JP2018035295A - Inkjet ink set, ink cartridge set, inkjet recording device and inkjet recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet ink set having suppressed bleeding between colors in an obtained image and excellent in discharge stability of an ink.SOLUTION: There is provided an inkjet ink set having a first ink containing an infrared absorber and water, second ink containing the infrared absorber and water and having value of factor a of the formula (1), which is a relational expression of viscosity and evaporation rate of the ink of 1.5 times or more difference from the first ink. y=a×exp(10x)+b (1), where x is mass evaporation rate of the ink and represents 0 to 0.6, y represents viscosity (mPa s) of the ink at 30°C and b represents a y-section.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ink jet ink set, an ink cartridge set, an ink jet recording apparatus, and an ink jet recording method.

  Inkjet printing technology has been greatly increasing in recent years in the printing field because it is easy to increase the width and speed.

As conventional inkjet recording methods, for example, those described in Patent Documents 1 to 3 are known.
For example, Patent Document 1 states that “the conveying means that conveys the recording medium and the ink that is arranged in a line along the conveying direction of the recording medium and that contains the color-specific ink containing the colorant and the infrared absorber is conveyed. A plurality of inkjet heads ejected onto a recording medium and the same number as the plurality of inkjet heads are disposed on the downstream side of each of the plurality of inkjet heads in the transport direction of the recording medium, and the recording is performed by the plurality of inkjet heads. A plurality of laser irradiation means for irradiating each color ink ejected on the medium with an infrared laser, satisfying all of the following conditions (1) to (3), or satisfying the following conditions (1) and An ink jet recording apparatus satisfying (4).
(1): The infrared absorbent contained in the color-specific inks has a maximum absorption wavelength that is the same as or close to the oscillation wavelength of the infrared laser irradiated first after the ink is ejected. (2): (a) In each color ink, there is an ink containing an infrared absorber having the same or approximate maximum absorption wavelength, and (b) after the ink is ejected in the ink. The infrared absorption rate with respect to the oscillation wavelength of the infrared laser irradiated first is increased in the order of ejection from the inkjet head from the upstream side to the downstream side in the conveyance direction of the recording medium (3): (a) Among the laser irradiation means, there is a laser irradiation means for irradiating an infrared laser having the same oscillation wavelength, and (b) an infrared laser of the laser irradiation means (4): Laser irradiation that irradiates infrared lasers having different oscillation wavelengths in the plurality of laser irradiation means. A means exists ”has been proposed.

Patent Document 2 discloses an image recording method including an ink applying step of applying a plurality of water-based inks to a recording medium and a drying step of drying the recording medium to which the ink has been applied. The water absorption coefficient Ka of water is 0.3 mL / m ² · ms ^1/2 or less, and the higher the viscosity of the plurality of water-based inks, the lower the viscosity of the water-removing ink obtained by removing water from the ink. In the ink application process, an image recording method is proposed in which, among the plurality of inks, an ink having a higher ink viscosity is applied to a recording medium in order.

  Further, Patent Document 3 discloses an “ink jet recording method in which ink droplets are ejected from an orifice of a recording head in accordance with a recording signal to form a multi-color image on a recording sheet. Two or more types of inks with different hues that thicken, and before or when the ink droplets land on the recording sheet, the recording sheet is heated to 70 ° C. or higher, and the ink has a low viscosity at 70 ° C. An inkjet recording method characterized in that printing is performed in order "has been proposed.

JP2013-188920A Japanese Patent Application Laid-Open No. 2015-150695 JP 2011-201037 A

  The problem to be solved by the present invention is that the value of a in all inks other than the ink is 1.0 times or more to 1.5 with respect to the value of a in the ink having the smallest value of the coefficient a in the formula (1). Compared to the case of using an inkjet ink set in a range of less than twice, it is to provide an inkjet ink set that suppresses intercolor bleeding in an obtained image and is excellent in ink ejection stability.

  The above problem is solved by the following means.

The invention according to claim 1
The first ink containing the infrared absorber and water, the infrared absorber and water, and the value of the coefficient a in the following formula (1), which is the relational expression between the viscosity and the evaporation rate of the ink, An ink-jet ink set having a second ink different from the first ink by 1.5 times or more.
y = a * exp (10x) + b (1)
In formula (1), x is a mass evaporation rate in the ink and represents 0 or more and 0.6 or less, y represents the viscosity (mPa · s) of the ink at 30 ° C., and b represents a y-intercept.

The invention according to claim 2
2. The inkjet ink set according to claim 1, wherein all inks of the inkjet ink set have a viscosity at 30 ° C. of 4 mPa · s or more and 10 mPa · s or less.

The invention according to claim 3
The inkjet ink set according to claim 1, wherein each of the first ink and the second ink further contains an organic solvent.

The invention according to claim 4
4. The first ink cartridge containing the first ink in the inkjet ink set according to claim 1, and the inkjet ink according to any one of claims 1 to 3. An ink cartridge set having a second ink cartridge containing the second ink in the set.

The invention according to claim 5
A first ejection head that contains the inkjet ink set according to claim 1, ejects the first ink onto a recording medium, and ejects the second ink onto a recording medium. An inkjet recording apparatus comprising: a two-ejection head; and an infrared irradiation unit that dries at least one of the first ink and the second ink ejected on the recording medium.

The invention according to claim 6
The inkjet ink according to any one of claims 1 to 3, wherein the inkjet ink set according to any one of claims 1 to 3 is ejected onto a recording medium. A step of discharging the second ink of the set onto a recording medium, and a step of drying at least one of the first ink and the second ink discharged onto the recording medium by irradiation with infrared rays. Inkjet recording method.

According to the first aspect of the present invention, the value of a in all the inks other than the ink is 1.0 times or more and 1.5 with respect to the value of a in the ink having the smallest value of the coefficient a in Expression (1). Compared to the case of using an inkjet ink set in a range of less than double, an inkjet ink set is provided in which bleeding between colors in an obtained image is suppressed and ink ejection stability is excellent.
According to the second aspect of the present invention, compared to the case where the ink-jet ink set has an ink viscosity at 30 ° C. of less than 4 mPa · s or more than 10 mPa · s, inter-color bleeding in the obtained image is more An inkjet ink set that is suppressed and is superior in ejection stability of each ink is provided.
According to the invention according to claim 3, it is easy to prepare an ink in which the value of the coefficient a in formula (1) is 1.5 times or more different from that in the case of an ink set having an ink not containing an organic solvent, An ink jet ink set that is superior in the ejection stability of each ink is provided.

According to the invention of claim 4, the value of a in all inks other than the ink is 1.0 times or more and 1.5 with respect to the value of a in the ink having the smallest value of the coefficient a in the formula (1). Compared to the case of using an ink set that is less than double, an ink cartridge set that suppresses intercolor bleeding in an obtained image and is excellent in ink ejection stability is provided.
According to the fifth aspect of the present invention, the value of a in all inks other than the ink is 1.0 times or more and 1.5 with respect to the value of a in the ink having the smallest value of the coefficient a in the formula (1). Compared to the case of using an ink set in a range less than double, an ink jet recording apparatus is provided in which intercolor bleeding in an obtained image is suppressed and ink ejection stability is excellent.
According to the invention of claim 6, the value of a in all inks other than the ink is 1.0 times or more and 1.5 with respect to the value of a in the ink having the smallest value of the coefficient a in the formula (1). Compared with a case where an ink set within a range of less than double is provided, there is provided an ink jet recording method in which bleeding between colors in an obtained image is suppressed and ink ejection stability is excellent.

It is a schematic structure figure showing an example of a recording device concerning this embodiment.

Hereinafter, the present embodiment will be described.
In addition, description with "mass part" and "mass%" is synonymous with "weight part" and "weight%", respectively.

<Inkjet ink set>
The ink-jet ink set according to the present embodiment (hereinafter, also simply referred to as “ink set”) contains a first ink containing an infrared absorbent and water, an infrared absorbent and water, and the viscosity of the ink. The value of the coefficient a in the following formula (1), which is a relational expression between the evaporation rate and the evaporation rate, includes a second ink that differs from the first ink by 1.5 times or more.
y = a * exp (10x) + b (1)
In the formula (1), x is a mass evaporation rate (hereinafter also simply referred to as “evaporation rate”) in the ink, and represents 0 or more and 0.6 or less, and y represents the viscosity (mPa · s) of the ink at 30 ° C. And b represents the y-intercept.

  The ink-jet ink set according to the present embodiment is excellent in the ejection stability of each ink because the inter-color blur in the obtained image is suppressed by the above configuration. The reason for this is not clear, but is presumed to be as follows.

