Paint composition

Abstract

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

Description

paint composition

[0001] The present invention relates to a coating composition.

[0002] Conventionally, a widely adopted method for forming multi-layer coatings on automobile bodies or automobile parts is to form a multi-layer coating by a three-coat, two-bake method, in which an intermediate coating is applied to an object to be coated (electrodeposition-coated steel plate, plastic, etc.), followed by heat curing, then a base coat is applied, then a clear coat is applied, and then heat curing is carried out in that order.

[0003] In response to this, in recent years, from the viewpoint of shortening the line process and saving energy, studies have been conducted on a 3-coat, 1-bake method in which the heat curing step after application of an intermediate coat or the intermediate coat application step is omitted, and the steps are applied in the order of intermediate coat application → base coat application → clear coat application → heat curing, and a 2-coat, 1-bake method in which the steps are applied in the order of base coat application → clear coat application → heat curing (a preheating step may be inserted after application of the paint). Of these, from the viewpoint of suppressing environmental pollution due to the volatilization of organic solvents, there is a particular demand for the 3-coat, 1-bake method and the 2-coat, 1-bake method in which a water-based paint is used as the base paint.

[0004] In the painting of automobile exterior panels, even with the three-coat one-bake method, there is a demand for a high-quality design that is as good as or even better than the conventional method.

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

[0006] On the other hand, if the paint thickens and / or settles during storage, it becomes difficult to apply the paint, and therefore storage stability is also required for the paint.

[0007] In the above-mentioned water-based base coat paint, one method for controlling viscosity is to incorporate an associative viscosity modifier into the paint. Such an associative viscosity modifier generally has a hydrophilic portion and a hydrophobic portion in one molecule, and in the water-based paint, the hydrophilic portion contributes to stability in the aqueous solution, while the hydrophobic portion adsorbs to the surface of the pigment and / or resin particles incorporated in the water-based paint, or the hydrophobic portions associate with each other to form a network structure, thereby effectively thickening the paint.

[0008] The associative viscosity modifier generally forms a network structure through hydrophobic interactions, thereby developing viscosity.

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

[0010] However, when an associative viscosity modifier is used in an aqueous base coat paint containing the above-mentioned surfactant and / or hydrophilic organic solvent, the viscosity provided by the associative viscosity modifier is not easily expressed, which can result in unevenness, etc., and this has been a problem. Specifically, if the viscosity of the aqueous base paint is low when applied to the substrate, a mixed layer can form between the paint applied in the upper and / or lower layers, and if the aqueous paint contains a luster pigment, the luster pigment in the paint can move after application, causing the orientation of the luster pigment to become irregular, resulting in unevenness.

[0011] Patent Document 1 describes an aqueous coating composition containing acrylic resin particles (A), a hydroxyl group-containing resin (B), a crosslinking agent (C), a viscosity modifier (D), and a pigment (E), in which the acrylic resin particles (A) have a core-shell structure in a mass ratio of 10 / 90 to 90 / 10, the core portion is crosslinked, and the amount of polymerizable unsaturated monomer (a1) having a linear, branched, or cyclic saturated or unsaturated hydrocarbon group having 4 or more carbon atoms is 3 to 70 parts by mass relative to 100 parts by mass of the total amount of polymerizable unsaturated monomers constituting the acrylic resin particles (A), the hydroxyl group-containing resin (B) has a weight average molecular weight of 1,000 or more and less than 100,000, and the viscosity modifier (D) is 100,000 parts by mass. The present invention discloses an aqueous coating composition having a weight-average molecular weight of 100.00 or more, and characterized in that the aqueous coating composition contains, relative to 100 parts by mass of the total amount of constituent monomers, 5 to 50 parts by mass of a polymerizable unsaturated monomer (d1) having a polyoxyalkylene chain, 5 to 90 parts by mass of at least one hydrophilic functional group-containing polymerizable unsaturated monomer (d2) having no polyoxyalkylene chain selected from N-vinyl-2-pyrrolidone, N-substituted (meth)acrylamide, hydroxyl group-containing polymerizable unsaturated monomers, and acid group-containing polymerizable unsaturated monomers, and 5 to 90 parts by mass of another polymerizable unsaturated monomer (d3), and the aqueous coating composition has a high viscosity development property, and the viscosity decreases with increasing shear rate.

[0012] Japanese Patent Application Publication No. 2013-221041

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

[0014] An object of the present invention is to provide a coating composition which has excellent storage stability and is capable of forming a multi-layer coating film having an excellent appearance with suppressed metallic unevenness.

[0015] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using a coating composition comprising a hydroxyl group-containing resin (A), a curing agent (B), a scaly luster 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.

[0016] That is, the present invention relates to <1> to <7>. <1> A coating composition comprising a hydroxyl group-containing resin (A), a curing agent (B), a scaly luster 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. <2> The coating composition according to <1>, wherein the scaly luster pigment (C) comprises a scaly aluminum pigment (C1) coated with silica. <3> The coating composition according to <1> or <2>, wherein the viscosity modifier (D) comprises cellulose nanocrystals (D1). <4> The coating composition according to any one of <1> to <3>, wherein the organic solvent (E) having a solubility in water of 4% by mass or more at 20°C includes an organic solvent (E1) having a solubility in water of 4 to 10% by mass at 20°C. <5> The coating composition according to any one of <1> to <4>, further comprising water. <6> A method for forming a multilayer coating film, comprising the steps of: Step (I-1): applying a base coat coating composition (Y) to an object to be coated to form an uncured base coat film; Step (I-2): applying a clear coat coating composition (Z) onto the uncured base coat film to form an uncured clear coat film; and Step (I-3): heating the uncured base coat film and the uncured clear coat film to simultaneously cure both films, wherein the base coat coating composition (Y) is the coating composition according to any one of <1> to <5>.<7> A method for forming a multilayer coating film, comprising: step (II-1): applying a colored coating composition (X) to an object to be coated to form an uncured colored coating film; step (II-2): applying a base coat coating composition (Y) onto the uncured colored coating film to form an uncured base coat coating film; step (II-3): applying a clear coat coating composition (Z) onto the uncured base coat coating film to form an uncured clear coat coating film; and step (II-4): heating the uncured colored coating film, the uncured base coat coating film, and the uncured clear coat coating film to simultaneously cure them, wherein the base coat coating composition (Y) is the coating composition described in any one of <1> to <5>.

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

[0018] As used herein, the singular forms "a," "an," "the," etc. are intended to include both the singular and the plural unless otherwise expressly stated herein or otherwise clearly contradicted by context.

[0019] The present invention will be described in detail below, but these are examples of preferred embodiments, and the present invention is not limited to these details.

[0020] The coating composition of the present invention comprises a hydroxyl group-containing resin (A), a curing agent (B), a scaly luster 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.

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

[0022] The hydroxyl value of the hydroxyl-containing resin (A) is preferably in the range of 1 to 200 mgKOH / g, more preferably in the range of 2 to 180 mgKOH / g, and particularly preferably in the range of 5 to 170 mgKOH / g, from the viewpoints of the storage stability of the resulting coating composition and the suppression of metallic unevenness in the coating film formed.

[0023] The content of the hydroxyl group-containing resin (A) in the coating composition of the present invention is preferably 20 to 90 mass %, more preferably 25 to 87 mass %, and particularly preferably 30 to 85 mass %, based on the resin solid content in the coating composition, from the viewpoints of the storage stability and anti-fouling properties of the resulting coating composition.

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

[0025] In addition, in this specification, the "solid content concentration" means the mass ratio of the solid content in the composition. Therefore, for example, the solid content concentration of the composition can be calculated by weighing out the composition into 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 in the composition remaining after drying, and determining the ratio of the mass of the components remaining after drying to the total mass of the composition before drying.

[0026] The hydroxyl-containing resin (A) preferably contains a hydroxyl-containing acrylic resin (A1) from the viewpoints of the storage stability of the resulting coating composition and the prevention of metallic unevenness in the coating film formed.

[0027] From the viewpoints of the flake resistance of the resulting coating composition and the appearance of the coating film formed, it is preferable that the hydroxyl-containing resin (A) contains a hydroxyl-containing polyester resin (A2).

