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

Abstract

The present invention relates to a coating composition with a high solids content that includes: (A) a hydroxyl group- and alkoxysilyl group-including acrylic resin; (B) a hydroxyl group-including polyester resin; and (C) a polyisocyanate compound, wherein the acrylic resin (A) content is 20-50 parts by mass per 100 parts by mass of the resin solids content of the coating composition with a high solids content, the polyester resin (B) has an acid number of 10 mg KOH / g or less, a hydroxyl number of 180-300 mg KOH / g, and a number average molecular weight of 400-1500, and at the time of coating, the solids content of the coating composition with a high solids content is 50 mass% or greater.

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 (scratch resistance, hardness, etc.) and finished appearance, solvent-based clear paints are still the predominant method of application.

[0005] 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).

[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 and finish. Furthermore, the topcoat paint composition described in Patent Document 2 has good scratch resistance, but is insufficient in hardness 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 and finished appearance. [Means for solving the problem]

[0011] As a result of extensive research into achieving the above object, the present inventors have found that the above problems can be solved by the following coating composition, etc., and have thus completed the present invention.

[0012] <1> A high solids coating composition containing (A) a hydroxyl group- and alkoxysilyl group-containing acrylic resin, (B) a hydroxyl group-containing polyester resin, and (C) a polyisocyanate compound, the content of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is 20 to 50 parts by mass based on 100 parts by mass of the resin solids of the high solid content coating composition; The hydroxyl group-containing polyester resin (B) has an acid value of 10 mgKOH / g or less, a hydroxyl group value of 180 to 300 mgKOH / g, and a number average molecular weight of 400 to 1,500, and A high-solids coating composition characterized by having a solids content of 50% by mass or more when applied. <2> The content of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is 31 to 45 parts by mass based on 100 parts by mass of the resin solid content of the high solid content coating composition. <1> The high solids coating composition according to claim 1. <3> The hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) has an alkoxysilyl group content of 50 to 200 mmol / g. <1> or <2> The high solids coating composition according to claim 1. <4> The content of the hydroxyl group-containing polyester resin (B) is 5 to 12 parts by mass based on 100 parts by mass of the resin solid content of the high solid content coating composition. <1> ~ <3> 1. The high solids coating composition according to claim 1 . <5> The hydroxyl group-containing polyester resin (B) is obtained by using a dihydric alcohol and a trihydric or higher alcohol in combination as a polyhydric alcohol. <1> ~ <4> 1. The high solids coating composition according to claim 1 . <6> The content ratio of the dihydric alcohol and the trihydric or higher alcohol is 90 / 10 to 30 / 70 in terms of a mass ratio of the dihydric alcohol / the trihydric or higher alcohol. <5> The high solids coating composition according to claim 1. <7> Furthermore, a melamine resin (D) is contained <1> ~ <6> 1. The high solids coating composition according to claim 1 . <8> 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): On the base coat film formed in step (2), <1> ~ <7> A step of applying the high solids content coating composition according to any one of the above to form a clear coat film; 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]

[0013] The high solids coating composition of the present invention is capable of forming a coating film that is excellent in hardness, scratch resistance and finished appearance. DETAILED DESCRIPTION OF THE INVENTION

[0014] The high solids coating composition of the present invention (hereinafter sometimes abbreviated as "the coating") will be described in further detail below.

[0015] The high solids coating composition of the present invention is a high solids coating composition containing (A) a hydroxyl group- and alkoxysilyl group-containing acrylic resin, (B) a hydroxyl group-containing polyester resin, and (C) a polyisocyanate compound, wherein the content of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is 20 to 50 parts by mass based on 100 parts by mass of the resin solids of the high solids coating composition, and the hydroxyl group-containing polyester resin (B) has an acid value of 10 mgKOH / g or less, a hydroxyl value of 180 to 300 mgKOH / g, and a number average molecular weight of 400 to 1,500, and the solids content at the time of application is 50 mass% or more.

[0016] 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.

[0017] Furthermore, in this specification, "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.

[0018] In this specification, the weight-average molecular weight and number-average molecular weight are values ​​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). The mobile phase was tetrahydrofuran, the measurement temperature was 40°C, the flow rate was 1 cc / min, and the detector was RI.

