JP2019166454A - Double layer coating film formation method - Google Patents

Abstract

To provide a method capable of forming a double layer coating film having excellent image clarity to a metallic member and a plastic member of an automobile body.SOLUTION: In a double layer coating film formation method for successively executing (1) a primer coating film formation process, (2) a process of forming a coating film by solvent system first color pigmented paint (X) on the coating film of the process (1), (3) a process of forming the coating film by solvent system second color pigmented paint (Y) on the coating film of the process (2), (4)a process of forming a clear coating film by solvent system 2-liquid type clear paint (Z) on the coating film of the process (3) and (5) a process of hardening by heating the coating film of the processes (1)-(4), the double layer coating film formation method, wherein the paint (X) includes a hydroxyl group-containing resin (A) and a polyisocyanate compound (I), and the paint (Y) includes a hydroxyl group-containing resin (B), and a solubility parameter δA of the resin (A) and a solubility parameter δB of the resin (B) is the relationship of 0.6<δA-δB<1.2.SELECTED DRAWING: None

Description

  The present invention relates to a method for forming a multilayer coating film capable of forming a multilayer coating film having excellent image clarity on both a metal member and a plastic member used in an automobile body.

  In general, an automobile body has a metal member forming the body and a plastic member such as a bumper.

  In such car body painting, conventionally, a metal member and a plastic member, separate paints suitable for the respective members, and a separate painting process are applied, and then the plastic member is attached to the metal member. ing.

  However, in recent years, there has been a demand for a method of painting in a state in which the plastic member is mounted on the metal member in order to reduce the equipment cost in the manufacturing process of the automobile body or to match the color tone of the metal member and the plastic member.

  For example, in Patent Document 1, a metal member pre-coated with a cationic electrodeposition paint and a plastic member are assembled into an automobile outer plate part, and a composition comprising an olefin resin and a urethane resin is formed on both members. There is disclosed a method for coating an automobile outer plate, characterized in that an aqueous barrier coat having a vehicle main component is applied, and then an intermediate coating is applied as necessary, and then a top coating is applied.

In Patent Document 2, an electrodeposited metal member and a plastic member are assembled and integrated, and on both surfaces, an isocyanate-modified polybutadiene resin, a polyol component having a number average molecular weight of 150 to 50,000, and conductivity A solvent-based paint that can form a coating film having a filler as a main component and a static glass transition temperature of −100 to 0 ° C. is coated with an intermediate coating as necessary, and then a top coating is applied. A method for forming a film is disclosed.
However, in any of the coating methods described in Patent Document 1 and Patent Document 2, it is difficult to say that the resulting multilayer coating film still has sufficient impact resistance in a low temperature environment (−30 ° C.).

  Regarding securing physical properties in a low temperature environment, for example, Patent Document 3 discloses a multilayer coating film forming method in which an electrodeposition coating film, an intermediate coating film, a base coating film, and a clear coating film are sequentially laminated on an object to be coated. A method for forming a multilayer coating film in which the clear coating film has a tensile strength at −20 ° C. of 60 MPa or more and an elongation at break of 5% or more is disclosed.

Japanese Patent Laid-Open No. 4-122474 JP-A-1-288372 JP 2011-020104 A

  However, the design characteristics of automobiles are very important, and the finished quality after painting, especially where excellent sharpness is required, Patent Documents 1 to 3 relate to the sharpness of the formed coating film. Has not been studied, and its effect was unknown.

  The present invention has been made in consideration of these points, and it is possible to form a multilayer coating film having excellent sharpness on both a metal member and a plastic member used in an automobile body. An object of the present invention is to provide a method for forming a multilayer coating film.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above problems can be solved by the following multilayer coating film forming method, and have completed the present invention.

That is, the present invention relates to the following <1> to <3>.
<1> (1) A process of forming an uncured primer coating by applying primer paint (P) to the surface of an automobile outer plate including at least one of a metal member and a plastic member;
(2) A step of coating the solvent-based first colored paint (X) on the uncured primer coating obtained in step (1) to form an uncured first colored coating,
(3) A step of coating the solvent-based second colored paint (Y) on the uncured first colored coating film obtained in the step (2) to form an uncured second colored coating film,
(4) A step of applying a solvent-based two-component clear coating (Z) on the uncured second colored coating film obtained in the step (3) to form an uncured clear coating film, and (5) Heat the uncured primer coating, uncured first colored coating, uncured second colored coating and uncured clear coating formed in steps (1) to (4) to 75 to 95 ° C. By simultaneously curing these coating films,
The solvent-based first colored paint (X) is a two-component paint composition containing a hydroxyl group-containing resin (A) and a polyisocyanate compound (I), The solvent-based second colored paint (Y) is a one-component paint composition containing a hydroxyl group-containing resin (B), wherein the solubility parameter δA of the hydroxyl group-containing resin (A) and the hydroxyl group-containing resin (B) ) Is a relationship of 0.6 <δA−δB <1.2.
<2> The method for forming a multilayer coating film according to <1>, wherein the hydroxyl group-containing resin (A) has a weight average molecular weight in the range of 29,000 to 47,000.
<3> The method for forming a multilayer coating film according to <1>, wherein the hydroxyl group-containing resin (B) has a weight average molecular weight of 15,000 to 40,000.

According to the method for forming a multilayer coating film of the present invention, a multilayer coating film having excellent sharpness can be formed on a metal member and a plastic member used in an automobile body.
Moreover, according to the method for forming a multilayer coating film of the present invention, a multilayer coating film having excellent flip-flop properties and high hardness can be formed.

Hereinafter, the multilayer coating film forming method of the present invention will be described in more detail.
In the present invention, (meth) acrylate means acrylate or methacrylate, (meth) acryl means acryl or methacryl, (meth) acryloyl means acryloyl or methacryloyl, and (meth) acrylo means acrylo or methacrylo. To do.

In the multilayer coating film forming method of the present invention, the following steps (1) to (5) are sequentially performed.
The automobile outer plate is a member constituting the outer surface of the automobile, and includes opening and closing members such as a front door, a rear door, and a bonnet in addition to a roof panel and a fender panel.

[Step (1)]
In the step (1) of the present invention, the primer coating (P) is applied to the surface of the automobile outer plate including at least one of the metal member and the plastic member to form an uncured primer coating.

(Metal member and plastic member)
Examples of the metal member include iron, aluminum, brass, copper, tinplate, stainless steel, galvanized steel, and zinc alloy (eg, Zn—Al, Zn—Ni, Zn—Fe, etc.) plated steel.

  The metal member may have a surface subjected to a surface treatment such as a phosphate treatment, a chromate treatment, or a complex oxide treatment, and an undercoat film is formed on the surface of the metal member. May be. Examples of the undercoat paint include electrodeposition paints, and among them, cationic electrodeposition paints are preferable.

  As the plastic member, for example, a polyolefin obtained by (co) polymerizing one or more of olefins having 2 to 10 carbon atoms such as ethylene, propylene, butylene and hexene is particularly suitable. , Polycarbonate, ABS resin, urethane resin, polyamide and the like.

  These plastic members are used for bumpers, spoilers, grills, fenders and the like, for example. Prior to the application of the primer paint (P), these plastic members can be appropriately subjected to a degreasing treatment, a water washing treatment or the like by a method known per se.

