Pigment dispersion liquid, aqueous coating composition, and methods for producing pigment dispersion liquid and aqueous coating composition

Abstract

A pigment dispersion liquid containing a copolymer (A) having a first segment (a1) derived from a nitrogen-containing polymerizable unsaturated monomer having a tertiary amino group and / or a nitrogen-containing heterocyclic group, and a second segment (a2) derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain, a hydrocarbon group-containing acidic compound (B), a pigment (C), and an aqueous solvent (D), and a hydrocarbon group-containing acidic compound (B) having a C5-23 saturated or unsaturated hydrocarbon group (b1) and at least one acid group (b2) selected from the group consisting of a carboxyl group, a phosphate group, a sulfonic acid group, and a phenol group.

Description

TECHNICAL FIELD

[0001] The present application relates to a pigment dispersion liquid and an aqueous coating composition, and a method for producing the same. BACKGROUND

[0002] In recent years, in order to protect the environment, reduction of emission of volatile organic compounds (VOC) from factories and the like is required. As one of the methods for reducing the emission of VOC, an aqueous coating composition has been proposed. However, pigments are generally not easily wetted by an aqueous solvent, and have poor dispersibility.

[0003] In this regard, Patent Literature 1 discloses an aqueous coating composition characterized by containing a copolymer of a plurality of monomers, a pigment, and an acrylic resin containing an acid group and a hydroxyl group, the plurality of monomers including a polymerizable unsaturated monomer having a cationic functional group represented by a specific formula.

[0004] PRIOR ART DOCUMENTS PATENT LITERATURE Patent Literature 1: Japanese Patent Application Laid-Open No. 2014-5399 SUMMARY

[0005] PROBLEMS TO BE SOLVED BY THE INVENTION However, in the copolymer of Patent Literature 1, it is difficult to sufficiently and stably disperse pigments.

[0006] MEANS FOR SOLVING THE PROBLEMS In order to solve the above problems, the present application provides the following solutions.

[0007] [1] A pigment dispersion liquid comprising: a copolymer (A), a hydrocarbyl group-containing acidic compound (B), a pigment (C), and an aqueous solvent (D), the copolymer (A) has: a first segment (al) derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amino group and a nitrogen-containing heterocyclic group, and a second segment (a2) derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain, the hydrocarbyl group-containing acidic compound (B) has: a saturated or unsaturated hydrocarbyl group (bl) having a carbon number of 5 to 23, and at least one acid group (b2) selected from a carboxyl group, a phosphoric acid group, a sulfonic acid group, and a phenolic group.

[0008] [2] The pigment dispersion liquid according to the above [1], wherein a ratio of an acid group equivalent possessed by the hydrocarbyl group-containing acidic compound (B) to a total equivalent of a tertiary amino group and a nitrogen-containing heterocyclic group possessed by the copolymer (A) (acid group / tertiary amino group and nitrogen-containing heterocyclic group) is 0.5 or more and 2 or less.

[0009] [3] The pigment dispersion liquid according to the above [1] or [2], wherein the copolymer (A) further has a third segment (a3) derived from a polymerizable unsaturated monomer other than the nitrogen-containing polymerizable unsaturated monomer and the polymerizable unsaturated monomer having a polyoxyalkylene chain, the copolymer (A) has, the first segment (al) has a mass ratio of 5 mass% or more and 30 mass% or less, the second segment (a2) has a mass ratio of 20 mass% or more and 80 mass% or less, the third segment (a3) has a mass ratio of 10 mass% or more and 60 mass% or less.

[0010] [4] The pigment dispersion liquid according to the above [3], wherein the third segment (a3) contains a segment (a31) derived from a hydroxyl group-containing polymerizable saturated monomer, the segment (a31) in the copolymer (A) has a mass ratio of 10 mass% or more and 30 mass% or less.

[0011] [5] An aqueous coating composition, comprising: the pigment dispersion liquid according to the above [1] or [2]; and a coating film-forming resin.

[0012] [6] A method for producing a pigment dispersion liquid, comprising: a step of adding and mixing a hydrocarbon group-containing acidic compound (B) in a first mixture containing an aqueous solvent (D) and a copolymer (A) to obtain a second mixture; and a step of adding and mixing a pigment (C) in the second mixture, the copolymer (A) has: a first segment (al) derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amino group and a nitrogen-containing heterocyclic group, and a second segment (a2) derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain, the hydrocarbon group-containing acidic compound (B) has: a saturated or unsaturated hydrocarbon group (bl) having a carbon number of 5 to 23, and at least one acid group (b2) selected from a carboxyl group, a phosphoric acid group, a sulfonic acid group, or a phenolic group.

[0013] [7] A method for producing an aqueous coating composition, comprising a step of mixing a pigment dispersion liquid produced by the method according to the above [6] and a coating film-forming resin.

[0014] Effects of the Invention According to the present disclosure, there is provided a pigment dispersion liquid which is low in viscosity and excellent in pigment dispersibility regardless of the kind of pigment. DETAILED DESCRIPTION

[0015] A pigment dispersant is an additive for uniformly dispersing a pigment in a solvent, and has a hydrophilic site and a hydrophobic site like a surfactant. The hydrophilic site is various in kind. The hydrophilic site can be ionized to generate an anion or a cation, and there are cases where it does not have ionic dissociation property.

[0016] A pigment generally has an acid site, a basic site, or an inert site on its surface, and shows properties of acidity, basicity, hydrophobicity, or hydrophilicity. These properties are not clearly distinguished between each pigment, and there are cases where a compound property is present. It is difficult to select a pigment dispersant suitable for a pigment having various properties described above. Therefore, it is desired to have a pigment dispersant which can be used for any pigment. However, if one pigment dispersant (compound) has a plurality of functional groups which can correspond to each site described above, there arise problems such as an increase in viscosity of a pigment dispersion liquid due to association or the like. In the case where a plurality of pigment dispersants are used in combination, there also arise adverse cases in viscosity increase of a pigment dispersion liquid, or in affinity of a pigment dispersant to a solvent or the like. An increase in viscosity of a pigment dispersion liquid results in difficulty in preparation of a paint composition, and also becomes a cause of reduction in dispersibility of a pigment in a pigment dispersion liquid.

[0017] The smaller the particle size of a certain pigment in a coating film (i.e., the higher the dispersibility of the pigment in a paint composition, and further in a pigment dispersion liquid), the higher the color development of the coating film. Generally, the smaller the particle size of a pigment (the higher the dispersibility of the pigment), the higher the viscosity of a pigment dispersion liquid. That is, in order to improve the color development of a coating film by improving the dispersibility of a pigment in a pigment dispersion liquid, the viscosity of the pigment dispersion liquid increases. Therefore, it is difficult to mix the pigment dispersion liquid with a coating film-forming resin, and as a result, the dispersibility of the pigment in a paint composition can be reduced. Generally, the improvement of the color development of a coating film (the improvement of the dispersibility of a pigment) and the reduction in viscosity of a pigment dispersion liquid can be said to be in a trade-off relationship.

[0018] The present disclosure has found a combination of compounds (pigment dispersants) which does not cause an increase in viscosity regardless of the properties of a pigment, and can disperse a pigment well in a polar solvent (aqueous solvent). A paint composition obtained using the pigment dispersion liquid according to the present disclosure has high color development.

[0019] The pigment dispersion liquid according to the present disclosure contains a copolymer (A), a hydrocarbon group-containing acidic compound (B) (hereinafter, sometimes referred to as "organic acid (B)"), a pigment (C), and an aqueous solvent (D). The copolymer (A) has a first segment (a1) derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amino group and a nitrogen-containing heterocyclic group, and a second segment (a2) derived from a polymerizable unsaturated monomer having a polyoxyalkylene chain. The organic acid (B) has a saturated or unsaturated hydrocarbon group (b1) having a carbon number of 5 to 23, and at least one acid group (b2) selected from a carboxylic acid group, a phosphoric acid group, a sulfonic acid group, and a phenolic group.

[0020] In the copolymer (A), the tertiary amino group and / or the nitrogen-containing heterocyclic group (hereinafter, sometimes referred to as "nitrogen-containing group") of the first segment (a1) and the polyoxyalkylene chain of the second segment (a2) are each disposed as a side chain. The main chain of the copolymer (A) is composed of carbon-carbon bonds. In the organic acid (B), the acid group (b2) is generally located at the terminal of the hydrocarbon group (b1).

[0021] The nitrogen-containing group in the first segment (a1) of the copolymer (A) generates a cation in the aqueous solvent. The acid group of the organic acid (B) generates an anion in the aqueous solvent. Thus, the copolymer (A) and the organic acid (B) can exist as counter ions to each other in the aqueous solvent. The saturated or unsaturated hydrocarbon group (hereinafter, sometimes simply referred to as "hydrocarbon group") of the organic acid (B) has substantially no ionic dissociation property.

[0022] With the combination of the copolymer (A) and the organic acid (B), the dispersibility of various pigments is improved without causing an increase in viscosity. The reason for this is considered as follows, but is not bound by a particular theory.

[0023] In the case where the pigment (C) has an acidic property (hereinafter, for convenience, sometimes referred to as "acidic pigment". Typical examples are carbon blacks), the copolymer (A) can be adsorbed to the pigment (C) through the nitrogen-containing group. Specifically, the nitrogen-containing group is adsorbed to the pigment (C), and the polyoxyalkylene chain is disposed outside the pigment (C). Further, the polyoxyalkylene chain is arranged in a manner extending to the outside of the pigment (C) through chemical repulsion and steric repulsion from the hydrophobic main chain of the copolymer (A). Through this polyoxyalkylene chain extending to the outside, the coagulation between the pigments (C) to which the copolymer (A) is adsorbed can be suppressed.

