Water-based pigment dispersions and water-based inks

Abstract

The present invention provides an aqueous pigment dispersion that does not result in a decrease in print quality due to white streaks or color unevenness when printed on coated paper, and that has good abrasion resistance, as well as an aqueous ink containing the aqueous pigment dispersion. [Solution] An aqueous pigment dispersion comprising a pigment and a polymer dispersant, wherein the polymer dispersant contains a polymer comprising one or more constituent units (A) selected from the group consisting of hydrocarbon compounds having vinyl groups and alkyl (meth)acrylates, a constituent unit (B) derived from a sulfonic acid having a polymerizable unsaturated group, and a constituent unit (C) derived from a carboxylic acid having a polymerizable unsaturated group, and at least a portion of the carboxyl groups of the polymer are crosslinked by a crosslinking agent.

Description

Technical Field

[0001] The present invention relates to an aqueous pigment dispersion and an aqueous ink.

Background Art

[0002] The inkjet recording method is a recording method in which ink droplets are directly ejected from fine nozzles and adhered to a recording medium to obtain characters and images. This method has many advantages such as being easy to achieve full color, inexpensive, being able to use plain paper as a recording medium, and being non-contact with the printed material, so it has become extremely popular. In recent years, due to the spread of digital printing, it has been used not only for consumer printing but also for commercial printing and industrial printing using low-absorbency coated paper and the like. The demand for aqueous inkjet inks is increasing more and more for the purpose of increasing printing speed, improving image quality, and reducing environmental impact.

[0003] For example, Patent Document 1 has an object of providing a dispersion liquid or the like that enables the easily redispersion of a solidified coloring material and can improve clogging prevention and ejection stability. It includes water, a coloring material, and a dispersion resin that disperses the coloring material. The dispersion resin has a structural unit A containing a hydrophobic monomer, a structural unit B containing a hydrophilic acrylic acid monomer, and a structural unit C containing an acrylamide monomer having a sulfonic acid group. The weight average molecular weight of the dispersion resin is 5000 to 100000, and the content of the structural unit A is 60 mol% or more based on the total amount of the dispersion resin. A dispersion liquid is disclosed.

[0004] Patent Document 2 discloses a dispersion that enables easy redispersion of solidified colorants and improves stability during drying and re-dispensing, comprising water, a colorant, and a dispersion resin for dispersing the colorant, wherein the dispersion resin comprises constituent unit A containing a hydrophobic monomer, constituent unit B containing a hydrophilic acrylic acid monomer, and constituent unit C containing a hydrophilic vinyl monomer having a sulfonic acid group, the weight-average molecular weight of the dispersion resin is 10,000 to 100,000, and the content of constituent unit A is 60 mol% or more of the total amount of the dispersion resin.

[0005] Furthermore, Patent Document 3 discloses an aqueous inkjet ink that aims to solve problems such as scratch resistance and glossiness of recorded images formed using pigment ink, wherein resin A contributes to the dispersion of the pigment, resin B does not contribute to the dispersion of the pigment compared to resin A, resin A is a copolymer that does not precipitate in the pH range of 4.0 to 6.0, and is at least one copolymer selected from the group consisting of copolymers having vinyl alcohol monomer units, copolymers having monomer units having sulfonic acid groups, and copolymers in which the monomer units contributing as hydrophilic groups are only (meth)acrylic acid units, and resin B is a copolymer having (meth)acrylic acid monomer units that precipitate in the pH range of 4.0 to 6.0. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-020902 [Patent Document 2] Japanese Patent Publication No. 2022-052812 [Patent Document 3] Japanese Patent Publication No. 2010-090191 [Overview of the project] [Problems that the invention aims to solve]

[0007] Water-based inks containing aqueous pigment dispersions described in Patent Documents 1 and 2 had problems when printed on coated paper, a low-liquid-absorbent media with a smooth surface that does not spread easily. This resulted in insufficient ink wetting and a decrease in print quality due to white streaks and uneven coloring. Furthermore, the ink described in Patent Document 3 did not provide satisfactory abrasion resistance.

[0008] The present invention aims to provide an aqueous pigment dispersion and an aqueous ink containing the aqueous pigment dispersion that, when printed on coated paper, does not result in a decrease in print quality due to white streaks or color unevenness, and has good abrasion resistance. [Means for solving the problem]

[0009] The present invention relates to the following [1] and [2]. [1] An aqueous pigment dispersion comprising a pigment and a polymer dispersant, The polymer dispersant contains a polymer comprising one or more hydrophobic monomers (A) selected from the group consisting of hydrocarbon compounds having vinyl groups and alkyl (meth)acrylates, a structural unit (B) derived from a sulfonic acid having a polymerizable unsaturated group, and a structural unit (C) derived from a carboxylic acid having a polymerizable unsaturated group. An aqueous pigment dispersion in which at least a portion of the carboxyl groups of the polymer are crosslinked with a crosslinking agent. [2] A water-based ink containing the water-based pigment dispersion described in [1] above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an aqueous pigment dispersion and an aqueous ink containing the aqueous pigment dispersion that do not cause a decrease in print quality due to white streaks or color unevenness even when printed on coated paper, and that have good abrasion resistance. [Modes for carrying out the invention]

[0011] <Water-based pigment dispersion> The aqueous pigment dispersion of the present invention is an aqueous pigment dispersion comprising a pigment and a polymer dispersant, The polymer dispersant contains a polymer comprising one or more hydrophobic monomers (A) selected from the group consisting of hydrocarbon compounds having vinyl groups and alkyl (meth)acrylates, a structural unit (B) derived from a sulfonic acid having a polymerizable unsaturated group, and a structural unit (C) derived from a carboxylic acid having a polymerizable unsaturated group. This is an aqueous pigment dispersion in which at least a portion of the carboxyl groups of the polymer are crosslinked with a crosslinking agent. In this invention, "aqueous system" means that water accounts for the largest proportion by mass in the medium. Water-based ink is sometimes simply referred to as "ink." A polymer containing the above-mentioned constituent units (A) to (C), in which at least a portion of the carboxyl groups of the polymer are crosslinked by a crosslinking agent, may be referred to as "the polymer according to this embodiment."

[0012] By using the above-described configuration for the aqueous pigment dispersion, even when printing on coated paper with a smooth surface that does not easily wet, the deterioration of print quality due to white streaks and color unevenness is suppressed, and the dispersion also exhibits excellent abrasion resistance. The reason for this is not entirely clear, but it is presumed to be due to the following reasons. The polymer according to this embodiment comprises a structural unit (C) having a highly hydrophilic carboxyl group and a structural unit (B) having a more hydrophilic sulfonic acid group, and further comprises a structural unit (A) derived from one or more hydrophobic monomers selected from the group consisting of hydrocarbon compounds having vinyl groups and alkyl (meth)acrylate esters. By including structural units (B) and (C), the aggregation rate associated with the drying of ink droplets is mitigated, and at least a portion of the carboxyl groups are crosslinked by the crosslinking agent, which is thought to improve not only the wettability but also the abrasion resistance of the ink.

[0013] This is thought to be because crosslinking suppresses the desorption of resin from the pigment surface, thereby suppressing the increase in ink viscosity when the ink becomes solvent-rich during the drying process, and thus improving the ink's wettability and spreadability. Furthermore, it is thought that crosslinking suppresses the interaction between the hydrophobic groups of the polymer according to this embodiment, improving the adhesion between the polymer according to this embodiment and the coated paper, and thus improving abrasion resistance.

