JP2000288465A - Coating method of automobile body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a coating film free from the generation of sag, each of hiding, popping, or the like, and exhibiting uniform metallic feeling by uniformly and regularly orienting a metallic pigment in parallel to the coating surface when the coating film is metallic. SOLUTION: An organic solvent based thermosetting 1st colored coating material B containing a neutralized material of a polycarboxylic acid resin having 5-100 mgKOH/g acid value and an amino resin is applied on the outside and inside both plates of an automobile body having a coating film formed by applying a cationic electrodeposition coating material A and hardening by heating and, after a thermosetting 2nd colored coating material C and a thermosetting aq. transparent coating material D are successively applied on the outside plate, the coating material B, C and D are hardened at the same time by heating and a thermosetting transparent coating material E is applied further on the outside plate and the coating film is hardened by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating an inner plate and an outer plate of an automobile body.

[0002]

2. Description of the Related Art The body of an automobile is mainly composed of an inner plate portion such as a trunk room, an engine room and a door, and an outer portion such as a roof, a hood, a trunk lid, a door panel and a fender. The inner and outer plates are coated by, for example, a method described below.

[0003] (1) An organic solvent-based intermediate coating is applied to the outer plate of the body which has been electrodeposited and heat-cured, and after being heat-cured, an organic solvent-based colored topcoat is applied to both the inner and outer plates. A method in which an organic solvent-based clear top coating is applied to the outer plate, and then both the coatings are simultaneously heated and cured; (2)
Apply an organic solvent-based coloring paint for the inner plate to the inner plate of the body that has been electrodeposited and heat-cured, then apply an organic solvent-based intermediate coating to the outer plate, heat and cure, then water-color the outer plate A method in which a paint and an organic solvent-based clear paint are applied, and then these coatings are simultaneously heated and cured; (3) An intermediate coating is applied to the outer plate portion of the body which has been electrodeposited and heated and then cured by heating. A method in which a water-based colored topcoat is applied to both parts of the inner and outer panels, an organic solvent-based clearcoat is applied to the outer panel, and both the coatings are cured.

However, these coating methods have various problems, and there is a strong demand for solving these problems. For example, in the coating method (1), since both the colored paint and the clear paint are organic solvent type, it is not preferable from the viewpoint of pollution prevention and resource saving. In the coating method (2), the organic solvent for the inner plate is not used. The mold paint must be prepared separately, and the finished appearance of the coating with the water-based coloring paint on the outer plate is not sufficient. In the method (3), the coating with the water-based coloring paint applied on both the inner and outer plates There is a problem that the finished appearance is not sufficient.

An object of the present invention is to provide a novel coating method for an inner plate and an outer plate of an automobile body, which solves these problems in the coating methods (1) to (3).

[0006]

According to the present invention, an acid value of 5 to 100 mg is applied to both the inner and outer plates of an automobile body obtained by applying a cationic electrodeposition coating (A) and heat-curing the coating.
An organic solvent-based thermosetting first colored paint (B) containing a neutralized polyvalent carboxylic acid resin of KOH / g and an amino resin is applied, and then a thermosetting aqueous second colored paint is applied to the outer panel. After sequentially applying (C) and the thermosetting water-based transparent coating (D), the three-layer coatings of the coatings (B), (C) and (D) are simultaneously heated and cured, and further applied to the outer plate portion. A coating method for an automobile body, characterized in that a thermosetting transparent coating material (E) is applied and the coating film is heated and cured.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the coating method for an automobile body according to the present invention (hereinafter referred to as the present method) will be described in more detail.

[0008] The present invention relates to an automobile to be painted
For example, passenger cars, RV cars, mini cars, wagon cars, buses,
Trucks, etc. are mentioned, and the bodies of these automobiles are mainly composed of trunk room, engine room, the inner plate which is hard to see from the outside such as inside the door, roof, bonnet, trunk lid, Door panels, fenders,
And an "external plate" which is exposed to the outside such as a bumper. The material of these two parts is mainly metal, but plastic parts may coexist. In the present specification, these inner and outer plates of a vehicle are referred to as "body".
May be referred to collectively.

According to the present method, first, a cationic electrodeposition paint (A) is applied to the metal portions on both the inner and outer plates of the body. The cationic electrodeposition paint (A) is a water-based undercoat, and a known one can be used. Specifically, for example, a paint containing an aqueous resin obtained by neutralizing a cationic resin such as an epoxy resin modified with an amino group-containing compound, an acrylic resin, or a polybutadiene resin with a neutralizing agent, and further comprising a crosslinking agent ( For example, an electrodeposition paint prepared by blending, if necessary, a block polyisocyanate, an alicyclic epoxy resin, a coloring pigment, a rust-preventive pigment, an extender pigment, a hydrophilic organic solvent, and the like. Examples of the neutralizing agent include organic acids such as acetic acid, hydroxyacetic acid, propionic acid, butyric acid, lactic acid, and glycine; and inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid.

