JP2000317394A - Method for forming coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a novel method for forming a coating film in which an electrodeposition coating film is coated directly with a colored finish coating and a clear coating in turn without applying an intermediate coating. SOLUTION: In a method in which a multilayer coating film is formed by coating an electrodeposition coating film with a first colored finish coating and a clear coating in turn, the first finish coating contains a resin which is crosslinked/cured by a urethane-forming reaction as a main component. In a method for forming a multilayer coating film by coating the electrodeposition coating film with a first colored finish coating, a second colored finish coating, and a clear coating in turn, the first finish coating contains a resin which is crosslinked/cured by a urethane-forming reaction as a main component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel coating film forming method in which a colored top coat and a clear paint are sequentially applied directly to the surface of an electrodeposited coat without applying an intermediate coat.

[0002]

2. Description of the Related Art An electrodeposition paint is applied to a metal object such as an automobile outer panel, and a colored top coat and a clear paint are sequentially applied to the surface of the electrodeposition without applying an intermediate coat. To form a multilayer coating film has already been adopted. In particular, a thermosetting resin composition containing a hydroxyl group-containing polyester resin and a melamine resin is often used as a resin component of these colored topcoat paints.

[0003] However, a multilayer coating film formed by applying a colored top coating material and a clear coating material to an electrodeposition coated surface without applying an intermediate coating material has insufficient chipping resistance and rust prevention performance. There is a strong desire to improve these performances

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-layer coating film which is formed by applying a colored top coat and a clear paint directly to the surface of an electrodeposition coating film without applying an intermediate coat. As a result of intensive research, they have found that the purpose can be achieved by using a paint containing a resin that is crosslinked and cured mainly by a urethane-forming reaction. The invention has been completed.

That is, according to the present invention, there is provided a method for forming a multi-layer coating film by sequentially applying a first colored top coating material and a clear coating material on an electrodeposition coating film surface. A coating film forming method is provided, which is a coating material containing a resin mainly crosslinked and cured by a urethanization reaction.

The present invention also includes applying the second colored topcoat after applying the first colored topcoat and before applying the clear paint.

Hereinafter, the method of the present invention will be described in more detail.

The object to be coated in the present method includes a conductive metal product that can be electrodeposited, and it is preferable to use an automobile outer panel that requires particularly excellent chipping resistance as the object to be coated. It is desirable that the surface of the object to be coated is subjected to a chemical conversion treatment or a cleaning treatment.

The electrodeposition paint to be applied to these objects may be either an anionic type or a cationic type, but a cationic type having good anticorrosion is preferred. Known cationic electrodeposition paints can be used. For example, an aqueous paint containing a base resin (a) having a hydroxyl group and a cationic group and a block polyisocyanate compound (b) is preferable. Examples of the base resin (a) include the following.

1) a reaction product of an epoxy resin and a cationizing agent; 2) a polycondensate of a polycarboxylic acid and a polyamine (see US Pat. No. 2,450,940) protonated with an acid; 3) polyisocyane A protonated compound or a polyadduct of a polyol and a mono or polyamine with an acid; 4) a protonated copolymer of an acrylic or vinyl monomer containing a hydroxyl group and an amino group with an acid ( Japanese Patent Publication No. 45-12395, Japanese Patent Publication No. 45
4) A product obtained by protonating an adduct of a polycarboxylic acid resin and an alkyleneimine with an acid (see U.S. Pat. No. 3,403,088). Of these, a base resin obtained by reacting a cationizing agent with an epoxy resin obtained by reacting the polyphenol compound and epichlorohydrin contained in 1) is particularly preferable because it forms an electrodeposition coating film having excellent anticorrosion properties. This epoxy resin has two or more epoxy groups in one molecule, a number average molecular weight of 200 to 2,000, and an epoxy equivalent of 190 to 20.
Those in the range of 00 are particularly suitable. Examples of such an epoxy resin include bis (4-hydroxyphenyl) -2,2-propane, 4,4'-dihydroxybenzophenone, and bis (4-hydroxyphenyl) -1,1.
-Ethane, bis- (4-hydroxyphenyl) -1,1
-Isobutane, bis (4-hydroxy-tert-butyl-phenyl) -2,2-propane, bis (2-hydroxybutyl) methane, 1,5-dihydroxynaphthalene, bis (2,4-dihydroxyphenyl) methane, tetra (4-hydroxyphenyl) -1,1,2,2-ethane, 4,4′-dihydroxydiphenyl ether,
4,4'-dihydroxydiphenyl sulfone, pheno-
And polyglycidyl ether compounds of polyphenol compounds selected from lunovolak, cresol-novolak and the like.

