HK1190745A - Ink and printing process - Google Patents

Abstract

An ink comprising an encapsulated particulate solid and a liquid vehicle wherein: I) the encapsulated particulate solid comprises a particulate solid encapsulated with a cross-linked dispersant shell; and II) the ink comprises the components: a. from 0.1 to 20 parts of the encapsulated particulate solid; b. from 20 to 40 parts of glycerol; c. from 1 to 30 parts of ethylene glycol; d. from 0 to 20 parts of 2-pyrrolidone; e. from 0.01 to 3 parts of surfactant; f. from 0 to 10 parts of water-soluble polymer; g. from 0 to 20 parts of polymer particles; h. from 0 to 2 parts of biocide; i. from 20 to 75 parts of water; wherein all the parts are by weight and the sum of the components a. to i. is 100 parts.

Description

Ink and printing process

Technical Field

The present invention relates to inks, and in particular to ink jet printer inks and vessels containing such inks. The invention also relates to printing processes (in particular, single pass inkjet printing processes) using the above inks.

Background

Homes, offices, and many wide format inkjet printers use scanning printer head technology (scanning inkjet printers). Scanning inkjet printers tend to have relatively limited printing speeds. Thus, scanning inkjet printers are not well suited for high throughput commercial applications. In a scanning inkjet printer, the printer head is moved (scanned) across the substrate while the substrate is stationary. As the printer head scans across the surface of the substrate (typically across the width of the substrate), droplets of ink are ejected toward the substrate to form an image. Typically, to achieve the best resolution or highest print density, the scanning head will scan the same substrate area multiple times to cover the ink droplets. The result of the scanning operation is a relatively thin print ribbon formed on the substrate. Only after the scanning head has formed the desired print swath, the substrate is moved by the printer device (typically along the length of the substrate) so that another swath can be printed. In this way, the scanning inkjet printer slowly prints the desired image.

Single pass inkjet printers have recently been developed. Single pass inkjet printers offer higher printing speeds and allow for the need for high throughput commercial applications in the design. In single pass inkjet printing, one or more inkjet printer heads are in a fixed position and the substrate is typically printed in a single pass as it travels under the printer head. In single pass inkjet printers, the printhead is larger, typically as wide as the substrate.

Single pass inkjet printing has more stringent requirements for inkjet printing inks and colorants when compared to scanning inkjet printing. In a scanning inkjet printer, the inkjet printer head may be cleaned multiple times during single page printing of the substrate. In contrast, in a single pass printer, the head cannot be cleaned so frequently. In addition, the higher printing speeds and the larger ink jet per minute indicate that the ink has to work extremely robustly in a single pass printer mechanism. Accordingly, ink jet printing inks and colorants for single pass ink jet printers should desirably provide even higher levels of reliable operation in the printer.

More specifically, ink jet printer inks and colorants for single pass ink jet printers should desirably provide:

i) long open time (good delay) so that the ink components do not dry on the printer nozzles even when the nozzles are inactive for a period of time;

ii) high stability such that no ink components tend to flocculate, aggregate, precipitate or produce oversized particulate matter;

iii) high optical density (even in a single pass);

iv) excellent droplet formation and droplet dispersion characteristics, even in very short time scales or at high droplet ejection frequencies;

v) high reliability when the ink is ejected through the nozzle for a period of time;

vi) once printed onto the substrate, the droplets dry relatively quickly;

vii) good toxicology and the use of the lowest possible amount of volatile organic liquids;

viii) low foaming properties;

ix) good light fastness and image permanence;

x) excellent ink storage stability;

xi) clear printing on highly porous media, such as corrugated substrates.

Single pass inkjet printers typically utilize a very different substrate than home and office printers. Home printers may well use expensive substrates (such as high quality photographic paper). Photographic paper generally has a microporous structure of high whiteness, high gloss and high controlled properties, which is particularly suitable for controlled spreading and penetration of ink jet printing inks. For single pass inkjet printing, the substrate tends to be less expensive and the coating (if present) tends to be less suitable for absorbing inkjet printing inks. For these substrates, known ink jet printing inks typically tend to penetrate too deeply into the substrate, resulting in loss of optical density, wicking, and/or strike-through.

Pigment-based inks include pigment particles dispersed in the ink, however, dye-based inks include dyes dissolved in the ink. Pigment-based inks tend to have some advantages in certain applications. For example, pigment-based inks tend to have light and ozone fastness properties that are superior to those of dye-based inks.

That is, if the ink is a pigment-based ink rather than a dye-based ink, it may be even more difficult to meet many of the above requirements. For example, it is well known that in pigment-based inks, pigment particles can tend to agglomerate or flocculate over time to produce particles of excessive size that can clog or impair printing of tiny inkjet printer nozzles. Meanwhile, it is well known that pigment-based inks generally tend to flocculate if the ink includes a higher relative amount of organic liquid or strongly adsorbed surfactant. Thus, in many aspects, dye-based inks are more suitable for the high printer reliability requirements of single pass printing than pigment-based inks.

In our studies, we have found that it is quite difficult to meet many or all of the above requirements simultaneously. Some of the requirements that are particularly difficult to achieve simultaneously are high optical density, high colloidal stability of pigment-based inks, and high printer reliability.

Prior Art

PCT patent publication WO2005/080513 discloses ink jet printing inks comprising glycerol. This patent publication does not mention encapsulated pigments, single pass inkjet printing or corrugated substrates.

Disclosure of Invention

Definition of

Unless otherwise specified, word expressions such as "a" or "an" include the possibility of having more than one. For example, "an" encapsulated particulate solid also includes particulate solids that may have more than one encapsulation.

In the present invention, all parts are by weight unless otherwise specified.

Detailed description of the invention

First aspect

According to a first aspect of the present invention there is provided an ink comprising an encapsulated particulate solid and a liquid medium, wherein:

I) the encapsulated particulate solid comprises a particulate solid encapsulated with a cross-linked dispersant shell; and

II) the ink comprises the following components:

0.1 to 20 parts of an encapsulated particulate solid;

15 to 60 parts of glycerol;

1 to 30 parts of ethylene glycol;

0 to 20 parts of 2-pyrrolidone;

0.01 to 3 parts of a surfactant;

f.0 to 10 parts of a water soluble polymer;

g.0 to 20 parts of polymer microparticles;

h.0 to 2 parts of an antimicrobial agent;

from 20 to 75 parts of water;

wherein all parts are by weight and the sum of the parts of components a.to i.is 100 parts.

Meanwhile, the addition of the components a to i of 100 parts does not indicate that other ink components are not present in the ink. The ink comprises components a to i, and corresponding further ink components may also be present.

Components a and g are usually in the form of dispersions. Components e, f and h are generally solutions. The parts of components a, e, f, g and h are taken into account on a solid basis. Thus, for example, 10 parts by weight of a polymer emulsion having a solids content of 10% by weight are 1 part by weight of polymer particles. Similarly, 20 parts by weight of the encapsulated particulate solid dispersion with a solids content of 15% by weight is 3 parts by weight of encapsulated particulate solid. As another example, 1 part of a 50% (by weight) antimicrobial solution is considered 0.5 parts antimicrobial.

a.Encapsulated particulate solids

Preferably, the encapsulated particulate solid has a particle size of less than 1 micron, more preferably a diameter of 30 to 500nm, even more preferably a diameter of 50 to 300nm, and particularly preferably a diameter of 70 to 200 nm.

