JP2014125558A - Coating composition and method of forming multilayer coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a clear coating composition capable of providing a multilayer coating film free from an effect of a surface roughness of a base material (excellent in masking performance of surface conditions (uneven) of the base material), excellent in smoothness and sharpness when forming the multilayer coating film by coating an aqueous first pigment coating, an aqueous second pigment coating and a clear coating on a matter to be coated in order and hardening once, and to provide a method of forming the multilayer coating film using the clear coating composition.SOLUTION: There is provided a coating composition containing a hydroxyl group-containing acrylic resin (A), a melamine resin (B) and polyol having a specific number average molecular weight of 300 to 1500 (C). There is provided a method of forming a multilayer coating film using the coating composition as a clear coating material by coating an aqueous first pigment coating, an aqueous second pigment coating and a clear coating on a matter to be coated in order and heat hardening them once.

Description

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

  Conventionally, as a method of forming a coating film on an automobile body, an electrodeposition coating is applied to an object to be coated, followed by heat curing, followed by intermediate coating coating → heat curing → base coating coating → preheating (preheating) → clear coating. There are a wide variety of methods for forming multi-layer coatings using the 3-coat 2-bake method in which coating is sequentially applied and heat-cured, and the 2-coat 2-bake method in which intermediate coating is applied, heat-curing, top-coating is applied, and heat-curing is sequentially performed. Has been done.

  In general, the 3-coat 2-bake method is performed when a so-called metallic-colored coating film is formed using a base coat paint containing a luster pigment, and the 2-coat 2-bake method contains a color pigment. This is carried out when a so-called solid color film such as white or black is formed using a top coating.

  In recent years, from the viewpoint of energy saving, the heat curing process after painting of the intermediate coating is omitted, and the coating of the intermediate coating is applied → preheating (preheating) → base coating is applied → preheating (preheating) → clear coating is applied → heating A 3-coat 1-bake system in which curing is performed sequentially and a 2-coat 1-bake system in which intermediate coating is applied, preheated (preliminary heating), top coating is applied, and heat-cured are sequentially studied.

  Among these, from the viewpoint of suppressing environmental pollution due to volatilization of organic solvents, the above-mentioned 3-coat 1-bake method and 2-coat 1-bake method using water-based paints as the above-mentioned intermediate coating, base coating, and top coating are particularly required. .

  However, in the three-coat one-bake method using the water-based intermediate coating material and the water-based base coat paint and the two-coat one-bake method using the water-based intermediate coating material and the water-based top coating material, The smoothness and sharpness of the formed film may be reduced due to the interlayer, the interlayer between the aqueous base coat paint and the clear paint, or the interlayer between the aqueous intermediate coat and the aqueous top coat. It was.

  In the coating specifications of the 3-coat 1-bake method and the 2-coat 1-bake method in which the heat curing step is omitted, the heat curing step after the intermediate coating is reduced, so the heat curing step is performed once. . In terms of concealment of the surface condition (irregularity) of the substrate, it is a harsh condition that tends to be insufficient compared to the conventional coating specifications, so that the surface roughness of the substrate such as the electrodeposition coating surface is particularly bad. In this case, the smoothness and sharpness of the formed coating film tend to be deteriorated by becoming more sensitive to the influence of the substrate during painting of the intermediate coating. It was an issue.

  For example, Patent Document 1 discloses a method in which a specific solid content is adjusted in a coating process of a multilayer coating film by a 3-coat 1-bake method using an aqueous intermediate coating, an aqueous base coating, and a clear coating. After applying a specific aqueous base paint on the coating film and adjusting it to a specific solid content, a clear paint containing a carboxyl group-containing compound and a polyepoxide is applied, and further, specific heating conditions are applied. A method for forming a multi-layer coating film in which an intermediate coating film, a base coating film and a clear coating film are cured at once is described. However, the multilayer coating film obtained by the coating film forming method sometimes has insufficient smoothness and sharpness.

  For example, in Patent Document 2, a water-based first colored paint, a water-based second colored paint, and a clear paint are sequentially applied to an object to be coated. In the three-coat one-bake method in which the three-layered coating film obtained by coating is heated and cured at the same time, the aqueous first colored paint (X) comprises an acrylic resin (A), a curing agent (B), and a urethane resin emulsion ( C), and the first colored coating film formed from the aqueous first colored paint (X) has a water swelling rate of 100% or less and an organic solvent swelling rate of 300% or less before the second base coating. There is described a method for forming a multilayer coating film characterized in that it is. However, the smoothness and sharpness of the multilayer coating film obtained by the coating film forming method may be insufficient.

  Further, for example, Patent Document 3 includes an acrylic resin (A), a curing agent (B), a polyisocyanate component containing an alicyclic diisocyanate, and an alicyclic diol having a cycloalkylene group having 6 or more carbon atoms. The aqueous coating composition containing the urethane resin emulsion (C) obtained from the structural component containing the polycarbonate diol component obtained from the diol component to contain is described.

  Further, a three-layered multi-layer coating film obtained by sequentially coating a water-based first colored paint, a water-based second colored paint, and a clear paint on an object to be coated using the water-based paint composition as a water-based first colored paint. A three-coat one-bake method for forming a multi-layer coating film in which heat-curing is simultaneously performed is described, and a coating composition containing a specific oligomer is further described as a preferred embodiment of the aqueous first colored coating material. However, there are cases where the effect of improving the finished appearance such as smoothness and sharpness is insufficient even by the coating film forming method.

  For example, Patent Document 4 discloses an intermediate coating film, a base coating, and the like, in which the appearance of the multilayer coating film is improved by preventing the mixing between the multilayer coating films and further controlling the internal stress of the coating film. In the 3-coat 1-bake method including the step of baking and curing the film and the clear coating film simultaneously, the water-based intermediate coating composition used for forming the intermediate coating film contains a specific acrylic resin emulsion, a fully alkyl etherified melamine resin and a carbodiimide compound. A multilayer coating film forming method is described, characterized in that the aqueous base coating material used for forming the base coating film contains a specific acrylic resin emulsion and a specific polyether polyol. Yes. However, by controlling the internal stress of the intermediate coating film, the appearance of the multilayer coating film obtained by the coating film forming method for preventing the mixed layer between the intermediate coating film and the base coating film is insufficient. There was a case.

JP 2009-028576 A WO2010 / 082607 JP 2010-215885 A JP 2009-262002 A

  The object of the present invention is to apply a surface of a substrate when a water-based first colored paint, a water-based second colored paint, and a clear paint are sequentially applied on an object to be cured to form a multilayer coating film. A clear coating composition that is less susceptible to roughness (excellent concealment of the surface state (unevenness) of the substrate), can provide a multilayer coating film excellent in smoothness, sharpness, and weather resistance, and the It is an object of the present invention to provide a method for forming a multilayer coating film using a clear coating composition.

  In order to improve the concealability of the surface state (unevenness) of the substrate in the coating process of the multi-layer coating film by the 3-coat 1-bake method, the present inventor has conducted intensive studies to achieve the above object. According to the coating composition containing the specific polyol in the clear paint, the clear paint contains the hydroxyl group-containing acrylic resin (A), the melamine resin (B) and the specific polyol (C). The inventors have found that the above object can be achieved and have completed the present invention.

That is, the present invention provides an article to be coated with the following steps (1) to (4),
Step (1): A step of forming the first colored coating film by coating the aqueous first colored paint (X),
Step (2): A step of forming a second colored coating film by applying an aqueous second colored coating material (Y) on the first colored coating film formed in the step (1).
Step (3): A step of applying a clear paint (Z) on the second colored coating film formed in the step (2) to form a clear coating film, and a step (4): the step (1). A step of heating and curing the first colored coating film, the second colored coating film and the clear coating film formed in (3) at a time;
A coating composition used as a clear coating (Z) in a method for forming a multilayer coating film, wherein the coating composition comprises a hydroxyl group-containing acrylic resin (A), a melamine resin (B), and a number average molecular weight of 300. Containing a polyol (C) in the range of ˜1500,
The polyol (C) provides a coating composition characterized by being at least one of a polyoxyalkylene group-containing polyol (C1) and a polycarbonate polyol (C2).

Furthermore, the present invention provides the following steps (1) to (4),
Step (1): A step of forming the first colored coating film by coating the aqueous first colored paint (X),
Step (2): A step of forming a second colored coating film by applying an aqueous second colored coating material (Y) on the first colored coating film formed in the step (1).
Step (3): A step of coating the above-mentioned coating composition as the clear coating (Z) on the second colored coating formed in the step (2) to form a clear coating, and step (4) ): Provided is a multilayer coating film forming method for sequentially performing the steps of heating and curing the first colored coating film, the second colored coating film and the clear coating film formed in the steps (1) to (3) at a time. To do.

  Furthermore, the present invention provides an article coated by the multilayer coating film forming method.

  Since the polyol in the coating composition of the present invention has a low molecular weight, it can improve the heat flow property during the curing process of the multilayer coating film, improve the hiding power of the substrate, and reduce the finished appearance. Since the influence of the surface shape (irregularity) of the substrate that causes the film to be formed can be effectively reduced, a three-coat one-bake multilayer coating film excellent in finished appearance such as smoothness and sharpness can be obtained. It is considered a thing.

  This effect can be obtained by making the polyol present in the clear coating film.

  In addition, the polyol has a hydroxyl group that is a crosslinkable functional group, and is excellent in reactivity, and therefore is suitable from the viewpoint of coating performance such as weather resistance.

  As described above, according to the coating composition of the present invention, in the coating method for forming a three-coat one-bake system, the surface condition (unevenness) of the substrate is excellent, so that it is excellent in smoothness and sharpness, and weather resistance. A multilayer coating film having excellent properties can be formed.

  Hereinafter, the coating composition and the coating film forming method of the present invention will be described in more detail.

The coating composition of the present invention (hereinafter sometimes abbreviated as “present coating”)
To the article to be coated, the following steps (1) to (4),
Step (1): A step of forming the first colored coating film by coating the aqueous first colored paint (X),
Step (2): A step of forming a second colored coating film by applying an aqueous second colored coating material (Y) on the first colored coating film formed in the step (1).
Step (3): a step of applying a clear paint (Z) on the second colored coating film formed in the step (2) to form a clear coating film, and a step (4): the step (1). A step of heating and curing the first colored coating film, the second colored coating film and the clear coating film formed in (3) at a time;
A coating composition used as a clear coating (Z) in a method for forming a multilayer coating film, wherein the coating composition comprises a hydroxyl group-containing acrylic resin (A), a melamine resin (B), and a number average molecular weight of 300. Containing a polyol (C) in the range of ˜1500,
The polyol (C) is at least one of a polyoxyalkylene group-containing polyol (C1) and a polycarbonate polyol (C2).

Coating composition of the present invention
Hydroxyl group-containing acrylic resin (A)
The hydroxyl group-containing acrylic resin (A) of the coating composition of the present invention can be produced by copolymerizing a hydroxyl group-containing unsaturated monomer and other unsaturated monomers by a conventional method.

  Examples of the hydroxyl group-containing unsaturated monomer include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate and hydroxyalkyl having 2 to 8 carbon atoms of acrylic acid or methacrylic acid such as hydroxybutyl (meth) acrylate. Esters; monoesters of polyether polyols such as polyethylene glycol, polypropylene glycol, polybutylene glycol, and unsaturated carboxylic acids such as (meth) acrylic acid; polyether polyols such as polyethylene glycol, polypropylene glycol, polybutylene glycol; Monoethers with (meth) acrylic acid hydroxyalkyl esters such as hydroxyethyl (meth) acrylate; unsaturated groups containing acid anhydride groups such as maleic anhydride and itaconic anhydride Monoesterification or diesterification of a compound with glycols such as ethylene glycol, 1,6-hexanediol and neopentyl glycol; hydroxyalkyl vinyl ethers such as hydroxyethyl vinyl ether; allyl alcohol and the like; 2-hydroxypropyl ( (Meth) acrylate; an α, β-unsaturated carboxylic acid and a monoepoxy compound such as “Cardura E10P” (trade name, manufactured by HEXION Specialty Chemicals, a glycidyl ester of a synthetic highly branched saturated fatty acid) and an α-olefin epoxide Adduct; Adduct of glycidyl (meth) acrylate and monobasic acid such as acetic acid, propionic acid, p-tert-butylbenzoic acid and fatty acids; hydroxyl group-containing unsaturated monomer and lactone (for example, ε Caprolactone, etc. γ- valerolactone) and adduct can be mentioned.