The cationizing agent in the above 1) reacts almost or all of the epoxy groups in the epoxy resin to form a cationic group such as a secondary amino group, a tertiary amino group or a quaternary ammonium base. The base resin having a hydroxyl group and a cationic group (a)
Is obtained. Such cationizing agents include, for example, amine compounds such as primary amines, secondary amines, tertiary amines, and polyamines.

The introduction of hydroxyl groups in the base resin (a) can be carried out, for example, by reacting an alkanolamine as an cationizing agent with an epoxy group. In particular, primary hydroxyl groups can be introduced into a block polyisocyanate compound (crosslinking agent). ) Is preferred because of its excellent cross-linking reactivity with). The amount of the hydroxyl group in the base resin (a) is 20 to 500 in terms of the hydroxyl equivalent.
0, particularly preferably 100 to 1000 mgKOH / g.
Further, the amount of the cationic group is preferably at least the minimum necessary for stably dispersing the base resin (a) in water, and is 3 to 3 in KOH (mg / g solid content) (in terms of amine value).
200 is preferred. It is desirable that the base resin (a) does not have a free epoxy group.

Block Polyisocyanate as Crosslinking Agent
The compound (b) is a compound in which substantially all of the isocyanate groups of the polyisocyanate compound are blocked with a volatile blocking agent. When heated above a predetermined temperature, the blocking agent is dissociated and the isocyanate group is dissociated. -The group regenerates,
It participates in a crosslinking reaction with the base resin (a).

The polyisocyanate compound is a compound having two or more free isocyanate groups in one molecule, and is a known aliphatic diisocyanate, alicyclic diisocyanate, aromatic diisocyanate or polyisocyanate. −
And urethanated adducts, biuret-type adducts, isocyanuric ring-type adducts, and the like. Known blocking agents such as phenols, alcohols, active methylenes, mercaptans, oximes, sulfites, and lactams can be used.

The cationic electrodeposition paint is prepared by neutralizing the cationic group in the base resin (a) with an acidic compound such as acetic acid, formic acid, lactic acid or phosphoric acid, and then neutralizing the cationic group together with the block polyisocyanate compound (b). It can be prepared by mixing with water, and the pH at the time of coating is generally 3 to 9, particularly 5 to 7, and the solid content concentration is suitably in the range of 5 to 30% by weight.

The object to be coated is immersed in a cationic electrodeposition coating bath as a cathode, the bath temperature is 20 to 35 ° C., and the voltage is 100 to 400.
V for 1 to 10 minutes to perform electrodeposition coating. The thickness of the cured coating is preferably 10 to 40 μm. Lift the object to be coated from the paint bath and wash it appropriately
The coating film can be cured by heating to 0 to 200 ° C.
The first colored top coating used in the present method is a coating applied to the cured or uncured electrodeposition coating film surface prior to the clear coating, and is mainly composed of a resin component and a coloring pigment which are cross-linked and cured by a urethane reaction. And a single coating film having a solid color tone or a metallic tone, and a base coating hiding power that is at least as high as the color tone of an adjacent lower electrodeposition coating film cannot be visually recognized through the coating film. To form

Examples of the resin component which is used in the first colored top coat and which is crosslinked and cured by a urethanization reaction include, for example,
Examples include a self-crosslinkable resin having a hydroxyl group and an isocyanate group in the same molecule, and a composition obtained by mixing a resin (compound) having these functional groups separately.

A resin having a hydroxyl group and an isocyanate group in the same molecule is self-curing, and it is not essential to use a cross-linking agent together. Specifically, known resins exemplified below can be used. it can.

