JP2017165955A - High solid content coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high solid content coating composition capable of obtaining a coating film which is excellent in a pot life and is also excellent in scratch resistance, acid resistance and finished appearance (returning resistance), and to provide a multilayer coating film formation method using the coating composition.SOLUTION: There is provided a coating composition which contains (A) a secondary hydroxyl group-containing acrylic resin having a weight average molecular weight of 3,000-7,000, (B) an aliphatic polyisocyanate compound and/or its derivative, (C) an alkyl-etherified melamine resin having a weight average molecular weight of 1,000 or less and (D) a sulfonic acid compound and/or a phosphate compound, where an amount of the (C) component is in a range of 1.5-20 mass% with respect to the total amount of the (B) component.SELECTED DRAWING: None

Description

  The present invention relates to a high solid content coating composition and a method for forming a multilayer coating film using the coating composition.

  In recent years, from the viewpoint of protecting the global environment, it has been required to reduce volatile organic compounds (VOC) released from paints, and in each field, replacement of solvent-based paints with water-based paints is rapidly progressing.

  Also in automobile painting, a large amount of solvent-based paint was used before, and there was an urgent need to reduce the VOC discharged from these paints. Various paints used in automobile undercoating, intermediate coating and topcoating processes With regard to the above, replacement of organic solvent-based paints with water-based paints has been promoted, and at present, water-based paints are mainly used.

  However, the top clear coating is particularly required to have a high level of paint film performance (scratch resistance, acid resistance, finished appearance, etc.) and finished appearance level, and it also has coating workability such as resistance to warping and sagging. Since the level of this is insufficient, solvent-based clear paint is still mainly applied.

  One technique for reducing VOCs that does not rely on water-based clear paint is high solid differentiation of the paint (increasing solid content concentration).

  For example, Patent Document 1 discloses a high solid content coating composition in which a polyisocyanate compound and a melamine resin are used in combination with a reaction product of a specific carboxyl group-containing compound and an epoxy group-containing compound, and further contains a specific hydroxyl group-containing resin. Things are disclosed.

  However, since this coating composition contains a reaction product of a carboxyl group-containing compound and an epoxy group-containing compound having a low molecular weight and a high hydroxyl group concentration, the pot life of the coating becomes insufficient, or 2 coats 1 In the bake metallic coating specification, the low molecular weight component may erode the lower metallic layer, resulting in poor metallic appearance (so-called mottle phenomenon).

  Patent Document 2 discloses a top coating composition containing, as essential components, a vinyl copolymer containing a side chain having a specific group (lactone-modified hydroxyl group), an alkoxymonomeric melamine, a blocked isocyanate, and a rheology control agent. Is disclosed.

  However, in this overcoating composition, since the vinyl copolymer has a structure derived from a specific group (lactone-modified hydroxyl group), the scratch resistance is improved, but the acid resistance is insufficient. was there. Furthermore, since the specific group (lactone-modified hydroxyl group) of the vinyl-based copolymer is highly polar, the mist phenomenon is likely to occur like the coating composition of Patent Document 1, and the metallic in the 2-coat 1-bake metallic coating specification. In some cases, the appearance was poor.

  Patent Document 3 discloses a clear paint comprising a specific acrylic resin, a specific polyester resin, a specific melamine resin, a specific acid catalyst, and a blocked isocyanate.

  However, this clear paint has a problem that high solid differentiation is difficult and the amount of melamine resin is relatively large, so that the acid resistance of the coating film is insufficient.

JP 2002-201430 A JP 2002-020682 A Japanese Patent Laid-Open No. 4-130168

  An object of the present invention is to provide a high solid content coating composition capable of obtaining a coating film excellent in pot life, scratch resistance, acid resistance, and finished appearance, and a multi-layer coating using the coating composition It is to provide a film forming method.

  As a result of intensive studies to achieve the above object, the present inventors have (A) a secondary hydroxyl group-containing acrylic resin having a specific molecular weight range, (B) an aliphatic polyisocyanate compound and / or a derivative thereof, and ( C) It has been found that according to a coating composition containing an alkyl etherified melamine resin in a specific molecular weight range, and the amount of the (C) component to the (B) component is within the specific range, the above object can be achieved. It came to be completed.

  That is, this invention includes the following aspects.

Item 1, (A) a secondary hydroxyl group-containing acrylic resin having a weight average molecular weight of 3000 to 7000,
(B) an aliphatic polyisocyanate compound and / or a derivative thereof,
(C) a coating composition containing an alkyl etherified melamine resin having a weight average molecular weight of 1000 or less, and (D) a sulfonic acid compound and / or a phosphoric acid compound,
(C) The amount of a component exists in the range of 1.5-20 mass% with respect to the total amount of (B) component, The high solid content coating composition characterized by the above-mentioned.

  Item 2, The high hydroxyl group according to Item 1, wherein the secondary hydroxyl group-containing polymerizable unsaturated monomer (a) is 50 to 100% by mass of the total amount of the hydroxyl group-containing polymerizable unsaturated monomer that is a constituent of the acrylic resin (A). Solid content paint composition.

  Item 3. The high solid content coating composition according to Item 1 or 2, wherein the alkyl etherified melamine resin (C) has substantially no imino group.

  Item 4. The high solid content coating composition according to any one of Items 1 to 3, further comprising an acylated hindered amine and / or an amino ether-based hindered amine.

  Item 5. An article having a coating film of the coating composition according to any one of Items 5 and 1-4.

  Item 6. A method for forming a multilayer coating film by applying at least one layer of a colored base coat paint and at least one layer of a clear coat paint to a substrate in order, wherein the top layer is a clear coat paint. A method for forming a multilayer coating film comprising coating the coating composition according to any one of -4.

  The coating composition of the present invention comprises a secondary hydroxyl group-containing acrylic resin having a specific weight average molecular weight range as a base resin, an aliphatic polyisocyanate compound and / or a derivative thereof as a crosslinking agent, and an alkyl etherified melamine resin having a specific weight average molecular weight range. In addition, it contains a sulfonic acid compound and / or a phosphoric acid compound, and contains the alkyl etherified melamine resin in a specific amount range with respect to the total amount of the aliphatic polyisocyanate compound and / or its derivative. It is characterized by doing.

  A coating film excellent in acid resistance and scratch resistance because it uses an aliphatic polyisocyanate compound and / or a derivative thereof as a main component of a crosslinking agent and an alkyl etherified melamine resin in a specific low molecular weight range as a secondary component. Can be obtained.

  In addition, since the acrylic resin as the base resin contains a secondary hydroxyl group that has a milder reactivity than the primary hydroxyl group in the specific low molecular weight range, a coating film excellent in pot life and finished appearance is obtained. Can be obtained.

  As described above, according to the coating composition of the present invention, these synergistic effects can form a coating film excellent in any of scratch resistance, acid resistance, and finished appearance, and has a high pot life. The effect that a solid content coating composition can be obtained can be produced.

