Coating composition

Abstract

Provided is a paint composition containing a hydroxyl group-containing resin (A), a curing agent (B), a scale-like photoluminescent pigment (C), a viscosity adjusting agent (D), and an organic solvent (E) having solubility in water at 20ºC of 4 mass% or higher. The viscosity adjusting agent (D) contains at least one viscosity adjusting agent selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2), and the content of the organic solvent (E) having solubility in water at 20ºC of 4 mass% or higher is within a range of 10-25 mass% on the basis of volatile components in the paint composition.

Description

[Technical Field]

[0001] This invention relates to a paint composition. [Background technology]

[0002] Conventionally, a widely adopted method for forming multi-layer coatings on automobile bodies or automobile parts is the 3-coat 2-bake method, in which the coating process is performed sequentially on the substrate (electrodeposited steel plate, plastic, etc.) in the following steps: application of an intermediate coating → heat curing → application of a base coat coating → application of a clear coating coating → heat curing.

[0003] In response to this, in recent years, from the viewpoint of shortening line processes and saving energy, a 3-coat 1-bake method, in which the heat curing process after the application of the intermediate coat paint or the application of the intermediate coat paint is omitted and the intermediate coat paint application → base coat paint application → clear coat paint application → heat curing is performed in order, and a 2-coat 1-bake method, in which the base coat paint application → clear coat paint application → heat curing is performed in order (a preheating process may be added after the paint is applied). In particular, from the viewpoint of suppressing environmental pollution caused by the volatilization of organic solvents, the 3-coat 1-bake method and the 2-coat 1-bake method using water-based paint as the base coat are especially in demand.

[0004] In the painting of automobile exteriors, even with the above-mentioned 3-coat, 1-bake method, there is a requirement to achieve a high-quality aesthetic appearance, similar to or even better than conventional methods.

[0005] Furthermore, water-based paints containing glossy pigments have the problem of being more prone to metallic unevenness compared to organic solvent-based paints.

[0006] On the other hand, since thickening and / or sedimentation of paint during storage can make painting difficult, paint also requires storage stability.

[0007] In the above-mentioned water-based base coat paint, one means of controlling viscosity is to incorporate an associated viscosity modifier into the paint. Generally, this associated viscosity modifier has a hydrophilic portion and a hydrophobic portion in one molecule. In water-based paints, the hydrophilic portion contributes to stability in aqueous solution, while the hydrophobic portion adsorbs to the surface of pigments and / or resin particles incorporated in the water-based paint, or the hydrophobic portions associate with each other, thereby forming a network structure and effectively exhibiting a thickening effect.

[0008] The above-mentioned associated viscosity modifiers typically form a network structure through hydrophobic interactions, thereby exhibiting viscosity.

[0009] The above-mentioned water-based basecoat paints generally contain surfactants to disperse hydrophobic resin components in water. Furthermore, if they contain water-soluble resins, additives, or pigment dispersion pastes, the hydrophilic organic solvents they contain may be introduced into the water-based paint.

[0010] However, in aqueous base coat paints containing the above-mentioned surfactant and / or hydrophilic organic solvent, when an aggregate viscosity modifier is used, the viscosity due to the aggregate viscosity modifier may not be easily achieved, which can lead to unevenness and other problems. Specifically, if the viscosity of the aqueous base coat is low when applied to the substrate, a mixed layer may form between it and the paint applied to the upper and / or lower layers. If the aqueous paint contains a glossy pigment, the glossy pigment in the paint may move after application, causing the orientation of the glossy pigment to become irregular and resulting in unevenness.

[0011] Patent Document 1 describes an aqueous coating composition containing acrylic resin particles (A), a hydroxyl group-containing resin (B), a crosslinking agent (C), a viscosity modifier (D), and a pigment (E), wherein the acrylic resin particles (A) have a core-shell structure with a mass ratio of 10 / 90 to 90 / 10, the core portion is crosslinked, and the amount of polymerizable unsaturated monomer (a1) having linear, branched, or cyclic saturated or unsaturated hydrocarbon groups with 4 or more carbon atoms is 3 to 70 parts by mass per 100 parts by mass of the total amount of polymerizable unsaturated monomers constituting the acrylic resin particles (A), the hydroxyl group-containing resin (B) has a weight-average molecular weight of 1,000 or more and less than 100,000, and the viscosity modifier (D) is 100,0 It has been disclosed that an aqueous coating composition having a weight-average molecular weight of 00 or more, and comprising 5 to 50 parts by mass of a polymerizable unsaturated monomer (d1) having a polyoxyalkylene chain, 5 to 90 parts by mass of a hydrophilic functional group-containing polymerizable unsaturated monomer (d2) without a polyoxyalkylene chain, selected from N-vinyl-2-pyrrolidone, N-substituted (meth)acrylamide, hydroxyl group-containing polymerizable unsaturated monomer and acid group-containing polymerizable unsaturated monomer, and 5 to 90 parts by mass of other polymerizable unsaturated monomers (d3) per 100 parts by mass of the total amount of constituent monomers, exhibits high viscosity development and viscosity decreases with increasing shear rate. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 2013-221041 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] In the technology described in Patent Document 1, it was sometimes difficult to achieve both the storage stability of the resulting paint composition and the suppression of metallic unevenness in the formed coating film. In particular, when a hydrophilic solvent was included in the aqueous paint composition, sufficient viscosity could not be obtained, making it difficult to achieve both the storage stability of the resulting paint composition and the suppression of metallic unevenness in the formed coating film.

[0014] The object of the present invention is to provide a coating composition that can form a multi-layer coating film having excellent storage stability and a superior appearance with suppressed metallic unevenness. [Means for solving the problem]

[0015] As a result of diligent research to solve the above problems, the present inventors have found that the above problems can be solved by using a paint composition comprising a hydroxyl group-containing resin (A), a curing agent (B), a flake-like glossy pigment (C), a viscosity modifier (D), and an organic solvent (E) having a water solubility of 4% by mass or more at 20°C, wherein the viscosity modifier (D) comprises at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2), and the content of the organic solvent (E) having a water solubility of 4% by mass or more at 20°C is in the range of 10 to 25% by mass, based on the volatile components in the paint composition.

[0016] In other words, the present invention <1> ~ <7> This concerns... <1> A paint composition comprising a hydroxyl group-containing resin (A), a curing agent (B), a flake-like glossy pigment (C), a viscosity modifier (D), and an organic solvent (E) having a water solubility of 4% by mass or more at 20°C, wherein the viscosity modifier (D) comprises at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2), and the content of the organic solvent (E) having a water solubility of 4% by mass or more at 20°C is in the range of 10 to 25% by mass, based on the volatile components in the paint composition. <2> The aforementioned flake-like luminous pigment (C) includes a flake-like aluminum pigment (C1) coated with silica, <1> The paint composition described above. <3> The viscosity modifier (D) includes cellulose nanocrystals (D1). <1> or <2> The paint composition described above. <4> The organic solvent (E) having a solubility in water at 20°C of 4% by mass or more includes an organic solvent (E1) having a solubility in water at 20°C in the range of 4 to 10% by mass. <1> ~ <3> A paint composition as described in any one of the following. <5> Furthermore, it contains water, <1> ~ <4> A paint composition as described in any one of the following. <6> Step (I-1): A step of applying a base coat paint composition (Y) to the object to be coated to form an uncured base coat film. Step (I-2): A step of applying a clear coat coating composition (Z) onto the uncured base coat coating to form an uncured clear coat coating, and Step (I-3): A method for forming a multilayer coating film, which includes a step of heating the uncured base coat film and the uncured clear coat film to cure both coating films simultaneously, The base coat paint composition (Y) <1> ~ <5> A method for forming a multilayer coating film using a paint composition described in any one of the following. <7> Step (II-1): A step of applying a colored paint composition (X) to the object to be coated to form an uncured colored coating film. Step (II-2): A step of applying a base coat paint composition (Y) onto the uncured colored coating to form an uncured base coat coating, Step (II-3): A step of applying a clear coat coating composition (Z) onto the uncured base coat coating to form an uncured clear coat coating, and Step (II-4): A method for forming a multilayer coating film, comprising the step of heating the uncured colored coating film, the uncured base coat coating film, and the uncured clear coat coating film to cure them simultaneously, The base coat paint composition (Y) <1> ~ <5> A method for forming a multilayer coating film using a paint composition described in any one of the following. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a coating composition capable of forming a multilayer coating film having excellent storage stability and an excellent appearance with suppressed metallic unevenness.

Mode for Carrying Out the Invention

[0018] In this specification, the singular form (a, an, the, etc.) includes the singular and plural unless otherwise specified in the specification or clearly contradictory in the context.

[0019] Hereinafter, the present invention will be described in detail, but these show an example of a preferred embodiment, and the present invention is not limited to these contents.

[0020] The coating composition of the present invention is a coating composition containing a hydroxyl group-containing resin (A), a curing agent (B), a flaky bright pigment (C), a viscosity modifier (D), and an organic solvent (E) having a solubility in water at 20°C of 4% by mass or more, wherein the viscosity modifier (D) contains at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2), and the content of the organic solvent (E) having a solubility in water at 20°C of 4% by mass or more is in the range of 10 to 25% by mass based on the volatile components in the coating composition.

[0021] 〔Hydroxyl Group-Containing Resin (A)〕 The hydroxyl group-containing resin (A) is a resin having at least one hydroxyl group in one molecule. Examples of the hydroxyl group-containing resin (A) include hydroxyl group-containing acrylic resins (A1), hydroxyl group-containing polyester resins (A2), hydroxyl group-containing polyurethane resins (A3), hydroxyl group-containing acrylic-modified polyester resins, hydroxyl group-containing polyether resins, hydroxyl group-containing polycarbonate resins, hydroxyl group-containing epoxy resins, hydroxyl group-containing alkyd resins, and the like. These can be used alone or in combination of two or more.

[0022] The hydroxyl value of the above-mentioned hydroxyl group-containing resin (A) is preferably in the range of 1 to 200 mg KOH / g, more preferably in the range of 2 to 180 mg KOH / g, and particularly preferably in the range of 5 to 170 mg KOH / g, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness in the formed coating film.

[0023] The content of the hydroxyl group-containing resin (A) in the paint composition of the present invention is preferably 20 to 90% by mass, more preferably 25 to 87% by mass, and particularly preferably 30 to 85% by mass, based on the amount of resin solids in the paint composition, from the viewpoint of storage stability and resistance to wilting of the obtained paint composition.

[0024] In this specification, "solid content" refers to non-volatile components such as resins, curing agents, and pigments that remain after drying at 110°C for 1 hour. The solid content can be determined, for example, by weighing a sample into a heat-resistant container such as an aluminum foil cup, spreading the sample on the bottom surface of the container, drying it at 110°C for 1 hour, and then weighing the mass of the components remaining after drying.

[0025] Furthermore, in this specification, "solid content concentration" means the mass percentage of the solid content in the composition. For example, the solid content concentration of a composition can be calculated by measuring the composition into a heat-resistant container such as an aluminum foil cup, spreading the composition on the bottom surface of the container, drying it at 110°C for 1 hour, weighing the mass of the components remaining in the composition after drying, and determining the ratio of the mass of the components remaining after drying to the total mass of the composition before drying.

[0026] As the hydroxyl group-containing resin (A) mentioned above, it is preferable that it contains a hydroxyl group-containing acrylic resin (A1) from the viewpoint of storage stability of the resulting paint composition and suppression of metallic unevenness in the formed coating film.

[0027] Furthermore, the hydroxyl group-containing resin (A) preferably includes a hydroxyl group-containing polyester resin (A2) from the viewpoint of the wilt resistance of the resulting paint composition and the appearance of the formed coating film.

[0028] Furthermore, from the viewpoint of the chipping resistance of the resulting paint composition, it is preferable that the hydroxyl group-containing resin (A) contains a hydroxyl group-containing polyurethane resin (A3).

[0029] Hydroxyl group-containing acrylic resin (A1) A hydroxyl group-containing acrylic resin (A1) can usually be produced by copolymerizing a hydroxyl group-containing polymerizable unsaturated monomer (a) and another polymerizable unsaturated monomer (b) copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer (a) by a known method, such as solution polymerization in an organic solvent or emulsion polymerization in an aqueous medium.

[0030] The above-mentioned hydroxyl group-containing polymerizable unsaturated monomer (a) is a compound having at least one hydroxyl group and at least one polymerizable unsaturated group in one molecule. Examples include monoesters of (meth)acrylic acid with a dihydric alcohol having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone modified forms of these monoesters; N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular terminus.

[0031] However, in the present invention, monomers corresponding to the polymerizable unsaturated monomer having an ultraviolet-absorbing functional group (xvii) described later should be defined as the hydroxyl group-containing polymerizable unsaturated monomer (a) and other polymerizable unsaturated monomers (b) that can copolymerize with the hydroxyl group-containing polymerizable unsaturated monomer (a), and are excluded from the hydroxyl group-containing polymerizable unsaturated monomer (a). The hydroxyl group-containing polymerizable unsaturated monomer (a) can be used alone or in combination of two or more types.

[0032] In this specification, a polymerizable unsaturated group means an unsaturated group that can undergo radical polymerization. Examples of such polymerizable unsaturated groups include vinyl groups, (meth)acryloyl groups, (meth)acrylamide groups, vinyl ether groups, allyl groups, propenyl groups, isopropenyl groups, and maleimide groups.

[0033] In this specification, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acrylic acid" means acrylic acid or methacrylic acid. Also, "(meth)acryloyl" means acryloyl or methacryloyl. Furthermore, "(meth)acrylamide" means acrylamide or methacrylamide.

[0034] The hydroxyl group-containing polymerizable unsaturated monomer (a) and the copolymerizable other polymerizable unsaturated monomer (b) can be appropriately selected and used according to the desired properties of the hydroxyl group-containing acrylic resin (A1). Specific examples of monomer (b) are listed in (i) to (xix) below. These can be used individually or in combination of two or more. (i) Alkyl or cycloalkyl (meth)acrylates: For example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate, tricyclodecanyl (meth)acrylate, etc. (ii) Polymerizable unsaturated monomers having an isobornyl group: for example, isobornyl (meth)acrylate, etc. (iii) Polymerizable unsaturated monomers having an adamantyl group: for example, adamantyl (meth)acrylate, etc. (iv) Polymerizable unsaturated monomers having a tricyclodecenyl group: for example, tricyclodecenyl (meth)acrylate, etc. (v) Polymerizable unsaturated monomers containing aromatic rings: for example, benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, etc. (vi) Polymerizable unsaturated monomers having an alkoxysilyl group: for example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, etc. (vii) Polymerizable unsaturated monomers having a fluorinated alkyl group: for example, perfluoroalkyl (meth)acrylates such as perfluorobutylethyl (meth)acrylate and perfluorooctylethyl (meth)acrylate; fluoroolefins, etc. (viii) A polymerizable unsaturated monomer having a photopolymerizable functional group such as a maleimide group. (ix) Vinyl compounds: For example, N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, etc. (x) Carboxylate-containing polymerizable unsaturated monomers: for example, (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl acrylate, etc. (xi) Nitrogen-containing polymerizable unsaturated monomers: for example, (meth)acrylonitrile, (meth)acrylamide, N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, methylenebis(meth)acrylamide, ethylenebis(meth)acrylamide, 2-(methacryloyloxy)ethyltrimethylammonium chloride, adducts of glycidyl (meth)acrylate and amine compounds, etc. (xii) Polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule: for example, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, etc. (xiii) Polymerizable unsaturated monomers containing epoxy groups: for example, glycidyl (meth)acrylate, β-methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3,4-epoxycyclohexylethyl (meth)acrylate, 3,4-epoxycyclohexylpropyl (meth)acrylate, allyl glycidyl ether, etc. (xiv) A (meth)acrylate having a polyoxyethylene chain with an alkoxy group at the molecular terminus. (xv) Polymerizable unsaturated monomers having a sulfonic acid group: for example, 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allylsulfonic acid, 4-styrenesulfonic acid, etc.; sodium salts, ammonium salts, etc. of these sulfonic acids. (xvi) Polymerizable unsaturated monomers having a phosphate group: acid phosphooxyethyl (meth)acrylate, acid phosphooxypropyl (meth)acrylate, acid phosphooxypoly(oxyethylene) glycol (meth)acrylate, acid phosphooxypoly(oxypropylene) glycol (meth)acrylate, etc. (xvii) Polymerizable unsaturated monomers having UV-absorbing functional groups: for example, 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2-hydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4-(3-acryloyloxy-2-hydroxypropoxy)benzophenone, 2-(2'-hydroxy-5'-methacryloyloxyethylphenyl)-2H-benzotriazole, etc. (xviii) Photostable polymerizable unsaturated monomers: e.g., 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloylamino-2,2,6 ,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, etc. (xix) Polymerizable unsaturated monomers having a carbonyl group: for example, acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formyl styrene, vinyl alkyl ketones having 4 to 7 carbon atoms (for example, vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), etc.