[0014] (Polymer dispersant) The polymer dispersant contains a polymer comprising one or more hydrophobic monomers (A) selected from the group consisting of hydrocarbon compounds having vinyl groups and alkyl (meth)acrylates, a structural unit (B) derived from a sulfonic acid having polymerizable unsaturated groups, and a structural unit (C) derived from a carboxylic acid having polymerizable unsaturated groups, wherein at least a portion of the carboxyl groups of the polymer are crosslinked by a crosslinking agent. In other words, the polymer according to this embodiment is a crosslinked polymer, and an uncrosslinked polymer (hereinafter also simply referred to as "uncrosslinked polymer a") containing one or more hydrophobic monomers (A) selected from the group consisting of hydrocarbon compounds having vinyl groups and alkyl (meth)acrylates, a sulfonic acid (B) having polymerizable unsaturated groups, and a carboxylic acid (C) having polymerizable unsaturated groups is crosslinked with a crosslinking agent.

[0015] [Component Unit (A)] The polymer according to this embodiment contains one or more constituent units (A) derived from hydrophobic monomers selected from the group consisting of hydrocarbon compounds having a vinyl group and alkyl (meth)acrylates. As for hydrocarbon compounds having a vinyl group, aromatic hydrocarbon compounds having a vinyl group are preferred. From the viewpoint of ink wettability, the number of carbon atoms in the aromatic group of an aromatic hydrocarbon compound having a vinyl group is preferably 6 or more, preferably 10 or less, and more preferably 7 or less. Examples of the aromatic hydrocarbon compound having a vinyl group include styrene, α-methylstyrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 2,4-dimethylstyrene, vinyl naphthalene, vinyl anthracene, etc. From the viewpoint of the ink wetting and spreading property, styrene is preferable among them from the viewpoints of availability and economy. From the viewpoints of the ink wetting and spreading property and abrasion resistance, the number of carbon atoms of the alkyl group of the (meth)acrylic acid alkyl ester is preferably 4 or more, more preferably 5 or more, still more preferably 6 or more, and from the same viewpoints, preferably 24 or less, more preferably 18 or less, still more preferably 12 or less, and even more preferably 7 or less. Note that "(meth)acrylic" includes methacrylic, acrylic, or both of them.

[0016] In the (meth)acrylic acid alkyl ester, the structure of the alkyl group is not particularly limited, and a linear, branched or alicyclic alkyl group can be used. Examples of the linear alkyl group include n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-dodecyl group (lauryl group), stearyl group, behenyl group, etc. Examples of the branched alkyl group include 2-ethylhexyl group, isohexyl group, isodecyl group, 3,5,5-trimethylhexyl group, isostearyl group, etc. Examples of the alicyclic alkyl group (cycloalkyl group) include cyclohexyl group, cyclooctyl group, 3,3,5-trimethylcyclohexyl group, isobornyl group, adamantyl group, etc. The linear, branched or alicyclic alkyl group may have an aromatic group, and for example, it may be an aromatic group-containing alkyl group (arylalkyl group) such as a benzyl group. Among the above, from the viewpoint of the ink wetting and spreading property, the alkyl group of the (meth)acrylic acid alkyl ester is preferably an alicyclic alkyl group and an aromatic group-containing alkyl group. Also, from the viewpoint of abrasion resistance, an alicyclic alkyl group and a linear alkyl group are preferable. Furthermore, from the viewpoint of achieving both ink wettability and abrasion resistance, the alkyl group of the (meth)acrylate alkyl ester is preferably an alicyclic alkyl group, more preferably a cyclohexyl group and an isobornyl group, and even more preferably a cyclohexyl group.

[0017] The constituent unit (A) may consist solely of constituent units derived from hydrocarbon compounds having vinyl groups, or solely of constituent units derived from alkyl (meth)acrylates, or may contain both constituent units derived from hydrocarbon compounds having vinyl groups and constituent units derived from alkyl (meth)acrylates. Furthermore, the hydrocarbon compound having vinyl groups may consist of only one type or two or more types, and the alkyl (meth)acrylate may consist of only one type or two or more types.

[0018] From the viewpoint of ink wettability and abrasion resistance, the total content of constituent units derived from aromatic hydrocarbon compounds having vinyl groups in constituent unit (A) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and more preferably 100% by mass.

[0019] Furthermore, from the viewpoint of the ink's wettability, the total content of constituent units derived from alkyl (meth)acrylate containing aromatic group-containing alkyl groups in constituent unit (A) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and more preferably 100% by mass.

[0020] Furthermore, from the viewpoint of abrasion resistance, the total content of constituent units derived from (meth)acrylic acid ester having a linear alkyl group in constituent unit (A) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and more preferably 100% by mass.

[0021] Furthermore, from the viewpoint of ink wettability and abrasion resistance, the content of constituent units derived from alkyl (meth)acrylate having an alicyclic alkyl group in constituent unit (A) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and more preferably 100% by mass.

[0022] From the viewpoint of abrasion resistance, it is preferable that the constituent unit (A) does not contain aromatic hydrocarbon groups. Specifically, it is preferable that the constituent unit (A) does not contain constituent unit (a1) derived from a monomer containing an aromatic hydrocarbon group selected from the group consisting of aromatic hydrocarbon compounds having a vinyl group and alkyl (meth)acrylates containing an aromatic group-containing alkyl group. The content of constituent unit (a1) in constituent unit (A) is preferably 50% by mass or less, more preferably 10% by mass or less, and even more preferably 1% by mass or less.

[0023] [Component Unit (B)] The polymer according to this embodiment contains a constituent unit (B) derived from a sulfonic acid having a polymerizable unsaturated group (hereinafter also simply referred to as "unsaturated sulfonic acid"). Examples of polymerizable unsaturated groups include vinyl groups, vinylidene groups, vinylene groups, etc., and from the viewpoint of ink wettability and abrasion resistance, vinyl groups are preferred. "Derived from sulfonic acid having polymerizable unsaturated groups" includes not only sulfonic acid having polymerizable unsaturated groups itself, but also sulfonates having polymerizable unsaturated groups. Examples of unsaturated sulfonic acids include styrene sulfonic acid, vinyl sulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid, from the viewpoint of availability and cost-effectiveness. Examples of salts include ammonium salts and alkali metal salts. Among the above, vinyl sulfonic acid and 2-acrylamido-2-methylpropanesulfonic acid are preferred as unsaturated sulfonic acids from the viewpoint of ink wetting spreadability and abrasion resistance. The unsaturated sulfonic acid that constitutes the constituent unit (B) may be only one type or two or more types. That is, constituent unit (B) may consist only of constituent units derived from one type of unsaturated sulfonic acid, or it may consist of constituent units derived from two or more types of unsaturated sulfonic acid. For example, constituent unit (B) may consist only of constituent units derived from vinyl sulfonic acid, or it may consist of constituent units derived from vinyl sulfonic acid and constituent units derived from acrylamide-2-methylpropanesulfonic acid.

[0024] [Component unit (C)] The polymer according to this embodiment contains a constituent unit (C) derived from a carboxylic acid having a polymerizable unsaturated group (hereinafter also simply referred to as "unsaturated carboxylic acid"). Examples of polymerizable unsaturated groups include vinyl groups, vinylidene groups, vinylene groups, etc., and from the viewpoint of ink wettability and abrasion resistance, vinyl groups are preferred. "Derived from carboxylic acids having polymerizable unsaturated groups" includes not only carboxylic acids themselves that have polymerizable unsaturated groups, but also carboxylic acid salts that have polymerizable unsaturated groups. Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethylsuccinate. Examples of salts include ammonium salts and alkali metal salts. Among the above, acrylic acid and methacrylic acid are preferred as unsaturated carboxylic acids from the viewpoint of ink wetting and abrasion resistance, availability, and cost-effectiveness. The unsaturated carboxylic acid that constitutes the constituent unit (C) may be one type or two or more types. That is, the constituent unit (C) may consist only of constituent units derived from one type of unsaturated carboxylic acid, or it may consist of constituent units derived from two or more types of unsaturated carboxylic acids. For example, the constituent unit (C) may consist only of constituent units derived from acrylic acid, or it may consist of constituent units derived from acrylic acid and constituent units derived from methacrylic acid.

