Coating composition

Abstract

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

Description

Technical Field

[0001] This invention relates to a coating composition. Background Technology

[0002] Previously, the method for forming multi-layer coatings on automobile bodies or parts was widely adopted, which involved forming multi-layer coatings on the substrate (steel plates, plastics, etc. that have undergone electrophoretic coating) through the following three-coat, two-bake process: applying intermediate coating → heating and curing → applying base coating → applying clear coating → heating and curing.

[0003] In contrast, in recent years, from the perspective of shortening production line processes and saving energy, research has been conducted on three-coat-one-bake methods that omit the heating and curing process after applying the intermediate coating or the intermediate coating application process, and instead sequentially apply the intermediate coating → primer → clear coat → heat curing; and two-coat-one-bake methods that sequentially apply the primer → clear coat → heat curing (a preheating process can also be added after coating). Among these, from the perspective of suppressing environmental pollution caused by the volatilization of organic solvents, the use of water-based coatings as primers in the three-coat-one-bake and two-coat-one-bake methods is particularly recommended.

[0004] In the painting of automotive exterior panels, the aforementioned three-coat-one-bake method is also required to have the same or even more advanced design sense as before.

[0005] Furthermore, water-based coatings with glossy pigments are more prone to developing metallic mottling compared to organic solvent-based coatings.

[0006] On the other hand, if thickening and / or sedimentation occurs during the storage of coatings, it becomes difficult to apply them, so storage stability is also required for coatings.

[0007] As a method for controlling viscosity in the aforementioned water-based primer coatings, one approach is to incorporate an associative viscosity modifier into the coating. This associative viscosity modifier typically comprises a hydrophilic portion and a hydrophobic portion within a single molecule. In water-based coatings, the hydrophilic portion contributes to stability in aqueous solutions, while the hydrophobic portion adsorbs onto the surface of pigments and / or resin particles incorporated into the water-based coating, or the hydrophobic portions associate with each other, thereby forming a network structure that effectively exhibits a thickening effect.

[0008] The aforementioned associative viscosity modifiers typically form a network structure through hydrophobic interactions, thus exhibiting viscosity.

[0009] The aforementioned water-based primer coatings often contain surfactants to disperse the hydrophobic resin components in water. Furthermore, in cases containing water-soluble resins, additives, or pigment dispersants, hydrophilic organic solvents may sometimes be introduced into the water-based coating.

[0010] However, when using associative viscosity modifiers in water-based primer coatings containing surfactants and / or hydrophilic organic solvents, the viscosity of these modifiers is not easily controlled, sometimes resulting in spots, which poses a technical problem. Specifically, when the viscosity of the water-based primer is low when applied to the substrate, interlayering occurs between it and the coatings applied to the upper and / or lower layers. Furthermore, when the water-based coating contains glossy pigments, these pigments migrate after application, causing irregular orientation and sometimes resulting in spots.

[0011] Patent Document 1 discloses a water-based coating composition with high viscosity performance and a viscosity characteristic that decreases with increasing shear rate. The water-based coating composition is characterized by containing: acrylic resin particles (A), a hydroxyl-containing resin (B), a crosslinking agent (C), a viscosity modifier (D), and a pigment (E). The acrylic resin particles (A) have a core / shell structure with a mass ratio of 10 / 90 to 90 / 10, the core is crosslinked, and relative to 100 parts by mass of the total amount of polymerizable unsaturated monomers constituting the acrylic resin particles (A), the amount of polymerizable unsaturated monomers (a1) having linear, branched, or cyclic saturated or unsaturated hydrocarbon groups with 4 or more carbon atoms is [not specified]. The amount is 3 to 70 parts by mass. The hydroxyl-containing resin (B) has a weight-average molecular weight of 1,000 or more and less than 100,000. The viscosity modifier (D) has a weight-average molecular weight of 100,000 or more. Relative to the total amount of monomers constituting 100 parts by mass, the amount of polymeric unsaturated monomer (d1) having a polyoxyalkylene chain is 5 to 50 parts by mass. The amount of polymeric unsaturated monomer (d2) having a hydrophilic functional group without a polyoxyalkylene chain selected from N-vinyl-2-pyrrolidone, N-substituted (meth)acrylamide, hydroxyl-containing polymeric unsaturated monomers and acid-containing polymeric unsaturated monomers is 5 to 90 parts by mass. The amount of other polymeric unsaturated monomers (d3) is 5 to 90 parts by mass.

[0012] Existing technical documents

[0013] Patent documents

[0014] Patent Document 1: Japanese Patent Application Publication No. 2013-221041 Summary of the Invention

[0015] The problem the invention aims to solve

[0016] The technique described in Patent Document 1 sometimes struggles to balance the storage stability of the resulting coating composition with the suppression of metallic spots in the formed coating film. In particular, when the waterborne coating composition contains a hydrophilic solvent, it is difficult to obtain sufficient viscosity, and it is sometimes difficult to balance the storage stability of the resulting coating composition with the suppression of metallic spots in the formed coating film.

[0017] The purpose of this invention is to provide a coating composition that has excellent storage stability and can form a multilayer coating film with an excellent appearance that suppresses metal spots.

[0018] Technical solution

[0019] In order to solve the aforementioned technical problem, the inventors have conducted repeated and in-depth research and found that the above-mentioned technical problem can be solved by using the following coating composition, which comprises: a hydroxyl-containing resin (A), a curing agent (B), a flake-like glossy pigment (C), a viscosity modifier (D), and an organic solvent (E) having a solubility in water of 4% by mass or more at 20°C. The viscosity modifier (D) comprises at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2). The content of the organic solvent (E) having a solubility in water 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 coating composition.

[0020] That is, the present invention relates to... <1> ~ <7> .

[0021] <1> A coating composition comprising: a hydroxyl-containing resin (A), a curing agent (B), a flake-like glossy pigment (C), a viscosity modifier (D), and an organic solvent (E) having a solubility in water 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 solubility in water 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 coating composition.

[0022] <2> according to <1> The coating composition wherein the flake-like glossy pigment (C) comprises flake-like aluminum pigment (C11) coated with silica.

[0023] <3> according to <1> or <2> The coating composition wherein the viscosity modifier (D) comprises cellulose nanocrystals (D1).

[0024] <4> according to <1> ~ <3> The coating composition according to any one of the following, wherein the organic solvent (E) having a solubility of 4% by mass or more in water at 20°C comprises an organic solvent (E1) having a solubility of 4% to 10% by mass in water at 20°C.

[0025] <5> according to <1> ~ <4> The coating composition according to any one of the following, wherein the coating composition further comprises water.

[0026] <6> A method for forming a multilayer coating film includes: step (I-1): applying a primer coating composition (Y) to a workpiece to form an uncured primer coating film; step (I-2): applying a clear coating composition (Z) to the uncured primer coating film to form an uncured clear coating film; and step (I-3): heating the uncured primer coating film and the uncured clear coating film to simultaneously cure both coating films, wherein the primer coating composition (Y) is as follows: <1> ~ <5> The coating composition described in any one of the following statements.

[0027] <7> A method for forming a multilayer coating film includes: step (II-1): applying a coloring paint composition (X) to a workpiece to form an uncured coloring coating film; step (II-2): applying a primer paint composition (Y) to the uncured coloring coating film to form an uncured primer coating film; step (II-3): applying a clear coating paint composition (Z) to the uncured primer coating film to form an uncured clear coating film; and step (II-4): heating the uncured coloring coating film, the uncured primer coating film, and the uncured clear coating film to cure them simultaneously, wherein the primer paint composition (Y) is as follows: <1> ~ <5> The coating composition described in any one of the following statements.

[0028] Beneficial effects

[0029] According to the present invention, a coating composition is provided that has excellent storage stability and can form a multilayer coating film with an excellent appearance that suppresses metal spots. Detailed Implementation

[0030] In this specification, the singular form (a, an, the, etc.) is assumed to include both singular and plural forms, unless otherwise stated in this specification or in cases where the context clearly contradicts it.

[0031] The present invention will now be described in detail, illustrating one example of a preferred embodiment, but the invention is not limited thereto.

[0032] The coating composition of the present invention comprises: a hydroxyl-containing resin (A), a curing agent (B), a flake-like glossy pigment (C), a viscosity modifier (D), and an organic solvent (E) having a solubility in water of 4% by mass or more at 20°C. The viscosity modifier (D) comprises at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2). The content of the organic solvent (E) having a solubility in water 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 coating composition.

[0033] [Hydroxy-containing resin (A)]

[0034] A hydroxyl-containing resin (A) is a resin having at least one hydroxyl group in one molecule. Examples of hydroxyl-containing resins (A) include: hydroxyl-containing acrylic resins (A1), hydroxyl-containing polyester resins (A2), hydroxyl-containing polyurethane resins (A3), hydroxyl-containing acrylic-modified polyester resins, hydroxyl-containing polyether resins, hydroxyl-containing polycarbonate resins, hydroxyl-containing epoxy resins, and hydroxyl-containing alkyd resins. They can be used alone or in combination of two or more.

[0035] From the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the hydroxyl value of the above-mentioned hydroxyl-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.

[0036] The content of the hydroxyl-containing resin (A) in the coating 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 coating composition, from the viewpoint of storage stability and foaming resistance of the obtained coating composition.

[0037] It should be noted that, in this specification, "solid components" refers to non-volatile components such as resin, curing agent, and pigments that remain after drying at 110°C for 1 hour. The aforementioned solid components can be determined, for example, by measuring a sample in a heat-resistant container such as an aluminum foil cup, spreading the sample on the bottom of the container, drying it at 110°C for 1 hour, and weighing the mass of the components remaining after drying.

[0038] Furthermore, in this specification, "solid component concentration" refers to the mass ratio of the aforementioned solid components in the composition. Therefore, for example, the solid component concentration of the composition can be calculated by measuring the composition in a heat-resistant container such as an aluminum foil cup, spreading the composition on the bottom 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.

[0039] From the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the hydroxyl-containing acrylic resin (A1) is preferred as the above-mentioned hydroxyl-containing resin (A1).

[0040] Furthermore, from the viewpoints of foam resistance and appearance of the formed coating film, a hydroxyl-containing polyester resin (A2) is preferred as the aforementioned hydroxyl-containing resin (A2).

[0041] Furthermore, from the viewpoint of stone chip resistance, a polyurethane resin containing hydroxyl groups (A3) is preferred as the aforementioned hydroxyl-containing resin (A3).

[0042] Hydroxyl-containing acrylic resin (A1)

[0043] Hydroxyl-containing acrylic resins (A1) can generally be manufactured by copolymerizing a hydroxyl-containing polymeric unsaturated monomer (a) with other polymeric unsaturated monomers (b) that can copolymerize with the hydroxyl-containing polymeric unsaturated monomer (a) by methods known per se, such as solution polymerization in an organic solvent or emulsion polymerization in an aqueous medium.

[0044] The aforementioned hydroxyl-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: 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, etc., monoesters of (meth)acrylic acid with diols having 2 to 8 carbon atoms; ε-caprolactone-modified forms of these monoesters; N-hydroxymethyl (meth)acrylamide; allyl alcohol; (meth)acrylates having polyoxyethylene chains with hydroxyl groups at the ends of the molecules, etc.

[0045] However, in this invention, the monomer equivalent to the (xvii) ultraviolet-absorbing functional group described later should be defined as another polymeric unsaturated monomer (b) capable of copolymerizing with the aforementioned hydroxyl-containing polymeric unsaturated monomer (a), and excluded from the hydroxyl-containing polymeric unsaturated monomer (a). The aforementioned hydroxyl-containing polymeric unsaturated monomer (a) can be used alone or in combination of two or more.

[0046] It should be noted that, in this specification, a polymerizable unsaturated group refers to an unsaturated group capable of free radical polymerization. Examples of such polymerizable unsaturated groups include: vinyl, (meth)acryloyl, (meth)acrylamido, vinyl ether, allyl, propenyl, isopropenyl, maleimide, etc.

[0047] It should be noted that in this specification, "(meth)acrylate" refers to acrylate or methacrylate, and "(meth)acrylic acid" refers to acrylic acid or methacrylic acid. Furthermore, "(meth)acryloyl" refers to acryloyl or methacryloyl. And "(meth)acrylamide" refers to acrylamide or methacrylamide.

[0048] Other polymerizable unsaturated monomers (b) capable of copolymerizing with the hydroxyl-containing polymerizable unsaturated monomer (a) can be appropriately selected and used according to the desired properties of the hydroxyl-containing acrylic resin (A1). Specific examples of such monomers (b) include the monomers described in (i) to (xix) below. They can be used alone or in combination of two or more.

[0049] (i) Alkyl methacrylates or cycloalkyl methacrylates: for example, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, dodecyl methacrylate, tridecyl methacrylate, stearyl methacrylate, isostearyl methacrylate, cyclohexyl methacrylate, methylcyclohexyl methacrylate, tert-butylcyclohexyl methacrylate, cyclododecyl methacrylate, tricyclodecyl methacrylate, etc.

[0050] (ii) Polymerizable unsaturated monomers having isoborneol groups: for example, isoborneol ester (meth)acrylate, etc.

[0051] (iii) Polymerizable unsaturated monomers having adamantyl groups: for example, adamantyl acrylate (meth)acrylate, etc.

[0052] (iv) Polymerizable unsaturated monomers having a tricyclic decenyl group: for example, tricyclic decenyl ester of (meth)acrylate, etc.

[0053] (v) Polymerizable unsaturated monomers containing aromatic rings: for example, benzyl (meth)acrylate, styrene, α-methylstyrene, vinyltoluene, etc.

[0054] (vi) Polymerizable unsaturated monomers having alkoxysilyl groups: for example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, γ-(meth)acryloyloxypropyltrimethoxysilane, γ-(meth)acryloyloxypropyltriethoxysilane, etc.

[0055] (vii) Polymerizable unsaturated monomers having fluoroalkyl groups: for example, perfluorobutyl ethyl (meth)acrylate, perfluorooctyl ethyl (meth)acrylate, etc.; perfluoroalkyl (meth)acrylates; fluoroolefins, etc.

[0056] (viii) Polymerizable unsaturated monomers having photopolymerizable functional groups such as maleimide groups.

[0057] (ix) Vinyl compounds: for example, N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate, vinyl acetate, etc.

[0058] (x) Polymerizable unsaturated monomers containing carboxyl groups: for example, (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl acrylate, etc.

[0059] (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, methylene bis(meth)acrylamide, ethylene bis(meth)acrylamide, 2-(methacryloyloxy)ethyltrimethylammonium chloride, adducts of glycidyl (meth)acrylate and amine compounds, etc.

[0060] (xii) Polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule: for example, allyl (meth)acrylate, ethylene (meth)acrylate, 1,4-butanediol (meth)acrylate, neopentyl (meth)acrylate, 1,6-hexanediol (meth)acrylate, etc.

