Water-based ink for inkjet printing

Abstract

To provide a water-based ink for ink-jet printing which has excellent ejection stability and water resistance and can give a recorded matter with suppressed bleeding. [Solution] A water-based ink for inkjet printing containing water-insoluble polymer particles (A) and water, wherein the water-insoluble polymer particles (A) contain a structure derived from a water-dispersible polymer (A') having an acid group, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy crosslinking agent, and the molecular weight of the carboxylic acid compound is 150 or more and 1,000 or less.

Description

[Technical Field]

[0001] The present invention relates to a water-based ink for ink-jet printing. [Background technology]

[0002] Inkjet recording is a method of directly ejecting ink droplets from minute nozzles and depositing them on a recording medium to produce a recorded product with characters or images. This method has become extremely popular due to its many advantages, including ease of full-color printing, low cost, the ability to use plain paper as the recording medium, and non-contact with the recording medium. In particular, from the perspective of weather resistance and water resistance of the recorded product, the use of pigments as colorants has become mainstream. On the other hand, water-based inks for ink-jet recording that use pigments as colorants tend to have poor ejection stability because the pigment particles are dispersed in an aqueous medium.

[0003] As a technology for addressing the above-mentioned problems, for example, Patent Document 1 describes a water-based ink containing water-insoluble polymer particles (A), an organic solvent (B), and water, with the aim of providing a water-based ink that has excellent ejection stability and is capable of producing printed matter that has excellent drying properties and abrasion resistance when printed on a low-water-absorbency printing medium, wherein the polymer that constitutes the water-insoluble polymer particles (A) is crosslinked, the organic solvent (B) contains a polyhydric alcohol ether, and the viscosity change rate of the organic solvent (B), represented by the following formula (1), is 140% or less. Viscosity change rate (%) = (η B / η 50 )×100 (1) η B : Viscosity of organic solvent (B) at 32°C η 50 : Viscosity of a 50% by mass aqueous solution of organic solvent (B) at 32°C [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-116598 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, there has been a demand for even higher resolution in inkjet recording, and there has been an increasing demand for further improvements in the ejection stability of water-based inks for inkjet printing, as well as for improved water resistance and suppression of bleeding in recorded materials. The water-based ink in Patent Document 1 achieves a certain degree of effectiveness in terms of ejection stability. However, Patent Document 1 makes no mention of improving the water resistance or suppressing bleeding in recorded materials. The present invention relates to a water-based ink for ink-jet printing that has excellent ejection stability, excellent water resistance, and is capable of producing printed matter with reduced bleeding. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by providing a water-based ink for inkjet printing that uses, as a fixing agent, a water-insoluble crosslinked polymer that includes a structure derived from a water-dispersible polymer having an acid group, a structure derived from a carboxylic acid compound of a specific molecular weight, and a structure derived from a polyfunctional epoxy crosslinking agent.

[0007] That is, the present invention relates to the following [1]. [1] A water-based ink for ink-jet printing containing water-insoluble polymer particles (A) and water, the water-insoluble polymer particles (A) contain a structure derived from the water-dispersible polymer (A') having an acid group, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy crosslinking agent; A water-based ink for ink-jet printing, wherein the molecular weight of the carboxylic acid compound is 150 or more and 1,000 or less. [Effects of the Invention]

[0008] The present invention can provide a water-based ink for ink-jet printing that has excellent ejection stability, excellent water resistance, and is capable of producing printed matter with reduced bleeding. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Water-based ink for inkjet printing] The water-based ink for ink-jet printing of the present invention (hereinafter also simply referred to as "water-based ink") contains water-insoluble polymer particles (A) and water, wherein the water-insoluble polymer particles (A) contain a structure derived from a water-dispersible polymer (A') having an acid group, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy crosslinking agent, and the molecular weight of the carboxylic acid compound is 150 or more and 1,000 or less.

[0010] In this specification, "aqueous" means that water accounts for the largest proportion of the medium in which the pigment is dispersed. Furthermore, "recording" is a concept that includes printing or printing characters or images. Furthermore, the term "crosslinking" is intended to encompass the concept of bonding between water-dispersible polymers (A') having acid groups via a polyfunctional epoxy crosslinking agent, and the concept of bonding between a water-dispersible polymer (A') having acid groups and a carboxylic acid compound having a molecular weight of 150 or more and 1000 or less via a polyfunctional epoxy crosslinking agent.

[0011] The water-based ink of the present invention has excellent ejection stability. Furthermore, by using the water-based ink of the present invention, it is possible to obtain recorded matter that has excellent water resistance and suppressed bleeding. Although the reason for this is not clear, it is thought to be as follows. The aqueous ink of the present invention contains water-insoluble polymer particles (A), which have a structure derived from a water-dispersible polymer (A') having an acid group, a structure derived from a carboxylic acid compound having a molecular weight of 150 to 1000, and a structure derived from a multifunctional epoxy crosslinker, with the carboxylic acid compound reacting with the epoxy group to incorporate the crosslinked polymer. The structure derived from the carboxylic acid compound having a molecular weight of 150 to 1000 improves the hydrophobicity of the water-insoluble polymer particles (A), thereby allowing the ink to dry quickly on the recording medium, such as paper, and preventing excessive wetting and spreading of the droplets. Furthermore, the hydrophobicity of the resulting printed image is also enhanced, resulting in excellent water resistance and reduced bleeding. Furthermore, since the water-insoluble polymer particles (A) are crosslinked polymer particles with enhanced hydrophobicity, swelling in organic solvents is suppressed, which is thought to improve ejection stability.

[0012] [Water-insoluble polymer particles (A)] The water-based ink of the present invention contains water-insoluble polymer particles (A). The water-insoluble polymer particles (A) contain a structure derived from the water-dispersible polymer (A') having an acid group, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy crosslinking agent, and the molecular weight of the carboxylic acid compound is 150 or more and 1,000 or less. Here, with regard to "water-insolubility," when water-insoluble polymer particles (A) that have reached a constant weight after drying at 105°C for 2 hours are dissolved in 100 g of water at 25°C until saturation is reached, the polymer is deemed to be water-insoluble if the dissolved amount is 10 g or less. The dissolved amount of the water-insoluble polymer particles (A) is preferably 5 g or less, more preferably 1 g or less. The "dissolved amount" refers to the amount dissolved when the acid groups of the water-insoluble polymer particles (A) are 100% neutralized with a neutralizing agent. The water-based ink of the present invention contains the water-insoluble polymer particles (A) as at least pigment-free polymer particles. The water-based ink of the present invention may further contain the water-insoluble polymer particles (A) as polymer particles constituting pigment-containing polymer particles.

[0013] <Water-dispersible polymer (A') having acid groups> The water-dispersible polymer (A') having an acid group (hereinafter simply referred to as "water-dispersible polymer (A')") has an acid group such as a carboxy group, a sulfonic acid group, or a phosphate group, with the carboxy group being preferred. In the present invention, the "water-dispersible polymer" refers to a polymer that is dispersible in water or an aqueous medium at room temperature (25°C).

[0014] The water-dispersible polymer (A') may be at least one selected from polyester, polyurethane, and vinyl polymers, but vinyl polymers obtained by addition polymerization of vinyl monomers are preferred in terms of ejection stability of aqueous inks, water resistance of recorded materials, and suppression of bleeding. Examples of vinyl monomers include vinyl compounds, vinylidene compounds, and vinylene compounds.

[0015] From the viewpoints of ejection stability of aqueous inks, water resistance of recorded materials, and suppression of bleeding, the water-dispersible polymer (A') is preferably a vinyl polymer containing structural units derived from acid group-containing monomers, more preferably a carboxy group-containing vinyl polymer, and even more preferably a vinyl polymer containing structural units derived from carboxy group-containing monomers and structural units derived from hydrophobic monomers. When the water-dispersible polymer (A') contains structural units derived from carboxy group-containing monomers and structural units derived from hydrophobic monomers, it is preferably one obtained by copolymerizing raw material monomers containing carboxy group-containing monomers and hydrophobic monomers.