1) The isocyanate group in the skeleton of a polymer mainly containing an isocyanate group-containing radical polymerizable monomer
A self-curable resin obtained by blocking a part of the hydroxyl group and then reacting the remaining unblocked isocyanate group with an alkanolamine to introduce a hydroxyl group (for details, see JP-A-3-25.
No. 8826).

2) Tertiary amino groups and / or 4 in one molecule
A part of the isocyanate group in a polymer skeleton having a number average molecular weight of 500 to 50,000 having a quaternary ammonium group and two or more isocyanate groups, and then the remaining unblocked isocyanate group A self-curable resin obtained by introducing a hydroxyl group by reacting an alkanolamine with the resin (for details, see JP-A-4-39322).

3) A glycidyl group and two or more isocyanate groups in one molecule having a number average molecular weight of 500 to 5
A part of the isocyanate group in the polymer skeleton of 0000 is blocked, and then the glycidyl group and the remaining unblocked isocyanate group are reacted with an alkanolamine to form a polymer.
Self-curable resin having a tertiary amino group or a quaternary ammonium base and a hydroxyl group introduced therein (for details, see JP-A-4-45120).
Reference).

4) A glycidyl group and two or more isocyanate groups in one molecule having a number average molecular weight of 500 to 5
All the isocyanate groups in the polymer skeleton of 0000 are blocked, and then the glycidyl group is reacted with an alkanolamine to form a blocked isocyanate group and a secondary or tertiary amino group or quaternary group in one molecule. Self-curing resin having an ammonium base and a hydroxyl group introduced therein (for details, see JP-A-4-4512).
No. 0).

5) A glycidyl group and two or more isocyanate groups in one molecule having a number average molecular weight of 500 to 5
All the isocyanate groups in the polymer skeleton of 0000 are blocked, and a glycidyl group is reacted with a primary or secondary tertiary amine to form a blocked isocyanate group and a glycidyl group in one molecule.
Self-curing resin having a tertiary amino group or a quaternary ammonium base and a hydroxyl group introduced therein (for details, see JP-A-4-45120).

6) A hydroxyl-containing vinyl monomer is allowed to react with the-part of the isocyanate group in a vinyl polymer skeleton having two or more isocyanate groups in one molecule to form a polymerizable unsaturated bond. After completely introducing the isocyanate group remaining in the polymer skeleton, the unsaturated monomer composition containing a hydroxyl group-containing vinyl monomer as an essential component is introduced into the polymerizable unsaturated monomer. Self-curable resin obtained by polymerizing to a saturated bond (for details, see JP-A-4-275319).

7) The-part of the isocyanate group in a vinyl polymer skeleton having two or more isocyanate groups in one molecule is blocked with a blocking agent, and then the polymer remains in the polymer skeleton. After reacting a hydroxyl group-containing vinyl monomer with the isocyanate group to introduce a polymerizable unsaturated bond,
A self-curable resin obtained by polymerizing an unsaturated monomer composition containing a hydroxyl group-containing vinyl monomer as an essential component into the above-mentioned polymerizable unsaturated bond (for details, see JP-A-4-2753)
No. 19).

8) In a vinyl polymer having two or more free isocyanate groups in one molecule, a part of the free isocyanate group in an acrylic resin having two or more hydroxyl groups in one molecule is used. A self-curing resin in which a blocked isocyanate group and a hydroxyl group coexist in one molecule obtained by reacting a part of hydroxyl groups and then reacting a blocking agent with all remaining free isocyanate groups (for details, See JP-A-5-247175).

9) All of the free isocyanate groups in a vinyl polymer in which a free isocyanate group and a block isocyanate group coexist in one molecule have two or more hydroxyl groups in one molecule. A self-curing resin in which a block isocyanate group and a hydroxyl group coexist in one molecule obtained by reacting a part of the hydroxyl group in an acrylic resin (for details, see JP-A-5-24)
No. 7175).