[0019] [Hydroxyl group- and alkoxysilyl group-containing acrylic resin (A)] The hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is an acrylic resin having one or more hydroxyl groups and one or more alkoxysilyl groups in one molecule.

[0020] The hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) can be obtained, for example, by copolymerizing a hydroxyl group-containing polymerizable unsaturated monomer, an alkoxysilyl group-containing polymerizable unsaturated monomer, and other polymerizable unsaturated monomers (polymerizable unsaturated monomers other than the hydroxyl group-containing polymerizable unsaturated monomer and the alkoxysilyl group-containing polymerizable unsaturated monomer).

[0021] 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., "Cardura E10P" (trade name, manufactured by Hexion Specialty Chemicals, glycidyl ester of synthetic highly branched saturated fatty acid (neodecanoic acid glycidyl ester)); N-hydroxymethyl (meth)acrylamide; allyl alcohol; and (meth)acrylates having a polyoxyethylene chain with a hydroxyl group at the molecular terminal.

[0022] The above hydroxyl group-containing polymerizable unsaturated monomers can be used alone or in combination of two or more.

[0023] As the hydroxyl group-containing polymerizable unsaturated monomer, it is preferable to use a primary hydroxyl group-containing polymerizable unsaturated monomer from the viewpoint of the scratch resistance, weather resistance, hardness, etc. of the coating film to be formed.

[0024] 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. These can be used alone or in combination of two or more. Of these, 2-hydroxyethyl (meth)acrylate is preferred from the viewpoint of the scratch resistance, water resistance, hardness, etc. of the coating film to be formed.

[0025] In producing the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A), the amount of the hydroxyl group-containing polymerizable unsaturated monomer used is 5 to 60 mass %, preferably 15 to 50 mass %, and more preferably 25 to 45 mass %, based on the total amount of copolymerizable monomer components, from the viewpoints of the scratch resistance, weather resistance, hardness, and finished appearance of the coating film to be formed.

[0026] When the primary hydroxyl group-containing polymerizable unsaturated monomer is used in producing the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A), the content of the primary hydroxyl group-containing polymerizable unsaturated monomer in the total amount of the hydroxyl group-containing polymerizable unsaturated monomer is 50 to 100% by mass, preferably 55 to 100% by mass, and more preferably 60 to 100% by mass, from the viewpoints of the scratch resistance, weather resistance, hardness, and finished appearance of the coating film to be formed.

[0027] Examples of the alkoxy moiety of the alkoxysilyl group contained in the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) 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.

[0028] The alkoxysilyl group includes a trialkoxysilyl group, a dialkoxysilyl group, and a monoalkoxysilyl group. As the alkoxysilyl group, a trialkoxysilyl group is preferred from the viewpoint of the hardness and scratch resistance of the coating film to be formed.

[0029] When the alkoxysilyl group is a dialkoxysilyl group or a monoalkoxysilyl group, the group bonded to the silicon atom other than alkoxy can be alkyl having about 1 to 6 carbon atoms, preferably about 1 to 3 carbon atoms (e.g., methyl, ethyl, propyl).

[0030] 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.

[0031] 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.

[0032] The alkoxysilyl group-containing polymerizable unsaturated monomer may be commercially available, 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," "A-174" (manufactured by Momentive Performance Materials Japan, LLC), and "OFS-6030" and "Z-6033" (manufactured by Dow Corning Toray Co., Ltd.).

[0033] The above alkoxysilyl group-containing polymerizable unsaturated monomers can be used alone or in combination of two or more.

[0034] In producing the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A), the amount of the alkoxysilyl group-containing polymerizable unsaturated monomer used is 3 to 50 mass %, preferably 10 to 45 mass %, and more preferably 20 to 40 mass %, based on the total amount of copolymerizable monomer components, from the viewpoints of the hardness, finished appearance, and scratch resistance of the coating film to be formed.

[0035] As the other polymerizable unsaturated monomer, 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.

[0036] (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 can be used alone or in combination.

[0037] When an acid group-containing polymerizable unsaturated monomer is used, it is preferably used in an amount such that the acid value of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is 0.5 to 15 mgKOH / g, particularly 1 to 10 mgKOH / g.