[0061] (xiii) Polymerizable unsaturated monomers containing epoxy groups: for example, glycidyl methacrylate, β-methyl glycidyl methacrylate, methyl 3,4-epoxycyclohexyl methacrylate, ethyl 3,4-epoxycyclohexyl methacrylate, propyl 3,4-epoxycyclohexyl methacrylate, allyl glycidyl ether, etc.

[0062] (xiv) A (meth)acrylate having a polyoxyethylene chain with an alkoxy group at the end of the molecule.

[0063] (xv) Polymerizable unsaturated monomers having sulfonic acid groups: for example, 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allyl sulfonic acid, 4-styrene sulfonic acid, etc.; sodium salts, ammonium salts, etc. of these sulfonic acids.

[0064] (xvi) Polymerizable unsaturated monomers with phosphate groups: (meth)acrylate acid phosphonoethyl acrylate, (meth)acrylate acid phosphonopropyl acrylate, acid phosphonoethyl acrylate poly(oxyethylene) glycol (meth)acrylate, acid phosphonoethyl acrylate poly(oxypropylene) glycol (meth)acrylate, etc.

[0065] (xvii) Polymerizable unsaturated monomers having ultraviolet 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.

[0066] (xviii) Photostable polymerizable unsaturated monomers: for example, 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-cyano-4-(meth)acryloami-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-(meth)acryloami-2,2,6,6-tetramethylpiperidine, 1-(meth)acryloyl-4-cyano-4-(meth)acryloami-2,2,6,6-tetramethylpiperidine, 4-crotonyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonylamino-2,2,6,6-tetramethylpiperidine, 1-crotonyl-4-crotonyloxy-2,2,6,6-tetramethylpiperidine, etc.

[0067] (xix) Polymerizable unsaturated monomers with carbonyl groups: for example, acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formyl styrene, vinyl alkyl ketones having 4 to 7 carbon atoms (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl butyl ketone), etc.

[0068] The hydroxyl-containing acrylic resin (A1) can also be used in combination with so-called urethane-modified acrylic resins, which are produced by extending and increasing the molecular weight of the resin by reacting a portion of the hydroxyl groups in the resin with a polyisocyanate compound through a urethane esterification reaction.

[0069] The hydroxyl-containing polymeric unsaturated monomer (a) can typically be used in the range of 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-containing polymeric unsaturated monomer (a) and the other copolymerizable polymeric unsaturated monomer (b).

[0070] The hydroxyl value of the hydroxyl-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 storage stability of the obtained coating composition.

[0071] Furthermore, from the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the acid value of the hydroxyl-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.

[0072] Furthermore, from the viewpoint of the storage stability of the obtained coating composition, the weight-average molecular weight of the hydroxyl-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.

[0073] It should be noted that, in this specification, the number-average molecular weight and weight-average molecular weight are values ​​obtained by converting the retention time (retention capacity) determined by gel permeation chromatography (GPC) to the molecular weight of polystyrene based on the retention time (retention capacity) of a standard polystyrene with a known molecular weight determined under the same conditions. Specifically, the "HLC-8120GPC" (trade name, manufactured by Tosoh Co., Ltd.) can be used as the gel permeation chromatography apparatus, and four columns—"TSKgel G4000HXL", "TSKgel G3000HXL", "TSKgel G2500HXL" and "TSKgel G2000HXL" (trade names, all manufactured by Tosoh Co., Ltd.)—can be used as chromatographic columns. A differential refractometer can be used as the detector, and the determination can be performed under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 mL / min.

[0074] In the case of a water-based coating composition of the present invention, the hydroxyl-containing acrylic resin (A1) preferably comprises a water-dispersible hydroxyl-containing acrylic resin (A11) having a core / shell type multilayer structure (hereinafter, sometimes simply referred to as "water-dispersible hydroxyl-containing acrylic resin (A11)") from the viewpoint of the storage stability and foaming resistance of the obtained coating composition. The core / shell type multilayer structure comprises a core and a shell as constituent components: the core is a copolymer (I) obtained by copolymerizing a polymeric unsaturated monomer (c) having at least two polymeric unsaturated groups in one molecule and a polymeric unsaturated monomer (d) having one polymeric unsaturated group in one molecule, and the shell is a copolymer (II) obtained by copolymerizing the hydroxyl-containing polymeric unsaturated monomer (a) and a polymeric unsaturated monomer (b) other than the hydroxyl-containing polymeric unsaturated monomer (a).

[0075] Polymerizable unsaturated monomers (c) that constitute the core and have at least two polymerizable unsaturated groups in one molecule include, for example: allyl (meth)acrylate, ethylene (meth)acrylate, triethylene (meth)acrylate, tetraethylene (meth)acrylate, 1,3-butanediol (meth)acrylate, trimethylolpropionic acid (trimethylol)acrylate, 1,4-butanediol (meth)acrylate, neopentyl (meth)acrylate, and di(meth)acrylate. Hexanediol acrylate, pentaerythritol dimethacrylate, pentaerythritol tetramethacrylate, glycerol dimethacrylate, 1,1,1-trimethylol ethyl dimethacrylate, 1,1,1-trimethylol ethyl trimethacrylate, 1,1,1-trimethylol propyl trimethacrylate, triallyl isocyanurate, diallyl terephthalate, divinylbenzene, etc., can be used alone or in combination of two or more.

[0076] The polymeric unsaturated monomer (c) having at least two polymeric unsaturated groups in one molecule can typically be used in the range of 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).

[0077] Furthermore, the polymeric unsaturated monomer (d) constituting the core, having one polymeric unsaturated group in one molecule, is a polymeric unsaturated monomer capable of copolymerizing with the polymeric unsaturated monomer (c) having at least two polymeric unsaturated groups in one molecule, and includes compounds containing one polymeric unsaturated group (e.g., vinyl, (meth)acryloyl, allyl, etc.) in one molecule.

[0078] Specific examples of polymerizable unsaturated monomers (d) having a polymerizable unsaturated group in one molecule include: methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, tridecyl methacrylate, lauryl methacrylate, stearyl methacrylate, "isostearyl acrylate" (trade name, manufactured by Osaka Organic Chemicals Co., Ltd.), cyclohexyl methacrylate, methylcyclohexyl methacrylate, tert-butylcyclohexyl methacrylate, cyclododecyl methacrylate, and other alkyl or cycloalkyl methacrylates; polymerizable unsaturated monomers having an isoborneol group, such as methyl methacrylate; propylene methacrylate, etc. Polymerizable unsaturated monomers with adamantyl groups, such as adamantyl esters; vinyl aromatic compounds such as styrene, α-methylstyrene, and vinyltoluene; monoesters of (meth)acrylic acid with diols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylic acid, 2-hydroxypropyl (meth)acrylic acid, 3-hydroxypropyl (meth)acrylic acid, and 4-hydroxybutyl (meth)acrylic acid); ε-caprolactone-modified forms of these monoesters; allyl alcohol; and compounds with molecular ends of... Hydroxyl-containing polymeric unsaturated monomers such as (meth)acrylates with hydroxyl polyoxyethylene chains; carboxyl-containing polymeric unsaturated monomers such as (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate; nitrogen-containing polymeric unsaturated monomers such as (meth)acrylonitrile, (meth)acrylamide, dimethylaminopropyl (meth)acrylamide, dimethylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, and amine compound adducts, etc., can be used alone or in combination of two or more.

[0079] On the other hand, the hydroxyl-containing polymeric unsaturated monomer (a) constituting the shell can be, as described above, for example, monoesterified compounds of (meth)acrylic acid with diols having 2 to 8 carbon atoms, such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, and 4-hydroxybutyl methacrylate; ε-caprolactone modified monoesterified compounds of (meth)acrylic acid with diols having 2 to 8 carbon atoms; allyl alcohol; and (meth)acrylic acid esters having polyoxyethylene chains with hydroxyl groups at the molecular ends. These can be used alone or in combination of two or more.

[0080] The aforementioned hydroxyl-containing polymerizable unsaturated monomer (a) can typically be used in the range of 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).

[0081] Furthermore, other than the hydroxyl-containing polymeric unsaturated monomer (a) constituting the shell, polymeric unsaturated monomer (b) may be used. They may be used individually or in combination of two or more.

[0082] From the perspective of ensuring the smoothness of the formed coating film, the polymeric unsaturated monomer (b) other than the hydroxyl-containing polymeric unsaturated monomer (a) preferably contains a carboxyl-containing polymeric unsaturated monomer (e) as at least part of its composition.

[0083] Examples of the above-mentioned carboxyl-containing polymerizable unsaturated monomers (e) include (meth)acrylic acid, maleic acid, crotonic acid, β-carboxyethyl acrylate, etc., with (meth)acrylic acid being preferred.

[0084] From the viewpoint of the stability of water-dispersible hydroxyl-containing acrylic resin (A11) in aqueous media, the above-mentioned carboxyl-containing polymerizable unsaturated monomer (e) is generally preferably used in the range of 1 to 40% by mass, particularly preferably in the range of 1 to 25% by mass, and even more particularly preferably in the range of 1 to 19% by mass, based on the total mass of monomer (a) and monomer (b).

[0085] The hydroxyl value of the water-dispersible hydroxyl-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 obtained coating composition.

[0086] Furthermore, from the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the acid value of the above-mentioned water-dispersible hydroxyl-containing acrylic resin (A11) is preferably in the range of 3 to 90 mg KOH / g, more preferably in the range of 4 to 70 mg KOH / g, and particularly preferably in the range of 5 to 50 mg KOH / g.

[0087] Furthermore, from the viewpoints of storage stability of the obtained coating composition and suppression of metal spots in the formed coating film, it is preferable to use a polymeric unsaturated monomer having only one polymeric unsaturated group in one molecule as said monomer (a) and said monomer (b), and to set the shell of the above-mentioned water-dispersible hydroxyl-containing acrylic resin (A11) as non-crosslinked.

[0088] The aforementioned water-dispersible hydroxyl-containing acrylic resin (A11) can be obtained, for example, by adding monomer mixture (II) to an emulsion obtained by emulsion polymerization of monomer mixture (I), thereby further polymerizing them. The monomer mixture (I) contains 0.1 to 30% by mass of the polymeric unsaturated monomer (c) having at least two polymeric unsaturated groups in one molecule and 70 to 99.9% by mass of the polymeric unsaturated monomer (d) having one polymeric unsaturated group in one molecule. The monomer mixture (II) contains 1 to 35% by mass of the hydroxyl-containing polymeric unsaturated monomer (a) and 65 to 99% by mass of the polymeric unsaturated monomer (b) other than the monomer (a).

[0089] The emulsion polymerization of the above monomer mixture can be carried out by methods known per se, such as using a polymerization initiator in the presence of an emulsifier.

[0090] As the aforementioned emulsifier, anionic or nonionic emulsifiers are preferred. Examples of anionic emulsifiers include sodium and ammonium salts of organic acids such as alkyl sulfonic acids, alkylbenzene sulfonic acids, and alkyl phosphoric acids. 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, sorbitol monolaurate, sorbitol monostearate, sorbitol trioleate, and polyoxyethylene sorbitol monolaurate.

[0091] Anionic emulsifiers containing polyoxyalkylene groups, such as polyoxyethylene or polyoxypropylene, can be used in one molecule; or reactive anionic emulsifiers containing the anionic group and free radical polymerizable unsaturated groups in one molecule, wherein reactive anionic emulsifiers are preferred.

[0092] Examples of reactive anionic emulsifiers include sodium and ammonium salts of sulfonic acid compounds having free radical polymerizable unsaturated groups such as (meth)allyl, (meth)acryloyl, propenyl, and butenyl. Among these, ammonium salts of sulfonic acid compounds having free radical polymerizable unsaturated groups are preferred to achieve excellent water resistance in the formed coating. Commercially available products such as "Latemul S-180A" (trade name, manufactured by Kao Corporation) are examples of commercially available ammonium salts of such sulfonic acid compounds.

[0093] Among the ammonium salts of sulfonic acid compounds having the aforementioned free radical polymerizable unsaturated groups, ammonium salts of sulfonic acid compounds having both free radical polymerizable unsaturated groups and polyoxyalkylene groups are further preferred. Examples of commercially available products that are such ammonium salts of sulfonic acid compounds having both free radical polymerizable unsaturated groups and polyoxyalkylene groups include: "Aqualon KH-10" (trade name, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) and "SR-1025A" (trade name, manufactured by Asahi Denka Kogyo Co., Ltd.).

[0094] The emulsifier described above can typically be used in the range of 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 all monomers used.

[0095] The polymerization initiator can be any type, whether oil-soluble or water-soluble, and examples include: benzoyl peroxide, octanoyl peroxide, lauroyl peroxide, stearyl peroxide, cumene hydroperoxide, tert-butyl peroxide, tert-butyl peroxylaurate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxyacetate, diisopropylbenzene hydroperoxide, and other organic peroxides; azobisisobutyronitrile, azobis(2,4-dimethylpentanonitrile), azobis(2-methylpropionitrile), azobis(2-methylbutyronitrile), 4,4'-azobis(4-cyanobutyric acid), dimethylazobis(2-methylpropionate), azobis[2-methyl-N-(2-hydroxyethyl)-propionamide], azobis{2-methyl-N-[2-(1-hydroxybutyl)]-propionamide}, and other azo compounds; persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate. These can be used individually or in combination of two or more.

[0096] In addition, the above-mentioned polymerization initiators can also be optionally used in combination with reducing agents such as sugars, sodium formaldehyde sulfoxylate, and iron complexes to form a redox polymerization system.

[0097] The polymerization initiator described above is preferably used in the range of 0.1 to 5% by mass, and particularly in the range of 0.2 to 3% by mass, based on the total mass of all monomers used. There are no particular restrictions on the method of adding the polymerization initiator, and it can be appropriately selected according to its type, amount, etc. For example, the polymerization initiator can be pre-included in the monomer mixture or aqueous medium, or it can be added all at once or dropwise during polymerization.

[0098] The water-dispersible hydroxyl-containing acrylic resin (A11) can be obtained by adding a monomer mixture (II) to the emulsion obtained as described above, and further polymerizing them, wherein the monomer mixture (II) comprises the hydroxyl-containing polymeric unsaturated monomer (a) and polymeric unsaturated monomers (b) other than the monomer (a).

[0099] The monomer mixture (II) may optionally contain, appropriately, the polymerization initiators, chain transfer agents, reducing agents, emulsifiers, etc. listed above.

[0100] Furthermore, the monomer mixture (II) described above can be added dropwise as is, but ideally, the monomer mixture (II) should be dispersed in an aqueous medium and added dropwise as a monomer emulsion. There are no particular limitations on the particle size of the monomer emulsion in this case.