The article to be coated in the present invention includes at least one of the two members, and it is preferable that the painted surface is configured to at least partially contain the two members. The form containing these and each content ratio are not limited. However, it is preferable that 20% or more of the painted surface is composed of 5 to 95% of metal members and 95 to 5% of plastic members.
The metal member and the plastic member can be assembled by a known method.

(Primer paint (P))
The primer paint (P) is preferably a water-based paint used mainly for the purpose of providing adhesion of a colored paint laminated on at least one of a plastic member and a metal member.
As the primer paint (P), for example, an aqueous polyolefin resin that may be chlorinated, an aqueous polyurethane resin, an aqueous polyester resin, a base resin such as an aqueous acrylic resin, a crosslinking agent such as a block polyisocyanate compound, a melamine resin, and the like Paints mainly used in the field of paints, such as water as the main component, and if necessary, rheology control agents, organic solvents, colored pigments, extender pigments, conductive pigments, anticorrosion pigments, pigment dispersants, plasticizers, etc. And those containing additives. These paint additives can be used alone or in combination of two or more.

  The primer coating is obtained by coating the primer coating (P) on the above-mentioned article by a method known per se, for example, air spray, airless spray, rotary atomization coating, curtain coat coating, etc. In this case, electrostatic application may be performed. Of these, methods such as air spray coating and rotary atomization coating are preferred.

  The amount of primer paint (P) applied is preferably such that the heat-cured film thickness is in the range of 2 to 15 μm, particularly preferably in the range of 5 to 10 μm.

  The obtained primer coating film may be subjected to preheating, air blowing, or the like at a temperature of about 50 to about 90 ° C. for about 1 to 60 minutes, if necessary.

[Step (2)]
In the step (2) of the present invention, the solvent-based first colored paint (X) is applied on the uncured primer coating film obtained in the step (1) to form an uncured first colored coating film. .

<Solvent-based first colored paint (X)>
The solvent-based first colored paint (X) is a two-component paint composition containing a hydroxyl group-containing resin (A) and a polyisocyanate compound (I). The solvent-based first colored paint (X) includes a main agent containing the hydroxyl group-containing resin (A) and a curing agent containing the polyisocyanate compound (I). The solvent-based first colored paint (X) includes those in which the main agent and the curing agent are not mixed and those in which these are mixed.
The solvent-based paint is a term contrasted with a water-based paint, and is a paint that does not substantially contain water as a solvent.

(Hydroxyl-containing resin (A))
The hydroxyl group-containing resin (A) is a resin having at least one hydroxyl group in one molecule. Examples of the hydroxyl group-containing resin (A) include a resin having a hydroxyl group, such as an acrylic resin, a polyester resin, a polycarbonate resin, a polyurethane resin, an epoxy resin, and an alkyd resin. These can be used alone or in combination of two or more. Especially, it is preferable that a hydroxyl-containing resin (A) is a hydroxyl-containing acrylic resin and / or a hydroxyl-containing polyester resin from a viewpoint of coating-film hardness and a weather resistance.

  The hydroxyl group-containing resin (A) preferably has a hydroxyl value in the range of 30 to 300 mgKOH / g, and in the range of 40 to 250 mgKOH / g, from the viewpoint of reactivity with the polyisocyanate compound (I) described later. It is particularly preferable to have a hydroxyl value.

  In addition, in this specification, the hydroxyl value (mgKOH / g) of resin represents the amount of hydroxyl group contained in 1 g of resin in terms of mg of potassium hydroxide when converted to potassium hydroxide. The molecular weight of potassium hydroxide is 56.1.

  The hydroxyl group-containing resin (A) preferably has an acid value in the range of 20 mgKOH / g or less, and has an acid value in the range of 1 to 15 mgKOH / g, from the viewpoint of the sharpness of the resulting coating film. Is particularly preferred.

  In addition, in this specification, the acid value (mgKOH / g) of the resin is a numerical value when the mass of potassium hydroxide necessary for neutralizing the protonic acid contained in 1 g of the resin is expressed in mg, and measured. Can be performed based on JIS K-2501-2003.

  The hydroxyl group-containing resin (A) is preferably in the range of 29,000 to 47,000, particularly preferably in the range of 29,000 to 45,000, and more particularly preferably, from the viewpoint of the sharpness of the resulting coating film. Has a weight average molecular weight in the range of 29,000 to 40,000.

  In the present specification, the weight average molecular weight and the number average molecular weight are the retention time (retention capacity) measured using a gel permeation chromatograph (GPC), and the retention time of standard polystyrene with a known molecular weight measured under the same conditions. (Retention capacity) is a value obtained by converting to the molecular weight of polystyrene.

  For the weight average molecular weight, “HLC-8120GPC” (trade name, manufactured by Tosoh Corporation) is used as a gel permeation chromatograph, and one “TSKgel GMHHR-L” (trade name, manufactured by Tosoh Corporation) is used as a column. A differential refractometer is used as a detector, mobile phase: N, N-dimethylformamide (containing 10 mM each of lithium bromide and phosphoric acid), measurement temperature: 25 ° C., flow rate: 1 mL / min Can be measured below.

  The number average molecular weight is “HLC-8120GPC” (trade name, manufactured by Tosoh Corporation) as a gel permeation chromatograph, and “TSKgel G4000HXL”, “TSKgel G3000HXL”, “TSKgel G2500HXL” Using a total of four “TSKgel G2000HXL” (trade name, all manufactured by Tosoh Corporation), using a differential refractometer as the detector, mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., flow rate: 1 mL / min Can be measured under the following conditions.

  The solubility parameter δA of the hydroxyl group-containing resin (A) is preferably 10.5 to 11.0, more preferably 10.5 to 10.7, from the viewpoint of the sharpness of the resulting coating film.

In the present specification, the “solubility parameter value” (SP value) of the hydroxyl group-containing resin represents a measure of the intermolecular interaction of liquid molecules, and can be calculated by the following method.
The solubility parameter value (SP value) of the hydroxyl group-containing resin obtained by copolymerization of at least two kinds of polymerizable monomers can be calculated by the following formula.

SP value = SP1 × fW1 + SP2 × fW2 +... + SPn × fWn
In the above formula, SP1, SP2,... SPn represents the SP value of the homopolymer of each polymerizable monomer, and fW1, fW2,... FWn represents the weight of each monomer relative to the total amount of monomers. Represents a fraction. The SP value of the homopolymer of the polymerizable monomer is J.P. Paint Technology, vol. 42, 176 (1970).

  The blending amount (solid content) of the hydroxyl group-containing resin (A) is preferably based on the total solid content of 100 parts by mass of the solvent-based first colored paint (X) from the viewpoint of the sharpness of the resulting coating film. It exists in the range of 18-30 mass parts, More preferably, it exists in the range of 20-25 mass parts.

  The hydroxyl group-containing acrylic resin is usually a copolymer of a hydroxyl group-containing polymerizable unsaturated monomer and another polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer. Examples of the method for obtaining the copolymer include a method known per se, such as a solution polymerization method in an organic solvent.

