JPH10140077A - Automotive top coating material and formation of coating film using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject material capable of forming a coating film excellent in fouling, acid and weather resistances, etc., by compounding an curable resin of an acid epoxy curable type coating material and a low condensate such as tetramethyl silicate. SOLUTION: This composition is obtained by compounding 100 pts.wt. curable resin of an acid epoxy curable type coating material prepared by compounding an epoxy group- and hydroxyl group-containing acrylic copolymer with a carboxyl group-containing compound with 0.1-50 pts.wt. low condensate of tetramethyl silicate and/or tetraethyl silicate having 2-10 degree of condensation. The surface of an automotive outside plate is coated with a colored base coat as a top coating material and subsequently coated with a clear top coating material prepared therefrom in an uncured state thereof and the colored base coat and the clear top coat are then simultaneously baked and cured according to a two-coat and one-bake method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel automotive top coating and a method for forming a coating film using the same, and more particularly, to a coating film having excellent stain resistance, acid resistance, weather resistance and the like. The present invention relates to an automotive top coating and a method for forming a coating film thereof.

[0002]

2. Description of the Related Art Conventionally, air pollution has progressed, and damage caused by acid rain such as forest withering has become a serious social problem. However, it has been applied to articles used outdoors such as automobile outer panels. Also in the coating film, there are problems that the coating film is etched, and that the coating film is whitened, stained, and the like.

[0003] A melamine-curable coating is generally used as a coating for automobile outer panels, and a coating film formed from the melamine-curable coating is subjected to a hydrolysis reaction by an acid to form a melamine resin crosslinked portion. It becomes water soluble and the coating deteriorates. When contaminants such as smoke adhere to such a poorly acid-resistant coating film, there is a problem that dirt is hardly removed and the coating film appearance is extremely deteriorated.

[0004] Acid epoxy-curable paints have been developed as non-melamine-curable paints that form coatings having excellent acid resistance. However, as with melamine-curable paints, these stains are difficult to remove once they adhere. There was a problem.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, by adding a specific silicone compound to an acid epoxy-curable coating composition, an automobile has been developed. The present inventors have found that a contaminant adhered to the outer plate is washed away by rain or the like, and that a car wash-free coating film having excellent stain resistance can be provided without the need for removal work using wax or the like, and the present invention has been completed.

That is, the present invention provides: 0.1 to 50 low-condensates of tetramethyl silicate and / or tetraethyl silicate having a degree of condensation of 2 to 10 are added to 100 parts by weight of the curable resin of the acid epoxy-curable coating.
1. An automotive topcoat paint characterized by being blended in parts by weight. 2. The automotive topcoat paint according to 1 above, wherein the acid epoxy curable paint is obtained by blending a carboxyl group-containing compound with an epoxy group- and hydroxyl group-containing acrylic copolymer. 3. The automotive topcoat paint according to 1 or 2 above, wherein the acid epoxy-curable coating composition is obtained by blending a carboxyl group-containing compound with an acrylic copolymer containing an epoxy group, a hydroxyl group and a hydrolyzable alkoxysilyl group. After a colored base coat is applied as a top coat on the surface of an automobile outer panel, the degree of condensation of tetramethyl silicate and / or tetraethyl silicate with respect to 100 parts by weight of the curable resin of the acid-epoxy-curable paint in an uncured state is 2 Coating a clear top coat comprising 0.1 to 50 parts by weight of a low condensate of 10 to 10 and then simultaneously baking and curing the colored base coat and the clear top coat in a two-coat one-bake method 4. forming method; After applying a colored base coat as a top coat on the outer surface of the automobile, applying a first clear coat in a state where the colored base coat is uncured, then simultaneously baking and curing the colored base coat and the first clear coat, and then curing with an acid epoxy. A second clear top coat was prepared by blending 0.1 to 50 parts by weight of a low-condensation product having a degree of condensation of 2 to 10 of tetramethyl silicate and / or tetraethyl silicate with respect to 100 parts by weight of the curable resin of the mold paint. Thereafter, the present invention relates to a coating film forming method characterized by baking.