[0025] The polymer according to this embodiment may further have a constituent unit (D) derived from polymerizable monomers other than constituent units (A) to (C). However, from the viewpoint of ink wettability and abrasion resistance, the total content of constituent unit (D) in the polymer according to this embodiment is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably less than 1% by mass, and more preferably 0% by mass.

[0026] In the polymer according to this embodiment, at least a portion of the carboxyl groups of the constituent unit (C) derived from an unsaturated carboxylic acid are crosslinked by a crosslinking agent. In other words, the polymer according to this embodiment has a crosslinked structure due to the crosslinking agent, and it is considered that the polymer according to this embodiment has a three-dimensional structure due to the components derived from the crosslinking agent. Because the polymer according to this embodiment has such a crosslinked structure, when an aqueous pigment dispersion is applied to an aqueous ink, even if the water in the aqueous ink evaporates and the proportion of water-soluble organic solvent in the aqueous ink increases, the polymer according to this embodiment is less likely to swell and is less likely to detach from the pigment.

[0027] The crosslinking agent has two or more reactive groups in its molecule, and the functional group (reactive group) is preferably one or more selected from the group consisting of carbodiimide group, oxazoline group, epoxy group, isocyanate group, azilidino group, and amino group. Note that the concept of epoxy group includes glycidyl group. Among these, from the viewpoint of ink wettability and abrasion resistance, it is preferable that the functional group has one or more functional groups selected from the group consisting of epoxy group and oxazoline group. These functional groups generally react with carboxyl groups but have low reactivity with sulfonic acid groups. In other words, the crosslinking agent is preferably one or more selected from the group consisting of polyfunctional epoxy compounds and polyfunctional oxazoline compounds, and more preferably a polyfunctional epoxy compound from the viewpoint of ink wettability.

[0028] (Polyfunctional epoxy compound) A polyfunctional epoxy compound is a compound that has two or more epoxy groups in its molecule. As the polyfunctional epoxy compound, compounds containing two or more glycidyl ether groups in the molecule are preferred, polyglycidyl ethers of polyhydric alcohols are more preferred, and polyglycidyl ethers of polyhydric alcohols having 3 to 8 carbon atoms are even more preferred.

[0029] Examples of polyfunctional epoxy compounds include polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, and hydrogenated bisphenol A type diglycidyl ether. Among these, the polyfunctional epoxy compound is preferably one or more selected from trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether, and diethylene glycol diglycidyl ether; more preferably one or more selected from trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, 1,6-hexanediol diglycidyl ether, and 1,4-butanediol diglycidyl ether; and even more preferably one or more selected from trimethylolpropane polyglycidyl ether and sorbitol polyglycidyl ether.

[0030] The epoxy equivalent of the polyfunctional epoxy compound is preferably 90 g / eq. or more, more preferably 115 g / eq. or more, even more preferably 130 g / eq. or more, and preferably 250 g / eq. or less, more preferably 220 g / eq. or less, and even more preferably 200 g / eq. or less, from the viewpoint of ink wettability and abrasion resistance.

[0031] (Polyfunctional oxazoline compounds) A polyfunctional oxazoline compound is a compound having two or more oxazoline groups in its molecule. A polymer containing two or more oxazoline groups (hereinafter also referred to as an "oxazoline group-containing polymer") is preferred as the polyfunctional oxazoline compound. From the viewpoint of increasing reactivity, the number-average molecular weight of the oxazoline group-containing polymer is preferably 1,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, and preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. Examples of oxazoline group-containing polymers include polymers with an acrylic backbone, polymers with a styrene / acrylic backbone, polymers with a styrene backbone, and polymers with an acrylonitrile / styrene backbone.

[0032] The oxazoline group equivalent of the oxazoline group-containing polymer is preferably 100 g / eq. or more, more preferably 170 g / eq. or more, even more preferably 200 g / eq. or more, and preferably 500 g / eq. or less, more preferably 400 g / eq. or less, and even more preferably 300 g / eq. or less, from the viewpoint of ink wettability and abrasion resistance. Note that the oxazoline group equivalent refers to the mass of the oxazoline group-containing polymer per mole of oxazoline groups. Examples of commercially available oxazoline group-containing polymers include the "Epocross WS" series, such as "Epocross WS-300," "Epocross WS-500," and "Epocross WS-700" (all manufactured by Nippon Shokubai Co., Ltd., and are water-soluble).

[0033] The crosslinking ratio of the crosslinking agent to the carboxyl groups of the polymer according to this embodiment can be calculated as the ratio of the number of moles of the functional groups (e.g., epoxy groups) of the crosslinking agent to the number of moles of carboxyl groups of the polymer before crosslinking (uncrosslinked polymer a) according to this embodiment. Crosslinking ratio (mol%) of crosslinked polymer particles = [Number of moles of functional groups of the crosslinking agent reacted with the polymer before crosslinking × 100 / Number of moles of carboxyl groups present in the polymer before crosslinking] Specifically, you can calculate it using the following formula. Crosslinking ratio (mol%) of crosslinked polymer particles = [Amount of crosslinking agent (g) / Equivalent amount of functional groups of crosslinking agent (g / eq.)] × 100 / [Number of moles of carboxyl groups in 1g of polymer before crosslinking (mol / g) × Amount of polymer before crosslinking (g)] The crosslinking ratio of the polymer according to this embodiment is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 40 mol% or more, and even more preferably 50 mol% or more, from the viewpoint of ink wetting spreadability and abrasion resistance, and preferably 90 mol% or less, more preferably 80 mol% or less, and even more preferably 70 mol% or less, from the viewpoint of abrasion resistance.

[0034] The acid value of the polymer before crosslinking (uncrosslinked polymer a) according to this embodiment is preferably 100 mg KOH / g or more, more preferably 115 mg KOH / g or more, even more preferably 150 mg KOH / g or more, and even more preferably 200 mg KOH / g or more, and from the viewpoint of ink wetting spreadability and abrasion resistance, and similarly, preferably 420 mg KOH / g or less, more preferably 400 mg KOH / g or less, even more preferably 300 mg KOH / g or less, and even more preferably 250 mg KOH / g or less. The acid value of the polymer before crosslinking (uncrosslinked polymer a) according to this embodiment can also be calculated from the mass ratio of the constituent monomers. The acid value of the constituent unit (C) (carboxylic acid) of the polymer before crosslinking (uncrosslinked polymer a) according to this embodiment is preferably 90 mg KOH / g or more, more preferably 100 mg KOH / g or more, even more preferably 150 mg KOH / g or more, and even more preferably 180 mg KOH / g or more, and from the viewpoint of ink wettability and abrasion resistance, preferably 400 mg KOH / g or less, more preferably 350 mg KOH / g or less, even more preferably 300 mg KOH / g or less, and even more preferably 240 mg KOH / g or less. The acid value of the polymer before crosslinking (uncrosslinked polymer a) according to this embodiment can also be calculated from the mass ratio of the constituent monomers.

