High solids content paint composition and method for forming multi-layer paint 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 that has a glass transition temperature (Tg) in the range of 20-70°C and a weight average molecular weight in the range of 3,000-10,000; (B) a hydroxyl group-containing polyester resin that is the reaction product of a polyfunctional compound (b1) which has a total of at least three carboxyl groups and hydroxyl groups in each molecule, a monoepoxide compound (b-2) which contains a hydrocarbon group having at least four carbon atoms, and a caprolactone compound (b-3); 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, for topcoat clear paints, particularly high levels of coating film performance (scratch resistance, hardness, water resistance, etc.) and finished appearance are required, so solvent-based clear paints are still the norm.

[0005] One method of reducing VOCs without using water-based clear paints is to increase the solids content of the paint (increasing the solids concentration).

[0006] 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.

[0007] Furthermore, Patent Document 2 discloses a topcoat paint composition containing, as essential components, a vinyl copolymer containing a side chain with a specific group (a lactone-modified hydroxyl group), an alkoxymonomeric melamine, a blocked isocyanate, and a rheology control agent. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2002-201430 [Patent Document 2] Japanese Patent Publication No. 2002-020682 Summary of the Invention [Problem to be solved by the invention]

[0009] However, although the coating composition described in Patent Document 1 has high hardness, it is insufficient in scratch resistance, water resistance and finish. Furthermore, the topcoat paint composition described in Patent Document 2 has good scratch resistance, but is insufficient in hardness, water resistance and finish.

[0010] An object of the present invention is to provide a high solids coating composition capable of forming a coating film that is excellent in hardness, scratch resistance, water resistance and finished appearance. [Means for solving the problem]

[0011] 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 a glass transition temperature (Tg) in the range of 20 to 70°C and a weight-average molecular weight in the range of 3,000 to 10,000; (B) a hydroxyl-containing polyester resin which is a reaction product of a polyfunctional compound (b-1) having a total of three or more carboxyl groups and three or more hydroxyl groups per molecule, a monoepoxide compound (b-2) having a hydrocarbon group of four or more carbon atoms, and a caprolactone compound (b-3); and (C) a polyisocyanate compound, and which has a solids content of 50 mass% or more when applied.

[0012] According to the present invention, there is provided a high solids coating composition comprising the following aspects:

[0013] Item 1. A high solids coating composition comprising: (A) a hydroxyl-containing acrylic resin having a glass transition temperature (Tg) in the range of 20 to 70°C and a weight-average molecular weight in the range of 3,000 to 10,000; (B) a hydroxyl-containing polyester resin which is a reaction product of a polyfunctional compound (b-1) having a total of three or more carboxyl groups and hydroxyl groups in one molecule, a monoepoxide compound (b-2) having a hydrocarbon group of four or more carbon atoms, and a caprolactone compound (b-3); and (C) a polyisocyanate compound, and wherein the solids content at the time of coating is 50 mass% or more. Item 2. The high solids coating composition according to Item 1, wherein the hydroxyl-containing acrylic resin (A) comprises a hydroxyl-containing acrylic resin (A') containing an alkoxysilyl group. Item 3. The high solids coating composition according to Item 1 or 2, wherein the hydroxyl group-containing polyester resin (B) has an acid value of 30 mgKOH / g or less. Item 4. The high solids coating composition according to any one of Items 1 to 3, wherein the polyfunctional compound (b-1) having a total of three or more carboxyl groups and hydroxyl groups is a compound having one carboxyl group and two hydroxyl groups. Item 5. The high solids coating composition according to any one of Items 1 to 4, wherein the hydroxyl group-containing polyester resin (B) further contains a polybasic acid compound (b-4) as a reaction component. Item 6. Step (1): A step of applying an intermediate coating composition to an object to be coated to form an intermediate coating film; Step (2): A step of applying a base coat paint composition onto the intermediate coating film formed in step (1) to form a base coat coating film; Step (3): A step of applying the high solids coating composition according to any one of items 1 to 5 onto the base coat coating film formed in step (2) to form a clear coat coating film; and Step (4): A method for forming a multi-layer coating film, comprising a step of simultaneously heating and curing the intermediate coating film, base coating film, and clear coating film formed in steps (1) to (3). [Effects of the Invention]

[0014] The high solids coating composition of the present invention is capable of forming a coating film that is excellent in hardness, scratch resistance, water resistance and finished appearance. DETAILED DESCRIPTION OF THE INVENTION

[0015] The high solids coating composition of the present invention (hereinafter sometimes abbreviated as "the coating") will be described in further detail below.

[0016] The high solids coating composition of the present invention is a high solids coating composition characterized by containing (A) a hydroxyl-containing acrylic resin having a glass transition temperature (Tg) in the range of 20 to 70°C and a weight-average molecular weight in the range of 3,000 to 10,000, (B) a hydroxyl-containing polyester resin which is a reaction product of a polyfunctional compound (b-1) having a total of three or more carboxyl groups and three or more hydroxyl groups per molecule, a monoepoxide compound (b-2) having a hydrocarbon group of four or more carbon atoms, and a caprolactone compound (b-3), and (C) a polyisocyanate compound, and having a solids content of 50% or more when applied.

[0017] 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.

[0018] <Hydroxyl group-containing acrylic resin (A)> The hydroxyl group-containing acrylic resin (A) is an acrylic resin having a glass transition temperature (Tg) in the range of 20 to 70°C and a weight average molecular weight in the range of 3,000 to 10,000. When the glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (A) is 20°C or higher, the hardness and scratch resistance of the formed coating film are good, and when the glass transition temperature (Tg) is 70°C or lower, the finished appearance of the formed coating film is good. In particular, from the viewpoints of the hardness, scratch resistance and finished appearance of the formed coating film, the glass transition temperature (Tg) of the hydroxyl group-containing acrylic resin (A) is preferably in the range of 25 to 65°C, more preferably in the range of 30 to 60°C.