The acid-epoxy-curable paint used in the present invention is obtained by blending an epoxy group- and hydroxyl group-containing acrylic copolymer as a base resin with a carboxyl group-containing compound as a curing agent. Is preferred. Further, the acrylic copolymer may contain a functional group such as a hydrolyzable alkoxysilyl group.

The epoxy- and hydroxyl-containing acrylic copolymers include, for example, epoxy-containing acrylic monomers such as glycidyl (meth) acrylate, hydroxyl-containing radically polymerizable unsaturated monomers, and other radical polymerizable if necessary. Copolymers obtained by subjecting unsaturated monomers to a radical copolymerization reaction are exemplified.

Examples of the hydroxyl group-containing radical polymerizable unsaturated monomer include 2-hydroxyethyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, and caprolactone-modified hydroxyethyl. .

As other radically polymerizable unsaturated monomers, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl ( Alkyl or cycloalkyl esters of acrylic acid such as meth) acrylate, stearyl (meth) acrylate, perfluorobutylethyl (meth) acrylate, perfluoroisononylethyl (meth) acrylate, and cyclohexyl (meth) acrylate; fragrance such as styrene Group compounds; γ
Hydrolyzable alkoxy such as-(meth) acryloyloxypropyltrimethoxysilane, γ- (meth) acryloyloxypropyltriethoxysilane, γ- (meth) acryloyloxypropylmethyldimethoxysilane, vinyltrimethoxysilane, vinylmethyldimethoxysilane Examples include silyl group-containing acrylic monomers. These unsaturated monomers can be used alone or in combination of two or more.

The acrylic copolymer containing epoxy groups and hydroxyl groups has an epoxy group content of 0.5 to 5.0 mmol / g, particularly 0.8 to 2.5 mmol / g, and a hydroxyl group content of 10 to 10 mmol / g. 200 mgKOH / g, especially 30-120 mgKOH / g
Is preferable. When a hydrolyzable alkoxysilyl group is contained in the copolymer, the functional group may be added in an amount of 0.1.
The range is preferably 1 to 5.0 mmol / g, particularly preferably 1.0 to 3.0 mmol / g.

When the epoxy group content of the epoxy group- and hydroxyl group-containing acrylic copolymer is less than 0.5 mmol / g, the curability of the resulting composition is reduced and the acid resistance and scratch resistance of the coating film are reduced. , The stain resistance tends to decrease,
Further, when the epoxy group content is more than 5.0 mmol / g, the stain resistance tends to decrease, and thus both are not preferred.

When the hydroxyl value of the acrylic copolymer containing an epoxy group and a hydroxyl group is less than 10 mgKOH / g, the curability of the resulting composition is lowered and the acid resistance of the coating film is reduced.
Both abrasion resistance and stain resistance tend to decrease, and when the hydroxyl value is more than 200 mgKOH / g, the water resistance of the coating film tends to decrease.

When a hydrolyzable alkoxysilyl group is contained in the acrylic copolymer containing an epoxy group and a hydroxyl group, the functional group is used in an amount of 0.1 to 5.0 mmol / g, particularly 1.0 to 3.0 mmol / g. 0 mmol / g is preferred.

When the content of the hydrolyzable alkoxysilyl group in the copolymer is less than 0.1 mmol / g, the curability of the resulting composition is reduced, and the acid resistance and scratch resistance of the coating film are reduced. When the content of the hydrolyzable alkoxysilyl group is more than 5.0 mmol / g, the cost increases, and neither is preferred.

The epoxy group- and hydroxyl group-containing copolymer preferably has a number average molecular weight of 2,000 to 10,000. If the number average molecular weight is less than 2,000, the weather resistance and durability of the stain resistance of the cured coating film tend to decrease, and if it exceeds 10,000, the stain resistance tends to decrease.

As the carboxyl group-containing compound, those having an acid value in the range of 50 to 500 mgKOH / g, particularly 80 to 300 mgKOH / g can be used. Acid value is 50mgKOH /
If it is smaller than g, the curability tends to decrease, and the acid resistance and stain resistance of the coating film tend to decrease.
If it exceeds 0 mgKOH / g, the water resistance, weather resistance,
This is not preferable because the durability of the stain resistance tends to decrease.