Preferably, the average particle diameter is the Z-average diameter. Preferably, the particle diameter is measured by, for example, laser light scattering. Suitable instruments for measurement include those sold by Malvern (Malvern) and Coulter (Coulter). The preferred apparatus is a Malvern Zetasizer^TM。

In our investigations, we have found that the encapsulated particulate solids used in the present invention provide inks with good optical density, that the encapsulated particulate solids are stable in inks with high amounts of glycerol and ethylene glycol, and that in inkjet printers and single pass inkjet printers the encapsulated particulate solids assist the inks in printing with extreme reliability. The dispersants used to prepare the encapsulated particulate solids also provide excellent rheology, droplet formation and droplet dispersion characteristics when used with glycerol and ethylene glycol. Whilst not wishing to be bound by any particular theory, it is believed that the encapsulated particulate solid, the dispersant used to prepare the encapsulated particulate solid, and the single pass printer mechanism according to the first aspect of the present invention cooperate to provide particularly satisfactory ink jetting and print performance characteristics.

Preparation of encapsulated granular solids

Preferably, the encapsulated particulate solid is prepared by a process comprising cross-linking the dispersant in the presence of the particulate solid and a liquid medium.

The amount of the encapsulated particulate solid in the ink is preferably 0.1 to 20 parts by weight, more preferably 0.1 to 15 parts by weight, further preferably 0.1 to 10 parts by weight and particularly preferably 1 to 10 parts by weight.

Granular solid

The particulate solid may be of any type without limitation. Preferably, the particulate solid is substantially insoluble in the ink. By substantially insoluble is meant a solubility in the ink of less than 1% by weight, more preferably less than 0.1% by weight. Preferably, the solubility is measured at a temperature of 25 ℃. Preferably, the solubility is measured at a pH of 8. The preferred granular solid is insoluble in a mixture comprising 18 parts ethylene glycol, 30 parts glycerol, 5 parts pyrrolidone and 46 parts water at a temperature of 25 ℃ and a pH adjusted to 8.

Preferably, the particulate solid is or comprises a colorant, more preferably the particulate solid is or comprises a pigment.

The pigment may be organic or inorganic.

Preferred particulate solids are organic pigments, for example, all types of pigments described in the third Edition of the color Index (1971), and the subsequent revisions and supplements thereto, entitled "pigments". Examples of organic pigments are azo (including disazo and condensed azo), thioindigo, indanthrone, isoindolinone, anthanthrone, anthraquinone, isoanthrone violet, trithiophenedioxazine, quinacridone, and the phthalocyanine series, especially copper phthalocyanine and its nuclear halogenated derivatives, and also lakes of acid, base and mordant dyes. Preferred organic pigments are phthalocyanines, especially copper phthalocyanine pigments, azo pigments, indanthrones and anthanthrones, quinacridones.

Preferred inorganic pigments include: metal oxides, sulfides, nitrides and carbides (e.g., titanium dioxide and silicon dioxide), metal pigments (e.g., aluminum flakes), and particularly carbon black. Carbon black is particularly preferred for these pigments.

A preferred carbon black is gas black, particularly sold by Evonik under the trade name Nipex^RTMGas black.

In the case of carbon black pigments, carbon black pigments are prepared in such a way that some of the carbon black surface has oxidized groups (e.g., carboxylic acid and/or hydroxyl groups). However, the amount of these groups is preferably not too high, if so the pigment may be dispersed into water without the aid of a dispersant (not self-dispersible).

Preferably, the pigment cannot be dispersed into the aqueous liquid medium (especially pure water) without the aid of a dispersant, i.e. the presence of a dispersant is required to aid dispersion. Preferably, the pigment is not chemically surface treated, e.g., has ionic groups (especially other than-CO) covalently bound to its surface₂H or-SO₃H）。

Preferably, the pigment is a cyan, magenta, yellow or black pigment.

More than one pigment may be used in the present invention.

For a print color ink set, the pigments are preferably carbon black, c.i. pigment blue 15:3, c.i. pigment red 122 and c.i. pigment yellow 74.

Preferably, the particulate solid has been comminuted (e.g. milled) in the presence of a liquid (preferably a liquid comprising water) and a dispersing agent prior to cross-linking. By pulverizing we mean preferably those processes which significantly reduce the particle size of the particulate solid. Examples of the pulverization method include a microfluidization method, a high-pressure homogenization method, an ultrasonication method, and a milling method (particularly, a bead milling method). Preferably, the only dispersants present during the comminution step are those cross-linking agents which subsequently cross-link to encapsulate the particulate solid. This minimizes any free (unencapsulated) dispersant. Preferably, the dispersant is present in an amount of 5 to 100 parts by weight, more preferably 10 to 80 parts by weight and particularly preferably 20 to 50 parts by weight, relative to 100 parts by weight of the particulate solid.

After the pulverization, the particulate solid preferably has a particle size of less than 1 μm, more preferably a diameter of 30 to 500nm, further preferably a diameter of 50 to 300nm and particularly preferably a diameter of 70 to 200 nm.

The average particle diameter is preferably the Z-average diameter. The particle diameter is preferably measured by, for example, laser light scattering. Suitable instruments for measurement include those sold by Malvern (Malvern) and Coulter (Coulter). The preferred apparatus is a Malvern Zetasizer^TM。

Dispersing agent

Preferably, the dispersant is a polymer.

Preferably, the number average molecular weight of the dispersant is 1000 to 1000000, more preferably 5000 to 100000 and particularly preferably 20000 to 80000. The molecular weight is preferably measured by gel permeation chromatography. Preferably, the solvent used for GPC is water, tetrahydrofuran or dimethylformamide. Preferably, the molecular weight is calibrated by known methods for polystyrene or more specifically polyethylene glycol standards.

Preferably, the polymeric dispersant is or includes a polyester, polyurethane, polyether, polystyrene, poly (meth) acrylate, or grafted and physical combinations thereof. Of these, poly (meth) acrylates are preferred.

Preferably, the polymeric dispersant is obtained or obtainable by copolymerizing at least components i) and ii):

i) 70 to 95 parts of one or more (meth) acrylate monomers each having no ionic group;

ii) 5 to 30 parts of one or more (meth) acrylate monomers each having at least one ionic group;

wherein the sum of the parts of components i) and ii) is 100 and all parts are by weight.

More preferably, the polymeric dispersant is obtained or obtainable by copolymerizing at least components i) to iii):

i) 70 to 95 parts of one or more (meth) acrylate monomers each having no ionic group;

ii) 5 to 30 parts of one or more (meth) acrylate monomers each having at least one ionic group;

iii) not more than 20 parts by weight of one or more ethylenically unsaturated monomers each having a polyethyleneoxy group;

wherein the sum of the parts of components i) to iii) is 100 and all parts are by weight.

