Water-based pigment dispersion

Abstract

The present invention provides a water-based pigment dispersion and a water-based ink containing the water-based pigment dispersion, which, when incorporated into ink and used for printing, exhibits excellent thermal stability, particularly suppressing the occurrence of burnt ink in the heater portion of the thermal head and providing excellent continuous ejection stability. [Solution] An aqueous pigment dispersion comprising crosslinked polymer particles containing a pigment, wherein the crosslinked polymer contained in the pigment-containing crosslinked polymer particles comprises a structure derived from an acidic water-dispersible polymer a, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy compound.

Description

Technical Field

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

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 a recorded matter such as a printed matter on which characters and images are recorded. This method has many advantages such as being easy to achieve full color and inexpensive, being able to use plain paper as a recording medium, and being non-contact with the recording medium, so it has become extremely popular. Particularly from the viewpoints of the weather resistance and water resistance of the recorded matter, those using a pigment as a colorant have become mainstream. On the other hand, an aqueous inkjet recording aqueous ink in which the colorant is a pigment has a problem that the ejection property is poor because pigment particles are dispersed in an aqueous medium. Therefore, various proposals have been made to improve the characteristics of an aqueous inkjet recording aqueous ink in which the colorant is a pigment.

[0003] For example, Patent Document 1 aims to provide a pigment aqueous dispersion and a method for producing the same, which have excellent thermal stability, particularly suppress the generation of coking in the heater portion of a thermal head, and have excellent continuous ejection stability when blended and printed in an ink. There is described a pigment aqueous dispersion containing crosslinked polymer particles containing a pigment, wherein the crosslinked polymer is a polymer having a specific structure and the pigment is carbon black, and an aqueous ink containing the aqueous pigment dispersion.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Patent Document 1 describes that a water-based ink using carbon black as a pigment exhibits good suppression of cogation and continuous ejection stability. However, with the remarkable increase in printing speed in recent years, further improvements in cogation suppression and continuous ejection stability are required for water-based inks using various pigments, including carbon black.

[0006] The present invention relates to an aqueous pigment dispersion and an aqueous ink containing the aqueous pigment dispersion, which, when incorporated into ink and used for printing, can produce an aqueous ink that exhibits excellent thermal stability, particularly by suppressing the occurrence of burn in the heater portion of the thermal head and providing excellent continuous ejection stability. [Means for solving the problem]

[0007] The present inventors have found that the above problem can be solved by an aqueous pigment dispersion in which a pigment is contained in a crosslinked polymer that includes a structure derived from an acidic water-dispersible polymer a, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy compound, and the pigment-containing crosslinked polymer particles are dispersed in an aqueous medium.

[0008] In other words, the present invention relates to the following [1] and [2]. [1] An aqueous pigment dispersion comprising crosslinked polymer particles containing a pigment, An aqueous pigment dispersion in which the crosslinked polymer contained in pigment-containing crosslinked polymer particles comprises a structure derived from an acidic water-dispersible polymer a, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy compound. A water-based ink containing the water-based pigment dispersion described in [2][1]. [Effects of the Invention]

[0009] The present invention provides an aqueous pigment dispersion and an aqueous ink containing the aqueous pigment dispersion, which, when incorporated into ink and used for printing, exhibits excellent thermal stability, particularly suppressing the occurrence of burnt ink in the heater portion of the thermal head and providing excellent continuous ejection stability. [Modes for carrying out the invention]

[0010] [Water-based pigment dispersion] The aqueous pigment dispersion of the present invention comprises crosslinked polymer particles containing a pigment, wherein the crosslinked polymer contained in the pigment-containing crosslinked polymer particles includes a structure derived from an acidic water-dispersible polymer a, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy compound.

[0011] In this specification, "aqueous system" means a medium in which the pigment is dispersed, in which water constitutes the largest proportion. Furthermore, "recording" is a concept that includes printing and inscription, which record characters and images. Furthermore, "crosslinking" is defined as a concept that includes the bonding of two water-dispersible polymers a having acid groups via a polyfunctional epoxy compound, and the bonding of a water-dispersible polymer a having acid groups with a carboxylic acid compound via a polyfunctional epoxy compound.

[0012] The reason why the aqueous pigment dispersion of the present invention, when incorporated into ink and used for printing, suppresses the occurrence of coagulation in the heater portion of the thermal head and exhibits excellent continuous ejection stability is not entirely clear, but it is thought to be as follows. The aqueous pigment dispersion of the present invention comprises a structure derived from a water-dispersible polymer a, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy compound, in which the pigment is dispersed in an aqueous medium by crosslinked polymer particles. The carboxylic acid compound reacts with the epoxy group and is incorporated into the crosslinked polymer, acting as a hydrophobic group within the crosslinked polymer particles. This allows the crosslinked polymer particles to be strongly adsorbed onto the pigment surface, suppressing the detachment of the crosslinked polymer particles from the pigment. As a result, the dispersion stability of the pigment in the aqueous pigment dispersion is improved, continuous ejection performance is enhanced, and adhesion to the heater of a thermal inkjet recording device is suppressed, thus providing excellent suppression of cogation.

[0013] [Pigments] The pigment may be either an inorganic pigment or an organic pigment. Examples of inorganic pigments include carbon black and metal oxides. For black inks, carbon black is preferred. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. For white inks, examples of metal oxides include titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide. 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. 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, red, blue, orange, and green can be used. Pigments can be used individually or in combination of two or more types.

[0014] The aqueous pigment dispersion of the present invention is an aqueous pigment dispersion comprising crosslinked polymer particles containing a pigment, wherein the pigment is dispersed in an aqueous medium with a crosslinked polymer. The form in which the pigment and crosslinked polymer exist in the aqueous pigment dispersion and the aqueous ink containing the aqueous pigment dispersion of the present invention are common to both, and are in the form of crosslinked polymer particles containing the pigment (hereinafter also referred to as "pigment-containing crosslinked polymer particles"), with the form of pigment-encapsulated crosslinked polymer particles in which the crosslinked polymer encapsulates the pigment being preferred.

