High solids content coating composition and method for forming multi-layer coating film

Abstract

The present invention relates to a coating composition having a high solid content, said coating composition being characterized by containing: (A) a hydroxyl group-containing acrylic resin having an acid value in the range of 0-30 mg KOH / g; (B) a hydroxyl group-containing acrylic resin having an acid value in the range of 60-120 mg KOH / g, and (C) a polyisocyanate compound, wherein the solid content at the time of application is at least 50 mass%.

Description

[Technical Field]

[0001] The present invention relates to a high solids coating composition and a method for forming a multi-layer coating film. [Background technology]

[0002] In recent years, from the perspective of protecting the global environment, there has been a demand to reduce the volatile organic compounds (VOCs) emitted from paints, and the replacement of solvent-based paints with water-based paints is progressing rapidly in various fields.

[0003] In the past, large amounts of solvent-based paints were used in the painting of automobiles, and reducing the VOCs emitted from these paints was an urgent task. However, progress has been made in replacing organic solvent-based paints with water-based paints for the various paints used in the primer, undercoat, and topcoat painting processes of automobiles, and water-based paints are now the mainstream.

[0004] However, since top-coat clear paints require particularly high levels of coating film performance (such as resistance to smudges) and finished appearance, solvent-based clear paints are still the predominant method of application. One method of reducing VOCs without using water-based clear paints is to increase the solid content of the paint (increasing the solid content concentration).

[0005] For example, Patent Document 1 discloses a high solids coating composition that uses a reaction product of a specific carboxyl group-containing compound and an epoxy group-containing compound in combination with a polyisocyanate compound and a melamine resin, and further contains a specific hydroxyl group-containing resin.

[0006] Patent Document 2 also discloses a clear coating composition characterized by containing an acrylic resin obtained from a monomer mixture including a long-chain (meth)acrylic acid ester monomer in which the ester moiety is a linear hydrocarbon group having 9 to 15 carbon atoms, a carboxyl group-containing (meth)acrylic monomer, and a hydroxyl group-containing (meth)acrylic monomer. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2002-201430 [Patent Document 2] Japanese Patent Application Publication No. 2009-155396 Summary of the Invention [Problem to be solved by the invention]

[0008] However, although the coating composition described in Patent Document 1 has a good finished appearance, it sometimes has insufficient resistance to mold. Furthermore, the clear coating composition described in Patent Document 2 has good resistance to sludge, but when the solid content is increased, the finished appearance is insufficient.

[0009] An object of the present invention is to provide a high solids coating composition capable of forming a coating film having excellent resistance to sludge and excellent finished appearance. [Means for solving the problem]

[0010] As a result of extensive research into achieving the above-mentioned object, the present inventors have found that the above-mentioned object can be achieved by a high solids coating composition comprising (A) a hydroxyl-containing acrylic resin having an acid value in the range of 0 to 30 mgKOH / g, (B) a hydroxyl-containing acrylic resin having an acid value in the range of 60 to 120 mgKOH / g, and (C) a polyisocyanate compound, and having a solids content of 50 mass% or more at the time of application. According to the present invention, there is provided a high solids coating composition comprising the following aspects: Item 1. A high solids coating composition comprising (A) a hydroxyl-containing acrylic resin having an acid value in the range of 0 to 30 mgKOH / g, (B) a hydroxyl-containing acrylic resin having an acid value in the range of 60 to 120 mgKOH / g, and (C) a polyisocyanate compound, and having a solids content of 50 mass% or more at the time of coating. Item 2. The high solids coating composition according to Item 1, wherein the weight average molecular weight of the hydroxyl group-containing acrylic resin (A) is within the range of 3,000 to 10,000. Item 3. The high solids coating composition according to Item 1 or 2, wherein the weight average molecular weight of the hydroxyl group-containing acrylic resin (B) is within the range of 1,000 to 4,000. Item 4. The high solids coating composition according to any one of Items 1 to 3, wherein the content ratio of the hydroxyl-containing acrylic resin (A) and the hydroxyl-containing acrylic resin (B) is a mass ratio of hydroxyl-containing acrylic resin (A) / hydroxyl-containing acrylic resin (B) of 99 / 1 to 70 / 30. Item 5. The high solids coating composition according to any one of Items 1 to 4, further comprising a hydroxyl group-containing polyester resin (D). Item 6. The following steps (1) to (3): Step (1): A step of applying a glitter coating composition to an object to be coated to form a glitter coating film; Step (2): A step of applying the high solids coating composition according to any one of items 1 to 5 onto the glossy coating film obtained in step (1) to form a clear coating film; Step (3): A method for forming a multilayer coating film, comprising a step of simultaneously curing the multilayer coating film including the glossy coating film and the clear coating film formed in steps (1) and (2) by heating the multilayer coating film. [Effects of the Invention]

[0011] The high solids coating composition of the present invention can form a coating film that is excellent in resistance to sludge and in finished appearance. DETAILED DESCRIPTION OF THE INVENTION

[0012] The high solids coating composition of the present invention (hereinafter sometimes abbreviated as "the coating") will be described in further detail below.

[0013] The high solids coating composition of the present invention is a high solids coating composition characterized by containing (A) a hydroxyl group-containing acrylic resin having an acid value in the range of 0 to 30 mgKOH / g, (B) a hydroxyl group-containing acrylic resin having an acid value in the range of 60 to 120 mgKOH / g, and (C) a polyisocyanate compound, and having a solids content of 50 mass% or more at the time of application. In this specification, a high solids content coating composition means a coating composition having a solids content of 50 mass % or more at the time of application.

[0014] <Hydroxyl group-containing acrylic resin (A) having an acid value in the range of 0 to 30 mgKOH / g> The hydroxyl group-containing acrylic resin (A) is an acrylic resin having at least one hydroxyl group in one molecule and an acid value within the range of 0 to 30 mgKOH / g.

[0015] An acid value in the range of 0 to 30 mgKOH / g results in a good finished appearance of the coating film that is formed. In particular, from the viewpoint of the finished appearance of the coating film that is formed, the acid value of the hydroxyl group-containing acrylic resin (A) is preferably in the range of 1 to 25 mgKOH / g, and more preferably in the range of 3 to 15 mgKOH / g.

[0016] The hydroxyl group-containing acrylic resin (A) can be obtained, for example, by copolymerizing a hydroxyl group-containing polymerizable unsaturated monomer, an acid group-containing polymerizable unsaturated monomer, and other polymerizable unsaturated monomers (polymerizable unsaturated monomers other than the hydroxyl group-containing polymerizable unsaturated monomer and the acid group-containing polymerizable unsaturated monomer).

[0017] The hydroxyl-containing polymerizable unsaturated monomer is a compound having one or more hydroxyl groups and one or more polymerizable unsaturated bonds per molecule. Examples of the hydroxyl-containing polymerizable unsaturated monomer 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; adducts of (meth)acrylic acid with epoxy-containing compounds (e.g., neodecanoic acid glycidyl ester, "Cardura E10P" (trade name), manufactured by Momentive Specialty Chemicals); N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular terminal.

[0018] As the hydroxyl group-containing polymerizable unsaturated monomer, it is preferable to use a secondary hydroxyl group-containing polymerizable unsaturated monomer from the viewpoints of the pot life of the present coating material and the finished appearance of the coating film formed.