[0038] (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.

[0039] (3) Aromatic vinyl monomers Specific examples include styrene, α-methylstyrene, and vinyltoluene.

[0040] 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.

[0041] When an aromatic vinyl monomer is used as a constituent component, the blending ratio thereof is preferably 3 to 50 mass %, particularly preferably 5 to 40 mass %, based on the total amount of the monomer components.

[0042] (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.

[0043] (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.

[0044] (6) Other vinyl compounds Examples include vinyl acetate, vinyl propionate, vinyl chloride, and versatate vinyl ester. Examples of versatate vinyl ester include commercially available products such as "Veova 9" and "Veova 10" (both trade names, manufactured by Mitsubishi Chemical Corporation).

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The copolymerization method for obtaining the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) by copolymerizing the hydroxyl group-containing polymerizable unsaturated monomer, the alkoxysilyl group-containing polymerizable unsaturated monomer, and other polymerizable unsaturated monomers is not particularly limited, and any copolymerization method known per se can be used. Among these, a solution polymerization method in which polymerization is carried out in an organic solvent in the presence of a polymerization initiator can be preferably used.

[0049] 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.

[0050] 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.

[0051] Examples of polymerization initiators that can be used in copolymerizing the hydroxyl group- and alkoxysilyl 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).

[0052] The weight average molecular weight of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is preferably 2,000 to 50,000, particularly 3,000 to 30,000, and even more particularly 4,000 to 20,000, from the viewpoint of the finished appearance and curing properties of the coating film.

[0053] The glass transition temperature of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is preferably from -50 to 60°C, particularly from -15 to 45°C, and even more particularly from 0 to 40°C, from the viewpoint of the hardness and finished appearance of the coating film to be formed.

[0054] In this specification, the glass transition temperature (°C) of the acrylic resin was calculated by the following formula.

[0055] 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 the copolymerization, and T1, T2, ... represent the glass transition temperatures Tg (K) of the homopolymers of the respective monomers.

[0056] 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 (°C) 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.

[0057] The hydroxyl value of the hydroxyl- and alkoxysilyl-containing acrylic resin (A) is preferably 70 to 200 mgKOH / g, particularly 80 to 190 mgKOH / g, and even more particularly 100 to 180 mgKOH / g, from the viewpoints of the scratch resistance, weather resistance, curing property, and finished appearance of the coating film to be formed.

[0058] The alkoxysilyl group content of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is preferably 50 to 200 mmol / g, more preferably 70 to 190 mmol / g, and even more preferably 90 to 180 mmol / g, from the viewpoints of the scratch resistance, weather resistance, hardness, and finished appearance of the coating film to be formed.

[0059] The hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) can be used alone or in combination of two or more kinds.

[0060] The content of the hydroxyl- and alkoxysilyl-containing acrylic resin (A) in the high solid content coating composition of the present invention is 20 to 50 parts by mass based on 100 parts by mass of the resin solids of the high solid content coating composition.

[0061] When the content of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is 20 parts by mass or more based on 100 parts by mass of the resin solids of the high solid content coating composition, a coating film with excellent abrasion resistance, weather resistance, and hardness can be formed. Furthermore, when the content is 50 parts by mass or less, a coating film with excellent finished appearance can be formed. In particular, from the viewpoints of the abrasion resistance, weather resistance, hardness, and finished appearance of the coating film formed, the content of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is preferably 31 to 45 parts by mass, more preferably 35 to 45 parts by mass, based on 100 parts by mass of the resin solids of the high solid content coating composition.

[0062] [Hydroxyl group-containing polyester resin (B)] The hydroxyl group-containing polyester resin (B) has an acid value of 10 mgKOH / g or less, a hydroxyl value of 180 to 300 mgKOH / g, and a number average molecular weight of 400 to 1,500.

[0063] When the acid value of the hydroxyl-containing polyester resin (B) is 10 mgKOH / g or less, the finished appearance of the formed coating film is good. In particular, from the viewpoint of the finished appearance of the formed coating film, the acid value of the hydroxyl-containing polyester resin (B) is preferably 5 mgKOH / g or less, and more preferably 3 mgKOH / g or less.

