JPH06233965A - Two coat one bake coating - Google Patents

Abstract

PURPOSE:To apply a water-based paint composition obtained by adding pigment in a dispersion manner to a specific ratio mixture composition of specific vinyl polymer containing amide group and an oligomer water dispersion material containing urethane to a base and clear-coat powder without curing the composition, and finally bake it to obtain a satisfactory coated appearance. CONSTITUTION:A water-based paint composition obtained by adding 2 to 100 pts.wt. of pigment to 100 pts.wt. (solid) of a water dispersion composition which contains 95 to 10wt.% of a film formable vinyl polymer obtained by copolymerizing a variety of ethylene monomers and neutralizing part of its acid group and 5 to 90wt.% (solid) of an oligmer water dispersion material containing urethane, is applied to the surface of a base. Next, a powder clear- coating crude composition with the ratio of number of epoxy groups in acrylic resin to that of carboxylic groups in polyvalent carboxylic acid being 10/6 to 10/10 is applied, and then is baked. Consequently, the objective two coat one backing method ideal from a viewpoint of sanitation and environment integrity and giving a satisfactory coat appearance is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention applies a metallic base paint and a clear paint to each other in the coating of automobiles.
The present invention relates to a two-coat / one-bake coating method in which curing is performed together.

[0002]

2. Description of the Related Art Up to now, in the coating of automobiles, a metallic base paint containing a metallic pigment as a top coat has been applied to an undercoated or middle-coated coated plate, and then this coat is wet-on-wet without curing. A two-coat / one-bake coating method (2C1B coating method) in which a clear coating is repeatedly applied and the metallic base coating and the clear coating are cured together is performed.

From the viewpoint of hygiene and environmental protection, it is preferable to replace these paints with solvent-based paints by water-based paints or powder paints. However, in the 2C1B coating method, metallic base paints are replaced with water-based paints and clear paints are powdered. Most practical is to use body paint.

As an attempt to convert a metallic base coating material into an aqueous coating material, for example, JP-A-58-168664 discloses a metallic base coating material using an aqueous polyurethane dispersant, and JP-A-1-287183 discloses an acrylic emulsion and urethane. Aqueous metallic base paints containing emulsions and crosslinkers are disclosed.

However, such a coating has a problem in the orientation of the metal pigment contained therein and a problem in the appearance of the resulting coating film.

The present inventors have previously described (a) an amide group-containing ethylenic monomer, an acidic group-containing ethylenic monomer,
Number average molecular weight 6000-5 obtained by copolymerizing hydroxyl group-containing ethylenic monomer and other ethylenic monomer
95 to 10% by weight (solid content) of a film-forming polymer obtained by neutralizing at least a part of the acidic groups of the 0000 copolymer, and (b) a molecular weight of 10 having a terminal hydroxyl group.
Hydrophilic group-containing oligomers obtained by reacting 0 to 5000 diol compounds, diisocyanate compounds and compounds having at least one active hydrogen in the molecule and having hydrophilic groups are primary and / or secondary. An aqueous metallic base paint using a mixture with 5 to 90% by weight (solid content) of a urethane-containing aqueous dispersion obtained by dispersing in an aqueous medium containing a polyamine has been proposed (JP-A-4-25582).

The above aqueous metallic base paint is used in combination with a solvent-based clear paint prepared by mixing fine acrylic resin particles in an acrylic resin varnish and a melamine resin varnish or a solvent-based clear paint composed of an acrylic resin varnish and an isocyanate curing agent in a 2C1B coating form. When used, it has a large non-volatile content, and the orientation of the metallic pigment is extremely excellent, so that a high-appearance coating film can be provided.

However, Japanese Patent Laid-Open No. 25582/1992 makes no mention of a powder clear coating composition.

In the case of a coating method in which a water-based base coating is used and then a powder clear coating is applied without curing, the powder coating generally has a large coating viscosity at the time of baking and a cooling shrinkage degree as compared with the base coating. Since it is large, the coating film interface is disturbed and the appearance tends to be deteriorated, and the 2C1B-based coating method using an aqueous base coating material and a powder clear coating material has not yet been successful.

For example, in Japanese Unexamined Patent Publication No. 52-69446, after coating with an aqueous base paint, preheating is carried out under extremely specific conditions so that the volatile content in the paint film is 6% or less, and then the powder is used. Paint is applied and baked.

[0011]

Therefore, after coating the water-based base coating, powder clear coating is performed without curing,
There is a demand for a 2C1B coating method capable of obtaining a high-appearance coating film by baking, and it is an object of the present invention to meet such a problem.