  The hydroxyl group-containing polymerizable unsaturated monomer is a compound having at least one hydroxyl group and one polymerizable unsaturated bond in one molecule. Specifically, for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxy Propyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, 7-hydroxyheptyl (meta ) Monoesterified product of (meth) acrylic acid such as acrylate and 8-hydroxyoctyl (meth) acrylate and a dihydric alcohol having 2 to 8 carbon atoms (preferably 2 to 4 carbon atoms); (meth) acrylic acid and carbon number Ε-caprolactone modified product of monoesterified product with 2-8 dihydric alcohol N- hydroxymethyl (meth) acrylamide; allyl alcohol, furthermore, may be mentioned molecular ends having a polyoxyethylene chain is a hydroxyl group (meth) acrylate.

  In the present invention, the polymerizable unsaturated monomer having an ultraviolet absorbing functional group such as 2-hydroxy-4- (3-methacryloyloxy-2-hydroxypropoxy) benzophenone described later is a hydroxyl group-containing polymerizable unsaturated monomer. Instead, it is included in other polymerizable unsaturated monomers copolymerizable with a hydroxyl group-containing polymerizable unsaturated monomer.

  Examples of the other polymerizable unsaturated monomer copolymerizable with the hydroxyl group-containing polymerizable unsaturated monomer include 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, n-octyl (meth) acrylate, 2-ethylhexyl (meth) Acrylate, nonyl (meth) acrylate, tridecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, “isostearyl acrylate” (trade name, manufactured by Osaka Organic Chemical Industry Co., Ltd.), cyclohexyl (meth) acrylate, methyl Cyclohexyl Alkyl or cycloalkyl (meth) acrylate such as (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate; polymerizable unsaturated monomer having an isobornyl group such as isobornyl (meth) acrylate; adamantyl ( Polymerizable unsaturated monomers having an adamantyl group such as (meth) acrylate; vinyl aromatic compounds such as styrene, α-methylstyrene and vinyltoluene; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, polymerizable unsaturated monomers having alkoxysilyl groups such as γ- (meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane; Perfluoroalkyl (meth) acrylates such as ethyl (meth) acrylate and perfluorooctylethyl (meth) acrylate; polymerizable unsaturated monomers having fluorinated alkyl groups such as fluoroolefins; and photopolymerizable functional groups such as maleimide groups Polymerizable unsaturated monomers having: vinyl compounds such as N-vinylpyrrolidone, ethylene, butadiene, chloroprene, vinyl propionate and vinyl acetate; carboxyl groups such as (meth) acrylic acid, maleic acid, crotonic acid and β-carboxyethyl acrylate Containing polymerizable unsaturated monomer: (meth) acrylonitrile, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, glycidyl (meth) acrylate and amino Nitrogen-containing polymerizable unsaturated monomers such as adducts with compounds; polymerizable having two or more polymerizable unsaturated groups in one molecule such as allyl (meth) acrylate and 1,6-hexanediol di (meth) acrylate Unsaturated monomer: glycidyl (meth) acrylate, β-methylglycidyl (meth) acrylate, 3,4-epoxycyclohexylmethyl (meth) acrylate, 3,4-epoxycyclohexylethyl (meth) acrylate, 3,4-epoxycyclohexylpropyl Epoxy group-containing polymerizable unsaturated monomers such as (meth) acrylate and allyl glycidyl ether; (meth) acrylate having a polyoxyethylene chain whose molecular terminal is an alkoxy group; 2-acrylamido-2-methylpropanesulfonic acid, allyl sulfone Acid, styrene sulfonic acid Polymerizable unsaturated monomers having a sulfonic acid group such as sodium salt, sulfoethyl methacrylate and its sodium salt, ammonium salt; 2-acryloyloxyethyl acid phosphate, 2-methacryloyloxyethyl acid phosphate, 2-acryloyloxypropyl acid phosphate; Polymerizable unsaturated monomers having a phosphate group such as 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 Polymerizable unsaturation having UV-absorbing functional groups such as -4- (3-acryloyloxy-2-hydroxypropoxy) benzophenone and 2- (2'-hydroxy-5'-methacryloyloxyethylphenyl) -2H-benzotriazole Monomer; 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-tetramethylpiperidine, 1- (meth) Acryloyl-4-cyano-4- (meth) acryloylamino-2,2,6,6-tetramethylpiperidine, 4-chloro Tonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoylamino-2,2,6,6-tetramethylpiperidine, 1-crotonoyl-4-crotonoyloxy-2,2,6,6- UV-stable polymerizable unsaturated monomers such as tetramethylpiperidine; acrolein, diacetone acrylamide, diacetone methacrylamide, acetoacetoxyethyl methacrylate, formylstyrol, vinyl alkyl ketones having 4 to 7 carbon atoms (eg, vinylmethyl Examples thereof include polymerizable unsaturated monomer compounds having a carbonyl group such as ketone, vinyl ethyl ketone, and vinyl butyl ketone, and these can be used alone or in combination of two or more.

  The hydroxyl group-containing acrylic resin preferably has a hydroxyl value in the range of 30 to 300 mgKOH / g, and has a hydroxyl value in the range of 40 to 250 mgKOH / g, from the viewpoint of reactivity with the polyisocyanate compound (I) described later. It is particularly preferred to have

  The hydroxyl group-containing acrylic resin preferably has an acid value in the range of 20 mgKOH / g or less, and particularly preferably has an acid value in the range of 1 to 15 mgKOH / g, from the viewpoint of the sharpness of the resulting coating film. preferable.

  The hydroxyl group-containing acrylic resin is a weight average molecular weight in the range of 29,000 to 47,000, particularly in the range of 29,000 to 45,000, from the viewpoint of the sharpness of the resulting coating film. It is particularly preferred to have a weight average molecular weight in the range of 29,000 to 40,000.

  The solubility parameter δA of the hydroxyl group-containing acrylic resin is preferably 10.5 to 11.0, more preferably 10.5 to 10.7, from the viewpoint of the sharpness of the resulting coating film.

  The above-mentioned hydroxyl group-containing polyester resin can be usually obtained by esterifying a polybasic acid and a polyhydric alcohol with a hydroxyl group excess by a method known per se.

  As said polybasic acid, the compound normally used as an acid component can be used at the time of manufacture of a polyester resin. Examples of the acid component include an aliphatic polybasic acid, an alicyclic polybasic acid, an aromatic polybasic acid, and the like.

  The aliphatic polybasic acid is generally an aliphatic compound having two or more carboxyl groups in one molecule, an acid anhydride of the aliphatic compound, and an esterified product of the aliphatic compound.

  Examples of the aliphatic polybasic acid include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassic acid, octadecanedioic acid, citric acid, butane. Aliphatic polyvalent carboxylic acids such as tetracarboxylic acid; anhydrides of the aliphatic polyvalent carboxylic acids; and esterified products of lower alkyl having about 1 to 4 carbon atoms of the aliphatic polyvalent carboxylic acids. The said aliphatic polybasic acid can be used individually or in combination of 2 or more types.

  As the aliphatic polybasic acid, it is particularly preferable to use adipic acid and / or adipic anhydride from the viewpoints of smoothness and sharpness of the resulting coating film.

  The alicyclic polybasic acid is generally a compound having one or more alicyclic structures and two or more carboxyl groups in one molecule, an acid anhydride of the compound, and an esterified product of the compound. The alicyclic structure is mainly a 4- to 6-membered ring structure.

  Examples of the alicyclic polybasic acid include 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 3-methyl- Alicyclic polycarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 1,3,5-cyclohexanetricarboxylic acid; An anhydride of an alicyclic polyvalent carboxylic acid; an esterified product of a lower alkyl having about 1 to 4 carbon atoms of the alicyclic polyvalent carboxylic acid. The said alicyclic polybasic acid can be used individually or in combination of 2 or more types.