In recent years, an ink jet recording method for recording an image using a water-based ink on a printing paper that is a poorly permeable recording medium or glass, plastic, or film that is a non-permeable recording medium has been studied.
The intercolor bleeding is a phenomenon in which the line shape of the edge (edge portion) between two colors is roughly disturbed by color bleeding in the image to be formed, and the ink applied on the recording medium is sufficiently dry. In the state where the ink is not discharged, the discharged ink spreads and when other ink is discharged, the previously discharged ink droplet and the other ink droplet are merged or come into contact with the other ink droplet. As a result, the previously ejected ink droplets move due to surface tension.
In the case of using a hardly permeable or non-permeable recording medium, the intercolor bleeding is often seen even if the ink is dried.
On the other hand, when ink having a high viscosity is used in order to simply suppress the intercolor bleeding, the intercolor bleeding is suppressed, but the discharge stability is lowered in the inkjet discharge.

In the water-based ink, the viscosity of the ink increases exponentially in accordance with the evaporation of the ink components, particularly the evaporation of water or organic solvent that tends to volatilize. The relationship between the viscosity of the ink and the evaporation rate is expressed by an approximate expression as the following expression (1).
y = a * exp (10x) + b (1)
In formula (1), x is a mass evaporation rate in the ink and represents 0 or more and 0.6 or less, y represents the viscosity (mPa · s) of the ink at 30 ° C., and b represents a y-intercept.
Needless to say, exp (10x) = ^e10x . e represents the Napier number that is the base of the natural logarithm.
In addition, since the region where the ink evaporation rate exceeds 60% by mass depends on the solid content of the ink and the like, it is not considered in the above formula (1) in this embodiment.
Furthermore, since the equation (1) is an approximate equation, the value of b may be different from the viscosity of the ink at 30 ° C. (viscosity of 0% by mass evaporation rate).

  The value of a which is a coefficient of exp (10x) in the formula (1) is a value indicating an increasing tendency of the viscosity according to the evaporation rate in the ink. The larger the value of a, the larger the amount of increase in viscosity according to the increase in the evaporation rate, and the smaller the value of a, the smaller the amount of increase in viscosity according to the increase in the evaporation rate.

The first ink containing the infrared absorber and water, the infrared absorber and water, and the coefficient a of the above formula (1), which is an approximate expression when the ink has an evaporation rate of 0% by mass to 60% by mass. Using an inkjet ink set having a second ink that is 1.5 times or more different from the first ink, and after ejecting one ink, the ink on the recording medium is irradiated with an infrared laser, and then the other By discharging this ink, wetting and spreading of the ink can be suppressed by suppressing the wetting and spreading of the previously discharged ink.
Further, the first ink and the second ink are inks having different viscosity increasing tendencies, and do not affect the viscosity at the time of ejection, which is the viscosity when the evaporation rate is 0% by mass, and do not use a high viscosity ink. In both cases, since the intercolor bleeding is suppressed, the ejection stability in the inkjet ejection is excellent.

  Hereinafter, the details of the inkjet ink set according to the present embodiment will be described.

The calculation method of a and b in the formula (1) in the inkjet ink set according to the present embodiment is calculated by the following method.
Using a rheometer HAAKE MARS (manufactured by Thermo Fisher Scientific Co., Ltd.), the ink evaporation rate was 0% by mass, 15% by mass ± 5% by mass, 30% by mass ± 5% by mass, 45% by mass. The viscosity of the ink is measured at a stage temperature of 30 ° C. and a shear rate of 1/750 s at at least 5 points in the range of ± 5% by mass and 60% by mass to 5% by mass.
Using the measurement values of the five points, the equation (1) is regressed by the method of least squares, and the values of a and b in the equation (1) are calculated.

Each ink in the inkjet ink set according to the present embodiment (all inks included in the ink set unless otherwise specified) preferably contains water, and more preferably is a water-based ink.
Further, from the viewpoint of ejection stability and drying speed, each of the inks preferably contains 50% by mass to 95% by mass of water, more preferably 60% by mass to 90% by mass, and more preferably 70% by mass to 85% by mass. Is particularly preferred.
As water, ion-exchanged water, pure water, ultrapure water, distilled water, and ultrafiltered water are particularly preferable from the viewpoint of preventing contamination of impurities or generation of microorganisms.

Each ink in the inkjet ink set according to the present embodiment preferably contains an organic solvent from the viewpoint of ejection stability and ink preparation ease.
Although there is no restriction | limiting in particular as an organic solvent, It is preferable that it is an organic solvent which melt | dissolves in water, and it is more preferable that it is the aqueous organic solvent mentioned later.

There is no particular limitation on the method for preparing the first ink and the second ink in which the value of the coefficient a in the formula (1) differs from the first ink by 1.5 times or more, but the resin content is changed. Method, method of changing the content ratio of resins having different glass transition temperatures, method of changing the content ratio of organic solvents having different boiling points, method of changing the content ratio of water and organic solvent, or a method combining two or more of these methods Is preferred.
Among them, a method of changing the content ratio of organic solvents having different boiling points, a method of changing the content ratio of water and organic solvent, or a method combining these methods is particularly preferable.

The inkjet ink set according to the present embodiment may have one or more inks other than the first ink and the second ink.
The ink other than the first ink and the second ink may be an ink in which the value of a in the formula (1) corresponds to the first ink or the second ink, or may not correspond to the ink. However, it is preferable that the ink corresponds to the first ink or the second ink.

From the viewpoints of intercolor bleeding and ejection stability, the viscosity at 30 ° C. of all the inks included in the inkjet ink set according to the present embodiment is preferably 4 mPa · s to 10 mPa · s, and preferably 5 mPa · s to 7 mPa. In particular, from the viewpoint of intercolor bleeding and ejection stability, all inks of the inkjet ink set according to the present embodiment have a high viscosity at 30 ° C. and a low viscosity at 30 ° C. The difference from the viscosity of the ink is preferably 3 mPa · s or less, more preferably 2 mPa · s or less, and particularly preferably 1 mPa · s or less.
The viscosity of the ink in this embodiment is measured using a rheometer HAAKE MARS (manufactured by Thermo Fisher Scientific Co., Ltd.) at a stage temperature of 30 ° C. and a shear rate of 1/750 s, as described above in Formula (1). It shall be.

As described later, each of the first ink and the second ink (each ink) in the inkjet ink set according to the present embodiment preferably contains a colorant.
The first ink and the second ink in the ink set according to the present embodiment are preferably different color inks, and are at least two types of inks selected from the group consisting of cyan ink, magenta ink, and yellow ink. Is more preferable.
In addition, the inkjet ink set according to the present embodiment preferably includes cyan ink, magenta ink, and yellow ink from the viewpoint of forming a full color image, and more preferably includes cyan ink, magenta ink, yellow ink, and black ink. preferable.
The inkjet ink set according to the present embodiment includes a cyan ink in which the value of the coefficient a in the formula (1) is 1.5 times or more larger than that of the magenta ink and the yellow ink from the viewpoint of intercolor bleeding and ejection stability. It is more preferable that the value of the coefficient a in the formula (1) has a cyan ink that is 1.5 times or more larger than that of magenta ink, yellow ink, and black ink.

Of the ink set according to the present embodiment, it is preferable that the ink that is irradiated with the laser has a lower light absorption rate as the printing order is earlier and a higher light absorption rate as the printing order is slower.
The light absorption rate of the ink in the present embodiment is measured by the following method.
Using a UV-visible near-infrared spectrophotometer V-560 (manufactured by JASCO Corporation) and a 10 mm square quartz cell, the absorbance A at the laser wavelength of the ink diluted with pure water was measured, and the Lambert-Beer rule. The absorptance in the ink film thickness at the time of printing is obtained from the conversion formula by That is, the absorbance A of a solution obtained by mixing the ink weight W _ink = 1 g and pure water W _water = 200 g was measured, and the absorption rate% A = 1-10 ^{− ((Wink) of the} ink film thickness d = 5 × 10 ⁻³ mm. ^{/ Wwater) × (d / 10) × A)} .

  In addition, the ink-jet ink set according to the present embodiment has an ink temperature at the time of drying even if it has an ink having a high light absorption rate such as a black ink that tends to cause a decrease in image density or blistering due to a high temperature. The image density is not increased, the decrease in image density is suppressed, and the generation of blisters is suppressed.

  Each ink used in the present embodiment preferably contains an infrared absorber, a colorant, and a solvent containing water and an aqueous organic solvent, the infrared absorber, the colorant, and polymer particles, More preferably, it contains water and a solvent containing an aqueous organic solvent, and includes an infrared absorber, a colorant, polymer particles, a polymer dispersant, a surfactant, water and an aqueous organic solvent. It is particularly preferable to contain a solvent.