[0012]

According to the present invention, the above objects are (a) 5 to 40% by weight of an amide group-containing ethylenic monomer, 3 to 15% by weight of an acidic group-containing ethylenic monomer, and 10 to 40% by weight. Film formation obtained by neutralizing at least a part of acidic groups of a copolymer having a number average molecular weight of 6000 to 50,000 obtained by copolymerizing a weight% of a hydroxyl group-containing ethylenic monomer and the remaining amount of another ethylenic monomer. Vinyl polymer 95 to 10% by weight (solid content), and (b) a diol compound having a terminal hydroxy group and a molecular weight of 100 to 5000, a diisocyanate compound and a hydrophilic group having at least one active hydrogen in the molecule. The hydrophilic group-containing oligomer obtained by reacting the compound having the above with an isocyanate-rich condition is used as a primary polyamine or a secondary polyamine. Alternatively, 100 parts by weight of the pigment (c) is added to an aqueous dispersion composition containing 5 to 90% by weight (solid content) of a urethane-containing aqueous dispersion obtained by dispersing in an aqueous medium containing both of them. 2-10 for solid content)
An aqueous base coating composition containing 0 parts by weight of a dispersion is coated on a substrate, and then 35 to 65% by weight of an epoxy group-containing monomer and 65 to 35% by weight of another ethylenic monomer which does not react with an epoxy group. It is composed of an epoxy group-containing acrylic resin obtained by copolymerizing and a polyvalent carboxylic acid, and the number ratio of epoxy groups in the acrylic resin / carboxyl groups in the polyvalent carboxylic acid is 10/6 to 10/10. It is achieved by a two-coat, one-bake coating method, which comprises applying a powder clear coating composition and then baking.

The aqueous base coating composition used in the present invention is a mixture containing a specific amide group-containing vinyl polymer and a urethane-containing oligomeric water dispersion in a specific ratio and a pigment dispersed therein.

The amide group-containing ethylenic monomer used to obtain the film-forming vinyl polymer (a) of the present invention is
Usually (meth) acrylamides. Examples of such (meth) acrylamides include acrylamide, methacrylamide, N, N-dimethylacrylamide,
N, N-dimethylmethacrylamide, N, N-dibutylacrylamide, N, N-dibutylmethacrylamide,
N, N-dioctyl acrylamide, N, N-dioctyl methacrylamide, N-monobutyl acrylamide,
Examples thereof include N-monobutyl methacrylamide, N-monooctyl acrylamide and N-monooctyl methacrylamide. Preferred (meth) acrylamides are acrylamide or methacrylamide.

Examples of the acidic group of the acidic group-containing ethylenic monomer include a carboxyl group and a sulfonic acid group. Examples of the carboxyl group-containing monomer include styrene derivatives (eg, 3-vinylsalicylic acid, 3-vinylacetylsalicylic acid, etc.); (meth) acrylic acid derivatives (eg, acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, etc.) Can be mentioned. Further, examples of the sulfonic acid group-containing ethylenic monomer include p-vinylbenzene sulfonic acid and 2-acrylamidopropane sulfonic acid.

The acidic group-containing ethylenic monomer may be a half ester, half amide or half thioester of a dibasic acid monomer. Examples of such are maleic acid, fumaric acid, half esters of itaconic acid, half amides, half thioesters. Alcohol forming an ester has 1 to 12 carbon atoms, for example, methanol, ethanol, propanol, butanol, methyl cellosolve, ethyl cellosolve, dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol, propargyl alcohol and the like. Preferred are butanol, dimethylaminoethanol, diethylaminoethanol, acetol, allyl alcohol, and propargyl alcohol.

The mercaptan forming the half thioester includes those having 1 to 12 carbon atoms, such as ethyl mercaptan, propyl mercaptan and butyl mercaptan. Examples of the amine forming the half amide include those having 1 to 12 carbon atoms, such as ethylamine, diethylamine, butylamine, dibutylamine, cyclohexylamine, aniline and naphthylamine. Of these, the half thioester compounds have some problems in terms of odor, and half esters and half amides are preferably used. The half-esterification, half-thioesterification or half-amidation reaction is carried out according to a conventional method at a temperature from room temperature to 120 ° C., and in some cases, using a tertiary amine as a catalyst.

Examples of the hydroxyl group-containing ethylenic monomer are 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2,4-dihydroxy-4'-vinylbenzophenone, N- (2-hydroxyethyl) acrylamide, N
Examples include-(2-hydroxyethyl) methacrylamide.

