HK1222668B - Ink formulations and film constructions thereof - Google Patents

Description

Ink formulations and film structures thereof

FIELD AND BACKGROUND OF THE DISCLOSURE

The present invention relates to ink formulations suitable for inkjet printing systems, and more particularly suitable for indirect printing systems. Ink film constructions produced using these inks are also disclosed, including ink dots, and more particularly continuous ink dots, adhered to a printing substrate.

Currently, offset printing is the most commonly used process for producing newspapers and magazines. Lithographic printing involves preparing plates bearing the image to be printed, which are placed on a plate cylinder. The ink image produced on the plate cylinder is transferred to a blanket cylinder carrying a rubber blanket. From the blanket, the image is applied to paper, card, or another print medium (called a substrate), which is fed between the blanket cylinder and the impression cylinder. For various well-known reasons, offset lithography is only suitable and economically viable for long printing runs.

More recently, digital printing technologies have been developed that allow printing devices to receive instructions directly from a computer without the need to prepare printing plates. These include color laser printers that use a xerographic printing process. Color laser printers that use dry toner are suitable for some applications, but they do not produce images of acceptable quality for publications such as magazines.

A process better suited for short-run, high-quality digital printing is used in HP Indigo digital presses. In this process, an electrostatic image is created on an electrically charged image cylinder by exposure to a laser. The electrostatic charge attracts oil-based ink, forming a color ink image on the image cylinder. This ink image is then transferred to the substrate via a blanket cylinder. While these systems are more suitable for high-quality digital printing, the use of oil-based inks raises environmental concerns.

Various printing devices using an indirect inkjet printing process have also been proposed previously. This process is a process in which an inkjet print head is used to print an image onto the surface of an intermediate transfer member, which is then used to transfer the image to a substrate. The intermediate transfer member (also referred to as an image transfer member or ITM) can be a rigid drum or a flexible belt guided on rollers, also referred to herein as a blanket.

Many problems related to direct inkjet printing on substrates are overcome using indirect printing technology. For example, direct inkjet printing on porous paper or other fibrous materials obtains poor image quality because the distance between the print head and the substrate surface changes and because the substrate acts as a core. Fibrous substrates such as paper generally require specific coatings that are engineered to absorb liquid ink or prevent it from penetrating below the surface of the substrate in a controlled manner. However, using a specially coated substrate is a costly option that is not suitable for certain printing applications. In addition, the problem inherent in using a coated substrate is that the surface of the substrate remains moist and requires an additional costly step to dry the ink so that the ink will not be wiped off when the substrate is processed, such as when stacked or wound into a roller. In addition, excessively wetting the substrate causes wrinkling and makes printing on both sides of the substrate (also referred to as two-sided printing or duplex printing) difficult, if not impossible.

On the other hand, using indirect technology allows the distance between the image transfer surface and the inkjet print head to remain constant, reducing substrate moisture because the ink can dry on the image transfer surface (also known as the release layer) before being applied to the substrate. Therefore, the final image quality of the ink film on the substrate is less affected by the physical properties of the substrate.

These complex indirect printing systems can operate under multiple sets of interrelated variables, including the ink formulation, the composition of the release layer to which it is coupled, the temperature at which the ink is deposited, dried, and transferred, and the pressure applied to the dried ink image to enable transfer.

While ink formulations have been proposed, and while each is excellent in the printing systems to which it has been adapted, further improvements are needed in ink formulations suitable for inkjetting, and particularly for inkjetting onto intermediate transfer members of indirect printing systems. There is also a need for superior ink film construction.

SUMMARY OF THE INVENTION

According to some teachings of the present invention, there is provided an ink product comprising (a) at least one colorant; and (b) at least one organic polymeric resin; the ink product exhibiting, as a substantially dry residue: (i) a dynamic viscosity in a range of 10 ⁶ cP to 5·10 ⁷ cP in at least a portion of a first temperature range of 60°C to 87.5°C; and (ii) a dynamic viscosity of at least 6·10 ⁷ cP in at least a portion of a second temperature range of 50°C to 55°C.

According to one aspect of the present invention, there is provided an ink product comprising (a) at least one colorant; and (b) at least one organic polymeric resin; the ink product exhibiting as a substantially dry residue: (i) a dynamic viscosity in the range of 10 ⁶ cP to 5·10 ⁷ cP, 8·10 7 cP, 1·10 8 cP, 2·10 8 cP or 3·10 ⁸ cP in at least a portion of a first temperature range of 60°C to 87.5°C, 60°C to 100 ^° C, 60°C to ¹⁰⁵ °C or 60°C to 110°C; and (ii) a dynamic viscosity of at least 6·10 ⁷ cP in at least a portion of a second temperature range of 50°C to ⁵⁵ °C.

According to another aspect of the present invention, an ink film construction is provided comprising an ink product and a printing substrate; the ink product being provided as at least one substantially dry ink film fixedly adhered to a surface of the printing substrate.

According to another aspect of the present invention, the ink product is an ink formulation comprising the ink product and an aqueous solvent, the at least one colorant being dispersed or at least partially dissolved in the solvent, and the at least one organic polymeric resin being dispersed in the solvent.

According to further features in the described preferred embodiments, the ink formulation is an aqueous inkjet ink that typically has at least one of: (i) a viscosity of 2 to 25 cP at at least one specific temperature within the jetting temperature range of 20-60°C; and (ii) a surface tension of at most 50 millinewtons/meter at at least one specific temperature within the jetting temperature range.

According to another aspect of the present invention, there is provided a water-based inkjet ink formulation comprising: (a) an aqueous solvent; (b) at least one colorant dispersed or at least partially dissolved in the solvent; and (c) at least one organic polymeric resin dispersed in the solvent; the ink formulation, when dried, forms a substantially dry ink residue having: (i) a dynamic viscosity in the viscosity range of 10 ⁶ cP to 5·10 ⁷ cP in at least a portion of a first temperature range of 60°C to 87.5°C; and (ii) a dynamic viscosity of at least 6·10 ⁷ cP in at least a portion of a second temperature range of 50°C to 55°C.

According to another aspect of the present invention, there is provided an ink film construction comprising: (a) a printing substrate; and (b) at least one substantially dry ink film fixedly adhered to a surface of the printing substrate, the ink film comprising at least one colorant dispersed in an organic polymeric resin; the ink film having a dynamic viscosity in the range of 10 ⁶ cP to 5·10 ⁷ cP in at least a portion of a first temperature range of 60° C. to 87.5° C., and at least 6·10 ⁷ cP in at least a portion of a second temperature range of 50° C. to 55° C.

According to another aspect of the present invention, there is provided a water-based inkjet ink formulation comprising: (a) an aqueous solvent; (b) at least one colorant dispersed or at least partially dissolved in the solvent; and (c) at least one organic polymeric resin dispersed in the solvent; the ink formulation, when dried, forming a substantially dry ink residue having: (i) a first dynamic viscosity in the range of 10 ⁶ cP to 3·10 8 cP in at least a portion of a first temperature range of 60° C. to 100° C., 60° C. to 105° C., or 60° C. to 110° C.; and (ii) a first dynamic viscosity in the range of at least 6·10 7 cP to 3·10 ^{8 cP} in at least a portion of a second temperature range of 50° C. to 55° C. cP; the second dynamic viscosity at 55°C exceeds the first dynamic viscosity at 85°C; the ink formulation satisfies at least one of the following structural properties: (A) at least one specific resin of the organic polymeric resin has an elevated glass transition temperature (Tg) of at least 52°C, at least 54°C, at least 56°C, at least 58°C, at least 60°C, at least 65°C, at least 70°C, at least 75°C, at least 80°C, at least 85°C, at least 90°C, or at least 95° _C ); (B) a substantially dry ink residue having an overall transferability rating of at least 0.90 at at least one of 100°C, 90°C, 85°C, 80°C, 75°C, and 70°C; (C) at least one specific resin having a minimum film forming temperature (MFFT) of at least 48°C, at least 50°C, at least 52°C, at least 54°C, at least 56°C, at least 58°C, at least 60°C, at least 65°C, at least 70°C, or at least 75°C; (D) the formulation comprises a film forming temperature (MFFT) of at most 0.40 kPa, at most 0.60 kPa, at most 0.70 kPa, at most 0.80 kPa, at least 0.90 kPa, at least ... (E) the formulation includes a softener selected to lower the elevated glass transition temperature by at least 5°C, at least 7°C, at least 10°C, at least 15°C, at least 20°C, at least 25°C, at least 30°C, at least 40°C, or at least 50°C.

According to another aspect of the present invention, there is provided an ink film construction comprising: (a) a printing substrate; and (b) at least one substantially dry ink film fixedly adhered to a surface of the printing substrate, the ink film comprising at least one colorant dispersed in an organic polymeric resin; the ink film satisfying at least one of the following structural properties: (A) at least one specific resin of the organic polymeric resin has an elevated glass transition temperature (Tg) of at least 52°C, at least 54°C, at least 56°C, at least 58°C, at least 60°C, at least 65°C, at least 70°C, at least 75°C, at least 80°C, at least 85°C, at least 90°C, or at least 95°C _; ); (B) the substantially dry ink residue has an overall transferability rating of at least 0.90 at at least one of 100°C, 90°C, 85°C, 80°C, 75°C, and 70°C; (C) at least one specific resin has a minimum film forming temperature (MFFT) of at least 48°C, at least 50°C, at least 52°C, at least 54°C, at least 56°C, at least 58°C, at least 60°C, at least 65°C, at least 70°C, or at least 75°C; (D) the formulation comprises a minimum film forming temperature (MFFT) of at most 0.40 kPa, at most 0.35 kPa, at most 0.25 kPa, at most 0.20 kPa, at most 0 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, at most 0.06 kPa, or at most 0.05 kPa; and (E) the formulation includes a softening agent selected to lower the elevated glass transition temperature by at least 5°C, at least 7°C, at least 10°C, at least 15°C, at least 20°C, at least 25°C, at least 30°C, at least 40°C, or at least 50°C; the ink film exhibiting at least one of the following structural properties: (I) a softening agent having a vapor pressure of at most ...I) a softening agent having a vapor pressure of at most 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, at most 0.06 kPa, or at most 0.05 kPa and a second dynamic viscosity of at least ^{6.10 7} cP in at least a portion of a second temperature range of 50° C. to ⁵⁵ ° C., the second dynamic viscosity at 55° C. exceeding the first dynamic viscosity at 85° C.; (II) the ink film comprises a single ink dot covering a surface area; the ink dot achieving a structural state wherein, with respect to a direction normal to the surface over the entire area, the single ink dot is disposed entirely over the area, and an average or characteristic thickness of the single ink dot is at most 1,800 nm; (III) the ink film comprises a set or field of ink dots contained within a square geometric projection projected onto a printing substrate, the set of ink dots containing at least 10 different ink dots, the ink dots being fixedly adhered to the surface of the printing substrate, all ink dots within the square geometric projection being counted as individual members of the set, each of the dots having an average thickness of less than 2,000 nm and a diameter of 5 to 300 microns; each of the ink dots having a generally convex shape, wherein a deviation from convexity (DC _point ) is defined as follows:

DC _point = 1-AA/CSA,

AA is the calculated projected area of the dot, the area being disposed generally parallel to the first fibrous printing substrate; and CSA is the surface area of a convex shape that minimally defines the outline of the projected area; the average deviation from convexity ( _DCdotavg ) of the ink dot set is at most 0.085; and (IV) the above-mentioned set of ink dots, each of the dots having an average thickness of less than 2,000 nm and a diameter of 5 to 300 microns; each of the ink dots having a deviation from a smooth circle ( _DRdot ) represented by:

DR _point = [P ² /(4π·A)]-1,

P is the measured or calculated perimeter of the ink dot; A is the maximum measured or calculated area encompassed by the perimeter; and the mean deviation of the ink dot set (DR _{dot average} ) is at most 0.85.

According to still further features in the described preferred embodiments, the dynamic viscosity in the first temperature range is at most 2·10 ⁸ cP, 1·10 ⁸ cP, or 8·10 ⁷ cP.

According to further features in the described preferred embodiments, the ratio of the second dynamic viscosity at 55°C to the first dynamic viscosity at 85°C is at least 1.7, at least 2, at least 2.5, at least 3, at least 4, at least 4.5, at least 5, at least 6, at least 7, at least 8, or at least 10.

According to still further features in the described preferred embodiments, the viscosity ratio is at most 30, at most 25, at most 20, at most 15, or at most 12.

According to still further features in the described preferred embodiments, the colorant includes at least one pigment.

According to still further features in the described preferred embodiments, the total concentration of colorant and resin within the ink dot is at least 7%, at least 10%, at least 15%, at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, or at least 85%.

According to still further features in the described preferred embodiments, the weight ratio of resin to colorant in the plurality of ink films is at least 1:1, at least 1.25:1, at least 1.5:1, at least 1.75:1, at least 2:1, at least 2.5:1, at least 3:1, at least 3.5:1, at least 4:1, at least 5:1, at least 7:1, or at least 10:1.

According to still further features in the described preferred embodiments, the ink dot contains less than 2%, less than 1%, less than 0.5%, or less than 0.1% of one or more charge directors, or is substantially free of charge directors.

According to still further features in the described preferred embodiments, the ink film contains at most 5%, at most 3%, at most 2%, at most 1%, or at most 0.5% by weight of inorganic filler particles (such as silica or titania).

According to further features in the described preferred embodiments, the formulation contains at most 20%, at most 16%, at most 13%, at most 10%, at most 8%, at most 6%, at most 4%, at most 3%, at most 2%, at most 1% or at most 0.2% (by weight) glycerol.

According to still further features in the described preferred embodiments, the ink dot contains less than 5%, less than 3%, less than 2%, or less than 0.5% of one or more hydrocarbons or oils, or is substantially free of such hydrocarbons or oils.

According to still further features in the described preferred embodiments, the ink film is configured to be laminated to a surface of the printing substrate.

According to still further features in the described preferred embodiments, fibers of the fibrous printing substrate directly contact the ink dots.

According to still further features in the described preferred embodiments, the mass-coated fibrous printing substrate comprises a coating having less than 10%, less than 5%, less than 3%, or less than 1% by weight of a water-absorbing polymer.

According to still further features in the described preferred embodiments, the fibrous printing substrate is paper, optionally selected from the group consisting of bond paper, uncoated offset paper, coated offset paper, copy paper, wood paper, coated wood paper, freesheet paper, coated freesheet paper, and laser paper.

According to still further features in the described preferred embodiments, the average (total) thickness of the ink film is in the range of 100-1,200 nm, 200-1,200 nm, 200-1,000 nm, 100-800 nm, 100-600 nm, 100-500 nm, 100-450 nm, 100-400 nm, 100-350 nm, 100-300 nm, 200-450 nm, 200-400 nm or 200-350 nm.

According to still further features in the described preferred embodiments, the average (total) ink film thickness or single ink dot thickness is at least 150 nm, at least 200 nm, at least 250 nm, at least 300 nm, or at least 350 nm.

According to still further features in the described preferred embodiments, the average thickness of a single ink dot is in the range of 100-800 nm, 100-600 nm, 100-500 nm, 100-450 nm, 100-400 nm, 100-350 nm, 100-300 nm, 200-450 nm, 200-400 nm or 200-350 nm.

According to still further features in the described preferred embodiments, the ink film has an average thickness or height of at most 5,000 nm, at most 4,000 nm, at most 3,500 nm, at most 3,000 nm, at most 2,500 nm, or at most 2,000 nm.

According to still further features in the described preferred embodiments, the ink film has an average thickness or height of at most 1,800 nm, at most 1,500 nm, at most 1,200 nm, at most 1,000 nm, at most 800 nm, at most 650 nm, at most 500 nm, at most 450 nm, or at most 400 nm.

According to still further features in the described preferred embodiments, the square geometric projection has a side length in the range of 0.5 mm to 15 mm, or approximately 10 mm, 5 mm, 2 mm, 1 mm, 0.8 mm, or 0.6 mm.

According to still further features in the described preferred embodiments, the diameter of the inkjet dot is at least 7, at least 10, at least 12, at least 15, at least 18, or at least 20 microns.

According to further features in the described preferred embodiments, the first dynamic viscosity is at most 4·10 ⁷ cP, at most 3·10 ⁷ cP, at most 2.5·10 ⁷ cP, at most 2·10 ⁷ cP, at most 1.5·10 ⁷ cP, or at most 1·10 ⁷ cP.

According to still further features in the described preferred embodiments, the first dynamic viscosity is at least 2·10 ⁶ cP, at least 4·10 ⁶ cP, at least 6·10 ⁶ cP, at least 7·10 ⁶ cP, at least 8·10 ⁶ cP, or at least 9·10 ⁶ cP.

According to still further features in the described preferred embodiments, the first dynamic viscosity is between 10 ⁶ cP and 4·10 ⁷ cP, 10 ⁶ cP and 3·10 ⁷ cP, 10 ⁶ cP and 2·10 ⁷ cP, 3·10 ⁶ cP and 4·10 ⁷ cP, 3·10 ⁶ cP and 3·10 ⁷ cP, 5·10 ⁶ cP and 3·10 ⁷ cP, 7·10 ⁶ cP and 3·10 ⁷ cP, 8·10 ⁶ cP and 3·10 ⁷ cP, 9·10 ⁶ cP and 3·10 ⁷ cP, 10 ^{7 cP and 5·10 7} cP, 10 ⁷ cP and 5·10 ⁷ cP, 10 ⁷ cP and 4·10 ⁷ cP, 10 ⁷ cP and 3·10 ⁷ cP, 15·10 ⁷ cP and 10 ^{7 cP.} cP to 3·10 ⁷ cP or 10 ⁷ cP to 3·10 ⁷ cP.

According to still further features in the described preferred embodiments, the second dynamic viscosity in the second temperature range is at least 8·10 ⁷ cP, at least 9·10 ⁷ cP, at least 10 ⁸ cP, at least 1.2·10 ⁸ cP, at least 1.5·10 ⁸ cP, at least 2.0·10 ⁸ cP, at least 2.5·10 ⁸ cP, at least 3.0·10 ⁸ cP, at least 3.5·10 ⁸ cP, at least 4.0·10 ⁸ cP, at least 5.0·10 ⁸ cP or at least 7.5·10 ⁸ cP.

According to still further features in the described preferred embodiments, the second dynamic viscosity is at most 6·10 ⁹ cP, at most 4·10 ⁹ cP, at most 3·10 ⁹ cP, at most 2·10 ⁹ cP, at most 1.5·10 ⁹ cP, or at most 10 ⁹ cP.

According to still further features in the described preferred embodiments, the second dynamic viscosity is between 7·10 ⁷ cP and 5·10 ⁹ cP, 7·10 ⁷ cP and 3·10 ⁹ cP, 7·10 ⁷ cP and 2·10 ⁹ cP, 7·10 ⁷ cP and 1·10 ⁹ cP, 8·10 ⁷ cP and 5·10 ^{9 cP, 9·10 7} cP and 5·10 ⁹ cP, 9·10 ⁷ cP and 3·10 ⁹ cP, 9·10 ⁷ cP and 2·10 ⁹ cP, 9·10 ⁷ cP and 1.5·10 ⁹ cP, 1·10 ⁸ cP and 5·10 ⁹ cP, 1·10 ⁸ cP and 3·10 ⁹ cP, 1·10 ⁸ cP and 2·10 ⁹ cP ^, or 1.5·10 ^{8 cP.} The range is from cP to 1.5·10 ⁹ cP.

According to further features in the described preferred embodiments, the upper temperature limit of the first temperature range is 87°C, 86°C, 85°C, 84°C, 82°C, 80°C, 78°C, 76°C, 74°C, 72°C, 70°C or 68°C.

According to still further features in the described preferred embodiments, the lower temperature limit of the range is 61°C, 62°C, 63°C, 64°C, or 65°C.

According to still further features in the described preferred embodiments, the ink film or dried ink residue has a glass transition temperature (Tg) of at least 52°C, at least 54°C, at least 56°C, at least 58°C, at least 60°C, at least 65°C, at least 70°C, at least 75°C, at least 80°C, at least 85°C, at least 90°C, or at least 95° _C .

According to still further features in the described preferred embodiments, the plurality of ink films or dried ink residues contain at least one water-soluble substance or at least one water-dispersible substance, optionally including an aqueous dispersant.

According to still further features in the described preferred embodiments, the ink film or dried ink residue contains at least 2%, at least 3%, at least 5%, or at least 8% (by weight) of water-soluble materials.

According to still further features in the described preferred embodiments, the ink film or dried ink residue contains at least 1.2%, at least 1.5%, at least 2%, at least 3%, at least 4%, at least 6%, at least 8%, at least 10%, at least 12%, at least 15% or at least 20% (by weight) colorant.

According to still further features in the described preferred embodiments, the ink film or dried ink residue contains at least 20%, at least 30%, at least 40%, at least 50%, at least 60%, or at least 70% by weight resin.

According to still further features in the described preferred embodiments, ΔT defines the temperature difference between a temperature ( _TF ) at which the ink film or dried ink residue begins to exhibit a certain degree of fluidity and a baseline temperature ( _TB ):

ΔT＝ _TF - _TB

The degree of fluidity is defined by the critical viscosity ( _μCR ) that achieves the degree of fluidity, and wherein, when the baseline temperature is equal to 50°C and the critical viscosity is equal to ¹⁰⁸ cP, the temperature difference is at least 3°C, at least 4°C, at least 5°C, at least 7°C, at least 12°C, at least 15°C, at least 18°C, at least 20°C, or at least 25°C.

According to still further features in the described preferred embodiments, the printing substrate is a fibrous printing substrate, a commodity coated printing substrate, an uncoated printing substrate, or a coated or uncoated offset printing substrate.

According to still further features in the described preferred embodiments, a continuous ink film of the continuous ink film is defined as an ink dot, and the dimensionless aspect ratio ( _Raspect ) is defined as follows:

R _{vertical and horizontal} = D _point / H _point

wherein: D _point is the average diameter of the point; H _point is the average thickness of the point; and the dimensionless aspect ratio is at least 15, at least 20, at least 25, or at least 30, at least 40, at least 50, at least 60, at least 75, at least 85, at least 95, at least 110, or at least 120.

According to still further features in the described preferred embodiments, the dimensionless aspect ratio is at most 200 or at most 175.

According to still further features in the described preferred embodiments, the plurality of continuous ink films are fixedly adhered directly to the surface of the printing substrate.

According to still further features in the described preferred embodiments, the colorant comprises at least 0.3%, at least 0.5%, at least 0.7%, at least 0.85%, at least 1%, at least 1.2%, at least 1.4%, at least 1.6%, at least 1.8% or at least 2% (by weight) of the formulation.

According to further features in the described preferred embodiments, the formulation further includes a softener, optionally having a vapor pressure at 150°C of at most 0.40 kPa, at most 0.35 kPa, at most 0.25 kPa, at most 0.20 kPa, at most 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, at most 0.06 kPa or at most 0.05 kPa.