(Infrared absorber)
The first ink and the second ink used in the present embodiment contain an infrared absorber. By containing an infrared absorbing agent, drying is also utilized for drying the ink by irradiation with infrared rays by an infrared laser or the like.
In addition, the inks other than the first ink and the second ink used in the present embodiment preferably contain an infrared absorber from the viewpoints of drying speed and space saving in the ink jet recording apparatus.
The “infrared absorber” refers to a compound that generates heat by absorbing infrared rays.
“Infrared radiation” refers to light in a wavelength range of 700 nm to 1 mm, and the infrared absorbent used in the present embodiment preferably has a maximum absorption in a wavelength range of 800 nm to 1,500 nm.

There is no restriction | limiting in particular as an infrared absorber used for this embodiment, A well-known infrared absorber is used. A black pigment such as carbon black may function as an infrared absorber.
In addition, as the infrared absorber, it is preferable to use an inorganic material or an organic dye, and it is preferable to use an inorganic material from the viewpoint of the calorific value. From the viewpoint of fading the color of itself and not hindering the formation of an image with ink, it is preferable to use an organic dye.
As said inorganic material, a metal oxide is preferable and an antimony tin oxide (ATO), an indium tin oxide (ITO), etc. are illustrated preferably.
Examples of the organic dye include a cyanine dye, a phthalocyanine dye, a merocyanine dye, a squarylium dye, an onium compound, an indolenine cyanine, a pyrylium salt, and a nickel thiolate complex. Among these, at least one organic dye selected from the group consisting of a cyanine dye, a phthalocyanine dye, a merocyanine dye, and a squarylium dye is preferable.

Each ink used in the present embodiment may contain an infrared absorber alone or in combination of two or more.
The content of the infrared absorbent in each ink is preferably 0.001% by mass or more and 3% by mass or less, and more preferably 0.005% by mass or more and 2% by mass or less with respect to the total mass of the ink. . If it is the said range, the emitted-heat amount is sufficient and there is little influence on the image formation by an ink.

  Commercially available infrared absorbers can also be used as the infrared absorber, such as NIR series (manufactured by Nagase ChemteX Corporation), KAYASORB series (manufactured by Nippon Kayaku Co., Ltd.), T-1 series (Mitsubishi Materials Electronics). Kasei Co., Ltd.).

(Aqueous organic solvent)
Examples of the aqueous organic solvent include polyhydric alcohols, polyhydric alcohol derivatives, nitrogen-containing solvents, alcohols, and sulfur-containing solvents. Other examples of the aqueous organic solvent include propylene carbonate and ethylene carbonate.
Preferred examples of the aqueous organic solvent include aqueous organic solvents having a boiling point of 150 ° C. or higher.

Examples of the polyhydric alcohol include ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,5-pentanediol, 1,2-hexanediol, 1,2,6-hexanetriol, and glycerin. .
Examples of polyhydric alcohol derivatives include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and diglycerin. Examples include ethylene oxide adducts.
Examples of the nitrogen-containing solvent include pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, triethanolamine and the like.
Examples of the alcohol include ethanol, isopropyl alcohol, butyl alcohol, benzyl alcohol and the like.
Examples of the sulfur-containing solvent include thiodiethanol, thiodiglycerol, sulfolane, dimethyl sulfoxide and the like.

The aqueous organic solvent may be used alone or in combination of two or more.
Among these, each ink preferably contains a polyhydric alcohol as an aqueous organic solvent from the viewpoints of adjusting the drying speed and clogging resistance of the head, and propylene glycol and 1,2-hexanediol. More preferably, it contains an aqueous organic solvent selected from the group consisting of propylene glycol and 1,2-hexanediol.

  The content of the aqueous organic solvent in each ink is preferably 1% by mass to 60% by mass and more preferably 1% by mass to 40% by mass with respect to water.

(Coloring agent)
Each ink used in the present embodiment preferably contains a colorant.
As the colorant, those according to the target color ink may be used, and specific examples include pigments and dyes. Examples of the pigment include organic pigments and inorganic pigments.

Specific examples of the cyan pigment include C.I. I. Pigment Blue-1, -2, -3, -15, -15: 1, -15: 2, -15: 3, -15: 4, -16, -22, -60, and the like. It is not limited.
Specific examples of the magenta color pigment include C.I. I. Pigment Red-5, -7, -12, -48, -48: 1, -57, -112, -122, -123, -146, -168, -177, -184, -202, C.I. I. Pigment Violet-19 and the like, but are not limited thereto.
Specific examples of yellow pigments include C.I. I. Pigment Yellow-1, -2, -3, -12, -13, -14, -16, -17, -73, -74, -75, -83, -93, -95, -97, -98, -114, -128, -129, -138, -151, -154, -180, and the like, but are not limited thereto.
Examples of black pigments include, but are not limited to, carbon black, copper oxide, manganese dioxide, activated carbon, nonmagnetic ferrite, magnetite and the like.
In addition, other known pigments and dyes are used.

  Here, when a pigment is used as the colorant, it is preferable to use a pigment dispersant together. Examples of the pigment dispersant used include a polymer dispersant, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant described later.

  As the polymer dispersant, a polymer having a hydrophilic structure portion and a hydrophobic structure portion is preferably used. As the polymer having a hydrophilic structure part and a hydrophobic structure part, for example, a condensation polymer and an addition polymer are used. Examples of the condensation polymer include known polyester dispersants. Examples of the addition polymer include addition polymers of monomers having an α, β-ethylenically unsaturated group. By copolymerizing a monomer having an α, β-ethylenically unsaturated group having a hydrophilic group and a monomer having an α, β-ethylenically unsaturated group having a hydrophobic group, A molecular dispersant is obtained. A homopolymer of a monomer having an α, β-ethylenically unsaturated group having a hydrophilic group is also used.

  Monomers having an α, β-ethylenically unsaturated group having a hydrophilic group include monomers having a carboxyl group, a sulfonic acid group, a hydroxyl group, a phosphoric acid group, such as acrylic acid, methacrylic acid, and croton. Acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, fumaric acid monoester, vinyl sulfonic acid, styrene sulfonic acid, sulfonated vinyl naphthalene, vinyl alcohol, acrylamide, methacryloxyethyl phosphate, bis Examples include methacryloxyethyl phosphate, methacryloxyethyl phenyl acid phosphate, ethylene glycol dimethacrylate, and diethylene glycol dimethacrylate.

  Examples of the monomer having an α, β-ethylenically unsaturated group having a hydrophobic group include styrene derivatives such as styrene, α-methylstyrene, vinyltoluene, vinylcyclohexane, vinylnaphthalene, vinylnaphthalene derivatives, and alkyl acrylate esters. Methacrylic acid alkyl ester, methacrylic acid phenyl ester, methacrylic acid cycloalkyl ester, crotonic acid alkyl ester, itaconic acid dialkyl ester, maleic acid dialkyl ester and the like.

Examples of preferred copolymers as the polymer dispersant include styrene-styrene sulfonic acid copolymer, styrene-maleic acid copolymer, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, vinyl naphthalene- Maleic acid copolymer, vinyl naphthalene-methacrylic acid copolymer, vinyl naphthalene-acrylic acid copolymer, alkyl acrylate ester-acrylic acid copolymer, alkyl methacrylate ester-methacrylic acid copolymer, styrene-methacrylic acid Alkyl ester-methacrylic acid copolymer, styrene-alkyl acrylate ester-acrylic acid copolymer, styrene-phenyl methacrylate-methacrylic acid copolymer, styrene-methacrylic acid cyclohexyl ester-methacrylic acid copolymer, or these Examples of salt It is. Moreover, you may copolymerize the monomer which has a polyoxyethylene group and a hydroxyl group with these polymers.
Among these, a polymer dispersant selected from the group consisting of a styrene-acrylic acid copolymer and a styrene-acrylate copolymer is preferable, a styrene-acrylate copolymer is more preferable, and a styrene-acrylic acid is preferable. Alkali metal salt copolymers are particularly preferred.

  The weight average molecular weight of the polymer dispersant is preferably 2,000 or more and 50,000 or less. Unless otherwise specified, the weight average molecular weight in the present embodiment is a value measured by gel permeation chromatography (GPC) and converted to standard polystyrene.

  These polymer dispersants may be used alone or in combination of two or more. The content of the polymer dispersant varies greatly depending on the pigment and cannot be generally stated, but it is preferably 0.1% by mass or more and 100% by mass or less based on the pigment.

