JPH11104550A - Formation of multilayered coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a multilayered coating film excellent in finish appearance, designing property, decorating property and adhesion property between layers, and especially to form the film by using a water-based color coating material including a water-based metallic coating material. SOLUTION: In this forming method of a coating film, a cationic electrodeposition coating material (A) is applied on a metal objective body and hardened by heating. Then, an org. solvent-type or nonwater dispersion liquid-type thermosetting first color coating material (B) containing a neutralized polyvalent carboxylic acid resin having 5 to 100 acid value and an amino resin as the essential components and having base shielding property, a thermosetting water- based second color coating material (C) and a thermosetting water-based transparent coating material (D) are applied, and the three layers of the coating films (B), (C) and (D) are hardened by heating at one time. Then, a thermosetting transparent coating material (E) is applied and 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 forming a multilayer coating film having excellent finished appearance, design, aesthetics, and adhesion between layers. In particular, it relates to an improved method of forming a multilayer coating using an aqueous colored paint, including an aqueous metallic paint.

[0002]

2. Description of the Related Art Metallic coatings have a unique appearance that is excellent in cosmetics and shines with reflection of incident light from the outside on the flaky metallic pigment contained in the coating. In particular, it is often applied to outer panels of automobiles and motorcycles. As a method for forming such a metallic coating film, a two-coat one-bake method (2C1) is used by using a metallic coating material and a clear coating material for forming a transparent coating film.
B) or a two-coat two-bake method (2C2B), or a three-coat two-bake method (3C2B) in which a clear paint is further applied to a coated surface formed by the two-coat method. I have.

[0003] Among them, as 3C2B, there is known a method in which a colored paint and a colored clear paint are applied to a heat-cured cationic electrodeposition coated surface, heated and cured, and then a clear paint is applied and cured. However, this multilayer coating film has a defect that sunlight from the outside passes through the colored coating film and reaches the electrodeposition coating film, and the interlayer adhesion between the two coating films is reduced. As a measure to solve the defect, when the amount of the coloring pigment in the colored coating film is increased, the chipping resistance is reduced, and when the amount of the coloring pigment in the colored clear coating film is increased, sharpening for removal of dust and dust sometimes occurs after baking. When this was performed, another defect that the hue was different from the unsharpened portion and the aesthetic appearance was inferior occurred, which was not preferable.

On the other hand, a neutralized product of a polyvalent carboxylic acid resin having an acid value of 5 to 100 and an organic solvent type paint, an aqueous metallic paint and a clear paint containing an amino resin as essential components are applied, and then heated to form a three-layer paint. There is also known a method of forming a multilayer coating film of 3C2B by simultaneously curing the coating films. However, in order to apply the clear paint to the uncured paint surface, it is necessary to prevent the clear paint from being mixed with, for example, an undercoat film, and there is a defect that the selection range is limited.

[0005]

According to the present invention, there is provided 3C2B, which is obtained by applying the above-mentioned colored paint and colored clear paint, heating and curing, then applying the clear paint, and heating and curing, and a polyvalent resin having an acid value of 5 to 100. Various defects in 3C1B, in which a neutralized carboxylic acid resin and an amino resin are coated with an organic solvent-based paint, an aqueous metallic paint, and a clear paint, which are essential components, and then heated to simultaneously cure the three-layer coating, have been eliminated. The present invention relates to a method for forming a multilayer coating film. As a result, a first colored paint having an organic solvent-type base concealing property, a thermosetting water-based colored paint, and a thermosetting resin, which comprises a neutralized product of a polycarboxylic acid resin having an acid value of 5 to 100 and an amino resin as essential components, After applying a water-soluble water-based transparent paint and heating it to simultaneously cure the three-layer coating film, the present inventors have found that the above object can be achieved by applying a thermosetting transparent paint and heating and curing, thereby completing the present invention. Reached.

According to the present invention, a cationic electrodeposition coating material (A) is applied to a metal object to be coated, heated and cured, and then neutralized with a polycarboxylic acid resin having an acid value of 5 to 100. Solvent-based or non-aqueous dispersion type thermosetting first color coating (B), thermosetting aqueous second color coating (C) and thermosetting curable resin containing organic matter and amino resin as essential components After applying the water-based transparent coating (D), the coating is heated to simultaneously cure the three-layer coatings (B), (C) and (D), and then the thermosetting transparent coating (E) is applied. And a method of forming a multilayer coating film, wherein the method is cured by heating.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, an aqueous second colored paint is applied to the uncured surface of an organic solvent-based first colored paint (B) having a base concealing property containing a neutralized polyvalent carboxylic acid resin. (C) is applied, and the applied first colored paint (B) coating shows strong water absorption due to the neutralization of the polycarboxylic acid resin contained therein, and is applied to the coated surface. The moisture in the colored coating (C) thus absorbed is absorbed, and the viscosity sharply increases. In this case, when a metallic paint is used as the colored paint (C), a flaky metallic pigment is uniformly and regularly oriented in parallel to the coating surface to form a metallic coating film having a uniform metallic feeling without metallic unevenness. Can be formed.