The film-forming vinyl polymer of the present invention can be obtained by copolymerizing the above monomers with other ethylenic monomers by a known method. Examples of other ethylenic monomers include styrene, α-methylstyrene, acrylates (eg methyl acrylate, ethyl acrylate, butyl acrylate or 2-ethylhexyl acrylate), methacrylic acid esters (eg methacrylic acid). And methyl, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, p-butyl methacrylate) and the like.

The amount of the amide group-containing ethylenic monomer used for preparing the film-forming vinyl polymer is 5-40.
%, Preferably 8 to 30% by weight. If the amount is less than 5% by weight, the orientation of the scaly pigment is not sufficient and the appearance of the coating film is deteriorated, and if it exceeds 40% by weight, the water resistance of the obtained coating film is deteriorated. The amount of the acidic group-containing ethylenic monomer used is 3 to 15% by weight, preferably 5 to 13% by weight. If the amount is less than 3% by weight, the water dispersibility will be poor.
If it exceeds 5% by weight, the water resistance of the coating film decreases.

The amount of the hydroxyl group-containing ethylenic monomer used is 10 to 40% by weight, preferably 13 to 30% by weight. If it is less than 10% by weight, the curability of the film is poor. 40
If it exceeds 5% by weight, the water resistance of the coating film decreases. The number average molecular weight of the obtained polymer is 6,000 to 50,000, preferably 8,000 to 30,000. If it is less than 6000, the workability and curability are not sufficient, and if it exceeds 50,000, the non-volatile content at the time of coating becomes too low, and the workability is rather poor. The molecular weight was measured by the GPC method.

A molecular weight of 100 to 50 having a hydroxyl group at the terminal used in the production of the aqueous dispersion (b) of the present invention.
The diol compound of 00 is generally polyether diol or polyester diol. Examples of such compounds include those obtained by polymerizing or copolymerizing alkylene oxides (ethylene oxide, propylene oxide, methylene oxide, etc.) or heterocyclic ethers (tetrahydrofuran, etc.), such as polyethylene glycol, polypropylene glycol, polyethylene-propylene glycol. , Polytetramethylene ether glycol, polyhexamethylene ether glycol, polyoctamethylene ether glycol; polyethylene adipate, polybutylene adipate, polyhexamethylene adipate,
Polyneopentyl adipate, poly-3-methylpentyl adipate, polyethylene-butylene adipate, polyneopentyl-hexyl adipate; polylactone diol, for example, polycaprolactone diol, poly-
Examples thereof include 3-methylvalerolactone diol; polycarbonate diol; or a mixture thereof.

The diisocyanate compound used in the present invention is an aliphatic diisocyanate such as hexamethylene diisocyanate, 2,2,4-trimethylhexane diisocyanate, lysine diisocyanate; carbon number 4 to 1
8 alicyclic diisocyanates, for example, 1,4-cyclohexane diisocyanate, 1-isocyanato-3-isocyanatomethyl-3,5-trimethylcyclohexane (isophorone diisocyanate), 4,4′-dicyclohexylmethane diisocyanate, methylcyclohexylene diisocyanate , Isopropylidene dicyclohexyl-4,4'-diisocyanate; modified products of these diisocyanates; mixtures thereof and the like. Preferred examples of these include hexamethylene diisocyanate and isophorone diisocyanate.

The compound having at least one active hydrogen and having a hydrophilic group in the molecule used in the present invention is
For example, a compound having a hydroxyl group and a carboxyl group, examples of the compound include dimethylol acetic acid, dimethylol propionic acid, dimethylol butyric acid, and the like,
Preferred is dimethylolpropionic acid. When preparing the hydrophilic group-containing oligomer of the present invention, the reaction is carried out under isocyanate-rich conditions, for example, in the ratio of NCO / OH equivalent ratio within the range of 1.1 to 1.9. The reaction occurs easily by mixing all compounds. The reaction may be carried out in a solvent if necessary.

The resulting hydrophilic group-containing oligomer is the first
Dispersion in an aqueous medium containing a primary polyamine or a secondary polyamine or both. In this dispersion step, the hydrophilic groups in the hydrophilic group-containing oligomer are neutralized. Neutralization is carried out with a base (eg, monomethylamine, dimethylamine, trimethylamine, triethylamine, diisopropylamine, monoethanolamine, diethanolamine, dimethylethanolamine, etc.) according to a conventional method.