[0035] The hydroxyl group-containing acrylic resin (A1) can also be used in combination with a so-called urethane-modified acrylic resin, which is obtained by elongating some of the hydroxyl groups in the resin through a urethane reaction with a polyisocyanate compound to increase its molecular weight.

[0036] The hydroxyl group-containing polymerizable unsaturated monomer (a) can be used in a range of generally 1 to 50% by mass, preferably 2 to 40% by mass, and more preferably 3 to 30% by mass, based on the total amount of the hydroxyl group-containing polymerizable unsaturated monomer (a) and the other copolymerizable polymerizable unsaturated monomer (b).

[0037] The hydroxyl value of the hydroxyl group-containing acrylic resin (A1) is preferably in the range of 1 to 200 mg KOH / g, more preferably in the range of 2 to 150 mg KOH / g, and particularly preferably in the range of 5 to 100 mg KOH / g, from the viewpoint of the storage stability of the resulting paint composition.

[0038] Furthermore, the acid value of the hydroxyl group-containing acrylic resin (A1) is preferably in the range of 1 to 200 mg KOH / g, more preferably in the range of 2 to 150 mg KOH / g, and particularly preferably in the range of 5 to 80 mg KOH / g, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness in the formed coating film.

[0039] Furthermore, the weight-average molecular weight of the hydroxyl group-containing acrylic resin (A1) is preferably in the range of 2,000 to 5,000,000, more preferably in the range of 4,000 to 1,000,000, and particularly preferably in the range of 8,000 to 500,000, from the viewpoint of the storage stability of the resulting paint composition.

[0040] In this specification, the number-average molecular weight and weight-average molecular weight are values ​​obtained by converting the retention time (retention volume) measured using gel permeation chromatography (GPC) to the molecular weight of polystyrene based on the retention time (retention volume) of standard polystyrene with a known molecular weight measured under the same conditions. Specifically, the measurement can be performed using the "HLC-8120GPC" (product name, manufactured by Tosoh Corporation) as the gel permeation chromatograph, with a total of four columns: "TSKgel G4000HXL", "TSKgel G3000HXL", "TSKgel G2500HXL", and "TSKgel G2000HXL" (product names, all manufactured by Tosoh Corporation), a differential refractometer as the detector, and under the conditions of mobile phase: tetrahydrofuran, measurement temperature: 40°C, and flow rate: 1 mL / min.

[0041] When the paint composition of the present invention is an aqueous paint, the hydroxyl group-containing acrylic resin (A1) preferably contains a water-dispersible hydroxyl group-containing acrylic resin (A11) (hereinafter sometimes abbreviated as "water-dispersible hydroxyl group-containing acrylic resin (A11)") having a core / shell type multilayer structure, comprising a core of copolymer (I) obtained by copolymerizing a polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and a polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule, and a shell of copolymer (II) obtained by copolymerizing the hydroxyl group-containing polymerizable unsaturated monomer (a) and a polymerizable unsaturated monomer (b) other than the hydroxyl group-containing polymerizable unsaturated monomer (a) as constituent components, from the viewpoint of storage stability and resistance to wilting of the resulting paint composition.

[0042] Examples of polymerizable unsaturated monomers (c) having at least two polymerizable unsaturated groups constituting the core in one molecule include allyl(meth)acrylate, ethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, and 1,6-hexanediol di(meth)acrylate. Examples include acrylates, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, glycerol di(meth)acrylate, 1,1,1-trishydroxymethylethane di(meth)acrylate, 1,1,1-trishydroxymethylethane tri(meth)acrylate, 1,1,1-trishydroxymethylpropane tri(meth)acrylate, triallyl isocyanurate, diallyl terephthalate, and divinylbenzene, which can be used individually or in combination of two or more.

[0043] The polymerizable unsaturated monomer (c), which has at least two polymerizable unsaturated groups in one molecule, can be used in a range of generally 0.1 to 30% by mass, preferably 0.1 to 10% by mass, and more preferably 0.1 to 5% by mass, based on the total mass of monomer (c) and monomer (d).

[0044] Furthermore, the polymerizable unsaturated monomer (d) having one polymerizable unsaturated group per molecule that constitutes the core is a polymerizable unsaturated monomer copolymerizable with the polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups per molecule, and includes compounds containing one polymerizable unsaturated group per molecule, such as a vinyl group, (meth)acryloyl group, allyl group, etc.

[0045] Specific examples of polymerizable unsaturated monomers (d) having one polymerizable unsaturated group per molecule include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, tridecyl (meth)acrylate, and Alkyl or cycloalkyl (meth)acrylates such as uryl (meth)acrylate, stearyl (meth)acrylate, "isostearyl acrylate" (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, tert-butylcyclohexyl (meth)acrylate, cyclododecyl (meth)acrylate; polymerizable unsaturated monomers having an isobornyl group such as isobornyl (meth)acrylate; polymerizable monomers having an adamantyl group such as adamantyl (meth)acrylate Unsaturated monomers; vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyltoluene; monoesters of (meth)acrylic acid with a dihydric alcohol having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone modified forms of the monoesters of (meth)acrylic acid with a dihydric alcohol having 2 to 8 carbon atoms; allyl alcohol; polyoxyethylene chains with hydroxyl groups at the molecular ends. Examples include hydroxyl group-containing polymerizable unsaturated monomers such as (meth)acrylate; carboxyl group-containing polymerizable unsaturated monomers such as (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate; and nitrogen-containing polymerizable unsaturated monomers such as adducts of (meth)acrylonitrile, (meth)acrylamide, dimethylaminopropyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate with amine compounds. These can be used individually or in combination of two or more.

[0046] On the other hand, as the hydroxyl group-containing polymerizable unsaturated monomer (a) constituting the shell, as mentioned above, examples include monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone modified monoesters of (meth)acrylic acid and dihydric alcohols having 2 to 8 carbon atoms; allyl alcohol; and (meth)acrylates having polyoxyethylene chains with hydroxyl groups at the molecular ends. These can be used individually or in combination of two or more.

[0047] The above-mentioned hydroxyl group-containing polymerizable unsaturated monomer (a) can be used in a range of generally 1 to 35% by mass, preferably 2 to 25% by mass, and more preferably 3 to 20% by mass, based on the total mass of monomer (a) and monomer (b).

[0048] Furthermore, as polymerizable unsaturated monomers (b) other than the hydroxyl group-containing polymerizable unsaturated monomer (a) that constitute the shell, any polymerizable unsaturated monomer (b) other than the hydroxyl group-containing polymerizable unsaturated monomer (a) mentioned above can be used. These can be used individually or in combination of two or more types.

[0049] The polymerizable unsaturated monomer (b), other than the hydroxyl group-containing polymerizable unsaturated monomer (a) described above, preferably contains a carboxyl group-containing polymerizable unsaturated monomer (e) as at least a part of its components, in order to ensure the smoothness of the coating film formed.

[0050] Examples of the carboxyl group-containing polymerizable unsaturated monomer (e) include (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate, among which (meth)acrylic acid is preferred.

[0051] The carboxyl group-containing polymerizable unsaturated monomer (e) is preferably used in a range of generally 1 to 40% by mass, particularly 1 to 25% by mass, and even more particularly 1 to 19% by mass, based on the total mass of monomer (a) and monomer (b), from the viewpoint of the stability of the water-dispersible hydroxyl group-containing acrylic resin (A11) in an aqueous medium.

[0052] The hydroxyl value of the water-dispersible hydroxyl group-containing acrylic resin (A11) is preferably in the range of 1 to 100 mg KOH / g, more preferably in the range of 2 to 90 mg KOH / g, and particularly preferably in the range of 5 to 85 mg KOH / g, from the viewpoint of the storage stability of the resulting paint composition.

[0053] Furthermore, the acid value of the water-dispersible hydroxyl group-containing acrylic resin (A11) is preferably in the range of 3 to 90 mgKOH / g, more preferably in the range of 4 to 70 mgKOH / g, and particularly preferably in the range of 5 to 50 mgKOH / g, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness in the formed coating film.

[0054] Furthermore, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness in the formed coating film, it is preferable to use polymerizable unsaturated monomers having only one polymerizable unsaturated group per molecule as monomer (a) and monomer (b), and to make the shell of the water-dispersible hydroxyl group-containing acrylic resin (A11) uncrosslinked.

[0055] The above-mentioned water-dispersible hydroxyl group-containing acrylic resin (A11) can be obtained, for example, by emulsion polymerization of a monomer mixture (I) containing 0.1 to 30% by mass of a polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups per molecule and 70 to 99.9% by mass of a polymerizable unsaturated monomer (d) having one polymerizable unsaturated group per molecule, to which a monomer mixture (II) containing 1 to 35% by mass of the hydroxyl group-containing polymerizable unsaturated monomer (a) and 65 to 99% by mass of polymerizable unsaturated monomers other than monomer (a) is added, and further polymerization is carried out.

[0056] The emulsion polymerization of the above monomer mixture can be carried out by a method known in itself, for example, by using a polymerization initiator in the presence of an emulsifier.

[0057] As the emulsifier mentioned above, anionic or nonionic emulsifiers are preferred. Examples of anionic emulsifiers include sodium salts and ammonium salts of organic acids such as alkyl sulfonic acid, alkylbenzene sulfonic acid, and alkyl phosphoric acid. Examples of nonionic emulsifiers include polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan triolate, and polyoxyethylene sorbitan monolaurate.

[0058] A polyoxyalkylene group-containing anionic emulsifier having an anionic group and a polyoxyalkylene group such as a polyoxyethylene group or a polyoxypropylene group in one molecule, or a reactive anionic emulsifier having the anionic group and a radically polymerizable unsaturated group in one molecule may be used, and among these, the use of a reactive anionic emulsifier is preferred.

[0059] Examples of the above-mentioned reactive anionic emulsifiers include sodium salts and ammonium salts of sulfonic acid compounds having radically polymerizable unsaturated groups such as (meth)allyl groups, (meth)acryloyl groups, propenyl groups, and butenyl groups. Among these, ammonium salts of sulfonic acid compounds having radically polymerizable unsaturated groups are preferred because they provide excellent water resistance to the formed coating film. Examples of such ammonium salts of sulfonic acid compounds include commercially available products such as "Latemul S-180A" (trade name, manufactured by Kao Corporation).

[0060] Among the ammonium salts of sulfonic acid compounds having the above-mentioned radical polymerizable unsaturated group, ammonium salts of sulfonic acid compounds having both a radical polymerizable unsaturated group and a polyoxyalkylene group are even more preferred. Examples of commercially available ammonium salts of sulfonic acid compounds having both a radical polymerizable unsaturated group and a polyoxyalkylene group include "Aqualon KH-10" (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and "SR-1025A" (trade name, manufactured by Asahi Denka Kogyo Co., Ltd.).

[0061] The emulsifier described above can be used in an amount of typically 0.1 to 15% by mass, preferably 0.5 to 10% by mass, and more preferably 1 to 5% by mass, based on the total amount of monomers used.

[0062] The polymerization initiator may be of either oil-soluble or water-soluble type, and examples include organic peroxides such as benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearoyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl peroxylaurate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, and diisopropylbenzene hydroperoxide; azobisisobutyronite Examples include azo compounds such as lyl, azobis(2,4-dimethylvaleronitrile), azobis(2-methylpropionnitrile), azobis(2-methylbutyronitrile), 4,4'-azobis(4-cyanobutanoic acid), dimethylazobis(2-methylpropionate), azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], and azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide}; and persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate. These can be used individually or in combination of two or more.

[0063] Furthermore, the polymerization initiator may be optionally combined with a reducing agent such as sugar, sodium formaldehyde sulfoxylate, or an iron complex to form a redox polymerization system.

[0064] The polymerization initiator described above is preferably used in an amount of 0.1 to 5% by mass, and particularly 0.2 to 3% by mass, based on the total mass of all monomers used. The method of adding the polymerization initiator is not particularly limited and can be appropriately selected depending on its type, amount, etc. For example, the polymerization initiator may be included in the monomer mixture or aqueous medium beforehand, or it may be added all at once during polymerization, or added dropwise.

[0065] The water-dispersible hydroxyl group-containing acrylic resin (A11) can be obtained by adding a monomer mixture (II) containing the hydroxyl group-containing polymerizable unsaturated monomer (a) and a polymerizable unsaturated monomer other than monomer (a) (b) to the emulsion obtained as described above, and further polymerization.

[0066] The above monomer mixture (II) may optionally contain, as appropriate, the polymerization initiators, chain transfer agents, reducing agents, emulsifiers, and other components listed above.

[0067] Furthermore, while the monomer mixture (II) can be added dropwise as is, it is preferable to disperse the monomer mixture (II) in an aqueous medium and add it dropwise as a monomer emulsion. In this case, the particle size of the monomer emulsion is not particularly limited.

[0068] Polymerization of the above monomer mixture (II) can be carried out, for example, by adding the monomer mixture (II), which may be emulsified, to the emulsion all at once or dropwise, and heating it to a suitable temperature while stirring.

[0069] The water-dispersible hydroxyl group-containing acrylic resin (A11) obtained as described above may have a core / shell type multilayer structure in which a copolymer (I) formed from the monomer mixture (I) containing a polymerizable unsaturated monomer (c) having at least two polymerizable unsaturated groups in one molecule and a polymerizable unsaturated monomer (d) having one polymerizable unsaturated group in one molecule is the core, and a copolymer (II) formed from the monomer mixture (II) containing the hydroxyl group-containing polymerizable unsaturated monomer (a) and a polymerizable unsaturated monomer (b) other than monomer (a) is the shell.

[0070] Furthermore, the water-dispersible hydroxyl group-containing acrylic resin (A11) may be obtained as resin particles consisting of three or more layers by adding a step of supplying polymerizable unsaturated monomers (one or a mixture of two or more) to form other resin layers and performing emulsion polymerization between the step of obtaining copolymer (I) and the step of obtaining copolymer (II).

[0071] In this invention, the "shell" of the water-dispersible hydroxyl group-containing acrylic resin (A11) refers to the polymer layer present on the outermost layer of the resin particles, the "core" refers to the polymer layer in the inner layer of the resin particles excluding the shell portion, and the "core / shell type structure" refers to a structure having the core and the shell. The core / shell type structure is generally a layered structure in which the core is completely covered by the shell, but depending on the mass ratio of the core to the shell, the amount of monomer in the shell may be insufficient to form a layered structure. In such cases, it is not necessary to have a complete layered structure as described above, and it may be a structure in which a part of the core is covered by the shell, or a structure in which polymerizable unsaturated monomers, which are components of the shell, are graft polymerized onto a part of the core. Furthermore, the concept of a multilayer structure in the core / shell type structure also applies when a multilayer structure is formed in the core of the water-dispersible hydroxyl group-containing acrylic resin (A11).

[0072] In the water-dispersible hydroxyl group-containing acrylic resin (A11) having a core / shell type multilayer structure, the ratio of copolymer (I) to copolymer (II) is preferably within the range of 10 / 90 to 90 / 10, particularly 50 / 50 to 85 / 15, and even more preferably 65 / 35 to 80 / 20 in terms of the solid content mass ratio of copolymer (I) to copolymer (II), from the viewpoint of storage stability of the resulting paint composition.