[0016] (Carboxy group-containing monomer) Preferred examples of the carboxy group-containing monomer include carboxylic acid monomers. The molecular weight of the carboxylic acid monomer is preferably 50 or more, more preferably 60 or more, and preferably less than 150, more preferably 140 or less. The carboxylic acid monomer may be at least one selected from the group consisting of unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid; and unsaturated dicarboxylic acids such as itaconic acid, maleic acid, fumaric acid, citraconic acid, and α,β-unsaturated dicarboxylic acids. Among these, the carboxyl group-containing monomer is preferably (meth)acrylic acid, more preferably acrylic acid, from the viewpoints of ejection stability of the aqueous ink, water resistance of the recorded matter, and suppression of bleeding. The unsaturated dicarboxylic acid may be an anhydride. In this specification, the term "(meth)acrylic" such as (meth)acrylic acid is a concept that includes both acrylic and methacrylic.

[0017] (hydrophobic monomer) In the present invention, the term "hydrophobic monomer" refers to a monomer that dissolves in 100 g of deionized water at 25° C. to saturation in an amount of less than 10 g. Specific examples of hydrophobic monomers include alkyl (meth)acrylates, aromatic group-containing monomers, and macromonomers described in paragraphs

[0020] to

[0022] of JP 2018-83938 A. Among these, from the viewpoint of the ejection stability of aqueous inks, the water resistance of recorded materials, and suppression of bleeding, the hydrophobic monomer is preferably at least one selected from alkyl (meth)acrylates having an alkyl group preferably having 1 to 18 carbon atoms, more preferably having 1 to 10 carbon atoms, and aromatic group-containing monomers having an aromatic group preferably having 6 to 22 carbon atoms, more preferably having 6 to 18 carbon atoms, more preferably at least one selected from ethyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, styrene, α-methylstyrene, and benzyl (meth)acrylate, more preferably at least one selected from styrene, α-methylstyrene, and benzyl (meth)acrylate, even more preferably at least one selected from styrene and α-methylstyrene, and even more preferably styrene.

[0018] The raw material monomers for the water-dispersible polymer (A') can be used singly or in combination of two or more.

[0019] <Content of each structural unit in water-dispersible polymer (A')> The content of structural units derived from carboxyl group-containing monomers in the water-dispersible polymer (A') is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and preferably 55% by mass or less, more preferably 45% by mass or less, even more preferably 35% by mass or less. The content of structural units derived from hydrophobic monomers in the water-dispersible polymer (A') is preferably 45% by mass or more, more preferably 55% by mass or more, even more preferably 65% ​​by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less. The total content of the structural units derived from the carboxyl group-containing monomer and the structural units derived from the hydrophobic monomer in the water-dispersible polymer (A') is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, from the viewpoints of ejection stability of the water-based ink, water resistance of the recorded matter, and suppression of bleeding, and is 100% by mass or less, preferably 100% by mass. The mass ratio of the content of structural units derived from carboxyl group-containing monomers to the content of structural units derived from hydrophobic monomers in the water-dispersible polymer (A') [carboxyl group-containing monomer / hydrophobic monomer] is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, and is preferably 1.2 or less, more preferably 1.0 or less, even more preferably 0.7 or less.

[0020] <Method for producing water-dispersible polymer (A')> The water-dispersible polymer (A') can be produced, for example, by copolymerizing raw material monomers including an acid group-containing monomer and a hydrophobic monomer by a known polymerization method, preferably a solution polymerization method. There are no limitations on the solvent used in the solution polymerization method, but polar solvents such as water, aliphatic alcohols having 1 to 3 carbon atoms, ketones, ethers, and esters are preferred, and water, methanol, ethanol, acetone, methyl ethyl ketone, and the like are more preferred. A known polymerization initiator can be used during polymerization. A polymerization chain transfer agent may also be used as needed. Preferred polymerization initiators include azo compounds such as 4,4'-azobis(4-cyanovaleric acid) and 2,2'-azobis(2,4-dimethylvaleronitrile), and preferred polymerization chain transfer agents include mercaptan compounds such as 2-mercaptoethanol and 3-mercaptopropionic acid. Although preferred polymerization conditions vary depending on the type of polymerization initiator, the polymerization temperature is preferably 50° C. to 90° C., and the polymerization time is preferably 1 hour to 10 hours. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.

[0021] <Degree of Neutralization of Water-Dispersible Polymer (A')> The acid groups of the water-dispersible polymer (A') may be neutralized with a neutralizing agent, which increases the charge repulsion force of the acid groups after neutralization, thereby suppressing aggregation of the water-insoluble polymer particles (A) in the water-based ink of the present invention and further improving dispersion stability. Examples of the neutralizing agent include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, and bases such as organic amines. Among these, from the viewpoint of water resistance, alkali metal hydroxides and ammonia are preferred, and ammonia is more preferred. From the viewpoints of ejection stability of the water-based ink, water resistance of the recorded material, and suppression of bleeding, the degree of neutralization of the acid groups of the water-dispersible polymer (A') is preferably 30 mol% or more, more preferably 35 mol% or more, even more preferably 40 mol% or more, and is preferably 80 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less. Here, the degree of neutralization is the value obtained by dividing the molar equivalents of the neutralizing agent by the molar equivalents of the acid groups of the water-dispersible polymer (A'), i.e., the percentage of "the molar equivalents of the neutralizing agent / the molar equivalents of the acid groups of the water-dispersible polymer (A')." Normally, the degree of neutralization does not exceed 100 mol%, but in the present invention, since it is calculated from the molar equivalents of the neutralizing agent, it exceeds 100 mol% when an excess amount of the neutralizing agent is used. When a divalent or higher neutralizing agent is used, the "molar equivalent number of the neutralizing agent" is synonymous with the functional group equivalent number.

[0022] <Acid value of water-dispersible polymer (A')> The acid value of the water-dispersible polymer (A') is preferably 100 mgKOH / g or more, more preferably 150 mgKOH / g or more, even more preferably 200 mgKOH / g or more, and preferably 340 mgKOH / g or less, more preferably 310 mgKOH / g or less, even more preferably 280 mgKOH / g or less. The acid value of the water-dispersible polymer (A') can be determined by neutralization titration as described in the Examples, or can be calculated from the mass ratio of the monomers constituting the water-dispersible polymer (A').

[0023] <Weight-average molecular weight of water-dispersible polymer (A')> From the viewpoints of ejection stability of the aqueous ink, water resistance of the recorded matter, and suppression of bleeding, the weight average molecular weight of the water-dispersible polymer (A') is preferably 1,000 or more, more preferably 5,000 or more, even more preferably 10,000 or more, and is preferably 50,000 or less, more preferably 30,000 or less, even more preferably 20,000 or less. The weight average molecular weight of the water-dispersible polymer (A') is measured by the method described in the examples.

[0024] <Carboxylic acid compounds> The carboxylic acid compound is a compound having a carboxy group and a molecular weight of 150 or more and 1,000 or less. From the viewpoint of ejection stability of the water-based ink, water resistance of the recorded material, and suppression of bleeding, the molecular weight of the carboxylic acid compound is preferably 900 or less, more preferably 800 or less, and even more preferably 750 or less.

[0025] The carboxylic acid compound preferably has 9 or more carbon atoms, more preferably 12 or more carbon atoms, and even more preferably 17 or more carbon atoms, and preferably has 60 or less carbon atoms, more preferably 50 or less carbon atoms, and even more preferably 40 or less carbon atoms.

[0026] The number of carboxy groups in the carboxylic acid compound is preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and even more preferably 1 or 2, from the viewpoints of ejection stability of the water-based ink, water resistance of the recorded matter, and suppression of bleeding. From the viewpoints of ejection stability of the water-based ink, water resistance of the recorded material, and suppression of bleeding, the carboxylic acid compound preferably has a hydrocarbon group. The hydrocarbon group may be linear or branched. The hydrocarbon group is preferably an unsaturated hydrocarbon group from the viewpoints of ejection stability of the aqueous ink, water resistance of the recorded material, and suppression of bleeding. The number of unsaturated bonds in the unsaturated hydrocarbon group is preferably 1 or 2, and more preferably 1. The carboxylic acid compound is preferably composed of a hydrocarbon group and one or two carboxy groups, from the viewpoints of ejection stability of the water-based ink, water resistance of the recorded material, and suppression of bleeding.

