JP2003026989A - Thermosetting powder coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a thermosetting powder coating composition with excellent storage stability and finished appearance. SOLUTION: The thermosetting powder coating composition comprises containing a resin (A) containing an epoxy group; an acid anhydride curing agent (B) and a crystal nucleating agent (C) as indispensable component. A coating film-forming method for an automobile comprises coating a surface of a substance to be coated with a thermosetting aqueous coloring base coat for an automobile; electrostatically coating a surface of the uncured aqueous base coat with the thermosetting clear powder coating composition in which the thermosetting powder coating composition described in any one of claims 1-4 is adjusted to a clear containing substantially no coloring agent; and simultaneously heating and curing the formed both coating films of the thermosetting aqueous base coat and the thermosetting powder coating composition.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel thermosetting powder coating composition capable of forming a coating film having excellent storage stability and excellent finished appearance, and an automobile using the coating composition. It is based on a method for forming a coating film, and is particularly suitable for a powder clear coating material to be coated on an aqueous base coating material.

[0002]

2. Description of the Related Art Conventionally, a thermosetting powder coating is applied as an overcoat clear for automobile outer panels, and the coating film formed thereon has a finished appearance, solvent resistance, acid resistance, and weather resistance depending on its application. Must meet requirements such as sex. In recent years, the requirements for coating film performance of topcoat clears for automobile outer panels have become increasingly strict. In order to satisfy these requirements, a powder clear paint using a dibasic acid such as dodecane diacid or an anhydride thereof as a curing agent for an acrylic resin-based powder clear paint has been studied so far. However, in a system using a dibasic acid such as dodecane diacid, sufficient curability cannot be obtained, and the coating film performance as a topcoat clear for automobile outer panels is not satisfied. Also, when a dibasic acid anhydride curing agent is used, a highly crosslinkable coating film can be obtained, but during storage of the powder coating, moisture in the air causes the acid anhydride group to open and become a carboxyl group. Reacts with the epoxy group to lower the fluidity of the coating material, resulting in a problem that the finished appearance and coating film performance are degraded.

[0003]

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, the epoxy group-containing resin (A), acid anhydride curing agent (B) and In the thermosetting powder coating composition containing the crystal nucleating agent (C) as an essential component, the acid anhydride curing agent (B) whose crystallinity is increased by the crystal nucleating agent (C) is affected by moisture in the air. It is difficult to receive the acid anhydride group and it is possible to suppress the ring opening of the acid anhydride group to become a carboxyl group, and with excellent storage stability of the paint,
The present invention has been completed by finding that it is possible to provide a powder coating material which has an excellent finished appearance and which is suitable as a top coat clear for automobile outer panels and which satisfies high finish properties and coating film physical properties.

That is, the present invention relates to a thermosetting powder coating composition containing an epoxy group-containing resin (A), an acid anhydride curing agent (B) and a crystal nucleating agent (C) as essential components, and for automobiles. Apply a thermosetting water-based colored base coat on the surface of the object to be coated,
Then, the surface of the uncured aqueous base coat is prepared by thermosetting the thermosetting powder coating composition according to any one of claims 1 to 4 into a clear substantially containing no colorant. Electrostatically coating a clear clear powder coating composition,
Then, the present invention relates to a method for forming a coating film for an automobile, which comprises simultaneously heating and curing both coating films of the thermosetting aqueous base coat and the thermosetting clear powder coating composition.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the epoxy-containing resin (A) used in the present invention include a bisphenol type epoxy resin. For example, “Epicoat 1001” (epoxy equivalent of 450 to 50 manufactured by Yuka Shell Chemical Co., Ltd.) is used.
0) "Epicoat 1004" (epoxy equivalent 875-9
75), "Epicoat 1007" (epoxy equivalent 175
0-2200) and the like.

