JPH11300271A - Method for forming multilayer powder coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a pollution-free coating film excellent in finishing appearance and coating film properties by a method in which a primer powder coating is applied on a substrate, the obtained coating film is heated or not heated, and a finishing powder coating, after being applied on the surface of the coating film, is heated. SOLUTION: When a multilayer powder coating film excellent in finishing appearance and coating film properties is formed on an automobile and others, first, a primer powder coating (powder coating A) is applied on a substrate. next, with the obtained primer powder coating film heated or not heated, a finishing powder coating (powder coating B) is applied on the surface of the coating film, and heated to form a required multilayer powder coating film. As each powder coating A, B, substances whose resin components are incompatible or poorly compatible with each other are used preferably, and equivalent or a substance in which the surface tension of the resin of the powder coating B is smaller by, for example, at least 0.1 dyne/cm than that of the resin of the powder coating A is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a powder coating for forming a multilayer coating film capable of providing a multilayer powder coating film having excellent finished appearance and coating film performance.

[0002]

2. Description of the Related Art Powder coatings have many features, such as being less polluting than solvent-based coatings, easier line management, and easier collection of coatings. Because of these features, they have received particular attention in the automotive field.
Generally, coating of an automobile outer panel is performed by electrodepositing a primer on the automobile outer panel, applying a middle coat, and then a top coat. In such a coating method, a melamine-curable polyester-based water-based or solvent-based paint is often used as an intermediate coating, and even if this is simply replaced with a thermosetting powder-based paint, the crosslink density is large. Since a coating film cannot be obtained, the workability, chipping resistance, adhesion, etc., are not sufficient, and the powder coating is melted by a baking process to form a coating film with the same film thickness. Since it is necessary, there is a problem that the finished appearance of the coating film is inferior to that of the solvent type or water-based paint. When a powder coating is used as a top coat on the surface of an intermediate coating film formed by an organic solvent type or water-based coating, there is a problem that the finished appearance and adhesion are inferior because the affinity with the intermediate coating film is poor. .

[0003] Further, as a coating for an automobile outer panel, a method of applying an intermediate coating without baking an electrodeposition coating film and then baking both coating films simultaneously, or after evaporating a solvent of the intermediate coating film, and then applying a top coating material. A so-called two-coat one-bake system, in which a coating is applied and both coating films are baked and cured at the same time, is generally employed. In this two-coat, one-bake method, when a powder coating is used as the intermediate coating, the powder coating has cracks and the adhesion between the intermediate coating powder and the electrodeposition coating and the top coating. And it is difficult to balance with the coating film performance. However, problems such as poor wettability and adhesion are left.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a multilayer powder coating film having excellent finished appearance and coating film performance.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, by combining two types of powder coatings as coatings to be applied to a substrate,
That is, after coating the powder coating functioning as the undercoat, the powder coating functioning as the top coating is applied and the two functions are efficiently shared, so that a pollution-free coating film with excellent finished appearance and coating film performance can be obtained. They found that they could be formed and completed the present invention.

That is, according to the present invention, an undercoat powder coating (hereinafter sometimes abbreviated as “powder coating A”) is applied to a substrate, and then the obtained undercoat powder coating is heated or A top coat powder coating (hereinafter sometimes abbreviated as "powder coating B") is applied to the surface of the coating without heating, and the coating is heated. It relates to a forming method.

The substrate used in the present invention includes, for example,
What has been conventionally used for powder coating, which can perform electrostatic powder coating and does not cause deformation of the substrate by heating, can be used. Specific examples include metals such as steel, copper, stainless steel, alloy steel, aluminum and its alloys, zinc, galvanized steel, zinc alloy, tin-plated steel, zinc phosphate or iron phosphate-treated steel. The substrate may be a plate, a pipe, a box, a line, a frame, a wheel, a vehicle, or the like. Further, a primer coating such as cationic electrodeposition coating may be applied to the surface of the base material, if necessary. Among these base materials, it is particularly preferable to apply to applications requiring undercoating and topcoating, for example, base materials for vehicles such as automobile bodies, parts of vehicles, and home appliances.

The powder coating used in the present invention can be applied by, for example, corona electrostatic coating, triboelectric powder coating, or the like. The powder thickness is preferably in the range of about 20-80 microns, preferably about 30-70 microns.