The application of the cationic electrodeposition coating (A) to the body is carried out, for example, at a solid concentration of about 5 to 40% by weight and a pH of 5.5.
This can be carried out by immersing the body in a bath of the cationic electrodeposition coating composition (A) adjusted to ~ 8 and performing electrodeposition coating according to a usual method. The coating thickness is preferably about 10 to about 60 μm for the cured coating, and the coating is about 140 to about 2 μm.
The composition can be cured by heating at 10 ° C. for about 5 to 40 minutes.

According to the present method, the body coated with the cationic electrodeposition paint (A) as described above is coated with an organic solvent-based first paint.
The coloring paint (B) is applied. The organic solvent-based first colored coating (B) is a neutralized polycarboxylic acid resin having an acid value of 5 to 100 mgKOH / g (B-1), and an amino resin (B-2).
And an organic solvent-based coating containing a coloring pigment (B-3), and which forms a solid-colored or metallic-like coating film having a base concealing property are advantageously used. This organic solvent-based first colored paint (B) is applied to the cured coating surface of the cationic electrodeposition paint (A) prior to the thermosetting aqueous second colored paint (C).

By using the first colored paint (B), the coating film of the second colored paint (C) described later, which is coated on the coated surface, is not affected by the coating atmosphere humidity and is uniform and smooth. Can be painted.

The above (B) of the organic solvent-based first colored paint (B)
The polyvalent carboxylic acid resin in the component -1) is a resin containing an average of at least two carboxyl groups in one molecule and having an acid value of 5 to 100 mgKOH / g. Resins can be used.

I) Acrylic resin or vinyl resin obtained by copolymerizing a carboxyl group-containing polymerizable monomer, a hydroxyl group-containing polymerizable monomer and another polymerizable monomer.

The carboxyl group-containing polymerizable monomer is a compound having a carboxyl group and a polymerizable unsaturated bond in one molecule, such as acrylic acid, methacrylic acid, maleic acid, itaconic acid and crotonic acid. . The hydroxyl group-containing polymerizable monomer is a compound having a hydroxyl group and a polymerizable unsaturated bond in one molecule, for example, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth)
(Meth) acrylic acid such as acrylate having 1 to 1 carbon atoms
And eight hydroxyalkyl esters.
The other polymerizable monomer is a compound having a polymerizable unsaturated bond in one molecule, which can be copolymerized with the carboxyl group-containing polymerizable monomer and the hydroxyl group-containing polymerizable monomer. (Meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth)
Acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, alkyl or cycloalkyl ester of (meth) acrylic acid having 1 to 24 carbon atoms such as decyl acrylate; (meth) acrylamide, N
-Methyl (meth) acrylamide, N-ethyl (meth)
Functional (meth) acrylamides such as acrylamide, diacetone acrylamide, N-methylol (meth) acrylamide, and N-butoxymethylacrylamide; glycidyl group-containing vinyl monomers such as glycidyl (meth) acrylate, glycidyl (meth) acrylamide, and allyl glycidyl ether Styrene, vinyltoluene, vinyl propionate, α-methylstyrene, vinyl acetate,
Vinyl monomers such as (meth) acrylonitrile, vinyl propionate, vinyl pivalate, and beova monomer (shell chemical products) are included.

The acrylic resin or vinyl resin can generally have a number average molecular weight in the range of 5,000 to 40,000.

Ii) A polyester resin obtained by subjecting a polyhydric alcohol and a polybasic acid to an esterification reaction.

The polyhydric alcohol is a compound having two or more alcoholic hydroxyl groups in one molecule, for example, ethylene glycol, diethylene glycol, propylene glycol, butanediol, pentanediol, 2,2
-Dimethylpropanediol, glycerin, trimethylolpropane, pentaerythritol and the like. A polybasic acid is a compound having two or more carboxyl groups in one molecule. For example, phthalic acid, isophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, maleic acid, succinic acid, adipic acid, sebacic acid, Examples include melitic acid, pyromellitic acid, and anhydrides thereof. Furthermore, in the esterification reaction of these polyhydric alcohols and polybasic acids, if necessary, monohydric alcohols and monoepoxy compounds having a glycidyl group are used as a part of the alcohol component, and / or a part of the acid component is used. And monobasic acids such as benzoic acid and t-butylbenzoic acid. The polyester resin also includes polyester components modified with oil components such as castor oil, tung oil, safflower oil, soybean oil, linseed oil, tall oil, and coconut oil, or fatty acids thereof. These polyester resins can generally have a number average molecular weight in the range of 500 to 10,000.