According to still further features in the described preferred embodiments, the softening agent is chemically stable up to a temperature of at least 170°C, at least 185°C, at least 200°C, or at least 220°C.

According to further features in the described preferred embodiments, the formulation or at least one organic polymeric resin further includes an aqueous dispersant, which optionally comprises at most 5%, at most 4.5%, at most 4%, at most 3.5 wt.%, at most 3 wt.%, at most 2.5 wt.%, at most 2 wt.%, at most 1.5 wt.%, at most 1 wt.% or at most 0.5 wt.% of the formulation.

According to still further features in the described preferred embodiments, the dispersant is selected from the group consisting of high molecular weight polyurethanes or aminocarbamates, styrene-acrylic acid copolymers, modified polyacrylate polymers, acrylic block copolymers made by controlled free radical polymerization, sulfosuccinates, acetylenic diols, ammonium salts of carboxylic acids, alkylol ammonium salts of carboxylic acids, aliphatic polyethers having acid groups, and ethoxylated nonionic fatty alcohols.

According to still further features in the described preferred embodiments, the polymeric resin comprises or consists essentially of an acrylic-based polymer selected from the group consisting of acrylic polymers and acrylic-styrene copolymers; or comprises or consists essentially of a linear or branched chain resin of a polyester or co-polyester.

According to still further features in the described preferred embodiments, the ink formulation is formulated so that when diluted at least 50%, at least 100%, at least 150%, at least 200%, at least 250%, at least 300%, at least 350%, or at least 400% on a weight/weight basis with a dilution solvent or water, the resulting mixture is an aqueous inkjet ink having: (i) a viscosity of 2 to 25 cP at at least one specific temperature in the range of 20-60°C; and (ii) a surface tension of at most 50 millinewtons/meter at at least one specific temperature in the range.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be further described by way of example with reference to the accompanying drawings, in which:

FIG1 is an exploded schematic perspective view of a printing system according to which an embodiment of the present invention may be used;

FIG2 is a schematic longitudinal section through the printing system of FIG1 , wherein the various components of the printing system are not drawn to scale;

FIG3 is a schematic illustration of a printing system of the present invention, according to which an embodiment of the present invention may be used;

FIG4A provides a temperature sweep plot of dynamic viscosity as a function of temperature for the dried ink residue of various ink formulations;

FIG4B provides a temperature sweep curve of dynamic viscosity as a function of temperature for the dried ink residue of the ink formulation of the present invention;

FIG5 provides a temperature sweep plot of dynamic viscosity as a function of temperature for a representative dried ink residue of each of the ink formulations provided in FIG4A and 4B;

FIG6 provides temperature sweep plots of dynamic viscosity as a function of temperature for representative dried ink residues of ink formulations of the present invention and dried ink residues of several commercially available inkjet inks;

FIG7A provides a first plurality of temperature sweep curves of dynamic viscosity as a function of temperature for dried ink residues of five ink formulations using a first thermoplastic resin and a first softener having the same composition and different ratios of softeners;

FIG7B provides a second plurality of temperature sweeps of dynamic viscosity as a function of temperature for dried ink residues of five ink formulations having the same components and different ratios of softeners relative to those used in FIG7A using different thermoplastic resins and different softeners;

8A-8D are temperature sweep plots of dynamic viscosity as a function of temperature for residual films of ink formulations having different softening agents and different concentrations of those agents;

FIG9 provides temperature sweep curves of dynamic viscosity as a function of temperature for dried ink residues of four ink formulations having different colorants (C, M, Y, K) but otherwise having the same formulation composition;

Figures 10A-F show magnified images acquired by laser microscopy in two dimensions (Figures 10A-C) and three dimensions (Figures 10D-F) of ink films on coated paper substrates obtained using various printing techniques, wherein: Figures 10A and 10D are magnified images of a liquid electrophotographic film (LEP); Figures 10B and 10E are magnified images of offset print spots; and Figures 10C and 10F are magnified images of inkjet ink film constructions according to the present invention;

Figures 11A-F show magnified images acquired by laser microscopy in two dimensions (Figures 11A-C) and three dimensions (Figures 11D-F) of ink films on uncoated paper substrates obtained using various printing techniques, wherein: Figures 11A and 11D are magnified images of a liquid electrophotographic film (LEP); Figures 11B and 11E are magnified images of offset print spots; and Figures 11C and 11F are magnified images of inkjet ink film constructions according to the present invention;

Figures 12A-1 to 12E-1 provide magnified views of fields of ink dots or films on mass-coated fibrous substrates (Figures 12A-1 to 12C-1) and uncoated fibrous substrates (Figures 12D-1 and 12E-1) produced using the ink formulations of the present invention;

Figures 12A-2 through 12E-2 provide further enlarged views of a portion of the panels of Figures 12A-1 through 12E-1, with ink films disposed on mass-coated paper provided in Figures 12A-2 through 12C-2, and with ink films disposed on uncoated paper provided in Figures 12D-2 and 12E-2; corresponding optical uniformity distributions are provided in Figures 12A-3 through 12E-3;

Figures 12A-4 through 12E-4 provide magnified views of ink films disposed on coated paper (Figures 12A-4 through 12C-4) and uncoated paper (Figures 12D-4 and 12E-4), and their corresponding image processor-calculated profile and convexity projections, the ink films produced using the ink formulations of the present invention;

FIG13A provides a magnified view of a field of ink dots on a mass-coated fibrous substrate produced using a commercially available, aqueous, direct inkjet printer;

FIG13B provides a magnified view of a field of ink dots on an uncoated fibrous substrate produced using the same commercially available, aqueous, direct inkjet printer;

Figures 14A-2 to 14F-2 provide images of ink spots or films obtained on uncoated (Figures 14A-2 to 14C-2) and coated (Figures 14D-2 to 14F-2) paper using various prior art printing techniques, as well as their optical uniformity distribution (14A-1 to 14F-1);

FIG15A illustrates a two-dimensional shape having the mathematical properties of a convex set;

FIG15B illustrates a two-dimensional shape having the mathematical properties of a non-convex set;

FIG15C is a schematic top projection of an ink film with small rivulets and inlets, which shows a smooth projection of the ink image;

Figures 16A and 16B provide schematic cross-sectional views of an ink film construction of the present invention and a prior art inkjet ink dot construction, respectively, wherein the substrate is a fibrous paper substrate; and

17A and 17C each show an image of the surface of an outer layer of an intermediate transfer member; and Figs. 17B and 17D are corresponding images of the surface of an ink film produced using those outer layers in accordance with the present invention.

Detailed Description of the Illustrated Embodiments

The ink formulations and ink film constructions according to the present invention may be better understood with reference to the drawings and accompanying description.

Before explaining at least one embodiment of the present invention in detail, it should be understood that the present invention is not limited in its application to the details of the construction and the configuration of the components set forth in the following description or illustrated in the drawings. The present invention may have other embodiments or be implemented or carried out in various ways. Furthermore, it should be understood that the wording and terminology employed herein are for descriptive purposes only and should not be construed as limiting.

The ink formulations of the present invention can be used, and ink film constructions can be obtained, in particular, by the following printing processes or by using any printing system that implements these processes. A printing process suitable for using the ink formulations disclosed herein and for preparing ink films according to the present invention comprises directing droplets of ink comprising an organic polymeric resin and a colorant (e.g., a pigment or dye) in an aqueous vehicle onto an intermediate transfer member to form an ink image, the ink comprising an organic polymeric resin and a colorant (e.g., a pigment or dye) in an aqueous vehicle, and the transfer member having a hydrophobic outer surface, wherein each ink droplet in the ink image expands upon impact with the intermediate transfer member to form a wet ink film (e.g., a film that preserves a substantial portion of the flattening and horizontal extension of the droplet present upon impact or covers an area depending on the mass of ink in the droplet). The ink is dried by evaporating the aqueous vehicle from the ink image to leave a dry or substantially dry residual film comprising the resin and colorant while the ink image is transported by the intermediate transfer member. The residual film is then transferred to a substrate (e.g., by pressing the intermediate transfer member against the substrate to emboss the residual film thereon). The chemical composition of the ink and the chemical composition of the surface of the intermediate transfer member are selected so that the intermolecular forces of attraction between the molecules in the outer skin of each droplet and on the surface of the intermediate transfer member resist the tendency of the ink film produced by each droplet to bead up under the surface tension of the aqueous vehicle, rather than causing each droplet to spread out by wetting the surface of the intermediate transfer member. Further details regarding these printing processes and exemplary printing systems suitable for use with the ink formulations of the present invention and achieving the ink film construction thereof are disclosed in PCT Publication Nos. WO 2013/132418, WO 2013/132419, and WO 2013/132420.

This printing process is described as preserving or solidifying the pancake-disc shape of each aqueous ink droplet, which is caused by the flattening of the ink droplet upon impact with the surface of an intermediate transfer member (also known as a release layer), despite the layer's low surface energy and hydrophobic nature. To achieve this, the novel process relies on electrostatic interactions between molecules in the ink and the outer surface of the transfer member, which are charged in their respective media or can be charged against each other, and thus become oppositely charged upon interaction between the ink and the release layer. Further details regarding the printing process are provided below.

General overview of printing processes and systems

The printing system shown in Figures 1 and 2 generally comprises three separate and interacting systems: a blanket system 100, an imaging system 300 above the blanket system 100, and a substrate transport system 500 below the blanket system 100. The blanket passes through each station while circulating in a loop. Although the following description is provided for the case where the intermediate transfer member is an endless belt, the ink formulation according to the present invention is equally applicable to printing systems in which the intermediate transfer member is a drum, with the specific design of each station being modified accordingly.

The blanket system 100 includes an endless belt or blanket 102, which serves as an intermediate transfer member and is guided over two rollers 104 and 106. An image composed of dots of aqueous ink is applied to the upper branch of the blanket 102 by the imaging system 300 at locations referred to herein as imaging stations. The lower branch selectively interacts with two impression cylinders 502 and 504 of the substrate transport system 500 at two impression stations to impress the image onto the substrate pressed between the blanket 102 and the respective impression cylinders 502 and 504. As will be explained below, the presence of two impression cylinders 502 and 504 is intended to allow for duplex printing. Although not illustrated, duplex printing can also be achieved with a single impression station using a modified two-sided system that feeds the opposite side of the printed substrate to the impression station. In the case of a single-sided printing press, only one impression station would be required.

In operation, ink images, each a mirror image of the image to be impressed on the final substrate, are printed onto the upper run of blanket 102 by imaging system 300. In this context, the term "run" is used to refer to the length or segment of blanket between any two given rollers guiding the blanket upward. While being transported by blanket 102, the ink is heated to dry it by evaporating most, if not all, of the liquid vehicle. Furthermore, the ink image is heated to impart a tacky film to the remaining ink solids after evaporation of the liquid vehicle, referred to as a residual film to distinguish it from the liquid film formed by flattening each ink droplet. At impression cylinders 502, 504, the image is impressed onto a single sheet 501 of substrate that is transported from an input stack 506 via impression cylinders 502, 504 to an output stack 508 by substrate transport system 500. Although not shown, the substrate can be a continuous web, in which case the input and output stacks can be replaced by supply and delivery rollers. Therefore, the substrate transport system needs to be modified accordingly, for example by using guide rollers and dancer rollers to relax the web so that it is properly aligned with the imprinting station.

Imaging system

Imaging system 300 includes print bars 302, each of which can be slidably mounted on a frame positioned at a fixed height above the surface of blanket 102. Each print bar 302 can include a print head strip as wide as the printing area on blanket 102 and each includes a controllable print nozzle. The imaging system can have a plurality of bars 302, each of which can contain aqueous inks of different or the same color, typically each ejecting cyan (C), magenta (M), yellow (Y), or black (K). It is possible for the print bars to deposit different shades of the same color (e.g., various shades of gray, including black), or for two or more print bars to deposit the same color (e.g., black). In addition, the print bars can be used for non-pigmented liquids (e.g., decorative or protective varnishes) and/or for specialized colors (e.g., to achieve visual effects such as metallic, shimmering, glowing, or sparkling appearances, or even olfactory effects).

Because some print bars may not be needed during a particular print job, the print head is movable between an operative position where it is positioned above the blanket 102, where the bars remain stationary, and an inoperative position where the bars are accessible for maintenance.

Within each print bar, the ink may be constantly recirculated, filtered, degassed, and maintained at a desired temperature and pressure, as is known to those skilled in the art and does not require further description.

Because the different print bars 302 are spaced apart from one another along the length of the blanket, their operation must of course be properly synchronized with the movement of the blanket 102 .

If desired, it is possible to provide an air blower after each print bar 302 to blow a slow stream of hot air (preferably air) onto the intermediate transfer member to begin drying the ink droplets deposited by the print bars 302. This helps to immobilize the droplets deposited by each print bar 302, that is, to resist their shrinkage and prevent them from moving on the intermediate transfer member, and also prevent them from merging with droplets subsequently deposited by other print bars 302. These post-jet treatments of the newly deposited ink droplets do not essentially dry them, but only allow a skin to form on their outer surfaces.

Blankets and Blanket Support Systems

In one variation, the blanket 102 is seamed. Specifically, the blanket can be formed from an initially flat strip whose ends are releasably or permanently fastened to each other to form a continuous loop often referred to as a band. The releasable fastening can be a zipper fastener or a hook and loop fastener positioned substantially parallel to the axis of the rollers 104 and 106 guiding the blanket. Permanent fastening can be achieved using an adhesive or tape. The continuous band can be formed from more than one elongated strip of blanket and thus include more than one seam. Alternatively, the band can be seamless.

To avoid abrupt changes in the stretch of the blanket as the seam passes over rollers or other parts of the support system, it is necessary to make the seam as close as possible to the same thickness as the rest of the blanket.

The main purpose of rubber blanket is to accept the ink image from imaging system and that dry but undisturbed image is transferred to the impression site. For making the ink image be easy to transfer at each impression site, rubber blanket has a thin upper release layer, and this upper release layer can be highly hydrophobic. Under suitable conditions, it has been found that silanol-, silicon- or silane-modified or end-blocked polydialkylsiloxane silicone materials and amino silicones are effective in the composition of the release layer. However, the exact formulation of cured silicone is not critical, as long as selected material allows the image to be discharged to final base material from the transfer member.

The strength of the blanket can be derived from a support or reinforcement layer. In one embodiment, the reinforcement layer is formed of a fabric. If the fabric is woven, the warp and weft threads of the fabric can have the same or different compositions or physical structures so that the blanket can have greater elasticity in its transverse direction (parallel to the axis of rollers 104 and 106) than in its longitudinal direction (for reasons discussed below).

The blanket may include additional layers between the reinforcement layer and the release layer, for example to provide the release layer with improved surface compressibility and compressibility to the substrate. Other layers may further be included to serve as a heat reservoir or thermal barrier. An inner layer may further be provided to control the frictional drag on the blanket as it rotates on its support structure. Other layers may be included to adhere or connect the layers to each other or to prevent molecules from migrating therebetween.

The blanket support system may include a thermally conductive support plate 130 that forms a continuous flat support surface on the top and bottom sides of the support frame. Electrical heating elements may be inserted into the plate's transverse holes to apply heat to the plate 130 and through the plate 130 to the blanket 102. Other means for heating the blanket will occur to those skilled in the art and may include heating from below, above, or within the blanket itself.

Also mounted on the blanket support frame are two pressure rollers or nip rollers 140 and 142, which can be raised and lowered relative to the lower leg of the blanket. The pressure rollers are located in the gap between the support plates 130 on the underside of the support frame, thereby covering the underside of the frame. The pressure rollers 140 and 142 are aligned with the impression cylinders 502 and 504 of the substrate transport system, respectively. Each impression roller and its corresponding pressure roller form an impression station when they engage the blanket transported therebetween.

In some cases, the blanket support system further includes a continuous rail that engages structures on the side edges of the blanket to maintain tension in its transverse direction. These structures can be spaced protrusions, such as half of the teeth of a zipper fastener sewn or otherwise attached to the side edges of the blanket. Alternatively, these structures can be continuous flexible beads having a greater thickness than the blanket. The lateral structures can be attached to the edges of the blanket directly or via intermediate strips, which can optionally provide suitable elasticity to engage these structures in their respective guide rails while maintaining the blanket flat, particularly at the imaging station. The lateral rail guide channels can have any cross-section suitable for receiving and holding the blanket lateral structures and maintaining tension. To reduce friction, the guide channels can include rolling bearing elements to retain the protrusions or beads within the channels. Further details regarding exemplary lateral blanket structures or seams that may be suitable for use with the ink formulations of the present invention are disclosed in PCT Publication No. WO 2013/136220.

To properly form an image on the blanket and transfer it to the final substrate, and to achieve alignment of the front and back images during duplex printing, many different components of the system must be properly synchronized. To properly position the image on the blanket, both the position and speed of the blanket must be known and controlled. To achieve this, the blanket can be marked at or near its edge with one or more markings spaced along the direction of the blanket's motion. One or more sensors 107 sense the timing of these markings as they pass through the sensors. To ensure proper image transfer from the transfer blanket to the substrate, the speed of the blanket and the speed of the surface of the platen roller should be the same. Signals from sensor 107 are sent to controller 109, which also receives indications of the platen roller's rotational speed and angular position, for example from encoders (not shown) on the shafts of one or both platen rollers. Sensor 107 or another sensor (not shown) also measures the time it takes for the seam of the blanket to pass through the sensors. To maximize the use of the available length of the blanket, the image on the blanket needs to begin as close to the seam as possible. Further details regarding exemplary control systems that may be suitable for printing systems suitable for use with the ink formulations of the present invention are disclosed in PCT Publication No. WO 2013/132424.

Blanket pretreatment

Figure 1 schematically shows a roller 190 positioned just outside the blanket next to roller 106. Such a roller 190 may optionally be used to apply a pre-treatment solution containing conditioning chemicals to the film.

While rollers can be used to apply a uniform film, a pretreatment or conditioning substance can alternatively be sprayed onto the surface of the blanket, for example, by using an air knife jet, and optionally spread more evenly. Alternatively, the optional conditioning solution can be applied by passing the blanket over a thin film of conditioning solution that is permeated through the blanket without directly contacting the surface of the release layer. Regardless of the method used to apply the optional conditioning solution, the location where such pre-printing treatment can be performed, if desired, may be referred to herein as a conditioning station. The alternative printing system illustrated in FIG3 may also include a conditioning station.

As noted, when an ink droplet strikes a transfer member, the momentum of the droplet causes it to expand into a relatively flat volume. In the prior art, this droplet flattening is almost immediately counteracted by a combination of the surface tension of the droplet and the hydrophobicity of the surface of the transfer member.

In some cases, the shape of the ink droplet is "frozen" so that at least some, and preferably most, of the flattening and horizontal extension of the droplet present upon impact is preserved. It will be appreciated that, because the droplet shape recovers very quickly after impact, prior art methods do not achieve phase change through coalescence and/or coagulation and/or migration.

Without wishing to be bound by theory, it is believed that upon impact, the positive charges already located on the surface of the transfer member attract the negatively charged polymer resin particles in the ink droplet that are immediately adjacent to the member surface. This effect is believed to occur as the droplet spreads, along a region of the interface between the spreading droplet and the transfer member sufficient to delay or prevent the droplet from beading, at least on the timescale of the printing process (typically on the order of seconds).

When the amount of charge is too small to attract more than a few charged resin particles in the ink, it is believed that the concentration and distribution of the charged resin particles in the ink droplet are substantially unchanged by contact with the chemical agent on the release layer. Furthermore, because the ink is aqueous, the effect of the positive charge is very localized, especially during the very short time interval required to solidify the shape of the droplet.

Without wishing to be bound by theory, it is believed that when the conditioning agent or solution is applied to the surface of the intermediate transfer member, at least one type of positively charged functional group of the conditioning agent is adsorbed onto or otherwise attached to the surface of the release layer. On the opposite side of the release layer, facing the ejected ink droplets, at least one type of positively charged functional group of the conditioning agent is available and positioned to interact with negatively charged species in the ink (e.g., in the resin).

An intermediate transfer member that can be subjected to such treatment can, for example, include a silanol-, silyl-, or silane-modified or terminated polydialkyl-siloxane silicone, or a combination thereof, in its release layer. Further details regarding exemplary release layers that may be suitable for use with the ink formulations of the present invention are disclosed in PCT Publication No. WO 2013/132432.

Chemical agents suitable for preparing these conditioning solutions (if necessary) have a relatively high charge density and can be polymers containing amine nitrogen atoms in multiple functional groups, which do not need to be the same and can be combinations (e.g., primary, secondary, tertiary, or quaternary ammonium salts). Although macromolecules with molecular weights of several hundred to several thousand can be suitable conditioning agents, the inventors believe that polymers with high molecular weights of 10,000 g/mole or greater are preferred. Suitable conditioning agents include cationic guar gum, guar gum-based polymers, cationic methacrylamide, methacrylamide-based polymers, and linear, branched, or modified polyethyleneimine (PEI). Further details on exemplary conditioning agents and solutions thereof that may be suitable in printing systems suitable for use with the ink formulations of the present invention are disclosed in PCT Publication No. WO2013/132339.

The efficacy of this method and its associated aqueous treatment solution (also referred to as a "conditioning solution") was determined in preliminary pilot printing experiments in a laboratory test facility. As disclosed in the aforementioned application, the use of these solutions was highly beneficial, as assessed by the print quality of the image after transfer from the intermediate transfer member to the printed substrate. The optical density of the print was found to be of particular relevance, and the use of this blanket treatment method prior to inkjet printing significantly improved the measured results for the printed substrate.

According to a method originally developed by the applicant, a very thin coating of a conditioning solution is applied to a transfer member, immediately removed and evaporated, leaving behind no more than a few molecular layers of the appropriate chemical. Ink droplets are then ejected onto this pretreated blanket, dried, and transferred to the printing substrate. Typically, the ink film image thus printed can be identified by the presence of the conditioning agent on its outer surface. In other words, the dried ink droplets strip off the underlying conditioning agent during transfer, which is then impressed onto the final substrate in the opposite orientation.

Exemplary conditioning solutions are provided below, including Conditioning Solution A, and its planar counterpart, in which the conditioning agent is diluted in distilled water (1:99) without additives.

Adjustment solution A

Sucrose 4

Water 95

Ink image heating

Heaters inserted into support plate 130 or positioned above the blanket as intermediate drying system 224 and drying station 214 are used to heat the blanket to a temperature suitable for rapid evaporation of the ink vehicle and compatible with the composition of the blanket. For blankets comprising, for example, silanol-modified or end-capped polydialkylsiloxane silicones in the release layer, the heating temperature can vary from 70°C to 180°C, depending on various factors, such as the composition of the ink and/or conditioning solution (if necessary). Blankets comprising amino silicones can generally be heated to temperatures between 70°C and 130°C. Exemplary blankets comprising cured amino-functionalized silicones in the release layer are disclosed in PCT Publication No. WO 2013/132438.