[0101] The polymerization of the monomer mixture (II) can be carried out, for example, by adding the optionally emulsified monomer mixture (II) to the emulsion in a one-time or dropwise manner while stirring and heating to a suitable temperature.

[0102] The water-dispersible hydroxyl-containing acrylic resin (A11) obtained as described above can have a core / shell multilayer structure, wherein the core is a copolymer (I) formed by a monomer mixture (I) containing a polymeric unsaturated monomer (c) having at least two polymeric unsaturated groups in one molecule and a polymeric unsaturated monomer (d) having one polymeric unsaturated group in one molecule, and the shell is a copolymer (II) formed by a monomer mixture (II) containing the hydroxyl-containing polymeric unsaturated monomer (a) and a polymeric unsaturated monomer (b) other than the monomer (a).

[0103] Furthermore, regarding the aforementioned water-dispersible hydroxyl-containing acrylic resin (A11), an emulsion polymerization step may be performed between the step of obtaining the aforementioned copolymer (I) and the step of obtaining the aforementioned copolymer (II), by supplying polymerizable unsaturated monomers (a mixture of one or more monomers) to form other resin layers, thereby producing resin particles formed of three or more layers.

[0104] It should be noted that, in this invention, the "shell" of the aforementioned water-dispersible hydroxyl-containing acrylic resin (A11) refers to the outermost polymer layer existing in the resin particles, the "core" refers to the inner polymer layer of the resin particles excluding the shell, and the "core / shell structure" refers to a structure having both a core and a shell. Regarding the aforementioned core / shell structure, a layered structure in which the core is completely covered by the shell is generally the case; however, depending on factors such as the mass ratio of the core to the shell, sometimes the amount of monomer in the shell is insufficient to form a layered structure. In this case, it is not necessary to have a complete layered structure as described above; it could be a structure in which a portion of the core is covered by the shell, or it could be a structure formed by graft polymerization of a portion of the core with a polymerizable unsaturated monomer that is a component of the shell. Furthermore, the concept of a multilayer structure in the aforementioned core / shell structure also applies to the case where a multilayer structure is formed on the core in this water-dispersible hydroxyl-containing acrylic resin (A11).

[0105] From the viewpoint of storage stability of the obtained coating composition, the ratio of copolymer (I) to copolymer (II) in the above-mentioned water-dispersible hydroxyl-containing acrylic resin (A11) having a core / shell multilayer structure is generally preferably 10 / 90 to 90 / 10, particularly preferably 50 / 50 to 85 / 15, and even more particularly preferably in the range of 65 / 35 to 80 / 20, based on the mass ratio of the solid components of copolymer (I) to copolymer (II).

[0106] The water-dispersible hydroxyl-containing acrylic resin (A11) obtained as described above can have an average particle size typically in the range of 10 to 1000 nm, particularly in the range of 20 to 500 nm.

[0107] In this specification, the average particle size of the aforementioned hydroxyl-containing acrylic resin is a value measured at 20°C after dilution with deionized water using a particle size distribution measuring device employing dynamic light scattering, via conventional methods. For example, the "ELSZ-2000" (trade name, manufactured by Otsuka Electronics Co., Ltd.) can be used as the particle size distribution measuring device employing dynamic light scattering.

[0108] To improve the mechanical stability of the aqueous dispersion particles of the aforementioned water-dispersible hydroxyl-containing acrylic resin (A11), it is ideal to neutralize the acidic groups such as carboxyl groups present in the water-dispersible hydroxyl-containing acrylic resin (A11) using a neutralizing agent. As the neutralizing agent, any neutralizing agent capable of neutralizing acidic groups can be used without particular limitation; examples include sodium hydroxide, potassium hydroxide, trimethylamine, 2-(dimethylamino)ethanol, 2-amino-2-methyl-1-propanol, triethylamine, and ammonia. Ideally, these neutralizing agents are used in an amount such that the pH of the neutralized aqueous dispersion of the water-dispersible hydroxyl-containing acrylic resin (A11) is approximately 6.5 to approximately 9.0.

[0109] Furthermore, the aforementioned water-dispersible hydroxyl-containing acrylic resin (A11) may contain a water-dispersible hydroxyl-containing acrylic resin (A11') comprising a gradient polymer layer.

[0110] The gradient polymer layer of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer refers to a polymer layer with a continuously varying composition (having a compositional gradient) layer structure.

[0111] More specifically, for example, it refers to a polymer layer having a compositional gradient in which the composition of monomers (or monomer mixtures) changes continuously from monomer A (or monomer mixture A) to monomer B (or monomer mixture B).

[0112] The aforementioned gradient polymer layer can typically be obtained using a well-known polymerization method known as power feed polymerization. Specifically, for example, when monomer A (or monomer mixture A) and monomer B (or monomer mixture B) are undergoing polymerization, the gradient polymer layer can be obtained by simultaneously adding monomer B (or monomer mixture B) dropwise into a container holding monomer A (or monomer mixture A) while introducing monomer A (or monomer mixture A) into a reaction vessel for polymerization.

[0113] In the above-mentioned dynamic feed polymerization, a gradient polymer layer with a desired composition gradient can be obtained by setting the synthesis conditions (such as the start time of mixing monomer A (or monomer mixture A) and monomer B (or monomer mixture B), the rate at which monomer B (or monomer mixture B) is added dropwise 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).

[0114] The water-dispersible hydroxyl-containing acrylic resin (A11') comprising a gradient polymer layer is an acrylic resin formed of a core, a shell, and a gradient polymer layer present between the core and the shell, wherein the core is a copolymer (I) with a polymerizable unsaturated monomer as a copolymer component, and the shell is a copolymer (II) with a polymerizable unsaturated monomer as a copolymer component.

[0115] The polymeric unsaturated monomers that constitute the core and shell as described above can be used in appropriate combinations of the hydroxyl-containing polymeric unsaturated monomers and other polymeric unsaturated monomers that can copolymerize with the hydroxyl-containing polymeric unsaturated monomers.

[0116] In order to manufacture the above-mentioned water-dispersible hydroxyl-containing acrylic resin (A11') containing a gradient polymer layer, firstly, a mixture of polymerizable unsaturated monomers is emulsion polymerized to prepare an emulsion of the core copolymer (I).

[0117] Emulsion polymerization of the emulsion used to prepare the core copolymer (I) can be carried out by methods known in the past. For example, it can be carried out by emulsion polymerization of a mixture of polymerizable unsaturated monomers in the presence of an emulsifier using a polymerization initiator. As the emulsifier and polymerization initiator, for example, the emulsifier and polymerization initiator described above can be used.

[0118] To obtain the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer described above, the gradient polymer layer is then formed. This gradient polymer layer can be formed by methods such as dynamic feed polymerization.

[0119] In the formation of gradient polymer layers, a mixture of polymeric unsaturated monomers used in the emulsion polymerization of the core copolymer (I) and the mixture of polymeric unsaturated monomers used in the emulsion polymerization of the shell copolymer (II) can typically be used.

[0120] The aforementioned water-dispersible hydroxyl-containing acrylic resin (A11') containing a gradient polymer layer can be further obtained by forming a shell copolymer (II).

[0121] The monomer mixture used to form the shell copolymer (II) described above may optionally contain the polymerization initiator, chain transfer agent, reducing agent, emulsifier, and other components. Furthermore, the monomer mixture may be added dropwise as is, but it is preferred to add it dropwise as a monomer emulsion obtained by dispersing the monomer mixture in an aqueous medium. In this case, there is no particular limitation on the particle size of the monomer emulsion.

[0122] As a method for polymerizing the monomer mixture used to form the shell copolymer (II), for example, the following method can be listed: the monomer mixture or its emulsion is added dropwise or slowly to the emulsion of the core copolymer (I) while stirring and heating to an appropriate temperature.

[0123] From the viewpoint of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer, the ratio of the gradient polymer layer in the above-mentioned water-dispersible hydroxyl-containing acrylic resin (A11') containing the 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.

[0124] From the viewpoint of curability, stone chip resistance, adhesion and finished product appearance, the hydroxyl value of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer is preferably 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.

[0125] From the viewpoint of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer, the hydroxyl value of the core is preferably 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.

[0126] From the viewpoint of the water-dispersible hydroxyl-containing acrylic resin (A11') shell containing the gradient polymer layer, the hydroxyl value is preferably 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.

[0127] From the viewpoint of the storage stability of the obtained coating and the water resistance of the formed coating film, the acid value of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer is preferably in the range of 1 to 80 mg KOH / g, more preferably in the range of 5 to 50 mg KOH / g, and particularly preferably in the range of 5 to 30 mg KOH / g.

[0128] From the viewpoint of manufacturing stability and storage stability of the obtained coating, the core of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer has an acid value preferably in the range of 0 to 50 mg KOH / g, more preferably in the range of 0 to 30 mg KOH / g, and particularly preferably in the range of 0 to 10 mg KOH / g.

[0129] From the viewpoint of the storage stability of the obtained coating and the water resistance of the formed coating film, the acid value of the shell of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer is preferably 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.

[0130] From the viewpoint of the water resistance, hardness, and stone impact resistance of the formed coating film, the glass transition temperature of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer is preferably 20°C or higher, more preferably 30°C or higher, and particularly preferably 30 to 100°C.

[0131] From the viewpoint of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer, the glass transition temperature of the core is preferably 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.

[0132] From the viewpoint of the hardness and water resistance of the formed coating film, the glass transition temperature of the shell portion of the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer is preferably 40°C or higher, more preferably 50°C or higher, and particularly preferably in the range of 50 to 100°C.

[0133] It should be noted that, in this specification, the glass transition temperature Tg of the water-dispersible hydroxyl-containing acrylic resin (A11') containing a gradient polymer layer is a value calculated using the following formula.

[0134] 1 / Tg(K)=W1 / T1+W2 / T2+……Wn / Tn

[0135] Tg(℃)=Tg(K)-273

[0136] 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.

[0137] It should be noted that the glass transition temperatures of the homopolymers of each monomer are based on the values ​​in the fourth edition of Polymer Handbook, edited by J. Brandrup, Eh Immergut, and E.A. Grulke (1999). For monomers not recorded in this literature, the glass transition temperatures were determined by synthesizing homopolymers of the monomers with a weight-average molecular weight of approximately 50,000 and using differential scanning calorimetry.

[0138] When the coating composition of the present invention contains the above-mentioned hydroxyl-containing acrylic resin (A1), the content of the hydroxyl-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 coating composition, from the viewpoint of the flip-flop properties and stone chip resistance of the formed coating film.

[0139] Hydroxyl-containing polyester resin (A2)

[0140] The hydroxyl-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.

[0141] As the aforementioned polyol, polyols having two or more hydroxyl groups in one molecule are preferred. Examples of such polyols 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-dimethyltrimethylenediol, tetramethylenediol, 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, neopentanediol. Diols such as 1,4-cyclohexanediethanol, tricyclodecanediethanol, neopentyl glycol hydroxypentanoate, hydrogenated bisphenol A, hydrogenated bisphenol F, and dimethylolpropionic acid; polylactone diols formed by adding lactone compounds such as ε-caprolactone to these diols; ester diols such as bis(hydroxyethyl) terephthalate; epoxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, polybutane glycol, and other polyether diols; glycerol, trimethylolethane, trimethylolpropane, diglycerol, triglycerides, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tri(2-hydroxyethyl) isocyanurate, sorbitol, and mannitol; polylactone polyols formed by adding lactone compounds such as ε-caprolactone to these ternary or higher alcohols; fatty acid esters of glycerol, etc.

[0142] In addition, alcohol components other than the aforementioned polyols may also be used. There are no particular limitations on the alcohol components mentioned above; examples include: monohydric alcohols such as methanol, ethanol, propanol, butanol, stearyl alcohol, and 2-phenoxyethanol; alcohol compounds obtained by reacting monoepoxides with acids, such as propylene oxide, butane oxide, and "Cardura E10" (trade name, manufactured by HEXION, a synthetic glycidyl ester of highly branched saturated fatty acids).

[0143] The polycarboxylic acid can be a compound commonly used in the manufacture of polyester resins. Examples of such polycarboxylic acids include aliphatic polycarboxylic acids, alicyclic polycarboxylic acids, and aromatic polycarboxylic acids.

[0144] The aforementioned aliphatic polycarboxylic acids are typically aliphatic compounds having two or more carboxyl groups in one molecule, their anhydrides, and their esters. Examples of aliphatic polycarboxylic acids include: succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, azelaic acid, sebacic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, octadecanoic acid, citric acid, butanetetracarboxylic acid, and other aliphatic polycarboxylic acids; their anhydrides; and their lower alkyl esters having 1 to 6 carbon atoms, preferably 1 to 4. These aliphatic polycarboxylic acids can be used alone or in combination of two or more.

[0145] The aforementioned alicyclic polycarboxylic acids are typically compounds having one or more alicyclic structures and two or more carboxyl groups in one molecule, their anhydrides, and their esterifications. The alicyclic structure can primarily be a 4- to 6-membered ring structure. Examples of alicyclic polycarboxylic acids include: 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, 1,3,5-cyclohexanetricarboxylic acid, etc.; the anhydrides of these alicyclic polycarboxylic acids; and lower alkyl esterifications of these alicyclic polycarboxylic acids having 1 to 6 carbon atoms, preferably 1 to 4. The aforementioned alicyclic polycarboxylic acids can be used alone or in combination of two or more.

[0146] The aforementioned aromatic polycarboxylic acids are typically aromatic compounds having two or more carboxyl groups in one molecule, their anhydrides, and their esters. Examples of aromatic polycarboxylic acids include: phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyl dicarboxylic acid, trimellitic acid, and pyromellitic acid; their anhydrides; and lower alkyl esters of the aromatic polycarboxylic acid having 1 to 6 carbon atoms, preferably 1 to 4. These aromatic polycarboxylic acids can be used individually or in combination of two or more. Phthalic acid, phthalic anhydride, isophthalic acid, trimellitic acid, and trimellitic anhydride are preferred as the aforementioned aromatic polycarboxylic acids, with trimellitic anhydride being more preferred.

[0147] In addition, acid components other than the aforementioned aliphatic polybasic acids, alicyclic polybasic acids, and aromatic polybasic acids may also be used. There are no particular limitations on the acid components mentioned, and examples include: fatty acids such as 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, linoleic acid fatty acids, tung oil fatty acids, rapeseed oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, and safflower oil fatty acids; 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-phenylstearic acid; and hydroxycarboxylic acids such as lactic acid, 3-hydroxybutyric acid, and 3-hydroxy-4-ethoxybenzoic acid. These acid components may be used alone or in combination of two or more.

[0148] The method for manufacturing the hydroxyl-containing polyester resin (A2) is not particularly limited and can be carried out according to conventional methods. For example, the hydroxyl-containing polyester resin (A2) can be manufactured by heating the alcohol component and the acid component in a nitrogen stream at a temperature of about 150 to 250°C for about 5 to 10 hours to carry out an esterification reaction or transesterification reaction between the alcohol component and the acid component.

