JPH09206665A - Topcoat film-forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a multi-layer topcoat film of good resistance to acids, resistance to chipping, interlaminar adhesion, water resistance, watherability and the like. SOLUTION: A material to be coated is coated with an aqueous coloring base-coating material composition (A) composed of acryl resin (A-1) containing hydroxyl and carboxyl groups, melamine resin (A-2), a cycloaliphatic epoxy group-containing compound (A-3), a neutralizer (A-4) and a colored pigment (A-5) as main components, and then the surface is coated with a clear coating material composition (B) dissolved in an organic solvent for curing by the crosslinking reaction of carboxyl and epoxy groups.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to chipping resistance,
Excellent in interlayer adhesion, water resistance, acid resistance and weather resistance,
The present invention relates to a novel method for forming a multi-layer top coating film comprising a colored base coating film and a clear coating film.

[0002]

2. Description of the Related Art Generally, an object to be coated such as an outer panel of an automobile is usually finished by sequentially coating an undercoat paint such as a cationic electrodeposition paint, an intermediate coat paint and a topcoat paint. Among them, as a top coating, a two-coat method using two kinds of a solid color coating or a colored base coating which is a metallic coating and a clear coating is often adopted.

Conventionally, for forming an overcoat film, a water-based paint containing a hydroxyl group- and carboxyl group-containing acrylic resin, a melamine resin, a neutralizing agent and a coloring pigment as a main component is used as a colored base paint, while a hydroxyl group-containing water-based paint is used as a clear paint. Paints containing resins and melamine resins as main components are frequently used. However, an overcoat film formed from such a coating is not sufficient in chipping resistance, interlayer adhesion between a colored base coating and a clear coating (hereinafter simply referred to as interlayer adhesion), water resistance and weather resistance. It was

From the viewpoint of improving the acid resistance of the top coating composition, the clear coating composition contains no melamine resin,
It has been proposed to use a paint that is cured by a crosslinking reaction between a carboxyl group and an epoxy group, but in this case as well, chipping resistance, interlayer adhesion, water resistance, weather resistance and the like were not sufficient.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method capable of forming a multi-layer top coating film having good acid resistance, chipping resistance, interlayer adhesion, water resistance and weather resistance. .

[0006]

Means for Solving the Problems As a result of intensive research, the present inventor has mainly used a hydroxyl group- and carboxyl group-containing acrylic resin, a melamine resin, an alicyclic epoxy group-containing compound, a neutralizing agent and a coloring pigment as a coloring base paint. It was found that the above object can be achieved by using an aqueous paint as a component and an organic solvent-based paint that is cured by a cross-linking reaction between a carboxyl group and an epoxy group as a clear paint, and completed the present invention. .

That is, according to the present invention, an acrylic resin (A-1) containing a hydroxyl group and a carboxyl group, a melamine resin (A-2), and an alicyclic epoxy group-containing compound (A-
3), a water-based colored base coating composition (A) containing a neutralizing agent (A-4) and a coloring pigment (A-5) as main components is applied, and then the coating surface is cross-linked with a carboxyl group and an epoxy group. The present invention relates to a method for forming a topcoat coating film, which comprises coating an organic solvent-based clear coating composition (B) which is cured by a reaction.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The water-based pigmented base coating composition (A) and the clear coating composition (B) used in the method of the present invention will be described in detail.

The aqueous colored base coating composition (A) comprises a hydroxyl group- and carboxyl group-containing acrylic resin (A-1), a melamine resin (A-2), an alicyclic epoxy group-containing compound (A-3), and a neutralizing agent. Agent (A-4) and Color Pigment (A-5)
Is a water-based paint containing as a main component and water as a main solvent or dispersion medium.

The component (A-1) is an acrylic resin in which one or more hydroxyl groups and one or more carboxyl groups coexist in one molecule.

The acrylic resin is obtained by copolymerizing a hydroxyl group-containing monomer, a carboxyl group-containing monomer and an acrylic monomer as essential components and, if necessary, other monomers.

The hydroxyl group-containing monomer is a compound having at least one hydroxyl group and at least one polymerizable unsaturated bond in one molecule, and examples thereof include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate. Examples thereof include monoesters of acrylic acid or methacrylic acid with glycols having 2 to 10 carbon atoms (having two hydroxyl groups).

The carboxyl group-containing monomer is a compound having at least one carboxyl group and at least one polymerizable unsaturated bond in one molecule, and examples thereof include acrylic acid, methacrylic acid, maleic acid, fumaric acid and mesaconic acid. , Citraconic acid, itaconic acid, their anhydrides, half-esterified products and the like.

The acrylic monomer is a monoester compound of acrylic acid or methacrylic acid and a monoalcohol having 1 to 20 carbon atoms (having one hydroxyl group), such as methyl (meth) acrylate and ethyl (meth). Acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate and the like are preferable.

The other monomer is a monomer other than the above, and examples thereof include styrene, vinyltoluene, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl acetate, glycidyl acrylate and glycidyl methacrylate. The amount of the other polymerizable monomer used is preferably equal to or less than the amount of the acrylic monomer.

The component (A-1) is obtained by polymerizing the above-mentioned monomer by a known method such as solution polymerization or emulsion polymerization, and its number average molecular weight is about 3,000.
To about 100,000, especially about 5,000 to about 50,000
0, hydroxyl value is about 20 to about 150 mgKOH / g, especially about 30
The acid value is preferably about 5 to about 100 mgKOH / g, and more preferably about 10 to about 70 mgKOH / g.

The acrylic resin (A-1) is described in (A-
The carboxyl group is neutralized by the component 4) and used in a state of being dissolved or dispersed in water.

