Method for producing a pigment aqueous dispersion

Abstract

This invention provides a method for producing a pigment aqueous dispersion that is used in the manufacture of water-based inks and yields a pigment aqueous dispersion with excellent storage stability. [Solution] A method for producing an aqueous pigment dispersion comprising the following steps 1 to 3. Step 1: Disperse pigment (I) with carboxyl group-containing vinyl polymer (II) to obtain an uncrosslinked polymer aqueous pigment dispersion (A). Step 2: Add the crosslinking agent (III) to the uncrosslinked polymer aqueous pigment dispersion (A) obtained in Step 1, and perform a heat crosslinking treatment at 40°C or higher to obtain a crosslinked polymer aqueous pigment dispersion (B). Step 3: Adding alkanediol (IV) to the crosslinked polymer aqueous pigment dispersion (B) obtained in Step 2 to obtain an aqueous pigment dispersion. Here, the solid content of the pigment aqueous dispersion obtained in step 3 is 10% by mass or more and 50% by mass or less, and the content of the alkanediol(IV) is 0.05% by mass or more and 1.6% by mass or less.

Description

Technical Field

[0001] The present invention relates to a method for producing a pigment dispersion.

Background Art

[0002] The inkjet recording method is a recording method in which ink droplets are directly ejected from a fine nozzle and adhered to a recording medium to obtain a recording in which characters and images are recorded. This method has many advantages such as easy full-colorization and low cost, the use of plain paper as a recording medium, and non-contact with the recording medium, and thus has become extremely popular. Particularly from the viewpoints of the weather resistance and water resistance of the recording, those using a pigment as a coloring material have become the mainstream.

[0003] For example, Patent Document 1 discloses a pigment dispersion liquid comprising at least a pigment, a water-insoluble polymer that coats the pigment and enables it to be dispersed in water, a wetting agent, and water, and a pigment dispersion liquid having excellent dispersion stability (storage stability) and a method for producing the pigment dispersion liquid. It is described that 1,2-alkanediols may be contained as a water-soluble organic solvent. Patent Document 2 discloses an aqueous pigment dispersion containing an organic solvent, a pigment, and a pigment dispersant, which can sufficiently enhance the dispersibility and storage stability of the pigment. It is described that alkanediols are used as a water-soluble nonpolar solvent in the organic solvent. Patent Document 3 discloses a pigment dispersion containing bisacetoacetallylide pigment (a), styrene-acrylic acid copolymer (b), basic compound (c), and wetting agent (d), wherein the wetting agent (d) contains a diol compound (e), and has excellent dispersion stability and little sedimentation even at low viscosity. Examples of the diol compound include 1,2-hexanediol.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] Patent documents 1 to 3 disclose pigment dispersions that can contain alkanediol compounds as described above, but there is a need for pigment dispersions with even better storage stability. The object of this invention is to provide a method for producing a pigment aqueous dispersion that can be used in the manufacture of water-based inks and yields a pigment aqueous dispersion with excellent storage stability. [Means for solving the problem]

[0006] The inventors have found that the above problem can be solved by dispersing the pigment in a carboxyl group-containing vinyl polymer, adding a crosslinking agent, performing a heat crosslinking treatment, and then adding an alkanediol in the production of an aqueous pigment dispersion.

[0007] In other words, the present invention relates to the following [1]. [1] A method for producing an aqueous pigment dispersion comprising the following steps 1 to 3. Step 1: Disperse pigment (I) with carboxyl group-containing vinyl polymer (II) to obtain an uncrosslinked polymer aqueous pigment dispersion (A). Step 2: Adding a crosslinking agent (III) to the uncrosslinked polymer aqueous pigment dispersion (A) obtained in Step 1, and performing a heat crosslinking treatment at 40°C or higher to obtain a crosslinked polymer aqueous pigment dispersion (B). Step 3: Adding alkanediol (IV) to the crosslinked polymer aqueous pigment dispersion (B) obtained in Step 2 to obtain an aqueous pigment dispersion. Here, the nonvolatile component of the pigment aqueous dispersion obtained in step 3 is 10% by mass or more and 50% by mass or less, and the content of the alkanediol(IV) is 0.05% by mass or more and 1.6% by mass or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing a pigment aqueous dispersion that can be used in the manufacture of water-based inks and yields a pigment aqueous dispersion with excellent storage stability. [Modes for carrying out the invention]

[0009] [Method for producing a pigment aqueous dispersion] The present invention provides a method for producing an aqueous pigment dispersion, comprising the following steps 1 to 3, each of which will be described below. Step 1: Disperse pigment (I) with carboxyl group-containing vinyl polymer (II) to obtain an uncrosslinked polymer aqueous pigment dispersion (A). Step 2: Adding a crosslinking agent (III) to the uncrosslinked polymer aqueous pigment dispersion (A) obtained in Step 1, and performing a heat crosslinking treatment at 40°C or higher to obtain a crosslinked polymer aqueous pigment dispersion (B). Step 3: Adding alkanediol (IV) to the crosslinked polymer aqueous pigment dispersion (B) obtained in Step 2 to obtain an aqueous pigment dispersion. Here, the nonvolatile component of the pigment aqueous dispersion obtained in step 3 is 10% by mass or more and 50% by mass or less, and the content of the alkanediol(IV) is 0.05% by mass or more and 1.6% by mass or less.

[0010] In this specification, "aqueous system" means that water constitutes the largest proportion of the medium in which the pigment is dispersed. Furthermore, "crosslinking" means that carboxyl group-containing vinyl polymers are bonded together via a crosslinking agent. Furthermore, "storage stability" means that the dispersion stability of the polymer particles containing the pigment is good in the aqueous pigment dispersion, and that the formation of aggregated foreign matter is suppressed.

[0011] The aqueous pigment dispersion obtained by the manufacturing method of the present invention exhibits excellent storage stability. The reason for this is not entirely clear, but it is thought to be as follows. The method for producing the pigment aqueous dispersion of the present invention finally involves a crosslinked polymer (crosslinked polymer) obtained by subjecting a carboxy group-containing vinyl polymer (II) and a crosslinking agent (III) to a heat crosslinking treatment, which acts as a dispersant for the pigment (I). Here, in the present invention, an alkanediol (IV) is blended into the dispersion for the purpose of improving storage stability and imparting antiseptic properties. However, after the heat crosslinking treatment, the alkanediol (IV) is added and blended. By adding the alkanediol (IV) at a predetermined timing in this way, the crosslinking reaction by the heat crosslinking treatment can be sufficiently carried out, whereby the crosslinking degree of the crosslinked polymer can be increased, and thus the generation of aggregated foreign substances is suppressed, and it is considered that the storage stability is improved. On the other hand, if the alkanediol (IV) is added before the heat crosslinking treatment, the alkanediol (IV) swells the carboxy group-containing vinyl polymer (II), and this swelling reduces the crosslinking reactivity of the carboxy group-containing vinyl polymer (II). As a result, it is considered that the storage stability is not sufficiently improved.

[0012] Hereinafter, each step and component in the method for producing the pigment aqueous dispersion of the present invention will be described in detail.

[0013] [Step 1] Step 1 is a step of dispersing the pigment (I) with the carboxy group-containing vinyl polymer (II) to obtain an uncrosslinked polymer aqueous pigment dispersion (A). That is, in this Step 1, in an aqueous medium, the pigment (I) and the carboxy group-containing vinyl polymer (II) are mixed, and the pigment (I) is dispersed by the carboxy group-containing vinyl polymer (II) to obtain an uncrosslinked polymer aqueous pigment dispersion (A).

[0014] More specifically, in this Step 1, it is preferable to prepare a polymer aqueous dispersion in which the carboxy group-containing vinyl polymer (II) is dispersed in water, and add a neutralizing agent, water, and the pigment (I) in this order, or a polymer aqueous dispersion preliminarily neutralized with a neutralizing agent, and then add water and the pigment (I) in this order as necessary.