[0028] From the viewpoint of chipping resistance of the resulting coating composition, the hydroxyl-containing resin (A) preferably contains a hydroxyl-containing polyurethane resin (A3).

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

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

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

[0032] In this specification, the term "polymerizable unsaturated group" refers to an unsaturated group that can undergo radical polymerization, such as a vinyl group, a (meth)acryloyl group, a (meth)acrylamide group, a vinyl ether group, an allyl group, a propenyl group, an isopropenyl group, or a maleimide group.

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

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

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

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

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

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

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

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

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

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

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

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

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

[0046] On the other hand, as described above, examples of the hydroxyl group-containing polymerizable unsaturated monomer (a) that constitutes the shell include monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms; allyl alcohol; and (meth)acrylates having a polyoxyethylene chain whose molecular terminal is a hydroxyl group, and these can be used either alone or in combination of two or more.

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

[0048] In addition, as the polymerizable unsaturated monomer (b) other than the hydroxyl group-containing polymerizable unsaturated monomer (a) constituting the shell, the above-mentioned polymerizable unsaturated monomer (b) other than the hydroxyl group-containing polymerizable unsaturated monomer (a) can be used. These can be used alone or in combination of two or more.

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

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

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

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

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

[0054] Furthermore, from the viewpoints of the storage stability of the resulting coating composition and suppression of metallic unevenness in the coating film formed, it is preferred that polymerizable unsaturated monomers having only one polymerizable unsaturated group per molecule are used as the monomer (a) and the monomer (b), and that the shell of the water-dispersible hydroxyl group-containing acrylic resin (A11) is uncrosslinked.

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

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

[0057] The emulsifier is preferably an anionic emulsifier or a nonionic emulsifier. Examples of the anionic emulsifier include sodium salts and ammonium salts of organic acids such as alkylsulfonic acid, alkylbenzenesulfonic acid, and alkylphosphate. Examples of the nonionic emulsifier include polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene tridecyl ether, polyoxyethylene phenyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene monolaurate, polyoxyethylene monostearate, polyoxyethylene monooleate, sorbitan monolaurate, sorbitan monostearate, sorbitan trioleate, and polyoxyethylene sorbitan monolaurate.

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

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

[0060] Among the ammonium salts of sulfonic acid compounds having a radically polymerizable unsaturated group, ammonium salts of sulfonic acid compounds having a radically polymerizable unsaturated group and a polyoxyalkylene group are more preferred. Examples of the ammonium salts of sulfonic acid compounds having a radically polymerizable unsaturated group and a polyoxyalkylene group include commercially available products such as "Aqualon KH-10" (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and "SR-1025A" (trade name, manufactured by Asahi Denka Kogyo Co., Ltd.).

[0061] The emulsifier can be used in an amount of usually 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 the monomers used.

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

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

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

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

[0066] The monomer mixture (II) may optionally contain the above-listed components such as a polymerization initiator, a chain transfer agent, a reducing agent, an emulsifier, and the like.

[0067] Although the monomer mixture (II) can be dropped as it is, it is preferable to disperse the monomer mixture (II) in an aqueous medium and dropwise ...

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

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

[0070] The water-dispersible hydroxyl group-containing acrylic resin (A11) may be made into resin particles having three or more layers by adding a step of supplying a polymerizable unsaturated monomer (one or a mixture of two or more) that forms another resin layer and carrying out emulsion polymerization between the step of obtaining the copolymer (I) and the step of obtaining the copolymer (II).

[0071] In the present invention, the "shell" of the water-dispersible hydroxyl-containing acrylic resin (A11) refers to the polymer layer present in the outermost layer of the resin particle, the "core" refers to the polymer layer present in the inner layer of the resin particle excluding the shell portion, and the "core / shell structure" refers to a structure having the core and shell. The core / shell structure is generally a layer structure in which the core is completely covered by the shell. However, depending on the mass ratio of the core to the shell, the amount of shell monomer may be insufficient to form a layer structure. In such cases, the complete layer structure described above is not necessary, and the core may be partially covered by the shell, or a polymerizable unsaturated monomer, a component of the shell, may be graft-polymerized onto a portion of the core. The concept of a multilayer structure in the core / shell structure also applies to the case in which a multilayer structure is formed on the core of the water-dispersible hydroxyl-containing acrylic resin (A11).

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

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

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

[0075] In order to improve the mechanical stability of the resulting aqueous dispersion particles of the water-dispersible hydroxyl-containing acrylic resin (A11), it is desirable to neutralize the acidic groups, such as carboxyl groups, of the water-dispersible hydroxyl-containing acrylic resin (A11) with a neutralizing agent. Any neutralizing agent can be used as long as it is capable of neutralizing the acidic groups, and examples of such neutralizing agents include sodium hydroxide, potassium hydroxide, trimethylamine, 2-(dimethylamino)ethanol, 2-amino-2-methyl-1-propanol, triethylamine, and aqueous ammonia. These neutralizing agents are desirably used in an amount such that the pH of the aqueous dispersion of the dispersible hydroxyl-containing acrylic resin (A11) after neutralization is about 6.5 to about 9.0.

[0076] The water-dispersible hydroxyl-containing acrylic resin (A11) may also contain a water-dispersible hydroxyl-containing acrylic resin (A11') containing a gradient polymer layer.

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

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

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

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

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

[0082] The polymerizable unsaturated monomers constituting the core and shell portions can be an appropriate combination of the hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer.

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

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

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

[0086] To form the gradient polymer layer, the polymerizable unsaturated monomer mixture used in the emulsion polymerization of the core copolymer (I) and the polymerizable unsaturated monomer mixture used in the emulsion polymerization of the shell copolymer (II) can usually be used.

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

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

[0089] Examples of a method for polymerizing the monomer mixture for forming the shell copolymer (II) include a method in which the monomer mixture or an emulsion thereof is added dropwise all at once or gradually to the emulsion of the core copolymer (I), and the mixture is heated to a suitable temperature while stirring.

[0090] From the viewpoint of the water resistance of the resulting coating film, the ratio of the gradient polymer layer in the water-dispersible hydroxyl-containing acrylic resin (A11′) containing the gradient polymer layer is preferably within a range of 20 to 80% by mass, more preferably within a range of 25 to 75% by mass, and particularly preferably within a range of 30 to 70% by mass, relative to the total amount of all copolymerization components of the water-dispersible hydroxyl-containing acrylic resin (A11′) containing the gradient polymer layer.

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

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

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

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

[0095] From the viewpoints of production stability and storage stability of the resulting coating material, the core portion of the water-dispersible hydroxyl group-containing acrylic resin (A11') comprising the gradient polymer layer preferably has an acid value in the range of 0 to 50 mgKOH / g, more preferably in the range of 0 to 30 mgKOH / g, and particularly preferably in the range of 0 to 10 mgKOH / g.

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

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

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

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

[0100] In this specification, the glass transition temperature Tg of the water-dispersible hydroxyl group-containing acrylic resin (A11') containing a gradient polymer layer is a value calculated by the following formula: 1 / Tg(K)=W1 / T1+W2 / T2+...Wn / Tn Tg(°C)=Tg(K)-273 In the formula, W1, W2,...Wn are the mass fractions of each monomer, and T1, T2,...Tn are the glass transition temperatures Tg(K) of the homopolymers of each monomer. The glass transition temperatures of the homopolymers of each monomer are calculated by the ... The glass transition temperature of a monomer not described in the document is determined by synthesizing a homopolymer of the monomer so as to have a weight-average molecular weight of about 50,000 and measuring the glass transition temperature by differential scanning calorimetry.

[0101] 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 mass %, more preferably in the range of 10 to 55 mass %, and particularly preferably in the range of 15 to 50 mass %, based on the resin solid content in the coating composition, from the viewpoints of the flip-flop properties and chipping resistance of the coating film to be formed.

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

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

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

[0105] The polycarboxylic acid may be a compound that is commonly used in the production of polyester resins, such as an aliphatic polybasic acid, an alicyclic polybasic acid, or an aromatic polybasic acid.