The component (A-2) is a melamine resin.
This is a cross-linking agent for the acrylic resin (A-1) component, and methylolated melamine, alkyl etherified melamine obtained by etherifying a part or all of the methylol group with a monoalcohol having 1 to 10 carbon atoms, etc. are used. it can. The number average molecular weight of the component (B) is about 400 to about 3,000,
Particularly preferred is about 500 to about 1,200. The melamine resin may be hydrophobic or hydrophilic.

The alicyclic epoxy group-containing compound (A-3) is a compound having one or more alicyclic epoxy groups in one molecule. The alicyclic epoxy group of the compound means a functional group in which two adjacent carbon atoms and one oxygen atom forming the ring of the alicyclic hydrocarbon skeleton form an epoxy group. . The alicyclic hydrocarbon skeleton has 4
It may be a saturated hydrocarbon ring having 10 to 10 members, preferably 5 to 6 members, or a condensed hydrocarbon ring formed by condensing two or more of these rings, and these hydrocarbon rings are bonded to each other through a bridge such as an alkylene group. The bridged hydrocarbon ring may be formed.

Specific examples of such alicyclic epoxy compounds include compounds represented by the following structural formulas.

For example, the expression

[0022]

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Epoxidized tetrahydrobenzyl alcohol represented by the formula:

[0024]

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(Where m is an integer of 2 to 12 and n is 1 to
An integer of 20 (average) is shown. ) Lactone-modified epoxidized tetrahydrobenzyl alcohol represented by the formula:

[0026]

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Cyclohexene oxide represented by the formula:

[0028]

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Α-pinene oxide represented by the formula:

[0030]

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A vinyl group-containing cyclohexene oxide represented by:

[0032]

[Chemical 6]

[0033]

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(In each formula, n'is an integer of 1 to 8 and k is 0.
Each of the integers of -15 is shown. ).

A compound having the following unit formula

[0036]

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(Wherein Y is an alicyclic epoxy residue,
X is

[0038]

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Wherein R ₁ is a C _1-18 alkyl group or a cycloalkyl group, R ₂ is a C _1-6 alkylene group, and q is 0 to
An integer of 100 and p are integers of 1 to 100, respectively. )etc.

Y in the above unit formula is

[0041]

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An organic group having an alicyclic epoxy group such as

Examples of the compound having the above unit formula include those described in Japanese Patent Application No. 1-209667, for example, the following compounds.

That is, as the compound having the above unit formula, for example, 3,4-epoxycyclohexyl methyl acrylate, 3,4-epoxy cyclohexyl acrylate, and commercially available products "METHB" and "AETHB" (all manufactured by Daicel Chemical Industries, Ltd.) , Trade name) or a radical-polymerizable epoxy monomer alone or with another radical-polymerizable monomer.

The following compounds are also included as the alicyclic epoxy compound as the component (A-3). That is, a polymer obtained by using a compound having an alicyclic epoxy group and a polymerizable unsaturated bond in the same molecule can be used as the component (A-3).

Examples of the compound having an alicyclic epoxy group and a polymerizable unsaturated bond in the same molecule include polymerizable epoxy monomers represented by the following general formulas (6) to (17).

[0047]

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[0048]

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(In each formula, R ₄ is a hydrogen atom or a methyl group, R ₅ is a divalent saturated aliphatic hydrocarbon group having 1 to ₆ carbon atoms, and R ₆ is a divalent aliphatic group having 1 to 10 carbon atoms. Hydrocarbon groups are respectively shown.).

In the above polymerizable epoxy monomer, R ₅
Examples of the divalent saturated aliphatic hydrocarbon group having 1 to 6 carbon atoms represented by are linear or branched alkylene groups such as methylene, ethylene, propylene, tetramethylene, ethylethylene, pentamethylene, and hexa. Methylene etc. can be mentioned. Further, the carbon number represented by R ₆ is 1 to 1.
Examples of the divalent hydrocarbon group of 0 include methylene, ethylene, propylene, tetramethylene, ethylethylene,
Pentamethylene, hexamethylene, polymethylene, phenylene,

[0051]

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Examples thereof include groups.

Specific examples of the polymerizable epoxy monomers represented by the above general formulas (6) to (17) include 3,4-epoxycyclohexylmethyl acrylate and 3,4-epoxycyclohexylmethyl methacrylate. Examples of these commercially available products include "METHB" and "AETHB" (both are trade names) manufactured by Daicel Chemical Industries, Ltd. Further, 4-vinylcyclohexene oxide can also be used as the polymerizable epoxy monomer.

By polymerizing one or more monomers selected from the polymerizable epoxy monomers, (A
A polymer as the component (3) can be produced, but other polymerizable unsaturated monomers can be copolymerized at that time.

As the other polymerizable unsaturated monomer,
A wide range of selection can be made according to the desired performance of the obtained polymer, and typical examples thereof are as follows.

(A) Ester of acrylic acid or methacrylic acid For example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, lauryl acrylate, methyl methacrylate , Ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, hexyl methacrylate, octyl methacrylate, lauryl methacrylate and the like, acrylic acid or a methacrylic acid alkyl ester having 1 to 18 carbon atoms; methoxybutyl acrylate, C2 to C18 of acrylic acid or methacrylic acid such as methoxybutyl methacrylate, methoxyethyl acrylate, methoxyethyl methacrylate, ethoxybutyl acrylate, ethoxybutyl methacrylate Alkoxyalkyl ester; C2-8 alkenyl ester of acrylic acid or methacrylic acid such as allyl acrylate and allyl methacrylate; Carbon of acrylic acid or methacrylic acid such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate A hydroxyalkyl ester of the number 2 to 8.