[0073] The water-dispersible hydroxyl group-containing acrylic resin (A11) obtained as described above can generally have an average particle size in the range of 10 to 1,000 nm, and particularly in the range of 20 to 500 nm.

[0074] In this specification, the average particle size of the hydroxyl group-containing acrylic resin is the value measured at 20°C after dilution with deionized water by a conventional method using a particle size distribution analyzer based on dynamic light scattering. As a particle size distribution analyzer based on dynamic light scattering, for example, "ELSZ-2000" (product name, manufactured by Otsuka Electronics Co., Ltd.) can be used.

[0075] To improve the mechanical stability of the aqueous dispersion particles of the water-dispersible hydroxyl group-containing acrylic resin (A11) obtained, it is desirable to neutralize the acidic groups such as carboxyl groups present in the water-dispersible hydroxyl group-containing acrylic resin (A11) with a neutralizing agent. The neutralizing agent is not particularly limited as long as it can neutralize the acidic groups, and examples include sodium hydroxide, potassium hydroxide, trimethylamine, 2-(dimethylamino)ethanol, 2-amino-2-methyl-1-propanol, triethylamine, and aqueous ammonia. It is desirable to use these neutralizing agents in an amount such that the pH of the aqueous dispersion of the dispersible hydroxyl group-containing acrylic resin (A11) after neutralization is approximately 6.5 to approximately 9.0.

[0076] Furthermore, the water-dispersible hydroxyl group-containing acrylic resin (A11) may include a water-dispersible hydroxyl group-containing acrylic resin (A11') containing a gradient polymer layer.

[0077] The gradient polymer layer of the water-dispersible hydroxyl group-containing acrylic resin (A11') including the above gradient polymer layer refers to a polymer layer having a layer structure in which the composition changes continuously (has a compositional gradient).

[0078] More specifically, it refers to a polymer layer having a compositional gradient, where the monomer (or monomer mixture) composition changes continuously, for example, from monomer A (or monomer mixture A) to monomer B (or monomer mixture B).

[0079] The above gradient polymer layer can generally be obtained by a known polymerization method called power feed polymerization. Specifically, for example, when polymerizing two types of monomer A (or monomer mixture A) and monomer B (or monomer mixture B), a gradient polymer layer can be obtained by introducing monomer A (or monomer mixture A) into a reaction vessel while dropping monomer B (or monomer mixture B) into a container containing monomer A (or monomer mixture A) and carrying out the polymerization reaction.

[0080] In the power feed polymerization described above, a gradient polymer layer having a desired composition gradient can be obtained by adjusting the synthesis conditions (such as the timing of the start of mixing between monomer A (or monomer mixture A) and monomer B (or monomer mixture B), the rate at which monomer B (or monomer mixture B) is dropped into the container containing monomer A (or monomer mixture A), and the rate at which monomer A (or monomer mixture A) is introduced into the reaction vessel).

[0081] The water-dispersible hydroxyl group-containing acrylic resin (A11') containing a gradient polymer layer is an acrylic resin comprising a core portion which is a copolymer (I) with polymerizable unsaturated monomers as copolymer components, a shell portion which is a copolymer (II) with polymerizable unsaturated monomers as copolymer components, and a gradient polymer layer present between the core portion and the shell portion.

[0082] The polymerizable unsaturated monomers that constitute the core and shell portions can be appropriately combined with the hydroxyl group-containing polymerizable unsaturated monomer and other polymerizable unsaturated monomers copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer.

[0083] To produce the water-dispersible hydroxyl group-containing acrylic resin (A11') containing the above gradient polymer layer, first, a polymerizable unsaturated monomer mixture is emulsion-polymerized to prepare an emulsion of the core copolymer (I).

[0084] Emulsion polymerization for preparing the core copolymer (I) emulsion can be carried out by conventionally known methods. For example, it can be carried out by emulsion polymerization of a polymerizable unsaturated monomer mixture using a polymerization initiator in the presence of an emulsifier. As the emulsifier and polymerization initiator, for example, the emulsifier and polymerization initiator mentioned above can be used.

[0085] To obtain a water-dispersible hydroxyl group-containing acrylic resin (A11') containing the above-mentioned gradient polymer layer, a gradient polymer layer is subsequently formed. This gradient polymer layer can be formed by the power feed polymerization described above.

[0086] For the formation of the gradient polymer layer, a polymerizable unsaturated monomer mixture used for the emulsion polymerization of the core copolymer (I) and a polymerizable unsaturated monomer mixture used for the emulsion polymerization of the shell copolymer (II) can typically be used.

[0087] The water-dispersible hydroxyl group-containing acrylic resin (A11') containing the above gradient polymer layer can be further obtained by forming a shell copolymer (II).

[0088] The monomer mixture for forming the shell copolymer (II) described above may optionally contain components such as polymerization initiators, chain transfer agents, reducing agents, and emulsifiers. While the monomer mixture can be added dropwise as is, it is preferable to add it as a monomer emulsion obtained by dispersing the monomer mixture in an aqueous medium. In this case, the particle size of the monomer emulsion is not particularly limited.

[0089] A method for polymerizing the monomer mixture to form the shell copolymer (II) is, for example, to add the monomer mixture or its emulsion to the emulsion of the core copolymer (I) either all at once or gradually, and then heat it to a suitable temperature while stirring.

[0090] The ratio of the gradient polymer layer in the water-dispersible hydroxyl group-containing acrylic resin (A11') containing the above-mentioned gradient polymer layer is preferably in the range of 20 to 80% by mass, more preferably in the range of 25 to 75% by mass, and particularly preferably in the range of 30 to 70% by mass, based on the total amount of all copolymer components of the water-dispersible hydroxyl group-containing acrylic resin (A11') containing the gradient polymer layer, from the viewpoint of the water resistance of the resulting coating film.

[0091] The water-dispersible hydroxyl group-containing acrylic resin (A11') containing the above gradient polymer layer preferably has a hydroxyl value in the range of 1 to 150 mg KOH / g, more preferably in the range of 2 to 120 mg KOH / g, and particularly preferably in the range of 5 to 100 mg KOH / g, from the viewpoint of the curability, chipping resistance, adhesion, and finished appearance of the resulting coating film.

[0092] The core portion of the water-dispersible hydroxyl group-containing acrylic resin (A11') including the above gradient polymer layer preferably has a hydroxyl value in the range of 0 to 150 mg KOH / g, more preferably in the range of 5 to 120 mg KOH / g, and particularly preferably in the range of 10 to 100 mg KOH / g, from the viewpoint of the water resistance and chipping resistance of the resulting coating film.

[0093] The shell portion of the water-dispersible hydroxyl group-containing acrylic resin (A11') including the above gradient polymer layer preferably has a hydroxyl value in the range of 0 to 150 mg KOH / g, more preferably in the range of 2 to 120 mg KOH / g, and particularly preferably in the range of 5 to 100 mg KOH / g, from the viewpoint of the water resistance and chipping resistance of the resulting coating film.

[0094] The water-dispersible hydroxyl group-containing acrylic resin (A11') containing the above-mentioned gradient polymer layer preferably has an acid value in the range of 1 to 80 mgKOH / g, more preferably in the range of 5 to 50 mgKOH / g, and particularly preferably in the range of 5 to 30 mgKOH / g, from the viewpoint of storage stability of the resulting paint and water resistance of the formed coating film.

[0095] The core portion of the water-dispersible hydroxyl group-containing acrylic resin (A11') including the above gradient polymer layer preferably has an acid value in the range of 0 to 50 mgKOH / g, more preferably in the range of 0 to 30 mgKOH / g, and particularly preferably in the range of 0 to 10 mgKOH / g, from the viewpoint of manufacturing stability and storage stability of the resulting paint.

[0096] The shell portion of the water-dispersible hydroxyl group-containing acrylic resin (A11') including the above gradient polymer layer preferably has an acid value in the range of 1 to 100 mg KOH / g, more preferably in the range of 5 to 80 mg KOH / g, and particularly preferably in the range of 10 to 50 mg KOH / g, from the viewpoint of storage stability of the resulting paint and water resistance of the formed coating film.

[0097] The water-dispersible hydroxyl group-containing acrylic resin (A11') containing the above-mentioned gradient polymer layer preferably has a glass transition temperature of 20°C or higher, more preferably 30°C or higher, and particularly preferably 30 to 100°C, from the viewpoint of the water resistance, hardness, and chipping resistance of the formed coating film.

[0098] The core portion of the water-dispersible hydroxyl group-containing acrylic resin (A11') including the above gradient polymer layer preferably has a glass transition temperature in the range of -50 to 50°C, more preferably in the range of -30 to 50°C, and particularly preferably in the range of 0 to 50°C, from the viewpoint of the water resistance, hardness, film-forming properties, and chipping resistance of the formed coating film.

[0099] The shell portion of the water-dispersible hydroxyl group-containing acrylic resin (A11') including the above gradient polymer layer preferably has a glass transition temperature of 40°C or higher, more preferably 50°C or higher, and particularly preferably in the range of 50 to 100°C, from the viewpoint of the hardness and water resistance of the formed coating film.

[0100] In this specification, the glass transition temperature Tg of the water-dispersible hydroxyl group-containing acrylic resin (A11') including the gradient polymer layer is calculated using the following formula. 1 / Tg(K)=W1 / T1+W2 / T2+...Wn / Tn Tg(°C) = Tg(K) - 273 In the formula, W1, W2, ...Wn are the mass fractions of each monomer, and T1, T2, ...Tn are the glass transition temperatures Tg(K) of the homopolymers of each monomer. The glass transition temperatures of each monomer homopolymer are based on the values ​​in POLYMER HANDBOOK Fourth Edition, edited by J. Brandrup, Eh Immergut, and E.A. Grulke (1999). For monomers not listed in this literature, the glass transition temperature of the monomer homopolymer was synthesized to have a weight-average molecular weight of approximately 50,000, and the glass transition temperature was measured by differential scanning thermal analysis.

[0101] When the paint composition of the present invention contains the above-mentioned hydroxyl group-containing acrylic resin (A1), the content of the hydroxyl group-containing acrylic resin (A1) is preferably in the range of 1 to 60% by mass, more preferably in the range of 10 to 55% by mass, and particularly preferably in the range of 15 to 50% by mass, based on the amount of resin solids in the paint composition, from the viewpoint of the flip-flop properties and chipping resistance of the formed coating film.

[0102] Hydroxyl group-containing polyester resin (A2) The hydroxyl group-containing polyester resin (A2) can be obtained, for example, by using a polyol having two or more hydroxyl groups as the alcohol component and a polycarboxylic acid having two or more carboxyl groups as the acid component, and by condensing the alcohol component and the acid component.

[0103] As the above polyol, polyhydric alcohols having two or more hydroxyl groups in one molecule can be suitably used. Examples of such polyhydric alcohols include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 3-methyl-1,2-butanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, tricycline Examples include dihydric alcohols such as rodecane dimethanol, neopentyl glycol hydroxypivalate, hydrogenated bisphenol A, hydrogenated bisphenol F, and dimethylolpropionic acid; polylactone diols obtained by adding lactone compounds such as ε-caprolactone to these dihydric alcohols; ester diol compounds such as bis(hydroxyethyl) terephthalate; polyether diol compounds such as alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, and polybutylene glycol; trihydric or higher alcohols such as glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tris(2-hydroxyethyl)isocyanuric acid, sorbitol, and mannitol; polylactone polyol compounds obtained by adding lactone compounds such as ε-caprolactone to these trihydric or higher alcohols; and fatty acid esters of glycerin.

[0104] In addition, alcohol components other than the polyols mentioned above can also be used. Such alcohol components are not particularly limited and include, for example, monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, and 2-phenoxyethanol; and alcohol compounds obtained by reacting monoepoxy compounds such as propylene oxide, butylene oxide, and "Cardura E10" (trade name, manufactured by HEXION, a glycidyl ester of a synthetic highly branched saturated fatty acid) with an acid.

[0105] As the polycarboxylic acid, compounds commonly used in the production of polyester resins can be used. Examples of such polycarboxylic acids include aliphatic polybasic acids, alicyclic polybasic acids, aromatic polybasic acids, and the like.

[0106] The above-mentioned aliphatic polybasic acids are generally aliphatic compounds having two or more carboxyl groups in one molecule, acid anhydrides of the aliphatic compounds, and esters of the aliphatic compounds. Examples of aliphatic polybasic acids include aliphatic polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanediic acid, dodecanediic acid, brassic acid, octadecanediic acid, citric acid, and butanetetracarboxylic acid; anhydrides of the aliphatic polycarboxylic acids; and lower alkyl esters of the aliphatic polycarboxylic acids having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. The above-mentioned aliphatic polybasic acids can be used individually or in combination of two or more types.

[0107] The above-mentioned alicyclic polybasic acids are generally compounds having one or more alicyclic structures and two or more carboxyl groups in one molecule, acid anhydrides of the same, and esters of the same. The alicyclic structure can mainly be a 4- to 6-membered ring structure. Examples of alicyclic polybasic acids include alicyclic polycarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 3-methyl-1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 1,3,5-cyclohexanetricarboxylic acid; anhydrides of the alicyclic polycarboxylic acids; and lower alkyl esters of the alicyclic polycarboxylic acids having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. The above-mentioned alicyclic polybasic acids can be used individually or in combination of two or more.

[0108] The above-mentioned aromatic polybasic acids are generally aromatic compounds having two or more carboxyl groups in one molecule, acid anhydrides of the aromatic compounds, and esterified products of the aromatic compounds. Examples of aromatic polybasic acids include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, trimellitic acid, and pyromellitic acid; anhydrides of the aromatic polycarboxylic acids; and lower alkyl esters of the aromatic polycarboxylic acids having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. The above-mentioned aromatic polybasic acids can be used individually or in combination of two or more. It is preferable to use phthalic acid, phthalic anhydride, isophthalic acid, trimellitic acid, and trimellitic anhydride as the above-mentioned aromatic polybasic acids, and among these, it is more preferable to use trimellitic anhydride.

[0109] Furthermore, acid components other than the above-mentioned aliphatic polybasic acids, alicyclic polybasic acids, and aromatic polybasic acids can also be used. Such acid components are not particularly limited and include, for example, fatty acids such as coconut oil fatty acid, cottonseed oil fatty acid, hemp seed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, and safflower oil fatty acid; monocarboxylic acids such as lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butylbenzoic acid, cyclohexanoic acid, and 10-phenyloctadecanoic acid; and hydroxycarboxylic acids such as lactic acid, 3-hydroxybutanoic acid, and 3-hydroxy-4-ethoxybenzoic acid. These acid components can be used individually or in combination of two or more.

[0110] The method for producing the hydroxyl group-containing polyester resin (A2) is not particularly limited and can be carried out according to conventional methods. For example, the hydroxyl group-containing polyester resin (A2) can be produced by heating the alcohol component and the acid component in a nitrogen stream at approximately 150 to 250°C for approximately 5 to 10 hours to carry out an esterification reaction or transesterification reaction between the alcohol component and the acid component.

[0111] When carrying out the esterification or transesterification reaction of the above alcohol component and the above acid component, these components may be added to the reaction vessel all at once, or one or both may be added in several stages. Alternatively, a hydroxyl group-containing polyester resin may be synthesized first, and then the resulting hydroxyl group-containing polyester resin may be reacted with an acid anhydride to perform half-esterification to obtain a carboxyl group and hydroxyl group-containing polyester resin. Alternatively, a carboxyl group-containing polyester resin may be synthesized first, and then the above alcohol component may be added to produce the above hydroxyl group-containing polyester resin.

[0112] In the aforementioned esterification or transesterification reaction, known catalysts such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, and tetraisopropyl titanate can be used as catalysts to accelerate the reaction.

[0113] Furthermore, the hydroxyl group-containing polyester resin (A2) can be modified with fatty acids, monoepoxy compounds, polyisocyanate compounds, etc., during or after the manufacture of the resin.