Examples of the pigment include pigments that are self-dispersed in water (hereinafter referred to as self-dispersing pigments).
The self-dispersing pigment refers to a pigment that has a water-solubilizing group on the pigment surface and disperses in water without the presence of a polymer dispersant. The self-dispersing pigment can be obtained, for example, by subjecting the pigment to surface modification treatment such as acid / base treatment, coupling agent treatment, polymer graft treatment, plasma treatment, oxidation / reduction treatment, and the like.

  As self-dispersing pigments, in addition to pigments that have been surface-modified to the above pigments, Cab-o-jet-200, Cab-o-jet-300, Cab-o-jet-400 manufactured by Cabot Corporation. IJX-157, IJX-253, IJX-266, IJX-273, IJX-444, IJX-55, Cab-o-jet-250C, Cab-o-jet-260M, Cab-o-jet-270Y, Cab -O-jet-450C, Cab-o-jet-465M, Cab-o-jet-470Y, Cab-o-jet-480M, Microjet Black CW-1, CW-2 manufactured by Orient Chemical Industries, Ltd. Commercially available self-dispersing pigments can also be mentioned.

  The self-dispersing pigment is preferably a pigment having at least a sulfonic acid, a sulfonate, a carboxylic acid or a carboxylate as a functional group on the surface, and has at least a carboxylic acid or a carboxylate as a functional group on the surface. More preferably, it is a pigment.

Here, examples of the pigment include a pigment coated with a resin. This is called a microcapsule pigment, and there are commercially available microcapsule pigments such as those manufactured by DIC Corporation and Toyo Ink Corporation. In addition, it is not restricted to a commercially available microcapsule pigment, You may use the microcapsule pigment produced according to the objective.
Examples of the pigment also include a resin dispersion type pigment in which a polymer compound is physically adsorbed or chemically bonded to the pigment.
In addition to the three primary color pigments of cyan, magenta, and yellow, specific pigments such as red, green, blue, brown, white, and black, metallic luster pigments such as gold and silver, and colorless or light-colored constitutions Examples include pigments and plastic pigments.
Examples of the pigment include particles in which silica, alumina, polymer beads or the like are used as a core, and a dye or pigment is fixed on the surface thereof, an insoluble lake of the dye, a colored emulsion, a colored latex, or the like.

  As colorants, in addition to pigments, hydrophilic anionic dyes, direct dyes, cationic dyes, reactive dyes, dyes such as polymer dyes and oil-soluble dyes, wax powders colored with dyes, resin powders, Or an emulsion, a fluorescent dye, a fluorescent pigment, etc. are mentioned.

The volume average particle diameter of the colorant is, for example, from 10 nm to 1,000 nm.
The volume average particle diameter of the colorant refers to the particle diameter of the colorant itself, or the particle diameter to which the additive has adhered when an additive such as a dispersant is attached to the colorant.
The volume average particle size is measured with a Microtrac UPA particle size analyzer UPA-UT151 (manufactured by Microtrac). The measurement is performed by placing 1,000-fold diluted ink in a measurement cell. As the input value at the time of measurement, the viscosity of the ink diluent is adopted as the viscosity, and the refractive index of the colorant is adopted as the particle refractive index.

  The content (concentration) of the colorant is, for example, preferably from 1% by mass to 25% by mass and more preferably from 2% by mass to 20% by mass with respect to the ink.

(Polymer particles)
The polymer particles will be described.
Each ink used in the present embodiment preferably includes polymer particles.
The polymer particles are components that enhance the fixability of an image with ink on a recording medium.
The polymer particles are obtained by granulating a polymer compound and are components different from the polymer dispersant described above.

Examples of the polymer particles include styrene-acrylic acid copolymer, styrene-acrylic acid-sodium acrylate copolymer, styrene-butadiene copolymer, polystyrene, acrylonitrile-butadiene copolymer, and acrylate copolymer. , Polyurethane, polyester, silicone-acrylic acid copolymer, acrylic modified fluororesin particles (latex particles).
Examples of the polymer particles include core / shell type polymer particles having different compositions at the center and outer edge of the particles.

The polymer particles may be dispersed in the ink using an emulsifier, or may be dispersed in the ink without using an emulsifier.
As an emulsifier, a polymer having a hydrophilic group such as a surfactant, a sulfonic acid group, or a carboxyl group (for example, a polymer having a hydrophilic group grafted thereto, a hydrophilic monomer and a hydrophobic portion) Polymers obtained from monomers).

The volume average particle diameter of the polymer particles is preferably 10 nm or more and 300 nm or less, more preferably 10 nm or more and 200 nm or less, from the viewpoint of glossiness and scratch resistance of the image.
The volume average particle diameter of the polymer particles is measured with a Microtrac UPA particle size analyzer UPA-UT151 (manufactured by Microtrac). The measurement is performed by placing 1,000-fold diluted ink in a measurement cell. As input values at the time of measurement, the viscosity of the ink diluent is used as the viscosity, and the refractive index of the polymer particles is used as the particle refractive index.

The glass transition temperature of the polymer particles is preferably 40 ° C. or higher and 90 ° C. or lower, and more preferably 70 ° C. or higher and 90 ° C. or lower from the viewpoint of suppressing landing unevenness. On the other hand, the glass transition temperature of the polymer particles is preferably −20 ° C. or higher and 80 ° C. or lower, more preferably −10 ° C. or higher and 60 ° C. or lower, from the viewpoint of image scratch resistance.
The glass transition temperature of the polymer particles is determined from the DSC curve obtained by differential scanning calorimetry (DSC). More specifically, the method for determining the glass transition temperature in JIS K7121-1987 “Method for Measuring Plastic Transition Temperature”. It is calculated | required by description "extrapolated glass transition start temperature" of description.

  The content of the polymer particles is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more with respect to the ink, from the viewpoint of enhancing the fixing property of the image, the ejection stability, and the film forming property. 5 mass% or less is more preferable.

(Surfactant)
The surfactant will be described.
Each ink used in the present embodiment preferably contains a surfactant.
The ink preferably contains, as a surfactant, for example, a surfactant having an HLB (hydrophilic-lipophilic balance) of 14 or less. The surface tension of the ink can be easily adjusted by adjusting the amount of the surfactant having an HLB of 14 or less, or by using a plurality of surfactants having different HLB.

The HLB (hydrophilic group / hydrophobic group balance “Hydrophile-Lipophile Balance”) is defined by the following formula (Griffin method).
・ HLB = 20 × (sum of formula weight of hydrophilic part / molecular weight)

  Examples of such a surfactant include at least one selected from the group consisting of an ethylene oxide adduct of acetylene glycol and a polyether-modified silicone.

The ethylene oxide adduct of acetylene glycol is, for example, an —O— (CH ₂ CH ₂ O) _n —H structure in which ethylene oxide is added to at least one hydroxyl group of acetylene glycol (for example, n is 1 to 30). A compound having an integer)
Examples of commercially available acetylene glycol ethylene oxide adducts (numbers in parentheses indicate HLB catalog values) include, for example, Olphine E1004 (from 7 to 9), Olphine E1010 (from 13 to 14), Olphine EXP. . 4001 (8 to 11), Olphin EXP. 4123 (11 to 14), Olphin EXP. 4300 (from 10 to 13), Surfinol 104H (4), Surfinol 420 (4), Surfinol 440 (4), Dinol 604 (8) (all manufactured by Nissin Chemical Industry Co., Ltd.) and the like. .

The polyether-modified silicone is, for example, a compound in which a polyether group is bonded to a silicone chain (polysiloxane main chain) in a graft form or a block form. Examples of the polyether group include a polyoxyethylene group and a polyoxypropylene group. The polyether group may be, for example, a polyoxyalkylene group in which an oxyethylene group and an oxypropylene group are added in a block form or randomly.
As commercial products of polyether-modified silicone (the numbers in parentheses indicate catalog values of HLB), Silface SAG002 (12), Silface SAG503A (11), Silface SAG005 (7) (the above, Nissin) Chemical Industry Co., Ltd.).

Other surfactants other than acetylene glycol ethylene oxide adduct and polyether-modified silicone may be used for the ink.
Examples of other surfactants include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants. Preferably, anionic surfactants and nonionic surfactants are used. is there.

Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonate of higher fatty acid ester, sulfuric acid of higher alcohol ether. Examples thereof include ester salts and sulfonates, higher alkyl sulfosuccinates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether sulfates, alkyl phosphates, polyoxyethylene alkyl ether phosphates, and the like.
Among these, as anionic surfactants, dodecylbenzenesulfonate, isopropylnaphthalenesulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenylsulfonate, monobutylbiphenylsulfonate, dibutylphenylphenol A disulfonate is preferable.

Nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, poly Examples thereof include oxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, sucrose fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, alkyl alkanol amide, polyethylene glycol polypropylene glycol block copolymer, acetylene glycol and the like.
Among these, nonionic surfactants include polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene Oxyethylene sorbitan fatty acid ester, fatty acid alkylolamide, polyethylene glycol polypropylene glycol block copolymer, and acetylene glycol are preferred.

  Other nonionic surfactants include silicone surfactants such as polysiloxane oxyethylene adducts; fluorine-based surfactants such as perfluoroalkyl carboxylates, perfluoroalkyl sulfonates, and oxyethylene perfluoroalkyl ethers. Agents; biosurfactants such as spicrispolic acid, rhamnolipid, lysolecithin; and the like.

  The hydrophilic / hydrophobic balance (HLB) of other surfactants is preferably in the range of 3 to 20, for example, in consideration of solubility.

The surfactant may be used alone or in combination of two or more.
Among these, as the surfactant, an ethylene oxide adduct of acetylene glycol is preferable, and each ink more preferably contains two or more ethylene oxide adducts of acetylene glycol.

  The total content of the surfactant in each ink is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, and 0.2% by mass with respect to the ink. More preferred is 3% by mass or less.

(Other additives)
Other additives will be described.
Each ink used in this embodiment may contain other additives.
Other additives include ink ejection improvers (polyethyleneimine, polyamines, polyvinylpyrrolidone, polyethylene glycol, ethylcellulose, carboxymethylcellulose, etc.), conductivity / pH adjusters (potassium hydroxide, sodium hydroxide, lithium hydroxide) Etc.), organic solvents other than the above aqueous organic solvents, reactive diluent solvents, penetrants, pH buffers, antioxidants, antifungal agents, viscosity modifiers, conductive agents, chelating agents And ultraviolet absorbers.

(Physical properties of each ink)
The preferred physical properties of each ink will be described.
When each ink is a water-based ink, the pH of each water-based ink is preferably in the range of 4 to 10 and more preferably in the range of 5 to 9.
Here, the pH of the water-based ink has a temperature of 23 ± 0.5 ° C. and a humidity of 55 ± 5% RP. H. Under the environment, a value measured by a pH / conductivity meter (MPC227 manufactured by METTLER TOLEDO) is adopted.

When each ink is a water-based ink, the conductivity of each water-based ink is preferably in the range of 0.01 S / m to 0.5 S / m, and in the range of 0.01 S / m to 0.25 S / m. Is more preferable, and a range of 0.01 S / m to 0.20 S / m is even more preferable.
The conductivity is measured by MPC227 (pH / Conductivity Meter, manufactured by METTLER TOLEDO).

(Use)
Here, each ink used in the present embodiment includes, for example, cyan ink, magenta ink, yellow ink, black ink, white ink and intermediate color inks other than these colors, special color inks such as green ink, orange ink, and violet ink, In addition, any of metallic ink and the like may be used.

〔recoding media〕
The recording medium to be recorded using the inkjet ink set according to the present embodiment is not particularly limited, and includes any known recording medium.
According to the ink jet recording method according to the present embodiment and the ink jet recording apparatus according to the present embodiment, intercolor bleeding is suppressed even for a low-penetration or non-penetrable recording medium in which intercolor bleeding is likely to occur.

In addition, a plain paper etc. are mentioned as a permeable recording medium. Specifically, the permeable recording medium means a recording medium having a maximum ink absorption amount exceeding 15 ml / m ² within a contact time of 500 ms as measured by a dynamic scanning absorption meter.
On the other hand, examples of the impermeable recording medium include films, plates, and the like made of resin, metal, glass, ceramics, silicon, rubber, and the like. Specifically, the non-permeable recording medium means a recording medium having a maximum ink absorption amount of less than 3 ml / m ² within a contact time of 500 ms as measured by a dynamic scanning absorption meter.
Examples of the low permeability recording medium include coated paper such as coated paper, art paper, and cast paper. Specifically, the low-penetration recording medium is a recording in which the maximum ink absorption amount within a contact time of 500 ms measured with a dynamic scanning absorption meter is in the range of 3 ml / m ^{2 to} 15 ml / m ^2. Means medium.

  Preferred examples of the recording medium include coated paper and resin film, and more preferred is coated paper.

[Ink cartridge set]
The ink cartridge according to the present embodiment includes a first ink cartridge that stores the first ink in the ink-jet ink set according to the present embodiment, and a second ink that stores the second ink in the ink-jet ink set according to the present embodiment. 2 ink cartridges.
Each ink cartridge in the ink cartridge set according to the present embodiment is preferably provided in a form that is detachable from, for example, an ink jet recording apparatus.
The ink cartridge according to this embodiment may include an ink cartridge other than the first ink cartridge and the second ink cartridge.

[Inkjet recording apparatus and inkjet recording method]
The ink jet recording apparatus according to the present embodiment accommodates the ink jet ink set according to the present embodiment, a first discharge head that discharges the first ink onto the recording medium, and a first discharge head that discharges the second ink onto the recording medium. A two-ejection head, and infrared irradiation means for drying at least one of the first ink and the second ink ejected on the recording medium.
In addition, the ink jet recording apparatus according to the present embodiment accommodates the ink set according to the present embodiment, and a yellow ink ejection head that ejects yellow ink onto the recording medium, and a magenta ink ejection head that ejects magenta ink onto the recording medium. A cyan ink discharge head for discharging cyan ink onto the recording medium; a black discharge head for discharging black ink onto the recording medium; a first infrared irradiation means for drying the yellow ink discharged onto the recording medium; A second infrared irradiation means for drying the magenta ink ejected on the medium; and a third infrared irradiation means for drying the cyan ink ejected on the recording medium. The inks are yellow ink, magenta ink, cyan ink and black ink, respectively. Aspect is at least one ink selected from that group are preferred.

  In the ink jet recording apparatus according to the present embodiment, the step of ejecting the first ink from the ink jet ink set according to the present embodiment onto the recording medium, and the second ink of the ink jet ink set according to the present embodiment as the recording medium. An ink jet recording method comprising: a step of discharging the ink, and a step of drying at least one of the first ink and the second ink discharged on the recording medium by irradiation with infrared rays (the ink jet according to the present embodiment) Recording method) is performed.

The ejection head used for ejecting ink droplets is not particularly limited, and a known inkjet head is used. Examples thereof include a piezo inkjet head and a thermal inkjet head.
The discharge temperature of each ink is not particularly limited and can be adjusted according to the ink used.
In the ink jet recording apparatus and the ink jet recording method according to the present embodiment, each ink may be ejected a plurality of times as necessary. For example, one type of ink may be ejected multiple times to the same location on the recording medium, two or more types of ink may be ejected once, or two or more types of ink may be ejected multiple times. May be.

  In the ink jet recording apparatus according to the present embodiment, from the viewpoint of inter-color bleeding, according to the light absorption rate of each ink, the discharge head that discharges ink having a low light absorption rate is disposed upstream of the recording medium conveyance direction. It is preferable to dispose the ejection head for ejecting high-density ink in order on the downstream side.

The infrared irradiation means is not particularly limited, but is preferably a means capable of irradiating the recording medium with infrared rays having a wavelength range of at least 760 nm or more and 1,500 nm or less. For example, an infrared laser irradiation apparatus is preferably used. .
Moreover, as an infrared irradiation means, an infrared laser irradiation apparatus, an infrared light emitting diode (infrared LED), etc. are mentioned. Among these, an infrared laser irradiation device is preferable.
Further, as the infrared irradiation means, an infrared laser irradiation unit in which a plurality of infrared laser light emitting elements are arranged along the width direction of the recording medium can be used.
In the infrared laser irradiation unit, the laser irradiation timing, irradiation position, and irradiation amount of each infrared laser light emitting element are adjusted for each infrared laser light emitting element according to the current value supplied to each infrared near laser light emitting element, for example. It is preferable that it is adapted. Such an infrared laser irradiation unit has a mechanism for controlling the irradiation timing of an infrared laser, a mechanism for controlling the irradiation amount of the infrared laser, and a mechanism for controlling the irradiation amount of the infrared laser, It is possible to have a mechanism for correcting variations.
Examples of such an infrared laser irradiation unit include a laser drying unit described in JP-A-2015-112792.

Irradiation with the infrared laser may be performed on the entire surface of the recording medium or may be performed on a part of the recording medium, but it is preferable to irradiate at least a region including a portion where ink is ejected.
Infrared irradiation amount may be an amount suitable for the drying of the ink, preferably from 1,000 J / m ² or more 100,000J / m ² or less, is 3,000 J / m ² or more 70,000J / m ² or less More preferably, it is more preferably 5,000 J / m ² or more and 50,000 J / m ² or less. The amount of infrared irradiation is the amount of infrared irradiation on the surface of the recording medium.
The infrared irradiation time is not particularly limited and may be irradiated until the ink is dried, but is preferably 100 μs to 1 s, more preferably 500 μs to 0.5 s, and further preferably 0.1 ms to 0.3 s. .