(B) Vinyl aromatic compound For example, styrene, α-methylstyrene, vinyltoluene, p-chlorostyrene.

(C) Polyolefin compound For example, butadiene, isoprene and chloroprene.

(D) Others For example, acrylonitrile, methacrylonitrile, methyl isopropenyl ketone, vinyl acetate, "veova monomer" (trade name, manufactured by Shell Chemical Co.), vinyl propionate, vinyl pivalate, vinyl compound having a polycaprolactone chain. (For example, "FM-3X monomer", trade name, manufactured by Daicel Chemical Industries, Ltd.).

The composition ratio of the polymerizable epoxy monomer and the other polymerizable unsaturated monomer can be arbitrarily selected according to the purpose, and one molecule of the component (A-3) obtained by the copolymerization reaction of them can be selected. Per alicyclic epoxy group is at least 1, preferably 2 or more, more preferably 4
It can be selected in the range that contains more than one,
In order to utilize as a functional group that imparts sufficient curability, the content of the polymerizable epoxy monomer in the solid content of the component (A-3) is 5 to 100% by weight, preferably 20 to 1
It is suitable to set it within the range of 00% by weight.

The polymer as the above-mentioned component (A-3) can be produced by using the same method and conditions as the polymerization reaction based on the polymerizable unsaturated bond of the usual acrylic resin or vinyl resin. As an example of such a polymerization reaction, a method of dissolving or dispersing each monomer component in an organic solvent and heating it with stirring at a temperature of about 60 to 180 ° C. in the presence of a radical polymerization initiator can be shown. . Reaction time is usually 1
It can be about 10 hours. Further, as the organic solvent, an alcohol solvent, an ether solvent, an ester solvent, a hydrocarbon solvent and the like can be used. When a hydrocarbon solvent is used, it is preferable to use another solvent in combination from the viewpoint of solubility. Further, as the radical polymerization initiator, any of those usually used can be used, and specific examples thereof include benzoyl peroxide and t-butylperoxy-.
Examples thereof include peroxides such as 2-ethylhexanoate; azo compounds such as azoisobutyronitrile and azobisdimethylvaleronitrile.

The alicyclic epoxy compound as the component (A-3) has excellent compatibility with the components (A-1) and (A-2) and is preferably stable in water. The number average molecular weight is about 90 to 50,000, preferably about 200 to 5,000. Further, the number of alicyclic epoxy groups in one molecule is preferably 2 to 200. When the number average molecular weight exceeds about 50,000, the storage stability of the aqueous basecoat composition may decrease, which is not preferable. If the number of alicyclic epoxy groups is less than 2, the chipping resistance cannot be improved. On the other hand, if the number of the epoxy groups is more than about 200, the smoothness of the aqueous base coat film may be deteriorated, which is not preferable.

If a compound having an epoxy group other than the alicyclic epoxy group is used instead of the alicyclic epoxy compound, the storage stability of the water-based paint will be insufficient, which is not preferred in the present invention. Further, in this case, as shown in Comparative Examples described later, the coating performance such as chipping resistance and water resistance of the cured coating becomes insufficient, which is not preferable.

The component (A-4) is a neutralizing agent, which neutralizes the carboxyl group of the component (A-1) to impart solubility or dispersibility with water, Examples thereof include ammonia, trimethylamine, triethylamine, dimethylethanolamine, triethanolamine, tetraethylammonium hydroxide, diethylaminoethanol and the like, of which dimethylethanolamine is preferable.

The component (A-5) is a coloring pigment, which is a coloring material for coloring the coating film of the water-based coloring base composition (A) into a solid color or a metallic color. Pigments are included. Specific examples of color pigments include titanium white, carbon black, chrome vermilion, molybdenum red, chrome yellow, yellow iron oxide, chrome green, ultramarine, inorganic violet pigments such as cobalt violet, phthalocyanine blue, phthalocyanine red, phthalocyanine green, Known as color pigments for paints such as monoazo pigments, organic coloring pigments such as quinacridone violet, aluminum flakes, copper flakes, mica-like iron oxide, mica, metallic pigments such as scale-like powders of mica surface-coated with metal oxides, etc. Things can be used.

The aqueous colored base coating composition (A) used in the present invention comprises the above-mentioned components (A-1), (A-2),
The component (A-3), the component (A-4) and the component (A-5) are the main components, and the blending ratio of each of these components can be arbitrarily selected according to the purpose. ) Ingredient 10
20 to 60 parts by weight of the component (A-2) per 0 parts by weight,
In particular, 25 to 50 parts by weight, component (A-3) is 0.5 to 15
Parts by weight, particularly 3 to 10 parts by weight, and the amount of the component (A-4) is 0.2 to 1.
It is preferable that 5 equivalents, particularly 0.5 to 1.2 equivalents, are incorporated respectively.

The component (A-5) can be added in an appropriate amount necessary for coloring the coating film of the coating composition (A) into a desired solid color or metallic color.

If necessary, the coating composition (A) may further contain an organic resin such as polyester resin, urethane resin or polyamide resin, an extender pigment, an anti-settling agent and an antifoaming agent.

As a medium for the coating composition (A), water or a mixture of water and an appropriate amount of an organic solvent is used. The organic solvent is not particularly limited, but suitable examples include isobutyl alcohol, butyl cellosolve, butyl carbitol, and isopropanol.

The aqueous colored base coating composition (A) can be prepared by mixing and dispersing the above components in the medium, and the solid content is preferably about 30 to 80% by weight at the time of coating.