The aqueous base coating composition of the present invention is usually used as a curable aqueous base coating composition by incorporating a curing agent. Melamine resin is a common example of a curing agent that can be used. The melamine resin is preferably a water-soluble melamine resin, for example, Cymel-commercially available from Mitsui Toatsu Co., Ltd.
303, Sumimar N commercially available from Sumitomo Chemical Co., Ltd.
Examples thereof include -W and the like, but the water-insoluble melamine resin can be used without any particular limitation. The amount of the melamine resin used is 5 to 60% by weight based on the film-forming vinyl polymer (a) (solid content). If the amount of the melamine resin is too small, the curability will be insufficient, and if it is too large, the cured film will be too hard and brittle.

Further, the aqueous base coating composition of the present invention contains a metal pigment (eg, aluminum pigment, bronze pigment, mica, gold pigment, silver pigment, etc.). The metal pigment is blended in an amount of 2 to 100 parts by weight based on 100 parts by weight (solid content) of the aqueous base coating composition. In addition, various additives (for example, an ultraviolet ray inhibitor, an antifoaming agent, a surface conditioner, etc.) and ordinary inorganic pigments may be added to the water-based coating composition of the present invention, if necessary.

When the above water-based base coating composition is used, both the amide group-containing vinyl polymer and the urethane bond-containing oligomer have extremely large cohesive force, so that a wet coating film excellent in coating strength can be obtained. It has been found that even if a powder clear paint is applied without curing, the interface is less disturbed and a high appearance coating film can be produced.

As described above, in the present invention, the powder clear coating composition is applied without being cured after the above-mentioned aqueous base coating composition is applied. The powder clear coating composition is epoxy. It is preferable to use a powder clear coating composition comprising a group-containing acrylic resin and a polycarboxylic acid.

In this case, the epoxy group-containing acrylic resin is
35 to 65% by weight of an epoxy group-containing monomer such as glycidyl acrylate and glycidyl methacrylate
And a resin having a glass transition temperature of 25 to 80 ° C., which is obtained by copolymerizing 65 to 35% by weight of another ethylenically unsaturated monomer that does not react with an epoxy group. As the polyvalent carboxylic acid, aliphatic, alicyclic, aromatic dicarboxylic acid, or any other polyvalent carboxylic acid,
For example, decanedicarboxylic acid is preferred. These resins and polyvalent carboxylic acid are mixed at an epoxy group / carboxyl group equivalent ratio of 10/6 to 10/10, and if desired, a coating surface modifier, an cissing inhibitor, etc. are added, for example, mixing, melting, It can be manufactured by known powder manufacturing processes such as kneading, cooling, pulverizing, and classifying. The epoxy group-containing monomer is 35
If it is less than 65% by weight, the flexibility of resin design is lowered and it is not practical, and if it exceeds 65% by weight, curability is lowered. The ratio of the epoxy group to the carboxyl group is preferably the above ratio from the viewpoint of curability and the hardness of the coating film.

The average particle size of the powder clear paint is 15
It has also been confirmed that the thickness of μm or less is necessary in order to effectively volatilize the volatile matter when forming a coating film and obtain a high-appearance coating film. In addition, the average particle size is 0.
It is particularly preferable to use resin fine particles having 001 to 10 μm, a glass transition temperature of 50 to 150 ° C. and a solubility parameter (SP) value of 9 to 15 on at least the surface of the powder particles.

In the present invention, after applying the above-mentioned water-based base coating composition, the above powder clear coating composition is applied by a conventional method without curing, and then baked and cured by a two-coat one-bake method. That is, an automobile top coat having a particularly high appearance can be obtained.

Since the water-based base coating composition of the present invention contains a special resin component, the disturbance of the base / powder interface is effectively prevented during the flow of the powder clear coating composition and the shrinkage upon curing, whereby a high appearance is obtained. The coating film is obtained by the two-coat one-bake method, and it is possible to provide a coating method which is free from problems of hygiene and pollution caused by solvents and which is economically excellent.

[0034]

EXAMPLES The present invention will be described in more detail below with reference to Production Examples, Examples and Comparative Examples, but the present invention is not limited thereto.