[0106] The aliphatic polybasic acid is generally an aliphatic compound having two or more carboxyl groups per molecule, an acid anhydride of the aliphatic compound, or an ester of the aliphatic compound. Examples of the aliphatic polybasic acid include aliphatic polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, octadecanedioic acid, citric acid, and butanetetracarboxylic acid; anhydrides of the aliphatic polycarboxylic acids; and lower alkyl esters of the aliphatic polycarboxylic acids having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. The aliphatic polybasic acids can be used alone or in combination of two or more.

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

[0108] The aromatic polybasic acid is generally an aromatic compound having two or more carboxyl groups per molecule, an acid anhydride of the aromatic compound, or an ester of the aromatic compound. Examples of the aromatic polybasic acid include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, trimellitic acid, and pyromellitic acid; anhydrides of the aromatic polycarboxylic acids; and lower alkyl esters of the aromatic polycarboxylic acids having 1 to 6 carbon atoms, preferably 1 to 4 carbon atoms. The aromatic polybasic acids can be used alone or in combination of two or more. Phthalic acid, phthalic anhydride, isophthalic acid, trimellitic acid, and trimellitic anhydride are preferred as the aromatic polybasic acid, with trimellitic anhydride being more preferred.

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

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

[0111] When the alcohol component and the acid component are subjected to an esterification reaction or transesterification reaction, these components may be added to a reaction vessel all at once, or one or both may be added in several portions. Alternatively, a hydroxyl-containing polyester resin may be first synthesized, and then the resulting hydroxyl-containing polyester resin may be reacted with an acid anhydride to half-esterify it into a carboxyl- and hydroxyl-containing polyester resin. Alternatively, a carboxyl-containing polyester resin may be first synthesized, and then the alcohol component may be added to produce the hydroxyl-containing polyester resin.

[0112] In the esterification or transesterification reaction, a catalyst known per se, such as dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, or tetraisopropyl titanate, can be used as a catalyst for promoting the reaction.

[0113] The hydroxyl group-containing polyester resin (A2) can be modified with a fatty acid, a monoepoxy compound, a polyisocyanate compound, or the like during or after the production of the resin.

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

[0115] As the polyisocyanate compound, the polyisocyanate compounds exemplified below in the polyisocyanate compound (B2) can be used. These can be used alone or in combination of two or more kinds.

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

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

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

[0119] The hydroxyl group-containing polyester resin (A2) preferably contains a carboxyl group from the viewpoint of the storage stability of the resulting coating composition.

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

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

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

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

[0124] Examples of polyisocyanates that can be reacted with the polyols include aliphatic polyisocyanate compounds such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; isophorone diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and methylcyclohexane-2,4-(or -2,6-)diisocyanate. alicyclic diisocyanate compounds such as 1,3-(or 1,4-)di(isocyanatomethyl)cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, and 1,2-cyclohexane diisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethylxylylene diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, aromatic diisocyanate compounds such as 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, (m- or p-)phenylene diisocyanate, 4,4'-biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, bis(4-isocyanatophenyl)sulfone, and isopropylidenebis(4-phenylisocyanate); and polyisocyanates thereof. biuret-type adducts and isocyanurate ring adducts of isocyanates; polyisocyanate compounds having three or more isocyanate groups in one molecule, such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, and 4,4'-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate; and biuret-type adducts and isocyanurate ring adducts of these polyisocyanates.

[0125] The hydroxyl value of the hydroxyl-containing polyurethane resin (A3) is preferably in the range of 1 to 150 mgKOH / g, more preferably in the range of 1 to 100 mgKOH / g, and particularly preferably in the range of 1 to 50 mgKOH / g, from the viewpoints of the storage stability of the resulting coating composition and the suppression of metallic unevenness in the coating film formed.

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

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

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

[0129] [Curing Agent (B)] The curing agent (B) is not particularly limited, and for example, a crosslinking agent reactive with the hydroxyl group of the hydroxyl group-containing resin (B) can be used.

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

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

[0132] Amino Resin (B1) The amino resin (B1) may be a partially methylolated amino resin or a fully methylolated amino resin obtained by reacting an amino component with an aldehyde component. Examples of the amino component include melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, and dicyandiamide. Examples of the aldehyde component include formaldehyde, paraformaldehyde, acetaldehyde, and benzaldehyde.

[0133] The methylolated amino resins may also be used in which the methylol groups have been partially or completely etherified with a suitable alcohol, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethyl-1-butanol, or 2-ethyl-1-hexanol.

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

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

[0136] As the melamine resin, commercially available products can be used, for example, under the trade names of "Cymel 202," "Cymel 203," "Cymel 211," "Cymel 238," "Cymel 251," "Cymel 254," "Cymel 303," "Cymel 325," "Cymel 327," "Cymel 350," "Cymel 370," "Cymel 385," "Cymel 1156," "Cymel 1158," and "Cymel 1130" (all manufactured by Allnex Japan Co., Ltd.); "U-Ban 20SE60" and "U-Ban 28-60" (all manufactured by Mitsui Chemicals, Inc.); and the like.

[0137] When the above-mentioned melamine resin is used as the curing agent (B), a curing catalyst may optionally be used, such as a sulfonic acid such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, or dinonylnaphthalenesulfonic acid; a neutralized salt of such a sulfonic acid with an amine; or a neutralized salt of a phosphoric acid ester compound with an amine.

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

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

[0140] Examples of the polyisocyanate compound (B2) include aliphatic polyisocyanates, alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates, and derivatives of the polyisocyanates.

[0141] Examples of the aliphatic polyisocyanate 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 acid diisocyanate, methyl 2,6-diisocyanatohexanoate (common name: lysine diisocyanate), aliphatic diisocyanates such as 2-isocyanatoethyl 2,6-diisocyanatohexanoate, 1,6-diisocyanato-3-isocyanatomethylhexane, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanatoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, and 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane.

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

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

[0144] Examples of the aromatic polyisocyanate include aromatic diisocyanates such as 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-tolylene diisocyanate or mixtures thereof, 4,4'-toluidine diisocyanate, and 4,4'-diphenyl ether diisocyanate; aromatic triisocyanates such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanates such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0145] Examples of the polyisocyanate derivatives include dimers, trimers, biurets, allophanates, uretdione, uretoimine, isocyanurates, oxadiazinetriones, polymethylene polyphenyl polyisocyanates (crude MDI, polymeric MDI), crude TDI, and the like of the above-mentioned polyisocyanate compounds.

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

[0147] Furthermore, as the polyisocyanate compound (B2), a prepolymer obtained by subjecting the above polyisocyanate or a derivative thereof to a urethanization reaction with a polyhydric alcohol, a low-molecular-weight polyester resin or water under conditions of an excess of isocyanate groups can also be used.

[0148] When a polyisocyanate compound (B2) is used as the curing agent (B), an organometallic compound, an acid compound, a base compound, or the like may be optionally used as a curing catalyst.

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

[0150] Blocked Polyisocyanate Compound (B3) The blocked polyisocyanate compound (B3) is a compound in which the isocyanate groups of the polyisocyanate compound (B2) are blocked with a blocking agent.

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

[0152] Among them, oxime-based blocking agents, active methylene-based blocking agents, pyrazole or pyrazole derivatives are suitable as blocking agents.

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

[0154] When the above-mentioned blocked polyisocyanate is used in the coating composition of the present invention, a blocked polyisocyanate compound can be preferably used which has been imparted with water dispersibility by blocking the isocyanate groups with the above-mentioned hydroxycarboxylic acid and then neutralizing the carboxyl groups of the hydroxycarboxylic acid.

[0155] From the viewpoints of the appearance of the coating film to be formed and the adhesion between the coating film to be formed and the substrate, the blocked polyisocyanate compound (B3) preferably contains a structure derived from a spacer having at least two isocyanate-reactive functional groups.

[0156] The functional group is not particularly limited as long as it is a functional group reactive with an isocyanate group. Examples of the isocyanate-reactive functional group include a hydroxyl group, an amino group, a carboxyl group, and a thiol group. Among these, a hydroxyl group and an amino group are preferred, and a hydroxyl group is particularly preferred.