10) In a vinyl polymer having two or more free isocyanate groups in one molecule, the hydroxyl group in a polyolefin resin having two or more hydroxyl groups in one molecule in a part of the free isocyanate groups Is reacted with a blocking agent on all remaining free isocyanate groups. A self-curing resin having both a blocked isocyanate group and a hydroxyl group in one molecule (for details, see JP-A-Hei. 5-3314
No. 13). 11) In a polyolefin resin having two or more hydroxyl groups in one molecule in all of the free isocyanate groups in a vinyl polymer in which a free isocyanate group and a block isocyanate group coexist in one molecule. A self-curable resin having both a block isocyanate group and a hydroxyl group in one molecule obtained by reacting a part of the hydroxyl group (see JP-A-5-3314).
No. 13).

12) Two or more isocyanates in one molecule
A hydroxyl group-containing vinyl monomer is reacted with a part of the isocyanate group in the vinyl polymer skeleton having a hydroxyl group to introduce a polymerizable double bond, and then the isocyanate group remaining in the polymer skeleton is introduced. After completely blocking the hydroxyl group with a blocking agent, an unsaturated monomer component having a hydroxyl group-containing vinyl monomer and a carboxyl group (including an acid anhydride group) -containing monomer as an essential component is introduced into the above polymerizable polymer. Self-curing resin having both a block isocyanate group formed by polymerization to a double bond and a hydroxyl group (for details, see JP-A-5-178958).

13) Two or more isocyanates in one molecule
A part of the isocyanate group in the vinyl polymer skeleton having a hydroxyl group is blocked with a blocking agent, and then the hydroxyl group-containing vinyl monomer is allowed to react with the isocyanate group remaining in the polymer skeleton. After the introduction of the polymerizable double bond, the unsaturated monomer component having a hydroxyl group-containing vinyl monomer and a carboxyl group (including an acid anhydride group) -containing monomer as essential components is added to the above-mentioned polymerizable double bond. Self-curing resins having both a block isocyanate group and a hydroxyl group polymerized by bonding (see JP-A-5-178958).

14) Two or more isocyanates in one molecule
A hydroxyl group-containing vinyl monomer is caused to react with a part of the isocyanate group in the vinyl polymer having a hydroxyl group to introduce a polymerizable double bond, and then the isocyanate remaining in the polymer is introduced. After the group is completely blocked with a blocking agent, the unsaturated monomer component having a hydroxyl group-containing vinyl monomer, a tertiary amino group and / or a quaternary ammonium group-containing vinyl monomer as an essential component is introduced into the above-mentioned polymerization. Self-curable resin having both a block isocyanate group and a hydroxyl group which are polymerized into a carboxylic double bond (for details, see JP-A-5-178959).

15) Two or more isocyanates in one molecule
A part of the isocyanate group in the vinyl polymer skeleton having a hydroxyl group is blocked with a blocking agent, and then the hydroxyl group-containing vinyl monomer is allowed to react with the isocyanate group remaining in the polymer skeleton. After introducing a polymerizable double bond, the unsaturated monomer component having a hydroxyl group-containing vinyl monomer, a tertiary amino group and / or a quaternary ammonium group-containing vinyl monomer as an essential component, Self-curable resin having both a block isocyanate group and a hydroxyl group which are polymerized into a carboxylic double bond (for details, see JP-A-5-178959).

16) Two or more isocyanates in one molecule
A hydroxyl group-containing vinyl monomer is reacted with a part of the isocyanate group in the vinyl polymer skeleton having a hydroxyl group to introduce a polymerizable double bond, and then the isocyanate group remaining in the polymer skeleton is introduced. After completely blocking the hydroxyl group with a blocking agent, an unsaturated monomer component having a hydroxyl group-containing vinyl monomer and a glycidyl group-containing vinyl monomer as an essential component is polymerized to the polymerizable double bond introduced above. And then the second
A self-curing resin having a hydroxyl group and a block isocyanate group formed by reacting a tertiary amine with a tertiary amine (for details, see JP-A-5-178959).