[0015] [Crosslinked polymers] The crosslinked polymer contained in the crosslinked polymer particles includes structures derived from a water-dispersible polymer a having acid groups, structures derived from carboxylic acid compounds, and structures derived from polyfunctional epoxy compounds. Crosslinked polymers can be used individually or in combination of two or more types.

[0016] <Water-dispersible polymer a containing acidic groups> The water-dispersible polymer a having an acid group (hereinafter also simply referred to as "polymer a") is a polymer having the ability to disperse pigments in an aqueous medium. Examples of the acid group include a carboxy group, a sulfonic acid group, and a phosphoric acid group, and a carboxy group is preferred. The "water-dispersible polymer" means a polymer that can be dispersed in water or an aqueous medium at normal temperature (25°C).

[0017] Examples of polymer a include at least one selected from polyester, polyurethane, and vinyl polymers. From the viewpoints of suppressing the occurrence of cogellation and the continuous discharge stability of the aqueous ink, vinyl polymers obtained by addition polymerization of vinyl monomers are preferred. The vinyl polymer preferably contains a structural unit derived from a carboxy group-containing monomer, and a vinyl polymer obtained by copolymerizing a monomer mixture A containing a carboxy group-containing monomer (hereinafter referred to as "(a-1) component") and a hydrophobic monomer (hereinafter referred to as "(a-2) component") is more preferred. The vinyl polymer has a structural unit derived from the (a-1) component and a structural unit derived from the (a-2) component. As the carboxy group-containing monomer, a carboxylic acid monomer is preferred, more preferably one or more selected from acrylic acid, methacrylic acid, and maleic acid, still more preferably one or more selected from acrylic acid and maleic acid, and still more preferably acrylic acid. The carboxy group-containing monomer includes not only the compound but also its anhydride. Specific examples of the hydrophobic monomer include those described in paragraphs

[0020] to

[0022] of JP-A-2018-83938, and styrene is preferred.

[0018] Polymer a can further use a nonionic monomer (hereinafter referred to as "(a-3) component"). Specific examples of the (a-3) component include those described in paragraph

[0018] of JP-A-2018-83938. Among these, one or more selected from methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate and polypropylene glycol (n = 2 to 30) (meth)acrylate are preferred. From the above viewpoint, polymer a is preferably at least one selected from styrene-acrylic acid copolymers and styrene-maleic acid copolymers, having a constituent unit derived from acrylic acid or maleic acid as component (a-1) and a constituent unit derived from styrene as component (a-2), and more preferably a styrene-acrylic acid copolymer.

[0019] (Content of each component in monomer mixture A or each constituent unit in polymer a) The content of each component in monomer mixture A during the production of polymer a (content as unneutralized amount; the same applies hereinafter) or the content of each constituent unit in polymer a is as follows, from the viewpoint of pigment dispersion stability, suppression of cogation, and continuous ejection stability of water-based ink. The content of component (a-1) is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less. The content of component (a-2) is preferably 98% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and preferably 45% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more. (a-3) If component is present, its content is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less. The mass ratio of component (a-1) to component (a-2) [(a-1) / (a-2)] is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.25 or more, and preferably 1.2 or less, more preferably 1.0 or less, and even more preferably 0.8 or less. In the present invention, the content of constituent units derived from components (a-1) to (a-3) in polymer a can be determined by measurement, or it can be substituted by the charging ratio of raw material monomers containing components (a-1) to (a-3) during the production of polymer a.

[0020] (Manufacturing of polymer a) Polymer a can be produced by copolymerizing monomer mixture A using a known polymerization method. Solution polymerization is preferred as the polymerization method. There are no restrictions on the solvent used in solution polymerization, but polar solvents such as water, lower aliphatic alcohols, ketones such as methyl ethyl ketone, ethers, and esters are preferred. During polymerization, polymerization initiators such as azo compounds and persulfates, and polymerization chain transfer agents such as mercaptans can be used. The polymerization temperature varies depending on the type of polymerization initiator, monomer, and solvent used, but is preferably 30°C or higher, more preferably 50°C or higher, and preferably 95°C or lower, more preferably 80°C or lower.

[0021] Commercially available polymers can also be used as polymer a. Examples of such commercially available polymers include styrene-acrylic resins such as Joncryl JDX-C3000, Joncryl 586, and Joncryl 690 manufactured by BASF Japan Ltd., and styrene-maleic anhydride copolymers such as XIRAN3000 manufactured by Polyscope Polymers.

[0022] The weight-average molecular weight of polymer a is preferably 3,000 or more, more preferably 5,000 or more, even more preferably 8,000 or more, and preferably 80,000 or less, more preferably 40,000 or less, and even more preferably 20,000 or less, from the viewpoint of improving the dispersion stability of the pigment in aqueous inks. From the same viewpoint as above, the acid value of polymer a is preferably 50 mg KOH / g or more, more preferably 60 mg KOH / g or more, even more preferably 70 mg KOH / g or more, and 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 260 mg KOH / g or less. The weight-average molecular weight and acid value of the polymer can be measured by the method described in the examples.

[0023] <Carboxylic acid compounds> Carboxylic acid compounds are compounds that contain a carboxyl group. The term "carboxylic acid compound" includes salts of carboxylic acid compounds. The counterions forming the salts of carboxylic acid compounds are preferably alkali metal ions, more preferably sodium ions and potassium ions, and even more preferably sodium ions. From the viewpoint of suppressing the occurrence of coagulation and ensuring the continuous discharge stability of water-based inks, the molecular weight of the carboxylic acid compound is preferably 150 or more, more preferably 200 or more, even more preferably 250 or more, and preferably 700 or less, more preferably 500 or less, and even more preferably 350 or less.

[0024] The number of carbon atoms in the carboxylic acid compound is preferably 8 or more, more preferably 12 or more, even more preferably 16 or more, and preferably 40 or less, more preferably 30 or less, and even more preferably 20 or less.