[0024] Further, in the vicinity of the nitrogen-containing group, the acid group of the organic acid (B) can exist as a counter ion. Thus, the charge balance is maintained, and the coagulation between the pigments (C) is further suppressed.

[0025] Further, both the main chain of the copolymer (A) and the hydrocarbon group of the organic acid (B) are hydrophobic and have high affinity. Therefore, in addition to the copolymer (A), the organic acid (B) can also be firmly adsorbed to the pigment (C). On the other hand, the polyoxyalkylene chain has high affinity with the aqueous solvent (D). That is, it is considered that the pigment (C) adsorbed with the copolymer (A) and the organic acid (B) is dispersed in the aqueous solvent (D) in a state where the hydrophobic portions of the copolymer (A) and the organic acid (B) are surrounded by the hydrophilic polyoxyalkylene chain, and thus is not easily aggregated, and it is also considered that the state can be maintained unchanged.

[0026] Viewed from another perspective, the copolymer (A) having the polyoxyalkylene chain allows the organic acid (B) having a hydrocarbon group with a long chain to be uniformly dispersed in the aqueous solvent (D). The organic acid (B) having the hydrocarbon group (bl) can reduce the surface tension of the aqueous solvent (D). By reducing the surface tension of the aqueous solvent (D), the wettability of the pigment (C) to the aqueous solvent is improved. As described above, the organic acid (B) and the pigment (C) are uniformly dispersed in the aqueous solvent (D), and thus the effect of reducing the surface tension is further improved, and the wettability of the pigment (C) to the aqueous solvent (D) can be further improved. As a result, the aggregation force between the pigments (C) is further weakened, and the pigment dispersibility in the aqueous solvent (D) is further improved. The dispersion stability of the pigment (C) is also improved.

[0027] By using the organic acid (B) in combination, the copolymer (A) can be selected more freely as long as it has the first segment (al) and the second segment (a2). In other words, when the aqueous paint composition is prepared, the degree of freedom in design is expanded, and a copolymer (A) more suitable for the pigment (C) can be used.

[0028] In the case where the pigment (C) has basic properties (hereinafter, sometimes referred to as "basic pigment" for convenience), the organic acid (B) is adsorbed to the pigment (C) via the acid group (b2). A nitrogen-containing group as a counter ion can exist in the vicinity of the acid group. That is, in this case, the copolymer (A) and the organic acid (B) can exist in close proximity to each other. Therefore, the polyoxyalkylene chain of the copolymer (A) is arranged in a manner extending to the outside of the pigment (C) by chemical and steric repulsion with the hydrocarbon group (bl) of the organic acid (B) and the hydrophobic main chain of the copolymer (A), and the aggregation between the pigments is suppressed. Further, as in the case of the acidic pigment, the pigment dispersibility, and further the dispersion stability of the pigment (C) is improved by the effect of reducing the surface tension of the aqueous solvent, and the like, caused by the organic acid (B).

[0029] When pigment (C) has hydrophobic properties (hereinafter, for convenience, it is sometimes referred to as "hydrophobic pigment," typically phthalocyanine blue), organic acids (B) are adsorbed onto pigment (C) through hydrophobic interactions with the hydrocarbon group (B1). Thus, through the same effect as in the case of basic pigments, the dispersibility and dispersion stability of pigment (C) are improved.

[0030] As described above, various pigments (C) can be dispersed by combining a copolymer (A) with groups that readily adsorb onto acidic pigments and an organic acid (B) with groups that readily adsorb onto basic or hydrophobic pigments. Furthermore, by having the copolymer (A) and organic acid (B) exist as counterions to each other, charge balance is maintained, the surface tension reduction effect is enhanced, and pigment (C) can remain stably in a finely dispersed state in the pigment dispersion. In addition, by placing the nitrogen-containing and acid groups in different compounds, interactions between them are suppressed, thus inhibiting an increase in the viscosity of the pigment dispersion. Since the polyoxyethylene chain is non-ionic and dissociable, it is difficult for it to interact with the nitrogen-containing groups within the same compound.

[0031] Although the pigment dispersion disclosed herein contains pigment in a finely micronized state, it has low viscosity. Therefore, when preparing waterborne coating compositions, the pigment dispersion and film-forming resin can be easily mixed, and the pigment dispersibility in the waterborne coating composition is also improved.

[0032] [Pigment Dispersion] The pigment dispersion disclosed herein comprises a copolymer (A), an organic acid (B), a pigment (C), and an aqueous solvent (D). The copolymer (A) has a first segment (a1) derived from a nitrogen-containing polymeric unsaturated monomer having a nitrogen-containing group and a second segment (a2) derived from a polymeric unsaturated monomer having a polyoxyolefin chain. The organic acid (B) has a hydrocarbon group (b1) having 5 to 23 carbon atoms and an acid group (b2). The pigment dispersion comprises an aqueous solvent (D), which is aqueous.

[0033] Through the aforementioned copolymer (A) and organic acid (B), various pigments (C) can be well dispersed in an aqueous solvent (D) without causing an increase in viscosity. That is, the pigment dispersions involved in this disclosure are of low viscosity, in which the pigments are fully dispersed (in other words, the average particle size of the pigments is small).

[0034] The copolymer (A) and the organic acid (B) can be blended, for example, in a ratio (acid group / nitrogen group) of the equivalent amount of acid groups (b2) in the organic acid (B) to the total equivalent amount of nitrogen-containing groups in the copolymer (A) being 0.5 or more and 2 or less. If the equivalent ratio (acid group / nitrogen group) is 0.5 or more, it is easier to obtain an improvement in pigment dispersibility. If the equivalent ratio (acid group / nitrogen group) is 2 or less, the dispersion effect of the organic acid (B) caused by the copolymer (A) is further improved, and it is easier to obtain an improvement in dispersion stability. The equivalent ratio (acid group / nitrogen group) can be 0.6 or more, or 0.8 or more. The equivalent ratio (acid group / nitrogen group) can be 1.8 or less, or 1.5 or less.

[0035] For example, 30 parts by mass and 3000 parts by mass of pigment (C) are blended into 100 parts by mass of the solid content of copolymer (A). The above-mentioned blending amount of pigment (C) can be 45 parts by mass or more, or 60 parts by mass or more. The above-mentioned blending amount of pigment (C) can be 2800 parts by mass or less, or 2700 parts by mass or less.

[0036] The solid content concentration of the pigment dispersion is, for example, 5% by mass or more and 90% by mass or less. The solid content concentration of the pigment dispersion can be 8% by mass or more, or 10% by mass or more. The solid content concentration of the pigment dispersion can be 88% by mass or less, or 85% by mass or less.

[0037] The concentration of solid components in the pigment dispersion was determined according to the JIS K 5601-1-2 method for determining residual content upon heating.

[0038] Pigment (C) is micro-dispersed in the pigment dispersion. The average particle size of pigment (C) in the pigment dispersion can be, for example, more than 90% and less than 1000% of the primary particle size of pigment (C). If the average particle size of pigment (C) in the pigment dispersion is within this range, the aggregation of pigment (C) is suppressed, and it can be said that micronization has occurred. The average particle size of pigment (C) in the pigment dispersion can be less than 900% or less than 800% of the primary particle size of pigment (C).

[0039] The average particle size refers to the volume average particle size D50. The volume average particle size D50 is the 50% average particle size in the volume-based particle size distribution, as measured using a particle size distribution measuring device based on laser diffraction / scattering (e.g., trade name: UPA-150, manufactured by Microtrac).

[0040] Pigment dispersions have various viscosities depending on the type of pigment. For ease of preparation of coating compositions, a low viscosity is preferred for the pigment dispersion. The viscosity of a pigment dispersion at 25°C and 5 rpm can be, for example, below 5000 cps or below 2000 cps. The lower limit of the viscosity of the pigment dispersion is appropriately set according to the type and size of the pigment (C), and is not particularly limited.

[0041] Compared to other pigment dispersions that disperse the same pigment to the same particle size using pigment dispersants other than copolymer (A) and / or organic acid (B), the viscosity of the pigment dispersion disclosed herein is sufficiently low. For example, the viscosity of the pigment dispersion disclosed herein may be less than 1 / 2 or less than 1 / 3 of the viscosity of the aforementioned other pigment dispersions. Alternatively, compared to other pigment dispersions that disperse to a degree where viscosity does not increase using pigment dispersants other than copolymer (A) and / or organic acid (B), the particle size of the pigment in the pigment dispersion disclosed herein can be smaller. For example, the average particle size of the pigment contained in the pigment dispersion disclosed herein may be less than 80%, less than 75%, or less than 70% of the average particle size of the pigment contained in the aforementioned other pigment dispersions.

[0042] (A) copolymer The copolymer (A) has: a first segment (a1) derived from a nitrogen-containing polymeric unsaturated monomer (hereinafter, sometimes referred to as "nitrogen-containing monomer") having a nitrogen-containing group, and a second segment (a2) derived from a polymeric unsaturated monomer (hereinafter, sometimes referred to as "hydrophilic monomer") having a polyoxyethylene chain.

[0043] The first segment (a1) has at least one nitrogen-containing group. The nitrogen-containing group can generate a cation in an aqueous solvent, thereby adsorbing onto the acidic pigment. Furthermore, since the nitrogen-containing group does not possess active hydrogen that can chemically react with components (typically curing agents) mixed in the waterborne coating composition, it is difficult to hinder the curing reaction of the waterborne coating composition.

[0044] The second segment (a2) has at least one polyoxyethylene chain. The polyoxyethylene chain hinders the approach between pigments, helps to suppress aggregation, and at the same time improves the hydrophilicity of the copolymer (A).

[0045] The copolymer (A) may further have a third segment (a3) ​​derived from polymerizable unsaturated monomers other than nitrogen-containing monomers and hydrophilic monomers.