[0149] When performing esterification or transesterification reactions with the aforementioned alcohol and acid components, these components can be added to the reaction vessel all at once, or one or both can be added to the reaction vessel in multiple batches. Alternatively, a hydroxyl-containing polyester resin can be synthesized first, and then the resulting hydroxyl-containing polyester resin can be reacted with an acid anhydride for half-esterification to produce a polyester resin containing both carboxyl and hydroxyl groups. Alternatively, a carboxyl-containing polyester resin can be synthesized first, and then the aforementioned alcohol component can be added to produce the aforementioned hydroxyl-containing polyester resin.

[0150] During the esterification or transesterification reaction, catalysts known in themselves, 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 promote the reaction.

[0151] Furthermore, the hydroxyl-containing polyester resin (A2) may be modified with fatty acids, monoepoxides, polyisocyanates, etc., during or after the manufacture of the resin.

[0152] Examples of the aforementioned 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, flaxseed oil fatty acids, tung oil fatty acids, rapeseed oil fatty acids, castor oil fatty acids, dehydrated castor oil fatty acids, safflower oil fatty acids, etc. As for the aforementioned monoepoxide compounds, "Cardura E10P" (trade name, manufactured by HEXION Corporation, a glycidyl ester for synthesizing highly branched saturated fatty acids) can be preferred, for example.

[0153] Furthermore, as the aforementioned polyisocyanate compounds, the polyisocyanate compounds exemplified in the polyisocyanate compound (B2) described later can be used. They can be used alone or in combination of two or more.

[0154] The hydroxyl value of the hydroxyl-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 the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film.

[0155] Furthermore, from the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the weight-average molecular weight of the hydroxyl-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.

[0156] Furthermore, from the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the glass transition temperature (Tg) of the hydroxyl-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.

[0157] From the viewpoint of storage stability of the resulting coating composition, the hydroxyl-containing polyester resin (A2) is preferably carboxyl-containing.

[0158] When the hydroxyl-containing polyester resin (A2) has a carboxyl group, the acid value of the hydroxyl-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 obtained coating composition and suppression of metal spots in the formed coating film.

[0159] When the coating composition of the present invention contains the above-mentioned hydroxyl-containing polyester resin (A2), the content of the hydroxyl-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 metal spots in the formed coating film.

[0160] Hydroxyl-containing polyurethane resin (A3)

[0161] As an example of the hydroxyl-containing polyurethane resin (A3), a hydroxyl-containing polyurethane resin obtained by reacting a polyol with a polyisocyanate can be cited.

[0162] Examples of polyols include, for example, low molecular weight polyols such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, and hexamethylene glycol; triols such as trimethylolpropane and glycerol; 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 condensations of the aforementioned diols, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and dicarboxylic acids such as adipic acid, azelaic acid, and sebacic acid; lactone-based ring-opening polymer polyols such as polycaprolactone; and polycarbonate diols. Furthermore, polyols containing carboxyl groups, such as 2,2-dimethylolpropionic acid and 2,2-dimethylolbutyric acid, can also be used.

[0163] Examples of polyisocyanates that react with the aforementioned polyols include: hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, lysine diisocyanate, and other aliphatic polyisocyanate compounds; as well as biuret adducts and isocyanurate cycloadditions of these polyisocyanates; isophorone diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), methylcyclohexane-2,4-(or -2,6-)diisocyanate. Alicyclic diisocyanate compounds such as esters, 1,3-(or 1,4-)bis(isocyanomethyl)cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, and 1,2-cyclohexane diisocyanate; and biuret adducts and isocyanurate cycloadditions of these polyisocyanates; phenyl diisocyanate, isophenyl diisocyanate, tetramethylphenyl diisocyanate, toluene diisocyanate, and 4,4'-diphenyl Aromatic diisocyanate compounds such as methyl methane diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, (m- or p-)phenyl diisocyanate, 4,4'-biphenyl diisocyanate, 3,3'-dimethyl-4,4'-biphenyl diisocyanate, bis(4-isocyanatophenyl) sulfone, and isopropylidene bis(4-phenylisocyanate); and these polyisocyanates. Biuret adducts and isocyanurate cycloadditions of esters; polyisocyanate compounds having three or more isocyanate groups in one molecule, such as triphenylmethane-4,4',4”-triisocyanate, 1,3,5-triisocyanobenzene, 2,4,6-triisocyanotoluene, and 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate; and biuret adducts and isocyanurate cycloadditions of these polyisocyanate compounds.

[0164] From the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the hydroxyl value of the above-mentioned hydroxyl-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.

[0165] From the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the acid value of the above-mentioned hydroxyl-containing polyurethane resin (A3) is preferably in the range of 3 to 90 mg KOH / g, more preferably in the range of 4 to 70 mg KOH / g, and particularly preferably in the range of 5 to 50 mg KOH / g.

[0166] The number-average molecular weight of the hydroxyl-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 obtained coating composition and suppression of metal spots in the formed coating film.

[0167] When the coating composition of the present invention contains the above-mentioned hydroxyl-containing polyurethane resin (A3), the content of the hydroxyl-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 the storage stability of the obtained coating composition and the inhibition of metal spots in the formed coating film.

[0168] [Curing agent (B)]

[0169] There are no particular restrictions on the curing agent (B). For example, a crosslinking agent that reacts with the hydroxyl groups of the hydroxyl-containing resin (A) can be used.

[0170] As curing agents (B), known crosslinking agents can be listed, specifically, for example: amino resins (B1), polyisocyanate compounds (B2), end-capped polyisocyanate compounds (B3), polyhydrazide compounds, polyaminourea compounds, carbodiimide compounds, compounds containing oxazoline groups, epoxy compounds, polycarboxylic acids, etc. Crosslinking agents can be used alone, or two or more can be used in combination.

[0171] From the viewpoint of the stone chip resistance of the formed coating, the curing agent (B) preferably includes at least one crosslinking agent selected from amino resin (B1), polyisocyanate compound (B2), and capped polyisocyanate compound (B3), and more preferably includes amino resin (B1) and / or capped polyisocyanate compound (B3), and particularly preferably includes amino resin (B1) and capped polyisocyanate compound (B3).

[0172] Amino resin (B1)

[0173] As the aforementioned amino resin (B1), a partially hydroxymethylated amino resin or a fully hydroxymethylated amino resin obtained by reacting an amino component with an aldehyde component can be used. Examples of amino components include melamine, urea, benzoguanamine, methylguanamine, steroidal guanamine, spiroguanamine, dicyandiamide, etc. Examples of aldehyde components include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde, etc.

[0174] Alternatively, a substance obtained by partially or completely etherifying the hydroxymethyl group of the above-mentioned hydroxymethylated amino resin with a suitable alcohol can be used. Examples of alcohols that can be used for etherification include: methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, 2-ethyl-1-butanol, 2-ethyl-1-hexanol, etc.

[0175] As the aforementioned amino resin (B1), melamine resin is preferred. In particular, methyl etherified melamine resin, which is formed by partially or completely etherifying the hydroxymethyl group of a partially or completely hydroxymethylated melamine resin with methanol, butyl etherified melamine resin, which is formed by partially or completely etherifying the hydroxymethyl group of a partially or completely hydroxymethylated melamine resin with butanol, and methyl-butyl mixed etherified melamine resin, which is formed by partially or completely etherifying the hydroxymethyl group of a partially or completely hydroxymethylated melamine resin with methanol and butanol, are preferred, and methyl-butyl mixed etherified melamine resin is even more preferred.

[0176] Furthermore, the weight-average molecular weight of the aforementioned melamine resin is preferably in the range of 450 to 6000, more preferably in the range of 500 to 4000, and particularly preferably in the range of 550 to 3000.

[0177] Commercially available melamine resins can be used. Examples of commercially available product names include: “CYMEL202”, “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”, “CYMEL 1130” (all manufactured by Allnex Japan Co., Ltd.); “U-VAN 20SE60”, “U-VAN28-60” (all manufactured by Mitsui Chemicals Co., Ltd.); etc.

[0178] When using the above-mentioned melamine resin as curing agent (B), sulfonic acids such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, and dinonylnaphthalenesulfonic acid; neutral salts of the sulfonic acid and amine; and neutral salts of phosphate ester compounds and amines can optionally be used as curing catalysts.

[0179] The amino resin (B1) can, for example, be used as a crosslinking agent for resins containing hydroxyl groups.

[0180] Polyisocyanate compound (B2)

[0181] The polyisocyanate compound (B2) is a compound having two or more isocyanate groups in one molecule.

[0182] The polyisocyanate compound (B2) includes, for example, aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic aliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of the polyisocyanate.

[0183] Examples of the aforementioned 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, dimer diisocyanate, and methyl 2,6-diisocyanate hexanoate (common name: Aliphatic diisocyanates such as lysine diisocyanate; aliphatic triisocyanates such as 2,6-diisocyanohexanoate 2-isocyanoethyl ester, 1,6-diisocyano-3-isocyanomethylhexane, 1,4,8-triisocyanooctane, 1,6,11-triisocyanoundecane, 1,8-diisocyano-4-isocyanomethyloctane, 1,3,6-triisocyanohexane, and 2,5,7-trimethyl-1,8-diisocyano-5-isocyanomethyloctane, etc.

[0184] Examples of alicyclic polyisocyanates include: 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanomethyl-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(isocyanomethyl)cyclohexane (common name: hydrogenated phenyl dimethyl diisocyanate) or mixtures thereof, norbornene diisocyanate, etc.; 1,3,5-triisocyanocyclohexane, 1,3,5-trimethylisocyanocyclohexane, 2-(3-isocyanopropyl)-2,5-bis(isocyanomethyl)-bicyclo(2.2.1)heptane, 2-(3 3-(3-isocyanopropyl)-2,5-di(isocyanomethyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanoethyl)-2-isocyanomethyl-3-(3-isocyanopropyl)-bicyclo(2.2.1)heptane, 6-(2-isocyanoethyl)-2- Alicyclic triisocyanates such as isocyanomethyl-3-(3-isocyanopropyl)-bicyclo(2.2.1)heptane, 5-(2-isocyanoethyl)-2-isocyanomethyl-2-(3-isocyanopropyl)-bicyclo(2.2.1)heptane, and 6-(2-isocyanoethyl)-2-isocyanomethyl-2-(3-isocyanopropyl)-bicyclo(2.2.1)heptane.

[0185] Examples of aromatic aliphatic polyisocyanates include: 1,3- or 1,4-phenylenedimethyl diisocyanate or mixtures thereof, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,3- or 1,4-bis(1-isocyanate-1-methylethyl)benzene (common name: tetramethylphenyldimethyl diisocyanate) or mixtures thereof, etc.; aromatic aliphatic triisocyanates such as 1,3,5-triisocyanate-toluene, etc.

[0186] Examples of aromatic polyisocyanates include: m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4'- or 4,4'-diphenylmethane diisocyanate or mixtures thereof, 2,4- or 2,6-toluene diisocyanate or mixtures thereof, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, and other aromatic diisocyanates; triphenylmethane-4,4',4”-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, and other aromatic triisocyanates; 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate, and other aromatic tetraisocyanates.

[0187] Examples of derivatives of the aforementioned polyisocyanate include: dimers, trimers, biuret, urethane, urea diketone, urea imine, isocyanurate, oxadiazine trione, polymethylene polyphenyl polyisocyanate (crude MDI, polymeric MDI), crude TDI, etc.

[0188] The aforementioned polyisocyanates and their derivatives can be used individually or in combination of two or more. Among these polyisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and their derivatives are preferably used individually or in combination of two or more.

[0189] Furthermore, as the polyisocyanate compound (B2), a prepolymer prepared by reacting the above-mentioned polyisocyanate and its derivatives with polyol, low molecular weight polyester resin or water under conditions of excess isocyanate groups can also be used.

[0190] When using a polyisocyanate compound (B2) as a curing agent (B), organometallic compounds, acid compounds, alkali compounds, etc., can optionally be used as curing catalysts.

[0191] The aforementioned polyisocyanate compound (B2) can, for example, be used as a crosslinking agent for resins containing hydroxyl or amino groups.

[0192] End-capped polyisocyanate compound (B3)

[0193] The terminated polyisocyanate compound (B3) is a compound formed by terminating the isocyanate group of the polyisocyanate compound (B2) with a terminating agent.

[0194] Examples of end-capping agents include: phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxybiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, methyl hydroxybenzoate, and other phenolic end-capping agents; β-caprolactam, δ-valerolactam, γ-butyrolactam, β-propiolactam, and other lactam end-capping agents; methanol, ethanol, propanol, butanol, pentanol, lauryl alcohol, and other aliphatic alcohol end-capping agents; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, and diethylene glycol monoethyl ether. Ether-based end-capping agents such as propylene glycol monomethyl ether and methoxymethanol; alcohol-based end-capping agents such as benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, hydroxymethylurea, hydroxymethyl melamine, diacetone alcohol, 2-hydroxyethyl acrylate, and 2-hydroxyethyl methacrylate; oxime-based end-capping agents such as formamide oxime, acetamide oxime, acetone oxime, methyl ethyl ketone oxime, diacetylmonoxime, benzophenone oxime, and cyclohexane oxime; dimethyl malonate, diethyl malonate, ethyl acetoacetate, and acetoacetic acid. Methylene-based end-capping agents such as methyl esters and acetylacetone; thiol-based end-capping agents such as butyl mercaptan, tert-butyl mercaptan, hexyl mercaptan, tert-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methyl thiophenol, and ethyl thiophenol; amide-based end-capping agents such as acetanilide, acetanilide, acetyltoluidine, acrylamide, methacrylamide, acetamide, stearamide, and benzamide; imide-based end-capping agents such as succinimide, phthalimide, and maleimide; diphenylamine, phenylnaphthylamine, dimethylaniline, and N-phenylene oxide. Amine-based end-capping agents such as dimethylaniline, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylaniline; imidazole-based end-capping agents such as imidazole and 2-ethylimidazole; urea-based end-capping agents such as urea, thiourea, ethylene urea, ethylene thiourea, and diphenylurea; carbamate-based end-capping agents such as N-phenylcarbamate; imine-based end-capping agents such as ethyleneimine and propyleneimine; sulfite-based end-capping agents such as sodium bisulfite and potassium bisulfite; and azole-based end-capping agents, etc. Examples of azole-based end-capping agents include: pyrazole, 3,5-dimethylpyrazole, 3-methylpyrazole, 4-benzyl-3,5-dimethylpyrazole, 4-nitro-3,5-dimethylpyrazole, 4-bromo-3,5-dimethylpyrazole, 3-methyl-5-phenylpyrazole, and other pyrazoles or pyrazole derivatives; imidazole, benzimidazole, 2-methylimidazolium, 2-ethylimidazolium, 2-phenylimidazolium, and other imidazoles or imidazole derivatives; and 2-methylimidazoline, 2-phenylimidazoline, and other imidazoline derivatives.