Preferably, the polymeric dispersant comprises or consists of repeating units of a (meth) acrylate monomer.

Monomers in component i)

Preferably, component i) comprises at least 40 parts by weight, more preferably at least 45 parts by weight, further preferably at least 50 parts by weight, particularly preferably at least 60 parts by weight and more particularly preferably at least 70 parts by weight of benzyl methacrylate. Preferably, component i) consists only of benzyl methacrylate. We have found that increasing the amount of benzyl methacrylate provides improved ink properties such as optical density, printer reliability in single pass printers and colloidal stability in the ink.

In case component i) comprises monomers other than benzyl methacrylate, it preferably comprises (meth) acrylic acid C_1-20A hydrocarbon ester. Preferably, C_1-20The hydrocarbyl group is an alkyl group. The alkyl group may be linear or branched. Preferred examples include butyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, methyl (meth) acrylate, isobornyl acrylate, dodecyl acrylate, and octadecyl acrylate.

Preferably, component i) is from 70 parts by weight to 92 parts by weight, more preferably from 70 parts by weight to 90 parts by weight and particularly preferably from 75 parts by weight to 85 parts by weight.

Monomers in component ii)

Preferably, the ionic groups in the monomers in component ii) are anionic. Preferred examples of anionic groups include phosphorus-containing acidic groups (phosphonic and phosphorus-containing), sulfonic acid groups, and in particular carboxylic acid groups. Preferably, each (meth) acrylate monomer in component ii) has from 1 to 3, more preferably 1 or 2 and especially only one ionic group.

Preferred examples of (meth) acrylate monomers having a carboxylic acid group include itaconic acid, fumaric acid, maleic acid, crotonic acid, beta carboxy ethyl acrylate, acrylic acid and, in particular, methacrylic acid. Preferably component ii) comprises methacrylic acid, more preferably component ii) comprises only methacrylic acid.

Preferably, component ii) is from 8 parts by weight to 30 parts by weight, more preferably from 10 parts by weight to 30 parts by weight and in particular from 15 parts by weight to 25 parts by weight.

Monomers in component iii)

In increasing order of preference, component iii) is not more than 10 parts, 5 parts, 2 parts, 1 part, 0.5 part and 0 part of ethylenically unsaturated monomers each having a polyethyleneoxy group. For ethylenically unsaturated monomers, we preferably mean C = C. For the purposes of the present invention, a monomer belongs to component iii) if it belongs to components i) and iii) or components ii) and iii). Thus, the ethylenically unsaturated monomers having polyethyleneoxy groups are always included in component iii), irrespective of other groups.

By polyethyleneoxy group, we mean any of or including (CH)₂CH₂O)_n-wherein n is 2 or more. The terminal groups of the polyethyleneoxy chains can be of any type. Thus, the number of ethylenically unsaturated monomers having alkyl, aryl, heterocyclic and H-terminated polyethyleneoxy groups is also limited by component iii).

When any monomer is present in component iii), the ethylenically unsaturated monomer having a polyethyleneoxy group is preferably a (meth) acrylate.

We have found that the low amount requirements expressed in component iii) for these kinds of monomers result in encapsulated particulate solids that provide improved optical density, stability and printer reliability in single pass inkjet printers.

Optional monomers

In addition to those monomers in components i) to iii), optional monomers may additionally be present.

Optionally, the copolymerized components comprise not more than 50 parts by weight, more preferably not more than 20 parts by weight, particularly preferably not more than 10 parts by weight and more particularly not more than 5 parts by weight of optional monomers other than those mentioned in components i) to iii). Particularly preferably, the polymer is obtained or obtainable by copolymerizing components consisting only of components i) to iii).

Preferred polymeric dispersants

In view of the above, preferred polymeric dispersants are obtained or obtainable by copolymerizing at least components i) to iii):

i) 70 to 95 parts of one or more (meth) acrylate monomers each having no ionic group, including at least 40 parts of benzyl methacrylate;

ii) 5 to 30 parts of methacrylic acid;

iii) not more than 5 parts, more preferably 0 parts, of one or more ethylenically unsaturated monomers each having a polyethyleneoxy group;

wherein the sum of the parts of i) to iii) is 100 and all parts are by weight.

Further preferably, the polymeric dispersant is obtained or obtainable by copolymerizing at least components i) to iii):

i) 70 to 95 parts of benzyl methacrylate;

ii) 5 to 30 parts of methacrylic acid;

iii) not more than 5 parts, more preferably 0 parts, of one or more ethylenically unsaturated monomers each having a polyethyleneoxy group;

wherein the sum of the parts of i) to iii) is 100 and all parts are by weight.

In these polymeric dispersants, preferably, there are no further monomers other than those mentioned in components i) to iii).

Preparation of dispersants

The dispersant may be prepared by any type of polymerization method, and is not particularly limited. Emulsion polymerization, bulk polymerization, suspension polymerization and, in particular, solution polymerization processes may be used. The initiator used in the polymerization may be a cationic initiator, an anionic initiator or more preferably a free radical initiator. The polymerization can be carried out in the presence of a chain transfer agent, thereby limiting the molecular weight.

Cross-linking

Preferably, the dispersant is crosslinked in the presence of the particulate solid and a liquid medium to produce an encapsulated particulate solid.

The crosslinking reaction may be achieved by using a self-crosslinkable dispersant or by using a combination of a dispersant and a crosslinking agent.

Any suitable crosslinking chemistry may be employed. Suitable crosslinking chemistries are described in PCT patent publication WO2005/061087, page 6, Table 1. Preferably, the crosslinking reaction is achieved by using an epoxy crosslinker.

We have found that it is preferable to cross-link the polymeric dispersant shell by a cross-linking reaction between carboxylic acid and epoxy groups. We have found that this approach is a particularly effective cross-linking approach which does not tend to destabilise particulate solids dispersed in a liquid medium. Preferably, the carboxylic acid groups are present in the dispersant and the epoxide is added as a cross-linking agent.

Low temperatures are preferred for crosslinking because this causes a lower level of flocculation and particle size growth of the particulate solids in the liquid medium. Preferably, the crosslinking reaction is carried out at a temperature of 10 ℃ to 90 ℃ and more preferably 30 ℃ to 70 ℃.

The pH of the crosslinking reaction is preferably 7 to 14, more preferably 7 to 12 and particularly preferably 8 to 11.

The borate compound is preferably present during the crosslinking reaction. We have found that this increases the efficiency of the crosslinking reaction.

The borate compound preferably comprises boric acid, metaboric acid, tetraboric acid or pyroboric acid, or combinations thereof, or salts thereof.

The time of the crosslinking reaction depends to some extent on the temperature and the pH. However, the preferred time is 1 to 24 hours, more preferably 1 to 8 hours.

Liquid medium

The liquid medium as used in the present invention refers to the liquid component present during the preparation of the encapsulated granular solid. The liquid component in the final ink is referred to as the liquid medium.

The liquid medium is preferably polar.

Examples of suitable polar liquid media include ethers, glycols, alcohols, polyols, amides, ketones, and in particular water.