Further, since the first colored paint (B) has an excellent base concealing property, it is possible to improve the adhesion between the layers without external rays of sunlight reaching the electrodeposition coating film. Further, since the second colored paint (C) has good wettability with the first colored paint (B), there is no occurrence of defects such as rough skin even when applied in a low humidity atmosphere.

Further, in the present invention, 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. Was. Further, in the method of the present invention, since the transparent paint (D) has transparency, it has a solid feeling, smoothness,
It is characterized in that it can be finished to a coated surface excellent in finished appearance such as sharpness, depth, high gloss and high metallic feeling.

Hereinafter, the method for forming a multilayer coating film of the present invention will be described in more detail.

[0011] Metallic object to be coated : The object to be coated according to the method of the present invention is not particularly limited as long as it is a metal product which can be cationically electrodeposited, and examples thereof include iron, copper, aluminum, and the like.
Examples include tin, zinc, and alloys containing these metals, and plated or vapor-deposited products thereof.
Specifically, there are car bodies such as passenger cars, trucks, motorcycles, and buses formed by using these metal members. These metal coatings are phosphate,
It is preferable to carry out a chemical conversion treatment with a chromate or the like.

[0012] Cationic electrodeposition coating (A ): A coating for directly coating a metal object to be coated. The type of the coating is not limited, and various kinds of known cationic electrodeposition coatings can be used. . Specifically, epoxy resin modified with an amino group-containing compound, an acrylic resin, a coating mainly composed of an aqueous resin neutralized with an organic acid or an inorganic acid such as a polybutadiene resin, and further a crosslinking agent (for example, Block polyisocyanate, alicyclic epoxy resin, etc.)
Examples thereof include those obtained by blending a coloring pigment, a rust-preventive pigment, an extender, a hydrophilic organic solvent, and the like as necessary. Here, as a neutralizing agent, organic acids such as acetic acid, hydroxyl acetic acid, propionic acid, butyric acid, lactic acid, and glycine; sulfuric acid, hydrochloric acid,
An inorganic acid such as phosphoric acid can be used. The amount of the neutralizing agent used is suitably in the range of a neutralization equivalent of about 0.1 to 0.4 with respect to the base number (about 30 to 200) of the resin.

This electrodeposition paint has a solid content of about 5 to about 4
It can be diluted with deionized water or the like so as to be within the range of 0% by weight, and can be electrodeposited by a conventional method while maintaining the pH within the range of 5.5 to 8.0. It can be cured by heating to ° C. The coating thickness is preferably in the range of about 10 to about 60 μm based on the cured coating.

On the cured coating surface of the cationic electrodeposition coating material (A), an intermediate coating material can be applied as needed.

The intermediate coating composition contains a resin component and a solvent as main components, and further contains a coloring pigment, an extender pigment, and other paint additives as required. The resin component is preferably a thermosetting resin composition, for example, an acrylic resin having a crosslinkable functional group, a polyester resin, a melamine resin on a base resin such as an alkyd resin,
Examples thereof include those in which a crosslinking agent such as a urea resin and a polyisocyanate compound (including a block body) is used in combination, and an organic solvent or water can be used as a solvent. The intermediate coating is applied on the cured coating surface of the cationic electrodeposition coating (A) in a film thickness of 10 to 50 μm based on the cured coating film.
Heat and cure at 0 to about 150 ° C.

First colored coating material (B ): Organic solvent type or non-aqueous dispersion type thermosetting base hiding which contains a neutralized polyvalent carboxylic acid resin having an acid value of 5 to 100 and an amino resin as essential components. This is a colored paint having a property, and is a paint for applying to the heat-cured coating surface of the electrodeposition paint (A) or the intermediate paint, and forms a coating film having a base concealing property.

When the thermosetting water-based second colored paint (C) is applied to the paint-coated surface, it can be finished uniformly and smoothly without being affected by the atmospheric humidity.

The base resin used in the first colored paint (B) is a polycarboxylic acid resin having an acid value of 5 to 100, and various known resins can be used as long as the requirements are satisfied. Among them, the following resins can be mentioned as typical examples.