[0064] The hydroxyl value of the hydroxyl-containing polyester resin (B) is 180 to 300 mgKOH / g. When the hydroxyl value of the hydroxyl-containing polyester resin (B) is 180 mgKOH / g or more, the resulting coating film has good abrasion resistance, water resistance, and hardness, while when the hydroxyl value is 300 mgKOH / g or less, the resulting coating film has a good finished appearance. In particular, the hydroxyl value of the hydroxyl-containing polyester resin (B) is preferably 190 to 280 mgKOH / g, more preferably 200 to 250 mgKOH / g, from the viewpoints of the abrasion resistance, water resistance, hardness, and finished appearance of the resulting coating film.

[0065] The number average molecular weight of the hydroxyl group-containing polyester resin (B) is 400 to 1,500. When the number average molecular weight of the hydroxyl group-containing polyester resin (B) is 400 or more, the weather resistance and hardness of the coating film formed will be good, and when the number average molecular weight is 1,500 or less, the finished appearance of the coating film formed will be good. In particular, from the viewpoints of the weather resistance, hardness, and finished appearance of the coating film formed, the number average molecular weight of the hydroxyl group-containing polyester resin (B) is preferably 500 to 1,200, and more preferably 600 to 1,000.

[0066] The hydroxyl-containing polyester resin (B) 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.

[0067] Examples of polyhydric alcohols include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3-butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, and 2,3-dimethyltrimethylol. Dihydric alcohols such as ethylene 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; polylactones 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 [trade 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, but from the viewpoint of the scratch resistance, weather resistance and finished appearance of the coating film formed, it is preferable to use a dihydric alcohol and a trihydric or higher alcohol in combination.

[0068] When the above-mentioned dihydric alcohol and trihydric or higher alcohol are used in combination as the polyhydric alcohol of the hydroxyl group-containing polyester (B), the content ratio, in terms of the mass ratio of dihydric alcohol to trihydric or higher alcohol, is preferably 90 / 10 to 30 / 70, more preferably 85 / 15 to 50 / 50, and even more preferably 80 / 20 to 60 / 40, from the viewpoints of the scratch resistance, weather resistance, and finished appearance of the coating film to be formed.

[0069] As the dihydric alcohol, from the viewpoint of the scratch resistance and finished appearance of the coating film to be formed, it is preferable to use an aliphatic dialcohol, and it is more preferable to use 1,6-hexanediol.

[0070] As the trihydric or higher alcohol, it is preferable to use a trihydric alcohol, and it is more preferable to use trimethylolpropane, from the viewpoint of the scratch resistance, water resistance and finished appearance of the coating film to be formed.

[0071] 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.

[0072] The above polybasic acids can be used alone or in combination of two or more.

[0073] From the viewpoint of the scratch resistance, hardness and finished appearance of the coating film to be formed, it is preferable to use an alicyclic dicarboxylic acid or an anhydride thereof, and it is more preferable to use hexahydrophthalic acid or an anhydride thereof as the polybasic acid.

[0074] Furthermore, during the reaction of the polyhydric alcohol and polybasic acid, a monobasic acid, an oil component (including its fatty acid), or the like may be further used as needed. Examples of monobasic acids include benzoic acid and t-butylbenzoic acid, and examples of oil components include castor oil, dehydrated castor oil, safflower oil, soybean oil, linseed oil, tall oil, coconut oil, and their fatty acids, and these can be used alone or in combination. Furthermore, the polyester resin may be modified with an epoxy compound such as butyl glycidyl ether, alkylphenyl glycidyl ether, or neodecanoic acid glycidyl ester as needed. The content of the hydroxyl group-containing polyester (B) in the high solid content coating composition of the present invention is preferably 5 to 12 parts by mass, more preferably 6 to 11 parts by mass, and even more preferably 6 to 10 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 scratch resistance, weather resistance, hardness, and finished appearance of the coating film to be formed.

[0075] [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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] The above polyisocyanate compounds and derivatives thereof may be used alone or in combination of two or more kinds.

[0082] 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.

[0083] 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 scratch 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.

[0084] The polyisocyanate compound (C) may have an isocyanate group blocked with a blocking agent.

[0085] 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.