Production Example of Film Forming Vinyl Polymer (I)

Production Example 1 76 parts by weight of ethylene glycol monobutyl ether was charged into a 1 L reaction vessel equipped with a stirrer, a temperature controller and a cooling tube, and further 15 parts by weight of styrene, 63 parts by weight of methyl methacrylate and 48 parts of 2-hydroxydiethyl methacrylate 48. 61 parts by weight of a monomer solution consisting of 1 part by weight, 117 parts by weight of n-butyl acrylate, 27 parts by weight of methacrylic acid, 30 parts by weight of acrylamide and 3 parts by weight of azobisisobutyronitrile were added and the temperature was raised to 120 ° C. with stirring. did. After adding 245 parts by weight of the above monomer solution in 3 hours, stirring was continued for 1 hour. Further, 28 parts by weight of dimethylethanolamine and 200 parts by weight of deionized water were added to obtain an acrylic resin varnish (A) having a volatile content of 50% and a resin number average molecular weight of 12,000. This resin has an OH number of 70,
It had an acid number of 58.

Production Example 2 ₂ L was placed in a 3 L reaction vessel equipped with a cooling tube equipped with an N ₂ introduction tube, a temperature control section, a dropping funnel, a stirrer, and a decanter.
-500 parts by weight of ethoxypropanol were charged and the temperature was brought to 100 ° C. 50 parts by weight of styrene monomer, 50 parts by weight of methyl methacrylate, methacrylic acid-
200 parts by weight of 2-hydroxyethyl, methacrylic acid-2
-Ethylhexyl 120 parts by weight, butyl acrylate 38
0 parts by weight and 300 parts by weight of methanol, 100 parts by weight of monobutyl maleate and 100 parts by weight of acrylamide, and further 30 azobisisobutyronitrile as a polymerization initiator.
A solution consisting of parts by weight was charged. While maintaining the temperature at 100 ° C., a solution containing a monomer and an initiator was added dropwise over 3 hours while distilling methanol off with a decanter. After stirring for another 30 minutes, a solution of 50 parts by weight of butyl acetate and 3 parts by weight of t-butylperoxy-2-ethylhexanoate was added dropwise over 0.5 hours. After the dropping, the temperature was kept at 100 ° C. for 1.5 hours. During that time, 300 parts by weight of methanol was distilled off. Then, 220 parts by weight of the solvent was distilled off under reduced pressure. Further, 100 parts by weight of dimethylethanolamine and 570 parts by weight of deionized water were added and dissolved to obtain a nonvolatile content of 50
%, A transparent, viscous acrylic resin water-solubilized varnish (B) having a number average molecular weight of 10,000 was obtained.

Production Example 3 (Film-forming vinyl polymer used in Comparative Example) The same procedure as in Production Example 1 was carried out except that the amount of styrene was 45 parts by weight and acrylamide was not used. Acrylic resin varnish (C) was obtained.

Production Example of Urethane Group-Containing Water Dispersion (II) Production Example 4 Synthesis of Hydrophilic Group-Containing Oligomer 40.2 parts by weight of dimethylolpropionic acid in a 1000 ml reaction vessel equipped with a thermometer, a stirrer and a condenser.
30 parts by weight of triethylamine and 3 of N-methylpyrrolidone
12 parts by weight was added and the mixture was heated and dissolved at 90 ° C. Next, 290 parts by weight of isophorone diisocyanate and 700 parts by weight of polypropylene glycol (molecular weight: 1000) were added, and after stirring for 10 minutes, 1.03 parts by weight of dibutyltin dilaurate was added. Next, the temperature was raised to 95 ° C. and the reaction was carried out for 1 hour.

Preparation of water dispersion 5 equipped with a thermometer, stirrer, condenser and dropping funnel
1757 parts by weight of deionized water and 9.2 parts by weight of hydrazine hydrate were added to a 000 ml reaction vessel, and the hydrophilic group-containing oligomer (urethane prepolymer solution) obtained above was added with stirring. Then, the mixture was stirred for 30 minutes. The obtained composition was a cloudy and stable aqueous dispersion (D). The acid value of the solid content was 16.2 and the nonvolatile content was 33%.
Met.

Production Example 5 Synthesis of Hydrophilic Group-Containing Oligomer Using the same apparatus as in Production Example 3, dimethylolpropionic acid 40.
2 parts by weight, 30 parts by weight of triethylamine, and 402 parts by weight of N-methylpyrrolidone were added, and the mixture was heated and dissolved at 90 ° C.
Next, 290 parts by weight of isophorone diisocyanate, 400 parts by weight of polypropylene glycol (molecular weight: 1000) and polypropylene glycol (molecular weight: 2000) 6
After adding 00 parts by weight and stirring for 10 minutes, 1.3 parts by weight of dibutyltin dilaurate was added. Next, raise the temperature to 95 ° C.,
The reaction was carried out for 1 hour.