[0019] In this specification, the glass transition temperature (Tg) 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, ... represent the mass fractions of the respective monomers used in copolymerization, and T1, T2, ... represent the Tg (K) of the homopolymer of each monomer. Note that T1, T2, ... are values ​​according to pages III-139 to 179 of Polymer Handbook (Second Edition, edited by J. Brandup and EH Immergut). When the Tg of the homopolymer of a monomer is unclear, the glass transition temperature (Tg) is taken as the static glass transition temperature. For example, using a differential scanning calorimeter "DSC-220U" (manufactured by Seiko Instruments Inc.), a sample is placed in a measuring cup and vacuum suction is used to completely remove the solvent, after which the change in calorific value is measured in the range of -20°C to +200°C at a heating rate of 3°C / min, and the first change point in the baseline on the low temperature side is taken as the static glass transition temperature.

[0020] When the weight-average molecular weight of the hydroxyl group-containing acrylic resin (A) is 3,000 or more, the hardness and scratch resistance of the formed coating film are good, and when the weight-average molecular weight is 10,000 or less, the finished appearance of the formed coating film is good. In particular, from the viewpoints of the hardness, scratch resistance and finished appearance of the formed coating film, the weight-average molecular weight of the hydroxyl group-containing acrylic resin (A) is preferably in the range of 3,500 to 9,500, and more preferably in the range of 4,000 to 9,000.

[0021] 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.

[0022] The hydroxyl group-containing acrylic resin (A) can be obtained, for example, by copolymerizing a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer (a polymerizable unsaturated monomer other than a hydroxyl group-containing polymerizable unsaturated monomer).

[0023] 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.

[0024] 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.

[0025] Examples of the secondary hydroxyl group-containing polymerizable unsaturated monomer include polymerizable unsaturated monomers having a secondary hydroxyl group, such as 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 3-hydroxybutyl (meth)acrylate, 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; 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. Of these, 2-hydroxypropyl (meth)acrylate is preferred from the viewpoints of the pot life of the coating material and the finished appearance of the coating film formed.

[0026] As other polymerizable monomers copolymerizable with the above-mentioned hydroxyl group-containing polymerizable unsaturated monomers, for example, the following monomers (1) to (6) can be used. These polymerizable unsaturated monomers can be used alone or in combination of two or more.

[0027] (1) Acid group-containing polymerizable unsaturated monomer 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 monomers may be used alone or in combination. When using an acid group-containing polymerizable unsaturated monomer, the amount is preferably adjusted so that the acid value of the hydroxyl group-containing acrylic resin (A) is 0.5 to 30 mgKOH / g, particularly 1 to 20 mgKOH / g.

[0028] (2) 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.

[0029] (3) 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.

[0030] (4) 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.

[0031] (5) 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.

[0032] (6) 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.).

[0033] As the other polymerizable unsaturated monomers, the monomers shown in (1) to (6) above can be used alone or in combination of two or more.

[0034] 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.

[0035] 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.

[0036] In producing 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 50 mass %, more preferably 20 to 40 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] These organic solvents can be used alone or in combination of two or more, but from the viewpoint of solubility of acrylic resin, it is preferable to use ester-based solvents and ketone-based solvents. Furthermore, aromatic solvents can also be used in suitable combinations.

[0041] 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).

[0042] The above hydroxyl group-containing acrylic resins (A) can be used alone or in combination of two or more.

[0043] From the viewpoints of the hardness, scratch resistance, 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.

[0044] As another embodiment of the hydroxyl group-containing acrylic resin (A), a hydroxyl group-containing acrylic resin (A') containing an alkoxysilyl group can be preferably used from the viewpoints of the hardness, scratch resistance, water resistance, and finished appearance of the coating film to be formed.

[0045] <Hydroxyl-containing acrylic resin (A') containing an alkoxysilyl group> The hydroxyl-containing acrylic resin (A') containing an alkoxysilyl group is a resin having one or more alkoxysilyl groups and one or more hydroxyl groups in one molecule.

[0046] By using a hydroxyl group-containing acrylic resin (A') containing alkoxysilyl groups, crosslinking bonds are formed by condensation reactions between alkoxysilyl groups and reactions between alkoxysilyl groups and hydroxyl groups, thereby improving the hardness and scratch resistance of the coating film formed.

[0047] Examples of the alkoxy moiety of the alkoxysilyl group contained in the hydroxyl group-containing acrylic resin (A') containing an alkoxysilyl group include alkoxy moieties having about 1 to 6 carbon atoms, preferably about 1 to 3 carbon atoms, such as methoxy, ethoxy, and propoxy. From the viewpoint of the hardness and scratch resistance of the coating film to be formed, methoxy and ethoxy are more preferred as the alkoxy moiety, and methoxy is particularly preferred.

[0048] The alkoxysilyl group includes, for example, a trialkoxysilyl group, a dialkoxysilyl group, and a monoalkoxysilyl group. As the alkoxysilyl group, a trialkoxysilyl group is preferred from the viewpoint of the scratch resistance of the coating film to be formed.

[0049] When the alkoxysilyl group is a dialkoxysilyl group or a monoalkoxysilyl group, the group bonded to the silicon atom other than the alkoxy can be, for example, an alkyl having about 1 to 6 carbon atoms, preferably about 1 to 3 carbon atoms (e.g., methyl, ethyl, propyl).