These polyvalent carboxylic acid resins have a content of 5 to 100.
mgKOH / g, preferably 10-50 mgKOH /
g, more preferably in the range of 30 to 50 mg KOH / g. When the acid value is less than 5, the affinity with the second colored paint (C) applied to the painted surface becomes poor, and the second colored paint (C) does not absorb moisture. Defects such as uneven flow and sagging of the coating film of the paint (C) occur, and the aesthetics of the coating film deteriorates. On the other hand, if the acid value is more than 100, the water resistance of the coating film itself of the first colored paint (B) is undesirably reduced.

The polycarboxylic acid resin in the component (B-1) preferably has a hydroxyl group in order to promote a crosslinking reaction with the amino resin (B-2). And the performance such as water resistance and weather resistance is improved. The content of the hydroxyl group is 10 to 20 in terms of hydroxyl value.
0 mgKOH / g, preferably in the range of 25 to 70 mgKOH / g.

These polycarboxylic acid resins can be made water-soluble or water-dispersible by neutralizing them with a basic substance. As the basic substance, for example, various basic substances such as ammonia, methylamine, ethylamine, dimethylamine, diethylamine, trimethylamine, triethylamine, dimethylethanolamine, diethanolamine, and triethanolamine can be used. The amount is preferably about 0.1 to about 2 equivalents, particularly about 0.3 to about 1.2 equivalents, based on the carboxyl groups in the resin.

The amino resin (B-2) serves as a cross-linking agent for curing the polycarboxylic acid resin. Or those obtained by co-condensation and those obtained by modifying them with a modifier. Of these, melamine-formaldehyde resins are preferred.

The compounding ratio of the neutralized polycarboxylic acid resin (B-1) and the amino resin (B-2) is based on the total weight of the solid content of both, and the component (B-1) is 50%. ~ 90%,
In particular, the content is preferably in the range of 60 to 85% and the component (B-2) in the range of 10 to 50%, particularly 15 to 40%.

The first colored paint (B) contains the components (B-1) and (B-2) described above, and these are added to the color pigment (B).
An organic solvent system which is dissolved or dispersed in an organic solvent together with -3). In particular, a so-called high solid in which the solid content at the time of coating is adjusted to about 35% by weight or more, particularly about 40 to about 60% by weight. The type is preferable from the viewpoint of preventing pollution.

The color pigment (B-3) is for imparting solid color or metallic base hiding power to the coating film of the first color paint (B), and specifically, for example, titanium dioxide, Zinc flower, carbon black, red iron, cadmium red, molybdenum red, cadmium yellow, chrome yellow, titanium yellow, phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyridine, azo orange, flavanthrone yellow, isoindoline yellow, azo yellow Solid color pigments such as Indathlon Blue, Dibromo Anzathrone Red, Perylene Red, Azo Red, Anthraquinone Red, Quinacridone Red, and Violet; Scale-like aluminum, mica, mica coated with metal oxide, etc. Tarik pigments. These can be used alone or in combination of two or more.

The amount of the coloring pigment (B-3) is such that the light transmittance at a wavelength of 400 to 700 nm is 5% or less at a film thickness (cured coating film) of the first colored coating material (B) of 30 μm.
Preferably, the amount is 3% or less. Specifically, although it depends on the coloring power of the pigment, it is usually in the range of 1 to 250 parts by weight, preferably 5 to 150 parts by weight per 100 parts by weight of the resin solid content (total amount of the base resin and the curing agent). can do. The light transmittance of the coating film of the first colored coating material (B) is such that the coating material (B) is applied to a glass plate so as to have a predetermined cured film thickness, cured, immersed in warm water of 60 to 70 ° C., and peeled. , A coated film obtained by drying, as a sample, a self-recording spectrophotometer (type EPS-3T, manufactured by Hitachi, Ltd.)
Is the average spectral transmittance when measured at a wavelength of 400 to 700 nm using.

As the organic solvent in the first colored paint (B), ordinary paint solvents can be used.
Ester solvents, ether solvents, alcohol solvents,
Amide solvents, ketone solvents, aliphatic hydrocarbon solvents,
An alicyclic hydrocarbon solvent, an aromatic hydrocarbon solvent and the like can be mentioned. Among them, particularly, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl Ether, diethylene glycol monobutyl ether, methyl alcohol, ethyl alcohol, allyl alcohol, n-propyl alcohol, isopropyl alcohol, tertiary butyl alcohol, ethylene glycol, 1,2-propylene glycol and its monoether, 1,3-butylene glycol, , 3-butylene Recall, hexylene glycol, hexanediol, dipropylene glycol and the monobutyl ether, acetone, be used a hydrophilic organic solvent such as diacetone alcohol as at least a part of the organic solvent preferable. As the hydrophilic organic solvent, an organic solvent that dissolves at 50 ° C. or more per 100 parts by weight of water at 20 ° C. is preferable. The ratio of the hydrophilic organic solvent to the total organic solvent is suitably 20% by weight or more, particularly 40 to 100% by weight, based on the total weight of the organic solvent contained in the first colored paint (B) at the time of coating.