[0019] Examples of the secondary hydroxyl group-containing polymerizable unsaturated monomer include polymerizable unsaturated monomers having a secondary hydroxyl group, in which the alkyl group in the ester moiety has 2 to 8 carbon atoms, preferably 3 to 6 carbon atoms, and more preferably 3 or 4 carbon atoms, such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-hydroxybutyl (meth)acrylate; and adducts of (meth)acrylic acid and epoxy group-containing compounds (e.g., "Cardura E10P" (trade name), manufactured by Momentive Specialty Chemicals, neodecanoic acid glycidyl ester). These can be used alone or in combination of two or more. Among these, 2-hydroxypropyl (meth)acrylate is preferred from the viewpoint of the finished appearance of the coating film to be formed. The acid group-containing polymerizable unsaturated monomer is a compound having one or more acid groups and one or more polymerizable unsaturated bonds per molecule. Examples of such monomers include carboxyl group-containing monomers such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, and maleic anhydride; sulfonic acid group-containing monomers such as vinyl sulfonic acid and 2-sulfoethyl (meth)acrylate; and acidic phosphate ester monomers such as 2-(meth)acryloyloxyethyl acid phosphate, 2-(meth)acryloyloxypropyl acid phosphate, 2-(meth)acryloyloxy-3-chloropropyl acid phosphate, and 2-methacryloyloxyethylphenyl phosphoric acid. These may be used alone or in combination.

[0020] As other polymerizable unsaturated monomers copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomer and acid group-containing polymerizable unsaturated monomer, for example, the following monomers (1) to (5) can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more.

[0021] (1) Esterification products of acrylic acid or methacrylic acid with monohydric alcohols having 1 to 20 carbon atoms Specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isomyristyl (meth)acrylate, stearyl (meth)acrylate, isostearyl acrylate (trade name, manufactured by Osaka Organic Chemical Industry Ltd.), lauryl (meth)acrylate, tridecyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate.

[0022] (2) Aromatic vinyl monomers Specific examples include styrene, α-methylstyrene, and vinyltoluene. By using an aromatic vinyl monomer as a constituent component, the glass transition temperature of the resulting resin is increased, and a coating film with a high refractive index and hydrophobicity can be obtained, which can improve the gloss of the coating film and thereby the finished appearance. When an aromatic vinyl monomer is used as a constituent component, the blending ratio thereof is preferably within the range of 3 to 50 mass %, particularly 5 to 40 mass %, based on the total amount of the monomer components.

[0023] (3) Glycidyl group-containing polymerizable unsaturated monomer The glycidyl group-containing polymerizable unsaturated monomer is a compound having one or more glycidyl groups and one or more polymerizable unsaturated bonds in one molecule, and specific examples thereof include glycidyl acrylate and glycidyl methacrylate.

[0024] (4) Polymerizable unsaturated bond-containing nitrogen atom-containing compound Examples include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-[3-(dimethylamino)propyl](meth)acrylamide, N-butoxymethyl(meth)acrylamide, diacetone(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylate, vinylpyridine, vinylimidazole, acrylonitrile, and methacrylonitrile.

[0025] (5) Other vinyl compounds Examples include vinyl acetate, vinyl propionate, vinyl chloride, vinyl versatate, etc. Examples of vinyl versatate include commercially available products such as "Veoba 9" and "Veoba 10" (both trade names, manufactured by Japan Epoxy Resin Co., Ltd.).

[0026] As the other polymerizable unsaturated monomer, the monomers shown in (1) to (5) above can be used alone or in combination of two or more.

[0027] In the present invention, the polymerizable unsaturated monomer refers to a monomer having one or more (e.g., 1 to 4) polymerizable unsaturated groups. The polymerizable unsaturated group refers to an unsaturated group that can undergo radical polymerization. Examples of such polymerizable unsaturated groups include vinyl groups, (meth)acryloyl groups, (meth)acrylamide groups, vinyl ether groups, allyl groups, propenyl groups, isopropenyl groups, and maleimide groups.

[0028] In addition, in this specification, "(meth)acrylate" means acrylate or methacrylate. "(meth)acrylic acid" means acrylic acid or methacrylic acid. "(meth)acryloyl" means acryloyl or methacryloyl. "(meth)acrylamide" means acrylamide or methacrylamide.

[0029] In the production of the hydroxyl group-containing acrylic resin (A), the amount of the hydroxyl group-containing polymerizable unsaturated monomer used is preferably within the range of 15 to 55 mass %, more preferably 20 to 45 mass %, based on the total amount of copolymerizable monomer components, from the viewpoints of the water resistance and finished appearance of the coating film to be formed.

[0030] The hydroxyl value of the hydroxyl-containing acrylic resin (A) is preferably within the range of 50 to 210 mgKOH / g, particularly 80 to 200 mgKOH / g, and even more particularly 100 to 190 mgKOH / g, from the viewpoint of the water resistance and finished appearance of the coating film formed.

[0031] In the production of the hydroxyl group-containing acrylic resin (A), the amount of the acid group-containing polymerizable unsaturated monomer used is preferably within the range of 0 to 5 mass %, more preferably 0.5 to 3 mass %, based on the total amount of copolymerizable monomer components, from the viewpoints of the water resistance and finished appearance of the coating film to be formed.

[0032] Furthermore, from the viewpoint of the water resistance and finished appearance of the coating film to be formed, the weight average molecular weight of the hydroxyl group-containing acrylic resin (A) is preferably within the range of 3,000 to 10,000, more preferably within the range of 3,500 to 9,000, and even more preferably within the range of 4,000 to 8,000.

[0033] In this specification, the average molecular weight is a value calculated from a chromatogram measured by gel permeation chromatography using the molecular weight of standard polystyrene as a reference. The gel permeation chromatograph used was an "HLC8120GPC" (manufactured by Tosoh Corporation). Four columns were used: "TSKgel G-4000HXL," "TSKgel G-3000HXL," "TSKgel G-2500HXL," and "TSKgel G-2000HXL" (all manufactured by Tosoh Corporation, trade names). The analysis was performed under the following conditions: mobile phase: tetrahydrofuran, measurement temperature: 40°C, flow rate: 1 cc / min, and detector: RI.

[0034] The glass transition temperature of the hydroxyl group-containing acrylic resin (A) is preferably within the range of 0 to 70°C, particularly 10 to 60°C, and even more particularly 20 to 55°C, from the viewpoint of the water resistance and finished appearance of the coating film formed.

[0035] In this specification, the glass transition temperature (°C) of the acrylic resin was calculated by the following formula. 1 / Tg(K)=(W1 / T1)+(W2 / T2)+ (1) Tg(℃)=Tg(K)-273 (2) In each formula, W1, W2, and... represent the mass fractions of the monomers used in the copolymerization, and T1, T2, and... represent the Tg (K) of the homopolymer of each monomer. Note that T1, T2, and... are values ​​taken from pages III-139-179 of Polymer Handbook (Second Edition, edited by J. Brandup and E. H. Immergut). When the Tg of the homopolymer of a monomer is unclear, the glass transition temperature (°C) is taken as the static glass transition temperature. For example, using a differential scanning calorimeter "DSC-220U" (Seiko Instruments Inc.), a sample is placed in a measuring cup, and the solvent is completely removed by vacuum suction. Then, the heat change is measured in the range of -20°C to +200°C at a heating rate of 3°C / min. The first change point in the baseline on the low-temperature side is taken as the static glass transition temperature.

[0036] As a copolymerization method for obtaining the hydroxyl group-containing acrylic resin (A) by copolymerizing the above-mentioned polymerizable unsaturated monomer mixture, a solution polymerization method in which polymerization is carried out in an organic solvent in the presence of a polymerization initiator can be suitably used.

[0037] Examples of organic solvents used in the solution polymerization method include aromatic solvents such as toluene, xylene, and "Swasol 1000" (trade name, high-boiling point petroleum solvent, manufactured by Cosmo Oil Co., Ltd.); ester solvents such as ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2-ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol ethyl ether acetate, and propylene glycol methyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; and alcohol solvents such as isopropanol, n-butanol, isobutanol, and 2-ethylhexanol.

[0038] These organic solvents can be used alone or in combination of two or more, but from the viewpoint of the solubility of the acrylic resin, it is preferable to use ester-based solvents and ketone-based solvents. Furthermore, aromatic solvents can also be used in suitable combinations.

[0039] Examples of polymerization initiators that can be used in copolymerizing the hydroxyl group-containing acrylic resin (A) include known radical polymerization initiators such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, di-t-amyl peroxide, t-butyl peroctoate, 2,2'-azobis(2-methylbutyronitrile), and 2,2'-azobis(2,4-dimethylvaleronitrile).