  Hereinafter, the coating composition of the present invention (which may be referred to as “the present coating” in the present specification) and the method for forming a coating film will be described in more detail.

The coating composition of the present invention (hereinafter sometimes abbreviated as “present coating”)
(A) A secondary hydroxyl group-containing acrylic resin having a weight average molecular weight of 3000 to 7000,
(B) an aliphatic polyisocyanate compound and / or a derivative thereof,
(C) a coating composition containing an alkyl etherified melamine resin having a weight average molecular weight of 1000 or less, and (D) a sulfonic acid compound and / or a phosphoric acid compound,
(C) It is the high solid content coating composition characterized by being in the range of 1.5-20 mass% with respect to the total amount of (B) component.

<Secondary hydroxyl group-containing acrylic resin (A)>
The secondary hydroxyl group-containing acrylic resin (A) (in the present specification, sometimes referred to as “component (A)”) is an acrylic resin containing a secondary hydroxyl group. Specifically, for example, (a) It can synthesize | combine by copolymerizing the monomer component which consists of a secondary hydroxyl-containing polymerizable unsaturated monomer and (b) other polymerizable unsaturated monomers by a conventional method.

  The secondary hydroxyl group-containing polymerizable unsaturated monomer (a) is a compound having one secondary hydroxyl group and one polymerizable unsaturated bond in one molecule. The polymerizable unsaturated bond means an unsaturated bond capable of radical polymerization. Examples of the polymerizable unsaturated bond include (meth) acryloyl group, acrylamide group, vinyl group, allyl group, (meth) acryloyloxy group, vinyl ether group and the like.

  As the secondary hydroxyl group-containing polymerizable unsaturated monomer (a), for example, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-hydroxybutyl (meta) from the viewpoint of the finished appearance of the coating film. ) A polymerizable unsaturated monomer having a secondary hydroxyl group having an alkyl group in the ester part such as acrylate having 2 to 8, particularly 3 to 6, more particularly 3 or 4, a (meth) acrylic acid and an epoxy group-containing compound ( Examples include adducts with Cardura E10 (trade name), Hexion Specialty Chemical Co., Ltd., neodecanoic acid glycidyl ester, and the like. Among these, 2-hydroxypropyl (meth) acrylate is particularly preferable. The monomer (a) can be used alone or in combination of two or more.

  In the present specification, “(meth) acrylate” means “acrylate or methacrylate”. “(Meth) acrylic acid” means “acrylic acid or methacrylic acid”. “(Meth) acryloyl” means “acryloyl or methacryloyl”. “(Meth) acryloyl” means “acryloyl or methacryloyl”.

  The other polymerizable unsaturated monomer (b) is a monomer other than the above-mentioned secondary hydroxyl group-containing polymerizable unsaturated monomer (a), and specifically has one polymerizable unsaturated bond in one molecule. A compound can be mentioned. Specific examples of the unsaturated monomer (b) are listed in the following (1) to (8).

(1) Acid group-containing polymerizable unsaturated monomer The acid group-containing polymerizable unsaturated monomer is a compound having one acid group and one polymerizable unsaturated bond in each molecule. Examples of the monomer 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 sulfoethyl (meth) acrylate, and the like. Can be mentioned. These can be used alone or in combination of two or more. When an acid group-containing polymerizable unsaturated monomer is used, the acid value of the acrylic resin (A) is 1.0 to 15.0 mgKOH / g, particularly 3. from the viewpoint of pot life and scratch resistance of the coating composition. The amount is preferably 0 to 8.0 mgKOH / g.

(2) Hydroxyl (excluding secondary hydroxyl group) -containing polymerizable unsaturated monomer A compound having one hydroxyl group (excluding secondary hydroxyl group) and one polymerizable unsaturated bond in one molecule. The hydroxyl group excluding the secondary hydroxyl group is a primary hydroxyl group or a tertiary hydroxyl group. Examples of the monomer include (meth) acrylic acid such as 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate, and a dihydric alcohol having 2 to 10 carbon atoms. And monoesterified products (excluding those having secondary hydroxyl groups); hydroxyl group-containing monomers modified by ring-opening polymerization reaction of ε-caprolactone (excluding those having secondary hydroxyl groups), and the like.

  As the hydroxyl group-containing monomer modified by ring-opening polymerization reaction of ε-caprolactone, a commercially available product can be used. Examples of commercially available products include “Placcel FA-1”, “Placcel FA-2”, “ Plaxel FA-3, Plaxel FA-4, Plaxel FA-5, Plaxel FM-1, Plaxel FM-2, Plaxel FM-3, Plaxel FM-4, Plaxel FM-5 "(all of which are trade names manufactured by Daicel Chemical Industries, Ltd.).

(3) Esterified product of acrylic acid or methacrylic acid and C1-C20 monohydric alcohol Specifically, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meta ) Acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, isomyristyl (meth) acrylate, stearyl (meth) acrylate, isostearyl acrylate ( Osaka Organic Chemical Industry, trade name), lauryl (meth) acrylate, tridecyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, etc. I can make it.

(4) Alkoxysilyl group-containing polymerizable unsaturated monomer Specifically, vinyltrimethoxysilane, vinyltriethoxysilane, acryloxyethyltrimethoxysilane, methacryloxyethyltrimethoxysilane, acryloxypropyltrimethoxysilane, methacryloxy Examples thereof include propyltrimethoxysilane, acryloxypropyltriethoxysilane, methacryloxypropyltriethoxysilane, and vinyltris (β-methoxyethoxy) silane. Among these, preferred alkoxysilyl group-containing polymerizable unsaturated monomers include vinyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and the like.

  By using an alkoxysilyl group-containing polymerizable unsaturated monomer as a constituent component, curability can be improved because a cross-linking bond is generated by a condensation reaction between alkoxylyl groups and a reaction between an alkoxysilyl group and a hydroxyl group.

(5) Aromatic vinyl monomer Specific examples include styrene, α-methylstyrene, vinyltoluene and the like.

  By using an aromatic polymerizable unsaturated monomer as a constituent component, the glass transition temperature of the resulting resin is increased, and a hydrophobic coating film having a high refractive index can be obtained. The effect of improving the finished appearance can be obtained.

  When an aromatic polymerizable unsaturated monomer is used as a constituent component, the blending ratio is preferably 5 to 50% by mass, particularly 10 to 40% by mass, based on the total amount of monomer components.

(6) Glycidyl group-containing polymerizable unsaturated monomer The glycidyl group-containing polymerizable unsaturated monomer is a compound having one glycidyl group and one polymerizable unsaturated bond in one molecule, specifically, glycidyl acrylate. And glycidyl methacrylate.

(7) Polymerizable unsaturated bond-containing nitrogen atom-containing compound For example, acrylamide, methacrylamide, dimethylacrylamide, N, N-dimethylpropylacrylamide, N-butoxymethylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, diacetone Examples include acrylamide, N, N-dimethylaminoethyl (meth) acrylate, vinyl pyridine, vinyl imidazole, acrylonitrile, methacrylonitrile and the like.