The color tone of the first colored paint (B) is such that the first colored paint (B) and the aqueous second colored paint (C) to be applied to the outer plate portion.
It is preferable that the color tone is similar to the color tone of the multilayer coating film composed of the water-based transparent paint (D) and the transparent paint (E).

The first colored coating (B) is prepared by applying a cationic electrodeposition coating (A) and heat-curing the coating to form a coating on both the inner and outer plates of the body. Painted.
The coating is carried out, for example, by a method such as air spraying, airless spraying, electrostatic coating or the like, and the viscosity at the time of coating is adjusted for about 15 to about 60 seconds, particularly 15 to 35 seconds (20 ° C.) with a Ford cup # 4.
About 2 to about 60 μm, especially about 5 μm, based on the cured coating film.
It is preferable to perform the process so that the film thickness is about 25 μm.

In the present method, the first colored paint (B) is applied to the electrodeposited coating surfaces of both the inner plate portion and the outer plate portion of the body as described above, and is applied at room temperature to 100 ° C. or lower. After leaving for 10 minutes, the thermosetting aqueous second colored paint (C) is applied to the uncured coating surface of the first colored paint (B) on the outer plate portion.

The thermosetting water-based second colored coating (C) is an aqueous liquid coating containing water as a main solvent or dispersion medium and containing a water-soluble or water-dispersible thermosetting resin composition. -Or those which form a metallic coating film are used.

As the thermosetting resin composition, for example,
Examples of the composition include a water-soluble or water-dispersible base resin having a crosslinkable functional group such as a hydroxyl group, such as an acrylic resin, a vinyl resin, or a polyester resin, and an amino resin as a crosslinker.

Examples of the water-soluble acrylic resin and vinyl resin include an acid value of about 20 obtained by copolymerizing a carboxyl group-containing polymerizable monomer, a hydroxyl group-containing polymerizable monomer and other polymerizable monomers. ~ 100 and hydroxyl value about 20 ~
About 200 resins can be given.

As these polymerizable monomers, (B-
The polymerizable monomers exemplified in i) of the component 1) can be suitably used, and the polymerization reaction of these monomers is carried out by subjecting the polymerizable monomer to azobisisobutyronitrile, benzoyl peroxide, dibutyl peroxide. The reaction can be carried out in a water-compatible organic solvent such as butyl cellosolve using a radical polymerization initiator such as oxide.

The water-soluble acrylic resin and vinyl resin may be ammonia or basic substances such as amines such as triethylamine, monoethanolamine, diethanolamine, triethanolamine and dimethylaminoethanol, or alkali metal hydroxides such as sodium hydroxide. Then, water and, if necessary, an organic solvent compatible with water are added to obtain an appropriate solid content, followed by dilution with water.

As the water-dispersible acrylic resin, for example, an ionic or nonionic low-molecular or high-molecular surfactant, a water-soluble resin or the like is used as a dispersion stabilizer, and the above-mentioned polymerizable monomer is dissolved in an aqueous medium. And by emulsion polymerization in a manner known per se.

The water-soluble polyester resin is, for example,
Among the polyester resins described in the color paint (B), the acid value is 15 to 100 mgKOH / g, and the hydroxyl value is 20 to 2
It can be obtained by using 100 mg KOH / g and neutralizing it with a basic substance in the same manner as in the above-mentioned water-soluble acrylic resin.

As a crosslinking agent, it is preferable to use an amino resin, which reacts with a base resin by heating to form a three-dimensional cured coating film. Examples of such amino resins include those obtained by condensation or co-condensation of melamine, benzoguanamine, urea, dicyandiamide, and the like with formaldehyde. Amino resin containing etc. can also be used. These amino resins are usually used in an alkaline or acidic condition by using about 0.5 to about 2 equivalents of formaldehyde to 1 equivalent of an amino group using a pH adjuster (eg, ammonia, sodium hydroxide, amines). It can be produced by reacting by a method known per se. A preferred crosslinking agent in the second colored paint (C) is a water-soluble melamine formaldehyde resin.

The mixing ratio of the base resin and the crosslinking agent in the second colored coating composition (C) is about 50 to about 90 parts by weight, particularly about 60 to about 85 parts by weight, based on the total solids weight ratio of both components. About 10 to about 50 parts by weight, especially about 15 to about 40 parts by weight.
It is preferably within the range of parts by weight.

The second colored paint (C) is an aqueous paint obtained by blending a solid color pigment and / or a metallic pigment with these thermosetting resin compositions. Those described for the paint (B) are preferably used. These pigments can be used alone or in combination of two or more.

The amount of these pigments is determined by coloring the coating film of the second colored coating material (C) and imparting the color cosmetics to the multi-layer coating film formed on the outer panel by the present method.
It is preferable that the amount is such that the color tone of the coating film of the first colored coating material (B) under the coating film is imparted to the base layer so that the color tone of the coating film cannot be visually recognized. Therefore, the light transmittance of a single coating film (15 μm in cured coating film) of the second colored coating material (C) at a wavelength of 400 to 700 nm is 5% or less, particularly 3%.
% Is preferable.