(I) At least one kind of a carboxyl group-containing polymerizable unsaturated monomer as shown in the following group (a) and at least one polymerizable unsaturated monomer as a group (c) copolymerizable therewith. One and, if necessary, at least one of the hydroxyl group-containing polymerizable unsaturated monomers as in (b) are copolymerized, preferably having a number average molecular weight of about 5,000 to about 40.
000 acrylic or vinyl resin.

(A) α, β-ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid, crotonic acid, etc .; (b) 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) A) hydroxyalkyl esters of (meth) acrylic acid having 1 to 8 carbon atoms, such as acrylates; methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) Carbon atoms of (meth) acrylic acid such as acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, decyl acrylate, etc. Alkyl or cycloal number of 1 to 24 Functional (meth) acrylamides such as (meth) acrylamide, N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, diacetoneacrylamide, N-methylol (meth) acrylamide, N-butoxymethylacrylamide and the like; 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, (meth) acrylonitrile, vinylpro Vinyl monomers such as pionates, vinyl pivalates, and veova monomers (shell chemical products).

(Ii) ethylene glycol, diethylene glycol, propylene glycol, butanediol,
Monohydric alcohols such as pentanediol, 2,2-dimethylpropanediol, glycerin, trimethylolpropane, pentaerythritol, etc. and monohydric alcohols used together if necessary or monoepoxy compounds having one glycidyl group in the molecule, For example, Kajura E
(Trade name, product of Shell Chemical Co., Ltd.) as alcohol component, phthalic anhydride, isophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic anhydride,
Polybasic acids such as succinic anhydride, adipic acid, sebacic acid, trimellitic anhydride, and pyromellitic anhydride, and monobasic acids such as benzoic acid and t-butylbenzoic acid used in combination as needed as an acid component. An oil-free alkyd resin obtained by condensing the alcohol component and the acid component, or, in addition to the alcohol component and the acid component, castor oil, tung oil, safflower oil, soybean oil, linseed oil,
An oil-modified alkyd resin obtained by adding an oil component, which is one or a mixture of two or more of tall oil, coconut oil, and their fatty acids, to the acid component and the alcohol component, and reacting the three components. The number average molecular weight is preferably 500 to 10,000.

(Iii) A graft copolymer obtained by grafting an acrylic resin or a vinyl resin to an alkyd resin, preferably having a number average molecular weight of about 5,000 to about 4,000.
0, for example, a graft copolymer obtained by reacting a vinyl monomer and / or an acrylic monomer with an alkyd resin having a polymerizable unsaturated group.

The acid value of the above polyvalent carboxylic acid resin is 5-1.
00, preferably 10 to 5
0, more preferably in the range of 30 to 50. When the acid value of the resin is less than 5, the water-based second colored paint (C) applied to the coated surface has poor adaptability and does not absorb moisture in the colored paint (C). Defects such as uneven flow and sagging of (C) are caused, and the aesthetics of the coating film is remarkably deteriorated. On the other hand, when the acid value is more than 100, the water resistance of the coating film deteriorates, which is not preferable.

When the polycarboxylic acid resin has a hydroxyl group, performances such as coating film hardness, water resistance and weather resistance are improved. Its hydroxyl value is about 10 to about 200, especially 2
It is preferably in the range of 5 to 70 mgKOH / g.

Examples of the basic substance that neutralizes these polyvalent carboxylic acid resins include ammonia, methylamine, ethylamine, dimethylamine, diethylamine, and the like.
Various basic substances such as trimethylamine, triethylamine, dimethylethanolamine, diethanolamine, and triethanolamine can be used. The amount of the neutralizing agent used is generally about 0.1 to about 2.0 equivalents, especially about 0.3 to about 1.2, based on the carboxyl group in the resin.
Equivalents are preferred.

The amino resin used in the first colored paint (B) is a crosslinking agent for curing the polycarboxylic acid resin, and various known crosslinking agents are used. Examples thereof include melamine, benzoguanamine, and triazine-based resins. It includes those obtained by condensation or co-condensation of compounds, urea, dicyandiamide and the like with formaldehyde, and those obtained by modifying them with a modifier. Of these, melamine formaldehyde resin is preferred.

The compounding ratio of the polycarboxylic acid resin to the amino resin is about 50 to about 90 parts by weight, preferably about 60 to about 85 parts by weight, and Is used in the range of about 10 to about 50 parts by weight, preferably about 15 to about 40 parts by weight.