[0195] As capping agents, oxime-based capping agents, active methylene-based capping agents, pyrazoles, or pyrazole derivatives are preferred. Furthermore, hydroxycarboxylic acids having one or more hydroxyl groups and one or more carboxyl groups, such as hydroxypentanoic acid and dimethylolpropionic acid, can also be used as capping agents.

[0196] In the coating composition of the present invention, when using the above-mentioned capped polyisocyanate, it is preferable to use a compound that is a capped polyisocyanate compound that, after using the above-mentioned hydroxycarboxylic acid capped isocyanate group, neutralizes the carboxyl group of the hydroxycarboxylic acid and imparts water dispersibility.

[0197] From the viewpoint of the appearance of the formed coating and the adhesion between the formed coating and the substrate, the above-mentioned end-capped polyisocyanate compound (B3) preferably contains a structure derived from a spacer having at least two isocyanate reactive functional groups.

[0198] There are no particular limitations on the functional groups mentioned above, as long as they are reactive to the isocyanate group. Examples of such reactive functional groups for the isocyanate group include hydroxyl, amino, carboxyl, and thiol groups, among which hydroxyl and amino groups are preferred, and hydroxyl is particularly preferred.

[0199] Therefore, the spacer is preferably a compound having at least two hydroxyl groups or a compound having at least two amino groups, wherein a compound having at least two hydroxyl groups is preferred.

[0200] Examples of compounds having at least two hydroxyl groups include, for example, diols such as ethylene glycol, diethylene glycol, propylene glycol, butanediol, and hexamethylene glycol, which are low molecular weight compounds; triols such as trimethylolpropane and glycerol; and pentaerythritol, which are high molecular weight compounds. Examples of high molecular weight compounds include polyether polyols, polyester polyols, acrylic polyols, and epoxy polyols. Among these, polyether polyols are preferred from the viewpoint of storage stability of the obtained coating composition.

[0201] As the aforementioned polyether polyol, epoxide adducts of compounds having at least two hydroxyl groups, ring-opening (co)polymers of epoxides or cyclic ethers (such as tetrahydrofuran) can be used. Specifically, examples include: polyethylene glycol, polypropylene glycol, ethylene glycol-propylene glycol (block or random) copolymers, polytetramethylene glycol, polyhexamethylene glycol, polyoctamethylene glycol, etc.

[0202] Among them, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol can be preferred as the polyether polyols mentioned above.

[0203] The aforementioned polyether polyols can be used alone or in combination of two or more.

[0204] Furthermore, polyetheramines can be listed as an example of compounds having at least two amino groups.

[0205] The aforementioned polyetheramines can also be commercially available products. 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" manufactured by HUNTSMAN.

[0206] The molecular weight of the spacer is preferably in the range of 500 to 6000, more preferably in the range of 800 to 5000, and even more preferably in the range of 1500 to 3500, from the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film.

[0207] From the viewpoint of the storage stability of the obtained coating composition, the number of functional groups used as the spacers is preferably 2 to 3, and more preferably 2.

[0208] By reacting a portion 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 foaming resistance of the obtained coating composition, the ratio of the polyisocyanate compound to the spacer is preferably in 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 end-capping the polyisocyanate compound containing a structure derived from the spacer, a end-capped polyisocyanate compound containing a structure derived from the spacer can be formed.

[0209] From the viewpoint of storage stability and foaming resistance of the obtained coating composition, the above-mentioned capped polyisocyanate compounds preferably include capped polyisocyanate compounds with a weight average molecular weight in the range of 20,000 to 200,000.

[0210] When using a capped polyisocyanate compound (B3) as a curing agent (B), organometallic compounds, acid compounds, alkali compounds, etc., can optionally be used as curing catalysts.

[0211] In the coating 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 coating composition, from the viewpoint of storage stability of the obtained coating composition and suppression of metal spots in the formed coating film.

[0212] [Flake-like glossy pigment (C)]

[0213] Examples of flaky, bright pigments (C) include: flaky metallic pigments made of aluminum, copper, nickel alloys, stainless steel, etc.; flaky metallic pigments with metal oxide coatings; flaky metallic pigments with coloring pigments chemically adsorbed on their surfaces; flaky aluminum pigments that form an aluminum oxide layer through a redox reaction on their surfaces; aluminum solid solution plate-shaped iron oxide pigments; glass sheet pigments; glass sheet pigments with metal oxide coatings; glass sheet pigments with coloring pigments chemically adsorbed on their surfaces; glass sheet pigments with metal coatings; interference mica pigments with titanium dioxide coatings; reduced mica pigments obtained by reducing interference mica pigments; coloring mica pigments with coloring pigments chemically adsorbed on their surfaces or with iron oxide coatings; graphite pigments with titanium dioxide coatings; silica flakes with titanium dioxide coatings; aluminum oxide flake pigments; plate-shaped iron oxide pigments; holographic pigments; synthetic mica pigments; cholesteric liquid crystal polymer pigments with helical structures; bismuth oxychloride pigments, etc.

[0214] Furthermore, from the viewpoint of the gloss of the formed coating, the aforementioned flake-shaped glossy pigment (C) preferably includes a flake-shaped aluminum pigment (C1).

[0215] The aforementioned flake-like aluminum pigment (C1) is typically manufactured by pulverizing and grinding aluminum in a ball mill or vertical ball mill in the presence of a pulverizing liquid medium, using pulverizing aids. In addition to higher fatty acids such as oleic acid, stearic acid, isostearic acid, lauric acid, palmitic acid, and myristic acid, aliphatic amines, aliphatic amides, and aliphatic alcohols can also be used as pulverizing aids. Aliphatic hydrocarbons such as mineral oil can be used as the pulverizing liquid medium.

[0216] The aforementioned flake-like aluminum pigments (C1) can be broadly classified into floating and non-floating types based on the type of pulverizing aid. Floating type pigments, when incorporated into coating compositions, align (float) on the surface of the resulting coating film, resulting in a strong metallic appearance, heat reflection, and rust prevention. Therefore, they are widely used in various building materials, such as tanks / pipes / wiring systems and roofing materials. In the coating composition of this invention, considering the depth of the resulting coating film, non-floating flake-like aluminum pigments are preferred.

[0217] From the viewpoints of glossiness of the formed coating and suppression of metal spots, the average particle size of the aforementioned 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. Furthermore, the thickness of the aforementioned flake-like aluminum pigment (C1) is preferably in the range of 0.05 to 5 μm. The average particle size referred to here is the median particle size of the volumetric reference particle size distribution measured using a Microtrac particle size distribution measuring device MT3300 (trade name, manufactured by Nikkiso Co., Ltd.) by laser diffraction scattering. Thickness is defined as follows: the thickness of the coating containing the flake-like aluminum pigment (C1) is measured using image processing software by observing the cross-section of the coating under a microscope, and the average value of 100 or more measurements is taken.

[0218] Furthermore, when the above-mentioned flake-shaped glossy pigment (C) includes the above-mentioned flake-shaped aluminum pigment (C1), from the viewpoint of suppressing metallic spots and water resistance of the formed coating film, it is preferable that the flake-shaped aluminum pigment (C1) is coated with silica.

[0219] As aluminum pigments coated with silica, commercially available products such as the "Hydrolan series" (trade name, manufactured by ECKART) and the "ALPASTE EMR series" (trade name, manufactured by Toyo Aluminum Co., Ltd.) can be used.

[0220] When the coating composition of the present invention contains the above-mentioned flake-shaped aluminum pigment (C1) as the flake-shaped glossy pigment (C), the amount of the flake-shaped aluminum pigment (C1) is preferably in the range of 1 to 50 parts by mass relative to 100 parts by mass of the resin solids in the coating composition, 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, from the viewpoint of gloss of the formed coating film and suppression of metallic spots.

[0221] Furthermore, when the coating composition of the present invention includes the aforementioned silica-coated flake-shaped aluminum pigment (C11) as the flake-shaped glossy pigment (C), the amount of the silica-coated flake-shaped aluminum pigment (C11) is preferably in the range of 1 to 50 parts by mass relative to 100 parts by mass of the resin solids in the coating composition, 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, from the viewpoint of gloss of the formed coating film and suppression of metallic spots.

[0222] Furthermore, from the viewpoint of the chroma of the formed coating film, the aforementioned flake-shaped glossy pigment (C) preferably includes a flake-shaped light interference pigment (C2).

[0223] Examples of the aforementioned flake-like optical interference pigments (C2) include coloring pearlescent pigments and interference pearlescent pigments made of translucent flake-like substrates coated with metal oxides such as iron oxide and titanium oxide.

[0224] Examples of translucent, flaky substrates include: natural mica, artificial mica, alumina sheets, silicon dioxide sheets, and glass sheets.

[0225] Natural mica refers to the flake-like substrate obtained by crushing mica ore. Artificial mica, on the other hand, is synthesized by heating industrial raw materials such as SiO2, MgO, Al2O3, K2SiF6, and Na2SiF6 to a high temperature of approximately 1500℃, then cooling and crystallizing them. Compared to natural mica, artificial mica has fewer impurities and is more uniform in size and thickness. Specifically, fluorophlogopite (KMg3AlSi3O3) is known to be... 10 F2), potassium tetrasilicon mica (KMg) 25 AlSi4O 10 F2), sodium tetrasilicon mica (NaMg) 25 AlSi4O 10 F2), Na-bearing mica (NaMg2LiSi4O) 10 F2), LiNa-bearing mica (LiMg2LiSi4O) 10 F2), etc.

[0226] Alumina flakes refer to flaky (thin) aluminum oxide, which is colorless and transparent. Alumina does not need to be a single component and can also contain oxides of other metals.

[0227] Silica sheets refer to substances obtained by heat-treating the following flaky gels: dissolving silicon alkoxides, such as methanol, ethanol, propoxide, and butoxide, in solvents such as methanol, ethanol, propanol, and butanol to obtain a solution; coating this solution onto a smooth metal plate or similar material; and then drying and peeling it off to obtain a flaky gel. Glass sheets refer to smooth-surfaced substrates obtained by shaping flaky C or E glass.

[0228] The aforementioned flake-like optical interference pigment (C2) can also be used for surface treatments to improve dispersibility, water resistance, chemical resistance, weather resistance, etc.

[0229] From the viewpoint of improving the chroma of the formed coating and suppressing metallic spots, the average particle size of the aforementioned flake-like optical interference 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. Furthermore, the thickness of the aforementioned flake-like optical interference pigment (C2) is preferably in the range of 0.05 to 5 μm. The average particle size referred to here is the median particle size of the volumetric reference particle size distribution measured using a Microtrac particle size distribution measuring device MT3300 (trade name, manufactured by Nikkiso Co., Ltd.) by laser diffraction scattering. Thickness is defined as follows: the thickness of the coating containing the flake-like optical interference pigment (C2) is measured using image processing software by observing the cross-section of the coating under a microscope, and the average value of more than 100 measurements is taken.

[0230] Furthermore, when the coating composition of the present invention includes the above-mentioned flake-like glossy pigment (C2) as the flake-like glossy pigment (C), the amount of the flake-like glossy pigment (C2) is preferably in the range of 1 to 50 parts by mass relative to 100 parts by mass of the resin solids in the coating, 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, from the viewpoint of storage stability of the coating composition and suppression of metallic spots in the formed coating film.

[0231] [Viscosity modifier (D)]

[0232] The coating composition of the present invention contains a viscosity modifier, which comprises 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 present, the storage stability of the resulting coating composition is reduced.

[0233] Furthermore, from the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the above-mentioned viscosity modifier preferably includes the above-mentioned cellulose nanocrystals (D1).

[0234] In this specification, the number-average fiber length to number-average fiber diameter ratio (number-average fiber length / number-average fiber diameter) of the cellulose nanocrystals (D1) is less than 50.

[0235] Furthermore, in this specification, the number-average fiber length to number-average fiber diameter ratio (number-average fiber length / number-average fiber diameter) of the cellulose nanofibers (D2) is 50 or more.

[0236] Cellulose nanocrystals (D1)

[0237] Cellulose nanocrystals (D1) can be obtained by known methods. For example, cellulose nanocrystals (D1) can be obtained by treating cellulose raw materials with acids such as sulfuric acid to hydrolyze and remove the non-crystalline portion, followed by mechanical defibrillation.

[0238] As a cellulose raw material, there are no particular limitations as long as it contains cellulose. Examples include various wood pulps, non-wood pulps, bacterial cellulose, regenerated cellulose, waste paper pulp, cotton, *Fagopyrum cylindrica* cellulose, and sea squirt cellulose. In addition, various commercially available cellulose powders and microcrystalline cellulose powders can also be used.

[0239] Furthermore, there are no particular limitations on mechanical defiber treatment; existing known methods can be used, such as those employing high-pressure homogenizers, ultra-high-pressure homogenizers, ball mills, roller mills, cutter mills, planetary mills, jet mills, grinders, juice mixers, homogenizers, ultrasonic homogenizers, nanogenerators, underwater counter-collision, single-screw or twin-screw extruders, etc.

[0240] Furthermore, the aforementioned cellulose nanocrystals (D1) can be cellulose nanocrystals that have undergone various chemical modifications. Examples of chemical modifications include: esterification such as carboxymethylation, acylation, and phosphorylation; acidification such as carboxylation; sulfonation; fluorination; cationization; and treatment using silane coupling agents.

[0241] In cases where the cellulose nanocrystals have undergone chemical modification, sulfonation is the preferred type of chemical modification, considering factors such as the storage stability of the resulting coating composition and the suppression of metal spots in the formed coating film.

[0242] In addition, the aforementioned cellulose nanocrystals (D1) can also undergo the above-mentioned chemical modification after defibrillation treatment.

[0243] Furthermore, the aforementioned cellulose nanocrystals (D1) can be neutralized with a neutralizing agent. For example, the neutralizing agent described in the description of the water-dispersible hydroxyl-containing acrylic resin (A11) can be used.

[0244] From the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the number-average fiber diameter of the above-mentioned cellulose nanocrystals (D1) 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 particularly preferably in the range of 1 to 5 nm.

[0245] Furthermore, from the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, 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 particularly preferably in the range of 30 to 150 nm.

[0246] The number-average fiber diameter and number-average fiber length were determined and calculated, for example, based on the following image: a sample obtained by dispersing cellulose nanocrystals (D1) diluted with water onto a hydrophilically treated carbon film-coated grid, and observing it using a transmission electron microscope (TEM). Specifically, the observation field was adjusted to observe at least 100 cellulose nanocrystal particles, and the diameter and fiber length of 100 randomly selected cellulose nanocrystal particles were measured to calculate the number-average diameter and number-average fiber length.