  Examples of the alicyclic polybasic acid include 1,2-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic anhydride, 1,3-cyclohexanedicarboxylic acid, from the viewpoint of smoothness and sharpness of the resulting coating film. It is preferable to use an acid, 1,4-cyclohexanedicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid, 4-cyclohexene-1,2-dicarboxylic acid anhydride, etc., among them, 1,2-cyclohexanedicarboxylic acid It is more preferable to use an acid and / or 1,2-cyclohexanedicarboxylic anhydride.

  The aromatic polybasic acid is generally an aromatic compound having two or more carboxyl groups in one molecule, an acid anhydride of the aromatic compound, and an esterified product of the aromatic compound, for example, phthalic acid , Isophthalic acid, terephthalic acid, naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, trimellitic acid, pyromellitic acid and other aromatic polycarboxylic acids; anhydrides of the aromatic polycarboxylic acids; aromatics Examples thereof include esterified products of lower alkyl having about 1 to 4 carbon atoms of polyvalent carboxylic acid. The said aromatic polybasic acid can be used individually or in combination of 2 or more types.

  As the aromatic polybasic acid, it is preferable to use phthalic acid, phthalic anhydride, isophthalic acid, trimellitic acid, trimellitic anhydride, and the like.

  Examples of fatty acid components used in the production of the alkyd resin 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, Fatty acids such as rapeseed oil fatty acid, castor oil fatty acid, dehydrated castor oil fatty acid, safflower oil fatty acid; lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, benzoic acid, p-tert-butyl Examples thereof include monocarboxylic acids such as benzoic acid, cyclohexane acid, and 10-phenyloctadecanoic acid; hydroxycarboxylic acids such as lactic acid, 3-hydroxybutanoic acid, and 3-hydroxy-4-ethoxybenzoic acid. These fatty acid components can be used alone or in combination of two or more.

  Moreover, as fats and oils, glycerol esterification products, such as the said fatty acid, etc. can be mentioned.

  Examples of the polyhydric alcohol include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, tetraethylene glycol, triethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, 2,3 -Butanediol, 1,2-butanediol, 2-methyl-1,3-propanediol, 3-methyl-1,2-butanediol, 2-butyl-2-ethyl-1,3-propanediol, 1, 2-pentanediol, 1,5-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 2,3-dimethyltrimethylene glycol, tetramethylene glycol, 3-methyl-4,3-pentanediol, 3-methyl-1,5-pentanediol, 2 2,4-trimethyl-1,3-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-hexanediol, 2,5-hexanediol, neopentyl glycol, 1,4-cyclohexane Dihydric alcohols such as dimethanol, tricyclodecane dimethanol, hydroxypivalic acid neopentyl glycol ester, hydrogenated bisphenol A, hydrogenated bisphenol F, dimethylolpropionic acid; lactone compounds such as ε-caprolactone in these dihydric alcohols A polylactone diol with an addition of an ester diol compound such as bis (hydroxyethyl) terephthalate; an alkylene oxide adduct of bisphenol A, a polyethylene glycol such as polyethylene glycol, polypropylene glycol, polybutylene glycol, etc. -Terdiol compounds; glycerin, trimethylolethane, trimethylolpropane, diglycerin, triglycerin, 1,2,6-hexanetriol, pentaerythritol, dipentaerythritol, tris (2-hydroxyethyl) isocyanuric acid, sorbitol, mannitol, etc. A trilactone or higher alcohol; a polylactone polyol compound obtained by adding a lactone compound such as ε-caprolactone to the trihydric or higher alcohol; a fatty acid esterified product of glycerin, and the like.

  The monoalcohol is not particularly limited, and examples thereof include monoalcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, stearyl alcohol, and 2-phenoxyethanol.

  It was obtained by reacting a monoepoxy compound such as propylene oxide, butylene oxide, “Cardura E10” (trade name, manufactured by Momentive Specialty Chemicals, glycidyl ester of synthetic hyperbranched saturated fatty acid) and an acid as other alcohol components. Alcohol compounds can also be used.

  The manufacturing method of a hydroxyl-containing polyester resin is not specifically limited, It can implement according to a normal method. For example, the polybasic acid and the alcohol component are heated in a nitrogen stream at about 150 to 250 ° C. for about 5 to 10 hours to perform an esterification reaction or a transesterification reaction between the polybasic acid and the alcohol component. Thus, a hydroxyl group-containing polyester resin can be produced.

  When the polybasic acid and the alcohol component are esterified or transesterified, they may be added to the reaction vessel at one time, or one or both may be added in several portions. Also good. First, after synthesizing a hydroxyl group-containing polyester resin, the resulting hydroxyl group-containing polyester resin is reacted with an acid anhydride to form a half ester to obtain a carboxyl group and a hydroxyl group-containing polyester resin, and further adding the alcohol component. It may be a hydroxyl group-containing polyester resin.

  In the esterification or transesterification reaction, as a catalyst for promoting the reaction, dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, tetraisopropyl A catalyst known per se, such as titanate, can be used.

  The hydroxyl group-containing polyester resin can be modified with a polyisocyanate compound or the like during or after preparation of the resin.

  Examples of the polyisocyanate compound include aliphatic diisocyanate compounds such as lysine diisocyanate, hexamethylene diisocyanate, and trimethylhexane diisocyanate; hydrogenated xylylene diisocyanate, isophorone diisocyanate, methylcyclohexane-2,4-diisocyanate, methylcyclohexane-2,6. -Alicyclic diisocyanate compounds such as diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), 1,3- (isocyanatomethyl) cyclohexane; Aromatic diisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate; Organic polyisocyanate such as triisocyanate These are: adducts of these organic polyisocyanates with polyhydric alcohols, low molecular weight polyester resins, water, etc .; cyclized polymers (for example, isocyanurates) of these organic polyisocyanates, biuret type adducts, etc. Is mentioned. These polyisocyanate compounds can be used individually by 1 type or in mixture of 2 or more types.

  The hydroxyl value of the hydroxyl group-containing polyester resin is preferably in the range of 30 to 300 mg KOH / g, more preferably in the range of 40 to 250 mg KOH / g, particularly preferably 50 to 200 mg KOH, from the viewpoint of water resistance of the resulting coating film. / G.

  The number average molecular weight of the hydroxyl group-containing polyester resin is preferably in the range of 29,000 to 47,000, particularly preferably in the range of 29,000 to 45,000, from the viewpoint of the sharpness of the resulting coating film. More preferably, it is in the range of 29,000 to 40,000.

  The acid value of the hydroxyl group-containing polyester resin is preferably in the range of 0 to 10 mgKOH / g, more preferably in the range of 0 to 5 mgKOH / g, from the viewpoint of the storage stability of the coating composition.

  The solubility parameter δA of the hydroxyl group-containing polyester resin is preferably 10.5 to 11.0, more preferably 10.5 to 10.7, from the viewpoint of the sharpness of the resulting coating film.

(Polyisocyanate compound (I))
The polyisocyanate compound (I) is a compound having two or more free isocyanate groups in one molecule, and the isocyanate groups are not blocked with a blocking agent.