[0015] <Pigment (I)> The pigment (I) used in the present invention may be either an inorganic pigment or an organic pigment, and a lake pigment or a fluorescent pigment can also be used. Further, if necessary, these pigments can be used in combination with a extender pigment. Specific examples of the inorganic pigment include metal oxides such as carbon black, titanium oxide, iron oxide, red iron oxide, chromium oxide, and nacreous pearlescent pigments. Particularly in the case of black ink, carbon black is preferred. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Specific examples of the organic pigment include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and perylene pigments. The hue is not particularly limited, and any of the chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of the preferred organic pigment include one or more product numbers selected from the group consisting of C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green. Examples of the extender pigment include silica, calcium carbonate, and talc. The above pigments can be used alone or in combination of two or more.

[0016] The pigment (I) used in the present invention is a constituent material of a pigment aqueous dispersion, and in the form of the pigment, it is used as crosslinked polymer particles containing the pigment (hereinafter also simply referred to as "pigment-containing crosslinked polymer particles"). In the present invention, the polymer constituting the pigment-containing crosslinked polymer particles is a crosslinked polymer obtained by crosslinking a carboxyl group-containing vinyl polymer (II) with a crosslinking agent (III), as described later, so that the pigment (I) can exist stably in a dispersed state in an aqueous medium. Note that uncrosslinked polymer particles containing the pigment before the crosslinking treatment are also called "pigment-containing polymer particles" and are referred to separately from crosslinked polymer particles containing the pigment (pigment-containing crosslinked polymer particles).

[0017] <Carboxyloid-containing vinyl polymer (II)> The carboxyl group-containing vinyl polymer (II) used in the present invention (hereinafter also simply referred to as "polymer (II)") is a polymer having carboxyl groups and acting as a dispersant. This carboxyl group-containing vinyl polymer (II) has the function of a pigment dispersant that exhibits a dispersing effect on pigment (I) and the function of a fixing agent on a recording medium.

[0018] The acid value of polymer (II) is derived from the carboxyl groups, and is preferably 80 mg KOH / g or more, more preferably 140 mg KOH / g or more, even more preferably 200 mg KOH / g or more, and preferably 320 mg KOH / g or less, more preferably 300 mg KOH / g or less, and even more preferably 270 mg KOH / g or less. If the acid value is within the above range, even after crosslinking, the amount of carboxyl groups and their neutralized carboxyl groups is sufficient, and the dispersion stability of the pigment is ensured. This is also preferable in terms of the balance between the affinity of polymer (II) to the aqueous medium and the interaction between polymer (II) and pigment (I). The acid value of polymer(II) can be calculated from the mass ratio of its constituent monomers. Alternatively, it can be determined by dissolving or swelling polymer(II) in a suitable organic solvent and then titrating it. More specifically, it can be determined by the method described in the examples.

[0019] The polymer (II) used in the present invention is a vinyl polymer obtained by copolymerizing a vinyl monomer mixture (hereinafter simply referred to as "monomer mixture") containing (a) a carboxyl group-containing vinyl monomer (hereinafter also referred to as "component (a)") and (b) a hydrophobic vinyl monomer (hereinafter also referred to as "component (b)"). This polymer (II) has structural units derived from component (a) and structural units derived from component (b). This polymer (II) may further contain structural units derived from (c) a macromonomer (hereinafter also referred to as "component (c)") and structural units derived from (d) a nonionic monomer (hereinafter also referred to as "component (d)").

[0020] (a) Carboxylate-containing vinyl monomers (a) Carboxylate-containing vinyl monomers are used as monomer components of polymer(II) from the viewpoint of improving the storage stability of the pigment aqueous dispersion. Carboxylate monomers are used as carboxylate-containing vinyl monomers. The carboxylic acid monomer is preferably one or more selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethylsuccinic acid, and the like, and more preferably one or more selected from the group consisting of acrylic acid and methacrylic acid.

[0021] (b) Hydrophobic vinyl monomer (b) Hydrophobic vinyl monomers are used as monomer components of polymer(II) from the viewpoint of improving the storage stability of the pigment aqueous dispersion. Examples of hydrophobic vinyl monomers include alkyl (meth)acrylates and aromatic group-containing monomers, and preferably one or more selected from the group consisting of alkyl (meth)acrylates having an alkyl group with 1 to 22 carbon atoms and aromatic group-containing monomers having an aryl group with 6 to 22 carbon atoms. The alkyl (meth)acrylate is preferably a (meth)acrylic monomer having an alkyl group with 1 to 22 carbon atoms, more preferably 6 to 18 carbon atoms. Examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, amyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, tertiary butyl (meth)acrylate, isoamyl (meth)acrylate, isooctyl (meth)acrylate, isodecyl (meth)acrylate, isododecyl (meth)acrylate, and isostearyl (meth)acrylate. Note that "(meth)acrylate" refers to one or more substances selected from the group consisting of acrylates and methacrylates. "(meta)" below also has the same meaning.

[0022] The aromatic group-containing monomer is preferably a vinyl monomer having an aromatic group with 6 to 22 carbon atoms, which may have substituents including heteroatoms, and more preferably a styrene monomer or an aromatic group-containing (meth)acrylate. The styrene monomer is preferably styrene, α-methylstyrene, vinyltoluene, divinylbenzene, and more preferably styrene or α-methylstyrene. Furthermore, the aromatic group-containing (meth)acrylate is preferably phenyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and more preferably benzyl (meth)acrylate. This (b) hydrophobic vinyl monomer may use two or more of the above-mentioned monomers, for example, a styrene monomer and an aromatic group-containing (meth)acrylate may be used in combination. The molecular weight of the aromatic group-containing monomer is preferably less than 500.

[0023] (c) Macromonomers (c) The macromonomer is a compound having a number average molecular weight of 500 to 100,000 and having a polymerizable functional group at one end, and may be used as a monomer component of polymer(II) from the viewpoint of improving the storage stability of the pigment aqueous dispersion. The polymerizable functional group at one end is preferably an acryloyloxy group or a methacryloyloxy group, and more preferably a methacryloyloxy group. (c) The number-average molecular weight of the macromonomer is preferably 1,000 or more and 10,000 or less. The number-average molecular weight is measured using gel permeation chromatography (GPC) with chloroform containing 1 mmol / L dodecyldimethylamine as the solvent, with polystyrene as the standard substance. (c) As macromonomers, from the viewpoint of improving the storage stability of the pigment aqueous dispersion, aromatic group-containing monomer-based macromonomers and silicone-based macromonomers are preferred, and aromatic group-containing monomer-based macromonomers are more preferred. Aromatic group-containing monomers that constitute the macromonomers of aromatic group-containing monomer systems include the aromatic group-containing monomers described in (b) Hydrophobic monomers above, with styrene and benzyl (meth)acrylate being preferred, and styrene being more preferred. Specific examples of styrene-based macromonomers include AS-6(S), AN-6(S), and HS-6(S) (all manufactured by Toagosei Co., Ltd., trade names). Examples of silicone-based macromonomers include organopolysiloxanes having a polymerizable functional group at one end.

[0024] (d) Nonionic monomers From the viewpoint of improving the storage stability of the pigment aqueous dispersion, (d) nonionic monomers may also be used as monomer components in the carboxyl group-containing vinyl polymer (II). (d) Examples of nonionic monomers include polyalkylene glycol (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, polypropylene glycol (meth)acrylate (n=2 to 30, where n is the average number of moles added of oxyalkylene groups; the same applies hereinafter), polyethylene glycol (meth)acrylate (n=2 to 30), alkoxy polyalkylene glycol (meth)acrylates such as methoxy polyethylene glycol (meth)acrylate (n=1 to 30), and phenoxy(ethylene glycol-propylene glycol copolymer) (meth)acrylate (n=1 to 30, of which ethylene glycol: n=1 to 29). Among these, polypropylene glycol (meth)acrylate (n=2 to 30) and phenoxy(ethylene glycol-propylene glycol copolymer) (meth)acrylate (n=1 to 30) are preferred, and polypropylene glycol (meth)acrylate (n=2 to 30) is more preferred.