[0247] The ratio of the number-average fiber length to the number-average fiber diameter (number-average fiber length / number-average fiber diameter) of the cellulose nanocrystals (D1) is preferably 3 or more and less than 50 from the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film. More preferably, it is 5 or more and less than 50. More particularly preferably, it is 10 or more and less than 50.

[0248] In addition, commercially available products of the aforementioned cellulose nanocrystals (D1) include, for example, "Celluforce NCC" (sodium sulfonate cellulose nanocrystals manufactured by Celluforce Corporation).

[0249] Cellulose nanofibers (D2)

[0250] The aforementioned cellulose nanofibers (D2) can be obtained by known methods. For example, cellulose nanofibers (D2) can be produced by defibrillating cellulose raw materials to refine them until the fiber diameter reaches the nanoscale. Examples of defibrillation methods for cellulose raw materials include mechanical defibrillation, chemical treatment using liquid oxidizing catalysts containing N-oxygen compounds, and so on.

[0251] As a cellulose raw material, there are no particular limitations as long as it contains cellulose, and the same cellulose raw material as the raw material of the cellulose nanocrystals (D1) can be used.

[0252] Furthermore, the aforementioned cellulose nanofibers (D2) can be cellulose nanofibers that have undergone various chemical modifications. Examples of chemical modifications include: esterification such as carboxymethylation, acylation, and phosphorylation; acidification such as carboxylation; sulfonation; fluorination; cationization; and treatment using silane coupling agents.

[0253] Furthermore, the aforementioned cellulose nanofibers (D2) can be neutralized using a neutralizing agent. For example, the neutralizing agent described in the description of the water-dispersible hydroxyl-containing acrylic resin (A11) can be used.

[0254] 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 viewpoints of storage stability of the obtained coating composition and suppression of metal spots in the formed coating film.

[0255] The number-average fiber length of the cellulose nanofibers (D2) is preferably in the range of 200 to 10000 nm, more preferably in the range of 200 to 5000 nm, particularly preferably in the range of 200 to 2500 nm, and even more particularly preferably in the range of 200 to 1000 nm, from the viewpoint of storage stability of the obtained coating composition and suppression of metal spots in the formed coating film.

[0256] The ratio of the number-average fiber length to the number-average fiber diameter (number-average fiber length / number-average fiber diameter) of the cellulose nanofibers (D2) 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 the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film.

[0257] Commercially available products of the aforementioned cellulose nanofibers (D2) include, for example: "Nanocellulose Fiber" (manufactured by Chugoku Pulp & Paper Co., Ltd.), "BiNFi-s" (manufactured by Sugino Machine Co., Ltd.), "Rheocrysta" (manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.), "Cellulcellulose Nanofiber" (manufactured by MORI MACHINERY Co., Ltd.), "cellenpia" (manufactured by Nippon Paper Co., Ltd.), and "AUROVISCO" (manufactured by Oji Holding Co., Ltd.).

[0258] As the viscosity modifier (D), viscosity modifiers other than the aforementioned cellulose nanocrystals (D1) and cellulose nanofibers (D2) can also be used. Known substances other than these cellulose nanocrystals (D1) and cellulose nanofibers (D2) can be used as viscosity modifiers, for example: silica-based micro powders, mineral-based viscosity modifiers, barium sulfate micronized powders, polyamide-based viscosity modifiers, organic resin micronized viscosity modifiers, diurea-based viscosity modifiers, urethane-associated viscosity modifiers, and acrylic swelling-type polyacrylic acid-based viscosity modifiers, etc.

[0259] As viscosity modifiers for the aforementioned mineral systems, examples include bentonite layered silicates with a 2:1 crystal structure. Specifically, examples include: natural or synthetic montmorillonite, succinate, lithium montmorillonite, magnesium montmorillonite, betolite, chlorodiazepine, bentonite, synthetic laponite, and other montmorillonite group clay minerals; bentonite group clay minerals such as Na-type tetrasilicic fluoromica, Li-type tetrasilicic fluoromica, Na-salt type fluorinated mica, and Li-type fluorinated mica; vermiculite; their substitutes or derivatives; and mixtures thereof.

[0260] As the urethane-associated viscosity modifier, a urethane-associated viscosity modifier having a hydrophobic group at the end and urethane bonds in the molecular chain is preferably used. Commercially available products can be used as such urethane-associated viscosity modifiers. Examples of trade names for these commercially available products include: “UH-420”, “UH-462”, “UH-472”, “UH-540”, “UH-752”, “UH-756VF”, “UH-814N” (all manufactured by ADEKA Co., Ltd.); “SNTHICKENER 612”, “SN THICKENER 621N”, “SN THICKENER 625N”, “SN THICKENER 627N”, “SN THICKENER 660T” (all manufactured by SAN NOPCO Co., Ltd.).

[0261] Examples of such polyacrylic acid-based viscosity modifiers include sodium polyacrylate and polyacrylic acid-(meth)acrylate copolymer.

[0262] Commercially available polyacrylic acid viscosity modifiers include, for example, "PRIMAL ASE-60", "PRIMAL TT615", and "PRIMAL RM5" (trade names) manufactured by Dow Chemical Co., Ltd.; and "SN THICKENER 613", "SN THICKENER 618", "SN THICKENER 630", "SN THICKENER 634", and "SN THICKENER 636" (trade names) manufactured by SAN NOPCO Co., Ltd. The acid value of the polyacrylic acid 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.

[0263] In this invention, the content of the above-mentioned viscosity modifier (D) is preferably in the range of 0.6 to 7 parts by mass relative to 100 parts by mass of the resin solids in the coating composition, 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, from the viewpoint of storage stability of the obtained coating composition and suppression of metal spots in the formed coating film.

[0264] Furthermore, in this invention, the content of at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2) is preferably in the range of 0.6 to 7 parts by mass relative to 100 parts by mass of the resin solids in the coating composition, 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, from the perspective of storage stability of the obtained coating composition and inhibition of metal spots in the formed coating film.

[0265] [An organic solvent (E) with a solubility of 4% by mass or more in water at 20°C]

[0266] The coating composition of the present invention contains 10 to 25% by mass of an organic solvent (E) that is 4% by mass or more soluble in water at 20°C, based on the volatile components in the coating composition. If the content of the organic solvent (E) that is 4% by mass or more soluble in water at 20°C is outside the above range, the formed coating film is prone to developing metallic spots.

[0267] From the viewpoints of storage stability of the obtained coating composition and suppression of metal spots in the formed coating film, the content of the organic solvent (E) with a solubility of 4% by mass or more in water at 20°C 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 coating composition.

[0268] It should be noted that, in this specification, "volatile components" refers to components that evaporate when dried at 110°C for 1 hour. Therefore, the volatile components in the coating composition can be calculated, for example, by measuring the coating composition in a heat-resistant container such as an aluminum foil cup, spreading the coating composition on the bottom of the container, drying it at 110°C for 1 hour, weighing the mass of the remaining components after drying, and subtracting the mass of the remaining components after drying from the total mass of the coating composition before drying.

[0269] Examples of organic solvents (E) that have a solubility of 4% by mass or more in water 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; and solvents such as methanol, ethanol, isopropanol, n-butanol, sec-butanol, isobutanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol isopropyl ether, and propylene glycol monomethyl ether. Alcohol solvents such as propylene glycol monobutyl ether, propylene 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 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, can be used alone or in combination of two or more.

[0270] The organic solvent (E) with a solubility of 4% by mass or more in water at 20°C is preferably an organic solvent (E1) with a solubility of 4% to 10% by mass in water at 20°C.

[0271] Organic solvents (E1) with a solubility in water of 4–10% by mass at 20°C include, for example, 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 solvents can be used alone or in combination of two or more.

[0272] When the coating 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) in the range of 4 to 10% by mass at 20°C 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 coating composition, from the viewpoint of the storage stability of the obtained coating composition and the spot suppression of the formed coating film.

[0273] From the viewpoint of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the organic solvent (E) with a solubility of 4% by mass or more in water at 20°C is preferably propylene glycol monobutyl ether.

[0274] [Other ingredients]

[0275] The coating composition of the present invention may optionally contain: resins other than hydroxyl-containing resins (A) and curing agents (B), pigments other than flake-like glossy pigments (C), organic solvents other than organic solvents (E) with a solubility of 4% by mass or more in water at 20°C, curing catalysts, dispersants, anti-settling agents, defoamers, ultraviolet absorbers, light stabilizers, surface modifiers, etc.

[0276] Examples of resins other than the hydroxyl-containing resin (A) and curing agent (B) include: hydroxyl-free acrylic resins, hydroxyl-free polyester resins, hydroxyl-free acrylic-modified polyester resins, hydroxyl-free acrylic-modified polyurethane resins, hydroxyl-free polyurethane resins, hydroxyl-free polyether resins, hydroxyl-free polycarbonate resins, hydroxyl-free epoxy resins, hydroxyl-free alkyd resins, and hydroxyl-free polyolefin resins. Preferably, the coating composition of the present invention contains a hydroxyl-free polyurethane resin as at least one of the resins other than the hydroxyl-containing resin (A) and curing agent (B).

[0277] When the coating composition of the present invention contains the above-mentioned hydroxyl-free polyurethane resin, the content of the hydroxyl-free polyurethane resin 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 the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film.

[0278] Pigments other than the aforementioned flaky glossy pigments (C) include, for example, coloring pigments and extender pigments. These pigments can be used alone or in combination of two or more types.

[0279] When the coating 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 weight based on 100 parts by weight of the resin solids in the coating composition, more preferably in the range of 5 to 160 parts by weight, and particularly preferably in the range of 5 to 140 parts by weight.

[0280] Examples of pigments used for coloring include: titanium dioxide, zinc oxide, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne pigments, perylene pigments, dioxazine pigments, and diketolpyrrolopyrrole pigments. Among these, titanium dioxide and carbon black are preferred.

[0281] When the coating composition contains the above-mentioned coloring pigment, the amount of the coloring pigment is preferably in the range of 1 to 180 parts by weight based on 100 parts by weight of the resin solids in the coating composition, more preferably in the range of 5 to 150 parts by weight, and particularly preferably in the range of 15 to 130 parts by weight.

[0282] Furthermore, examples of extender pigments include barium sulfate, talc, clay, kaolin, barium carbonate, calcium carbonate, silica, and alumina. From the viewpoint of coating stability and smoothness, barium sulfate and talc are preferred as extender pigments.

[0283] When the coating composition contains the above-mentioned extender pigment, the amount of the extender pigment is preferably in the range of 1 to 180 parts by weight based on 100 parts by weight of the resin solids in the coating composition, more preferably in the range of 5 to 140 parts by weight, and particularly preferably in the range of 10 to 120 parts by weight.

[0284] Organic solvents other than the organic solvents (E) with a solubility of 4% by mass or more in water at 20°C include, for example: hydrocarbon solvents such as mineral oil, 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, methyl amyl acetate, ethylene glycol monobutyl ether acetate, and n-butyl propionate; ether solvents such as diethylene glycol dibutyl ether; and ketone solvents such as methyl isobutyl ketone, 2-heptanone, ethyl n-pentyl ketone, diisobutyl ketone, and isophorone. These can be used individually or in combination of two or more.

[0285] Examples of ultraviolet absorbers include benzotriazole absorbers, triazine absorbers, salicylic acid derivative absorbers, and benzophenone absorbers.

[0286] Examples of light stabilizers include hindered amine light stabilizers.

[0287] [Coating Composition]

[0288] The coating composition of the present invention can be prepared by mixing a hydroxyl-containing resin (A), a curing agent (B), a flake-like glossy pigment (C), a viscosity modifier (D), an organic solvent (E) having a solubility of 4% by mass or more in water at 20°C, and optionally other components in a solvent using a conventional coating method. For example, organic solvents, water, etc., can be used as the solvent.

[0289] Furthermore, from the viewpoints of the storage stability of the obtained coating composition and the suppression of metal spots in the formed coating film, the concentration of the coating solids in the coating 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 even more particularly preferably in the range of 17 to 30% by mass.

[0290] The concentration of the solid components in the coating can be adjusted, for example, by adjusting the amount of solvent.

[0291] From the viewpoint of storage stability, the coating composition of the present invention preferably contains water as a solvent.

[0292] When the coating composition of the present invention contains the water described above, the water content, from the viewpoint of the storage stability of the obtained coating composition, is preferably in the range of 30 to 80% by mass, more preferably in the range of 40 to 75% by mass, and even more preferably in the range of 50 to 70% by mass, based on the total amount of the coating composition.

[0293] Furthermore, considering the suppression of metallic spots in the formed coating film, the coating composition of the present invention exhibits excellent performance at a temperature of 25°C and a shear rate of 1500 sec. -1 The viscosity measured under the specified conditions is preferably in the range of 5 to 150 mPa·s, more preferably in the range of 7 to 125 mPa·s, and particularly preferably in the range of 10 to 100 mPa·s.

[0294] Furthermore, from the viewpoint of suppressing metallic spots in the formed coating film, the coating composition of the present invention exhibits excellent performance at a temperature of 25°C and a shear rate of 0.1 sec. -1 The viscosity measured under the specified conditions is preferably in the range of 5,000 to 70,000 mPa·s, more preferably in the range of 8,000 to 60,000 mPa·s, and particularly preferably in the range of 10,000 to 50,000 mPa·s.

[0295] The coating composition can be either a one-component coating or a multi-component coating. From the viewpoints of eliminating the need for a coating mixing process, excellent productivity, and simplification of maintenance of coating machinery, a one-component coating is preferred.

[0296] The coating composition can be applied to the substrate by methods known per se, such as air spraying, airless spraying, rotary atomization, curtain coating, etc. Electrostatic application can also be used during coating. Air spraying and rotary atomization are preferred methods. Furthermore, the coating method can be performed in one step or in multiple steps until the desired film thickness is achieved.

[0297] The coating amount of the coating composition, measured by the cured film thickness, is typically 0.5 to 50 μm, preferably 2 to 40 μm, and more preferably 5 to 30 μm.

[0298] [Multilayer Coating Formation Method]

[0299] The coating composition of the present invention can be used as a coating composition for forming a base coat film when a multilayer coating film consisting of a base coat film and a clear coat film is formed on the workpiece by a two-coat, one-bake process. In this case, the coating film forming method can be carried out according to Method I described below.

[0300] <Method I>

[0301] A method for forming a multilayer coating film includes: step (I-1): applying a primer coating composition (Y) to a workpiece to form an uncured primer coating film; step (I-2): applying a clear coating composition (Z) to the uncured primer coating film to form an uncured clear coating film; and step (I-3): heating the uncured primer coating film and the uncured clear coating film to cure both films simultaneously, wherein the primer coating composition (Y) is the coating composition of the present invention.