  Specifically, those conventionally used for polyurethane production can be used. Such polyisocyanates include aliphatic polyisocyanate compounds, alicyclic polyisocyanate compounds, araliphatic polyisocyanate compounds, aromatic polyisocyanate compounds and crude products thereof, modified products of these polyisocyanate compounds (urethane groups, Carbodiimide groups, allophanate groups, urea groups, burette groups, uretdione groups, uretoimine groups, isocyanurate groups, oxazolidone group-containing modified products, and the like, and mixtures of two or more of these.

  Specific examples of the aliphatic polyisocyanate compound include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), dodecamethylene diisocyanate, 1,6,11-undecane triisocyanate, 2,2,4-trimethylhexamethylene diisocyanate. Lysine diisocyanate, 2,6-diisocyanatomethyl caproate, bis (2-isocyanatoethyl) fumarate, bis (2-isocyanatoethyl) carbonate, 2-isocyanatoethyl-2,6-diisocyanatohexano Eate.

  Specific examples of the alicyclic polyisocyanate compound include isophorone diisocyanate (IPDI), dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI), cyclohexylene diisocyanate, methylcyclohexylene diisocyanate (hydrogenated TDI), bis ( 2-isocyanatoethyl) -4-cyclohexene-1,2-dicarboxylate, 2,5- and / or 2,6-norbornane diisocyanate.

  Specific examples of the araliphatic polyisocyanate compound include m- or p-xylylene diisocyanate (XDI), α, α, α ′, α′-tetramethylxylylene diisocyanate (TMXDI), and the like.

  Specific examples of the aromatic polyisocyanate compound include 1,3- or 1,4-phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate (TDI), crude TDI, 2,4'- or 4 , 4′-biphenylmethane diisocyanate (MDI), 4,4′-diisocyanatobiphenyl, 3,3′-dimethyl-4,4′-diisocyanatobiphenyl, 3,3′-dimethyl-4,4′- Examples include diisocyanatodiphenylmethane, crude MDI, 1,5-naphthylene diisocyanate, 4,4 ′, 4 ″ -triphenylmethane triisocyanate, m- or p-isocyanatophenylsulfonyl isocyanate.

  The modified products of the polyisocyanate compound (I) include modified MDI (urethane modified MDI, carbodiimide modified MDI, trihydrocarbyl phosphate modified MDI), urethane modified TDI, biuret modified HDI, isocyanurate modified HDI, isocyanurate modified IPDI. And a mixture of two or more thereof [for example, combined use of modified MDI and urethane-modified TDI (isocyanate group-containing prepolymer)]. Among these, isocyanurate-modified HDI and the like are preferable.

  What is preferable as said polyisocyanate compound (I) is an aliphatic polyisocyanate compound and an alicyclic polyisocyanate compound from the surface of chemical resistance or corrosion resistance. The number average molecular weight of the polyisocyanate compound (I) is preferably 3,000 or less, and particularly preferably within the range of 100 to 1,500.

  Commercially available products of such polyisocyanate compound (I) include Bayhydr (TP) LS2550, Sumidur N3300 (manufactured by Sumika Bayer Urethane Co., Ltd.), TPA100 (manufactured by Asahi Kasei Chemicals Corporation), BASONAT (BASONAT) HI100 (manufactured by BASF Corporation) and the like.

  The blending amount of the polyisocyanate compound (I) is preferably in the range of 60 to 90 parts by mass based on the total solid content of the hydroxyl group-containing resin (A) of 100 parts by mass from the viewpoint of the sharpness of the resulting coating film. Of these, more preferably within the range of 65 to 85 parts by mass.

  The blending amount of the polyisocyanate compound (I) is such that the isocyanate group (NCO) contained in the polyisocyanate compound (I) is usually an equivalent ratio of NCO / OH to the hydroxyl group (OH) in the hydroxyl group-containing resin (A). It is appropriate to select it within the range of 1.0 to 2.5, preferably within the range of 1.0 to 2.0.

  Further, the solvent-based first colored paint (X) preferably further contains a pigment. Examples of the pigment include coloring pigments, extender pigments, and bright pigments. These can be used alone or in combination of two or more.

  When the solvent-based first colored paint (X) contains the pigment, the total amount of the pigment is generally 1 based on 100 parts by mass of the total resin solid content in the solvent-based first colored paint (X). It is preferably within the range of ˜170 parts by mass, more preferably within the range of 5 to 165 parts by mass, and even more preferably within the range of 10 to 160 parts by mass.

  Examples of the color pigment include titanium oxide, zinc white, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment, quinacridone pigment, isoindoline pigment, selenium pigment, and perylene pigment. And dioxazine pigments and diketopyrrolopyrrole pigments. Of these, titanium oxide and carbon black are preferable.

  When the solvent-based first colored paint (X) contains the color pigment, the blending amount of the color pigment is usually 1 to 4 parts by weight based on 100 parts by mass of the total resin solid content in the solvent-based first colored paint (X). It is preferably in the range of 180 parts by mass, more preferably in the range of 3 to 160 parts by mass, and still more preferably in the range of 5 to 140 parts by mass.

Examples of the extender pigment include talc, clay, kaolin, barium sulfate, barium carbonate, calcium carbonate, silica, and alumina white.

  When the solvent-based first colored paint (X) contains the extender pigment, the blending amount of the extender pigment is usually 1 to 4, based on 100 parts by mass of the total resin solid content in the solvent-based first colored paint (X). It is preferably within the range of 150 parts by mass, more preferably within the range of 5 to 130 parts by mass, and even more preferably within the range of 10 to 110 parts by mass.

  Examples of the bright pigment include aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, aluminum oxide, mica, aluminum oxide coated with titanium oxide and iron oxide, titanium oxide and iron oxide. Mention may be made of coated mica, glass flakes, hologram pigments and the like. These glitter pigments can be used alone or in combination of two or more. The aluminum pigment includes non-leafing aluminum and leafing aluminum, and any of them can be used.

  When the solvent-based first colored paint (X) contains the glitter pigment, the blending amount of the glitter pigment is usually based on 100 parts by mass of the total resin solid content in the solvent-based first colored paint (X). It is preferably within the range of 1 to 50 parts by mass, more preferably within the range of 2 to 30 parts by mass, and even more preferably within the range of 3 to 20 parts by mass.

  The solvent-based first colored paint (X) contains the hydroxyl group-containing resin (A) and the polyisocyanate compound (I) as essential resin components, and, if necessary, the above-mentioned pigments, other resin components, and organic solvents. , Thickeners, anti-settling agents, curing catalysts, pigment dispersants, UV absorbers, light stabilizers, surface conditioners, antifoaming agents, plasticizers, etc. It can be dispersed into a paint.

  The solvent-based first colored paint (X) described above is a method known per se, such as air spray, airless spray, and rotary atomization coating, on the uncured primer coating obtained in step (1). Can be painted with a machine. Electrostatic application may be performed during coating. Among these, electrostatic coating by air spray and electrostatic coating by a rotary atomizing coating machine are preferable, and electrostatic coating by a rotary atomizing coating machine is particularly preferable.

  The coating film thickness of the solvent-based first colored paint (X) is a cured film thickness, usually preferably in the range of 10 to 100 μm, more preferably in the range of 10 to 50 μm, and more preferably 15 to 35 μm. More preferably, it is within the range.