The clear coating composition (B) is a transparent coating film-forming coating material applied to the coating surface of the water-based colored base coating composition (A), which is a thermosetting composition that is cured by a crosslinking reaction between a carboxyl group and an epoxy group. Organic solvent-based clear paint.

The coating composition (B) is specifically a clear coating composition (having a mixture of a carboxyl group-containing resin (B-1a) and an epoxy group-containing resin (B-1b) as a main component ( B-1), and a clear coating composition (B-2) containing a resin (B-2a) in which a carboxyl group and an epoxy group coexist in the same molecule as a main component, and the like.

Examples of the carboxyl group-containing resin (B-1a) include a carboxyl group-containing vinyl resin and a carboxyl group-containing polyester resin, and any one of them can be used alone, or both can be used in combination.

The carboxyl group-containing vinyl resin contained in the component (B-1a) is a vinyl resin obtained by polymerizing the carboxyl group-containing polymerizable monomer alone or together with other polymerizable monomers.

The carboxyl group-containing polymerizable monomer is a compound having a carboxyl group and a polymerizable double bond in one molecule, and the carboxyl group also includes an acid anhydride group. Specific examples thereof include acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, fumaric acid, mesaconic acid, itaconic acid, itaconic anhydride and aconitic acid. These may be used alone or in combination of two or more. Can be used. In addition, those obtained by half-esterifying a dibasic acid (including an acid anhydride group) among these can also be used as the carboxyl group-containing polymerizable monomer. This half-esterification is carried out by reacting a dibasic acid with an aliphatic monohydric alcohol such as methanol, ethanol, propanol, butanol or methyl cellosolve in the presence of a tertiary amine (catalyst). This half-esterification reaction may be carried out either before or after the polymerization.

The other polymerizable monomer is a compound having one or more polymerizable double bonds in one molecule, and may have a functional group other than a carboxyl group and an epoxy group. For example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate,
Hydroxyl (meth) acrylate, a hydroxyl group-containing monomer such as a monoester of polyethylene glycol and (meth) acrylic acid; an aliphatic or alicyclic monohydric alcohol having 1 to 24 carbon atoms and (meth) acrylic acid Monoesters; monoesters of C2-18 alkoxyalkyl monohydric alcohol and (meth) acrylic acid; vinyl ethers such as ethyl vinyl ether, pentyl vinyl ether, cyclohexyl vinyl ether, benzyl vinyl ether, allyl glycidyl ether; styrene, α
-Styrenes such as methylstyrene; (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N-methyl (meth) acrylamide, vinylpyridine, acrylonitrile, etc. Examples of the nitrogen-containing monomer include vinyl acetate and vinyl chloride. These are one or two
More than one species can be used.

The carboxyl group-containing vinyl resin is obtained by polymerizing only the above-mentioned carboxyl group-containing polymerizable monomer or this and another monomer, and the resin has an epoxy group substantially. Absent. The polymerization is carried out by a known method, but an organic solution type radical polymerization method is preferable. The acid value of the vinyl resin is about 30 to 250 mg KOH / g, especially about 5
0 ~ 150mgKOH / g, number average molecular weight is about 1,000 ~ 1
0,000, especially about 3,000 to 50,000 is preferred. Further, a hydroxyl group may coexist in the resin, and the hydroxyl value is about 150 mgKOH / g or less, particularly about 10 to 10
0 mg KOH / g is suitable.

Examples of the carboxyl group-containing polyester resin contained in the component (B-1a) include polyhydric alcohols such as ethylene glycol, butylene glycol, hexanediol, trimethylolpropane and pentaerythritol, and succinic anhydride, adipic acid, It can be obtained by reacting with a polyvalent carboxylic acid such as terephthalic acid, isophthalic acid, phthalic anhydride, and hexahydrophthalic anhydride in an excess ratio of carboxyl groups.

It is also obtained by reacting in a hydroxyl group excess ratio to synthesize a hydroxyl group-terminated polyester resin, and then adding a carboxylic acid anhydride such as succinic anhydride, phthalic anhydride, or hexahydrophthalic anhydride to the hydroxyl group. To be

The acid value of the polyester resin is about 10 to 10
0 mgKOH / g, especially about 15-80 mgKOH / g, number average molecular weight of about 1,000-80,000, especially about 2,000-3
10,000 is preferable. Further, the resin may have a hydroxyl group, and the hydroxyl value is about 150 mgKOH / g or less,
Particularly, about 10 to 100 mg KOH / g is suitable.

Examples of the epoxy group-containing resin (B-1b) include an epoxy group-containing vinyl resin obtained by polymerizing an epoxy group-containing polymerizable monomer alone or together with other polymerizable monomers.

The epoxy group-containing polymerizable monomer is a compound having at least one epoxy group and at least one polymerizable double bond in one molecule. Specific examples thereof include glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether, and these can be used alone or in combination of two or more.

As other polymerizable monomers, the above (B
-1a) 1 type or 2 types or more selected from the other polymerizable monomers described in the component can be used.

The epoxy group-containing vinyl resin is obtained by polymerizing the above-mentioned epoxy group-containing polymerizable monomer alone or with other monomer, and the resin has a carboxyl group substantially. Absent. The polymerization is carried out by a known method, but an organic solution type radical polymerization method is preferable. The vinyl resin has an epoxy group content of about 0.8 to 3.2 mmol / g, particularly about 1.2 to 2.8 mmol / g, and a number average molecular weight of about 2,000 to 15,000, particularly about 3 1,000 ~
11,000 is preferred. Further, the vinyl resin may have a hydroxyl group, and the hydroxyl value is about 150 mgKOH /
g or less, especially about 20-60 mg KOH / g is suitable.