[0114] Examples of the above fatty acids include coconut oil fatty acids, cottonseed oil fatty acids, hemp seed oil fatty acids, rice bran oil fatty acids, fish oil fatty acids, tall oil fatty acids, soybean oil fatty acids, linseed oil fatty acids, tung oil fatty acids, rapeseed oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, and safflower oil fatty acids. As for the above monoepoxy compound, for example, "Cardura E10P" (trade name, manufactured by HEXION, a glycidyl ester of synthetic highly branched saturated fatty acids) can be suitably used.

[0115] Furthermore, the polyisocyanate compounds exemplified in polyisocyanate compound (B2) described later can be used as the above-mentioned polyisocyanate compounds. These can be used individually or in combination of two or more.

[0116] The hydroxyl value of the hydroxyl group-containing polyester resin (A2) is preferably in the range of 1 to 200 mg KOH / g, more preferably in the range of 2 to 180 mg KOH / g, and particularly preferably in the range of 5 to 170 mg KOH / g, from the viewpoint of storage stability of the obtained coating composition and suppression of metallic unevenness in the formed coating film.

[0117] Furthermore, the weight-average molecular weight of the hydroxyl group-containing polyester resin (A2) is preferably in the range of 500 to 50,000, more preferably in the range of 1,000 to 30,000, and particularly preferably in the range of 1,200 to 20,000, from the viewpoint of storage stability of the obtained coating composition and suppression of metallic unevenness in the formed coating film.

[0118] Furthermore, the glass transition temperature (Tg) of the hydroxyl group-containing polyester resin (A2) is preferably in the range of -20°C to 50°C, more preferably in the range of -10°C to 40°C, and particularly preferably in the range of -5°C to 35°C, from the viewpoint of storage stability of the obtained coating composition and suppression of metallic unevenness in the formed coating film.

[0119] The hydroxyl group-containing polyester resin (A2) described above preferably has carboxyl groups from the viewpoint of storage stability of the resulting paint composition.

[0120] When the hydroxyl group-containing polyester resin (A2) has carboxyl groups, the acid value of the hydroxyl group-containing polyester resin (A2) is preferably in the range of 5 to 150 mg KOH / g, more preferably in the range of 10 to 140 mg KOH / g, and particularly preferably in the range of 15 to 120 mg KOH / g, from the viewpoint of storage stability of the resulting paint composition and suppression of metallic unevenness in the formed coating film.

[0121] When the coating composition of the present invention contains the above-mentioned hydroxyl group-containing polyester resin (A2), the content of the hydroxyl group-containing polyester resin (A2) is preferably in the range of 1 to 45% by mass, more preferably in the range of 5 to 40% by mass, and particularly preferably in the range of 10 to 35% by mass, based on the amount of resin solids in the coating composition, from the viewpoint of storage stability of the obtained coating composition and suppression of metallic unevenness of the formed coating film.

[0122] Hydroxyl group-containing polyurethane resin (A3) Examples of the hydroxyl group-containing polyurethane resin (A3) include hydroxyl group-containing polyurethane resins obtained by reacting a polyol with a polyisocyanate.

[0123] Examples of polyols include low molecular weight polyols such as dihydric alcohols like ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, and hexamethylene glycol, and trihydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol. Examples of high molecular weight polyols include polyether polyols, polyester polyols, acrylic polyols, and epoxy polyols. Examples of polyether polyols include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Examples of polyester polyols include the aforementioned dihydric alcohols, polycondensates of alcohols such as dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol with dibasic acids such as adipic acid, azelaic acid, and sebatic acid, lactone-based ring-opening polymer polyols such as polycaprolactone, and polycarbonate diols. In addition, carboxyl group-containing polyols such as 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid can also be used.

[0124] Examples of polyisocyanates to be reacted with the above polyols include aliphatic polyisocyanate compounds such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; isophorone diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and methylcyclohexane-2,4-(or-2,6-) diisocyanate. Alicyclic diisocyanate compounds such as 1,3-(or 1,4-)di(isocyanatomethyl)cyclohexane, 1,4-cyclohexanediisocyanate, 1,3-cyclopentanediisocyanate, and 1,2-cyclohexanediisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethylxylylene diisocyanate, tolylenediisocyanate, and 4,4'-diphenylmethanedi Aromatic diisocyanate compounds such as socyanates, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, (m- or p-)phenylene diisocyanate, 4,4'-biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, bis(4-isocyanatophenyl)sulfone, isopropylidene bis(4-phenylisocyanate), and their polypropylene Examples include biuret-type adducts and isocyanurate ring adducts of socyanates; polyisocyanate compounds having three or more isocyanate groups in one molecule, such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, and 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates.

[0125] The hydroxyl value of the above-mentioned hydroxyl group-containing polyurethane resin (A3) is preferably in the range of 1 to 150 mg KOH / g, more preferably in the range of 1 to 100 mg KOH / g, and particularly preferably in the range of 1 to 50 mg KOH / g, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness in the formed coating film.

[0126] The acid value of the hydroxyl group-containing polyurethane resin (A3) is preferably in the range of 3 to 90 mgKOH / g, more preferably in the range of 4 to 70 mgKOH / g, and particularly preferably in the range of 5 to 50 mgKOH / g, from the viewpoint of storage stability of the resulting paint composition and suppression of metallic unevenness in the formed coating film.

[0127] The number-average molecular weight of the hydroxyl group-containing polyurethane resin (A3) is preferably 10,000 or more, more preferably 50,000 or more, and particularly preferably 100,000 or more, from the viewpoint of storage stability of the resulting paint composition and suppression of metallic unevenness in the formed coating film.

[0128] When the coating composition of the present invention contains the above-mentioned hydroxyl group-containing polyurethane resin (A3), the content of the hydroxyl group-containing polyurethane resin (A3) is preferably in the range of 3 to 60% by mass, more preferably in the range of 5 to 40% by mass, and particularly preferably in the range of 7 to 30% by mass, based on the amount of resin solids in the coating composition, from the viewpoint of storage stability of the obtained coating composition and suppression of metallic unevenness of the formed coating film.

[0129] [Hardening agent (B)] The curing agent (B) is not particularly limited. For example, a crosslinking agent that is reactive with the hydroxyl groups of the hydroxyl group-containing resin (B) can be used.

[0130] Examples of the curing agent (B) include known crosslinking agents, specifically, amino resins (B1), polyisocyanate compounds (B2), blocked polyisocyanate compounds (B3), polyhydrazide compounds, polysemicarbazide compounds, carbodiimide compounds, oxazoline group-containing compounds, epoxy compounds, polycarboxylic acids, etc. The crosslinking agent may be used alone or in combination of two or more types.

[0131] The curing agent (B) described above preferably contains at least one crosslinking agent selected from amino resin (B1), polyisocyanate compound (B2), and blocked polyisocyanate compound (B3), from the viewpoint of chipping resistance of the formed coating film, more preferably contains amino resin (B1) and / or blocked polyisocyanate compound (B3), and particularly preferably contains amino resin (B1) and blocked polyisocyanate compound (B3).

[0132] Amino resin (B1) As the above amino resin (B1), a partially methylolated amino resin or a fully methylolated amino resin obtained by the reaction of an amino component and an aldehyde component can be used. Examples of amino components include melamine, urea, benzoguanamine, acetoganaamine, steroguanamine, spiloganamine, and dicyandiamide. Examples of aldehyde components include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

[0133] A methylolated amino resin can also be used in which the methylol group has been partially or completely etherified with a suitable alcohol. Examples of alcohols that can be used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethyl-1-butanol, and 2-ethyl-1-hexanol.

[0134] As the above amino resin (B1), melamine resin is preferred. In particular, methyl etherified melamine resin, in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with methyl alcohol, butyl etherified melamine resin, in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with butyl alcohol, and methyl-butyl mixed etherified melamine resin, in which the methylol groups of a partially or completely methylolated melamine resin are partially or completely etherified with methyl alcohol and butyl alcohol, are preferred, and methyl-butyl mixed etherified melamine resin is more preferred.

[0135] Furthermore, the weight-average molecular weight of the melamine resin is preferably in the range of 450 to 6,000, more preferably in the range of 500 to 4,000, and particularly preferably in the range of 550 to 3,000.

[0136] Commercially available melamine resins can be used. Examples of commercially available product names include "Cymel 202", "Cymel 203", "Cymel 211", "Cymel 238", "Cymel 251", "Cymel 254", "Cymel 303", "Cymel 325", "Cymel 327", "Cymel 350", "Cymel 370", "Cymel 385", "Cymel 1156", "Cymel 1158", and "Cymel 1130" (all manufactured by Ornex Japan Co., Ltd.); and "Uban 20SE60" and "Uban 28-60" (both manufactured by Mitsui Chemicals, Inc.).

[0137] When using the above-mentioned melamine resin as the curing agent (B), the following can be optionally used as curing catalysts: a sulfonic acid such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, or dinonylnaphthalenesulfonic acid; a neutralized salt of the sulfonic acid with an amine; or a neutralized salt of a phosphate ester compound with an amine.

[0138] The amino resin (B1) can be used, for example, as a crosslinking agent for resins containing hydroxyl groups.

[0139] Polyisocyanate compound (B2) The polyisocyanate compound (B2) is a compound having two or more isocyanate groups in one molecule.

[0140] The polyisocyanate compound (B2) includes, for example, aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of said polyisocyanates.

[0141] Examples of the above aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate, diisocyanate dimer, and methyl 2,6-diisocyanatohexanoate (common name: lysine). Examples include aliphatic diisocyanates such as diisocyanates; and aliphatic triisocyanates such as 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

[0142] Examples of the alicyclic polyisocyanates include alicyclic diisocyanates such as 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or mixtures thereof, norbornane diisocyanate, etc.; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)hepta , 2-(3-isocyanatopropyl)-2,6-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 3-(3-isocyanatopropyl)-2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanatoethyl)-2-isocyana Examples include alicyclic triisocyanates such as tomethyl-3-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanatoethyl)-2-isocyanatomethyl-2-(3-isocyanatopropyl)-bicyclo(2.2.1)heptane.

[0143] Examples of the aforementioned aromatic aliphatic polyisocyanates include aromatic aliphatic diisocyanates such as 1,3- or 1,4-xylylene diisocyanate or mixtures thereof, ω,ω'-diisocyanato-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanato-1-methylethyl)benzene (common name: tetramethylxylylene diisocyanate) or mixtures thereof; and aromatic aliphatic triisocyanates such as 1,3,5-triisocyanatomethylbenzene.

[0144] Examples of the aromatic polyisocyanates include aromatic diisocyanates such as m-phenylenediisocyanate, p-phenylenediisocyanate, 4,4'-diphenyldiisocyanate, 1,5-naphthalenediisocyanate, 2,4'- or 4,4'-diphenylmethanediisocyanate or mixtures thereof, 2,4- or 2,6-tolylenediisocyanate or mixtures thereof, 4,4'-toluidinediisocyanate, and 4,4'-diphenyletherdiisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0145] Examples of the polyisocyanate derivatives include dimers, trimers, biuretes, allophanates, uretodiones, uretoimines, isocyanurates, oxadiazinetriones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like.

[0146] The above-mentioned polyisocyanates and their derivatives may be used individually or in combination of two or more. Among these polyisocyanates, it is preferable to use aliphatic diisocyanates, alicyclic diisocyanates, and their derivatives individually or in combination of two or more.

[0147] Furthermore, as the polyisocyanate compound (B2), a prepolymer obtained by urethane reaction of the above-mentioned polyisocyanate and its derivatives with a polyhydric alcohol, a low molecular weight polyester resin, or water under conditions of excess isocyanate groups can also be used.

[0148] When using a polyisocyanate compound (B2) as the curing agent (B), organometallic compounds, acid compounds, basic compounds, etc., can be optionally used as the curing catalyst.

[0149] The above polyisocyanate compound (B2) can be used, for example, as a crosslinking agent for resins containing hydroxyl groups or amino groups.

[0150] Blocked polyisocyanate compound (B3) The blocked polyisocyanate compound (B3) is a compound obtained by blocking the isocyanate group of the polyisocyanate compound (B2) with a blocking agent.

[0151] Examples of the above-mentioned blocking agents include phenolic blocking agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactam blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohol blocking agents such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, and lauryl alcohol; ether blocking agents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, and butyrolactamic acid. Alcohol-based blocking agents such as methylolurea, methylolmelamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate; oxime-based blocking agents such as formamide oxime, acetamide oxime, acetoxime, methylethyl ketoxime, diacetylmonoxime, benzophenone oxime, and cyclohexane oxime; active methylene-based blocking agents such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; mercaptan-based blocking agents such as butyl mercaptan, tert-butyl mercaptan, hexyl mercaptan, tert-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, and ethylthiophenol; acid amide-based blocking agents such as acetanilide, acetanisidide, acetoluid, acrylamide, methacrylamide, acetic acid amide, stearic acid amide, and benzamide; imide-based blocking agents such as succinimide, phthalimide, and maleimide;Examples include amine-based blocking agents such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazole-based blocking agents such as imidazole and 2-ethylimidazole; urea-based blocking agents such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamic acid ester-based blocking agents such as phenyl N-phenylcarbamate; imine-based blocking agents such as ethyleneimine and propyleneimine; sulfite-based blocking agents such as sodium bisulfite and potassium bisulfite; and azole-based blocking agents. Examples of the above-mentioned azole-based blocking agents include pyrazoles or pyrazole derivatives such as pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, and 3-methyl-5-phenylpyrazole; imidazoles or imidazole derivatives such as imidazole, benzimidazole, 2-methylimidazole, 2-ethylimidazole, and 2-phenylimidazole; and imidazoline derivatives such as 2-methylimidazoline and 2-phenylimidazoline.

[0152] Among the blocking agents, oxime-based blocking agents, active methylene-based blocking agents, pyrazoles, or pyrazole derivatives are particularly preferred.

[0153] Furthermore, as the blocking agent, a hydroxycarboxylic acid having one or more hydroxyl groups and one or more carboxyl groups, such as hydroxypivalic acid or dimethylolpropionic acid, can also be used.

[0154] In the paint composition of the present invention, when using the blocked polyisocyanate, a blocked polyisocyanate compound can be suitably used, which is obtained by blocking the isocyanate group with the hydroxycarboxylic acid and then neutralizing the carboxyl group of the hydroxycarboxylic acid to impart water dispersibility.

[0155] The above-mentioned blocked polyisocyanate compound (B3) preferably includes a structure derived from a spacer having at least two isocyanate-reactive functional groups, from the viewpoint of the appearance of the formed coating film and the adhesion between the formed coating film and the substrate.

[0156] The above functional group is not particularly limited as long as it is a functional group that is reactive with an isocyanate group. Examples of such isocyanate-reactive functional groups include hydroxyl groups, amino groups, carboxyl groups, and thiol groups, with hydroxyl groups and amino groups being preferred, and hydroxyl groups being particularly preferred.

[0157] Therefore, the spacer is preferably a compound having at least two hydroxyl groups or at least two amino groups, and more preferably a compound having at least two hydroxyl groups.

[0158] Examples of compounds having at least two hydroxyl groups include, as low molecular weight compounds, dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, and hexamethylene glycol, and trihydric alcohols such as trimethylolpropane, glycerin, and pentaerythritol, and as high molecular weight compounds, polyether polyols, polyester polyols, acrylic polyols, and epoxy polyols. Among these, polyether polyols are preferred from the viewpoint of storage stability of the resulting paint composition.

[0159] As the above-mentioned polyether polyol, alkylene oxide adducts of low molecular weight compounds having at least two hydroxyl groups, ring-opening (co)polymers of alkylene oxides or cyclic ethers (such as tetrahydrofuran) can be used. Specifically, examples include polyethylene glycol, polypropylene glycol, (block or random) copolymers of ethylene glycol-propylene glycol, polytetramethylene glycol, polyhexamethylene glycol, and polyoctamethylene glycol.

[0160] In particular, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol can be suitably used as the above-mentioned polyether polyols.

[0161] The above-mentioned polyether polyols can be used individually or in combination of two or more types.