Preferably, the liquid medium is or includes water, as this tends to produce a particularly stable and well encapsulated particulate solid. Preferably, the liquid medium comprises from 1 to 100% by weight, more preferably from 10 to 100% by weight, especially from 30 to 100% by weight, more especially from 50 to 100% by weight, especially from 60 to 100% by weight, and most especially from 80 to 100% by weight of water. The remainder is preferably one or more polar organic liquids. In some cases, it is preferred that the liquid medium comprises water and less than 5%, more preferably less than 2%, particularly less than 1% and most particularly 0% of an organic liquid. A liquid medium comprising almost only water offers the best choice for ink formation and is more environmentally friendly.

When the liquid medium comprises more than one liquid, the liquid medium may be in the form of a multi-phase liquid (e.g. a liquid-liquid emulsion), but is preferably in the form of a single-phase (homogeneous) liquid.

Preferably, the polar liquid other than water is water soluble.

In one instance, the liquid medium includes water and a water-soluble organic liquid. Such liquid media are useful because they help to dissolve and/or disperse a wider range of cross-linking agents and facilitate the use of more hydrophobic dispersants.

Preferred water-soluble organic liquids contained in the liquid medium include:

i）C_1-6alkanols, preferably methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol, n-pentanol, cyclopentanol and cyclohexanol;

ii) a linear amide, preferably dimethylformamide or dimethylacetamide;

iii) ethers, preferably tetrahydrofuran and dioxane;

iv) glycols, preferably diols having from 2 to 12 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol and thiodiglycol, and also oligoalkylene glycols and polyalkylene glycols, preferably diethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol;

v) triols, preferably glycerol and 1,2, 6-hexanetriol;

vi) ethers of diols, preferably mono C of diols having 2 to 12 carbon atoms_1-4Alkyl ethers, in particular 2-ethylene glycol monomethyl ether, 2- (2-methoxyethoxy) ethanol, 2- (2-ethoxyethoxy) -ethanol, 2- [2- (2-methoxyethoxy) ethoxy]Ethanol, 2- [2- (2-ethoxyethoxy) -ethoxy]-ethanol and ethylene glycol monoallyl ether;

vii) cyclic amides, preferably 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, caprolactam and 1, 3-dimethylimidazolidinone.

In some cases, the liquid medium comprises water and 1 part or more, specifically 1 to 8 parts, of a water-soluble organic liquid.

In many cases, it is preferred to remove all of the organic liquid from the dispersion of encapsulated particulate solid prior to formulating the ink, in accordance with the first aspect of the present invention.

This removal can be accomplished by methods including distillation, isolation and redispersion, or more preferably by membrane washing.

Purification of encapsulated particulate solids

Preferably, the encapsulated particulate solid is purified prior to formulating the ink. Preferably, impurities such as unwanted free unencapsulated dispersant, unused crosslinker and borate material (when present) are substantially removed. Preferred purification methods include filtration washing, and in particular membrane treatment.

b.Glycerol

Glycerol is also known under other common names including glycerol (glycerin and glycerol). The formal IUPAC name is 1,2, 3-trihydroxypropane.

Preferably, the amount of glycerol in the ink is from 15 to 50 parts by weight, more preferably from 15 to 40 parts by weight, especially more preferably from 17 to 40 parts by weight, in particular from 20 to 40 parts by weight and more especially from 25 to 35 parts by weight. In particularly preferred cases, the amount of glycerol in the ink is 30+/-2 parts by weight. In many cases, it is preferred that the amount of glycerin is at least 17 parts by weight.

c.Ethylene glycol

Ethylene glycol is also known by the simpler name glycol. The formal IUPAC name is 1, 2-dihydroxyethane.

Preferably, the amount of ethylene glycol in the ink is from 5 parts by weight to 30 parts by weight, more preferably from 5 parts by weight to 25 parts by weight, especially more preferably from 7 parts by weight to 25 parts by weight and especially from 10 parts by weight to 25 parts by weight. In a particularly preferred case, the amount of ethylene glycol in the ink is 18+/-2 parts by weight. In many cases, it is preferred that the amount of ethylene glycol is at least 7 parts by weight.

d.2-pyrrolidone

2-pyrrolidone (in this case, this is the formal IUPAC name) is also less commonly referred to as 2-pyrrolidone (2-pyrrolidone) or 2-pyrrole (2-Pyrol).

Preferably, the amount of 2-pyrrolidone in the ink is from 0.1 to 20 parts by weight, more preferably from 1 to 15 parts by weight, particularly from 1 to 10 parts by weight, more particularly from 2.5 to 7.5 parts by weight. In some cases, the amount of 2-pyrrolidone in the ink is 0 to 20 parts by weight, more preferably 0 to 10 parts by weight.

e.Surface active agent

The amount of the surfactant in the ink is preferably 0.1 part by weight to 2 parts by weight, more preferably 0.1 part by weight to 1.5 parts by weight, particularly preferably 0.15 part by weight to 1.5 parts by weight, particularly preferably 0.5 part by weight to 1.5 parts by weight. In a particularly preferred case, the amount of surfactant in the ink is 0.8+/-0.2 parts by weight. In other instances, the amount of surfactant is 0.4+ parts/-0.2 parts by weight.

The surfactant may be of any kind and is not subject to any particular limitation. Preferred surfactants are amphoteric (having a hydrophobic group and a hydrophilic group). Preferred hydrophilic groups are sulfonic acid groups, phosphonic acid groups, carboxylic acid groups and vinyloxy groups. Preferred hydrophobic groups are aryl groups, alkyl groups, propenyloxy groups, and butenyloxy groups, and combinations thereof.

Surfactants having an acetylenic diol structure (especially 2,4,7, 9-tetramethyl-5-decyne-4, 7-diol and the corresponding ethoxylates) are preferred. Preferred examples include those sold by air products under the trade name Surfynol^TMAnd especially Surfynol^TM465. 104E, and 440. Among these surfactants, Surfynol^TM104E is preferred, it is 2,4,7, 9-tetramethyl-5-decyne-4, 7-diol (CAS code 126-86-3).

One or more of these surfactants may be used.

We have found that these large amounts and preferred types of surfactants provide excellent droplet ejection and dispersion characteristics when used in combination with glycerol and ethylene glycol, which are particularly important for inkjet printing and in particular single pass inkjet printing. These preferred acetylenic diol surfactants also desirably provide the ink with a low foaming tendency.

The process of inkjet printing is a dynamic process in which the surface of the ink is constantly disturbed. In such an environment, the surface tension of the ink at very low surface times is significant and can affect drop speed, required voltage, retardance, print quality, and optical density. It is desirable to carefully select the type, flow and amount of surfactant at the time of ink formulation in order to provide better droplet formation and jetting characteristics to the ink.

f.Water-soluble polymers

For clarity, when the polymer is water soluble and is a surfactant, it is considered herein to be a surfactant (component e.).

The water-soluble polymer may be of any type and is not particularly limited. As used herein, the phrase "water soluble" includes polymers having a solubility in water of at least 5% by weight. Preferably, the water is distilled water. Preferably, any acidic groups in the polymer are neutralized with sodium hydroxide and any basic groups in the polymer are neutralized with acetic acid. Preferably, the neutralization is 100% based on the stoichiometry of the acidic or basic groups present. Preferably, the solubility is measured at 25 ℃. Soluble polymers tend to dissolve to form completely (or almost completely) clear polymer solutions in water.