[0050] The hydroxyl-containing acrylic resin (A') containing the alkoxysilyl group can be obtained, for example, by using the hydroxyl-containing polymerizable unsaturated monomer and an alkoxysilyl-containing polymerizable unsaturated monomer as one of the other polymerizable unsaturated monomers in the method for producing the hydroxyl-containing acrylic resin (A).

[0051] As the hydroxyl group-containing polymerizable unsaturated monomer, it is preferable to use a primary hydroxyl group-containing polymerizable unsaturated monomer from the viewpoints of the hardness, scratch resistance, water resistance, and finished appearance of the coating film to be formed.

[0052] Examples of the primary hydroxyl group-containing polymerizable unsaturated monomer include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and other polymerizable unsaturated monomers having a primary hydroxyl group in the alkyl group of the ester moiety having 2 to 8 carbon atoms, preferably 2 to 6 carbon atoms, and more preferably 2 to 4 carbon atoms. These may be used alone or in combination of two or more kinds.

[0053] The hydroxyl value of the alkoxysilyl-containing 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.

[0054] The alkoxysilyl group-containing polymerizable unsaturated monomer is a compound having one or more alkoxysilyl groups and one or more polymerizable unsaturated bonds in one molecule. Examples of the alkoxysilyl group-containing polymerizable unsaturated monomer include vinyltrimethoxysilane, vinyltriethoxysilane, acryloxyethyltrimethoxysilane, methacryloxyethyltrimethoxysilane, acryloxypropyltrimethoxysilane, methacryloxypropyltrimethoxysilane, acryloxypropyltriethoxysilane, methacryloxypropyltriethoxysilane, and vinyltris(β-methoxyethoxy)silane.

[0055] As the alkoxysilyl group-containing polymerizable unsaturated monomer, vinyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane are preferred, with γ-methacryloxypropyltrimethoxysilane being more preferred, from the viewpoint of the scratch resistance of the coating film to be formed. Commercially available alkoxysilyl group-containing polymerizable unsaturated monomers can be used, such as KBM-1003, KBE-1003, KBM-502, KBM-503, KBE-502, KBE-503, KBM-5103, and KBM-5803 (all manufactured by Shin-Etsu Chemical Co., Ltd.), Y-9936 and A-174 (manufactured by Momentive Performance Materials Japan, LLC), and OFS-6030 and Z-6033 (manufactured by Dow Corning Toray Co., Ltd.).

[0056] The alkoxysilyl group-containing polymerizable unsaturated monomers can be used alone or in combination of two or more.

[0057] In the production of the hydroxyl group-containing acrylic resin (A') containing the alkoxysilyl group, the amount of the alkoxysilyl group-containing polymerizable unsaturated monomer used is preferably 3 to 50 mass %, more preferably 10 to 45 mass %, and even more preferably 20 to 40 mass %, based on the total amount of copolymerizable monomer components, from the viewpoints of the hardness, scratch resistance, water resistance, and finished appearance of the coating film to be formed.

[0058] When the hydroxyl-containing acrylic resin (A) contains an alkoxysilyl-containing hydroxyl-containing acrylic resin (A') as one embodiment of the hydroxyl-containing acrylic resin (A), the content of the alkoxysilyl-containing hydroxyl-containing acrylic resin (A') in the hydroxyl-containing acrylic resin (A) is preferably 50 to 100% by mass, more preferably 55 to 100% by mass, and even more preferably 60 to 100% by mass, from the viewpoints of the hardness, scratch resistance, water resistance, and finished appearance of the coating film to be formed.

[0059] <Hydroxyl group-containing polyester resin (B)> The hydroxyl group-containing polyester resin (B) is a polyester resin that is a reaction product of a polyfunctional compound (b-1) having a total of three or more carboxyl groups and hydroxyl groups in one molecule, a monoepoxide compound (b-2) having a hydrocarbon group with four or more carbon atoms, and a caprolactone compound (b-3).

[0060] <Compound (b-1)> The compound (b-1) is a compound having a total of three or more carboxyl groups and hydroxyl groups in one molecule.

[0061] When the hydroxyl group-containing polyester resin (B) contains the compound (b-1) as a reactive component, the finished appearance of the coating film formed is excellent.

[0062] Examples of the compound (b-1) include the following compounds (1) to (4). (1) Compounds that have one hydroxyl group and two carboxyl groups in one molecule: malic acid, etc. (2) Compounds with one hydroxyl group and three carboxyl groups in one molecule: citric acid, etc. (3) Compounds containing two hydroxyl groups and two carboxyl groups in one molecule: tartaric acid, etc. (4) Compounds having two hydroxyl groups and one carboxyl group in one molecule: dimethylolpropionic acid, dimethylolbutanoic acid, etc.

[0063] Among the above compounds (b-1), it is preferable to use a compound having two hydroxyl groups and one carboxyl group in one molecule, from the viewpoint of the finished appearance of the coating film to be formed.

[0064] The above compounds (b-1) can be used either alone or in combination of two or more.

[0065] In the production of the hydroxyl group-containing polyester resin (B), the amount of the compound (b-1) used is preferably within a range of 3 to 40 mass %, more preferably 5 to 30 mass %, based on the total amount of the reaction components, from the viewpoint of the finished appearance of the coating film to be formed.

[0066] <Compound (b-2)> The compound (b-2) is a monoepoxide compound having a hydrocarbon group with 4 or more carbon atoms.

[0067] When the hydroxyl group-containing polyester resin (B) contains the compound (b-2) as a reactive component, the coating film formed has excellent water resistance.