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

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

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

[0160] Among these, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol can be suitably used as the polyether polyol.

[0161] The polyether polyols may be used alone or in combination of two or more.

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

[0163] The polyetheramine may be a commercially available product, such as "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," or "JEFFAMINE T-5000," manufactured by Huntsman.

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

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

[0166] By reacting some of the isocyanate groups in the 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 the storage stability and blisters resistance of the resulting coating composition, the ratio of the polyisocyanate compound to the spacer is preferably such that the number of moles of active hydrogen in the spacer is within the range of 0.03 to 0.6 moles per mole of isocyanate groups in the polyisocyanate compound. By blocking the polyisocyanate compound containing a structure derived from the spacer, a blocked polyisocyanate compound containing a structure derived from the spacer can be formed.

[0167] From the viewpoint of the storage stability and blisters resistance of the resulting coating composition, the blocked polyisocyanate compound preferably contains a blocked polyisocyanate compound having a weight average molecular weight in the range of 20,000 to 200,000.

[0168] When a blocked polyisocyanate compound (B3) is used as the curing agent (B), an organometallic compound, an acid compound, a base compound, or the like may be optionally used as a curing catalyst.

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

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

[0171] In addition, from the viewpoint of the brightness of the coating film to be formed, the above-mentioned scaly luster pigment (C) preferably contains a scaly aluminum pigment (C1).

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

[0173] The above-mentioned scaly aluminum pigment (C1) can be broadly classified into leafing type and non-leafing type depending on the type of grinding aid. When incorporated into a coating composition, the leafing type arranges (leafs) on the surface of the coating film obtained by application, resulting in a finish with a strong metallic feel, and has heat reflecting properties and rust prevention properties. Therefore, it is often used in various building materials, including tanks, ducts, piping, and rooftop roofing. In the coating composition of the present invention, it is preferable to use a non-leafing type scaly aluminum pigment, from the viewpoint of the depth of the coating film obtained by application.

[0174] From the viewpoints of the brightness of the coating film formed and the suppression of metallic unevenness, the average particle size of the scaly 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 scaly aluminum pigment (C1) is preferably in the range of 0.05 to 5 μm. The average particle size here refers to the median diameter of the volume-based particle size distribution measured by a laser diffraction scattering method using a Microtrac particle size distribution analyzer MT3300 (trade name, manufactured by Nikkiso Co., Ltd.). The thickness is defined as the average value of measurements of 100 or more pieces of the scaly aluminum pigment (C1) observed under a microscope and the thickness of the scaly aluminum pigment (C1) measured using image processing software.

[0175] Furthermore, when the above-mentioned scaly luster pigment (C) contains the above-mentioned scaly aluminum pigment (C1), it is preferable that the scaly aluminum pigment (C1) contains a scaly aluminum pigment (C11) coated with silica, from the viewpoints of suppressing metallic unevenness in the coating film formed and improving water resistance, etc.

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

[0177] When the coating composition of the present invention contains the above-mentioned scaly aluminum pigment (C1) as the scaly luster pigment (C), the blending amount thereof is preferably within the range of 1 to 50 parts by mass, more preferably 3 to 30 parts by mass, and particularly preferably 5 to 20 parts by mass, per 100 parts by mass of the resin solids in the coating composition, from the viewpoints of the luster of the coating film to be formed and suppression of metallic unevenness.

[0178] Furthermore, when the coating composition of the present invention contains the above-mentioned silica-coated scaly aluminum pigment (C11) as the scaly luster pigment (C), the blending amount thereof is preferably within the range of 1 to 50 parts by mass, more preferably within the range of 3 to 30 parts by mass, and particularly preferably within the range of 5 to 20 parts by mass, per 100 parts by mass of the resin solids in the coating composition, from the viewpoints of the luster of the coating film formed and suppression of metallic unevenness.

[0179] In addition, from the viewpoint of the saturation of the coating film to be formed, the above-mentioned scaly luster pigment (C) preferably contains a scaly light interference pigment (C2).

[0180] Examples of the scaly light interference pigment (C2) include colored pearl pigments and interference pearl pigments in which a translucent scaly substrate is coated with a metal oxide such as iron oxide or titanium oxide.

[0181] Examples of the translucent scaly substrate include natural mica, artificial mica, alumina flakes, silica flakes, and glass flakes.

[0182] Natural mica is a scaly base material made by crushing mica ore, and artificial mica is a SiO ２ , MgO, Al ２ 0 ３ , K. ２ SiF ６ , Na ２ SiF ６ It is synthesized by heating industrial raw materials such as KMg, melting them at a high temperature of about 1500°C, and then cooling and crystallizing them. Compared to natural mica, it has fewer impurities and is uniform in size and thickness. ３ AlSi ３ O １０ F２ ), potassium tetrasilicic mica (KMg ２５ AlSi ４ O １０ F ２ ), sodium tetrasilicic mica (NaMg ２５ AlSi ４ O １０ F ２ ), Na taeniolite (NaMg ２ LiSi ４ O １０ F ２ ), LiNa taeniolite (LiMg ２ LiSi ４ O １０ F ２ ) are known.

[0183] The alumina flakes refer to scaly (thin) aluminum oxide, which is colorless and transparent. They do not necessarily have to be composed solely of aluminum oxide, and may contain oxides of other metals.

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

[0185] Glass flakes are substrates with smooth surfaces obtained by molding scaly C glass or E glass.

[0186] The above-mentioned scaly light interference pigment (C2) may be subjected to a surface treatment in order to improve dispersibility, water resistance, chemical resistance, weather resistance, and the like.

[0187] From the viewpoint of suppressing the saturation of the coating film formed and metallic unevenness, the average particle size of the scaly light-interference pigment (C2) is preferably within the range of 5 to 30 μm, more preferably within the range of 7 to 25 μm, and particularly preferably within the range of 8 to 23 μm. Furthermore, the thickness of the scaly light-interference pigment (C2) is preferably within the range of 0.05 to 5 μm. The average particle size here refers to the median diameter of the volume-based particle size distribution measured by laser diffraction scattering using a Microtrac particle size distribution analyzer MT3300 (product name, manufactured by Nikkiso Co., Ltd.). The thickness is defined as the average value of measurements of 100 or more pieces of the scaly light-interference pigment (C2) observed under a microscope and measured using image processing software.

[0188] Furthermore, when the coating composition of the present invention contains the above-mentioned scaly luster pigment (C2) as the scaly luster pigment (C), the content thereof is preferably within a range of 1 to 50 parts by mass in total, more preferably within a range of 3 to 30 parts by mass, and particularly preferably within a range of 7 to 20 parts by mass, per 100 parts by mass of resin solids in the coating, from the viewpoints of the storage stability of the coating composition and suppression of metallic unevenness in the coating film formed.

[0189] [Viscosity modifier (D)] The coating composition of the present invention contains a viscosity modifier including at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2). If the coating composition does not contain at least one viscosity modifier selected from cellulose nanocrystals (D1) and cellulose nanofibers (D2), the storage stability of the resulting coating composition will be reduced.

[0190] Furthermore, from the viewpoints of the storage stability of the resulting coating composition and the suppression of metallic unevenness in the coating film formed, it is preferable that the viscosity modifier contains the cellulose nanocrystal (D1).

[0191] In this specification, the cellulose nanocrystal (D1) has a ratio of the number average fiber length to the number average fiber diameter (number average fiber length / number average fiber diameter) of less than 50.

[0192] In this specification, the cellulose nanofibers (D2) have a ratio of the number average fiber length to the number average fiber diameter (number average fiber length / number average fiber diameter) of 50 or more.

[0193] <Cellulose nanocrystals (D1)> Cellulose nanocrystals (D1) can be obtained by known methods. For example, cellulose raw materials can be treated with an acid such as sulfuric acid to hydrolyze and remove the amorphous portion, followed by mechanical defibration to obtain cellulose nanocrystals (D1).

[0194] The cellulose raw material is not particularly limited as long as it contains cellulose, and examples thereof include various wood pulps, non-wood pulps, bacterial cellulose, regenerated cellulose, waste paper pulp, cotton, valonia cellulose, sea squirt cellulose, etc. Commercially available cellulose powders, microcrystalline cellulose powders, etc. may also be used.

