Copolymer, pigment dispersant, and pigment dispersion liquid

Abstract

To provide a copolymer that is excellent in initial dispersibility and dispersion stability of pigment and also has low foamability.SOLUTION: A copolymer contains a constitutional unit (A) derived from a styrenic monomer, a constitutional unit (B) derived from a monomer that is formed by reacting an unsaturated dicarboxylic acid or an anhydride thereof with a compound represented by e.g. the following general formula (3): R4O-(A1O)n1-H (3) (where A1 is a C2 to 4 alkylene group and n1 is a number selected from 3-100), and a constitutional unit (C) derived from a monomer represented by the following general formula (2) (where R6 is a hydrogen atom or a methyl group, A3 is a C2 to 4 alkylene group, p is a number selected from 1-30, q is 1 or 2, M2 is a hydrogen atom, alkali metal, alkaline-earth metal, ammonium, or organic ammonium).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a copolymer, a pigment dispersant containing the same, and a pigment dispersion liquid.

Background Art

[0002] In recent years, due to efforts towards environmental issues and safety reasons, the water-based conversion of inks and paints has been progressing. However, both inorganic pigments and organic pigments have low affinity for water and are not easily dispersed in water. Against this background, in pigment dispersion compositions such as inks and paints, dispersants capable of improving the dispersibility of pigments have been developed.

[0003] As dispersants for pigments, polymer dispersants such as styrene-acrylic acid copolymers, polyacrylates, and formalin condensates of naphthalenesulfonates are known. These polymer dispersants have an effect on the long-term storage stability of pigment dispersions due to the steric hindrance effect. However, because of their large molecular weight, almost no wetting property (wetting effect) of the solvent on the pigment can be obtained. In addition, in polymer dispersants, so-called bridging aggregation in which one molecule is adsorbed to a plurality of particles due to a plurality of adsorption groups in the molecule easily occurs, and particularly when the pigment is at a high concentration, aggregation and sedimentation of pigment particles may be caused.

[0004] On the other hand, as pigment dispersants having a wetting action, nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymers, and alkoxypolyoxyethylene fatty acid esters, and anionic surfactants such as sulfate esters of polyoxyethylene alkyl ethers are known (see Patent Documents 1 and 2). In addition, a wetting and dispersing agent including a comb-shaped copolymer in which a polyalkylene glycol chain is grafted onto a styrene-maleic anhydride copolymer, and a pigment dispersion resin composition in which the comb-shaped copolymer and a surfactant are used in combination are known (see Patent Documents 3 and 4).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, although a pigment dispersant composed of a nonionic surfactant has an effect on the initial dispersibility of pigments because it has wettability with respect to pigment particles, the repulsive force acting between pigment particles is insufficient, and aggregation and sedimentation of pigment particles may occur under long-term storage. In addition, although the sulfate ester salt of polyoxyethylene alkyl ether has an effect on the initial dispersibility and long-term storage stability of pigments, it has a problem of high foaming property. On the other hand, the comb-shaped copolymer described in Patent Document 3 and Patent Document 4 has a problem that the adsorption power to hydrophilized pigment particles such as titanium oxide is weak and a sufficient viscosity reduction effect cannot be obtained. The present invention has been made in view of the problems of the above prior art, and an object thereof is to provide a copolymer excellent in the initial dispersibility and dispersion stability of pigments and having low foaming property.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by using a specific copolymer as a pigment dispersant, and have completed the present invention. That is, the present invention relates to the following [1] to [6]. [1] A structural unit (A) derived from a styrene-based monomer, A structural unit (B) represented by the following general formula (1), [Chemical formula] (In the formula, R 1 , R 2 , and R 3 each independently represents a hydrogen atom, a hydrocarbon group having 1 to 10 carbon atoms, -(CH2) m2 -COOM 1 , or -(CH2) m2 -COX 2 -(A 2 O) n2 -R 5 , provided that one of them is -(CH2) m2 -COOM 1 , or -(CH2) m2 -COX 2 -(A 2 O) n2 -R 5 , M 1 represents a hydrogen atom, an alkali metal, an alkaline earth metal, ammonium, or an organic ammonium. m1 and m2 each independently represent 0 or 1, X 1 and X 2 each independently represent -O-, or -NH-, or, R 1 or R 2 and X 1 together represent -CON<, A 1 and A 2 each independently represent an alkylene group having 2 to 4 carbon atoms, n1 and n2 are the average number of moles of alkylene oxide added, and each independently represents a number from 3 to 100, R 4 and R 5 each independently represent a hydrocarbon group having 1 to 24 carbon atoms.) And, a structural unit (C) derived from a monomer represented by the following general formula (2) [Chemical formula] (In the formula, R 6 represents a hydrogen atom or a methyl group, A 3 is an alkylene group having 2 to 4 carbon atoms, p is the average number of moles of alkylene oxide added, and is a number from 1 to 30, q is 1 or 2, M 2 represents a hydrogen atom, an alkali metal, an alkaline earth metal, ammonium, or an organic ammonium.) A copolymer having [2] The copolymer according to [1], wherein the structural unit (B) is derived from a monomer obtained by reacting an unsaturated dicarboxylic acid or its anhydride with a compound represented by the following general formula (3) or (4). R 4 O-(A 1 O) n1 -H (3) R 4 O-(A 1 O) n1 -NH2(4) (In the formula, R 4 , A 1 , and n1 have the same meanings as described above.) [3] The copolymer according to [1] or [2], wherein the ratio of each structural unit in all the structural units of the copolymer is 1 to 30% by mass of the structural unit (A), 20 to 85% by mass of the structural unit (B), and 1 to 30% by mass of the structural unit (C). [4] The copolymer according to any one of [1] to [3], having a weight average molecular weight of 10,000 or more and 50,000 or less. [5] A pigment dispersant containing the copolymer according to any one of [1] to [4]. [6] A pigment dispersion liquid containing the copolymer according to any one of [1] to [4], a pigment, and a dispersion medium.