Examples of suitable water-soluble polymers include polymers of ethylenically unsaturated monomers (e.g., polyacrylic acid, polyacrylamide, polyvinyl alcohol, and polyvinylpyrrolidone), polyesters, polyurethanes, cellulose, and, in particular, polyethylene glycol (sometimes referred to as polyethylene oxide).

Preferably, the water soluble polymer is or includes polyethylene glycol.

Preferably, the molecular weight of the water-soluble polymer is from 150 to 200000, more preferably from 1000 to 100000; particularly preferably 5000 to 50000 and especially 10000 to 30000. In one case, the water-soluble polymer preferably has a molecular weight of 30000 to 40000. Preferably the molecular weight is the number average molecular weight as determined by gel permeation chromatography.

Preferably, the amount of water-soluble polymer in the ink is not more than 7 parts by weight, more preferably not more than 5 parts by weight, and more particularly not more than 3 parts by weight. In some cases, it is desirable that the amount of water-soluble polymer in the ink is at least 0.1 parts by weight, more preferably at least 0.2 parts by weight.

The preferred amount of water-soluble polymer is 0.01 to 7 parts by weight, more preferably 0.05 to 5 parts by weight, particularly 0.1 to 3 parts by weight.

Also, without wishing to be bound by any particular theory, it is believed that the water-soluble polymer, and in particular polyethylene glycol, tends to assist in adjusting the rheology of the ink, thereby facilitating particularly good inkjet ejection (printing) and printing.

In some cases, two or more different water-soluble polymers may be used, in particular two or more different polyethylene glycols. Preferably, the two or more polyethylene glycols have different molecular weights. Preferably, one polyethylene glycol has a molecular weight of 1000 to 50000 and the other polyethylene glycol has a molecular weight of 150 to 999.

In some cases, it may be advantageous for component f. to include a water soluble polymer other than polyethylene glycol. In some cases, component f comprises a water soluble polymer other than polyethylene glycol and polyethylene glycol. Preferred water-soluble polymers other than polyethylene glycol include polyesters, polymers polymerized from ethylenically unsaturated monomers, and particularly polyurethanes.

For clarity, the water-soluble polymer does not encapsulate the particulate solid, nor does it act as a dispersant in any way.

g.Polymer microparticles

The ink may optionally include polymeric microparticles. Any kind of polymer microparticles may be used without limitation. When present, the polymeric microparticles are separate and distinct from the encapsulated particulate solid. The polymer in the polymeric microparticles may be polystyrene, poly (meth) acrylic acid, styrene-methacrylic acid copolymers, polyesters, polyethers, polyurethanes, polycarbonates or polyamides, including grafted polymers and physical mixtures thereof. The polymer may also be a natural polymer such as cellulose, protein or wax.

Preferably, the average particle diameter of the polymeric particles is no more than 1 micron, more preferably from 10 to 500nm, especially from 30 to 200nm, and most especially from 30 to 150 nm. A preferred method for determining the particle size of the polymer particles is photon correlation spectroscopy.

When present, the polymeric microparticles may be used to aid in the bonding of the particulate solid to the substrate, or to improve the gloss of the final print. In a typical dilution process, the polymer particles tend to have little effect on the rheology of the ink.

Particularly, preferred polymer fine particles are those prepared by polymerizing ethylenically unsaturated monomers (particularly, acrylic acid esters, methacrylic acid esters, styrene, etc.). Other useful polymeric microparticles include polyesters and polyurethanes. In water, the polymer particles tend to have a solubility of less than 5%, more preferably less than 1% by weight, measured using the same method as mentioned above for the water-soluble polymers.

We have found that the presence of a large amount of polymer particles can be detrimental to the operability and delay of ink jetting. Thus, preferably, the amount of polymer microparticles in the ink is no more than 15 parts by weight, more preferably no more than 12 parts by weight, particularly no more than 10 parts by weight, more particularly no more than 5 parts by weight, and most particularly no more than 3 parts by weight. In some cases, the amount of the polymer microparticles in the ink is 0.1 to 15 parts by weight, more preferably 1 to 12 parts by weight, and particularly 3 to 10 parts by weight. We have found that these high amounts of polymeric microparticles tend to improve the adhesion and wet fastness properties of the final ink printed on the substrate.

In some cases, it is preferred that no polymeric microparticles are present in the ink. Of course, when the dispersant is a polymer, the word polymer microparticle does not mean an encapsulated particulate solid.

The polymer microparticles can be produced by many possible methods including solution dispersion polymerization, melt dispersion polymerization, suspension polymerization, and particularly emulsion polymerization.

The polymer particles may be colloidally stabilized by adsorbed surfactants and/or water-dispersing groups that are part of the structure of the polymer particles.

h.Antimicrobial agents

The ink may optionally include an antimicrobial agent or a mixture of antimicrobial agents.

Any antimicrobial agent can be used without any particular limitation. We have found that 1, 2-benzisothiazolin-3-one is a particularly suitable antimicrobial agent for the inks of the invention and that 1, 2-benzisothiazolin-3-one is a Proxel^TMGXL was purchased commercially. The amount of the antimicrobial agent in the ink is preferably not more than 1.5 parts by weight, in particular not more than 1 part by weight.

The amount of the antimicrobial agent in the ink is preferably 0.0001 part by weight to 1.5 parts by weight, more preferably 0.01 part by weight to 1 part by weight, particularly 0.01 part by weight to 0.3 part by weight.

i.Water (W)

The amount of water in the ink is preferably 25 parts by weight to 70 parts by weight, more preferably 30 parts by weight to 60 parts by weight, particularly 35 parts by weight to 55 parts by weight, and more particularly 40 parts by weight to 55 parts by weight. In a preferred case, the amount of water in the ink is 46+/-2 parts by weight.

The water is preferably purified prior to formulation into the ink. Preferably, the water is purified by contact with a deionizing resin, distillation and/or reverse osmosis.

j.Optional ink Components

The ink may optionally include ink components other than components a.

Examples of suitable optional ink components include:

a metal chelator; scale (kogation) inhibitors; rheology modifiers other than water-soluble polymers, dyes; further dispersants, water-soluble organic liquids (other than glycerol, ethylene glycol and 2-pyrrolidone); unencapsulated particulate solids (e.g., pigments), defoamers; bases and buffers, and the like.

Preferably, the ink comprises not more than 10 parts by weight, more preferably not more than 5 parts by weight, and especially not more than 3 parts by weight of all optional ink components present in the ink.

Preferably, the ink does not include a dispersant other than a dispersant that is crosslinked to encapsulate the particulate solid.

Preferred ink Components

Preferably, components b, c and d add up to at least 30 parts by weight, more preferably at least 35 parts by weight, more particularly at least 40 parts by weight.