As the carboxyl group-containing compound, a conventionally known compound can be used without any particular limitation as long as the above conditions are satisfied. Specifically, for example, a maleic anhydride, an acid anhydride group-containing vinyl monomer such as itaconic anhydride half-esterified with a low molecular weight monoalcohol such as methanol or ethanol, or a half-esterified non-esterified monomer as required. Obtained by a radical polymerization reaction with a radically polymerizable unsaturated monomer (e.g., the same alkyl or cycloalkyl esters of acrylic acid, aromatic compounds, etc. as described above), provided that the monomer is not half-esterified. Half-ester polymer obtained by subjecting the obtained polymer to half-esterification with a low-molecular-weight monoalcohol; a C2-10 polyol component such as ethylene glycol, propanediol, pentanediol, neopentyl glycol, and trimethylolpropane; and succinic acid Anhydride, maleic anhydride , Phthalic anhydride, tetrahydrophthalic acid anhydride, half ester and a carboxyl group-containing polyester resin with the acid anhydride component of C2-20 such as hexahydrophthalic acid anhydride.

In the acid-epoxy-curable coating material used in the present invention, the epoxy resin and the hydroxyl-containing acrylic resin, and the carboxyl group-containing compound are organic solvents (for example, aromatic resins such as toluene and xylene, and ester resins such as butyl acetate). And ketones such as methyl ethyl ketone and methyl isobutyl ketone, and alcohols such as propyl alcohol and butanol) dissolved or dispersed in an organic solvent-based coating composition. Resin solid part of paint (when spraying)
Is usually in the range of 30 to 80% by weight, especially 40 to 75% by weight.

The acid-epoxy curable paint used in the present invention may contain, if necessary, a curing catalyst, a coloring pigment, an extender pigment, an ultraviolet absorber, an antioxidant, a surface conditioner, and polymer fine particles. Can be. Further, if necessary, a curing agent such as a melamine resin other than the carboxyl group-containing compound and a blocked polyisocyanate compound can be used in combination with the carboxyl group-containing compound.

The low condensate of tetramethyl silicate and / or tetraethyl silicate used in the present invention having a degree of condensation of 2 to 10 (hereinafter, these are abbreviated as "silicate low condensate") are tetramethyl silicate or tetraethyl silicate. It may be a single low-condensate of a silicate or a co-low condensate of a combination thereof. When the number of carbon atoms of the alkoxyl group bonded to silicon is 3 or more, the compatibility with the acid-epoxy-curable coating material is improved, so that the silicate component is hardly separated on the surface of the coating film and the stain resistance cannot be exhibited. If the degree of condensation of the low-condensate is less than 2, the stain resistance becomes poor. On the other hand, if it exceeds 10, the viscosity of the silicate component becomes high, so that it is difficult to separate on the coating film surface, and the stain resistance becomes poor.

The compounding ratio of the low silicate condensate is preferably about 0.1 to 50 parts by weight, more preferably about 1 to 20 parts by weight, based on 100 parts by weight of the resin solid content of the acid-epoxy curable coating. If the compounding ratio of the low silicate condensate is less than about 0.1 part by weight, the stain resistance of the coating film tends to be inferior. On the other hand, if it exceeds about 50 parts by weight, defects such as cracking and gloss reduction may occur. Is not preferred.

The automotive top coating composition of the present invention can be applied to an automobile outer panel and then heated to form a cured coating. When the formed cured coating film is exposed outdoors, the contaminants attached to the coating film surface are washed out by gradually decreasing the contact angle of the coating film surface with water due to acid components such as acid rain. This can prevent the coating film surface from being stained.

Before the coating film is exposed to the outdoors, it is treated with an acid (for example, about 5 to 98% in an acidic aqueous solution having a pH of 6 or less).
° C). By treating with an acid, it is possible to prevent stains on the coating film surface from an early stage.