[0195] Furthermore, the mechanical fiberization treatment is not particularly limited, and conventionally known methods can be used, for example, methods using equipment such as a high-pressure homogenizer, ultra-high-pressure homogenizer, ball mill, roll mill, cutter mill, planetary mill, jet mill, attritor, grinder, juicer mixer, homomixer, ultrasonic homogenizer, nanogenizer, underwater counter-impingement system, single-screw or twin-screw extruder, etc.

[0196] The cellulose nanocrystal (D1) may be chemically modified in various ways, such as esterification (e.g., carboxymethylation, acylation, phosphorylation), oxidation (e.g., carboxylation), sulfonation, fluorination, cationization, or treatment with a silane coupling agent.

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

[0198] The cellulose nanocrystals (D1) may be chemically modified after being defibrated.

[0199] The cellulose nanocrystals (D1) may be neutralized with a neutralizing agent, such as those described in the description of the water-dispersible hydroxyl-containing acrylic resin (A11).

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

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

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

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

[0204] Furthermore, examples of commercially available cellulose nanocrystals (D1) include "Celluforce NCC" (sodium sulfonate salt-type cellulose nanocrystals manufactured by Celluforce).

[0205] <Cellulose nanofibers (D2)> The cellulose nanofibers (D2) can be obtained by known methods. For example, cellulose raw materials can be defibrated and refined to nano-sized fiber diameters to produce cellulose nanofibers (D2). Examples of methods for defibrating cellulose raw materials include mechanical defibration and chemical treatments such as treatment with an oxidation catalyst solution containing an N-oxyl compound.

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

[0207] The cellulose nanofibers (D2) may be chemically modified in various ways, such as esterification (e.g., carboxymethylation, acylation, phosphorylation), oxidation (e.g., carboxylation), sulfonation, fluorination, cationization, and treatment with a silane coupling agent.

[0208] The cellulose nanofibers (D2) may be neutralized with a neutralizing agent, such as the neutralizing agents described in the description of the water-dispersible hydroxyl-containing acrylic resin (A11).

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

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

[0211] Examples of commercially available products of the cellulose nanofiber (D2) include "Nanocellulose Fiber" (manufactured by Chuetsu Pulp Industries Co., Ltd.), "BiNFi-s" (manufactured by Sugino Machine Co., Ltd.), "Leocrysta" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), "Cellulose Nanofiber" (manufactured by Mori Machinery Co., Ltd.), "Cellenpia" (manufactured by Nippon Paper Industries Co., Ltd.), and "Aurovisco" (manufactured by Oji Holdings Co., Ltd.).

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

[0213] The mineral viscosity adjuster may include swellable layered silicates having a 2:1 crystal structure.Specific examples include natural or synthetic smectite clay minerals such as montmorillonite, saponite, hectorite, stevensite, beidellite, nontronite, bentonite, and laponite; swellable mica clay minerals such as Na-type tetrasilicic fluorine mica, Li-type tetrasilicic fluorine mica, Na-salt-type fluorine taeniolite, and Li-type fluorine taeniolite; vermiculite; substitution products or derivatives thereof; and mixtures thereof.

[0214] As the urethane associative viscosity modifier, for example, it is preferable to use a urethane associative viscosity modifier having a hydrophobic group at the terminal and a urethane bond in the molecular chain. Commercially available products can be used as the urethane associative viscosity modifier. Examples of commercially available products under the trade names include "UH-420", "UH-462", "UH-472", "UH-540", "UH-752", "UH-756VF", and "UH-814N" (all manufactured by ADEKA Corporation); "SN Thickener 612", "SN Thickener 621N", "SN Thickener 625N", "SN Thickener 627N", and "SN Thickener 660T" (all manufactured by San Nopco Ltd.).

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

[0216] Commercially available polyacrylic acid viscosity modifiers include, for example, "Primal ASE-60," "Primal TT615," and "Primal RM5" (all trade names) manufactured by The Dow Chemical Company, and "SN Thickener 613," "SN Thickener 618," "SN Thickener 630," "SN Thickener 634," and "SN Thickener 636" (all trade names) manufactured by San Nopco Ltd. The acid value of the polyacrylic acid viscosity modifier is preferably in the range of 30 to 300 mgKOH / g, and more preferably in the range of 80 to 280 mgKOH / g.

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

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

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

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

[0221] In this specification, "volatile components" refers to components that volatilize when dried for 1 hour at 110° C. Therefore, the volatile components in a coating composition can be calculated, for example, by weighing out the coating composition into 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 components remaining after drying, and subtracting the mass of the components remaining after drying from the total mass of the coating composition before drying.

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

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

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

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

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

[0227] [Other Components] The coating composition of the present invention may further optionally contain a resin other than the hydroxyl group-containing resin (A) and the curing agent (B), a pigment other than the scaly luster pigment (C), an organic solvent other than the organic solvent (E) having a solubility in water at 20°C of 4 mass% or more, a curing catalyst, a dispersant, an anti-settling agent, an antifoaming agent, an ultraviolet absorber, a light stabilizer, a surface conditioner, etc.

[0228] 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, hydroxyl-free polyolefin resins, etc. Among these, it is preferable that 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).

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

[0230] Examples of pigments other than the scaly luster pigment (C) include coloring pigments, extender pigments, etc. These pigments may be used alone or in combination of two or more.

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

[0232] Examples of the color pigment include titanium oxide, 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 diketopyrrolopyrrole pigments. Of these, titanium oxide and carbon black are particularly preferred.

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

[0234] Examples of the extender pigment include barium sulfate, talc, clay, kaolin, barium carbonate, calcium carbonate, silica, alumina white, etc. From the viewpoints of paint stability, smoothness, etc., barium sulfate and talc are preferably used as the extender pigment.

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

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

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

[0238] Examples of the light stabilizer include hindered amine light stabilizers.

[0239] [Coating Composition] The coating composition of the present invention can be prepared by mixing the hydroxyl group-containing resin (A), the curing agent (B), the scaly luster pigment (C), the viscosity modifier (D), the organic solvent (E) having a solubility in water of 4% by mass or more at 20°C, and optionally other components, in a solvent by a conventional coating method. Examples of the solvent that can be used include organic solvents and water.

[0240] Furthermore, from the viewpoints of the storage stability of the resulting coating composition and suppression of metallic unevenness in the coating film formed, the coating solids concentration of the coating composition of the present invention is preferably within the range of 10 to 45 mass %, more preferably within the range of 15 to 40 mass %, and even more preferably within the range of 17 to 30 mass %.

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

[0242] In particular, the coating composition of the present invention preferably contains water as a solvent from the viewpoint of storage stability and the like.

[0243] When the coating composition of the present invention contains the above-mentioned water, from the viewpoint of the storage stability of the resulting coating composition, the water content is preferably in the range of 30 to 80 mass %, more preferably in the range of 40 to 75 mass %, and even more preferably in the range of 50 to 70 mass %, based on the total amount of the coating composition.

[0244] Furthermore, from the viewpoint of suppressing metallic unevenness in the coating film formed, the coating composition of the present invention is preferably applied at a temperature of 25°C and a shear rate of 1,500 sec. －１The viscosity measured under the above 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.

[0245] Furthermore, from the viewpoint of suppressing metallic unevenness in the coating film formed, the coating composition of the present invention is preferably applied at a temperature of 25°C and a shear rate of 0.1 sec. －１ The viscosity measured under the above 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.

[0246] The coating composition may be either a one-component coating or a multi-component coating, but a one-component coating is preferred from the viewpoints of excellent productivity due to the absence of a coating mixing step and simplification of maintenance of coating machines.

[0247] The coating composition can be applied to a substrate by a known method, such as air spray coating, airless spray coating, rotary atomization coating, curtain coating, etc., and electrostatic application may be performed during coating. Of these, air spray coating and rotary atomization coating are preferred. Furthermore, such coating methods can be performed in one or several batches until the desired film thickness is obtained.

[0248] The coating amount of the coating composition is usually an amount that results in a cured film thickness of 0.5 to 50 μm, preferably 2 to 40 μm, and more preferably 5 to 30 μm.