(8) Other vinyl compounds Examples include vinyl acetate, vinyl propionate, vinyl chloride, and vinyl versatate. Examples of the versatic acid vinyl ester include “Veoba 9” and “Veoba 10” (trade names, manufactured by Japan Epoxy Resin Co., Ltd.), which are commercially available products.

  As the other polymerizable unsaturated monomer (b), the monomers represented by the above (1) to (8) can be used alone or in combination of two or more.

  The weight average molecular weight of the acrylic resin (A) is from 3000 to 7000, particularly from 3500 to 6500, more preferably from 4000 to 6000, from the viewpoint of high solid differentiation and the finished appearance of the coating film. .

  In the present specification, the average molecular weight is a value calculated based on the molecular weight of standard polystyrene from a chromatogram measured by gel permeation chromatography. As the gel permeation chromatograph, “HLC8120GPC” (manufactured by Tosoh Corporation) was used. As the columns, four columns of “TSKgel G-4000HXL”, “TSKgel G-3000HXL”, “TSKgel G-2500HXL”, “TSKgel G-2000HXL” (both manufactured by Tosoh Corporation, trade name) were used, Mobile phase: Tetrahydrofuran, measurement temperature: 40 ° C., flow rate: 1 cc / min, detector: RI

  The glass transition temperature of the acrylic resin (A) is preferably in the range of 10 to 50 ° C, particularly 20 to 45 ° C, from the viewpoint of the hardness of the coating film and the finished appearance.

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

1 / Tg (K) = (W1 / T1) + (W2 / T2) + (1)
Tg (° C.) = Tg (K) -273 (2)
In each formula, W1, W2,... Represent the respective mass fractions of the monomers used for copolymerization, and T1, T2,... Represent the Tg (K) of the homopolymer of each monomer.

  T1, T2,... Are values according to Polymer Hand Book (Second Edition, edited by J. Brandup / E.H. Immergut) pages III-139-179. The glass transition temperature (° C.) when the Tg of the monomer homopolymer is not clear is a static glass transition temperature, for example, using a differential scanning calorimeter “DSC-220U” (manufactured by Seiko Instruments Inc.), Take the sample in a measuring cup, remove the solvent completely by vacuum suction, measure the change in calorie in the range of -20 ° C to + 200 ° C at a rate of temperature rise of 3 ° C / min. The change point was defined as the static glass transition temperature.

  The mixing ratio of the secondary hydroxyl group-containing polymerizable unsaturated monomer (a) and the other polymerizable unsaturated monomer (b) is 20 to 20 for the secondary hydroxyl group-containing polymerizable unsaturated monomer (a) with respect to the total monomer amount. It is preferable that it is in the range of 45% by mass, especially 25 to 40% by mass, and that the other unsaturated monomer (b) is in the range of 55 to 80% by mass, particularly 60 to 75% by mass. preferable. When the amount of the secondary unsaturated hydroxyl group-containing polymerizable unsaturated monomer (a) is less than 20% by mass, the curability and the finished appearance of the cured coating film may be insufficient. The finished appearance of the coating film may be insufficient.

  From the viewpoint of improving the pot life and the finished appearance of the coating film, 50 to 100% by mass of the secondary hydroxyl group-containing polymerizable unsaturated monomer (a) in the total amount of the hydroxyl group-containing polymerizable unsaturated monomer in the acrylic resin (A), In particular, it is preferable to contain 75 to 100% by mass, and more particularly 85 to 100% by mass.

  The hydroxyl value of the acrylic resin (A) is preferably in the range of 70 to 200 mgKOH / g, particularly 80 to 185 mgKOH / g, more particularly 100 to 170 mgKOH / g, from the viewpoints of curability and scratch resistance. .

  The acid value of the acrylic resin (A) is in the range of 1.0 to 15.0 mgKOH / g, particularly 3.0 to 8.0 mgKOH / g, from the viewpoint of the pot life and finished appearance of the coating composition. It is preferable.

  The copolymerization method for obtaining the secondary hydroxyl group-containing acrylic resin (A) by copolymerizing the monomer mixture is not particularly limited and can be carried out by a conventional method, but in particular in an organic solvent. A solution polymerization method in which polymerization is performed in the presence of a polymerization initiator can be preferably used.

  Examples of the organic solvent used in the solution polymerization method include aromatic solvents such as toluene, xylene, and swazole 1000 (trade name, high-boiling petroleum solvent) manufactured by Cosmo Oil; ethyl acetate, butyl acetate, propyl Ester solvents such as propionate, butyl propionate, methoxypropyl acetate, ethoxyethyl propionate, 3-methoxybutyl acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate; methyl ethyl ketone, methyl isobutyl ketone, methyl amyl Examples thereof include ketone solvents such as ketones, and alcohol solvents such as isopropanol, n-butanol, iso-butanol, and 2-ethylhexanol.

  These organic solvents can be used alone or in combination of two or more, but it is preferable to use an ester solvent or a ketone solvent from the viewpoint of the solubility of the acrylic resin. Further, aromatic solvents can be used in suitable combinations.

  Examples of the polymerization initiator that can be used for copolymerization of the secondary hydroxyl group-containing acrylic resin (A) include 2,2′-azobisisobutyronitrile, benzoyl peroxide, di-t-butyl peroxide, and di-t. -Known radical polymerization initiators such as amyl peroxide, t-butyl peroctoate, 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile) Can be mentioned.

  The secondary hydroxyl group-containing acrylic resin (A) can be used alone or in combination of two or more.

  In the coating composition of the present invention, resins other than the secondary hydroxyl group-containing acrylic resin (A) can be used together as necessary. Specifically, for example, an acrylic resin other than the acrylic resin (A), a polyester resin, a polyurethane resin, a polyether resin, and the like can be mentioned. Preferred examples thereof include a hydroxyl group-containing polyester resin and a hydroxyl group-containing polyurethane resin. it can.

  The hydroxyl group-containing polyester resin can be produced by an ordinary method, for example, by an esterification reaction of a polybasic acid and a polyhydric alcohol. The polybasic acid is a compound having two or more carboxyl groups in one molecule. For example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic acid, hexa Examples include hydrophthalic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid, pyromellitic acid, and anhydrides thereof. The polyhydric alcohol has two or more hydroxyl groups in one molecule. For example, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-diethyl-1,3 -Propanediol, neopentyl glycol, 1,9-nonanediol, 1,4-cyclohexanediol, hydroxy Diols such as neopentyl glycol phosphate, 2-butyl-2-ethyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 2,2,4-trimethylpentanediol, hydrogenated bisphenol A, etc. , And trivalent or higher polyol components such as trimethylolpropane, trimethylolethane, glycerin, pentaerythritol, and the like, and 2,2-dimethylolpropionic acid, 2,2-dimethylolbutanoic acid, 2,2-dimethylol Examples thereof include hydroxycarboxylic acids such as pentanoic acid, 2,2-dimethylolhexanoic acid, and 2,2-dimethyloloctanoic acid.