[0302] In method I described above, the object to be coated is preferably a car body with a primer coating or a car body with a colored coating formed on the primer coating. The primer coating is preferably formed by electrophoretic coating, and more preferably by cationic electrophoretic coating. Furthermore, the uncured coating includes a touch-dry coating and a semi-cured coating.

[0303] When the coating composition of the present invention is applied by the two-coat-one-bake method of Method I, the coating film thickness, measured by the cured 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 particularly preferably in the range of 8 to 27 μm.

[0304] Furthermore, the aforementioned uncured primer coating film is typically formed using one primer coating composition, but it can also be formed using two or more primer coating compositions.

[0305] It should be noted that when using two or more primer coating compositions, it is preferable to use two primer coating compositions.

[0306] Specifically, for example, a first base coat coating, optionally using the coating composition of the present invention, can be applied to the object to form a first base coat film, and then a second base coat coating using the coating composition of the present invention can be applied to the first base coat film to form a second base coat film.

[0307] In this case, from the viewpoint of suppressing metal spots in the formed coating film, the first base coating film, in terms of cured film thickness, is preferably in the range of 5 to 15 μm, and more preferably in the range of 7 to 13 μm. Furthermore, the second base coating film, in terms of cured film thickness, is preferably in the range of 0.5 to 15 μm, and more preferably in the range of 2 to 13 μm.

[0308] Furthermore, the coating film thickness of the above-mentioned transparent coating composition (Z), measured by the cured film thickness, is preferably in the range of 10 to 80 μm, and more preferably in the range of 15 to 60 μm.

[0309] Furthermore, in Method I, after applying the coating composition of the present invention, from the viewpoint of preventing coating defects such as blistering, it is preferable to perform preheating, blowing, etc., under heating conditions where the coating film is substantially uncured. The preheating temperature is preferably in the range of 40–100°C, more preferably in the range of 50–90°C, and particularly preferably in the range of 60–80°C. The preheating time is preferably in the range of 30 seconds to 15 minutes, more preferably in the range of 1–10 minutes, and particularly preferably in the range of 2–5 minutes. Furthermore, the aforementioned blowing can be performed, for example, by blowing air at room temperature or heated to 25°C–80°C onto the coated surface of the workpiece for 30 seconds to 15 minutes. Additionally, after applying the above-mentioned transparent coating composition (Y), an interval of 1–60 minutes can optionally be set at room temperature, or preheating can be performed at 40–80°C for 1–60 minutes.

[0310] The coating film can be cured using the known heating method described above. The heating temperature is preferably in the range of 60–180°C, more preferably in the range of 65–170°C, and particularly preferably in the range of 70–160°C. Furthermore, the heating time is preferably in the range of 10–60 minutes, more preferably in the range of 20–40 minutes. This heating allows both the base coat and the clear coat to cure simultaneously.

[0311] Furthermore, when the coating composition of the present invention forms a multilayer coating film consisting of a colored coating film, a base coating film, and a transparent coating film on a substrate such as an automobile body using a three-coat, one-bake process, it can preferably be used as the coating composition for forming the base coating film. In this case, the coating film forming method can be performed according to Method II described below.

[0312] <Method II>

[0313] A method for forming a multilayer coating film includes: step (II-1): applying a coloring paint composition (X) to a workpiece to form an uncured coloring coating film; step (II-2): applying a primer paint composition (Y) to the uncured coloring coating film to form an uncured primer coating film; step (II-3): applying a clear coating paint composition (Z) to the uncured primer coating film to form an uncured clear coating film; and step (II-4): heating the uncured coloring coating film, the uncured primer coating film, and the uncured clear coating film to cure them simultaneously, wherein the primer paint composition (Y) is the paint composition of the present invention.

[0314] Method II described above is a method for forming a coating film using the method described in Method I on an uncured colored coating film. As the object to be coated in Method II, a car body or the like with a primer coating film formed thereon is preferred. The primer coating film is preferably formed using an electrophoretic coating, and more preferably using a cationic electrophoretic coating.

[0315] In Method II, the coating film thickness of the coloring paint composition, measured by the cured film thickness, is preferably in the range of 10 to 60 μm, more preferably in the range of 20 to 40 μm. Furthermore, the coating film thickness of the paint composition of the present invention, measured by the cured 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 particularly preferably in the range of 8 to 27 μm. Furthermore, the coating film thickness of the transparent coating composition (Z), measured by the cured film thickness, is preferably in the range of 10 to 80 μm, more preferably in the range of 15 to 60 μm.

[0316] Furthermore, in method II, preheating is preferably performed after the above-mentioned coloring paint composition (X) has been applied. 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.

[0317] Furthermore, preheating is preferably performed after the coating composition of the present invention has been applied. 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.

[0318] Furthermore, in Method II, the aforementioned uncured primer coating film is typically formed using one primer coating composition, but it can also be formed using two or more primer coating compositions. In this case, the coating composition of the present invention can be used as the primer coating composition for at least forming the uppermost primer coating film.

[0319] It should be noted that when using two or more primer coating compositions, it is preferable to use two primer coating compositions.

[0320] Specifically, for example, a first base coat coating, optionally using the coating composition of the present invention, can be applied to the object to form a first base coat film, and then a second base coat coating using the coating composition of the present invention can be applied to the first base coat film to form a second base coat film.

[0321] In this case, from the viewpoint of suppressing metal spots in the formed coating film, the first base coating film, in terms of cured film thickness, is preferably in the range of 5 to 15 μm, and more preferably in the range of 7 to 13 μm. Furthermore, the second base coating film, in terms of cured film thickness, is preferably in the range of 0.5 to 15 μm, and more preferably in the range of 2 to 13 μm.

[0322] After applying the above-mentioned transparent coating composition (Z), an interval of 1 to 60 minutes can be optionally set at room temperature, or preheating can be performed at 40 to 80°C for 1 to 60 minutes.

[0323] The curing of the three coating layers—the uncured coloring coating, the uncured primer coating, and the uncured clear coating—can be carried out using the known heating method described above. The heating temperature is preferably in the range of 60–180°C, more preferably in the range of 65–170°C, and particularly preferably in the range of 70–160°C. Furthermore, the heating time is preferably in the range of 10–60 minutes, and particularly preferably in the range of 20–40 minutes. This heating allows the three coating layers—the coloring coating, the primer coating, and the clear coating—to cure simultaneously.

[0324] As the transparent coating composition (Z) used in methods I and II above, any thermosetting transparent coating composition known for coating automobile bodies, etc., can be used. Examples include: organic solvent-based thermosetting coating compositions containing a matrix resin having crosslinking functional groups and a crosslinking agent, water-based thermosetting coating compositions, powder thermosetting coating compositions, etc.

[0325] Examples of crosslinking functional groups found in the aforementioned matrix resins include carboxyl, hydroxyl, epoxy, and silanol groups. Examples of types of matrix resins include acrylic resins, polyester resins, alkyd resins, urethane resins, epoxy resins, and fluoropolymers. Examples of crosslinking agents include polyisocyanate compounds, end-capped polyisocyanate compounds, melamine resins, urea-formaldehyde resins, carboxyl-containing compounds, carboxyl-containing resins, epoxy-containing resins, and epoxy-containing compounds.

[0326] Furthermore, the aforementioned transparent coating material can be a one-component coating or a multi-component coating such as a two-component urethane resin coating.

[0327] Furthermore, the above-mentioned transparent coating composition (Z) may optionally contain coloring pigments, gloss pigments, dyes, etc., to a degree that does not impede transparency, and may also contain appropriate extender pigments, ultraviolet absorbers, light stabilizers, defoamers, thickeners, rust inhibitors, surface conditioners, etc.

[0328] The combination of matrix resin and crosslinking agent in the transparent coating composition (Z) is preferably a combination of carboxyl-containing resin / epoxy-containing resin, hydroxyl-containing resin / polyisocyanate compound, hydroxyl-containing resin / terminated polyisocyanate compound, hydroxyl-containing resin / melamine resin, etc. Among these, the combination of hydroxyl-containing resin / polyisocyanate compound is preferred from the viewpoint of the particle texture of the formed coating film.

[0329] As the coloring paint composition used in Method II above, any known thermosetting coloring paint composition can be used. For example, a thermosetting paint composition containing a matrix resin having crosslinking functional groups, a crosslinking agent, a coloring pigment, and an extender pigment is preferably used.

[0330] Examples of crosslinking functional groups found in the aforementioned matrix resins include carboxyl, hydroxyl, and epoxy groups. Examples of types of matrix resins include acrylic resins, polyester resins, alkyd resins, and urethane resins. Examples of crosslinking agents include melamine resins, polyisocyanate compounds, and end-capped polyisocyanate compounds.

[0331] As a coloring coating composition, any of the following can be used: organic solvent-based coating composition, water-based coating composition, and powder coating composition. Among them, coating composition is preferred.

[0332] In methods I and II above, coating can be performed using known methods, such as air spray coating, airless spray coating, rotary atomization coating, etc.

[0333] Example

[0334] The present invention will be further described in detail below by providing manufacturing examples, embodiments, and comparative examples. However, the present invention is not limited to these examples. In each example, unless otherwise specified, "parts" and "%" are based on mass. Furthermore, the film thickness is based on the thickness of the cured coating.

[0335] Manufacturing of hydroxyl-containing acrylic resins (A1)

[0336] Manufacturing Example 1

[0337] 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (trade name, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., emulsifier, 97% active ingredient) were added to a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube and dropping device. The mixture was stirred and mixed in a nitrogen stream and heated to 80°C.

[0338] 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 kept at 80°C for 15 minutes. Then, the remaining monomer emulsion (1) was added dropwise to the reaction vessel, which was kept at the same temperature, over a period of 3 hours. After the addition was completed, the mixture was allowed to mature for 1 hour. Then, the monomer emulsion (2) was added dropwise over a period of 1 hour. After maturation for 1 hour, 20 parts of a 5% N-methylmorpholine aqueous solution were slowly added to the reaction vessel while cooling to 30°C. The mixture was then filtered through a 100-mesh nylon cloth and discharged 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-containing acrylic resin (A1-1) is equivalent to the water-dispersible hydroxyl-containing acrylic resin (A11) having the core / shell type multilayer structure.

[0339] Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of “Aqualon 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 monomer emulsion (1).

[0340] 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).

[0341] Manufacturing Example 2

[0342] 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (trade name, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., emulsifier, 97% active ingredient) were added to a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube and dropping device. The mixture was stirred and mixed in a nitrogen stream and heated to 80°C.

[0343] Next, 1.72 parts of monomer emulsion (1) and 5.3 parts of 6% ammonium persulfate aqueous solution were introduced into the reaction vessel and kept at 80°C for 15 minutes. Then, over a period of 1 hour, 35.4 parts of monomer emulsion (1) were added dropwise into the reaction vessel, which was maintained at the same temperature. Immediately after the addition was completed, the remaining 55.6 parts of monomer emulsion (1) were added dropwise into the reaction vessel. At the same time, 55.6 parts of monomer emulsion (2) were added dropwise into monomer emulsion (1). After 2 hours, the addition of monomer emulsion (1) and monomer emulsion (2) was completed. Then, over a period of 1 hour, 37.17 parts of the remaining monomer emulsion (2) were added dropwise to the reaction vessel. After aging for 1 hour, 20 parts of a 5% N-methylmorpholine aqueous solution were slowly added to the reaction vessel while cooling to 30°C. The solution was then filtered through a 100-mesh nylon cloth while being discharged, resulting in an aqueous dispersion of hydroxyl-containing acrylic resin (A1-2) with a solid content of 30%. The obtained hydroxyl-containing acrylic resin (A1-2) 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 above-mentioned hydroxyl-containing acrylic resin (A1-2) is equivalent to the aqueous dispersion of hydroxyl-containing acrylic resin (A11') containing a gradient polymer layer.

[0344] Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of “Aqualon 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 monomer emulsion (1).

[0345] 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).

[0346] Manufacturing Example 3

[0347] A mixed solvent consisting of 27.5 parts methoxypropanol and 27.5 parts isobutanol was added to a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device, and heated to 110°C. Then, over a period of 4 hours, 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 Chemicals Co., Ltd., a branched higher alkyl acrylate), 7.5 parts 4-hydroxybutyl acrylate, 15 parts of the following phosphoric acid-containing polymerizable monomer, 12.5 parts 2-methacryloyloxyethyl phosphate, 10 parts isobutanol, and 4 parts tert-butylperoxyoctanoate was added to the above mixed solvent. Further, over a period of 1 hour, a mixture consisting of 0.5 parts tert-butylperoxyoctanoate and 20 parts isopropanol was added dropwise. The mixture was then stirred and matured for 1 hour to obtain a 50% solids concentration acrylic resin solution containing hydroxyl and phosphoric acid groups (A1-3). The resin has an acid value based on phosphate groups of 83 mg KOH / g, a hydroxyl value of 29 mg KOH / g, and a weight-average molecular weight of 10,000.

[0348] Polymerizable monomers containing phosphate groups: 57.5 parts of monobutyl phosphate and 41 parts of isobutanol were added to a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device. The temperature was raised to 90°C, and then 42.5 parts of glycidyl methacrylate were added dropwise over 2 hours, followed by further stirring and maturation for 1 hour. Then, 59 parts of isopropanol were added to obtain a 50% solids concentration polymerizable monomer solution containing phosphate groups. The phosphate-based acid value of the obtained monomer was 285 mg KOH / g.

[0349] Manufacturing of hydroxyl-containing polyester resin (A2)

[0350] Manufacturing Example 4

[0351] 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 anhydride were added to a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and water separator. The temperature was raised from 160°C to 230°C over 3 hours. While removing the generated condensation water by distillation using the water separator, the temperature was maintained at 230°C until the acid value fell below 3 mg KOH / g. 59 parts of trimellitic anhydride were added to the reaction product, and an addition reaction was carried out at 170°C for 30 minutes. The mixture was then cooled to below 50°C, and N-methylmorpholine (in equivalent to the acid group) was added for neutralization. Deionized water was then slowly added, resulting in a hydroxyl-containing polyester resin (A2-1) solution with a solid content of 45% and a pH of 7.2. The obtained hydroxyl-containing polyester resin has a hydroxyl value of 128 mgKOH / g, an acid value of 35 mgKOH / g, and a weight-average molecular weight of 13000.

[0352] Manufacturing of hydroxyl-containing polyurethane resin (A3)

[0353] Manufacturing Example 5

[0354] A reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser was loaded with 316.0 parts of "PTMG1000" (trade name, manufactured by MITSUBISHI CHEMICAL Co., Ltd., 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 "NEOSTANN U-600" (trade name, manufactured by Nitto Kasei Corporation, bismuth-based catalyst), and 235.0 parts of methyl ethyl ketone. After purging the reaction system with nitrogen, the reaction was carried out at 80°C with 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 for emulsification. Then, 96.4 parts of 5% N-(2-hydroxyethyl)ethylenediamine aqueous solution were added. After stirring for 120 minutes, the methyl ethyl ketone was removed by distillation under reduced pressure and heating. The concentration was adjusted with deionized water to obtain a hydroxyl-containing polyurethane resin (A3-1) dispersion 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.