[0035] The weight-average molecular weight of the polymer before crosslinking (uncrosslinked polymer a) according to this embodiment is preferably 10,000 or more, more preferably 13,000 or more, even more preferably 15,000 or more, and even more preferably 17,000 or more, from the viewpoint of ink wetting spreadability and abrasion resistance, and preferably 50,000 or less, more preferably 40,000 or less, even more preferably 30,000 or less, and even more preferably 27,000 or less, from the viewpoint of abrasion resistance. The weight-average molecular weight of the polymer before crosslinking (uncrosslinked polymer a) according to this embodiment can be measured by the method described in the examples.

[0036] The content of constituent unit (A) in the polymer according to this embodiment is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, from the viewpoint of ink wettability and abrasion resistance, and from the same viewpoint, preferably 90% by mass or less, more preferably 82% by mass or less, and even more preferably 70% by mass or less. The content of unsaturated sulfonic acid-derived constituent units (B) in the polymer according to this embodiment is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, from the viewpoint of ink wettability and abrasion resistance, and from the same viewpoint, preferably 60% by mass or less, more preferably 45% by mass or less, even more preferably 30% by mass or less, even more preferably 15% by mass or less, and even more preferably 12% by mass or less. The content of unsaturated carboxylic acid-derived constituent units (C) in the polymer according to this embodiment is preferably 3% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of ink wettability and abrasion resistance, and similarly preferably 60% by mass or less, more preferably 45% by mass or less, and even more preferably 30% by mass or less. The total content of unsaturated sulfonic acid-derived constituent units (B) and unsaturated carboxylic acid-derived constituent units (C) in the polymer according to this embodiment is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of ink wettability and abrasion resistance, and similarly, preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0037] In the polymer according to this embodiment, the mass ratio of the content of constituent unit (A) to the total content of constituent unit (B) and constituent unit (C) [content of constituent unit (A) / [content of constituent unit (B) + content of constituent unit (C)]] is preferably 0.2 or more, more preferably 0.5 or more, and even more preferably 1.0 or more, from the viewpoint of ink wettability and abrasion resistance, and from the same viewpoint, preferably 15 or less, more preferably 10 or less, even more preferably 4 or less, and even more preferably 2.5 or less.

[0038] At least a portion of the sulfonic acid group of constituent unit (B) and the carboxyl group of constituent unit (C) of the polymer according to this embodiment may be neutralized with a neutralizing agent from the viewpoint of ink wettability. The neutralizing agent is preferably one or more selected from the group consisting of alkali metal hydroxides, organic amines, and ammonia. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide. Examples of organic amines include alkanolamines, alkylamines, aminoalkanediols, alkoxyamines, and heterocyclic amines. Among these, one or more selected from the group consisting of alkanolamines and alkylamines are preferred, with alkanolamines being more preferred. Preferred alkanolamines include those miscible with water and having 2 to 8 carbon atoms, such as monoethanolamine, monoisopropanolamine, monoisobutanolamine, N-methylethanolamine, 2-dimethylaminoethanol, N-methyldiethanolamine, and triethanolamine. More preferably, one or more selected from the group consisting of alkali metal hydroxides and organic amines, and even more preferably sodium hydroxide, potassium hydroxide, and 2-dimethylaminoethanol. The degree of neutralization of the sulfonic acid group and carboxyl group in the polymer according to this embodiment is preferably 15 mol% or more, more preferably 20 mol% or more, from the viewpoint of ink wettability and abrasion resistance, and similarly, preferably 100 mol% or less, more preferably 95 mol% or less, and even more preferably 91 mol% or less.

[0039] Here, the degree of neutralization can be determined by the following formula as the equivalent amount of neutralizing agent used relative to the sulfonic acid groups and carboxyl groups of the polymer according to this embodiment. When the equivalent amount of neutralizing agent used is 100 mol% or less, it is synonymous with the degree of neutralization. When the equivalent amount of neutralizing agent used exceeds 100 mol%, it means that the neutralizing agent is in excess relative to the sulfonic acid groups and carboxyl groups of the polymer according to this embodiment, and in this case, the degree of neutralization of the polymer according to this embodiment is considered to be 100 mol%. Note that the degree of neutralization is the degree of neutralization of the uncrosslinked polymer before crosslinking. Amount of neutralizing agent used (mol%) = [(Mass of neutralizing agent added (g) / Equivalent amount of neutralizing agent) / [(Acid value of polymer according to this embodiment (mgKOH / g) × Mass of polymer according to this embodiment (g)) / (56.1 × 1000)] × 100

[0040] (Composition of aqueous pigment dispersion) The solid content concentration of the aqueous pigment dispersion of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more, from the viewpoint of the degree of freedom in designing the ink formulation, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, from the viewpoint of the dispersion stability of the aqueous pigment dispersion.

[0041] The water content in the aqueous pigment dispersion of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, from the viewpoint of dispersion stability of the aqueous pigment dispersion and reduction of environmental impact, and preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less, from the viewpoint of freedom in designing the ink formulation.

[0042] The method for producing the aqueous pigment dispersion of the present invention preferably involves first synthesizing the polymer before crosslinking (uncrosslinked polymer a) according to this embodiment, and then dispersing it using a known method with the pigment, uncrosslinked polymer a, a crosslinking agent, and optionally a neutralizing agent, a surfactant, etc. At this time, the ratio of pigment to uncrosslinked polymer a (pigment / uncrosslinked polymer a) is preferably 40 / 60 or more, more preferably 50 / 50 or more, even more preferably 60 / 40 or more, and even more preferably 70 / 30 or more, on a mass basis, from the viewpoint of ink wetting spreadability, and preferably 95 / 5 or less, more preferably 90 / 10 or less, even more preferably 85 / 15 or less, and even more preferably 80 / 20 or less, from the viewpoint of abrasion resistance. The following methods can be used to produce aqueous pigment dispersions. A pigment mixture containing pigment, uncrosslinked polymer a, organic solvent, and water is dispersed to obtain a dispersion. Subsequently, the organic solvent is removed from the dispersion, and a crosslinking agent is added to the resulting aqueous pigment dispersion to crosslink the uncrosslinked polymer a. The mixture is then filtered to remove coarse particles, thereby obtaining an aqueous pigment dispersion in which pigment-containing polymer particles are dispersed in an aqueous medium.

[0043] The cumulant average particle size of the pigment-containing polymer particles in the aqueous pigment dispersion of the present invention is preferably 50 nm or more, more preferably 70 nm or more, even more preferably 90 nm or more, from the viewpoint of ink wetting spreadability and abrasion resistance, and similarly, preferably 600 nm or less, more preferably 300 nm or less, even more preferably 200 nm or less, and even more preferably 160 nm or less. The cumulant average particle size of pigment-containing polymer particles in an aqueous pigment dispersion can be measured by the method described in the examples.

[0044] The polymer dispersant may further contain known pigment dispersants other than the polymer according to this embodiment, but from the viewpoint of ink wettability and abrasion resistance, the content of the polymer according to this embodiment in the polymer dispersant is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass.

[0045] (Pigment) The pigments used in this invention may be either inorganic or organic pigments, and lake pigments and fluorescent pigments may also be used. Furthermore, these may be used in combination with extender pigments as needed. Specific examples of inorganic pigments include metal oxides such as carbon black, titanium dioxide, iron oxide, red iron oxide, and chromium oxide, as well as pearlescent pigments. Carbon black is particularly preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and slene pigments. Specific examples of preferred organic pigments include one or more products from each product code selected from CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green. Examples of extender pigments include silica, calcium carbonate, and talc. For achromatic inks, achromatic pigments such as white, black, and gray can be used, while for chromatic inks, chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. The above pigments can be used individually or in combination of two or more.