  The multilayer coating film forming method according to the present invention has an advantage that a multilayer coating film having excellent sharpness can be formed without performing the preliminary heating.

  In this specification, the cured coating is a cured and dried state as defined in JIS K 5600-1-1, that is, the center of the coating surface is strongly sandwiched between the thumb and index finger, and the coating surface has dents due to fingerprints. It is a coating film in which the movement of the coating film is not felt, and the center of the coating surface is rubbed rapidly with a fingertip so that no trace is left on the coating surface. On the other hand, an uncured coating film is a state in which the coating film has not reached the above-mentioned cured and dried state, and includes a finger-touch dried state and a semi-cured dried state defined in JIS K 5600-1-1.

[Step (3)]
In the step (3) of the present invention, the solvent-based second colored paint (Y) is applied on the uncured first colored coating film obtained in the above step (2) to thereby form an uncured second colored coating film. Form.

<Solvent-based second colored paint (Y)>
The solvent-based second colored paint (Y) is a one-component paint composition containing a hydroxyl group-containing resin (B), and is a paint generally used for the purpose of imparting an excellent appearance to the object to be coated. .

(Hydroxyl-containing resin (B))
The hydroxyl group-containing resin (B) is a resin having at least one hydroxyl group in one molecule. Examples of the hydroxyl group-containing resin (B) include resins having a hydroxyl group, such as acrylic resin, polyester resin, polycarbonate resin, polyurethane resin, epoxy resin, and alkyd resin. These can be used alone or in combination of two or more. Especially, it is preferable that a hydroxyl-containing resin (B) is a hydroxyl-containing acrylic resin and / or a hydroxyl-containing polyester resin from a viewpoint of coating-film hardness and a weather resistance.

  The hydroxyl group-containing resin (B) preferably has a hydroxyl value in the range of 30 to 300 mgKOH / g, and preferably has a hydroxyl value in the range of 40 to 250 mgKOH / g, from the viewpoint of water resistance of the resulting coating film. Particularly preferred.

  The hydroxyl group-containing resin (B) preferably has an acid value in the range of 20 mgKOH / g or less, and has an acid value in the range of 1 to 15 mgKOH / g, from the viewpoint of the sharpness of the resulting coating film. Is particularly preferred.

  The hydroxyl group-containing resin (B) preferably has a weight average molecular weight in the range of 15,000 to 40,000, and in the range of 16,000 to 35,000, from the viewpoint of the sharpness of the resulting coating film. It is particularly preferred to have a weight average molecular weight of

  The solubility parameter δB of the hydroxyl group-containing resin (B) is preferably 9.0 to 10, more preferably 9.2 to 9.9, from the viewpoint of the sharpness of the resulting coating film.

  The blending amount (solid content) of the hydroxyl group-containing resin (B) is preferably based on 100 parts by mass of the total solid content of the solvent-based first colored paint (Y) from the viewpoint of the sharpness of the resulting coating film. It is in the range of 40 to 97 parts by mass, more preferably in the range of 50 to 90 parts by mass.

  The hydroxyl group-containing acrylic resin can be obtained using the method and monomer described for the hydroxyl group-containing acrylic resin.

  The hydroxyl group-containing acrylic resin preferably has a hydroxyl value in the range of 30 to 300 mgKOH / g, and particularly preferably has a hydroxyl value in the range of 40 to 250 mgKOH / g, from the viewpoint of water resistance of the resulting coating film. preferable.

  The hydroxyl group-containing acrylic resin preferably has an acid value in the range of 20 mgKOH / g or less, and particularly preferably has an acid value in the range of 1 to 15 mgKOH / g, from the viewpoint of the sharpness of the resulting coating film. preferable.

  The hydroxyl group-containing acrylic resin preferably has a weight average molecular weight in the range of 25,000 to 40,000, and a weight in the range of 26,000 to 33,000, from the viewpoint of the sharpness of the resulting coating film. It is particularly preferred to have an average molecular weight.

  The solubility parameter δB of the hydroxyl group-containing acrylic resin is preferably 9.0 to 10, more preferably 9.2 to 9.9, from the viewpoint of the sharpness of the coating film obtained.

  The hydroxyl group-containing polyester resin can be obtained using the method and monomer described in the hydroxyl group-containing polyester resin.

  The hydroxyl value of the hydroxyl group-containing polyester resin is preferably in the range of 30 to 300 mgKOH / g, more preferably in the range of 40 to 250 mgKOH / g, particularly preferably 50 to 200 mgKOH / g, from the viewpoint of water resistance of the resulting coating film. Within the range of g.

  The number average molecular weight of the hydroxyl group-containing polyester resin is preferably in the range of 15,000 to 20,000, particularly preferably in the range of 15,000 to 18,000, from the viewpoint of the sharpness of the resulting coating film.

  The acid value of the hydroxyl group-containing polyester resin is preferably in the range of 0 to 10 mgKOH / g, more preferably in the range of 0 to 5 mgKOH / g, from the viewpoint of the storage stability of the coating composition.

  The solubility parameter δB of the hydroxyl group-containing polyester resin is preferably 9.0 to 10, more preferably 9.2 to 9.9, from the viewpoint of the sharpness of the resulting coating film.

  The solvent-based second colored paint (Y) can contain a curing agent. Examples of the curing agent include melamine resin, polyisocyanate compound, blocked polyisocyanate compound, carbodiimide group-containing compound, and the like.

  The solvent-based second colored paint (Y) contains the hydroxyl group-containing resin (B) as an essential resin component, and if necessary, pigments, other resin components, organic solvents, thickeners, anti-settling agents, and curing. It contains a catalyst, a pigment dispersant, an ultraviolet absorber, a light stabilizer, a surface conditioner, an antifoaming agent, a plasticizer and the like, and these can be dissolved or dispersed in an aqueous medium to form a paint.

As the pigment, a color pigment, a bright pigment, and the like can be used.
Examples of the color pigment include titanium oxide, zinc white, carbon black, molybdenum red, Prussian blue, cobalt blue, azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, and selenium (anthraquinone) pigments, Examples include perylene pigments, dioxazine pigments, diketopyrrolopyrrole pigments, and the like. These may be used alone or in combination of two or more.

  Examples of the bright pigment include aluminum (including vapor-deposited aluminum), copper, zinc, brass, nickel, aluminum oxide, mica, aluminum oxide coated with titanium oxide and iron oxide, and titanium oxide and iron oxide. Mica, glass flakes, hologram pigments and the like, which can be used alone or in combination of two or more. The glitter pigment is preferably scaly.

  The solvent-based second colored paint (Y) may be applied to the uncured first colored coating film by a method known per se, for example, air spray, airless spray, rotary atomization coating, curtain coating, etc. Yes, electrostatic application may be performed during painting. Of these, methods such as air spray coating and rotary atomization coating are preferred.

  The coating amount of the solvent-based second colored paint (Y) is preferably an amount such that the cured film thickness is in the range of 6 to 20 μm, within the range of 8 to 15 μm, from the viewpoint of the sharpness of the obtained multilayer coating film. Is more preferred. In particular, when the water-based second colored paint (Y) contains a glitter pigment, the glitter pigment in the second colored coating film is oriented and glittered if the coating amount is within the above range. It is possible to obtain an appearance having excellent design properties with a sense of brightness and light interference.