[0068] Examples of the compound (b-2) include glycidyl esters of aliphatic carboxylic acids such as 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, and "Cardura E10P" (trade name, manufactured by Momentive Specialty Chemicals, neodecanoic acid monoglycidyl ester); alkyl glycidyl ethers such as butyl glycidyl ether and decyl glycidyl ether; aryl glycidyl ether such as phenyl glycidyl ether; styrene oxide; and α-olefin monoepoxides such as AOEX24 (manufactured by Daicel Chemical Industries, Ltd., α-olefin monoepoxide mixture). Among these, from the viewpoint of the water resistance of the coating film to be formed, it is preferable to use glycidyl esters of aliphatic carboxylic acids, such as "Cardura E10P" (trade name, manufactured by Momentive Specialty Chemicals, It is more preferable to use neodecanoic acid monoglycidyl ester (manufactured by Daiichi Sankyo Chemicals Co., Ltd.).

[0069] Furthermore, the hydrocarbon group having 4 or more carbon atoms may have a substituent such as a hydroxyl group, and specific examples of monoepoxide compounds having a hydrocarbon group with such a substituent include 1,2-epoxyoctanol and hydroxyoctyl glycidyl ether.

[0070] The above compounds (b-2) can be used either alone or in combination of two or more.

[0071] In the production of the hydroxyl group-containing polyester resin (B), the amount of the compound (b-2) used is preferably within a range of 10 to 70 mass %, more preferably 20 to 60 mass %, based on the total amount of the reaction components, from the viewpoint of the water resistance of the coating film to be formed, etc.

[0072] <Compound (b-3)> The compound (b-3) is a caprolactone compound.

[0073] When the hydroxyl group-containing polyester resin (B) contains the compound (b-3) as a reactive component, the resulting coating film has excellent abrasion resistance and water resistance.

[0074] Examples of the compound (b-3) include γ-caprolactone, ε-caprolactone, δ-caprolactone, lactone, and valerolactone. Of these, ε-caprolactone is preferred from the viewpoint of the scratch resistance and water resistance of the coating film to be formed.

[0075] The above compounds (b-3) can be used either alone or in combination of two or more.

[0076] In the production of the hydroxyl group-containing polyester resin (B), the amount of the compound (b-3) used is preferably within a range of 5 to 60 mass %, more preferably 10 to 50 mass %, based on the total amount of reaction components, from the viewpoint of the scratch resistance and water resistance of the coating film to be formed.

[0077] The hydroxyl group-containing polyester resin (B) can be produced by known methods such as melt polycondensation and solution polycondensation.

[0078] In the production of the hydroxyl group-containing polyester resin (B), a polybasic acid compound (b-4) and / or a polyhydric alcohol compound (b-5) can also be used. However, in the present invention, a compound corresponding to the compound (b-1) should be defined as the compound (b-1) and is excluded from the compounds (b-4) and (b-5).

[0079] <Compound (b-4)> The compound (b-4) is a compound having two or more carboxyl groups in one molecule.

[0080] Examples of the compound (b-4) include aromatic polybasic acids and anhydrides thereof, such as terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, and diphenylmethane-4,4'-dicarboxylic acid; alicyclic dicarboxylic acids and anhydrides thereof, such as hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid, and tetrahydrophthalic acid; and adipic acid, sebacic acid, suberic acid, succinic acid, glutaric acid, maleic acid, chloromaleic acid, fumaric acid, and dodecanedioic acid. aliphatic polybasic acids such as pimelic acid, azelaic acid, itaconic acid, citraconic acid, and dimer acid, and their anhydrides; 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 their anhydrides. Among these, it is preferable to use alicyclic dicarboxylic acids and their anhydrides.

[0081] The above compounds (b-4) can be used either alone or in combination of two or more.

[0082] When the compound (b-4) is used in the production of the hydroxyl group-containing polyester resin (B), the amount used is preferably within a range of 5 to 30 mass %, more preferably 10 to 25 mass %, based on the total amount of the reaction components, from the viewpoint of the finished appearance of the coating film to be formed.

[0083] <Compound (b-5)> The compound (b-5) is a compound having two or more hydroxyl groups in one molecule. Examples of the compound (b-5) 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, 2,3-dimethyltrimethylene 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 neopentyl glycol hydroxypivalate. dihydric alcohols such as esters; ester diols such as bis(hydroxyethyl) terephthalate; polyether diols such as alkylene oxide adducts of bisphenol A, polyethylene glycol, polypropylene glycol, and polybutylene glycol; trihydric or higher alcohols such as glycerin, trimethylolpropane, trimethylolethane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, sorbitol, and mannitol; alicyclic polyhydric alcohols such as 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, hydrogenated bisphenol A, hydrogenated bisphenol F, hydrogenated bisphenol A, and hydrogenated bisphenol F; and cyclic polyol compounds having a nurate structure such as tris(hydroxyalkyl)isocyanurate and tris(hydroxyethyl)isocyanurate.

[0084] The above compounds (b-5) can be used either alone or in combination of two or more.

[0085] When the compound (b-5) is used in the production of the hydroxyl group-containing polyester resin (B), the amount used is preferably within a range of 3 to 20 mass %, more preferably 5 to 15 mass %, based on the total amount of the reaction components, from the viewpoint of the water resistance of the coating film to be formed, etc.

[0086] The acid value of the hydroxyl group-containing polyester resin (B) is preferably 30 mgKOH / g or less, more preferably 24 mgKOH / g or less, and even more preferably 18 mgKOH / g or less, from the viewpoint of the water resistance and finished appearance of the coating film to be formed.

[0087] The hydroxyl value of the hydroxyl-containing polyester resin (B) is preferably within a range of 50 to 250 mgKOH / g, more preferably within a range of 80 to 200 mgKOH / g, from the viewpoint of the scratch resistance of the coating film to be formed.