The second colored paint (C) has a solid content concentration of 15 to 65% by weight and a viscosity of 15 to 60% at the time of coating.
Seconds, preferably 20-50 seconds / Ford Cup # 4/2
The temperature was adjusted to 0 ° C., and the uncured coating surface of the coating material (B) applied to the outer panel portion was cured by a method such as air spraying, airless spraying, or electrostatic coating to a thickness of 5 to 25 μm, particularly 10 to 2 μm.
The coating is preferably performed so as to have a thickness of 0 μm.

In this method, the second colored paint (C) is applied to the outer plate.
Is applied, a thermosetting aqueous transparent paint (D) is applied to the uncured coated surface. Prior to the application of the thermosetting aqueous transparent paint (D), both coating films of the first colored paint (B) and the second colored paint (C) are pre-dried at a temperature of about 50 to about 100 ° C. It is also possible to put. In this preliminary drying, the crosslinking reaction between the two coating films hardly or not progresses at all (the gel fraction is 0 to 5%), and the volatile components such as organic solvent and water contained in both the coating films are removed. It is preferable that most or all of the reaction be carried out by evaporation.

Next, the thermosetting aqueous transparent paint (D) is
It is applied to the uncured coating surface of the second colored paint (C) applied to the outer panel of the body. The water-based transparent coating (D) contains a water-soluble or water-dispersible thermosetting resin composition,
An aqueous liquid paint which forms a colorless transparent or colored transparent coating film, which is mixed with a solid color pigment or a metallic pigment, if necessary, is used.

The transparent paint (D) can be prepared by blending the above-mentioned second colored paint (C) by removing a part or all of a solid color pigment or a metallic pigment from the composition of the second colored paint (C). The content of the pigment is desirably such that the single coating film of the transparent coating (D) has transparency and the color tone of the coating film of the second colored coating (C) can be visually observed through the coating film. It is preferable that the content of the pigment in the second colored paint (C) is smaller than that in the second colored paint (C).

Specifically, the light transmittance of the cured coating film of the transparent coating material (D) at a film thickness of 15 μm in the wavelength range of 400 to 700 nm is 6 to 95%, particularly 10 to 90%, and more particularly 20 to 80%. It is desirable to blend the pigment in such an amount as to fall within the range described above.

The viscosity of the transparent paint (D) is adjusted to about 10 to about 50 seconds (20 ° C.) using a Ford cup # 4 and applied by a method such as air spray coating, airless spray coating, or rotary electrostatic coating. On the uncured surface of the second colored paint (C), based on the cured coating film, 5 to 30 μm, especially 10 to 2 μm.
The coating is preferably performed so as to have a thickness of 5 μm.

In the present method, the second colored paint (C) and the transparent paint (D) preferably have an affinity, and specifically, a part of the thermosetting resin composition contained in both paints. Alternatively, it is desirable that all of them are common or similar, or that they are different but have an affinity between them.

In the present method, a cationic electrodeposition paint (A) is applied to the inner plate and the outer plate of the automobile body, the coating film is cured by heating, and then the first plate is applied to the inner plate and the outer plate. After applying the colored paint (B) and applying the second colored paint (C) and the transparent paint (D) sequentially on the outer surface without heating and curing the coating film, the paint is applied at about 100 to about 170 ° C. After heating for about 40 minutes to simultaneously cure these three-layer coating films, a thermosetting transparent coating material (E) is applied to the cured coating surface of the transparent coating material (D).

The thermosetting transparent paint (E) is a paint which forms a colorless transparent or colored transparent coating, and is, for example, a known organic solvent solution type, non-aqueous dispersion type (NAD), or the like.
A liquid paint such as a powder slurry type or a powder paint containing little or no solvent can be used. Further, the solid content at the time of coating is 35% by weight or more, preferably 4% by weight.
High solid content type paints of 0 to 80% by weight can also be suitably used.

The transparent paint (E) further improves the aesthetics, finished appearance, weather resistance, chemical resistance, water resistance, moisture resistance, sharpness, etc. of the multilayer coating film formed on the outer panel. For the purpose, it is applied as the uppermost coating film on the cured coating surface of the transparent coating material (D), specifically, an acrylic resin or a vinyl resin having a crosslinkable functional group such as a hydroxyl group or a carboxyl group. And a coating containing a thermosetting resin composition comprising a base resin and a crosslinking agent such as an amino resin, a block polyisocyanate compound, or an epoxy group-containing compound.