  The solubility parameter δA of the hydroxyl group-containing resin (A) and the solubility parameter δB of the hydroxyl group-containing resin (B) contained in the solvent-based second colored paint (Y) are 0.6 <δA−δB <1.2. The relationship is preferably 0.6 <δA−δB ≦ 1.1.

If δA−δB is a value exceeding 0.6, the hydroxyl group-containing resin (A) in the solvent-based first colored paint (X) and the hydroxyl group-containing resin (B) in the solvent-based second colored paint (Y) Since mixing can be suppressed, a coating film excellent in sharpness, flip-flop (FF) properties and hardness can be obtained.
If δA−δB is less than 1.2, in the following step (4), the solvent-based two-component clear paint (Z) spreads uniformly on the second colored coating film, and the second colored coating film A clear coating film can be formed on the entire surface.

[Step (4)]
In step (4) of the present invention, a solvent-based two-component clear coating (Z) is applied onto the uncured second colored coating film obtained in the above step (3) to form an uncured clear coating film. Form.

(Solvent-based two-component clear paint (Z))
As the solvent-based two-component clear coating composition (Z), any of known solvent-based and two-component thermosetting clear coating compositions for coating automobile bodies can be used. Examples of the thermosetting clear coating composition include an organic solvent type thermosetting coating composition containing a base resin having a crosslinkable functional group and a crosslinking agent.

  Examples of the crosslinkable functional group that the base resin has include a carboxyl group, a hydroxyl group, an epoxy group, and a silanol group.

  Examples of the base resin include acrylic resin, polyester resin, alkyd resin, urethane resin, epoxy resin, and fluorine resin.

  Examples of the crosslinking agent include polyisocyanate compounds, blocked polyisocyanate compounds, melamine resins, urea resins, carboxyl group-containing compounds, carboxyl group-containing resins, epoxy group-containing resins, and epoxy group-containing compounds.

  As the base resin / crosslinking agent combination of the solvent-based two-component clear coating (Z), a hydroxyl group-containing resin / polyisocyanate compound and the like are preferable.

  The solvent-based two-component clear paint (Z) can contain a color pigment, a bright pigment, a dye, and the like as long as it does not hinder transparency. An ultraviolet absorber, a light stabilizer, an antifoaming agent, a thickener, a rust inhibitor, a surface conditioner, and the like can be appropriately contained.

  The solvent-based two-component clear paint (Z) can be applied to the second colored coating film by a method known per se, for example, airless spray, air spray, rotary atomizer, etc. Alternatively, electrostatic application may be performed.

  The film thickness of the coating with the solvent-based two-component clear paint (Z) is a cured film thickness, and is usually preferably in the range of 10 to 80 μm, more preferably in the range of 15 to 70 μm. More preferably, it is within the range of 60 μm.

  In addition, after application of the solvent-based two-component clear paint (Z), an interval of 1 to 60 minutes may be provided at room temperature, or preheating may be performed at 40 to 80 ° C. for about 1 to 60 minutes as necessary. preferable.

[Step (5)]
In step (5) of the method for forming a multilayer coating film of the present invention, the uncured primer coating film, the uncured first colored coating film, and the uncured first coating film formed in the above steps (1) to (4). The two colored coating and the uncured clear coating are simultaneously cured by heating to 75-95 ° C, preferably 80-90 ° C.

  When the heating temperature is 75 ° C. or higher, a multilayer coating film having excellent hardness can be obtained, and when the heating temperature is 95 ° C. or lower, a multilayer coating film having excellent sharpness is obtained. Can do.

Curing of the primer coating, the first colored coating, the second colored coating, and the clear coating can be performed by ordinary coating baking means such as hot air heating, infrared heating, and high-frequency heating.
The heating time is preferably 10 to 60 minutes, and more preferably 15 to 40 minutes.

  Hereinafter, the present invention will be described more specifically with reference to examples. The scope of the present invention is not limited to these examples. In the examples, “parts” and “%” indicate “parts by mass” and “% by mass”, respectively.

[Preparation of test plate]
As a metal member, a zinc phosphate treated cold rolled steel sheet (450 mm × 300 mm × 0.8 mm), a thermosetting epoxy resin cationic electrodeposition coating composition (trade name “Electron GT-10”, manufactured by Kansai Paint Co., Ltd.) ) Was electrodeposited to a film thickness of 20 μm and prepared by heating at 170 ° C. for 30 minutes to cure.

  As a plastic member, a 2 mm thick polypropylene plate (350 mm × 10 mm × 2 mm) was prepared.

  And the surface of the metal member prepared above and the plastic member was wiped with gauze containing petroleum benzine and degreased, and they were arranged adjacently to obtain a test plate.

[Production of hydroxyl group-containing resins (A) and (B)]
(Production Example 1)
In a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, a thermostat and a dropping pump, 60 parts of xylene were charged, and the temperature was raised to 145 ° C. while stirring while blowing nitrogen gas,
52 parts of methyl methacrylate,
22 parts ethyl acrylate,
10 parts of methoxyethyl acrylate,
15 parts 2-hydroxyethyl methacrylate and
1 part of acrylic acid A mixture of the above monomer and polymerization initiator was dropped into the reaction vessel at a constant rate over 3 hours using a dropping pump. Thereafter, a mixture of 0.5 part of 2,2′-azobisisobutyronitrile and 10 parts of xylene was added dropwise at a constant rate over 1 hour. After completion of dropping, the reaction was terminated by aging at the same temperature for 3 hours to obtain a solution of a hydroxyl group-containing acrylic resin (A-1).

  The obtained solution of the hydroxyl group-containing acrylic resin (A-1) was a uniform transparent solution having a solid content of 50%. Further, the solubility parameter δA of the hydroxyl group-containing acrylic resin (A-1) was 10.6, the weight average molecular weight was 29,000, and the hydroxyl value was 65 mgKOH / g.

(Production Examples 2 to 5)
Hydroxyl-containing resins (A-2) to (A-5) were obtained in the same manner as in Production Example 1 except that the monomer composition shown in Table 1 was used in Production Example 1. Table 1 shows the solubility parameter δA, the weight average molecular weight, and the hydroxyl value of the hydroxyl group-containing resins (A-2) to (A-5).

(Production Examples 6 to 10)
Hydroxyl-containing resins (B-1) to (B-5) were obtained in the same manner as in Production Example 1 except that the monomer composition shown in Table 2 was used in Production Example 1. The solubility parameter δB, the weight average molecular weight, and the hydroxyl value of the hydroxyl group-containing resins (B-1) to (B-5) were as shown in Table 2.
The hydroxyl group-containing resins (A-1) to (A-5) and the hydroxyl group-containing resins (B-1) to (B-5) obtained above are “hydroxyl group-containing acrylic resins”.

[Production of Solvent-Based First Colored Paint (X)]
(Production Example 11)
10.6 parts (solid content) of a hydroxyl group-containing resin (A-1) solution having a solid content of 50%, a hydroxyl group-containing polyester resin (A-6) having a solid content of 60% (hydroxyl value: 105, solubility parameter value: 10. 6) 2.6 parts (solid content) of the solution, “Sumijour N3300” (trade name, manufactured by Sumika Cobestrourethane Co., Ltd., polyisocyanate compound) 9.5 parts (solid content), “JR-806” (trade name) 28.3 parts (solid content) manufactured by Teica Co., Ltd. (solid content), “MA-100” (trade name, manufactured by Mitsubishi Chemical Corporation, carbon black) 0.2 parts, “Varifine BF-20” (trade name) 7.4 parts, manufactured by Sakai Chemical Industry Co., Ltd., barium sulfate having an average particle size of 0.03 μm) was uniformly mixed.
Furthermore, the solid content was adjusted with butyl acetate so that the viscosity at 20 ° C. measured with “Viscosity Cup NK-2” manufactured by Anest Iwata Co., Ltd. was adjusted, and the solvent-based first colored paint (X -1) was obtained.