According to the above preferences, preferred inks comprise the following components:

from 0.1 to 10 parts of an encapsulated particulate solid;

from 20 parts to 40 parts of glycerol;

from 5 parts to 25 parts of ethylene glycol;

0 to 10 parts of 2-pyrrolidone;

e.0.1 to 2 parts of a surfactant;

f.0 to 5 parts of polyethylene glycol;

g.0 parts to 15 parts of polymeric microparticles;

h.0 parts to 1 part of an antimicrobial agent;

from 35 parts to 55 parts of water;

wherein all parts are by weight and the sum of the parts of components a to i is 100.

We have found that these inks can be printed particularly reliably by inkjet printers and in particular single pass inkjet printers. In addition, these inks are effective for printing on corrugated substrates and newsprint substrates.

Ink characteristics

Preferably, the ink is an ink jet printing ink (i.e., an ink that can be printed by an ink jet printer).

The following ink requirements provide inks that are particularly well suited for ink jet printing and single pass ink jet printing.

The pH of the ink according to the first aspect of the present invention is preferably equal to or greater than 7, more preferably from 7 to 12, and particularly from 8 to 11. Preferably, the dispersant used to encapsulate the particulate solid is neutralised with a base. The base may be an alkali metal hydroxide, an organic amine, an alkanolamine or ammonia. Thus, any ionic (preferably acidic) group in the dispersant may be in the form of a salt, a free acid or a free base.

Preferably, the surface tension of the ink is from 20 to 50mN/m, more preferably from 20 to 40mN/m, and particularly from 25 to 35 mN/m. Preferably, the surface tension is measured by a Kibron Aquapi tensiometer device. Preferably, the surface tension of the ink is measured at a temperature of 25 ℃.

Preferably, the ink is filtered through a filter having an average pore size of no more than 5 microns, more preferably no more than 2 microns, and especially no more than 1 micron.

Preferably, the viscosity of the ink is not more than 50mpa.s, more preferably not more than 30mpa.s, and especially not more than 20mpa.s, when measured at 30 ℃. A preferred apparatus for measuring viscosity is a Brookfield DV II viscometer, preferably using spindle number 0 or 18. Preferred viscosities for the inks are from 1 to 20mpa.s, more preferably from 2 to 17mpa.s, and especially from 3 to 15 mpa.s.

Preferably, the ink comprises less than 500ppm, more preferably less than 250ppm, and especially less than 100ppm of multi-valent (divalent or higher valent) metal ions. Ppm as used herein means parts per million by weight.

Ink preparation method

The ink components may be mixed together in any order and using any suitable apparatus or method. Preferably, the encapsulated particulate solid is mixed with the other ingredients in a form that is dispersed in water.

A preferred method for preparing the ink comprises the steps of:

i) adding a surfactant and ethylene glycol together to form a surfactant solution;

ii) adding other ink components than the encapsulated particulate solid to the surfactant solution formed in step i) to form a liquid medium;

iii) adding the liquid medium formed in step ii) to an aqueous dispersion of the encapsulated particulate solid.

Preferably, all steps i) to iii) are carried out while mixing the ink components. Suitable mixers are paddle mixers or homogenizers.

Second aspect of the invention

According to a second aspect of the present invention there is provided a process for printing an ink according to the first aspect of the present invention onto a substrate.

Ink jet printing

Preferably, the printer is an inkjet printer, and in particular a single pass inkjet printer. Preferably, the printing is carried out by means of an ink jet printer. Preferably, the single pass inkjet printer has one or more inkjet printheads which individually or in combination extend across the entire width of the print zone. The print zone can be wider than 2.5cm, 5cm, 10cm, 20cm, 50cm, 100cm, etc. In fact, in some printers, the print zone is wider than 1m, 1.5m, or even wider than 2 m. Preferably, the printing is performed in a single pass using a single pass inkjet printer.

Inkjet printers may eject ink droplets using a piezoelectric head, a thermal head, or a voice activated head.

Substrate

The inks of the present invention are generally suitable for use on a wide range of substrates such as paper, textile, glass, ceramic, metal and plastic substrates.

That is, the inks of the present invention are particularly suitable for use on porous substrates. Among these porous substrates, the most preferred is a porous substrate comprising paper.

A preferred substrate is a corrugated substrate (also known as corrugated paper). Corrugated substrates tend to be thicker and have a higher mass per square meter than many substrates due to their good properties. A preferred corrugated substrate has a mass of 40g/m²To 800g/m²More preferably 100g/m²To 800g/m²And in particular 200g/m²To 800g/m². The term corrugated substrate as used herein preferably means those paper substrates comprising paper having a corrugated shape. The corrugated substrate may (and preferably does) have one, two and or more linerboards. The corrugated substrate may be a single ply or multiple plies of linerboard, optionally interposed between corrugated paper plies.

While the ink may be printed onto a corrugated surface, it is preferably printed onto a flat paper linerboard.

The ink is particularly suitable for printing inks having a porous surface and a mass of 40g/m²To 800g/m²The substrate of (1).

Corrugated substrates tend to be highly absorbent and have surfaces on which it tends to be particularly difficult to form high quality prints by means of ink jet printing. A particular problem with printing on corrugated substrates is capillary action, where the ink tends to spread out over the surface reducing image quality. Another problem is that the ink may penetrate too deeply into the corrugated substrate and, therefore, the indentations exhibit low optical density at the surface. We have found that the inks of the present invention provide a good balance of properties, including good optical density and image quality (even on corrugated substrates). It is more difficult to achieve high optical density printing when printing is performed in a single pass. In such systems, there is no subsequent opportunity to reapply more ink layers to the print zone.

Another preferred substrate is newsprint. Newsprint is a substrate comprising porous paper. Newsprint (as opposed to corrugated substrates) is typically a flat single sheet. Newsprint tends to have a significantly lower mass per square meter than corrugated substrates. The preferred newsprint substrate mass is 10g/m²To 200g/m²In particular 20g/m²To 200g/m²And more particularly 40g/m²To 200g/m². A problem with existing inks is that they tend to show through on thinner newsprint substrates, making the ink visible on the back of the substrate. It has been found that the ink according to the first aspect of the invention can be printed well, with high optical density, while minimizing show-through.

Ink container

To provide a means for storing ink, and to provide an ink jet printer with ink according to the first aspect of the invention, the ink may be stored in a vessel (vessel).

Accordingly, in a third aspect of the invention, there is provided a vessel containing ink according to the first aspect of the invention.

A suitable vessel is preferred so that it can be connected to an inkjet printer and ultimately to a print head, allowing ink to be conducted out of the vessel, through the printer and to the head. Examples of suitable vessels include cartridges, bottles, buckets, cans, and the like. Preferably, the vessel has a connection point that can be connected to the printer so that ink can be delivered to the printer head without ink spilling and air being entrained into the ink stream.

Ink-jet printer

According to a fourth aspect of the present invention there is provided an ink jet printer comprising an ink jet print head and a vessel according to the third aspect of the present invention. During printing, ink flows from the vessel through conduits, channels, tubes, etc. to the inkjet printer head.

Detailed Description

Examples of the invention

The invention will now be described by the following examples in which all parts are by weight unless otherwise indicated.