[0025] From the viewpoint of suppressing cogation and ensuring the continuous ejection stability of water-based inks, the number of carboxyl groups in the carboxylic acid compound is preferably 4 or less, more preferably 3 or less, even more preferably 1 or 2, and even more preferably 1. From the viewpoint of suppressing cogation and ensuring the continuous ejection stability of water-based inks, carboxylic acid compounds are preferably those that have a hydrocarbon group. The hydrocarbon group may be linear or branched. The hydrocarbon group is preferably an unsaturated hydrocarbon group from the viewpoint of suppressing cogation and ensuring the continuous discharge stability of the water-based ink. The number of unsaturated bonds in the unsaturated hydrocarbon group is preferably one or two. From the viewpoint of suppressing cogation and ensuring the continuous ejection stability of water-based inks, the carboxylic acid compound is preferably composed of a hydrocarbon group and one or two carboxyl groups, and more preferably composed of a hydrocarbon group and one carboxyl group.

[0026] The acid value of the carboxylic acid compound is preferably 50 mg KOH / g or more, more preferably 100 mg KOH / g or more, even more preferably 150 mg KOH / g or more, and preferably 400 mg KOH / g or less, more preferably 300 mg KOH / g or less, and even more preferably 210 mg KOH / g or less, from the viewpoint of suppressing the occurrence of cogation and the continuous discharge stability of water-based inks.

[0027] In the raw materials for the crosslinked polymer, the weighted average acid value of polymer a and the carboxylic acid compound is preferably 60 mg KOH / g or more, more preferably 70 mg KOH / g or more, even more preferably 80 mg KOH / g or more, and preferably 320 mg KOH / g or less, more preferably 300 mg KOH / g or less, even more preferably 290 mg KOH / g or less, even more preferably 280 mg KOH / g or less, and even more preferably 260 mg KOH / g or less. If the weighted average acid value of polymer a and the carboxylic acid compound is within the above range, the amount of acid groups crosslinked by the polyfunctional epoxy compound and the amount of acid groups neutralized can be ensured, and the dispersion stability of the pigment dispersed by the crosslinked polymer can be guaranteed. Furthermore, the weighted average acid value of polymer a and the carboxylic acid compound can also be calculated from the acid value of the crosslinked polymer (described later) and the degree of crosslinking of the crosslinked polymer (also described later) using the following formula. The acid value of polymer a (mgKOH / g) = 100 × (acid value of crosslinked polymer) / (100 - (degree of crosslinking of crosslinked polymer)) Here, the unit for the acid value of the crosslinked polymer is "mgKOH / g", and the unit for the degree of crosslinking of the crosslinked polymer is "mol%".

[0028] Specific examples of carboxylic acid compounds include oleic acid, caprylic acid, linoleic acid, stearic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, polyoxyethylene lauryl ether acetate, polyoxyethylene oleyl ether acetate, dimer acid, and salts thereof. Among these, oleic acid, caprylic acid, linoleic acid, and stearic acid are preferred, oleic acid, linoleic acid, and stearic acid are more preferred, and oleic acid and linoleic acid are even more preferred. Carboxylic acid compounds can be used individually or in combination of two or more.

[0029] In the crosslinked polymer, the ratio of the mass of the structure derived from polymer a to the mass of the structure derived from the carboxylic acid compound [structure derived from polymer a / structure derived from the carboxylic acid compound] is preferably 1 or more, more preferably 3.5 or more, even more preferably 7.5 or more, and preferably 20 or less, more preferably 15 or less, and even more preferably 11 or less, from the viewpoint of suppressing cogation and ensuring the continuous ejection stability of the water-based ink.

[0030] <Polyfunctional epoxy compounds> The polyfunctional epoxy compound may be water-insoluble or water-soluble. From the viewpoint of efficiently reacting the acid group of polymer a and the carboxyl group of the carboxylic acid compound in an aqueous medium to form a crosslinked structure, the water solubility of the polyfunctional epoxy compound is 0% by mass or more, preferably 5% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and 100% by mass or less, preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. When two or more polyfunctional epoxy compounds are used in combination, the water solubility of the polyfunctional epoxy compound refers to the water solubility of the mixture of polyfunctional epoxy compounds. The water solubility of polyfunctional epoxy compounds is calculated as follows: 90 parts by mass of deionized water and 10 parts by mass of a polyfunctional epoxy compound are added to a glass tube (25 mmφ × 250 mmh) at 25°C, and the glass tube is left standing for 1 hour in a constant temperature bath adjusted to a water temperature of 25°C. Next, the glass tube is shaken for 1 minute at 1500 rpm using a small vibrator (manufactured by AS ONE Corporation, product name: Test Tube Mixer TRIO (High Type) HM-1N), and then left standing again in the constant temperature bath for 10 minutes. Then, the undissolved material is collected, dried, and weighed, and the water solubility (mass%) is calculated using the following formula. Water solubility (mass %) = 100 × (10 - parts by mass of undissolved material) / 10

[0031] The number of epoxy groups in a polyfunctional epoxy compound is 2 or more, preferably 2.1 or more, more preferably 2.5 or more, and preferably 7 or less, more preferably 5 or less, from the viewpoint of suppressing coging and ensuring the continuous ejection stability of water-based inks. The polyfunctional epoxy compound preferably has epoxy groups in a form having glycidyl ether groups. The number of glycidyl ether groups in the polyfunctional epoxy compound is 2 or more, preferably 2.1 or more, more preferably 2.5 or more, and preferably 7 or less, more preferably 5 or less, from the viewpoint of suppressing cogation and ensuring the continuous ejection stability of water-based inks. The term "polyfunctional" in polyfunctional epoxy compound means having 2 or more epoxy groups. Furthermore, when using a combination of polyfunctional epoxy compounds with different numbers of epoxy groups, the "number of epoxy groups in the polyfunctional epoxy compound" refers to the weighted average value. The same applies to the number of glycidyl ether groups. Furthermore, the polyfunctional epoxy compound may also be a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group with 3 to 8 carbon atoms.

[0032] In the structure derived from the polyfunctional epoxy compound, the content of the structure derived from the polyfunctional epoxy compound having three or more epoxy groups is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and 100% by mass or less, from the viewpoint of suppressing the occurrence of cogation and the continuous ejection stability of the water-based ink.