The liquid transparent paint (E) is adjusted to have a viscosity of about 10 to about 60 seconds / Ford Cup # 4 / (20 ° C.) at the time of coating, and is applied by a method such as air spray, airless spray, or electrostatic coating. And about 5 to about 60 μm, especially about 10 to about 50 μm, based on the cured coating film on the cured coating surface of the transparent paint (D).
It is preferable to apply the coating so as to have a film thickness of m. The transparent coating (E) is coated at a temperature of about 100 to about 170 ° C.
It can be cured by heating for about 40 minutes.

[0053]

According to the method of the present invention described above, the following effects can be obtained.

(1) The neutralized polycarboxylic acid resin contained in the uncured coating film of the first colored coating (B) exhibits strong water absorption, and therefore the colored coating (C) applied to the coated surface thereof The moisture inside is absorbed and the viscosity rises sharply. As a result, the coating of the colored paint (C) is free of sagging, scum, and abrasion, and if the coating has a metallic tone, the metallic pigment is uniformly and regularly parallel to the coating surface. It is possible to form a coating film which is oriented and has a uniform metallic feeling without metallic unevenness.

(2) Since the first colored paint (B) coating film has excellent base concealing property, the solar light from the outside in the multi-layer coating film formed on the outer plate portion of the body is an electrodeposition coating film. , And the interlayer adhesion can be improved.

(3) Since the second colored paint (C) has good wettability with the first colored paint (B), it does not cause defects such as rough skin even when painted in a low humidity atmosphere.

(4) Since the transparent paint (E) is applied to the surface of the cured transparent paint (D), defects such as mixed layers do not occur and the selection range is not limited.

(5) Since the transparent coating (D) has transparency, the coated surface is excellent in finished appearance such as feeling of holding, smoothness, sharpness, depth, high gloss and high metallic feeling. Can be finished.

(6) Since both the inner plate portion and the outer plate portion of the body are coated with the first colored paint (B) forming a hydrophilic coating film, the inner plate portion having a complicated shape is applied. There is no invisibility or sagging.

(7) Even if the transparent paint (D) is applied and cured by heating to thereby remove the defective portions such as dusts and bumps generated before this step by polishing, the paint (E) is then removed.
The multi-layer coating film formed by coating with has remarkably excellent sharpness and gloss.

[0061]

The present invention will be described below more specifically with reference to examples and comparative examples. The parts and percentages are based on weight, and the thickness of the coating is based on the cured coating.

1. Preparation of Sample 1) Electroplated steel sheet "Electron # 9400" (manufactured by Kansai Paint Co., Ltd., trade name, polyamide-modified epoxy resin / block polyisocyanate-based cationic electrodeposition paint) having a solid content of 16%
And dilute with deionized water to adjust the pH to 5.5-8.
0, a steel plate (size 10)
.Times.10.times.0.8 mm), and electrodeposited by a conventional method, and heated at about 175.degree. C. for 30 minutes to cure the coating. The thickness is 20 μm.

2) Organic solvent-based thermosetting first colored paint (B) Base resin (B1) : 1 part by adding 60 parts of ethyl cellosolve
In a reaction vessel heated to 20 ° C., 30 parts of methyl methacrylate, 23 parts of ethyl acrylate, 30 parts of butyl acrylate, 12 parts of hydroxyethyl methacrylate,
A monomer mixture consisting of 5 parts of acrylic acid and 2 parts of α, α'-azobisisobutyronitrile was added over 3 hours using a metering pump, and polymerized to obtain an acid value of 40 mg KO.
An acrylic resin solution having a H / g, a hydroxyl value of 52 mg KOH / g, a number average molecular weight of about 10,000 and a resin solid content of 60% was obtained. To 100 parts of this acrylic resin solution was added 2-amino-2-
The mixture was neutralized by adding 3.5 parts of methyl propanol, and then diluted with isopropyl alcohol to obtain an acrylic resin neutralized solution (B1) having a resin solid content of 50%.

Substrate resin (B2) : 0.7 mol of neopentyl glycol, trimethylolpropane 0.1 mol in a reaction vessel.
3 mol, 0.4 mol of phthalic anhydride and 0.5 adipic acid
After reacting at 200-230 ° C. for 5 hours,
After adding 0.03 mol of trimellitic anhydride and reacting at 180 ° C. for another 1 hour, butyl cellosolve was added thereto to obtain an acid value of 40 mg KOH / g and a number average molecular weight of about 600.
0, a polyester resin solution having a resin solid content of 70% was obtained.
To 100 parts of this polyester resin solution was added 2-amino-2-
The mixture was neutralized by adding 4 parts of methylpropanol, and then diluted with isopropyl alcohol to obtain a polyester resin neutralized solution (B2) having a resin solid content of 60%.

Preparation of first colored paint (B) : The above-mentioned components were mixed in the mixing ratio shown in Table 1 below to obtain first colored paints a, b and c.

[0066]

[Table 1] (Note 1) Trade name, manufactured by Mitsui Cytec, water-soluble melamine.