[0025] Examples of commercially available components (d) include NK ester M-20G, 40G, 90G, 230G, etc. from Shin Nakamura Chemical Industry Co., Ltd., and Bremmer PE-90, 200, 350, etc., PME-100, 200, 400, etc., PP-500, 800, 1000, etc., AP-150, 400, 550, etc., 50PEP-300, 50POEP-800B, 43PAPE-600B, etc. from NOF Corporation. The components (a) to (d) can each be used individually or in combination of two or more.

[0026] The polymer (II) used in the present invention preferably includes a vinyl polymer containing one or more (a) carboxyl group-containing vinyl monomers selected from the group consisting of acrylic acid and methacrylic acid, and one or more (b) hydrophobic vinyl monomers selected from the group consisting of acrylate monomers having an alkyl group with 1 to 22 carbon atoms or an aryl group with 6 to 22 carbon atoms, methacrylate monomers, and aromatic group-containing monomers.

[0027] <Content of each component or constituent unit in the monomer mixture or polymer> The content of component (a) is preferably 8% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and even more preferably 20% by mass or more, and preferably 65% ​​by mass or less, more preferably 55% by mass or less, even more preferably 45% by mass or less, and even more preferably 35% by mass or less. The content of component (b) is preferably 15% by mass or more, more preferably 25% by mass or more, even more preferably 35% by mass or more, even more preferably 45% by mass or more, even more preferably 50% by mass or more, and preferably 80% by mass or less, more preferably 75% by mass or less, and even more preferably 70% by mass or less. If component (c) is present, the content of component (c) is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. If component (d) is present, the content of component (d) is preferably 3% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0028] <Manufacturing of carboxyl group-containing vinyl polymer (II)> Carboxy group-containing vinyl polymer (II) is produced by copolymerizing the monomer mixture using known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these polymerization methods, solution polymerization is preferred. There are no particular restrictions on the solvent used in the solution polymerization method, but polar organic solvents are preferred. If the polar organic solvent is miscible with water, it can be used in combination with water. Examples of polar organic solvents include aliphatic alcohols having 1 to 3 carbon atoms, ketones having 3 to 5 carbon atoms, ethers, esters such as ethyl acetate, and preferably methanol, ethanol, acetone, methyl ethyl ketone, or a mixed solvent of one or more of these with water, and more preferably methyl ethyl ketone or a mixed solvent of methyl ethyl ketone with water.

[0029] Polymerization initiators and polymerization chain transfer agents can be used during polymerization. As polymerization initiators, known radical polymerization initiators such as azo compounds like 2,2'-azobisisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile), or organic peroxides like t-butylperoxyoctoate and benzoyl peroxide can be used. The amount of radical polymerization initiator is preferably 0.001 moles to 5 moles, more preferably 0.01 moles to 2 moles, per mole of monomer mixture. As polymerization chain transfer agents, known chain transfer agents such as mercaptans (octyl mercaptan, 2-mercaptoethanol, etc.) and thiuram disulfides can be used. Furthermore, there are no restrictions on the chain configuration of the polymerization monomers; any polymerization method such as random, block, or graft is acceptable.

[0030] The preferred polymerization conditions vary depending on the type of polymerization initiator, monomer, and solvent used, but typically the polymerization temperature is preferably 30°C or higher, more preferably 50°C or higher, and preferably 95°C or lower, and more preferably 80°C or lower. The polymerization time is preferably 1 hour or more, more preferably 2 hours or more, and preferably 20 hours or less, and more preferably 10 hours or less. The polymerization atmosphere is preferably an inert gas atmosphere such as nitrogen gas or argon. After the polymerization reaction is complete, the resulting polymer can be isolated from the reaction solution by known methods such as reprecipitation and solvent removal. Furthermore, the obtained polymer can be purified by removing unreacted monomers and other impurities using methods such as reprecipitation, membrane separation, chromatography, and extraction.

[0031] The weight-average molecular weight of polymer(II) used in the present invention is preferably 6,000 or more, more preferably 8,000 or more, and preferably 80,000 or less, and more preferably 40,000 or less. If the molecular weight of polymer(II) is within the above range, it can exhibit sufficient adsorption to the pigment and good dispersion stability. The weight-average molecular weight can be measured by the method described in the examples.

[0032] It is preferable to disperse the polymer (II) obtained in this manner in water such as pure water or deionized water to obtain a polymer aqueous dispersion in which the pigment (I) in step 1 is dispersed. The concentration (solid content concentration) of polymer (II) in this polymer aqueous dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, and also preferably 30% by mass or less, more preferably 25% by mass or less, from the viewpoint of improving the dispersion stability of the uncrosslinked polymer aqueous pigment dispersion (A) and facilitating its preparation. The solid content concentration of the polymer aqueous dispersion is measured by the method described in the examples.

[0033] <Content of pigment (I) and carboxyl group-containing vinyl polymer (II) in uncrosslinked polymer aqueous pigment dispersion (A)> From the viewpoint of improving the storage stability and productivity of the resulting aqueous pigment dispersion, the content of pigment (I) and polymer (II) in the uncrosslinked polymer aqueous pigment dispersion (A) obtained in step 1 is preferably within the following range. The pigment (I) content in the uncrosslinked polymer aqueous pigment dispersion (A) is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 12.5% ​​by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. The polymer (II) content in the uncrosslinked polymer aqueous pigment dispersion (A) is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and preferably 8% by mass or less, more preferably 7% by mass or less, and even more preferably 6% by mass or less.

[0034] Furthermore, in the uncrosslinked polymer aqueous pigment dispersion (A), the mass ratio of pigment (I) to polymer (II) [pigment (I) / carboxyl group-containing vinyl polymer (II)] is preferably 40 / 60 or more, more preferably 50 / 50 or more, even more preferably 60 / 40 or more, even more preferably 70 / 30 or more, and preferably 90 / 10 or less, more preferably 85 / 15 or less, and even more preferably 80 / 20 or less.

[0035] <Neutralization> At least some of the carboxyl groups of polymer(II) are neutralized using an alkali metal compound. The alkali metal compound used as a neutralizing agent here is a compound that generates alkali metal ions in an aqueous medium, and can be one or more selected from, for example, alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; alkali metal salts of silica such as sodium orthosilicate, sodium metasilicate, and sodium sesquisilicate; alkali metal salts of phosphoric acid such as trisodium phosphate; alkali metal salts of carbonic acid such as disodium carbonate, sodium bicarbonate, and dipotassium carbonate; and alkali metal salts of boric acid such as sodium borate. Two or more alkali metal compounds may be combined. The alkali metal compound is preferably an alkali metal hydroxide, more preferably sodium hydroxide and potassium hydroxide. 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 viewpoint of the above, the concentration of the aqueous solution of the neutralizing agent is preferably 3% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and preferably 50% by mass or less, more preferably 25% by mass or less. Furthermore, the polymer (II) may be neutralized beforehand, which eliminates the need to add a neutralizing agent in step 1.

[0036] From the viewpoint of improving the storage stability of the resulting aqueous pigment dispersion, the degree of neutralization of the carboxyl groups of polymer(II) before crosslinking is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, and even more preferably 65 mol% or less. Here, the degree of neutralization is the percentage (mol%) obtained by dividing the molar equivalents of the alkali metal compound by the molar equivalents of the carboxyl groups of the polymer (II), that is, the percentage (mol%) of "mollar equivalents of the alkali metal compound / molar equivalents of the carboxyl groups of the carboxyl group-containing vinyl polymer (II)". In this invention, since the degree of neutralization is calculated from the molar equivalents of the alkali metal compound, it will exceed 100 mol% if an excess of the alkali metal compound is used.