The first colored paint (B) contains a neutralized polycarboxylic acid resin and an amino resin, and is dissolved or dispersed in an organic solvent together with a color pigment in an organic solvent type or non-aqueous dispersion type. The paint is a so-called high solid type in which the solid content concentration at the time of painting is adjusted to about 35% by weight or more, particularly about 40 to about 60% by weight, from the viewpoint of preventing pollution.

As the organic solvent, those which are commonly used for coatings can be used, such as ester solvents, ether solvents, alcohol solvents, amide solvents, ketone solvents, and the like.
Examples thereof include aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents, and one or more selected from these can be used. Particularly, among them, 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 Monoether, 1,3-butylene glycol, 2,3-butylene glycol, hexylene glycol, hexanediol,
It is preferable to use a hydrophilic organic solvent such as dipropylene glycol and its monoether, acetone, diacetone alcohol and the like. These hydrophilic organic solvents are 1
Species or two or more species can be used. The hydrophilic organic solvent is an organic solvent that dissolves at 50 ° C. or more per 100 parts by weight of water at 20 ° C. The ratio of the hydrophilic organic solvent is 20% by weight or more, especially 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.
It is suitable to contain.

The coloring pigment which can be blended with the first coloring coating material (B) gives a base concealing property. Specifically, titanium dioxide, carbon black, phthalocyanine blue, phthalocyanine green, carbazole violet, anthrapyridine, azo Solid color for ordinary paints such as coloring pigments such as orange, yellow, flavanthrone yellow, isoindoline yellow, azo yellow, indathrone blue, dibromo anzathrone red, perylene red, azo red, anthraquinone red, quinacridone red, violet, etc. -Pigments.
These pigments can be used alone or in combination of two or more.

The coloring pigment is for imparting a base concealing property to the coating film of the first coloring paint (B).
At a film thickness (cured coating film) of 30 μm, a wavelength of 40
Light transmittance of 0 to 700 nm is 5% or less, preferably 3% or less.
% Is appropriate. Specifically, although it depends on the coloring power of the pigment, it is usually from 1 to 250 per 100 parts by weight of the resin solid content (total amount of the base resin and the curing agent).
Parts by weight, preferably in the range of 5 to 150 parts by weight.

The light transmittance of the coating film is determined by applying a coating material on a glass plate so as to have a predetermined cured film thickness, and after curing, at 60 to 70 ° C.
Immersed in hot water, peeled off, and dried, and used as a sample an isolated coating film as a sample, using a self-recording spectrophotometer (EPS-, manufactured by Hitachi, Ltd.).
It is an average spectral transmittance when measured at a wavelength of 400 to 700 nm using (3T type).

In the present invention, the first colored paint (B) is
After applying and curing the cationic electrodeposition coating material (A) on the metal object to be coated, an intermediate coating material may be applied as necessary, and the cured surface may be applied. The painting is
By air spray coating, airless spray coating or rotary electrostatic coating, etc., the coating viscosity at the time of coating is about 15 to about 60 seconds, particularly 15 to 35 seconds (20
C), and applied to a film thickness of about 2 to about 60 µm, especially about 5 to about 25 µm based on the cured coating film.

Thermosetting water-based second colored coating (C ): This is a coating applied to the uncured coating surface of the first colored coating (B), using water as its main solvent, water-soluble or water-dispersible. And a solid color paint and a metallic paint.

Examples of the water-soluble or water-dispersible thermosetting resin include acrylic resins and polyester resins having a crosslinkable functional group such as a hydroxyl group.

As the water-soluble acrylic resin, one or two kinds selected from α, β-monoethylenically unsaturated carboxylic acids, hydroxyalkyl esters thereof and other α, β-monoethylenically unsaturated monomers are used. The acid value obtained by polymerizing the above monomers is about 20 to about 100 and the hydroxyl value is about 20 to
About 200 acrylic resins can be mentioned.

These polymerizable unsaturated monomers include, for example, α, β-monoethylenically unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid and itaconic acid; 2-hydroxy (meth) acrylate Hydroxyalkyl esters of α, β-monoethylenically unsaturated carboxylic acids such as ethyl and 2-hydroxypropyl (meth) acrylate;
Methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, (meth) acryl Alkyl esters of α, β-monoethylenically unsaturated carboxylic acids such as decyl acid; acrylamide derivatives such as (meth) acrylamide, N-methylol (meth) acrylamide and diacetone acrylamide; α such as glycidyl (meth) acrylate Glycidyl esters of α, β-monoethylenically unsaturated carboxylic acids; vinyl esters of saturated carboxylic acids such as vinyl acetate and vinyl propionate; aromatic unsaturated monomers such as styrene, α-methylstyrene, vinyltoluene, etc. Can be mentioned.