(Note 2) Blu-Pigment, trade name, manufactured by Sanyo Dyeing Co., Ltd.

(Note 3) Ford cup # 4/20 ° C.

(Note 4) Measured value for a coating film having a thickness of 20 μm.

3) Preparation of thermosetting aqueous second colored coating material (C) 20% acrylic resin emulsion (C1): 140 parts of deionized water and 30% "Newcol 7" in a reaction vessel.
07SF "(surfactant, manufactured by Nippon Emulsifier Co., Ltd.) 2.5
And 1 part of the following monomer mixture (1) (Note 5)
The mixture was stirred and mixed in a stream of nitrogen gas, and 3 parts of a 3% aqueous solution of ammonium persulfate was added at 60 ° C. Then, after raising the temperature to 80 ° C., 79 parts of the monomer mixture (1) (Note 5), 3 parts
A monomer emulsion consisting of 2.5 parts of 0% “Newcol 707SF”, 4 parts of a 3% aqueous ammonium persulfate solution and 42 parts of deionized water was added to the reaction vessel over 4 hours using a metering pump. After completion of the addition, aging was performed for 1 hour. Further, at 80 ° C., the following monomer mixture (2) (Note 6): 20.
5 parts and 4 parts of a 3% ammonium persulfate aqueous solution were simultaneously added to 1.
The solution was dropped in parallel into the reaction vessel over 5 hours. After completion of addition, 1
Aged for 30 hours, diluted with 30 parts of deionized water,
The mixture was filtered through a 0 mesh nylon cloth. Deionized water was further added to the filtrate, and the pH was adjusted to 7.5 with dimethylaminoethanol to obtain an acrylic resin emulsion (C1) having an average particle diameter of 0.1 μm and a nonvolatile content of 20%.

(Note 5) Monomer mixture (1): 55 parts of methyl methacrylate, 8 parts of styrene, 9 parts of n-butyl acrylate, 5 parts of 2-hydroxyethyl acrylate,
A mixture consisting of 2 parts of 1,6-hexanediol diacrylate and 1 part of methacrylic acid.

(Note 6) Monomer mixture (2): 5 parts of methyl methacrylate, 7 parts of n-butyl acrylate, 5 parts of 2-ethylhexyl acrylate, 3 parts of methacrylic acid and 30% “Newcol 707SF” Mixture of 5 parts.

Preparation of water-based second colored paint (C): The above components were mixed in the mixing ratio shown in Table 2 below to obtain thermosetting second colored paints a and b.

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[Table 2] (Note 7) Scaly aluminum paste manufactured by Toyo Aluminum Co., Ltd.

(Note 8) The light transmittance is a value measured on a coating film having a thickness of 15 μm.

4) Thermosetting water-based transparent coating material (D)
A material prepared in the same manner except that “G316” was used is referred to as a transparent paint d.

5) Thermosetting water-based transparent coating material (E) Base resin (E1): 30 parts of styrene, 30 parts of acryl were added to a reaction vessel which was heated at 120 ° C. with 40 parts of swazole # 1000 (manufactured by Maruzen Oil Co., Ltd.). A monomer mixture consisting of 35 parts of butyl acrylate, 10 parts of 2-ethylhexyl acrylate, 25 parts of hydroxyethyl acrylate and 4 parts of α, α'-azobisisobutyronitrile was added over 3 hours using a metering pump. And polymerized. As a result, the hydroxyl value was 120 mgKOH / g, the number average molecular weight was about 6000,
An acrylic resin solution (E1) having a resin solid content of 70% was obtained.

A 60% acrylic resin non-aqueous dispersion (E2):
A reaction vessel was charged with 58 parts of 60% Uban 28-60 (a melamine resin solution manufactured by Mitsui Toatsu Chemicals, Inc.), 30 parts of n-heptane, and 0.15 part of benzoyl peroxide, and heated to 95 ° C. In addition, styrene 15
Part, acrylonitrile 9 parts, methyl methacrylate
13 parts, methyl acrylate 15 parts, n-butyl acrylate 1.8 parts, 2-hydroxyethyl methacrylate 10 parts, acrylic acid 1.2 parts, benzoyl peroxide 0.5 parts, n-butanol 5 parts, Shellsol 140 ( Note 9) A mixture consisting of 30 parts and 9 parts of n-heptane was added dropwise over 3 hours, and after 1 hour at the same temperature, 0.65 part of t-butyl peroctoate and Shellsol 140 (Note 9) 3 0.5 part of the mixture was added dropwise over 1 hour. Thereafter, stirring was continued for 2 hours while maintaining the temperature at 95 ° C. Then, the pressure was reduced to remove 34 parts of the solvent,
An acrylic resin non-aqueous dispersion (E2) having a resin solid content of 60% and a varnish viscosity A (Gardner bubble viscosity) was obtained.