The clear coating composition (B-1) is a clear coating composition containing a mixture of the above-mentioned carboxyl group-containing resin (B-1a) and epoxy group-containing resin (B-1b) as a main component. The mixing ratio of -1a) and (B-1b) can be arbitrarily selected according to the purpose. Usually, the former is about 10 to 90% by weight, especially about 3% by weight based on the total weight of the both resins.
0 to 70% by weight, the latter about 90 to 10% by weight, especially about 7
0-30% by weight is suitable.

The clear coating composition (B-2) is a clear coating composition containing as a main component a resin (B-2a) in which a carboxyl group and an epoxy group coexist in the same molecule.

As the resin (B-2a), for example, the above-mentioned carboxyl group-containing polymerizable monomer and epoxy group-containing polymerizable monomer are used, or these are further combined with other monomers. Thus, a vinyl resin obtained by polymerization is preferable. As these monomers, one kind or two or more kinds selected from those exemplified above can be used, and the polymerization thereof is carried out by a known method, but an organic solution type radical polymerization method is preferable. The acid value of the resin is about 30 to 250 mg KOH / g, especially about 50 to 150 mg KOH / g, and the epoxy group content is about 0.8.
-3.2 mmol / g, especially about 1.2-2.8 mmol / g, number average molecular weight of about 1,000-100,000,
Particularly, about 2,000 to 50,000 is preferable. further,
A hydroxyl group may coexist in the resin, and the hydroxyl value is preferably about 150 mgKOH / g or less, particularly about 10 to 100 mgKOH / g.

The clear coating compositions (B-1) and (B-2) further include a vinyl polymer (B-Si) having a hydrolyzable silyl group or a group and a hydroxyl group in one molecule.
By blending, the acid resistance and scratch resistance of the clear coating film can be further improved.

The vinyl polymer (B-Si) contains a hydrolyzable silyl group-containing polymerizable monomer as an essential component, and further contains a hydroxyl group-containing polymerizable monomer and other polymerizable monomers as necessary. It can be obtained by polymerizing by a known method,
The polymerization method is preferably an organic solution type radical polymerization method.

The hydrolyzable silyl group-containing polymerizable monomer is
A compound having at least one hydrolyzable silyl group and at least one polymerizable double bond in one molecule, specifically, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, γ- (Meth) acryloyloxypropyltrimethoxysilane,
γ- (meth) acryloyloxypropyltriethoxysilane and the like can be mentioned, and these can be used alone or in combination of two or more.

The hydroxyl group-containing polymerizable monomer is a compound having at least one hydroxyl group and at least one polymerizable double bond in one molecule, and specific examples thereof include hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate. , Hydroxybutyl (meth) acrylate, monoesters of polyethylene glycol and (meth) acrylic acid, α,
Addition product of β-unsaturated carboxylic acid and cardura E10 (trade name of Shell Petroleum Co., Ltd.) or monoepoxy compound such as α-olefin epoxide, glycidyl methacrylate and acetic acid, propionic acid, p-tert-butylbenzoic acid , And addition products with monobasic acids such as fatty acids.

As the other polymerizable monomer, one kind or two or more kinds selected from the above-mentioned ones can be used.

In the vinyl polymer (B-Si), the composition ratio of these monomers is not particularly limited, but based on the total weight of these monomers, the hydrolyzable silyl group-containing polymerizable monomer is used. Is 10 to 60% by weight, particularly 20 to 50% by weight, the hydroxyl group-containing polymerizable monomer is 0 to 50% by weight, and particularly 10 to 4% by weight.
0% by weight, other polymerizable monomers are 40 to 90% by weight,
Particularly, 50 to 80% by weight is preferable. And (B-S
The number average molecular weight of i) is preferably 2,000 to 15,000.

The blending amount of the vinyl polymer (B-Si) in the composition (B-1) is 100 parts by weight of the total solids of the component (B-1a) and the component (B-1b). B-
In 2), 25 to 65 parts by weight is preferable per 100 parts by weight of the solid content of the component (B-2a).

The clear coating composition (B) can be prepared by mixing and dispersing the above components in an organic solvent for coating, and the solid content is preferably 30 to 80% by weight at the time of coating. Various organic solvents for paints can be used as the solvent, for example, aromatic, alicyclic or aliphatic hydrocarbon solvents,
Examples thereof include alcohol solvents, ester solvents, ketone solvents, ether solvents and the like. The clear paint (B) may further contain additives for paints such as fine particles of non-aqueous polymer, melamine resin, blocked isocyanate, curing catalyst, ultraviolet absorber, antioxidant, surface modifier, defoaming agent and the like. Can be blended.

In the method for forming a topcoat coating film of the present invention, an aqueous colored base coating composition (A) is applied to an object to be coated and then heat-cured, and then an organic solvent-based clear coating composition (B) is applied and then heat-cured. 2 coat 1 bake method or 2 coat 1 bake method in which the clear coating composition (B) is applied without curing after coating the base coating composition (A), and then both coating films are simultaneously heat-cured. It is preferably carried out according to the method.

As the article to which the method of the present invention is applied,
An automobile outer panel, etc., which is formed by applying an undercoat paint such as a cationic electrodeposition paint and an intermediate paint (optional) and curing by heating,
Preferred are mentioned.