[0088] The number average molecular weight of the hydroxyl group-containing polyester resin (B) is preferably within the range of 500 to 5,000, more preferably within the range of 1,000 to 3,500, from the viewpoint of the water resistance and finished appearance of the coating film to be formed.

[0089] The content of the hydroxyl group-containing polyester resin (B) in the high solid content coating composition of the present invention 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 viewpoints of the hardness, scratch resistance, water resistance, and finished appearance of the coating film to be formed.

[0090] <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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] The above polyisocyanate compounds and derivatives thereof may be used alone or in combination of two or more kinds.

[0097] 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.

[0098] As the aliphatic polyisocyanate compound and / or derivative thereof, from the viewpoints of high solid content of the resulting coating composition and the finished appearance of the coating film formed, 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.

[0099] The polyisocyanate compound (C) may have an isocyanate group blocked with a blocking agent.

[0100] 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.

[0101] From the viewpoints of the hardness, scratch resistance, water resistance and 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.

[0102] <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-containing acrylic resin having a glass transition temperature (Tg) in the range of 20 to 70°C and a weight-average molecular weight in the range of 3,000 to 10,000, (B) a hydroxyl-containing polyester resin which is a reaction product of a polyfunctional compound (b-1) having a total of three or more carboxyl groups and three or more hydroxyl groups per molecule, a monoepoxide compound (b-2) having a hydrocarbon group of four or more carbon atoms, and a caprolactone compound (b-3), and (C) a polyisocyanate compound, and having a solids content of 50% or more when applied.

[0103] 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.

[0104] 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.

[0105] The reason why the high-solids coating composition of the present invention can form coating films with excellent hardness, scratch resistance, water resistance, and finished appearance is unclear, but the high glass transition temperature (Tg) of the hydroxyl-containing acrylic resin (A) in the range of 20 to 70°C results in good hardness and scratch resistance, and the weight-average molecular weight in the range of 3,000 to 10,000 reduces the coating viscosity, allowing for the formation of coating films with excellent finished appearance despite the high solids content. Furthermore, the hydroxyl-containing polyester resin (B) contains, as a reactive component, a multifunctional compound (b-1) having a total of three or more carboxyl and hydroxyl groups per molecule, which reduces molecular chain entanglement, thereby reducing the coating viscosity and allowing for the formation of coating films with excellent finished appearance despite the high solids content. The monoepoxide compound (b-2) with a hydrocarbon group having four or more carbon atoms enhances hydrophobicity, allowing for the formation of coating films with excellent water resistance. Furthermore, since the composition contains the caprolactone compound (b-3), the flexibility of the coating film is improved, allowing the formation of a coating film with excellent abrasion resistance, and since the low molecular weight components in the hydroxyl group-containing polyester resin (B) are reduced, a coating film with excellent water resistance can be formed. Furthermore, since both the hydroxyl group-containing acrylic resin (A) and the hydroxyl group-containing polyester resin (B) contain hydroxyl groups, it is presumed that the reaction with the polyisocyanate compound is favorable, allowing the formation of a coating film with excellent hardness, water resistance, and abrasion resistance.

[0106] <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.

[0107] Examples of resins other than those mentioned above include acrylic resins other than the hydroxyl group-containing acrylic resin (A) that may contain hydroxyl groups, polyester resins other than the hydroxyl group-containing polyester resin (B) that may 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. Of these, it is preferable to contain an acrylic resin other than the hydroxyl group-containing acrylic resin (A) that may contain hydroxyl groups, and it is preferable to contain a hydroxyl group-containing acrylic resin (D) other than the hydroxyl group-containing acrylic resin (A).

[0108] The hydroxyl-containing acrylic resin (D) can be produced, for example, by the method described in the explanation section for the hydroxyl-containing acrylic resin (A).

[0109] From the viewpoint of the modulus resistance of the coating film formed, it is preferable to use a hydroxyl group-containing acrylic resin (D1) having an acid value within the range of 60 to 120 mgKOH / g as the hydroxyl group-containing acrylic resin (D).

[0110] When the high solids coating composition of the present invention contains a hydroxyl group-containing acrylic resin (D), 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 solids coating composition, from the viewpoint of the resistance to mold of the coating film to be formed.

[0111] Examples of the crosslinking agent other than the polyisocyanate compound (C) include melamine resins.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] Commercially available melamine resins can be used, including, for example, 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.).

[0117] The above melamine resins can be used either alone or in combination of two or more.

[0118] 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 hardness and scratch resistance of the coating film to be formed.

[0119] 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.

[0120] 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.

[0121] Examples of the luster pigment include aluminum powder, mica powder, and mica powder coated with titanium oxide.

[0122] Examples of extender pigments include talc, clay, kaolin, baryta, barium sulfate, barium carbonate, calcium carbonate, and alumina white.

[0123] Each of the above pigments can be used alone or in combination of two or more.

[0124] 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.

[0125] 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.

[0126] 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 can be used alone or in combination of two or more.

[0127] 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.

[0128] 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.

[0129] 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).

[0130] 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.

[0131] 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.

[0132] As the light stabilizer, a conventionally known light stabilizer can be used, for example, a hindered amine light stabilizer.

[0133] 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).

[0134] 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.

[0135] 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.

[0136] 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.

[0137] The high solids coating composition of the present invention can form a coating film that is excellent in hardness, scratch resistance, water resistance, and 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.