Preparation of Aqueous Dispersion 2293 parts by weight of deionized water and 11.5 parts by weight of hydrazine hydrate were added to the same apparatus as in Production Example 3 and stirred to obtain the hydrophilic group-containing oligomer (urethane prepolymer) obtained above. Solution) was added. Then, the mixture was stirred for 30 minutes. The obtained composition was a cloudy and stable aqueous dispersion (E). The acid value of the solid content was 12.5 and the non-volatile content was 33%.

Production Example 6 Polypropylene glycol (molecular weight: 100 in Production Example 4)
0) is a polycarbonate diol (manufactured by Daicel Chemical Industries Ltd., PLACCEL CD-211PL; molecular weight: 10).
Except that it was changed to (00)
An aqueous dispersion (F) having a solid content acid value of 16.0 and a nonvolatile content of 33% was obtained.

Production Example 7 (Production Example of Acrylic Resin Varnish (G) Used for Preparation of Pigment Paste) 40 parts by weight of ethoxypropanol was charged into a 1 L reaction vessel equipped with a stirrer, a temperature controller and a cooling tube, and styrene was further added. 4 parts by weight, n-butyl acrylate 35.96 parts by weight, ethylhexyl methacrylate 1
40 parts by weight of 8.45 parts by weight, 13.92 parts by weight of 2-hydroxyethyl methacrylate, 7.67 parts by weight of methacrylic acid and 20 parts by weight of ethoxypropanol and 20 parts by weight of acid phosphooxyhexa (oxypropylene) monomethacrylate. And 1.7 parts by weight of azobisisobutyronitrile were added dropwise over a period of 3 hours, and then stirring was continued for 1 hour. The obtained product has an acid value of 105, an OH value of 60, and a number average molecular weight of 60.
The acrylic varnish (G) of No. 00 had a nonvolatile content of 63%.

Preparation of Aqueous Base Coating Composition Production Example 8 Aluminum pigment paste (Alpaste 7160N,
To 15 parts by weight of an Al metal content of 65%, manufactured by Toyo Aluminum Co., Ltd., 30 parts by weight of Cymel 303 (methoxylated methylol melamine manufactured by Mitsui Toatsu Co., Ltd.) was added and uniformly mixed. Further, 2 parts by weight of isostearyl acid phosphate (Pholex A-180L, manufactured by Sakai Chemical Industry Co., Ltd.) was uniformly mixed to obtain an aluminum pigment solution. Next, the above aluminum pigment solution was added to 112 parts by weight of the film-forming polymer varnish (A) obtained in Production Example 1 and uniformly dispersed, and then the urethane emulsion (D) 4 obtained in Production Example 4 was obtained.
An aqueous base coating composition (1) was obtained by uniformly dispersing 3 parts by weight.

Production Examples 9 and 10 In the same manner as in Production Example 8, the film-forming polymer varnish and the urethane emulsion were changed as follows to prepare aqueous base coating compositions (2) and (3). Production Example 9 Aqueous base coating composition (2) Film-forming polymer varnish (B) 80 parts by weight Urethane emulsion (D) 91 parts by weight Production Example 10 Aqueous-based coating composition (3) Film-forming polymer varnish (A) ) 112 parts by weight Urethane emulsion (E) 43 parts by weight

Production Examples 11 to 13 Aluminum pigment paste (Alpaste 7160N,
To 15 parts by weight of Al metal content of 65%, manufactured by Toyo Aluminum Co., Ltd., 30 parts by weight of Cymel 303 (methoxylated methylol melamine manufactured by Mitsui Toatsu Co., Ltd.) was added, and the acrylic resin varnish (G) obtained in Production Example 7 was added thereto. 4 parts by weight were added and uniformly mixed, and further 2 parts by weight of isostearyl acid phosphate (phoslex A-180L, manufactured by Sakai Chemical Industry Co., Ltd.) were uniformly mixed to obtain an aluminum pigment solution. Then, in the same manner as in Production Example 8, the respective components having the following compositions were blended to obtain aqueous base coating compositions (4) to (6). Production Example 11 Water-based base coating composition (4) 80 parts by weight of film-forming polymer varnish (A) Urethane emulsion (D) 91 parts by weight Production Example 12 Water-based base coating composition (5) Film-forming polymer varnish (B) ) 112 parts by weight Urethane emulsion (D) 43 parts by weight Production Example 13 Water-based base coating composition (6) Film-forming polymer varnish (B) 80 parts by weight Urethane emulsion (F) 91 parts by weight

Production Example 14 (Comparative water-based base coating composition (P)) In the same manner as in Production Example 8, except that the film-forming polymer (A) was replaced by the comparative film-forming polymer of Production Example 3. An aqueous base coating composition (P) was obtained using (C).