[0046] The mass percentage of the first segment (a1) should be 5% or more and 30% or less, the mass percentage of the second segment (a2) should be 20% or more and 80% or less, and the mass percentage of the third segment (a3) ​​should be 10% or more and 60% or less.

[0047] If the mass percentage of the first segment (a1) is 5% by mass or more, the adsorption performance to the pigment is improved. If the mass percentage of the first segment (a1) is 30% by mass or less, the excessive increase in hydrophilicity of the copolymer (A) is suppressed, and the decrease in the water resistance of the coating film is inhibited. The mass percentage of the first segment (a1) can be 7% by mass or more, 10% by mass or more, or 12% by mass or more. The mass percentage of the first segment (a1) can be 27% by mass or less, 25% by mass or less, or 22% by mass or less.

[0048] If the mass percentage of the second segment (a2) is 20% or more, the dispersibility of the pigment adsorbed by the copolymer (A) is improved. If the mass percentage of the second segment (a2) is 80% or less, the excessive increase in hydrophilicity of the copolymer (A) is suppressed, and the decrease in the water resistance of the coating film is inhibited. The mass percentage of the second segment (a2) can be 30% or more, 35% or more, or 40% or more. The mass percentage of the second segment (a2) can be 75% or less, 70% or less, or 65% or less.

[0049] The mass percentage of the third segment (a3) ​​can be, for example, 10% or more and 60% or less by mass. The mass percentage of the third segment (a3) ​​can be 15% or more by mass, or 20% or more by mass. The mass percentage of the third segment (a3) ​​can be 55% or less by mass, or 50% or less by mass.

[0050] The third segment (a3) ​​may contain segments derived from polymerizable unsaturated monomers containing hydroxyl groups (hereinafter referred to as hydroxyl-containing segments (a31)). The hydroxyl groups can chemically react with components blended in the water-based coating composition. The copolymer (A) adsorbed onto the pigment inhibits pigment detachment (exudation) from the coating film through a chemical reaction with the curing agent. The mass percentage of the hydroxyl-containing segment (a31) can be 10% by mass or more and 30% by mass or less. If the mass percentage of the hydroxyl-containing segment (a31) is within this range, the exudation inhibition effect is easily achieved, and the viscosity of the pigment dispersion is less likely to increase. The mass percentage of the hydroxyl-containing segment (a31) can be 12% by mass or more, or 15% by mass or more. The mass percentage of the hydroxyl-containing segment (a31) can be 25% by mass or less, or 20% by mass or less.

[0051] The content of the first segment (a1) relative to the total constituent units can be calculated by dividing the mass of the nitrogen-containing polymerizable unsaturated monomer used in the synthesis of copolymer (A) by the total mass of all raw material monomers. The content of other segments relative to the total constituent units can also be calculated by dividing the mass of the monomer that forms that segment used in the synthesis of copolymer (A) by the total mass of all raw material monomers.

[0052] The weight-average molecular weight of copolymer (A) can be 10,000 or more and 40,000 or less. The weight-average molecular weight of copolymer (A) can be 15,000 or more or 20,000 or more. The weight-average molecular weight of copolymer (A) can be 38,000 or less or 35,000 or less.

[0053] The weight-average molecular weight can be calculated based on the molecular weight of standard polystyrene from the chromatogram determined by gel permeation chromatography. The acid value and hydroxyl value are calculated from the monomer composition used in the preparation according to JIS specifications.

[0054] (Nitrogen-containing polymerizable unsaturated monomers) Nitrogen-containing polymerizable unsaturated monomers (nitrogen-containing monomers) have at least one of a tertiary amine group and a nitrogen-containing heterocyclic group, as well as a polymerizable unsaturated group, in one molecule. The tertiary amine group and the nitrogen-containing heterocyclic group are basic. Therefore, the (a1) first segment derived from the nitrogen-containing monomer can be well adsorbed onto pigments (e.g., carbon black) with acidic sites.

[0055] Examples of monomers containing tertiary amino groups include: N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N,N-dimethylaminopropyl methacrylate, N,N-di-tert-butylaminoethyl methacrylate, N,N-dimethylaminobutyl methacrylate, and other N,N-dialkylaminoalkyl methacrylates; N,N-dimethylaminoethyl (meth)acrylamide, N,N-diethylaminoethyl (meth)acrylamide, N,N-dimethylaminopropyl (meth)acrylamide, and other N,N-dialkylaminoalkyl (meth)acrylamides. These can be used alone or in combination of two or more.

[0056] It can be N,N-dialkylaminoalkyl ester of (meth)acrylate, or N,N-dimethylaminoethyl ester of (meth)acrylate and N,N-diethylaminoethyl ester of (meth)acrylate.

[0057] In this specification, "(meth)acrylic acid" is a concept that includes both acrylic acid and methacrylic acid.

[0058] Examples of nitrogen-containing heterocyclic groups include: pyridine cyclic group, quinoline cyclic group, thiazole cyclic group, thiazole cyclic group, benzothiazole cyclic group, imidazole cyclic group, pyrazole cyclic group, imidazoleline cyclic group, pyrimidine cyclic group, pyrazine cyclic group, triazole cyclic group, and tetraazole cyclic group.

[0059] Examples of polymerizable unsaturated monomers (vinyl monomers) having a pyridine ring include 2-vinylpyridine and 4-vinylpyridine. Examples of polymerizable unsaturated monomers having a thiazole ring include 2-vinylthiazole and 4-methyl-5-vinylthiazole. Examples of polymerizable unsaturated monomers having a benzothiazole ring include 2-phenyl-5-vinylbenzothiazole. Examples of polymerizable unsaturated monomers having a benzothiazole ring include 2-vinylbenzothiazole, 2-[2-(1-naphthyl)vinyl]benzothiazole, and 2-[2-(dimethylamino)vinyl]benzothiazole. Examples of polymerizable unsaturated monomers having an imidazole ring include 1-vinylimidazolium, 2-methyl-1-vinylimidazolium, 2-vinylimidazolium, 4-vinylimidazolium, 2-phenyl-1-vinylimidazolium, 1-vinylcarbazole, and 2-(1H-imidazol-1-yl)ethyl (meth)acrylate. Examples of polymerizable unsaturated monomers having a pyrazole ring include 1-vinylpyrazole and 3-vinylpyrazole. Examples of polymerizable unsaturated monomers having an imidazoline ring include 1-vinyl-2-imidazoline, 1-vinyl-2-methylimidazoline, 2-vinyl-2-imidazoline, and 2-(1H-imidazoline-1-yl)ethyl methacrylate. Examples of polymerizable unsaturated monomers having a pyrimidine ring include 5-vinylpyrimidine and 2,4-dichloro-6-vinylpyrimidine. Examples of polymerizable unsaturated monomers having a pyrazine ring include 2-vinylpyrazine, 2,5-dimethyl-3-vinylpyrazine, and 2-methyl-5-vinylpyrazine. Examples of vinyl monomers having a triazole ring include 2,4-diamino-6-vinyltriazine. Examples of polymerizable unsaturated monomers having a tetrazolium ring include 1-vinyl-1H-tetrazole, 2-vinyl-2H-tetrazole, 5-vinyl-1H-tetrazole, and 1-methyl-5-vinyl-1H-tetrazole. These are used alone or in combination of two or more.

[0060] It can be at least one of a vinyl monomer having a pyridine ring group and a vinyl monomer having an imidazole ring group.

[0061] The nitrogen-containing monomer can be N,N-dialkylaminoalkyl methacrylate. This further improves the dispersibility of the pigment. Preferred N,N-dialkylaminoalkyl methacrylates are represented by the following general formula.

[0062] [Chemical Formula 1] In the formula, A represents hydrogen or methyl, B 1 and B 2 Each group independently represents a straight-chain or branched hydrocarbon group with 1 to 4 carbon atoms, where n is an integer from 1 to 3. In the formula, A can be a methyl group, B... 1 and B 2 It can be a hydrocarbon group with 1 or 2 carbon atoms, and n can be 1 or 2.

[0063] (polymerizable unsaturated monomers with polyoxyethylene chains) Polymerizable unsaturated monomers (hydrophilic monomers) with polyoxyethylene chains have both polyoxyethylene chains and polymerizable unsaturated groups in one molecule. The second segment (a2) derived from the hydrophilic monomer imparts hydrophilicity to the copolymer (A).

[0064] Examples of polyoxyethylene chains include: polyethylene oxide chains, polypropylene oxide chains, and chains containing polyethylene oxide blocks and polypropylene oxide blocks. The proportion of polyethylene oxide chains in the total polyoxyethylene chains can be 65% by mass or more, 70% by mass or more, 75% by mass or more, or 80% by mass or more. In one embodiment, the polyoxyethylene chains are composed of polyethylene oxide.

[0065] The molecular weight of the polyoxyethylene chain is, for example, 200 or more and 5,000 or less. From the viewpoint of dispersion stability, the molecular weight of the polyoxyethylene chain can be 300 or more, 400 or more, 800 or more, or 1,000 or more. The molecular weight of the polyoxyethylene chain can be 3,500 or less or 2,500 or less. In particular, if the molecular weight of the polyoxyethylene chain is 800 or more, long-term dispersion stability is easily obtained.

[0066] Examples of hydrophilic monomers include: tetraethylene glycol (meth)acrylate, methoxytetraethylene glycol (meth)acrylate, ethoxytetraethylene glycol (meth)acrylate, n-butoxytetraethylene glycol (meth)acrylate, polyethylene glycol (meth)acrylate, methoxy polyethylene glycol (meth)acrylate, ethoxy polyethylene glycol (meth)acrylate, and other acrylates with polyoxyethylene chains; and tetrapropylene glycol (meth)acrylate, methoxytetrapropylene glycol (meth)acrylate, ethoxytetrapropylene glycol (meth)acrylate, n-butoxytetrapropylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, and other acrylates with polyoxypropylene chains. These can be used alone or in combination of two or more.