[0138] <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. Step (1): A step of applying an intermediate coating composition to an object to be coated to form an intermediate coating film; Step (2): A step of applying a base coat paint composition onto the intermediate coating film formed in step (1) to form a base coat coating film; Step (3): A step of applying the high solids paint composition of the present invention onto the base coat film formed in step (2) to form a clear coat film; and Step (4): A method for forming a multi-layer coating film, comprising a step of simultaneously heating and curing the intermediate coating film, base coating film, and clear coating film formed in steps (1) to (3).

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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 necessary, and a primer coating film may be formed thereon. For example, when the substrate to be coated is an automobile body, the primer coating film may be formed using a known primer coating composition that is commonly used in painting automobile bodies.

[0143] The above-mentioned primer coating composition is usually applied to an object to impart corrosion resistance to the object to be coated.

[0144] As the undercoat paint composition for forming the undercoat paint film, for example, an electrodeposition paint, preferably a cationic electrodeposition paint, can be used.

[0145] In addition, the undercoat coating film is preferably a cured coating film from the viewpoint of the finished appearance of the multi-layer coating film to be formed.

[0146] The intermediate coating composition can be a thermosetting intermediate coating composition known for use in painting automobile bodies, etc. Suitable intermediate coating compositions include, for example, thermosetting coatings containing a base resin having a crosslinkable functional group, a crosslinking agent, a color pigment, and an extender pigment.

[0147] The intermediate coating composition is usually applied to an object to impart smoothness, chipping resistance and adhesion between coating films to the object.

[0148] Examples of the crosslinkable functional group contained in the base resin include a carboxyl group, a hydroxyl group, and an epoxy group.

[0149] Examples of the base resin include acrylic resin, polyester resin, alkyd resin, and urethane resin.

[0150] Examples of the crosslinking agent include melamine resins, polyisocyanate compounds, and blocked polyisocyanate compounds.

[0151] The intermediate 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.

[0152] The amount of intermediate coating composition to be applied is preferably an amount that results in a cured film thickness of 10 to 60 μm, more preferably an amount that results in a cured film thickness of 10 to 60 μm, even more preferably an amount that results in a cured film thickness of 15 to 50 μm, and even more preferably an amount that results in a cured film thickness of 20 to 40 μm.

[0153] The base coat paint composition can be a known thermosetting base coat paint composition for painting automobile bodies, etc. Suitable examples of the base coat paint composition include a thermosetting paint composition containing a base resin having a crosslinkable functional group, a crosslinking agent, a color pigment, a luster pigment, and an extender pigment.

[0154] The above-mentioned base coat paint composition is usually applied for the purpose of imparting excellent design properties (for example, color, metallic look, gloss, etc.) to the substrate.

[0155] Examples of the crosslinkable functional group contained in the base resin include a carboxyl group, a hydroxyl group, and an epoxy group.

[0156] Examples of the base resin include acrylic resin, polyester resin, alkyd resin, and urethane resin.

[0157] Examples of the crosslinking agent include melamine resins, polyisocyanate compounds, and blocked polyisocyanate compounds.

[0158] The base coat paint composition may be either an aqueous paint composition or an organic solvent-based paint composition, but from the viewpoint of reducing the environmental load, an aqueous paint composition is preferred.

[0159] The amount of base coat paint 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.

[0160] 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]

[0161] 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.

[0162] [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) so that the film thickness based on the cured coating was 20 μm, and the plate was heated at 170°C for 20 minutes to crosslink and cure, forming an electrodeposition coating film, which was then used as the coated object.

[0163] [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, 46.2 parts of isobutyl methacrylate, 1.3 parts of acrylic acid, and 3.2 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 10.1 mgKOH / g, a hydroxyl value of 140 mgKOH / g, a weight average molecular weight of 8,000, and a glass transition temperature of 39°C.

[0164] 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.

[0165] [Table 1]

[0166] <Production of Hydroxyl-Containing Acrylic Resin (A') Containing Alkoxysilyl Groups> Production Example 5 A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser, nitrogen inlet tube, and dropping device was charged with 30 parts of "Swasol 1000" (trade name, aromatic organic solvent, manufactured by Cosmo Oil Co., Ltd.) and 10 parts of n-butanol. The charged liquid was stirred at 125°C while nitrogen gas was blown into the reaction vessel, and a monomer mixture consisting of 15 parts of γ-methacryloxypropyltrimethoxysilane, 32.5 parts of 2-hydroxyethyl methacrylate, 10 parts of styrene, 10 parts of 2-ethylhexyl acrylate, 32.5 parts of isobutyl methacrylate, and 7.0 parts of 2,2'-azobis(2-methylbutyronitrile) (polymerization initiator) was added dropwise at a uniform rate over 4 hours. After aging for 30 minutes at 125°C, a solution consisting of 0.5 parts of 2,2'-azobis(2-methylbutyronitrile) and 5.0 parts of "Swasol 1000" was added dropwise at a uniform rate over 1 hour. After aging for 1 hour at 125°C, the mixture was cooled and further diluted with 6 parts of isobutyl acetate to obtain a solution of hydroxyl-containing acrylic resin (A'-1) containing alkoxysilyl groups with a solids concentration of 65%. The resulting hydroxyl-containing acrylic resin (A'-1) containing alkoxysilyl groups had an alkoxysilyl group content of 60 mmol / g, a hydroxyl value of 140 mg KOH / g, a weight-average molecular weight of 7,000, and a glass transition temperature of 32°C.

[0167] <Production of Hydroxyl-Containing Acrylic Resin (D)> Manufacturing Example 6 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, 46.2 parts of isobutyl methacrylate, 1.3 parts of acrylic acid, and 2.0 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 (D-1) solution with a solids concentration of 65%. The resulting hydroxyl-containing acrylic resin (D-1) had an acid value of 10.1 mgKOH / g, a hydroxyl value of 140 mgKOH / g, a weight average molecular weight of 11,000, and a glass transition temperature of 39°C.