[0086] From the viewpoints of the scratch resistance, weather resistance, hardness 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 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.

[0087] [High solid content paint composition] The high solids coating composition of the present invention is a high solids coating composition containing (A) a hydroxyl group- and alkoxysilyl group-containing acrylic resin, (B) a hydroxyl group-containing polyester resin, and (C) a polyisocyanate compound, wherein the content of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is 20 to 50 parts by mass based on 100 parts by mass of the resin solids of the high solids coating composition, and the hydroxyl group-containing polyester resin (B) has an acid value of 10 mgKOH / g or less, a hydroxyl value of 180 to 300 mgKOH / g, and a number average molecular weight of 400 to 1500, and the solids content at the time of application is 50 mass% or more.

[0088] From the viewpoint of reducing VOCs, the high solids coating composition of the present invention preferably has a solids content of 53 mass % or more, more preferably 55 mass % or more, at the time of application.

[0089] Although the reason why the high-solids coating composition of the present invention can form coating films with excellent hardness, scratch resistance, and finished appearance is unclear, it is believed that the content of the hydroxyl- and alkoxysilyl-containing acrylic resin (A) of 20 to 50 parts by mass leads to high crosslink density due to the rapid self-condensation of the alkoxysilyl groups, thereby forming coating films with excellent hardness and scratch resistance. Furthermore, the hydroxyl value of the hydroxyl-containing polyester resin (B) of 180 to 300 mgKOH / g improves reactivity with the polyisocyanate compound (C), increasing the crosslink density and forming coating films with excellent hardness and scratch resistance. Furthermore, the acid value of the hydroxyl-containing polyester resin (B) of 10 mgKOH / g or less and the number-average molecular weight of 400 to 1,500 reduce the coating viscosity, enabling high solids content and the formation of coating films with excellent finished appearance.

[0090] From the viewpoint of the scratch resistance and hardness of the coating film formed, the high solids coating composition of the present invention preferably further contains a melamine resin (D).

[0091] [Melamine resin (D)] The melamine resin (D) 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.

[0092] 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.

[0093] The melamine resin (D) is preferably a methyl-etherified melamine resin in which the methylol groups of a partially or fully methylolated melamine resin are partially or completely etherified with methyl alcohol, a butyl-etherified melamine resin in which the methylol groups of a partially or fully methylolated melamine resin are partially or completely etherified with butyl alcohol, or a methyl-butyl mixed etherified melamine resin in which the methylol groups of a partially or fully methylolated melamine resin are partially or completely etherified with methyl alcohol and butyl alcohol.

[0094] The melamine resin (D) has a weight average molecular weight of 400 to 6,000, preferably 500 to 5,000, and more preferably 800 to 4,000.

[0095] 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.).

[0096] The above melamine resins (D) can be used either alone or in combination of two or more.

[0097] When the high solid content coating composition of the present invention contains a melamine resin (D), the content thereof is preferably 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 and hardness of the coating film to be formed.

[0098] [Other ingredients] The high solids coating composition of the present invention may further contain, as necessary, other resins, pigments, organic solvents, curing catalysts, dispersants, anti-settling agents, antifoaming agents, thickeners, ultraviolet absorbers, light stabilizers, surface conditioners, etc.

[0099] Examples of resins other than those mentioned above include acrylic resins that do not contain hydroxyl groups and / or alkoxysilyl 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. However, from the viewpoint of the hardness of the coating film to be formed and the finished appearance, it is preferable to use a hydroxyl group-containing resin that does not contain alkoxysilyl groups.

[0100] The hydroxyl-containing resin not containing an alkoxysilyl group can be obtained by copolymerizing a hydroxyl-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer (a polymerizable unsaturated monomer other than a hydroxyl-containing polymerizable unsaturated monomer and an alkoxysilyl-containing polymerizable unsaturated monomer) as explained in the section on the hydroxyl- and alkoxysilyl-containing acrylic resin (A).

[0101] When the high solids coating composition contains a hydroxyl group-containing resin that does not contain the above-mentioned alkoxysilyl group, the content thereof is preferably 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 hardness of the coating film formed and the finished appearance, etc.

[0102] 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.

[0103] 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.