In the present invention, the reason why the effect of excellent stain resistance is exhibited without deteriorating the finished appearance and performance as a top coating for automobiles is considered as follows. When a coating material obtained by mixing a highly polar acid-epoxy curable resin component and a low-polarity silicate low-condensate is applied to a substrate, the low-polarity silicate low-condensate component separates on the coating film surface and the low-condensate A wet coating film containing many components near the coating film surface is formed. Then, when the coating film is heated, the silicate low-condensate is converted into an acid component (curing agent) of the acid epoxy-curable resin at the interface (mixed layer) between the acid epoxy-curable resin and the silicate low-condensate inside the coating film. It is presumed that the finish and performance suitable for a coating film for automobiles were obtained because a strong coating film was formed by hydrolysis and condensation simultaneously with the hydroxyl group in the resin at the same time as the hydrolysis and condensation by the catalytic action of.

With respect to the coating method of applying the automotive top coating composition of the present invention to an automobile outer panel, particularly preferred two-coat one-bake system and three-coat two-bake system will be described.

As the automobile outer panel used in the above-described coating method, a conventionally known automobile outer panel can be used. Specifically, iron, steel, aluminum, zinc, stainless steel, galvanized steel sheets, and chromic acid,
Metallic substrates such as those that have been surface-treated with zinc phosphate or the like are subjected to primer coating such as (cationic) electrodeposition primer coating and intermediate coating, and the like.

Two-coat, one-bake method: After coating a colored base coat on the outer surface of an automobile in which the above-mentioned metal base material has been coated with a base coat, the automobile top coat paint of the present invention is cleared in a state where the colored base coat is uncured. It can be carried out by applying as a top coat and then heating and simultaneously baking and curing the colored base coat and the clear top coat.

The colored base coat is formed by mixing a thermosetting resin with a metallic pigment (for example, flaky aluminum powder, copper powder, nickel powder, stainless steel powder, colored mica powder, etc.) and, if necessary, a colored pigment. Alternatively, an organic solvent type paint can be used. The amount of the metallic pigment varies depending on the type and shape of the pigment, but it is generally considered that a range of about 1 to 50 parts by weight per 100 parts by weight of the resin solid content is sufficient.

As the thermosetting resin used in the colored base coat, in particular, a melamine resin is blended with a hydroxyl group-containing resin. It is preferable to use this. Examples of the hydroxyl group-containing resin include a hydroxyl group-containing acrylic resin, a hydroxyl group-containing polyester resin, and a hydroxyl group-containing alkyd resin. The hydroxyl group-containing resin has a hydroxyl value of 20 to 200 mg KOH /
g, especially 25 to 180 mg KOH / g.

The hydroxyl group-containing acrylic resin includes:
Those having a hydroxyl group in the skeleton can be used, and can be obtained by copolymerizing a polymerizable unsaturated monomer having a hydroxyl group and another monomer copolymerizable with this monomer. Examples of the hydroxyl group-containing unsaturated monomer include hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxyethyl vinyl ether, ω-hydroxybutyl vinyl ether, and the like. As the carboxyl group-containing unsaturated monomer, acrylic acid, methacrylic acid , Itaconic acid, maleic acid and the like.
Other monomers copolymerized with these monomers include alkyl esters of acrylic acid or methacrylic acid; alkyl vinyl ethers such as ethyl vinyl ether and butyl vinyl ether; styrene, vinyl toluene, vinyl acetate, and acrylonitrile. The acrylic resin has a number average molecular weight of 2,000 to 1
A range of 00,000 is preferred.