[0037] Furthermore, in step 1, a volatile basic compound can be used in combination with the alkali metal compound. Examples of volatile basic compounds include ammonia, trimethylamine, and triethylamine, but ammonia is preferred from the viewpoint of high volatility. There are no particular restrictions on the amount of volatile basic compounds used, but they should either not be used at all, or if used, the amount should be 10 mol% or more, preferably 20 mol% or more, more preferably 25 mol% or more, even more preferably 30 mol% or more relative to the carboxyl groups of polymer(II), and preferably 100 mol% or less, more preferably 90 mol% or less, even more preferably 80 mol% or less, and even more preferably 75 mol% or less. Note that only the amount of alkali metal compounds used is used to calculate the degree of neutralization, and the amount of volatile basic compounds used is not used in calculating the degree of neutralization in this invention.

[0038] <Distributed Processing> In step 1, it is preferable to disperse the raw material mixture containing the above components to obtain a dispersion of pigment-containing polymer particles. There are no particular restrictions on the dispersion method used to obtain the dispersion. The average particle size of the pigment (I) may be finened to a desired particle size by this dispersion alone, but it is preferable to pre-disperse the raw material mixture and then apply shear stress to perform the final dispersion to control the average particle size of the pigment (I) to a desired particle size. The temperature in step 1, particularly the temperature in the preliminary dispersion, is preferably 0°C or higher, more preferably 40°C or lower, more preferably 30°C or lower, and even more preferably 25°C or lower. The dispersion time is preferably 0.5 hours or more, more preferably 0.8 hours or more, more preferably 30 hours or less, more preferably 10 hours or less, and even more preferably 5 hours or less. When pre-dispersing, commonly used mixing and stirring devices such as anchor blades and disperser blades can be used, but high-speed stirring and mixing devices are preferred.

[0039] Means of applying shear stress to this dispersion include, for example, kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers (manufactured by Microfluidic), and media-type dispersers such as paint shakers and bead mills. Examples of commercially available media-type dispersers include the Ultra Apex Mill (manufactured by Kotobuki Kogyo Co., Ltd.) and the Pico Mill (manufactured by Asada Iron Works Co., Ltd.). Multiple of these devices can also be combined. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment. When performing this dispersion using a high-pressure homogenizer, the pigment particle size can be controlled to the desired level by controlling the processing pressure and the number of passes. From the viewpoint of productivity and economic efficiency, the processing pressure is preferably 60 MPa or higher, more preferably 100 MPa or higher, even more preferably 130 MPa or higher, and preferably 250 MPa or lower, more preferably 220 MPa or lower. Furthermore, the number of passes is preferably 3 or more, more preferably 8 or more, and preferably 30 or less, more preferably 20 or less.

[0040] In this way, an uncrosslinked polymer aqueous pigment dispersion (A) (an aqueous dispersion of pigment-containing polymer particles) can be obtained. Furthermore, if an organic solvent is used, the organic solvent may be removed from the dispersion of pigment-containing polymer particles by known methods, if necessary. It is preferable that the organic solvent in the obtained aqueous pigment dispersion (A) is substantially removed, but it may remain as long as it does not impair the objective of the present invention. The amount of residual organic solvent is preferably 0.1% by mass or less, more preferably 0.01% by mass or less. The obtained uncrosslinked polymer aqueous pigment dispersion (A) is in which pigment-containing polymer particles are dispersed in a medium mainly composed of water. There are no particular restrictions on the morphology of the pigment-containing polymer particles; it is sufficient that the particles are formed from at least pigment (I) and polymer (II), but it is preferable that the particles are in a form in which pigment (I) is encapsulated within polymer (II).

[0041] The average particle size of the pigment-containing polymer particles in the uncrosslinked polymer aqueous pigment dispersion (A) is preferably 50 nm or larger, more preferably 60 nm or larger, even more preferably 70 nm or larger, and preferably 200 nm or smaller, more preferably 160 nm or smaller, and even more preferably 140 nm or smaller, from the viewpoint of reducing coarse particles and improving the storage stability of the pigment aqueous dispersion. The average particle size of the pigment-containing polymer particles is measured by the method described in the examples. Furthermore, the average particle size of the pigment-containing crosslinked polymer particles in the aqueous pigment dispersion is approximately the same as the average particle size in the aqueous pigment dispersion (A) described above, and the preferred range of average particle size is the same as the preferred range of average particle size in the aqueous pigment dispersion (A).

[0042] [Process 2] Step 2 involves adding a crosslinking agent (III) to the uncrosslinked polymer aqueous pigment dispersion (A) obtained in Step 1, and then performing a heat crosslinking treatment at 40°C or higher to obtain a crosslinked polymer aqueous pigment dispersion (B). In this step 2, from the viewpoint of improving the storage stability of the resulting crosslinked polymer aqueous pigment dispersion (B), the polymer (II) in the uncrosslinked polymer aqueous pigment dispersion (A) obtained in step 1 is crosslinked with a crosslinking agent (III) described later to obtain a crosslinked polymer aqueous pigment dispersion (B) containing the crosslinked polymer (II). In this step, some of the carboxyl groups of the polymer (II) constituting the pigment-containing polymer particles are crosslinked, resulting in pigment-containing crosslinked polymer particles in which a crosslinked structure is formed on the surface.

[0043] <Cross-linking reaction> In this invention, a portion of the carboxyl groups of polymer (II) is neutralized with an alkali metal compound to disperse pigment (I) and obtain an uncrosslinked polymer aqueous pigment dispersion (A). Subsequently, a portion of the carboxyl groups of polymer (II) is reacted with a crosslinking agent (III) to form a crosslinked structure. That is, polymer (II) in this invention becomes a crosslinked polymer in which polymer (II) and the crosslinking agent (III) are crosslinked on the pigment surface in the uncrosslinked polymer aqueous pigment dispersion (A). By performing this crosslinking reaction, pigment (I) is dispersed in an aqueous medium in the form of pigment-containing crosslinked polymer particles in a crosslinked polymer aqueous pigment dispersion (B).

[0044] The reaction temperature in this crosslinking reaction is preferably 40°C or higher, more preferably 50°C or higher, more preferably 60°C or higher, even more preferably 65°C or higher, and preferably 95°C or lower, more preferably 85°C or lower, and even more preferably 80°C or lower, from the viewpoint of improving storage stability. Furthermore, the reaction time is preferably 0.5 hours or more, more preferably 1 hour or more, even more preferably 1.5 hours or more, and even more preferably 3 hours or more, and preferably 12 hours or less, more preferably 10 hours or less, even more preferably 8 hours or less, and even more preferably 6 hours or less, from the viewpoint of completion of the reaction and economic efficiency. The amount of crosslinking agent (III) used here should be such that the degree of crosslinking with polymer (II) is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, and preferably 85 mol% or less, more preferably 80 mol% or less, and even more preferably 75 mol% or less. This degree of crosslinking is a calculated degree of crosslinking calculated from the acid value of polymer (II) and the equivalent amount of epoxy groups of crosslinking agent (III). That is, the degree of crosslinking is the percentage (mol%) of "molar equivalents of epoxy groups of crosslinking agent (III) / molar equivalents of carboxyl groups of carboxyl group-containing vinyl polymer (II)".

[0045] <Crosslinking agent (III)> The crosslinking agent (III) used in the present invention is a crosslinking agent for carrying out a crosslinking reaction with the carboxyl groups of polymer (II) in a dispersion mainly composed of water. The crosslinking agent (III) is preferably a polyfunctional epoxy compound containing multiple epoxy groups, and more preferably a water-insoluble polyfunctional epoxy compound. From the viewpoint of efficiently crosslinking the carboxyl groups of polymer (II) in an aqueous medium, the amount of crosslinking agent (III) dissolved in 100 g of water at 20°C is preferably 55 g or less, more preferably 44 g or less, and even more preferably 39 g or less. Furthermore, from the viewpoint of improving the storage stability of the resulting pigment aqueous dispersion, the water solubility of the polyfunctional epoxy compound is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. Here, water solubility (mass%) refers to the solubility (mass%) when 10 parts by mass of the epoxy compound are dissolved in 90 parts by mass of water at room temperature (25°C), and more specifically, it is measured by the method described in the examples.