The polymerization reaction is carried out by using the above monomer in a water-compatible organic solvent such as butyl cellosolve using a radical polymerization initiator such as azobisisobutyronitrile, benzoyl peroxide and dibutyl peroxide. Can be.

As the water-soluble acrylic resin, use is made of ammonia or a basic substance such as amines such as triethylamine, monoethanolamine, diethanolamine, triethanolamine and dimethylaminoethanol or hydroxides of alkali metals such as sodium hydroxide. And neutralize. Thereafter, water and, if necessary, an organic solvent compatible with water are added to obtain an appropriate solid content, followed by dilution with water.

The water-dispersible acrylic resin can be prepared, for example, by using an ionic or nonionic or both low-molecular or high-molecular surfactant, or a water-soluble resin as the dispersion stabilizer to form the polymerizable unsaturated monomer. It is prepared by emulsion polymerization of the monomer in an aqueous medium by a known method.

The water-soluble polyester resin is, for example,
Among the polyester resins described in the color paint (B), those having an acid value of 15 to 100 and a hydroxyl value of 20 to 200 are used, and are obtained by neutralizing the same in the same manner as the above water-soluble acrylic resin. .

In the second colored paint (C), it is preferable to use an amino resin as a crosslinking agent for these acrylic resin and polyester resin.

The amino resin is, for example, a resin obtained by condensation or co-condensation of melamine, benzoguanamine, urea, dicyandiamide and the like with formaldehyde, further modified with an alcohol having 1 to 8 carbon atoms, or carboxyl. A group-containing amino resin is also used. These amino resins usually contain about 0.5 to about 2.0 equivalents of formaldehyde per equivalent of amino group.
It is prepared by using an H regulator (eg, ammonia, sodium hydroxide, amines) and reacting in a known manner under alkaline or acidic conditions. Preferred in the present invention are water-soluble melamine formaldehyde resins.

In the second colored paint (C), the mixing ratio of the acrylic resin and / or polyester resin to the amino resin component is such that the acrylic resin and / or polyester resin component is about 50 to about 90, based on the weight of the solid content. Parts by weight,
Preferably about 60 to about 85 parts by weight, the amino resin component is used in the range of about 10 to about 50 parts by weight, preferably about 15 to about 40 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 water-soluble or water-dispersible thermosetting resins. Is the first colored paint (B)
Examples of the metallic pigment include, for example, flake-like aluminum, mica, mica coated with a metal oxide, mica-like iron oxide, and other ordinary solid color pigments for paint and metallic pigments. . These pigments can be used alone or in combination of two or more.

These solid color pigments and metallic pigments are used for coloring the second colored paint (C) coating to impart aesthetics to the multi-layered coating formed by the present invention, and to provide the same. It is preferable that the undercoat layer has an undercoat concealing property that is at least such that the color tone of the coating film of the first colored paint (A) in the lower layer cannot be visually recognized.

Therefore, the light transmittance of a single coating film (15 μm as a cured coating film) of the second colored paint (C) at a wavelength of 400 to 700 nm is preferably 5% or less, particularly preferably 3% or less.

Thermosetting water-based transparent coating (D ): This is a coating applied to the uncured coating surface of the second colored coating (C).
Using water as its main solvent, containing a water-soluble or water-dispersible thermosetting resin, and blending a solid color pigment or a metallic pigment as necessary, to form a colorless transparent or colored transparent coating film. It is a water-based paint.

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 transparent coating (D) coating has transparency and the color tone of the second coloring coating (C) coating can be visually recognized through the coating. It is preferably smaller than the pigment content of the coloring paint (C).

Specifically, a wavelength of 400 to 700 nm at 15 μm of a cured coating film formed by the transparent coating material (D)
Light transmittance in the range of 6 to 95%, especially 10 to 90%,
More preferably, the pigment is blended in such an amount that it falls within the range of 20 to 80%. The transparent paint (D) has a viscosity of about 10 to about 50 seconds (20
° C), and air spray coating, airless spray coating or rotary electrostatic coating, etc., is applied to the uncured coating surface of the second colored coating (C) on the basis of the cured coating film in an amount of about 5 to about 3
It is preferable to apply the coating to a thickness of 0 μm, especially about 10 to about 25 μm.

In the present invention, the second colored paint (C) and the transparent paint (D) preferably have an affinity, and more specifically, one of the thermosetting resin compositions contained in the paints of the two coats. It is desirable that even if the parts or all are common or similar, or even if they are different, there is affinity between them.