[0104] Examples of the luster pigment include aluminum powder, mica powder, and mica powder coated with titanium oxide.

[0105] Examples of extender pigments include talc, clay, kaolin, baryta, barium sulfate, barium carbonate, calcium carbonate, and alumina white.

[0106] Each of the above pigments can be used alone or in combination of two or more.

[0107] When the high solid content coating composition of the present invention is used as a clear coat and contains a pigment, the amount of pigment is preferably an amount that does not impair the transparency of the resulting coating film, and for example, is usually 0.1 to 20 mass %, particularly 0.3 to 10 mass %, and even more particularly 0.5 to 5 mass %, relative to the total amount of solids in the high solid content coating composition.

[0108] 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 1 to 200 mass%, particularly 2 to 100 mass%, and even more particularly 5 to 50 mass%, based on the total amount of solids in the high solid content coating composition.

[0109] Examples of organic solvents that can be contained in the high solids coating composition of the present invention 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.

[0110] Examples of curing catalysts that can be contained in the high solids coating composition of the present invention 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 tetradecanoate. Examples of suitable organic compounds include bismuth naphthenate, 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. These may be used alone or in combination of two or more.

[0111] 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 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.

[0112] The thickener that can be contained in the high solids coating composition of the present invention can be any of the conventionally known thickeners, and examples thereof include clay minerals (e.g., metal silicates, montmorillonite), acrylics (e.g., those containing a structure consisting of a polymer or oligomer of an acrylic acid ester or methacrylic acid ester 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, acetylcellulose, cellulose ether, etc.), and 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).

[0113] The ultraviolet absorber that can be contained in the high solids coating composition of the present invention may be any conventionally known ultraviolet absorber, such as a benzotriazole-based absorber, a triazine-based absorber, a salicylic acid derivative-based absorber, a benzophenone-based absorber, etc. These may be used alone or in combination of two or more.

[0114] When the high solid content coating composition of the present invention contains an ultraviolet absorber, the amount of the ultraviolet absorber to be blended is usually 0.1 to 10 mass %, particularly 0.2 to 5 mass %, and more particularly 0.3 to 2 mass %, relative to the total amount of solids in the high solid content coating composition.

[0115] As the light stabilizer that can be contained in the high solids coating composition of the present invention, conventionally known ones can be used, and examples thereof include hindered amine light stabilizers.

[0116] 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).

[0117] 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.

[0118] 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, and particularly 20 to 40 seconds, at 20°C as measured using a Ford Cup No. 4 viscometer.

[0119] The wet coating film formed by applying the present coating material to the substrate can be cured by heating. Heating can be carried out by known heating means, for example, 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 preferably 60 to 160°C, and more preferably 80 to 140°C. The heating time is not particularly limited, but is preferably 10 to 60 minutes, and more preferably 15 to 30 minutes.

[0120] The high solids coating composition of the present invention can form a coating film that is excellent in hardness, scratch 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.

[0121] [Multi-layer coating film formation method] 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.

[0122] 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).

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] The above-mentioned primer coating composition is usually applied to an object to impart corrosion resistance to the object to be coated.

[0128] As the undercoat paint composition for forming the undercoat paint film, for example, an electrodeposition paint, preferably a cationic electrodeposition paint, can be used.

[0129] 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.

[0130] 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.

[0131] The intermediate coating composition is usually applied to an object to impart smoothness, chipping resistance and adhesion between coating films to the object.

[0132] Examples of the crosslinkable functional group contained in the base resin include a carboxyl group, a hydroxyl group, and an epoxy group.

[0133] Examples of the base resin include acrylic resin, polyester resin, alkyd resin, and urethane resin.

[0134] Examples of the crosslinking agent include melamine resins, polyisocyanate compounds, and blocked polyisocyanate compounds.

[0135] 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.

[0136] 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.

[0137] The base coat paint composition can be a known thermosetting base coat paint composition for painting automobile bodies, etc. For example, a thermosetting paint composition containing a base resin having a crosslinkable functional group, a crosslinking agent, a color pigment, and an extender pigment can be suitably used as the base coat paint composition.

[0138] 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.

[0139] Examples of the crosslinkable functional group contained in the base resin include a carboxyl group, a hydroxyl group, and an epoxy group.