[0168] Manufacturing Examples 7-9 Solutions of hydroxyl-containing acrylic resins (D-2) to (D-4) with a solid content concentration of 65% were obtained in the same manner as in Production Example 6, except that the blending compositions in Production Example 6 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.

[0169] [Table 2]

[0170] Manufacturing Example 10 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 11.5 parts of 2-ethylhexyl methacrylate, 40 parts of 2-hydroxyethyl methacrylate, 38 parts of isobutyl acrylate, 10.5 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-containing acrylic resin (D1-1) solution with a solids concentration of 65%. The resulting hydroxyl group-containing acrylic resin (D1-1) had an acid value of 81.8 mgKOH / g, a hydroxyl value of 173 mgKOH / g, a weight average molecular weight of 3,500, and a glass transition temperature of 17°C.

[0171] <Production of Hydroxyl Group-Containing Polyester Resin (B)> 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 (B-1) solution with a solids concentration of 80%. The resulting hydroxyl-containing polyester resin (B-1) had an acid value of 4 mgKOH / g, a hydroxyl value of 120 mgKOH / g, and a number average molecular weight of 2,100.

[0172] Manufacturing 12~17 Solutions of hydroxyl-containing polyester resins (B-2) to (B-7) with a solid content concentration of 80% were obtained in the same manner as in Production Example 11, except that the blending compositions in Production Example 11 were as shown in Table 3. The acid value, hydroxyl value, and number average molecular weight of each hydroxyl-containing polyester resin are also shown in Table 3.

[0173] [Table 3]

[0174] <Production of Hydroxyl-Containing Polyester Resin (E) Other than Hydroxyl-Containing Polyester Resin (B)> Manufacturing Example 18 A reactor equipped with a stirrer, reflux condenser, and thermometer was charged with 90 parts of lactic acid, 490 parts of "Cardura E10P" (trade name, manufactured by Momentive Specialty Chemicals, neodecanoic acid monoglycidyl ester), and 154 parts of hexahydrophthalic anhydride, and the mixture was allowed to react at 190°C for 3 hours. 228 parts of ε-caprolactone was then 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 (E-1) solution with a solids concentration of 80%. The resulting hydroxyl-containing polyester resin (E-1) had an acid value of 1 mgKOH / g, a hydroxyl value of 176 mgKOH / g, and a number average molecular weight of 961.

[0175] Manufacturing Example 19 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, neodecanoic acid monoglycidyl ester, manufactured by Momentive Specialty Chemicals), and 308 parts of hexahydrophthalic anhydride. The mixture was reacted at 190°C for 6 hours, and then diluted with butyl acetate to obtain a hydroxyl-containing polyester resin (E-2) solution with a solids concentration of 80%. The resulting hydroxyl-containing polyester resin (E-2) had an acid value of 1 mgKOH / g, a hydroxyl value of 142 mgKOH / g, and a number average molecular weight of 1,190.

[0176] Manufacturing Example 20 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 reacted at 230°C for 6 hours. The mixture was then diluted with butyl acetate to obtain a solution of hydroxyl-containing polyester resin (E-3) with a solids concentration of 80%. The resulting hydroxyl-containing polyester resin (E-3) had an acid value of 2 mgKOH / g, a hydroxyl value of 192 mgKOH / g, and a number average molecular weight of 578.

[0177] <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, 10 parts (8 parts solids) of the hydroxyl-containing polyester resin (B-1) solution obtained in Production Example 11, 0.5 parts (0.3 parts solids) of "SETALUX 61767 VX-60" (trade name, manufactured by Allnex, viscosity modifier, 60% solids), and 0.4 parts (0.2 parts solids) of "BYK-300" (trade name, manufactured by BYK-Chemie, 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 homogeneously mixed just before application, and butyl acetate was added to adjust the solids content at application to 58%, yielding high solids coating composition No. 1.

[0178] Examples 2 to 18 and Comparative Examples 1 to 9 High solid content coating compositions Nos. 2 to 27 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 4 to 8. The blending compositions shown in Tables 4 to 8 are based on the solid content by mass of each component.

[0179] <Creating test panels> On the substrate prepared in [1] above, "WP-523H" (trade name, acrylic-melamine resin-based water-based primer coating composition, manufactured by Kansai Paint Co., Ltd.) was electrostatically coated using a rotary atomizing electrostatic coater to a cured film thickness of 20 μm, and the coating was left to stand for 5 minutes to form an uncured primer coating film.

[0180] Next, "WBC-713T No. 1F7" (product name, manufactured by Kansai Paint Co., Ltd., acrylic-melamine resin-based water-based base coat paint, silver paint color) was electrostatically applied onto the uncured primer coating using a rotary atomizing electrostatic coating machine 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 coating.

[0181] 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.

[0182] In preparing the test panels of the above-mentioned high solid content coating composition No. 1, the test panels of Examples 2 to 18 and Comparative Examples 1 to 9 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 27.

[0183] Each test panel obtained above was evaluated by the following test methods. The evaluation results are shown in Tables 4 to 8 together with the coating composition.

[0184] (Test Method) Tukon hardness: After leaving the test plate in a constant temperature room at 20°C for 4 hours, the "Tukon hardness" was measured using a Tukon (micro hardness tester manufactured by American Chain & Cable Company). Tukon hardness, which is a Knoop hardness test method, is a numerical value measured using a Tukon micro hardness tester manufactured by American Chain & Cable Company. Tukon hardness, also known as the Knoop Hardness Number (KHN), is the hardness of the coating film read from the size of the diamond-shaped indentation that occurs when a square pyramidal diamond indenter is pressed into the test surface of the material with a certain test load. The higher the value, the harder the film. A value of 10 or above is considered a pass.