Also, a copolymer of an epoxy group-containing vinyl monomer and another polymerizable vinyl monomer can be used. The polymerization method is not particularly specified, but the radical polymerization method is often used industrially. Examples of the epoxy group-containing vinyl monomer used here include glycidyl (meth) acrylate, glycidyl allyl ether,
Examples thereof include 3,4-epoxycyclohexyl (meth) acrylate, β-methylglycidyl (meth) acrylate, and allylglycidyl ether. These monomers can be used alone or in combination of two or more. Glycidyl (meth) acrylate and β-methylglycidyl (meth) acrylate are particularly preferable.

Other polymerizable vinyl monomers include vinyl aromatic compounds such as styrene, α-methylstyrene, vinyltoluene and α-chlorostyrene; methyl (meth) acrylate, ethyl (meth) acrylate, n- Butyl (meth) acrylate, i-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate,
acrylic acid such as n-octyl (meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecanyl (meth) acrylate or Examples thereof include an alkyl ester of methacrylic acid having 1 to 24 carbon atoms or a cyclic alkyl ester.

The epoxy group-containing vinyl monomer is contained in the copolymer in the range of 20 to 70% by weight, preferably 30 to 60% by weight. When the epoxy group-containing vinyl monomer is less than 20% by weight, acid resistance, weather resistance and solvent resistance are deteriorated, while 70% by weight
If it exceeds the range, the storage stability of the coating material and the finished appearance (smoothness) of the coating film deteriorate, which is not preferable.

The resin (A) component having an epoxy group used in the present invention has a glass transition temperature of 40 to 80 ° C., preferably 50 to 70 ° C. and a number average molecular weight of 1000.
It is preferably from 1 to 10,000, preferably from 2000 to 6000.

When the glass transition temperature is lower than 40 ° C., the powder coating material obtained is not preferable because the particles are fused with each other and the blocking resistance is deteriorated. On the other hand, if the temperature is higher than 80 ° C, not only the viscosity at the time of heat flow increases and the finishability decreases but also the solubility decreases, which is not preferable.

If the number average molecular weight is less than 1000, the powder coating composition is inferior in blocking resistance, and the coating performance such as acid resistance and solvent resistance is deteriorated. On the other hand, if the number average molecular weight exceeds 10,000, the finish appearance (smoothness) of the coating film is deteriorated, which is not preferable.

The glass transition temperature can be determined by DSC (differential scanning calorimeter).

Acid anhydride curing agent (B) used in the present invention
Any known material can be used without particular limitation. Specific examples include JP-A-2001-55536 and the like.

In addition to the above acid anhydride curing agent (B), for example, suberic acid, azelaic acid, sebacic acid,
Aliphatic dibasic acids such as undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, pentadecanedioic acid and eicosanedioic acid can be used in combination.

The curing agent (B) component is a carboxyl group /
The molar ratio of acid anhydride groups is 0.15 to 2.0, preferably 0.1.
It is preferably from 2 to 1.8. When the molar ratio of carboxyl group / acid anhydride group is less than 0.15, sufficient curability cannot be obtained, and when it exceeds 2.0, the curing start time is short and the coating film is cracked or smooth. It is inferior in sex.

The melting point of the curing agent (B) used in the present invention is preferably 60 ° C. or higher, particularly 70 ° C. to 140 ° C. If it is lower than 60 ° C., the blocking resistance of the powder coating composition is lowered, which is not preferable.

Examples of the crystal nucleating agent (C) used in the present invention include talc, silica, graphite, alumina, zinc oxide, magnesium oxide, aluminum oxide in the inorganic system.
Organic compounds such as calcium sulphate, barium sulphate, etc., such as calcium benzoate, calcium oxalate, magnesium stearate, zinc salicylate, etc., metal carboxylates such as sodium benzoate, aluminum dibenzoate, potassium dibenzoate, lithium benzoate Salt type, benzylidene sorbitol and its derivative type, polyvinyl cycloalkane, polyvinyl trialkylsilane, copolymer of ethylene and propylene,
Polymer-based materials such as Kepler fiber and high melting point nylon,
It is at least one selected from phosphoric acid, organic phosphoric acid metal salts and the like.