[0067] (Other polymerizable unsaturated monomers) Other polymerizable unsaturated monomers (hereinafter, sometimes referred to as "other raw material monomers") have polymerizable unsaturated groups in one molecule, but on the other hand, they do not have polyoxyolefin chains and nitrogen-containing groups. The (a3) ​​third segment derived from other raw material monomers can impart various functions to the copolymer (A).

[0068] Other raw material monomers preferably do not have acid groups such as carboxyl, phosphate, sulfonic acid, and phenol groups. The reason is that if an interaction occurs between the acid group and the nitrogen-containing group, intermolecular forces will be generated in the copolymer (A), and the viscosity of the pigment dispersion will become excessively high.

[0069] Other raw material monomers may contain hydroxyl groups and polymerizable unsaturated groups in one molecule. The hydroxyl groups can chemically react with the curing agent blended in the water-based coating composition, thus improving the water resistance of the resulting coating film. Moreover, the copolymer (A) adsorbed on the pigment (C) chemically reacts with the curing agent, thereby easily inhibiting the pigment from falling out of the coating film (exudation).

[0070] Examples of polymerizable unsaturated monomers containing hydroxyl groups (hereinafter sometimes referred to as "hydroxyl-containing monomers") include: 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, etc.; monoesters of (meth)acrylate with diols having 2 to 8 carbon atoms; ε-caprolactone-modified monoesters of (meth)acrylate with diols having 2 to 8 carbon atoms; and allyl alcohol. These can be used alone or in combination of two or more.

[0071] Other raw material monomers besides hydroxyl-containing monomers include, for example: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, and other alkyl methacrylates; styrene, α-methylstyrene, vinyltoluene, and other vinyl aromatic compounds; and methacrylonitrile, methacrylamide, and vinyl acetate. These can be used alone or in combination of two or more.

[0072] (B) Organic acids Organic acids (B) have a hydrocarbon group (b1) and an acid group (b2). The acid group (b2) is typically located at the end of the hydrocarbon group (b1).

[0073] The hydrocarbon group (b1) can be saturated or unsaturated. The hydrocarbon group (b1) can be chain-like, alicyclic, or aromatic. From a colorimetric point of view, the hydrocarbon group (b1) can be chain-like. The chain-like hydrocarbon group (b1) can be straight-chain or branched.

[0074] The hydrocarbon group (b1) has 5 to 23 carbon atoms. By giving the organic acid (B) a hydrocarbon group (b1) of a certain length, hydrophobic pigments are easily adsorbed onto the organic acid (B), or the polyoxyethylene chain is easily extended outward, or the surface tension of the aqueous solvent is easily reduced. Furthermore, when formulating an aqueous coating composition, the dissociation of the organic acid (B) from the pigment adsorbed with the organic acid (B) is suppressed, and the dispersibility of the pigment in the aqueous coating composition is maintained. On the other hand, if the hydrocarbon group (b1) has too many carbon atoms, it is difficult to uniformly disperse the pigment in the aqueous solvent. The hydrocarbon group (b1) can have 6 or more carbon atoms, 7 or more carbon atoms, or 12 or more carbon atoms. The hydrocarbon group (b1) can have 21 or fewer carbon atoms, or 19 or fewer carbon atoms.

[0075] The acid group (b2) is selected from at least one of carboxyl, phosphoric acid, sulfonic acid, and phenolic groups. An organic acid (B) may have multiple acid groups (b2) of the same or different kinds, or it may have only one acid group (b2).

[0076] Examples of organic acids (B) containing a carboxyl group include monocarboxylic, dicarboxylic, and tricarboxylic acids. Examples of monocarboxylic acids include octanoic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, isostearic acid, undecenoic acid, phellandrene acid, oleic acid, ricinoleic acid, linoleic acid, linolenic acid, and cyclohexanecarboxylic acid. Examples of dicarboxylic acids include fumaric acid, maleic acid, adipic acid, pimelic acid, octanoic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, and 1,4-cyclohexanedicarboxylic acid. Examples of tricarboxylic acids include aconitic acid. Other examples of organic acids (B) containing a carboxyl group include amino acids and their derivatives (trimethylated amino acids such as trimethylglycine).

[0077] Examples of organic acids (B) having a phosphoric acid group include: alkylphosphonic acids (e.g., octylphosphonic acid, etc.), alkenylphosphonic acids (e.g., oleyl phosphate), and phenylphosphonic acid.

[0078] Examples of organic acids (B) with sulfonic acid groups include: p-phenylbenzenesulfonic acid, β-naphthalenesulfonic acid, naphthol-1-sulfonic acid, p-toluenesulfonic acid, p-chlorobenzenesulfonic acid, and 5-chloro-α,α-bis(3,5-dichloro-2-hydroxyphenyl)toluenesulfonic acid.

[0079] Examples of organic acids (B) containing phenolic groups include: nonylphenol, tert-butylphenol, and tert-butylcatechol.

[0080] (C) Pigment As pigments, examples include: coloring pigments, extender pigments, rust-preventing pigments, and glossy pigments.

[0081] Coloring pigments can be inorganic or organic. They can be colored or achromatic. Examples of organic coloring pigments include: azo chelate pigments, insoluble azo pigments, condensed azo pigments, diketopyrrolopyrrole pigments, phthalocyanine pigments, indigo pigments, pyrene pigments, perylene pigments, dialkyl pigments, quinacridone pigments, isoindolinone pigments, and metal complex pigments. Examples of inorganic coloring pigments include: chrome yellow, iron oxide yellow, iron oxide red, carbon black, and titanium dioxide. These can be used individually or in combination of two or more.

[0082] Examples of pigments used as extenders include calcium carbonate, barium sulfate, clay, and talc. These can be used individually or in combination of two or more.

[0083] Examples of glossy pigments include: mica pigments such as interference mica, muscovite, and colored mica; graphite pigments; glass flake pigments; and metallic pigments such as aluminum, copper, zinc, iron, nickel, tin, aluminum oxide, chromium oxide, and alloys containing these. These can be used individually or in combination of two or more. Glossy pigments can be colored.

[0084] (D) Aqueous solvents The aqueous solvent (D) accounts for more than 50% by mass of the total solvent in the pigment dispersion. Examples of aqueous solvent (D) include water and mixtures of water and hydrophilic solvents.

[0085] Examples of hydrophilic solvents include: glycols such as ethylene glycol, propylene glycol, butanediol, pentanediol, diethylene glycol, dipropylene glycol, and triethylene glycol; glycol ethers such as ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol monobutyl ether, diethylene glycol dibutyl ether, triethylene glycol monoethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and propylene glycol monomethyl ether acetate; alcohols such as methanol, ethanol, and isopropanol; ketones such as acetone; and N-methyl-2-pyrrolidone. These can be used individually or in combination of two or more.

[0086] (other) Pigment dispersions may contain other components such as defoamers, UV absorbers, light stabilizers, antioxidants, surface modifiers, film-forming aids, and rust inhibitors.

[0087] [Method for manufacturing pigment dispersion] The pigment dispersion disclosed herein is manufactured by a method comprising the following steps: adding an organic acid (B) to a first mixture comprising an aqueous solvent (D) and a copolymer (A) and mixing to obtain a second mixture; and adding a pigment (C) to the second mixture and mixing.

[0088] By first mixing the copolymer (A) with an aqueous solvent (D), and then mixing in an organic acid (B), the dispersibility of the pigment (C) is further improved, as the organic acid (B) is easily dissolved and / or dispersed in the aqueous solvent (D).

[0089] Each mixing process is carried out, for example, by a disperser (mixer). Examples of dispersers include: low-speed mixers such as propeller mixers, paddle mixers, and anchor mixers; and high-speed mixers such as homogenizers, dispersive mixers, and ultra mixers.

[0090] The resulting pigment dispersion can be further mixed using a disperser with a dispersion medium (beads). This promotes the micronization of the pigment (C). Specific examples of dispersers include: Ultra Apex Mill (trade name: Dual Apex Mill, Kotobukuri Co., Ltd.), Pico Grain Mill (trade name: Eco Mill, Asada Iron Works Co., Ltd.), Star Mill ZRS, Star Mill, Nano Getter (trade name: Max Nano Getter, Asizawa Finetech Ltd.), Micro Media (Bühler Ltd.), MSC Mill (Nippon Coke & Engineering Co., Ltd.), NPM (Shinmaru Enterprises Corp.), and SandGrind (SG) Mill.

[0091] Materials used as dispersion media include, for example, alumina, zirconium oxide, silicon carbide, silicon nitride, glass, steel, stainless steel, and ceramics. The particle size of the dispersion media can be, for example, less than 0.3 mm, less than 0.1 mm, or less than 0.05 mm. This further promotes the micronization of the pigment (C).

[0092] The stirring speed of the disperser can be, for example, 500 rpm or higher and 5000 rpm or lower. The mixing time can be, for example, 30 minutes or higher and 200 minutes or lower. The mixing temperature can be, for example, 5°C or higher and 45°C or lower.

[0093] [Water-based coating composition] The waterborne coating composition may comprise the pigment dispersion and film-forming resin described above. The waterborne coating composition may further comprise a curing agent and a waterborne solvent that can react with the film-forming resin. Examples of waterborne solvents include those identical to those used as examples of waterborne solvents contained in the pigment dispersion. The waterborne coating composition may be further diluted with a suitable solvent before use during coating.