[0046] The number of epoxy groups in a polyfunctional epoxy compound is 2 or more, preferably 2.5 or more, more preferably 3 or more, and preferably 7 or less, and more preferably 5 or less, from the viewpoint of efficiently crosslinking with the carboxyl groups of polymer(II) in an aqueous medium. Similarly, the number of glycidyl ether groups in a polyfunctional epoxy compound is 2 or more, preferably 2.5 or more, more preferably 3 or more, and preferably 7 or less, and more preferably 5 or less. Note that "polyfunctional" in a 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 a polyfunctional epoxy compound" refers to the weighted average value. The same applies to the number of glycidyl ether groups. Furthermore, the polyfunctional epoxy compound is preferably a polyglycidyl ether compound of a polyhydric alcohol having hydrocarbon groups with 3 to 8 carbon atoms.

[0047] The epoxy equivalent of the polyfunctional epoxy crosslinking agent 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 more preferably 180 g / eq or less. The molecular weight of the polyfunctional epoxy compound is preferably 120 or more, more preferably 150 or more, even more preferably 200 or more, and preferably 2000 or less, more preferably 1500 or less, and even more preferably 1000 or less, from the viewpoint of ease of reaction and storage stability of the resulting crosslinked polymer.

[0048] Specific examples of polyfunctional epoxy compounds include one or more selected from the group consisting of polyglycidyl ethers such as polypropylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydrogenated bisphenol A type diglycidyl ether. Among these, the polyfunctional epoxy compound is preferably one or more selected from the group consisting of polypropylene glycol diglycidyl ether (water solubility 31%), trimethylolpropane polyglycidyl ether (water solubility 27%), and pentaerythritol polyglycidyl ether (water solubility 0%), more preferably trimethylolpropane polyglycidyl ether.

[0049] In this step 2, the acid value of the crosslinked polymer constituting the pigment-containing crosslinked polymer particles becomes lower than that of the carboxyl group-containing vinyl polymer(II) due to the crosslinking reaction. The acid value of this crosslinked polymer is preferably 50 mg KOH / g or more, more preferably 60 mg KOH / g or more, even more preferably 65 mg KOH / g or more, and preferably 180 mg KOH / g or less, more preferably 150 mg KOH / g or less, and even more preferably 100 mg KOH / g or less. If the acid value is within the above range, the dispersion stability of the pigment in the pigment aqueous dispersion is ensured. This crosslinked polymer is obtained by crosslinking a neutralized polymer aqueous dispersion with crosslinking agent (III) as described above, and the acid value of the crosslinked polymer includes the acid groups in the neutralized state. This crosslinked polymer is the polymer that constitutes the pigment-containing crosslinked polymer particles in the pigment aqueous dispersion described later. Furthermore, the acid value of a crosslinked polymer can be calculated from the acid value of the carboxyl group-containing vinyl polymer (II) and the type and amount of crosslinking agent added. Alternatively, it can be determined by dissolving or swelling the polymer in a suitable organic solvent and titrating it. More specifically, 2 g of a pigment aqueous dispersion of pigment-containing crosslinked polymer particles is accurately weighed, diluted with 50 g of deionized water, and 3 mL of a 0.1 N sodium hydroxide / ethanol solution is added to obtain a titration sample. The titration sample is titrated with 0.1 N hydrochloric acid using a potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and after measuring two pH inflection points, the number of moles of hydrochloric acid used is calculated from the difference in the amount of 0.1 N hydrochloric acid added between the two points. The acid value (mgKOH / g) of the pigment-containing crosslinked polymer particles is calculated from the number of moles of hydrochloric acid used, the solid content of the pigment aqueous dispersion of the pigment-containing crosslinked polymer particles, and the ratio of the pigment and the crosslinked polymer dispersant constituting the pigment-containing crosslinked polymer particles.

[0050] [Step 3] Step 3 is a step in which alkanediol (IV) is added to the crosslinked polymer aqueous pigment dispersion (B) obtained in Step 2 to obtain an aqueous pigment dispersion. Since alkanediol (IV) has a high affinity for polymer (II), it is thought to contribute to improving the storage stability of the aqueous pigment dispersion. Thus, by reacting polymer (II) and crosslinking agent (III) in step 2 to form crosslinked polymer particles (pigment-containing crosslinked polymer particles) having pigment (I), and then adding alkanediol (IV), the storage stability of the pigment aqueous dispersion can be improved.

[0051] <Alkanediol (IV)> The alkanediol(IV) used in the present invention is not particularly limited as long as it is an alkyl alcohol having two hydroxyl groups, but from the viewpoint of improving the storage stability of the pigment aqueous dispersion, it is preferably an alkanediol having 4 to 10 carbon atoms, more preferably 5 to 9 carbon atoms, and even more preferably 6 to 8 carbon atoms. The alkyl chain of the alkanediol(IV) may be either a straight chain or a branched chain, and is preferably a straight chain. Examples of alkanediols having 4 to 10 carbon atoms include butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, and decanediol, which may have an alkyl group having 1 to 3 carbon atoms. Among these, alkanediols having hydroxyl groups on adjacent carbon atoms are preferred. The alkanediol(IV) used in the present invention is preferably a 1,2-alkanediol having 4 to 10 carbon atoms, more preferably a 1,2-alkanediol having 5 to 9 carbon atoms, even more preferably a 1,2-alkanediol having 6 to 8 carbon atoms, even more preferably a 1,2-hexanediol, a 1,2-octanediol, and even more preferably a 1,2-hexanediol.

[0052] The addition of alkanediol (IV) to the crosslinked polymer aqueous pigment dispersion (B) is preferably carried out at a temperature of 40°C or lower, more preferably 35°C or lower, even more preferably 30°C or lower, and preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher, from the viewpoint of improving the storage stability of the aqueous pigment dispersion.

[0053] Furthermore, alkanediol(IV) is added in such a way that its content in the pigment aqueous dispersion is between 0.05% by mass and 1.6% by mass. From the viewpoint of improving the storage stability of the pigment aqueous dispersion, the content of alkanediol(IV) is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.4% by mass or more, even more preferably 0.5% by mass or more, and preferably 1.5% by mass or less, more preferably 1.2% by mass or less, even more preferably 1.0% by mass or less, and even more preferably 0.8% by mass or less.

[0054] The pigment aqueous dispersion of the present invention may further contain a preservative. By incorporating a preservative, the storage stability of the pigment aqueous dispersion can be improved, and the formation of insoluble substances due to spoilage of the pigment aqueous dispersion can be prevented. Here, a preservative means a substance that has the function of preventing the occurrence and growth of microorganisms, especially bacteria and fungi (mold), and is preferably soluble or stably dispersed in water, has sufficient antibacterial performance, preservative performance and stability for practical use, is highly safe and has a low environmental impact. In this invention, organic and inorganic preservatives can be used without particular limitation. For example, those listed in "Antibacterial and Antifungal Handbook" (Gihodo Publishing, 1986), edited by the Japan Society for Antibacterial and Antifungal Agents, and "Dictionary of Antibacterial and Antifungal Agents," edited by the Japan Society for Antibacterial and Antifungal Agents, can be used.

[0055] Examples of organic preservatives include nitrogen-containing heterocyclic compounds, quaternary ammonium salts, phenols, alcohols, carboxylic acids or their salts and esters. Examples of inorganic preservatives include inorganic substances containing heavy metal ions (such as silver ion-containing substances) and their salts. Among the above, nitrogen-containing heterocyclic compounds, phenols, carboxylic acids or their salts and esters are more preferred, and preferred examples include thiabendazole, 2-benzoisothiazolin-3-one, 1,2-benzoisothiazol-3(2H)-one, 1,2-benzoisothiazolin-3-one, 3,4-isothiazolin-3-one, benzoisothiazolone, alkylisothiazolone, chloralkylisothiazolone, benzisothiazolone, benzimidazole, thiabendazole, thiazosulfamide, pyridinethiol oxide, dichlorophene, hexachlorophene, bromonitro alcohol, chloroxylenol, sodium benzoate, potassium sorbate, and the like.