The compounding ratio of the crystal nucleating agent (C) is 0.01 to 0.2 parts by weight, preferably 100 parts by weight, based on 100 parts by weight of the resin (A) having an epoxy group and the acid anhydride curing agent (B). 0.02 to 0.1 part by weight is suitable. If it is less than 0.01 part by weight, a sufficient effect of improving the crystallinity cannot be obtained,
If the amount is more than 1 part by weight, the baked coating film may have abnormalities such as spots on the baking surface and the transparency may be deteriorated, which is not suitable as a top coating film for automobiles.

In the present invention, in addition to the above components, if necessary, anti-armpit agents, surface modifiers, antioxidants, ultraviolet absorbers, ultraviolet stabilizers, antiblocking agents, flow modifiers, charge control agents, color pigments, Other compounds such as fillers and curing accelerators can be added as needed.

The thermosetting powder coating composition of the present invention is not particularly limited in its powder coating method. For example, a resin (A) containing an epoxy group, an acid anhydride curing agent (B), and a crystal nucleus. Mixer containing agent (C) and other ingredients as required
It can be produced by dry-blending in, followed by heating, melt-kneading, cooling, coarse pulverization, fine pulverization, and filtration.

The thermosetting powder coating composition of the present invention comprises electrostatically powder coating an object to be coated and baking it (for example, at a temperature of about 160 ° C. or higher for about 30 minutes) to form a cured coating film. You can As the article to be coated, any conventionally known material can be used without particular limitation as long as it is a material capable of electrostatic powder coating. Examples of the article to be coated include metals,
Examples thereof include surface-treated metals, plastics, and materials coated with paint.

The powder coating is preferably performed by a method known per se, such as electrostatic powder coating or triboelectric powder coating. The coating film thickness is not particularly limited, but is about 20 microns to 1000 microns, preferably about 20 microns.
A range of 80 microns is preferred.

The thermosetting powder coating composition of the present invention can be applied without limitation to applications in which the powder coating has been used conventionally, such as automobiles, home appliances, steel furniture, office supplies, and building materials. Especially, it is preferable to use it for an outer panel or an inner panel of an automobile where smoothness of a coating film is desired.

Next, a method for forming a coating film for an automobile, in which the thermosetting powder coating composition of the present invention is applied as a powder coating composition for an automobile, will be described below.

The coating film for automobiles is a one-coat system in which a colored thermosetting powder coating composition of the present invention is applied to an object to be coated, which is obtained by applying an undercoating material and optionally an intermediate coating material to a substrate. The present invention can be applied to any of these two-coat methods in which the thermosetting clear powder coating composition of the present invention is applied to the coated surface of the base coat paint, and in particular, the thermosetting powder coating composition of the present invention. The object is to apply a colored metallic paint or an aqueous colored interference pattern paint as an aqueous colored base coat, and then apply the thermosetting clear powder coating composition of the present invention to the surface of the base coating film in an uncured state, and then In the case of the two-coat one-bake system (2C1B) in which both the coating film of the invention powder coating composition and the coating film of the aqueous colored base coat are simultaneously heat-cured, the effect of the coating composition of the present invention can be fully utilized. In is suitable.

In this 2C1B, a metal or plastic object to be coated, such as an automobile body, was directly coated, or an undercoating material such as a cationic electrodeposition coating and optionally an intermediate coating material was applied and cured. Later, the solid content concentration at the time of applying the water-based colored base coat was 10 to 60
The amount is adjusted to be within the range of 10% by weight, and is spray-coated such as airless spray, air spray, electrostatic coating, etc., and is 10 to 60 μm, preferably 10 to 4 on the basis of the cured coating film on the above-mentioned object.
The coating is applied to a thickness of 0 μm and left at room temperature for about 1 to 10 minutes, or after drying at a temperature of about 50 to about 100 ° C. for about 1 to 10 minutes, the uncured coated surface is The thermosetting powder coating composition of the present invention is applied by a method such as electrostatic powder coating or triboelectric powder coating based on the coating film formed.
To 100 μm, preferably 30 to 80 μm, and then 1 at a temperature of about 120 to about 180 ° C.
The method of the present invention can be carried out by heating both coating films at the same time by heating for about 0 to 50 minutes.