(Production Examples 12 to 15)
Solvent-based first colored paints (X-2) to (X-5) were obtained in the same manner as in Production Example 11 except that the monomer composition shown in Table 3 was used in Production Example 11.

[Production of solvent-based second colored paint (Y)]
(Production Example 16)
21.6 parts (solid content) of a hydroxyl group-containing acrylic resin (B-1) solution having a solid content of 50%, a hydroxyl group-containing polyester resin (B-6) having a solid content of 70% (hydroxyl value: 60, solubility parameter value: 9) .9) Solution 4.5 parts (solid content), "GX180A" (trade name, manufactured by Asahi Kasei Corporation, aluminum paste) 5.4 parts (solid content), "Varifine BF-20" (trade name, Sakai Chemical Industry) 3.1 parts of barium sulfate having an average particle size of 0.03 μm and extender pigment) were mixed uniformly.
Furthermore, the solid content was adjusted with butyl acetate so that the viscosity at 20 ° C. measured with “Viscosity Cup NK-2” manufactured by Anest Iwata Co., Ltd. was adjusted to butyl acetate, and the solvent-based second colored paint (Y -1) was obtained.

(Production Examples 17-20)
Solvent-based second colored paints (Y-2) to (Y-5) were obtained in the same manner as in Production Example 16 except that the monomer composition shown in Table 4 was used in Production Example 11.
It was.

[Preparation of test plate]
Example 1
The test plate obtained above was spray-coated with a water-based primer paint “SOFLEX 3100” (trade name, manufactured by Kansai Paint Co., Ltd.) to a cured film thickness of 10 μm, and allowed to stand at room temperature for 6 minutes. The solvent-based first colored paint (X-1) produced in (1) was electrostatically coated so as to have a cured film thickness of 20 μm, allowed to stand at room temperature for 6 minutes, and further the solvent-based second colored paint (Y-) produced above. 1) was electrostatically coated to a cured film thickness of 10 μm.

Next, the solvent-based two-component clear paint (Z) “Soflex 7500” (trade name, manufactured by Kansai Paint Co., Ltd.) was electrostatically applied to a dry film thickness of 35 μm and left at room temperature for 5 minutes. The test coating plate in which the multilayer coating film was formed was obtained by heating in an oven at 85 ° C. for 30 minutes.
The obtained multilayer coating film was subjected to various coating film performance tests described below. The results are shown in Table 5.

(Examples 2-5 and Comparative Examples 1-4)
In Example 1, a multilayer coating film was formed in the same manner as in Example 1 except that the solvent-based first colored paint (X), the solvent-based second colored paint (Y) and the baking temperature were as shown in Table 5. A formed test coating was obtained. About each obtained multilayer coating film, the various coating-film performance tests described below were done.
In Comparative Example 2, the solvent-based two-component clear paint (Z) “Soflex 7500” (trade name, manufactured by Kansai Paint Co., Ltd.) did not spread evenly on the coating film, and the clear coating film was applied to the entire coating film surface. Since the film could not be formed, various coating film performance tests were not performed. The results are shown in Table 5.

[Film performance test]
(Vividness)
About each test coating plate obtained above, Wb value was measured by DOI (Determination of image clarity) measuring apparatus "Wave Scan DOI" (trade name, manufactured by BYK Gardner).
The smaller the Wb value, the higher the clearness of the coating surface. The smaller the Wb value, the better. At least the condition of less than 20 must be satisfied.

(Flip-flop (FF))
About each test coating board obtained above, using a laser type metallic feeling measuring device “ALCORP LMR-200” (trade name, manufactured by Kansai Paint Co., Ltd.), a which is a Y value of a light receiving angle of 15 ° and a light receiving angle of 110 °. B which is Y value of was measured, and FF value was calculated | required by the following formula.
FF value = (ab) / [(a + b) / 2]

  The larger the FF value, the larger the change in the Y value (brightness) depending on the observation angle (light receiving angle), indicating that the flip-flop property is excellent. The upper limit of the FF value is 2.00.

(Pencil hardness)
Based on JIS K 5600-5-4 (1999) “Scratch hardness (pencil method)”, the pencil hardness of the coated surface of each test coated plate obtained above was measured.
If the pencil hardness is F or H, the hardness is good.

  As can be seen from Table 5, the test coated plates of Examples 1 to 5 were excellent in sharpness, flip-flop (FF) properties and hardness.

On the other hand, the test coated plate of Comparative Example 1 in which δA−δB was 0.5 was inferior to the test coated plates of Examples 1 to 5 in sharpness and flip-flop (FF) properties.
In Comparative Example 2 where δA-δB is 1.4, the solvent-based two-component clear paint (Z) “Soflex 7500” (trade name, manufactured by Kansai Paint Co., Ltd.) does not spread evenly on the coating film. Since a clear coating film could not be formed on the entire coating film surface, various coating film performance tests were not conducted.

Furthermore, the test coating board of the comparative example 3 whose heating temperature of the coating film was 60 degreeC was inferior to the test coating board of Examples 1-5 in flip-flop (FF) property and hardness.
Moreover, the test coating board of the comparative example 4 whose heating temperature of the coating film was 110 degreeC was inferior to the test coating board of Examples 1-5.

Claims (3)

(1) A step of applying a primer paint (P) to form an uncured primer coating on the surface of an automobile outer plate including at least one of a metal member and a plastic member;
(2) A step of coating the solvent-based first colored paint (X) on the uncured primer coating obtained in step (1) to form an uncured first colored coating,
(3) A step of coating the solvent-based second colored paint (Y) on the uncured first colored coating film obtained in the step (2) to form an uncured second colored coating film,
(4) A step of applying a solvent-based two-component clear coating (Z) on the uncured second colored coating film obtained in the step (3) to form an uncured clear coating film, and (5) Heat the uncured primer coating, uncured first colored coating, uncured second colored coating and uncured clear coating formed in steps (1) to (4) to 75 to 95 ° C. By simultaneously curing these coating films,
A multilayer coating film forming method for sequentially performing,
The solvent-based first colored paint (X) is a two-component paint composition containing a hydroxyl group-containing resin (A) and a polyisocyanate compound (I),
The solvent-based second colored paint (Y) is a one-component paint composition containing a hydroxyl group-containing resin (B),
The multilayer coating, wherein the solubility parameter δA of the hydroxyl group-containing resin (A) and the solubility parameter δB of the hydroxyl group-containing resin (B) are in a relationship of 0.6 <δA−δB <1.2. Film forming method.   The method for forming a multilayer coating film according to claim 1, wherein the hydroxyl group-containing resin (A) has a weight average molecular weight in the range of 29,000 to 47,000.   The method for forming a multilayer coating film according to claim 1, wherein the hydroxyl group-containing resin (B) has a weight average molecular weight of 15,000 to 40,000.