In some printing systems, the temperature of the blanket can be kept relatively similar along the loop it follows, with optional localized transient variations (e.g., to facilitate transfer of the dried ink image from the transfer member to the printing substrate). In other printing systems, the temperature of the blanket can be varied as needed between the locations it traverses. For example, the ink formulation can be jetted onto the blanket at the imaging location at a relatively low temperature (e.g., between 60°C and 100°C, typically between 70°C and 90°C), below the evaporation temperature of the ink vehicle. The deposited ink droplets can then be dried on the blanket, which then has a higher temperature (e.g., up to 200°C) to facilitate evaporation of the ink vehicle. The blanket temperature can be further modified to be sufficient to enable transfer of the dried ink image at the imprinting location. In high-temperature transfer processes, where the blanket is further heated at the nip of the imprinting station (e.g., via 231), the surface temperature can transiently rise to 170°C. In low-temperature transfer processes, where the blanket is not further heated after the ink has dried, the surface temperature at the impression station can be below 140°C, typically below 120°C. Following the impression station, the blanket temperature can be additionally modified to suit the optimal operating conditions of any stations that the printing system may include. For example, the blanket can be further heated or cooled to suit the coating station, where a varnish can optionally be applied to the printed ink image. Finally, the blanket temperature can be further modified to allow it to enter the imaging station at the desired temperature. For this purpose, a printing system suitable for use with the ink formulations according to the present invention can include a blanket cooling station.

When using a bottom-heated transfer member, it may be desirable for the blanket to have a relatively high heat capacity and low thermal conductivity so that the temperature of the bulk of the blanket 102 does not change significantly as it moves between the optional pre-treatment or conditioning station, the imaging station, and the impression station. When using a top-heated transfer member, the blanket will preferably include a thermal insulation layer to prevent excessive dissipation of the applied heat. To apply heat to the ink image carried by the transfer surface at different rates, regardless of the configuration of the particular printing system, additional external heaters or energy sources (not shown) can be used to apply energy locally, for example, before reaching the impression station to make ink residue tacky (see 231 in FIG. 3 ), before the imaging station to dry the conditioning agent (if necessary), and at the inkjet station to begin evaporating the vehicle from the ink droplets as soon as possible after the ink droplets impact the surface of the blanket. Conversely, the printing system can include cooling stations to locally remove excess heat.

The external heater can be, for example, a hot air or air blower 306 (as schematically presented in Figure 1) or a radiant heater that focuses, for example, infrared radiation onto the surface of the blanket, which can achieve temperatures exceeding 50°C, 75°C, 100°C, 125°C, 150°C, 175°C, 190°C, 200°C, 210°C or even 220°C.

After evaporation of the aqueous vehicle, including any liquid humectant, from the ink image, a dry or substantially dry residual film comprising the resin and colorant is obtained. The remaining dry residual film may have an average single drop ink film thickness of 1,500 nm or less, 1,200 nm or less, 1,000 nm or less, 800 nm or less, 600 nm or less, 500 nm or less, 400 nm or less, or 300 nm or less.

For multi-drop ink films, the average thickness may be 2,500 nm or less, 2,000 nm or less, 1,600 nm or less, 1,400 nm or less, 1,200 nm or less, 1,000 nm or less, 800 nm or less, or 600 nm or less.

As explained above, temperature control is crucial for a printing system if high-quality printed images are to be achieved. This is greatly simplified in the embodiment of FIG. 3 because the belt has a much lower thermal capacity than the blanket 102 in the embodiments of FIG. 1 and 2 . The exemplary printing system schematically illustrated in FIG. 3 includes an endless belt 210 that circulates through an imaging station 212, a drying station 214, and an impression station 216, each of which functions as previously described. For example, the imaging station 212 of FIG. 3 is similar to the imaging system 300 described previously, such as that illustrated in FIG. 1 . Following each print bar 222 in the imaging station, an intermediate drying system 224 is provided to blow hot air (typically air) onto the surface of the belt 210, thereby partially drying the ink droplets. This hot air flow helps prevent inkjet nozzle clogging and also prevents droplets of different colored ink on the belt 210 from merging. In the drying station 214, the ink droplets on the belt 210 are exposed to radiation and/or hot air to dry the ink more thoroughly, driving off most (not necessarily all) of the liquid vehicle and leaving only a layer of resin and colorant that is heated to the point of becoming tacky.

At the impression station 216, the belt 210 passes between an impression cylinder 220 and a pressure cylinder 218 carrying a compressible blanket 219. The length of the blanket 219 is equal to or greater than the maximum length of the sheet 226 of substrate to be printed. The impression cylinder 220 has a diameter twice that of the pressure cylinder 218 and can simultaneously support two sheets 226 of substrate. The sheets 226 of substrate are carried from a supply stack 228 by a suitable transport mechanism (not shown in FIG. 3 ) and passed through the nip between the impression cylinder 220 and the pressure cylinder 218. Within the nip, the surface of the belt 220 carrying the ink image is firmly pressed against the substrate by the blanket 219 of the pressure cylinder 218, so that the ink image is impressed onto the substrate and then cleanly separated from the surface of the belt. The substrate is then transported to an output stack 230.

In some printing systems, a heater 231 may be provided just beyond the nip between the two cylinders 218 and 220 at the image impression station to help make the ink film tacky, thereby facilitating transfer to the substrate.

In order for the ink to separate cleanly from the surface of the belt 210, it is necessary to have a hydrophobic release layer on the latter surface. In the embodiment of FIG1 , this hydrophobic release layer is formed as part of a thick blanket that also includes a compressible conformable layer necessary to ensure proper contact between the release layer and the substrate at the imprint station. The resulting blanket is a very heavy and costly item that needs to be replaced if any of the many functions it performs fail.

In the embodiment of Figure 3, the hydrophobic release layer forms part of a separate element of a thick blanket 219 which is required to be pressed against the substrate sheet 226. In Figure 3, the release layer is formed on a flexible thin inextensible tape 210 which is preferably fiber reinforced to increase tensile strength along its longitudinal dimension.

It should be appreciated that the description of the printing system as illustrated in FIG. 3 has provided a sufficient level of detail for one of ordinary skill in the art to understand and perform the present invention.

With respect to embodiments utilizing a thick blanket 102, it is also suggested above that an additional layer be included to affect the blanket's thermal capacity, given that the blanket is heated from below. In the embodiment of FIG. 3 , the separation of the belt 210 from the blanket 219 allows for the use of less energy in the drying section 214 to dry the ink droplets and heat them to the softening temperature of the resin. Furthermore, the belt can be cooled before returning to the imaging station, which reduces or avoids problems associated with attempting to spray ink droplets very close to a hot surface where the inkjet nozzles operate. Alternatively, or in addition, a cooling station can be added to the printing system to reduce the belt's temperature to a desired value before it enters the imaging station. Cooling can be achieved by passing the belt 210 through rollers whose lower half is immersed in a coolant (which can be water or a cleaning/treatment solution), by spraying a coolant onto the belt 210, or by passing the belt through a coolant reservoir.

To illustrate, a conventional hydrophobic surface, such as a silicone-coated surface, will readily generate electrons and be considered negatively charged. Polymeric resins in aqueous vehicles are also generally negatively charged. Therefore, without taking additional steps, net intermolecular forces will cause the intermediate transfer member to repel the ink and the droplets will tend to bead into spherical beads.

In a novel printing process suitable for producing ink film constructions according to the present invention, the chemical composition of the surface of the intermediate transfer member is modified to provide a positive charge. This can be achieved, for example, by including molecules having one or more Bronsted base functional groups, particularly nitrogen, in the surface of the intermediate transfer member (e.g., embedded in a release layer). Suitable positively charged or positively chargeable groups include primary, secondary, and tertiary amines. These groups can be covalently bonded to the polymeric backbone, and, for example, the outer surface of the intermediate transfer member can include aminosilicone.

These positively chargeable functional groups of the release layer molecules can interact with the Bronsted acid functional groups of the ink molecules. Suitable negatively charged or negatively chargeable groups include carboxylic acids, such as those with carboxylic acid groups (-COOH), acrylic acid groups ( _-CH2 =CH-COOH), methacrylic acid groups ( _-CH2 =C( _CH3 )-COOH); and sulfonates, such as those with sulfonic acid groups ( _-SO3H ). These groups can be covalently bonded to the polymer backbone and are preferably water-soluble or water-dispersible. Suitable ink molecules can, for example, include acrylic acid-based resins, such as acrylic polymers and acrylic acid-styrene copolymers, having carboxylic acid functional groups.

ink

Inks according to embodiments of the presently claimed invention suitable for use in this process and in conjunction with the systems described herein are aqueous inkjet inks containing (i) a solvent including water and optionally a cosolvent, (ii) a polymeric resin that can be negatively charged (the ink can include a small amount of a pH-raising substance to ensure that the polymer is negatively charged), and (iii) at least one colorant.

Prior to jetting, the ink typically has (i) a viscosity of 2 to 25 centipoise (cP) at at least one temperature in the range of 20-60° C.; and (ii) a surface tension of no more than 50 millinewtons/m at at least one temperature in the range of 20-60° C. The colorant may contain a pigment, preferably a nanopigment, e.g., having an average particle size (d ₅₀ ) of no more than 120 nm.

In some embodiments, the polymeric resin primarily or exclusively includes one or more negatively chargeable polymers, such as polyanionic polymers. "Negatively chargeable polymer" or "negatively chargeable polymer resin" means a polymer or polymeric resin from which at least one proton can be readily removed to yield a negative charge; as used herein, the term refers to an inherent property of the polymer and thus encompasses the polymer in an environment in which these protons have been removed, as well as the polymer in an environment in which these protons have not been removed.

In contrast, the term "negatively charged polymer resin" refers to a resin in an environment from which one or more of these protons has been removed.

Examples of negatively chargeable groups are carboxylic acid groups (—COOH), including acrylic acid groups (—CH ₂ ═CH—COOH) and methacrylic acid groups (—CH ₂ ═C(CH ₃ )—COOH); and sulfonic acid groups (—SO ₃ H). These groups may be covalently bound to the polymeric backbone; for example, styrene-acrylic acid copolymer resins have carboxylic acid functional groups that readily lose a proton to yield a negatively charged moiety. Many polymers suitable for use in embodiments of the present invention will be negatively charged when dissolved in water; other polymers may require the presence of a compound that raises the pH to become negatively charged. Typically, a polymer will have many of these negatively chargeable groups on a single polymer molecule and is therefore referred to as a polyanionic polymer.

Examples of polyanionic polymers include, for example, polysulfonates, such as polyvinylsulfonate; poly(styrenesulfonates), such as poly(sodium styrenesulfonate) (PSS); sulfonated poly(tetrafluoroethylene); polysulfates, such as polyvinylsulfate; polycarboxylates, such as acrylic acid polymers and salts thereof (e.g., ammonium, potassium, sodium, etc.), such as those available from BASF and DSM Resins; methacrylic acid polymers and salts thereof (e.g., copolymers of methacrylic acid and ethyl acrylate); carboxymethylcellulose; carboxylic acid derivatives of carboxymethyl amylose and various other polymers; polyanionic peptides and proteins, such as homopolymers and copolymers of acidic amino acids (e.g., glutamic acid, aspartic acid, or combinations thereof), homopolymers and copolymers of uronic acids (e.g., mannuronic acid, galacturonic acid, and guluronic acid), and salts thereof; alginic acid and salts thereof; hyaluronic acid and salts thereof; gelatin; carrageenan; polyphosphates, such as phosphoric acid derivatives of various polymers; polyphosphonates, such as polyvinylphosphonate; and copolymers, salts, derivatives, and combinations of the foregoing, and the like. In some embodiments, the polymeric resin comprises an acrylic acid-based polymer, i.e., a polymer or copolymer formed from acrylic acid or an acrylic acid derivative (e.g., methacrylic acid or an acrylate), such as polyacrylic acid or an acrylic acid-styrene copolymer. Nominally, the polymeric resin can be, or comprises, an acrylic acid-styrene copolymer. In some embodiments, the polymeric resin primarily or exclusively comprises an acrylic acid-based polymer selected from acrylic acid polymers and acrylic acid-styrene copolymers. In some cases, the polymeric resin is at least partially water-soluble; in some cases, the polymeric resin is water-dispersible and can be provided in the form of an emulsion or colloid.

There are many organic polymeric resins, and many of those identified as being useful for preparing ink compositions are commercially available and known to those skilled in the art. Generally speaking, these polymers (whether established ink resins or less typical for this field) serve to capture (e.g., encapsulate) or otherwise immobilize or associate the relevant colorants via physical, covalent, or ionic interactions, ultimately also enabling adhesion of the ink image to the printed substrate. These polymeric resins are therefore often referred to as binders. Some polymers may alternatively or additionally act as dispersants, thereby maintaining the ink formulation in the desired suspension or emulsion form. While the exact function of an organic polymeric resin may vary in the context of a particular formulation, or may include more than one function, it is used herein to refer to a predominant binder function, which typically accounts for the presence of most of these polymers in the final ink composition.

Water-dispersible thermoplastic resins include, but are not limited to, linear and branched acrylic polymers, acrylic styrene copolymers, styrene polymers, polyesters, copolyesters, polyethers, polyamides or polyesteramides, polyurethanes, and polyamines. These polymers are typically supplied with basic information regarding their average molecular weight (MW), their glass transition ( _Tg ) or softening temperature, their minimum film forming temperature (MFFT), their hardness, their ability to contribute to the gloss of the final printed ink, or their ability to adhere to the printed substrate or resist abrasion. Some polymers can be defined by their reactivity or by the density of their functional groups, the acid number or hydroxyl number being but examples of such limitations.

Ink formulators are familiar with these parameters and will readily appreciate that the selection of a suitable organic polymeric resin can depend on the intended purpose. For example, if the printed image is intended to be matte or if the ink image is to be further laminated or coated with a varnish that will independently provide the desired optical effect, then the adhesive need not provide a high gloss. Such gloss-related information is generally provided by the supplier but can be independently measured, for example, using a glossmeter at a fixed angle of incidence. Using a Micro-gloss (BYK-Gardner, Germany) single-angle glossmeter at 75°, prints exhibiting a gloss of 65-70 or above are considered glossy, whereas prints with a gloss below 65 are considered matte.

Similarly, the presence of a laminate or varnish can reduce the need to select a polymer that provides good to excellent abrasion resistance. Each supplier can use a variation of the standard resistance test ASTM D5264 to assess this property. In the absence of a coating protection and if the printed product is expected or likely to be subjected to rubbing, polymers with higher abrasion resistance should be preferred. It will be understood that the hardness of a polymer may be related to its ability to form an ink film image that can have the desired abrasion resistance (if required). Therefore, for some purposes, resins with good to high hardness are preferred.

This coating can also improve the adhesion of ink images to certain base materials. Understandably, the degree of adhesion that polymer will need to have will depend on predetermined base material. Some organic resins provide good adhesion to the coated or synthesized base materials that typically have relatively low surface roughness. Other resins have excellent abilities and can additionally or alternatively adhere to base materials with higher surface roughness, such as most of the uncoated printing base materials. Resin can also be selected to be suitable for the printing base materials commonly used in the commercial printing field based on cellulose, cellulose-free, based on plastics or based on metal. Advantageously (but not necessarily), suitable organic polymer resins should be suitable for the possible base materials of a wide range. The ability of this adhesion to selected base materials, if not provided by resin manufacturers, can be easily evaluated using the tape adhesion test to the predetermined printing base material.

Acid number (also referred to as acid value or neutralization number) is related to the mass (in milligrams) of potassium hydroxide (KOH) required to neutralize one gram of a chemical. Acid number is typically provided by the manufacturer, but can be easily measured according to its definition. Resins with high acid numbers are expected to produce less stable ink films (water fastness) when exposed to water and should therefore be avoided when the intended use of the printed matter may expose them to conditions that would be harmful to films containing these resins. Resins suitable for the present invention generally have an acid number of less than 220, less than 180, less than 150, less than 120, less than 100, or less than 90. In some embodiments, the organic polymeric resin has an acid number between 20 and 220, between 60 and 100, and particularly between 70 and 90.

In some embodiments, and particularly for embodiments employing polyester or polyester-based resins, the acid number may be 15 or less, 12 or less, 10 or less, 7 or less, 5 or less, or 2.5 or less. These polymeric resins may have an acid number between 0 and 15, between 0 and 10, and particularly between 0 and 5 or between 1 and 5.

Polymeric resins (such as acrylic acid-based polymers) can be negatively charged at alkaline pH values. Therefore, in some embodiments, the polymeric resin has a negative charge at a pH value of more than 7.5, more than 8, or more than 9. In addition, the solubility or dispersibility of the polymeric resin in water may be affected by the pH value. Therefore, in some embodiments, the formulation includes compounds that increase the pH value. Examples of these compounds are diethylamine, monoethanolamine, and 2-amino-2-methylpropanol. These compounds that increase the pH value, when included in the ink, are generally included in small amounts, such as about 1 wt.% of the formulation and generally not more than about 2 wt.% of the formulation.

Some resins are characterized by a hydroxyl number (also known as a hydroxyl value), which is a measure of the free hydroxyl content in a compound and is therefore typically used for ester linkage. This value (if not provided) can be determined by acetylation of the free hydroxyl groups of the compound of interest, as well as standard titration and calculation, as known in the art. Because other functional groups (such as primary or secondary amines) can participate in the chemical reactions used to assess this number, they can also be reported as hydroxyl groups. Therefore, the hydroxyl number can be used to assess the more general reactivity/functionality of a resin. It is expressed in milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl content in one gram of the chemical, corrected for carboxyl hydroxyl groups by titrating an unacetylated sample of the same substance. Some suitable resins (e.g., polyesters or polyester-based resins, including copolyester resins, linear and branched polyesters, or copolyester resins) may have a hydroxyl number between 15 and 60, between 25 and 55, or between 35 and 50.

In addition, suitable resins will preferably meet the thermorheological conditions described in more detail in the following sections. Once again, these rheological patterns can be adapted to the intended purpose. For example, when used with a printing substrate having a low surface roughness, the viscosity of the dried ink film at high temperature can be higher than the viscosity of the dried ink film intended to be adhered to a substrate having a higher surface roughness. In other words, an ink composition suitable for an uncoated substrate will require a relatively low viscosity of the dried film, which will allow the image to better follow the contours of the surface topography, thereby increasing the contact area and thus better adhesion. Generally speaking, when used in the printing process described herein, the selection of the organic polymeric (binder) resin to be included in the ink formulation of the present invention can further take into account the temperature at which the ink is ejected at the imaging station, the type of inkjet head (such as continuous inkjet (CIJ) or drop-on-demand (DOD)), its temperature when it contacts the intermediate transfer member, its temperature when it is dried on the transfer member, and its temperature when it is transferred from the transfer member to the intended printing substrate at the imprint station.

In some embodiments, suitable organic polymeric resins include acrylic polymers, acrylic styrene copolymers, styrene polymers, and polyesters. In other embodiments, the resin is one or more polymers selected from the group consisting of: 90, 530, 537E, 538, 631, 1158, 1180, 1680E, 1908, 1925, 2038, 2157, Eco 2189, LMV 7051, 8055, 8060, 8064, 8067, all acrylic-based polymers available from BASF; 7150, XP2607, and F-37070, all polyester-based polymers available from Evonik, Bayer, and Synthesia International, respectively; and any other commercially available chemical equivalents thereof. For convenience, data regarding these materials are reproduced below as provided by their respective suppliers. The dispersant Joncryl HPD 296 is included for comparative purposes.

The molecular weight of the resin need not be limited. In some embodiments, the resin has an average molecular weight of at least 1,200, at least 1,500, at least 2,000, or at least 5,000, at least 25,000, at least 50,000, at least 100,000, at least 150,000, or at least 200,000. In some embodiments, suitable organic polymeric resins and in particular polyesters or polyester-based resins (including copolyester resins, linear and branched polyesters or copolyester resins) may have an average molecular weight of at most 12,000, at most 10,000, at most 8,000, at most 6,000, at most 5,000, at most 4,000, at most 3,500, or at most 3,000.

Example

The following examples illustrate inkjet ink formulations according to the teachings of the present invention.

Substances and chemicals were purchased from various manufacturers, including:

Although the following formulations were prepared using substances supplied by the respective manufacturers under the indicated trademarks, these ingredients may be replaced by other commercially available compounds having similar chemical formulas.

For simplicity, the formulations presented below use carbon black as the pigment to produce a black (K) ink. Some of the following formulations were prepared with a cyan pigment (e.g., PV Fast Blue BG), a magenta pigment (e.g., Jet Magenta DMQ), or a yellow pigment (e.g., Hansa Brilliant Yellow 5GX03) at the same concentrations as indicated for the black pigment, resulting in cyan (C), magenta (M), and yellow (Y) inks, respectively. Results obtained with black ink will be referred to by their appropriate example number. If the results are presented or discussed with reference to a color other than black, a one-letter code indicating the specific color will be used. For example, 'Example 4C' would correspond to a cyan version of the formulation disclosed in Example 4. Similarly, some of the following formulations were prepared using dyes in place of pigments. Dyes tested in conjunction with the ink formulations of the present invention include Red 485 and Blue 636. Alternative colorants (pigments or dyes) that may be suitable for these formulations are readily known to those skilled in the art of formulating printing inks.

Polymeric binder resins are commercially available in many forms, including various solid forms, such as amorphous or crystalline structures. The resins are available in the form of free-flowing powders and pellets. The resins are available in liquid forms such as emulsions or dispersions, typically blended with suitable additives. In addition, each of these commercially available resins may have a specific characteristic particle size distribution.

As is known, the viscosity of a composition can be affected by the types of ingredients it contains, their respective inherent rheological properties, and their concentrations. As those skilled in the art of ink formulation understand, particle size can also affect viscosity to some extent, as the same amount of material with a lower particle size provides a higher surface area available for interactions that can alter some of its original physicochemical properties. However, particle size is merely one parameter and, as such, need not be limiting.

In some embodiments, the resin has an average particle size _d50 of 3 micrometers (μm) or less, or less than 1 μm, or less than 0.5 μm, or less than 400 nm, or less than 300 nm, or less than 200 nm, or less than 100 nm.

The general procedure for preparing inks according to embodiments of the present invention for resins available in liquid form is as follows: First, a pigment or dye concentrate is prepared by mixing distilled water, at least a portion (typically about 20%) of the polymeric resin or dispersant (if used), and the colorant, and grinding using any suitable equipment according to procedures known in the art until a suitable particle size is achieved. If a dispersant is used in this step, it is typically used in a 1:1 ratio with the colorant. Alternatively, commercially available nanopigments (e.g., having a _d50 of less than 1 μm) or submicron to low micron range resins (e.g., having a _d50 of less than 5 μm) can readily be used to prepare the ink formulations of the present invention. If a pH-raising compound is used, it can be included in this step. The grinding process is monitored based on particle size measurement using a dynamic light scattering particle size analyzer (ZETASIZER ^™ Nano-S, ZEN1600, available from Malvern Instruments, England) using standard operating procedures. Unless stated otherwise, the process was stopped when the average particle size ( _d50 ) reached approximately 70 nm.