[0140] Examples of the base resin include acrylic resin, polyester resin, alkyd resin, and urethane resin.

[0141] Examples of the crosslinking agent include melamine resins, polyisocyanate compounds, and blocked polyisocyanate compounds.

[0142] 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.

[0143] 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.

[0144] 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 10 to 40 minutes, and more preferably 20 to 40 minutes. [Example]

[0145] 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.

[0146] [Hydroxyl group- and alkoxysilyl group-containing acrylic resin (A)] (Production Example 1) 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 hydroxyl- and alkoxysilyl-containing acrylic resin (A-1) solution with a solids concentration of 65% by mass. The resulting hydroxyl- and alkoxysilyl-containing acrylic resin (A-1) 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.

[0147] (Manufacturing Examples 2-3) Solutions of hydroxyl- and alkoxysilyl-containing acrylic resins (A-2) and (A-3) 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. Table 1 also shows the alkoxysilyl group content, hydroxyl value, weight average molecular weight, and glass transition temperature of each hydroxyl- and alkoxysilyl-containing acrylic resin.

[0148] [Production of hydroxyl-containing acrylic resin (E) containing no alkoxysilyl groups] (Production Example 4) 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. The reaction vessel was stirred at 150°C while nitrogen gas was blown into the reaction vessel. 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 6.0 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 solution of hydroxyl-containing acrylic resin (E-1) containing no alkoxysilyl groups with a solids concentration of 65% by mass. The resulting alkoxysilyl-free hydroxyl-containing acrylic resin (E-1) had a hydroxyl value of 140 mgKOH / g, an acid value of 5.5 mgKOH / g, a weight average molecular weight of 5,500, and a glass transition temperature of 38°C.

[0149] [Table 1]

[0150] [Production of Hydroxyl-Containing Polyester Resin (B)] (Production Example 5) A reactor equipped with a stirrer, reflux condenser, water separator, and thermometer was charged with 107.8 parts of hexahydrophthalic anhydride, 86.1 parts of 1,6-hexanediol, and 36.9 parts of trimethylolpropane, and the mixture was reacted at 230°C for 6 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 2 mg KOH / g, a hydroxyl value of 226 mg KOH / g, and a number average molecular weight of 709.

[0151] (Examples 6 to 16) Solutions of hydroxyl-containing polyester resins (B-2) to (B-12) with a solid content concentration of 80% were obtained in the same manner as in Production Example 5, except that the monomer composition, reaction time, and reaction temperature in Production Example 5 were as shown in Table 2. The acid value, hydroxyl value, and number average molecular weight of each hydroxyl-containing polyester resin are also shown in Table 2.

[0152] [Table 2]

[0153] [Production of high solids coating composition] Example 1 61.5 parts (solid content 40 parts) of the hydroxyl- and alkoxysilyl-containing acrylic resin (A-1) solution obtained in Production Example 1, 7.7 parts (solid content 5 parts) of the alkoxysilyl-free hydroxyl-containing acrylic resin (E-1) obtained in Production Example 4, 10 parts (solid content 8 parts) of the hydroxyl-containing polyester resin (B-1) obtained in Production Example 5, 16.7 parts (solid content 10 parts) of "U-BAN 20SE60" (trade name, manufactured by Mitsui Chemicals, Inc., melamine resin, solid content 60%), and "SETALUX 61767 A base compound consisting of 0.5 parts (0.3 parts solids) of "VX-60" (trade name, manufactured by Allnex, viscosity modifier, solids content 60%) and 0.4 parts (0.2 parts solids) of "BYK-300" (trade name, manufactured by BYK-Chemie, surface modifier, active ingredient 52%) was uniformly mixed with 37 parts of "Sumidur N3300" (trade name, manufactured by Sumika Covestro Urethane Co., Ltd., isocyanurate of hexamethylene diisocyanate, solids content 100%) as a curing agent. Just before painting, butyl acetate was added to adjust the solids content at the time of painting to 58%, yielding High Solids Paint Composition No. 1.

[0154] Examples 2 to 14 and Comparative Examples 1 to 9 High solid content coating compositions Nos. 2 to 23 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.