[0056] Commercially available preservatives include the following products from Abyssia Co., Ltd.: Proxel CRL, Proxel BDN, Proxel LV, Proxel LVS, Proxel GXL, Proxel XL2, Proxel IB, and Proxel TN; the following products from Nippon Soda Co., Ltd.: Bestside 200K, Bestside 300, Bestside 1000, Bestside 1200, and Bestside NS; and the following product from Clariant: JMAC-LP10%. The aforementioned preservatives can be used individually or in combination of two or more types. These preservatives are preferably water-soluble, and when using two or more preservatives in combination, it is preferable to use those with different chemical structures. For example, a combination of nitrogen-containing heterocyclic compounds and phenols is an example. The preservative content in the pigment aqueous dispersion is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.3% by mass or less. If the preservative content is within the above range, sufficient preservative effect can be obtained and it will not cause problems such as poor dispersion.

[0057] Furthermore, the aforementioned alkanediol(IV) is a component that can impart preservative properties to a dispersion containing, for example, 1,2-hexanediol. Therefore, when an alkanediol with such preservative properties is included, the amount of preservative added to impart the desired preservative properties can be reduced.

[0058] In addition to preservatives, the pigment aqueous dispersion of the present invention may also contain additives such as humectants to prevent drying. These additives may be added in step 1, or they may be added simultaneously with alkanediol(IV) in step 3. Examples of humectants include glycerin and polyethylene glycol, which may be added to the pigment aqueous dispersion in an amount of 1% to 10% by mass.

[0059] <Content of non-volatile components in the aqueous pigment dispersion> From the viewpoint of improving the storage stability of the pigment aqueous dispersion, the concentration of nonvolatile components in the obtained pigment aqueous dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, and also preferably 30% by mass or less, more preferably 25% by mass or less. Here, the content of nonvolatile components in the pigment aqueous dispersion is the nonvolatile components added as needed, such as the pigment (I), polymer (II), crosslinking agent (III), alkanediol (IV), and preservative, as described above. The concentration of non-volatile components in the pigment aqueous dispersion is measured by the method described in the examples.

[0060] Furthermore, the content of pigment (I) in this pigment aqueous dispersion is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 12.5% ​​by mass or more, and preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less. The content of the crosslinked polymer in the pigment aqueous dispersion is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and preferably 8% by mass or less, more preferably 7% by mass or less, and even more preferably 6% by mass or less.

[0061] Furthermore, in the aqueous pigment dispersion, the mass ratio of pigment (I) to the crosslinked polymer [pigment (I) / crosslinked polymer] is preferably 40 / 60 or more, more preferably 50 / 50 or more, even more preferably 60 / 40 or more, even more preferably 70 / 30 or more, and preferably 90 / 10 or less, more preferably 85 / 15 or less, and even more preferably 80 / 20 or less.

[0062] Furthermore, the pH of the pigment aqueous dispersion obtained in step 3 is preferably 8 or higher. If the pH is 8 or higher, the dissociation of anionic groups is promoted, the charge amount of the pigment aqueous dispersion is sufficient, and this can improve the storage stability of the pigment aqueous dispersion. The pH of the pigment aqueous dispersion is more preferably 8.5 or higher, and there is no particular upper limit, but if the pH exceeds 11, when manufacturing ink using the pigment aqueous dispersion, the pH of the ink becomes too high, which is undesirable because it adversely affects the components of printers and printing presses that use the ink. For this reason, the pH of the pigment aqueous dispersion is even more preferably 10.5 or lower. There are no particular restrictions on the method of measuring pH, but a pH measurement method using a glass electrode is specified in JIS Z8802, and this method is preferred because it is simple and accurate.

[0063] [Water-based ink] The pigment aqueous dispersion obtained by the manufacturing method of the present invention can be used in the production of water-based ink. This water-based ink can be prepared by adding to the pigment aqueous dispersion obtained above a penetrating agent, dispersant, defoaming agent, rust inhibitor, surfactant, etc., which are commonly used in water-based inks. In the water-based ink, the content of crosslinked polymer particles containing pigment (I) (pigment-containing crosslinked polymer particles) is preferably 1% by mass or more, more preferably 3% by mass or more, and preferably 10% by mass or less, and more preferably 8% by mass or less. The content of preservatives is preferably 0.1% by mass or more, and preferably 1% by mass or less, and more preferably 0.5% by mass or less.

[0064] The resulting water-based ink 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. Examples of recording media include low-absorbent recording paper such as coated paper, and non-absorbent resin films such as PET film and polypropylene film. Plain paper can also be used as a recording medium. [Examples]

[0065] 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.

[0066] (1) Measurement of the weight-average molecular weight of carboxyl group-containing vinyl polymer (II) 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 SuperAW-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: 1mL / min Standard material: Monodisperse polystyrene kits with known molecular weight, manufactured by Tosoh Corporation: "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)".

[0067] (2) Measurement of the acid value of carboxyl group-containing vinyl polymers (II) and crosslinked polymers Using a potentiometric automatic titrator (manufactured by Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), for polymers (II) without a crosslinked structure, the polymer (II) was dissolved in a titration solvent of toluene and acetone (2:1) and titrated with a 0.1N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve as the endpoint. The acid value (mgKOH / g) was calculated from the amount of potassium hydroxide solution titrated to the endpoint. In the case of crosslinked polymers in which polymer (II) was crosslinked, the acid value after crosslinking was calculated from the degree of crosslinking based on the polymer raw materials and the amount of crosslinking agent used.

[0068] (3) Measurement of solid content concentration of polymer(II) aqueous dispersion Using an infrared moisture meter (FD-230, manufactured by Kett Scientific Research Institute Co., Ltd.), 1.0 g of the sample was dried at a drying temperature of 150°C and measurement mode 96 (monitoring time 2.5 minutes / variation range 0.05%). The moisture content (%) of the sample was then measured, and the solid content concentration (%) was calculated using the following formula. Solid content concentration (%) = 100 - Moisture content of the sample (%)

[0069] (4) Measurement of the concentration of non-volatile components in the pigment aqueous dispersion 10.0 g of sodium sulfate, which had been stabilized in a desiccator, was weighed into a 30 mL ointment container. Approximately 1.0 g of the sample was added and mixed, then accurately weighed. The mixture was kept at 105°C for 2 hours to remove volatile components, and then left in a desiccator for another 15 minutes before the mass was measured. The mass of the sample after removing 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.

[0070] (5) Measurement of the water solubility of the crosslinking agent At room temperature of 25°C, 90 parts by mass of deionized water and 10 parts by mass of crosslinking agent (W1) were added to a glass tube (25 mmφ × 250 mmh), and the glass tube was left to stand for 1 hour in a constant temperature bath adjusted to 25°C. Next, the glass tube was shaken vigorously for 1 minute, and then left to stand again in the constant temperature bath for 12 hours. Then, the undissolved material that separated from the water and settled or floated was collected, dried for 6 hours at 40°C and a gauge pressure of -0.08 MPa, and weighed (W2). The water solubility (mass%) was calculated using the following formula. Water solubility (mass%)={(W1-W2) / W1}×100

[0071] (6) Measurement of the average particle size of pigment-containing crosslinked polymer particles Cumulant analysis was performed using a laser particle analysis system (ELS-8000, manufactured by Otsuka Electronics Co., Ltd.), and the resulting average cumulant particle size was taken as the average particle size of the pigment-containing crosslinked polymer particles in the pigment aqueous dispersion. For each example of the pigment aqueous dispersion, the concentration of the particles to be measured was 5 × 10⁻⁶. -3 A dispersion solution diluted with water to a concentration of % (converted to solid content) was used. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion medium.