[0040] The above hydroxyl group-containing acrylic resins (A) can be used alone or in combination of two or more.

[0041] From the viewpoint of the water resistance and finished appearance of the coating film formed, the content of the hydroxyl group-containing acrylic resin (A) in the high solid content coating composition of the present invention is preferably within the range of 20 to 60 parts by mass, more preferably 25 to 55 parts by mass, and even more preferably 30 to 50 parts by mass, based on 100 parts by mass of the resin solids of the high solid content coating composition.

[0042] <Hydroxyl group-containing acrylic resin (B) with an acid value in the range of 60 to 120 mgKOH / g> The hydroxyl group-containing acrylic resin (B) is an acrylic resin having at least one hydroxyl group in one molecule and an acid value within the range of 60 to 120 mgKOH / g.

[0043] An acid value in the range of 60 to 120 mgKOH / g improves the resistance to deformation of the coating film formed. In particular, the acid value of the hydroxyl group-containing acrylic resin (B) is preferably in the range of 65 to 110 mgKOH / g, and more preferably in the range of 70 to 100 mgKOH / g, from the viewpoint of the resistance to deformation of the coating film formed.

[0044] The hydroxyl group-containing acrylic resin (B) can be obtained, for example, by copolymerizing a hydroxyl group-containing polymerizable unsaturated monomer, an acid group-containing polymerizable unsaturated monomer, and other polymerizable unsaturated monomers (polymerizable unsaturated monomers other than the hydroxyl group-containing polymerizable unsaturated monomer and the acid group-containing polymerizable unsaturated monomer).

[0045] As the hydroxyl group-containing polymerizable unsaturated monomer, for example, the hydroxyl group-containing polymerizable unsaturated monomers described in the description section of the hydroxyl group-containing acrylic resin (A) can be used, and among them, from the viewpoint of the water resistance of the coating film to be formed, it is preferable to use a primary hydroxyl group-containing polymerizable unsaturated monomer.

[0046] Examples of the primary hydroxyl group-containing polymerizable unsaturated monomer include polymerizable unsaturated monomers having a primary hydroxyl group, in which the alkyl group in the ester moiety has 2 to 8 carbon atoms, preferably 2 to 6 carbon atoms, and more preferably 2 to 4 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; and adducts of (meth)acrylic acid and epoxy group-containing compounds (e.g., "Cardura E10P" (trade name), manufactured by Momentive Specialty Chemicals, neodecanoic acid glycidyl ester). These can be used alone or in combination of two or more. Among these, 2-hydroxyethyl (meth)acrylate is preferred from the viewpoint of the water resistance of the coating film to be formed.

[0047] As the acid group-containing polymerizable unsaturated monomer and other copolymerizable polymerizable unsaturated monomers, for example, the polymerizable unsaturated monomers described in the explanation section for the hydroxyl group-containing acrylic resin (A) can be used.

[0048] In the production of the hydroxyl group-containing acrylic resin (B), the amount of the hydroxyl group-containing polymerizable unsaturated monomer used is preferably within the range of 15 to 50 mass %, more preferably 20 to 40 mass %, based on the total amount of copolymerizable monomer components, from the viewpoint of the water resistance of the coating film to be formed, etc.

[0049] From the viewpoint of the water resistance of the coating film formed, the hydroxyl value of the hydroxyl-containing acrylic resin (B) is preferably within the range of 50 to 210 mgKOH / g, particularly 80 to 200 mgKOH / g, and even more particularly 100 to 190 mgKOH / g.

[0050] In the production of the hydroxyl group-containing acrylic resin (B), the amount of the acid group-containing polymerizable unsaturated monomer used is preferably within a range of 5 to 20 mass %, more preferably 7 to 15 mass %, based on the total amount of copolymerizable monomer components, from the viewpoint of the modulus resistance of the coating film to be formed.

[0051] The weight average molecular weight of the hydroxyl group-containing acrylic resin (B) is preferably within the range of 1,000 to 4,000, particularly 1,250 to 3,750, and even more particularly 1,500 to 3,500, from the viewpoint of achieving a high solid content of the coating material.

[0052] The glass transition temperature of the hydroxyl group-containing acrylic resin (B) is preferably within the range of -20 to 60°C, particularly -10 to 50°C, and more particularly 0 to 40°C, from the viewpoint of the resistance to deformation of the coating film formed.

[0053] As a copolymerization method for obtaining the hydroxyl group-containing acrylic resin (B) by copolymerizing the above-mentioned polymerizable unsaturated monomer mixture, a solution polymerization method in which polymerization is carried out in an organic solvent in the presence of a polymerization initiator can be suitably used.

[0054] Examples of organic solvents used in the solution polymerization method include aromatic solvents such as toluene, xylene, and "Swasol 1000" (trade name, high-boiling point petroleum solvent, manufactured by Cosmo Oil Co., Ltd.); ester solvents such as ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2-ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol ethyl ether acetate, and propylene glycol methyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; and alcohol solvents such as isopropanol, n-butanol, isobutanol, and 2-ethylhexanol.

[0055] These organic solvents can be used alone or in combination of two or more, but from the viewpoint of the solubility of the acrylic resin, it is preferable to use ester-based solvents and ketone-based solvents. Furthermore, aromatic solvents can also be used in suitable combinations.

[0056] Examples of polymerization initiators that can be used in copolymerizing the hydroxyl group-containing acrylic resin (B) include known radical polymerization initiators such as 2,2'-azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, di-t-amyl peroxide, t-butyl peroctoate, 2,2'-azobis(2-methylbutyronitrile), and 2,2'-azobis(2,4-dimethylvaleronitrile). The above hydroxyl group-containing acrylic resins (B) can be used alone or in combination of two or more.

[0057] From the viewpoints of high solid content of the paint and resistance to mold of the formed coating film, the content of the hydroxyl group-containing acrylic resin (B) in the high solid content paint composition of the present invention is preferably within the range of 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, and even more preferably 3 to 10 parts by mass, based on 100 parts by mass of the resin solid content of the high solid content paint composition.

[0058] From the viewpoint of forming a coating film excellent in resistance to mold and finished appearance, the content ratio of the hydroxyl-containing acrylic resin (A) and the hydroxyl-containing acrylic resin (B) in the high solids coating composition of the present invention is preferably 99 / 1 to 70 / 30, more preferably 95 / 5 to 75 / 25, and even more preferably 90 / 10 to 80 / 20, in terms of the mass ratio of hydroxyl-containing acrylic resin (A) / hydroxyl-containing acrylic resin (B).

[0059] <Polyisocyanate compound (C)> The polyisocyanate compound (C) is a compound having at least two isocyanate groups in one molecule, and examples thereof include an aliphatic polyisocyanate compound, an alicyclic polyisocyanate compound, an aromatic aliphatic polyisocyanate compound, an aromatic polyisocyanate compound, and derivatives of the polyisocyanate compounds.

[0060] Examples of the aliphatic polyisocyanate compound 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), isocyanate); and aliphatic triisocyanate compounds 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.

[0061] Examples of the alicyclic polyisocyanate compound include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: isophorone diisocyanate), 4-methyl-1,3-cyclohexylene diisocyanate (common name: hydrogenated TDI), 2-methyl-1,3-cyclohexylene diisocyanate, Alicyclic diisocyanate compounds such as 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane (common name: hydrogenated xylylene diisocyanate) or its mixture, methylenebis(4,1-cyclohexanediyl)diisocyanate (common name: hydrogenated MDI), norbornane diisocyanate; 1,3,5-triisocyanatocyclohexane, 1,3,5-trimethylisocyanatocyclohexane, 2-(3-isocyanatopropyl) -2,5-di(isocyanatomethyl)-bicyclo(2.2.1)heptane, 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-isocyanatopropyl)-bicyclo(2.2.1)heptane, Examples of such compounds include alicyclic triisocyanate compounds such as 2-isocyanatoethyl-2-isocyanatomethyl-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.