[0155] [Preparation of test panels] (Preparation of test specimens) A cold-rolled steel sheet that had been subjected to zinc phosphate conversion treatment was electrocoated with "Elecron GT-10" (product name, cationic electrodeposition paint, manufactured by Kansai Paint Co., Ltd.) to a dry film thickness of 20 μm, and then heated at 170°C for 30 minutes to cure, resulting in a coated test specimen.

[0156] (Preparation of test plates) The test substrate obtained above was electrostatically coated with "WP-523H" (product name, Kansai Paint Co., Ltd., acrylic-melamine resin-based water-based primer coating composition) using a rotary atomizer electrostatic coater to a cured film thickness of 20 μm, and then left for 5 minutes to form an uncured primer coating film.

[0157] Next, "WBC-720H" (product name, acrylic-melamine resin-based water-based base coat paint composition, manufactured by Kansai Paint Co., Ltd.) was electrostatically applied onto the uncured primer coating using a rotary atomizer electrostatic coater to a dry film thickness of 12 μm. After leaving it for 3 minutes, the coating was preheated at 80°C for 5 minutes to form an uncured base coat coating.

[0158] 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.

[0159] In preparing the test panels of the above-mentioned high solid content coating composition No. 1, the test panels of Examples 2 to 14 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 23.

[0160] 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.

[0161] (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 coating. A rating of 10 or higher is considered a pass.

[0162] 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 rating of A, B, or C was considered a pass.

[0163] 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: 70% or more but less than 80% D: Gloss retention rate 50% or more but less than 70% E: Gloss retention rate less than 50%

[0164] Finished appearance: The finished appearance of each test panel was evaluated based on the Long Wave (LW) value measured using a "Wave Scan" (trade name, manufactured by BYK Gardner). The smaller the LW value, the smoother the painted surface. A rating of 10 or less is considered a pass.

[0165] [Table 3]

[0166] [Table 4]

[0167] [Table 5]

[0168] From the above results, it can be seen that the coating compositions of the examples were able to form coating films that were excellent in hardness, scratch resistance and finished appearance. The coating films formed from the coating compositions of Comparative Examples 1 to 3 and 5 to 9 did not meet the standard values ​​for hardness, scratch resistance, or finished appearance. The coating film formed from the coating composition of Comparative Example 4 was excellent in hardness, scratch resistance, and finished appearance, but the solid content did not meet the standard.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2020-132067) filed on August 4, 2020, the contents of which are incorporated herein by reference.

Claims

1. A high solids coating composition comprising (A) a hydroxyl group- and alkoxysilyl group-containing acrylic resin, (B) a hydroxyl group-containing polyester resin, and (C) a polyisocyanate compound, the content of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is 20 to 50 parts by mass based on 100 parts by mass of the resin solids of the high solid content coating composition; the hydroxyl group-containing polyester resin (B) has an acid value of 10 mgKOH / g or less, a hydroxyl group value of 180 to 300 mgKOH / g, and a number average molecular weight of 400 to 1,500; The hydroxyl group-containing polyester resin (B) is obtained by using a dihydric alcohol and a trihydric or higher alcohol in combination as the polyhydric alcohol, 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 solid content coating composition according to claim 1, wherein the content of the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is 31 to 45 parts by mass based on 100 parts by mass of the resin solids of the high solid content coating composition.

3. A high solids coating composition as described in claim 1 or 2, wherein the hydroxyl group- and alkoxysilyl group-containing acrylic resin (A) is obtained by using an alkoxysilyl group-containing polymerizable unsaturated monomer in an amount of 3 to 50 mass% relative to the total amount of copolymerizable monomer components.

4. 4. The high solid content coating composition according to claim 1, wherein the content of the hydroxyl group-containing polyester resin (B) is 5 to 12 parts by mass based on 100 parts by mass of the resin solid content of the high solid content coating composition.

5. 5. The high solids coating composition according to claim 1, wherein the content ratio of the dihydric alcohol and the trihydric or higher alcohol is 90 / 10 to 30 / 70 in terms of a mass ratio of the dihydric alcohol / the trihydric or higher alcohol.

6. The high solids coating composition according to any one of claims 1 to 5, further comprising a melamine resin (D).

7. 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 6 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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