  Also, by reacting mono-epoxy compounds such as α-olefin epoxides such as propylene oxide and butylene oxide, Cardura E10 (product name, glycidyl ester of synthetic hyperbranched saturated fatty acid) and the like with acids, A compound may be introduced into the polyester resin.

  When introducing a carboxyl group into a polyester resin, for example, it can be introduced by adding an acid anhydride to a hydroxyl group-containing polyester and half-esterifying it.

  The hydroxyl value of the hydroxyl group-containing polyester resin is preferably in the range of 100 to 250 mgKOH / g, more preferably 120 to 220 mgKOH / g. The weight average molecular weight of the hydroxyl group-containing polyester resin is preferably 500 to 3000, more preferably 500 to 2000.

  Examples of the hydroxyl group-containing polyurethane resin include a hydroxyl group-containing polyurethane resin obtained by reacting a polyol and a polyisocyanate.

  Examples of the polyol include dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, butylene glycol and hexamethylene glycol, and trihydric alcohols such as trimethylolpropane, glycerin and pentaerythritol as low molecular weight substances. Can do. Examples of the high molecular weight material include polyether polyol, polyester polyol, acrylic polyol, and epoxy polyol. Examples of the polyether polyol include polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. Examples of the polyester polyol include alcohols such as the divalent alcohols, dipropylene glycol, 1,4-butanediol, 1,6-hexanediol, and neopentyl glycol, and dibasic acids such as adipic acid, azelaic acid, and sebacic acid. Lactone-based ring-opening polymer polyol such as polycaprolactone, polycarbonate diol, and the like. Moreover, for example, carboxyl group-containing polyols such as 2,2-dimethylolpropionic acid and 2,2-dimethylolbutanoic acid can also be used.

  Examples of the polyisocyanate to be reacted with the above polyol include aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; and burette type addition of these polyisocyanates. Product, isocyanurate cycloadduct; isophorone diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4- (or-2,6-) diisocyanate, 1,3- (or 1,4-) Alicyclic diisocyanates such as di (isocyanatomethyl) cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1,2-cyclohexane diisocyanate; And burette type adducts, isocyanurate cycloadducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethyl xylylene diisocyanate, tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate, (m- or p-) phenylene diisocyanate, 4,4′-biphenylene diisocyanate, 3,3′-dimethyl-4,4 Aromatic diisocyanates such as' -biphenylene diisocyanate, bis (4-isocyanatophenyl) sulfone, isopropylidenebis (4-phenylisocyanate) And burette type adducts, isocyanurate cycloadducts of these polyisocyanates; triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 1,3,5-triisocyanatobenzene, 2, Polyisocyanates having three or more isocyanate groups in one molecule such as 4,6-triisocyanatotoluene, 4,4′-dimethyldiphenylmethane-2,2 ′, 5,5′-tetraisocyanate; And polyisocyanate burette type adducts, isocyanurate ring adducts, and the like.

  The hydroxyl value of the hydroxyl group-containing polyurethane resin is preferably in the range of 100 to 250 mgKOH / g, more preferably 120 to 220 mgKOH / g. The weight average molecular weight of the hydroxyl group-containing polyurethane resin is preferably in the range of 1000 to 4000, more preferably 1000 to 2000.

  When a resin other than the secondary hydroxyl group-containing acrylic resin (A) (more specifically, a polyester resin, a polyurethane resin, a polyether resin, etc.) is used in combination, a resin other than the secondary hydroxyl group-containing acrylic resin (A) Is preferably 50% by mass or less, more preferably in the range of 0 to 20% by mass, based on the total solid content of the secondary hydroxyl group-containing acrylic resin (A).

<Aliphatic polyisocyanate compound and / or its derivative (B)>
The aliphatic polyisocyanate compound and / or its derivative (B) may be referred to as “component (B)” in the present specification.

  As the aliphatic polyisocyanate compound, an aliphatic compound having two or more isocyanate groups in one molecule known for polyurethane production, for example, ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, pentamethylene diisocyanate, Dodecamethylene diisocyanate, lysine diisocyanate, 1,2-propylene diisocyanate, 1,2-butylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, 2,4,4- or 2,2,4-trimethylhexa Methylene diisocyanate, bis (2-isocyanatoethyl) fumarate, bis (2-isocyanatoethyl) carbonate, 2,6-diisocyanatomethyl Aliphatic diisocyanates such as proate, 2-isocyanatoethyl-2,6-diisocyanatohexanoate, such as lysine ester triisocyanate, 1,4,8-triisocyanatooctane, 1,6,11-triisocyanate Fats such as natoundecane, 1,8-diisocyanato-4-isocyanatomethyloctane, 1,3,6-triisocyanatohexane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanatomethyloctane Group triisocyanate and the like.

  Examples of the derivative of the aliphatic polyisocyanate compound include various derivatives such as dimer, trimer, biuret, allophanate, carbodiimide, uretdione, uretoimine, isocyanurate, iminooxadiazinedione of the above-described aliphatic polyisocyanate compound. Can do.

  Of the aliphatic polyisocyanate compounds and derivatives thereof, aliphatic diisocyanates and isocyanurates thereof can be suitably used from the viewpoints of high solid differentiation and scratch resistance.

  Of these, hexamethylene diisocyanate and its isocyanurate are particularly preferably used.

  In the present specification, “and / or” means “at least one”. For example, “aliphatic polyisocyanate compound and / or derivative thereof” is “at least one of aliphatic polyisocyanate compound and derivative thereof” or “at least one selected from the group consisting of aliphatic polyisocyanate compound and derivative thereof”. In other words.

  As the polyisocyanate compound, in addition to the aliphatic polyisocyanate compound and derivatives thereof, those known for polyurethane production, such as alicyclic polyisocyanates, araliphatic polyisocyanates, aromatic polyisocyanates and derivatives of these polyisocyanates, etc. Can also be used to such an extent that the coating composition performance such as high solid differentiation of the coating composition and scratch resistance of the resulting coating film is not impaired.

  Examples of the alicyclic polyisocyanate include 1,3-cyclopentene diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-cyclohexane diisocyanate, 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (common name: Isophorone diisocyanate), 4,4'-methylenebis (cyclohexyl isocyanate), methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 1,3-bis (isocyanatomethyl) cyclohexane, 1,4-bis (Isocyanatomethyl) cyclohexane, norbornane diisocyanate, dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methyl Alicyclic diisocyanates such as lohexylene diisocyanate (hydrogenated TDI) and bis (2-isocyanatoethyl) -4-cyclohexene-1,2-dicarboxylate, such as 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) Tan, 6- (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, 6- (2-isocyanatoethyl) -2-isocyanatomethyl-2- (3-isocyanatopropyl) -An alicyclic triisocyanate such as bicyclo (2.2.1) heptane can be used.

  Examples of the araliphatic polyisocyanate include 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, for example, an araliphatic triisocyanate such as 1,3,5-triisocyanatomethylbenzene Etc.