[0046] <Water-based ink> The aqueous ink of the present invention comprises the aqueous pigment dispersion of the present invention. The water-based ink of the present invention contains a water-based pigment dispersion that does not cause a decrease in print quality due to white streaks or color unevenness even when printed on coated paper, and has good abrasion resistance, making it suitable for use as a water-based ink for inkjet printing. The water-based ink of the present invention may further contain, as necessary, various additives such as water-soluble organic solvents, fixing resins, surfactants, humectants, wetting agents, wetting / penetrating agents, viscosity modifiers, defoaming agents, preservatives, fungicides, and rust inhibitors. The water-based ink of the present invention is preferably obtained by mixing the water-based pigment dispersion of the present invention with a water-soluble organic solvent and a surfactant, from the viewpoint of ink wettability and abrasion resistance. There are no particular restrictions on the method of mixing each component.

[0047] (Water-soluble organic solvent) The water-based ink of the present invention preferably contains a water-soluble organic solvent from the viewpoint of ink wetting spreadability, abrasion resistance, and discharge stability. In the present invention, "water-soluble organic solvent" refers to an organic solvent in which the amount of solvent dissolved when dissolved in 100 mL of water at 25°C is 5 mL or more. Water-soluble organic solvents can be used individually or in combination of two or more. Examples of water-soluble organic solvents include polyhydric alcohols; ethers such as polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers; nitrogen-containing heterocyclic compounds; amides; amines; and sulfur-containing compounds. Among these, one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers are preferred.

[0048] Examples of polyhydric alcohols include diols such as ethylene glycol, diethylene glycol, propylene glycol (1,2-propanediol), 1,3-propylene glycol, dipropylene glycol (isomer mixture), 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-hexanediol, triethylene glycol, polyethylene glycol, and polypropylene glycol.

[0049] Examples of polyhydric alcohol alkyl ethers include (poly)alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol monobutyl ether, triethylene glycol dimethyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, and dipropylene glycol dimethyl ether. Examples of polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether. As for the water-soluble organic solvent, from the viewpoint of ink wettability and abrasion resistance, one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers is preferred, and one or more selected from diethylene glycol, 1,2-hexanediol, and dipropylene glycol monopropyl ether is preferred.

[0050] (Surfactants) Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants. Among these, nonionic surfactants are preferred from the viewpoint of ink wetting spreadability and abrasion resistance. Examples of nonionic surfactants include polyoxyalkylene alkyl ether type surfactants, acetylene glycol type surfactants, polyhydric alcohol type surfactants, fatty acid alkanolamides, silicone type surfactants, and fluorine type surfactants. Among these, from the viewpoint of ink wetting spreadability and abrasion resistance, one or more nonionic surfactants selected from the group consisting of acetylene glycol type surfactants and silicone type surfactants are preferred. Preferred acetylene glycol-based surfactants include acetylene glycol having 8 to 22 carbon atoms and ethylene oxide adducts of the acetylene glycol, with 2,4,7,9-tetramethyl-5-decine-4,7-diol or its ethylene oxide adduct being more preferred. Examples of silicone-based surfactants include polyether-modified silicones, amino-modified silicones, carboxy-modified silicones, fatty acid-modified silicones, alcohol-modified silicones, aliphatic alcohol-modified silicones, epoxy-modified silicones, fluorine-modified silicones, and alkyl-modified silicones. Examples of commercially available nonionic surfactants include the KF series from Shin-Etsu Chemical Co., Ltd., the BYK series from BIC Chemie Japan Co., Ltd., the Surfinol series from Nisshin Chemical Industry Co., Ltd. and Air Products & Chemicals, and the Acetyleneol series from Kawaken Fine Chemical Co., Ltd.

[0051] (Composition and physical properties of water-based inks) The total content of pigment and polymer dispersant in the aqueous ink of the present invention is preferably 4% by mass or more, more preferably 6% by mass or more, and even more preferably 7% by mass or more, from the viewpoint of scratch resistance, and preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of ink wetting spreadability.

[0052] The pigment content in the aqueous ink of the present invention is preferably 4.0% by mass or more, more preferably 5.0% by mass or more, and even more preferably 5.5% by mass or more, from the viewpoint of print density, and preferably 10% by mass or less, more preferably 8% by mass or less, even more preferably 7% by mass or less, and even more preferably 6.5% by mass or less, from the viewpoint of ink dispersion stability. The content of polymer dispersant a in the aqueous ink of the present invention is preferably 0.5% by mass or more, more preferably 0.6% by mass or more, even more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, from the viewpoint of scratch resistance, and preferably 6% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less, and even more preferably 3.5% by mass or less, from the viewpoint of ink wettability.

[0053] The content of the water-soluble organic solvent in the water-based ink of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more, from the viewpoint of ink wettability and abrasion resistance, and similarly, preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less.

[0054] The water content in the water-based ink of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, from the viewpoint of ink dispersion stability and reduction of environmental impact, and preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less, from the viewpoint of freedom in designing the ink formulation.

[0055] (Inkjet printing) The aqueous ink of the present invention can be suitably used as an aqueous ink for inkjet printing. In particular, it is suitable for printing on coated paper as a printing substrate. In inkjet printing methods, a piezoelectric system is preferred as the method for ejecting water-based ink from the viewpoint of ejection performance. Examples of coated paper include general-purpose glossy paper and multi-color foam glossy paper. [Examples]

[0056] In the following manufacturing examples, embodiments, and comparative examples, "parts" and "%" refer to "parts by mass" and "mass%" unless otherwise specified. The measurement and calculation methods for each physical property are as follows.

[0057] (1) Measurement of the weight-average molecular weight of uncrosslinked polymer a The results were obtained by gel permeation chromatography. The measurement conditions are shown below. GPC device: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolum Super AW-H" manufactured by Tosoh Corporation. Eluent: A solution prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits with known molecular weight [PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500)] (all manufactured by Tosoh Corporation) Measurement sample: 0.1 g of the polymer according to this embodiment was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and filtered through a syringe filter "DISMIC-13HP" (made of PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.).

[0058] (2) Measurement of solid content concentration 10.0 g of sodium sulfate, which had been stabilized in a desiccator, was weighed into a 30 mL polypropylene container (φ=40 mm, height=30 mm). Approximately 1.0 g of the sample was added and mixed, then accurately weighed and maintained at 105°C for 2 hours to remove volatile components. After standing in the desiccator for another 15 minutes, the mass was measured. The mass of the sample after removal of volatile components was taken as the solid content, and the solid content concentration (%) was obtained by dividing it by the mass of the added sample.

[0059] (3) Measurement of the average particle size of aqueous pigment dispersion Cumulant analysis was performed using the "ELS-8000" laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd.), and the average particle size of the resulting cumulant was used to measure the average particle size of the aqueous pigment dispersion or aqueous ink. The sample to be measured had a particle concentration of 5 × 10⁻¹⁶ -3 A dispersion solution diluted with water to a concentration of % (converted to solid content) was used. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent.

[0060] (Preparation of uncrosslinked polymer a) <Preparation Example 1> In a reaction vessel equipped with a stirrer, reflux condenser, and dropping tank, 6.3 parts butyl acrylate, 1.0 part acrylamide-2-methylpropanesulfonic acid, 2.7 parts acrylic acid, and 6.6 parts N,N-dimethylformamide (hereinafter referred to as "DMF") as the polymerization solvent were added as the initial charge, and the reaction vessel was stirred for 10 minutes while maintaining the temperature at 70°C. Next, a mixture containing 56.7 parts butyl acrylate, 9.0 parts acrylamide-2-methylpropanesulfonic acid, 24.3 parts acrylic acid, 60 parts DMF, 0.2 parts 2-mercaptoethanol as a chain transfer agent, and 1.0 part 2,2'-azobis(2,4-dimethylvalenonitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) as a polymerization initiator was continuously added dropwise to a reaction vessel over 5 hours. After the addition was complete, the polymerization reaction was carried out for 1 hour, and then the polymerization reaction was terminated by cooling to room temperature. After the reaction was complete, the polymerization solvent was removed by vacuum distillation, diluted with tetrahydrofuran, and precipitated as a solid by dropwise addition to hexane. The precipitated solid was collected and dried under reduced pressure at 60°C for 24 hours to obtain uncrosslinked polymer a1 (weight-average molecular weight: 18000).