17) Two or more isocyanates in one molecule
A part of the isocyanate group in the vinyl polymer skeleton having a hydroxyl group is blocked with a blocking agent, and then the hydroxyl group-containing vinyl monomer is allowed to react with the isocyanate group remaining in the polymer skeleton. After the introduction of the polymerizable double bond, an unsaturated monomer component having a hydroxyl group-containing vinyl monomer and a glycidyl group-containing vinyl monomer as an essential component is polymerized to the polymerizable double bond introduced above. A self-curable resin having a hydroxyl group and a block isocyanate group obtained by reacting a secondary amine with the secondary amine to introduce a tertiary amine (see JP-A-5-178959).

18) In a vinyl polymer having two or more free isocyanate groups in one molecule, a part of the free isocyanate group in a polyester resin having two or more hydroxyl groups in one molecule is used. A self-curing resin in which a blocked isocyanate group and a hydroxyl group coexist in one molecule obtained by reacting a part of hydroxyl groups and then reacting a blocking agent with all remaining free isocyanate groups (for details, Kaihei 6-4917
No. 2).

19) All of the free isocyanate groups in a vinyl polymer in which a free isocyanate group and a block isocyanate group coexist in one molecule have two or more hydroxyl groups in one molecule. A self-curing resin in which a block isocyanate group and a hydroxyl group coexist in one molecule obtained by reacting a part of the hydroxyl group in a polyester resin (for details, see Japanese Patent Application Laid-Open No.
-49172).

A composition comprising a mixture of a resin having a hydroxyl group and a compound having an isocyanate group can also be used as the resin composition in the first colored top coat. As the resin having a hydroxyl group, a known acrylic resin or polyester resin having two or more hydroxyl groups in one molecule can be used. The hydroxyl value of these hydroxyl-containing resins is 30 to 300, especially 60 to 250 mg KO.
H / g, acid value is 0-30, especially 2-10 mgKOH /
g, the number average molecular weight is 1,000 to 100,000, particularly 20
It is preferably in the range of 00 to 50,000.

On the other hand, the compound having an isocyanate group has two or more isocyanate groups in one molecule, for example, known aliphatic diisocyanate, alicyclic diisocyanate, aromatic diisocyanate, and the like. Polyisocyanate
Urethanized adducts, biuret-type adducts, isocyanuric ring-type adducts, and the like of the compound can be used. These are used as a crosslinking agent for a resin having a hydroxyl group. Since these isocyanate groups easily react with the above-mentioned hydroxyl groups at room temperature, from the viewpoint of storage stability, the isocyanate groups are blocked with a blocking agent, and when heated above a predetermined temperature, the blocking agent is dissociated. It is preferred that the isocyanate group be regenerated to participate in a crosslinking reaction with the hydroxyl group-containing resin. Known blocking agents such as phenol-based, alcohol-based, active methylene-based, mercaptan-based, oxime-based, sulfurous-based, and lactam-based blocking agents can be used.

The first colored top coat may further contain a melamine resin as a resin component in addition to the resin component which is crosslinked and cured by the above-described urethane-forming reaction. Such melamine resins include, for example, methylo-
Part or all of the methylol group of the fluorinated melamine has 1 carbon atom.
And a partially or fully etherified melamine resin etherified with a monohydric alcohol having a number average molecular weight of 300-2.
000 is preferred. These may be those in which the methylol group is entirely etherified or partially etherified and the methylol group or imino group remains. The amount of the melamine resin used is, for example, 10 to 50 parts by weight, particularly 2 parts by weight, per 100 parts by weight of the resin component which is crosslinked and cured by the urethanization reaction in terms of solid content.
0-30 parts by weight are suitable.

The color pigments usable in the first colored top coat include solid color pigments, metallic pigments, and light interference pattern pigments. As solid color pigments, for example, titanium oxide, zinc white, carbon black,
Cadmium red, molybdenum red, chrome erotic,
Inorganic pigments such as chromium oxide, Prussian blue, and cobalt blue; organic pigments such as azo pigments, phthalocyanine pigments, quinacridone pigments, isoindoline pigments, sulene pigments and perylene pigments, and scaly metallic pigments Examples of the light interference pattern pigment include aluminum, mica-like iron oxide, and the like, and examples thereof include mica and mica whose surface is coated with a metal oxide, but is not limited thereto. The amount of these color pigments varies depending on the coloring power of each pigment, but it is preferable that the color pigments are blended to such an extent that the color tone of the electrodeposition coating film on the coated surface cannot be visually recognized through the single coating film. .