Specifically, the above-mentioned article to be coated is coated with the aqueous colored base coating composition (A) by a coating method such as an electrostatic method or a spray method so that the film thickness based on the cured coating film becomes 10 to 50 μm. On the coated surface of the base coating composition (A) without being cured by heating or with heat.
By a coating method such as an electrostatic method or a spray method so that the film thickness based on the cured coating film is 20 to 80 μm, and only the clear coating film or both the base coating film and the clear coating film are coated. Heat cure. Here, the heat curing of these coating films,
Usually, a condition of heating at a temperature of about 100 to 160 ° C. for about 10 to 60 minutes is suitable.

[0099]

EXAMPLES Hereinafter, Production Examples, Examples and Comparative Examples will be given,
The present invention will be described more specifically. Parts and% in each example are based on weight.

Production Example 1 Production of Acrylic Resin Containing Hydroxyl Group and Carboxyl Group (A-1) 50 parts of butyl cellosolve were placed in a reaction vessel, and 10 parts of styrene as a monomer and 25 parts of methyl methacrylate were added.
Parts, n-butyl methacrylate 20 parts, n-butyl acrylate 25 parts, hydroxyethyl methacrylate 15
Parts, 5 parts of acrylic acid, and 6 parts of azoisobutyronitrile as a radical polymerization initiator, and polymerized at 120 ° C. for 3 hours to contain the solid content of the hydroxyl group- and carboxyl group-containing acrylic resin of the component (A-1). A 65% solution was obtained. The hydroxyl value of the resin is 65 mgKOH / g, the acid value is 40 mgKOH / g,
The number average molecular weight was 12,000.

This resin solution was neutralized with dimethylethanolamine [component (A-4)] to an equivalent amount of the carboxyl group of the resin, and then 100 parts of water was added to obtain (A-1)-.

Production Example 2 Production of Aqueous Colored Base Coating Composition (A) The components (A-1) and (A-4) are Production Example 1
The (A-1) -obtained in 1. was used.

As the component (A-2), "Cymel 37
0 ”[(A-2)-] (trade name, manufactured by Cytec, methylol group / methyl ether group mixed melamine resin, number average molecular weight 600) was used.

As the component (A-3), a lactone-modified epoxidized tetrabenzyl alcohol [(A-3)-] in which m is 5 and n is 1.5 in the above formula (2), “Ceroxide 2021” is used. [(A-3)-] (manufactured by Daicel Chemical Industries, Ltd., trade name, structure

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), "ERC-4299" [(A-3)-
] (Product name, structure, manufactured by Union Carbide

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), "Eporide GT-300" [(A-
3)-] (manufactured by Daicel Chemical Industries, Ltd., trade name, structure

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)) Or "EHPE3150" [(A-
3)-] (trade name, manufactured by Daicel Chemical Industries, Ltd., epoxidized polyvinyl cyclohexene oxide (1 of epoxy group)
Carbon atoms and one of the carbon atoms forming the cyclohexene ring are bonded together), the number average molecular weight is about 1,
500, for comparative example) was used.

As the metallic pigment, "aluminum paste N-519" (trade name, aluminum flake pigment manufactured by Toyo Aluminum Industry Co., Ltd.) was used.

The above components were mixed in water according to the formulation shown in Table 1 below to prepare water-based colored (metallic) base coating compositions (A)-(1) to (A)-(4) for Examples and a comparison. Aqueous pigmented (metallic) base coating composition (A)-(5) -for example
(A)-(6) was prepared. The solids content of the paint was 22% by weight and the viscosity was 40 at Ford Cup # 4/20 ° C.
Adjusted to seconds.

The storage stability of each coating composition obtained above was examined by the following test method.

Storage Stability Test Each coating composition was treated with Ford Cup # 4/2 in deionized water.
Dilute to a viscosity of 30 seconds at 0 ° C, put 300g in a beaker, lightly cover with aluminum foil, store at 40 ° C for 2 weeks, and measure the viscosity (Ford cup # 4/20 ° C). The storage stability was evaluated by examining the degree of thickening.
The evaluation criteria are as follows.

A shows that the storage stability is good when the viscosity is within 50 seconds, B shows that the storage stability is slightly inferior when the viscosity is within 70 seconds, and C shows that the storage stability is inferior when the viscosity is 70 seconds or more. , Respectively.

The results of the storage stability test are also shown in Table 1 below.

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[Table 1]

The numerical values of the compounding amounts in Table 1 above are parts by weight of solid content.

Production Example 3 Carboxyl group-containing resin (B-
Production of 1a) A 5 liter glass flask equipped with a stirrer, a thermometer, and a cooling tube was charged with 553 parts of xylene and 276 parts of 3-methoxybutyl acetate, and heated to 125 with an electric heating mantle.
The mixture was heated to 0 ° C., and at that temperature, a mixture having the following monomer composition was added dropwise uniformly over 4 hours. Incidentally, p-tert-butylperoxy-2-ethylhexanoate is a polymerization initiator.

Methanol half ester of maleic anhydride 288 parts (20%) 4-hydroxy n-butyl acrylate 288 parts (20%) n-butyl acrylate 576 parts (40%) Styrene 288 parts (20%) p-tert -Butylperoxy-2-ethylhexanoate 72 parts.

Then, after aging for 30 minutes, further 3-
A mixture of 277 parts of methoxybutyl acetate and 14.4 parts of p-tert-butylperoxy-2-ethylhexanoate was added dropwise over 2 hours and then aged for 2 hours to give a carboxyl group having a final polymerization rate of 98%. A solution of the contained vinyl resin (B-1a) -was obtained.

The polymer solid content of the obtained polymer liquid was 55.
%, Gardner viscosity (25 ° C.) M. The number average molecular weight of this polymer was 3,500. The acid value of this polymer was 86 mgKOH / g and the hydroxyl value was 78 mgKOH / g.