1.Preparation of encapsulated granular solids

1.1Preparation of dispersant (1)

The dispersant was prepared by solution copolymerization of benzyl methacrylate and methacrylic acid in 78.5 and 21.5 parts by weight, respectively. The dispersant is isolated as a dry solid. This is dispersant (1). The acid value of the dispersant (1) was 2.5 mmol of acid groups/g.

1.2Preparation of dispersant solution (1)

200 parts of the dispersant (1) was dissolved in water to form 1000 parts, and neutralized with an aqueous potassium hydroxide solution to give an aqueous solution having a pH of about 9. This step produces a dispersant solution (1) comprising about 20% by weight of dispersant (1).

1.3Preparation of color paste

1.3.1Black color paste (1)

The pigment powder (90 parts carbon black pigment) and the dispersant solution (1) (180 parts) were mixed together to form a premix. Water is added to the premix in appropriate amounts to provide a suitable viscosity for mixing and grinding.

The pre-mix was mixed together thoroughly. After mixing, mixingThe material was transferred to a bead mill containing milling beads. The mixture is then milled for several hours until the desired particle size of about 110nm is reached. The particle size is determined by a Malvern Zetasizer^TMThe measured Z-average particle size.

The beads are then removed from the milled mixture. This step produces a black paste (1).

1.3.2Magenta color paste (1)

A magenta color paste (1) was prepared by exactly the same method as the black color paste (1) except that a magenta pigment (85 parts of c.i. pigment 122) and a dispersant solution (1) (127.5 parts) were used instead of the corresponding components in the black pulverized pigment (1). For the magenta pulverized pigment (1), milling was continued for several hours until a particle size of about 120nm was obtained. The particle size is determined by a Malvern Zetasizer^TMThe measured Z-average particle size. This step produces a magenta paste (1).

1.3.3Yellow color paste (1)

A yellow color paste (1) was prepared by exactly the same method as the black color paste (1) except that the yellow pigment (100 parts of c.i. pigment yellow 74) and the dispersant solution (1) (250 parts) were used instead of the corresponding components in the black pulverized pigment (1). For the yellow milled pigment (1), milling was continued for several hours until a particle size of about 120nm was obtained. The particle size is determined by a Malvern Zetasizer^TMThe measured Z-average particle size. This procedure produced yellow paste (1).

1.3.4Blue-green color paste (1)

Pigment powder (150 parts of c.i. pigment blue 15:3 powder) and dispersant solution (1) (225 parts) were mixed together to form a premix. Water is added to the premix in appropriate amounts to provide a suitable viscosity for mixing and grinding.

The pre-mix was mixed together thoroughly. After mixing, the mixture is transferred to beads containing milling beadsIn a grinding mill. The mixture is then milled for several hours until the desired particle size of about 120nm is reached. The particle size is determined by a Malvern Zetasizer^TMThe measured Z-average particle size.

The beads are then removed from the milled mixture. This step produces a cyan color paste (1).

1.4Preparation of encapsulated granular solids

All color pastes in sections 1.3.1 to 1.3.4 were adjusted to a solids content of about 10% by weight by adding pure water.

Then, a cross-linking agent (Denacol from Nagase ChemteX) was used^TMEX-321, epoxy equivalent =140, hereinafter abbreviated as EX-321) cross-linking the dispersant in each mill base. This step crosslinks the carboxylic acid groups in the dispersant and thus encapsulates the pigment. The crosslinking reaction was controlled by the presence of a small amount of boric acid (available from Aldrich). The crosslinking reaction was induced by heating the mixture described previously to a temperature of about 65 ℃ for 5 hours. This procedure produced a series of different encapsulated granular solids, see column 1 of table 1.

Table 1:cross-linking

Encapsulated particulate solids	Color paste (parts)	Cross-linking agent (in parts)	Boric acid part number
				EPS1	Blue-green color paste 1 (3)	EX321(6.3)	2.78
EPS2	Magenta color paste 1 (3)	EX321(3.57)	1.58
				EPS3	Yellow color paste 1 (3)	EX321(4.9)	2.16
EPS4	Black paste 1 (3)	EX321(5.04)	2.23

1.5Purification of encapsulated particulate solids

The encapsulated granular solids prepared in 1.4 above were each purified by the method of ultrafiltration. The encapsulated pigment dispersion was diafiltered using pure water. The encapsulated dispersion is then concentrated using ultrafiltration membranes to bring the solids content back to about 10 to 13% by weight.

2.Preparation of the inks

Ink components 1 to 11 were prepared by mixing the ingredients shown in tables 2 to 4, wherein the number of each ingredient represents the number of parts by weight.

The mixing method used to prepare the ink was as follows:

step 1-surfactant Surfynol^TM104E into a vessel containing ethylene glycol and stirring the mixture to form the surfactantAnd (3) solution.

Step 2-add other ink components to the surfactant solution in addition to the encapsulated particulate solid dispersion. Stirring was carried out for 10 minutes. This step forms a liquid medium.

Step 3-the liquid medium formed above is added to the encapsulated particulate solid dispersion while stirring to ensure particle stability during formulation. The resulting ink was further stirred for 20 minutes or until a uniform ink was obtained. The stirring may be carried out by means of a paddle stirrer.

Table 2: inks 1 to 4

Components		Ink 1	Ink 2	Ink 3	Ink 4
						a. Encapsulated particulate solids
a. Blue-green pigment	EPS1	4
						a. Magenta pigment	EPS2		4

a. Yellow pigment	EPS3			4
						a. Black pigment	EPS4				4
b. Glycerol		30	30	30	30
						c. Ethylene glycol		18	18	18	18
d.2-pyrrolidone		5	5	5	5
						e. Surface active agent	SurfynolRTM104E	0.8	0.8	0.8	0.8
f. Polyethylene glycol	Mn20000	0	0	0	0
						h. Antimicrobial agent	ProxelRTM GXL	0.02	0.02	0.02	0.02
i. Water (W)	Deionized	46.18	46.18	46.18	46.18

Table 3: inks 5 to 8

Components		Ink 5	Ink 6	Ink 7	Ink 8
						a. Encapsulated particulate solids
Blue-green pigment	EPS1	4
						Magenta pigment	EPS2		4
Yellow pigment	EPS3			4
						Black pigment	EPS4				4
b. Glycerol		30	30	30	30
						c. Ethylene glycol		18	18	18	18
d.2-pyrrolidone		5	5	5	5
						e. Surface active agent	SurfynolRTM104E	0.8	0.8	0.8	0.8
f. Polyethylene glycol	Mn20000	1.87	1.73	1.27	1.47
						h. Antimicrobial agent	ProxelRTM GXL	0.02	0.02	0.02	0.02
i. Water (W)	Deionized	44.31	44.45	44.91	44.71

Table 4: inks 9 to 11

Components		Ink 9	Ink 10	Ink 11
					a. Encapsulated particulate solids
Blue green color	EPS1

Magenta color	EPS2
					Yellow colour	EPS3
Black color	EPS4	4	4	4
					b. Glycerol		30	28	18
c. Ethylene glycol		18	10	10
					d.2-pyrrolidone		0	5	5
e. Surface active agent	SurfynolRTM104E	0.4	0.4	0.4
					f. Polyethylene glycol	Mn200	0	0	10
	Mn10000	0	0.633	0.5
					h. Antimicrobial agent	ProxelRTM GXL	0.02	0.02	0.02
i. Water (W)	Deionized	47.58	51.95	52.08

In each case, the amount of encapsulated pigment (e.g., cyan, yellow, magenta, and black) in tables 2-4 is based on the effective (or solids) amount of the pigment. Thus, 4 parts of pigment (used in inks 1 to 11) correspond to 40 parts of EPS dispersion having a pigment content of 10% by weight.