[0062] Examples of the aromatic aliphatic polyisocyanate compound include aromatic aliphatic diisocyanate compounds such as methylenebis(4,1-phenylene)diisocyanate (common name: MDI), 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 aromatic aliphatic triisocyanate compounds such as 1,3,5-triisocyanatomethylbenzene.

[0063] Examples of the aromatic polyisocyanate compound include aromatic diisocyanate compounds such as m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenyl diisocyanate, 1,5-naphthalene diisocyanate, 2,4-tolylene diisocyanate (common name: 2,4-TDI) or 2,6-tolylene diisocyanate (common name: 2,6-TDI) or mixtures thereof, 4,4'-toluidine diisocyanate, and 4,4'-diphenyl ether diisocyanate; aromatic triisocyanate compounds such as triphenylmethane-4,4',4''-triisocyanate, 1,3,5-triisocyanatobenzene, and 2,4,6-triisocyanatotoluene; and aromatic tetraisocyanate compounds such as 4,4'-diphenylmethane-2,2',5,5'-tetraisocyanate.

[0064] Furthermore, examples of derivatives of the polyisocyanate compounds 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.

[0065] The above polyisocyanate compounds and derivatives thereof may be used alone or in combination of two or more kinds.

[0066] As the polyisocyanate compound (C), from the viewpoint of the weather resistance of the coating film to be formed, it is preferable to use at least one selected from aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds and derivatives thereof, and from the viewpoint of high solid content of the resulting coating composition, and the finished appearance and scratch resistance of the coating film to be formed, it is more preferable to use an aliphatic polyisocyanate compound and / or a derivative thereof.

[0067] As the aliphatic polyisocyanate compound and / or derivative thereof, from the viewpoints of high solid content of the resulting coating composition, the finished appearance and mold resistance of the formed coating film, etc., it is preferable to use an aliphatic diisocyanate compound and / or its isocyanurate, and it is more preferable to use hexamethylene diisocyanate and / or its isocyanurate.

[0068] The polyisocyanate compound (C) may have an isocyanate group blocked with a blocking agent.

[0069] Examples of the blocking agent include phenol-based agents such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and methyl hydroxybenzoate; lactam-based agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; aliphatic alcohol-based agents such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, and lauryl alcohol; ether-based agents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and methoxymethanol; benzyl alcohol, glycolic acid, methyl glycolate, ethyl glycolate, butyl glycolate, lactic acid, methyl lactate, ethyl lactate, butyl lactate, methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate ... Alcohol-based compounds such as hydroxyethyl methacrylate; oxime-based compounds such as formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, and cyclohexane oxime; active methylene-based compounds such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone; butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, and methylthiophene mercaptans such as acetanilide, acetanisidide, acetotoluide, acrylamide, methacrylamide, acetic amide, stearic acid amide, benzamide, and other acid amides; imides such as succinimide, phthalic acid imide, and maleic acid imide; amines such as diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine, dibutylamine, and butylphenylamine; imidazoles such as imidazole and 2-ethylimidazole;Examples of suitable azole compounds include urea-based compounds such as urea, thiourea, ethyleneurea, ethylenethiourea, and diphenylurea; carbamate ester-based compounds such as N-phenylphenylcarbamate; imine-based compounds such as ethyleneimine and propyleneimine; sulfite-based compounds such as sodium bisulfite and potassium bisulfite; and azole-based compounds. Examples of suitable azole-based compounds 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.

[0070] From the viewpoint of the resistance to mold and the finished appearance of the coating film formed, the content of the polyisocyanate compound (C) in the high solid content coating composition of the present invention is preferably within the range of 5 to 60 parts by mass, more preferably 15 to 50 parts by mass, and even more preferably 25 to 45 parts by mass, based on 100 parts by mass of the resin solids of the high solid content coating composition.

[0071] <High solid content paint composition> The high solids coating composition of the present invention is a high solids coating composition characterized by containing (A) a hydroxyl group-containing acrylic resin having an acid value in the range of 0 to 30 mgKOH / g, (B) a hydroxyl group-containing acrylic resin having an acid value in the range of 60 to 120 mgKOH / g, and (C) a polyisocyanate compound, and having a solids content of 50% or more at the time of application.

[0072] The high solids coating composition of the present invention has a solids content of 50% by mass or more at the time of application, which effectively reduces VOCs. From the viewpoint of VOC reduction, the solids content at the time of application is preferably 53% by mass or more, and more preferably 55% by mass or more.

[0073] As used herein, "solid content" refers to non-volatile components, such as resins, curing agents, and pigments, contained in a paint composition that remain after the paint composition has been dried for 1 hour at 110° C. Therefore, for example, the total solid content of a paint composition can be calculated by weighing out the paint composition into a heat-resistant container such as an aluminum foil cup, spreading the paint composition on the bottom of the container, drying it for 1 hour at 110° C., weighing the mass of the components in the paint composition that remain after drying, and determining the ratio of the mass of the components that remain after drying to the total mass of the paint composition before drying.

[0074] Although the reason why the high-solids coating composition of the present invention can form coating films with excellent muddiness resistance and finished appearance is unclear, it is believed that the low acid value of the hydroxyl-containing acrylic resin (A), ranging from 0 to 30 mg KOH / g, slows the reaction rate between the hydroxyl groups contained in the resin and the polyisocyanate compound (C), allowing time for the resin to flow before curing, resulting in a good finished appearance. Furthermore, the low acid value of the hydroxyl-containing acrylic resin (A), ranging from 0 to 30 mg KOH / g, reduces the coating viscosity and enables a high solids content. Furthermore, the high acid value of the hydroxyl-containing acrylic resin (B), ranging from 60 to 120 mg KOH / g, inhibits migration of the polyisocyanate compound (C) to the lower layer, resulting in good muddiness resistance.

[0075] The high solids coating composition of the present invention preferably further contains a hydroxyl group-containing polyester resin (D) from the viewpoint of forming a coating film that is excellent in resistance to muddiness and finished appearance.

[0076] <Hydroxyl group-containing polyester resin (D)> The hydroxyl-containing polyester resin (D) can generally be obtained by esterifying a polyhydric alcohol and a polybasic acid with an excess of hydroxyl groups by a method known per se. The polyhydric alcohol is a compound having two or more hydroxyl groups per molecule, and the polybasic acid is a compound having two or more carboxyl groups per molecule.

[0077] Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, and 2,3-dimethyl- Dihydric alcohols such as dimethylmethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-4,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, and hydroxypivalic acid neopentyl glycol ester; polylactohydric alcohols obtained by adding lactones such as ε-caprolactone to these dihydric alcohols; diols; ester diols such as bis(hydroxyethyl) terephthalate; polyether diols such as alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, and polybutylene glycol; α-olefin epoxides such as propylene oxide and butylene oxide, and monoepoxy compounds such as Cardura E10 [product name, glycidyl ester of synthetic highly branched saturated fatty acid, manufactured by Shell Chemical Co., Ltd.]; trihydric or higher alcohols such as glycerin, trimethylolpropane, trimethylolethane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, and mannitol; polylactone polyols obtained by adding lactones such as ε-caprolactone to these trihydric or higher alcohols; alicyclic polyhydric alcohols such as 1,4-cyclohexanedimethanol, tricyclodecanedimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol A, and hydrogenated bisphenol F;Examples include cyclic polyol compounds having a nurate structure such as tris(hydroxyalkyl) isocyanurate, ε-caprolactone-modified tris(hydroxyalkyl) isocyanurate, and tris(hydroxyethyl) isocyanurate. The above polyhydric alcohols can be used alone or in combination of two or more kinds.