The first colored top coat can be prepared by dissolving or dispersing, in an organic solvent, a resin component which is crosslinked and hardened by the above-mentioned urethanization reaction, and if necessary, a melamine resin, a coloring pigment and the like. Examples of the organic solvent include hydrocarbon-based, ester-based, ether-based, alcohol-based, and ketone-based coating solvents. The first colored top coat has a viscosity at the time of application of 10 to 35.
The temperature is adjusted to seconds / ford cup # 4/20 ° C., and the cured or uncured electrodeposited film is applied by air spray, airless spray, electrostatic method or the like. The coating film thickness may be at least the thickness of the base concealment film.
0 μm, especially 15-30 μm, is suitable. The coating film of the first colored top coat is cross-linked and cured by heating at 100 to 180 ° C. for about 10 to 40 minutes. After the coating film is cured by heating or in an uncured state, The method can be achieved by applying clear paint.

The clear paint used in the present method is a paint to be applied to the cured or uncured coating surface of the first colored top coat, and is a resin component known per se that forms a colorless transparent or colored transparent coating film. And a thermosetting paint containing an organic solvent.

The resin component used in the clear paint includes an acrylic resin having a crosslinkable functional group (for example, a hydroxyl group, an epoxy group, a carboxyl group, an alkoxysilane group, etc.), a vinyl resin, a polyester resin, an alkyd resin, and a urethane resin. A base resin selected from such as, a melamine resin alkylated to cure and crosslink these, a urea resin, a guanamine resin, a polyisocyanate compound which may be blocked, an epoxy compound,
A component comprising a crosslinking agent selected from a carboxyl group-containing compound and the like can be suitably used. These ratios are preferably 50 to 90% for the base resin and 50 to 10% for the crosslinking agent, based on the total weight of both components. Further, a resin component which is cross-linked and cured by a urethanization reaction exemplified in the first colored top coating material can also be used as a resin component in the clear coating material.

Any organic solvent may be used as long as it can mix, dissolve, and disperse these two components. For example, ordinary organic solvents such as hydrocarbons, esters, ethers, alcohols, and ketones can be used. Paint solvents can be used.

The clear paint may be appropriately blended with the solid color pigments, metallic pigments, light interference pigments, etc. to such an extent that the transparency of the clear coating film is not impaired.

The viscosity at the time of application of the clear paint is 15 to 40 seconds (for ford cup # 4/20 ° C.), and the solid content is 30.
６５65% by weight, and the cured or uncured coating surface of the first colored top coat is applied by airless spraying, air spraying, electrostatic coating, or the like so that the thickness of the cured coating film is about 20 to 80 μm. By coating and heating at 100 to 180 ° C. for 10 to 40 minutes, the coating film is cross-linked and cured, and the present method is achieved.

In this method, the above-mentioned electrodeposition coating material, first colored top coating material and clear coating material are coated in a three-coat one-bake system (3C
1B), a three-coat two-bake system (3C2B) and a three-coat three-bake system (3C3B) to form a multi-layer coating film. Further, the present invention also includes a method in which after applying the electrodeposition paint and the first colored topcoat, a second colored topcoat is applied, and then a clear paint is applied to form a multilayer coating film. In this method, the above-mentioned paints can be suitably used as the electrodeposition paint, the first colored overcoat paint, and the clear paint.

The second colored top coat is a paint to be applied to the cured or uncured surface of the first colored top coat prior to the application of the clear paint, and the single coated film is solid color tone or metallic tone. This is a thermosetting liquid paint that forms a transparent or opaque coating film with optical interference tone. By coating this second colored top coat, performance such as smoothness and sharpness can be improved.

The second colored top coat is prepared by mixing and dispersing a resin component and a color pigment in an organic solvent to form a solid color tone, a metallic tone, and a light interference tone.