[0094] Pigment (C) is sufficiently and stably dispersed even in water-based coating compositions. Therefore, the resulting coating film exhibits excellent color rendering. Color rendering is obtained by comprehensively evaluating gloss, transparency, color depth, etc., based on the type of pigment. "Excellent color rendering" can also be expressed as the color envisioned by the pigment being realized in the coating film.

[0095] A pigment dispersion is blended in such a way that, relative to 100 parts by weight of solid components, such as pigment (C), contained in the film-forming resin of the water-based coating composition, is 1 part by weight or more and 30 parts by weight or less. The aforementioned blending amount of pigment (C) can be 2 parts by weight or more, or 3 parts by weight or more. The aforementioned blending amount of pigment (C) can be 25 parts by weight or less, or 20 parts by weight or less.

[0096] The solids concentration of the water-based coating composition is, for example, 3% by mass or more and 50% by mass or less. The solids concentration of the water-based coating composition may be 5% by mass or more, or 7% by mass or more. The solids concentration of the water-based coating composition may be 45% by mass or less, or 40% by mass or less.

[0097] The concentration of solid components in the water-based coating composition was determined according to the JIS K 5601-1-2 method for determining residual content upon heating.

[0098] (Resin film formation) Examples of coating-forming resins include: acrylic resins, acrylic silicone resins, polyester resins, polyurethane resins, epoxy resins, fluoropolymers, and silicone resins. These can be used individually or in combination of two or more. Among these, acrylic resins may be used.

[0099] The coating-forming resin may include hydroxyl-containing resins. Examples of hydroxyl-containing resins include: hydroxyl-containing acrylic resins, hydroxyl-containing polyester resins, polycarbonate polyol resins, polyether polyol resins, and polycaprolactone polyol resins. These may be used alone or in combination of two or more. Among them, hydroxyl-containing acrylic resins may be used.

[0100] The hydroxyl value (OHV) of hydroxyl-containing resins can be, for example, above 20 mg KOH / g and below 180 mg KOH / g. If the hydroxyl value of the hydroxyl-containing resin is above 20 mg KOH / g, the tensile strength of the coating film is easily improved. If the hydroxyl value of the hydroxyl-containing resin is below 180 mg KOH / g, the hydrophilicity of the coating film is suppressed, and the water resistance is easily improved. The hydroxyl value of hydroxyl-containing resins can be above 30 mg KOH / g or above 40 mg KOH / g. The hydroxyl value of hydroxyl-containing resins can be below 150 mg KOH / g, below 140 mg KOH / g, below 100 mg KOH / g, or below 80 mg KOH / g.

[0101] The weight-average molecular weight (Mw) of the hydroxyl-containing resin (A) can be, for example, above 2,000 and below 50,000.

[0102] The weight-average molecular weight was determined using the GPC method with polystyrene as the standard. The acid value and hydroxyl value were calculated from the monomer composition used in the formulation, according to JIS specifications.

[0103] The coating-forming resin can be contained in the form of an emulsion, a dispersion, or dissolved in a solvent. For example, an acrylic resin dispersion can be prepared by solution polymerization of the aforementioned α,β-olefinic unsaturated monomers and dispersing them with an alkaline compound. Water-soluble acrylic resins can be prepared, for example, by solution polymerization of the aforementioned α,β-olefinic unsaturated monomers and dissolving them in water with an alkaline compound.

[0104] Emulsions of hydroxyl-containing acrylic resins can be formulated, for example, by emulsion polymerization of α,β-olefinically unsaturated monomers. Examples of α,β-olefinically unsaturated monomers include (meth)acrylates, α,β-olefinically unsaturated monomers with acid groups, and α,β-olefinically unsaturated monomers with hydroxyl groups. Monomers can be used alone or in combination of two or more.

[0105] Examples of (meth)acrylates include: methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, phenyl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, tert-butylcyclohexyl methacrylate, dicyclopentadienyl methacrylate, and dihydrodicyclopentadienyl methacrylate. (Methacryl acrylates) refer to both acrylates and methacrylates.

[0106] Examples of α,β-olefinic unsaturated monomers with acid groups include: acrylic acid, methacrylic acid, crotonic acid, 2-acryloyloxyethyl phthalate, 2-acryloyloxyethyl succinate, ω-carboxy-polycaprolactone mono(meth)acrylate, isocrotonic acid, α-hydro-ω-((1-oxo-2-propenyl)oxy)poly(oxy(1-oxo-1,6-hexadiyl)), maleic acid, fumaric acid, itaconic acid, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, 2-acrylamido-2-methylpropanesulfonic acid, p-hydroxystyrene, and 2,4-dihydroxy-4'-vinylbenzophenone.

[0107] Examples of α,β-olefinic unsaturated monomers with hydroxyl groups include: hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, allyl alcohol, methyl allyl alcohol, and their adducts with ε-caprolactone.

[0108] Other α,β-olefinic unsaturated monomers may be used in conjunction. Examples of other α,β-olefinic unsaturated monomers include: polymerizable amide compounds, polymerizable aromatic compounds, polymerizable nitriles, polymerizable epoxide compounds, polyfunctional vinyl compounds, polymerizable amine compounds, α-olefins, dienes, polymerizable carbonyl compounds, polymerizable alkoxysilyl compounds, and other polymerizable compounds.

[0109] There are no particular limitations on the method of emulsion polymerization. For example, an emulsifier is dissolved in water or an aqueous medium containing organic solvents such as alcohols or ethers (e.g., dipropylene glycol methyl ether, propylene glycol methyl ether, etc.) as needed, and α,β-olefinic unsaturated monomers and polymerization initiators are added dropwise under heating and stirring. The α,β-olefinic unsaturated monomers can be pre-emulsified with the emulsifier.

[0110] The polymerization initiator and emulsifier can be substances commonly used by those skilled in the art. The molecular weight can be adjusted as needed using chain transfer agents such as thiols (e.g., lauryl thiol) and α-methylstyrene dimers. The reaction temperature, reaction time, etc., can be appropriately selected within the range commonly used by those skilled in the art. The resulting acrylic resin emulsion is neutralized with alkali as needed.

[0111] The number-average molecular weight of the hydroxyl-containing acrylic resin obtained by emulsion polymerization can be 3,000 or higher. The hydroxyl value (solid component hydroxyl value) of the hydroxyl-containing acrylic resin can be 20 mg KOH / g or higher and 180 mg KOH / g or lower. The acid value (solid component acid value) of the hydroxyl-containing acrylic resin can be 1 mg KOH / g or higher and 80 mg KOH / g or lower.

[0112] (Curing agent) Waterborne coating compositions may include a curing agent. The curing agent reacts with the coating film-forming resin to simultaneously form a cured coating film.

[0113] Examples of curing agents include: melamine resins, blocked isocyanate compounds, epoxy compounds, aziridine compounds, carbodiimide compounds, α-azoline compounds, and metal ions. These can be used alone or in combination of two or more. At least one of melamine resins and blocked isocyanate compounds may be used.

[0114] Melamine resins can be water-soluble or water-insoluble. Melamine resins consist of a melamine core (triazine core) surrounded by three nitrogen atoms bonded to hydrogen atoms or substituents (alkyl ether groups, hydroxymethyl groups, etc.). Melamine resins are typically composed of polynuclear bodies formed by multiple melamine cores bonded together. Melamine resins can also be mononuclear bodies composed of a single melamine core.

[0115] Commercially available melamine resins can be used. Examples of commercially available melamine resins include: the Cymel series (trade names) manufactured by Allnex, specifically Cymel 202, Cymel 204, Cymel 211, Cymel 232, Cymel 235, Cymel 236, Cymel 238, Cymel 250, Cymel 251, Cymel 254, Cymel 266, Cymel 267, Cymel 272, Cymel 285, Cymel 301, Cymel 303, Cymel 325, Cymel 327, Cymel 350, Cymel 370, Cymel 701, Cymel 703, and Cymel 1141; and the U-VAN series (trade name) manufactured by Mitsui Chemicals. These can be used individually or in combination of two or more.

[0116] Blocked isocyanate compounds can be modulated by adding a blocking agent with active hydrogen to polyisocyanates composed of trimethylene diisocyanate, hexamethylene diisocyanate, phenyl diisocyanate, isophorone diisocyanate, etc.

[0117] The content of the curing agent can be 10% by mass or more and 80% by mass or less of the resin solids contained in the water-based coating composition. The above-mentioned content of the curing agent can be 15% by mass or more. The above-mentioned content of the curing agent can be 60% by mass or less.

[0118] (other) Waterborne coating compositions may contain other components such as defoamers, UV absorbers, light stabilizers (e.g., hindered amines), antioxidants, surface modifiers, film-forming aids, and rust inhibitors.

[0119] [Method for manufacturing water-based coating compositions] The waterborne coating composition disclosed herein is manufactured by a method comprising the step of mixing a pigment dispersion prepared by the above method with a coating film forming resin.

[0120] The mixing conditions and mixing apparatus may be the same as those listed in the method for manufacturing pigment dispersions.

[0121] [Painted Items] Using the waterborne coating composition disclosed herein, a coated article having a coating film with excellent color development can be obtained. Such a coated article comprises a substrate and a primer film formed from the aforementioned waterborne coating composition. The coated article may comprise a substrate, a primer film formed from the aforementioned waterborne coating composition, and a transparent coating film disposed on the primer film.

[0122] The primer film may be one or more layers. At least one primer film is formed from the water-based coating composition disclosed herein. The components contained in each primer film may be the same or different.

[0123] (Object to be painted) Examples of materials that can be coated include: metals, plastics, and foams. Among these, metals (especially castings) can be used, and these can be metals suitable for electrodeposition coating. Examples of such metals include: iron, copper, aluminum, tin, zinc, and alloys containing these metals.

[0124] There are no particular limitations on the shape of the object to be coated; it can be flat or three-dimensional. Specifically, examples of objects to be coated include: the bodies and components of cars, trucks, motorcycles, buses, etc.