[0033] The epoxy equivalent of the polyfunctional epoxy compound 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, and even more preferably 180 g / eq or less, from the viewpoint of suppressing the occurrence of cogation and ensuring the continuous discharge stability of the water-based ink.

[0034] Specific examples of polyfunctional epoxy compounds include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, polypropylene glycol diglycidyl ether, resorcinol glycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, phthalate diglycidyl ester, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, aliphatic epoxy compounds, and trimethylolpropane polyglycidyl ether. Among these, sorbitol polyglycidyl ether and trimethylolpropane polyglycidyl ether are preferred.

[0035] Examples of commercially available polyfunctional epoxy compounds include the following (all manufactured by Nagase ChemteX Corporation): 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-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) Denacol EX-521 (Polyglycerol polyglycidyl ether, epoxy equivalent 183 g / eq, water solubility: 100% by mass) Among these, Denacol EX-612 and Denacol EX-321 are preferred, with Denacol EX-321 being more preferred.

[0036] In the crosslinked polymer, the ratio of the mass of the structure derived from the polyfunctional epoxy compound to the total mass of the structure derived from the water-dispersible polymer a having acid groups and the structure derived from the carboxylic acid compound [structure derived from polyfunctional epoxy compound / (structure derived from water-dispersible polymer a having acid groups + structure derived from carboxylic acid compound)] is preferably 0.05 or higher, more preferably 0.1 or higher, even more preferably 0.15 or higher, even more preferably 0.2 or higher, and preferably 0.6 or lower, more preferably 0.5 or lower, even more preferably 0.4 or lower, and even more preferably 0.3 or lower.

[0037] (Degree of cross-linking of cross-linked polymers) The degree of crosslinking of the crosslinked polymer is preferably 25 mol% or more, more preferably 35 mol% or more, even more preferably 45 mol% or more, even more preferably 50 mol% or more, and preferably 95 mol% or less, more preferably 75 mol% or less, and even more preferably 60 mol% or less, from the viewpoint of suppressing the occurrence of cogation and the continuous discharge stability of water-based inks. Here, the degree of crosslinking of a crosslinked polymer refers to the percentage obtained by dividing the molar equivalents of epoxy groups in the polyfunctional epoxy compound by the molar equivalents of acid groups in the crosslinked polymer and the carboxylic acid compound.

[0038] (Acid value of cross-linked polymers) The acid value of the crosslinked polymer is preferably 25 mg KOH / g or more, more preferably 30 mg KOH / g or more, even more preferably 35 mg KOH / g or more, and preferably 190 mg KOH / g or less, more preferably 180 mg KOH / g or less, and even more preferably 170 mg KOH / g or less, from the viewpoint of suppressing the occurrence of cogation and the continuous discharge stability of water-based inks. Here, the acid value of a crosslinked polymer can be calculated from the degree of crosslinking of the crosslinked polymer using the following formula, and represents the amount of acid groups remaining that do not participate in the formation of the crosslinked structure through reaction with the polyfunctional epoxy compound, out of the acid groups of polymer a and the carboxylic acid compound. Acid value of crosslinked polymer (mgKOH / g) = (Weighted average acid value of water-dispersible polymer and carboxylic acid compound) × (100 - (Degree of crosslinking of crosslinked polymer)) / 100 Here, the unit for the acid value of water-dispersible polymers and carboxylic acid compounds is "mgKOH / g", and the unit for the degree of crosslinking of crosslinked polymers is "mol%".

[0039] [Method for producing aqueous pigment dispersions] The aqueous pigment dispersion is preferably manufactured by a method comprising the following steps 1 to 3. Step 1: A step of neutralizing polymer a, which has an acid group, with a neutralizing agent. Step 2: Mix the neutralized polymer a, the carboxylic acid compound, and the pigment. Disperse the pigment in an aqueous medium using the neutralized polymer a and the carboxylic acid compound as dispersants to obtain an aqueous pigment dispersion. Step 3: The aqueous pigment dispersion obtained in Step 2 is crosslinked with a polyfunctional epoxy compound to obtain an aqueous pigment dispersion in which polymer a and a carboxylic acid compound are crosslinked.

[0040] [Process 1] Step 1 is a step of neutralizing polymer a having an acid group with a neutralizing agent. In Step 1, first, the neutralizing agent and polymer a are mixed in an aqueous medium. The neutralizing agent is preferably one or more selected from the group consisting of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and amine compounds, with alkali metal hydroxides being preferred. The aqueous medium may contain an organic solvent. Preferred organic solvents include aliphatic alcohols having 1 to 3 carbon atoms, ketones having 3 to 8 carbon atoms, ethers, esters, etc., with ketones having 4 to 8 carbon atoms being more preferred, and methyl ethyl ketone being even more preferred. If polymer a is synthesized by solution polymerization, the solvent used in polymerization may be used as is.

[0041] From the viewpoint of promoting sufficient and uniform neutralization, the neutralizing agent is preferably used as an aqueous solution of the neutralizing agent. From the same viewpoint as above, the concentration of the aqueous solution of the neutralizing agent is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 50% by mass or less, more preferably 25% by mass or less. From the viewpoint of suppressing the occurrence of coagulation and ensuring the continuous discharge stability of water-based ink, it is preferable to use an amount of the neutralizing agent such that the degree of neutralization is preferably 20 mol% or more, more preferably 25 mol% or more, even more preferably 30 mol% or more, and preferably 95 mol% or less, more preferably 90 mol% or less, and even more preferably 85 mol% or less. Here, the degree of neutralization is the value obtained by dividing the molar equivalent of the neutralizing agent by the sum of the molar equivalents of the acid groups of polymer a and the molar equivalents of the carboxyl groups of the carboxylic acid compound, i.e., the percentage of "molar equivalent of the neutralizing agent / sum of the molar equivalents of the acid groups of polymer a and the molar equivalents of the carboxyl groups of the carboxylic acid compound". Normally, the degree of neutralization does not exceed 100 mol%, but in this invention, since it is calculated from the molar equivalent of the neutralizing agent, it will exceed 100 mol% if an excess of the neutralizing agent is used. Furthermore, when using a neutralizing agent with two or more valent properties, the "molar equivalent of the neutralizing agent" shall be considered synonymous with the functional group equivalent.