Production Example 15 (Comparative aqueous base coating composition (Q)) In the same manner as in Production Example 8, except that the aluminum pigment solution was uniformly dispersed in 140 parts by weight of the film-forming polymer (A) for comparison. An aqueous base coating composition (Q) was obtained.

Production Example 16 (Preparation of base resin (I) for powder clear coating composition) 2
63 parts by weight of xylene was placed in L-Kolben and the temperature was raised to 130 ° C. A mixture of 55 parts by weight of glycidyl methacrylate, 25 parts by weight of styrene, 20 parts by weight of methyl methacrylate, and 8 parts by weight of t-butylperoxy-2-ethylhexanoate was added dropwise thereto over 3 hours while blowing nitrogen. . After 30 minutes from the completion of the dropping, 0.5 part by weight of t-butylperoxyhexanoate was dropped over 30 minutes. After aging for 1 hour, the solvent was removed to obtain a solid resin. The conditions for removing the solvent are 5 mmHg and 130 after depressurization.
Was held for 1 hour. The base resin (I) thus obtained has a glass transition temperature of 50 ° C. and a number average molecular weight of 25.
It was 00.

Production Example 17 (Preparation of base resin (II) for powder clear coating composition)
55 parts by weight of glycidyl methacrylate, 25 parts by weight of styrene, 5.3 parts by weight of methyl methacrylate, 14.7 parts by weight of ethylhexyl methacrylate, t
A base resin (II) was obtained in the same manner as in Production Example 16 except that the mixture was changed to 8 parts by weight of -butylperoxy-2-ethylhexanoate. The obtained base resin (I
I) has a glass transition temperature of 35 ° C. and a number average molecular weight of 250.
It was 0.

Production Example 18 (Preparation of powder clear coating composition (1)) 70 parts by weight of the base resin (I) obtained in Production Example 16 and 23.4 parts by weight of 1,10-decanedicarboxylic acid (DDA). , Benzoin 1.0 part by weight, polysiloxane-based surface conditioner YF-39
After mixing 0.3 parts by weight of 19 (manufactured by Toshiba Silicone Co., Ltd.), the mixture is melt-kneaded in a Buscon Kneader (manufactured by Buss Co.), crushed and classified (150 mesh) to obtain a powder clear coating composition (1). Obtained. COO in this resin composition for powder coatings
The H / epoxy functional group ratio was 0.75. The average particle size was 25 μm. Microtrac MK-2 (manufactured by Nikkiso Co., Ltd.) was used for particle size measurement.

Production Example 19 (Preparation of powder clear coating composition (2)) 70 parts by weight of the base resin (II) obtained in Production Example 17, 23.4 parts by weight of 1,10-decanedicarboxylic acid, and benzoin 1 0.0 parts by weight and 0.3 parts by weight of a polysiloxane surface modifier YF-3919 (manufactured by Toshiba Silicone Co., Ltd.) and a powder clear coating composition (2) having an average particle diameter of 25 μm in the same manner as in Production Example 18. Got The resin composition for powder clear coating had a COOH / epoxy functional group ratio of 0.75.

Production Example 20 (Preparation of powder clear coating composition (3)) A powder clear coating composition (3) was produced in the same manner as in Production Example 18 except that jet pulverization was adopted as the pulverization method after kneading. Obtained. The average particle size was 10 μm. The resin composition for powder clear coating had a COOH / epoxy functional group ratio of 0.75.

Production Example 21 (Preparation of powder clear coating composition (4)) By the same operation as in Production Example 20, a powder coating having an average particle size of 9 μm was produced by jet pulverization. Next, this powder coating 100
2 parts by weight of the non-crosslinked resin fine particles obtained in the following Production Example 22 are blended with parts by weight and dry-mixed by a Henschel mixer, and the non-crosslinked resin fine particles are adhered to the surface of the powder coating particles. A composition (4) was obtained. The resin composition for powder clear coating had a COOH / epoxy functional group ratio of 0.75.

Production Example 22 (Production of Non-Crosslinked Resin Fine Particles) 380 parts by weight of deionized water and 2 parts by weight of nonionic surfactant MON2 (manufactured by Sanyo Kasei Co.) were placed in a reaction vessel equipped with a stirrer, a cooler and a temperature controller. Parts were charged and dissolved while maintaining the stirring temperature at 80 ° C., and a solution prepared by dissolving 1 part by weight of ammonium persulfate in 10 parts by weight of deionized water as a polymerization initiator was added thereto.