The hydroxyl group-containing polyester resin is mainly an esterified product of a polybasic acid and a polyhydric alcohol. Examples of the polybasic acid include phthalic anhydride, isophthalic acid, terephthalic acid, succinic acid, adipic acid, fumaric acid, and the like. One or more dibasic acids selected from maleic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride and the like are mainly used, and if necessary, one or more dibasic acids such as benzoic acid, crotonic acid, p-tertbutylbenzoic acid, etc. Tribasic or higher polybasic acids such as basic acid, trimellitic anhydride, methylcyclohexentricarboxylic acid, and pyromellitic anhydride are used. Examples of polyhydric alcohols include ethylene glycol, propylene glycol, diethylene glycol, butanediol, and neopentyl glycol. , Cyclohexanedimethanol, 1,6-hexanediol and the like The alcohol is mainly used, and if necessary, a trihydric or higher polyhydric alcohol such as glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol may be used in combination. The esterification reaction of both components can be performed by a known method at a mixing ratio in which the number of hydroxyl groups is excessive with respect to the number of acid groups.

The hydroxyl group-containing alkyd resin is obtained by reacting the above oil-free polyester resin with an oil fatty acid. Examples of the oil fatty acid include coconut oil fatty acid,
Soybean oil fatty acids, linseed oil fatty acids, safflower oil fatty acids,
Examples include tall oil fatty acids, dehydrated castor oil fatty acids, tung oil fatty acids, and the like. The reaction between the polyester resin and the oil fatty acids can be performed by a known method, and the oil length is preferably 30% or less.

The above-mentioned hydroxyl group-containing polyester resin and hydroxyl group-containing alkyd resin have a number average molecular weight of 1,000-1.
Those in the range of 000 are preferred.

The melamine resin is a cross-linking agent compounded for cross-linking with the hydroxyl group-containing resin, and specifically, a methylolated or C1-5 alkyl etherified one can be used.

The mixing ratio of the hydroxyl group-containing resin and the melamine resin is in the range of 50 to 90% by weight, preferably 55 to 80% by weight, based on the total weight of both, 100% by weight. The range is preferably from 50 to 50% by weight, more preferably from 20 to 45% by weight.

The coating of the colored base coat and the clear top coat can be performed by spray coating. The coating amount (cured film thickness) of the colored base coat is generally in the range of about 10 to 50 μm, especially about 15 to 40 μm, and the coated amount (cured film thickness) of the clear top coat is generally About 20 to 100 μm, especially about 25 to
A range of 80 μm is preferred.

The baking of the colored base coat and the clear top coat is performed at a baking temperature of about 130 to 200 ° C. for about 10 minutes.
Preferred is a range of ６０60 minutes, preferably about 20-40 minutes.

Three-coat two-bake method: After coating a colored base coat on the surface of an automobile outer panel in which the above-mentioned metal base material is coated with a base coat, a first clear coat is applied in a state where the colored base coat is uncured. Next, the colored base coat and the first clear coat are heated and baked and cured at the same time, and then the automotive top coating composition of the present invention is further applied as a second clear top coat and then baked and cured. As the colored base coat, the same base coat as used in two coats and one bake can be used. As the first clear top coat, a colored base coat which does not contain any metallic pigment or which contains metallic pigment to such an extent that the coating film is not completely hidden can be used. For the first clear coat, the melamine-curable paint or the acid epoxy-curable paint can be used.

Coating Method of Colored Base Coat and First Clear Coat The coating film thickness and baking conditions can be performed under the same conditions as described in the two-coat one-bake method. The second clear top coat is spray-coated to a thickness (cured) of about 10
80 μm, preferably in the range of about 20 to 70 μm,
30 to 200 ° C. for about 10 to 60 minutes, preferably about 20
The coating film can be formed by baking for a period of up to 40 minutes.

[0041]

【Example】

Preparation of Acid-Epoxy-Curable Coating Material Preparation Example of Acid-Epoxy-Curable Coating Material I Epoxy- and hydroxyl-containing acrylic copolymer solution (glycidyl methacrylate / 2-hydroxyethyl acrylate / n-butyl acrylate / γ-methacryloxypropyl triacrylate) Methoxysilane / styrene = 35/1
5/15/15/20 wt% copolymer, number average molecular weight 2,000, solid content 70 wt% xylene solution, epoxy group content 2.12 mmol / g, hydroxyl value 78 mgKOH /
g) 96 g of a carboxyl group-containing compound solution (methanol half-esterified maleic anhydride / acrylic acid 2)
-Hydroxyethyl / n-butyl acrylate / styrene = 20/20/40/20% by weight, number average molecular weight 3,
500, solid content 55% by weight, acid value 86mgKOH / g) 60g
Was blended to obtain Paint I.