[0042] [Process 2] Step 2 involves mixing the neutralized polymer a, the carboxylic acid compound, and the pigment, and then using the neutralized polymer a and the carboxylic acid compound as dispersants to disperse the pigment in an aqueous medium to obtain an aqueous pigment dispersion. There are no particular restrictions on the aqueous medium used here, but one mainly composed of water is preferred. From the viewpoint of improving the wettability to the pigment and the adsorption of polymers and carboxylic acid compounds to the pigment, an organic solvent may be added to the aqueous medium. Examples of organic solvents include those listed in step 1. In step 2, the dispersion treatment can be performed solely by shear stress to finely atomize the pigment particles to the desired particle size. However, from the viewpoint of obtaining a uniform aqueous pigment dispersion, it is preferable to pre-disperse the pigment mixture before the final dispersion. For preliminary dispersion, a mixing and stirring device equipped with commonly used stirring blades such as anchor blades and disperser blades can be used as the disperser. Means of applying shear stress for this dispersion include, for example, kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersers such as paint shakers and bead mills.

[0043] Preferably, the organic solvent in the pigment aqueous dispersion obtained in step 2 is substantially removed, but it may remain as long as it does not impair the purpose of the present invention.

[0044] The concentration of non-volatile components in the pigment aqueous dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating the preparation of water-based inks. The concentration of non-volatile components in the pigment aqueous dispersion is measured by the method described in the examples.

[0045] The pigment content in the non-volatile components of the pigment aqueous dispersion is preferably 55% by mass or more, more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less, from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating the preparation of water-based inks. The content of polymer a in the nonvolatile components of the pigment aqueous dispersion is preferably 9% by mass or more, more preferably 12% by mass or more, even more preferably 15% by mass or more, and also preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating the preparation of water-based inks. The content of carboxylic acid compounds in the non-volatile components of the pigment aqueous dispersion is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, and also preferably 21% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less, from the viewpoint of improving the dispersion stability of the pigment aqueous dispersion and facilitating the preparation of water-based inks.

[0046] The average particle size of the pigment-containing polymer particles in the pigment aqueous dispersion is preferably 60 nm or larger, more preferably 80 nm or larger, even more preferably 100 nm or larger, and preferably 160 nm or smaller, more preferably 140 nm or smaller, and even more preferably 135 nm or smaller, from the viewpoint of reducing coarse particles and improving the discharge performance of the resulting aqueous ink. The average particle size of pigment-containing polymer particles in aqueous pigment dispersions and aqueous inks is approximately the same as the average particle size in aqueous pigment dispersions, and the preferred embodiment of the average particle size is the same as the preferred embodiment of the average particle size in aqueous pigment dispersions. The average particle size of pigment-containing polymer particles is measured in the same manner as the method for measuring the average particle size of pigment-containing crosslinked polymer particles in an aqueous pigment dispersion described in the Examples.

[0047] [Step 3] Step 3 is a step in which the aqueous pigment dispersion obtained in Step 2 is crosslinked with a polyfunctional epoxy compound to obtain an aqueous pigment dispersion in which polymer a and carboxylic acid compounds are crosslinked. In step 3, a portion of the acid groups of polymer a and the carboxylic acid compound constituting the pigment-containing polymer particles in the pigment aqueous dispersion are crosslinked, forming a crosslinked structure on the surface of the pigment-containing polymer particles, thereby transforming the pigment aqueous dispersion into a predetermined aqueous pigment dispersion. In this aqueous pigment dispersion, the pigment is dispersed in an aqueous medium by a crosslinked polymer that includes structures derived from polymer a, structures derived from the carboxylic acid compound, and structures derived from the polyfunctional epoxy compound.

[0048] The concentration of nonvolatile components in the aqueous pigment dispersion obtained by step 3 is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, from the viewpoint of improving the dispersion stability of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion and facilitating the preparation of the aqueous ink.

[0049] The pigment content in the nonvolatile components of the aqueous pigment dispersion is preferably 45% by mass or more, more preferably 50% by mass or more, and even more preferably 55% by mass or more, from the viewpoint of facilitating the preparation of aqueous inks, and from the viewpoint of improving the dispersion stability of the aqueous pigment dispersion, it is preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less.

[0050] The content of the crosslinked polymer in the nonvolatile components of the aqueous pigment dispersion is preferably 15% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, from the viewpoint of improving the dispersion stability of the aqueous pigment dispersion, and preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less, from the viewpoint of facilitating the preparation of aqueous inks and improving the dispersion stability of the aqueous pigment dispersion.

[0051] In an aqueous pigment dispersion, the mass ratio of pigment to the total mass of pigment and crosslinked polymer [pigment / (pigment + crosslinked polymer)] is preferably 0.45 or higher, more preferably 0.5 or higher, even more preferably 0.55 or higher, and preferably 0.8 or lower, more preferably 0.75 or lower, and even more preferably 0.7 or lower, from the viewpoint of suppressing cogation and ensuring the continuous ejection stability of the aqueous ink.

[0052] The average particle size of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion is preferably 60 nm or more, more preferably 80 nm or more, even more preferably 100 nm or more, and also preferably 160 nm or less, more preferably 140 nm or less, and even more preferably 135 nm or less, from the viewpoint of suppressing the occurrence of cogation and ensuring the continuous ejection stability of the aqueous ink. The average particle size of pigment-containing crosslinked polymer particles in an aqueous pigment dispersion is measured by the method described in the examples.

[0053] The pH of the aqueous pigment dispersion at 20°C is preferably 8 or higher, more preferably 8.5 or higher, even more preferably 9 or higher, and preferably 12 or lower, more preferably 11 or lower, and even more preferably 10.5 or lower, from the viewpoint of suppressing the occurrence of coagulation and ensuring the continuous ejection stability of the aqueous ink. The pH of the aqueous pigment dispersion at 20°C can be adjusted by the acid value of polymer a, the type of carboxylic acid compound, the degree of crosslinking of the crosslinked polymer, etc. The pH of the aqueous pigment dispersion at 20°C is measured by the method described in the examples.