Production Example 4 Carboxyl group-containing resin (B-
Production of 1a) A solution of a carboxyl group-containing vinyl resin (B-1a)-having a final polymerization rate of 95% was obtained in the same manner as in Production Example 3, except that only the monomer composition was changed as follows. It was

Methanol half ester of maleic anhydride 288 parts (20%) 2-hydroxyethyl acrylate 230 parts (16%) n-butyl acrylate 634 parts (44%) Styrene 288 parts (20%) p-tert-butyl 72 parts of peroxy-2-ethylhexanoate.

The polymer solid content of the obtained polymer liquid was 55.
%, Gardner viscosity (25 ° C.) was O. The number average molecular weight of this polymer was 3,500. The acid value of this polymer was 86 mgKOH / g and the hydroxyl value was 78 mgKOH / g.

Production Example 5 Epoxy group-containing resin (B-1
Production of b) In a 5 liter glass flask equipped with a stirrer, a thermometer and a condenser, 580 parts of xylene and 2 parts of n-butanol were added.
Charge 50 parts, heat to 125 ° C with an electric heating mantle,
At that temperature, the mixture of the following monomer compositions was added dropwise uniformly over 4 hours. Azobisisobutyronitrile is a polymerization initiator.

Glycidyl methacrylate 432 parts (30%) 4-hydroxy n-butyl acrylate 288 parts (20%) n-butyl acrylate 432 parts (30%) Styrene 288 parts (20%) Azobisisobutyronitrile 72 parts .

Then, after aging for 30 minutes, a mixture of 90 parts of xylene, 40 parts of n-butanol and 14.4 parts of azobisisobutyronitrile was added dropwise over 2 hours and then aging for 2 hours. A solution of an epoxy group-containing vinyl resin (B-1b)-having a final polymerization rate of 100% was obtained.

The polymer solid content of the obtained polymer liquid was 60.
% And Gardner viscosity (25 ° C.) S. The number average molecular weight of this polymer was 3,000. The epoxy group content of this polymer was 2.12 mmol / g, and the hydroxyl value was 78 mgKOH / g.

Production Example 6 Production of Hydrolyzable Silyl Group-Containing Vinyl Polymer (B-Si) Final Production Rate in the same manner as in Production Example 5 except that only the monomer composition was changed as follows. 99% hydrolyzable silyl group-containing vinyl polymer (B-Si)-
Was obtained.

Γ-methacryloxypropyltriethoxysilane 288 parts (20%) 2-hydroxy n-propyl acrylate 288 parts (20%) n-butyl methacrylate 576 parts (40%) styrene 288 parts (20%).

The polymer solid content of the obtained polymer liquid was 60.
%, Gardner viscosity (25 ° C.) U. The number average molecular weight of this polymer was 4,000. The hydroxyl value of this polymer was 86 mgKOH / g.

Production Example 7 Production of Organic Solvent-based Clear Coating Composition (B) After preparing a mixed solution of each component with the composition (solid content) shown in Table 2 below, an equivalent mixture of tetrabutylammonium bromide and monobutylphosphoric acid was prepared. 2 parts (curing catalyst), 1 part of "Tinuvin 900" (trade name, manufactured by Ciba-Geigy, UV absorber) and 0.1 part of "BYK-300" (brand name, manufactured by Big Chemie, surface conditioner) "Swasol 1
000 ”(trade name, manufactured by Cosmo Oil Co., Ltd., hydrocarbon solvent), and the viscosity is 25 seconds (Ford Cup # 4/20.
(° C), and an organic solvent-based clear coating composition (B)
-(1) to (B)-(4) were prepared. The results of measuring the solid content at the time of coating are also shown in Table 2.

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[Table 2]

Examples 1 to 4 and Comparative Examples 1 and 2 The aqueous colored base coating composition (A) obtained in the above Production Example 2 and the organic solvent-based clear coating composition (B) obtained in the Production Example 7.
By using the 2 coat 1 bake method,
It was formed as follows.

Thickness 0.8 m after zinc phosphate conversion treatment
m on a dull steel plate, electrodeposited an epoxy-based cationic electrodeposition paint so as to have a dry film thickness of about 20 μm.
After baking for a minute, sharpen with # 400 sandpaper,
After degreased by wiping with petroleum benzine, air spray coating was applied to an automotive intermediate coating surfacer to a dry film thickness of about 25 μm and baked at 140 ° C. for 30 minutes.
The sample was sanded with 400 sandpaper, drained and dried, and then degreased by wiping with petroleum benzene to obtain a test object.

Then, the above-mentioned aqueous colored (metallic) base coating composition (A) was applied onto the coated object in a cured film thickness of 20 μm.
m, and allowed to stand at room temperature for 5 minutes, then the organic solvent-based clear coating composition (B) was coated on the coated surface so that the cured film thickness was 40 μm, and heated at 140 ° C. for 30 minutes. Then, both coating films were cured to form a top coating film.

The multi-layer top coating film thus obtained was examined for coating film performance by the following test method.

Chipping resistance test Using a "Q-G-R gravelometer" (manufactured by Q-Panel, trade name) as a test device, about 500 ml of crushed stone having a diameter of about 15 to 20 mm and about 4 kg / cm ² of air are used. After the pressure was applied to the test plate at an angle of 45 ° under a temperature condition of about 20 ° C. to impact the coating film, the state of the coated surface was visually observed and evaluated according to the following criteria.

⊚: Slight scratches are observed on a part of the top coat film, peeling of the electrodeposition coat film is not observed at all, and chipping resistance is good.

◯: Scratches due to impact were observed in the top coating film and the intermediate coating film, and peeling of the electrodeposition coating film was slightly observed, and chipping resistance was slightly poor.