In the present invention, the metallic electrodeposition coating is coated with the cationic electrodeposition coating (A) and cured by heating, and then, if necessary, the intermediate coating is coated and cured by heating.
After sequentially applying the colored paint (B), the second colored paint (C) and the transparent paint (D), the paint is applied at 100 to 170 ° C. for 10 to 4 times.
After heating for three minutes to simultaneously cure these three-layer coating films, a thermosetting transparent paint (E) is applied.

Thermosetting transparent coating (E ): This is a coating applied to the cured coating surface of the transparent coating (D), and forms a colorless transparent or colored transparent coating, for example, an organic solvent solution type Known thermosetting paints such as non-aqueous dispersion type (NAD), powder type, and powder slurry type can be applied. Further, a high solid content paint having a solid content of 35% by weight or more, preferably 40 to 80% by weight at the time of coating can be suitably used.

The transparent paint (E) can further improve the aesthetics, finished appearance, weather resistance, chemical resistance, water resistance, moisture resistance, sharpness, etc. of the multilayer coating film formed by the present invention. Therefore, it is a paint that forms a transparent coating film to be applied as the uppermost coating film on the cured coating surface of the transparent coating material (D), specifically, an acrylic resin (base resin) and an amino resin (crosslinking agent)
And a vehicle component.

The viscosity of the transparent paint (E) is adjusted to about 10 to about 60 seconds (20 ° C.) using a Ford cup # 4, and the transparent paint (E) is made transparent by air spray coating, airless spray coating, or rotary electrostatic coating. About 5 to about 60 μm, especially about 10 to about 5 μm,
It is preferable to apply a thickness of 0 μm.

In the method for forming a multilayer coating film of the present invention, a cationic electrodeposition coating material (A) is applied to a metal substrate and cured by heating, and then, if necessary, an intermediate coating material is coated and cured by heating. After the first colored paint (B), the second colored paint (C) and the transparent paint (D) are sequentially applied to the painted surface of
After heating at 10 ° C. for 10 to 40 minutes to simultaneously cure these three-layer coating films, a thermosetting transparent paint (E) is applied,
Heating is performed at 100 to 170 ° C. for 10 to 40 minutes to cure the coating film.

[0057]

[Effects of the present invention]

1. The neutralized polyvalent carboxylic acid resin contained in the first colored paint (B) coating film shows strong water absorption, and the moisture in the colored paint (C) applied to the coated surface is absorbed and the viscosity sharply increases. As a result, the metallic pigment contained in the colored paint (C) coating film is uniformly and regularly oriented parallel to the coated surface to form a metallic coating film having a uniform metallic feeling without metallic unevenness. be able to.

2. Since the coating film of the first colored paint (B) has excellent undercoat concealing property, the solar light and the like from the outside of the formed multilayer coating film do not reach the electrodeposition coating film and improve the interlayer adhesion. I was able to.

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 applied in a low humidity atmosphere.

4. Since the transparent paint (E) is applied to the coated 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 paint (D) has transparency, it is possible to finish the coated surface with excellent finished appearance such as feeling of touch, smoothness, sharpness, depth, high gloss and high metallic feeling. Was.

[0062]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. Hereinafter, “parts” and “%” are “parts by weight”.
And "% by weight".

I. Preparation of sample 1) Cationic electrodeposition paint (A) (A-1): "Electron # 9400" (manufactured by Kansai Paint Co., Ltd., trade name, polyamide-modified epoxy resin / block polyisocyanate) having a solid concentration of about Dilute to 16% by weight with deionized water or the like, and adjust the pH to 5.5.
Steel plate (size 10 × 10 ×
0.8 mm) by electrodeposition coating according to a conventional method. The coating thickness was about 20 μm based on the cured coating, and the coating was cured by heating to about 175 ° C.

2) First colored paint (B) 60% acrylic resin solution (a-1): 60 parts of butyl cellosolve was added to a reaction vessel and heated to 120 ° C., and the following monomer mixture was added thereto for 3 hours. Using a metering pump.

Methyl methacrylate 30 parts Ethyl acrylate 23 parts Butyl acrylate 30 parts Hydroxyethyl methacrylate 12 parts Acrylic acid 5 parts α, α'-azobisisobutyronitrile 2 parts As described above, acid value 40, hydroxyl value 52, an acrylic resin solution (a-1) having a number average molecular weight of about 10,000 and a resin solid content of 60% was obtained.

A 50% acrylic resin neutralized solution (a-1)
N): Neutralized by adding 3.5 parts of 2-amino-2-methylpropanol to 100 parts of the acrylic resin solution (a-1),
Thereafter, the resultant was diluted with isopropyl alcohol to obtain an acrylic resin neutralized solution (a-1N) having a resin solid content of 50%.