[0078] Examples of the polybasic acid include aromatic polybasic acids such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and diphenylmethane-4,4'-dicarboxylic acid, and anhydrides thereof; alicyclic dicarboxylic acids such as hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid, and tetrahydrophthalic acid, and anhydrides thereof; adipic acid, sebacic acid, suberic acid, succinic acid, glutaric acid, maleic acid, and chloromaleic acid. aliphatic polybasic acids and anhydrides thereof, such as carboxylic acid, fumaric acid, dodecanedioic acid, pimelic acid, azelaic acid, itaconic acid, citraconic acid, and dimer acid; lower alkyl esters, such as methyl esters and ethyl esters, of these dicarboxylic acids; and tri- or higher valent polybasic acids, such as trimellitic acid, trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, trimesic acid, methylcyclohexene tricarboxylic acid, and tetrachlorohexene polybasic acid and anhydrides thereof. The above polybasic acids can be used alone or in combination of two or more.

[0079] Furthermore, a compound having at least one hydroxyl group and at least one carboxyl group in one molecule can also be used as a reaction component for the hydroxyl group-containing polyester resin (D).

[0080] Examples of the compound having at least one hydroxyl group and at least one carboxyl group in one molecule include malic acid, citric acid, tartaric acid, dimethylolpropionic acid, dimethylolbutanoic acid, lactic acid, etc. Among these, from the viewpoint of the finished appearance of the coating film to be formed, a compound having two hydroxyl groups and one carboxyl group in one molecule is preferred.

[0081] When the compound having at least one hydroxyl group and at least one carboxyl group in one molecule is used as a reaction component for the hydroxyl group-containing polyester resin (D), it is preferable to use a monoepoxide compound having a hydrocarbon group having 4 or more carbon atoms in combination, from the viewpoint of the water resistance of the coating film to be formed.

[0082] Examples of the monoepoxide compound having a hydrocarbon group having 4 or more carbon atoms include pivalic acid glycidyl ester, hexanoic acid glycidyl ester, cyclohexanecarboxylic acid glycidyl ester, 2-ethylhexanoic acid glycidyl ester, isononanoic acid glycidyl ester, decanoic acid glycidyl ester, undecanoic acid glycidyl ester, lauric acid glycidyl ester, myristic acid glycidyl ester, palmitic acid glycidyl ester, stearic acid glycidyl ester, Cardura E10P (manufactured by Japan Epoxy Resins Co., Ltd.), and neodecanoic acid monoglycidyl ester. Examples of suitable glycidyl esters include glycidyl esters of aliphatic carboxylic acids such as butyl glycidyl ether and decyl glycidyl ether; alkyl glycidyl ethers such as butyl glycidyl ether and decyl glycidyl ether; aryl glycidyl ether such as phenyl glycidyl ether; and α-olefin monoepoxides such as styrene oxide and AOEX24 (manufactured by Daicel Chemical Industries, Ltd., α-olefin monoepoxide mixture). Among these, it is preferable to use a monoepoxide compound having a hydrocarbon group with 6 to 20 carbon atoms, and it is even more preferable to use a glycidyl ester compound having a hydrocarbon group with 6 to 20 carbon atoms.

[0083] From the viewpoint of the finished appearance of the coating film to be formed, the hydroxyl value of the hydroxyl-containing polyester resin (D) is preferably within the range of 50 to 210 mgKOH / g, particularly 80 to 200 mgKOH / g, and even more particularly 100 to 190 mgKOH / g.

[0084] From the viewpoint of the finished appearance of the coating film to be formed, the acid value of the hydroxyl group-containing polyester resin (D) is preferably 20 mgKOH / g or less, particularly 10 mgKOH / g or less, and even more particularly 5 mgKOH / g or less. The number average molecular weight of the hydroxyl group-containing polyester resin (D) is preferably within the range of 500 to 6,000, particularly 750 to 5,000, and even more particularly 1,000 to 4,500, from the viewpoint of the finished appearance of the coating film to be formed.

[0085] When the high solids coating composition of the present invention contains the above-mentioned hydroxyl group-containing polyester resin (D), the content thereof is preferably within the range of 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, and even more preferably 3 to 10 parts by mass, based on 100 parts by mass of the resin solids of the high solids coating composition, from the viewpoints of the resistance to mold and the finished appearance of the coating film to be formed.

[0086] <Other ingredients> The high solids coating composition of the present invention may further contain, as necessary, resins other than those mentioned above, crosslinking agents other than the polyisocyanate compound (C), pigments, organic solvents, curing catalysts, dispersants, anti-settling agents, antifoaming agents, thickeners, ultraviolet absorbers, light stabilizers, surface conditioners, scratch resistance improvers, etc.

[0087] Examples of resins other than those mentioned above include acrylic resins other than the hydroxyl group-containing acrylic resin (A) and the hydroxyl group-containing acrylic resin (B) that may contain hydroxyl groups, polyester resins that do not contain hydroxyl groups, polyurethane resins that may contain hydroxyl groups, polyether resins that may contain hydroxyl groups, polycarbonate resins that may contain hydroxyl groups, and epoxy resins that may contain hydroxyl groups.

[0088] Examples of the crosslinking agent other than the polyisocyanate compound (C) include melamine resins.

[0089] The melamine resin may be a partially methylolated melamine resin or a fully methylolated melamine resin obtained by reacting a melamine component with an aldehyde component, such as formaldehyde, paraformaldehyde, acetaldehyde, or benzaldehyde.

[0090] Alternatively, the methylolated melamine resin may be partially or completely etherified with an appropriate alcohol, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethyl-1-butanol, or 2-ethyl-1-hexanol.

[0091] As the melamine resin, preferred are methyl-etherified melamine resins in which the methylol groups of a partially or fully methylolated melamine resin have been partially or completely etherified with methyl alcohol, butyl-etherified melamine resins in which the methylol groups of a partially or fully methylolated melamine resin have been partially or completely etherified with butyl alcohol, and methyl-butyl mixed etherified melamine resins in which the methylol groups of a partially or fully methylolated melamine resin have been partially or completely etherified with methyl alcohol and butyl alcohol.

[0092] The melamine resin preferably has a weight average molecular weight in the range of 400 to 6,000, more preferably in the range of 500 to 5,000, and even more preferably in the range of 800 to 4,000.

[0093] As the melamine resin (D), commercially available products can be used. Examples of commercially available product names include "Cymel 202", "Cymel 203", "Cymel 238", "Cymel 251", "Cymel 303", "Cymel 323", "Cymel 324", "Cymel 325", "Cymel 327", "Cymel 350", "Cymel 385", "Cymel 1156", "Cymel 1158", "Cymel 1116", and "Cymel 1130" (all manufactured by Allnex Japan Co., Ltd.), "U-Van 120", "U-Van 20HS", "U-Van 20SE60", "U-Van 2021", "U-Van 2028", and "U-Van 28-60" (all manufactured by Mitsui Chemicals, Inc.). The above melamine resins can be used either alone or in combination of two or more.

[0094] When the high solid content coating composition of the present invention contains a melamine resin, the content thereof is preferably within the range of 1 to 30 parts by mass, more preferably 2 to 25 parts by mass, and even more preferably 3 to 20 parts by mass, based on 100 parts by mass of the resin solids of the high solid content coating composition, from the viewpoint of the scratch resistance of the coating film formed, etc.

[0095] Examples of the pigment include color pigments, luster pigments, extender pigments, etc. The pigments can be used alone or in combination of two or more.

[0096] Examples of color pigments include titanium oxide, zinc oxide, carbon black, cadmium red, molybdenum red, chrome yellow, chromium oxide, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, threne pigments, and perylene pigments.

[0097] Examples of the luster pigment include aluminum powder, mica powder, and mica powder coated with titanium oxide.

[0098] Examples of extender pigments include talc, clay, kaolin, baryta, barium sulfate, barium carbonate, calcium carbonate, and alumina white.

[0099] Each of the above pigments can be used alone or in combination of two or more.