In addition, the inkjet recording apparatus according to the present embodiment preferably includes the infrared irradiation unit between the respective ejection heads (ejection units) from the viewpoint of intercolor bleeding.
Furthermore, the inkjet recording apparatus according to the present embodiment preferably has a drying unit other than the infrared irradiation unit on the downstream side in the recording medium conveyance direction of all the ejection heads (ejection units) from the viewpoint of intercolor bleeding. There is no restriction | limiting in particular as a drying means, A well-known means is used, For example, a drying drum, a warm air blower, a near-infrared heater, etc. are mentioned.

  The ink jet recording apparatus and the ink jet recording method according to the present embodiment, by using the ink jet ink set according to the present embodiment, form an image with excellent ink ejection stability and suppressed intercolor bleeding.

  The ink jet recording apparatus according to the present embodiment may include an ink cartridge set that accommodates each ink in the ink jet ink set according to the present embodiment and is made into a cartridge so as to be attached to and detached from the recording apparatus.

  Hereinafter, an example of a recording apparatus according to the present embodiment will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram illustrating an example of an ink jet recording apparatus according to the present embodiment.
As shown in FIG. 1, the inkjet recording apparatus 10 is a recording apparatus that includes ejection heads 122 </ b> Y, 122 </ b> M, 122 </ b> C, and 122 </ b> K that eject each ink onto a recording medium P. In the inkjet recording apparatus 10, an inkjet recording apparatus having an ejection unit that ejects water-based ink onto the recording medium P is realized. As a result, an image using water-based ink is recorded on the recording medium P.

Specifically, the inkjet recording apparatus 10 includes an image recording unit 12 that records an image on a continuous paper (hereinafter, also referred to as “continuous paper P”) as a recording medium P, for example.
The ink jet recording apparatus 10 adjusts the preprocessing unit 14 in which the continuous paper P supplied to the image recording unit 12 is accommodated, and the conveyance amount of the continuous paper P supplied from the preprocessing unit 14 to the image recording unit 12. And a buffer unit 16. The buffer unit 16 is disposed between the image recording unit 12 and the preprocessing unit 14.
The recording apparatus 10 includes, for example, a post-processing unit 18 that stores the continuous paper P discharged from the image recording unit 12, and a conveyance amount of the continuous paper P discharged from the image recording unit 12 to the post-processing unit 18. A buffer unit 20 to be adjusted. The buffer unit 20 is disposed between the image recording unit 12 and the post-processing unit 18.
The ink jet recording apparatus 10 includes a cooling unit 22 that is disposed between the image recording unit 12 and the buffer unit 20 and cools the continuous paper P that is carried out of the image recording unit 12.

The image recording unit 12 includes, for example, a roll member (not shown) that guides the continuous paper P along the conveyance path 124 of the continuous paper P, and a continuous paper that is conveyed along the conveyance path 124 of the continuous paper P. And an ejection device 121 that ejects water-based ink (water-based ink droplets) onto the paper P to record an image.
The ejection device 121 includes ejection heads 122Y, 122M, 122C, and 122K that eject each ink onto the continuous paper P. The ejection head has, for example, an effective recording area (arrangement area of nozzles that eject ink) equal to or greater than the width of the continuous paper P (the length in a direction intersecting (eg, orthogonal to) the continuous paper P conveyance direction). This is a long recording head.
The ejection head is not limited to this, and is an ejection head that is shorter than the width of the continuous paper P, and is a system that moves in the width direction of the continuous paper P to discharge aqueous ink (so-called carriage). Type) discharge head.

The ejection heads 122Y, 122M, 122C, and 122K may be a so-called thermal system that ejects ink droplets by heat, or may be a so-called piezo system that ejects ink droplets by pressure. Well known ones are applied.
The inkjet recording apparatus 10 includes, for example, an ejection head 122Y that ejects ink onto the continuous paper P to record a Y (yellow) color image, an ejection head 122M that records an M (magenta) color image, and a C ( It has an ejection head 122C for recording a cyan) color image and an ejection head 122K for recording a K (black) color image. The ejection head 122Y, the ejection head 122M, the ejection head 122C, and the ejection head 122K are in this order in the transport direction of the continuous paper P (hereinafter, simply referred to as “paper transport direction”). Are arranged so as to face the continuous paper P from the upstream side to the downstream side. When Y, M, C, and K are not distinguished in the description of the ejection head, Y, M, C, and K attached to the reference numerals are omitted.

The discharge device 121 is not limited to the form in which the four first discharge heads and the four second discharge heads corresponding to each of the four colors are arranged, and each of four or more colors including other intermediate colors depending on the purpose. 4 or more first discharge heads and four or more second discharge heads corresponding to the above may be arranged.
Here, as the ejection heads 122Y, 122M, 122C, and 122K, for example, a low-resolution ejection head (for example, a 600 dpi ejection head) that ejects ink in a range of an ink droplet amount to 15 pl or less, an ink droplet amount of less than 10 pl. Any of high-resolution ejection heads (for example, 1,200 dpi ejection heads) that eject ink in a range may be provided. Further, the ejection device 121 may include both a low resolution ejection head and a high resolution ejection head. In addition, dpi means “dot per inch”.
Infrared laser irradiation devices 128A, 128B, and 128C are provided as drying means between the ejection heads 122Y, 122M, 122C, and 122K, respectively. Further, an infrared laser irradiation device may be further provided on the downstream side of the ejection head 122K in the paper conveyance direction.
The discharge device 121 is driven in contact with the transported continuous paper P by, for example, the back surface of the continuous paper P being wound around the discharge heads 122Y, 122M, 122C, and 122K in the downstream of the paper transport direction. A drying drum 126 (an example of a drying device) that dries images (ink) on the continuous paper P while rotating is disposed.
A heating source (for example, a halogen heater or the like: not shown) is built in the drying drum 126. The drying drum 126 dries the image (water-based ink) on the continuous paper P by heating with a heating source.
Around the drying drum 126, a hot air blower 128 (an example of a drying device) that dries an image (ink) on the continuous paper P is disposed. The image (ink) on the continuous paper P wound around the drying drum 126 is dried by the warm air from the warm air blower 128.

  On the other hand, the preprocessing unit 14 includes a supply roll 14B around which the continuous paper P supplied to the image recording unit 12 is wound. The supply roll 14B is rotatably supported by a frame member (not shown). ing.

  In the buffer unit 16, for example, a first pass roller 16A, a dancer roller 16B, and a second pass roller 16C are arranged along the paper transport direction. The dancer roller 16 </ b> B moves up and down in FIG. 1 to adjust the tension of the continuous paper P conveyed to the image recording unit 12 and the conveyance amount of the continuous paper P.

  The post-processing unit 18 includes a winding roll 18A as an example of a transport unit that winds the continuous paper P on which images are recorded. The take-up roll 18 </ b> A receives a rotational force from a motor (not shown) and rotates so that the continuous paper P is transported along the transport path 124.

In the buffer unit 20, for example, a first pass roller 20A, a dancer roller 20B, and a second pass roller 20C are arranged along the paper transport direction. The dancer roller 20 </ b> B moves up and down in FIG. 1 to adjust the tension of the continuous paper P discharged to the post-processing unit 18 and the conveyance amount of the continuous paper P.
The cooling unit 22 is provided with a plurality of cooling rollers 22A. The continuous paper P is cooled by conveying the continuous paper P between the plurality of cooling rollers 22A.