[0054] [Water-based ink] The aqueous ink of the present invention contains the aqueous pigment dispersion of the present invention. That is, the aqueous ink of the present invention contains the components contained in the aqueous pigment dispersion of the present invention, and preferably contains an organic solvent from the viewpoint of further improving the continuous discharge stability of the ink. The aqueous ink may further contain, as needed, penetrating agents, dispersants, surfactants, viscosity modifiers, defoaming agents, rust inhibitors, preservatives, fungicides, etc.

[0055] The amount of the aqueous pigment dispersion of the present invention is preferably 15% by mass or more, more preferably 25% by mass or more, even more preferably 40% by mass or more, and preferably 70% by mass or less, more preferably 65% ​​by mass or less, and even more preferably 55% by mass or less, from the viewpoint of suppressing the occurrence of coging and improving the continuous ejection stability of the aqueous ink. From the viewpoint of print density, suppression of coagulation, and improvement of continuous ejection stability of the water-based ink, the pigment content in the water-based ink is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 4% by mass or more, 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 suppressing the occurrence of coging and improving the continuous ejection stability of the water-based ink, the content of the crosslinked polymer in the water-based ink is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 6% by mass or less.

[0056] [Organic solvents] The organic solvent can contain polyhydric alcohols, polyhydric alcohol alkyl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, and the like. Among these, the organic solvent is preferably one or more selected from the group consisting of polyhydric alcohols and polyhydric alcohol alkyl ethers.

[0057] Preferably, the polyhydric alcohol is one or more selected from diols and polyhydric alcohols of trihydric or higher valency. Examples of diols include ethylene glycol, propylene glycol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-octanediol, 1,8-octanediol, 1,2-decanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, 1,3-propanediol, and 1,4-butanediol. Examples of polyhydric alcohols with a valency of 3 or higher include glycerin, trimethylolpropane, and pentaerythritol. Examples of polyhydric alcohol alkyl ethers include ethylene 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 alkylene glycol monoalkyl ethers such as tripropylene glycol monomethyl ether. Organic solvents may be used individually or in combination of two or more.

[0058] From the viewpoint of improving the continuous ejection stability of the ink, polyhydric alcohols are preferred as the organic solvent, and polyethylene glycol is more preferred. The average molecular weight of polyethylene glycol is preferably 150 or more, more preferably 200 or more, even more preferably 300 or more, and preferably 2,000 or less, more preferably 1,000 or less.

[0059] From the viewpoint of improving the continuous ejection stability of the ink, the content of the organic solvent in the water-based ink is preferably 5% by mass or more, more preferably 8% by mass or more, and preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0060] [Surfactants] The water-based ink of the present invention may contain a surfactant from the viewpoint of improving continuous ejection stability. Examples of surfactants include nonionic surfactants, anionic surfactants, and amphoteric surfactants, but nonionic surfactants are preferred, one or more selected from acetylene glycol-based surfactants and polyoxyalkylene alkyl ether-based surfactants are more preferred, and acetylene glycol-based surfactants are even more preferred. Examples of 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 preferred. A specific example of a polyoxyalkylene alkyl ether surfactant is polyoxyethylene lauryl ether. The water-based ink of the present invention may contain a combination of an acetylene glycol-based surfactant and a polyoxyethylene alkyl ether.

[0061] From the viewpoint of suppressing an increase in the viscosity of the water-based ink and improving the continuous ejection stability of the water-based ink, the surfactant content is preferably 0.2% by mass or more, more preferably 0.4% by mass or more, even more preferably 0.6% by mass or more, and preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2.5% by mass or less in the water-based ink.

[0062] 〔water〕 From the viewpoint of improving the continuous ejection stability of the water-based ink, the water content is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0063] It is preferable that the pigment-containing crosslinked polymer particles in the water-based ink do not swell, shrink, or aggregate between particles, and that the average particle size of the pigment-containing crosslinked polymer particles in the water-based ink is the same as the average particle size in the water-based pigment dispersion.

[0064] [Method for manufacturing water-based ink] The aqueous ink of the present invention can be prepared by adding a solvent or surfactant as needed to the aqueous pigment dispersion of the present invention, dispersing it by a known method, and filtering it as needed to remove coarse particles. In the production of the aqueous ink of the present invention, if an alkali metal hydroxide is further included in addition to the aqueous pigment dispersion described above, the alkali metal hydroxide added to the aqueous pigment dispersion is added together with the alkali metal hydroxide that neutralizes the carboxyl groups of the crosslinked polymer contained in the aqueous pigment dispersion.

[0065] [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 or images. Inkjet recording devices include thermal and piezo types, but the thermal type is preferred. In other words, the water-based ink of the present invention is preferably used for thermal inkjet recording. Plain paper can be used as the recording medium. Alternatively, low-absorbent recording paper such as coated paper, or non-absorbent resin films such as polyethylene terephthalate (PET) film or polypropylene film can also be used. Furthermore, "low water absorption" and "non-water absorption" refer to the amount of water absorbed by the recording medium during a 100 msecond contact time with pure water being 10 g / m³. 2 This means that the water absorption is 10 g / m². 2 Ultra-absorbent recording media are highly absorbent, and ordinary paper is classified as highly absorbent. [Examples]

[0066] In the following manufacturing examples, embodiments, and comparative examples, "parts" and "%" refer to "parts by mass" and "mass%" unless otherwise specified. The measurement methods for each physical property are as follows.