[0027] The acid value of the carboxylic acid compound is preferably 50 mgKOH / g or more, more preferably 70 mgKOH / g or more, even more preferably 90 mgKOH / g or more, and is preferably 400 mgKOH / g or less, more preferably 300 mgKOH / g or less, even more preferably 210 mgKOH / g or less.

[0028] The weighted average acid value of the water-dispersible polymer (A') and the carboxylic acid compound in the raw materials for the water-insoluble polymer particles (A) is preferably 100 mgKOH / g or more, more preferably 140 mgKOH / g or more, even more preferably 180 mgKOH / g or more, and is preferably 320 mgKOH / g or less, more preferably 300 mgKOH / g or less, even more preferably 280 mgKOH / g or less. When the weighted average acid value of the water-dispersible polymer (A') and the carboxylic acid compound is within the above ranges, the amount of acid groups crosslinked by the polyfunctional epoxy crosslinking agent and the amount of acid groups neutralized can be ensured, and the dispersion stability of the pigment dispersed by the water-insoluble polymer particles (A) can be ensured. In addition, the weighted average acid value of the water-dispersible polymer (A') and the carboxylic acid compound can also be calculated using the acid value of the water-insoluble polymer particles (A) described below and the degree of crosslinking of the water-insoluble polymer particles (A) also described below, using the following formula. Acid value (mg KOH / g) of water-dispersible polymer (A') = 100 × (acid value of water-insoluble polymer particles (A)) / (100 - (degree of crosslinking of water-insoluble polymer particles (A))) Here, the acid value of the water-insoluble polymer particles (A) is expressed in units of "mgKOH / g", and the crosslinking degree of the water-insoluble polymer particles (A) is expressed in units of "mol %".

[0029] The melting point of the carboxylic acid compound is preferably 80°C or lower, more preferably 50°C or lower, even more preferably 30°C or lower, even more preferably 25°C or lower, and is preferably 3°C or higher, more preferably 7°C or higher.

[0030] Specific examples of carboxylic acid compounds include oleic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, polyoxyethylene lauryl ether acetic acid, polyoxyethylene oleyl ether acetic acid, and dimerized oleic acid, of which oleic acid, lauric acid, myristic acid, palmitic acid, and dimerized oleic acid are preferred, and oleic acid and dimerized oleic acid are more preferred. The carboxylic acid compounds can be used alone or in combination of two or more.

[0031] <Multifunctional epoxy crosslinking agent> The polyfunctional epoxy crosslinking agent may be water-insoluble or water-soluble, and is preferably water-soluble. From the viewpoint of efficiently reacting with the water-dispersible polymer (A') and the acid groups in the carboxylic acid compound in an aqueous medium to form a crosslinked structure, the water-solubility of the polyfunctional epoxy crosslinking agent is preferably 15% by mass or more, more preferably 45% by mass or more, even more preferably 75% by mass or more, and preferably 100% by mass or less. The polyfunctional epoxy crosslinking agent may be used alone or in combination of two or more. When two or more polyfunctional epoxy crosslinking agents are used in combination, the water solubility of the polyfunctional epoxy crosslinking agent means the water solubility of the mixture of the polyfunctional epoxy crosslinking agents. The water solubility of the polyfunctional epoxy crosslinking agent is measured by the method described in the examples.

[0032] The number of epoxy groups in the multifunctional epoxy crosslinking agent is 2 or more, preferably 2.5 or more, more preferably 3 or more, and preferably 7 or less, more preferably 5 or less. The number of glycidyl ether groups in the multifunctional epoxy crosslinking agent is 2 or more, preferably 2.5 or more, more preferably 3 or more, and preferably 7 or less, more preferably 5 or less. The term "multifunctional" in the context of a multifunctional epoxy crosslinking agent means that the agent has two or more epoxy groups. When multifunctional epoxy crosslinking agents with different numbers of epoxy groups are used in combination, the "number of epoxy groups in the multifunctional epoxy crosslinking agent" refers to a weighted average value. The same applies to the number of glycidyl ether groups. The polyfunctional epoxy crosslinking agent is preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms.

[0033] Among the structures derived from polyfunctional epoxy crosslinkers, the content of structures derived from tri- or higher functional epoxy crosslinkers is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more, and 100% by mass or less, from the viewpoints of ejection stability of the aqueous ink, water resistance of the recorded matter, and suppression of bleeding.

[0034] The epoxy equivalent of the multifunctional epoxy crosslinker is preferably 90 g / eq or more, more preferably 100 g / eq or more, even more preferably 110 g / eq or more, and preferably 300 g / eq or less, more preferably 220 g / eq or less, more preferably 180 g / eq or less.

[0035] Specific examples of polyfunctional epoxy crosslinkers include sorbitol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, diglycerol polyglycidyl ether, and polyglycerol polyglycidyl ether. Among these, sorbitol polyglycidyl ether and trimethylolpropane polyglycidyl ether are preferred, and sorbitol polyglycidyl ether is more preferred.

[0036] Commercially available polyfunctional epoxy crosslinkers include Denacol EX-612 (sorbitol polyglycidyl ether, epoxy equivalent: 166 g / eq, water solubility: 42% by mass), Denacol EX-614 (sorbitol polyglycidyl ether, epoxy equivalent: 167 g / eq, water solubility: 78% by mass), Denacol EX-614B (sorbitol polyglycidyl ether, epoxy equivalent: 173 g / eq, water solubility: 94% by mass), Denacol EX-313 (glycerol polyglycidyl ether, epoxy equivalent: 141 g / eq, water solubility: 99% by mass), Denacol EX-314B (glycerol polyglycidyl ether, epoxy equivalent: 141 g / eq, water solubility: 99% by mass), Denacol EX-314C (glycerol polyglycidyl ether, epoxy equivalent: 141 g / eq, water solubility: 99% by mass), Denacol EX-314D (glycerol polyglycidyl ether, epoxy equivalent: 141 g / eq, water solubility: 99% by mass), Denacol EX-314E (glycerol polyglycidyl ether, epoxy equivalent: 141 g / eq, water solubility: 99% by mass), Denacol EX-314F (glycerol polyglycidyl ether, epoxy equivalent: 141 g / eq, water solubility: 99% by mass), Denacol EX-314H ...

[0043] Examples of such epoxy resins include Denacol EX-321 (trimethylolpropane polyglycidyl ether, epoxy equivalent: 140 g / eq, water solubility: 27% by mass), Denacol EX-421 (diglycerol polyglycidyl ether, epoxy equivalent: 159 g / eq, water solubility: 88% by mass), Denacol EX-512 (polyglycerol polyglycidyl ether, epoxy equivalent: 168 g / eq, water solubility: 100% by mass), and Denacol EX-521 (polyglycerol polyglycidyl ether, epoxy equivalent: 183 g / eq, water solubility: 100% by mass) (all manufactured by Nagase ChemteX Corporation). Among these, Denacol EX-614B and Denacol EX-321 are preferred, and Denacol EX-614B is more preferred.

[0037] In the water-insoluble polymer particles (A), the ratio of the mass of the structure derived from a carboxylic acid compound to the total mass of the structure derived from the water-dispersible polymer (A') and the structure derived from a carboxylic acid compound [structure derived from a carboxylic acid compound / (structure derived from the water-dispersible polymer (A') having acid groups + structure derived from a carboxylic acid compound)] is preferably 0.03 or more, more preferably 0.08 or more, even more preferably 0.13 or more, even more preferably 0.17 or more, and is preferably 0.6 or less, more preferably 0.5 or less.

[0038] In the water-insoluble polymer particles (A), the ratio of the mass of the structure derived from the crosslinking agent to the total mass of the structure derived from the water-dispersible polymer (A') and the structure derived from the carboxylic acid compound [structure derived from the crosslinking agent / (structure derived from the water-dispersible polymer (A') having acid groups + structure derived from the carboxylic acid compound)] is preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.2 or more, and is preferably 0.9 or less, more preferably 0.8 or less, even more preferably 0.7 or less.