In tables 2 to 4, the amount of water in i) includes all water from any of the ink components, such as encapsulated particulate solid dispersion (about 90% water). Thus, for example, in ink 9, 47.58 parts of water included 36 parts of water from ESP4, with the remainder (11.58 parts) being added directly to achieve the specified amount.

3.Physical Properties of the ink

The pH values of inks 1 to 11 were measured by a pH meter.

The viscosities of inks 1 to 11 were measured at a temperature of 30 ℃ using the preferred method described hereinbefore.

The surface tension was measured using a Kibron Aquapi apparatus with the ink at 25 ℃.

The physical properties of the inks are summarized in table 5.

Table 5: physical Properties of the ink of the present invention

Printing ink	Viscosity (mPa.s)	Surface tension (mN/m)	pH
				1	7.6	33.1
2	6.76	32.1
				3	7.23	31.8
4	7	31.3
				5	12.5	33.1	9.5
6	12.3	32	9.2
				7	11.8	31.8	9.3
8	11.4	31.3	9.3
				9	6.3	34.2	9.2
10	5.94	34.4	9.2
				11	5.89	35.1	9.2

4.Ink jet printing

It was found that the inks of the invention allow particularly good printing to be achieved by means of ink jet printers. Excellent ink droplet formation and dispersion was observed. The inventors contemplate that the synergistic effect of the encapsulated particulate solid, the dispersant used to prepare the encapsulated particulate solid, and the glycerol/glycol/water ink medium results in excellent droplet formation and dispersion characteristics.

After a long period of printing, the ink can be reliably ejected. The ink prints well on corrugated cardboard and newsprint. The inks provide high optical density, fast drying, and a low degree of substrate penetration.

Claims (26)

1. An ink comprising an encapsulated particulate solid and a liquid medium, wherein:

I) the encapsulated particulate solid comprises a particulate solid encapsulated with a cross-linked dispersant shell; and

II) the ink comprises the following components:

from 0.1 parts to 20 parts of said encapsulated particulate solid;

from 20 parts to 40 parts of glycerol;

1 to 30 parts of ethylene glycol;

0 to 20 parts of 2-pyrrolidone;

0.01 to 3 parts of a surfactant;

f.0 to 10 parts of a water soluble polymer;

g.0 parts to 20 parts of polymer microparticles;

h.0 parts to 2 parts of an antimicrobial agent;

from 20 parts to 75 parts of water;

wherein all parts are by weight and the sum of the parts of components a to i is 100 parts.

2. The ink according to claim 1, wherein the surfactant has an acetylene glycol structure.

3. An ink according to any preceding claim, in which the surfactant is a 2,4,7, 9-tetramethyl-5-decyne-4, 7-diol surfactant.

4. An ink according to any one of the preceding claims, in which the amount of ethylene glycol is from 10 to 25 parts.

5. An ink according to any one of the preceding claims, in which the amount of water is from 30 to 60 parts.

6. An ink according to any one of the preceding claims, in which the amount of 2-pyrrolidone is from 1 part to 10 parts.

7. An ink according to any one of the preceding claims, in which the amount of 2-pyrrolidone is from 2.5 parts to 7.5 parts.

8. An ink according to any one of the preceding claims, in which the water-soluble polymer is or includes polyethylene glycol.

9. The ink of claim 8, wherein the amount of the polyethylene glycol is 0.1 to 3 parts by weight.

10. The ink of claim 9, wherein the polyethylene glycol has a number average molecular weight of 5000 to 500000.

11. An ink according to any one of the preceding claims, in which the amount of surfactant is from 0.1 to 2 parts by weight.

12. An ink according to any one of the preceding claims, in which the amount of surfactant is from 0.1 to 1.5 parts by weight.

13. An ink according to any one of the preceding claims comprising from 0 to 3 parts by weight of polymeric microparticles.

14. An ink according to any one of the preceding claims, in which the dispersant is a polymer and is obtained or obtainable by copolymerising at least components i) and ii):

i) from 70 parts to 95 parts of one or more (meth) acrylate monomers, each of said (meth) acrylate monomers having no ionic group;

ii) 5 to 30 parts of one or more (meth) acrylate monomers, each of said (meth) acrylate monomers having at least one ionic group;

wherein the sum of the parts of components i) and ii) is 100 and all parts are by weight.

15. An ink according to any one of the preceding claims, in which the dispersant is a polymer and is obtained or obtainable by copolymerising at least components i) to iii):

i) 70 to 95 parts of one or more (meth) acrylate monomers, each of the (meth) acrylate monomers having no ionic group and the (meth) acrylate monomers comprising at least 40 parts of benzyl methacrylate;

ii) 5 to 30 parts of methacrylic acid;

iii) not more than 5 parts, more preferably 0 parts, of one or more ethylenically unsaturated monomers, each of said ethylenically unsaturated monomers having a polyethyleneoxy group;

wherein the sum of the parts of i) to iii) is 100 and all parts are by weight.

16. An ink according to any one of the preceding claims, in which the dispersant housing is cross-linked by reaction between a carboxylic acid and an epoxy group.

17. The ink of claim 1, comprising the following components:

from 0.1 parts to 10 parts of said encapsulated particulate solid;

from 20 parts to 40 parts of glycerol;

from 5 parts to 25 parts of ethylene glycol;

0 to 10 parts of 2-pyrrolidone;

e.0.1 to 2 parts of a 2,4,7, 9-tetramethyl-5-decyne-4, 7-diol surfactant;

f.0 to 5 parts of polyethylene glycol;

g.0 parts to 15 parts of polymeric microparticles;

h.0 parts to 1 part of an antimicrobial agent;

from 35 parts to 55 parts of water;

wherein all parts are by weight and the amount of water is selected so that the sum of the parts of components a to i is 100 parts.

18. An ink according to any one of the preceding claims, in which the particulate solid is or includes a pigment.

19. An ink according to any preceding claim, comprising optional ink components other than components a.

20. The ink according to any one of the preceding claims, having a viscosity not exceeding 50mpa.s at a temperature condition of 30 ℃.

21. A process for printing the ink of any one of the preceding claims onto a substrate.

22. The process of claim 21, wherein printing is performed by means of an inkjet printer.

23. The process of claim 22, wherein inkjet printing is performed in a single pass using a single pass inkjet printer.

24. The process of any one of claims 21 to 23, wherein the substrate comprises a porous surface and the mass of the substrate is 40g/m²To 800g/m²。

25. A vessel containing the ink of any one of claims 1 to 20.

26. An inkjet printer comprising an inkjet printhead and a vessel according to claim 25.