The above-mentioned aqueous colored base coat can be used without limitation as long as it is known as an aqueous colored base coat for automobiles, but it is particularly preferable to use a melamine-curable aqueous colored base coat.

The melamine-curable aqueous colored base coat is preferably one containing a resin (i) having both a hydroxyl group and a carboxyl group in one molecule and a melamine resin curing agent (ii) as a curable resin component.

The resin (i) is preferably an acrylic resin or a polyester resin.

The acrylic resin is a C2 of (meth) acrylic acid such as a hydroxyl group-containing unsaturated monomer (hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate).
To C20 hydroxyalkyl ester, etc., carboxyl group-containing unsaturated monomer (monocarboxylic acid such as acrylic acid and methacrylic acid, maleic acid, itaconic acid, fumaric acid, mesaconic acid and their anhydrides and half-esterified products) Dicarboxylic acid or its modified products)
And, if necessary, other vinyl unsaturated monomers (eg, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, etc. ) C1 to C22 alkyl esters of acrylic acid,
Styrene, acrylonitrile, etc.).

The acrylic resin has a number average molecular weight of 5,000 to 100,000, particularly 15,000 to 80,000 and a hydroxyl value of 20 to 200 as characteristic values.
mgKOH / g, especially 40-150 mgKOH / g, and acid number 10-150 mgKOH / g, especially 20-1
It is preferably in the range of 00 mgKOH / g.

The polyester resin can be obtained by an ester reaction of a polybasic acid and a polyhydric alcohol. Examples of the polybasic acid include phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid and azelaic acid. , Sebacic acid, tetrahydrophthalic acid, hexahydrophthalic acid, het acid, maleic acid, fumaric acid, itaconic acid, trimellitic acid and their anhydrides, and the polyhydric alcohols include, for example, ethylene glycol. , Propylene glycol, butylene glycol, hexanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol and the like. The polyester resin has a number average molecular weight of 2,0.
00-100,000, especially 3,000-80,000
0, hydroxyl value is 30 to 120 mg KOH / g, especially 50
~ 80mgKOH / g, and acid value 15 ~ 100mg
It is preferably in the range of KOH / g, particularly 30 to 50 mg KOH / g.

As the above-mentioned melamine resin (ii) curing agent, a part or all of the methylol group of the partially methylolated or completely methylolated melamine resin is C1 to C1.
C8 alkanol, such as methanol, ethanol,
A partially etherified or fully etherified methylolmelamine resin etherified with propanol, butanol, etc., having 1 to 5 triazine rings in one molecule,
And the molecular weight is 300 to 3,000, particularly 500 to 2,000.
Those in the range of 00 are preferable. These resins may be water-insoluble or water-soluble.

The above aqueous colored base coat contains, in addition to the above-mentioned components, at least one of a color pigment, a metallic pigment and an interference pigment, and if necessary, an oxazoline group-containing compound, an extender pigment, an organic solvent, a catalyst and an anti-settling agent. It is possible to further mix an agent, an ultraviolet absorber and the like.

[0035]

EFFECTS OF THE INVENTION In the powder coating material of the present invention, the crystallinity of the acid anhydride curing agent is increased by adding a crystal nucleating agent to the acid anhydride curing agent, which reduces the influence of moisture in the air. As a result, the hydrolysis reaction of the acid anhydride curing agent is suppressed, and it is speculated that the outstanding effect of excellent storage stability was exhibited.