Advantages of the Invention

[0008] By using the copolymer of the present invention and the pigment dispersant containing the same, a pigment dispersion liquid excellent in initial dispersibility and dispersion stability of the pigment and having little foaming can be obtained.

Modes for Carrying Out the Invention

[0009] Hereinafter, the copolymer, pigment dispersant, and pigment dispersion of the present invention will be described in detail.

[0010] <Structural unit (A)> The copolymer of the present invention has a structural unit (A) derived from a styrenic monomer. Examples of the styrenic monomer include aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, styrene nuclear-substituted with halogen, 1-vinylnaphthalene, p-methylstyrene, p-propylstyrene, p-cyclohexylstyrene, and p-dodecylstyrene. Among these, styrene or α-methylstyrene is preferred.

[0011] In the total structural units of the copolymer of the present invention, the proportion of the structural unit (A) is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, from the viewpoint of making the adsorption to the pigment surface stronger and enhancing the drying property of the aqueous pigment dispersion, and is preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less, from the viewpoint of the dispersion stability of the aqueous pigment dispersion.

[0012] <Structural unit (B)> The copolymer of the present invention has a structural unit (B) represented by the general formula (1).

[0013] [Chemical formula] (In the formula, R 1 , R 2 , and R 3 are each independently a hydrogen atom, a hydrocarbon group having 1 to 10 carbon atoms, -(CH2) m2 -COOM 1 , or -(CH2) m2 -COX 2 -(A 2 O) n2 -R 5represents, provided that one of them is -(CH2) m2 -COOM 1 or -(CH2) m2 -COX 2 -(A 2 O) n2 -R 5 represents, M 1 represents a hydrogen atom, an alkali metal, an alkaline earth metal, ammonium, or an organic ammonium. m1 and m2 are each independently 0 or 1 X 1 and X 2 are each independently -O-, or -NH-, or, R 1 or R 2 and X 1 together represent -CON<, A 1 and A 2 are each independently an alkylene group having 2 to 4 carbon atoms n1 and n2 are each independently a number from 3 to 100 R 4 and R 5 each independently represent a hydrocarbon group having 1 to 24 carbon atoms.)

[0014] In general formula (1), A 1 O and A 2 O each independently represent an alkyleneoxy group having 2 to 4 carbon atoms, specifically, an ethyleneoxy group, a propyleneoxy group, and a butyleneoxy group. A 1 O and A 2 O may be composed only of an ethyleneoxy group, a propyleneoxy group, or a butyleneoxy group, or may contain two or more of these groups. When containing two or more groups, their addition forms may be either random addition or block addition. n1 and n2 represent the average number of moles of added alkyleneoxy groups, which is a number from 3 to 100. From the viewpoint of providing a steric repulsion between pigment particles and suppressing the aggregation of pigment particles, it is preferably a number from 10 to 80, more preferably a number from 20 to 70.