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

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

[0251] The substrate in Method I is preferably an automobile body on which a primer coating film has been formed or an automobile body on which a colored coating film has been formed over the primer coating film. The primer coating film is preferably formed using an electrodeposition paint, more preferably using a cationic electrodeposition paint. The uncured coating film includes a coating film that is dry to the touch and a coating film that is semi-cured and dry.

[0252] When the coating composition of the present invention is applied by the two-coat, one-bake method of Method I, the coating film thickness, as 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.

[0253] The uncured base coat film is usually formed using one type of base coat paint composition, but may also be formed using two or more types of base coat paint compositions.

[0254] When two or more types of base coat paint compositions are used, it is preferable to use two types of base coat paint compositions.

[0255] Specifically, for example, a first base coat paint, which may use the paint composition of the present invention, is applied to a substrate to form a first base coat film, and then a second base coat paint, which uses the paint composition of the present invention, is applied on top of the first base coat film to form a second base coat film.

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

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

[0258] In Method I, after application of the coating composition of the present invention, it is preferable to preheat, air blow, or the like under heating conditions that do not substantially cure the coating, in order to prevent the occurrence of coating defects such as popping. The preheating temperature is preferably within the range of 40 to 100°C, more preferably within the range of 50 to 90°C, and particularly preferably within the range of 60 to 80°C. The preheating time is preferably within the range of 30 seconds to 15 minutes, more preferably within the range of 1 to 10 minutes, and particularly preferably within the range of 2 to 5 minutes. The air blowing can be carried out, for example, by blowing air heated to room temperature or a temperature of 25 to 80°C onto the coated surface of the substrate for 30 seconds to 15 minutes. After application of the clear coat coating composition (Y), an interval of 1 to 60 minutes can be optionally allowed at room temperature, or the coating can be preheated at 40 to 80°C for 1 to 60 minutes.

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

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

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

[0262] In Method II, the coating film formation method of Method I is carried out on an uncured pigmented coating film. The substrate to be coated in Method II is preferably an automobile body or the like having a primer coating film formed thereon. The primer coating is preferably formed by an electrodeposition paint, more preferably by a cationic electrodeposition paint.

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

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

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

[0266] In Method II, the uncured base coat film is usually formed using one base coat paint composition, but it can also be formed using two or more base coat paint compositions, in which case the paint composition of the present invention can be used as the base coat paint composition that forms at least the top layer of the base coat film.

[0267] When two or more types of base coat paint compositions are used, it is preferable to use two types of base coat paint compositions.

[0268] Specifically, for example, a first base coat paint, which may use the paint composition of the present invention, is applied to a substrate to form a first base coat film, and then a second base coat paint, which uses the paint composition of the present invention, is applied on top of the first base coat film to form a second base coat film.

[0269] In this case, from the viewpoint of suppressing metallic unevenness in the coating film to be formed, the first base coat coating film preferably has a cured film thickness in the range of 5 to 15 μm, more preferably in the range of 7 to 13 μm, and the second base coat coating film preferably has a cured film thickness in the range of 0.5 to 15 μm, more preferably in the range of 2 to 13 μm.

[0270] After application of the clear coat paint composition (Z), an interval of 1 to 60 minutes can be allowed to stand at room temperature, or preheating can be carried out at 40 to 80°C for 1 to 60 minutes, if desired.

[0271] The three-layer coating film consisting of the uncured color coating film, the uncured base coating film, and the uncured clear coating film can be cured by the known heating means described above. The heating temperature is preferably within the range of 60 to 180°C, more preferably within the range of 65 to 170°C, and particularly preferably within the range of 70 to 160°C. The heating time is preferably within the range of 10 to 60 minutes, and particularly preferably within the range of 20 to 40 minutes. This heating allows the three-layer coating film consisting of the color coating film, the base coating film, and the clear coating film to be cured simultaneously.

[0272] The clear coat paint composition (Z) used in the above methods I and II can be any known thermosetting clear coat paint composition for painting automobile bodies, etc. Examples include organic solvent-based thermosetting paint compositions containing a base resin having a crosslinkable functional group and a crosslinking agent, aqueous thermosetting paint compositions, and powder thermosetting paint compositions.

[0273] Examples of crosslinkable functional groups possessed by the base resin include carboxyl groups, hydroxyl groups, epoxy groups, silanol groups, etc. Types of base resins include acrylic resins, polyester resins, alkyd resins, urethane resins, epoxy resins, fluororesins, etc. Examples of crosslinking agents include polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins, urea resins, carboxyl group-containing compounds, carboxyl group-containing resins, epoxy group-containing resins, epoxy group-containing compounds, etc.

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

[0275] The clear coat paint composition (Z) may optionally contain coloring pigments, luster pigments, dyes, etc. to the extent that transparency is not impaired, and may further contain extender pigments, ultraviolet absorbers, light stabilizers, antifoaming agents, thickeners, rust inhibitors, surface conditioners, etc. as appropriate.

[0276] Preferred combinations of base resin / crosslinking agent for the clear coat paint composition (Z) include carboxyl group-containing resin / epoxy group-containing resin, hydroxyl group-containing resin / polyisocyanate compound, hydroxyl group-containing resin / blocked polyisocyanate compound, hydroxyl group-containing resin / melamine resin, etc. Of these, from the viewpoint of the granular feel of the coating film to be formed, the combination of hydroxyl group-containing resin / polyisocyanate compound is preferred.

[0277] The colored coating composition used in Method II may be any known thermosetting colored coating composition, such as a thermosetting coating composition containing a base resin having a crosslinkable functional group, a crosslinking agent, a color pigment, and an extender pigment.

[0278] Examples of the crosslinkable functional group contained in the base resin include a carboxyl group, a hydroxyl group, and an epoxy group. Examples of the type of base resin include an acrylic resin, a polyester resin, an alkyd resin, and a urethane resin. Examples of the crosslinking agent include a melamine resin, a polyisocyanate compound, and a blocked polyisocyanate compound.

[0279] The colored coating composition may be any of an organic solvent-based coating composition, a water-based coating composition, and a powder coating composition, and among these, it is preferable to use a coating composition.

[0280] In the above methods I and II, the coating can be carried out by a known method such as air spray coating, airless spray coating, rotary atomization coating or the like.

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

[0282] Production of Hydroxyl Group-Containing Acrylic Resin (A1) Production Example 1 A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet tube, and a dropping device was charged with 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., emulsifier, active ingredient 97%), and the mixture was stirred and mixed in a nitrogen stream, and the temperature was raised to 80°C.

[0283] Next, 1.72 parts of the following monomer emulsion (1) and 5.3 parts of a 6% aqueous ammonium persulfate solution were introduced into a reaction vessel and maintained at 80°C for 15 minutes. Thereafter, the remaining monomer emulsion (1) was added dropwise over 3 hours to the reaction vessel maintained at the same temperature, and the mixture was aged for 1 hour after the completion of the dropwise addition. Thereafter, the following monomer emulsion (2) was added dropwise over 1 hour. After aging for 1 hour, the reaction vessel was cooled to 30°C while 20 parts of a 5% aqueous N-methylmorpholine solution was gradually added thereto, and the mixture was discharged while being filtered through a 100-mesh nylon cloth, yielding an aqueous dispersion of hydroxyl-containing acrylic resin (A1-1) with a solids concentration of 30%. The resulting hydroxyl-containing acrylic resin (A1-1) had an acid value of 16 mgKOH / g, a hydroxyl value of 66 mgKOH / g, and a glass transition temperature of 21°C. The hydroxyl-containing acrylic resin (A1-1) corresponds to the water-dispersible hydroxyl-containing acrylic resin (A11) having a core / shell type multilayer structure.

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

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

[0286] Production Example 2 A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet pipe, and a dropping device was charged with 130 parts of deionized water and 0.52 parts of "Aqualon KH-10" (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., emulsifier, active ingredient 97%), and the mixture was stirred and mixed in a nitrogen stream and heated to 80°C.