Preparation Example of Acid Epoxy-Curable Paint II In the paint I, an acrylic copolymer solution containing an epoxy group and a hydroxyl group was prepared as glycidyl methacrylate / 2-hydroxyethyl acrylate / n-butyl acrylate / methyl methacrylate / styrene = 35/15. / 15
/ 15/20 wt% copolymer, number average molecular weight 2,000
Paint II was obtained in the same manner as Paint I except that a xylene solution having a solid content of 70% by weight, an epoxy group content of 2.12 mmol / g, and a hydroxyl value of 78 mgKOH / g was used.

Examples 1 to 4 and Comparative Examples 1 and 2 After mixing the paint and the silicate low-condensate in the composition (solid content) shown in Table 1, 1 g of tetrabutylammonium bromide was added to 100 g of the resin. Swazole 100
0 (manufactured by Cosmo Oil Co., Ltd .; trade name) and adjusted to a viscosity of 25 seconds (Ford Cup No. 4/20 ° C.)
And the clear top coat of Comparative Examples 1-2 was obtained.

Method for forming a top coat by a two-coat one-bake method (2C1B): An epoxy-based cationic electrodeposition paint was coated on a 0.8 mm-thick dull steel plate subjected to a zinc phosphate chemical conversion treatment to a dry film thickness of about 20 μm. Electrodeposited so that
After baking at 70 ° C. for 20 minutes, sharpen with # 400 sandpaper, wipe off with petroleum benzene and degrease, then apply an air-sprayed automotive middle-coating surfacer to a dry film thickness of about 25 μm. After baking for minutes, the material was sanded with # 400 sandpaper, drained and dried, and then degreased by wiping with petroleum benzene to obtain a test material.

Then, on this material, a colored metallic base coat paint (70 g of a hydroxyl-containing acrylic resin having a hydroxyl value of 72 mgKOH / g and a number average molecular weight of 2,000 (solid content))
20g (solid content) of 30g (solid content) of Cymel 202 (trade name, melamine resin with a solid content of 80% by weight, manufactured by Mitsui Cytec Co., Ltd.) The mixture was diluted with a mixed solvent (toluene / isobutylarylol / cellosolve acetate = 40 g / 30 g / 30 g) to a viscosity of 16 seconds at Ford Cup No. 4/20 ° C.) to give a cured film thickness of 30 μm. After spray-drying at 80 ° C. for 10 minutes, the uncured coating surface was spray-coated with the clear top coat paints of Examples and Comparative Examples to a cured film thickness of 40 μm.
Heating at 30 ° C. for 30 minutes cured both coatings to form a topcoat coating.

Forming method of top coat by 3 coat 2 bake method (3C2B): The same colored metallic base coat paint as above is cured on a surface-coated test material used in 2 coat 1 bake method. Spray-painted to a thickness of 20 μm.
After forced drying for 0 minutes, a first clear coat (acrylic resin * 65 g / cymel 202 *) is applied to the uncured coating film surface.
, 35 g of Ford Cup No. 4/2 with mixed solvent *
Diluted to a viscosity of 25 seconds at 0 ° C. The * marks used were the same as those used for the colored metallic base coat. ) Is spray-coated so as to have a cured film thickness of 20 μm, and heated at 140 ° C. for 30 minutes to cure both coating films. After cooling, the clear top coats of Examples and Comparative Examples are replaced with a second clear top coat. And spray-coated so that the cured film thickness becomes 20 μm.
C. for 30 minutes to form a top coat.

Table 1 shows the appearance and performance of the coating films obtained by the two-coat one-bake and three-coat two-bake systems.

[0048]

[Table 1]

In Table 1, ethyl silicate 40 and ethyl silicate 48 are trade names manufactured by Colcoat Co., Ltd., each having a degree of condensation of 2 to 10 of tetraethoxysilicate.
Is shown.