[0015] In general formula (1), R 4 and R 5 each independently represent a hydrocarbon group having 1 to 24 carbon atoms, and specifically include a linear or branched alkyl group, an alkenyl group, and an aryl group. Among these, from the viewpoint of the dispersion stability of the pigment dispersion, an alkyl group having 1 to 4 carbon atoms is preferable, and a methyl group is particularly preferable.

[0016] As the structural unit (B), it may be derived from a monomer (b) obtained by reacting an unsaturated dicarboxylic acid or its anhydride with a compound having a polyoxyalkylene group represented by the following general formula (3) or (4), or may be a grafted product obtained by reacting a compound represented by the general formula (3) or (4) after copolymerizing an unsaturated dicarboxylic acid or its anhydride with another monomer. However, from the viewpoint of the ease of manufacturing the copolymer, those derived from the monomer (b) are preferable. R 4 O-(A 1 O) n1 -H (3) R 4 O-(A 1 O) n1 -NH2(4) (In the formula, R 4 , A 1 , and n1 have the same meanings as described above.)

[0017] Examples of the unsaturated dicarboxylic acid or its anhydride include maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic acid, citraconic anhydride, and the like. These can be used alone or in combination of two or more.

[0018] Examples of the monomer (b) include a monoester or diester obtained by an esterification reaction between an unsaturated dicarboxylic acid and the compound represented by the general formula (3), and a compound obtained by an amidation or imidization reaction between an unsaturated dicarboxylic acid and the compound represented by the general formula (4), and they can be obtained by known methods. Specifically, methoxypolyethylene glycol monomaleate, methoxypolypropylene glycol monomaleate, methoxypolyethylene glycol polypropylene glycol monomaleate, methoxypolyethylene glycol dimaleate, methoxypolypropylene glycol dimaleate, methoxypolyethylene glycol polypropylene glycol dimaleate, methoxypolyethylene glycol monoitaconate, methoxypolypropylene glycol monoitaconate, methoxypolyethylene glycol polypropylene glycol monoitaconate, methoxypolyethylene glycol diitaconate, methoxypolypropylene glycol diitaconate, methoxypolyethylene glycol polypropylene glycol diitaconate, methoxypolyethylene glycol monofumarate, methoxypolypropylene glycol monofumarate, methoxypolyethylene glycol polypropylene glycol monofumarate, methoxypolyethylene glycol difumarate, methoxypolypropylene glycol difumarate, methoxypolyethylene glycol polypropylene glycol difumarate, an amidated or imidized product of methoxypolyethylene glycol polypropylene glycol monoamine and an unsaturated dicarboxylic acid, and the like can be mentioned. These monomers can be used alone or in combination of two or more.

[0019] In all the structural units of the copolymer of the present invention, the proportion of the structural unit (B) is preferably 20% by mass or more, more preferably 30% by mass or more, still more preferably 40% by mass or more, from the viewpoint of suppressing aggregation between pigment particles and imparting dispersion stability, and preferably 85% by mass or less, more preferably 80% by mass or less, still more preferably 75% by mass or less, from the viewpoints of the drying property and defoaming property of the aqueous pigment dispersion.

[0020] <Structural unit (C)> The copolymer of the present invention has a structural unit (C) derived from a monomer (c) having a phosphate group represented by the general formula (2).

[0021]

Chemical formula

[0022] In the general formula (2), A 3 O represents an alkyleneoxy group having 2 to 4 carbon atoms, and specifically, an ethyleneoxy group, a propyleneoxy group, and a butyleneoxy group can be mentioned. A 3 O may be composed only of an ethyleneoxy group, a propyleneoxy group, or a butyleneoxy group, or may contain two or more of these groups. From the viewpoint of low foaming property, it is preferable that the propyleneoxy group is contained in an amount of 50% by mass or more based on the total mass of the alkyleneoxy groups, and more preferably 70% by mass or more. When two or more groups are contained, their addition forms may be either random addition or block addition. p represents the average number of moles of alkylene oxide added, which is a number from 1 to 30. From the viewpoint of the dispersibility of the pigment, it is preferably a number from 2 to 20, and more preferably a number from 3 to 10.