(Note 9): trade name, hydrocarbon solvent, manufactured by Shell Sekiyu KK

Preparation of thermosetting transparent paint (E) : 57 parts of 70% acrylic resin solution (E1), 50 parts of 60% acrylic resin non-aqueous dispersion (E2), Cymel 303 (Note 1)
0) 30 parts, 4 parts of a 25% dodecylbenzenesulfonic acid solution and 0.5 part of BYK-300 (Note 11) are mixed, and the viscosity is 30 seconds with Swazol # 1000 (Note 12) (Ford cup # 4/20 ° C.) To a resin solids content of 55
% Transparent paint e was obtained.

(Note 10) Monomeric melamine resin manufactured by Mitsui Cytec Co., Ltd.

(Note 11): manufactured by Big Chemie Japan,
Trade name, surface conditioner.

(Note 12): trade name, aromatic hydrocarbon solvent, manufactured by Cosmo Oil Co., Ltd.

2. Examples Examples 1 to 3 A viscosity of 25 seconds (Ford Cup #
4/20 ° C.) first colored paint (B) -a, b,
c is set to a relative humidity of 7 so that each has a thickness of 20 μm.
It was applied by air spray at 5% RH and left at room temperature for about 5 minutes. Then, a viscosity of 30 seconds (Ford Cup #) was applied to the uncured coating surface of the first colored paint in the lower half of the coated steel sheet.
(4/20 ° C.), the second colored paint (C) -a, b was adjusted to a relative humidity of 75% so that each had a thickness of 15 μm.
After coating by air spray at RH and leaving at room temperature for about 5 minutes, the thermosetting aqueous transparent coating (D) -d is coated by air spray at a relative humidity of 75% RH to a thickness of 5 μm, After leaving at room temperature for about 3 minutes,
By heating for 0 minutes, the three-layer coating film composed of the first coloring paint, the second coloring paint, and the transparent paint was simultaneously cross-linked and cured.

Thereafter, the cured coating film of the transparent paint was applied with a viscosity of 3
The thermosetting transparent coating material (E) -e adjusted to 0 seconds (Ford cup # 4/20 ° C.) is about 45 μm based on the cured film thickness.
The mixture was left standing at room temperature for about 5 minutes and then heated at 140 ° C. for 30 minutes to cure by crosslinking.

3. Performance Test Results Performance tests were performed on the multilayer coating films obtained in the above examples. Table 3 shows the test results.

The test method is as follows.

Smoothness: tension meter (RENAU)
LY). The higher the value, the better the smoothness.

Brightness: Measured by a sharpness measuring device NSIC (manufactured by Suga Test Instruments Co., Ltd.). The higher the value, the better the sharpness.

Water resistance: 240 g of the sample-coated plate in warm water of 40 ° C.
After immersion for a time, the state of the coated surface was visually evaluated. ：: No abnormality is observed, Δ: Slight defects such as gloss shrinkage and blistering are slightly recognized, and X: Defects such as gloss shrinking and blistering are remarkable.

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[Table 3]

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B05D 7/24 302 B05D 7/24 302S C09D 5/44 C09D 5/44 A 133/02 133/02 161/20 161 / 20 167/00 167/00 (72) Inventor Yoshiya Nakamura 300 Takatsukacho, Hamamatsu-shi, Shizuoka Suzuki Co., Ltd. (72) Inventor Hideyuki Kawashima 300 Takatsukacho, Hamamatsu-shi, Shizuoka Suzuki Co., Ltd. (72) Inventor Akira Kasari 4-7-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Paint Kansai Paint Co., Ltd. (72) Inventor Seio Kato 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd. (72) Inventor Takanobu Iizuka 4-171-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa F-term in Kansai Paint Co., Ltd. (Reference) 4D075 AA02 AA04 AA09 AE06 BB26Z BB89X CA32 CA38 CA40 CB01 CB04 CB07 CB13 DC12 EA02 EA06 EA19 EB1 EB01 EB43 EB01 EB01 CG031 CG071 CG141 CH121 CJ031 CJ041 CJ101 CJ131 DA111 DA141 DA161 DA171 DA181 DB391 DD041 DD051 DD061 DD121 GA06 KA08 MA07 MA08 NA01 NA23 NA27 PA04 PA19 PB07 PC02

Claims (1)

[Claims] 1. A method for applying a cationic electrodeposition coating material (A) to a vehicle body, wherein the coating film is cured by heating.
An organic solvent-based thermosetting first colored paint (B) containing a neutralized polyvalent carboxylic acid resin having an acid value of 5 to 100 mgKOH / g and an amino resin is applied, and then a thermosetting After sequentially applying the water-based second colored coating (C) and the thermosetting water-based transparent coating (D), the three-layer coatings of the coatings (B), (C) and (D) are simultaneously heated and cured. A coating method for an automobile body, characterized in that a thermosetting transparent paint (E) is applied to a plate portion and the coating film is heated and cured.