[0072] <Preparation of carboxyl group-containing vinyl polymer(II)> Preparation Example 1-1 (Preparation of Carboxylic Acid-Containing Vinyl Polymer (II-1)) A mixture of raw material monomers was prepared by mixing 30.8 parts of acrylic acid, 59.2 parts of styrene, and 10.0 parts of α-methylstyrene. In a reaction vessel, 10.0 parts of methyl ethyl ketone (hereinafter also referred to as "MEK"), 0.3 parts of 2-mercaptoethanol as a polymerization chain transfer agent, and 10% of the above raw material monomer mixture were added and mixed, and the mixture was thoroughly purged with nitrogen gas. Meanwhile, a dropping funnel was filled with the remaining (90%) of the raw material monomer mixture, 0.27 parts of 2-mercaptoethanol, 40.0 parts of MEK, and 1.1 parts of an azo radical polymerization initiator (V-65, 2,2'-azobis(2,4-dimethylvaleronitrile) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (hereinafter also referred to as "V-65"). Under a nitrogen atmosphere, the reaction vessel was heated to 65°C while stirring the raw material monomers, and the mixture in the dropping funnel was added dropwise over 3 hours. After stirring for 2 hours from the end of the dropwise addition, a solution of 0.15 parts of the azo radical polymerization initiator (V-65) dissolved in 2.5 parts of MEK was added, and the mixture was aged at 65°C for 2 hours, and then at 70°C for another 2 hours to obtain a solution of carboxyl group-containing vinyl polymer (II-1). The carboxyl group-containing vinyl polymer (II-1) had a weight-average molecular weight of 15,000 and an acid value of 240 mgKOH / g. Table 1 shows the amount used and the properties of the resulting carboxyl group-containing vinyl polymer (II).

[0073] Preparation Example 1-2 (Preparation of Carboxyloid-Containing Vinyl Polymer (II-2)) A mixture of raw material monomers was prepared by mixing 13.8 parts of methacrylic acid, 56.2 parts of benzyl acrylate, 40.0 parts of styrene macromer (AS-6S, manufactured by Toagosei Co., Ltd., number average molecular weight: 6,000, solid content concentration 50%) (hereinafter referred to as "styrene macromer") (20.0 parts as solid content), and 10.0 parts of polypropylene glycol monomethacrylate (Bremmer PP-800, manufactured by NOF Corporation, average number of moles of propylene oxide added: 13, terminal: hydroxyl group). 10 parts of MEK, 0.3 parts of 2-mercaptoethanol, and 10% of the raw material monomer mixture were added to the reaction vessel and mixed, followed by thorough nitrogen gas purging. Meanwhile, a mixture of the remaining (90%) of the raw material monomer mixture, 0.27 parts of 2-mercaptoethanol, 40 parts of MEK, and 1.1 parts of azo radical polymerization initiator (V-65) was placed in a dropping funnel, and the preparation proceeded in the same manner as in Preparation Example 1-1 to obtain a solution of carboxyl group-containing vinyl polymer (II-2). The weight-average molecular weight of carboxyl group-containing vinyl polymer (II-2) was 150,000, and the acid value was 90 mgKOH / g. The amount charged and the properties of the obtained carboxyl group-containing vinyl polymer (II) are shown in Table 1.

[0074] [Table 1]

[0075] <Preparation of polymer aqueous dispersion (P)> Preparation Example 2-1 (Preparation of Polymer Aqueous Dispersion (P1)) The solution of carboxyl group-containing vinyl polymer (II-1) obtained in Preparation Example 1-1 was dried under reduced pressure and then ground using a coffee mill to obtain carboxyl group-containing vinyl polymer (II-1). 80.0 parts of carboxyl group-containing vinyl polymer (II-1), 313.9 parts of deionized water, and 48.6 parts of 5N sodium hydroxide aqueous solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., reagent) as a neutralizing agent were added to a heat-resistant bottle (the amount of neutralizing agent used (the ratio of moles of sodium hydroxide to moles of carboxyl groups in carboxyl group-containing vinyl polymer (II-1)) was set to 60 mol% (degree of neutralization: 60 mol%)). The mixture was neutralized and dispersed by heating at 90°C for 5 hours while stirring at 150 rpm to obtain a polymer aqueous dispersion (P1) (solid content concentration: 20.0%). The amounts are shown in Table 2.

[0076] Preparation Example 2-2 (Preparation of Polymer Aqueous Dispersion (P2)) A polymer aqueous dispersion (P2) (solid content concentration: 20.0%) was obtained in the same manner as in Preparation Example 2-1, except that the type of carboxyl group-containing vinyl polymer (II), the amount of neutralizing agent added, and the amount of ion-exchanged water added were changed as shown in Table 2.

[0077] [Table 2]

[0078] <Preparation of uncrosslinked polymer aqueous pigment dispersion (A); Step 1> Example a (Preparation of an uncrosslinked polymer aqueous pigment dispersion (A1)) To 137.8 parts of the polymer aqueous dispersion (P1) obtained in Preparation Example 2-1, 370.0 parts of deionized water and 100.0 parts of carbon black pigment (CI Pigment Black 7, manufactured by Cabot, trade name: Monarch880) were added, and the mixture was stirred at 7,000 rpm for 60 minutes at 20°C using a disperser (Ultra Disperser, manufactured by Asada Iron Works Co., Ltd.). The obtained mixture was subjected to a 10-pass dispersion treatment at a pressure of 200 MPa using a microfluidizer (product name: Microfluidics, model name: M-110-EH) to obtain the dispersed product. The resulting dispersion was filtered using a 25 mL needleless syringe (Terumo Corporation) fitted with a 5 μm pore size syringe filter (Sartorius "Minisart", model number: S7594-FMOSK) to remove coarse particles, thereby obtaining an uncrosslinked polymer aqueous pigment dispersion (A1) (solid content concentration: 21.0%). The formulation amounts are shown in Table 3.

[0079] Example b (Preparation of uncrosslinked polymer aqueous pigment dispersion (A2)) In Example a, an aqueous pigment dispersion (A2) (solid content concentration: 21.0%) was obtained in the same manner as in Example a, except that the type and amount of polymer aqueous dispersion (P) were changed as shown in Table 3. The blending amounts are shown in Table 3.

[0080] Example c (Preparation of an uncrosslinked polymer aqueous pigment dispersion (A3)) In Example a, the pigment type was changed to PB15:3 (CI Pigment Blue 15:3, manufactured by DIC, trade name: FASTOGEN BLUE TGR-SD). The same procedure was followed to obtain an aqueous pigment dispersion (A3) (solid content concentration: 21.0%). The blending amounts are shown in Table 3.

[0081] [Table 3]

[0082] <Manufacturing of Pigment Aqueous Dispersion; Steps 2-3> Example 1 (Preparation of Pigment Aqueous Dispersion 1) 87.6 parts (solid content concentration: 21.0%) of the aqueous pigment dispersion (A1) obtained in Example a were placed in a screw-top glass bottle, and 1.59 parts of trimethylolpropane polyglycidyl ether (Denacol EX-321, manufactured by Nagase ChemteX Corporation, epoxy equivalent: 139 g / eq., water solubility: 27%) (hereinafter referred to as "EX-321") were added as a crosslinking agent (an amount sufficient to crosslink 70 mol% of the total carboxyl groups in the carboxyl group-containing vinyl polymer (II-1) (degree of crosslinking: 70 mol%)). The bottle was then sealed tightly and heated at 70°C for 5 hours while stirring with a stirrer. After that, the temperature was lowered to room temperature (25°C), and the mixture was filtered using a 25 mL needleless syringe fitted with the aforementioned 5 μm pore size syringe filter to obtain the crosslinked polymer aqueous pigment dispersion (B1). To the obtained crosslinked polymer aqueous pigment dispersion (B1), 0.1 parts of 1,2-hexanediol as an alkanediol, 0.17 parts of Proxel LVS as a preservative, and 10.54 parts of deionized water were added and mixed at room temperature (25°C) to perform preservation treatment. Subsequently, the mixture was filtered through the 5 μm syringe filter to obtain pigment aqueous dispersion 1 (solid content concentration: 20.0%). The obtained pigment aqueous dispersion 1 was evaluated for storage stability and preservative properties using the evaluation method described below. The composition and evaluation results are shown in Table 4.