[0023] Examples of the monomer (c) include a phosphoric acid monoester (when q in the formula (2) is 1), a phosphoric acid diester (when q is 2), or a mixture thereof. When using a mixture of a monoester and a diester, from the viewpoint of controlling the molecular weight during polymerization, the ratio of the monoester is preferably 60 mol% or more, and more preferably 80 mol% or more.

[0024] The monomer (c) can be produced by a known method. For example, it can be obtained by adding an alkylene oxide to a hydroxyalkyl (meth) acrylate and then reacting the resulting adduct with a phosphorylating agent to effect phosphoric esterification.

[0025] Examples of the hydroxyalkyl (meth) acrylate include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and the like.

[0026] Examples of the alkylene oxide include ethylene oxide, propylene oxide, butylene oxide, and the like. These can be used alone or in combination of two or more. By reacting these alkylene oxides, -(A 3 O)- in the general formula (2) is formed.

[0027] Examples of the phosphorylating agent include known phosphorus compounds such as orthophosphoric acid, phosphorus pentoxide (phosphoric anhydride), polyphosphoric acid, phosphorus oxychloride, and the like. These can be used alone or in combination of two or more.

[0028] In all the structural units of the copolymer of the present invention, the proportion of the structural unit (C) is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less, from the viewpoints of the dispersibility of the pigment and low foaming property.

[0029] <Other structural units> The copolymer of the present invention may contain other structural units other than the structural units (A), (B), and (C) as long as the effects of the present invention are not impaired. Examples of other structural units include structural units derived from unsaturated dicarboxylic acids such as acrylic acid, methacrylic acid or salts thereof, maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic acid, citraconic anhydride; (meth)acrylic acid alkyl ester compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate; (meth)acrylic acid ester compounds containing an aromatic ring such as benzyl (meth)acrylate, naphthyl (meth)acrylate; and (meth)acrylic acid hydroxyalkyl ester compounds such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate.

[0030] In all the constituent units of the copolymer of the present invention, the proportion of the other constituent units is preferably 35% by mass or less, more preferably 30% by mass or less, still more preferably 25% by mass or less, from the viewpoint of expressing the effects of the present invention.

[0031] <Method for Producing Copolymer> The copolymer of the present invention can be obtained by a known method such as polymerizing a monomer mixture containing a styrenic monomer (a), the monomer (b), and a phosphate ester monomer (c) by a solution polymerization method. Examples of the solvent used in solution polymerization include aromatic solvents such as toluene and xylene; alcohols such as ethanol and 2-propanol; ketone solvents such as acetone and methyl ethyl ketone; ether solvents such as tetrahydrofuran and diethylene glycol dimethyl ether; and ester solvents such as ethyl acetate, n-butyl acetate, isobutyl acetate, methoxypropyl acetate, ethylene glycol monomethyl ether acetate, and butyl carbitol acetate. The amount of the solvent is preferably 50 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of the total amount of the monomers.

[0032] As the polymerization initiator, known radical polymerization initiators can be used, such as azo polymerization initiators, hydroperoxides, dialkyl peroxides, diacyl peroxides, ketone peroxides, and the like. The amount of the polymerization initiator is preferably 1 mol or more, more preferably 2 mol or more, still more preferably 3 mol or more, and preferably 15 mol or less, more preferably 12 mol or less, still more preferably 9 mol or less, based on 100 mol of the total amount of the monomers. The polymerization reaction is preferably carried out in a nitrogen atmosphere, the reaction temperature is preferably 60°C or higher and 180°C or lower, and the reaction time is preferably 0.5 hours or more and 20 hours or less.

[0033] During the polymerization, a chain transfer agent may be further used. Examples of the chain transfer agent include mercaptans such as octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-tetradecyl mercaptan, mercaptoethanol, 3-mercapto-1,2-propanediol, and mercaptosuccinic acid; thiuram disulfides; hydrocarbons; unsaturated cyclic hydrocarbon compounds such as α-methylstyrene; unsaturated heterocyclic compounds; and the like. These can be used alone or in combination of two or more.

[0034] <Copolymer> In the copolymer of the present invention, the sequences of the structural unit (A), the structural unit (B), and the structural unit (C) may be any of random, block, or graft. From the viewpoint of ease of copolymer production, it is preferably at least one selected from random and block. Further, from the viewpoint of the dispersion stability of the aqueous pigment dispersion, it is preferable that the acid groups in the copolymer are partially neutralized or completely neutralized with a basic compound. Examples of the basic compound include organic amine compounds such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, 2-aminoethanol, and 2-dimethylaminoethanol, ammonia, hydroxides and carbonates of alkali metals or alkaline earth metals, and the like. These can be used alone or in combination of two or more.