  In this specification, (meth) acrylate is a general term for acrylate and methacrylate, and (meth) acrylic acid is a general term for acrylic acid and methacrylic acid.

  Examples of other unsaturated monomers include carboxyl group-containing unsaturated monomers, (meth) acrylic esters, vinyl ethers or allyl ethers, olefinic compounds and diene compounds, hydrocarbon ring-containing unsaturated monomers, nitrogen-containing unsaturated monomers. , Epoxy group-containing unsaturated monomers, hydrolyzable alkoxysilyl group-containing acrylic monomers, and the like.

  A carboxyl group-containing unsaturated monomer is a compound having one or more carboxyl groups and one unsaturated bond in one molecule. For example, (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, maleic anhydride Examples thereof include acids, fumaric acid, 2-carboxyethyl (meth) acrylate, 3-carboxypropyl (meth) acrylate, and 5-carboxypentyl (meth) acrylate.

  Examples of (meth) acrylic acid esters include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, hexyl acrylate, acrylic acid 2-ethylhexyl, n-octyl acrylate, decyl acrylate, lauryl acrylate, stearyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, Isobutyl methacrylate, tert-butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, lauryl methacrylate, stearyl methacrylate, C1-C24 alkyl ester or cycloalkyl ester of acrylic acid or methacrylic acid such as cyclohexyl tacrylate; methoxybutyl acrylate, methoxybutyl methacrylate, methoxyethyl acrylate, methoxyethyl methacrylate, ethoxybutyl acrylate, methacrylic acid Examples thereof include C2-C18 alkoxyalkyl esters of acrylic acid or methacrylic acid such as ethoxybutyl acid.

  Examples of the vinyl ether or allyl ether include chain alkyl vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, butyl vinyl ether, tert-butyl vinyl ether, pentyl vinyl ether, hexyl vinyl ether, octyl vinyl ether; cyclopentyl vinyl ether, cyclohexyl vinyl ether, and the like. Cycloalkyl vinyl ethers; aryl vinyl ethers such as phenyl vinyl ether and trivinyl benzyl ether; aralkyl vinyl ethers such as benzyl vinyl ether and phenethyl vinyl ether; and allyl ethers such as allyl ethyl ether.

  Examples of the olefinic compound and diene compound include ethylene, propylene, butylene, vinyl chloride, butadiene, isoprene, chloroprene, and the like.

  Examples of the hydrocarbon ring-containing unsaturated monomer include styrene, α-methylstyrene, phenyl (meth) acrylate, phenylethyl (meth) acrylate, phenylpropyl (meth) acrylate, benzyl (meth) acrylate, and phenoxyethyl (meth). Acrylate, cyclohexyl (meth) acrylate, 2-acryloyloxyethyl hydrogen phthalate, 2-acryloyloxypropyl hydrogen phthalate, 2-acryloyloxypropyl hexahydrohydrogen phthalate, 2-acryloyloxypropyl tetrahydrohydrogen phthalate, p-tert-butyl-benzoate Examples include esterified products of acid and hydroxyethyl (meth) acrylate, dicyclopentenyl (meth) acrylate, and the like.

  Examples of the nitrogen-containing unsaturated monomer include nitrogen-containing alkyls such as N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, and Nt-butylaminoethyl (meth) acrylate ( Meth) acrylate; acrylamide, methacrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N, N -Polymerizable amides such as dimethylaminoethyl (meth) acrylamide; Aromatic nitrogen-containing monomers such as 2-vinylpyridine, 1-vinyl-2-pyrrolidone, 4-vinylpyridine; Polymerizable nitriles such as acrylonitrile and methacrylonitrile ; Allylamine, etc. It is.

  Examples of the epoxy group-containing unsaturated monomer include aliphatic epoxy group-containing unsaturated monomers such as glycidyl (meth) acrylate and allyl glycidyl ether, and alicyclic epoxy group-containing unsaturated monomers such as 3,4-epoxycyclohexylmethyl (meth) acrylate. Mention may be made of saturated monomers.

  Examples of the hydrolyzable alkoxysilyl group-containing acrylic monomer include γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, and β- (meth) acryloyloxyethyltrimethoxysilane. Γ- (meth) acryloyloxypropyltriethoxysilane, γ- (meth) acryloyloxypropylmethyldiethoxysilane, and the like.

  Also, for example, vinyl compounds such as vinyl acetate, vinyl propionate, vinyl chloride, Verovac acid vinyl ester Veova 9 and Veova 10 (Japan Epoxy Resin) can be used.

  The synthesis of the hydroxyl group-containing acrylic resin (A) can be performed by using a general unsaturated monomer polymerization method, but is performed by a solution-type radical polymerization method in an organic solvent in consideration of versatility and cost. Is most suitable. For example, aromatic solvents such as xylene and toluene; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; ester solvents such as ethyl acetate, butyl acetate, isobutyl acetate and 3-methoxybutyl acetate; n-butanol and isopropyl alcohol It can be easily obtained by carrying out a copolymerization reaction at a temperature of about 60 to about 150 ° C. in the presence of a polymerization initiator such as an azo catalyst or a peroxide catalyst in a solvent such as an alcohol solvent. it can.

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

  The hydroxyl value of the hydroxyl group-containing acrylic resin (A) is 80 to 200 mgKOH / g, particularly 90 to 170 mgKOH / g, more particularly, from the viewpoint of the finished appearance such as smoothness and sharpness and the coating performance such as weather resistance. It is preferable to be within the range of 100 to 140 mgKOH / g.

  The weight average molecular weight of the hydroxyl group-containing acrylic resin (A) is 4000 to 20000, particularly 6000 to 16000, more particularly 8000 to 4,000,000 in terms of finished appearance such as smoothness and sharpness and coating performance such as weather resistance. It is preferably within the range of 12000.

  In this specification, the number average molecular weight and the weight average molecular weight are the retention time (retention capacity) measured using a gel permeation chromatograph (GPC), the retention time of standard polystyrene with a known molecular weight measured under the same conditions ( It is a value obtained by converting to the molecular weight of polystyrene by (retention capacity). Specifically, “HLC8120GPC” (trade name, manufactured by Tosoh Corporation) is used as a gel permeation chromatograph, and “TSKgel G-4000HXL”, “TSKgel G-3000HXL”, “TSKgel G-2500HXL” are used as columns. ”And“ TSKgel G-2000HXL ”(trade names, all manufactured by Tosoh Corporation), a differential refractometer is used as a detector, mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., flow rate: It can be measured under the condition of 1 mL / min.

  When the hydroxyl group-containing acrylic resin (A) has a carboxyl group, the acid value is 1 to 40 mgKOH / g, particularly 3 from the viewpoint of finished appearance such as smoothness and sharpness and coating performance such as weather resistance. It is preferable to be within the range of ˜30 mg KOH / g, more particularly 5 to 20 mg KOH / g.

Melamine resin (B)
As a melamine resin (B), what is used with a well-known coating composition can be used. As a melamine resin, the well-known partial obtained by reaction of a melamine and an aldehyde, or a complete methylol-ized melamine resin can be mention | raise | lifted, for example.

  Examples of the aldehyde include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde and the like.

  Further, this methylolated melamine resin etherified with alcohol can also be used, and examples of alcohol used for etherification include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, Examples thereof include 2-ethylbutanol and 2-ethylhexanol.

  Specific examples of the melamine resin (B) include methylol melamines such as dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, and hexamethylol melamine; alkyl etherified products or condensates of these methylol melamines; Examples thereof include condensates of alkyl ethers.

  As the melamine resin (B), a melamine resin containing a butyl ether group etherified with n-butyl alcohol can be suitably used from the viewpoint of coating performance such as weather resistance. In particular, a melamine resin in which all of the alkyl ether groups in the melamine resin are butyl ether groups can be used more suitably.

In addition, the melamine resin (B) is from the viewpoint of coating performance such as weather resistance,
The average number of imino groups per triazine nucleus is 0.3 to 3.5, especially 0.5 to 3.0, more particularly 1.0 to 2.5,
An average of 0.1 to 2.0 methylol groups per triazine nucleus, in particular 0.1 to 1.5, more particularly 0.1 to 1.0,
It is preferable to have an alkyl ether group having an average of 2.0 to 5.6, particularly 2.5 to 5.5, more particularly 3.0 to 5.0, on average per triazine nucleus.

  The melamine resin (B) has a weight average molecular weight of 600 to 6000, particularly 800 to 5,000, more particularly 1,000 to 4,000, from the viewpoint of finished appearance such as smoothness and sharpness, and coating performance such as weather resistance. The inside can be used suitably.

  A commercially available product can be used as the melamine resin (B). Commercially available product names include, for example, Cymel 323, Cymel 325, Cymel 327, Cymel 350, Cymel 370, Cymel 380, Cymel 385, Cymel 212, Cymel 251, Cymel 254, My Coat 776 manufactured by Nippon Cytec Industries, Inc .; Resin 735, Resimin 740, Resimin 741, Resimin 745, Resimin 746, Resimin 747 manufactured by Monsanto Co., Ltd. Sumimar M55, Sumimar M30W, Sumimar M50W manufactured by Sumitomo Chemical Co., Ltd. 28-60 etc. can be mentioned.

  A melamine resin (B) can be used by 1 type or in combination of 2 or more types.

  The amount of the hydroxyl group-containing acrylic resin (A) and the melamine resin (B) in this paint is 50 for the acrylic resin (A) on the basis of the total amount of the solid content of both from the viewpoint of the finished appearance and the curability of the coating film. It is preferable to be in the range of ˜90 mass%, particularly 60-80 mass%, and melamine resin (B) in the range of 10-50 mass%, particularly 20-40 mass%.

Polyol (C)
The polyol (C) is at least one of a polyoxyalkylene group-containing polyol (C1) and a polycarbonate polyol (C2).

  The number average molecular weight of the polyol (C) is in the range of 300 to 1500, preferably 350 to 1000, more preferably from the viewpoint of excellent coating performance such as smoothness and sharpness, finished appearance and weather resistance. It is in the range of 400-800.

  The hydroxyl value of the polyol (C) is preferably in the range of 60 to 400 mgKOH / g, more preferably 100 from the viewpoint of excellent coating performance such as smoothness and sharpness, finished appearance and weather resistance. It is -350 mgKOH / g, More preferably, it exists in the range of 150-300 mgKOH / g.

  Examples of the polyoxyalkylene group-containing polyol (C1) include compounds in which an alkylene oxide is added to an active hydrogen-containing compound such as a polyhydric alcohol, a polyhydric phenol, and a polycarboxylic acid. Examples of the active hydrogen atom-containing compound include water, polyhydric alcohols (ethylene glycol, diethylene glycol, trimethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4 -Dihydric alcohols such as dihydroxymethylcyclohexane and cyclohexylene glycol, glycerin, trioxyisobutane, 1,2,3-butanetriol, 1,2,3-pentanetriol, 2-methyl-1,2,3-propane Triol, 2-methyl-2,3,4-butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl- 3,4,5-heptanetriol, 2,4-dimethyl- , 3,4-pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4-butanetriol, 1,2,4-pentanetriol, trihydric alcohols such as trimethylolethane, trimethylolpropane, pentaerythritol, 1 , 2,3,4-pentanetetrol, 2,3,4,5-hexanetetrol, 1,2,4,5-pentanetetrol, 1,3,4,5-hexanetetrol, diglycerin, Tetravalent alcohols such as sorbitan, pentahydric alcohols such as adonitol, arabitol, xylitol, triglycerin, hexavalent alcohols such as dipentaerythritol, sorbitol, mannitol, iditol, inositol, dulcitol, talose, allose, etc., and octavalent alcohols such as sucrose Polyglycerin, etc.); Knols [polyhydric phenols (pyrogallol, hydroquinone, phloroglucin, etc.), bisphenols (bisphenol A, bisphenolsulfone, etc.)]; (Phthalic acid, terephthalic acid, trimellitic acid, etc.)].