[0100] When the high solids coating composition of the present invention is used as a clear coating and contains a pigment, the amount of pigment is preferably an amount that does not impair the transparency of the resulting coating film; for example, it is preferably usually within the range of 0.1 to 20 mass %, particularly 0.3 to 10 mass %, and even more particularly 0.5 to 5 mass %, relative to the total solids content of the high solids coating composition.

[0101] Furthermore, when the high solid content coating composition of the present invention is used as a colored coating and contains a pigment, the amount of the pigment to be blended is preferably usually within the range of 1 to 200 mass%, particularly 2 to 100 mass%, and even more particularly 5 to 50 mass%, relative to the total amount of solids in the high solid content coating composition.

[0102] Examples of organic solvents include aromatic solvents such as toluene, xylene, and "Swasol 1000" (trade name, high-boiling petroleum solvent, manufactured by Cosmo Oil Co., Ltd.); ester solvents such as ethyl acetate, butyl acetate, propyl propionate, butyl propionate, 1-methoxy-2-propyl acetate, 2-ethoxyethyl propionate, ethyl-3-ethoxypropionate, 3-methoxybutyl acetate, ethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether acetate, and propylene glycol monomethyl ether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; and alcohol solvents such as isopropanol, n-butanol, isobutanol, and 2-ethylhexanol. These may be used alone or in combination of two or more. Examples of curing catalysts include tin octylate, dibutyltin diacetate, dibutyltin di(2-ethylhexanoate), dibutyltin dilaurate, dioctyltin diacetate, dioctyltin di(2-ethylhexanoate), dibutyltin oxide, dibutyltin sulfide, dioctyltin oxide, dibutyltin fatty acid salts, lead 2-ethylhexanoate, zinc octylate, zinc naphthenate, zinc fatty acids, bismuth octanoate, bismuth 2-ethylhexanoate, bismuth oleate, bismuth neodecanoate, and bismuth versatate. organic metal compounds such as bismuth naphthenate, cobalt naphthenate, calcium octoate, copper naphthenate, and tetra(2-ethylhexyl)titanate; sulfonic acids such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, and dinonylnaphthalenesulfonic acid; alkyl phosphates such as monobutyl phosphate, dibutyl phosphate, mono(2-ethylhexyl)phosphate, and di(2-ethylhexyl)phosphate; and salts of these acids with amine compounds, and these can be used either alone or in combination of two or more.

[0103] When the high solid content coating composition of the present invention contains the above-mentioned curing catalyst, the content of the curing catalyst is preferably in the range of 0.005 to 2 mass %, particularly 0.01 to 1 mass %, relative to the total solid content of the high solid content coating composition of the present invention.

[0104] As the thickener, conventionally known thickeners can be used, and examples thereof include clay minerals (e.g., metal silicates, montmorillonite), acrylics (e.g., those containing a structure consisting of an acrylic acid ester or methacrylic acid ester polymer or oligomer in the molecule), polyolefins (e.g., polyethylene, polypropylene, etc.), amides (higher fatty acid amides, polyamides, oligomers, etc.), polycarboxylic acids (including derivatives having at least two carboxyl groups in the molecule), cellulose (including various derivatives such as nitrocellulose, acetyl cellulose, cellulose ether, etc.), urethanes (polymers, oligomers, etc. containing a urethane structure in the molecule), ureas (polymers, oligomers, etc. containing a urea structure in the molecule), and urethane ureas (polymers, oligomers, etc. containing a urethane structure and a urea structure in the molecule).

[0105] As the ultraviolet absorber, conventionally known ones can be used, for example, ultraviolet absorbers such as benzotriazole-based absorbers, triazine-based absorbers, salicylic acid derivative-based absorbers, benzophenone-based absorbers, etc. These can be used alone or in combination of two or more kinds.

[0106] When the high solid content coating composition of the present invention contains an ultraviolet absorber, the amount of the ultraviolet absorber is preferably in the range of usually 0.1 to 10 mass %, particularly 0.2 to 5 mass %, and even more particularly 0.3 to 2 mass %, relative to the total amount of solids in the high solid content coating composition.

[0107] As the light stabilizer, a conventionally known light stabilizer can be used, for example, a hindered amine light stabilizer.

[0108] As the hindered amine light stabilizer, from the viewpoint of pot life, a hindered amine light stabilizer with low basicity can be preferably used. Examples of such hindered amine light stabilizers include acylated hindered amines and aminoether hindered amines, and specific examples include "HOSTAVIN 3058" (trade name, manufactured by Clariant) and "TINUVIN 123" (trade name, manufactured by BASF).

[0109] The application method for the high solids coating composition of the present invention is not particularly limited, and examples thereof include air spray coating, airless spray coating, rotary atomization coating, and curtain coating, and wet coating films can be formed by these methods. These coating methods may also employ electrostatic application, if necessary. Of these, air spray coating and rotary atomization coating are particularly preferred. The coating amount of the present coating material is generally preferably an amount that results in a cured film thickness of 10 to 60 μm, particularly 25 to 50 μm.

[0110] When air spray coating, airless spray coating or rotary atomization coating is used, it is preferable to adjust the viscosity of the paint appropriately using a solvent such as an organic solvent and a thickener so that the viscosity is within a range suitable for the coating, usually 15 to 60 seconds, particularly 20 to 40 seconds, at 20°C as measured using a Ford Cup No. 4 viscometer.

[0111] The wet coating film formed by applying the present coating material to the substrate can be cured by heating, and heating can be carried out by known heating means, such as a drying oven such as a hot air oven, electric oven, or infrared induction heating oven. The heating temperature is not particularly limited, but is suitably within the range of, for example, 60 to 160°C, preferably 80 to 140°C. The heating time is not particularly limited, but is suitably within the range of, for example, 10 to 60 minutes, preferably 15 to 30 minutes.

[0112] The high solids paint composition of the present invention can form a paint film that is excellent in resistance to smudges and in finished appearance, and is therefore suitable for use as a top clear coat paint. This paint is particularly suitable for use as an automotive paint.

[0113] <Method for forming multi-layer coating film> As a method for forming a multi-layer coating film in which the present coating material is applied as a top clear coat coating material, for example, the following method can be suitably used. The following steps (1) to (3): Step (1): A step of applying a glitter coating composition to an object to be coated to form a glitter coating film; Step (2): A step of applying the high solids coating composition of the present invention onto the glossy coating film obtained in Step (1) to form a clear coating film; Step (3): A method for forming a multilayer coating film, comprising a step of simultaneously curing the multilayer coating film including the glossy coating film and the clear coating film formed in steps (1) and (2) by heating the multilayer coating film.

[0114] The substrate is not particularly limited, and examples thereof include outer panels of automobile bodies such as passenger cars, trucks, motorcycles, and buses; automobile parts; and outer panels of household electrical appliances such as mobile phones and audio equipment. Of these, outer panels of automobile bodies and automobile parts are preferred.

[0115] The material of these substrates is not particularly limited. Examples include metal materials such as iron, aluminum, brass, copper, tinplate, stainless steel, zinc-plated steel, and zinc alloy (Zn-Al, Zn-Ni, Zn-Fe, etc.)-plated steel; resins such as polyethylene resin, polypropylene resin, acrylonitrile-butadiene-styrene (ABS) resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, and epoxy resin; plastic materials such as various FRPs; inorganic materials such as glass, cement, and concrete; wood; and fibrous materials such as paper and cloth. Among these, metal materials and plastic materials are preferred.

[0116] Furthermore, the surface of the object to which the multilayer coating film is applied may be a metal surface such as an outer panel of an automobile body, an automobile part, a household electrical appliance, or a metal substrate such as the steel plate that constitutes these, which has been subjected to a surface treatment such as phosphate treatment, chromate treatment, or composite oxide treatment.

[0117] A coating film may be further formed on an object that may or may not have been surface-treated. For example, a substrate to be coated may be subjected to a surface treatment as needed, and a primer coating film and / or intermediate coating film may be formed thereon. For example, when the substrate to be coated is an automobile body, the primer coating film and / or intermediate coating film may be formed using a known primer and / or intermediate coating composition that is commonly used in painting automobile bodies.