[0039] <Method for producing water-insoluble polymer particles (A)> The water-insoluble polymer particles (A) can be obtained by reacting the acid groups of the water-dispersible polymer (A') with a carboxylic acid compound and a polyfunctional epoxy crosslinking agent. The reaction can be carried out in an aqueous medium. The reaction temperature of the acid groups of the water-dispersible polymer (A'), the carboxylic acid compound, and the polyfunctional epoxy crosslinking agent is preferably 60°C or higher, more preferably 75°C or higher, and preferably 110°C or lower, more preferably 100°C or lower, from the viewpoint of completing the reaction and from the viewpoint of economy. The reaction time is preferably 0.5 hours or higher, more preferably 1 hour or higher, and preferably 15 hours or lower, more preferably 8 hours or lower.

[0040] <<Degree of crosslinking of water-insoluble polymer particles (A)>> The degree of crosslinking of the water-insoluble polymer particles (A) is preferably 50 mol% or more, more preferably 55 mol% or more, and is preferably less than 100 mol%, more preferably 95 mol% or less, even more preferably 90 mol% or less, and even more preferably 85 mol% or less. Here, the degree of crosslinking of the water-insoluble polymer particles (A) means the percentage of the value obtained by dividing the molar equivalent number of epoxy groups of the polyfunctional epoxy crosslinking agent by the molar equivalent number of acid groups of the water-dispersible polymer (A') and the carboxylic acid compound.

[0041] <Acid value of water-insoluble polymer particles (A)> From the viewpoint of water resistance and bleeding prevention of recorded materials, the acid value of the water-insoluble polymer particles (A) is preferably 25 mgKOH / g or more, more preferably 30 mgKOH / g or more, even more preferably 35 mgKOH / g or more, and is preferably 65 mgKOH / g or less, more preferably 60 mgKOH / g or less, even more preferably 55 mgKOH / g or less.

[0042] The acid value of the water-insoluble polymer particles (A) can be calculated from the degree of crosslinking of the water-insoluble polymer particles (A) using the following formula, and indicates the amount of acid groups remaining among the acid groups of the water-dispersible polymer (A') and the carboxylic acid compound that are not involved in the formation of a crosslinked structure by reaction with the polyfunctional epoxy crosslinking agent. Acid value (mg KOH / g) of water-insoluble polymer particles (A) = (weighted average acid value of water-dispersible polymer (A') and carboxylic acid compound) × (100 - (degree of crosslinking of water-insoluble polymer particles (A))) / 100 Here, the acid values ​​of the water-dispersible polymer (A') and the carboxylic acid compound are expressed in units of "mgKOH / g," and the crosslinking degree of the water-insoluble polymer particles (A) is expressed in units of "mol %."

[0043] 〔water〕 The water-based ink of the present invention contains water. The water used in the water-based ink of the present invention is preferably pure water or deionized water from the viewpoint of preventing the inclusion of unintended substances.

[0044] [Pigments] The hue of the water-based ink of the present invention is not particularly limited, and may be any of a transparent ink containing no pigment, a chromatic ink such as yellow, magenta, cyan, red, blue, orange, or green, or an achromatic ink such as black. From the viewpoints of water resistance and bleeding prevention of recorded matter, it is preferable that the water-based ink of the present invention further contains a pigment. The pigment may be either an inorganic pigment or an organic pigment, and if necessary, an extender pigment may be used in combination with the inorganic pigment or an organic pigment. Examples of inorganic pigments include carbon black, metal oxides, metal sulfides, and metal chlorides. Of these, carbon black is preferred, particularly for black inks. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Furthermore, examples of metal oxides for white inks include titanium oxide, zinc oxide, silica, alumina, and magnesium oxide, with titanium oxide being preferred. Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. The hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, or green can be used. Specific examples of preferred chromatic organic pigments include one or more selected from CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green. The above pigments can be used alone or in combination of two or more.

[0045] The pigment used in the present invention is preferably used as an aqueous pigment dispersion obtained by dispersing the pigment in an aqueous medium, and the pigment is preferably used in the form of particles dispersed in a polymer dispersant. The polymer dispersant is used to disperse the pigment.

[0046] <Pigment particles dispersed with a polymer dispersant> Examples of particles in which a pigment is dispersed with a polymer dispersant include: 1) particles in which a pigment and a polymer dispersant are kneaded together and the kneaded mixture is dispersed in a medium such as water; 2) particles in which a pigment and a polymer dispersant are stirred in a medium such as water and the pigment is dispersed in the medium such as water; and 3) particles in which the raw materials for the polymer dispersant and the pigment are mechanically dispersed, and the raw materials for the polymer dispersant are polymerized, and the pigment is dispersed in a medium such as water by the resulting polymer dispersant. From the viewpoint of ejection stability of the water-based ink, water resistance of the recorded material, and suppression of bleeding, it is preferable to add a crosslinking agent to particles in which the pigment is dispersed in a polymer dispersant to crosslink the polymer dispersant. The form in which the pigment and polymer dispersant are present in the water-based ink may include a form in which the polymer dispersant is adsorbed to the pigment, a form in which the polymer dispersant contains the pigment, etc. Among these, from the viewpoint of the dispersion stability of the pigment, a form in which the polymer dispersant is in the form of polymer particles containing the pigment is preferred, and a form in which the polymer dispersant contains the pigment and contains the pigment is more preferred.

[0047] (Polymer dispersant) The polymer dispersant may be one or more selected from condensation polymers such as polyesters and polyurethanes; vinyl polymers, etc. From the viewpoint of pigment dispersion stability, vinyl polymers obtained by addition polymerization of vinyl monomers (vinyl compounds, vinylidene compounds, vinylene compounds) are preferred. The polymer dispersant may be appropriately synthesized or a commercially available product. When the polymer dispersant is a crosslinked polymer obtained by crosslinking the water-dispersible polymer (A') with a crosslinking agent, the polymer dispersant may contain the above-mentioned carboxylic acid compound.

[0048] <Method for producing water-based pigment dispersion> The water-based pigment dispersion is preferably produced by a method including the following steps 1 to 3. Step 1: A step of dispersing a pigment mixture containing a pigment and an aqueous dispersion of a water-dispersible polymer (A') having an acid group (hereinafter also referred to as "aqueous polymer dispersion (d)") by applying shear stress to obtain a pigment dispersion. Step 2: A step of obtaining a pigment aqueous dispersion (e) by filtering the pigment dispersion to remove coarse particles. Step 3: A step of reacting the acid groups of the water-dispersible polymer (A') in the pigment water dispersion (e) obtained in Step 1 with a polyfunctional epoxy crosslinking agent to form a crosslinked polymer, thereby obtaining an aqueous pigment dispersion (E) containing a pigment, a crosslinked polymer, and an aqueous medium.

[0049] [Process 1] Step 1 is a step of dispersing a pigment in an aqueous medium using a water-dispersible polymer (A') having an acid group as a dispersant to obtain a pigment dispersion. In step 1, the aqueous medium may contain an organic solvent from the viewpoint of improving the wettability of the pigment and the adsorption of the water-dispersible polymer (A') having an acid group to the pigment. Suitable examples of the organic solvent include alcohols having from 1 to 3 carbon atoms and ketones having from 3 to 6 carbon atoms. In the dispersion treatment in step 1, the pigment particles may be atomized to the desired particle size by main dispersion using shear stress alone. However, from the viewpoint of obtaining a uniform pigment dispersion, it is preferable to pre-disperse the pigment mixture and then further carry out main dispersion. As a dispersing machine used for preliminary dispersion, a commonly used mixing and stirring device such as an anchor blade or a disperser blade can be used. Examples of means for applying shear stress used in this dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersers such as paint shakers and bead mills. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment. When a dispersion treatment is carried out using a high-pressure homogenizer, the average particle size of the pigment particles in the pigment dispersion can be adjusted by controlling the treatment pressure and the number of passes. From the viewpoints of productivity and economy, the treatment pressure is preferably 60 MPa or more and 300 MPa or less, and the number of passes is preferably 3 or more and 30 or less.

[0050] In step 1, at least a portion of the acid groups of the water-dispersible polymer (A') is preferably neutralized with a neutralizing agent. That is, at least a portion of the acid groups of the water-dispersible polymer (A') constituting the crosslinked polymer become neutralized salts, and thereby at least a portion of the acid groups of the crosslinked polymer become neutralized salts. The water-dispersible polymer (A') having an acid group is preferably neutralized by mixing a neutralizing agent when the water-dispersible polymer (A') is dispersed in water to obtain the aqueous polymer dispersion (d). From the viewpoint of facilitating the production of the pigment dispersion, the non-volatile component concentration (solid content concentration) of the polymer aqueous dispersion (d) is preferably 5% by mass or more, more preferably 10% by mass or more, and is preferably 25% by mass or less, more preferably 20% by mass or less. The solid content concentration of the polymer aqueous dispersion (d) is measured by the method described in the Examples.