[0083] Examples 2-7 and Comparative Example 3 (Production of Pigment Aqueous Dispersions 2-7 and C3) Pigment aqueous dispersions 2-7 and C3 were obtained in the same manner as in Example 1, except that the type of uncrosslinked polymer aqueous pigment dispersion (A), the amount of crosslinking agent added, the type and amount of alkanediol added, and the amount of ion-exchanged water added were changed as shown in Tables 4 and 5. The storage stability and preservative properties of the obtained pigment aqueous dispersions 2-7 and C3 were evaluated using the evaluation method described below. The composition and evaluation results are shown in Tables 4 and 5.

[0084] Comparative Example 1 (Production of Pigment Aqueous Dispersion (C1)) 87.6 parts (solid content concentration: 21.0%) of the uncrosslinked polymer aqueous pigment dispersion (A1) obtained in production example a were placed in a screw-cap glass bottle, 0.6 parts of 1,2-hexanediol as the alkanediol were added, the bottle was tightly sealed, and the mixture was heated at 70°C for 5 hours while stirring with a stirrer. After that, the mixture was cooled to room temperature (25°C), and filtered using a 25 mL needleless syringe fitted with a syringe filter with a pore size of 5 μm to obtain an aqueous pigment dispersion. To the obtained aqueous pigment dispersion, 0.17 parts of Proxel LVS and 11.63 parts of deionized water were added as preservatives and mixed at room temperature (25°C) to perform preservation treatment. Subsequently, the mixture was filtered through the 5 μm syringe filter to obtain the aqueous pigment dispersion (C1) (solid content concentration: 20.0%). The obtained pigment aqueous dispersion (C1) was evaluated for storage stability and preservative properties using the evaluation method described below. The composition and evaluation results are shown in Table 5.

[0085] Comparative Example 2 (Production of Pigment Aqueous Dispersion (C2)) 87.6 parts (solids content: 21.0%) of the uncrosslinked polymer aqueous pigment dispersion (A1) obtained in Example a were placed in a screw-top glass bottle, 1.59 parts (degree of crosslinking: 70 mol%) of trimethylolpropane polyglycidyl ether as a crosslinking agent and 0.6 parts of 1,2-hexanediol as an alkanediol were added, the bottle was tightly sealed, and the mixture was heated at 70°C for 5 hours while stirring with a stirrer. After that, the mixture was cooled to room temperature (25°C), and filtered using a 25 mL needleless syringe fitted with a syringe filter with a pore size of 5 μm to obtain the crosslinked polymer aqueous pigment dispersion. To the obtained crosslinked polymer aqueous pigment dispersion, 0.17 parts of Proxel LVS and 10.04 parts of deionized water were added as preservatives and mixed at room temperature (25°C) to perform preservation treatment. Subsequently, the mixture was filtered through the 5 μm syringe filter to obtain the pigment aqueous dispersion (C2) (solid content concentration: 20.0%). The obtained pigment aqueous dispersion (C2) was evaluated for storage stability and preservative properties using the evaluation method described below. The composition and evaluation results are shown in Table 5.

[0086] [Evaluation of storage stability] 100 g of pigment aqueous dispersion was added to a 100 mL plastic container and stored in a sealed state at 40°C for 6 months. Afterward, each pigment aqueous dispersion, cooled to room temperature (25°C), was filtered using a 25 mL needleless syringe (Terumo Corporation) fitted with a 5 μm pore size syringe filter (Sartorius "Minisart", model number: S7594-FMOSK). The amount of liquid (g) that passed through until the syringe filter became blocked was measured. This amount of liquid was evaluated according to the following criteria. <Evaluation Criteria> 4:Liquid passing amount 100g or more 3: Fluid flow rate 50g or more but less than 100g 2: Fluid flow rate 5g or more but less than 50g 1: Fluid flow rate less than 5g

[0087] [Evaluation of preservative properties] 50 g of a pigment aqueous dispersion was mixed with 0.5 mL of a bacterial solution (containing Staphylococcus aureus, coliform bacteria, and Bacillus bacteria) and thoroughly stirred to obtain a bacterial solution-containing aqueous dispersion. To a test tube containing 9 mL of sterile LP diluent (manufactured by Nippon Shinyaku Co., Ltd.), 1 mL of the bacterial suspension-containing aqueous dispersion sample was added and mixed. Then, 0.1 mL of the mixed diluent was placed on the surface of a plate containing SCDLP agar medium (manufactured by Nippon Shinyaku Co., Ltd.), and uniformly spread with a sterile convection rod. After static incubation in a 30°C incubator, the formed colonies were counted. Sampling was performed on days 1, 3, 7, 14, and 28. The number of bacteria measured at this time was evaluated according to the following criteria. Regarding the practical pass criteria, 10 6 If you ingest a certain amount of bacteria per gram, the detection limit (10) will be reached on the third day. 2 ( / g) or less, or below the detection limit (10) on day 7. 2 The conditions for passing the test were that the bacterial count remained below 1 / g and no bacterial growth was observed during the test period (28 days). <Evaluation Criteria> 4: The detection limit of bacterial count on the plate within 3 days (10 2 Below 1 / g, no bacterial growth occurred. 3: The lower limit of bacterial count on the plate within 7 days (10 2 Below 1 / g, no bacterial growth occurred. 2: Detection limit of bacterial count on plate within 28 days (10 2 / g) or less 1: Detection limit of bacterial count on plate within 28 days (10 2 / g) super

[0088] [Table 4]

[0089] [Table 5]

[0090] Tables 4 and 5 show that the aqueous pigment dispersions obtained by the manufacturing method of the present invention have excellent storage stability (Examples 1-7). In contrast, Comparative Example 1, in which no crosslinking agent was added and the carboxyl group-containing vinyl polymer was not crosslinked, Comparative Example 2, in which alkanediol was added before crosslinking, and Comparative Example 3, in which a large amount of alkanediol was added, all showed poor storage stability. Furthermore, it was found that the aqueous pigment dispersions obtained by the manufacturing method of the present invention also exhibit good preservative properties, and in particular, alkanediols with 6 or more carbon atoms tend to exhibit good preservative properties.

Claims

1. A method for producing an aqueous pigment dispersion, comprising the following steps 1 to 3. Step 1: Disperse pigment (I) with carboxyl group-containing vinyl polymer (II) to obtain an uncrosslinked polymer aqueous pigment dispersion (A). Step 2: Adding a crosslinking agent (III) to the uncrosslinked polymer aqueous pigment dispersion (A) obtained in Step 1, and performing a heat crosslinking treatment at 40°C or higher to obtain a crosslinked polymer aqueous pigment dispersion (B). Step 3: Adding alkanediol (IV) to the crosslinked polymer aqueous pigment dispersion (B) obtained in Step 2 to obtain an aqueous pigment dispersion. Here, the nonvolatile component of the pigment aqueous dispersion obtained in step 3 is 10% by mass or more and 50% by mass or less, and the content of the alkanediol(IV) is 0.05% by mass or more and 1.6% by mass or less.

2. The method for producing an aqueous pigment dispersion according to claim 1, wherein the alkanediol(IV) comprises a 1,2-alkanediol.

3. The method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein the aqueous pigment dispersion further contains a preservative.

4. A method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein a polyfunctional epoxy compound is used as the crosslinking agent (III).

5. A method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein the acid value of the crosslinked polymer constituting the aqueous pigment dispersion is 50 mg KOH / g or more and 180 mg KOH / g or less.

6. A method for producing an aqueous pigment dispersion according to claim 1 or 2, wherein in step 3, the alkanediol(IV) is added at 35°C or below.

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