[0118] The undercoat paint composition for forming the undercoat paint film can be, for example, an electrodeposition paint, preferably a cationic electrodeposition paint. The intermediate paint composition for forming the intermediate paint film can be, for example, a paint prepared by mixing a base resin having a crosslinkable functional group such as a carboxyl group, a hydroxyl group, or the like, such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin, or an epoxy resin, with a crosslinking agent such as an amino resin such as a melamine resin or a urea resin, or an optionally blocked polyisocyanate compound, together with a pigment, a thickener, and optionally other components.

[0119] The glitter coating composition can be a known thermosetting glitter coating composition for use in coating automobile bodies, etc. As the glitter coating composition, for example, a thermosetting coating composition containing a base resin having a crosslinkable functional group, a crosslinking agent, and a glitter pigment can be suitably used.

[0120] The above-mentioned glitter coating composition is usually applied for the purpose of imparting excellent design properties (for example, color, metallic appearance, gloss, etc.) to the substrate.

[0121] Examples of the crosslinkable functional group contained in the base resin include a carboxyl group, a hydroxyl group, and an epoxy group.

[0122] Examples of the base resin include acrylic resin, polyester resin, alkyd resin, and urethane resin.

[0123] Examples of the crosslinking agent include melamine resins, polyisocyanate compounds, and blocked polyisocyanate compounds.

[0124] Examples of the bright pigment include aluminum powder, mica powder, and mica powder coated with titanium oxide.

[0125] The glittering coating composition may be either an aqueous coating composition or an organic solvent-based coating composition, but from the viewpoint of reducing the environmental load, an aqueous coating composition is preferred.

[0126] The amount of the glittering coating composition to be applied is preferably an amount that results in a cured film thickness of 5 to 40 μm, more preferably an amount that results in a cured film thickness of 6 to 35 μm, and even more preferably an amount that results in a cured film thickness of 7 to 30 μm.

[0127] The heating can be carried out by known means, for example, a drying oven such as a hot air oven, an electric oven, or an infrared induction heating oven. The heating temperature is preferably 60 to 180° C., more preferably 70 to 170° C., and even more preferably 80 to 160° C. The heating time is not particularly limited, but is preferably in the range of 10 to 40 minutes, and more preferably in the range of 20 to 40 minutes. [Example]

[0128] 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.

[0129] [1] Preparation of the object to be coated A degreased and zinc phosphate-treated steel plate (JIS G3141, size 400 mm x 300 mm x 0.8 mm) was electrodeposited with the cationic electrodeposition paint "Elecron GT-10" (product name: manufactured by Kansai Paint Co., Ltd., an epoxy resin polyamine-based cationic resin using a blocked polyisocyanate compound as a curing agent) to a film thickness of 20 μm based on the cured coating, and heated at 170°C for 20 minutes to crosslink and cure, forming an electrodeposition coating. The resulting electrodeposition coating surface of the steel plate was electrostatically coated with "WP-523H" (product name, manufactured by Kansai Paint Co., Ltd., an acrylic-melamine resin-based water-based intermediate coating composition) using a rotary atomizer electrostatic coating machine to a cured film thickness of 20 μm, and then left for 5 minutes to form an uncured intermediate coating film, thereby preparing the coated object.

[0130] [2] Preparation of paint <Production of Hydroxyl Group-Containing Acrylic Resin (A)> Manufacturing Example 1 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device was charged with 27 parts of "Swasol 1000" (trade name, Cosmo Oil Co., Ltd., aromatic organic solvent) and 5 parts of propylene glycol monomethyl ether acetate. While nitrogen gas was blown into the reaction vessel, the charged solution was stirred at 150°C. A monomer mixture consisting of 20 parts of styrene, 32.5 parts of 2-hydroxypropyl acrylate, 46.8 parts of isobutyl methacrylate, 0.7 parts of acrylic acid, and 3.5 parts of di-tertiary amyl peroxide (polymerization initiator) was added dropwise at a uniform rate over 4 hours. The mixture was then aged at 150°C for 1 hour, cooled, and further diluted with 21 parts of isobutyl acetate to obtain a hydroxyl-containing acrylic resin (A-1) solution with a solids concentration of 65%. The resulting hydroxyl-containing acrylic resin (A-1) had an acid value of 5.5 mgKOH / g, a hydroxyl value of 140 mgKOH / g, a weight average molecular weight of 7,500, and a glass transition temperature of 38°C.

[0131] Manufacturing Examples 2-4 Solutions of hydroxyl-containing acrylic resins (A-2) to (A-4) with a solid content concentration of 65% were obtained in the same manner as in Production Example 1, except that the blending compositions in Production Example 1 were as shown in Table 1. The acid value, hydroxyl value, weight-average molecular weight, and glass transition temperature of each hydroxyl-containing acrylic resin are also shown in Table 1.

[0132] [Table 1]

[0133] <Production of Hydroxyl Group-Containing Acrylic Resin (B)> Production Example 5 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device was charged with 27 parts of "Swasol 1000" (trade name, Cosmo Oil Co., Ltd., aromatic organic solvent) and 5 parts of propylene glycol monomethyl ether acetate. While nitrogen gas was blown into the reaction vessel, the charged solution was stirred at 150°C. A monomer mixture consisting of 13.7 parts of 2-ethylhexyl methacrylate, 40 parts of 2-hydroxyethyl methacrylate, 38 parts of isobutyl acrylate, 8.3 parts of acrylic acid, and 6.5 parts of di-tertiary amyl peroxide (polymerization initiator) was added dropwise at a uniform rate over 4 hours. The mixture was then aged at 150°C for 1 hour, cooled, and further diluted with 21 parts of isobutyl acetate to obtain a hydroxyl group-containing acrylic resin (B-1) solution with a solids concentration of 65%. The resulting hydroxyl-containing acrylic resin (B-1) had an acid value of 64.7 mgKOH / g, a hydroxyl value of 173 mgKOH / g, a weight average molecular weight of 3,500, and a glass transition temperature of 15°C.

[0134] Manufacturing Examples 6-8 Solutions of hydroxyl-containing acrylic resins (B-2) to (B-4) with a solid content concentration of 65% were obtained in the same manner as in Production Example 5, except that the blending compositions in Production Example 5 were as shown in Table 2. The acid value, hydroxyl value, weight average molecular weight, and glass transition temperature of each hydroxyl-containing acrylic resin are also shown in Table 2.

[0135] [Table 2]

[0136] <Production of Hydroxyl-Containing Acrylic Resin (E) Other than Hydroxyl-Containing Acrylic Resin (A) and Hydroxyl-Containing Acrylic Resin (B)> Manufacturing Example 9 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device was charged with 27 parts of "Swasol 1000" (trade name, Cosmo Oil Co., Ltd., aromatic organic solvent) and 5 parts of propylene glycol monomethyl ether acetate. While nitrogen gas was blown into the reaction vessel, the charged solution was stirred at 150°C. A monomer mixture consisting of 25 parts of styrene, 17.5 parts of 2-hydroxypropyl acrylate, 17.5 parts of 2-hydroxyethyl methacrylate, 34.8 parts of 2-ethylhexyl methacrylate, 5.2 parts of acrylic acid, and 5 parts of di-tertiary amyl peroxide (polymerization initiator) was added dropwise at a uniform rate over 4 hours. The mixture was then aged at 150°C for 1 hour, cooled, and further diluted with 21 parts of isobutyl acetate to obtain a hydroxyl-containing acrylic resin (E-1) solution with a solids concentration of 65%. The resulting hydroxyl group-containing acrylic resin (E-1) had an acid value of 40.5 mgKOH / g, a hydroxyl value of 151 mgKOH / g, a weight average molecular weight of 5,000, and a glass transition temperature of 28°C.