70% polyester resin solution (b-1):
Add 0.7 mol of neopentyl glycol, 0.3 mol of trimethylolpropane, 0.4 mol of phthalic anhydride and 0.5 mol of adipic acid to a reaction vessel, and add 200 to 230 ° C.
For 5 hours, add 0.03 mol of trimellitic anhydride and react at 180 ° C. for another 1 hour, then add butyl cellosolve, acid value 40, number average molecular weight about 6,000, resin solid content A 70% polyester resin solution (b-1) was obtained.

A 60% polyester resin neutralized solution (b-1)
N): 2-to 100 parts of polyester resin solution (b-1)
Neutralize by adding 4 parts of amino-2-methylpropanol,
Thereafter, the resultant was diluted with isopropyl alcohol to obtain a polyester resin neutralized solution (b-1N) having a resin solid content of 60%.

(B-1) to (B-3): First colored paints (B-1) to (B-3) were obtained at the compounding ratios shown in Table 1. The light transmittance of the coating films formed from the coats (B-1) to (B-3) was 0.1% or less at a cured film thickness of 20 μm.

[0070]

[Table 1]

3) Thermosetting aqueous second colored paint (C) 20% acrylic resin emulsion (c-1): 140 parts of deionized water in a reaction vessel, 30% "Newcol 707"
SF "(surfactant, manufactured by Nippon Emulsifier Co., Ltd.) and 1 part of the following monomer mixture (1) were added, and mixed by stirring in a stream of nitrogen gas. Three parts were added. Then, after raising the temperature to 80 ° C., 79 parts of the following monomer mixture (1), 30% “New
The monomer emulsion comprising 2.5 parts of col707SF ", 4 parts of a 3% aqueous solution of ammonium persulfate 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. In addition, 80 ° C
Then, 20.5 parts of the following monomer mixture (2) and 4 parts of a 3% ammonium persulfate aqueous solution were simultaneously dropped into the reaction vessel in parallel over 1.5 hours. After completion of the addition, the mixture was aged for 1 hour, diluted with 30 parts of deionized water, and filtered at 30 ° C. with a 200 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 (c-1) having an average particle diameter of 0.1 μm and a nonvolatile content of 20%. Monomer mixture (1) Methyl methacrylate 55 parts Styrene 8 parts N-butyl acrylate 9 parts 2-hydroxyethyl acrylate 5 parts 1,6-hexanediol diacrylate 2 parts Methacrylic acid 1 part Monomer mixture (2 ) Methyl methacrylate 5 parts n-butyl acrylate 7 parts 2-ethylhexyl acrylate 5 parts methacrylic acid 3 parts 30% "Newcol 707SF" 0.5 parts (C-1) to (C-2): shown in Table 2. Thermosetting aqueous second colored paints (C-1) to (C-2) were obtained at the mixing ratio. The light transmittance of the formed coating film of the coats (C-1) to (C-2) was 15 μm in cured film thickness, (C-1) was 40%, and (C-
2) was 50%.

[0072]

[Table 2]

4) Thermosetting water-based transparent coating material (D) A transparent coating material prepared in the same manner as in the above-mentioned thermosetting water-based second colored coating material (C-1) except that Blue-G316 was omitted. (D-1).

5) Clear coat (E) 70% acrylic resin solution (a-2): 40 parts of Swazol # 1000 (manufactured by Maruzen Oil Co., Ltd.) was added to the reaction vessel and heated to 120 ° C. The monomer mixture was added using a metering pump over 3 hours.

Styrene 30 parts Butyl acrylate 35 parts 2-Ethylhexyl acrylate 10 parts Hydroxyethyl acrylate 25 parts α, α′-azobisisobutyronitrile 4 parts As described above, the hydroxyl value is 120 and the number average molecular weight is about 6, 00
0, an acrylic resin solution (a-2) having a resin solid content of 70% was obtained.

A 60% acrylic resin non-aqueous dispersion (d-
1): 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. The mixture was heated and the following monomer mixture was added dropwise over 3 hours.

Styrene 15 parts 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 30 parts of Schelsol 140 9 parts of n-heptane One hour after the completion of dropping of the monomer mixture, 0.65 part of t-butyl peroctoate, and Shelsol 140
3.5 parts of the mixture were added dropwise over 1 hour. Thereafter, stirring was continued for 2 hours while maintaining the temperature at 95 ° C. Thereafter, the pressure was reduced to remove 34 parts of the solvent to obtain an acrylic resin non-aqueous dispersion (d-1) having a resin solid content of 60% and a varnish viscosity A (Gardner bubble viscosity).