  Among the above, the active hydrogen atom-containing compound is preferably a polyhydric alcohol from the viewpoint of reactivity, particularly preferably a polyhydric alcohol having an alkylene group having 3 or more carbon atoms, particularly an alkylene having 3 to 4 carbon atoms. A polyhydric alcohol having a group is preferred.

  Further, among the polyhydric alcohols, divalent alcohols are particularly preferable from the viewpoint of smoothness and sharpness of the resulting multilayer coating film.

  In particular, among the polyhydric alcohols, ethylene glycol, diethylene glycol, trimethylene glycol, propylene glycol, and 1,4-butanediol are preferable, and trimethylene glycol, propylene glycol, and 1,4-butanediol are particularly preferable.

  The polyoxyalkylene group-containing polyol (C1) is usually subjected to an addition reaction of alkylene oxide to the active hydrogen-containing compound in the presence of an alkali catalyst at a temperature of 60 to 160 ° C. under normal pressure or pressure by a conventional method. Can be obtained. Examples of the alkylene oxide include alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide. Among them, propylene oxide, butylene oxide, particularly propylene oxide can be preferably used. These can be used alone or in combination of two or more. When two or more types are used in combination, the addition format may be either block or random.

  As the polyoxyalkylene group-containing polyol (C1), polyoxyalkylene glycol can be preferably used.

  As the polyoxyalkylene glycol, commercially available products can be used. For example, as polypropylene glycol, Hyprox MP-600 (manufactured by Dainippon Ink & Chemicals, Inc.), Primepole PX-1000, Sanniks SP- 750, Sannix PP-400, Sannix PP-600, Sannix PP-1000 (manufactured by Sanyo Chemical Co., Ltd.), Diol-400, Diol-700, Diol-1000 (manufactured by Mitsui Chemicals, Inc.) ); Examples of polytetramethylene glycol include PTMG-650, PTMG-850, PTMG-1000 (manufactured by Mitsubishi Chemical Corporation), and the like.

  As the polycarbonate polyol (C2), for example, polycarbonate polyol produced by a known method can be used in addition to the commonly used 1,6-hexanediol as a basic skeleton. For example, the polycarbonate polyol obtained by making carbonate components or phosgene, such as alkylene carbonate, diaryl carbonate, and dialkyl carbonate, react with the aliphatic polyol component illustrated below is mentioned. Here, as the aliphatic polyol component, linear glycols such as 1,3-propanediol, 1,4-butanediol or 1,6-hexanediol; 1,2-propanediol, neopentyl glycol, 3 Examples of the aliphatic polyol component include branched glycols such as methyl-1,5-pentanediol and ethylbutylpropanediol; ether-based diols such as diethylene glycol and triethylene glycol.

  The polycarbonate polyol (C2) preferably has no ring structure such as an aromatic ring or an aliphatic ring in the molecular structure from the viewpoint of heat flow at the time of heat curing.

  The polycarbonate polyol can use a commercial item, and UH-50, UH-100, UM-90 (1/3) (above, Ube Industries, Ltd. make); C-1100, C-XP-2716 (above , Manufactured by Bayer).

  The polyol (C) is 1 to 20% by mass, particularly 2 to 10% by mass, more particularly 3 to 7% by mass, based on the total solid content of the hydroxyl group-containing acrylic resin (A) and melamine resin (B). It is preferable to use it.

  By using an amount in this range, the heat flow in the curing process of the multilayer coating film is improved, the surface shape (unevenness) of the substrate can be sufficiently concealed, and the influence of the surface shape of the substrate is suppressed. Thus, a multilayer coating film having excellent smoothness and sharpness in finished appearance and excellent coating performance such as weather resistance can be obtained.

Phosphate group-containing compound (D)
In the coating composition of the present invention, since the uniform curing property of the clear coating film is improved and the finished appearance is improved, the phosphate group-containing compound (D) can be used as necessary.

  Examples of the phosphoric acid group-containing compound (D) include phosphoric acid; mono-n-propyl phosphoric acid, monoisopropyl phosphoric acid, mono-n-butyl phosphoric acid, monoisobutyl phosphoric acid, mono-tert-butyl phosphoric acid, monooctyl Monoalkyl phosphoric acid such as phosphoric acid and monodecyl phosphoric acid; di-n-propyl phosphoric acid, diisopropyl phosphoric acid, di-n-butyl phosphoric acid, diisobutyl phosphoric acid, di-tert-butyl phosphoric acid, dioctyl phosphoric acid, didecyl phosphoric acid, etc. Dialkyl phosphoric acid; mono-n-propyl phosphorous acid, monoisopropyl phosphorous acid, mono-n-butyl phosphorous acid, monoisobutyl phosphorous acid, mono-tert-butyl phosphorous acid, monooctyl phosphorous acid, monodecyl Monoalkyl phosphorous acid such as phosphorous acid; di-n-propyl phosphorous acid, diisopropyl phosphorous acid, di-n- It can be mentioned phosphoric acid group-containing acrylic resin; chill phosphite, diisobutyl phosphite, di -tert- butyl phosphite, dioctyl phosphite, didecyl dialkyl phosphite such as phosphorous acid.

  Among the above, from the viewpoint of coating performance such as weather resistance, a phosphoric acid group-containing acrylic resin can be preferably used.

  The phosphoric acid group-containing acrylic resin can synthesize a phosphoric acid group-containing unsaturated monomer and other unsaturated monomers in the same manner as the hydroxyl group-containing acrylic resin (A).

  Examples of phosphoric acid group-containing unsaturated monomers include 2- (meth) acryloyloxyethyl acid phosphate, 2- (meth) acryloyloxypropyl acid phosphate, 2- (meth) acryloyloxy-3-chloropropyl acid phosphate, 2-methacryloyl Examples thereof include acidic phosphate ester monomers such as oxyethylphenyl phosphoric acid. Specific product names include Kayamar PM21 manufactured by Nippon Kayaku Co., Ltd. and Light Ester PM manufactured by Kyoei Yushi Co., Ltd. The phosphate group-containing unsaturated monomers can be used alone or in combination of two or more.

  Examples of the other unsaturated monomer include the hydroxyl group-containing unsaturated monomer and other unsaturated monomers exemplified in the hydroxyl group-containing acrylic resin (A).

  In the coating composition of the present invention, when the phosphoric acid group-containing acrylic resin also has a hydroxyl group, it is not a hydroxyl group-containing acrylic resin (A) but a phosphoric acid group-containing compound (D).

  In the phosphoric acid group-containing acrylic resin, the phosphoric acid group-containing unsaturated monomer is 1 to 20% by mass, particularly 5 to 15% by mass, based on the total amount of each monomer component constituting the phosphoric acid group-containing acrylic resin. Is preferred.

  The weight average molecular weight of the phosphoric acid group-containing acrylic resin is preferably in the range of 3000 to 30000, particularly 5000 to 25000, and more particularly 10,000 to 20000 from the viewpoints of finished appearance and coating film performance.

  The phosphoric acid group-containing compound (D) is 10% by mass or less, particularly 1 to 6% by mass, more particularly 2 to 2%, based on the total solid content of the hydroxyl group-containing acrylic resin (A) and melamine resin (B). It is preferable to use 5% by mass.

  The phosphoric acid group-containing acrylic resin can be used alone or in combination of two or more.

Non-aqueous dispersion type acrylic resin (E)
The non-aqueous dispersion type acrylic resin (E) has less influence on the finished appearance of the coating film than the polymer fine particles called microgel, which is usually used as a rheology control agent in the field of paint. It can be suitably used as a rheology control agent for the coating composition of the invention.

  The non-aqueous dispersion type acrylic resin (E) is an acrylic resin obtained by dispersion polymerization of at least one unsaturated monomer in the presence of a polymer dispersion stabilizer and an organic solvent.

  The polymer dispersion stabilizer used in the production of the non-aqueous dispersion type acrylic resin (E) is generally a polymer obtained by copolymerizing a long-chain unsaturated monomer with another unsaturated monomer as required.

  The long-chain unsaturated monomer used in the polymer can be appropriately selected according to the performance required for the coating film, but can be preferably used from the viewpoints of copolymerizability, solubility in organic solvents, and the like. The following can be exemplified.

  For example, n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) C4-C18 alkyl or cycloalkyl ester of (meth) acrylic acid such as acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate; methoxybutyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxybutyl ( Alkoxyalkyl ester of (meth) acrylic acid such as (meth) acrylate; ester of aromatic alcohol such as benzyl (meth) acrylate with (meth) acrylic acid; glycidyl (meth) acrylate or (meth) acrylate Adducts of hydroxyalkyl esters of lauric acid and monocarboxylic acid compounds such as capric acid, lauric acid, linoleic acid, and oleic acid; adducts of (meth) acrylic acid and monoepoxy compounds such as “Cardula E10”; styrene , Α-methylstyrene, vinyltoluene, p-chlorostyrene, pt-butylstyrene, etc., vinyl aromatic compounds; itaconic acid, itaconic anhydride, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, etc. A mono or diester compound of an α, β-unsaturated carboxylic acid other than (meth) acrylic acid and a monoalcohol having 4 to 18 carbon atoms such as butyl alcohol, pentyl alcohol, heptyl alcohol, octyl alcohol, stearyl alcohol; 8F "," Biscoat 8FM "," Biscoat 3 " ”,“ Biscoat 3FM ”(both manufactured by Osaka Organic Chemical Co., Ltd., trade names, (meth) acrylate compounds having a fluorine atom in the side chain), fluorine atoms such as perfluorocyclohexyl (meth) acrylate, perfluorohexylethylene, etc. Examples thereof include compounds.

  The unsaturated monomer other than the long-chain unsaturated monomer used as necessary for the polymerization of the polymer dispersion stabilizer is particularly limited as long as it is an unsaturated monomer other than the long-chain unsaturated monomer as listed above. Although not, for example, alkyl esters of 1 to 3 carbon atoms of (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate; glycidyl (meth) acrylate and acetic acid, propionic acid, etc. Adducts with monocarboxylic acid compounds having 2 to 3 carbon atoms; α, β other than (meth) acrylic acid such as itaconic acid, itaconic anhydride, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid, etc. -Mono- or diesterification of unsaturated carboxylic acid with mono-alcohols having 1 to 3 carbon atoms such as methyl alcohol and propyl alcohol Compounds; Cyano group-containing unsaturated compounds such as (meth) acrylonitrile; Vinyl ester compounds such as vinyl acetate; Vinyl ether compounds such as ethyl vinyl ether and methyl vinyl ether; α-olefins such as ethylene, propylene, vinyl chloride and vinylidene chloride A compound etc. can be mentioned. Examples of unsaturated monomers other than long-chain unsaturated monomers include those obtained by substituting the unsaturated monomers listed above with hydroxyl groups or the like, such as 2-hydroxyethyl (meth) acrylate.

  The polymerization for producing the polymer dispersion stabilizer can usually be carried out using a radical polymerization initiator. Examples of the radical polymerization initiator include azo initiators such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile); benzoyl peroxide, lauryl peroxide, Examples thereof include peroxide initiators such as t-butyl peroctoate and t-butyl peroxy-2-ethylhexanoate, and these polymerization initiators are generally 0 per 100 parts by mass of monomers used for polymerization. .About 2 to 10 parts by mass, preferably 0.5 to 5 parts by mass. The reaction temperature at the time of polymerization is usually about 60 to 160 ° C., and the reaction time at the time of polymerization can be usually about 1 to 15 hours.

  The molecular weight of the copolymer used as the dispersion stabilizer is usually in the range of about 5000 to 100,000, preferably about 5000 to 50000 in terms of weight average molecular weight. Use of a copolymer having a molecular weight in the above range as a dispersion stabilizer is preferable because stabilization of the dispersed particles can suppress aggregation and sedimentation, and can provide a paint that is easy to handle without having a too high viscosity.