[0137] <Production of Hydroxyl Group-Containing Polyester Resin (D)> Manufacturing Example 10 A reactor equipped with a stirrer, reflux condenser, water separator, and thermometer was charged with 100.1 parts of hexahydrophthalic anhydride and 118 parts of 1,6-hexanediol, and the mixture was reacted at 230°C for 6 hours. The mixture was then diluted with butyl acetate to obtain a solution of hydroxyl-containing polyester resin (D-1) with a solids concentration of 80%. The resulting hydroxyl-containing polyester resin (D-1) had an acid value of 2 mgKOH / g, a hydroxyl value of 192 mgKOH / g, and a number average molecular weight of 578.

[0138] Manufacturing Example 11 A reactor equipped with a stirrer, reflux condenser, and thermometer was charged with 148 parts of dimethylolbutanoic acid, 735 parts of "Cardura E10P" (trade name, manufactured by Momentive Specialty Chemicals, neodecanoic acid monoglycidyl ester), and 308 parts of hexahydrophthalic anhydride, and the mixture was allowed to react at 190°C for 3 hours. After this, 342 parts of ε-caprolactone was added and the mixture was allowed to react at 190°C for 3 hours. The mixture was then diluted with butyl acetate to obtain a hydroxyl-containing polyester resin (D-2) solution with a solids concentration of 80%. The resulting hydroxyl-containing polyester resin (D-2) had an acid value of 4 mgKOH / g, a hydroxyl value of 120 mgKOH / g, and a number average molecular weight of 1,529.

[0139] <Production of high solids coating composition> Example 1 A mixture of 76.9 parts (50 parts solids) of the hydroxyl-containing acrylic resin (A-1) solution obtained in Production Example 1, 12.3 parts (8 parts solids) of the hydroxyl-containing acrylic resin (B-2) solution obtained in Production Example 6, 0.5 parts (0.3 parts solids) of "SETALUX 61767 VX-60" (trade name, manufactured by Allnex Corporation, viscosity modifier, 60% solids), and 0.4 parts (0.2 parts solids) of "BYK-300" (trade name, manufactured by BYK-Chemie Corporation, surface modifier, 52% active ingredient) was homogeneously mixed to form a base resin, and 42 parts of the curing agent "Sumidur N3300" (trade name, manufactured by Sumika Covestro Urethane Co., Ltd., isocyanurate of hexamethylene diisocyanate, solids content 100%) were mixed homogeneously just before application, and butyl acetate was added to adjust the solids content at application to 58%, yielding high solids coating composition No. 1.

[0140] Examples 2 to 13 and Comparative Examples 1 to 4 High solid content coating compositions Nos. 2 to 17 were obtained in the same manner as high solid content coating composition No. 1, except that the blending compositions and solid contents at the time of application were as shown in the following Tables 3 to 5. The blending compositions shown in Tables 3 to 5 are based on the solid content by mass of each component.

[0141] <Creating test panels> On the substrate prepared in [1] above, "WBC-713T No. 1F7" (product name, Kansai Paint Co., Ltd., acrylic-melamine resin-based water-based base coat paint, silver paint color) was electrostatically coated using a rotary atomizing electrostatic coater so that the dry film thickness was 12 μm. After leaving it for 3 minutes, it was preheated at 80°C for 5 minutes to form an uncured base coat film. Next, high solids paint composition No. 1 was electrostatically applied onto the uncured base coat film using a rotary atomizer electrostatic coater to form a clear coat film with a dry film thickness of 35 μm, and the applied film was left for 7 minutes.Then, the intermediate coat film, base coat film, and clear coat film were heat-cured by heating at 140°C for 30 minutes to prepare the test panel of Example 1. In preparing the test panels of the above-mentioned high solid content coating composition No. 1, the test panels of Examples 2 to 13 and Comparative Examples 1 to 4 were prepared in the same manner as in preparing the test panels of high solid content coating composition No. 1, except that high solid content coating composition No. 1 was replaced by any of high solid content coating compositions Nos. 2 to 17. Each test panel obtained above was evaluated by the following test methods. The evaluation results are shown in Tables 3 to 5 together with the coating composition.

[0142] (Test Method) Finished appearance: The finished appearance was evaluated based on the Long Wave (LW) value and Short Wave (SW) value measured by Wave Scan (trade name, manufactured by BYK Gardner).

[0143] LW value: An index of smoothness. The smaller the LW value, the smoother the coating surface. A value of 7 or less is considered a pass.

[0144] SW value: An index of image clarity. The smaller the SW value, the higher the image clarity of the coating surface. A value of 18 or less is considered a pass.

[0145] Modification resistance: Using a multi-angle spectrophotometer "MA-68II" (trade name, manufactured by X-Rite), the L value (brightness) was measured at a light receiving angle of 15° and a light receiving angle of 110°, and the flip-flop value was calculated using the following formula, which was used as an index of modification resistance. The higher the flip-flop value, the better the aluminum orientation and the better the modification resistance. A value of 86 or higher is considered acceptable. Flip-flop value = L value at 15° acceptance angle - L value at 110° acceptance angle

[0146] [Table 3]

[0147] [Table 4]

[0148] [Table 5]

[0149] Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical concept of the present invention are possible. For example, the configurations, methods, processes, shapes, materials, and numerical values ​​given in the above-described embodiments and examples are merely examples, and different configurations, methods, processes, shapes, materials, and numerical values ​​may be used as necessary. Furthermore, the configurations, methods, steps, shapes, materials, and numerical values ​​of the above-described embodiments can be combined with one another without departing from the spirit of the present invention.

[0150] This application is based on a Japanese patent application (Patent Application No. 2020-191308) filed on November 18, 2020, the contents of which are incorporated herein by reference.

Claims

1. (A) a hydroxyl group-containing acrylic resin having an acid value in the range of 1 to 30 mgKOH / g; (B) a hydroxyl group-containing acrylic resin having an acid value in the range of 60 to 120 mgKOH / g, and (C) containing a polyisocyanate compound, A high solids coating composition for top clear coat, having a solids content of 50% by mass or more when applied, the content of the hydroxyl group-containing acrylic resin (A) is 20 to 60 parts by mass based on 100 parts by mass of the resin solids of the high solid content coating composition, the content of the hydroxyl group-containing acrylic resin (B) is 1 to 20 parts by mass based on 100 parts by mass of the resin solids of the high solid content coating composition, the content of the polyisocyanate compound (C) is 5 to 60 parts by mass based on 100 parts by mass of the resin solid content of the high solid content coating composition, the hydroxyl value of the hydroxyl-containing acrylic resin (A) is 50 to 210 mgKOH / g; the hydroxyl value of the hydroxyl-containing acrylic resin (B) is 50 to 210 mgKOH / g; the content ratio of the hydroxyl group-containing acrylic resin (A) and the hydroxyl group-containing acrylic resin (B) is 95 / 5 to 70 / 30 in terms of a mass ratio of the hydroxyl group-containing acrylic resin (A) / the hydroxyl group-containing acrylic resin (B); A high solids coating composition for top clear coat, characterized in that:

2. 2. The high solids paint composition for top clear coat according to claim 1, wherein the weight average molecular weight of said hydroxyl group-containing acrylic resin (A) is within the range of 3,000 to 10,000.

3. 3. The high solids paint composition for top clear coat according to claim 1, wherein the weight average molecular weight of the hydroxyl group-containing acrylic resin (B) is within the range of 1,000 to 4,000.

4. 4. The high solids coating composition for top clear coat application according to claim 1, further comprising a hydroxyl group-containing polyester resin (D).

5. The following steps (1) to (3): Step (1): A step of applying a glitter coating composition to a substrate to form a glitter coating film; Step (2): A step of applying the high solids coating composition for top clear coat according to any one of claims 1 to 4 onto the glossy coating film obtained in step (1) to form a clear coating film; Step (3): A method for forming a multilayer coating film, comprising the step of simultaneously curing the multilayer coating film including the glossy coating film and the clear coating film formed in steps (1) and (2) by heating the multilayer coating film.

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