[0067] (1) Acid value of polymer a The measurement was performed according to the neutralization titration method described in JIS K0070-1992, 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)]. (2) Weight-average molecular weight of 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 guardcolumn 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 materials: 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)" (all manufactured by Tosoh Corporation) Measurement sample: 0.1 g of polymer a was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25°C for 10 hours, and the solution was filtered through a syringe filter "DISMIC-13HP" (material: polytetrafluoroethylene (PTFE) 0.2 μm, manufactured by ADVANTEC). (3) Non-volatile component concentration of Pigment A aqueous dispersion and Aqueous Pigment B 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, mixed, and weighed. The mixture was maintained at 105°C for 2 hours to remove volatile components, and then allowed to stand in the desiccator for another 15 minutes. The mass was then measured. The mass of the sample after removal of volatile components was used as the non-volatile component, and the concentration of the non-volatile component was obtained by dividing it by the mass of the added sample. (4) Average particle size of pigment-containing crosslinked polymer particles in aqueous pigment dispersion Using a laser particle analysis system (manufactured by Otsuka Electronics Co., Ltd., product name: ELS-8000), particle size was measured by dynamic light scattering 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 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. For the measurement sample, an aqueous pigment dispersion was weighed into a screw tube (Maruemu Co., Ltd., No. 5) and the non-volatile component concentration was 2 × 10⁻⁶. -4 Water was added to the solution to a mass percentage, and the mixture was stirred using a magnetic stirrer at 25°C for 1 hour. (5) pH of aqueous pigment dispersion The pH of an aqueous pigment dispersion at 20°C was measured using a benchtop pH meter "F-71" (manufactured by Horiba, Ltd.) equipped with a pH electrode "6337-10D" (manufactured by Horiba, Ltd.).

[0068] <Manufacturing of Pigment Aqueous Dispersion A> Manufacturing Example 1 (Manufacturing of Pigment Aqueous Dispersion A1) To 600 parts of deionized water, 9.22 parts of 5N sodium hydroxide aqueous solution (16.9% sodium hydroxide solids, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) and 44.82 parts of Joncryl JDX-C3000 (manufactured by BASF Japan Ltd., styrene-acrylic acid copolymer, acid value 75 mg KOH / g, weight-average molecular weight 10,000) as polymer a(a) were added, and the mixture was stirred at 80°C for 5 hours to obtain a polymer-containing solution. To the obtained polymer-containing solution, 4.98 parts of oleic acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 116 parts of magenta pigment (manufactured by DCL Corporation, Quindo® Magenta 122 (228-0066)) were added, and the mixture was stirred at 600 rpm for 60 minutes at room temperature using a Homodisper 2.5 type (manufactured by Primix Corporation) equipped with a 33 mm diameter disperser blade. The obtained mixture was subjected to a dispersion treatment for 4 hours while circulating in a vertical bead mill "Ultra Apex Mill (UAM-015)" (manufactured by Hiroshima Metal & Machinery Co., Ltd., total container capacity 0.17L) filled with 535 parts of 0.05 mmφ zirconia beads, at a tip peripheral speed of 10 m / s, flow rate of 80 g / min, and outlet temperature of 40-50°C. Subsequently, deionized water was added to obtain a pigment aqueous dispersion A1 with a non-volatile component concentration of 20%.

[0069] Manufacturing Example 2 (Manufacturing of Pigment Aqueous Dispersion A2) A pigment aqueous dispersion A2 with a non-volatile component concentration of 20% was obtained by the same procedure as in Production Example 1, except that 12.34 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 used, and Joncryl 586 (manufactured by BASF Japan Ltd., styrene-acrylic acid copolymer, acid value 108 mg KOH / g, weight-average molecular weight 4,600) was used as polymer a(b) instead of polymer a(a).

[0070] Manufacturing Example 3 (Manufacturing of Pigment Aqueous Dispersion A3) A pigment aqueous dispersion A3 with a non-volatile component concentration of 20% was obtained by the same procedure as in Production Example 1, except that 24.82 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 used, and Joncryl 690 (manufactured by BASF Japan Ltd., styrene-acrylic acid copolymer, acid value 240 mg KOH / g, weight-average molecular weight 16,500) was used as polymer a(c) instead of polymer a(a).

[0071] Manufacturing Example 4 (Manufacturing of Pigment Aqueous Dispersion A4) A pigment aqueous dispersion A4 with a non-volatile component concentration of 20% was obtained by the same procedure as in Production Example 1, except that 29.07 parts of a 5N sodium hydroxide aqueous solution (sodium hydroxide solid content 16.9%, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) were used, and XIRAN3000 (manufactured by Polyscope Polymers, styrene-maleic anhydride copolymer, acid value 285 mg KOH / g, weight-average molecular weight 10,000) was used as polymer a(d) instead of polymer a(a).

[0072] Manufacturing Examples 5-12 (Manufacturing of Pigment Aqueous Dispersions A5-A12) Pigment aqueous dispersions A5 to A12 with a non-volatile component concentration of 20% were obtained using the same procedure as in Production Example 3, except that the amount of polymer a(c), the amount of 5N sodium hydroxide aqueous solution, the type of carboxylic acid compound, and / or its amount were changed as shown in Table 1. The linoleic acid, stearic acid, and sodium oleate in Table 1 were all manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0073] Manufacturing Example 13 (Manufacturing of Pigment Aqueous Dispersion A13) A pigment aqueous dispersion A13 with a non-volatile component concentration of 20% was obtained using the same procedure as in Production Example 3, except that carbon black (Cabot Corporation, MONARCH 717) was used instead of magenta pigment.

[0074] Manufacturing example c1 (Manufacturing of pigment aqueous dispersion cA1) A pigment aqueous dispersion cA1 with a non-volatile component concentration of 20% was obtained by following the same procedure as in Production Example 3, except that oleic acid was not added, using 25.21 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) and 49.80 parts of Joncryl 690 (manufactured by BASF Japan Ltd.) as polymer a(c).

[0075] [Table 1]

[0076] Example 1 (Preparation of aqueous pigment dispersion B1) 100.00 parts of pigment aqueous dispersion A1 (non-volatile component concentration 20%) were placed in a screw-top glass bottle, and 0.74 parts of trimethylolpropane polyglycidyl ether (Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq) as a polyfunctional epoxy compound (an amount that results in a cross-linking degree of the cross-linked polymer of 56 mol%) and 2.95 parts of deionized water were added. The bottle was then tightly sealed and heated at 70°C for 5 hours while stirring with a stirrer. After 5 hours, the temperature was lowered to room temperature, and the mixture was filtered using a 25 mL needleless syringe (Terumo Corporation) fitted with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, Fujifilm Corporation) to obtain aqueous pigment dispersion B1 with a non-volatile component concentration of 20%.