[0061] <Preparation Examples 2-10> In Preparation Example 1, uncrosslinked polymers a2 to a10 were obtained in the same manner as in Preparation Example 1, except that the composition of the raw material monomers constituting uncrosslinked polymer a was changed to the conditions shown in Table 1. 10% by mass of each monomer was initially charged, and 90% by mass was added dropwise.

[0062] In Table 1, the values ​​in the "Hydroxide Compounds Containing Vinyl Groups (A)", "Unsaturated Sulfonic Acids (B)", and "Unsaturated Carboxylic Acids (C)" columns represent the mass percentage (%) of the total raw material monomers, while the values ​​in the "Chain Transfer Agents" and "Polymerization Initiators" columns represent the percentage (parts) relative to 10 parts of the total mass of all raw material monomers. Furthermore, the value in the "A / (B+C)" column represents the mass ratio of the amount of hydrocarbon compound (A) containing a vinyl group to the sum of the amounts of unsaturated sulfonic acid (B) and unsaturated carboxylic acid (C), and corresponds to the mass ratio of the content of constituent unit (A) to the sum of the content of constituent unit (B) and constituent unit (C) in uncrosslinked polymer a [Content of constituent unit (A) / [Content of constituent unit (B) + Content of constituent unit (C)]].

[0063] [Table 1]

[0064] (Manufacturing of aqueous pigment dispersions) <Manufacturing Example 1> (Process 1) In a reaction vessel equipped with a stirrer, 25 parts of uncrosslinked polymer a1 and 180 parts of deionized water were added. Then, 11.8 parts of a 5N sodium hydroxide aqueous solution (16.9% sodium hydroxide solids, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) was added so that the degree of neutralization of the sulfonic acid groups and carboxylic acid groups (total acid value) of uncrosslinked polymer a1 was 47 mol%. The reaction vessel was heated to 80°C and stirred for 5 hours, then cooled to 25°C to obtain a varnish solution of uncrosslinked polymer a1.

[0065] (Process 2) To the obtained varnish solution, 145 parts of deionized water and 50 parts of methyl ethyl ketone were added, and then 75 parts of cyanide pigment (manufactured by DIC Corporation, product name: Fastogen Blue FA5380, Pigment Blue 15:3) were added to obtain a pigment mixture. In Tables 2 and 3, Pigment Blue 15:3 is indicated as "PB15:3". The resulting pigment mixture was mixed for 1 hour at 6000 rpm and 20°C using a disperser blade (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disperser). Then, it was subjected to a 10-pass dispersion treatment at a pressure of 200 MPa using a microfluidizer (manufactured by Microfluidics, high-pressure homogenizer, product name: M-140K) to obtain a pigment dispersion.

[0066] (Step 3) To the obtained pigment dispersion, 135 parts of deionized water were added, and methyl ethyl ketone was removed under reduced pressure at 60°C. After removing some of the water, the mixture was filtered through a membrane filter (Sartorius, product name: Minisart syringe filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, and a pigment dispersion with a solid content of 20% was obtained.

[0067] (Step 4) 500 parts of the obtained pigment dispersion were placed in a screw-top glass bottle, and 7.9 parts of trimethylolpropane polyglycidyl ether (Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of the carboxylic acid: 60 mol%) and 31.5 parts of deionized water were added. The bottle was then tightly sealed and heated at 80°C for 5 hours while stirring with a stirrer. After 5 hours, the temperature was lowered to room temperature, and the mixture was filtered through a membrane filter (Sartorius, product name: Minisart syringe filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles. As a result, a pigment aqueous dispersion A1 (average particle size: 119 nm) with a solid content of 20% containing a polymer dispersant a1 in which uncrosslinked polymer a1 was crosslinked was obtained. The results are shown in Table 2.

[0068] <Manufacturing Examples 2-4> In Production Example 1, aqueous pigment dispersions A2 to A4 containing polymer dispersants a2 to a4 were obtained using the same procedure as in Production Example 1, except that 25 parts of uncrosslinked polymers a2, a3, or a4 obtained in Production Examples 2 to 4 were used instead of the uncrosslinked polymer a1 obtained in Production Example 1 (solids concentration: 20%). The results are shown in Table 2.

[0069] <Manufacturing Example 5> Aqueous pigment dispersion A5 containing polymer dispersant a5 was obtained using the same procedure as in Production Example 4, except that 500 parts of the pigment dispersion obtained in Production Example 4 (solids concentration: 20%) were mixed with 2.6 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of the carboxylic acid: 20 mol%) and 10.5 parts of deionized water. The results are shown in Table 2.

[0070] <Manufacturing Example 6> Aqueous pigment dispersion A6 containing polymer dispersant a6 was obtained using the same procedure as in Production Example 4, except that 500 parts of the pigment dispersion obtained in Production Example 4 (solids concentration: 20%) were mixed with 10.5 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of the carboxylic acid: 80 mol%) and 42.0 parts of ion-exchanged water. The results are shown in Table 2.

[0071] <Manufacturing Example 7> In Production Example 4, 5.0 parts of a 5N sodium hydroxide aqueous solution (16.9% sodium hydroxide solids, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added so that the degree of neutralization of the sulfonic acid groups and carboxylic acid groups (total acid value) of the uncrosslinked polymer a4 was 20 mol%. To the resulting pigment dispersion of 500 parts (solids concentration: 20%), 11.9 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of the carboxylic acid: 90 mol%) and 47.2 parts of deionized water were added. The procedure was the same as in Production Example 4 to obtain an aqueous pigment dispersion A7 containing polymer dispersant a7 (solids concentration: 20%). The results are shown in Table 2.

[0072] <Manufacturing Example 8> In Production Example 4, 22.8 parts of a 5N sodium hydroxide aqueous solution (16.9% sodium hydroxide solids, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added so that the degree of neutralization of the sulfonic acid groups and carboxylic acid groups (total acid value) of the uncrosslinked polymer a4 was 91 mol%. To 500 parts of the resulting pigment dispersion (solids concentration: 20%), 1.3 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of the carboxylic acid: 10 mol%) and 5.3 parts of deionized water were added. The procedure was the same as in Production Example 4 to obtain an aqueous pigment dispersion A8 containing polymer dispersant a8 (solids concentration: 20%). The results are shown in Table 2.

[0073] <Manufacturing Example 9> A water-based pigment dispersion A9 containing polymer dispersant a9 was obtained using the same procedure as in Production Example 4, except that 500 parts of the pigment dispersion obtained in Production Example 4 (solids concentration: 20%) were mixed with 10.7 parts of the crosslinking agent sorbitol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-622, epoxy equivalent 191 g / eq., insoluble in water) (degree of crosslinking relative to the acid value of the carboxylic acid: 60 mol%) and 43.0 parts of ion-exchanged water. The results are shown in Table 2.

[0074] <Manufacturing Example 10> Aqueous pigment dispersion A10 containing polymer dispersant a10 was obtained using the same procedure as in Production Example 4, except that 500 parts of the pigment dispersion obtained in Production Example 4 (solids concentration: 20%) were mixed with 8.5 parts of the crosslinking agent 1,6-hexanediol diglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-212, epoxy equivalent 151 g / eq., insoluble in water) (degree of crosslinking relative to the acid value of the carboxylic acid: 60 mol%) and 34.0 parts of deionized water. The results are shown in Table 2.