[0162] Furthermore, examples of compounds having at least two amino groups include polyetheramines.

[0163] The above-mentioned polyetheramines can also be commercially available. Examples of such commercially available products include "JEFFAMINE D-400", "JEFFAMINE D-2000", "JEFFAMINE D-4000", "JEFFAMINE ED-600", "JEFFAMINE ED-900", "JEFFAMINE ED-2003", "ELASTAMINE RT-1000", "JEFFAMINE T-403", "JEFFAMINE T-3000", and "JEFFAMINE T-5000" from HUNTSMAN.

[0164] The molecular weight of the above-mentioned spacer is preferably in the range of 500 to 6,000, more preferably in the range of 800 to 5,000, and even more preferably in the range of 1,500 to 3,500, from the viewpoint of storage stability of the resulting paint composition and suppression of metallic unevenness in the formed coating film.

[0165] The number of functional groups in the above-mentioned spacer is preferably 2 to 3, and more preferably 2, from the viewpoint of the storage stability of the resulting paint composition.

[0166] By reacting some of the isocyanate groups in a polyisocyanate compound with a spacer, a polyisocyanate compound containing a structure derived from the spacer can be formed. In this case, from the viewpoint of storage stability and resistance to wilting of the resulting paint composition, it is preferable that the ratio of the polyisocyanate compound to the spacer is within the range of 0.03 to 0.6 moles of active hydrogen in the spacer, based on 1 mole of isocyanate groups in the polyisocyanate compound. By blocking the polyisocyanate compound containing a structure derived from the spacer, a blocked polyisocyanate compound containing a structure derived from the spacer can be formed.

[0167] From the viewpoint of storage stability and resistance to wilting of the resulting paint composition, the above-mentioned blocked polyisocyanate compound preferably includes a blocked polyisocyanate compound having a weight-average molecular weight in the range of 20,000 to 200,000.

[0168] When using a blocked polyisocyanate compound (B3) as the curing agent (B), organometallic compounds, acid compounds, basic compounds, etc., can be optionally used as the curing catalyst.

[0169] In the paint composition of the present invention, the content of the curing agent (B) is preferably in the range of 5 to 55% by mass, more preferably in the range of 10 to 50% by mass, and particularly preferably in the range of 15 to 45% by mass, based on the amount of resin solids in the paint composition, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness of the formed paint film.

[0170] [Scaly glitter pigment (C)] Examples of flake-like luminous pigments (C) include flake-like metal pigments such as aluminum, copper, nickel alloys, and stainless steel; flake-like metal pigments coated with metal oxides; flake-like metal pigments with colored pigments chemically adsorbed onto the surface; flake-like aluminum pigments with an aluminum oxide layer formed by an oxidation-reduction reaction on the surface; aluminum solid-solution plate-like iron oxide pigments; glass flake pigments; glass flake pigments coated with metal oxides; glass flake pigments with colored pigments chemically adsorbed onto the surface; glass flake pigments coated with metal; interference mica pigments coated with titanium dioxide; reduced mica pigments obtained by reducing interference mica pigments; colored mica pigments with colored pigments chemically adsorbed onto the surface or coated with iron oxide; graphite pigments coated with titanium dioxide; silica flakes and alumina flake pigments coated with titanium dioxide; plate-like iron oxide pigments; hologram pigments; synthetic mica pigments; cholesteric liquid crystal polymer pigments with a helical structure; and bismuth oxychloride pigments.

[0171] Furthermore, the above-mentioned flake-like lustrous pigment (C) preferably contains a flake-like aluminum pigment (C1) from the viewpoint of the lustrousness of the formed coating film.

[0172] The above-mentioned flake-like aluminum pigment (C1) is generally produced by grinding and grinding aluminum in a ball mill or attritor mill in the presence of a grinding medium and using a grinding aid. As grinding aids, higher fatty acids such as oleic acid, stearic acid, isostearic acid, lauric acid, palmitic acid, and myristic acid are used, as well as aliphatic amines, aliphatic amides, and aliphatic alcohols. As the grinding medium, aliphatic hydrocarbons such as mineral spirits are used.

[0173] The above-mentioned flake-like aluminum pigment (C1) can be broadly classified into leafing type and non-leafing type depending on the type of grinding aid used. When the leafing type is incorporated into a paint composition, it forms (leafes) on the surface of the paint film obtained after painting, resulting in a finish with a strong metallic feel, possessing heat-reflective properties and exhibiting rust-preventive capabilities. For this reason, it is often used in tanks, ducts, pipes, roofing, and various other building materials. In the paint composition of the present invention, it is preferable to use the non-leafing type of flake-like aluminum pigment in terms of the depth of the paint film obtained after painting.

[0174] The average particle size of the above-mentioned flake-like aluminum pigment (C1) is preferably in the range of 5 to 30 μm, more preferably in the range of 7 to 25 μm, and particularly preferably in the range of 8 to 23 μm, from the viewpoint of the brilliance of the formed coating film and the suppression of metallic unevenness. Furthermore, the thickness of the above-mentioned flake-like aluminum pigment (C1) is preferably in the range of 0.05 to 5 μm. The average particle size referred to here means the median diameter of the volume-based particle size distribution measured by laser diffraction scattering using a Microtrac particle size distribution analyzer MT3300 (product name, manufactured by Nikkiso Co., Ltd.). The thickness is defined as the average value of 100 or more measurements obtained by observing a cross-section of the coating film containing the flake-like aluminum pigment (C1) under a microscope and measuring the thickness of the flake-like aluminum pigment (C1) using image processing software.

[0175] Furthermore, when the above-mentioned flake-like lustrous pigment (C) includes the above-mentioned flake-like aluminum pigment (C1), it is preferable that the flake-like aluminum pigment (C1) includes a silica-coated flake-like aluminum pigment (C11) from the viewpoint of suppressing metallic unevenness in the formed coating film and ensuring water resistance.

[0176] As silica-coated aluminum pigments, commercially available products such as the "Hydrolan series" (product name, manufactured by Ekart) and the "Alpaste EMR series" (product name, manufactured by Toyo Aluminum Co., Ltd.) can be used.

[0177] When the paint composition of the present invention contains the above-mentioned flake-like aluminum pigment (C1) as the flake-like lustrous pigment (C), the amount of the pigment blended is preferably in the range of 1 to 50 parts by mass, more preferably 3 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of resin solids in the paint composition, from the viewpoint of the lustrousness of the formed coating film and the suppression of metallic unevenness.

[0178] Furthermore, when the paint composition of the present invention includes a flake-shaped aluminum pigment (C11) coated with silica as the flake-shaped lustrous pigment (C), the amount of the pigment blended is preferably in the range of 1 to 50 parts by mass, more preferably in the range of 3 to 30 parts by mass, and particularly preferably in the range of 5 to 20 parts by mass, per 100 parts by mass of resin solids in the paint composition, from the viewpoint of the lustrousness of the formed coating film and the suppression of metallic unevenness.

[0179] Furthermore, the above-mentioned flake-like luminous pigment (C) preferably includes a flake-like optically coherent pigment (C2) from the viewpoint of the saturation of the formed coating film.

[0180] Examples of the above-mentioned flake-like light-interfering pigment (C2) include colored pearl pigments and interference pearl pigments obtained by coating a translucent flake-like substrate with a metal oxide such as iron oxide or titanium oxide.

[0181] Examples of translucent, flaky substrates include natural mica, artificial mica, alumina flakes, silica flakes, and glass flakes.

[0182] Natural mica is a flaky substrate obtained by crushing mica (mica) ore, while artificial mica is synthesized by heating industrial raw materials such as SiO2, MgO, Al2O3, K2SiF6, and Na2SiF6, melting them at a high temperature of approximately 1500°C, and then cooling and crystallizing them. Compared to natural mica, it has fewer impurities and is more uniform in size and thickness. Specifically, fluorinated mica (KMg3AlSi3O 10 F2), potassium tetrasilicate mica (KMg 25 AlSi4O10 F2), sodium tetrasilicon mica (NaMg 25 AlSi4O 10 F2), Na teniolite (NaMg2LiSi4O 10 F2), LiNa teniolite (LiMg2LiSi4O 10 F2, etc., are well known.

[0183] Alumina flakes refer to flaky (thin flake) aluminum oxide, which is colorless and transparent. They do not need to be solely aluminum oxide; they may also contain oxides of other metals.

[0184] Silica flakes are obtained by dissolving silicon alkoxides, such as methoxide, ethoxide, propoxide, and butoxide, in an alcohol compound, such as methanol, ethanol, propanol, or butanol, in a solvent, applying the solution to a smooth metal plate or the like, drying and peeling it off, and then heat-treating the resulting flake-like gel.

[0185] Glass flakes are a substrate with a smooth surface obtained by molding flaky C glass or E glass.

[0186] The above-mentioned flake-like optical interference pigment (C2) may be surface-treated to improve dispersibility, water resistance, chemical resistance, weather resistance, etc.

[0187] The average particle size of the above-mentioned flake-like optical coherence pigment (C2) is preferably in the range of 5 to 30 μm, more preferably in the range of 7 to 25 μm, and particularly preferably in the range of 8 to 23 μm, from the viewpoint of suppressing the saturation and metallic unevenness of the formed coating film. Furthermore, the thickness of the above-mentioned flake-like optical coherence pigment (C2) is preferably in the range of 0.05 to 5 μm. The average particle size referred to here means the median diameter of the volume-based particle size distribution measured by laser diffraction scattering using a Microtrac particle size distribution analyzer MT3300 (product name, manufactured by Nikkiso Co., Ltd.). The thickness is defined as the average value of 100 or more measurements obtained by observing a cross-section of the coating film containing the flake-like optical coherence pigment (C2) under a microscope and measuring the thickness of the flake-like optical coherence pigment (C2) using image processing software.

[0188] Furthermore, when the paint composition of the present invention contains the above-mentioned flake-like lustrous pigment (C2) as the flake-like lustrous pigment (C), the amount thereof is preferably in the range of 1 to 50 parts by mass, more preferably in the range of 3 to 30 parts by mass, and particularly preferably in the range of 7 to 20 parts by mass, per 100 parts by mass of resin solids in the paint, from the viewpoint of storage stability of the paint composition and suppression of metallic unevenness in the formed paint film.

[0189] [Viscosity modifier (D)] The paint composition of the present invention contains a viscosity modifier comprising at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2). If at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2) is not included, the storage stability of the resulting paint composition will be low.

[0190] Furthermore, the viscosity modifier preferably contains the cellulose nanocrystal (D1) from the viewpoint of improving the storage stability of the resulting paint composition and suppressing metallic unevenness in the formed coating film.

[0191] In this specification, cellulose nanocrystals (D1) are defined as those with a ratio of number-average fiber length to number-average fiber diameter (number-average fiber length / number-average fiber diameter) of less than 50.

[0192] Furthermore, in this specification, cellulose nanofibers (D2) are defined as those with a ratio of number-average fiber length to number-average fiber diameter (number-average fiber length / number-average fiber diameter) of 50 or more.

[0193] <Cellulose Nanocrystal (D1)> Cellulose nanocrystals (D1) can be obtained by known methods. For example, cellulose raw material can be hydrolyzed and the amorphous portion removed by treating it with an acid such as sulfuric acid, and then mechanically defibrillated to obtain cellulose nanocrystals (D1).

[0194] The cellulose raw material is not particularly limited as long as it contains cellulose, but examples include various wood pulps, non-wood pulps, bacterial cellulose, regenerated cellulose, recycled paper pulp, cotton, Valonia cellulose, and sea squirt cellulose. In addition, various commercially available cellulose powders and microcrystalline cellulose powders may be used.

[0195] Furthermore, the mechanical defibration process is not particularly limited, and conventionally known methods can be used, such as high-pressure homogenizers, ultra-high-pressure homogenizers, ball mills, roll mills, cutter mills, planetary mills, jet mills, attritors, grinders, juicer mixers, homomixers, ultrasonic homogenizers, nanogenizers, underwater counter-impacting machines, and single-screw or twin-screw extruders.

[0196] Furthermore, the cellulose nanocrystals (D1) described above can be those that have undergone various chemical modifications. Examples of chemical modifications include carboxymethylation, acylation, esterification such as phosphorylation, oxidation such as carboxylation, sulfonation, fluorination, cationization, and treatment with silane coupling agents.

[0197] In particular, when the cellulose nanocrystals are chemically modified, sulfonation is preferred as the type of chemical modification from the viewpoint of storage stability of the resulting paint composition and suppression of metallic unevenness in the formed coating film.

[0198] Furthermore, the cellulose nanocrystals (D1) may undergo the above-mentioned chemical modification after defibration treatment.

[0199] Furthermore, the cellulose nanocrystals (D1) may be neutralized with a neutralizing agent. As the neutralizing agent, for example, the neutralizing agent described in the description section for the water-dispersible hydroxyl group-containing acrylic resin (A11) can be used.

[0200] The number-average fiber diameter of the cellulose nanocrystals (D1) described above is preferably in the range of 1 to 50 nm, more preferably in the range of 1 to 30 nm, particularly preferably in the range of 1 to 15 nm, and even more preferably in the range of 1 to 5 nm, from the viewpoint of storage stability of the resulting coating composition and suppression of metallic unevenness in the formed coating film.

[0201] Furthermore, the number-average fiber length of the cellulose nanocrystals (D1) is preferably in the range of 10 to 500 nm, more preferably in the range of 10 to 300 nm, particularly preferably in the range of 20 to 250 nm, and even more preferably in the range of 30 to 150 nm, from the viewpoint of storage stability of the resulting coating composition and suppression of metallic unevenness in the formed coating film.

[0202] The number-average fiber diameter and number-average fiber length are measured and calculated from images obtained by, for example, dispersing a sample of cellulose nanocrystals (D1) diluted with water, casting it onto a hydrophilically treated carbon film-coated grid, and observing it with a transmission electron microscope (TEM). Specifically, the observation field is adjusted so that at least 100 cellulose nanocrystal particles are observed, the diameter and fiber length of 100 randomly selected cellulose nanocrystal particles are measured, and the number-average diameter and number-average fiber length are calculated.

[0203] The ratio of the number-average fiber length of the cellulose nanocrystal (D1) to the number-average fiber diameter (number-average fiber length / number-average fiber diameter) is preferably 3 or more and less than 50, more preferably 5 or more and less than 50, and most preferably 10 or more and less than 50, from the viewpoint of storage stability of the resulting coating composition and suppression of metallic unevenness in the formed coating film.

[0204] Furthermore, commercially available examples of the above-mentioned cellulose nanocrystal (D1) include, for example, "Celluforce NCC" (sodium sulfonate type cellulose nanocrystal manufactured by Celluforce).

[0205] <Cellulose nanofiber (D2)> The above-mentioned cellulose nanofibers (D2) can be obtained by known methods. For example, cellulose nanofibers (D2) can be obtained by defibrating a cellulose raw material and refining it until the fiber diameter reaches the nanoscale. Examples of methods for defibrating the cellulose raw material include mechanical defibration and chemical treatment such as treatment with an oxidation catalyst solution containing an N-oxyl compound.

[0206] The cellulose raw material is not particularly limited as long as it contains cellulose, and the same cellulose raw material as the raw material for the cellulose nanocrystal (D1) can be used.

[0207] Furthermore, the cellulose nanofiber (D2) described above can be used after undergoing various chemical modifications. Examples of chemical modifications include carboxymethylation, acylation, esterification such as phosphorylation, oxidation such as carboxylation, sulfonation, fluorination, cationization, and treatment with silane coupling agents.

[0208] Furthermore, the cellulose nanofiber (D2) may be neutralized with a neutralizing agent. As the neutralizing agent, for example, the neutralizing agent described in the description section for the water-dispersible hydroxyl group-containing acrylic resin (A11) can be used.