X: Many scratches due to impact were observed on the top coating film and the intermediate coating film, and peeling of the electrodeposition coating film was considerably observed, resulting in poor chipping resistance.

Interlayer adhesion test With a cutter knife so as to reach the substrate (dull steel plate), 11 parallel and 11 vertical and horizontal parallel lines were drawn at a distance of 1 mm in the center of the coating film of the test plate to form a 1 cm ² area. To make 100 squares, make cuts and scratches in the shape of a gobo, stick adhesive cellophane tape on the coated surface, and after peeling it off sharply, the painted surface of the goban is based on the following criteria. Evaluated.

◯: Peeling of the coating film is not observed at all, Δ: Peeling is slightly observed between the metallic base coating film and the clear coating film, ×: Delamination between the metallic base coating film and the clear coating film is observed. Many are recognized.

Water Resistance Test A test plate was immersed in warm water at 40 ° C. for 240 hours, washed with water, and the coated surface was visually observed, and evaluated based on the following criteria.

◯: No particular abnormality is observed, Δ: Slight glossiness is observed, X: Whitening of the coated surface is observed.

Acid resistance test A test coated plate was immersed 1/2 in a 40% sulfuric acid solution, and the test plate was subjected to 5 ° C at 50 ° C.
After leaving it for a period of time, it was washed with water and the coated surface was visually observed. The evaluation criteria are as follows.

◯: No particular abnormality was observed, Δ: There was no abnormality on the coated surface, but a slight step was observed at the boundary between the immersed portion and the non-immersed portion, ×: The coated surface was observed to be white. To be

Weather resistance test The coating film after being exposed to a sunshine weather meter for 1000 hours was visually observed. The evaluation criteria are as follows.

◯: No particular abnormality was observed, Δ: small cracks occurred a little, ×: cracks occurred.

Scratch resistance test A car with a test coated plate attached to the roof was washed with a car washer 15
The state of the coated surface of the coated plate after the car was washed was observed. As the car wash machine, "PO 20FWRC" manufactured by Yasui Sangyo Co., Ltd. was used.
The evaluation criteria are as follows.

◯: Almost no scratches are found by visual observation, Δ: Slight scratches are seen, but the degree thereof is very slight, ×: Scratches are noticeable by visual observation.

Gloss test According to JIS K-5400 7.6 (1990) 20 degree mirror surface glossiness, the degree of gloss of the coating film was measured by measuring the reflectance when the incident angle and the light receiving angle were 20 degrees, and the mirror surface was obtained. The glossiness is expressed as a percentage when the glossiness of the reference surface is 100.

The results of each test are shown in Table 3.

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[Table 3]

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【The invention's effect】

(1) A multi-layer top coating film consisting of a colored base coating film and a clear coating film having good acid resistance, chipping resistance, interlayer adhesion, water resistance and weather resistance, etc. Can be formed.

(2) In particular, the epoxy group of the alicyclic epoxy group-containing compound (A-3) in the aqueous colored base coating composition (A) used in the method of the present invention is a hydroxyl group- and carboxyl group-containing acrylic resin (A). -1) Crosslinking reaction with a carboxyl group introduced for water-solubilization in to improve coating strength such as chipping resistance, and at the same time, free carboxyl groups as hydrophilic groups in the coating are reduced, so that water resistance and The acid resistance is improved. The component (A-3) is
Since it is stable in water, there is an advantage that thickening, sedimentation and the like do not occur during storage of the composition (A).

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B05D 5/06 B05D 5/06 CG 7/24 301 7/24 301F 301R 302 302P 302S 302U C08G 59 / 42 NHY C08G 59/42 NHY C09D 163/00 PKC C09D 163/00 PKC (72) Inventor Mikio Shimakawa 4-17-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd.

Claims (5)

[Claims] 1. An acrylic resin (A-1) containing a hydroxyl group and a carboxyl group, a melamine resin (A-2), an alicyclic epoxy group-containing compound (A-3) and a neutralizing agent (A-
4) and an aqueous colored base coating composition (A) containing a coloring pigment (A-5) as a main component, and then an organic solvent-based clear coating composition which is cured by a crosslinking reaction between a carboxyl group and an epoxy group on the coated surface. A method for forming a topcoat coating film, which comprises coating the composition (B). 2. A two-coat, two-bake system in which the base coating composition (A) is heated and cured after coating, and then the clear coating composition (B) is cured by heating, or the base coating composition (A). The coating film forming method according to claim 1, wherein the clear coating composition (B) is coated without curing after coating, and then the coating composition is coated by a two-coat-one-bake method in which both coating films are simultaneously heated and cured. 3. In the base coating composition (A), (A
-1) The component (A-2) is 20 per 100 parts by weight of the component.
˜60 parts by weight, 0.5 to 15 parts by weight of the component (A-3),
The coating film forming method according to claim 1, wherein the component (A-4) and the component (A-4) are blended in an amount of 0.2 to 1.5 equivalents based on the carboxyl group of the component (A-1). 4. The clear coating composition (B) comprises a carboxyl group-containing resin (B-1a) and an epoxy group-containing resin (B).
-1b) as a main component, a clear coating composition (B-1) or a resin (B-2a) in which a carboxyl group and an epoxy group coexist in the same molecule as a main component The coating film forming method according to claim 1, which is (B-2). 5. The clear coating composition (B-1) or (B
The method for forming a coating film according to claim 4, wherein the vinyl polymer (B-Si) having a hydrolyzable silyl group or a hydroxyl group and a hydroxyl group in one molecule is further added to -2).