[0355] Manufacturing of hydroxyl-free polyurethane resin (U)

[0356] Manufacturing Example 6

[0357] 211.9 parts of "PTMG1000" (trade name, manufactured by MITSUBISHI CHEMICAL Co., Ltd., 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 into a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser. After purging the reaction system with nitrogen, the reaction was carried out at 80°C with 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 for emulsification. Then, 159.2 parts of 5% ethylenediamine aqueous solution were added and stirred for 60 minutes. The methyl ethyl ketone was removed by distillation under reduced pressure and heating. The concentration was adjusted with deionized water to obtain a hydroxyl-free 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.

[0358] Manufacturing of end-capped polyisocyanate compound (B3)

[0359] Manufacturing Example 7

[0360] 1650 parts of "Sumidur N-3300" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., containing a polyisocyanate structure derived from hexamethylene diisocyanate, 100% solids concentration, 21.8% isocyanate group content), 1100 parts of "PTMG2000" (trade name, manufactured by MITSUBISHI CHEMICAL Co., Ltd., polytetramethylene ether glycol, average molecular weight 2000, 100% solids concentration), and 0.9 parts of 2,6-di-tert-butyl-4-methylphenol were thoroughly mixed and heated at 130°C for 3 hours under a nitrogen atmosphere. Next, 1200 parts of ethyl acetate and 1200 parts of diisopropyl malonate were added, and 14 parts of a 28% methanol solution of sodium methoxide were added while stirring under a nitrogen stream. The mixture was stirred at 65°C for 8 hours. Then, it was diluted with ethyl acetate to achieve a final solids concentration of 70%, yielding a capped polyisocyanate compound (B3-1) with a solids concentration of 70% and a weight-average molecular weight of 40,000.

[0361] Manufacturing of pigment dispersions

[0362] Manufacturing Example 8

[0363] In a mixing container, 25 parts of "Hydroran2156" (trade name, manufactured by ECKART, a silica-coated aluminum pigment paste with 60% aluminum content) (15 parts solids), 10 parts of the acrylic resin (A1-3) solution with hydroxyl and phosphoric acid groups obtained in Manufacturing Example 3 (5 parts solids), 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).

[0364] Manufacturing Examples 9 to 28

[0365] In Manufacturing Example 8, the formulation composition was set as shown in Table 1 below, and otherwise, pigment dispersions (P-2) to (P-21) were obtained in the same manner as in Manufacturing Example 8.

[0366] In Table 1, the amount of organic solvents added is listed, and the solid content of substances other than organic solvents is listed. Furthermore, the components listed in Table 1 are described below.

[0367] [Table 1]

[0368] Table 1

[0369]

[0370] [Table 2]

[0371] Table 1 (continued - 1)

[0372]

[0373] [Table 3]

[0374] Table 1 (continued - 2)

[0375]

[0376] (Note 1) "ALPASTE 6360NS": Trade name, manufactured by Toyo Aluminum Co., Ltd., aluminum pigment paste.

[0377] (Note 2) "Xirallic T61-10 Micro Silver": Trade name, manufactured by MERCK Co., Ltd., titanium oxide coated alumina flake pigment.

[0378] (Note 3) "Iriodin 121RUTILE LUSTRE SATIN": Trade name, manufactured by MERCK Co., Ltd., titanium oxide coated mica pigment.

[0379] (Note 4) "Swazol 1000": Trade name, manufactured by Maruzen Petrochemical Co., Ltd., a hydrocarbon solvent.

[0380] In addition, the solubility of each organic solvent in water at 20°C is shown below.

[0381] Propylene glycol monobutyl ether: Solubility in water at 20°C is 6.4% by mass.

[0382] n-Butanol: Solubility in water at 20°C is 6.4% by mass.

[0383] Propylene glycol monomethyl ether: mixes freely with water at 20°C.

[0384] Ethylene glycol monobutyl ether: mixes freely with water at 20°C.

[0385] Dipropylene glycol monomethyl ether: mixes freely with water at 20°C.

[0386] Butyl acetate: Solubility in water at 20°C is 1.0% by mass.

[0387] 2-Ethyl-1-hexanol: Solubility in water at 20°C is 0.07% by mass.

[0388] Methyl isobutyl ketone: sparingly soluble in water at 20°C.

[0389] "Swazol 1000": Slightly soluble in water at 20℃.

[0390] Preparation of aqueous dispersion of cellulose nanocrystals (D1)

[0391] Manufacturing Example 29

[0392] Slowly add "Celluforce NCC" (trade name, manufactured by Celluforce Corporation, 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) to deionized water after stirring with a magnetic stirrer, at a solids concentration of 4%. 2 After obtaining sodium sulfonate cellulose nanocrystals (D1-1) with a solid content of 100% (9g, ζ potential of -37mV), the mixture was stirred continuously for 2 hours to obtain an aqueous dispersion of cellulose nanocrystals.

[0393] Adjustment of coating composition

[0394] Example 1

[0395] In a mixing vessel, 89.0 parts (20.0 parts solids) of pigment dispersion (P-1) obtained in Manufacturing Example 8, 133.3 parts (40.0 parts solids) of aqueous dispersion of hydroxyl-containing acrylic resin (A1-1) obtained in Manufacturing Example 1, 55.6 parts (25 parts solids) of hydroxyl-containing polyester resin solution (A2-1) obtained in Manufacturing Example 4, 28.6 parts (10 parts solids) of non-hydroxyl-containing polyurethane resin (U-1) dispersion obtained in Manufacturing Example 6, 6.25 parts (5.0 parts solids) of "CYMEL325" (trade name, manufactured by Allnex Japan Co., Ltd., methyl / butyl mixed etherified melamine resin, 80% solids concentration), and "Bayhydur VPLS2310" (trade name, Sumika Bayer) were mixed in. Urethane Corporation manufactured a capped polyisocyanate compound (38% solids concentration) of 39.5 parts (15.0 parts solids). The mixture was then further mixed with 75.0 parts (3.0 parts solids) of an aqueous dispersion of cellulose nanocrystals (D1-1) obtained in Manufacturing Example 29, 2-(dimethylamino)ethanol, and deionized water to obtain Waterborne Coating Composition No. 1 with pH 8.0 and a coating solids concentration of 25%.

[0396] Examples 2-25, Comparative Examples 1-8

[0397] In Example 1, the formulation composition was set as shown in Table 2 below, and otherwise, waterborne coating compositions No. 1 to No. 33 were obtained in the same manner as in Example 1.

[0398] In Table 2, the amount of organic solvent added is listed, and the solid content of substances other than organic solvents is listed. Furthermore, the components listed in Table 2 are described below.

[0399] (Note 5) "Rheocrysta I-2SX": Trade name, manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd., cellulose nanofiber, viscosity modifier.

[0400] (Note 6) "PRIMAL ASE-60": Trade name, manufactured by Dow Chemical Co., Ltd., a polyacrylic acid viscosity modifier.

[0401] (Note 7) "UH-752": Trade name, manufactured by ADEKA Co., Ltd., a carbamate associative viscosity modifier.

[0402] The coating compositions No. 1 to No. 33 obtained in Examples 1 to 25 and Comparative Examples 1 to 8 were evaluated using the test methods described below. The evaluation results are shown in Table 2 below.

[0403] Test methods

[0404] Storage stability

[0405] Storage stability tests were conducted on the coating compositions obtained in the above examples and comparative examples according to the following test methods.

[0406] Add 800g of each of the above coating compositions to a glass bottle with a capacity of approximately 1L and store for 10 days in a constant temperature chamber at 40°C. Then, allow to return to room temperature, and evaluate the storage stability by visually observing the state of the container according to the following criteria. A and B are considered acceptable. The results are shown in Table 2.

[0407] A: No evidence of sediment formation or viscosity changes has been found.

[0408] B: Slight confirmation of sedimentation and / or viscosity changes, but these were restored by stirring.

[0409] C: Confirmation of sediment formation and / or viscosity changes.

[0410] D: Confirmation of significant sediment formation and / or significant viscosity changes.

[0411] Preparation of test panels and evaluation of metallic spots under 80℃ heat curing conditions

[0412] On an alloyed molten galvanized steel sheet treated with zinc phosphate as the metallic material, "ELECRON GT-10" (trade name, manufactured by KANSAIPAINT Co., Ltd., cationic electrophoretic coating) was electrophoretically coated to a cured film thickness of 20 μm. The coated sheet was then cured at 170°C for 30 minutes to obtain an electrophoretically coated steel sheet. Next, a coloring coating composition (trade name "WP-505T", manufactured by KANSAIPAINT Co., Ltd., polyester / amino resin-based waterborne coating composition) was coated to the obtained electrophoretically coated steel sheet to a film thickness of 20 μm. After standing for 2 minutes, the coated sheet was preheated at 80°C for 3 minutes to obtain an uncured coloring coating film. Then, the coating compositions obtained in the above examples and comparative examples were coated to a cured film thickness of 15 μm on the uncured coloring coating film. After standing for 3 minutes, the coated sheet was preheated at 80°C for 3 minutes to obtain an uncured base coat film. Next, "KINO6510" (trade name, manufactured by KANSAIPAINT Co., Ltd., an acrylic resin / polyisocyanate compound solvent-based transparent topcoat) was electrostatically coated onto the uncured base coat to achieve a cured film thickness of 35 μm, resulting in an uncured transparent topcoat. Then, after standing for 7 minutes, the coating was heated at 80°C for 30 minutes to cure the multilayer coating formed by the uncured colored coating, the uncured base coat, and the uncured transparent topcoat, thereby producing various test panels.

[0413] The degree of metal spot formation was evaluated by visually inspecting each test plate according to the following criteria. A and B were deemed acceptable. The results are shown in Table 2.

[0414] A: No metal spots have been detected at all.

[0415] B: A small amount of metal spots has been detected, but it is within acceptable limits.

[0416] C: The formation of metal spots has been confirmed.

[0417] D: The formation of numerous metal spots has been confirmed.

[0418] Preparation of test panels and evaluation of metallic spot properties under 140℃ heat curing conditions

[0419] On an alloyed molten galvanized steel sheet treated with zinc phosphate as the metallic material, "ELECRON GT-10" (trade name, manufactured by KANSAIPAINT Co., Ltd., cationic electrophoretic coating) was electrophoretically coated to a cured film thickness of 20 μm. The coated sheet was then cured at 170°C for 30 minutes to obtain an electrophoretically coated steel sheet. Next, a coloring coating composition (trade name "WP-505T", manufactured by KANSAIPAINT Co., Ltd., polyester / amino resin-based waterborne coating composition) was coated to the obtained electrophoretically coated steel sheet to a film thickness of 20 μm. After standing for 2 minutes, the coated sheet was preheated at 80°C for 3 minutes to obtain an uncured coloring coating film. Then, the coating compositions obtained in the above examples and comparative examples were coated to a cured film thickness of 15 μm on the uncured coloring coating film. After standing for 3 minutes, the coated sheet was preheated at 80°C for 3 minutes to obtain an uncured base coat film. Next, "KINO6510" (trade name, manufactured by KANSAIPAINT Co., Ltd., an acrylic resin / polyisocyanate compound solvent-based transparent topcoat) was electrostatically coated onto the uncured base coat to achieve a cured film thickness of 35 μm, resulting in an uncured transparent topcoat. Then, after standing for 7 minutes, the coating was heated at 140°C for 30 minutes to cure the multilayer coating formed by the uncured colored coating, the uncured base coat, and the uncured transparent topcoat, thereby producing various test panels.

[0420] The degree of metal spot formation was evaluated by visually inspecting each test plate according to the following criteria. A and B were deemed acceptable. The results are shown in Table 2.

[0421] A: No metal spots have been detected at all.

[0422] B: A small amount of metal spots has been detected, but it is within acceptable limits.

[0423] C: The formation of metal spots has been confirmed.

[0424] D: The formation of numerous metal spots has been confirmed.

[0425] [Table 4]

[0426] Table 2

[0427]

[0428] [Table 5]

[0429] Table 2 (continued - 1)

[0430]

[0431] [Table 6]

[0432] Table 2 (continued - 2)

[0433]

[0434] [Table 7]

[0435] Table 2 (continued - 3)

[0436]

[0437] [Table 8]

[0438] Table 2 (continued - 4)

[0439]

Claims

1. A coating composition comprising: a hydroxyl-containing resin A, a curing agent B, a flake-like glossy pigment C, a viscosity modifier D, and an organic solvent E having a solubility in water 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. The flaky glossy pigment C comprises flaky aluminum pigment C11 coated with silica. Relative to 100 parts by weight of the resin solids in the coating composition, the content of the flake-like aluminum pigment C11 is in the range of 1 to 50 parts by weight, and The content of organic solvent E, which has a solubility of 4% by mass or more in water at 20°C, is in the range of 13% to 22% by mass, based on the volatile components in the coating composition. The organic solvent E, which has a solubility of 4% by mass or more in water at 20°C, is selected from at least one group consisting of propylene glycol monobutyl ether, n-butanol, propylene glycol monomethyl ether, ethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether.

2. The coating composition according to claim 1, wherein, The viscosity modifier D contains cellulose nanocrystals D1.

3. The coating composition according to claim 1, wherein, The organic solvent E, which has a solubility of 4% by mass or more in water at 20°C, includes organic solvent E1, which has a solubility of 4% to 10% by mass in water at 20°C.

4. The coating composition according to claim 1, wherein, The coating composition also contains water.

5. A method for forming a multilayer coating, the method comprising: Process I-1: The process of applying a primer coating composition Y to a substrate to form an uncured primer coating film; Step I-2: The step of applying the clear coating composition Z onto the uncured primer film to form an uncured clear coating film; and Step I-3: A step of heating the uncured base coating and the uncured transparent coating to cure both coatings simultaneously, wherein... The base coat coating composition Y is a coating composition as described in any one of claims 1 to 4.

6. A method for forming a multilayer coating, the method comprising: Process II-1: The process of applying coloring paint composition X to a substrate to form an uncured colored coating film; Step II-2: The step of applying primer coating composition Y onto the uncured colored coating film to form an uncured primer coating film; Step II-3: The step of applying the clear coating composition Z onto the uncured primer film to form an uncured clear coating film; and Step II-4: A step of heating the uncured colored coating, the uncured base coating, and the uncured transparent coating to cure them simultaneously, wherein... The base coat coating composition Y is a coating composition as described in any one of claims 1 to 4.

Images