  Examples of the aromatic polyisocyanate include m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4′-diphenyl diisocyanate, 3,3′-dimethyl-4,4′-diisocyanatobiphenyl, and 3,3′-dimethyl. -4,4'-diisocyanatodiphenylmethane, 1,5-naphthalene diisocyanate, 2,4'- or 4,4'-diphenylmethane diisocyanate (MDI) or mixtures thereof, 2,4- or 2,6-tolylene diisocyanate Or mixtures thereof, aromatic diisocyanates such as 4,4′-toluidine diisocyanate, 4,4′-diphenyl ether diisocyanate, m- and p-isocyanatophenylsulfonyl isocyanate, such as triphenylmethane-4,4 ′, 4 ″ -Triisocy Aromatic triisocyanates such as anate, 1,3,5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, for example, 4,4′-diphenylmethane-2,2 ′, 5,5′-tetra Examples thereof include aromatic tetraisocyanates such as isocyanate.

  Examples of the polyisocyanate derivative include various derivatives such as the dimer, trimer, biuret, allophanate, carbodiimide, uretdione, uretoimine, isocyanurate, and iminooxadiazinedione of the above polyisocyanate compound.

  These polyisocyanate compounds can be used alone or in combination of two or more.

  The weight average molecular weight of the aliphatic polyisocyanate compound and / or derivative thereof (B) is 1000 or less, particularly 150 to 1000, more particularly from the viewpoints of high solid differentiation and the finished appearance and scratch resistance of the resulting coating film. It is preferable to be within the range of 400 to 950.

  When a polyisocyanate compound other than the aliphatic polyisocyanate compound and / or its derivative (B) and its derivative are used in combination, the polyisocyanate compound other than the aliphatic polyisocyanate compound and / or its derivative (B) and its derivative Is preferably 50% by mass or less, more preferably in the range of 0 to 20% by mass, based on the total solid content of the aliphatic polyisocyanate compound and / or derivative (B) thereof.

<Alkyl etherified melamine resin (C)>
Alkyl etherified melamine resin (C) (may be described as “(C) component” in this specification) is an addition reaction or addition condensation reaction of aldehyde such as formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde and the like with melamine. Thus, a methylolated melamine resin can be obtained, and further, this methylol group can be synthesized by alkyl etherification with an alcohol.

  Examples of the alcohol used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, 2-ethylbutanol, and 2-ethylhexanol.

  As the alkyl etherified melamine resin, for example, a hydrogen atom of a hydroxyl group of a methylol group is substituted with an alkyl group, and examples of the alkyl group include a methyl group, an ethyl group, an n-butyl group, an isobutyl group, and a 2-ethylbutyl group. And 2-ethylhexyl group.

  The alkyl etherified melamine resin may be a condensate of an alkyl etherified melamine resin (one obtained by condensation reaction of an alkyl etherified melamine resin to increase the molecular weight).

  Of these, methyl and butyl mixed alkyl etherified melamine resins are particularly preferred.

  The alkyl etherified melamine resin (C) should preferably have a weight average molecular weight of 1000 or less, particularly 950 or less, from the viewpoints of high solid state differentiation and the finished appearance and scratch resistance of the resulting coating film. Can do.

  A commercially available product can be used as the alkyl etherified melamine resin (C). Examples of commercially available products include Cymel 235, Cymel 238, Cymel 232, Cymel 325, Cymel 327, Cymel 350, Cymel 370, Cymel 212, Cymel 211, Resimin 745, Resimin 747, manufactured by Ornex Japan. .

  The alkyl etherified melamine resin (C) is more preferable as the number of imino groups is smaller from the viewpoint of improving pot life, and more preferably substantially free of imino groups.

  More specifically, 5 or more, particularly 5.5 or more, more particularly preferably all methylolated so that substantially no imino group remains, and has 6 methylol groups per triazine nucleus. An alkyl etherified melamine resin synthesized by alkyl etherifying a methylolated melamine resin synthesized as described above is preferred.

  The alkyl etherified melamine resin (C) has 4.0 or more, particularly 5.0 or more, more particularly 5.5 or more alkyl ether groups out of a maximum of 6 per one triazine nucleus. Synthesized alkyl etherified melamine resins are preferred from the viewpoint of improving pot life.

  Alkyl etherified melamine resin (C) can be used individually or in combination of 2 or more types.

  In the coating composition of the present invention, the amount of the component (C) is in the range of 1.5 to 20% by mass with respect to the total amount of the component (B) from the viewpoint of finished appearance and scratch resistance, It is preferable to be in the range of 1.5 to 15% by mass, more particularly 1.5 to 10% by mass.

  The amount of the secondary hydroxyl group-containing acrylic resin (A), aliphatic polyisocyanate compound and / or derivative thereof (B), and alkyl etherified melamine resin (C) in the paint is such as the finished appearance and the curability of the coating film. From the viewpoint, the secondary hydroxyl group-containing acrylic resin (A) is 45 to 80% by mass, especially 50 to 70% by mass, fat based on the total solid content of the component (A), the component (B) and the component (C). Group polyisocyanate compound and / or derivative thereof (B) is 20 to 50% by mass, particularly 25 to 40% by mass, alkyl etherified melamine resin (C) is 0.5 to 10% by mass, particularly 1 to 7% by mass, In particular, it is preferable to be in the range of 1 to 5% by mass.

<Sulfonic acid compound and / or phosphoric acid compound (D)>
In the coating composition of the present invention, from the viewpoint of imparting scratch resistance, as the acid catalyst, a sulfonic acid compound and / or a phosphoric acid compound (D) (in this specification, may be referred to as component (D)). contains.

  The sulfonic acid compound is a compound containing a sulfonic acid group, for example, a sulfonic acid compound such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid; neutralized salt of these sulfonic acid compounds and amine compounds Etc.

  The phosphoric acid compound is a compound containing a phosphoric acid group. For example, phosphoric acid; mono-n-propyl phosphoric acid, monoisopropyl phosphoric acid, mono-n-butyl phosphoric acid, monoisobutyl phosphoric acid, mono-tert-butyl phosphoric acid Monoalkyl phosphoric acid such as monooctyl phosphoric acid, mono 2-ethylhexyl phosphoric acid, monodecyl phosphoric acid; di-n-propyl phosphoric acid, diisopropyl phosphoric acid, di-n-butyl phosphoric acid, diisobutyl phosphoric acid, di-tert-butyl phosphorous Dialkyl phosphoric acid such as acid, dioctyl phosphoric acid, di-2-ethylhexyl phosphoric acid, didecyl phosphoric acid; mono-n-propyl phosphorous acid, monoisopropyl phosphorous acid, mono-n-butyl phosphorous acid, monoisobutyl phosphorous acid Monoalkyl such as mono-tert-butylphosphorous acid, monooctylphosphorous acid, monodecylphosphorous acid, etc. Phosphorous acid: di-n-propyl phosphorous acid, diisopropyl phosphorous acid, di-n-butyl phosphorous acid, diisobutyl phosphorous acid, di-tert-butyl phosphorous acid, dioctyl phosphorous acid, didecyl phosphorous acid And dialkyl phosphorous acid such as phosphoric acid group-containing acrylic resin; neutralized salts of these phosphoric acid compounds and amine compounds.