The remaining materials are then added to the pigment concentrate and mixed. After mixing, the ink is filtered through a 0.5 μm filter. The viscosity of the ink thus obtained is measured at 25°C using a viscometer (DV II + Pro, available from Brookfield) and is typically in the range of about 2 cP to 25 cP. The surface tension is measured using a standard liquid tensiometer (EasyDyne, available from Krüss) and is generally in the range of about 20 to 30 mN/m. The resulting pH value is typically in the range of 6.5 to 10.5, and more typically in the range of 7.0 to 9.0.

In other embodiments, when polymeric resin is available in solid form, alternative procedures can be used. Typically, the resin is fully ground together with a dispersant and then mixed with any other ingredients of the colorant and ink formulation. For the preparation of some formulations disclosed herein, a slurry consisting of 37.5g 7150 (Evonik, flakes), 93.75g DispexUltra PX4575 (BASF, also known as 4575) and 131.25ml distilled water was ground for 48 hours at 5°C in a ball mill (Atrittor OS, Union Process, USA), which has a ceramic inner surface and 0.8mm zirconium oxide beads. The ground slurry is then mixed with a concentrate of the colorant in the presence of a dispersant (e.g., black pigment is dispersed in a standard grinding device in the presence of a dispersant). In an embodiment of the present invention, the pigment is dispersed with identical DispexUltra PX 4575 so that the final ratio of the resin to the dispersant is 1:0.35. As needed, softeners were added to the resin-pigment mixture and water was added if necessary to achieve the final formulation. The fully formulated ink was then mixed and filtered through a 0.5 μm filter. Viscosity, surface tension, and pH were measured as described above.

A partial list of ink formulations prepared by these exemplary methods is presented below, with the amount of each ingredient indicated as a weight percent (wt.%) of the stock material, whether a liquid or solid chemical or a diluted solution, dispersion, or emulsion containing the substance of interest, with the weight percent being relative to the total weight of the final formulation. Concentrated forms having a solids content of at least 45% (see Example 42) and about 80% (see Examples 40 and 41) are also provided. Those skilled in the art will readily appreciate that other preparation methods may be equally suitable.

Example 1

Example 2

Example 3

Example 4

Example 5

Example 6

Example 7

Example 8

Example 9

Example 10

Example 11

Example 12

Example 13

Example 14

Example 15

Example 16

Example 17

Example 18

Example 19

Example 20

Example 21

Example 22

Example 23

Example 24

Example 25

Example 26

Example 27

Example 28

Example 29

Example 30

Example 31

Example 32

Example 33

Example 34

Example 35

Example 36

Example 37

Example 38

Example 39

Example 40

Example 41

Example 42

A variety of commercially available nanopigments can be used in the ink formulations of the present invention. These include pigment formulations such as CAB-O-352K, available from Cabot; Hostajet Magenta E5B-PT and Hostajet Black O-PT, both available from Clariant; and pigments that require a post-dispersion process, such as Cromophtal Jet Magenta DMQ and Irgalite Blue GLO, both available from BASF.

Those skilled in the art can easily recognize that various known colorants and colorant preparations can be used for ink of the present invention or inkjet ink preparation.In one embodiment, these pigments and pigment preparations can comprise inkjet colorant and inkjet colorant preparation, or are basically made up of inkjet colorant and inkjet colorant preparation.

Alternatively or in addition, the colorant can be a dye. Examples of dyes suitable for use in the ink formulations of the present invention include: Duasyn Yellow 3GF-SF liquid, Duasyn Acid Yellow XX-SF, Duasyn Red 3B-SF liquid, Duasynjet Cyan FRL-SF liquid (all manufactured by Clariant International Ltd.); Basovit Yellow 133, Fastusol Yellow 30L, Basacid Red 495, Basacid Red 510 liquid, Basacid Blue 762 liquid, Basacid Black X34 liquid, Basacid Black X38 liquid, Basacid Black X40 liquid (all manufactured by BASF).

Those skilled in the art can select various suitable dispersants, including commercially available products. These dispersants can include high molecular weight polyurethane or aminocarbamate (e.g., 198), styrene-acrylic acid copolymer (e.g., HPD296), modified polyacrylate polymers (e.g., 4560, 4580), acrylic block copolymers prepared by controlled radical polymerization (e.g., 4585, 7702), sulfosuccinates (e.g., Triton GR, Empimin OT), acetylenic diols (e.g., Surfynol CT), ammonium salts of carboxylic acids (e.g., 7571), alkyl alcohol ammonium salts of carboxylic acids (e.g., 5071), aliphatic polyethers with acid groups (e.g., EFKA 6230), or ethoxylated nonionic fatty alcohols (e.g., N-OC 30).

In some embodiments, except polymeric resin, it may be necessary to include colorant, water and optional cosolvent, a small amount of surfactant, for example the 0.5-1.5wt.% of printing ink. These surfactants can serve as wetting agent and/or leveling agent. In some embodiments, surfactant is a nonionic surfactant. The wetting agent and/or leveling agent of exemplary types include silicone, modified organopolysiloxane and polyether-modified siloxane (for example from BYK -307, -333, 345, -346, -347, -348 or -349; Or from BASF's Hydropalat WE 3240). Fluorosurfactant can also be suitable, such as Capstone FS-10, Capstone FS-22, Capstone FS-31, Capstone FS-65 (DuPont), Hydropalat WE 3370 and Hydropalat WE 3500. Hydrocarbon surfactants can be used as wetting agents and/or leveling agents, such as block copolymers (eg Hydropalat WE 3110, WE 3130), sulfosuccinates (eg Hydropalat WE 3475) and acetylene glycol derivatives (eg Hydropalat WE 3240).

In some embodiments, it may be desirable to include at least one wetting agent. Examples of water-miscible wetting agents are glycols such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, oligo- or polyethylene glycols, oligo- or polypropylene glycols, glycerol, and glycol ethers; nitrogen-containing solvents such as N-methylpyrrolidone and 2-pyrrolidone; and sulfur-containing solvents such as dimethyl sulfoxide (DMSO); and mixtures thereof.

Various other or additional dispersants, humectants, and wetting and leveling agents that may be suitable for use in the ink formulations of the present invention will be readily apparent to those of ordinary skill in the art.

Thermo-rheological properties

The present process, in which these ink formulations may be used, may include heating the ink film or image during transport on the surface of the image transfer member to evaporate the aqueous vehicle from the ink image. Heating may also facilitate reducing the viscosity of the ink to achieve transfer conditions from the ITM to the substrate. The ink image may be heated to a temperature that renders the residual film of organic polymeric resin and colorant remaining after evaporation of the aqueous vehicle tacky (e.g., by softening the resin).

Immediately prior to transfer to the printing substrate, the residual ink film on the surface of the image transfer member may be dry or substantially dry. The film comprises the resin and colorant from the ink formulation. The residual film may further comprise a small amount of one or more surfactants or dispersants, which are typically water-soluble at the pH of the ink (i.e., prior to jetting).

The residual ink film may become tacky before it reaches the impression cylinder. In this case, the film can be cooled at the impression station by contact with the substrate and exposure to the environment. The already tacky ink film may immediately adhere to the substrate onto which it is impressed under pressure, and the cooling of the film may be sufficient to reduce the film's adhesion to the image transfer surface to the point where the film can be cleanly peeled off from the image transfer member without compromising adhesion to the substrate.

Viscosity (or tackiness) can be defined as the property of a substance that enables it to adhere to a surface after direct contact under slight pressure. Viscous properties can be highly correlated with various viscoelastic properties of the substance (polymeric resin or ink solids). Both viscous and elastic properties appear to be important; the viscous properties at least partially characterize the ability of a substance to spread out on a surface and form intimate contact, while the elastic properties at least partially characterize the adhesive strength of the substance. These and other thermorheological properties are rate- and temperature-dependent.

Some of the significant difficulties associated with low-temperature operation of imaging stations have been described above. Simply put, while lower temperatures at the imaging station can reduce nozzle clogging caused by ink vehicle evaporation and extend the life of the blanket, which is subsequently subjected to less stringent operating conditions, lowering the temperature of the blanket portion below the station to below the temperature at which the vehicle evaporates creates its own problems. While the ink needs to remain jettable from the printhead nozzles, the deposited droplets need to readily adhere to the outer surface of the ITM at a viscosity that is lower than that achievable with the same formulation at higher temperatures, largely due to the much lower evaporation rate. These ink droplets need to be able to form a skin once on the ITM surface, as long as the ink vehicle has not completely evaporated, to prevent disturbances in the droplet position and shape on the blanket. If adhesion needs to be promoted by treating the blanket with a conditioning solution prior to inkjet and imaging, the type of interaction with the optional conditioning agent may also be affected by temperature.

The resulting ink droplets are then heated, dried, and transferred to a printing substrate to produce a residual ink film. These residual films, obtained from the ink formulations of the present invention and which can be processed substantially as described herein, can have several notable characteristics, including:

Ultra-thin film thickness (typically around 0.5 μm for a single layer);

Temperature gradient: Temperature varies with position along the Z-axis (thickness direction) of the film;

A substantially or completely dry membrane, including the interface between the ITM and its proximal membrane surface; and

• The conditioning layer of the present invention, which can advantageously be stripped of the ITM to form the major portion of the residual film.

In addition, the process may require that the residual film of the present invention has sufficient fluidity at low temperatures (e.g., below 140°C, below 120°C, below 100°C, or below 90°C) to facilitate transfer from the ITM to the printed substrate. The process may also require that the residual film of the present invention has sufficiently low fluidity at relatively low temperatures (e.g., below 55°C) so that the residual film is "permanently" adhered to the printed substrate at these temperatures without a tendency to adhere to other surfaces.

By appropriately selecting the thermorheological characteristics of the residual film, the cooling effect can be to increase the cohesive force of the residual film, thereby causing it to exceed its adhesive force to the transfer member, so that all or substantially all of the residual film is separated from the image transfer member and is imprinted onto the substrate in the form of a film. In this way, it is possible to ensure that the residual film is imprinted onto the substrate without significantly changing the area covered by the film or its thickness.

The present inventors have found that the dried or substantially dried ink residue or ink film may advantageously have a first dynamic viscosity in the range of 10 ⁶ cP to 5.10 ⁷ cP at at least one first temperature in the first range of 60° C. to 87.5° C. The present inventors have found that this first dynamic viscosity may be associated with efficient low temperature transfer of the dried ink film from the ITM to various fibrous (e.g., coated and uncoated paper and paperboard) and non-fibrous (e.g., various types of plastics) substrates at extremely low transfer pressures.

The present inventors have further discovered that the ink residual film can advantageously have a second dynamic viscosity of at least 7·10 ⁷ cP at at least one second temperature in a second temperature range of 50° C. to 55° C. At these viscosities and temperatures, the residual film can exhibit sufficient fluidity to achieve good contact with the surface of the printed substrate, while the surface tack is low enough to prevent sticking to other surfaces when the ink film is cooled.

Thermo-rheological measurements

Viscosity temperature step sweeps were performed using a Thermo Scientific HAAKE Mars III rheometer with a TM-PE-P Peltier plate temperature module and a P20Ti L measurement geometry or a PP20 disposable (spindle).

The sample was tested with a substantially dry ink residue of 1 mm in a 2 cm diameter module. Prior to thermorheological evaluation, the sample was dried in an oven at an operating temperature of 100°C to 110°C until the weight of the sample remained substantially constant, typically reaching the expected weight based on non-volatile matter. Typically, the sample was dried overnight (i.e., at least 12 and up to 18 hours) under 10 mbar vacuum (absolute) and found to be visibly and tactilely dry before introduction into the rheometer module.

A certain volume of sample (pellet) is inserted into a 2 cm diameter module and softened by gentle heating (typically at 80°C for less than one minute) to ensure adequate contact between the surface of the sample and the spindle. The sample volume is then reduced to the desired size by lowering the spindle to reduce the sample volume to the desired depth of 1 mm.

In the temperature ramp mode, the sample temperature is stabilized at low temperature (typically 45-55°C, in particular about 50°C) for 120 seconds and then ramped to high temperature (typically 150-190°C, in particular about 180°C).

The measurements were performed under two schemes, referred to as the "long method" and the "short method". In the long method, the temperature was set to increase at a rate of about 0.08°C/second to about 110°C, while at higher temperatures (above 110°C) it was performed at a rate of about 0.04°C/second. The viscosity measurements were performed at time intervals of about 10°C, with 20 repeated measurements at each time point. The sample temperature was then allowed to stabilize at the high temperature for 120 seconds and then gradually decreased to the low temperature at the same rate. The oscillating temperature sweep was performed at a frequency of 1 Hz (Ω = 6.2832 rad/second) at a stress of 1-500 Pa up to 110°C and 5 Pa between 110°C and 180°C.

In the short method, the temperature was set to increase at a rate of about 0.11°C/second to about 110°C, and at a rate of about 0.07°C/second at higher temperatures. Viscosity measurements were taken at intervals of about 90 seconds up to about 110°C, with ten replicates at each time point. The sample temperature was then increased to the target high temperature over 940 seconds, at which point the viscosity was measured for the final time, without being ramped back down to the lower temperature. The spindle was set to oscillate at a frequency of 1 Hz.

The rheometer used in this experimental setup provides up to ten replicate measurements at a given temperature and temperatures up to 100°C, with the rheometer arranging the mass of each measurement, thereby training the operator to manually select (if necessary) representative values within the linear viscoelastic range (typically at least the last three measurements in a series performed at a given temperature). Above 110°C, samples are generally viscous and generally have sufficient linear viscoelastic range to allow automated measurement.

For samples where repeatability proves to be an issue, sample "memory" may be reduced or essentially erased by oscillating at 120°C with a shear force of 10Pa (0.5Hz) for 60 seconds (20 points); oscillating under the same conditions between 120°C and 50°C for 600 seconds; and oscillating at 120°C with a shear force of 10Pa (0.5Hz) for 60 seconds (20 points).

It will be appreciated by those skilled in the art that a sample material that does not adhere sufficiently to the spindle and/or platform may exhibit results that do not reflect or adequately reflect the inherent thermorheological properties of the sample material. Those skilled in the art will readily appreciate that in such cases, viscosity must be assessed by other available means appropriate to the characteristics of the sample material.

For example, a melt flow indexer can be used to determine the melt flow index (MFI) of a dried ink formulation. These devices monitor the mass (in grams) that flows through a capillary tube of a specific diameter and length over a preset time period (e.g., ten minutes) due to the application of pressure via a specified weight at a specified temperature. Generally speaking, the melt flow rate, as measured by this method, is inversely proportional to the viscosity of the melt under the test conditions. Standards exist for these measurements. Such devices can be used to characterize the fluidity of a substance as a function of several discrete temperatures.

In this specification and in the claims that follow, the values of dynamic viscosity are determined quantitatively by the "short method" described above.

Experiments were performed in which the oscillation frequency was reduced from 1.0 Hz to 0.1 Hz, and/or in which the temperature increase rate was increased from about 2° C./min to about 10° C./min. These modifications did not significantly affect the observed thermorheological properties of the samples.

Thermo-rheological results

FIG4A provides temperature sweep curves showing the dynamic viscosity as a function of temperature for the residual films of various ink formulations, including the ink formulations of the present invention. The twenty curves provided correspond to dried ink residues of the ink formulations of Examples 1-4, 7-15, 18, 20, 23, 24, 28, 31, and 33, with the viscosity axis spanning from 1.10 ⁶ cP to 1.10 ⁹ cP. The dried ink residues were obtained using the drying procedure provided below.

As described above, it may be advantageous for the dried ink residue to exhibit a dynamic viscosity of at least 7.10 ⁷ cP at a temperature range of 50° C. to 55° C. The dried ink residue may advantageously exhibit a dynamic viscosity of at least 8.10 ⁷ cP, at least 9.10 ⁷ cP, at least 1.10 ⁸ cP, or at least 1.5.10 ⁸ cP. At these viscosities and temperatures, the residual film may exhibit good adhesion to the printed substrate while having a sufficiently low surface tack to prevent adhesion to other surfaces.

The first rectangular window (W1) plotted in FIG4A shows the viscosity suitable for dried ink residues within the temperature sweep range of 60° C. to about 87.5° C. The inventors have found that residual films exhibiting good transfer characteristics at low temperatures generally exhibit temperature sweep viscosity curves that fall within this window.

4A shows a suitable viscosity for dried ink residue at 50° C. to 55° C. over the temperature sweep range. Of course, the dried ink residue may advantageously have a viscosity exceeding the upper limit of the curve, i.e., 1·10 ⁹ cP.

In the ink film construction of the present invention and in the ink formulation of the present invention, the temperature sweep curve of the dynamic viscosity as a function of temperature for the residual film may belong to two windows (W1, W2).

Figure 4B provides a temperature sweep plot of dynamic viscosity as a function of temperature for dried ink residues of ink formulations of the present invention containing various polyester resins. The provided curves correspond to dried ink residues of ink formulations of Examples 34-39, with the viscosity axis spanning from ^1.10⁷ cP to ^1.10⁸ cP to magnify the region of interest. The dried ink residues were obtained using the drying procedure provided below.

In the ink film constructions of the present invention and in the ink formulations of the present invention, the temperature sweep curve of the dynamic viscosity as a function of temperature for a residual film containing a polyester-based resin may fall into two windows (W1, W2), both of which are shown in truncated form in FIG. 4B .

This is more clearly demonstrated using Figure 5, which provides temperature sweep curves of dynamic viscosity as a function of temperature for representative dried ink residues from various ink formulations, some of which are provided in Figures 4A and 4B. Near the top left-hand corner of the figure, the temperature sweep of Residue #16 (Formulation #16 of Example 16) passes through W2 at a viscosity of approximately ^1.109 cP. Above 55°C, the viscosity of Residue #16 decreases monotonically. However, the slope (or negative slope) is far from sufficient to allow the thermorheological curve of Residue #16 to pass through W1. Similarly, the temperature sweep of Residue #19 (from Example 19) appears to pass through W2 at a viscosity above ^1.109 cP. Above 55°C, the viscosity of Residue #19 decreases more sharply than that of Residue #16. However, the slope is still insufficient to allow the thermorheological curve of Residue #19 to pass through W1. However, both residue #16 and residue #19 pass through W' (not shown), which is a widened, enlarged version of W1, where the window extends to 100° C., 105° C., or 110° C., and upwards to 7.10 ⁷ cP, 1.10 ⁸ cP, 2.10 ⁸ cP, or 3.10 ⁸ cP. This region of W' is of interest and can be exploited with the systems, processes, and ink formulations disclosed herein.

The temperature of Residue #2 (from the inventive ink formulation provided in Example 2) sweeps through W2 with a viscosity close to 1·10 ⁹ cP, and the viscosity decreases monotonically above 55° C. However, in contrast to the thermorheological behavior exhibited by the previous examples, the slope is clearly sufficient for the thermorheological curve of Residue #2 to pass through W1.

The temperature sweep of Residue #34 (from the inventive ink formulation provided in Example 34) passes through W2 at a viscosity of approximately 7·10 ⁷ cP, and the viscosity decreases monotonically above 55° C. However, the slope is low for Residue #2 and Residue #19.

Referring now to Residue #8 (from the inventive ink formulation provided in Example 8), the temperature sweep passes through W2 at a viscosity close to 2·10 ⁸ cP. Above 55°C, the viscosity decreases monotonically with a slope similar to Residue #2. The temperature sweep passes through the central region of W2.

Similar to Residue #8, the temperature scan of Residue #7 (from the inventive ink formulation provided in Example 7) passed through W2 at a viscosity of approximately 2.10 ⁸ cP. Above 55°C, the viscosity dropped sharply, causing the scan to pass through W1 near the bottom left-hand angle, resulting in a viscosity of 1.10 ⁶ cP at approximately 70°C.

The slope of the temperature sweep for Residue #15 (from the ink formulation provided in Example 15) is similar to that of Residue #7, however the residue has sufficiently high fluidity at low temperatures that the temperature sweep falls outside the boundary of W1 and W2.

The temperature sweep of residue #14 (from the ink formulation provided in Example 14) passed through W1 but failed to produce the necessary viscosity for a dried ink residue according to the present invention at the lower temperatures of 50-55°C.

Figure 6 provides temperature sweep plots of dynamic viscosity as a function of temperature for representative dried ink residues of an inventive ink formulation and dried ink residues of several commercially available inkjet inks. The dried ink residues of inventive ink formulations 2, 7, and 8 are those described above with reference to Figure 5; residue #35 was obtained by drying the inventive ink formulation provided in Example 35. The commercially available inkjet inks are black inks from Canon, Epson, HP, and Toyo and are labeled accordingly.

It is evident from these curves and the viscosity values that the dried ink residues of various prior art ink formulations exhibit no or essentially no flow properties across the entire measured temperature range. The peaks observed at very high viscosities in some of the curves for the prior art formulations appear to have no physical significance. Notably, within the temperature range of 60°C to 87.5°C, all prior art film residues exhibit minimum viscosities exceeding 1.10 ¹⁰ cP, exceeding the upper limit of W2, 5.10 ⁷ cP, by more than two and a half orders of magnitude.

In practice, the inventors of the present invention successfully transferred all of the inventive ink residues to a printed substrate, but were unable to transfer any of the prior art ink films to a printed substrate even after heating to above 160°C.

The transferability of ink formulations prepared as described in the previous examples to a printed substrate was assessed as follows: the formulation being tested was applied to the outer surface of a printing blanket approximately 20 cm x 30 cm in size on a hot plate preheated to a predetermined surface temperature typically between 70°C and 130°C, with temperatures between 70°C and 90°C being of particular interest. Unless otherwise specified, the surface comprised a silanol-terminated polydimethylsiloxane silicone (PDMS) release layer. A conditioning solution, typically comprising a 0.3 wt.% aqueous solution of polyethyleneimine (1:100 water-diluted PS; PEI), was manually applied to the release layer surface by wetting a Statitech 100% polyester dust-free cloth with the solution and wiping the release layer surface. The conditioning solution was then allowed to dry naturally on the heated blanket, and the temperature of the release layer was monitored using an IR thermometer dual-wavelength laser available from Extech Instruments. Unless otherwise specified, standard transferability experiments were conducted at 90°C.

Thereafter, the ink formulation (e.g., about 1-2 ml) is applied and smoothed using a coating rod (e.g., a Mayer rod) on the surface of a heated and optionally preconditioned rubber blanket, resulting in a wet layer with a characteristic thickness of about 24 microns. The ink film thus formed is dried with hot air (at about 200° C.) until visually dry. While still hot, the dried film is transferred to the desired printing substrate, such as Condat 135 gsm coated paper, flat office printer uncoated paper, and polyester plastic foil. The substrate is placed on the surface of a metal roller weighing 1.5 kg and rolled over with the dried ink, applying a manual pressure equivalent to a force of 10 kg. The roller is rolled at a pace such that the printed substrate contacts 1 cm of dried ink in about 1 second.