[0077] Examples 2-14, 16 (Preparation of aqueous pigment dispersions B2-B14, B16) Except for changing the type of pigment aqueous dispersion and the amount of deionized water as shown in Table 2, aqueous pigment dispersions B2 to B14 and B16 with a non-volatile component concentration of 20% were obtained using the same procedure as in Example 1.

[0078] Example 15 (Preparation of aqueous pigment dispersion B15) Using pigment aqueous dispersion A3, an aqueous pigment dispersion B15 with a non-volatile component concentration of 20% was obtained by the same procedure as in Example 1, except that 2.35 parts of sorbitol polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-612, epoxy equivalent 166 g / eq) as a polyfunctional epoxy compound (an amount that results in a cross-linking degree of the cross-linked polymer of 56 mol%) and 9.41 parts of deionized water were used.

[0079] Comparative Example 1 (Preparation of aqueous pigment dispersion cB1) Using the pigment aqueous dispersion cA1, an aqueous pigment dispersion cB1 with a non-volatile component concentration of 20% was obtained by the same procedure as in Example 1, except that 2.02 parts of trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, Denacol EX-321, epoxy equivalent 140 g / eq) was added as a polyfunctional epoxy compound (an amount that results in a cross-linking degree of the cross-linked polymer of 56 mol%) and 8.06 parts of deionized water were added.

[0080] [Table 2]

[0081] Preparation of water-based inks (Preparation of water-based inks 1-16 and c1) The following amounts of each component were mixed. Water-based pigment dispersion 50 parts (pigment 6-7 parts) Polyethylene glycol 400, 10 parts (Manufactured by Fujifilm Wako Pure Chemical Corporation, reagent) One part of a propylene glycol solution of an acetylene glycol-based surfactant. (Product name: Surfinol 104PG-50, manufactured by Nisshin Chemical Industry Co., Ltd., active ingredient 50%) Polyoxyethylene lauryl ether 0.5 parts (Product name: Emulgen 120, manufactured by Kao Corporation) Deionized water 38.5 parts The resulting mixture was filtered using a syringe fitted with a 5 μm acetylcellulose filter manufactured by Sartorius to obtain aqueous inks 1-16 and c1.

[0082] [evaluation] [Suppression of coagulation] Using a modified inkjet printer (LG Electronics, LPP-6010N) equipped with a thermal head, the ink supply tube was pulled out and inserted into the ink tank for printing. Printing was performed in the best mode at a resolution of 1,600 dpi vertically x 1,600 dpi horizontally with a duty cycle of 100% in an environment of 25±1°C and 30±5% relative humidity. To evaluate the suppression of coagulation, continuous printing was performed on A4-sized plain paper, and after printing 10,000 sheets, the heater portion inside the thermal head chamber was washed with pure water, and the heater surface was observed with an optical microscope. The ratio of the heater surface area with deposits to the total heater surface area was evaluated as an indicator of coagulation suppression. A smaller value indicates better suppression of coagulation. The results are shown in Table 3.

[0083] [Continuous Discharge Stability] Continuous ejection stability was evaluated in the same way as for coagulation suppression: continuous printing was performed on A4 size plain paper, and the number of sheets that could be printed before the print density fell below that of the first sheet was measured. All-in-One paper (Office Max) was used as the plain paper. A higher number of sheets that could be printed indicates better continuous ejection performance. The results are shown in Table 3. The print density was determined by measuring the print density (value output as black optical density) of the printed material on plain paper obtained above at a total of 5 points using a Macbeth densitometer (X-Rite, model number: Spectro-I, measurement conditions: observation field of view: 2 degrees, observation light source: D65, white reference: Abs, polarizing filter: none, density reference: DIN), and the average value was used as the print density of the printed material.

[0084] [Table 3]

[0085] Table 3 shows that the aqueous inks obtained by incorporating the aqueous pigment dispersion of the present invention suppress the occurrence of cogas in the heater portion of the thermal head during printing and exhibit excellent continuous ejection stability (aqueous inks 1-16). In contrast, aqueous inks in which the crosslinked polymer does not have a structure derived from a carboxylic acid compound are inferior in both evaluation of cogas suppression and evaluation of continuous ejection (aqueous ink c1).

Claims

1. A water-based pigment dispersion containing crosslinked polymer particles containing pigment, An aqueous pigment dispersion in which the crosslinked polymer contained in pigment-containing crosslinked polymer particles comprises a structure derived from an acidic group-containing water-dispersible polymer a, a structure derived from a carboxylic acid compound, and a structure derived from a polyfunctional epoxy compound.

2. The aqueous pigment dispersion according to claim 1, wherein the molecular weight of the carboxylic acid compound is 150 or more and 1,000 or less.

3. The aqueous pigment dispersion according to claim 1 or 2, wherein the ratio of the mass of the structure derived from the polyfunctional epoxy compound to the total mass of the structure derived from the water-dispersible polymer a having acid groups and the structure derived from the carboxylic acid compound [structure derived from polyfunctional epoxy compound / (structure derived from water-dispersible polymer a having acid groups + structure derived from carboxylic acid compound)] is 0.05 or more and 0.6 or less.

4. The aqueous pigment dispersion according to claim 1 or 2, wherein the degree of crosslinking of the crosslinked polymer is 25 mol% or more and 95 mol% or less.

5. The aqueous pigment dispersion according to claim 1 or 2, wherein the carboxylic acid compound has an unsaturated hydrocarbon group.

6. The aqueous pigment dispersion according to claim 1 or 2, wherein the ratio of the mass of the structure derived from the water-dispersible polymer a having acid group to the mass of the structure derived from the carboxylic acid compound in the crosslinked polymer [structure derived from water-dispersible polymer a having acid group / structure derived from the carboxylic acid compound] is 1 or more.

7. A water-based ink containing the water-based pigment dispersion described in claim 1 or 2.

Images