[0075] <Manufacturing Example 11> Aqueous pigment dispersion A11 containing polymer dispersant a11 was obtained using the same procedure as in Production Example 4, except that 500 parts of the pigment dispersion obtained in Production Example 4 (solids concentration: 20%) were mixed with 6.5 parts of the crosslinking agent 1,4-butanediol diglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-214L, epoxy equivalent 115 g / eq., water solubility 100%) (degree of crosslinking relative to the acid value of the carboxylic acid: 60 mol%) and 25.9 parts of deionized water. The results are shown in Table 2.

[0076] <Manufacturing Example 12> A aqueous pigment dispersion A12 containing polymer dispersant a12 was obtained using the same procedure as in Production Example 4, except that 500 parts of the pigment dispersion obtained in Production Example 4 (solid content concentration: 20%) were mixed with 49.5 parts of an oxazoline-based crosslinking agent (manufactured by Nippon Shokubai Co., Ltd., WS-700, oxazoline equivalent 220 g / eq., number average molecular weight 20,000, water-soluble, active ingredient 25%) (degree of crosslinking relative to the acid value of carboxylic acid: 60 mol%) and 12.4 parts of ion-exchanged water. The results are shown in Table 2.

[0077] <Manufacturing Examples 13-14> In Production Example 4, aqueous pigment dispersions A13 to A14 containing polymer dispersant a13 or a14 were obtained using the same procedure as in Production Example 4, except that 8.2 parts of 8N potassium hydroxide aqueous solution (KOH) (potassium hydroxide solids content 33.8%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration: degree of neutralization 47 mol%) or 4.4 parts of 2-dimethylaminoethanol (DMAE) (Fujifilm Wako Pure Chemical Industries, Ltd., degree of neutralization 47 mol%) were used instead of 5N sodium hydroxide aqueous solution. The results are shown in Table 2.

[0078] <Manufacturing Example 15> In Production Example 4, 25 parts of uncrosslinked polymer a5 obtained in Production Example 5 were used instead of uncrosslinked polymer a4 obtained in Production Example 4, and 11.9 parts of 5N sodium hydroxide aqueous solution (sodium hydroxide solids content 16.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added so that the degree of neutralization of the sulfonic acid groups and carboxylic acid groups (total acid value) of uncrosslinked polymer a5 was 47 mol%. To the resulting pigment dispersion of 500 parts (solids concentration: 20%), 4.4 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of carboxylic acid: 60 mol%) and 17.5 parts of deionized water were added, except that the procedure was the same as in Production Example 4 to obtain an aqueous pigment dispersion A15 containing polymer dispersant a15 (solids concentration: 20%). The results are shown in Table 3.

[0079] <Manufacturing Example 16> In Production Example 4, 25 parts of uncrosslinked polymer a6 obtained in Production Example 6 were used instead of uncrosslinked polymer a4 obtained in Production Example 4, and 19.4 parts of 5N sodium hydroxide aqueous solution (sodium hydroxide solids content 16.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added so that the degree of neutralization of the sulfonic acid groups and carboxylic acid groups (total acid value) of uncrosslinked polymer a6 was 47 mol%. To the resulting pigment dispersion of 500 parts (solids concentration: 20%), 13.1 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of carboxylic acid: 60 mol%) and 52.5 parts of deionized water were added, except that the procedure was the same as in Production Example 4 to obtain an aqueous pigment dispersion A16 containing polymer dispersant a16 (solids concentration: 20%). The results are shown in Table 3.

[0080] <Manufacturing Examples 17-21> In Production Example 4, aqueous pigment dispersions A17 to A21 containing polymer dispersant a4 were obtained using the same procedure as in Production Example 4, except that the cyan pigment was replaced with 75 parts magenta pigment (manufactured by DIC Corporation, product name: Fastogen Super Magenta JM03, Pigment Red 122 / Pigment Violet 19 solid solution), 75 parts red pigment (manufactured by Fuji Pigment Co., Ltd., product name: FUJI FAST CARMINE 522-1D, Pigment Red 150), 75 parts yellow pigment (manufactured by Sanyo Pigment Co., Ltd., product name: Fast Yellow 7423, Pigment Yellow 74), 75 parts yellow pigment (manufactured by Heubach Color Japan Co., Ltd., product name: Inkjet Yellow 4GC, Pigment Yellow 155), or 75 parts black pigment (manufactured by Cabot, product name: Monarch 880, Pigment Black 7). The results are shown in Table 3. In Table 3, Pigment Red 122 is abbreviated as "PR122", Pigment Violet 19 as "PV19", Pigment Red 150 as "PR150", Pigment Yellow 74 as "PY74", Pigment Yellow 155 as "PY155", and Pigment Black 7 as "PBk7".

[0081] <Manufacturing Example 22> In Production Example 4, 25 parts of uncrosslinked polymer a7 obtained in Production Example 7 were used instead of uncrosslinked polymer a4 obtained in Production Example 4, and 5.7 parts of 5N sodium hydroxide aqueous solution (sodium hydroxide solids content 16.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added so that the degree of neutralization of the sulfonic acid groups and carboxylic acid groups (total acid value) of uncrosslinked polymer a7 was 47 mol%. To the resulting pigment dispersion of 500 parts (solids concentration: 20%), 3.8 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of carboxylic acid: 60 mol%) and 15.2 parts of deionized water were added, except that the procedure was the same as in Production Example 4 to obtain an aqueous pigment dispersion A22 containing polymer dispersant a17 (solids concentration: 20%). The results are shown in Table 3.

[0082] <Manufacturing Example 23> In Production Example 4, 25 parts of uncrosslinked polymer a8 obtained in Production Example 8 were used instead of uncrosslinked polymer a4 obtained in Production Example 4, and 10.1 parts of 5N sodium hydroxide aqueous solution (sodium hydroxide solids content 16.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added so that the degree of neutralization of the sulfonic acid groups and carboxylic acid groups (total acid value) of uncrosslinked polymer a8 was 47 mol%. To the resulting pigment dispersion of 500 parts (solids concentration: 20%), 6.6 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of carboxylic acid: 60 mol%) and 26.4 parts of deionized water were added, except that the procedure was the same as in Production Example 4 to obtain an aqueous pigment dispersion A23 containing polymer dispersant a18 (solids concentration: 20%). The results are shown in Table 3.

[0083] <Manufacturing Example 24> In Production Example 4, 25 parts of uncrosslinked polymer a9 obtained in Production Example 9 were used instead of uncrosslinked polymer a4 obtained in Production Example 4, and 13.0 parts of 5N sodium hydroxide aqueous solution (sodium hydroxide solids content 16.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added so that the degree of neutralization of the sulfonic acid groups and carboxylic acid groups (total acid value) of uncrosslinked polymer a9 was 47 mol%. To the resulting pigment dispersion of 500 parts (solids concentration: 20%), 7.9 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of carboxylic acid: 60 mol%) and 31.5 parts of ion-exchanged water were added, except that the procedure was the same as in Production Example 4 to obtain an aqueous pigment dispersion A24 containing polymer dispersant a19 (solids concentration: 20%). The results are shown in Table 3.