[0035] From the perspective of improving dispersibility, the weight-average molecular weight of the copolymer of the present invention is preferably 10,000 or more, more preferably 15,000 or more, still more preferably 18,000 or more. And from the perspectives of improving dispersibility and ease of manufacturing the copolymer, it is preferably less than 50,000, more preferably 40,000 or less, still more preferably 30,000 or less. The method for measuring the weight-average molecular weight is the method described in the examples.

[0036] <Pigment dispersant> Since the copolymer of the present invention can impart excellent initial dispersibility and dispersion stability to pigments, it can be suitably used as a pigment dispersant. In addition to the above copolymer, the pigment dispersant of the present invention may contain unreacted monomers, by-products, reaction solvents, water and organic solvents during the production of the copolymer, as long as the effects of the present invention are not inhibited.

[0037] <Pigment dispersion> The pigment dispersion of the present invention can be obtained by dispersing pigment powders, raw ore of the powders or coarse particles in a dispersion medium such as an aqueous medium using the copolymer of the present invention. Examples of pigments include organic pigments and inorganic pigments. Examples of organic pigments include soluble azo pigments such as β-naphthol-based, β-oxynaphthoic acid-based anilide-based, acetoacetic acid anilide-based, pyrazolone-based, etc.; insoluble azo pigments such as β-naphthol-based, β-oxynaphthoic acid-based, β-oxynaphthoic acid anilide-based, acetoacetic acid anilide-based monoazo, acetoacetic acid anilide-based disazo, pyrazolone-based, etc.; phthalocyanine-based pigments such as copper phthalocyanine blue, halogenated copper phthalocyanine blue, sulfonated copper phthalocyanine blue, metal-free phthalocyanine, etc.; polycyclic or heterocyclic compounds such as isodrinone-based, quinacridone-based, dioxazine-based, perinone-based and perylene-based. Examples of inorganic pigments include lead yellow, zinc yellow, ultramarine blue, barium sulfate, cadmium red, titanium oxide, zinc white, red iron oxide, alumina, calcium carbonate, ultramarine, carbon black, graphite and titanium black.

[0038] The dispersion medium is not particularly limited and examples include water, a mixed solution of water and a water-soluble organic solvent such as ethanol or ethylene glycol, and an organic solvent, with water being preferred. Examples of the organic solvent include xylene, ethyl acetate, toluene, tetrahydrofuran, methyl ethyl ketone, acetone, butyl cellosolve, dimethylformamide, n-propanol, ethanol, dimethyl sulfoxide, n-butanol, and methanol.

[0039] Although there is no particular regulation on the content of the pigment in the pigment dispersion of the present invention, it is usually 50 to 90% by mass, preferably 55 to 85% by mass, and more preferably 60 to 80% by mass. Also, although there is no particular regulation on the content of the copolymer of the present invention in the pigment dispersion, it is usually preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, and particularly preferably 0.05 to 3 parts by mass with respect to 100 parts by mass of the pigment.

[0040] As a method for obtaining a pigment dispersion using the pigment dispersant of the present invention, a normal slurrying method is used. For example, a method of adding a pigment to an aqueous solution in which the pigment dispersant of the present invention is dissolved and stirring and mixing, a method of adding water and the pigment dispersant of the present invention to the pigment and stirring and mixing, etc. can be mentioned. As a method of stirring and mixing, for example, a commonly used wet grinder such as a high-speed disper, a homomixer, a ball mill, or a bead mill can be used.

Examples

[0041] The present invention will be described in more detail based on examples below, but the present invention is not limited thereto. Unless otherwise specified, the blending amounts are shown in parts by mass.