Next, the operation (recording apparatus) by the inkjet recording apparatus 10 according to the present embodiment will be described.
In the inkjet recording apparatus 10 according to the present embodiment, first, the continuous paper P is conveyed from the supply roll 14 </ b> B of the preprocessing unit 14 to the image recording unit 12 through the buffer unit 16.
Next, in the image recording unit 12, ink is ejected from the ejection heads 122Y, 122M, 122C, and 122K of the ejection device 121 onto a recording medium. As a result, an image of water-based ink is formed on the continuous paper P. The ink ejected by the ejection head 122Y is irradiated with infrared rays by the infrared laser irradiation device 128A, and at least a part of a solvent such as water is volatilized. The ink ejected by the ejection head 122M is irradiated with infrared rays by the infrared laser irradiation device 128B, and at least a part of a solvent such as water is volatilized. Further, the ink ejected by the ejection head 122C is irradiated with infrared rays by the infrared laser irradiation device 128C, and at least a part of a solvent such as water is volatilized. Further, the ink ejected by the ejection head 122K may be irradiated with infrared rays by an infrared laser irradiation device. In this case, at least a part of the solvent such as water is volatilized in the ink ejected by the ejection head 122K. . Thereafter, the image (water-based ink) on the continuous paper P is dried from the back side (the surface opposite to the recording surface) of the continuous paper P by the drying drum 126. Then, the water-based ink (image) discharged onto the continuous paper P is dried from the surface side (recording surface) of the continuous paper P by the hot air blower 128. That is, the ink discharged onto the continuous paper P is dried by the drying drum 126 and the hot air blowing device 128. Although the hot air blower 128 may not be provided, there is an effect of eliminating the evaporated water.
Next, in the cooling unit 22, the continuous paper P on which the images are recorded is cooled by the cooling roller 22A.
Next, through the buffer unit 16, the post-processing unit 18 winds the continuous paper P on which the images are recorded by the winding roll 18A.

Through the above means, an image with water-based ink is recorded on the continuous paper P as the recording medium P.
In the inkjet recording apparatus 10, the method of directly ejecting ink droplets onto the surface of the recording medium P by the ejection device 121 has been described. However, the present invention is not limited to this. For example, after ejecting ink droplets to the intermediate transfer member Alternatively, a method of transferring ink droplets on the intermediate transfer member to the recording medium P may be used.

  Further, in the inkjet recording apparatus 10, the method of recording an image by ejecting ink onto the continuous paper P as the recording medium P has been described. However, the method of recording the image by ejecting ink onto a sheet as the recording medium P It may be.

  It is needless to say that the above-described embodiment is not limited to the embodiment and is realized within a range satisfying the requirements of the present invention. For example, instead of the drying drum 126 and the hot air blowing device 128, drying may be performed with an infrared lamp.

  EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples. Unless otherwise specified, “part” represents “part by mass” and “%” represents “% by mass”.

Example 1
<Preparation of cyan ink 2>
Pigment Blue 15: 4 (cyan pigment, manufactured by DIC Corporation): 4.0% by mass
Styrene-acrylate copolymer (pigment dispersant, manufactured by BASF): 0.4% by mass
Propylene glycol (Wako Pure Chemical Industries, Ltd.): 10% by mass
Diethylene glycol monoisopropyl ether: 5% by mass
1,2-hexanediol (manufactured by Wako Pure Chemical Industries, Ltd.): 1% by mass
Polyacrylate emulsion (solid content 25%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.): 4% by mass
Infrared absorber dispersion (including 2% by mass of squarylium compound, 18% by mass of styrene / ethyl methacrylate / acrylic acid-2-carboxyethyl copolymer (30/60/10), 80% by mass of aqueous solvent): 5% by mass
Olfine E1010 (surfactant, manufactured by Nissin Chemical Industry Co., Ltd.): 0.5% by mass
Olfine E1004 (surfactant, manufactured by Nissin Chemical Industry Co., Ltd.): 0.5% by mass
Pure water: 69.6% by mass
After mixing the above components, the mixture was filtered with a 5 μm filter to obtain cyan ink 2.

<Calculation Method of Formula (1), which is an Approximate Formula for Ink Evaporation Rates of 0% to 60%>
Using rheometer HAAKE MARS (manufactured by Thermo Fisher Scientific Co., Ltd.), ink evaporation rate of 0%, 15%, 30%, 45%, 60% and 60% or less The viscosity of the ink at 30 ° C. was measured. Five measured values were regressed to the formula (1) by the least square method, and the values of a and b in the formula (1) were calculated.

The value of a in cyan ink 2 was 1.2, and the value of b was 4.55.
Further, the viscosity (evaporation rate 0%) of cyan ink 2 at 30 ° C. was 5.7 mPa · s.

<Preparation of magenta ink 2>
PigmentRed 122 (magenta pigment, manufactured by DIC Corporation): 6.0% by mass
Styrene-acrylate copolymer (pigment dispersant, manufactured by BASF): 0.6% by mass
Propylene glycol (Wako Pure Chemical Industries, Ltd.): 10% by mass
Diethylene glycol monoisopropyl ether: 5% by mass
1,2-hexanediol (manufactured by Wako Pure Chemical Industries, Ltd.): 1% by mass
Polyacrylate emulsion (solid content 25%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.): 4% by mass
Infrared absorber dispersion (including 2% by mass of squarylium compound, 18% by mass of styrene / ethyl methacrylate / acrylic acid-2-carboxyethyl copolymer (30/60/10), 80% by mass of aqueous solvent): 4% by mass
Olfine E1010 (surfactant, manufactured by Nissin Chemical Industry Co., Ltd.): 0.6% by mass
Olfine E1004 (surfactant, manufactured by Nissin Chemical Industry Co., Ltd.): 0.4% by mass
Pure water: 68.4% by mass

<Preparation of yellow ink 2>
A yellow ink 2 was obtained in the same manner as the cyan ink 2 except that Pigment Yellow 74 (yellow pigment, manufactured by DIC Corporation) was used instead of Pigment Blue 15: 4.

<Preparation of black ink 2>
Carbon black (carbon black pigment, manufactured by Cabot Corporation): 5.3 wt. %
Styrene-methacrylate copolymer (pigment dispersant, manufactured by BASF): 0.53 wt%
Propylene glycol: 15 wt. %
Diethylene glycol monoisopropyl ether: 4 wt. %
1,2 hexanediol: 1.5 wt. %
Polyacrylate emulsion (solid content 25%, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.): 5% by mass
Olfine E1010 (surfactant, manufactured by Nissin Chemical Industry Co., Ltd.): 0.6% by mass
Olfine E1004 (surfactant, manufactured by Nissin Chemical Industry Co., Ltd.): 0.4% by mass
Pure water: 67.67% by mass

The value of a in magenta ink 2 is 1.27, the value of b is 4.23, the value of a in yellow ink 2 is 1.15, the value of b is 4.45, and the value of a in black ink 2 is The value was 1.16, and the value of b was 4.54.
The viscosity (evaporation rate 0%) of magenta ink 2 at 30 ° C. was 5.5 mPa · s.
The viscosity (evaporation rate 0%) of yellow ink 2 at 30 ° C. was 5.6 mPa · s.
The viscosity (evaporation rate 0%) of the black ink 2 at 30 ° C. was 5.7 mPa · s.

<Preparation of cyan inks 1, 3 and 4>
In cyan ink 1, the amount of polyacrylate emulsion and pure water was increased and the amount of propylene glycol was decreased relative to cyan ink 2 so that a was about the target value shown in Table 1. For cyan ink 3, the amount of polyacrylate emulsion was reduced and the amount of propylene glycol and pure water was increased relative to cyan ink 2 so that a was about the target value shown in Table 1. In the cyan ink 4, the polyacrylate emulsion was reduced with respect to the cyan ink 2 so that a was about the target value shown in Table 1, and pure water, propylene glycol and 1,2-hexanediol were increased.
Further, the viscosity (evaporation rate 0%) of cyan ink 1 at 30 ° C. was 5.8 mPa · s.
The viscosity (evaporation rate 0%) of cyan ink 3 at 30 ° C. was 5.7 mPa · s.
The viscosity (evaporation rate 0%) of cyan ink 4 at 30 ° C. was 5.4 mPa · s.

<Preparation of magenta inks 1, 3 and 4>
In the magenta ink 1, the amount of polyacrylate emulsion and pure water was increased and the amount of propylene glycol was decreased with respect to the magenta ink 2 so that a was about the target value shown in Table 1. In magenta ink 3, the amount of polyacrylate emulsion was reduced and the amount of propylene glycol and pure water was increased with respect to magenta ink 2 so that a was about the target value shown in Table 1. In magenta ink 4, the amount of polyacrylate emulsion was reduced to about magenta ink 2 so that a was the target value shown in Table 1, and pure water, propylene glycol and 1,2-hexanediol were increased.
The viscosity (evaporation rate 0%) of magenta ink 1 at 30 ° C. was 5.6 mPa · s.
The viscosity (evaporation rate 0%) of magenta ink 3 at 30 ° C. was 5.5 mPa · s.
The viscosity (evaporation rate 0%) of the magenta ink 4 at 30 ° C. was 5.2 mPa · s.