  The sulfonic acid compound and / or the phosphoric acid compound (D) can be used alone or in combination of two or more.

  In the coating composition of the present invention, a sulfonic acid compound can be suitably used from the viewpoint of scratch resistance and pot life.

  As the sulfonic acid, dodecylbenzenesulfonic acid and dinonylnaphthalenesulfonic acid are particularly preferable from the viewpoint of scratch resistance.

  Moreover, as an amine compound as a neutralizing agent of a sulfonic acid compound and / or a phosphoric acid compound, a tertiary amine compound such as triethylamine can be preferably used from the viewpoint of finished appearance.

  The amount of the sulfonic acid compound and / or phosphoric acid compound (D) is determined from the viewpoint of the finished appearance, secondary hydroxyl group-containing acrylic resin (A), aliphatic polyisocyanate compound and / or derivative (B), and alkyl etherified melamine. It is 1.5% by mass or less, particularly 0.1 to 1.0% by mass, and more particularly 0.3 to 0.8% by mass with respect to the total solid content of the resin (C). preferable.

  The paint can further contain a color pigment, a bright pigment, a dye, and the like, if necessary, and also an extender pigment, a catalyst, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a thickener, A rust inhibitor, a surface conditioner, an organic solvent, and the like can be appropriately contained.

  Examples of the coloring pigment include titanium oxide, zinc white, carbon black, cadmium red, molybdenum red, chromium yellow, chromium oxide, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, selenium pigment, Examples include perylene pigments.

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

  Examples of extender pigments include talc, clay, kaolin, barita, barium sulfate, barium carbonate, calcium carbonate, and alumina white.

  The above pigments can be used alone or in combination of two or more.

  When the coating composition of the present invention is used as a clear coating and contains a pigment, the amount of the pigment is preferably an amount that does not hinder the transparency of the resulting coating film. The total solid content in the coating composition is usually in the range of 0.1 to 20% by mass, particularly 0.3 to 10% by mass, more preferably 0.5 to 5% by mass.

  Further, when the coating composition of the present invention is used as a colored coating and contains a pigment, the amount of the pigment is usually 1 to 200% by mass with respect to the total solid content in the coating composition. In particular, the content is preferably in the range of 2 to 100% by mass, more preferably 5 to 50% by mass.

  As the ultraviolet absorber, conventionally known ones can be used, and examples thereof include ultraviolet absorbers such as benzotriazole absorbers, triazine absorbers, salicylic acid derivative absorbers, and benzophenone absorbers. it can. These can be used alone or in combination of two or more.

  When the coating composition of this invention contains a ultraviolet absorber, the compounding quantity of a ultraviolet absorber is 0.1-10 mass% normally with respect to the solid content total amount in a coating composition, Especially 0.2- It is preferably 5% by mass, more preferably in the range of 0.3-2% by mass.

  A conventionally well-known thing can be used as a light stabilizer, For example, a hindered amine light stabilizer etc. can be mentioned.

  As the hindered amine light stabilizer, a hindered amine light stabilizer having a low basicity can be suitably used from the viewpoint of pot life. Examples of such hindered amine light stabilizers include acylated hindered amines and amino ether-based hindered amines. Specific examples include HOSTAVIN 3058 (manufactured by Clariant) and TINUVIN 123 (manufactured by BASF).

  When the coating composition of the present invention contains a light stabilizer (for example, acylated hindered amine, amino ether-based hindered amine), the blending amount of the light stabilizer is usually 0 with respect to the total solid content in the coating composition. It is preferable to be within the range of 0.1 to 10% by mass, particularly 0.2 to 5% by mass, and more particularly 0.3 to 2% by mass.

  As the organic solvent, those usually used for paints can be used, and examples thereof include aromatic solvents, ester solvents, ketone solvents, alcohol solvents and the like that can be used in the above-described solution polymerization method. Is done. These organic solvents can be used alone or in combination of two or more.

  In a preferred embodiment, the coating composition of the present invention is an organic solvent type coating composition in which the solvent is mainly an organic solvent.

  In the present specification, the “high solid content coating composition” refers to a coating composition having a coating solid content concentration (solid content concentration during coating; coating NV (nonvolatile content) value) higher than usual. For example, when the coating composition of the present invention is used as a clear coating, the high solid content refers to one having a coating solid content concentration of about 50 to 55% by mass or more. The coating solid content concentration of the paint is usually 57 to 65% by mass, and particularly preferably 58 to 63% by mass from the viewpoint of achieving both high solid differentiation and a finished appearance.

  In addition, solid content can be calculated | required as a heating residue which is the mass fraction of the residue obtained by evaporation under the predetermined conditions prescribed | regulated to JISK5601.

  This paint is a base resin at room temperature because it normally comprises an aliphatic polyisocyanate compound having a free (free) isocyanate group and / or a derivative thereof as the component (B) which is a crosslinking agent (A ) Since the cross-linking reaction with the component proceeds, the main component containing the component (A) and the component (C) and the curing agent containing the component (B) are made into a two-component type. It is preferable to mix and adjust the viscosity.

  The coating object to which the coating composition of the present invention is applied is not particularly limited. For example, an outer plate part of an automobile body such as a passenger car, a truck, a motorcycle, or a bus; an automobile part; a mobile phone, an audio Examples of the outer plate of a household electric product such as a device can be given. Of these, the outer plate of an automobile body and automobile parts are preferable.

  In addition, the material of the object to be coated is not particularly limited. For example, iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, alloyed zinc (Zn-Al, Zn-Ni, Zn-Fe, etc.) Metal materials such as 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, epoxy resin And various plastic materials such as FRP; inorganic materials such as glass, cement and concrete; wood; fiber materials (paper, cloth, etc.), among which metal materials and plastic materials are suitable.

  The object to be coated may be one in which a surface treatment such as a phosphate treatment, a chromate treatment, or a complex oxide treatment is performed on a metal surface of the metal material or a vehicle body formed from the metal material. Further, the object to be coated may be one in which an undercoat film such as various electrodeposition paints is formed on the above-mentioned metal base material, vehicle body, etc., among which an undercoat film is formed by a cationic electrodeposition paint. A car body is particularly suitable.

  The coating method of the paint is not particularly limited, and examples thereof include air spray coating, airless spray coating, rotary atomization coating, curtain coat coating, and the like. Can be formed. In these coating methods, electrostatic application may be performed as necessary. Of these, air spray coating or rotary atomization coating is particularly preferred. The coating amount of the paint is usually preferably 10 to 60 μm, particularly preferably about 25 to 50 μm as the cured film thickness.