As the powder coating material A and the powder coating material B used in the present invention, conventionally known coating materials can be used as long as they are thermosetting types and exhibit a function as an undercoat or an overcoat. However, it is particularly preferable to use one satisfying at least one of the following requirements (1) to (7).

(1) As the powder coating A and the powder coating B, it is preferable to use one in which resin components are incompatible or hardly compatible. This incompatibility (P> 0.5) and poor compatibility (0 <
P ≦ 0.5) can be measured by the compatibility parameter described in JP-A-51-122137. When such a condition is satisfied, when both the coating films are baked simultaneously, the powder coating material A and the powder coating material B are hardly mixed at the interface, and the finished appearance of the coating film is improved.

(2) The powder coating material A and the powder coating material B are equivalent or the surface tension of the resin of the powder coating material B is 0.1 dyne / cm or more, preferably 0, or more than the surface tension of the resin of the powder coating material A. It is preferable to use a material smaller than 0.2 dyne / cm. This surface tension is as disclosed in JP-A-51-12213.
No. 7 can be measured. When such a condition is satisfied, the powder coating B easily spreads at the interface with the powder coating A when both coating films are baked simultaneously, and the finished appearance of the coating film is improved.

(3) The powder coating A has a softening temperature equal to or higher than that of the powder coating B (preferably about 1 to 40).
C., more preferably about 1 to 20 C.). As a result, the powder coating B easily spreads at the interface with the powder coating A, and the finished appearance of the coating film is improved. The softening temperature of the powder coating A is usually in the range of about 20 to 100C, preferably about 30 to 80C.

(4) The powder coating A and the powder coating B are preferably powder coating A and powder coating B, each having a particle size of 5 μm.
Particles having a size of m to 45 µm, particularly 10 µm to 40 µm, preferably account for 90% by weight or more, particularly 95% by weight or more. As a result, the coated powder coating is compactly filled, so that there is no possibility that a portion of the powder coating A will emerge on the surface of the powder coating B, thereby improving the appearance and performance of the coating.
Also, the powder coating B can be electrostatically powder coated on the surface of the powder coating A without deteriorating electrostatic repulsion, coating workability and the like.

(5) It is preferable to use the powder coating A containing the following onium salt.

The onium salt compound has a general formula
What is represented by [(R) 4Y] + X- or [(R) 3S] + X- is preferable. In the formula, R is the same or different and is a hydrogen atom, a lower alkyl group (eg, methyl, ethyl, propyl, butyl, hexyl, etc.), a hydroxy lower alkyl group (eg, hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, hydroxybutyl) Hexyl, etc.), halo-lower alkyl groups (eg, methyl bromide, ethyl bromide, etc.), lower alkoxy lower alkyl groups (eg, methoxymethyl, methoxyethyl,
Methoxypropyl, methoxybutyl, methoxyhexyl, etc.), cycloalkyl group (eg, cyclohexyl, cyclohexylmethyl, cyclopentyl, etc.), aryl group (eg, phenyl, toluyl, xylyl, etc.) or aralkyl group (eg, benzyl group, etc.) Organic groups are mentioned. Y is a nitrogen atom or a phosphorus atom. X represents a negative ion, for example, a halogen ion (eg, chlorine, bromine, fluorine, iodine, etc.), an inorganic acid group (eg, a sulfate group, a phosphate group, etc.), an organic acid group (eg, an acetate group,
Benzylsulfonic acid radicals, hydroxyl radicals, etc.). The above lower meaning means those having 6 or less carbon atoms. In the above-mentioned general formula, an ammonium or phosphonium salt compound in which R is a lower alkyl group, a phenyl group or a benzyl group and X is a halogen ion is particularly preferred.

The above onium salt compounds include, for example,
Phosphonium salt compounds such as tetramethylphosphonium chloride, tetraethylphosphonium chloride, tetrabutylphosphonium chloride, trimethylethylphosphonium chloride, triphenylbenzylphosphonium chloride, tetramethylphosphonium bromide and triphenylbenzylphosphonium bromide; tetramethylammonium chloride; Ammonium salt compounds such as tetraethylammonium chloride, tetrabutylammonium chloride, trimethylethylammonium chloride, triphenylbenzylammonium chloride, tetramethylammonium bromide, triphenylbenzylammonium bromide; trimethylsulfonium chloride, tetraethylsulfonium chloride, tetrachloride Butylsulfonium, trimethylethylsulfonium chloride,
And sulfonium salt compounds such as triphenylbenzylsulfonium chloride. The compounding ratio of the onium salt compound in the powder coating A is preferably in the range of 0.01 to 10% by weight, particularly preferably 0.01 to 5% by weight. By blending the onium salt, the finished appearance of the powder coating film B is improved.