[0036]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples. Unless otherwise specified, “part” or “%” represents the weight standard.

1) Production Example of Powder Coating Production Example of Resin for Powder (A-1) 60 parts of toluene was charged into a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser and a dropping device.
While blowing nitrogen gas, heat to 105 ° C. and mix with styrene 15 parts, methyl methacrylate 30 parts, iso-butyl methacrylate 20 parts, glycidyl methacrylate 35 parts, azobisisobutyronitrile 4 parts over about 3 hours. Was dropped. After completion of the dropping, the mixture was left standing at 105 ° C. for 1 hour, 0.5 parts of azobisisobutyronitrile and 10 parts of toluene were further added dropwise over 1 hour, and after the completion of dropping, the reaction was terminated at 105 ° C. for 1 hour. . Then, depressurizing operation was performed to remove the solvent in the system to produce a resin (A-1) for powder.

Production Example of Powder Resin (A-2) 60 parts of toluene was charged into a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a reflux condenser and a dropping device.
While blowing nitrogen gas, heat to 105 ° C., and mix with 10 parts of styrene, 30 parts of methyl methacrylate, 15 parts of iso-butyl methacrylate, 45 parts of glycidyl methacrylate, and 4 parts of azobisisobutyronitrile for about 3 hours. Was dropped. After completion of the dropping, the mixture was left standing at 105 ° C. for 1 hour, 0.5 parts of azobisisobutyronitrile and 10 parts of toluene were further added dropwise over 1 hour, and after the completion of dropping, the reaction was terminated at 105 ° C. for 1 hour. . Then, depressurizing operation was performed to remove the solvent in the system to produce a resin (A-1) for powder.

Production Example of Curing Agent (B-1) In a reaction vessel equipped with a thermometer, thermostat, stirrer and reflux condenser, 230 parts of dodecane diacid and 8 parts of acetic anhydride were used.
7 parts were charged, and the temperature was raised while acetic acid was distilled off to 170 ° C. with stirring. At this time, heating was adjusted so that acetic anhydride did not distill at the same time. When the acetic acid stopped distilling off, the pressure was immediately reduced. Gradually increase the degree of decompression, and finally 170 ° C
Depressurize at 30mmHg for 2 hours, then 100 ℃
Cooled down. 0.8 part of methanol was added dropwise to this over 1 hour, and then reacted for 1 hour. The product obtained by cooling this was a solid substance having a melting point of 82 ° C.

Production Example of Powder Coating (1) 100 parts of powder resin (A-1) and curing agent (B-1) 3
8.6 parts, crystal nucleating agent (C-1) phosphoric acid 2,2-methylenebis
0.1 part of (4,6-di-t-butylphenyl) sodium (Adeka Stab NA-11 manufactured by Asahi Denka Co., Ltd.) was dry-blended with a Henschel mixer at room temperature, and then melt-kneaded with an extruder. Next, after cooling, it was finely pulverized with a pin disk and filtered through 150 mesh to obtain a powder coating material (1).

Production Examples of Powder Coatings (2) to (5) Powder coatings (2) to (5) were produced in the same manner as in the production example of powder coating (1) with the formulations shown in Table 1.

2) Production Example of Aqueous Base Coat Coating The following (D-1) 45 parts of water-soluble acrylic resin (solid content),
The following (D-2) water-dispersible polyester resin 30 parts (solid content), the following (D-3) butyl etherified methylol melamine resin 25 parts, the following metallic pigment 10 parts, and blue organic pigment 2 parts were mixed and manufactured. .