The resin component used in the second colored top coat includes an acrylic resin having a crosslinkable functional group (for example, a hydroxyl group, an epoxy group, a carboxyl group, an alkoxysilane group, etc.), a vinyl resin, a polyester resin, and an alkyd resin. , A base resin selected from urethane resin and the like,
A component comprising a cross-linking agent selected from an alkyl etherified melamine resin, a urea resin, a guanamine resin, an optionally blocked polyisocyanate compound, an epoxy compound, a carboxyl group-containing compound, etc. for crosslinking and curing these is preferably used. Can be used. These ratios are 50 to 90% based on the total weight of both components.
%, And the crosslinking agent is preferably in the range of 50 to 10%. further,
The resin component which is crosslinked and hardened by the urethanization reaction exemplified in the first colored top coat can also be used as the resin component in the second colored top coat.

As an organic solvent, these components are mixed,
Any solvent can be used as long as it can be dissolved and dispersed, and a normal paint solvent such as a hydrocarbon-based, ester-based, ether-based, alcohol-based, or ketone-based paint can be used. As the coloring pigment, solid color pigments, metallic pigments, light interference pattern pigments and the like exemplified as the first colored top coat paint can be used,
The amount of these coloring pigments varies depending on the coloring power of each pigment, but is preferably within a range in which the single coating film of the second colored top coat has a transparent feeling. The viscosity of the second colored top coat at the time of application is adjusted to 10 to 35 seconds / ford cup # 4/20 ° C., and air spray,
The first colored top coat is applied to the cured or uncured coating surface by airless spray, electrostatic method, or the like. The thickness of the coating may be not more than the thickness of the underlayer concealment, and for example, 10 to 40 μm, particularly 15 to 30 μm is suitable for a cured coating film. The coating film of the second colored top coat is 100 to 180 ° C.
The film is crosslinked and cured by heating for about 10 to 40 minutes, but this method can be achieved by applying a clear paint to the coated surface after heating and curing the coated film or in an uncured state.

In this method, the above-mentioned electrodeposition paint, the first colored top coat, the second colored top coat and the clear paint are coated in four coats.
4-bake system (4C1B), 4-coat 2-bake system (4C2B), 4-coat 3-bake system (4C3B), 4
This is achieved by applying a coat 4 bake method (4C4B) to form a multilayer coating film.

[0053]

According to the present invention, a first colored top coat, a second colored top coat (optional), and a clear paint are sequentially applied to the electrodeposition coating surface without applying an intermediate coat, and a metal such as an automobile outer panel is applied. In forming a multi-layer coating film on an object to be coated, by using a coating material containing a resin which is cross-linked and cured by a urethane-forming reaction as the first colored overcoating material, the chipping resistance of the multi-layer coating film is improved. It has become possible to remarkably improve rust prevention and the like.

[0054]

EXAMPLES Examples and comparative examples according to the present invention will be described. All parts and percentages are based on weight.
The film thickness of the coating is for the cured coating.

1. Preparation of sample 1) Coating object: steel sheet surface-treated with zinc phosphate.

2) Cationic electrodeposition paint a): "Electron # 9600" (manufactured by Kansai Paint Co., Ltd.)
Epoxy resin / block iosocyanate cationic electrodeposition coating) 3) First colored top coating a) 100 parts of self-crosslinking resin (Note 1), 80 parts of titanium white pigment, 0.5 part of carbon black The solvent (xylene)
And dispersed into a mixture having a viscosity of 13 seconds (for ford cup # 4 /
20 ° C).

(Note 1) Self-crosslinking resin: m-isopropenyl-α, α'-dimethylbenzyl isocyanate 50
Part, n-butyl acrylate 30 parts and 2-ethylhexyl acrylate 20 parts polymerized isocyanate group-containing acrylic resin (weight average molecular weight about 6000, isocyanate value 100 g / kg) 240 parts (solid Minutes),
39 parts of n-butyl methacrylate, 20 parts of styrene, 2
-Hydroxy group-containing resin obtained by polymerizing 15 parts of ethylhexyl acrylate, 25 parts of 2-hydroxyethyl acrylate and 1 part of acrylic acid (having a hydroxyl value of 120 mgKOH /
g, acid value 7.7 mgKOH / g, weight average molecular weight about 10
262) (solid content) at room temperature and stirred, and the isocyanate value was measured. Mixed varnish isocyanate
The toning number was 47 (initial isocyanate number). Isocyanate after reaction for about 3 hours at 40 ° C with stirring
A self-crosslinkable resin obtained by adding methyl ethyl ketoxime (blocking agent) and reacting at 60 ° C. for 2 hours when the to-value reaches 45.