[0051] The neutralizing agent is preferably used as an aqueous solution of the neutralizing agent from the viewpoint of promoting sufficient and uniform neutralization. Examples of the neutralizing agent include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, ammonia, and bases such as organic amines. Among these, preferred is one or more selected from the group consisting of sodium hydroxide, potassium hydroxide, and organic amines, and more preferred is sodium hydroxide.

[0052] From the viewpoint of improving the dispersion stability of the pigment and thereby improving the ejection stability of the water-based ink, the degree of neutralization of the acid groups in the water-dispersible polymer (A') is preferably 25 mol% or more, more preferably 30 mol% or more, even more preferably 35 mol% or more, and is preferably 80 mol% or less, more preferably 60 mol% or less, even more preferably 50 mol% or less.

[0053] [Process 2] In step 2, the pigment dispersion is filtered to remove coarse particles, thereby obtaining a pigment aqueous dispersion (e). In step 2, it is preferable that the organic solvent in the obtained pigment aqueous dispersion (e) has been substantially removed, but it may remain as long as it does not impair the object of the present invention. The organic solvent can be removed, for example, by distillation under reduced pressure.

[0054] The pigment water dispersion (e) obtained in step 2 is prepared by dispersing a pigment in an aqueous medium using a water-dispersible polymer (A') having acid groups. The form in which the pigment and the water-dispersible polymer (A') having acid groups are present in the pigment water dispersion (e) is not particularly limited, as long as particles are formed from at least the pigment and the water-dispersible polymer (A') having acid groups. Examples of such forms include a particle form in which the pigment is encapsulated in the water-dispersible polymer (A') having acid groups, a particle form in which the pigment is uniformly dispersed in the water-dispersible polymer (A') having acid groups, and a particle form in which the pigment is exposed on the surface of the water-dispersible polymer (A') having acid groups, and mixtures thereof are also included.

[0055] The concentration of non-volatile components (solid content concentration) of the pigment water dispersion (e) obtained in step 2 is preferably 10% by mass or more, more preferably 15% by mass or more, from the viewpoint of improving the dispersion stability of the pigment in the pigment water dispersion (e) and facilitating the preparation of a water-based ink for inkjet printing, and is preferably 30% by mass or less, more preferably 25% by mass or less. The solid content concentration of the pigment water dispersion (e) is measured by the method described in the examples.

[0056] The content of the pigment in the pigment water dispersion (e) is preferably 4% by mass or more, more preferably 8% by mass or more, even more preferably 12% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less.

[0057] The content of the water-dispersible polymer (A') having an acid group in the pigment water dispersion (e) is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and is preferably 14% by mass or less, more preferably 10% by mass or less, even more preferably 6% by mass or less.

[0058] In the pigment water dispersion (e), the mass ratio of the pigment to the total mass of the pigment and the water-dispersible polymer (A') having an acid group [pigment / pigment + water-dispersible polymer (A') having an acid group] is, from the viewpoint of improving the dispersion stability of the pigment and improving the jetting stability of the water-based ink, preferably 0.3 or more, more preferably 0.5 or more, even more preferably 0.7 or more, and is preferably 0.95 or less, more preferably 0.9 or less, and even more preferably 0.85 or less.

[0059] [Step 3] Step 3 is a step of reacting the acid groups of the water-dispersible polymer (A') in the pigment aqueous dispersion (e) obtained in Step 2 with a polyfunctional epoxy crosslinking agent to obtain an aqueous pigment dispersion (E) in which the pigment is dispersed in an aqueous medium as a crosslinked polymer. The reaction between the acid groups of the water-dispersible polymer (A') and the polyfunctional epoxy crosslinking agent forms a crosslinked polymer containing a crosslinked structure. In Step 3, the above-mentioned carboxylic acid compound may be used to incorporate a structure derived from the carboxylic acid compound into the crosslinked polymer. That is, in Step 3, the crosslinked polymer may be water-insoluble polymer particles (A).

[0060] When a carboxylic acid compound is used in step 3, the ratio of the mass of the carboxylic acid compound to the total mass of the carboxylic acid compound and the water-dispersible polymer (A') having an acid group [carboxylic acid compound / (carboxylic acid compound + water-dispersible polymer (A') having an acid group)] is preferably 0.05 or more, more preferably 0.10 or more, even more preferably 0.15 or more, from the viewpoint of improving the dispersion stability of the pigment and thereby improving the ejection stability of the water-based ink, and is preferably 0.6 or less, more preferably 0.4 or less.

[0061] The reaction temperature between the acid groups of the water-dispersible polymer (A') and the polyfunctional epoxy crosslinking agent is preferably 60°C or higher, more preferably 75°C or higher, and preferably 110°C or lower, more preferably 100°C or lower, from the viewpoint of completing the reaction and from the viewpoint of economy. The reaction time is preferably 0.5 hours or higher, more preferably 1 hour or higher, and preferably 15 hours or lower, more preferably 8 hours or lower.

[0062] The content of the pigment in the aqueous pigment dispersion (E) of the present invention is preferably 3% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, and is preferably 28% by mass or less, more preferably 22% by mass or less, even more preferably 18% by mass or less.

[0063] The content of the crosslinked polymer in the aqueous pigment dispersion (E) is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and preferably 16% by mass or less, more preferably 12% by mass or less, even more preferably 8% by mass or less.

[0064] In the aqueous pigment dispersion (E), the mass ratio of the pigment to the total mass of the pigment and the crosslinked polymer [pigment / pigment+crosslinked polymer] is preferably 0.4 or more, more preferably 0.5 or more, even more preferably 0.6 or more, from the viewpoint of improving the dispersion stability of the pigment and thereby improving the ejection stability of the aqueous ink, and is preferably 0.95 or less, more preferably 0.85 or less, even more preferably 0.75 or less.

[0065] The average particle size of the particles in the aqueous pigment dispersion (E) is preferably 60 nm or more, more preferably 80 nm or more, even more preferably 100 nm or more, and is preferably 160 nm or less, more preferably 140 nm or less, even more preferably 120 nm or less, from the viewpoints of reducing coarse particles, improving the dispersion stability of the pigment, and thereby improving the ejection stability of the aqueous ink. The average particle size of the particles in the water-based pigment dispersion (E) is measured by the method described in the examples.

[0066] [Organic solvent] The water-based ink of the present invention preferably contains an organic solvent from the viewpoint of improving ejection stability. Examples of the organic solvent include polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, and sulfur-containing compounds. Among these, the organic solvent is preferably one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers.

[0067] The polyhydric alcohol is preferably one or more selected from the group consisting of diols and trihydric or higher polyhydric alcohols.

[0068] Examples of diols include ethylene glycol, propylene glycol, 1,2-butanediol, 1,2-hexanediol, 1,2-octanediol, 1,8-octanediol, 1,2-decanediol, 1,3-propanediol, 1,4-butanediol, 2-ethyl-1,3-hexanediol, diethylene glycol, and dipropylene glycol. Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, and pentaerythritol.

[0069] Examples of polyhydric alcohol alkyl ethers include alkylene glycol monoalkyl ethers such as ethylene glycol monoethyl ether and ethylene glycol monoisopropyl ether; diethylene glycol monoalkyl ethers such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether and diethylene glycol monobutyl ether; tetraethylene glycol monoalkyl ethers such as tetraethylene glycol monomethyl ether; propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether and propylene glycol monobutyl ether; dipropylene glycol monoalkyl ethers such as dipropylene glycol monomethyl ether; and tripropylene glycol monoalkyl ethers such as tripropylene glycol monomethyl ether. The organic solvent may be used alone or in combination of two or more kinds.