[0125] It can be used to perform chemical treatment and electrodeposition coating on metallic substrates using phosphoric acid-based chemical treatment agents, zirconium-based chemical treatment agents, etc. The electrodeposition coating composition can be cationic or anionic. Cationic electrodeposition coating compositions can form a coating film with excellent corrosion resistance.

[0126] Metallic substrates may have an electrodeposited coating and a mid-coat layer thereon. The mid-coat layer is typically designed to improve the adhesion and durability of multilayer coatings. Mid-coat paint compositions may, for example, contain film-forming resins, curing agents, coloring pigments, and extender pigments. Examples of film-forming resins and curing agents include components identical to those found in the waterborne paint compositions disclosed herein.

[0127] (Primer coating) At least one primer film is formed from the above-described water-based coating composition. The thickness of the primer film can be 0.2 μm or more and 50 μm or less. The thickness of the base coat film can be 3 μm or more. The thickness of the base coat film can be 40 μm or less, 30 μm or less, or 20 μm or less.

[0128] (Transparent coating) A transparent coating protects the substrate coating. The thickness of the transparent coating can be, for example, 10 μm or more but less than 80 μm. The thickness of the transparent coating can be 20 μm or more. The thickness of the transparent coating can be less than 60 μm.

[0129] A transparent coating film is formed from a transparent coating composition. The transparent coating composition can be solvent-based, water-based, or powder-based. Solvent-based transparent coating compositions, considering transparency or acid etching resistance, may contain acrylic resins and / or polyester resins as film-forming resins and amino resins and / or isocyanates as curing agents. Solvent-based transparent coating compositions may also contain acrylic resins and / or polyester resins having carboxylic acid and / or epoxy groups.

[0130] The transparent coating composition may contain the various pigments described above, without compromising transparency and the effects of the coating composition disclosed herein. The transparent coating composition may also contain various additives as needed. Examples of additives include, for instance, ultraviolet absorbers, antioxidants, defoamers, surface conditioners, and anti-pinhole agents.

[0131] [Manufacturing Method for Painted Items] Taking a coated article having a substrate, a primer film, and a transparent film as an example, the manufacturing method of the coated article will be explained.

[0132] Coated articles having a primer film and a clear coat film are obtained, for example, by sequentially applying the water-based coating composition and the clear coat composition disclosed herein to a substrate and then allowing both to cure simultaneously. Preheating can be performed after applying the water-based coating composition and before applying the clear coat composition.

[0133] Examples of coating methods include: air spraying, airless spraying, electrostatic spraying, multi-stage coating (preferably two-stage coating), and coating combining air electrostatic spraying with a rotary atomizing electrostatic coating machine.

[0134] The curing of each coating composition is carried out, for example, at a heating temperature of 80°C to 180°C (preferably 100°C to 160°C) and a heating time of 5 minutes to 60 minutes (preferably 10 minutes to 30 minutes). Example

[0135] The invention is further illustrated by the following examples, but the invention is not limited thereto. In the examples, "parts" and "%" are based on mass unless otherwise stated.

[0136] [Manufacturing Example 1-1] Manufacturing of Copolymer (A-1) 78 parts of dipropylene glycol monomethyl ether were loaded into a reaction vessel equipped with a stirrer, temperature regulator, condenser, and dropping device. The mixture was stirred and heated to 120°C, and then refluxed.

[0137] Then, a solution containing 15 parts of 2-(dimethylamino)ethyl methacrylate, 60 parts of a monomer with a polyoxyethylene structure (product name: PME-1000, manufactured by Nippon Yuko Co., Ltd., methoxy polyethylene glycol-methacrylate), 19 parts of a monomer mixture of 2-hydroxyethyl methacrylate and 6 parts of butyl acrylate, 0.5 parts of Kaya Ester O (manufactured by Nippon Yuko Co., Ltd.), and 76 parts of dipropylene glycol monomethyl ether was added dropwise over 3 hours to allow the reaction to proceed. As a subsequent feedstock, a polymerization initiator solution obtained by dissolving 0.3 parts of Kaya Ester O (manufactured by Nippon Yuko Co., Ltd.) as a polymerization initiator in 11 parts of dipropylene glycol monomethyl ether was added dropwise over 0.5 hours, and stirring was continued for another 0.5 hours to allow polymerization to proceed, yielding copolymer (A-1). Then, after removing the solvent by vacuum distillation at 90°C, 100 parts of deionized water were added relative to 1000 parts of copolymer (A-1), and stirring was performed to obtain an aqueous solution of copolymer (A-1) (solid content: 50% by mass).

[0138] The resulting copolymer (A-1) has a hydroxyl value of 82 mg KOH / g and a weight-average molecular weight of 30,000.

[0139] [Manufacturing Examples 1-2 to 1-14] Manufacturing of copolymers (A-2) to (A-12), (a-1) and (a-2) Except for using the monomers shown in the table below in the blending amounts recorded in Table 1, copolymers (A-2) to (A-12), (a-1) and (a-2) were prepared according to the same procedure as in Manufacturing Example 1-1.

[0140] [Table 1] [Manufacturing Example 2] Manufacturing of Acrylic Resin Emulsion 633 parts of deionized water were added to the reaction vessel, and the mixture was heated to 80°C while being stirred under a nitrogen stream. Separately, 75.65 parts by weight of styrene (ST), 178.96 parts by weight of methyl methacrylate (MMA), 75.94 parts by weight of n-butyl acrylate (BA), 64.45 parts by weight of 2-ethylhexyl acrylate (2-EHA), and 105 parts by weight of hydroxyethyl methacrylate (HEMA) were mixed to prepare the monomer mixture for the first stage. Then, this monomer mixture, 25 parts by weight of Aqualon HS-10 (polyoxyethylene alkylpropylene phenyl ether sulfate, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), 25.0 parts by weight of Adeka Reasoap NE-20 (α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxyoxyethylene, manufactured by Asahi Denka Co., Ltd.), and 400 parts by weight of deionized water were mixed to prepare a monomer emulsion. In addition, an initiator solution consisting of 1.2 parts ammonium persulfate and 500 parts deionized water was prepared. The monomer emulsion and initiator solution were added dropwise in parallel to the above reaction vessel over 1.5 hours. After the addition was complete, the mixture was aged at the same temperature for 1 hour.

[0141] In addition, 53.65 parts by weight of styrene (ST), 178.96 parts by weight of methyl methacrylate (MMA), 75.94 parts by weight of n-butyl acrylate (BA), 64.45 parts by weight of 2-ethylhexyl acrylate (2-EHA), 105 parts by weight of hydroxyethyl methacrylate (HEMA), and 22 parts by weight of acrylic acid were mixed to prepare the monomer mixture for the second stage. Then, this monomer mixture, 10 parts by weight of Aqualon HS-10, and 250 parts by weight of deionized water were mixed to prepare a monomer emulsion. Furthermore, an initiator solution consisting of 3.0 parts by weight of ammonium persulfate and 500 parts by weight of deionized water was prepared. The monomer emulsion and initiator solution were added dropwise in parallel to the above reaction vessel over 1.5 hours. After the addition was completed, the mixture was aged at the same temperature for 2 hours.

[0142] The reactants were then cooled to 40°C and filtered through a 400-mesh filter. Finally, 100 parts of deionized water and 1.6 parts of dimethylaminoethanol were added to the reactants to adjust the pH to 6.5. This process yielded an acrylic resin emulsion with an average particle size of 150 nm, a solid content of 35% by mass, a solid content acid value of 20 mg KOH / g, and a hydroxyl value of 100 mg KOH / g.

[0143] [Manufacturing Example 3] Manufacturing of Water-Soluble Acrylic Resin 23.89 parts of tripropylene glycol methyl ether and 16.11 parts of propylene glycol methyl ether were added to the reaction vessel, and the mixture was stirred and heated to 105°C under a nitrogen atmosphere. Then, a monomer mixture comprising 13.1 parts of methyl methacrylate, 68.4 parts of ethyl acrylate, 11.6 parts of 2-hydroxyethyl methacrylate, and 6.9 parts of methacrylic acid was prepared. Over 3 hours, 100 parts of this monomer mixture and an initiator solution consisting of 10.0 parts of tripropylene glycol methyl ether and 1 part of tert-butyl peroxide were added dropwise in parallel to the reaction vessel. After the addition was complete, the mixture was allowed to mature at the same temperature for 0.5 hours.

[0144] Then, over a period of 0.5 hours, an initiator solution consisting of 5.0 parts tripropylene glycol methyl ether and 0.3 parts tert-butyl peroxide was added dropwise to the reaction vessel. After the addition was complete, the mixture was allowed to mature at the same temperature for 2 hours.

[0145] After removing 16.1 parts of solvent using a solvent removal apparatus under reduced pressure (70 torr) and at 110°C, 204 parts of deionized water and 7.1 parts of dimethylaminoethanol were added to obtain a water-soluble acrylic resin solution. The resulting water-soluble acrylic resin solution had a solid content of 30% by mass, an acid value of 40 mg KOH / g, a hydroxyl value of 50 mg KOH / g, and a viscosity of 140 poise (E-type viscometer, 1 rpm / 25°C).

[0146] Regarding the weight-average molecular weight, the "HLC8220GPC" (trade name, manufactured by Tosoh Corporation) was used as the GPC apparatus, and four "Shodex KF-606M" and "Shodex KF-603" (both manufactured by Showa Denko Corporation, trade names) were used as columns. The measurements were performed under the following conditions: the mobile phase was tetrahydrofuran, the measurement temperature was 40°C, the flow rate was 0.6 cc / min, and the detector was RI.

[0147] The acid value and hydroxyl value are calculated based on the monomer composition used in the formulation, according to JIS specifications.