<Preparation of yellow inks 1, 3 and 4>
For yellow ink 1, the amount of polyacrylate emulsion and pure water was increased and the amount of propylene glycol was decreased with respect to yellow ink 2 so that a was about the target value shown in Table 1. For yellow ink 3, the amount of polyacrylate emulsion was reduced and the amount of propylene glycol and pure water was increased relative to yellow ink 2 so that a was about the target value shown in Table 1. In yellow ink 4, the amount of polyacrylate emulsion was reduced with respect to yellow ink 2 so that a was about the target value shown in Table 1, and pure water, propylene glycol and 1,2-hexanediol were increased.
The viscosity (evaporation rate 0%) of yellow ink 1 at 30 ° C. was 5.5 mPa · s.
The viscosity (evaporation rate 0%) of the yellow ink 3 at 30 ° C. was 5.3 mPa · s.
The viscosity (evaporation rate 0%) of the yellow ink 4 at 30 ° C. was 5.4 mPa · s.

<Preparation of black inks 1, 3 and 4>
For black ink 1, the amount of polyacrylate emulsion and pure water was increased and the amount of propylene glycol was decreased with respect to black ink 2 so that a was about the target value shown in Table 1. For black ink 3, the amount of polyacrylate emulsion was reduced and the amount of propylene glycol and pure water was increased with respect to black ink 2 so that a was about the target value shown in Table 1. For black ink 4, the amount of polyacrylate emulsion was reduced with respect to black ink 2 so that a was about the target value shown in Table 1, and pure water, propylene glycol and 1,2-hexanediol were increased.
Moreover, the viscosity (evaporation rate 0%) of the black ink 1 at 30 ° C. was 5.8 mPa · s.
The viscosity (evaporation rate 0%) of the black ink 3 at 30 ° C. was 5.7 mPa · s.
The viscosity (evaporation rate 0%) of the black ink 4 at 30 ° C. was 5.5 mPa · s.

  In Table 1, “C” represents cyan ink, “M” represents magenta ink, “Y” represents yellow ink, and “K” represents black ink. The same applies to the following.

<Measurement method of light absorption rate>
The light absorption rate of the ink was measured by the following method.
Using a UV-visible near-infrared spectrophotometer V-560 (manufactured by JASCO Corporation) and a 10 mm square quartz cell, the absorbance A at the laser wavelength of the ink diluted with pure water was measured, and the Lambert-Beer rule. The absorptance in the ink film thickness at the time of printing was calculated from the conversion formula by That is, the absorbance A of a solution obtained by mixing the ink weight W _ink = 1 g and pure water W _water = 200 g was measured, and the absorption rate% A = 1-10 ^{− ((Wink) of the} ink film thickness d = 5 × 10 ⁻³ mm. ^{/ Wwater) × (d / 10) × A)} .

The cyan, magenta, and yellow inks 1 to 4 all had a light absorption rate of 0.7, and the black inks 1 to 4 had a light absorption rate of 0.8.
The light absorptance was adjusted by changing the ratio of the infrared absorbent and the dispersion resin contained in the infrared absorbent dispersion.

<Image forming method>
A piezo-type inkjet head shown in FIG. 1 (resolution: 1,200 × 1,200 dpi, maximum ink droplet amount: 5 pL) and an inkjet recording system including an infrared laser and a heating roller as a drying device are prepared. Each color ink described (cyan ink, magenta ink, yellow ink and black ink) was loaded. The conveyance speed of the recording medium was set to 50 m / min.
As a recording medium, an OK top coat + paper (manufactured by Oji Paper Co., Ltd.) was prepared.
On the recording medium, each color ink was ejected from an inkjet head and dried with an infrared laser and a heating roller to obtain a recorded image.
As the recorded image, an image corresponding to each evaluation described later was formed.

<Evaluation>
[Blending between colors]
In the image forming method described above, a chart that draws a single-color 8-dot line is superimposed on the single-color coverage 100% patch and the secondary-color coverage 100% patch, and is dried by inkjet discharge, infrared laser, or the like. Obtained. In the obtained recorded image, the 8 dot line radiusness (Raggedness) was measured with PIAS II (manufactured by QEA) and evaluated according to the following criteria.
A: All of the radius values are less than 15 μm. B: Some places where the radius values are 15 μm or more and less than 30 μm are found, but both are less than 30 μm. C: Some places where the radius value is 30 μm or more.

[Problems caused by high temperatures (high temperature problems (decrease in image density, blister))]
In the above image forming method, ink jet ejection for drawing a patch having a monochrome printing rate of 100% was performed and dried by an infrared laser or the like to obtain a recorded image. Using the X-Rite 504 (manufactured by X-Rite), the optical density (OD) of the obtained patch image is measured, and further visually observed using a 10-fold magnifier to confirm the occurrence of blistering (swelling). did.
For comparison, a recorded image was obtained in the same manner as described above except that natural drying was performed instead of drying using the infrared laser or the like, and the optical density was measured.
The evaluation criteria are shown below.
A: ΔOD (difference in optical density from the naturally dried product) <0.3 with respect to the naturally dried optical density drop, and no blister is confirmed. B: Reduced optical density is naturally dried. On the other hand, ΔOD ≧ 0.3 and no blister is confirmed. C: ΔOD ≧ 0.3 and blister is confirmed with respect to a naturally dried optical density drop.

[Discharge stability]
Using a material printer DMP2891 manufactured by FUJIFILM Dimatix, continuous dots were printed using each ink, and dots were printed again after thinning out the number of dots corresponding to the pause time.
The reference (ink jet ejection for reference) was a pause time of 0.0015 seconds, and the evaluation target was a pause time of 0.8 seconds.
The amount of landing position deviation of the first dot after the pause (difference between the reference dot position in the printing direction and the dot position to be evaluated) was magnified by an optical microscope and measured.
The evaluation criteria are shown below.
A: The landing position deviation amount is less than 10 μm in any of the used inks. B: The landing position deviation amount in at least one of the used inks is 10 μm or more and less than 20 μm, and the landing position deviation is in any of the used inks. The amount is less than 20 μm.
C: The amount of landing position deviation in at least one of the used inks is 20 μm or more.

0 in a configuration employing a print order and ink shown in Table 2, with respect to 1.05J / ^cm 2, 3 color against 3.08J / ^cm 2, 2 color infrared irradiation energy per color. The following results were obtained when it was set to 57 J / cm ² and 0.65 J / cm ^{2 for} the fourth color. The evaluation results are shown in Table 2.

0 in a configuration employing a print order and inks described in Table 3, with respect to 1.31J / ^cm 2, 3 color against 1.59J / ^cm 2, 2 color infrared irradiation energy per color. The following results were obtained when 88J / cm ² and 0.77 J / cm ² were set for the fourth color. The evaluation results are shown in Table 3.

10: inkjet recording apparatus 12: image recording unit 14: pre-processing unit 14B: supply roll 16: buffer unit 16A: first pass roller 16B: dancer roller 16C: second pass roller 18: post-processing unit 18A: take-up roll 20: buffer Unit 20A: first pass roller 20B: dancer roller 20C: second pass roller 22: cooling unit 22A: cooling roller 121: discharge devices 122K, 122Y, 122M, 122C: discharge head 124: transport path 126: drying drum 128: hot air blowing Devices 128A, 128B, 128C: Infrared laser irradiation device P: Recording medium

Claims (6)

A first ink containing an infrared absorber and water;
A second ink containing an infrared absorber and water and having a value of a coefficient a of the following formula (1), which is a relational expression between the viscosity and the evaporation rate of the ink, different from the first ink by 1.5 times or more; Inkjet ink set.
y = a * exp (10x) + b (1)
In formula (1), x is a mass evaporation rate in the ink and represents 0 or more and 0.6 or less, y represents the viscosity (mPa · s) of the ink at 30 ° C., and b represents a y-intercept.   2. The inkjet ink set according to claim 1, wherein the viscosity at 30 ° C. of all inks of the inkjet ink set is 4 mPa · s or more and 10 mPa · s or less.   The inkjet ink set according to claim 1, wherein each of the first ink and the second ink further contains an organic solvent. A first ink cartridge containing the first ink in the inkjet ink set according to any one of claims 1 to 3,
An ink cartridge set comprising: a second ink cartridge containing the second ink in the inkjet ink set according to any one of claims 1 to 3. Containing the inkjet ink set according to any one of claims 1 to 3,
A first ejection head for ejecting the first ink onto a recording medium;
A second ejection head for ejecting the second ink onto a recording medium; and
An ink jet recording apparatus comprising: an infrared irradiation unit that dries at least one of the first ink and the second ink ejected on the recording medium. A step of ejecting the first ink of the inkjet ink set according to any one of claims 1 to 3 onto a recording medium;
A step of discharging the second ink from the inkjet ink set according to any one of claims 1 to 3 onto a recording medium; and
A step of drying at least one of the first ink and the second ink ejected on the recording medium by irradiation with infrared rays;