  The polymer dispersion stabilizer can be used alone or in combination of two or more. Further, if necessary, other dispersion stabilizers such as butyl etherified melamine-formaldehyde resin, alkyd resin and the like can be used in combination.

  In the production of the non-aqueous dispersion type acrylic resin (E), at least one unsaturated monomer is polymerized in an organic solvent in the presence of the polymer dispersion stabilizer, and the polymer particles are insoluble in the organic solvent. A non-aqueous dispersion of is prepared.

  The organic solvent used in the polymerization includes organic solvents that do not substantially dissolve the polymer particles produced by the polymerization, but are good solvents for the polymer dispersion stabilizer and the unsaturated monomer. Is done. Specific examples of such organic solvents include aliphatic hydrocarbon solvents such as hexane, heptane, and octane; aromatic hydrocarbons such as benzene, toluene, and xylene; methyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, octyl Alcohol solvents such as alcohol; ether solvents such as cellosolve, butyl cellosolve, diethylene glycol monobutyl ether; ketone solvents such as methyl isobutyl ketone, diisobutyl ketone, methyl ethyl ketone, methyl hexyl ketone, ethyl butyl ketone; ethyl acetate, isobutyl acetate, amyl acetate And ester solvents such as 2-ethylhexyl acetate. These organic solvents can be used alone or in combination of two or more.

  As the above-mentioned organic solvent, in particular, those mainly composed of aliphatic hydrocarbons and suitably combined with aromatic hydrocarbons, alcohol solvents, ether solvents, ketone solvents, ester solvents and the like are preferably used. Can do.

  As the unsaturated monomer to be used for the polymerization, an unsaturated monomer having excellent polymerizability and having a carbon number smaller than that of the monomer used as the monomer component of the polymer dispersion stabilizer is dispersed. This is preferable because it is easily formed as polymer particles.

  Examples of such unsaturated monomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, and t-butyl (meth) acrylate. Carbon number of (meth) acrylic acid such as 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, n-octyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate, etc. 1-18 alkyl or cycloalkyl esters; alkoxyalkyl esters of (meth) acrylic acid such as methoxybutyl (meth) acrylate, methoxyethyl (meth) acrylate, ethoxybutyl (meth) acrylate; Esters of aromatic alcohols such as (meth) acrylates with (meth) acrylic acid; monocarboxylic acids having 2 to 18 carbon atoms such as glycidyl (meth) acrylate and acetic acid, propionic acid, oleic acid, pt-butylbenzoic acid Adducts with acid compounds; Adducts of (meth) acrylic acid with monoepoxy compounds such as “Kardura E10”; Styrene, α-methylstyrene, vinyltoluene, p-chlorostyrene, pt-butylstyrene Vinyl aromatic compounds such as itaconic acid, itaconic anhydride, crotonic acid, maleic acid, maleic anhydride, fumaric acid, citraconic acid and other α, β-unsaturated carboxylic acids and methyl alcohol, Mono or di with mono-alcohol having 1 to 18 carbon atoms such as butyl alcohol, hexyl alcohol, stearyl alcohol Stealth compound; “Biscoat 8F”, “Biscoat 8FM”, “Biscoat 3F”, “Biscoat 3FM” (both manufactured by Osaka Organic Chemical Co., Ltd., trade name, (meth) acrylate compound having a fluorine atom in the side chain), Fluorine atom-containing compounds such as perfluorocyclohexyl (meth) acrylate and perfluorohexylethylene; cyano group-containing unsaturated compounds such as (meth) acrylonitrile; vinyl acetate, vinyl benzoate, “VEOVA” (Shell Co., Ltd.) Vinyl ester compounds such as n-butyl vinyl ether, ethyl vinyl ether, and methyl vinyl ether; 1,6-hexanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, divinylbenzene, etc. Polyvinyli And α-olefin compounds such as ethylene, propylene, vinyl chloride, and vinylidene chloride.

  As described above, the monomer component forming the polymer particles can stably form the particle component by using a polymer component having a carbon number smaller than that of the monomer component of the polymer dispersion stabilizer. From the viewpoint, (meth) acrylic acid ester compounds, vinyl aromatic compounds, (meth) acrylonitrile, and the like having 8 or less carbon atoms, preferably 4 or less carbon atoms can be suitably used. These unsaturated monomers can be used alone or in combination of two or more.

  The polymerization of the unsaturated monomer can usually be performed using a radical polymerization initiator. Usable radical polymerization initiators include, for example, azo initiators such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile); benzoyl peroxide, lauryl And peroxide initiators such as peroxide, t-butyl peroctoate, t-butyl peroxy-2-ethylhexanoate, etc., and these polymerization initiators are generally based on the total amount of monomers used for polymerization. And about 0.2 to 10 parts by mass, preferably 0.5 to 5 parts by mass.

  The ratio of the polymer dispersion stabilizer and the unsaturated monomer used in the polymerization is usually about 3 to 240 parts by weight, preferably 5 to 5 parts of the unsaturated monomer with respect to 100 parts by weight of the polymer dispersion stabilizer. About 82 parts by mass. Furthermore, the total concentration of the polymer dispersion stabilizer and the unsaturated monomer in the organic solvent is usually about 30 to 70% by mass, preferably about 30 to 60% by mass.

  The polymerization can be carried out by a method known per se, the reaction temperature during the polymerization is usually about 60 to 160 ° C., and the reaction time during the polymerization is usually about 1 to 15 hours.

  By carrying out the polymerization reaction as described above, the liquid phase is a solution of a polymer dispersion stabilizer in an organic solvent, and the solid phase is a polymer particle obtained by polymerizing an unsaturated monomer. A stable non-aqueous dispersion of resin can be obtained. The average particle size of the polymer particles is usually in the range of about 0.1 to 1.0 μm. By setting the average particle diameter of the polymer particles in the above range, it is preferable because the viscosity of the non-aqueous dispersion does not become too high and swelling or aggregation of the polymer particles during storage of the paint can be suppressed.

  In the production of the non-aqueous dispersion type acrylic resin (E), the storage stability and mechanical properties of the non-aqueous dispersion are improved by combining the polymer dispersion stabilizer and the polymer particles in the non-aqueous dispersion. Can be improved. Even when bonded, there is almost no change in the dispersed state in appearance, and the average particle diameter of the polymer particles is hardly changed.

  Examples of the method for bonding the polymer dispersion stabilizer and the polymer particles include a hydroxyl group, an acid group, an acid anhydride group, an epoxy group, a methylol group, an isocyanate group, an amide in the stage of preparing the polymer dispersion stabilizer in advance. A hydroxyl group, an acid group, an acid anhydride group, an epoxy group, or a methylol that has been partially copolymerized with a monomer component having a functional group such as an amino group or an amino group and further reacts with the functional group as a monomer component that forms polymer particles. It can be carried out by using a monomer having a functional group such as a group, an isocyanate group, an amide group or an amino group. Examples of these combinations include an isocyanate group and a hydroxyl group, an isocyanate group and a methylol group, an epoxy group and an acid (anhydrous) group, an epoxy group and an amino group, an isocyanate group and an amide group, and an acid (anhydrous) group and a hydroxyl group. Can do.

Examples of the monomer having such a functional group include (meth) acrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, citraconic acid, and the like. Saturated carboxylic acids; glycidyl group-containing compounds such as glycidyl (meth) acrylate, vinyl glycidyl ether, allyl glycidyl ether; (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N-alkoxymethyl (meth) acrylamide, diacetone Carboxylic acid amide compounds such as acrylamide and N-methylol (meth) acrylamide; containing sulfonic acid amide groups such as p-styrenesulfonamide, N-methyl-p-styrenesulfonamide, and N, N-dimethyl-p-styrenesulfonamide Compound; (meth) acryl Amino group-containing compounds such as tert-butylaminoethyl uric acid; condensates of 2-hydroxyethyl (meth) acrylate and phosphoric acid or phosphate ester compounds, glycidyl compounds having a glycidyl group such as glycidyl (meth) acrylate Phosphoric acid group-containing compounds such as phosphoric acid or phosphoric acid ester compounds added to groups; sulfonic acid group-containing compounds such as 2-acrylamido-2-methyl-propanesulfonic acid; m-isopropenyl-α, α- Examples include dimethylbenzyl isocyanate, isophorone diisocyanate or tolylene diisocyanate and hydroxy (meth) acrylate equimolar adducts, isocyanate group-containing compounds such as isocyanoethyl methacrylate, and the like.
Another method for bonding the polymer dispersion stabilizer and the polymer particles can be performed by polymerizing an unsaturated monomer in the presence of a polymer dispersion stabilizer having a polymerizable double bond.

  For example, a polymerizable double bond is introduced into the polymer dispersion stabilizer by using an acid group-containing monomer such as carboxylic acid, phosphoric acid, or sulfonic acid as a copolymerization component of the resin. The reaction can be carried out by reacting a glycidyl group-containing unsaturated monomer such as acrylate or allyl glycidyl ether. Conversely, it can also be carried out by allowing a polymer dispersion stabilizer to contain a glycidyl group and reacting it with an acid group-containing unsaturated monomer. These reactions can be performed according to known conditions.

  Further, as another method for bonding the polymer dispersion stabilizer and the polymer particles, a non-aqueous dispersion liquid in which functional groups that do not react with each other are introduced into the polymer dispersion stabilizer and the polymer particles is manufactured. It can also be carried out by reacting a binder that binds both to a product.

  Specifically, for example, a hydroxyl group-containing unsaturated monomer is polymerized alone or as a mixture with other unsaturated monomers in the presence of a hydroxyl group-containing polymer dispersion stabilizer and an organic solvent, and a non-aqueous dispersion containing a hydroxyl group in both. After producing the liquid, it can be carried out by blending a polyisocyanate compound and the like and reacting at room temperature for several hours to several days, or at about 60 to 100 ° C. for about 1 to 5 hours.

  The polyisocyanate compound may be any compound having two or more isocyanate groups in the molecule. For example, aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, 4,4′-diphenylmethane diisocyanate, or hydrides thereof. An aliphatic diisocyanate such as hexamethylene diisocyanate, lysine diisocyanate, dimer acid (dimer of tall oil fatty acid) diisocyanate; and an alicyclic diisocyanate such as isophorone diisocyanate.

  In addition to the above, polymer dispersion stabilizers containing acid groups and combinations of polymer particles and polyepoxides, polymer dispersion stabilizers containing epoxy groups and combinations of polymer particles and polycarboxylic acids, epoxy groups Alternatively, a polymer dispersion stabilizer containing an isocyanate group and a combination of polymer particles and a polysulfide compound can also be used.

  Examples of the polyepoxide include bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolac type epoxy resin, epoxy group-containing acrylic resin, and the like. Examples of polycarboxylic acids include adipic acid, sebacic acid, azelaic acid, isophthalic acid, and the like. ; Examples of polysulfide include pentamethylene disulfide, hexamethylene disulfide, poly (ethylene disulfide), and the like.

  As described above, the polymer dispersion stabilizer and the polymer particles can be chemically bonded. At this time, various functional groups and / or polymerizable double bonds are bonded to the polymer dispersion stabilizer and / or It is sufficient that the amount introduced into the polymerizable particles is an amount that averages at least 0.1 in one molecule of the dispersion stabilizer and / or particles. The amount is preferably 0, particularly 0.1 to 0.5, and more preferably 0.1 to 0.3.

  The non-aqueous dispersion thus obtained has excellent storage stability because the polymer dispersion stabilizer and polymer particles are chemically bonded, and the formed coating film is chemically and mechanically formed. Can exhibit excellent properties.

  When the non-aqueous dispersion type acrylic resin (E) is used in the coating composition of the present invention, the amount thereof depends on the coating workability (sag resistance) of the coating composition of the present invention and the coating surface of the resulting coating film. From the viewpoint of finished appearance such as smoothness, the solid content is 15% by mass or less, preferably 2 to 10% by mass, and more preferably based on the total solid content of the hydroxyl group-containing acrylic resin (A) and melamine resin (B). Is suitably in the range of 3-8% by weight.