(E-1): 70% acrylic resin solution (a-2) 57 parts 60% acrylic resin non-aqueous dispersion (d-1) 50 parts Cymel 303 (Note 5) 30 parts 25% dodecylbenzenesulfonic acid Solution 4 parts BYK-300 (Note 6) 0.5 part The above mixture was adjusted to a viscosity of 30 seconds (Ford cup # 4/20 ° C.) with Swazole # 1000, and resin solid content 55
% Clear coat (E-1) was obtained.

(Note 5) Cymel 303: trade name, manufactured by Mitsui Cytec, a monomeric melamine resin.

(Note 6) BYK-300: trade name and surface conditioner manufactured by BYK Japan KK

II. Examples and Comparative Examples Examples 1 to 3 A steel sheet surface-treated with “Bonderite # 3030” (manufactured by Nippon Parkerizing Co., Ltd., a zinc phosphate treating agent) is immersed in a bath of a cationic electrodeposition paint (A-1) and subjected to a conventional method. By electrodeposition coating. The thickness of the coating film was about 20 μm based on the cured coating film. The coating film was pulled out of the bath, washed with water, and heated to about 175 ° C. to cure the coating film.

The first colored paints (B-1) to (B-3) shown in Table 3 which were adjusted to a viscosity of 25 seconds (Ford cup # 4/20 ° C.) were cured on the cured coating surface of the electrodeposition paint. It was applied by air spray at a relative humidity of 75% RH so as to have a thickness of about 20 μm based on the film thickness, and left at room temperature for about 10 minutes.

Next, on the uncured coating surface of the first colored paint,
The second colored paints (C-1) to (C-2) shown in Table 3 adjusted to a viscosity of 30 seconds (Ford cup # 4/20 ° C.) were adjusted to a relative humidity of about 15 μm based on the cured film thickness. 75
% RH by air spray and left at room temperature for about 10 minutes, then apply the transparent paint (D-1) by air spray at a relative humidity of 75% RH so as to be about 5 μm based on the cured film thickness. After leaving at room temperature for about 10 minutes,
By heating at 140 ° C. for 30 minutes, the three-layer coating film composed of the first coloring paint, the second coloring paint and the transparent paint was simultaneously crosslinked and cured.

Thereafter, a clear coat (E-1) adjusted to a viscosity of 30 seconds (Ford cup # 4/20 ° C.) was applied to the cured coating surface of the transparent paint by about 45 μm based on the cured film thickness.
Paint by air spray so that at room temperature
After leaving it to stand for 0 minutes, it was heated at 140 ° C. for 30 minutes to cure by crosslinking.

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

Test Method Smoothness: Measured with a tension meter (manufactured by RENAULY). The higher the value, the better the smoothness.

Brightness: Measured by a sharpness measuring machine 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 according to the following criteria.

：: No abnormality is observed, Δ: Slight defects such as glossiness and blistering are observed, and X: Defects such as glossiness and blistering are remarkable.

[0090]

[Table 3]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B05D 7/24 303 B05D 7/24 303B

Claims (7)

[Claims] 1. A metallic electrodeposition coating composition is coated with a cationic electrodeposition coating composition (A) and cured by heating, after which a neutralized polyvalent carboxylic acid resin having an acid value of 5 to 100 and an amino resin are essential components. The organic solvent type or non-aqueous dispersion type thermosetting first coloring paint (B) having a base concealing property, the thermosetting aqueous second coloring paint (C) and the thermosetting aqueous transparent coating (D) After the coating, the coating is heated and the above (B), (C) and (D)
A method for forming a multilayer coating film, comprising simultaneously curing a layer coating film, then applying a thermosetting transparent coating material (E), and curing by heating. 2. The method according to claim 1, wherein the first colored paint (B) is a solid color paint. 3. The method according to claim 1, wherein the first colored paint (B) is a cured coating film having a thickness of 30 μm.
, The light transmittance at a wavelength of 400 to 700 nm is 5%
The method according to claim 1, wherein the amount is not more than 3%. 4. The method according to claim 1, wherein the second colored paint (C) is a solid color paint or a metallic paint. 5. The method according to claim 1, wherein the second colored coating material (C) has a cured coating film of 15 μm.
, The light transmittance at a wavelength of 400 to 700 nm is 5%
The method according to claim 1, wherein the amount is not more than 3%. 6. The method according to claim 1, wherein the transparent paint (D) contains a metallic pigment and / or a colored pigment. 7. The transparent coating material (D) has a light transmittance in the range of 6 to 95% at a cured film thickness of 15 μm.
The described method.