[0042] <Measurement method of weight average molecular weight> In this example, gel permeation chromatography (hereinafter also referred to as "GPC") was used to measure the weight average molecular weight. The sample was diluted with THF (tetrahydrofuran) to prepare a solution with a solid content concentration of 0.05% by mass of the sample as a sample solution, and 20 μL thereof was used for measurement. Using THF as an eluent, measurement was performed by GPC (apparatus: "HLC-8320GPC" manufactured by Tosoh Corporation, detector: differential refractometer (attached to the apparatus), column: "TSKgel SuperMultipore HZ-M × 2 pieces, TSKgel SuperMultipore HZ1000 × 1 piece, TSKgel SuperMultipore HZ2000 × 1 piece" manufactured by Tosoh Corporation, column temperature: 40 ° C, eluent flow rate: 1 mL / min). As a standard substance, standard polystyrene ("PStQuick" manufactured by Tosoh Corporation) was used.

[0043] [Production Example 1] 44 g of maleic acid, 756 g of polyethylene glycol monomethyl ether (methoxy PEG2000 manufactured by Toho Chemical Industry Co., Ltd. with an average molecular weight of 2,000), and 4 g of p-toluenesulfonic acid were charged into an autoclave equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet tube, and stirred and reacted at 150 ° C for 15 hours under a nitrogen stream. After cooling, a maleic acid esterified product (b-1) was obtained.

[0044] [Production Example 2] A maleic acid esterified product (b-2) was obtained in the same manner as in Production Example 1, except that polyethylene glycol polypropylene glycol monomethyl ether (EO / PO ratio = 2.4 / 1.0, molecular weight of about 2,000) was used instead of polyethylene glycol monomethyl ether.

[0045] [Production Example 3] A maleic acid amidated product (b-3) was obtained in the same manner as in Production Example 1, except that monoamine-terminated polypropylene glycol polyethylene glycol monomethyl ether (Jeffamine M2070 (manufactured by Huntsman)) was used instead of polyethylene glycol monomethyl ether.

[0046] [Production Example 4] Into an autoclave equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas inlet tube, 49 g of itaconic acid, 752 g of polyethylene glycol monomethyl ether (methoxy PEG2000, manufactured by Toho Chemical Industry Co., Ltd., average molecular weight 2,000), and 4 g of p-toluenesulfonic acid were charged, and the mixture was stirred and reacted at 150 °C for 15 hours under a nitrogen stream. After cooling, an itaconic acid esterified product (b-4) was obtained.

[0047] [Production Example 5] An itaconic acid esterified product (b-5) was obtained in the same manner as in Production Example 4, except that polyethylene glycol polypropylene glycol monomethyl ether (EO / PO ratio = 2.4 / 1.0, molecular weight about 2,000) was used instead of polyethylene glycol monomethyl ether.

[0048] [Production Example 6] An itaconic acid esterified product (b-6) was obtained in the same manner as in Production Example 4, except that monoamine-terminated polypropylene glycol polyethylene glycol monomethyl ether (Jeffamine M2070, manufactured by Huntsman) was used instead of polyethylene glycol monomethyl ether.

[0049] The following were used as the phosphate ester monomer (c). · Monomer (c-1): Methacryloyloxy polyoxypropylene phosphate (In General Formula (2), R 6 : Methyl group, A 3 : Propylene group, p: 5, q: 1) · Monomer (c-1): Methacryloyloxy polyoxyethylene phosphate (In General Formula (2), R 6 : Methyl group, A 3 : Ethylene group, p: 5, q: 1)

[0050] [Example 1] Into a five-necked flask equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas inlet tube, 2.7 g of styrene, 27.8 g of maleic acid ester (b-1), 5.1 g of butyl acrylate, 0.1 g of dodecyl mercaptan, and 12.2 g of methoxypropyl acetate were charged as an initial charge monomer solution. The temperature was raised to 80 °C under a nitrogen stream, and while maintaining the same temperature, a mixed solution of 0.2 g of azobisisobutyronitrile and 11.9 g of methoxypropyl acetate as an initiator solution was added dropwise and reacted for 2 hours. Next, while maintaining the same temperature, a mixed solution of 0.4 g of methyl methacrylate, 3.7 g of phosphate ester monomer (c-1), 0.1 g of dodecyl mercaptan, 0.03 g of azobisisobutyronitrile, and 35.7 g of methoxypropyl acetate as a dropwise monomer solution was added dropwise and reacted for 4 hours to obtain a solution of copolymer 1.