[0070] [Surfactant] The aqueous ink of the present invention preferably contains a surfactant from the viewpoint of improving ejection stability. Examples of the surfactant include nonionic surfactants, anionic surfactants, and amphoteric surfactants, with nonionic surfactants being preferred, and one or more surfactants selected from the group consisting of acetylene glycol surfactants and polyoxyalkylene alkyl ether surfactants being more preferred, with acetylene glycol surfactants being even more preferred. Preferred examples of the acetylene glycol surfactant include acetylene glycols having 8 to 22 carbon atoms and ethylene oxide adducts of the acetylene glycols, and more preferred is 2,4,7,9-tetramethyl-5-decyne-4,7-diol or an ethylene oxide adduct thereof. A specific example of the polyoxyalkylene alkyl ether surfactant is polyoxyethylene lauryl ether. The water-based ink of the present invention may contain a combination of an acetylene glycol surfactant and a polyoxyethylene alkyl ether.

[0071] [Other ingredients] The water-based ink of the present invention may further contain, if necessary, various additives commonly used in water-based inks for ink-jet printing, such as a humectant, wetting agent, penetrant, dispersant, viscosity modifier, antifoaming agent, preservative, antifungal agent and antirust agent.

[0072] [Content] The content of the water-insoluble polymer particles (A) in the water-based ink of the present invention is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, from the viewpoint of the ejection stability of the water-based ink and the water resistance and suppression of bleeding of the recorded matter, and is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 8% by mass or less.

[0073] The water content in the water-based ink of the present invention is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 60% by mass or more, from the viewpoint of the ejection stability of the water-based ink and the water resistance and suppression of bleeding of the recorded matter, and is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less.

[0074] When the aqueous ink of the present invention contains a crosslinked polymer other than the water-insoluble polymer particles (A), the content of the crosslinked polymer in the aqueous ink is, from the viewpoint of the ejection stability of the aqueous ink and the water resistance and suppression of bleeding of the recorded matter, preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and is preferably 12% by mass or less, more preferably 8% by mass or less, even more preferably 4% by mass or less.

[0075] When the water-based ink of the present invention contains a pigment, the content of the pigment in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, from the viewpoint of the ejection stability of the water-based ink and the water resistance and suppression of bleeding of the recorded matter, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 7% by mass or less.

[0076] When the water-based ink of the present invention contains an organic solvent, the content of the organic solvent in the water-based ink is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, from the viewpoint of the ejection stability of the water-based ink and the water resistance and suppression of bleeding of the recorded matter, and is preferably 35% by mass or less, more preferably 32% by mass or less, even more preferably 27% by mass or less. When the aqueous ink of the present invention contains a polyhydric alcohol, the content of the polyhydric alcohol in the aqueous ink is, from the viewpoint of the ejection stability of the aqueous ink and the water resistance and suppression of bleeding of the recorded matter, preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less.

[0077] When the aqueous ink of the present invention contains a polyhydric alcohol alkyl ether, the content of the polyhydric alcohol alkyl ether in the aqueous ink is, from the viewpoint of the ejection stability of the aqueous ink and the water resistance and suppression of bleeding of the recorded matter, preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less.

[0078] When the water-based ink of the present invention contains a surfactant, from the viewpoint of the ejection stability of the water-based ink, the water resistance of the recorded matter, and suppression of bleeding, the surfactant content is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, and is preferably 3% by mass or less, more preferably 2% by mass or less, even more preferably 1% by mass or less.

[0079] [Method of manufacturing water-based ink for inkjet printing] The water-based ink of the present invention is a method for producing a water-based ink for ink-jet printing containing water-insoluble polymer particles (A) and water, and includes the following step A: Step A: A step of obtaining water-insoluble polymer particles (A) by reacting a water-dispersible polymer (A') having an acid group, a carboxylic acid compound having a molecular weight of 150 to 1000, and a polyfunctional epoxy crosslinking agent. The reaction can be carried out in an aqueous medium. The water-based ink of the present invention can be produced by mixing the water-insoluble polymer particles (A), and, if necessary, water and various optional components such as a pigment, an organic solvent, a surfactant, etc. The water-based ink of the present invention is preferably produced by dispersing an aqueous dispersion of the water-insoluble polymer particles (A), the water-based pigment dispersion (E), and, if necessary, various optional components such as an organic solvent, a surfactant, etc., by a known method, and, if necessary, filtering to remove coarse particles.

[0080] [Inkjet recording] The water-based ink of the present invention can be loaded into a known inkjet recording device and ejected as ink droplets onto a recording medium to record characters and images. Ink jet recording apparatuses include thermal and piezo types, with the thermal type being preferred, and the water-based ink of the present invention is preferably used for thermal ink jet recording. Examples of recording media include low-water-absorbency recording paper such as coated paper, and non-water-absorbency resin films such as PET film and polypropylene film. Plain paper can also be used as the recording medium. The terms "low water absorption" and "non-water absorption" refer to a state in which the amount of water absorption of the recording medium is 10 g / m2 or less when the recording medium is in contact with pure water for 100 ms. 2 This means that the water absorption is 10 g / m or less. 2 Ultra-high absorbency recording media are highly absorbent, and plain paper is classified as highly absorbent. [Example]

[0081] In the following Production Examples, Examples, and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

[0082] (1) Measurement of weight average molecular weight of water-dispersible polymer (A') The measurement was performed by gel permeation chromatography under the following conditions. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: "TSKgel SuperAWM-H," "TSKgel SuperAW3000," and "TSKgel guardcolumn Super AW-H" manufactured by Tosoh Corporation Eluent: N,N-dimethylformamide dissolved with phosphoric acid and lithium bromide at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits with known molecular weights, "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)" (both manufactured by Tosoh Corporation) Measurement sample: 0.1 g of water-dispersible polymer (A'1) 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" (material: polytetrafluoroethylene (PTFE) 0.2 μm, manufactured by ADVANTEC).

[0083] (2) Measurement of the acid value of the water-dispersible polymer (A') Measurement was carried out in accordance with the neutralization titration method described in JIS K 0070-1992, except that the measurement solvent was changed from a mixed solvent of ethanol and ether to a mixed solvent of acetone and toluene [acetone:toluene=1:1 (volume ratio)].

[0084] (3) Water solubility of multifunctional epoxy crosslinking agent At room temperature (25°C), 90 parts by mass of deionized water and 10 parts by mass of a multifunctional epoxy crosslinker were added to a glass tube (25 mmφ × 250 mmh), and the glass tube was left to stand for 1 hour in a thermostatic bath with the water temperature adjusted to 25°C. The glass tube was then shaken at 1500 rpm for 1 minute using a small vibrator (manufactured by AS ONE Corporation, product name: Test Tube Mixer TRIO (High Type) HM-1N) and then left to stand again in the thermostatic bath for 10 minutes. The undissolved material was then recovered, dried, and weighed, and the water solubility (mass%) was calculated using the following formula: Water solubility (mass%) = 100 × (10 - mass parts of undissolved matter) / 10

[0085] (4) Measurement of the average particle size of water-insoluble polymer particles (A) in water-based pigment dispersions The particle size was measured by dynamic light scattering using a laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., product name: ELS-8000), and calculated by cumulant analysis. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 integration times. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measured concentration was 5 × 10 -3 The measurement was carried out in mass % (solid content conversion), and the obtained cumulant average particle size was taken as the average particle size of the particles.

[0086] (5) Measurement of solids concentration in polymer water dispersions, pigment water dispersions, and water-based pigment dispersions 10.0 g of sodium sulfate, brought to a constant weight in a desiccator, was weighed into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm), and approximately 1.0 g of the sample was added and mixed. The mixture was then accurately weighed and maintained at 105°C for 2 hours to remove volatiles. The mixture was then left to stand in the desiccator for an additional 15 minutes, and the mass was measured. The mass of the sample after devolatilization was taken as the solid content, and was divided by the mass of the added sample to obtain the solid content concentration.