[0148] Details of the organic acid (B) used in the examples and comparative examples are shown in Table 2.

[0149] [Table 2] [Example 1] Preparation of pigment dispersion (blue) 8.3 parts (solid mass) of copolymer (A-1) and 60 parts of deionized water were added to a mixer and stirred to obtain a first mixture. 2.2 parts of organic acid (B-1) were added to the first mixture and stirred, followed by 0.5 parts of defoamer (BYK-011, manufactured by ALTNA) and stirred to obtain a second mixture. 15 parts of phthalocyanine blue (blue pigment, manufactured by Toyo Color Materials Co., Ltd., trade name: LIONOL BLUE 7186-PM) were added to the second mixture and stirred, followed by deionized water to bring the total volume to 100 parts. The resulting mixture was dispersed using a batch SG mill filled with 0.5 mm zirconia beads at 70% volumetric filling rate as the dispersion medium to obtain a pigment dispersion (blue).

[0150] [Examples 2-19, Comparative Examples 1-8] Preparation of Pigment Dispersion (Blue) Except for changing the type or amount of copolymer (A) and organic acid (B) as described in Table 3, the pigment dispersion (blue) was prepared using the same procedure as in Example 1.

[0151] Manufacturing of [Example 20] 2.8 parts (solids mass) of copolymer (A-1) and 19 parts of deionized water were added to a mixer and stirred to obtain a first mixture. 0.8 parts of organic acid (B-1) were added to the first mixture and stirred, followed by 0.5 parts of defoamer (BYK-011, manufactured by ALTNA) and stirred to obtain a second mixture. 73.0 parts of titanium dioxide (white pigment, Ishihara Sangyo CR-97) were added to the second mixture and stirred, then deionized water was added to bring the total volume to 100 parts. The resulting mixture was dispersed using a paint conditioner filled with 0.6 mm zirconium beads at 70% volume fill as the dispersion medium to obtain a pigment dispersion (white).

[0152] [Example 21 and Comparative Examples 9 and 10] Preparation of Pigment Dispersion (White) Except for changing the type or amount of copolymer (A) and organic acid (B) as described in Table 4, a pigment dispersion (white) was obtained by the same procedure as in Example 20.

[0153] [Example 22] Preparation of Pigment Dispersion (Black) 12.5 parts (solids mass) of copolymer (A-1) and 50.0 parts of deionized water were added to a mixer and stirred to obtain a first mixture. 3.2 parts of organic acid (B-1) were added to the first mixture and stirred, followed by 0.5 parts of defoamer (BYK-011, manufactured by ALTNA) and stirred to obtain a second mixture. 17.5 parts of carbon black (black pigment, Raven 5000 manufactured by BILRA CARBON) were added to the second mixture and stirred, then deionized water was added to bring the total volume to 100 parts. The resulting mixture was dispersed using a batch SG mill filled with 0.5 mm zirconium beads at 70% volumetric filling rate as the dispersion medium to obtain a pigment dispersion (black).

[0154] [Example 23 and Comparative Examples 11, 12] Preparation of Pigment Dispersion (Black) Except for changing the type or amount of copolymer (A) and organic acid (B) as described in Table 5, a pigment dispersion (black) was obtained by the same procedure as in Example 22.

[0155] [Example 24] Preparation of Pigment Dispersion (Red) 7.8 parts (solids mass) of copolymer (A-1) and 45.0 parts of deionized water were added to a mixer and stirred to obtain a first mixture. 2.0 parts of organic acid (B-1) were added to the first mixture and stirred, followed by the addition of 0.5 parts of defoamer (BYK-011, manufactured by ALTNA) and stirred to obtain a second mixture. 34.5 parts of diketopyrrolopyrrole (red pigment, Irgazin Rubine L 4025 manufactured by BASF) were added to the second mixture and stirred, followed by the addition of deionized water to bring the total volume to 100 parts. The resulting mixture / pigment dispersion was dispersed using a batch SG mill filled with 0.6 mm zirconium beads at 70% volumetric filling rate as the dispersion medium to obtain a red pigment dispersion.

[0156] [Comparative Example 13] Preparation of Pigment Dispersion (Red) Except for changing the type or amount of copolymer (A) and the type or amount of organic acid (B) as described in Table 6, a pigment dispersion (red) was obtained by the same procedure as in Example 24.

[0157] [evaluate] The pigment dispersions of the examples and comparative examples were evaluated as follows.

[0158] (1) Average particle size The pigment dispersion was infinitely diluted with deionized water, and the 50% volume particle size (D50) of the pigment in the dispersion was measured using a particle size distribution measuring device (trade name: UPA-150, manufactured by Microtrac) based on dynamic light scattering. It can be said that the smaller the particle size, the higher the pigment dispersibility.

[0159] (2) Viscosity The viscosity was measured at 25°C and 5 rpm using a viscosity measuring device (product name: VISCOMETER TV-25, manufactured by Toki Sangyo Co., Ltd.).

[0160] (3) Color development of the coating (3-1) Pigment dispersion containing blue, red, and black pigments A transparent substrate was prepared by mixing 210 parts of water-soluble acrylic resin (30% solids content) from Manufacturing Example 3 and 30 parts of Cymel 327 (a mixed alkylated melamine resin, manufactured by Allnex, with 90% solids content). A pigment dispersion was then mixed into the transparent substrate such that the mass of the pigment was 10 parts relative to 90 parts by mass of the solids content of the transparent substrate, resulting in an evaluation waterborne coating composition.

[0161] The obtained water-based coating composition for evaluation was applied to a 15cm × 10cm glass plate and cured at 140°C for 20 minutes to obtain an evaluation coating film. The appearance of the obtained evaluation coating film was visually inspected, and the color development was evaluated according to the following criteria. The evaluation results are shown in Tables 3–5, 7, and 8. If the evaluation exceeds B, the color development can be considered excellent.

[0162] • Evaluation criteria for coatings formed from pigment dispersions (blue) A: It has a transparent feel, and the blue color is also strong; A-: It has a transparent feel, but the blue color is slightly weak; B: It has a slightly cloudy appearance, and the blue color is weaker; C: It has a white turbidity, and the blue color is also weak.

[0163] • Evaluation criteria for coatings formed from pigment dispersion (black) A: It has a glossy finish and a high degree of blackness; B: Between standard A and C; C: Pale.

[0164] • Evaluation criteria for coatings formed from pigment dispersion (red) A: It has a transparent feel, and the red is deep; B: It has a slightly cloudy appearance, and the red color is slightly weaker; C: It feels cloudy.

[0165] (3-2) Pigment dispersion containing white pigment The pigment dispersion was coated onto a 15cm × 10cm glass plate and heated at 140°C for 20 minutes to obtain an evaluation coating. After standing at 23°C, the 60° gloss value was measured using a micro-gloss meter (manufactured by BYK Gardner). The 60° gloss value was evaluated according to the following criteria. The evaluation results are shown in Table 6. A higher 60° gloss value indicates better color rendering of white. A rating exceeding B indicates excellent color rendering.

[0166] • Evaluation criteria for coatings formed from pigment dispersions (white) A: Gloss value of 80 or higher at 60°; B: A 60° gloss value of 60 or higher but lower than 80; C: 60° gloss value is below 60.

[0167] [Table 3] [Table 4] [Table 5] [Table 6] [Table 7] [Table 8] In the pigment dispersions of Examples 1-24, the average particle size of the pigments was small and the viscosity was suppressed to a low level.

[0168] In Comparative Examples 1 and 2, the average particle size of pigment (C) was relatively large. It is believed that because the pigment dispersions in Comparative Examples 1 and 2 did not contain organic acid (B), phthalocyanine blue, as a hydrophobic pigment, was not sufficiently dispersed. In Comparative Example 3, when oleylamine was used instead of organic acid (B), the average particle size of pigment (C) was relatively large. This is believed to be because the oleylamine used in Comparative Example 3 could not function as a counterion of copolymer (A), resulting in a disruption of charge balance and failure to suppress aggregation between pigments (C). In Comparative Example 4, when polyoxyethylene oil ether was used instead of organic acid (B), the average particle size of pigment (C) could not be sufficiently reduced, and the viscosity of the pigment dispersion increased. It is believed that the polyoxyethylene oil ether used in Comparative Example 4 could not function sufficiently as a counterion of copolymer (A), thus failing to sufficiently suppress aggregation between pigments (C), and a specific interaction occurred between the polyoxyethylene oil ether and phthalocyanine blue, resulting in a very high viscosity. In Comparative Examples 5 and 6, the average particle size of pigment (C) was relatively large, and the viscosity of the pigment dispersion was also high. It is believed that the aggregation between pigments was not sufficiently suppressed because the hydrocarbon groups of the organic acids used in Comparative Examples 5 and 6 were relatively short. In Comparative Example 7, the average particle size of pigment (C) was relatively large. This is believed to be because the copolymer (A) used in Comparative Example 7 does not have nitrogen-containing groups and therefore cannot act as a counterion to the organic acid (B), resulting in the aggregation between pigments (C) not being suppressed.

[0169] The coatings formed from the aqueous coating compositions made using the pigment dispersions of Comparative Examples 1 to 7 have particularly low transparency.

[0170] In Comparative Example 8, the pigment could not be dispersed. This is believed to be because the copolymer used in Comparative Example 8 does not have polyoxyolefin chains, thus its affinity for aqueous solvents is low, and the copolymer itself cannot be dispersed in aqueous solvents. As a result, pigment (C) cannot be dispersed either.

[0171] In Comparative Examples 9–13, no organic acid (B) was used.