Next, 61 parts by weight of methyl methacrylate,
A mixed solution of 36 parts by weight of styrene and 3 parts by weight of n-butyl methacrylate was added dropwise over 60 minutes. After completion of dropping, stirring was continued at 80 ° C. for 60 minutes. Thus, an emulsion having a nonvolatile content of 20% and a particle size of 0.03 to 0.05 μm was obtained. This emulsion is spray-dried to obtain a dissolution parameter of 10, a glass transition temperature of 110 ° C. and an average particle size of 0.03.
Non-crosslinked resin fine particles of ˜0.05 μm were obtained.

Examples 1 to 9 and Comparative Examples 1 to 2 The present invention and comparative aqueous base coating compositions (1) to (6) prepared in Production Examples 8 to 13 and Production Examples 14 and 15 on intermediate coated steel sheets. And (P) and (Q) each have a temperature of 2
In a environment of 3 ° C. and a humidity of 85%, a dry film thickness of 20 μm was coated in two stages at intervals of 1 minute by an air spray coating means, and then preheated at 80 ° C. for 2 minutes, and then prepared in Production Examples 18 to 21. The powder clear coating compositions (1) to (4) were wet-on-wet coated in one stage by air spray coating so that the dry film thickness was 60 μm. After setting for 7 minutes, the obtained coated plate was baked at 140 ° C. for 30 minutes in a dryer to prepare a test plate. The intermediate coated steel sheet used was a degreased chemical-treated polished mild steel sheet coated with an electrodeposition paint for automobiles and baked, and then an intermediate coating was applied and baked in the intermediate coating line. Table 1 shows the combination of the water-based base coating composition and the powder clear coating composition used in each Example and Comparative Example,
The evaluation results of the appearance of the coating film by visual judgment of the obtained test plate are shown. ◯ means good, and x means bad.

[0059]

[Table 1]

[0060]

EFFECTS OF THE INVENTION According to the present invention, after coating a base paint, powder clear coating is carried out without curing and then baking is performed, which is preferable from the viewpoint of hygiene and environmental protection, and gives a good coating appearance. A coat 1 bake coating method can be established.

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Claims (5)

[Claims] 1. (a) 5 to 40% by weight of an amide group-containing ethylenic monomer, 3 to 15% by weight of an acidic group-containing ethylenic monomer, 10 to 40% by weight of a hydroxyl group-containing ethylenic monomer, and the remaining amount of others. 95-10% by weight (solid content) of a film-forming vinyl polymer obtained by neutralizing at least a part of the acidic groups of the copolymer having a number average molecular weight of 6,000 to 50,000 obtained by copolymerizing the ethylenic monomer of
And (b) a molecular weight of 100 to 100 having a terminal hydroxyl group.
A hydrophilic group-containing oligomer obtained by reacting 5000 diol compounds, diisocyanate compounds and compounds having at least one active hydrogen in the molecule and having a hydrophilic group under isocyanate-rich conditions is a primary polyamine. Alternatively, a urethane-containing water dispersion 5 obtained by dispersing in a water medium containing a secondary polyamine or both
In an aqueous dispersion composition containing 90% by weight (solid content),
(C) An aqueous base coating composition comprising 2 to 100 parts by weight of a pigment dispersed in 100 parts by weight (solid content) of the above aqueous dispersion composition is coated on a substrate, and then 35 to 65% by weight of epoxy is used. An epoxy group-containing acrylic resin obtained by copolymerizing a group-containing monomer with another ethylenic monomer that does not react with 65 to 35% by weight of an epoxy group, and a polyvalent carboxylic acid. The number ratio of the carboxyl groups in the polycarboxylic acid is 10/6
And applying a powder clear coating composition of 10/10,
Then, a two-coat one-bake coating method characterized by baking. 2. The two-coat one-bake coating method according to claim 1, wherein the aqueous base coating composition is an aqueous metallic base coating composition. 3. The average particle size of the powder clear coating composition is 1
The two-coat one-bake coating method according to claim 1 or 2, which has a thickness of 5 μm or less. 4. The powder clear coating composition has an average particle size of 0.001 to 10 μm on at least the surface of each powder particle.
Glass transition temperature 50 to 150 ° C, dissolution parameter (S
The two-coat-one-bake coating method according to claim 1, wherein P) has resin fine particles of 9 to 15. 5. The two-coat one-bake coating method according to claim 1, wherein the polycarboxylic acid is decanedicarboxylic acid.