[0087] [Production of Water-Dispersible Polymer (A')] Production Example 1 (Production of Water-Dispersible Polymer (A'1)) A monomer mixture was prepared by mixing 31 parts of acrylic acid and 69 parts of styrene. Five parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.25 parts of 3-mercaptopropionic acid as a polymerization chain transfer agent, and 10% by mass of the monomer mixture were placed in a reaction vessel and mixed, followed by thorough nitrogen gas replacement. Separately, a mixture of the remaining 90% by mass of the monomer mixture, 2.0 parts of the polymerization chain transfer agent, 75 parts of MEK, and 1.5 parts of 4,4'-azobis(4-cyanovaleric acid) (Fujifilm Wako Pure Chemical Industries, Ltd., product name "V-501") as an azo-based radical polymerization initiator was placed in a dropping funnel. Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 77°C with stirring, and the mixture in the dropping funnel was added dropwise over 5 hours. After the dropwise addition was completed, a solution of 0.5 parts of the polymerization initiator in 5 parts of MEK was added, and the reaction was continued for another 2 hours at 77°C to obtain a solution of water-dispersible polymer (A'1). The acid value of the water-dispersible polymer (A'1) was 240 mgKOH / g and the weight-average molecular weight was 16,900.

[0088] [Production of polymer aqueous dispersion] Production Example 2-1 (Production of polymer aqueous dispersion (d1)) The solution of the water-dispersible polymer (A'1) obtained in Production Example 1 was dried under reduced pressure to obtain 80 parts of the water-dispersible polymer (A'1) having carboxy groups. 421 parts of deionized water and 32.4 parts of a 5N aqueous solution of sodium hydroxide (sodium hydroxide solids content 16.9%) as an alkali metal compound (neutralizing agent) were added, and the ratio of the number of moles of sodium hydroxide to the number of moles of carboxy groups in the water-dispersible polymer (A'1) was neutralized to 40 mol% (neutralization degree 40 mol%). The resulting dispersion was heated at 90°C for 5 hours while stirring at 150 rpm to obtain a polymer aqueous dispersion (d1) (solids concentration 15%).

[0089] Production Example 2-2 (Production of Polymer Aqueous Dispersion (D1)) The solution of water-dispersible polymer (A'1) obtained in Production Example 1 was dried under reduced pressure, and 80 parts of the resulting water-dispersible polymer (A'1) having carboxy groups was neutralized by adding 443 parts of deionized water and 10.5 parts of a 25% aqueous ammonia solution as a neutralizing agent, so that the ratio of the number of moles of ammonia to the number of moles of carboxy groups in the water-dispersible polymer (A'1) was 45 mol% (neutralization degree 45 mol%). The resulting dispersion was heated at 90°C for 5 hours while stirring at 150 rpm to obtain a polymer aqueous dispersion (D1) (solids concentration 15%).

[0090] [Production of Water-Based Pigment Dispersion (E)] Production Example 3-1 (Production of Water-Based Pigment Dispersion (E1)) (Process 1) To 155 parts of the polymer aqueous dispersion (d1) (solid content concentration 15%) were added 42 parts of MEK and 279 parts of deionized water, and then 90 parts of carbon black (manufactured by Cabot Corporation, trade name: Monarch 800) was added to obtain a pigment mixture. The resulting pigment mixture was mixed for 1 hour using a disper blade at 7000 rpm and 20° C. Thereafter, a dispersion treatment was further performed using a microfluidizer (Microfluidics Corporation, high-pressure homogenizer "M-140K") at a pressure of 180 MPa for 10 passes to obtain a pigment dispersion.

[0091] (Process 2) From the obtained pigment dispersion, MEK was removed under reduced pressure at 60°C, and then some of the water was removed. After centrifugation, the liquid phase was filtered through a membrane filter ("Minisart Syringe Filter" manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining a pigment aqueous dispersion (e1) (solid concentration: 20%) in which pigment-containing polymer particles were dispersed in an aqueous medium.

[0092] (Step 3) One hundred parts of the resulting pigment aqueous dispersion (e1) (20% solids concentration) was transferred to a screw-cap glass bottle, and 2.49 parts (enough to achieve a crosslinking degree of 80 mol%) of sorbitol polyglycidyl ether (Denacol EX-614B, manufactured by Nagase ChemteX Corporation, epoxy group equivalent: 173 g / eq, water solubility: 94%, hereinafter also referred to as "EX-614B") as a multifunctional epoxy crosslinker and 9.9 parts of deionized water were added. The bottle was then sealed and heated at 90°C for 5 hours with stirring. The temperature was then lowered to room temperature, and the mixture was filtered through a membrane filter (Minisart Syringe Filter, manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding aqueous pigment dispersion E1 (20% solids concentration), which consisted of pigment-containing crosslinked polymer particles dispersed in an aqueous medium. The average particle size of the particles in aqueous pigment dispersion E1 is shown in Table 1.

[0093] Production Example 3-2 (Production of Water-Based Pigment Dispersion (E2)) (Process 1) To 130 parts of the polymer aqueous dispersion (d1) (solid content concentration 15%) were added 41 parts of MEK and 287 parts of deionized water, and then 90 parts of carbon black (manufactured by Cabot Corporation, trade name: Monarch 800) was added to obtain a pigment mixture. The resulting pigment mixture was mixed for 1 hour using a disper blade at 7000 rpm and 20° C. Thereafter, a dispersion treatment was further performed using a microfluidizer (Microfluidics Corporation, high-pressure homogenizer "M-140K") at a pressure of 180 MPa for 10 passes to obtain a pigment dispersion.

[0094] (Process 2) From the obtained pigment dispersion, MEK was removed under reduced pressure at 60°C, and then some of the water was removed. After centrifugation, the liquid phase was filtered through a membrane filter ("Minisart Syringe Filter" manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining a pigment aqueous dispersion (e2) (solid concentration: 20%) in which pigment-containing polymer particles were dispersed in an aqueous medium.

[0095] (Step 3) One hundred parts of the resulting pigment aqueous dispersion (e2) (20% solids) was transferred to a screw-cap glass bottle, and 2.57 parts of EX-614B (a polyfunctional epoxy crosslinker, equivalent to 80 mol% crosslinking of the crosslinked polymer), 0.9 parts of oleic acid (Kao Corporation's "Lunac OV") as a carboxylic acid compound, and 13.9 parts of deionized water were added. The bottle was then sealed and heated to 90°C for 5 hours with stirring. The temperature was then lowered to room temperature, and the contents were filtered through a membrane filter (Sartorius "Minisart Syringe Filter," 5 μm pore size, cellulose acetate) to remove coarse particles, yielding aqueous pigment dispersion E2 (20% solids), which consisted of pigment-containing crosslinked polymer particles dispersed in an aqueous medium. The average particle size of the particles in aqueous pigment dispersion E2 is shown in Table 1.

[0096] [Table 1]

[0097] [Production of Water-Insoluble Polymer Particles (A)] Production Example 4-1 Production of Water-Insoluble Polymer Particles (A1) Twenty parts of the aqueous polymer dispersion (D1) (15% solids) were placed in a screw-cap glass bottle, and 1.94 parts of EX-614B (a polyfunctional epoxy crosslinker) (the amount required to achieve a crosslinking degree of 80 mol%), 0.33 parts of oleic acid (Kao Corporation's "Lunac OV"), and 21.7 parts of deionized water were added. The bottle was sealed and heated to 90°C for 5 hours with stirring. The temperature was then lowered to room temperature, and the mixture was filtered through a membrane filter (Sartorius "Minisart Syringe Filter," 5 μm pore size, cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of water-insoluble polymer particles (A1) (12% solids). The average particle size of the water-insoluble polymer particles (A1) is shown in Table 2.

[0098] Production Examples 4-2 to 4-13 (Production of Water-Insoluble Polymer Particles (A2) to (A13)) Water-insoluble polymer particles (A2) to (A13) were obtained in the same manner as water-insoluble polymer particles (A1), except that the type and amount of carboxylic acid compound, the type and amount of polyfunctional epoxy crosslinker, and the amount of deionized water were changed as shown in Table 2. The average particle sizes of water-insoluble polymer particles (A2) to (A13) are shown in Table 2.

[0099] Production Example c4-1 (Production of Water-Insoluble Polymer Particles (AC1)) An attempt was made to produce water-insoluble polymer particles (AC1) in the same manner as water-insoluble polymer particles (A1), except that the type and amount of carboxylic acid compound, the type and amount of crosslinking agent, and the amount of deionized water were changed as shown in Table 2. However, after the reaction, the water-insoluble polymer particles AC1 gelled, and no aqueous dispersion of water-insoluble polymer particles (AC1) was obtained.