The quality of the transferred image was assessed visually and assigned a score or rating from 0 to 5. A score of 0 indicates that less than 20% of the area of the dried ink film was transferred to the printed substrate, a rating of 1 indicates that between 20% and 40% of the dried ink area was transferred, a rating of 2 indicates that between 40% and 60% of the dried ink area was transferred, a rating of 3 indicates that between 60% and 80% of the dried ink area was transferred, a rating of 4 indicates between 80% and 95%, and a rating of 5 indicates that more than 95% of the dried ink area was transferred to the printed substrate. The surface of the release layer was also observed, especially if the transfer was incomplete. Two main types of incomplete transfer can be observed: (a) partial transfer, in which only a portion of the image is transferred to the printed substrate, while a complementary portion remains on the blanket; and (b) split transfer, in which the ink image transferred to the substrate and the ink remaining on the blanket at least partially overlap. The extent of transfer from the blanket was assessed by applying a scotch tape to the surface of the printing blanket and then peeling it away. The area of dried ink transferred to the tape (if any) is considered to substantially correspond to the area of untransferred ink remaining on the blanket. A score of 0 to 5 is assigned to estimate the percentage area of dried ink remaining on the blanket. A score of 5 indicates that less than 5% of the dried ink remains on the blanket, a score of 4.5 indicates that up to 10% of the ink image remains on the blanket, a score of 4 indicates that up to 20% of the ink image remains on the blanket, a score of 3 means up to 40%, a score of 2 means up to 60%, a score of 1 means up to 80%, and a score of 0 means that up to 100% of the dried ink remains on the blanket. It should be noted that if the ink formulation is only partially transferred, the sum of the area percentages on the printed substrate and on the blanket can be as high as approximately 100% ± 5-10%. However, it is possible that if there is a complete separation between the image transferred to the substrate and the image remaining on the blanket, the sum of the two values will produce a dried ink area of up to 200%. Combinations of partial transfer and partial separation are also possible and are reported accordingly. If the transferability score or assessment (transferred to the printing substrate) is at least 4.5, and preferably 5, and the untransferred ink score is at least 4.5, and preferably 5, then the ink is considered suitable for transfer from a specific blanket treated with a selected conditioning agent (if necessary) at a specific temperature. The overall transferability rating is generated by summing the two scores for transferred and untransferred ink and dividing by 10. A perfect score yields a rating of 1.0.

The percentage area on the surface can be visually assessed with sufficient certainty by a trained operator to assign the above-mentioned evaluation result. If necessary, a test image can be deposited by ejecting ink onto a blanket via a print head, thereby facilitating a more quantitative assessment of the ink transferability under the operating conditions of interest. This can be achieved, for example, by scanning the printed image at high resolution and performing image analysis on the scan using an appropriate image capture and analysis program.

Typically, the ink formulations of the present invention achieve an overall transferability rating of at least 0.9 and more typically 0.95 or 1.0.

In some embodiments, an ink formulation according to the teachings of the present invention deposited (e.g., manually or by jetting) onto a PDMS release layer heated to 90° C. and treated with PEI can transfer at least 90% of the dried ink image area, at least 95%, at least 97.5%, at least 99%, or substantially all of the image area to a coated fibrous printing substrate when dried on the release layer.

In some embodiments, an ink formulation according to the teachings of the present invention deposited on a PDMS release layer heated to 90° C. and treated with PEI can transfer at least 90% of the dried image area, or at least 95%, or at least 97.5%, or at least 99%, or substantially all of the image area to an uncoated fibrous printing substrate when dried on the release layer.

In some embodiments, an ink formulation according to the teachings of the present invention deposited on a PDMS release layer heated to 90° C. and treated with PEI can transfer at least 90% of the dried image area, or at least 95%, or at least 97.5%, or at least 99%, or substantially all of the image area to a plastic printing substrate when dried on the release layer.

In some embodiments, an ink formulation according to the teachings of the present invention deposited on a PDMS release layer heated to 90° C. and treated with PEI can be transferred to a coated fibrous printing substrate, an uncoated fibrous printing substrate, or a plastic printing substrate such that the area of the dried ink image that is not transferred to the substrate is at most 5%, at most 2.5%, at most 1%, at most 0.5%, or substantially 0%. For each formulation, transferability evaluations were performed at least three times for each transfer temperature and/or printing substrate. Between each experiment, the surface of the release layer of the blanket was cleaned with isopropyl alcohol (technical grade) and a lint-free wipe. The reported results correspond to the average of multiple replicates under the same experimental conditions.

softener

The present inventors have discovered that certain softening agents can be incorporated into the ink formulations according to the present invention. In some embodiments of the present ink formulations, the addition of these softening agents can enable the use of various resins that characteristically exhibit poor flow properties at low temperatures.

As described herein, the present inventors have developed a system and process for producing ink film constructions, and ink formulations suitable therefor, in which the transfer of a dry ink film from an intermediate transfer member to a printing substrate is performed at a low temperature, which can be between 60° C. and 140° C., depending on the duration of contact with the substrate and/or the temperature of the substrate, typically at the higher end of this range, e.g., between 100° C. and 130° C., for a printing substrate in contact with the ink film for a short duration (e.g., less than 100 milliseconds) at room temperature (approximately 23° C.), and typically at the lower end of this range, e.g., between 60° C. and 100° C., for a printing substrate in contact with the ink film on a blanket for a time sufficient to reduce the temperature gradient between the contacting surfaces (e.g., a few seconds). Other factors may influence the optimal transfer temperature, which may depend, among other things, on the printing system being used, the composition of the blanket release layer and conditioning solution (if any), the properties of the ink and substrate, their contact dwell time, the pressure applied at the imprint station, etc.

In the printing systems disclosed herein, temperatures of 40°C to 100°C or 70°C to 90°C can be used at the imaging station where the ink formulation is deposited on the transfer member. The ink needs to be sufficiently fixed to the surface of the release layer at this stage. Furthermore, the ink formulation needs to be jettable at the printhead temperature, and more specifically, at the nozzle plate temperature. Typically, the printhead operates at temperatures between about 20°C and about 50°C, or between about 25°C and about 40°C.

While this low-temperature dry transfer offers various advantages (e.g., energy savings), it also presents significant disadvantages. For example, one obvious design constraint is that the polymeric resin or adhesive needs to be softened to enable dry transfer at these temperatures. Consequently, various mechanical properties of the printed ink image or ink film construction may be compromised. Abrasion resistance may be poor, and the printed image may become tacky even in near-ambient conditions (e.g., in a vehicle exposed to sunlight).

Dry transfer can require a significant increase in viscosity (Δη) between the initial transfer temperature of the ink film and the temperature of the film after contacting a relatively cold print substrate. The inventors have discovered that low-temperature dry transfer processes can require a similarly substantial Δη. Moreover, the inventors have further discovered that because the initial transfer temperature of the film is now lowered relative to higher-temperature dry transfer processes, the ΔT available for achieving transfer can be significantly reduced. In some cases, this has been found to cause the ink film to separate during transfer and/or result in excessive softness or flowability of the printed ink film product.

Resins with relatively high _Tg can exhibit high viscosities at these low temperatures, substantially preventing proper transfer to the printing substrate. As explained below, this problem is particularly relevant when the ink film has a low overall thickness (e.g., 2.5 μm or less), resulting in rapid cooling within the film thickness and shortening the time window during which the ink film viscosity is suitable for transfer. Thus, while these high _Tg resins have favorable mechanical properties, they may be highly unsuitable for use in low-temperature dry transfer processes, let alone thin ink films according to the teachings of the present invention.

The present inventors have discovered that softening agents can be incorporated into ink formulations containing various high _Tg resins that would otherwise be suitable for low temperature ink film transfer. In these inventive formulations, the resins can be sufficiently hard _to inhibit or largely inhibit inkjet printhead clogging even when the blanket temperature near the printhead is 40°C-50°C or slightly higher.

Softeners can significantly improve the flowability of neat resins, as well as the flowability of dried ink solids in the presence of dry ink residue. Softeners can be selected and added in suitable proportions to achieve a significant reduction in the viscosity of high-Tg resins and/or dried ink solids containing them. Between 60°C and 110°C, the viscosity can be reduced by at least 20%, at least 35%, at least 50%, at least 75%, or at least 100% relative to the same high-Tg resin or dried ink solids without the softener. In many cases, the viscosity reduction is at least 150%, at least 200%, or at least 300%.

The softening agent selected may have a sufficiently low vapor pressure such that after the ink has been evaporated and heated, the softening agent remains or remains largely in the dry ink film. Thus, at 150° C., the vapor pressure of the at least one softening agent may be at most 1.0 kPa, at most 0.8 kPa, at most 0.7 kPa, at most 0.6 kPa, or at most 0.5 kPa. However, in some embodiments, the inventors have found that it is advantageous for the vapor pressure to be even lower: at most 0.40 kPa, at most 0.35 kPa, at most 0.25 kPa, at most 0.20 kPa, at most 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, at most 0.06 kPa, or at most 0.05 kPa.

For example, these low vapor pressures can significantly stabilize various properties of the ink formulation and, perhaps most notably, enable the dried ink film to retain or largely retain its transferable properties even during continued heating of the film (e.g., on an ITM) for at least one hour, at least six hours, at least 24 hours, or at least three days.

The present inventors have discovered that the introduction of these softeners into the ink formulations of the present invention may impair various mechanical properties of the printed image. Abrasion resistance may be reduced, and the printed image may become tacky at near-ambient temperatures of 35°C-45°C. However, the present inventors have further discovered that these detrimental tendencies can be significantly mitigated by at least one of the following:

Limiting the weight ratio of softener to high _Tg resin to at most 1, at most 0.50, at most 0.40, at most 0.30, at most 0.20, at most 0.17, at most 0.15, at most 0.12, or at most 0.10;

limiting the weight ratio of softener to total resin content to at most 0.25, at most 0.20, at most 0.15, at most 0.12, at most 0.10, at most 0.08, or at most 0.06;

• Limit the weight ratio of softener to total solids content to at most 0.20, at most 0.15, at most 0.12, at most 0.10, at most 0.08, at most 0.06, at most 0.05, or at most 0.04.

Typically, the weight ratio of the softener to the high _Tg resin is at least 0.02, at least 0.04, at least 0.06, at least 0.08, at least 0.10, at least 0.12, at least 0.15, or at least 0.20. The weight ratio of the softener to the total resin content can be at least 0.01, at least 0.02, at least 0.03, at least 0.04, at least 0.06, at least 0.08, at least 0.10, or at least 0.12. The weight ratio of the softener to the total solids content can be at least 0.01, at least 0.02, at least 0.03, at least 0.04, at least 0.06, at least 0.08, or at least 0.10.

These amounts of softener are still substantial and might be expected to more severely affect the mechanical properties of the printed image. Despite this, the inventors have surprisingly discovered that various affected mechanical properties of the printed image can still be maintained within suitable ranges. Without wishing to be bound by theory, the inventors believe that this phenomenon may be at least partially attributable to the uniquely thin ink films obtained using the systems and processes described herein. These thin ink films may have an average film thickness of at most 2.5 micrometers (μm) or at most 2.0 μm, and more typically at most 1.8 μm, at most 1.6 μm, at most 1.4 μm, at most 1.2 μm, at most 1.0 μm, at most 0.8 μm, or at most 0.6 μm.

While one of ordinary skill in the art can identify chemical families or groups that may be particularly suitable for a particular resin chemistry, the present inventors have discovered specific chemical families whose members can act as effective softeners for a variety of organic polymeric resins. These families include: low vapor pressure esters, more specifically sorbitan, polyoxyethylene sorbitan, and polysorbates; and low vapor pressure ethers, more specifically polyethylene glycol. Exemplary compounds are polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, sorbitan monolaurate, sorbitan stearate, sorbitan tristearate, sorbitan monooleate, sorbitan trioleate, and medium to high MW PEGs that are solid at room temperature. These materials are commercially available in the following forms, for example: 20, 40, 60, 65, 80, 85, 20, 60, 65, 80, 85, PEG 8,000 and PEG 20,000.

These softeners may be particularly suitable for resins selected from the group consisting of acrylic polymers, acrylic styrene copolymers, styrene polymers, and polyesters. Exemplary compounds are commercially available in the following forms: 90, 530, 537E, 538, 631, 1158, 1180, 1680E, 1908, 1925, 2038, 2157, Eco 2189, LMV 7051, 8055, 8060, 8064, 8067, all acrylic-based polymers available from BASF; 7150, XP2607, and F-37070, all polyester-based polymers available from Evonik, Bayer, and Synthesia International, respectively; and any other chemical equivalents thereof.

The molecular weight of the softening agents used in conjunction with the present invention can have a molecular weight of at least 300, at least 500, at least 600, at least 700, or at least 800; the molecular weight can be at most 20,000, at most 10,000, at most 5,000, at most 3,000, at most 2,500, at most 2,000, at most 1,750, at most 1,500, or at most 1,400.

The solubility of the softener in water may be at least 0.1% (weight:weight of water), and more typically, at least 0.2%, at least 0.3%, or at least 0.5%.

In this application, the term softening agent is used to refer to a compound that is capable of significantly lowering the glass transition temperature of the resin to which it is added. An agent is considered to have a significant effect if, when mixed 1:1 on a solids weight basis with the resin of interest, _{the Tg} of the mixture is lowered by at least 5°C, at least 10°C, at least 15°C, at least 20°C, or at least 25°C relative to the original Tg of the resin.

For example, FIG7A shows a plurality of temperature sweep curves of the first dynamic viscosity as a function of temperature for dried ink residues of five ink formulations using a first thermoplastic resin (1680E) and a first softener (polyethylene glycol (PEG) 20,000) with the same components and different ratios of softeners. The dried residues were obtained from ink formulations corresponding to Examples 5, 6, 7, 25, and 26.

FIG7B provides temperature sweep curves of the second batch dynamic viscosity as a function of temperature for dried ink residues of five ink formulations having the same components and different ratios of softeners using a second thermoplastic resin (i.e., 8060) and a second softener (i.e., PEG 8,000). The dried residues were obtained from ink formulations corresponding to Examples 16, 17, 21, 22, and 23.

Figures 8A-8D show temperature sweep curves of dynamic viscosity as a function of temperature for residual films of ink formulations containing different softeners and different concentrations of those agents. For ease of comparison, the pigment and polymeric resin were the same black pigment and 2038, and the ratio was maintained at 1:4 for all samples. Figure 8A provides the thermorheological behavior of the dried residue of ink formulations containing 20 (Examples 27-28); Figure 8B shows the sweep curves observed for formulations containing 40 (Examples 29-31); Figure 8C for formulations containing 60 (Examples 9-10); and Figure 8D for formulations containing 80 (Examples 32-33).

In some embodiments, the softening agent may have a vapor pressure of at most 0.40 kPa, at most 0.35 kPa, at most 0.25 kPa, at most 0.20 kPa, at most 0.15 kPa, at most 0.12 kPa, at most 0.10 kPa, at most 0.08 kPa, at most 0.06 kPa, or at most 0.05 kPa at 150°C.

In some embodiments, the softener may be stable at temperatures up to at least 170°C, at least 185°C, at least 200°C, or at least 220°C.

In some embodiments, the weight ratio of softener to resin in the formulation can be at least 0.05:1, at least 0.10:1, at least 0.15:1, at least 0.2:1, at least 0.25:1, at least 0.35:1, at least 0.4:1, at least 0.5:1, at least 0.6:1, at least 0.75:1, at least 1:1, at least 1.25:1, at least 1.5:1, at least 1.75:1, or at least 2:1.

In some embodiments, the weight ratio may be at most 3:1, at most 2.5:1, at most 2:1, at most 1.6:1, or at most 1.4:1.

Various analytical methods and apparatuses can be used to identify the various components of aqueous ink formulations and the ink films produced therefrom, and these will be readily apparent to those skilled in the art. It may be advantageous to separate the resin and any other polymeric material from the aqueous phase containing the softening agent. The softening agent can be identified using HPLC, MS, or other known analytical methods and apparatuses. The softening agent can be extracted from the resin and polymer by various means. In one approach, the resin can be swollen using a suitable solvent (e.g., ISOPAR) that can help release the softening agent. Nanofiltration may also be appropriate in some cases.

Colorants

As used herein in the specification and in the claims section that follows, the term "colorant" or "coloring agent" refers to a substance that is or will be considered a colorant in the printing art. The colorant may include at least one pigment. Alternatively or in addition, the colorant may include at least one dye.

As used herein in the specification and in the claims above, the term "pigment" refers to a solid colorant, typically finely divided. Pigments can have an organic and/or inorganic composition. Typically, pigments are insoluble in the medium or media in which they are incorporated and are generally physically and chemically unaffected by the medium or media in which they are incorporated. Pigments can be colored, fluorescent, metallic, magnetic, transparent or opaque. Pigments can change their appearance by selective absorption, interference and/or scattering of light. They are typically incorporated by being dispersed in a variety of systems and can maintain their crystalline or particle properties throughout the coloring process.

As used herein in the specification and in the claims section that follows, the term "dye" refers to at least one colored substance that is soluble in or goes into solution during application and imparts color by selective absorption of light.

While a wide range of average particle sizes ( _d50 ) or particle size distributions (PSD) may be suitable for the pigments utilized in various embodiments of the inks of the present invention, the inventors believe that optimal results are achieved when the pigment's _d50 is in the range of 20 nm to 300 nm (e.g., up to 120 nm, up to 100 nm, or 40-80 nm). Thus, the pigment can be a nanopigment; the particle size of the nanopigment can depend on the type of pigment and the size reduction method used in preparing the pigment. Pigments of various particle sizes used to produce different colors can be used in the same print. Some pigments of these particle sizes are commercially available and can be used as is in embodiments of the present invention; in other cases, the pigment can be ground to the appropriate size. It will be understood that, generally, the pigment is dispersed (or at least partially dissolved) in the solvent along with the polymeric resin, or can be first dispersed in the polymeric resin (e.g., by kneading) to obtain colored resin particles, which are then mixed with the solvent.

The concentration of the at least one colorant in the ink formulation can be at least 2%, at least 3%, at least 4%, at least 6%, at least 8%, at least 10%, at least 15%, at least 20%, or at least 22% by weight when the formulation is substantially dry. Typically, the concentration of the at least one colorant in the ink film is at most 40%, at most 35%, at most 30%, or at most 25%. More typically, the dry ink residue can contain 2-30%, 3-25%, or 4-25% of the at least one colorant.

In some applications, particularly when it is desired to have ultra-thin ink films laminated to a print substrate, the weight ratio of polymeric resin to colorant can be at most 10:1, at most 7:1, at most 5:1, at most 3:1, at most 2.5:1, at most 2:1, or at most 1.7:1.

Figure 9 provides temperature sweep curves of dynamic viscosity as a function of temperature for dried ink residues of four ink formulations having different colorants (C, M, Y, K) but otherwise the same formulation composition. The black formulation is as disclosed in Example 4.

Those skilled in the art will appreciate that the formulations of the present invention can be modified in a fairly predictable manner to achieve desired formulation properties, and in particular thermorheological properties. To this end, a large number of exemplary formulations and their thermorheological curves have been provided. In addition, these curves have been arranged in the figures to provide guidance on the effect of the resin-to-pigment ratio on thermorheological behavior. Figures 7A and 7B demonstrate the effect of the softener-to-resin ratio on thermorheological behavior for two different thermoplastic resins and two different softeners. A higher softener-to-resin ratio is generally associated with a lower viscosity. Relatively hard resins suitable for low-temperature transfer can be prepared by softening agents. Figures 8A-8D demonstrate the effect of different softeners in combination with different softener-to-resin ratios while keeping other formulation parameters constant on thermorheological properties. From the similarity of the curves in Figure 9, it is clear that the colorant plays a thermorheological role, but this role is generally not very important.

First, the "high temperature" viscosity (related to W1) provides a general indication of the film's transfer properties, which is important in transferring the film from the release layer of the ITM. The maximum viscosity value associated with this physical property can be represented by the top line or area of W1.

Secondly, the "low temperature" viscosity (related to W2 at 50-55°C) provides a general indication of how the film will behave on a printed substrate. The minimum viscosity value associated with this physical property can be represented by the bottom of W2.

For the drying of inks in thermorheological testing of dried ink samples, the present inventors have used various rigorous procedures and operating conditions to ensure that the ink residues achieve sufficient levels to enable comparative testing between samples and to achieve good repeatability of the thermorheological results of dried ink residues produced by the same ink formulation.

The inventors have discovered that some of these stringent procedures and operating conditions can be relaxed without significantly affecting thermorheological repeatability, such that the following definition of ink residue drying can be utilized: As used in this specification and in the claims section that follows, the term "substantially dry" and the like with respect to ink residue refers to an ink residue obtained by drying a particular ink that preferably contains no more solvents and other volatile compounds than a "standard" layer of the particular ink having an initial thickness of 1 mm, after the layer has been dried in an oven at 100° C. and under a vacuum of 10 mbar (absolute) for 12 hours. In the case of inks that prove difficult to dry, the depth of vacuum can be increased to 5 mbar. In the case of inks that prove particularly difficult to dry, the ink residue can be allowed to exhibit a loss on drying (LOD) % of up to 1% or up to 2% below the LOD % exhibited by the "standard" layer.

Similarly, an ink formulation that is dried to form a "substantially dry" ink residue is referred to as "substantially dry."

In some embodiments, the ink formulation is free of or substantially free of wax. Typically, the ink formulation contains less than 30 wt.% wax, less than 20 wt.% wax, less than 15 wt.% wax, less than 10 wt.% wax, less than 7 wt.% wax, less than 5 wt.% wax, less than 3 wt.% wax, less than 2 wt.% wax, or less than 1 wt.% wax. In other embodiments, wax is included in the ink formulation to impart greater abrasion resistance in the printed ink. These waxes can be natural or synthetic, such as esters or long-chain alkanes (paraffin waxes) based on fatty acids and fatty alcohols, or mixtures thereof. In these cases, the formulation can include, for example, 0.1-10 wt.% wax, for example, up to 0.1, 0.3, 0.5, 0.7, 1.0, 1.5, 2, 3, 4, 6, 8, or 10 wt.% wax. The wax can be incorporated into the formulation in the form of an aqueous dispersion of small wax particles, for example, with an average size of 10 microns or less, preferably with an average size of 1 μm or less.

In some embodiments, the ink formulation is free or substantially free of oils, such as mineral oils and vegetable oils (e.g., linseed oil and soybean oil). Typically, the ink formulation contains at most 20 wt.%, at most 12 wt.%, at most 8 wt.%, at most 5 wt.%, at most 3 wt.%, at most 1 wt.%, at most 0.5 wt.%, or at most 0.1 wt.% (by weight) of one or more oils, cross-linked fatty acids, or fatty acid derivatives produced upon air drying.

In some embodiments, the ink formulation is free or substantially free of glycerol. Typically, the ink formulation contains at most 10%, at most 8%, at most 6%, at most 4%, at most 2%, at most 1%, at most 0.5%, or at most 0.2% (by weight) glycerol.