[0287] Next, 1.72 parts of the following monomer emulsion (1) and 5.3 parts of a 6% aqueous solution of ammonium persulfate were introduced into a reaction vessel and maintained at 80°C for 15 minutes. Thereafter, 35.4 parts of the monomer emulsion (1) were added dropwise over 1 hour to the reaction vessel maintained at the same temperature. Immediately after completion of the dropwise addition, the remaining 55.6 parts of the monomer emulsion (1) began to be added dropwise to the reaction vessel. At the same time, 55.6 parts of the monomer emulsion (2) were added dropwise to the monomer emulsion (1), and the dropwise addition of the monomer emulsions (1) and (2) was completed over 2 hours. Thereafter, 37.17 parts of the remaining monomer emulsion (2) was added dropwise to the reaction vessel over 1 hour. After aging for 1 hour, 20 parts of a 5% aqueous solution of N-methylmorpholine was gradually added to the reaction vessel while the mixture was cooled to 30°C. The mixture was then discharged while being filtered through a 100-mesh nylon cloth, yielding an aqueous dispersion of hydroxyl-containing acrylic resin (A1-2) with a solids concentration of 30%. The resulting 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 hydroxyl-containing acrylic resin (A1-2) corresponds to the water-dispersible hydroxyl-containing acrylic resin (A11') containing the gradient polymer layer.

[0288] Monomer emulsion (1): 42 parts of deionized water, 0.72 parts of "Aqualon KH-10", 2 parts of methylenebisacrylamide, 5 parts of styrene, 15 parts of methyl methacrylate, 5 parts of 2-hydroxyethyl methacrylate, and 23 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (1).

[0289] 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 a monomer emulsion (2).

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

[0291] Phosphate group-containing polymerizable monomer: 57.5 parts of monobutyl phosphate and 41 parts of isobutanol were placed in a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and dropping device, and the mixture was heated to 90°C. Next, 42.5 parts of glycidyl methacrylate was added dropwise over 2 hours, and the mixture was further stirred and aged for 1 hour. Subsequently, 59 parts of isopropanol was added to obtain a phosphate group-containing polymerizable monomer solution with a solids concentration of 50%. The acid value due to the phosphate group of the resulting monomer was 285 mgKOH / g.

[0292] Preparation of Hydroxyl-Containing Polyester Resin (A2) Preparation Example 4: A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, and water separator was charged with 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. The mixture was heated from 160°C to 230°C over 3 hours, and the resulting condensed water was distilled off using a water separator while maintaining the temperature at 230°C until the acid value reached 3 mgKOH / g or less. 59 parts of trimellitic anhydride was added to the reaction product, and the mixture was subjected to an addition reaction at 170°C for 30 minutes. The mixture was then cooled to 50°C or less, and an equivalent amount of N-methylmorpholine was added to the acid groups to neutralize the mixture. Deionized water was then added gradually to obtain a hydroxyl-containing polyester resin (A2-1) solution with a solids concentration of 45% and a pH of 7.2. The resulting hydroxyl-containing polyester resin had a hydroxyl value of 128 mgKOH / g, an acid value of 35 mgKOH / g, and a weight-average molecular weight of 13,000.

[0293] Production of Hydroxyl Group-Containing Polyurethane Resin (A3) Production Example 5 A reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser was charged with 316.0 parts of "PTMG1000" (trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol having a number average molecular weight of 1000), 17.0 parts of 2,2-dimethylolpropionic acid, 21.9 parts of trimethylolpropane, 113.0 parts of isophorone diisocyanate, 0.19 parts of "Neostan U-600" (trade name, manufactured by Nitto Kasei Co., Ltd., bismuth catalyst), and 235.0 parts of methyl ethyl ketone. The reaction system was then purged with nitrogen gas, and the mixture was reacted at 80°C with stirring to obtain an NCO-terminated urethane prepolymer having a free isocyanate group content of 3.2%. The resulting 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 to emulsify, and then 96.4 parts of a 5% aqueous solution of N-(2-hydroxyethyl)ethylenediamine was added thereto and stirred for 120 minutes. The methyl ethyl ketone was then distilled off under reduced pressure and heating, and the concentration was adjusted with deionized water to obtain a hydroxyl group-containing polyurethane resin (A3-1) dispersion having a solids concentration of 35%, an acid value of 15 mgKOH / g, a hydroxyl value of 12 mgKOH / g, an average particle size of 120 nm, and a glass transition temperature of -7°C.

[0294] Production of Hydroxyl Group-Free Polyurethane Resin (U) Production Example 6 A reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser was charged with 211.9 parts of "PTMG1000" (trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol having 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, and after the reaction system was purged with nitrogen gas, the mixture was reacted at 80°C with stirring to obtain an NCO-terminated urethane prepolymer having a free isocyanate group content of 3.2%. The resulting 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 to emulsify the solution. Thereafter, 159.2 parts of a 5% aqueous ethylenediamine solution was added thereto and stirred for 60 minutes. The methyl ethyl ketone was then distilled off under reduced pressure and heating, and the concentration was adjusted with deionized water to obtain a hydroxyl-free polyurethane resin (U-1) dispersion having a solids content of 35%, an acid value of 14 mgKOH / g, and an average particle size of 120 nm.

[0295] Production of Blocked Polyisocyanate Compound (B3) Production Example 7 A reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser, a nitrogen inlet tube, and a dropping device was charged with 1,650 parts of "Sumidur N-3300" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., hexamethylene diisocyanate-derived isocyanurate structure-containing polyisocyanate, solids content 100%, isocyanate group content 21.8%), 1,100 parts of "PTMG2000" (trade name, manufactured by Mitsubishi Chemical Corporation, polytetramethylene ether glycol, average molecular weight 2,000, solids content 100%), and 0.9 parts of 2,6-di-t-butyl-4-methylphenol, which were thoroughly mixed and heated at 130°C for 3 hours under a nitrogen stream. Next, 1,200 parts of ethyl acetate and 1,200 parts of diisopropyl malonate were charged, and while stirring under a nitrogen stream, 14 parts of a 28% methanol solution of sodium methoxide was added, followed by stirring for 8 hours at 65° C. Next, the mixture was diluted with ethyl acetate to a final solids concentration of 70%, thereby obtaining a blocked polyisocyanate compound (B3-1) having a solids concentration of 70% and a weight average molecular weight of 40,000.

[0296] Production of Pigment Dispersion Production Example 8 In a stirring mixing vessel, 25 parts (solid content: 15 parts) of "Hydroran 2156" (trade name, manufactured by Ecart, silica-coated aluminum pigment paste, aluminum content: 60%), 10 parts (solid content: 5 parts) of the acrylic resin (A1-3) solution having hydroxyl groups and phosphate groups obtained in Production Example 3, 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 mixed uniformly to obtain a pigment dispersion (P-1).

[0297] Production Examples 9 to 28 Pigment dispersions (P-2) to (P-21) were obtained in the same manner as in Production Example 8, except that the blending compositions in Production Example 8 were as shown in Table 1 below.

[0298] In Table 1, the amount of organic solvent added is shown, and the solid content is shown for the components other than the organic solvent. The components shown in Table 1 are as follows.

[0299]

[0300]

[0301]

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

[0303] The solubilities of each organic solvent in water at 20°C are as follows: Propylene glycol monobutyl ether: solubility in water at 20°C is 6.4% by mass, n-butanol: solubility in water at 20°C is 6.4% by mass, Propylene glycol monomethyl ether: freely miscible with water at 20°C, Ethylene glycol monobutyl ether: freely miscible with water at 20°C, Dipropylene glycol monomethyl ether: freely miscible with water at 20°C, Butyl acetate: solubility in water at 20°C is 1.0% by mass, 2-ethyl-1-hexanol: solubility in water at 0°C is 0.07% by mass, Methyl isobutyl ketone: poorly soluble in water at 20°C, "Swasol 1000": poorly soluble in water at 20°C.