[0100] Production Example c4-2 (Production of Water-Insoluble Polymer Particles (AC2)) Water-insoluble polymer particles (AC2) were obtained in the same manner as water-insoluble polymer particles (A1), except that no carboxylic acid compound was used and the type and amount of crosslinking agent and the amount of deionized water were changed as shown in Table 2.

[0101] [Table 2]

[0102] (Details of carboxylic acid compounds) Oleic acid: "Lunac OV" manufactured by Kao Corporation Pelargonic acid: manufactured by Tokyo Chemical Industry Co., Ltd. Capric acid: "Lunac 10-98" manufactured by Kao Corporation Lauric acid: Kao Corporation's "Lunac L-98" Myristic acid: Kao Corporation's "Lunac MY-98" Palmitic acid: Kao Corporation's "Lunac P-95" Akipo RLM-100: Kao Corporation, polyoxyethylene (10) lauryl ether acetate, active ingredient 89% Akipo RO50VG: Kao Corporation, polyoxyethylene oleyl ether acetate, active ingredient 92% Tsunodim 216: Manufactured by Tsuno Foods Co., Ltd., dimerized oleic acid Caprylic acid: "Lunac 8-98" manufactured by Kao Corporation

[0103] (Details of multifunctional epoxy crosslinker) Denacol EX-614B: Nagase ChemteX Corporation, sorbitol polyglycidyl ether, epoxy equivalent: 173g / eq, water solubility: 94% Denacol EX-321: Nagase ChemteX Corporation, trimethylolpropane polyglycidyl ether, epoxy equivalent: 140g / eq, water solubility: 27%

[0104] Example 1 (Production of Water-Based Ink 1) 37.5 parts of aqueous pigment dispersion (E1) [solid content: 7.5 parts (pigment: 5.25 parts, crosslinked polymer: 2.3 parts)], 33.3 parts of aqueous dispersion of water-insoluble polymer (A1) (solid content: 4.0 parts)], 3.0 parts of propylene glycol mono-n-butyl ether (manufactured by Nippon Nyukazai Co., Ltd., trade name: BFG), 20.0 parts of propylene glycol (manufactured by AGC Corporation), acetylene glycol surfactant (manufactured by Nissin Chemical Industry Co., Ltd., trade name: Surfynol 104PG50, propylene glycol solution of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, HLB (Hydrophile-Lipophile) The ink had a balance value (Griffin method): 4 (catalog value), and an active ingredient: 0.6 parts of 50% by mass. Deionized water was then added to make the total amount 100 parts, and the mixture was stirred with a magnetic stirrer for 30 minutes. The mixture was then filtered using a syringe equipped with a 5 μm acetyl cellulose filter to obtain water-based ink 1.

[0105] Examples 2 to 14, Comparative Example 1 (Production of Water-Based Inks 2 to 14, C1) In the same manner as in Example 1, water-based inks 2 to 14 and C1 were obtained according to the formulations shown in Table 3.

[0106] <Evaluation of inkjet printing> The water-based inks 1 to 14 and C1 were evaluated for ejection stability, water resistance of printed matter, and bleeding of printed images (lines).

[0107] (1) Creation of inkjet printouts An image was formed on A4 size matte coated paper (trade name: Fitness Mat, manufactured by GRAFICAS Y FORMULARIOS) using a water-based ink by the following inkjet recording method. (inkjet recording method) A water-based ink was filled into a print evaluation device (manufactured by Tritec Corporation) equipped with an inkjet printhead (Kyocera Corporation, product name: KJ4B-HD06MHG-STDV, piezo type) in an environment with a temperature of 25±1°C and a relative humidity of 30±5%. The printhead voltage was set to 26V, the drive frequency to 10kHz, the ejection volume to 12pl, the printhead temperature to 32°C, the resolution to 600dpi, the number of pre-ejection flushes to 200, and the negative pressure to -4.0kPa. The printhead was fixed to the conveyor table under reduced pressure with the longitudinal direction of the printhead aligned with the conveying direction. A print command was sent to the print evaluation device, and a gradation image was printed in 5% increments with a duty cycle of 0 to 100% to obtain a printout.

[0108] (2) Evaluation of ejection stability After preparing the print in (1) above, the printer was stopped for 30 minutes and the recording head was exposed to the atmosphere. After 30 minutes had passed, the ink was purged from the inkjet recording head once, wiped, and printing resumed. The state of nozzle chipping was observed, and the nozzle recovery rate (%) was calculated using the following formula to evaluate the ejection stability. Nozzle recovery rate (%) = (number of normal nozzles / total number of nozzles) x 100 The higher the nozzle recovery rate (%), the better the nozzle recovery is judged to be, and a value of 90% or higher is practically usable.

[0109] (3) Water resistance evaluation The print obtained in (1) above was left to stand for 3 minutes, then immersed in a stainless steel tray containing 1000 mL of deionized water for 10 seconds, and the gradation images with a duty of 0 to 100% in 5% increments were gently rubbed with a finger in sequence, and the duty of the image where peeling was observed was recorded as the numerical value for the water resistance evaluation. The print with a higher duty that did not peel was judged to have higher water resistance.

[0110] (4) Measurement of line width on matte coated paper The same matte coated paper as above was prepared, and an inkjet printer (manufactured by Tritec Corporation) equipped with a piezo-driven inkjet head (manufactured by Kyocera Corporation, product name: KJ4B-600) was filled with water-based ink, and a line five dots wide was printed on the matte coated paper. The resulting print was observed under an optical microscope, and the line width was measured. The smaller the width, the more suppressed bleeding of the printed image was judged to be.

[0111] [Table 3]

[0112] Table 3 shows that the water-based ink for ink-jet printing of the present invention has excellent ejection stability, and that printed matter having excellent water resistance and suppressed bleeding can be obtained using the water-based ink for ink-jet printing of the present invention (Examples 1 to 14). In contrast, printed matter obtained using a water-based ink containing a water-insoluble polymer not containing a structure derived from a carboxylic acid compound having a molecular weight of 150 to 1000 had poor water resistance and insufficient suppression of bleeding (Comparative Example 1).

Claims

1. A water-based ink for ink-jet printing containing water-insoluble polymer particles (A) and water, the water-insoluble polymer particles (A) contain a structure derived from a water-dispersible polymer (A') having an acid group, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy crosslinking agent; A water-based ink for ink-jet printing, wherein the molecular weight of the carboxylic acid compound is 150 or more and 1,000 or less.

2. 2. The water-based ink for ink-jet printing according to claim 1, wherein in the water-insoluble polymer particles (A), a ratio of the mass of structures derived from carboxylic acid compounds to the total mass of structures derived from the water-dispersible polymer (A′) having acid groups and structures derived from carboxylic acid compounds [structures derived from carboxylic acid compounds / (structures derived from the water-dispersible polymer (A′) having acid groups+structures derived from carboxylic acid compounds)] is from 0.03 to 0.

6.

3. 3. The water-based ink for ink-jet printing according to claim 1, wherein the degree of crosslinking of the water-insoluble polymer particles (A) is 50 mol % or more but less than 100 mol %.

4. 3. The water-based ink for ink-jet printing according to claim 1, wherein the water-dispersible polymer (A') having an acid group has an acid value of 100 mgKOH / g or more and 320 mgKOH / g or less.

5. 3. The water-based ink for ink-jet printing according to claim 1, wherein the carboxylic acid compound has an unsaturated hydrocarbon group.

6. 3. The water-based ink for ink-jet printing according to claim 1, wherein the carboxylic acid compound has a melting point of 30[deg.] C. or lower.

7. 3. The water-based ink for ink-jet printing according to claim 1, wherein the polyfunctional epoxy crosslinking agent comprises a tri- or higher functional epoxy crosslinking agent.

8. The water-based ink for ink-jet printing according to claim 1 or 2, further comprising a pigment.

9. A method for producing a water-based ink for ink-jet printing containing water-insoluble polymer particles (A) and water, the method comprising the following step 1: Step 1: A step of reacting a water-dispersible polymer (A') having an acid group, a carboxylic acid compound having a molecular weight of 150 to 1000, and a polyfunctional epoxy crosslinking agent to obtain water-insoluble polymer particles (A).

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