In some embodiments, the ink formulation is free of or substantially free of one or more salts, including salts used to coagulate or precipitate the ink on the transfer member or substrate (e.g., calcium chloride). Typically, the ink formulation contains at most 8 wt.%, at most 5 wt.%, at most 3 wt.%, at most 1 wt.%, at most 0.5 wt.%, at most 0.1 wt.%, or substantially 0 wt.% of one or more salts. These salts may be referred to herein as "precipitants," and it should be understood that when a formulation is stated to not include salts or to contain salts in an amount less than a certain weight percentage, this does not refer to salts that may form between the polymers of the polymeric resin and the pH adjuster (e.g., an alcohol amine), or that may be present in the polymeric resin itself if the polymeric resin is provided in salt form. As discussed above, it is currently believed that the presence of negative charges in the polymeric resin is beneficial to the printing process.

In some embodiments, the ink formulation is free of or substantially free of inorganic particles, such as silica particles, titanium oxide particles, or aluminum oxide particles, containing less than 2 wt.%, less than 1 wt.%, less than 0.1 wt.%, or substantially no inorganic particles. "Silica particles" means fumed silica, silica flakes, silica colloids, and the like. Specific examples of these silica particles include those available from DuPont Company under the following names: AM-30, CL, HS-30; and those available from Nyacol Nanotechnologies Company under the following names: NexSil ^™ 12, NexSil ^™ 20, NexSil ^™ 8, NexSil ^™ 85. In the context of this application, the term "silica particles" does not include colorants.

Ink film structure

In the ink film construction of the present invention, the ink dots can be substantially laminated onto the top surface of the printing substrate. As described herein, the dot morphology can be determined or largely determined prior to the transfer operation, and the dots are transferred to the substrate as a unitary unit. This unitary unit can be substantially free of solvent, such that no material of any type can penetrate from the blanket transfer member into or between the fibers of the substrate. The continuous dots, which may primarily contain an organic polymeric resin and a colorant, adhere to the top surface of the fibrous printing substrate or form a laminated layer on the top surface of the fibrous printing substrate.

Printing tests using the previously disclosed ink compositions demonstrated good transfer to various and different paper and plastic substrates, as will be illustrated in some of the following figures.

Figures 10A-F show magnified images of two-dimensional (Figures 10A-C) and three-dimensional (Figures 10D-F) laser microscopy acquisition of ink films on mass-coated paper substrates obtained using various printing techniques, wherein: Figures 10A and 10D are magnified images of liquid electrophotography film (LEP); Figures 10B and 10E are magnified images of offset print spots; and Figures 10C and 10F are magnified images of inkjet ink film constructions according to the present invention. Laser microscopy imaging was performed using an Olympus LEXT 3D measurement laser microscope model OLS4000.

11A-F show magnified images acquired by laser microscopy in two dimensions (FIGS. 11A-C) and three dimensions (FIGS. 11D-F) of ink films on uncoated paper substrates obtained using various printing techniques, wherein: FIGs. 11A and 11D are magnified images of a liquid electrophotographic film (LEP); FIGs. 11B and 11E are magnified images of lithographic offset print spots; and FIGs. 11C and 11F are magnified images of inkjet ink film constructions according to the present invention.

The ink dots in the ink dot constructions of the present invention can exhibit consistently good shape properties (e.g., roundness, edge roughness, etc.) that are largely independent of the specific local topographical features of the substrate and largely independent of the type of printing substrate (coated or uncoated printing substrate, plastic printing substrate, etc.).

In contrast, the quality of ink dots in various known printing technologies, and in particular in direct aqueous inkjet technology, can vary significantly depending on the type of printed substrate and on the specific local topographical features of the substrate. It should be readily understood that, for example, when an ink droplet is jetted onto a particularly flat local contour with a relatively uniform substrate surface (such as a wide fiber), the resulting ink dot can exhibit significantly better shape characteristics relative to other or average ink dots disposed elsewhere on the substrate.

As best seen in Figures 11D-11F, in these prior art ink and substrate configurations, the inkjet ink droplets have penetrated the surface of the paper. This penetration can be a characteristic of various printing techniques using uncoated or commodity coated paper, where the paper can absorb ink carrier solvents and pigments within the matrix of the paper fibers.

In contrast to prior art ink constructions, the inkjet ink film constructions of the present invention can be characterized by well-defined individual ink films that are generally disposed over and adhered to coated (FIGS. 10C, 10F) and uncoated (FIGS. 11C, 11F) fibrous substrates.

An inkjet single drop ink film (or single ink dot) construction of the present invention was produced using the present invention systems and methods described herein using ink formulation Example 29 according to the present invention.

Point Perimeter Representation

The perimeter of an offset ink spot and a LEP ink spot has multiple protrusions or rivulets and multiple inlets or valleys. These ink morphologies can be irregular and/or discontinuous. In contrast, an inkjet ink dot produced according to the present invention (best seen in Figures 10C and 11C) has a distinctly rounded convex shape. The perimeter of the ink film is relatively smooth, regular, continuous, and well-defined.

More specifically, the projections of the ink films of the present invention relative to the substrate surface (i.e., projections from a top view) tend to be rounded convex projections that form convex sets, i.e., for every pair of points within the projection, every point on the line segment connecting those points is also within the projection. Such convex sets are illustrated in FIG15A. In stark contrast, the small streams and inlets in various prior art projections define those projections as non-convex sets, i.e., for at least one line segment within a particular projection, a portion of that line segment is located outside the projection, as illustrated in FIG15B.

It must be emphasized that an ink image can contain a very large number of individual or single ink films. For example, a 5 mm x 5 mm ink image at 600 dpi can contain over 10,000 such individual ink films. Therefore, it is possible to appropriately define the ink film construction of the present invention statistically: at least 10%, at least 20%, or at least 30%, and more typically at least 50%, at least 70%, or at least 90% of the individual ink dots (selected at random) or their projections can be convex sets.

It must be further emphasized that ink images may not have fragile boundaries, especially when those boundaries are viewed at high magnification. Therefore, it may be appropriate to relax the definition of a convex set, whereby non-convex surfaces (streams or inlets) having a radial length L _r of up to 3,000 nm, up to 1,500 nm, up to 1,000 nm, up to 700 nm, up to 500 nm, up to 300 nm, or up to 200 nm (as shown in FIG. 15C ) are ignored, excluded, or "smoothed," whereby the ink film or ink film projection is considered a convex set. The radial length L _r is measured by drawing a radial line L from the center point C of the ink film image through a particular stream or inlet. The radial length L _r is the distance between the actual edge of the stream or inlet and the smooth projection _{P s} of the ink image, which does not have that stream or inlet and matches the outline of the ink film image.

Relatively speaking, it may be appropriate to relax the definition of a convex set, whereby non-convex surfaces (small flows or inlets) having a radial length of up to 15%, up to 10% and more typically up to 5%, up to 3%, up to 2% or up to 1% of the film/drop/spot diameter or the average diameter are ignored, excluded or "smoothed" (as above), whereby the ink film or ink film projection is considered to be a convex set.

The perimeter of each prior art ink dot or film may typically have multiple protrusions or small streams and multiple inlets or indentations. These ink morphologies can be irregular and/or discontinuous. In sharp contrast, the inkjet ink dots produced according to the present invention typically have a distinctly rounded, convex, circular shape. The perimeter of the ink dot of the present invention can be relatively smooth, regular, continuous, and well-defined. Ink dot roundness, convexity, and edge roughness are structural parameters used to evaluate or characterize its shape or optical appearance.

By comparing the magnified images of the prior art ink morphologies of Figures 10A and 10B with the inventive ink dot configuration of Figure 10C , or by comparing the magnified images of the prior art ink morphologies of Figures 11A and 11B with the inventive ink dot configuration of Figure 11C , it can be readily observed that the appearance of the inventive ink dot is significantly different from these prior art ink morphologies. What is readily observable to the human eye can be quantified using image processing techniques. Following a description of the image acquisition method, various characterizations of the ink morphologies are described below.

Collection method

(1) For each of the known printing technologies to be compared in the study, single dot, spot, or film images printed on coated and uncoated paper were used, including a number of coated and uncoated fibrous substrates and various plastic printing substrates.

(2) Regarding the printing technique according to the present invention, single drop dot images were printed on coated and uncoated paper. Care was taken to select a substrate having similar characteristics to the substrate of the known ink dot configuration used in (1).

(3) Dot images were collected using an OLS4000 (Olympus) microscope. One skilled in the art would know how to adjust the microscope to achieve the necessary focus, brightness, and contrast so that image details are highly visible. These image details include dot outlines, color variations within the dot area, and the fiber structure of the substrate surface.

(4) The images were acquired using an X100 optical zoom lens with a resolution of 129 microns x 129 microns. This high resolution may be essential for obtaining fine details of the fiber structure of the dots and substrate surface.

(5) Save the image in an uncompressed format (Tiff) with a resolution of 1024×1024 pixels, because image data may be lost in a compressed format.

(6) Generally, a single dot or spot is evaluated for each printing technology. However, from a statistical point of view, it may be advantageous to obtain 15 dot images (at least) for each type of hard copy print being analyzed and manually select the 10 (at least) most representative dot images for image processing. The dot images selected should be representative with respect to dot shape, outline, and color variation within the dot area. Another method for print dot sampling, referred to as "field of view," is described below.

Point contour calculation

The dot images were loaded into the image processing software (ImageXpert). Each image was loaded in each of the red, green, and blue channels. The processing channel was selected based on the highest visibility criterion. For example, for cyan dots, the red channel typically gave the best dot feature visibility and was therefore selected for the image processing step; the green channel was typically best suited for magenta dots. Dot edge profiles were detected (automatically calculated) based on a single threshold. Using the "full screen view" mode on a 21.5" monitor, the threshold was manually selected for each image so that the calculated edge profile would best match the real and visible dot edge. Because a single image channel was processed, the threshold was a grayscale value (from 0 to 255, where a grayscale value is a colorless value).

Obtain the calculated perimeter value from image processing software (e.g., ImageXpert). This perimeter value is the sum of all distances between adjacent connected pixels at the edge of a point or blob. For example, if the XY coordinates of adjacent pixels are (x1, y1) and (x2, y2), then the distance is √[(x2-x1)²+(y2-y1)²], and the perimeter is equal to ∑{√[(xi ₊₁ - _xi )²+(yi ₊₁ - _yi )²]}.

In various embodiments of the present invention, it is necessary to measure the perimeter length of an ink dot. An alternative method for measuring perimeter length will now be described. As a first step, an image containing the ink dot is used as input to an algorithm that outputs the perimeter length. The pixel size MxN of the image can be stored in a two-element array or ordered pair, image_pixel_size. An example value for image_pixel_size is 1280,760, where M=1280 and N=760. This corresponds to 1280 pixels of the image in the horizontal axis and 760 pixels in the vertical axis. Subsequently, the image magnification ratio or scale is obtained and stored in the variable image_magnification. An example value for the variable image_magnification is 500. When comparing the perimeters between ink dots in a first image and a second image, it is mandatory that the variables image_pixel_size and image_magnification are equal for both images. It is now possible to calculate the corresponding length of one square pixel, i.e., a practical unit of length (e.g., micrometers) or the side length of a pixel. This value is stored in the variable pixel_pitch. An example of the variable pixel_pitch is 0.05 μm. The image is now converted to grayscale by methods known to the skilled artisan. One proposed method is to convert the input image (which is typically in the sRGB color space) into the L*a*b* color space. Once the image is in the Lab color space, the values of the variables a and b become zero. It is now possible to apply an edge detection operator to the image. A preferred operator is the Canny edge detection operator. However, any operator known in the art may be applied. These operators are not limited to first-order derivatives, such as the Canny operator, but are also open to second-order derivatives. In addition, combinations of operators may be used to obtain results that can be compared between operators and subsequently remove "unwanted" edges. It may be advantageous to apply a smoothing operator, such as a Gaussian blur, before applying the edge detection operator. The threshold level applied when applying the edge detection operator is such that the edge forming an endless ring is first obtained in the region between the ring containing the smallest perimeter ink dot and the ring surrounding the largest perimeter ink dot as previously described. Now, a thinning operator is performed so that the endless loop edge is essentially one pixel wide. Any pixel that is not part of the endless loop edge has its L* value reduced to zero, while any pixel that is part of the endless loop edge has its L* value reduced to 100. The endless loop edge is defined as the perimeter of the ink dot. Pixel links are defined as straight lines connecting pixels. Each pixel along the perimeter combines two pixel links: the first pixel link and the second pixel link. These two pixel links define a pixel link path within a single pixel. In this method of calculating perimeter length, each pixel is a square pixel. Therefore, each pixel link can form a line from the center of the pixel to one of eight possible nodes. Possible nodes are the corners of the pixel or the midpoint between two adjacent corners of the pixel. A node at a pixel corner is of type node_1, and a node at the midpoint between two corners is of type node_2. Therefore, there are six possible pixel link paths within a pixel. These pixel link paths can be divided into three groups: Groups A, B, and C. Each group has its own corresponding coefficients: coefficient_A, coefficient_B, and coefficient_C. The value of coefficient_A is 1, the value of coefficient_B is sqrt(2), and the value of coefficient_C is (1+sqrt(2))/2. Group A contains pixels whose pixel link paths correspond to nodes of type node_2. Group B contains pixels whose pixel link paths correspond to nodes of type node_1. Group C contains pixels whose pixel link paths correspond to nodes of type node_1 and type node_2. It is now possible to calculate the perimeter length of the pixels. The perimeter length of the pixels is calculated by summing the perimeter lengths of all pixels multiplied by their corresponding coefficients. This value is stored in the variable perimeter_pixel_length. It is now possible to calculate the actual length of the ink dot perimeter. This is done by multiplying pixel_pitch by perimeter_pixel_length.

Roundness

The dimensionless roundness factor (ER) can be defined as follows:

ER＝P ² /(4π·A)

Where P is the measured or calculated perimeter and A is the measured or calculated area within the ink film, dot or spot. For a perfectly smooth and round ink dot, ER equals 1.

The deviation from a circular, smooth shape can be expressed by the expression (ER-1). For a perfectly circular ideal ink dot, this expression is equal to zero.

The R-squared of the roundness factor may be calculated for each of the 10 most representative dot images selected for each type of printing technology and averaged into a single value.

For ink film constructions where the fibrous substrate (e.g., paper) is uncoated, or where the fibrous substrate is coated, such as a commercial coating in coated offset paper (or such coatings that enable the vehicle from conventional water-based inkjet inks to reach the paper fibers), the deviation from a round, smooth circular shape [(ER-1), hereinafter referred to as "deviation"] is undesirable for the ink dots of the present invention and will exceed zero.

In Figures 14A-2 to 14F2, exemplary magnified ink film images disposed on coated and uncoated substrates are provided for the following printers: direct inkjet: HP DeskJet 9000 (uncoated: Figure 14A-2; coated: Figure 14D-2); digital press: HP Indigo 7500 (uncoated: Figure 14B-2; coated: Figure 14E-2); and offset lithography: Ryobi 755 (uncoated: Figure 14C-2; coated: Figure 14F-2).

Figures 12A-2 through 12E-2 provide magnified views of ink films disposed on coated paper (12A-2 through 12C-2) and uncoated paper (12D-2 and 12E-2) according to the present invention. These ink film images were generally obtained according to the image acquisition method detailed above.

A quantitative analysis of the roundness deviation (ER-1) is provided below.

convexity

As previously described, prior art ink dots or films may typically have multiple protrusions or rivulets and multiple inlets or indentations. These ink morphologies can be irregular and/or discontinuous. In sharp contrast, inkjet ink films produced according to the present invention typically have a distinctly rounded, convex, circular shape. Dot convexity, or its deviation from it, is a structural parameter that can be used to evaluate or characterize its shape or optical appearance.

The image acquisition method may be substantially the same as described above.

Convexity measurement

The dot images were loaded into the image processing software (ImageXpert). Each image was loaded in each of the red, green, and blue channels. The processing channel was selected based on the highest visibility criterion. For example, for cyan dots, the red channel typically gave the best dot feature visibility and was therefore selected for the image processing step; the green channel was typically best suited for magenta dots. Dot edge profiles were detected (automatically calculated) based on a single threshold. Using the "full screen view" mode on a 21.5" monitor, the threshold was manually selected for each image so that the calculated edge profile would best match the real and visible dot edge. Because a single image channel was processed, the threshold was a grayscale value (from 0 to 255, where a grayscale value is a colorless value).

A MATLAB script was created to calculate the ratio between the area of the minimum convex shape that bounds the dot profile and the actual area of the dot.For each ink dot image, the (X,Y) point set of the dot edge profile created by ImageXpert was loaded into MATLAB.

To reduce the sensitivity of the measurement to noise, the spot edges were passed through a Savitzky-Golay filter (an image processing low-pass filter) to smooth the edge profile slightly, but without significantly changing its roughness characteristics. A window size of 5 pixels was found to be generally suitable.

Subsequently, a convex shape of minimum area is generated to constrain the smooth edge contour. The convexity ratio between the area of the convex shape (CSA) and the actual (calculated) point or film area (AA) is then calculated as follows:

CX＝AA/CSA

Deviations from this convexity ratio, or "non-convexity," are represented by the 1-CX or DC _point .

A quantitative analysis of this non-convexity is provided below.

Field of view

On both commercially available coated and uncoated fibrous substrates, the ink dots of the ink dot constructions of the present invention can exhibit consistently good shape properties (e.g., convexity, roundness, edge roughness, etc.), largely independent of the specific local topographical features of the substrate and, to some extent, independent of the type of printed substrate (coated or uncoated printing substrate, plastic printing substrate, etc.). In contrast, the quality of ink dots in various known printing technologies, and in particular in direct aqueous inkjet technology, can vary significantly depending on the type of printed substrate and on the specific local topographical features of the substrate.

However, using more robust statistical methods can better distinguish the ink dot configurations of the present invention from those of the prior art. Thus, in some embodiments of the present invention, the ink dot configuration can be characterized as a plurality of ink dots disposed on a substrate within a representative field of view. Assuming that the dot representation is obtained by image processing, the field of view contains a plurality of dot images, at least ten of which are suitable for image processing. Both the field of view and the dot images selected for analysis are preferably representative of the total population of ink dots on the substrate (e.g., in terms of dot shape).

program

A printed sample, preferably containing a high incidence of single ink dots, is manually scanned on a LEXT microscope using a x20 magnification to obtain a field containing at least 10 single dots in a single frame. Care should be taken to select a field whose ink dot quality is fairly representative of the overall ink dot quality of the printed sample.

Each dot within the selected canvas is analyzed independently. Dots "separated" by the canvas border (which can be viewed as a square geometric projection) are considered part of the canvas and analyzed. Any satellites and overlapping dots are excluded from the analysis. "Satellites" are defined as ink dots with an area less than 25% of the average dot area of the dots within the canvas for canvases with generally uniform dot size, or less than 25% of the area of the nearest neighboring dot for canvases with non-uniform dot size.

Each different ink dot is then magnified with a X100 zoom lens and image processing can be accomplished according to the procedures provided above with respect to the convexity and roundness procedures.

result

Figure 13A provides a magnified view of a field of ink dots on a commodity-coated fibrous substrate (coated, recycled Arjowiggins gloss, 170 gsm), produced using a commercially available aqueous direct inkjet printer. Figure 13B provides a magnified view of a field of ink dots on an uncoated fibrous substrate (uncoated offset Hadar Top, 170 gsm), produced using the same commercially available aqueous direct inkjet printer. While the frame of Figure 13A technically does not qualify as a "field" of ink dots, requiring at least 10 individual dots within a single frame, the frames are provided for illustrative purposes and the dots are depicted.

In FIG13A , ink image A is an appendage and is excluded from analysis. Dot B is separated by the frame border and is included in the analysis (i.e., the entire ink dot is analyzed). The tail or shadow C is considered part of the ink dot located to its left. Therefore, the field contains only six ink dots for image processing.

13B, it is apparent that only at high magnification are dots E and F distinct single dots. While several of the dots are reasonably circular and well-formed, most of the dots exhibit poor roundness and convexity, have poorly defined edges, and appear to contain multiple ink centers that are correlated or weakly correlated.

Figures 12A-1 through 12E-1 provide magnified views of fields of ink dots or films produced according to the present invention on a commodity-coated fibrous substrate (Figures 12A-1 through 12C-1) and an uncoated fibrous substrate (Figures 12D-1 and 12E-1). Printed images were prepared by jetting an ink corresponding to Example 29 onto a blanket having a release layer comprising a condensation-cured silanol-terminated polydimethylsiloxane. The blanket was heated to approximately 70°C and pretreated with a conditioning solution comprising PEI as described for the basic transferability test, which was subsequently removed and evaporated. A conventional inkjet head was used to jet black ink corresponding to Example 29 onto the treated release layer at a resolution of 600 x 1200 dpi (providing an average drop volume of 9 pL) to form ink images of varying ink coverage/dot density. The relative speed of the blanket relative to the print bar was 0.5 m/s. The ink images were dried at 200°C for up to 5 seconds and the dried images were transferred to the substrates indicated in the following table and Figures 12A-1 to 12E-3 by applying manual pressure.

Figures 12A-2 to 12E-2 provide further enlarged views of a portion of the panels of Figures 12A-1 to 12E-1, with enlarged views of ink films disposed on mass-coated paper provided in Figures 12A-2 to 12C-2, and enlarged views of ink films disposed on uncoated paper provided in Figures 12D-2 and 12E-2.

As is apparent from a comparison of these figures, the fields of ink dots from the inventive inks exhibit superior dot shape (roundness, convexity, and edge definition) and average dot shape relative to the prior art fields presented in Figures 13A and 13B. In fact, for the field of ink dots on the roughest and most challenging uncoated substrate, presented in Figure 12D-1, the inventive ink construction exhibits superior dot shape and average dot shape relative to the prior art field (Figure 13A) where the substrate is a relatively smooth coated substrate.

What is readily observable by the human eye can be quantified using the image processing techniques and field processing procedures provided above.

Table 1: Ink dot structure of the present invention - viewing field

Table 2: Prior Art Ink Dot Structure - Field of View

Substrate type ER-1 1-CX Optical uniformity (standard deviation) coated paper 0.943 0.085 4.0 Uncoated paper 3.347 0.253 19.1

These exemplary results have been confirmed on several additional fiber substrates, both commercially coated and uncoated.

For all mass-coated fibrous substrates tested, the fields of the ink dot constructions according to the present invention exhibited an average non-convexity of at most 0.05, at most 0.04, at most 0.03, at most 0.025, at most 0.020, at most 0.015, at most 0.012, at most 0.010, at most 0.009, or at most 0.008.

For all uncoated fibrous substrates tested, the fields of the ink dot constructions according to the present invention exhibited an average non-convexity of at most 0.085, at most 0.07, at most 0.06, at most 0.05, at most 0.04, at most 0.03, at most 0.025, at most 0.020, at most 0.018, or at most 0.015.

In some embodiments, the field non-convexity is at least 0.0005, at least 0.001, at least 0.002, at least 0.003, or at least about 0.004. In some cases, and particularly for uncoated fibrous substrates, the field or average non-convexity can be at least 0.05, at least 0.07, at least 0.10, at least 0.12, at least 0.15, at least 0.16, at least 0.17, or at least 0.18.