  Further, the present paint can further contain, if necessary, a color pigment, a bright pigment, a dye, and the like to the extent that transparency is not hindered. Further, other than extender pigments and phosphate group-containing compounds (D) Catalyst, ultraviolet absorber, light stabilizer, antifoaming agent, thickener, rust preventive agent, surface conditioner, organic solvent and the like can be appropriately contained.

  The solid content concentration of the paint is usually preferably 35 to 70% by mass, more preferably 40 to 70% by mass, and still more preferably 45 to 65% by mass.

  This paint can be applied by a method known per se, for example, airless spray, air spray, rotary atomizing coater, etc., and electrostatic application may be performed during the coating. The coating film thickness can be in the range of usually 10 to 60 μm, preferably 25 to 50 μm in terms of the cured film thickness.

Multi-layer coating formation method
Coating material The coating material to which the water-based first colored paint (X) can be applied according to the present invention is not particularly limited. For example, an outer plate portion of an automobile body such as a passenger car, a truck, a motorcycle, or a bus; Automobile parts; The outer plate part of home electric products such as mobile phones and audio devices can be mentioned, and among them, the outer plate part of an automobile body and the 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 them, an undercoat film is formed by a cationic electrodeposition paint. A car body is particularly suitable.

Process (1)
In this step, the first colored coating film is formed by applying the aqueous first colored paint (X) on the object to be coated.

Water-based first colored paint (X)
The water-based first colored paint (X) to be coated on the article to be coated contains a thermosetting resin component and water, and if necessary, an organic solvent, a colored pigment, an extender pigment, a bright pigment, a surface An aqueous liquid coating composition containing a regulator, an anti-settling agent, or the like can be used. In this specification, the water-based paint is a paint in which the main component of the solvent is water.

  Examples of the thermosetting resin component include base resins (ii) having a crosslinkable functional group such as a hydroxyl group and a hydrophilic functional group such as a carboxyl group, such as a polyester resin, an acrylic resin, a vinyl resin, an alkyd resin, and a urethane resin. Further, a coating resin composition known per se consisting of a crosslinking agent (b) such as a melamine resin and an optionally blocked polyisocyanate compound can be used.

  Among them, a hydroxyl group-containing acrylic resin (b) and / or a hydroxyl group-containing polyester resin (b) is used as the base resin (b), and an amino resin (b) and / or a block is used as the crosslinking agent (b). It is preferable to use a modified polyisocyanate compound (2).

  The hydroxyl group-containing acrylic resin (I) is prepared by, for example, containing at least one unsaturated monomer component including a hydroxyl group-containing unsaturated monomer and optionally another unsaturated monomer copolymerizable with the monomer under normal conditions ( It can be produced by co) polymerization.

  The hydroxyl group-containing unsaturated monomer is a compound having at least one hydroxyl group and polymerizable unsaturated bond in one molecule, such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, Monoesterified product of (meth) acrylic acid such as 3-hydroxypropyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate and a dihydric alcohol having 2 to 8 carbon atoms; (meth) acrylic acid and 2 to 2 carbon atoms Ε-caprolactone modified product of monoesterified product of 8 dihydric alcohol; allyl alcohol; (meth) acrylate having a polyoxyethylene chain whose molecular terminal is a hydroxyl group.

  Other unsaturated monomers copolymerizable with the hydroxyl group-containing unsaturated monomer include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n -Butyl (meth) acrylate, i-butyl (meth) acrylate, tert-butyl (meth) acrylate, n-hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, nonyl (meth) acrylate , Lauryl (meth) acrylate, tridecyl (meth) acrylate, stearyl (meth) acrylate, “isostearyl acrylate” (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate , Alkyl or cycloalkyl (meth) acrylates such as t-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate; unsaturated monomers having an isobornyl group such as isobornyl (meth) acrylate; adamantyl (meta ) Unsaturated monomer having an adamantyl group such as acrylate; aromatic ring-containing unsaturated monomer such as styrene, α-methylstyrene, vinyltoluene, phenyl (meth) acrylate; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2- Unsaturated monomers having an alkoxysilyl group such as methoxyethoxy) silane, γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane; Perfluoroalkyl (meth) acrylates such as tilethyl (meth) acrylate and perfluorooctylethyl (meth) acrylate; Unsaturated monomers having fluorinated alkyl groups such as fluoroolefins; Nonpolymers having photopolymerizable functional groups such as maleimide groups Saturated monomers; vinyl compounds such as N-vinyl pyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate and vinyl acetate; carboxyl group-containing unsaturated monomers such as (meth) acrylic acid, maleic acid, crotonic acid and β-carboxyethyl acrylate ; (Meth) acrylonitrile, (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, dimethylaminoethyl (meth) acrylate, adducts of glycidyl (meth) acrylate and amines, etc. Nitrogen unsaturated monomer: glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate, 3,4-epoxycyclohexyl Epoxy group-containing unsaturated monomers such as propyl (meth) acrylate and allyl glycidyl ether; (meth) acrylate having a polyoxyethylene chain whose molecular terminal is an alkoxy group; 2-acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid , Unsaturated monomers having a sulfonic acid group such as sodium styrenesulfonate, sulfoethyl methacrylate, and sodium salts and ammonium salts thereof; 2-acryloyloxyethyl acid phosphate; Unsaturated monomers having a phosphate group such as methacryloyloxyethyl acid phosphate, 2-acryloyloxypropyl acid phosphate, 2-methacryloyloxypropyl acid phosphate; 2-hydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone 2-hydroxy-4- (3-acryloyloxy-2-hydroxypropoxy) benzophenone, 2,2′-dihydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone, 2,2′-dihydroxy-4 UV rays such as-(3-acryloyloxy-2-hydroxypropoxy) benzophenone and 2- (2'-hydroxy-5'-methacryloyloxyethylphenyl) -2H-benzotriazole Unsaturated monomer having an astringent group; 4- (meth) acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4- (meth) acryloyloxy-2,2,6,6-tetramethylpiperidine 4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 1- (meth) acryloyl-4- (meth) acryloylamino-2,2,6,6-tetramethyl Piperidine, 1- (meth) acryloyl-4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6-tetramethyl Unsaturated monomers having UV-stabilizing performance such as lupiperidine; acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formylstyrol, vinyl alkyl ketone having 4 to 7 carbon atoms (for example, vinyl methyl ketone) , Vinyl ethyl ketone, vinyl butyl ketone) and the like, and these can be used alone or in combination of two or more.

  The hydroxyl group-containing acrylic resin (I) is generally from 1 to 200 mgKOH / g, preferably from 2 to 100 mgKOH / g, more preferably from 3 to 60 mgKOH / g, from the viewpoints of storage stability and water resistance of the resulting coating film. It can have a hydroxyl value within the range and generally an acid value within the range of 1 to 200 mg KOH / g, preferably 2 to 150 mg KOH / g, more preferably 5 to 100 mg KOH / g. The hydroxyl group-containing acrylic resin (A1) is generally in the range of 1,000 to 5,000,000, preferably 2,000 to 3,000,000, more preferably 3,000 to 1,000,000. It can have a weight average molecular weight.

  The compounding amount of the hydroxyl group-containing acrylic resin (I) is based on the total solid content of the base resin (I) and the crosslinking agent (B) (hereinafter referred to as the resin component) in the aqueous first colored paint (X). Usually, it can be in the range of 0 to 90% by mass, preferably 5 to 60% by mass, and more preferably 10 to 40% by mass.

  The hydroxyl group-containing polyester resin (ii) can be produced, for example, by an esterification reaction or a transesterification reaction between a polybasic acid component and a polyhydric alcohol component. Specifically, for example, the polybasic acid component It can manufacture by making the equivalent ratio (COOH / OH) of the carboxyl group in a polyhydric alcohol component into less than 1, and performing an esterification reaction in a state with many hydroxyl groups compared with a carboxyl group.

  The polybasic acid component is a compound having at least two carboxyl groups in one molecule. For example, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, glutaric acid, adipic acid, azelaic acid, sebacic acid, tetrahydro Polybasic acids such as phthalic acid, hexahydrophthalic acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid and pyromellitic acid; anhydrides of these polybasic acids; lower alkyl esterified products of these polybasic acids, etc. These may be used alone or in combination of two or more.

  The polyhydric alcohol component is a compound having at least two hydroxyl groups in one molecule, such as ethylene glycol, 1,2-propylene glycol, 1,2-butylene glycol. Α-glycol such as 2,3-butylene glycol, 1,2-hexanediol, 1,2-dihydroxycyclohexane, 3-ethoxypropane-1,2-diol, 3-phenoxypropane-1,2-diol -Neolyl glycol, 2-methyl-1,3-propanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol 2,2-diethyl-1,3-propanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-butyl-2-ethyl-1,3-propyl Pandiol, 2-phenoxypropane-1,3-diol, 2-methyl-2-phenylpropane-1,3-diol, 1,3-propylene glycol, 1,3-butylene glycol, 2-ethyl-1,3 -Octanediol, 1,3-dihydroxycyclohexane, 1,4-butanediol, 1,4-dihydroxycyclohexane, 1,5-pentanediol, 1,6-hexanediol, 2,5-hexanediol, 3-methyl- 1,5-pentanediol, 1,4-dimethylolcyclohexane, tricyclodecane dimethanol, 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate (this is hydroxypivalin) Acid and neopentyl glycol esterified product), bisphenol A, Bisphenol F, bis (4-hydroxyhexyl) -2,2-propane, bis (4-hydroxyhexyl) methane, 3,9-bis (1,1-dimethyl-2-hydroxyethyl) -2,4,8, 10-tetraoxaspiro [5,5] undecane, diethylene glycol, triethylene glycol, glycerol, diglycerol, triglycerol, pentaerythritol, dipentaerythritol, sorbitol, mannitol, trimethylolethane, trimethylolpropane, ditrimethylolpropane, Examples thereof include tris (2-hydroxyethyl) isocyanurate, and these can be used alone or in combination of two or more.

  The esterification or transesterification reaction of the polybasic acid component and the polyhydric alcohol component can be carried out by a method known per se. For example, the polybasic acid component and the polyhydric alcohol component are heated at about 180 to about 250 ° C. It can be carried out by polycondensation at a temperature.

  Further, the hydroxyl group-containing polyester resin (ii) can be modified with a fatty acid, a monoepoxy compound, or the like as necessary during the preparation of the polyester resin or after the esterification reaction. Examples of the fatty acid include coconut oil fatty acid, cottonseed oil fatty acid, hemp seed oil fatty acid, rice bran oil fatty acid, fish oil fatty acid, tall oil fatty acid, soybean oil fatty acid, linseed oil fatty acid, tung oil fatty acid, rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor Examples of the monoepoxy compound include “Cardura E10P” (trade name, manufactured by HEXION Specialty Chemicals, Inc., a glycidyl ester of a synthetic highly branched saturated fatty acid).

  The hydroxyl group-containing polyester resin (ii) is generally 10 to 300 mgKOH / g, preferably 25 to 250 mgKOH / g, more preferably 50 to 200 mgKOH / g, and generally 1 to 200 mgKOH / g, preferably The acid value may be in the range of 5 to 100 mg KOH / g, more preferably 10 to 60 mg KOH / g. The hydroxyl group-containing polyester resin (ii) generally has a weight average molecular weight in the range of 500 to 50,000, preferably 1,000 to 40,000, and more preferably 1,500 to 30,000. it can.

  The compounding amount of the hydroxyl group-containing polyester resin (ii) is usually 0 to 90% by mass, preferably 10 to 60% by mass, more preferably, based on the total amount of resin component solids in the aqueous first colored paint (X). It can be in the range of 15-50 mass%.