[0209] The number-average fiber diameter of the cellulose nanofibers (D2) is preferably in the range of 1 to 500 nm, more preferably in the range of 1 to 250 nm, and particularly preferably in the range of 2 to 50 nm, from the viewpoint of storage stability of the resulting coating composition and suppression of metallic unevenness in the formed coating film. The number-average fiber length of the cellulose nanofibers (D2) is preferably in the range of 200 to 10,000 nm, more preferably in the range of 200 to 5,000 nm, particularly preferably in the range of 200 to 2,500 nm, and even more preferably in the range of 200 to 1,000 nm, from the viewpoint of storage stability of the resulting coating composition and suppression of metallic unevenness in the formed coating film.

[0210] The ratio of the number-average fiber length of the cellulose nanofiber (D2) to the number-average fiber diameter (number-average fiber length / number-average fiber diameter) is preferably in the range of 50 to 500, more preferably in the range of 50 to 200, and particularly preferably in the range of 50 to 150, from the viewpoint of storage stability of the obtained coating composition and suppression of metallic unevenness in the formed coating film.

[0211] Examples of commercially available cellulose nanofibers (D2) include "Nanocellulose Fiber" (manufactured by Chuetsu Pulp & Paper Co., Ltd.), "BiNFi-s" (manufactured by Sugino Machinery Co., Ltd.), "Leocrista" (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), "Cellulose Nanofiber" (manufactured by Mori Machinery Co., Ltd.), "Selenpia" (manufactured by Nippon Paper Industries Ltd.), and "Auro Visco" (manufactured by Oji Holdings Corporation).

[0212] Other viscosity modifiers besides the cellulose nanocrystals (D1) and cellulose nanofibers (D2) mentioned above can also be used as the viscosity modifier (D). Known viscosity modifiers other than cellulose nanocrystals (D1) and cellulose nanofibers (D2) can be used, for example, silica-based fine powders, mineral-based viscosity modifiers, barium sulfate fine powders, polyamide-based viscosity modifiers, organic resin fine particle viscosity modifiers, diurea-based viscosity modifiers, urethane association-type viscosity modifiers, and acrylic swelling-type polyacrylic acid-based viscosity modifiers.

[0213] Examples of the mineral-based viscosity modifiers include swelling layered silicates having a 2:1 crystal structure. Specifically, these include natural or synthetic smectite group clay minerals such as montmorillonite, saponite, hectorite, stivunsite, bydelite, nontronite, bentonite, and laponite; swelling mica group clay minerals such as Na-type tetrasilicic fluorite, Li-type tetrasilicic fluorite, Na-salt type fluorite teniolite, and Li-type fluorite teniolite; vermiculite; substituted or derivative products thereof; and mixtures thereof.

[0214] As the urethane-associated viscosity modifier, it is preferable to use, for example, a urethane-associated viscosity modifier having hydrophobic groups at its terminals and urethane bonds in its molecular chain. Commercially available urethane-associated viscosity modifiers can be used. Examples of commercially available product names include "UH-420", "UH-462", "UH-472", "UH-540", "UH-752", "UH-756VF", and "UH-814N" (all manufactured by ADEKA Corporation); and "SN Thickener 612", "SN Thickener 621N", "SN Thickener 625N", "SN Thickener 627N", and "SN Thickener 660T" (all manufactured by Sunopco Co., Ltd.).

[0215] Examples of the polyacrylic acid-based viscosity modifiers include sodium polyacrylate and polyacrylic acid-(meth)acrylic acid ester copolymers.

[0216] Examples of commercially available polyacrylic acid-based viscosity modifiers include "Primal ASE-60," "Primal TT615," and "Primal RM5" (all trade names) from Dow Chemical Co., Ltd., and "SN Thickener 613," "SN Thickener 618," "SN Thickener 630," "SN Thickener 634," and "SN Thickener 636" (all trade names) from Sunnopco Corporation. The acid value of the polyacrylic acid-based viscosity modifier is preferably in the range of 30 to 300 mg KOH / g, and more preferably in the range of 80 to 280 mg KOH / g.

[0217] In the present invention, the content of the viscosity modifier (D) is preferably in the range of 0.6 to 7 parts by mass, more preferably in the range of 1.0 to 5.0 parts by mass, and particularly preferably in the range of 1.5 to 4.5 parts by mass, per 100 parts by mass of resin solids in the paint composition, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness of the formed paint film.

[0218] Furthermore, in the present invention, the content of at least one viscosity modifier selected from the cellulose nanocrystals (D1) and cellulose nanofibers (D2) is preferably in the range of 0.6 to 7 parts by mass, more preferably in the range of 1.0 to 5.0 parts by mass, and particularly preferably in the range of 1.5 to 4.5 parts by mass, per 100 parts by mass of resin solids in the paint composition, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness of the formed paint film.

[0219] [Organic solvent (E) with solubility in water at 20°C of 4% by mass or more] The paint composition of the present invention contains 10 to 25% by mass of an organic solvent (E) having a solubility in water of 4% by mass or more at 20°C, based on the volatile components in the paint composition. If the content of the organic solvent (E) having a solubility in water of 4% by mass or more at 20°C is outside the above range, metallic unevenness is likely to occur in the formed paint film.

[0220] In particular, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness of the formed paint film, the content of the organic solvent (E) having a solubility in water at 20°C of 4% by mass or more is preferably in the range of 12 to 23% by mass, more preferably in the range of 13 to 22% by mass, and especially preferably in the range of 14 to 21% by mass, based on the volatile components in the paint composition.

[0221] In this specification, "volatile components" refers to components that volatilize when dried at 110°C for 1 hour. Therefore, the volatile components in a paint composition can be calculated, for example, by measuring the paint composition into a heat-resistant container such as an aluminum foil cup, spreading the paint composition on the bottom surface of the container, drying it at 110°C for 1 hour, weighing the mass of the components remaining after drying, and subtracting the mass of the components remaining after drying from the total mass of the paint composition before drying.

[0222] Examples of organic solvents (E) having a solubility in water of 4% by mass or more at 20°C include: ester solvents such as ethyl acetate, ethylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether acetate, and 3-methoxybutyl acetate; ketone solvents such as acetone, methyl ethyl ketone, and cyclohexanone; methanol, ethanol, isopropanol, n-butanol, sec-butanol, isobutanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol isopropyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, and propylene glycol Examples of alcohol-based solvents include glycol monopropyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, dipropylene glycol monomethyl ether, and dipropylene glycol-n-butyl ether; and ether-based solvents such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, diethylene glycol butyl methyl ether, and dioxane. These can be used individually or in combination of two or more.

[0223] The organic solvent (E) having a solubility in water at 20°C of 4% by mass or more preferably contains an organic solvent (E1) having a solubility in water at 20°C in the range of 4 to 10% by mass.

[0224] Examples of organic solvents (E1) whose solubility in water at 20°C is in the range of 4 to 10% by mass include ester solvents such as ethyl acetate, diethylene glycol monobutyl ether acetate, and 3-methoxybutyl acetate; ketone solvents such as cyclohexanone; alcohol solvents such as n-butanol, sec-butanol, isobutanol, propylene glycol monobutyl ether, and dipropylene glycol-n-butyl ether; and ether solvents such as diethylene glycol butyl methyl ether. These can be used individually or in combination of two or more.

[0225] When the paint composition of the present invention contains an organic solvent (E1) whose solubility in water at 20°C is in the range of 4 to 10% by mass, the content of the organic solvent (E1) whose solubility in water at 20°C is in the range of 4 to 10% by mass is preferably in the range of 12 to 23% by mass, more preferably in the range of 13 to 22% by mass, and particularly preferably in the range of 14 to 21% by mass, based on the volatile components in the paint composition, from the viewpoint of storage stability of the obtained paint composition and suppression of unevenness in the formed paint film.

[0226] The organic solvent (E) having a solubility in water at 20°C of 4% by mass or more preferably contains propylene glycol monobutyl ether, from the viewpoint of storage stability of the resulting paint composition and suppression of metallic unevenness in the formed coating film.

[0227] [Other ingredients] The paint composition of the present invention may further optionally contain resins other than the hydroxyl group-containing resin (A) and curing agent (B), pigments other than the flake-like lustrous pigment (C), organic solvents other than the organic solvent (E) having a solubility in water at 20°C of 4% by mass or more, a curing catalyst, a dispersant, an anti-settling agent, an antifoaming agent, an ultraviolet absorber, a light stabilizer, a surface modifier, and the like.

[0228] Examples of resins other than the hydroxyl group-containing resin (A) and curing agent (B) mentioned above include acrylic resins without hydroxyl groups, polyester resins without hydroxyl groups, acrylic-modified polyester resins without hydroxyl groups, acrylic-modified polyurethane resins without hydroxyl groups, polyurethane resins without hydroxyl groups, polyether resins without hydroxyl groups, polycarbonate resins without hydroxyl groups, epoxy resins without hydroxyl groups, alkyd resins without hydroxyl groups, and polyolefin resins without hydroxyl groups. In particular, it is preferable that the coating composition of the present invention contains a polyurethane resin without hydroxyl groups as at least one of the resins other than the hydroxyl group-containing resin (A) and curing agent (B) mentioned above.

[0229] When the coating composition of the present invention contains a polyurethane resin that does not contain hydroxyl groups, the content of the polyurethane resin that does not contain hydroxyl groups is preferably in the range of 3 to 60% by mass, more preferably in the range of 5 to 40% by mass, and particularly preferably in the range of 7 to 30% by mass, based on the amount of resin solids in the coating composition, from the viewpoint of storage stability of the obtained coating composition and suppression of metallic unevenness of the formed coating film.

[0230] Examples of pigments other than the above-mentioned flake-like luminous pigment (C) include coloring pigments and extender pigments. These pigments can be used alone or in combination of two or more types.

[0231] When the paint composition of the present invention contains the above-mentioned pigment, the amount of the pigment is preferably in the range of 1 to 200 parts by mass, more preferably in the range of 5 to 160 parts by mass, and particularly preferably in the range of 5 to 140 parts by mass, based on 100 parts by mass of resin solids in the paint composition.

[0232] Examples of the above-mentioned coloring pigments include titanium dioxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, surene pigments, perylene pigments, dioxazine pigments, and diketopyrrolopyrrole pigments. Among these, titanium dioxide and carbon black can be preferably used.

[0233] When the paint composition contains the above-mentioned coloring pigment, the amount of the coloring pigment is preferably in the range of 1 to 180 parts by mass, more preferably in the range of 5 to 150 parts by mass, and particularly preferably in the range of 15 to 130 parts by mass, based on 100 parts by mass of resin solids in the paint composition.

[0234] Examples of the extender pigments include barium sulfate, talc, clay, kaolin, barium carbonate, calcium carbonate, silica, and alumina white. Barium sulfate and talc are particularly suitable as extender pigments from the viewpoint of paint stability and smoothness.

[0235] When the paint composition contains the above-mentioned extender pigment, the amount of the extender pigment is preferably in the range of 1 to 180 parts by mass, more preferably in the range of 5 to 140 parts by mass, and particularly preferably in the range of 10 to 120 parts by mass, based on 100 parts by mass of resin solids in the paint composition.

[0236] Examples of organic solvents other than organic solvent (E) whose solubility in water at 20°C is 4% by mass or more include hydrocarbon solvents such as mineral spirits, toluene, xylene, and solvent naphtha; alcohol solvents such as 1-hexanol, 1-octanol, 2-octanol, 2-ethyl-1-hexanol, 1-decanol, benzyl alcohol, ethylene glycol monohexyl ether, and ethylene glycol mono-2-ethylhexyl ether; ester solvents such as n-butyl acetate, isobutyl acetate, methylamyl acetate, ethylene glycol monobutyl ether, and n-butyl propionate; ether solvents such as diethylene glycol dibutyl ether; and ketone solvents such as methyl isobutyl ketone, 2-heptanone, ethyl n-amyl ketone, diisobutyl ketone, and isophorone. These can be used individually or in combination of two or more.

[0237] Examples of the aforementioned ultraviolet absorbers include benzotriazole-based absorbers, triazine-based absorbers, salicylic acid derivative-based absorbers, and benzophenone-based absorbers.

[0238] Examples of the aforementioned light stabilizers include hindered amine-based light stabilizers.

[0239] [Paint composition] The paint composition of the present invention can be prepared by mixing a hydroxyl group-containing resin (A), a curing agent (B), a flake-like glossy pigment (C), a viscosity modifier (D), an organic solvent (E) having a solubility in water at 20°C of 4% by mass or more, and optionally other components in a solvent using conventional paint-making methods. As the solvent, for example, an organic solvent or water can be used.

[0240] Furthermore, the paint solids content concentration of the paint mixture paint composition of the present invention is preferably in the range of 10 to 45% by mass, more preferably in the range of 15 to 40% by mass, and most preferably in the range of 17 to 30% by mass, from the viewpoint of storage stability of the obtained paint composition and suppression of metallic unevenness in the formed paint film.

[0241] The above paint solid content concentration can be adjusted, for example, by adjusting the amount of the solvent.

[0242] Among them, from the viewpoints such as storage stability, the paint composition of the present invention preferably contains water as a solvent.

[0243] When the paint composition of the present invention contains the above water, from the viewpoints such as storage stability of the obtained paint composition, the water content is preferably within the range of 30 to 80% by mass, more preferably within the range of 40 to 75% by mass, and even more preferably within the range of 50 to 70% by mass based on the total amount of the paint composition.

[0244] Further, from the viewpoint of suppressing metallic unevenness of the formed paint film, etc., the paint composition of the present invention has a viscosity of 5 to 150 mPa·s, preferably 7 to 125 mPa·s, and particularly preferably 10 to 100 mPa·s when measured under the conditions of a temperature of 25°C and a shear rate of 1,500 sec -1 -1.

[0245] Further, from the viewpoint of suppressing metallic unevenness of the formed paint film, etc., the paint composition of the present invention has a viscosity of 5,000 to 70,000 mPa·s, preferably 8,000 to 60,000 mPa·s, and particularly preferably 10,000 to 50,000 mPa·s when measured under the conditions of a temperature of 25°C and a shear rate of 0.1 sec -1 -1.

[0246] The paint composition may be either a one-component paint or a multi-component paint, but from the viewpoints such as excellent productivity without a paint mixing process and simplification of maintenance of painting machines, etc., it is preferably a one-component paint.

[0247] The paint composition can be applied to the object to be coated by known methods, such as air spray painting, airless spray painting, rotary atomization painting, or curtain coat painting, and electrostatic application may be performed during painting. Of these, air spray painting and rotary atomization painting are preferred. Furthermore, such painting methods can be carried out in one to several stages until the desired film thickness is achieved.

[0248] The amount of paint composition applied is typically such that the cured film thickness is 0.5 to 50 μm, preferably 2 to 40 μm, and more preferably 5 to 30 μm.

[0249] [Method for forming multi-layer coatings] The paint composition of the present invention can be used for forming the base coat film when forming a multilayer coating consisting of a base coat film and a clear coat film on the aforementioned substrate using a two-coat, one-bake method. In this case, the coating film formation method can be carried out according to Method I described below.

[0250] <Method I> Step (I-1): A step of applying a base coat paint composition (Y) to the object to be coated to form an uncured base coat film. Step (I-2): A step of applying a clear coat coating composition (Z) onto the uncured base coat coating to form an uncured clear coat coating, and A method for forming a multilayer coating film, comprising the step (I-3): heating the uncured base coat coating film and the uncured clear coat coating film to cure both coating films simultaneously, wherein the base coat coating composition (Y) is the coating composition of the present invention.

[0251] The object to be coated in Method I described above is preferably an automobile body with a primer coating film formed on it, or an automobile body with a colored coating film formed on the primer coating film. The primer coating film is preferably formed by electrodeposition paint, and more preferably by cationic electrodeposition paint. Furthermore, the uncured coating film includes coating films that are touch-dry and coating films that are semi-cured.

[0252] When the coating composition of the present invention is applied using the two-coat, one-bake method of Method I, the coating film thickness is preferably in the range of 0.5 to 50 μm, more preferably in the range of 2 to 40 μm, particularly preferably in the range of 5 to 30 μm, and even more preferably in the range of 8 to 27 μm as the cured film thickness.

[0253] Furthermore, while the above-mentioned uncured base coat film is usually formed using one type of base coat paint composition, it can also be formed using two or more types of base coat paint compositions.