For all tested mass-coated fibrous substrates, the fields of the ink dot constructions according to the present invention exhibited an average deviation from roundness of at most 0.60, at most 0.50, at most 0.45, at most 0.40, at most 0.35, at most 0.30, at most 0.25, at most 0.20, at most 0.17, at most 0.15, at most 0.12, or at most 0.10.

For all uncoated fibrous substrates tested, the fields of the ink dot constructions according to the present invention exhibited an average deviation from roundness of at most 0.85, at most 0.7, at most 0.6, at most 0.5, at most 0.4, at most 0.35, at most 0.3, at most 0.25, at most 0.22, or at most 0.20.

In some embodiments, the average deviation from roundness is at least 0.010, at least 0.02, at least 0.03, or at least about 0.04. In some cases, the deviation from roundness can be at least 0.05, at least 0.07, at least 0.10, at least 0.12, at least 0.15, at least 0.16, at least 0.17, or at least 0.18.

While the above non-convexity and deviation from roundness values are for fields having at least 10 dots suitable for evaluation, they are further applicable to fields having at least 20, at least 50, or at least 200 such dots. Furthermore, the inventors have discovered that the differences between the non-convexity and deviation from roundness values for the ink dot constructions of the present invention and prior art ink dot constructions become even more statistically significant as the field size increases.

For plastic substrates, fields of the ink dot construction according to the present invention may exhibit an average non-convexity of at most 0.075, at most 0.06, at most 0.05, at most 0.04, at most 0.03, at most 0.025, at most 0.020, at most 0.015, at most 0.012, at most 0.010, at most 0.009, or at most 0.008; fields of the ink dot construction according to the present invention may exhibit an average deviation from roundness of at most 0.8, at most 0.7, at most 0.6, at most 0.5, at most 0.4, at most 0.35, at most 0.3, at most 0.25, at most 0.20, at most 0.18, or at most 0.15. Smooth plastics such as random polypropylene and various polyesters typically exhibit a mean deviation from roundness of at most 0.35, at most 0.3, at most 0.25, at most 0.20, at most 0.18, at most 0.15, at most 0.12, at most 0.10, at most 0.08, at most 0.06, at most 0.05, at most 0.04, or at most 0.035.

Optical uniformity

The ink film images provided in Figures 5A and 5B are not optically uniform. Generally speaking, ink film images disposed on uncoated paper are less optically uniform than corresponding ink film images disposed on coated paper.

Furthermore, it was observed that the ink dots of the present invention exhibited superior optical uniformity compared to various prior art ink morphologies. This appeared to be true for both uncoated and coated printed substrates. What is readily observable by the human eye can be quantified using image processing techniques. A method for measuring ink dot uniformity is provided below.

Optical uniformity measurement

Preferably, the statistical rule provided above is used to load the dot image into ImageXpert software.Each image is loaded into each of red, green and blue channels.The channel selected for image processing is the channel that shows the highest visible details, and these details include the color deviation in dot profile and dot area, and substrate surface fiber structure.For example, the red channel is typically most suitable for cyan point, and the green channel is typically most suitable for magenta point.

For each of the selected points, a line profile is measured across the point area, across the center of the point (preferably 3 line profiles for each of at least the 10 most representative points). Because the line profile is measured on a single channel, the grayscale value (0-255, no color value) is measured. The line profile is acquired across the center of the point and only covers the inner two-thirds of the point diameter to avoid edge effects. The standard for sampling frequency is about 8 optical measurements along the line profile (8 measured grayscale values evenly spaced along each micrometer, or 125nm+/-25nm per measurement along the line profile), which is the automatic frequency of the ImageXpert software and has been found to be suitable and robust for the task at hand.

The standard deviation (STD) of each of the line distributions is calculated, and the plurality of line distribution STDs for each type of printed image are averaged into a single value.

Figures 14A-1 through 14F-2 provide images of ink spots or dots obtained using various printing technologies, and their optical uniformity distribution. More specifically, Figures 14A-2 through 14C-2 provide images of ink dots placed on uncoated paper for the following printing technologies: HP DeskJet 9000 (Figure 14A-2); digital press: HP Indigo 7500 (Figure 14B-2); and offset press: Ryobi 755 (Figure 14C-2). Similarly, Figures 14D-2 through 14F-2 provide images of ink dots placed on commodity-coated paper for those printing technologies.

Figures 14A-1 to 14F-1 provide graphs of the relative value of (achromatic) gray as a function of position on a line passing through the center of the ink dot image for each of the ink dot images provided by Figures 14A-2 to 14C-2 (on uncoated paper) and by Figures 14D-2 to 14F-2 (on coated paper).

Figures 14A-3 to 14-F3 provide profile analysis of these dots on uncoated and coated substrates as obtained by the aforementioned state of the art printing techniques.The profile distribution is used to calculate the convexity characteristics of the printed dots.

Figures 12A-3 to 12E-3 provide graphs that plot the relative value of (colorless) grayscale as a function of position on a line passing through the center of the ink dot image for each of the ink dot images provided by Figures 12A-3 to 12C-3 (on coated paper) and Figures 12D-3 to 12E-3 (on uncoated paper), respectively. The relatively flat linear distribution of a particular ink dot image indicates high optical uniformity along the line.

The results would appear to confirm that ink dots disposed on an uncoated fibrous printing substrate exhibit poor uniformity relative to corresponding ink dots disposed on a coated fibrous printing substrate.

Furthermore, for uncoated substrates, the line profiles of the ink films of the present invention produced by the system and process of the present invention had an average STD of about 4.7, which compares favorably to the STD (19) achieved using prior art techniques. For coated substrates, the line profiles of the ink dots of the present invention produced by the system and process of the present invention had an STD of about 2 to 2.7, which compares favorably, though less significantly, to the STD (4) achieved using prior art techniques.

When comparing films or dots on coated paper, the average of each of the standard deviations (STDs) of the dot distributions of the present invention is always less than 3.5. More generally, the STDs of the dot distributions of the present invention are less than 3.2, less than 3.0, less than 2.9, or less than 2.8.

When comparing films or dots on uncoated paper, the standard deviation (STD) of the dot distributions of the present invention is always less than 6. More typically, the STD of the dot distributions of the present invention is less than 15, less than 12, less than 10, less than 8, less than 7, or less than 6.

Because, as mentioned above, ink images can contain a very large number of individual or single ink dots (at least 20, at least 100, at least 1,000, at least 10,000, or at least 100,000), it may be of interest to statistically determine that the inventive ink dot constructions are those in which at least 10%, at least 20%, or at least 30%, and in some cases, at least 50%, at least 70%, or at least 90% of the inventive ink dots (or inventive single-drop ink dots) disposed on any uncoated or coated (or mass-coated) fibrous substrate exhibit the standard deviations described above for uncoated paper and for mass-coated paper.

penetrate

In the ink film construction of the present invention, the ink dots can be substantially laminated onto the top surface of the printing substrate. As described herein, the dot morphology can be determined or largely determined prior to the transfer operation, and the dot is transferred to the substrate as a unitary unit. The unitary unit can be substantially free of solvent, such that no material of any type can penetrate from the blanket transfer member into or between the fibers of the substrate. The continuous dots, which may primarily contain an organic polymeric resin and a colorant, adhere to the top surface of the fibrous printing substrate or form a laminated layer thereon.

These continuous dots are typically produced by various inkjet technologies, such as drop-on-demand and continuous jet technologies.

Referring again to the drawings, Figures 16A and 16B provide schematic cross-sectional views of an ink film construction 300 of the present invention and a prior art inkjet ink spot or film construction 370, respectively. Referring now to Figure 16B, the inkjet ink film construction 370 includes a single drop ink spot 305 adhered to or laminated to a plurality of substrate fibers 320 in a specific continuous area of a fibrous printing substrate 350. For example, the fibrous printing substrate 350 can be an uncoated paper, such as bond paper, copy paper, or offset paper. The fibrous printing substrate 350 can also be one of various commercially coated fibrous printing substrates, such as coated offset paper.

A portion of ink spot 305 is disposed between fibers 320 below the top surface of substrate 350. Various components of the ink, including a portion of the colorant, can penetrate the top surface along with the ink carrier solvent to at least partially fill volume 380 disposed between fibers 320. As shown, a portion of the colorant can diffuse or migrate beneath fibers 320 into volume 390 disposed below fibers 320. In many cases (not shown), some of the colorant can penetrate into the fibers.

In sharp contrast, the ink film construction 300 of the present invention (provided in FIG16A ) includes a unitary continuous ink dot, such as a single ink dot 310, disposed on and fixedly adhered (or laminated) to the top surface of a plurality of substrate fibers 320 in a specific continuous region of a fibrous printing substrate 350. The adhesion or lamination can be primarily or substantially physical. The adhesion or lamination can have little or substantially no chemical bonding characteristics, or more specifically, no ionic bonding characteristics.

Ink dot 310 contains at least one colorant dispersed in an organic polymeric resin. Within a specific continuous area of fibrous substrate 350, there is at least one direction perpendicular to the top surface of printing substrate 350 (indicated by arrow 360, which is one of several directions). Ink dot 310 is positioned completely above the area in all directions perpendicular to the top surface across the entire dot area. The volume 380 between fibers 320 and the volume 390 below fibers 320 are free or substantially free of colorant, resin, and any and all components of the ink.

The degree of ink penetration into the printed substrate can be quantitatively determined using various analytical techniques, many of which will be known to those of ordinary skill in the art. Various commercial analytical laboratories can perform such quantitative determinations of penetration.

These analytical techniques include the use of various staining techniques, such as osmium tetroxide staining (see Patrick Echlin, "Handbook of Sample Preparation for Scanning Electron Microscopy and X-Ray Microanalysis" (Springer Science+Business Media, LLC 2009, pp. 140-143).

An alternative to dyeing techniques may be particularly suitable for inks containing metals such as copper. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was performed using a TOF-SIMSV spectrometer [Ion-ToF (Münster, Germany)]. This instrument provides elemental and molecular information about the uppermost layers of organic and inorganic surfaces, and offers depth profiling and imaging with nanometer-scale depth resolution, submicron lateral resolution, and chemical sensitivity of approximately 1 ppm.

The raw data of TOF-SIMS is converted into concentration and can be carried out by the carbon (C+) concentration measured by X-ray photoelectron spectroscopy (XPS) in the sample by the obtained signal standardization. Use Thermo VG Scientific SigmaProbe (England) to obtain XPS data. Obtain the small area chemical analysis of the solid surface with chemical bonding information by using micro-focusing (15 to 400 μm) monochromatic x-ray source. Obtain angular resolved information when tilting the sample and not tilting the sample. This can obtain the depth distribution with good depth resolution.

As a baseline, the atomic concentration of copper within the fibrous paper substrate was measured as a function of depth. The atomic concentration of copper was found to be essentially zero from the surface down to a depth of several micrometers. This procedure was repeated for two cyan inkjet ink film constructions of the prior art and for a cyan ink film construction of the present invention.

The atomic concentration of copper (Cu) within the ink dot and within the fibrous paper substrate as a function of approximate depth within the first prior art cyan inkjet ink film construction was measured as described above. The initial Cu measured near the top surface of the cyan-containing ink film construction was approximately 0.8 atomic %. Within a depth of approximately 100 nm, the Cu steadily decreased to approximately 0.1 atomic %. Within a depth range of approximately 100 nm to 1,000 nm, the Cu decreased from approximately 0.1 atomic % to approximately 0. Thus, it is apparent that the inkjet ink pigment has penetrated into the fibrous paper substrate, potentially to a penetration depth of at least 700 nm, at least 800 nm, or at least 900 nm.

Additional measurements of the atomic concentration of copper within the ink dot construction as a function of approximate depth within a second prior art cyan inkjet ink film construction yielded the following findings: The initial atomic concentration of copper [Cu] within the ink dot construction, measured near the top surface, was approximately 0.02 atomic %. This concentration was generally maintained to a depth of approximately 3,000 nm. [Cu] decreased very gradually to approximately 0.01 atomic % within a depth range of approximately 3,000 nm to approximately 6,000 nm. It will be apparent that this prior art construction had little or no ink film on the surface of the substrate, and pigment penetration into the substrate was significant (at least 5-6 microns).

In view of the basic properties of the inventive laminate film transfer technique described above (particularly with respect to Figures 16A and 16B) and in view of the atomic concentration of copper [Cu] measurements performed by the inventors on similar ink film constructions, it will seem apparent that the ink films of the inventive constructions are disposed substantially only on the surface of the substrate and that penetration of the pigment into the substrate is substantially negligible both in terms of penetration depth and in terms of the amount or fraction of penetration.

Film height or thickness

The instrumental measurement height (H) or thickness of the single film ink dot or spot was obtained using a measuring laser microscope (Olympus LEXT 3D, Model OLS4000). LEP specimens typically had a height or thickness in the range of 900-1150 nm; lithographic offset specimens typically had a height or thickness in the range of 750-1200 nm.

With respect to ink dots or films produced from jetted ink droplets, we have found that the maximum average on-substrate thickness of the ink dots can be calculated from the following equation:

T _AVG(MAX) = V _drop / [A _film * R _VOL ] (I)

in:

T _AVG(MAX) is the maximum average thickness on the substrate;

_Vdrop is the volume of the ejected drop, or the nominal or characteristic volume of the ejected drop (e.g., the nominal volume provided by the inkjet head manufacturer or supplier);

A _film is the measured or calculated area of the ink dot; and

R _VOL is the dimensionless ratio of the volume of the original ink to the volume of the dried ink residue generated from that ink.

For example, an ink dot deposited on a plastic printing substrate has an area of 1075 square microns. The nominal size of the jetted droplet is 10.0 ± 0.3 picoliters. R _VOL is determined experimentally by heating a container containing 20.0 ml of ink at 130°C until a dry residue is obtained. The residue has a volume of 1.8 ml. Substituting into equation (I), T _AVG(MAX) = 10 picoliters / [1075 μm ² * (20.0 / 1.8)] = 837 nm.

For generally circular ink dots, the area of the ink dot can be calculated from the ink dot diameter. Additionally, it has been found that the dimensionless ratio R _VOL is generally about 10 for a wide variety of inkjet inks.

Although the actual average thickness may be slightly less than _TAVG(MAX) for inks that penetrate the substrate, this calculation can reliably serve as an upper bound for the average thickness. Furthermore, in the case of various plastic substrates and in the case of various premium coated substrates, the maximum average on-substrate thickness may be substantially equal to the average on-substrate thickness. In the case of various commodity coated substrates, the maximum average on-substrate thickness may be close to the average on-substrate thickness, often within 100 nm, 200 nm, or 300 nm.

With respect to ink dots or films produced from jetted ink droplets, it has been found that the maximum average on-substrate thickness of the ink dots can be calculated from the following equation:

T _AVG(MAX) = [V _drop * ρ _ink * F _{n residue} ] / [A _film * ρ _film ] (II)

in:

_ρink is the specific gravity of ink;

Fn _residue is the weight of dried ink residue divided by the weight of original ink; and

_ρfilm is the specific gravity of the ink.

Typically, the ratio of _pink to _pfilm is about 1, so that equation (II) can be simplified to:

T _AVG(MAX) = [V _drops * F _{n residue} ] / A _film (III)

For a wide variety of aqueous inkjet inks, the Fn _residue is approximately equal to the weight fraction of solids in the inkjet ink.

The height of the various ink dot configurations above the substrate surface was measured using the Olympus LEXT 3D measurement laser microscope described above.

Atomic force microscopy (AFM) is another high-precision measurement technique used to measure the height and determine the thickness of ink dots on substrates. AFM measurements can be performed using commercially available equipment, such as a Park Scientific Instruments Model Autoprobe CP scanning probe microscope equipped with Proscan version 1.3 software (or more recent). The use of AFM is described extensively in the literature, for example, by Renmei Xu et al., "The Effect of Ink Jet Papers Roughness on Print Gloss and Ink Film Thickness" [Department of Paper Engineering, Chemical Engineering, and Imaging Center for Ink and Printability, Western Michigan University (Kalamazoo, MI)].

With respect to the ink film constructions of the present invention, the inventors have discovered that the thickness of the dry ink film on the substrate can be adjusted by modifying the inkjet ink formulation. To achieve lower dot thicknesses, such modifications may require at least one of the following:

Reduce the resin to pigment ratio;

Select a resin that allows for adequate film transfer even at reduced resin-to-pigment ratios;

Utilize finer pigment particles;

Reduce the absolute amount of pigment.

To obtain thicker dots, at least one of the opposing modifications may be made (eg, increasing the resin to pigment ratio).

These formulation changes may necessitate or facilitate various modifications to the process operating conditions.The present inventors have discovered that lower resin to pigment ratios may require relatively high transfer temperatures.

For a given inkjet ink formulation, increased transfer temperature can reduce ink film thickness. Increasing the pressure of the pressure roller or cylinder toward the impression cylinder during transfer of the residual film to the substrate at the impression position can also reduce ink film thickness. Furthermore, ink film thickness can be reduced by increasing the contact time between the substrate and an intermediate transfer member, which is interchangeably referred to herein as an "image transfer member" and both are abbreviated as ITMs.

Nevertheless, the actual minimum characteristic (i.e., median) thickness or average thickness of the ink films produced according to the present invention can be about 100 nm. More typically, these ink films are single drop ink films having a dot thickness, average dot thickness, or height (of the top surface of the dot) of at least 125 nm, at least 150 nm, at least 175 nm, at least 200 nm, at least 250 nm, at least 300 nm, at least 350 nm, at least 400 nm, at least 450 nm, or at least 500 nm relative to the substrate.

Using the film thickness guidelines provided above, the inventors were able to obtain film constructions of the present invention having an average thickness of at least 600 nm, at least 700 nm, at least 800 nm, at least 1,000 nm, at least 1,200 nm, or at least 1,500 nm. The characteristic thickness or average thickness of a single drop film (or single ink dot) can be at most about 2,000 nm, at most 1,800 nm, at most 1,500 nm, at most 1,200 nm, at most 1,000 nm, or at most 900 nm. More typically, the characteristic thickness or average thickness of a single drop film can be at most 800 nm, at most 700 nm, at most 650 nm, at most 600 nm, at most 500 nm, at most 450 nm, at most 400 nm, or at most 350 nm.

Using the film thickness criteria described above, the inventors were able to obtain film constructions of the present invention in which the characteristic or average thickness of the ink film can be in the range of 100 nm, 125 nm, or 150 nm to 1,800 nm, 1,500 nm, 1,200 nm, 1,000 nm, 800 nm, 700 nm, 600 nm, 550 nm, 500 nm, 450 nm, 400 nm, or 350 nm. More typically, the characteristic or average thickness of the ink film can be in the range of 175 nm, 200 nm, 225 nm, or 250 nm to 800 nm, 700 nm, 650 nm, 600 nm, 550 nm, 500 nm, 450 nm, or 400 nm. Suitable optical density and optical uniformity can be achieved using the systems, processes, and ink formulations of the present invention.

The thickness (H _point ) of a single drop of ink film or a single ink dot (schematically shown as dot 310 in FIG. 16A ) can be at most 1,800 nm, at most 1,500 nm, at most 1,200 nm, at most 1,000 nm, or at most 800 nm, and more typically, at most 650 nm, at most 600 nm, at most 550 nm, at most 500 nm, at most 450 nm, or at most 400 nm. The thickness (H _point ) of a single drop of ink dot 310 can be at least 50 nm, at least 100 nm, or at least 125 nm, and more typically, at least 150 nm, at least 175 nm, at least 200 nm, or at least 250 nm.

Aspect ratio

The present inventors have discovered that the diameter of a single ink dot in the ink film construction of the present invention can be adjusted by, inter alia, selecting an ink delivery system suitable for applying (e.g., jetting) the ink to the ITM and by adjusting the ink formulation properties (e.g., surface tension) to the requirements of the specific ink head.

Such an ink film diameter D _dot or the average dot diameter D _{dot average} on the substrate surface may be at least 10 micrometers, at least 15 μm, or at least 20 μm, and more typically at least 30 μm, at least 40 μm, at least 50 μm, at least 60 μm, or at least 75 μm. D _dot or D _{dot average} may be at most 300 micrometers, at most 250 μm, or at most 200 μm, and more typically at most 175 μm, at most 150 μm, at most 120 μm, or at most 100 μm.

Generally, _Ddot or Ddot _average may be in the range of 10-300 μm, 10-250 μm, 15-250 μm, 15-200 μm, 15-150 μm, 15-120 μm, or 15-100 μm. More typically, using currently used ink formulations and specific ink heads, _Ddot or Ddot _average may be in the range of 20-120 μm, 20-120 μm, 20-100 μm, 20-80 μm, 20-60 μm, 20-50 μm, or 25-50 μm.

Each single droplet of ink film or single ink dot is characterized by a dimensionless aspect ratio defined by:

R _{vertical and horizontal} = D _point / H _point

Where _Raspect is the aspect ratio; _Dpoint is the longest diameter of the dot; and _Hpoint is the average height of the top surface of the dot relative to the substrate.

The aspect ratio may be at least 15, at least 20, at least 25, or at least 30 and more typically at least 40, at least 50, at least 60, at least 75. In many cases, the aspect ratio may be at least 95, at least 110, or at least 120. The aspect ratio is typically 200 or less or 175 or less.

surface roughness

Using laser microscopy imaging and other techniques, the present inventors have observed that the top surfaces of the ink dots in the ink film constructions of the present invention can be characterized by low surface roughness, particularly when the substrates of those constructions have high paper (or substrate) gloss.

Without wishing to be bound by theory, the inventors believe that the relative flatness or smoothness of the ink film constructions of the present invention may be due in large part to the smoothness of the release layer on the surface of the ITM, and to the systems and processes of the present invention, wherein the revealed ink film surface substantially complements the smoothness of that surface layer, and wherein the developed ink film image may substantially or completely retain that complementary topography upon transfer to the printing substrate.

Reference is now made to FIG. 17A , which is an image of the surface of a release layer of an ITM or blanket used in accordance with the present invention. Although the surface may be nominally flat, various pits (depressions) and protrusions, typically about 1-5 μm in size, can be observed. Many of these marks have sharp, irregular features. An image of the ink dot surface produced using the blanket, provided in FIG. 17B , shows topographical features that are qualitatively very similar to those shown in FIG. 17A . The dot surface is dotted with numerous marks having sharp, irregular features that closely resemble (and are within the same size range as) the irregular marks in the blanket surface.

A smoother blanket was applied; FIG17C provides an image of the release layer of this blanket. The irregular pits of FIG17A are conspicuously absent. Interspersed across the highly smooth surface are highly circular surface defects, likely formed by air bubbles, typically having a diameter of approximately 1-2 μm. FIG17D provides an image of an ink dot surface produced using this blanket, showing topographical features that are qualitatively very similar to those shown in FIG17C. This image is virtually devoid of distinct pits, but rather possesses numerous highly circular surface defects that closely resemble the surface defects shown on the blanket surface in size and morphology.