  In addition, the hydroxyl group-containing acrylic resin (I) and the hydroxyl group-containing polyester resin (I 2) are a part of or all of the carboxyl groups that may be contained in the base in order to facilitate water-solubilization or water-dispersion. It is preferable to neutralize with a functional compound. Examples of basic compounds include hydroxides of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, barium hydroxide; ammonia; ethylamine, propylamine, butylamine, Primary monoamines such as benzylamine, monoethanolamine, neopentanolamine, 2-aminopropanol, 2-amino-2-methyl-1-propanol, 3-aminopropanol; diethylamine, diethanolamine, di-n-propanolamine , Secondary monoamines such as di-iso-propanolamine, N-methylethanolamine, N-ethylethanolamine; dimethylethanolamine, trimethylamine, triethylamine, triisopropylamine, methyldiethanol Triethanolamine, 2- (dimethylamino) tertiary monoamines such as ethanol; diethylenetriamine, hydroxyethylaminoethylamine, ethylamino ethylamine, may be mentioned polyamines such as methylamino propylamine. The amount of the basic compound used is usually in the range of 0.1 to 1.5 equivalents, preferably 0.2 to 1.2 equivalents, relative to the acid groups of the base resin (ii).

  As the urethane resin, in addition to a normal urethane resin, a high molecular weight is obtained by extending a polyisocyanate compound to a part of hydroxyl groups in the hydroxyl group-containing acrylic resin (ii) and the hydroxyl group-containing polyester resin (ii) by a urethanization reaction. Examples of such urethane resins can be given.

  On the other hand, examples of the amino resin (b) include partial or completely methylolated amino resins obtained by reacting amino components such as melamine, urea, benzoguanamine, acetoguanamine, steroguanamine, spiroguanamine, dicyandiamide and the aldehyde. It is done. Examples of the aldehyde include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde and the like. In addition, a partially or completely etherified part of this partially or fully methylolated amino resin with alcohol can be used. Examples of alcohols used for etherification include methyl alcohol, ethyl alcohol, and n-propyl. Examples include alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, 2-ethylbutanol, and 2-ethylhexanol.

  As the amino resin (1), a melamine resin is preferable, and in particular, a methyl ether melamine resin partially or completely etherified with a methyl alcohol group of a partially or completely methylol melamine resin or partially with a butyl alcohol. Preference is given to alkyl etherified melamine resins such as partially or fully etherified butyl etherified melamine resins, methyl alcohol and methyl-butyl mixed etherified melamine resins partially or fully etherified with butyl alcohol.

  Moreover, it is preferable that a melamine resin has the weight average molecular weight in the range of 500-5,000 normally, especially 600-4,000, Furthermore, 700-3,000.

  When melamine resin is used as a crosslinking agent (b), sulfonic acids such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and salts of these acids and amines are used as catalysts. be able to.

  As the blocked polyisocyanate compound (2), the isocyanate group of the polyisocyanate compound having at least two isocyanate groups in one molecule is blocked with a blocking agent such as oxime, phenol, alcohol, active methylene compound, lactam, mercaptan, etc. Can be used.

  The ratio of the base resin (a) and the crosslinking agent (b) is based on the total solid content of both, the former is generally 40 to 90% by mass, particularly 50 to 80% by mass, the latter is generally 60 to 10% by mass, The range of 50 to 20% by mass is particularly suitable.

  Examples of the color pigment include titanium oxide, zinc oxide, carbon black, lead sulfate, calcium lead acid, zinc phosphate, aluminum phosphate, zinc molybdate, calcium molybdate, bitumen, ultramarine blue, cobalt blue, copper phthalocyanine blue. , Indanthrone Blue, Yellow lead, Synthetic yellow iron oxide, Transparent brown (yellow), Bismuth vanadate, Titanium yellow, Zinc yellow (Zinc yellow), Monoazo yellow, Isoindolinone yellow, Metal complex azo yellow, Quinophthalone yellow, Benz Imidazolone yellow, red bean, red lead, monoazo red, quinacridone red, azo lake (Mn salt), quinacridone magenta, ansanthrone orange, dianslaquinonyl red, perylene maroon, quinacridone magenta, perylene red, dike Examples include pyrrolopyrrole chromium vermilion, chlorinated phthalocyanine green, brominated phthalocyanine green, pyrazolone orange, benzimidazolone orange, dioxazine violet, and perylene violet. Among them, titanium oxide and carbon black are preferably used. it can.

  When the aqueous first colored paint (X) contains the above-mentioned colored pigment, the amount of the colored pigment is usually 1 to 120% by mass based on the total amount of solids of the resin component in the aqueous first colored paint (X). , Preferably 10 to 100% by mass, more preferably 15 to 90% by mass.

  Examples of the extender pigment include clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, talc, silica, and alumina white. Among them, it is preferable to use barium sulfate and / or talc.

  When the aqueous first colored paint (X) contains the above extender, the amount of the extender pigment is usually 1 to 100% by mass based on the total amount of solids of the resin component in the aqueous first colored paint (X). , Preferably 5 to 60% by mass, more preferably 8 to 40% by mass.

  Examples of the bright pigment include non-leafing type or leafing type aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, aluminum oxide, mica, aluminum oxide coated with titanium oxide or iron oxide, Examples thereof include mica coated with titanium oxide or iron oxide, glass flakes, and hologram pigments, and these can be used alone or in combination of two or more.

  When the water-based first colored paint (X) contains the glitter pigment, the blending amount of the glitter pigment is usually 1 to 50 on the basis of the total solid content of the resin component in the water-based first colored paint (X). It can be within the range of mass%, preferably 2-30 mass%, more preferably 3-20 mass%.

  The water-based first colored paint (X) can be applied onto the object by a method known per se, for example, air spray, airless spray, rotary atomizing coating machine, etc. You may go. The coating film thickness is usually 10 to 100 μm, preferably 10 to 50 μm, and more preferably 15 to 35 μm as a cured film thickness.

  The first colored coating film formed with the aqueous first colored paint (X) in step (1) before applying the aqueous second colored paint (Y) has a solid content of 70 to 100% by mass. In particular, it is preferably adjusted to be in the range of 75 to 99% by mass, more preferably 80 to 98% by mass.

  The solid content can be adjusted by means such as preheating (preheating) or air blowing. The preheating temperature can be room temperature to about 100 ° C., preferably about 40 to about 90 ° C., more preferably about 60 to about 80 ° C., and the preheating time is 30 seconds to 15 minutes, preferably 1 to 10 Minutes, more preferably about 3 to 5 minutes.

Step (2)
Next, an aqueous second colored paint (Y) is applied on the first colored coating film formed by the aqueous first colored paint in the step (1).

Water-based second colored paint (Y)
The aqueous second colored paint (Y) used in the present invention contains a thermosetting resin component and water, and if necessary, an organic solvent, a colored pigment, an extender pigment, a bright pigment, a surface conditioner. In addition, an aqueous liquid paint formed by blending an anti-settling agent or the like can be used.

  As the thermosetting resin component, polyester resin, acrylic resin, vinyl resin, alkyd resin having a crosslinkable functional group such as a hydroxyl group and a hydrophilic functional group such as a carboxyl group described for the aqueous first colored paint (X) It is possible to use a coating resin composition known per se, which comprises a base resin (A) such as urethane resin and a crosslinking agent (B) such as a melamine resin or an optionally blocked polyisocyanate compound.

  Among them, the above-mentioned hydroxyl group-containing acrylic resin (ii) and / or hydroxyl group-containing polyester resin (ii) is used as the base resin (ii), and the amino resin (ii) and / or the crosslinking agent (ii). Alternatively, it is preferable to use a blocked polyisocyanate compound (2).

  The water-based second colored paint (Y) may further include, if necessary, pigments such as the above-mentioned color pigments, extender pigments and glitter pigments; curing catalysts, ultraviolet absorbers, light stabilizers, antifoaming agents, plastics A normal coating additive such as an agent, an organic solvent, a surface conditioner, and an anti-settling agent can be contained alone or in combination of two or more.

  In particular, in the aqueous second colored paint (Y), when a bright pigment is used as at least one of the pigment components, it is possible to form a metallic or pearly coating film having a dense feeling, which is preferable.

  The water-based second colored paint (Y) can be applied by a method known per se, for example, air spray, airless spray, rotary atomizing coater, etc., and electrostatic application may be performed during the coating. The coating film thickness is usually 5 to 40 μm, preferably 10 to 30 μm as a cured film thickness.

  Before applying the clear paint (Z), the second colored coating film formed by the aqueous second colored paint (Y) in the step (2) has a solid content of 70 to 100% by mass, particularly 75. It is preferably adjusted to be in the range of ˜99 mass%, more particularly 80 to 98 mass%.

Step (3)
Next, the clear paint (Z) is applied on the second colored coating film formed by the aqueous second colored paint in the step (2). As the clear paint (Z), the above-described paint composition of the present invention (the present paint) is applied.

  The clear paint (Z) can be applied by a method known per se, for example, airless spray, air spray, rotary atomizing coating machine, etc., and electrostatic application may be performed during the coating. The coating film thickness can be in the range of usually 10 to 60 μm, preferably 25 to 50 μm in terms of the cured film thickness.

Step (4)
A multi-layer coating film composed of three layers of the first colored coating film, the second colored coating film, and the clear coating film formed as described above, It can be cured by heating at a temperature of about 80 to about 170 ° C., preferably about 120 to about 160 ° C. for about 20 to about 40 minutes, by hot air heating, infrared heating, high frequency heating or the like.

  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 and production example 1 of hydroxyl group-containing acrylic resin (I)
In a reaction vessel equipped with a thermometer, thermostat, stirring device, reflux condenser and dropping device, 70.7 parts of deionized water and “Aqualon KH-10” (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., emulsifier, active ingredient) 97%) 0.52 part was charged, stirred and mixed in a nitrogen stream, and heated to 80 ° C. Next, 1% of the total amount of the following monomer emulsion and 5 parts of a 6% aqueous ammonium persulfate solution were introduced into the reaction vessel and maintained at 80 ° C. for 15 minutes. Thereafter, the remaining monomer emulsion was dropped into a reaction vessel maintained at the same temperature over 3 hours, and after aging was completed for 1 hour, 40 parts of a 5% 2- (dimethylamino) ethanol aqueous solution was placed in the reaction vessel. While gradually adding, the mixture was cooled to 30 ° C. and discharged while filtering through a 100 mesh nylon cloth to obtain a hydroxyl group-containing acrylic resin emulsion (I-1-1) having a solid content concentration of 45%. The resulting hydroxyl group-containing acrylic resin had an acid value of 12 mgKOH / g and a hydroxyl value of 43 mgKOH / g.

  Monomer emulsion: 50 parts of deionized water, 10 parts of styrene, 40 parts of methyl methacrylate, 35 parts of ethyl acrylate, 3.5 parts of n-butyl methacrylate, 10 parts of 2-hydroxyethyl methacrylate, 1.5 parts of acrylic acid, Aqualon KH -10 1.0 part of ammonium persulfate and 0.03 part of ammonium persulfate were mixed and stirred to obtain a monomer emulsion.

Production Example 2
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device was charged with 130 parts of deionized water and 0.52 part of “AQUALON KH-10” and stirred and mixed in a nitrogen stream at 80 ° C. The temperature was raised to. Next, 1% of the total amount of the following monomer emulsion (1) and 5.3 parts of a 6% aqueous ammonium persulfate solution were introduced into the reaction vessel and maintained at 80 ° C. for 15 minutes. Then, the remaining monomer emulsion (1) was dripped in the reaction container hold | maintained at the same temperature over 3 hours, and it age | cure | ripened for 1 hour after completion | finish of dripping. Thereafter, the following monomer emulsion (2) was added dropwise over 1 hour, and after aging for 1 hour, the mixture was cooled to 30 ° C. while gradually adding 40 parts of 5% dimethylethanolamine aqueous solution to the reaction vessel, and 100 mesh nylon Drained while filtering through cloth, average particle size 100 nm (submicron particle size distribution measuring device “COULTER N4 type” (trade name, manufactured by Beckman Coulter, Inc.) diluted with deionized water and measured at 20 ° C.) Then, a hydroxyl group-containing acrylic resin emulsion (I-1-2) having a solid content concentration of 30% was obtained. The obtained hydroxyl group-containing acrylic resin had an acid value of 33 mgKOH / g and a hydroxyl value of 25 mgKOH / g.