(D-1) 70 parts of butyl cellosolve was charged into a reaction vessel equipped with a water-soluble acrylic resin thermometer, a thermostat, a stirrer, a reflux condenser and a dropping device, and heated to 115 ° C. while blowing nitrogen gas. , Styrene 30 parts, methyl methacrylate 15 parts, n
-Butyl acrylate 16.7 parts, 2-ethylhexyl acrylate 20 parts, hydroxyethyl methacrylate 12 parts, acrylic acid 6.3 parts, and azobisisobutyronitrile 1 part were added dropwise over about 3 hours. After completion of the dropping, the mixture was allowed to stand at 115 ° C. for 1 hour, 0.3 parts of azobisisobutyronitrile and 10 parts of butyl cellosolve were further added dropwise over 1 hour, and after completion of the dropping, the reaction was terminated at 115 ° C. for 1 hour. . The acid value of the obtained acrylic resin is 50 mg.
KOH / g, hydroxyl value was 50 mg KOH / g, and number average molecular weight was 45,000. Then, the carboxyl group of this acrylic resin was neutralized with dimethylaminoethanol in an equivalent amount, and an acrylic resin aqueous solution (D-
1) was obtained.

(D-2) Water-dispersible polyester resin 35.95 parts of neopentyl glycol and trimethylolpropane in a reaction vessel equipped with a thermometer, a thermostat, a stirrer, a Dean Stark water separator, and a reflux condenser.
68 parts, phthalic anhydride 25.34 parts and adipic acid 3
1.24 parts were charged and the temperature was raised to 230 ° C. over 3 hours while distilling off the water. Then add a small amount of xylol,
Under reflux, the reaction was continued for 5 hours while distilling off the water with a water separator. Furthermore, 6.57 parts of trimellitic anhydride was charged and reacted at 180 ° C. for 1 hour, butyl cellosolve was added,
Acid value 40 mgKOH / g, hydroxyl value 80 mgKOH / g
A polyester resin solution having a nonvolatile content of 70% and a number average molecular weight of 6000 was obtained. Dimethylaminoethanol was added to this polyester resin solution to neutralize it in an equivalent amount, and deionized water was then added to obtain a polyester emulsion (D-2) having a solid content of 35%.

(D-3) Butyl etherified methylol melamine resin "Uvan 28-60" (trade name, manufactured by Mitsui Chemicals, Inc.) The metallic pigment is "Aluminum paste N768".
0 "(manufactured by Toyo Aluminum Co., Ltd., product name) blue organic pigment used was" Heliogen Blue L6900 "(manufactured by BASF, product name, cyanine blue).

Preparation of coated plate (on aqueous base coat) Epoxy cationic electrodeposition coating was electrodeposited to a dry film thickness of 20 microns on a 0.8 mm thick dull steel sheet which had been subjected to zinc phosphate chemical conversion treatment, and baked. On the electro-deposited coating film, a surface coater for automobiles was air-sprayed to a dry film thickness of 40 microns, baked at 140 ° C for 30 minutes, sanded with # 400 sandpaper, drained and dried, then petroleum oil. It was wiped with benzine to be degreased and used as a test object. Then, the viscosity of the water-based paint obtained in 2) was changed to 45 seconds /
Ford cup # 4/20 ° C. was adjusted, and the above coated article was coated with air spray so that the cured coating film had a thickness of 15 μm, and dried at 80 ° C. for 10 minutes, and then the above-mentioned 1 After coating the powder coating material obtained in 1) so as to have a cured film thickness of about 60 μm, both coating films were simultaneously cured by heating at 160 ° C. for 30 minutes.

Table 1 shows the results of performance tests of the multilayer coating films obtained in 3-1) and 3-2). Table 1

[0048]

[Table 1]

The performance test method is as follows.

Blocking resistance: After the powder coating is left open for storage for a certain period under a constant temperature and humidity condition,
The state of the powder coating material was evaluated according to the following criteria. ○: Powder that is as smooth as before open storage, △: A lump of paint is formed but quickly collapses when you pinch it with your fingers, ×: A lump of paint that does not collapse easily Hygroscopicity: Constant powder coating Difference in water content in the powder coating before and after left open for a certain period under the temperature and humidity conditions. The water content of the powder coating material was determined by the Karl Fischer method.