[0172] In Comparative Example 9, the average particle size of pigment (C) was relatively large, and an increase in viscosity was particularly observed. It is believed that in Comparative Example 9, since no organic acid (B) was used, the normally alkaline titanium dioxide had difficulty adsorbing resin components, thus making it difficult to disperse. Furthermore, it is believed that due to the high specific gravity of titanium dioxide, in addition to its tendency to settle, its dispersion was also insufficient, leading to an excessive increase in viscosity. In Comparative Example 10, titanium dioxide was also difficult to disperse, making evaluation tests impossible.

[0173] In Comparative Examples 11 and 12, carbon black, used as an acidic pigment, could be dispersed through the copolymer (A), but the average particle size of the pigment (C) was large, resulting in insufficient dispersibility. An increase in viscosity was also observed in Comparative Example 12.

[0174] In Comparative Example 13, although the average particle size of the pigment was small, the color rendering was poor. It is believed that the dispersion state of the pigment in the pigment dispersion is unstable, and therefore the pigment partially aggregates during the manufacture of the water-based coating composition.

[0175] [Example 25] Preparation of water-based coating composition and coated articles (1) Manufacturing of water-based coating compositions 160 parts of the acrylic resin emulsion of Manufacturing Example 2, 1 part of dimethylaminoethanol, 33 parts of the water-soluble acrylic resin of Manufacturing Example 3 (solid content of 30% by mass), 38 parts of melamine resin (Cymel 204, manufactured by Mitsui Cytec, a mixed alkylated melamine resin with a solid content of 80%), 10 parts of difunctional polyether polyol (Primepol PX-1000, manufactured by Sanyo Chemical Industries, Ltd.) and 30 parts of the pigment dispersion of Example 1 (solid content of 26%) were mixed and diluted with deionized water to prepare an aqueous coating composition with a solid content concentration of 20%.

[0176] (2) Manufacturing of painted items On a matte steel plate with a thickness of 0.8 mm, a length of 30 cm, and a width of 40 cm, treated with zinc phosphate, a cationic electrodeposition coating composition, "Power Top U-50" (manufactured by Nippon Paint Aautomotive Coatings Co., Ltd.), was applied by electrodeposition to achieve a dry film thickness of 20 μm, and then baked at 160°C for 30 minutes. On the resulting coated plate, an intermediate coat coating composition, "OP-30P Middle Gray" (manufactured by Nippon Paint Aautomotive Coatings Co., Ltd., polyester / melamine-based coating, 25 seconds (measured at 20°C using a No. 4 Ford cup), pre-diluted), was applied by air spraying using an ANETIWATA air gun W-101-132G to achieve a dry film thickness of 35 μm, and then baked at 140°C for 30 minutes to cure. This process yielded a substrate with both an electrodeposited coating and an intermediate coat.

[0177] A water-based coating composition (manufactured by Nippon Paint Aautomotive Coatings Co., Ltd., water-based AR-3020-1 (gray metallic paint)) was air-sprayed onto a substrate to achieve a dry film thickness of 12 μm under ambient temperature of 23°C and humidity of 68%. After standing for 4 minutes, it was preheated at 80°C for 5 minutes. Then, the aforementioned water-based coating composition was air-sprayed onto the substrate to achieve a dry film thickness of 12 μm under ambient temperature of 23°C and humidity of 68%. After standing for 4 minutes, it was preheated at 80°C for 5 minutes.

[0178] Next, a rotary atomizing electrostatic coating machine was used to apply a clear coating (manufactured by Nippon Paint Aautomotive Coatings Co., Ltd., PolyureExcel O-1200 (trade name), a two-component acrylic polyurethane organic solvent-based clear coating containing polyisocyanate compounds) to achieve a dried film thickness of 35 μm. Finally, the coating was heated at 80°C for 20 minutes to obtain a coated article with multiple layers. The resulting coating has a transparent appearance and a strong blue tint.

[0179] This disclosure includes the following schemes.

[0180] [1] A pigment dispersion comprising: a copolymer (A), a hydrocarbon-containing acidic compound (B), a pigment (C), and an aqueous solvent (D), The copolymer (A) comprises: a first segment (a1) derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amine and a nitrogen-containing heterocyclic group, and a second segment (a2) derived from a polymerizable unsaturated monomer having a polyoxyolefin chain. The acidic compound (B) containing a hydrocarbon group has: a saturated or unsaturated hydrocarbon group (b1) having 5 to 23 carbon atoms and at least one acid group (b2) selected from carboxyl, phosphoric acid, sulfonic acid and phenolic groups.

[0181] [2] According to the pigment dispersion of [1] above, wherein the ratio of the acid equivalent of the hydrocarbon-containing acidic compound (B) to the total equivalent of the tertiary amino group and nitrogen-containing heterocyclic group of the copolymer (A) (acid group / tertiary amino group and nitrogen-containing heterocyclic group) is 0.5 or more and 2 or less.

[0182] [3] According to the pigment dispersion of [1] or [2] above, wherein the copolymer (A) further has a third segment (a3) ​​derived from a polymeric unsaturated monomer other than the nitrogen-containing polymeric unsaturated monomer and the polymeric unsaturated monomer having a polyoxyolefin chain. In the copolymer (A), The mass percentage of the first chain segment (a1) is more than 5% by mass and less than 30% by mass. The mass percentage of the second segment (a2) is 20% or more and 80% or less by mass. The mass percentage of the third segment (a3) ​​is more than 10% by mass and less than 60% by mass.

[0183] [4] According to the pigment dispersion of [3] above, wherein the third segment (a3) ​​comprises a segment (a31) derived from a hydroxyl-containing polymerizable saturated monomer. The mass percentage of the segment (a31) in the copolymer (A) is more than 10% by mass and less than 30% by mass.

[0184] [5] A water-based coating composition comprising: The pigment dispersion of any one of [1] to [4] above; and The coating forms a resin film.

[0185] [6] A method for manufacturing a pigment dispersion, comprising the following steps: The step of adding an acidic compound (B) containing a hydrocarbon group to a first mixture containing an aqueous solvent (D) and a copolymer (A) to obtain a second mixture; and The step of adding pigment (C) to the second mixture and mixing it. The copolymer (A) has: A first segment (a1) derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amine and a nitrogen-containing heterocyclic group, and a second segment (a2) derived from a polymerizable unsaturated monomer having a polyoxyolefin chain. The acidic compound (B) containing a hydrocarbon group has the following characteristics: A saturated or unsaturated hydrocarbon group having 5 to 23 carbon atoms (b1), and at least one acid group selected from carboxyl, phosphoric acid, sulfonic acid or phenolic groups (b2).

[0186] [7] A method for manufacturing an aqueous coating composition, comprising the step of mixing a pigment dispersion prepared by the method described above [6] with a coating film forming resin.

[0187] Industrial applicability The pigment dispersion of the present invention does not cause an increase in viscosity regardless of the type of pigment, and can fully and stably disperse the pigment, thus it can be used in various water-based coating compositions.

[0188] This application claims priority based on Japanese Patent Application No. 2023-107340 filed on June 29, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A pigment dispersion comprising a copolymer (A), a hydrocarbon-containing acidic compound (B), a pigment (C), and an aqueous solvent (D), The copolymer (A) comprises: a first segment (a1) derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amine and a nitrogen-containing heterocyclic group, and a second segment (a2) derived from a polymerizable unsaturated monomer having a polyoxyolefin chain. The acidic compound (B) containing a hydrocarbon group has: a saturated or unsaturated hydrocarbon group having 5 to 23 carbon atoms (b1), and at least one acid group selected from carboxyl, phosphoric acid, sulfonic acid and phenolic groups (b2).

2. The pigment dispersion according to claim 1, wherein, The ratio of the acid equivalent of the hydrocarbon-containing acidic compound (B) to the total equivalent of the tertiary amino groups and nitrogen-containing heterocyclic groups in the copolymer (A) (acid group / tertiary amino group and nitrogen-containing heterocyclic group) is 0.5 or more and 2 or less.

3. The pigment dispersion according to claim 1 or 2, wherein, The copolymer (A) also has a third segment (a3) ​​derived from polymeric unsaturated monomers other than the nitrogen-containing polymeric unsaturated monomer and the polymeric unsaturated monomer having a polyoxyethylene chain. In the copolymer (A), The mass percentage of the first chain segment (a1) is more than 5% by mass and less than 30% by mass. The mass percentage of the second segment (a2) is 20% or more and 80% or less by mass. The mass percentage of the third segment (a3) ​​is more than 10% by mass and less than 60% by mass.

4. The pigment dispersion according to claim 3, wherein, The third segment (a3) ​​comprises a segment (a31) derived from a hydroxyl-containing polymerizable saturated monomer. The mass percentage of the segment (a31) in the copolymer (A) is more than 10% by mass and less than 30% by mass.

5. A water-based coating composition comprising: The pigment dispersion according to any one of claims 1 to 4; and The coating forms a resin film.

6. A method for manufacturing a pigment dispersion, comprising the following steps: The step of adding an acidic compound (B) containing a hydrocarbon group to a first mixture containing an aqueous solvent (D) and a copolymer (A) to obtain a second mixture; and The step of adding pigment (C) to the second mixture and mixing it. The copolymer (A) comprises: a first segment (a1) derived from a nitrogen-containing polymerizable unsaturated monomer having at least one of a tertiary amine and a nitrogen-containing heterocyclic group, and a second segment (a2) derived from a polymerizable unsaturated monomer having a polyoxyolefin chain. The acidic compound (B) containing a hydrocarbon group has: a saturated or unsaturated hydrocarbon group having 5 to 23 carbon atoms (b1), and at least one acid group selected from carboxyl, phosphoric acid, sulfonic acid or phenolic groups (b2).

7. A method for manufacturing an aqueous coating composition, comprising the step of mixing a pigment dispersion prepared by the method of claim 6 with a coating film forming resin.

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