  Monomer emulsion (1): 42 parts deionized water, 0.72 parts Aqualon KH-10, 2.1 parts methylenebisacrylamide, 2.8 parts styrene, 16.1 parts methyl methacrylate, 28 parts ethyl acrylate and n- 21 parts of butyl acrylate was mixed and stirred to obtain a monomer emulsion (1).

  Monomer emulsion (2): 18 parts deionized water, 0.31 part Aqualon KH-10, 0.03 part ammonium persulfate, 5.1 parts methacrylic acid, 5.1 parts 2-hydroxyethyl acrylate, 3 parts styrene, 6 parts of methyl methacrylate, 1.8 parts of ethyl acrylate and 9 parts of n-butyl acrylate were mixed and stirred to obtain a monomer emulsion (2).

Production Example 3 of Hydroxyl-Containing Polyester Resin (I2)
In a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and water separator, 174 parts trimethylolpropane, 327 parts neopentyl glycol, 352 parts adipic acid, 109 parts isophthalic acid and 1,2-cyclohexanedicarboxylic acid After charging 101 parts of acid anhydride and heating from 160 ° C. to 230 ° C. over 3 hours, the condensed water produced was kept at 230 ° C. while distilling off with a water separator, and the acid value was 3 mgKOH / g or less The reaction was continued until To this reaction product, 59 parts of trimellitic anhydride was added, and after 30 minutes of addition reaction at 170 ° C., the reaction product was cooled to 50 ° C. or less, and 2- (dimethylamino) ethanol was added in an equivalent amount to the acid group. After neutralization, deionized water was gradually added to obtain a hydroxyl group-containing polyester resin solution (A2-1) having a solid content concentration of 45% and a pH of 7.2. The obtained hydroxyl group-containing polyester resin had an acid value of 35 mgKOH / g, a hydroxyl value of 128 mgKOH / g, and a weight average molecular weight of 13,000.

Production Example 4
A reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and water separator was charged with 109 parts of trimethylolpropane, 141 parts of 1,6-hexanediol, 126 parts of hexahydrophthalic anhydride and 120 parts of adipic acid. The mixture was heated and heated from 160 ° C. to 230 ° C. over 3 hours, and then subjected to a condensation reaction at 230 ° C. for 4 hours. Subsequently, in order to add a carboxyl group to the obtained condensation reaction product, 38.3 parts of trimellitic anhydride was further added and reacted at 170 ° C. for 30 minutes, followed by 1-octanol (alcohol having a boiling point of 195 ° C.). Then, a hydroxyl group-containing polyester resin solution (ii-2) having a solid content concentration of 70% was obtained. The obtained hydroxyl group-containing polyester resin had an acid value of 46 mgKOH / g, a hydroxyl value of 150 mgKOH / g, and a weight average molecular weight of 6,400.

Production and production example 5 of water-based first colored paint (X)
56 parts of a hydroxyl group-containing polyester resin solution (ii-1) obtained in Production Example 3 (resin solids content 25 parts), JR-806 (manufactured by Teica, trade name, rutile titanium dioxide) 60 parts, carbon MA-100 (Mitsubishi Chemical Corporation, trade name, carbon black) 1 part, Variace B-35 (trade name, Sakai Chemical Industry Co., Ltd., barium sulfate powder, average primary particle size 0.5 μm) 15 parts, MICRO ACE S-3 ( Product name, manufactured by Nippon Talc Co., Ltd., 3 parts of talc powder, average primary particle size 4.8 μm) and 5 parts of deionized water were mixed, adjusted to pH 8.0 with 2- (dimethylamino) ethanol, and then painted with a shaker. A pigment dispersion paste was obtained by dispersing for 30 minutes.

  Next, 140 parts of the obtained pigment dispersion paste, 33 parts of the hydroxyl group-containing acrylic resin emulsion (A-1) obtained in Production Example 1, and the hydroxyl group-containing polyester resin solution (A-1) 33 obtained in Production Example 3 Parts, Cymel 325 (trade name, manufactured by Nippon Cytec Industries, Inc., melamine resin, solid content 80%), 37.5 parts, Bihydur VPLS2310 (trade name, manufactured by Sumika Bayer Urethane Co., Ltd., blocked polyisocyanate compound, solid content 38% ) 26 parts and 43 parts of U-coat UX-8100 (trade name, manufactured by Sanyo Chemical Industries, urethane emulsion, solid content 35%) were mixed uniformly.

  Next, UH-752 (trade name, manufactured by ADEKA, thickener), 2- (dimethylamino) ethanol and deionized water were added to the obtained mixture, pH 8.0, paint solid content 48%, 20 Ford Cup No. A water-based first colored paint (X-1) having a viscosity of 4 according to 30 was obtained.

Production Example 6
In Production Example 5, 43 parts of U-coat UX-8100, 28.6 parts of U-coat UX-8100 and SANNICS PP-1000 (trade name, manufactured by Sanyo Kasei Co., Ltd., polyoxypropylene glycol, number average molecular weight 1000, active ingredient 100% ) A water-based first colored paint (X-2) was obtained in the same manner as in Production Example 5 except that it was replaced with 5 parts.

Production Example of Bright Pigment Concentrate Liquid Production Example 7
In a stirring and mixing vessel, 19 parts of aluminum pigment paste GX-180A (trade name, manufactured by Asahi Kasei Metals Co., Ltd., metal content 74%), 35 parts of 1-octanol (alcohol solvent having a boiling point of 195 ° C.), containing phosphate groups 8 parts of a resin solution (* 1) and 0.2 part of 2- (dimethylamino) ethanol were mixed uniformly to obtain a bright pigment concentrate (P-1).

  (* 1) Phosphate group-containing resin solution: Put a mixed solvent of 27.5 parts of methoxypropanol and 27.5 parts of isobutanol into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device. , Heated to 110 ° C., 25 parts of styrene, 27.5 parts of n-butyl methacrylate, 20 parts of “isostearyl acrylate” (trade name, Osaka Organic Chemical Industries, Ltd., branched higher alkyl acrylate), 4-hydroxybutyl acrylate 7 A mixture of 5 parts, 15 parts of a phosphoric acid group-containing polymerizable monomer (* 2), 12.5 parts of 2-methacryloyloxyethyl acid phosphate, 10 parts of isobutanol and 4 parts of t-butylperoxyoctanoate 121. 5 parts are added to the above mixed solvent over 4 hours, and t-butyl peroxyoctanoate 0.5 A mixture of 20 parts of isopropanol and was dropped for 1 hour. Thereafter, the mixture was aged and stirred for 1 hour to obtain a phosphate group-containing resin solution having a solid concentration of 50%. The acid value due to the phosphoric acid group of this resin was 83 mgKOH / g, the hydroxyl value was 29 mgKOH / g, and the weight average molecular weight was 10,000.

  (* 2) Phosphoric acid group-containing polymerizable monomer: Into a reaction vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device, put 57.5 parts of monobutyl phosphate and 41 parts of isobutanol and bring to 90 ° C. After raising the temperature, 42.5 parts of glycidyl methacrylate was added dropwise over 2 hours, followed by stirring and aging for another hour. Thereafter, 59 parts of isopropanol was added to obtain a phosphate group-containing polymerizable monomer solution having a solid content concentration of 50%. The acid value due to the phosphate group of the obtained monomer was 285 mgKOH / g.

Production and production example 8 of water-based second colored paint (Y)
100 parts of the hydroxyl group-containing acrylic resin emulsion (ii-2) obtained in Production Example 2, 57 parts of the hydroxyl group-containing polyester resin solution (ii-2) obtained in Production Example 4, and the bright pigment concentrate obtained in Production Example 7 62 parts of liquid (P-1) and 37.5 parts of Cymel 325 (trade name, manufactured by Nippon Cytec Industries, Inc., melamine resin, solid content 80%) were mixed uniformly, and further, Primal ASE-60 (trade name, ROHM) And Haas, a thickener), 2- (dimethylamino) ethanol and deionized water, pH 8.0, paint solids 25%, Ford Cup No. 20 at 20 ° C. An aqueous second colored paint (Y-1) having a viscosity according to 4 of 40 seconds was obtained.

Production example 9 of hydroxyl group-containing acrylic resin (A1)
45 parts of SWAZOL 1000 (hydrocarbon organic solvent; manufactured by Cosmo Oil Co., Ltd., trade name) and 20 parts of n-butyl alcohol were charged, and the temperature was raised to 125 ° C. under nitrogen gas flow. After reaching 125 ° C., the nitrogen gas flow was stopped, 20 parts of styrene, 47.5 parts of n-butyl acrylate, 30 parts of 2-hydroxyethyl methacrylate, 2.5 parts of acrylic acid and 2,2-azobisisobutyrate. A monomer mixture composed of 4 parts of nitrile (polymerization initiator) was added dropwise over 5 hours. After 30 minutes, a polymerization initiator solution in which 0.5 part of 2,2′-azobis (2,4-dimethylvaleronitrile) (polymerization initiator) was dissolved in 3 parts of Swazol 1000 was added dropwise over 1 hour. Thereafter, the mixture was aged for 1 hour while flowing nitrogen gas at 125 ° C. and then cooled to obtain a hydroxyl group-containing acrylic resin (A1) having a solid content of about 60%. The obtained hydroxyl group-containing acrylic resin (A1) had a hydroxyl value of 129 mgKOH / g, an acid value of 19 mgKOH / g, and a weight average molecular weight of about 10,000.

Production Example 10 of Phosphate Group-Containing Compound (D) (Phosphate Group-Containing Acrylic Resin (D1))
A four-necked flask equipped with a stirrer, a thermometer, a condenser, and a nitrogen gas inlet was charged with 70 parts of “Swazole 1000” and 30 parts of n-butyl alcohol, and the temperature was raised to 125 ° C. under nitrogen gas flow. After reaching 125 ° C., the nitrogen gas flow was stopped and 10 parts mono (2-hydroxyethyl methacrylate) phosphate, 30 parts styrene, 40 parts n-butyl acrylate, 20 parts 2-hydroxyethyl methacrylate, 2, 2′- A mixture of 2 parts of azobisisobutylnitrile monomer and polymerization initiator was added dropwise over 5 hours. Next, the mixture was aged for 2 hours while ventilating nitrogen gas at 125 ° C. and then cooled to obtain a phosphoric acid group-containing acrylic resin (D1) having a solid content of 50%.

  The phosphoric acid group-containing acrylic resin (D1) had a hydroxyl value of 86 mgKOH / g and a weight average molecular weight of about 20,000.

Production and production example 11 of non-aqueous dispersion type acrylic resin (E1)
A four-necked flask equipped with a stirrer, thermometer, condenser and nitrogen gas inlet is charged with 93 parts of heptane and 98 parts of the following 55% polymer dispersion stabilizer solution (* 1) and heated to reflux. A mixture of polymerization initiators was dropped over 3 hours and aged for 2 hours to obtain a non-aqueous dispersion type acrylic resin (E1).

(Mixture of monomer and polymerization initiator)
A mixture of 15 parts styrene, 40 parts methyl methacrylate, 30 parts acrylonitrile, 15 parts 2-hydroxyethyl methacrylate and 1.5 parts t-butylperoxy-2-ethylhexanoate.

  The obtained non-aqueous dispersion type acrylic resin (E1) is a milky white stable low-viscosity weight having a mass solid content concentration of 53%, a Gardner viscosity B, and an average particle size (measured by an electron microscope) of 0.2 to 0.3 μm. It was a dispersion of coalescence.

(Synthesis of polymer dispersion stabilizer solution (* 1))
A four-necked flask equipped with a stirrer, thermometer, condenser, and nitrogen gas inlet is charged with 40 parts of isobutyl acetate and 40 parts of toluene, heated to reflux, and a mixture of the following monomers and polymerization initiator is added over 3 hours. The polymer dispersion stabilizer solution was obtained by dripping and aging for 2 hours after dripping.