[0051] [Examples 2 to 11, Comparative Examples 1 to 7] Solutions of copolymers 2 to 18 were obtained in the same manner as in Example 1, except that the compositions of the "initial charge monomer", "initiator solution", and "dropwise monomer solution" were changed according to the description in Table 1. The non-volatile content and the weight average molecular weight are as shown in Table 1. The abbreviations in the table mean the following. ·St: Styrene ·AB: Butyl acrylate ·MMA: Methyl methacrylate ·MAA: Methacrylic acid ·PGMEA: Methoxypropyl acetate ·AIBN: Azobisisobutyronitrile ·DM: Dodecyl mercaptan

[0052] (Method for preparing an aqueous pigment dispersion) 2.5 g (1.0 g in terms of solid content) of the solution of copolymer 1 and 26.5 g of ion-exchanged water were placed in a 50 mL glass container, and 2-dimethylaminoethanol was added dropwise until the pH reached about 7 for neutralization. The neutralized solution was placed in a 200 mL polypropylene container, and 71 g of titanium dioxide (Ti-Pure R-902 manufactured by Kemira) was also placed in the same container. Subsequently, it was mixed and stirred (2,000 rpm × 15 minutes) with a homodisper to obtain a pigment dispersion. In Examples 2 to 11 and Comparative Examples 1 to 7, pigment dispersions were also prepared in the same process.

[0053] (Evaluation of foaming and dispersibility) As an evaluation of foaming, the foam height immediately after mixing and stirring with a homodisper was measured. As an evaluation of initial dispersibility and dispersion stability, viscosity measurement evaluations were performed immediately after adjusting the obtained pigment dispersion and after standing at 50°C for 7 days. Viscosity measurement was performed at room temperature (25°C) using a ViscoMETER TVB-10, rotor No. 2, and 30 rotations. The results are shown in Table 1.

[0054]

Table 1

[0055] As shown in Table 1, the pigment dispersions of Examples 1 to 11 using the copolymer of the present invention were superior in initial dispersibility and dispersion stability to Comparative Examples 1 to 7, and also had less foaming.

Claims

1. A structural unit (A) derived from a styrene monomer, A structural unit (B) represented by the following general formula (1), 【Chemical 1】 (In the formula, R １ 、 R ２ 、 and R ３ each independently represents a hydrogen atom, a hydrocarbon group having 1 to 10 carbon atoms, -(CH ２ ) ｍ２ -COOM １ or -(CH ２ ) ｍ２ -COX ２ -(A ２ O) ｎ２ -R ５ provided that one of them represents -(CH ２ ) ｍ２ -COOM １ or -(CH ２ ) ｍ２ -COX ２ -(A ２ O) ｎ２ -R ５ and M １ represents a hydrogen atom, an alkali metal, an alkaline earth metal, ammonium, or an organic ammonium. m1 and m2 are each independently 0 or 1, X １ and X ２ are each independently —O—, or —NH—, Or, R １ or R ２ and X １ together represent -CON<, A １ and A ２ each independently represents an alkylene group having 2 to 4 carbon atoms, n1 and n2 are the average number of moles of alkylene oxide added, and are each independently a number from 20 to 100, R ４ and R ５ each independently represents a hydrocarbon group having 1 to 24 carbon atoms.) And, A structural unit (C) derived from a monomer represented by the following general formula (2) 【Chemical 2】 (wherein, R ６ is a hydrogen atom or a methyl group, A ３ is an alkylene group having 2 to 4 carbon atoms, p is the average number of moles of alkylene oxide added, and is a number from 1 to 30, q is 1 or 2, M ２ represents a hydrogen atom, an alkali metal, an alkaline earth metal, ammonium, or an organic ammonium.) A copolymer having The proportion of each structural unit in all the structural units of the copolymer is such that the structural unit (A) is 5 to 30% by mass, the structural unit (B) is 40 to 85% by mass, and the structural unit (C) is 5 to 30% by mass Copolymer.

2. The copolymer according to claim 1, wherein the structural unit (B) is derived from a monomer obtained by reacting an unsaturated dicarboxylic acid or its anhydride with a compound represented by the following general formula (3) or (4). R ４ O-(A １ O) ｎ１ -H (3) R ４ O-(A １ O) ｎ１ -NH ２ (4) (wherein R ４ , A １ , and n1 represent the same meaning as described above.)

3. The copolymer according to claim 1 or 2, having a weight average molecular weight of 10,000 or more and 50,000 or less.

4. A pigment dispersant containing the copolymer according to any one of claims 1 to 3.

5. A pigment dispersion liquid containing the copolymer according to any one of claims 1 to 3, a pigment, and a dispersion medium.

Images