  When air spray coating, airless spray coating, and rotary atomization coating are performed, the viscosity of the coating is adjusted to a viscosity range suitable for the coating, usually Ford Cup No. In a 4-viscosity meter, it is preferable to adjust appropriately using a solvent such as an organic solvent so that the viscosity is within a range of 15 to 60 seconds, particularly about 20 to 40 seconds at 20 ° C.

  Curing of the wet coating film formed by applying the coating material to the object to be coated can be performed by heating, and heating can be performed by a known heating means, for example, a hot air furnace, an electric furnace, infrared induction heating. A drying furnace such as a furnace can be used. The heating temperature is not particularly limited, and is preferably in the range of 60 to 160 ° C., preferably 80 to 140 ° C., for example. The heating time is not particularly limited and is, for example, 10 to 60 minutes, preferably 15 to 30 minutes.

  This paint is capable of forming a coating film with excellent scratch resistance, acid resistance, and finished appearance, and is a high solids coating composition having an excellent pot life. It can be used suitably. This paint can be suitably used particularly as a paint for automobiles.

Multi-layer coating film forming method As a multi-layer coating film forming method in which this paint is applied as a top clear coating paint, at least one colored base coat paint and at least one clear coat paint are sequentially applied to the object to be coated. It is a method of forming a multilayer coating film by doing, Comprising: The multilayer coating-film formation method including apply | coating the coating composition of this invention as an uppermost clear coat coating material can be mentioned.

  Specifically, for example, a base coat paint is applied on an object to which electrodeposition coating and / or intermediate coating is applied, and the solvent in the base coat paint is cured as necessary without curing the coating film. In order to promote volatilization, for example, preheating is performed at 40 to 90 ° C. for about 3 to 30 minutes, and after applying this paint as a clear coat paint on the uncured base coat film, the base coat film is applied. And a two-coat one-bake method for forming a multi-layer coating film, in which a clear coat film is cured together.

  Moreover, this paint can be suitably used also as a top clear coat paint in the top coat of the 3-coat 2-bake method or the 3-coat 1-bake method.

  As the base coat paint used in the above, a conventionally known normal thermosetting base coat paint can be used. Specifically, for example, a base resin such as an acrylic resin, a polyester resin, an alkyd resin, a urethane resin type, or the like. In addition, a coating material obtained by appropriately combining a reactive functional group contained in the base resin with a crosslinking agent such as an amino resin, a polyisocyanate compound, or a block polyisocyanate compound can be used.

  As the base coat paint, for example, an aqueous paint, an organic solvent-based paint, and a powder paint can be used. Among these, a water-based paint is preferable from the viewpoint of reducing environmental burden and the finished appearance of the coating film.

  In the multilayer coating film forming method, when two or more clear coats are applied, a conventionally known normal thermosetting clear coat paint can be used as the clear coat paint other than the uppermost layer.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to only these examples. “Part” and “%” are based on mass.

Production of secondary hydroxyl group-containing acrylic resin (A) In an acrylic resin reaction vessel equipped with a stirrer, thermometer and reflux condenser, 27 parts of Swazol 1000 (Cosmo Oil Co., Ltd., aromatic solvent) and methoxy Charge 5 parts of propyl acetate (KH Neochem Co., Ltd., ester solvent), heat and stir under nitrogen gas flow, reach 150 ° C., stop nitrogen gas flow, 20 parts of styrene, 2-hydroxypropyl A monomer mixture having a composition comprising 32.5 parts of acrylate, 46.8 parts of isobornyl acrylate, 0.7 part of acrylic acid and 6.0 parts of ditertiary mil peroxide (polymerization initiator) was dropped over 4 hours. .

  Then, after aging at 150 ° C. for 1 hour, the mixture was cooled and further diluted by adding 21 parts of isobutyl acetate to obtain a hydroxyl group-containing acrylic resin (A1) having a solid content concentration of 65% by mass. The hydroxyl group-containing acrylic resin (A1) had a weight average molecular weight of 5,500, a hydroxyl value of 139 mgKOH / g, an acid value of 5.5 mgKOH / g, and a glass transition temperature of 25 ° C.

Production Examples 2 to 10
In Production Example 1, except that the monomer mixture is a monomer mixture having the composition shown in Table 1, it is the same as Production Example 1 (the amount of the polymerization initiator is adjusted to have a desired weight average molecular weight), and contains a hydroxyl group. Acrylic resins (A2) to (A10) were obtained. Table 1 also shows the glass transition temperature (Tg (° C.)) calculated from the weight average molecular weight, hydroxyl value, acid value, and monomer composition.

  The hydroxyl group-containing acrylic resins (A8) to (A10) are acrylic resins for comparative examples.

<Manufacture of coating composition>
Example 1
Hydroxyl-containing acrylic resin (A1) solution 93.8 parts (solid content 61 parts) obtained in Production Example 1 and melamine resin (C1) (trade name, Cymel 350, manufactured by Ornex Japan, methyl etherified melamine resin, weight Average molecular weight 550, imino group is substantially 0, methylol group: 1.3 per triazine nucleus 5.15 parts (solid content 5 parts), sulfonic acid compound (D1) (NACURE 5523: trade name, KING INDUSTRIES) 2.14 parts (solid content: 0.75 parts), HOSTAVIN3058 (trade name, manufactured by CLARIANT, hindered amine light stabilizer, acylated hindered amine, 100 parts of active ingredient) 1.0 part, TINUVIN400 (trade name, manufactured by BASF Corporation, Contains 3 parts Nzotriazole UV absorber, active ingredient 100%) and 0.4 part BYK-300 (trade name, manufactured by Big Chemie, surface conditioner, 52% active ingredient) (solid content 0.2 part) And the main agent to
Polyisocyanate compound (B1) which is a curing agent (crosslinking agent) (Sumijour N3300, trade name, manufactured by Sumika Corobestro Urethane Co., Ltd., isocyanurate of hexamethylene diisocyanate, solid content 100%) 34 parts (solid content 34 parts) ) Was mixed evenly just before coating, and butyl acetate was further added. 4 so that the viscosity according to No. 4 is 30 seconds. 1 was obtained.

Examples 2-14 and Comparative Examples 1-5
In the same manner as in Example 1, the Ford Cup No. 20 at 20 ° C. with the coating composition shown in Table 2 below. 4 with a viscosity of 30 seconds according to each coating composition No. 2-19 were obtained. Coating composition No. 15 to 19 are for comparative examples.

  In addition, each coating composition No. The paint blends 1 to 19 are solid blends.