(Mixture of monomer and polymerization initiator)
A mixture of 10 parts styrene, 49 parts isobutyl methacrylate, 30 parts 2-ethylhexyl methacrylate, 11 parts 2-hydroxyethyl methacrylate and 2 parts azobisisobutyronitrile.

  The resulting polymer dispersion stabilizer solution had a mass solids concentration of 55%, a Gardner viscosity G, and a weight average molecular weight of 16000.

Production and production example 12 of clear paint (Z)
110 parts of hydroxyl group-containing acrylic resin (A1) solution obtained in Production Example 9 (solid content: 66 parts), melamine resin A (methylol group and imino group-containing butyl etherified melamine resin, weight average molecular weight of 4000, per triazine nucleus, imino 68 parts of melamine resin synthesized under the synthesis conditions of 1.0 group, 0.4 methylol group, 4.6 butyl ether group, active ingredient 50%), Sanniks PP-1000 (trade name, manufactured by Sanyo Kasei Co., Ltd.) , Polyoxypropylene glycol, number average molecular weight 1000, active ingredient 100%) 5 parts, BYK-300 (trade name, manufactured by Big Chemie, surface conditioner, active ingredient 52%) 0.2 part, TINUVIN 900 (trade name, B Manufactured by ASF Corporation, 2.0 parts of benzotriazole ultraviolet absorber, active ingredient 100%) and TINUVIN 292 ( The product name, manufactured by BASF, hindered amine light stabilizer, active ingredient 100%, 1.0 part is mixed uniformly, and Swazol 1000 (trade name, manufactured by Cosmo Oil Co., hydrocarbon system). Solvent) and a Ford Cup No. 20 at 20 ° C. A clear paint (Z-1) having a viscosity according to 4 of 25 seconds was obtained.

Production Examples 13 to 26
In the same manner as in Production Example 12, a Ford Cup No. 20 at 20 ° C. with the coating composition shown in Table 1 below. The clear paints (Z-2) to (Z-15) having a viscosity of 4 having a viscosity of 25 seconds were obtained. Clear paints (Z-12) to (Z-15) are for comparative examples.

  The clear paints (Z-1) to (Z-15) in Table 1 have a solid content.

  (Note 1) to (Note 9) in Table 1 are as follows.

(Note 1) Melamine resin B: methylol and imino group-containing butyl etherified melamine resin, weight average molecular weight 2200, per triazine nucleus, 2.0 imino groups, 0.2 methylol groups, 3.8 butyl ether groups Melamine resin synthesized under the synthesis conditions of 60% active ingredient
(Note 2) Sannics PP-400; trade name, manufactured by Sanyo Chemical Industries, polyoxypropylene glycol, number average molecular weight 400, active ingredient 100%
(Note 3) Sannics PP-600; trade name, manufactured by Sanyo Kasei Co., Ltd., polyoxypropylene glycol, number average molecular weight 600, active ingredient 100%
(Note 4) Sannics PP-2000; trade name, manufactured by Sanyo Chemical Industries, polyoxypropylene glycol, number average molecular weight 2000, active ingredient 100%
(Note 5) GP-600; trade name, manufactured by Sanyo Chemical Industries, polyoxypropylene glyceryl ether, number average molecular weight 600, active ingredient 100%
(Note 6) PTMG-850; trade name, manufactured by Mitsubishi Chemical Corporation, polyoxytetramethylene glycol, number average molecular weight 850, active ingredient 100%
(Note 7) ETERNACOLL UH-50; trade name, manufactured by Ube Industries, 1,6-hexanediol-based polycarbonate diol, number average molecular weight 500, active ingredient 100%
(Note 8) ETERNACOLL UH-200; trade name, manufactured by Ube Industries, 1,6-hexanediol-based polycarbonate diol, number average molecular weight 2000, active ingredient 100%
(Note 9) Polylite OD-X-240; trade name, manufactured by DIC, polyester polyol, number average molecular weight 1000, active ingredient 100%
Aqueous first colored paints (X-1) to (X-2) obtained in coating film forming methods Production Examples 5 and 6, Aqueous second colored paint (Y-1) obtained in Production Example 8, and Production Example 12 Using the clear paints (Z-1) to (Z-15) obtained in ˜26, test plates were prepared as follows and subjected to evaluation tests.

(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 A test object 1 was obtained by heating and curing. Ra of the surface roughness of the test object 1 was 0.21.

  Furthermore, using the cold-rolled steel sheet that has been subjected to the zinc phosphate chemical conversion treatment having a rougher surface roughness than that used for the preparation of the test object 1, the test object 1 was tested in the same manner as the test object 1. A test object 2 having a surface roughness higher than that of the coated object 1 was also produced. Ra of the surface roughness of the test object 2 was 0.38.

(Preparation of test plate)
Example 1
The water-based first colored paint (X-1) obtained in Production Example 5 is applied to the test object 1 using a rotary atomizing electrostatic coater so that the dry film thickness is 25 μm. The coating was electrostatically coated and allowed to stand for 2 minutes, followed by preheating at 80 ° C. for 3 minutes.

  Next, the water-based second colored paint (Y-1) obtained in Production Example 8 on the uncured first colored coating film is 15 μm in dry film thickness using a rotary atomizing type electrostatic coating machine. Electrostatic coating was performed, and after standing for 2 minutes, preheating was performed at 80 ° C. for 3 minutes.

  Further, the clear paint (Z-1) obtained in Production Example 12 was electrostatically coated on the second colored coating film so as to have a dry film thickness of 35 μm, and left for 7 minutes. Subsequently, it heated at 140 degreeC for 20 minutes (keep time), and the test plate was produced by heat-hardening a 1st colored coating film, a 2nd colored coating film, and a clear coating film.

Examples 2-12 and Comparative Examples 1-6
In Example 1, the test target object is the test target object 1 or 2 shown in the following Table 1, and the aqueous first colored paint (X-1) is the aqueous first colored paint (X-) shown in the following Table 1. 1) or (X-2), except that the clear paint (Z-1) is any one of clear paints (Z-1) to (Z-15) shown in Table 1 below. A test plate was prepared.

Evaluation Test Each test plate obtained in Examples 1 to 12 and Comparative Examples 1 to 6 was evaluated by the following test method. The evaluation results are also shown in Table 1 below.

(Test method)
Smoothness: Evaluated using the Wc value measured by Wave Scan DOI (trade name, manufactured by BYK Gardner). The Wc value is an index of the amplitude of the surface roughness having a wavelength of about 1 to 3 mm, and the smaller the measured value, the higher the smoothness of the coated surface.

  Vividness: Evaluated using Wa values measured by Wave Scan DOI. The Wa value is an index of the amplitude of the surface roughness having a wavelength of about 0.1 to 0.3 mm.

  Accelerated weather resistance: Irradiation and rain conditions under the test conditions described in JIS K5600-7-7 (Method 1) using a Superxenon weather meter (trade name, Accelerated Weather Resistance Tester, manufactured by Suga Test Instruments Co., Ltd.) A combined cycle test was conducted. After a total cycle test time of 3000 hours, the film was further immersed in warm water at 40 ° C. for 2 days to evaluate the adhesion of the coating film. For adhesion, after making 100 square grids of 2 mm x 2 mm on the coating film according to JIS K 5600-5-6 (1990) on each test plate, affixing adhesive tape to the surface and peeling it off rapidly The number of cross-cut coating films remaining on the coating surface was evaluated. The 98 or more remaining cross-cut coating films are acceptable levels.

  In Example 2 using the clear paint (Z-2) and Example 4 using the clear paint (Z-4), the number of remaining cross-cut coating films was 100, and no flicking was observed. Therefore, the adhesion was further superior to the other examples having 100 remaining grids in the examples.

  Furthermore, for Example 1 using the clear paint (Z-1) and Example 6 using the clear paint (Z-6), the following sagging resistance (sag limit film thickness) was also evaluated as a comparison. It was.

  Sagging limit film thickness: 11 cm × 45 cm of the test article 1 having a punched hole having a diameter of 5 mm provided in a line of 3 cm from the end on the long side in a line of 21 at intervals of 2 cm. Use the water-based first colored paint (X-1) obtained in Production Example 5 on the test article 1 to be 25 μm in dry film thickness using a rotary atomizing electrostatic coater. Electrostatic coating was performed, and after standing for 2 minutes, preheating was performed at 80 ° C. for 3 minutes.

  Next, on the uncured first colored coating film, the water-based second colored paint (Y-1) obtained in Production Example 8 is dried at a film thickness of 15 μm using a rotary atomizing electrostatic coating machine. Electrostatic coating was performed, and after standing for 2 minutes, preheating was performed at 80 ° C. for 3 minutes.

Further, on the second colored coating film, a clear paint (Z-1) is used in Example 1, a clear paint (Z-6) is used in Example 6, and a minibell rotary atomizing electrostatic coating machine is used. With a discharge amount of 200 cc, a rotation speed of 40,000 rpm, a shaping air pressure of 1 kg / cm ² , a gun distance of 30 cm, and coating with a film thickness gradient so that a film thickness of approximately 30 μm to 60 μm is obtained in the longitudinal direction, By standing the paint plate almost vertically and heating for 7 minutes after coating, heating at 140 ° C for 20 minutes (keep time) to heat and cure the first colored coating, the second colored coating, and the clear coating A test plate was prepared.

  By examining the position at which the sagging of the 2 mm coating film is observed from the lower end of the punch hole of each test plate obtained, and measuring the film thickness (sag limit film thickness (μm)) at the position, Evaluation was performed. The larger the sagging limit film thickness, the better the sagging resistance.

Claims (8)

To the article to be coated, the following steps (1) to (4),
Step (1): A step of forming the first colored coating film by coating the aqueous first colored paint (X),
Step (2): A step of forming a second colored coating film by applying an aqueous second colored coating material (Y) on the first colored coating film formed in the step (1).
Step (3): a step of applying a clear paint (Z) on the second colored coating film formed in the step (2) to form a clear coating film, and a step (4): the step (1). A step of heating and curing the first colored coating film, the second colored coating film and the clear coating film formed in (3) at a time;
A coating composition used as a clear coating (Z) in a method for forming a multilayer coating film, wherein the coating composition comprises a hydroxyl group-containing acrylic resin (A), a melamine resin (B), and a number average molecular weight of 300. Containing a polyol (C) in the range of ˜1500,
The polyol (C) is at least one of a polyoxyalkylene group-containing polyol (C1) and a polycarbonate polyol (C2).   The coating composition according to claim 1, wherein the polyoxyalkylene group-containing polyol (C1) has an alkylene group having 3 or more carbon atoms.   The coating composition according to claim 1 or 2, wherein the amount of the polyol (C) is 1 to 20% by mass based on the total solid content of the hydroxyl group-containing acrylic resin (A) and the melamine resin (B).   Furthermore, the coating composition of any one of Claims 1-3 containing a phosphoric acid group containing compound (D).   Furthermore, the non-aqueous dispersion type acrylic resin (E) obtained by dispersing and polymerizing at least one kind of unsaturated monomer in the presence of a polymer dispersion stabilizer and an organic solvent is contained. The coating composition according to Item. To the article to be coated, the following steps (1) to (4),
Step (1): A step of forming the first colored coating film by coating the aqueous first colored paint (X),
Step (2): A step of forming a second colored coating film by applying an aqueous second colored coating material (Y) on the first colored coating film formed in the step (1).
Step (3): A coating composition according to any one of claims 1 to 5 is applied as a clear paint (Z) on the second colored coating film formed in the step (2), and the clear paint is applied. A step of forming a coating film, and a step (4): a step of heat-curing the first colored coating film, the second colored coating film and the clear coating film formed in the steps (1) to (3) at a time, A method for forming a multilayer coating film sequentially.   The multilayer coating film forming method according to claim 6, wherein the object to be coated is a vehicle body on which an undercoat film is formed by an electrodeposition paint.   An article coated by the multilayer coating film forming method according to claim 6 or 7.