[0185] Scratch resistance: The test panel was fixed to the test stand of a car wash tester (Amtec, Carwash Lab Apparatus) in a 20°C atmosphere. A test solution consisting of 1.5 g of "Sikron SH200" (product name, silica microparticles with a particle size of 24 μm, manufactured by Quarzwerke) mixed with 1 liter of water was sprayed onto the test panel, while a car wash brush was rotated at 127 rpm and moved back and forth across the test stand 10 times. The test panel was then rinsed with water and dried. The 20° gloss before and after the test was measured using a gloss meter (Byk-Gardner, Micro Tri Gloss), and the gloss retention was calculated using the following formula. The higher the gloss retention, the better the scratch resistance. A and B were considered pass. Gloss retention rate (%) = (gloss after test / gloss before test) x 100 A: Gloss retention rate of 85% or more B: Gloss retention rate 80% or more but less than 85% C: Gloss retention rate less than 80%

[0186] Water resistance: The test panel was immersed in 40°C warm water for 240 hours, then removed and the surface moisture was wiped off. Immediately afterwards, 100 2mm x 2mm cross-hatch patterns were made on the coating surface in accordance with JIS K 5600-5-6 (1990). Adhesive tape was then applied to the surface and quickly peeled off, and the number of cross-hatch patterns remaining on the coating surface was evaluated. A is considered a pass. A: Remaining number / total number = 100 / 100 with no chipped edges B: Remaining number / total number = 100 / 100 with chipped edges C: Remaining number / total number = 99 or less 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).

[0187] LW value: An index of smoothness. The smaller the LW value, the smoother the coating surface. A value of 6 or less is considered a pass.

[0188] SW value: An index of image clarity. The smaller the SW value, the higher the image clarity of the coating surface. A value of 17 or less is considered a pass.

[0189] Resistance to distortion: 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 resistance to distortion. The higher the flip-flop value, the better the orientation of the aluminum and the better the resistance to distortion. A value of 87 or higher is considered acceptable. Flip-flop value = L value at 15° acceptance angle - L value at 110° acceptance angle.

[0190] [Table 4]

[0191] [Table 5]

[0192] [Table 6]

[0193] [Table 7]

[0194] [Table 8]

[0195] 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.

[0196] This application is based on a Japanese patent application (Patent Application No. 2020-191307) filed on November 18, 2020, and a Japanese patent application (Patent Application No. 2021-066840) filed on April 12, 2021, the contents of which are incorporated herein by reference.

Claims

1. (A) a hydroxyl-containing acrylic resin having a glass transition temperature (Tg) in the range of 20 to 70°C and a weight average molecular weight in the range of 3,000 to 10,000, which is a copolymer of a hydroxyl-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer, wherein the hydroxyl-containing polymerizable unsaturated monomer has a hydroxyl group and a polymerizable unsaturated group selected from a vinyl group, a (meth)acryloyl group, a (meth)acrylamide group, a vinyl ether group, an allyl group, a propenyl group, an isopropenyl group, and a maleimide group, and the other polymerizable unsaturated monomer has the polymerizable unsaturated group; (B) a hydroxyl group-containing polyester resin which is a reaction product of a polyfunctional compound (b-1) having a total of three or more carboxyl groups and hydroxyl groups in one molecule, a monoepoxide compound (b-2) having a hydrocarbon group having four or more carbon atoms, and a caprolactone compound (b-3), wherein the polyfunctional compound (b-1) is selected from compounds having one hydroxyl group and two carboxyl groups in one molecule; compounds having one hydroxyl group and three carboxyl groups in one molecule; compounds having two hydroxyl groups and two carboxyl groups in one molecule; and compounds having two hydroxyl groups and one carboxyl group in one molecule, wherein the monoepoxide compound (b-2) is a glycidyl ester of an aliphatic carboxylic acid, and the caprolactone compound (b-3) is selected from γ-caprolactone, ε-caprolactone, δ-caprolactone, lactone, and valerolactone; and (C) a polyisocyanate compound containing at least one of an aliphatic polyisocyanate compound and a derivative thereof; and A high-solids coating composition characterized in that the solids content at the time of coating is 50% by mass or more.

2. 2. The high solids coating composition according to claim 1, wherein the hydroxyl-containing acrylic resin (A) comprises a hydroxyl-containing acrylic resin (A') containing an alkoxysilyl group.

3. 3. The high solids coating composition according to claim 1, wherein the hydroxyl-containing polyester resin (B) has an acid value of 30 mg KOH / g or less.

4. The high solids coating composition according to any one of claims 1 to 3, wherein the polyfunctional compound (b-1) having a total of three or more carboxyl groups and hydroxyl groups is a compound having one carboxyl group and two hydroxyl groups.

5. 5. The high solids coating composition according to claim 1, wherein the hydroxyl-containing polyester resin (B) further contains a polybasic acid compound (b-4) as a reaction component.

6. Step (1): A step of applying an intermediate coating composition to an object to be coated to form an intermediate coating film; Step (2): A step of applying a base coat paint composition onto the intermediate coating film formed in step (1) to form a base coat coating film; Step (3): A step of applying the high solids coating composition according to any one of claims 1 to 5 onto the base coat coating film formed in step (2) to form a clear coat coating film; and Step (4): A method for forming a multi-layer coating film, comprising a step of simultaneously heating and curing the intermediate coating film, base coating film, and clear coating film formed in steps (1) to (3).

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