(* 1) to (* 4) in Table 2 are as follows.
(* 1) Melamine resin (C2): Cymel 250, trade name, methylbutyl mixed etherified melamine resin, manufactured by Ornex Japan, weight average molecular weight 2700
(* 2) Phosphoric acid compound (D2): NACURE 4167, trade name, triethylamine salt of alkyl phosphoric acid, KING INDUSTRIES, active ingredient solid content 25%
(* 3) TINUVIN123: trade name, B.I. A. S. F. Hindered amine light stabilizer, 100% active ingredient
(* 4) Polyisocyanate compound (B2): XP2679, trade name, allophanate of hexamethylene diisocyanate, manufactured by Sumika Bayer Urethane Co., Ltd., 80% solid content
<Preparation of test plate>
(Preparation of test article)
Electrocolon-coated ELECRON GT-10 (trade name, manufactured by Kansai Paint Co., Ltd., cationic electrodeposition paint) on a cold-rolled steel sheet that has been subjected to zinc phosphate conversion treatment to a dry film thickness of 20 μm, at 170 ° C. for 30 minutes After heating and curing, "WP-306T" (trade name, manufactured by Kansai Paint Co., Ltd., polyester melamine resin-based aqueous intermediate coating) is applied onto the electrodeposition coating film using a rotary atomizing electrostatic coating machine. Electrostatic coating to a cured film thickness of 30 μm, left for 5 minutes, preheated at 80 ° C. for 3 minutes, and then heated at 140 ° C. for 30 minutes to form an intermediate coating film to be coated for testing. It was a thing.

(Preparation of test plate)
Using the rotary atomization type electrostatic coating machine, “WBC-713T No. 1F7” (trade name, manufactured by Kansai Paint Co., Ltd., acrylic melamine resin water-based base coat paint, silver coating color) is used for the above test object. Then, electrostatic coating was performed so that the cured film thickness was 15 μm, and after standing for 5 minutes, preheating was performed at 80 ° C. for 3 minutes.

  Subsequently, the coating composition No. obtained in Example 1 was applied onto the uncured base coat film. Using a rotary atomizing type electrostatic coating machine, No. 1 was electrostatically coated so as to have a dry film thickness of 40 μm to form a clear coat film and left for 7 minutes. Subsequently, the base coating film and the clear coating film were heated and cured at 140 ° C. for 30 minutes (keep time), thereby coating composition No. 1 test plate was produced.

  The coating composition No. In the preparation of the test plate of No. 1, the coating composition No. 1 is the coating composition no. 2 to 19 except that the coating composition No. In the same manner as in the preparation of the test plate of No. 1, the coating composition No. 2 to 19 test plates were prepared.

  Each test plate obtained above was evaluated by the following test method. The evaluation results are shown in Table 2 together with the paint composition.

  In addition, the coating solid content concentration of each coating composition (paint solid concentration at the time of coating (solid content mass% adjusted to viscosity of 30 seconds by Ford Cup No. 4 at 20 ° C .; “painting NV” in the table)) Pot life (Mixing of main agent and curing agent, adjusting viscosity to 30 seconds with Ford Cup No. 4 at 20 ° C., then increasing rate% after standing at 20 ° C. for 4 hours; Rate))) is also shown.

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

  LW: An index of smoothness. The smaller the LW value, the higher the smoothness of the coated surface.

  SW: An index of sharpness. The smaller the SW value, the higher the sharpness of the coating surface.

Flip-flop property (FF property): Using a multi-angle spectrocolorimeter MA-68 (trade name, manufactured by X-Rite), L values (lightness) at a light receiving angle of 15 ° and a light receiving angle of 110 ° are measured, The FF value was determined by the following formula.
FF value = L value at a light receiving angle of 15 ° −L value at a light receiving angle of 110 °.
The larger the FF value, the larger the change in the L value (brightness) depending on the observation angle (light receiving angle), indicating that the flip-flop property is excellent.

  Scratch resistance: Using an Atlas Clock Meter, using a 3M281Q polishing sheet (manufactured by Sumitomo 3M), rubbing the test plate 10 times and wiping with a mineral spirit. The test plate was cleaned.

  The 20-degree specular reflectance (20 ° gloss value) of the test plate after the test was measured, and the scratch resistance was evaluated by the gloss retention rate (%) with respect to the 20 ° gloss value before the test. Higher gloss retention (%) indicates better scratch resistance.

TU-CON Hardness: After leaving the test plate in a constant temperature room at 20 ° C. for 4 hours, TUKON (American
“Two-con hardness” was measured with a micro hardness tester manufactured by Chain & Cable Company. The TUCON hardness, which is a Knoop hardness test method, is a numerical value measured by the TUKON micro hardness tester manufactured by American Chain & Cable Company. It is the hardness of the coating film that is read from the size of the diamond-shaped indentation that was pressed into the test surface of the material. The higher the value, the harder it is.

  Acid resistance: Each test plate was immersed in a 10% sulfuric acid solution half, left at 50 ° C. for 5 hours, washed with water, the coated surface was observed, and evaluated according to the following criteria.

  S: No change is observed.

  A: Although there is no abnormality in the coating surface, a slight level difference is recognized at the boundary between the immersion part and the non-immersion part.

  B: Swelling or whitening occurs on the coated surface.

  NSR adherence (non-sand recoat adherence): Coating composition no. A test plate prepared at a heat curing temperature of 160 ° C. in the preparation of the test plate 1 was separately prepared for each coating composition.

  On the test plate, the coating composition No. In the same manner as the preparation of the test plate of No. 1, a base coat film and a clear coat film are formed again and recoated (the same coating composition as the base coat paint and the clear coat paint is applied again), and 130 ° C. Each recoat test plate was prepared by heating and curing the base coat film and the clear coat film for 30 minutes (keep time).

  The test was carried out by the adhesive cellophane tape peeling test described in JIS K5600 (100 gobangs having a size of 2 mm × 2 mm) and evaluated according to the following criteria.

  S: 100 gobangs remain, and no flickering is observed in each gobang.

  A: 100 gobangs remain, but spotting is observed on the gobangs.

  B: The remaining number of Gobang eyes is 99 or less.

Claims (6)

(A) A secondary hydroxyl group-containing acrylic resin having a weight average molecular weight of 3000 to 7000,
(B) an aliphatic polyisocyanate compound and / or a derivative thereof,
(C) a coating composition containing an alkyl etherified melamine resin having a weight average molecular weight of 1000 or less, and (D) a sulfonic acid compound and / or a phosphoric acid compound,
(C) The amount of a component exists in the range of 1.5-20 mass% with respect to the total amount of (B) component, The high solid content coating composition characterized by the above-mentioned.   2. The high solid content according to claim 1, wherein the secondary hydroxyl group-containing polymerizable unsaturated monomer (a) is 50 to 100% by mass in the total amount of the hydroxyl group-containing polymerizable unsaturated monomer which is a constituent component of the acrylic resin (A). Paint composition.   The high solid content coating composition according to claim 1 or 2, wherein the alkyl etherified melamine resin (C) has substantially no imino group.   The high solid content coating composition according to any one of claims 1 to 3, further comprising an acylated hindered amine and / or an amino ether-based hindered amine.   The article | item which has a coating film of the coating composition of any one of Claims 1-4. A method for forming a multi-layer coating film by coating at least one layer of a colored base coat paint and at least one layer of a clear coat paint on an object to be coated, wherein the clear coat paint is the uppermost layer. A method for forming a multilayer coating film, comprising coating the coating composition according to any one of the above.