[0084] <Manufacturing Example 25> In Production Example 4, instead of the uncrosslinked polymer a4 obtained in Production Example 4, 25 parts of the uncrosslinked polymer a10 obtained in Production Example 10 were used, and 11.8 parts of a 5N sodium hydroxide aqueous solution (sodium hydroxide solids content 16.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were added so that the degree of neutralization of the sulfonic acid groups and carboxylic acid groups (total acid value) of the uncrosslinked polymer a10 was 47 mol%. To the resulting pigment dispersion of 500 parts (solids concentration: 20%), 7.9 parts of the crosslinking agent trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq., water solubility 27%) (degree of crosslinking relative to the acid value of carboxylic acid: 60 mol%) and 31.5 parts of deionized water were added, otherwise the procedure was the same as in Production Example 4 to obtain an aqueous pigment dispersion A25 containing polymer dispersant a20 (solids concentration: 20%). The results are shown in Table 3.

[0085] <Manufacturing Example 26> In Production Example 1, the pigment dispersion containing the uncrosslinked polymer a1 obtained after the completion of (Step 3) was designated as aqueous pigment dispersion A26 (solid content concentration: 20%). The results are shown in Table 3.

[0086] <Manufacturing Example 27> In Production Example 2, the pigment dispersion containing the uncrosslinked polymer a2 obtained after the completion of (Step 3) was designated as aqueous pigment dispersion A27 (solid content concentration: 20%). The results are shown in Table 3.

[0087] [Table 2]

[0088] [Table 3]

[0089] (Preparation of water-based ink) <Example 1> To obtain the ink composition shown in Table 4 (total of 100 parts), 8.6 parts of aqueous pigment dispersion A1 (43 parts as aqueous pigment dispersion) as the total of pigment and polymer dispersant a1, 20.0 parts of diethylene glycol, 5.0 parts of 1,2-hexanediol, 0.5 parts of acetylene glycol-based surfactant (manufactured by Nisshin Chemical Industry Co., Ltd., product name: Surfinol 465), and deionized water were added and stirred, and filtered through a membrane filter (manufactured by Sartorius, product name: Minisart syringe filter, pore size: 5 μm, material: cellulose acetate) to obtain aqueous ink 1.

[0090] <Examples 2-26 and Comparative Examples 1-3> Water-based inks 2 to 29 were obtained in the same manner as in Example 1, except that the type or amount of water-based pigment dispersion A, water-soluble organic solvent, and surfactant were changed to those shown in Tables 4 to 6. The resin emulsion used to prepare water-based ink 29 in Comparative Example 3 shown in Table 6 is a styrene-acrylic emulsion (DSM NeoResins, "NeoCryl A-1091"). In Tables 4-6, the units for "Aqueous Pigment Dispersion A" other than the "Type" and "Evaluation Results" columns, and for the remainder, are in "parts".

[0091] <Creating printed materials> An inkjet printer (ImageXpert, product name: Jetxpert) equipped with a FUJIFILM Dimatix piezo-driven inkjet head, product name: Samba G3L, was filled with water-based ink. After adjusting the head voltage to 30V, frequency to 20kHz, push-pull drive waveform, and ink ejection volume to 3.0pL, a solid image (Duty 100%) was printed on gloss-coated paper (Oji Paper Co., Ltd., product name: OK Topcoat+) at a resolution of 1200 x 1200 dpi.

[0092] <Abrasion resistance> The resulting print was dried in a constant temperature bath set to 70°C for 1 minute, and a friction test was performed on the solid image area (Duty 100%) of the print using an AB-201 Sutherland type ink lab tester (manufactured by Tester Sangyo Co., Ltd.). The friction material used was the bottom surface of a weight (bottom surface area 50 cm²) on "OK Topcoat+" coated paper. 2 A load of 500g was applied using a tool, and the material was rubbed 20 times (back and forth). The condition of the printed surface of the rubbed material was visually inspected and evaluated according to the following evaluation criteria.

[0093] (Evaluation Criteria) A: No scratches can be seen on the surface of the printed material by visual inspection. B: A slight scratch is visible on the surface of the printed material, but there is no exposed surface of the printing medium. C: While scratches on the surface of the printed material are visible to the naked eye, there is no exposed surface on the printing medium, and it is usable for practical purposes. D: Visual inspection revealed scratches on the surface of the printed material, and some parts of the printing medium's surface were exposed, posing a practical problem.

[0094] <Wetting properties> White streaks and color unevenness were visually evaluated in the solid image areas of evaluation prints obtained on gloss-coated paper. The evaluation criteria are as follows: A: There are no white streaks or color inconsistencies visible in the printed material. B: Slight white streaks or color inconsistencies are visible in the printed material. C: White streaks or color unevenness may be visible in the printed material, but it is still usable for practical purposes. D: The printed material has many white streaks or color inconsistencies, which poses a practical problem.

[0095] [Table 4]

[0096] [Table 5]

[0097] [Table 6]

[0098] As can be seen from the comparison between Example 1 and Comparative Example 1, and between Example 2 and Comparative Example 2, when the dispersion polymer is not crosslinked (comparative example), the ink does not have good wetting properties or abrasion resistance. However, when the dispersion polymer is crosslinked, the ink exhibits excellent wetting properties and abrasion resistance, even when the hydrophobic groups of the dispersion polymer are short-chain butyl groups or aromatic groups. Furthermore, as can be seen from Examples 1-4 and 25, when the hydrophobic groups of the dispersion polymer are alicyclic alkyl groups, the ink exhibits better wetting properties and abrasion resistance than when they are linear alkyl groups or aromatic groups. [Industrial applicability]

[0099] According to the present invention, it is possible to provide an aqueous pigment dispersion and an aqueous ink containing the aqueous pigment dispersion that do not cause a decrease in print quality due to white streaks or color unevenness even when printed on coated paper, and that have good abrasion resistance.

Claims

1. A water-based pigment dispersion comprising a pigment and a polymer dispersant, The polymer dispersant contains a polymer comprising one or more hydrophobic monomers (A) selected from the group consisting of hydrocarbon compounds having vinyl groups and alkyl (meth)acrylates, a structural unit (B) derived from a sulfonic acid having a polymerizable unsaturated group, and a structural unit (C) derived from a carboxylic acid having a polymerizable unsaturated group. An aqueous pigment dispersion in which at least a portion of the carboxyl groups of the polymer are crosslinked with a crosslinking agent.

2. The aqueous pigment dispersion according to claim 1, wherein the crosslinking agent has one or more functional groups selected from the group consisting of epoxy groups and oxazoline groups.

3. The aqueous pigment dispersion according to claim 1, wherein the crosslinking rate of the crosslinking agent with respect to the carboxyl groups of the polymer is 10 mol% or more and 90 mol% or less.

4. The aqueous pigment dispersion according to any one of claims 1 to 3, wherein the content of the constituent unit (A) in the polymer is 30% by mass or more and 90% by mass or less.

5. The aqueous pigment dispersion according to any one of claims 1 to 3, wherein the mass ratio of the content of the constituent unit (A) to the total content of the constituent unit (B) and the content of the constituent unit (C) in the polymer [content of the constituent unit (A) / [content of the constituent unit (B) + content of the constituent unit (C)]] is 0.2 or more and 15 or less.

6. The aqueous pigment dispersion according to any one of claims 1 to 3, wherein the content of the constituent unit (B) in the polymer is 3% by mass or more and 60% by mass or less.

7. The aqueous pigment dispersion according to any one of claims 1 to 3, wherein the content of the constituent unit (C) in the polymer is 3% by mass or more and 60% by mass or less.

8. The aqueous pigment dispersion according to any one of claims 1 to 3, wherein the constituent unit (A) includes a constituent unit derived from the alkyl (meth)acrylate, and the alkyl group of the alkyl (meth)acrylate is an alicyclic alkyl group.

9. A water-based ink comprising the aqueous pigment dispersion described in any one of claims 1 to 3.

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