Coating surface smoothness: The coating surface condition was visually observed and judged according to the following evaluation criteria. ◎ indicates that the smoothness was good without any peeling, unevenness, etc., and x indicates that the smoothness was poor with the peeling, unevenness, etc., respectively.

6. Coating surface reflectance: JIS K-5400
6 (1990). (Reflection angle 60 degrees) Acid resistance: 0.5% of 40% sulfuric acid aqueous solution is dropped on the painted surface,
After heating at 70 ° C. for 20 minutes, it was washed with water and the state of the coated surface was evaluated. There are no abnormalities at all (◎) and abnormalities such as marked gloss and blisters (×).
△, △, × were determined in four stages.

Water contact angle after acid treatment: A test plate was immersed in 2.5% sulfuric acid solution at 20 ° C. for 24 hours, and the attached sulfuric acid solution was washed with water and dried, and then manufactured by Kyowa Chemical Co., Ltd. Using a contact angle meter DCAA, a drop of 0.03 cc of deionized water was dropped on the surface of the coating film, and the value was measured after 3 minutes at 20 ° C.

Outdoor exposure test: A test plate was installed at an angle of 30 degrees on the south side of the Tokyo Plant of Kansai Paint Co., Ltd. Respectively,
The test plate exposed for 3 months and 6 months was evaluated for coating film characteristics without adjusting the sample such as washing with water.

Initial water contact angle: A test plate before outdoor exposure was used as a contact angle meter DCAA manufactured by Kyowa Chemical Co., Ltd.
Using a mold, a drop of 0.03 cc of deionized water was dropped on the surface of the coating film, and the value was measured after 3 minutes at 20 ° C. Appearance (dirt): The degree of dirt on the coated surface was evaluated. And no change in dirt ○ = very slight change in dirt on the coated plate before test ○-= slight dirt change on the coated plate before test △ = coated plate before test ×: a change in stain is observed on the coated plate before the test.

[0055]

According to the present invention, since a specific silicate compound is blended with an acid-curable coating, a coating film excellent in stain resistance which is free from car washing can be obtained.

──────────────────────────────────────────────────の Continued on front page (51) Int.Cl. ⁶ Identification code FI C08G 59/30 C08G 59/30 59/42 59/42 (C08F 220/32 220: 26 220: 18 230: 08)

Claims (5)

[Claims] 1. A curable resin 100 of an acid epoxy curable paint
0.1 parts by weight of a low condensate of tetramethyl silicate and / or tetraethyl silicate having a degree of condensation of 2 to 10 with respect to parts by weight.
1 to 50 parts by weight of an automotive top coating. 2. The automotive top coating according to claim 1, wherein the acid epoxy curing type coating is obtained by blending a carboxyl group-containing compound with an epoxy group- and hydroxyl group-containing acrylic copolymer. 3. An acid epoxy-curable coating composition comprising a carboxyl group-containing compound mixed with an acrylic copolymer containing an epoxy group, a hydroxyl group and a hydrolyzable alkoxysilyl group. Automotive topcoat. 4. After coating a colored base coat as a top coating on the outer surface of an automobile, tetramethyl silicate and / or tetraethyl are added to 100 parts by weight of the curable resin of the acid epoxy-curable coating in a state where the colored base coat is uncured. 0.1 to 5 low condensates of silicate having a condensation degree of 2 to 10
A method for forming a coating film, comprising coating a clear top coat containing 0 parts by weight, and simultaneously baking and curing the colored base coat and the clear top coat in a two-coat one-bake method. 5. A method for applying a colored base coat as a top coat on the outer surface of an automobile, applying a first clear coat in a state where the colored base coat is uncured, and simultaneously baking and curing the colored base coat and the first clear coat;
Next, a low-condensation product having a condensation degree of 2 to 10 of tetramethyl silicate and / or tetraethyl silicate is added to 0.1 to 50 parts by weight based on 100 parts by weight of the curable resin of the acid epoxy curing type paint.
A method for forming a coating film, comprising coating a second clear top coat composed of parts by weight and baking the applied second clear top coat.