Hydrolysis rate: The powder coating is measured as a tablet with KBr. The ratio of the absorbance of absorption derived from CH at about 2950 cm -1 to the absorbance of absorption derived from acid anhydride group near 1818 cm -1 was compared before and after the storage test to obtain the ratio of hydrolyzed acid anhydride groups.

Appearance of coating film: The finished appearance of the coating film is glossy,
The smoothness was evaluated according to the following criteria. ○: good, △: slightly inferior, ×: inferior Acid resistance: 0.4% of 40% sulfuric acid was dropped on the test coated plate,
After heating for 15 minutes on a hot plate heated to 85 ° C., it was washed with water and the coated surface was observed and evaluated according to the following criteria.
◯: No change at all, Δ: A step is recognized at the boundary between the drop portion and the non-drop portion, X: Whitening of the coating film.

Gasoline resistance: This is the result of visual observation of the coated surface after the test piece was immersed in regular gasoline for 2 hours at room temperature. ◯ means good with no blister or whitening, Δ: slightly bad with blister or whitening, and x means bad occurrence due to remarkable occurrence of blister or decrease in gloss.

Xylene resistance: Xylol of 0.
Spot 5 mL and let stand for 30 minutes at room temperature. Then, the xylol is wiped off with a case, and the coated surface is visually evaluated. ○: There is no retrofitting. Δ: The contour of the spot portion can be confirmed. X: Clear swelling is observed in the spot part.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoto Adachi             Seki, 4-17-1, Higashi-Hachiman, Hiratsuka City, Kanagawa Prefecture             West Paint Co., Ltd. F term (reference) 4J038 CB102 CL002 CR072 DB001                       DB061 DB221 DH002 DJ022                       HA386 JA35 JA46 KA03                       MA13 MA14 NA01 NA03 NA04                       PB07 PC02

Claims (8)

[Claims] 1. A thermosetting powder coating composition comprising an epoxy group-containing resin (A), an acid anhydride curing agent (B) and a crystal nucleating agent (C) as essential components. 2. The crystal nucleating agent (C) component is at least one inorganic crystal nucleating agent selected from talc, silica, graphite, alumina, zinc oxide, magnesium oxide, aluminum oxide, calcium sulfate and barium sulfate. The thermosetting powder coating composition according to claim 1, wherein 3. The crystal nucleating agent (C) component is at least one carboxylic acid metal salt crystal nucleating agent selected from calcium benzoate, calcium oxalate magnesium stearate and zinc salicylate. The thermosetting powder coating composition according to 1. 4. The crystal nucleating agent (C) component is at least one organic polymer crystal nucleus selected from polyvinylcycloalkane, polyvinyltrialkylsilane, copolymer of ethylene and propylene, Kepler fiber, high melting point nylon. The thermosetting powder coating composition according to claim 1, which is an agent. 5. The thermosetting agent according to claim 1, wherein the crystal nucleating agent (C) component is at least one phosphoric acid-based crystal nucleating agent selected from phosphoric acid and organophosphoric acid metal salts. Type powder coating composition. 6. The resin (A) having an epoxy group has a glass transition temperature of 40 to 80 ° C. and a number average molecular weight of 1,000 to 1.
The thermosetting powder coating composition according to claim 1, which is in the range of 0000. 7. The thermosetting powder coating composition according to claim 1, wherein the curing agent (B) has a melting point of 60 ° C. or higher. 8. A thermosetting water-based colored base coat is applied to the surface of an article to be coated on an automobile, and then the surface of the uncured water-based base coat is applied.
The heat-curable powder coating composition according to the item (1) is electrostatically coated with a heat-curable clear powder coating composition that is substantially free of a colorant, and then a heat-curable aqueous base coat is formed. A method for forming a coating film for an automobile, which comprises simultaneously heating and curing both coating films of a thermosetting clear powder coating composition.