B): 100 parts of a self-crosslinkable resin (Note 1)
20 parts of melamine resin (Note 2), 80 parts of titanium white pigment, and 0.5 part of carbon black are mixed and dispersed in a solvent (xylene) to adjust the viscosity to 13 seconds (for ford cup # 4/20 ° C.). did.

(Note 2) Melamine resin: butyletherified melamine resin.

C): 70 parts of hydroxyl group-containing resin (Note 3), 20 parts of melamine resin (Note 2), 80 parts of titanium white pigment, car
0.5 parts of bon black was mixed and dispersed in a solvent (xylene) to adjust the viscosity to 13 seconds (Ford cup # 4/20 ° C.).

(Note 3) Hydroxy group-containing resin: An acrylic resin using 52 parts of methyl methacrylate, 32 parts of n-butyl acrylate, 15 parts of hydroxyethyl methacrylate, and 1 part of acrylic acid, and has a hydroxyl value. 65mgKOH /
g, number average molecular weight is about 12,000.

5) Preparation of Second Colored Paint a): 70 parts of a hydroxyl group-containing resin (Note 3), 20 parts of a melamine resin (Note 2), 80 parts of titanium white pigment, and 0.5 part of carbon black in a solvent ( The resulting mixture was mixed and dispersed in xylene) to adjust the viscosity to 13 seconds (for ford cup # 4/20 ° C).

6) Clear paint a): "MAGICRON KINO # 1001T2" (trade name, manufactured by Kansai Paint Co., Ltd., acid epoxy-based paint containing carboxyl group-containing acrylic resin and epoxy group-containing compound).
The viscosity was adjusted to 22 seconds (Ford cup # 4/20 ° C).

2. Examples and Comparative Examples Cationic electrodeposition paint a) The object to be coated was immersed in a bath as a cathode, electrodeposited at a voltage of 300 V to a thickness of 20 μm, washed with water, and then washed at 170 ° C. for 20 minutes. The coating was cured by heating. A first colored topcoat, a second colored topcoat, and a clear paint were sequentially applied to this electrodeposition coated steel sheet. Table 1 shows these coating steps and the performance test results of the obtained coating films.

[0065]

[Table 1]

The test method is as follows.

Chipping resistance: Using a gravelometer (manufactured by Q Panel Co., Ltd.), apply 500 g of No. 7 crushed stone 4 times on the coated surface.
At an angle of 5 ° and at 20 ° C., an air pressure of 0.3 MPa
To impact the coating. Then, an adhesive cellophane tape was stuck to the coated surface, and the state of peeling of the coating film due to impact after being rapidly peeled was examined. ○ indicates little peeling of the clear coating film, Δ indicates slight peeling of the clear coating film, and X indicates many peeling of the clear coating film.

Finish appearance: The smoothness of the coated surface was visually evaluated.は indicates good smoothness, 劣 indicates poor smoothness, and × indicates very poor smoothness.

Modification phenomenon: Visual evaluation.は indicates good glossiness, Δ indicates poor glossiness, and × indicates very poor glossiness.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // C25D 13/00 308 C25D 13/00 308C

Claims (2)

[Claims] 1. A method for forming a multi-layer coating film by sequentially applying a first colored top coating material and a clear coating material on an electrodeposition coating film surface, wherein the first colored top coating material is crosslinked mainly by a urethane-forming reaction. A method for forming a coating film, which is a paint containing a curable resin. 2. A method of forming a multi-layer coating by sequentially applying a first colored top coat, a second colored top coat, and a clear paint on an electrodeposition coating surface, wherein the first colored top coat is mainly composed of A method for forming a coating film, which is a coating material containing a resin which is crosslinked and cured by a urethanization reaction.