Plastic substrate

In view of the aforementioned results as observed on various fibrous substrates, and in view of the fundamental nature of the transfer technology of the present invention, the ink dots of the present invention are expected to exhibit excellent optical and topological properties, including roundness, convexity, edge raggedness, and surface roughness, on plastic printed substrates as well.

The non-convexity or deviation from convexity of ink dots printed on various plastic printing substrates can typically be at most 0.020, at most 0.018, at most 0.016, at most 0.014, at most 0.012, or at most 0.010. At least some ink dots can exhibit a non-convexity of at most 0.008, at most 0.006, at most 0.005, at most 0.004, at most 0.0035, at most 0.0030, at most 0.0025, or at most 0.0020. On some substrates (e.g., polyester and random polypropylene substrates), a typical ink dot can exhibit a non-convexity of at most 0.006, at most 0.004, at most 0.0035, and even more typically, at most 0.0030, at most 0.0025, or at most 0.0020.

On an all-plastic substrate, a single ink dot in an ink dot construction according to the present invention may exhibit a typical deviation from roundness of at most 0.8, at most 0.7, at most 0.6, at most 0.5, at most 0.4, at most 0.35, at most 0.3, at most 0.25, at most 0.20, at most 0.18, or at most 0.15. On various smooth plastics (such as random polypropylene and various polyesters), a single ink dot may exhibit a typical deviation from roundness of at most 0.35, at most 0.3, at most 0.25, at most 0.20, at most 0.18, at most 0.15, at most 0.12, at most 0.10, at most 0.08, at most 0.06, at most 0.05, at most 0.04, or at most 0.035.

Glass transition temperature of resin

The present inventors have discovered that the softening temperature (or glass transition temperature for at least partially amorphous resins) can be a useful indicator of resin suitability when selecting resins and resin combinations for use in formulations supporting the ink film constructions of the present invention. Specifically, resins used in ink formulations (and provided in the ink films of the present invention) can have a glass transition temperature ( _Tg ) of at least 42°C, at least 44°C, at least 46°C, at least 48°C, or at least 50°C. However, these resins can be too soft, which can negatively impact the abrasion resistance of the printed image and can also be associated with image tack and flow at near-ambient temperatures (e.g., about 40°C). More significantly, these resins can cause clogging of the inkjet printhead, particularly when the blanket is heated and delivering heat to the jetting elements. Thus, more typically, the Tg can be at least 52°C, at least 54°C, at least 56°C, at least 58°C, at least 60°C, at least 65°C, at least 70°C, at least 75°C, at least 80°C, at least 85°C, at least 90°C, or at least 95°C. The glass transition temperature is typically at most 120°C, at most 110°C, at most 105°C, or at most 100°C, and in some cases, at most 95°C, at most 90°C, or at most 85°C.

More generally, from a process standpoint, the ink formulation disposed on the ITM, after becoming free or substantially free of water, any co-solvents and other evaporable materials that would evaporate under process conditions, such as pH adjusters (yielding "ink solids,""dried ink residue," etc.), and/or its resin, can have a _Tg of at least 42°C, at least 44°C, at least 46°C, at least 48°C, or at least 50°C.

Where multiple glass transition temperatures are observed, the term _Tg as used herein refers to at least one of: (i) the glass transition temperature of the primary resin (by weight), and (ii) the highest Tg of the plurality of resins.

Analyzing ink films on printed substrates

Three thin sheets of printed material (750x530 mm in B2 format) were subjected to the following procedure: After one week, the sheets were cut into 3x3 cm pieces and introduced into 300 g of a solution containing 1% 2-amino-2-methyl-1-propanol dissolved in water, a solution that is capable of fully dissolving ink images printed using various water-soluble inks. However, if the solution remained colorless, the water was separated and the same weight of the less polar solvent ethanol was introduced. Once again, if the solution remained colorless, the solvent was separated and the same weight of the less polar solvent methyl ethyl ketone was introduced. The procedure was successfully continued with the following less polar solvents: ethyl acetate, toluene, and Isopar ^™ (a synthetic mixture of isoparaffins). After stirring for 5 hours at room temperature with the most appropriate solvent, the mixture was filtered through a 5-micron filter. The filtrate containing the dissolved ink was dried using a rotary evaporator. The residue was then dissolved in 5 g of DMSO (or one of the solvents listed above) and dried in an oven at 110° C. for 12 hours to obtain the “recovered residue”.

The thermorheological behavior of the recovered residue can then be characterized (e.g., by performing a viscosity "sweep" as a function of temperature as described above) and, when available, compared to the thermorheological behavior of the dried original ink sample. The inventors have found that this procedure provides a strong correlation between the thermorheological behavior of the recovered residue and the thermorheological behavior of the dried original ink sample. The inventors believe that this correlation may be due to the increased residence time and the use of additional solvents with different polarities.

This procedure can be advantageously used to generate and thermorheologically characterize dried ink residues recovered from printed materials such as magazines and brochures.

Those skilled in the art will readily appreciate that other potentially superior procedures may be used to deink the printed substrate and produce a recovered ink residue for rheological, thermorheological, and/or chemical analysis.

Ink formulations and ink film compositions

In particular, the inkjet inks of the present invention are aqueous inks in that they contain water, typically at least 30 wt. % and more commonly about 50 wt. % or more; optionally, one or more water-miscible cosolvents; at least one colorant, dispersed or at least partially dissolved in the water and the optional cosolvent; and an organic polymeric resin binder, dispersed or at least partially dissolved in the water and the optional cosolvent.

It should be understood that acrylic acid-based polymers can be negatively charged at alkaline pH. Therefore, in some embodiments, the resin binder has a negative charge at pH 8 or higher; in some embodiments, the resin binder has a negative charge at pH 9 or higher. In addition, the solubility or dispersibility of the resin binder in water may be affected by pH. Therefore, in some embodiments, the formulation includes a compound that increases pH, non-limiting examples of which include diethylamine, monoethanolamine, and 2-amino-2-methylpropanol. These compounds, when included in the ink, are generally included in small amounts, such as about 1 wt.% of the formulation and generally not more than about 2 wt.% of the formulation. In other embodiments, the ink formulation is not supplemented with a pH regulator.

The ink film of the ink film construction of the present invention contains at least one colorant. The concentration of the at least one colorant in the ink film can be at least 2%, at least 3%, at least 4%, at least 6%, at least 8%, at least 10%, at least 15%, at least 20%, or at least 22% by weight of the complete ink formulation. Typically, the concentration of the at least one colorant in the ink film is at most 40%, at most 35%, at most 30%, or at most 25%.

More typically, the ink film may contain 2-30%, 3-25%, or 4-25% of at least one colorant.

The particle size of the pigment may depend on the type of pigment and the size reduction method used in preparing the pigment. Generally, the _d50 of the pigment particles is expected to be in the range of 20 nm to 300 nm. Pigments of various particle sizes used to produce different colors can be used in the same print.

The ink film contains at least one resin or resin binder, typically an organic polymeric resin. The concentration of the at least one resin in the ink film may be at least 10%, at least 15%, at least 20%, at least 25%, at least 35%, at least 40%, at least 50%, at least 60%, at least 70%, or at least 80% by weight.

The total concentration of colorant and resin within the ink film may be at least 10%, at least 15%, at least 20%, at least 30%, or at least 40% by weight. More typically, however, the total concentration of colorant and resin within the ink film may be at least 50%, at least 60%, at least 70%, at least 80%, or at least 85%. In many cases, the total concentration of colorant and resin within the ink film may be at least 90%, at least 95%, or at least 97% by weight of the ink film.

Nominally, the resin dispersion can be or include a polyester (including co-polyesters) or acrylic styrene copolymer (or co(ethyl acrylate methacrylate)) dispersion. The acrylic styrene copolymer from the ink formulation ultimately remains in the ink film that adheres to the printed substrate.

In one embodiment, the ink film in the ink film construction according to the present invention is free or substantially free of wax. Typically, the ink film according to the present invention contains less than 30% wax, less than 20% wax, less than 15% wax, less than 10% wax, less than 7% wax, less than 5% wax, less than 3% wax, less than 2% wax, or less than 1% wax.

In one embodiment, the ink film according to the present invention is free or substantially free of oils, such as mineral oils and vegetable oils (e.g., linseed oil and soybean oil), or various oils used in offset ink formulations. Typically, the ink film according to the present invention contains up to 20%, up to 12%, up to 8%, up to 5%, up to 3%, up to 1%, up to 0.5%, or up to 0.1% (by weight) of one or more oils, cross-linked fatty acids, or fatty acid derivatives produced upon air drying.

In one embodiment, the ink film according to the present invention is free or substantially free of one or more salts, including salts used to coagulate or precipitate the ink on the transfer member or substrate (e.g., calcium chloride). Typically, the ink film according to the present invention contains at most 8%, at most 5%, at most 4%, at most 3%, at most 1%, at most 0.5%, at most 0.3%, or at most 0.1% of one or more salts.

In one embodiment, the ink film according to the present invention is free or substantially free of one or more photoinitiators. Typically, the ink film according to the present invention contains at most 2%, at most 1%, at most 0.5%, at most 0.3%, at most 0.2%, or at most 0.1% of one or more photoinitiators.

In one embodiment, the printing substrate of the ink film construction of the present invention is free or substantially free of one or more soluble salts, including salts used or suitable for causing the ink or its components to coagulate or precipitate on the substrate (e.g., calcium chloride). In one embodiment, the printing substrate of the ink film construction of the present invention contains at most 100 mg of soluble salts, at most 50 mg of soluble salts, or at most 30 mg of soluble salts per 1 m ² of paper, and more typically at most 20 mg of soluble salts, at most 10 mg of soluble salts, at most 5 mg of soluble salts, or at most 2 mg of soluble salts.

In one embodiment, the ink film and formulation are substantially free of sugar. Typically, the concentration of sugar (by weight) in the ink of the present invention is at most 6%, at most 4%, at most 3%, at most 1%, at most 0.5%, at most 0.3% or at most 0.1%.

In one embodiment, the ink film according to the present invention is free of or substantially free of one or more primers (e.g., coagulants or viscosity builders). As will be appreciated by one of ordinary skill in the art, these primers may be sprayed onto the surface of the substrate or applied in some other manner. The primer may be applied only in the vicinity of the subsequently jetted ink droplets, or may be applied over substantially the entire printed surface of the substrate. Typically, the ink film according to the present invention contains at most 2%, at most 1%, at most 0.5%, at most 0.3%, at most 0.2%, or at most 0.1% of these primers.

It will be appreciated that such primers can chemically interact with the printed substrate, or more generally, with the components of the inkjet ink, to produce a "bound primer." Thus, in one embodiment, the ink film according to the present invention is free of, or substantially free of, one or more bound primers. Typically, the ink film according to the present invention contains at most 2%, at most 1%, at most 0.5%, at most 0.3%, at most 0.2%, or at most 0.1% of such primers.

In one embodiment, the ink film in the ink film construction according to the present invention contains at most 5%, at most 3%, at most 2%, at most 1%, or at most 0.5% (by weight) of inorganic filler particles, such as silica.

In one embodiment, the dried resin present in the ink film of the present invention may have a solubility in water of at least 3%, at least 5%, or at least 10% at at least one specific temperature within the temperature range of 20° C. to 60° C., at a pH within the range of 7.5 to 10, or within the range of 8 to 11. In alternative embodiments, the polymeric resin is not highly soluble in water (e.g., less than 3% by weight at at least one pH value within the range of 7.5 to 10), but is dispersible therein.

In one embodiment, the solubility of the recovered ink film of the present invention in water at at least one specific temperature in the temperature range of 20°C to 60°C, at a pH in the range of 8 to 10 or in the range of 8 to 11 may be at least 3%, at least 5%, or at least 10%.

Water fastness of printed images

ASTM standard F2292-03 (2008), "Standard Practice for Determining the Waterfastness of Images Produced by Ink Jet Printers Utilizing Four Different Test Methods—Drip, Spray, Submersion, and Rub," can be used to evaluate the waterfastness of ink dots and films printed on various substrates. The waterfastness of ink constructions according to the present invention can be evaluated using these three test methods: drip, spray, and immersion.

In all three tests, several of the inventive ink film constructions exhibited perfect waterfastness; no ink bleeding, smearing, or transfer was observed.

In some embodiments, the upper film surface comprises at least one PEI; a polyquaternium cationic guar, such as guar hydroxypropyltrimonium chloride and hydroxypropyl guar hydroxypropyltrimonium chloride.

In some embodiments, the upper membrane surface contains a polymer having quaternary amine groups, such as the hydrochloride salts of various primary amines.

As used herein in the specification and in the claims section that follows, the term "dye" refers to at least one colored substance that is soluble in or goes into solution during application and imparts color by selective absorption of light.

As used herein in the specification and in the claims section that follows, the term "average particle size" or " _d50 " with respect to the particle size of a pigment refers to the average particle size (by volume) as determined by a laser diffraction particle size analyzer (e.g., Mastersizer ^™ 2000 from Malvern Instruments, England) or by a dynamic light scattering particle size analyzer (e.g., Zetasizer ^™ Nano-S, ZEN1600, also from Malvern Instruments, England) using standard operating procedures.

As used herein in the specification and in the claims section that follows, the term "geometric projection" refers to an imaginary geometric configuration projected onto the printing surface of a printing substrate.

As used herein in the specification and in the claims section that follows, the term "distinct ink dot" refers to any ink dot or ink dot image that is at least partially disposed within a "geometric projection" and is neither a "satellite" nor an overlapping dot or dot image.

As used herein in the specification and in the claims section that follows, the term "average deviation" of a plurality of "different ink dots" with respect to roundness, convexity, etc., refers to the sum of the deviations of the individual different ink dots divided by the number of the individual different ink dots.

As used herein in the specification and in the claims section that follows, the terms "weight" or "weight ratio" with respect to a resin in a formulation or dried ink residue are meant to include the total resin content within the formulation or residue, including, for example, the resin "binder" and any resin dispersant.

As used herein in the specification and in the claims section that follows, the term "softener" is used generically as one skilled in the art of polymer resins would normally understand the term. Thus, for example, a substance that is added to a particular polymer resin at a 1:1 ratio by weight and achieves insignificant softening of the resin (e.g., a decrease in Tg of less than 1°C) would not be considered a "softener" with respect to that particular polymer resin.

With respect to fibrous printing substrates, those skilled in the art of printing will appreciate that coated papers used for printing can be generally divided into two groups, functionally and/or chemically: coated papers designed for use with non-inkjet printing methods (e.g., offset printing), and coated papers designed specifically for use with inkjet printing methods employing aqueous inks. As is known in the art, the former type of coated paper utilizes mineral fillers, not only to replace some of the paper fibers to reduce costs, but also to impart specific properties to the paper, such as improved printability, brightness, opacity, and smoothness. In paper coatings, minerals are used as white pigments to hide the fibers, thereby improving brightness, whiteness, opacity, and smoothness. Minerals commonly used for this purpose include kaolin, calcined clay, ground calcium carbonate, precipitated calcium carbonate, talc, gypsum, aluminum oxide, satin white, barium sulfate powder, zinc sulfide, zinc oxide, and plastic pigments (polystyrene).

Coated papers designed for use in non-inkjet printing processes have heretofore been unsuitable for use with aqueous inkjet inks, or produce printed dots or spots that may differ significantly from the printed ink film construction of the present invention.

In contrast, specialized coated papers designed for use with inkjet inks, such coated papers, may in some cases have a filler pigment layer like other types of coated papers, and may also include a layer of a highly porous mineral (typically silica) combined with a water-soluble polymer (such as polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP)) that acts as a binder, onto which the ink is printed. These coated inkjet papers are designed to quickly remove water from the printed ink, thereby facilitating the printing of ink droplets with good uniformity and edge roughness. The present invention encompasses ink droplets printed on uncoated paper as well as coated paper not designed for inkjet use, but some embodiments of the present invention are not intended to encompass ink droplets printed on specialized coated inkjet papers.

Thus, in some embodiments, the substrate is an uncoated paper. In other embodiments, the substrate is a coated paper that does not contain a water-soluble polymeric binder in the layer onto which the ink is printed.

As used herein in the specification and in the claims section that follows, the term "commodity coated fibrous printing substrate" is meant to exclude specialty and high-end coated papers, including photographic papers and coated inkjet papers.

In a typical paper coating for commercially coated fibrous printing substrates, the coating formulation can be prepared by dispersing pigments such as kaolin clay and calcium carbonate in water and then adding a binder such as a polystyrene butadiene copolymer and/or an aqueous solution of cooked starch. Other paper coating ingredients, such as rheology modifiers, biocides, lubricants, defoaming compounds, crosslinking agents, and pH adjusting additives, may also be present in the coating in small amounts.

Examples of pigments that can be used in coating formulations are kaolin, calcium carbonate (chalk), china clay, amorphous silica, silicates, barium sulfate, satin white, aluminum trihydrate, talc, titanium dioxide, and mixtures thereof. Examples of binders are starch, casein, soy protein, polyvinyl acetate, styrene butadiene latex, acrylate latex, ethylene acrylic latex, and mixtures thereof. Other ingredients that can be present in paper coatings are, for example, dispersants such as polyacrylates; lubricants such as stearates; preservatives; defoamers, which can be oil-based, such as dispersed silica in hydrocarbon oil, or water-based, such as hexylene glycol; pH adjusters such as sodium hydroxide; rheology modifiers such as sodium alginate, carboxymethyl cellulose, starch, protein, high viscosity hydroxyethyl cellulose, and alkali-soluble lattices.

As used herein in the specification and in the claims section that follows, the term "fibrous printing substrate" of the present invention is specifically meant to include:

Newsprint, including standard newsprint, telephone directory paper, machine-processed paper, and supercalendered paper;

Coated mechanical papers, including lightweight coated papers, medium weight coated papers, heavyweight coated papers, machine-processed coated papers, and film-coated offset papers;

Uncoated paper that does not contain groundwood, including offset paper and lightweight paper;

Woodfree coated papers, including standard coated fine papers, low coat weight papers, and fine art papers;

Specialized high-grade paper, including copy paper, digital printing paper, and continuous letter paper;

Cardboard and paperboard; and

·Carton board.

As used herein in the specification and in the claims section that follows, the term "fibrous printing substrate" of the present invention is specifically meant to include all five types of fibrous offset printing substrates described in ISO 12647-2.

As used herein in the specification and in the claims section that follows, the term "dispersed" with respect to a polymeric resin is meant to include partially dissolved polymeric resin.

As used herein in the specification and in the claims section that follows, the term "jettable ink formulation" and the like refers to an ink formulation suitable for repeated drop-on-demand jetting using a drop-on-demand pressure printhead.

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

It will be appreciated that, for clarity, certain features of the present invention described in the context of independent embodiments may also be provided in combination in a single embodiment. Conversely, for simplicity, various features of the present invention described in the context of a single embodiment may also be provided independently or in any suitable sub-combination.

Although the present invention has been described in conjunction with its specific embodiment, it is obvious that many substitutions, modifications and variations will be apparent to those skilled in the art. Therefore, it is intended to encompass all these substitutions, modifications and variations within the spirit and broad scope of the appended claims. All disclosures, patents and patent applications mentioned in this specification, including PCT Publication Nos. WO 2013/132418, WO 2013/132419, WO 2013/132420, WO 2013/132424, WO 2013/136220, WO 2013/132339, WO 2013/132432 and WO 2013/132438 are hereby incorporated into the specification by reference in their entirety, and the extent of their quotations is as if each single disclosure, patent and patent application specifically and individually indicate that they are incorporated herein by reference. In addition, quoting or identifying any reference in this application should not be considered as admitting that the reference can be used as prior art for the present invention.

Claims (18)

1. A water-based inkjet ink formulation, comprising: (a) Aqueous solvents; (b) at least one colorant dispersed or at least partially dissolved in the solvent; and (c) at least one organic polymeric resin dispersed in the solvent; and (d) A softener, selected to lower the glass transition temperature ( _Tg ) of the polymeric resin, wherein the ink formulation forms a dry ink residue upon drying, the ink residue having: (i) a first dynamic viscosity in the range of ^10⁶ cP to ^3.10⁸ cP in at least a portion of a first temperature range of 60°C to 110°C; and (ii) a second dynamic viscosity of at least ^6.107 cP in at least a portion of a second temperature range of 50°C to 55°C; The second dynamic viscosity at 55°C exceeds the first dynamic viscosity at 85°C; The softener has a pure vapor pressure of up to 0.40 kPa at 150°C. 2. The formulation of claim 1, wherein at least one specific resin of the organic polymeric resin has an elevated glass transition temperature (T_{_g} ) of at least 60°C. 3. The formulation of claim 2, wherein the softener is selectively and/or added in a certain amount to reduce the elevated glass transition temperature by at least 10°C. 4. The formulation of claim 1, wherein at least one of the at least one organic polymeric resins has a minimum film-forming temperature (MFFT) of at least 48°C. 5. The formulation of claim 1, wherein the first temperature range is 60°C to 100°C. 6. The formulation of claim 1, wherein the first temperature range is 60°C to 87.5°C, and the first dynamic viscosity is in the range of ^10⁶ cP to ^5.10⁷ cP in at least a portion of the first temperature range. 7. The formulation of claim 1, wherein the weight ratio of the softener to the dry ink residue is in the range of 0.10 to 0.25. 8. The formulation of claim 1, wherein the weight ratio of the softener to the dry ink residue is in the range of 0.12 to 0.20. 9. The ink formulation of claim 1, wherein the formulation has a total solids content, and wherein the first weight ratio of the softener to the total solids content is at least 0.10. 10. The formulation of claim 9, wherein the first weight ratio is at most 0.20. 11. The ink formulation of claim 1, wherein the formulation has a total resin content, and wherein the second weight ratio of the softener to the total resin content is at least 0.08. 12. The formulation of claim 11, wherein the second weight ratio is at most 0.25. 13. The ink formulation of claim 1, wherein the formulation has at least one high _Tg resin with a _Tg of 50°C or higher, and wherein the third weight ratio of the softener to the at least one high _Tg resin is at least 0.08. 14. The formulation of claim 13, wherein the third weight ratio is at most 1.0. 15. The formulation of claim 1, wherein ΔT is defined as the temperature difference between the temperature at which the dried ink residue begins to exhibit a certain degree of fluidity ( _TF ) and the baseline temperature ( _TB ): ΔT＝T _F -T _B The fluidity level is defined by the critical viscosity ( _μCR ) at which the fluidity level is achieved. Furthermore, when the baseline temperature is 50°C and the critical viscosity is ^10⁸ cP, the temperature difference is at least 3°C. 16. The formulation of claim 1, wherein the polymeric resin comprises an acrylic acid-based polymer selected from the group consisting of acrylic acid polymers and acrylic acid-styrene copolymers. 17. The formulation of claim 1, wherein the viscosity of the dried ink residue increases monotonically as the temperature decreases from 85°C to 55°C. 18. The formulation of claim 1, wherein the dry ink residue comprises at least 20% by weight of the colorant.