[0254] Furthermore, when using two or more base coat paint compositions, it is preferable to use two base coat paint compositions.

[0255] Specifically, for example, a first base coat coating, which may use the coating composition of the present invention, can be applied to a workpiece to form a first base coat coating film, and then a second base coat coating using the coating composition of the present invention can be applied on the first base coat coating film to form a second base coat coating film.

[0256] In this case, from the viewpoint of suppressing metallic unevenness in the formed coating film, the first base coat coating film is preferably cured to a thickness of 5 to 15 μm, and more preferably to a thickness of 7 to 13 μm, and the second base coat coating film is preferably cured to a thickness of 0.5 to 15 μm, and more preferably to a thickness of 2 to 13 μm.

[0257] Furthermore, the coating film thickness of the above clear coat paint composition (Z) is preferably in the range of 10 to 80 μm as a cured film thickness, and more preferably in the range of 15 to 60 μm.

[0258] Furthermore, in Method I, after applying the coating composition of the present invention, it is preferable to perform preheating, air blowing, etc., under heating conditions that do not substantially harden the coating film, from the viewpoint of preventing the occurrence of coating defects such as blotches. The preheating temperature is preferably in the range of 40 to 100°C, more preferably in the range of 50 to 90°C, and particularly preferably in the range of 60 to 80°C. The preheating time is preferably in the range of 30 seconds to 15 minutes, more preferably in the range of 1 to 10 minutes, and particularly preferably in the range of 2 to 5 minutes. In addition, the air blowing can be performed, for example, by blowing air heated to room temperature or 25°C to 80°C onto the coated surface of the object to be coated for 30 seconds to 15 minutes. Furthermore, after applying the clear coat coating composition (Y), an interval of 1 to 60 minutes at room temperature or preheating at 40 to 80°C for 1 to 60 minutes can be optionally performed.

[0259] The coating film can be cured by the known heating method described above. The heating temperature is preferably in the range of 60 to 180°C, more preferably in the range of 65 to 170°C, and particularly preferably in the range of 70 to 160°C. The heating time is preferably in the range of 10 to 60 minutes, and more preferably in the range of 20 to 40 minutes. This heating allows both the base coat and the clear coat to be cured simultaneously.

[0260] Furthermore, the paint composition of the present invention can be suitably used as a base coat when forming a multi-layer coating consisting of a colored coating, a base coat coating, and a clear coat coating on an object to be coated, such as an automobile body, using a 3-coat 1-bake method. In this case, the coating film formation method can be carried out according to Method II below.

[0261] <Method II> Step (II-1): A step of applying a colored paint composition (X) to the object to be coated to form an uncured colored coating film. Step (II-2): A step of applying a base coat paint composition (Y) onto the uncured colored coating to form an uncured base coat coating, Step (II-3): A step of applying a clear coat coating composition (Z) onto the uncured base coat coating to form an uncured clear coat coating, and Step (II-4): A method for forming a multilayer coating film, comprising the step of heating the uncured colored coating film, the uncured base coat coating film, and the uncured clear coat coating film to cure them simultaneously, wherein the base coat coating composition (Y) is the coating composition of the present invention.

[0262] Method II described above involves performing the coating film formation method of Method I on an uncured colored coating film. The object to be coated in Method II is preferably an automobile body or the like, which has a primer coating film already formed on it. The primer coating film is preferably formed by electrodeposition paint, and more preferably by cationic electrodeposition paint.

[0263] In Method II, the coating film thickness of the colored paint composition is preferably in the range of 10 to 60 μm as a cured film thickness, and more preferably in the range of 20 to 40 μm. Furthermore, the coating film thickness of the paint composition of the present invention is preferably in the range of 0.5 to 50 μm as a cured film thickness, more preferably in the range of 2 to 40 μm, particularly preferably in the range of 5 to 30 μm, and even more particularly preferably in the range of 8 to 27 μm. Furthermore, the coating film thickness of the clear coat paint composition (Z) is preferably in the range of 10 to 80 μm as a cured film thickness, and more preferably in the range of 15 to 60 μm.

[0264] Also, in Method II, it is preferable to perform preheating after coating the coloring paint composition (X). The temperature for preheating is preferably within the range of 40 to 100°C, more preferably within the range of 50 to 90°C, and particularly preferably within the range of 60 to 80°C. The time for preheating is preferably within the range of 30 seconds to 15 minutes, more preferably within the range of 1 to 10 minutes, and particularly preferably within the range of 2 to 5 minutes.

[0265] Also, it is preferable to perform preheating after coating the paint composition of the present invention. The temperature for preheating is preferably within the range of 40 to 100°C, more preferably within the range of 50 to 90°C, and particularly preferably within the range of 60 to 80°C. The time for preheating is preferably within the range of 30 seconds to 15 minutes, more preferably within the range of 1 to 10 minutes, and particularly preferably within the range of 2 to 5 minutes.

[0266] Also, in Method II as well, the above-mentioned uncured base coat film is usually formed using one type of base coat paint composition, but it can also be formed using two or more types of base coat paint compositions. In that case, the paint composition of the present invention can be used as the base coat paint composition for forming at least the uppermost base coat film.

[0267] In addition, when using two or more types of base coat paint compositions, it is preferable to use two types of base coat paint compositions.

[0268] Specifically, for example, after coating a first base coat paint, which may be the paint composition of the present invention, on an object to be coated to form a first base coat film, a second base coat paint using the paint composition of the present invention can be coated on the first base coat film to form a second base coat film.

[0269] In this case, from the perspective of suppressing metallic unevenness of the formed coating film, etc., the above-mentioned first base coat film preferably has a cured film thickness within the range of 5 to 15 μm, more preferably within the range of 7 to 13 μm. Also, the above-mentioned second base coat film preferably has a cured film thickness within the range of 0.5 to 15 μm, more preferably within the range of 2 to 13 μm.

[0270] After coating the above clear coat paint composition (Z), optionally, an interval of 1 to 60 minutes can be provided at room temperature, or preheating can be performed at 40 to 80 °C for 1 to 60 minutes.

[0271] The curing of the three-layer coating film of the uncured colored coating film, uncured base coat film, and uncured clear coat film can be performed by the aforementioned known heating means. The heating temperature is preferably within the range of 60 to 180 °C, more preferably within the range of 65 to 170 °C, and particularly preferably within the range of 70 to 160 °C. Also, the heating time is preferably within the range of 10 to 60 minutes, and particularly preferably within the range of 20 to 40 minutes. By this heating, the three-layer coating film of the colored coating film, base coat film, and clear coat film can be cured simultaneously.

[0272] As the clear coat paint composition (Z) used in the above methods I and II, any of the thermosetting clear coat paint compositions known for coating automobile bodies, etc. can be used. For example, an organic solvent-based thermosetting paint composition containing a substrate resin having a crosslinkable functional group and a crosslinking agent, an aqueous thermosetting paint composition, a powder thermosetting paint composition, etc. can be mentioned.

[0273] Examples of crosslinkable functional groups in the above-mentioned base resin include carboxyl groups, hydroxyl groups, epoxy groups, and silanol groups. Examples of base resin types include acrylic resins, polyester resins, alkyd resins, urethane resins, epoxy resins, and fluororesins. Examples of crosslinking agents include polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins, urea resins, carboxyl group-containing compounds, carboxyl group-containing resins, epoxy group-containing resins, and epoxy group-containing compounds.

[0274] Furthermore, the clear coat paint may be a one-component paint or a multi-component paint such as a two-component urethane resin paint.

[0275] Furthermore, the above-mentioned clear coat paint composition (Z) may optionally contain coloring pigments, luminescence pigments, dyes, etc., to an extent that does not impair transparency, and may also appropriately contain extender pigments, ultraviolet absorbers, light stabilizers, defoamers, thickeners, rust inhibitors, surface modifiers, etc.

[0276] As for the base resin / crosslinking agent combination of the clear coat paint composition (Z), carboxyl group-containing resin / epoxy group-containing resin, hydroxyl group-containing resin / polyisocyanate compound, hydroxyl group-containing resin / blocked polyisocyanate compound, hydroxyl group-containing resin / melamine resin, etc., are preferred. Among these, the combination of hydroxyl group-containing resin / polyisocyanate compound is preferred from the viewpoint of the particle texture of the formed coating film.

[0277] Any known thermosetting colored paint composition can be used as the colored paint composition in Method II described above. For example, a thermosetting paint composition containing a base resin having a crosslinkable functional group, a crosslinking agent, a coloring pigment, and an extender pigment can be suitably used.

[0278] Examples of crosslinkable functional groups in the above-mentioned base resin include carboxyl groups, hydroxyl groups, epoxy groups, etc. Examples of types of base resin include acrylic resins, polyester resins, alkyd resins, urethane resins, etc. Examples of crosslinking agents include melamine resins, polyisocyanate compounds, blocked polyisocyanate compounds, etc.

[0279] As the colored paint composition, any of the following may be used: an organic solvent-based paint composition, an aqueous paint composition, or a powder paint composition. Of these, the use of a paint composition is preferred.

[0280] In methods I and II described above, painting can be carried out by known methods, such as air spray painting, airless spray painting, rotary atomization painting, etc. [Examples]

[0281] The present invention will be described in more detail below with reference to manufacturing examples, examples, and comparative examples. However, the present invention is not limited thereto. In each example, "parts" and "%" are based on mass unless otherwise specified. Furthermore, the film thickness of the coating is based on the cured coating.

[0282] Manufacturing of hydroxyl group-containing acrylic resin (A1) Manufacturing Example 1 In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device, 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., emulsifier, 97% active ingredient) were charged, stirred and mixed in a nitrogen atmosphere, and the temperature was raised to 80°C.

[0283] Next, 1.72 parts of the monomer emulsion (1) and 5.3 parts of a 6% ammonium persulfate aqueous solution were introduced into the reaction vessel and maintained at 80°C for 15 minutes. Then, the remaining monomer emulsion (1) was added dropwise over 3 hours to the reaction vessel, which was maintained at the same temperature, and the mixture was allowed to mature for 1 hour after the dropwise addition was complete. Subsequently, the monomer emulsion (2) was added dropwise over 1 hour and matured for 1 hour. Then, 20 parts of a 5% N-methylmorpholine aqueous solution were gradually added to the reaction vessel while cooling to 30°C, and the mixture was drained while filtering through a 100-mesh nylon cloth to obtain an aqueous dispersion of hydroxyl-containing acrylic resin (A1-1) with a solid content of 30%. The obtained hydroxyl-containing acrylic resin (A1-1) had an acid value of 16 mg KOH / g, a hydroxyl value of 66 mg KOH / g, and a glass transition temperature of 21°C. The hydroxyl group-containing acrylic resin (A1-1) corresponds to the water-dispersible hydroxyl group-containing acrylic resin (A11) having the core / shell type multilayer structure.

[0284] Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of "Aqualon KH-10", 2 parts of methylenebisacrylamide, 5 parts of styrene, 15 parts of methyl methacrylate, 5 parts of 2-hydroxyethyl methacrylate, and 23 parts of n-butyl acrylate were mixed and stirred to obtain monomer emulsion (1).

[0285] Monomer emulsion (2): 42 parts of deionized water, 0.72 parts of Aqualon KH-10, 0.05 parts of ammonium persulfate, 2.5 parts of methacrylic acid, 10 parts of 2-hydroxyethyl methacrylate, 5 parts of styrene, 12.5 parts of methyl methacrylate, 10 parts of n-butyl acrylate, and 10 parts of n-butyl methacrylate were mixed and stirred to obtain monomer emulsion (2).

[0286] Manufacturing Example 2 In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device, 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., emulsifier, 97% active ingredient) were charged, stirred and mixed in a nitrogen atmosphere, and the temperature was raised to 80°C.

[0287] Next, 1.72 parts of the following monomer emulsion (1) and 5.3 parts of a 6% aqueous ammonium persulfate solution were introduced into a reaction vessel and held at 80°C for 15 minutes. Then, 35.4 parts of the monomer emulsion (1) were dropped into the reaction vessel maintained at the same temperature over 1 hour. Immediately after the dropping was completed, 55.6 parts of the remaining monomer emulsion (1) were started to be dropped into the reaction vessel. At the same time, 55.6 parts of the monomer emulsion (2) were dropped with respect to the monomer emulsion (1), and the dropping of the monomer emulsion (1) and the monomer emulsion (2) was completed over 2 hours. Then, 37.17 parts of the remaining monomer emulsion (2) were dropped into the reaction vessel over 1 hour. After aging for 1 hour, 20 parts of a 5% aqueous N-methylmorpholine solution were gradually added to the reaction vessel while cooling to 30°C, and then discharged while filtering through a 100-mesh nylon cloth to obtain a hydroxyl group-containing acrylic resin (A1-2) aqueous dispersion with a solid content concentration of 30%. The obtained hydroxyl group-containing acrylic resin (A1-2) had an acid value of 16 mgKOH / g, a hydroxyl value of 66 mgKOH / g, and a glass transition temperature of 21°C. The above hydroxyl group-containing acrylic resin (A1-2) corresponds to the water-dispersible hydroxyl group-containing acrylic resin (A11’) containing the gradient polymer layer.

[0288] Monomer emulsion (1): 42 parts of deionized water, 0.72 part of “Aquaron KH-10”, 2 parts of methylene bisacrylamide, 5 parts of styrene, 15 parts of methyl methacrylate, 5 parts of 2-hydroxyethyl methacrylate, and 23 parts of n-butyl acrylate were mixed and stirred to obtain the monomer emulsion (1).

[0289] Monomer emulsion (2): 42 parts of deionized water, 0.72 part of “Aquaron KH-10”, 0.05 part of ammonium persulfate, 2.5 parts of methacrylic acid, 10 parts of 2-hydroxyethyl methacrylate, 5 parts of styrene, 12.5 parts of methyl methacrylate, 10 parts of n-butyl acrylate, and 10 parts of n-butyl methacrylate were mixed and stirred to obtain the monomer emulsion (2).

[0290] Production Example 3 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device contained a mixed solvent of 27.5 parts methoxypropanol and 27.5 parts isobutanol, and was heated to 110°C. Next, 121.5 parts of a mixture consisting of 25 parts styrene, 27.5 parts n-butyl methacrylate, 20 parts isostearyl acrylate (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd., branched higher alkyl acrylate), 7.5 parts 4-hydroxybutyl acrylate, 15 parts of the following phosphate group-containing polymerizable monomer, 12.5 parts 2-methacryloyloxyethyl acid phosphate, 10 parts isobutanol, and 4 parts t-butyl peroxyoctanoate were added to the mixed solvent over 4 hours. A mixture consisting of 0.5 parts t-butyl peroxyoctanoate and 20 parts isopropanol was then added dropwise over 1 hour. After that, the mixture was stirred and aged for 1 hour to obtain a hydroxyl and phosphate group-containing acrylic resin (A1-3) solution with a solid content of 50%. The acid value due to the phosphate group of this resin was 83 mgKOH / g, the hydroxyl value was 29 mgKOH / g, and the weight-average molecular weight was 10,000.

[0291] Phosphate-containing polymerizable monomer: In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device, 57.5 parts of monobutyl phosphate and 41 parts of isobutanol were added and the temperature was raised to 90°C. Then, 42.5 parts of glycidyl methacrylate were added dropwise over 2 hours, followed by stirring and aging for another 1 hour. After that, 59 parts of isopropanol were added to obtain a phosphate-containing polymerizable monomer solution with a solid content of 50%. The acid value of the obtained monomer due to the phosphate group was 285 mgKOH / g.