[0304] Preparation of cellulose nanocrystal (D1) aqueous dispersion Preparation Example 29: Celluforce NCC (trade name, manufactured by Celluforce Corporation, number average fiber diameter: 2.3 to 4.5 nm, number average fiber length: 44 to 108 nm, specific surface area: 400 m) was added to deionized water stirred with a magnetic stirrer so as to give a solids concentration of 4%. ２ Sodium sulfonate salt-type cellulose nanocrystals (solid concentration 100%) having a zeta potential of −37 mV and a 100% ethanol content of 1 / g were gradually added, and the mixture was stirred for 2 hours to obtain an aqueous dispersion of cellulose nanocrystals (D1-1).

[0305] Preparation of Coating Composition Example 1 Into a stirring mixing vessel were added 89.0 parts (solid content 20.0 parts) of the pigment dispersion (P-1) obtained in Production Example 8, 133.3 parts (solid content 40.0 parts) of the aqueous dispersion of hydroxyl-containing acrylic resin (A1-1) obtained in Production Example 1, 55.6 parts (solid content 25 parts) of the hydroxyl-containing polyester resin solution (A2-1) obtained in Production Example 4, 28.6 parts (solid content 10 parts) of the dispersion of hydroxyl-free polyurethane resin (U-1) obtained in Production Example 6, and "Cymel 325" (trade name, manufactured by Allnex Japan Co., Ltd., a methyl / butyl mixed etherified melamine). 6.25 parts (solids content: 5.0 parts) of a cellulose nanocrystal (D1-1) resin (solids concentration: 80%) and 39.5 parts (solids content: 15.0 parts) of "Bayhydur VPLS2310" (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., blocked polyisocyanate compound, solids concentration: 38%) were uniformly mixed, and 75.0 parts (solids content: 3.0 parts) of the cellulose nanocrystal (D1-1) aqueous dispersion obtained in Production Example 29, 2-(dimethylamino)ethanol, and deionized water were added to obtain aqueous coating composition No. 1 with a pH of 8.0 and a coating solids concentration of 25%.

[0306] Examples 2 to 25 and Comparative Examples 1 to 8 Aqueous coating compositions No. 1 to No. 33 were obtained in the same manner as in Example 1, except that the blending compositions in Example 1 were as shown in Table 2 below.

[0307] In Table 1, the amount of organic solvent added is listed, and for ingredients other than organic solvents, the solid content is listed. The ingredients listed in Table 2 are as follows: (Note 5) "Leocrysta I-2SX": Trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., cellulose nanofiber, viscosity modifier, (Note 6) "Primal ASE-60": Trade name, manufactured by The Dow Chemical Company, polyacrylic acid viscosity modifier, (Note 7) "UH-752": Trade name, manufactured by ADEKA Corporation, urethane associative viscosity modifier.

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

[0309] Test Method Storage Stability A storage stability test was carried out for each of the coating compositions obtained in the above Examples and Comparative Examples according to the following test method. 800 g of each of the above coating compositions was placed in a glass bottle with a capacity of approximately 1 L and stored in a thermostatic chamber at 40°C for 10 days. The bottle was then returned to room temperature, the condition inside the container was visually observed, and storage stability was evaluated according to the following criteria. A and B are acceptable. The results are shown in Table 2. A: No sediment formation or viscosity change was observed. B: Slight sediment formation and / or viscosity change was observed, but the viscosity returned to normal upon stirring. C: Sediment formation and / or viscosity change was observed. D: Significant sediment formation and / or significant viscosity change was observed.

[0310] Preparation of test panels under 80°C heat curing conditions and evaluation of metallic unevenness As the metal material, zinc phosphate-treated galvannealed steel sheets were electrocoated with "Elecron GT-10" (trade name, manufactured by Kansai Paint Co., Ltd., cationic electrodeposition paint) to a cured film thickness of 20 μm, and the steel sheets were heated and cured at 170°C for 30 minutes to obtain electrodeposition-coated steel sheets. Next, a colored coating composition (trade name "WP-505T", manufactured by Kansai Paint Co., Ltd., polyester resin / amino resin-based aqueous coating composition) was applied to the obtained electrodeposition-coated steel sheets to a film thickness of 20 μm, left for 2 minutes, and then preheated at 80°C for 3 minutes to obtain an uncured colored coating film. Next, each of the coating compositions obtained in the above Examples and Comparative Examples was applied to the uncured colored coating film to a cured film thickness of 15 μm, left for 3 minutes, and then preheated at 80°C for 3 minutes to obtain an uncured base coat coating film. Next, "KINO6510" (trade name, acrylic resin / polyisocyanate compound-based solvent-based topcoat clear coating, manufactured by Kansai Paint Co., Ltd.) was electrostatically applied onto the uncured base coat film to a cured film thickness of 35 μm, yielding an uncured clear coat film. After leaving for 7 minutes, the test panels were heated at 80°C for 30 minutes to cure the multilayer coating consisting of the uncured colored coating film, uncured base coat film, and uncured clear coat film, thereby producing test panels. Each test panel was visually observed, and the degree of metallic unevenness was evaluated according to the following criteria: A and B are acceptable. The results are shown in Table 2. A: No metallic unevenness was observed; B: Some metallic unevenness was observed, but within the acceptable range; C: Metallic unevenness was observed; D: Significant metallic unevenness was observed.

[0311] Preparation of test panels under 140°C heat curing conditions and evaluation of metallic unevenness As the metal material, zinc phosphate-treated galvannealed steel sheets were electrocoated with "Elecron GT-10" (trade name, manufactured by Kansai Paint Co., Ltd., cationic electrodeposition paint) to a cured film thickness of 20 μm, and the steel sheets were heated and cured at 170°C for 30 minutes to obtain electrodeposition-coated steel sheets. Next, a colored coating composition (trade name "WP-505T", manufactured by Kansai Paint Co., Ltd., polyester resin / amino resin-based aqueous coating composition) was applied to the obtained electrodeposition-coated steel sheets to a film thickness of 20 μm, left for 2 minutes, and then preheated at 80°C for 3 minutes to obtain an uncured colored coating film. Next, each of the coating compositions obtained in the above Examples and Comparative Examples was applied to the uncured colored coating film to a cured film thickness of 15 μm, left for 3 minutes, and then preheated at 80°C for 3 minutes to obtain an uncured base coat coating film. Next, "KINO6510" (trade name, acrylic resin / polyisocyanate compound-based solvent-based topcoat clear coating, manufactured by Kansai Paint Co., Ltd.) was electrostatically applied onto the uncured base coat film to a cured film thickness of 35 μm, yielding an uncured clear coat film. After leaving for 7 minutes, the test panels were heated at 140°C for 30 minutes to cure the multilayer coating consisting of the uncured colored coating film, uncured base coat film, and uncured clear coat film, thereby producing test panels. Each test panel was visually observed, and the degree of metallic unevenness was evaluated according to the following criteria: A and B are acceptable. The results are shown in Table 2. A: No metallic unevenness was observed; B: Some metallic unevenness was observed, but within the acceptable range; C: Metallic unevenness was observed; D: Significant metallic unevenness was observed.

[0312]

[0313]

[0314]

[0315]

[0316]

Claims

1. A coating composition comprising a hydroxyl-containing resin (A), a curing agent (B), a scaly luster pigment (C), a viscosity modifier (D), and an organic solvent (E) having a solubility in water of 4 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 mass% or more at 20°C is in the range of 10 to 25 mass% based on the volatile components in the coating composition.

2. 2. The coating composition according to claim 1, wherein the scaly luster pigment (C) comprises a scaly aluminum pigment (C11) coated with silica.

3. 2. The coating composition of claim 1, wherein the viscosity modifier (D) comprises cellulose nanocrystals (D1).

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

5. The coating composition of claim 1 further comprising water.

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

7. Step (II-1): A step of applying a colored coating composition (X) to a substrate to form an uncured colored coating film; Step (II-2): A step of applying a base coat paint composition (Y) onto the uncured colored coating film to form an uncured base coat coating film; Step (II-3): A step of applying a clear coat paint composition (Z) onto the uncured base coat film to form an uncured clear coat film; and Step (II-4): A method for forming a multilayer coating film, comprising a step of heating the uncured color coating film, the uncured base coat coating film, and the uncured clear coat coating film to simultaneously cure them, A method for forming a multi-layer coating film, wherein the base coat paint composition (Y) is the paint composition according to any one of claims 1 to 5.