[0292] Production of hydroxyl group-containing polyester resin (A2) Manufacturing Example 4 In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and water separator, 174 parts of trimethylolpropane, 327 parts of neopentyl glycol, 352 parts of adipic acid, 109 parts of isophthalic acid, and 101 parts of 1,2-cyclohexanedicarboxylic acid anhydride were charged. The temperature was raised from 160°C to 230°C over 3 hours, and the mixture was maintained at 230°C while the generated condensation water was removed by distillation using a water separator until the acid value was 3 mg KOH / g or less. To this reaction product, 59 parts of trimellitic anhydride were added, and an addition reaction was carried out at 170°C for 30 minutes. After cooling to below 50°C, N-methylmorpholine was added in an equivalent amount relative to the acid groups to neutralize the mixture, and then deionized water was gradually added to obtain a hydroxyl group-containing polyester resin (A2-1) solution with a solid content of 45% and a pH of 7.2. The obtained hydroxyl group-containing polyester resin had a hydroxyl value of 128 mgKOH / g, an acid value of 35 mgKOH / g, and a weight-average molecular weight of 13,000.

[0293] Manufacturing of hydroxyl group-containing polyurethane resin (A3) Manufacturing Example 5 In a reaction vessel equipped with a thermometer, stirrer, and reflux condenser, 316.0 parts of "PTMG1000" (trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol with a number average molecular weight of 1000), 17.0 parts of 2,2-dimethylolpropionic acid, 21.9 parts of trimethylolpropane, 113.0 parts of isophorone diisocyanate, 0.19 parts of "Neostan U-600" (trade name, manufactured by Nitto Kasei Co., Ltd., bismuth-based catalyst), and 235.0 parts of methyl ethyl ketone were charged. After purging the reaction system with nitrogen gas, the mixture was reacted at 80°C under stirring to obtain an NCO-terminated urethane prepolymer with a free isocyanate group content of 3.2%. The obtained methyl ethyl ketone solution was cooled to 40°C, and 764.5 g of deionized water containing 13.8 parts of N-methylmorpholine was added and emulsified. Then, 96.4 parts of a 5% N-(2-hydroxyethyl)ethylenediamine aqueous solution were added, and after stirring for 120 minutes, the methyl ethyl ketone was removed by distillation under reduced pressure and heating, and the concentration was adjusted with deionized water to obtain a dispersion of hydroxyl group-containing polyurethane resin (A3-1) with a solid content of 35%, an acid value of 15 mg KOH / g, a hydroxyl value of 12 mg KOH / g, an average particle size of 120 nm, and a glass transition temperature of -7°C.

[0294] Production of polyurethane resin (U) that does not contain hydroxyl groups Manufacturing Example 6 In a reaction vessel equipped with a thermometer, stirrer, and reflux condenser, 211.9 parts of "PTMG1000" (trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol with a number average molecular weight of 1000), 11.5 parts of 2,2-dimethylolpropionic acid, 6.9 parts of trimethylolpropane, 112.2 parts of isophorone diisocyanate, and 298.5 parts of methyl ethyl ketone were charged. After purging the reaction system with nitrogen gas, the mixture was reacted at 80°C under stirring to obtain an NCO-terminated urethane prepolymer with a free isocyanate group content of 3.2%. The obtained methyl ethyl ketone solution was cooled to 40°C, and 493.2 g of deionized water containing 9.8 parts of N-ethylmorpholine was added and emulsified. Then, 159.2 parts of a 5% aqueous ethylenediamine solution were added, and after stirring for 60 minutes, the methyl ethyl ketone was removed by distillation under reduced pressure and heating. The concentration was then adjusted with deionized water to obtain a polyurethane resin (U-1) dispersion with a solid content of 35%, an acid value of 14 mg KOH / g, and an average particle size of 120 nm, which does not contain hydroxyl groups.

[0295] Production of blocked polyisocyanate compounds (B3) Manufacturing example 7 In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropper, 1650 parts of "Sumijoule N-3300" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., polyisocyanate containing isocyanurate structure derived from hexamethylene diisocyanate, solid content concentration 100%, isocyanate group content 21.8%), 1100 parts of "PTMG2000" (trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol, average molecular weight 2,000, solid content concentration 100%), and 0.9 parts of 2,6-di-t-butyl-4-methylphenol were charged and thoroughly mixed, and heated at 130°C for 3 hours under a nitrogen stream. Next, 1200 parts of ethyl acetate and 1200 parts of diisopropyl malonate were charged, and while stirring under a nitrogen stream, 14 parts of a 28% methanol solution of sodium methoxide were added, and the mixture was stirred at 65°C for 8 hours. Next, the mixture was diluted with ethyl acetate to obtain a blocked polyisocyanate compound (B3-1) with a final solid content of 70% and a weight-average molecular weight of 40,000.

[0296] Manufacturing of pigment dispersions Manufacturing Example 8 In a stirring and mixing vessel, 25 parts (15 parts solids) of "Hydroran 2156" (trade name, manufactured by Ekart, silica-coated aluminum pigment paste, aluminum content 60%), 10 parts (5 parts solids) of the acrylic resin (A1-3) solution having hydroxyl and phosphate groups obtained in Production Example 3, and 8 parts of propylene glycol monomethyl ether, 3 parts of ethylene glycol monobutyl ether, 3 parts of dipropylene glycol monomethyl ether, and 40 parts of propylene glycol monobutyl ether were uniformly mixed to obtain a pigment dispersion (P-1).

[0297] Manufacturing Examples 9-28 In Production Example 8, pigment dispersions (P-2) to (P-21) were obtained in the same manner as in Production Example 8, except that the formulation composition was as shown in Table 1 below.

[0298] In Table 1, the amount of organic solvents added is listed, and the solid content of non-organic solvents is listed. Furthermore, the components listed in Table 1 are as follows:

[0299] [Table 1]

[0300] [Table 2]

[0301] [Table 3]

[0302] (Note 1) "Alpaste 6360NS": Product name, manufactured by Toyo Aluminum Co., Ltd., aluminum pigment paste. (Note 2) "Xirallic T61-10 Micro Silver": Product name, manufactured by Merck KGaA, titanium oxide coated alumina flake pigment. (Note 3) "Iriodin 121 RUTILE LUSTRE SATIN": Product name, manufactured by Merck KGaA, titanium dioxide coated mica pigment. (Note 4) "Swazol 1000": Product name, manufactured by Maruzen Petrochemical Co., Ltd., hydrocarbon solvent.

[0303] Furthermore, the solubility of each organic solvent in water at 20°C is as follows. Propylene glycol monobutyl ether: Solubility in water at 20°C is 6.4% by mass. n-butanol: Solubility in water at 20°C is 6.4% by mass. Propylene glycol monomethyl ether: Freely mixable with water at 20°C. Ethylene glycol monobutyl ether: freely mixes with water at 20°C. Dipropylene glycol monomethyl ether: freely mixes with water at 20°C. Butyl acetate: Solubility in water at 20°C is 1.0% by mass. 2-Ethyl-1-hexanol: Solubility in water at 0°C is 0.07% by mass. Methyl isobutyl ketone: Sparingly soluble in water at 20°C. "Swazol 1000": Sparingly soluble in water at 20°C.

[0304] Production of Cellulose Nanocrystal (D1) Aqueous Dispersion Manufacturing example 29 To the deionized water stirred with a magnetic stirrer, "Celluforce NCC" (product name, manufactured by Celluforce, with a number-average fiber diameter of 2.3-4.5 nm, a number-average fiber length of 44-108 nm, and a specific surface area of ​​400 m²) was added to achieve a solid content concentration of 4%. 2 A cellulose nanocrystal (D1-1) aqueous dispersion was obtained by gradually adding sodium sulfonate type cellulose nanocrystal (100% solid content) with a zeta potential of -37mV / g and continuing stirring for 2 hours.

[0305] Preparation of paint composition Example 1 In a stirring and mixing container, combine 89.0 parts (20.0 parts solids) of the pigment dispersion (P-1) obtained in Production Example 8, 133.3 parts (40.0 parts solids) of the aqueous dispersion of hydroxyl group-containing acrylic resin (A1-1) obtained in Production Example 1, 55.6 parts (25 parts solids) of the hydroxyl group-containing polyester resin solution (A2-1) obtained in Production Example 4, 28.6 parts (10 parts solids) of the polyurethane resin (U-1) dispersion that does not contain hydroxyl groups obtained in Production Example 6, and "Cymel 325" (product name, manufactured by Ornex Japan Co., Ltd., methyl / butyl mixed etherified melamine resin). 6.25 parts (5.0 parts solids) of fat (80% solids content) and 39.5 parts (15.0 parts solids) of "Bahijur VPLS2310" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., blocked polyisocyanate compound, 38% solids content) were uniformly mixed. Further, 75.0 parts (3.0 parts solids) of the cellulose nanocrystal (D1-1) aqueous dispersion obtained in Production Example 29, 2-(dimethylamino)ethanol, and deionized water were added to obtain aqueous paint composition No. 1 with a pH of 8.0 and a paint solids content of 25%.

[0306] Examples 2-25, Comparative Examples 1-8 In Example 1, aqueous paint compositions No. 1 to No. 33 were obtained in the same manner as in Example 1, except that the formulation was as shown in Table 2 below.

[0307] In Table 1, the amount of organic solvents added is listed, and the solid content of non-organic solvents is listed. Furthermore, the components listed in Table 2 are as follows: (Note 5) "Leocrysta I-2SX": Product name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., cellulose nanofiber, viscosity modifier, (Note 6) "Primal ASE-60": Product name, manufactured by Dow Chemical Co., Ltd., polyacrylic acid-based viscosity modifier. (Note 7) "UH-752": Product name, manufactured by ADEKA Corporation, urethane association type viscosity modifier.

[0308] The paint compositions No. 1 to No. 33 obtained in Examples 1 to 25 and Comparative Examples 1 to 8 were evaluated using the following test method. The evaluation results are shown in Table 2 below.

[0309] Test method Storage stability Each of the coating compositions obtained in the above examples and comparative examples was subjected to a storage stability test according to the following test method. Each of the above paint compositions was placed in a glass bottle with a capacity of approximately 1 liter (800 g) and stored in a constant temperature room at 40°C for 10 days. After that, the contents were returned to room temperature, and the condition of the contents of the container was visually observed to evaluate the storage stability according to the following criteria. A and B are considered acceptable. The results are shown in Table 2. A: No sedimentation or change in viscosity was observed at all. B: Slight sedimentation and / or viscosity changes are observed, but they return to normal with stirring. C: Sedimentation and / or changes in viscosity are observed. D: Significant sedimentation and / or significant viscosity changes are observed.

[0310] Preparation of test plates and evaluation of metallic unevenness under 80°C heat curing conditions As a metal material, a zinc phosphate-treated alloyed hot-dip galvanized steel sheet was electrodeposited with "Elecron GT-10" (product name, manufactured by Kansai Paint Co., Ltd., cationic electrodeposition paint) to a cured film thickness of 20 μm, and then heated at 170°C for 30 minutes to cure, thereby obtaining an electrodeposited steel sheet. Next, a colored paint composition (product name "WP-505T", manufactured by Kansai Paint Co., Ltd., polyester resin / amino resin-based aqueous paint composition) was applied to the obtained electrodeposited steel sheet to a film thickness of 20 μm, left for 2 minutes, and then preheated at 80°C for 3 minutes to obtain an uncured colored coating film. Next, each paint composition obtained in the above examples and comparative examples was applied to the uncured colored coating film to a cured film thickness of 15 μm, left for 3 minutes, and then preheated at 80°C for 3 minutes to obtain an uncured base coat coating film. Next, "KINO6510" (product name, manufactured by Kansai Paint Co., Ltd., acrylic resin / polyisocyanate compound solvent-based topcoat clear paint) was electrostatically applied onto the uncured basecoat film to a cured film thickness of 35 μm, thereby obtaining an uncured clearcoat film. Then, after being left for 7 minutes, the multilayer coating consisting of the uncured colored film, uncured basecoat film, and uncured clearcoat film was heated at 80°C for 30 minutes to cure the coating, thereby producing each test panel. Each test panel was observed visually, and the degree of metallic unevenness was evaluated according to the following criteria. A and B are considered acceptable. The results are shown in Table 2. A: No metallic unevenness is observed at all. B: Some metallic unevenness was observed, but it was within an acceptable range. C: Metallic unevenness was observed. D: Many instances of metallic unevenness were observed.

[0311] Preparation of test plates under 140°C heat curing conditions and evaluation of metallic unevenness. As a metal material, a zinc phosphate-treated alloyed hot-dip galvanized steel sheet was electrodeposited with "Elecron GT-10" (product name, manufactured by Kansai Paint Co., Ltd., cationic electrodeposition paint) to a cured film thickness of 20 μm, and then heated at 170°C for 30 minutes to cure, thereby obtaining an electrodeposited steel sheet. Next, a colored paint composition (product name "WP-505T", manufactured by Kansai Paint Co., Ltd., polyester resin / amino resin-based aqueous paint composition) was applied to the obtained electrodeposited steel sheet to a film thickness of 20 μm, left for 2 minutes, and then preheated at 80°C for 3 minutes to obtain an uncured colored coating film. Next, each paint composition obtained in the above examples and comparative examples was applied to the uncured colored coating film to a cured film thickness of 15 μm, left for 3 minutes, and then preheated at 80°C for 3 minutes to obtain an uncured base coat coating film. Next, "KINO6510" (product name, manufactured by Kansai Paint Co., Ltd., acrylic resin / polyisocyanate compound solvent-based topcoat clear paint) was electrostatically applied onto the uncured basecoat film to a cured film thickness of 35 μm, thereby obtaining an uncured clearcoat film. Then, after being left for 7 minutes, the multilayer coating consisting of the uncured colored film, uncured basecoat film, and uncured clearcoat film was heated at 140°C for 30 minutes to cure the coating, thereby producing each test panel. Each test panel was observed visually, and the degree of metallic unevenness was evaluated according to the following criteria. A and B are considered acceptable. The results are shown in Table 2. A: No metallic unevenness is observed at all. B: Some metallic unevenness was observed, but it was within an acceptable range. C: Metallic unevenness was observed. D: Many instances of metallic unevenness were observed.

[0312] [Table 4]

[0313] [Table 5]

[0314] Table 6

[0315] Table 7

[0316] Table 8

Claims

1. A paint composition comprising a hydroxyl group-containing resin (A), a curing agent (B), a flake-like lustrous pigment (C), a viscosity modifier (D), and an organic solvent (E) having a solubility in water at 20°C of 4% by mass or more, The aforementioned flake-like luminous pigment (C) comprises a flake-like aluminum pigment (C11) coated with silica, and the content of the flake-like aluminum pigment (C11) is 1 to 50 parts by mass per 100 parts by mass of resin solids in the paint composition. The viscosity modifier (D) comprises at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2). A paint composition in which the content of the organic solvent (E), which has a solubility in water at 20°C of 4% by mass or more, is in the range of 10 to 25% by mass, based on the volatile components in the paint composition.

2. The paint composition according to claim 1, wherein the viscosity modifier (D) comprises cellulose nanocrystals (D1).

3. The paint composition according to claim 1, wherein the organic solvent (E) having a solubility in water at 20°C of 4% by mass or more comprises an organic solvent (E1) having a solubility in water at 20°C in the range of 4 to 10% by mass.

4. The paint composition according to claim 1, further comprising water.

5. Step (I-1): A step of applying a base coat paint composition (Y) to the object to be coated to form an uncured base coat film. Step (I-2): A step of applying a clear coat coating composition (Z) onto the uncured base coat coating to form an uncured clear coat coating, and Step (I-3): A method for forming a multilayer coating film, which includes a step of heating the uncured base coat film and the uncured clear coat film to cure both coating films simultaneously, A method for forming a multilayer coating film, wherein the base coat coating composition (Y) is the coating composition according to any one of claims 1 to 4.

6. Step (II-1): A step of applying a colored paint composition (X) to the object to be coated to form an uncured colored coating film. Step (II-2): A step of applying a base coat paint composition (Y) onto the uncured colored coating to form an uncured base coat coating, Step (II-3): A step of applying a clear coat coating composition (Z) onto the uncured base coat coating to form an uncured clear coat coating, and Step (II-4): A method for forming a multilayer coating film, comprising the step of heating the uncured colored coating film, the uncured base coat coating film, and the uncured clear coat coating film to cure them simultaneously, A method for forming a multilayer coating film, wherein the base coat coating composition (Y) is the coating composition according to any one of claims 1 to 4.

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