(6) As the powder coating A, it is preferable to use an epoxy resin-based powder coating A which exhibits excellent effects on separability, corrosion resistance and adhesion to a substrate. As the epoxy resin-based powder coating A, a conventionally known powder coating which can be subjected to electrostatic powder coating or fluid immersion coating itself and is cured by heating, for example, a bisphenol / epichlorohydrin type epoxy base resin (for example, oil) Shell Co., Ltd., trade name: Epicoat 1004, Epicoat 100
7) an epoxy resin such as a novolak type epoxy base resin or the like; a polycarboxylic acid compound such as adipic acid and (trimellitic anhydride); an aromatic sulfonium such as benzyl-4-hydroxyphenylmethylsulfonium hexafluoroantimonate; Cationic polymerization catalysts for salts, amide compounds such as dicyandiamide, carboxylic acid dihydrazide compounds such as adipic dihydrazide, imidazoline compounds, imidazole compounds, phenolic resins, and known epoxy resin-containing high-acid-value polyester-based resin-containing crosslinking agents for epoxy. Powder coatings can be used. The mixing ratio of the base resin and the curing agent is in the range of about 0.01 to 10 parts by weight, preferably about 0.1 to 5 parts by weight in the case of the cationic polymerization catalyst per 100 parts by weight of the base resin. About 10-100 parts by weight, preferably about 15-8
A range of 0 parts by weight is preferred. Addition of paints such as coloring agents, fillers, rust inhibitors, curing catalysts, fluidity regulators, repelling inhibitors, ultraviolet stabilizers, ultraviolet absorbers (benzotriazole compounds, etc.) to powder coating A as required An agent can be compounded.

(7) As the powder coating B, thermosetting acrylic resin powder coating (B1), polyester resin powder coating (B2), and the like having excellent coating properties such as weather resistance and workability.
It is preferable to use a fluororesin-based powder coating (B3).

Thermosetting acrylic resin powder coating (B1)
Conventionally known powder coatings which can be electrostatic powder coated by themselves and are cured by heating, such as acid epoxy curing type acrylic resin type powder coating (a), block isocyanate curing type acrylic resin type powder Paint (b) and the like.

Examples of the powder coating (a) include a radical polymerizable unsaturated monomer containing an epoxy group (eg, glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate), and a hard acrylic monomer having a glass transition temperature of 40 ° C. or higher. (Eg, methyl methacrylate, ethyl methacrylate, iso-butyl methacrylate, te
r-butyl methacrylate, ter-butyl acrylate, etc.) and, if necessary, a soft acrylic monomer having a glass transition temperature of less than 40 ° C. (eg, methyl acrylate,
Ethyl acrylate, n-butyl methacrylate, is
o-butyl acrylate, 2ethylhexyl (meth) acrylate, stearyl methacrylate, etc.), radical polymerizable unsaturated monomers other than acrylic monomers (eg, styrene, vinyltoluene, α-methylstyrene,
Radical copolymerization reaction of (meth) acrylonitrile, (meth) acrylamide, etc.) and a functional group-containing radically polymerizable unsaturated monomer other than the above epoxy group (eg, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, etc.) A polycarboxylic acid crosslinking agent (for example,
Adipic acid, azelaic acid, dodecanedioic acid, adipic anhydride, trimellitic anhydride, etc.).

The powder coating (b) may be a hydroxyl-containing radically polymerizable unsaturated monomer (for example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, etc.), a hard resin having a glass transition temperature of 40 ° C. or higher. Acrylic monomers (eg, methyl methacrylate, ethyl methacrylate, iso-butyl methacrylate, ter-butyl methacrylate, ter-butyl acrylate, etc.) and optionally a glass transition temperature of 40
Soft acrylic monomers (e.g., methyl acrylate, ethyl acrylate, n-butyl methacrylate, iso-butyl acrylate, 2-ethylhexyl (meth) acrylate, stearyl methacrylate, and the like) having a temperature of less than or equal to or lower than C, and radical polymerizable unsaturated monomers other than acrylic monomers (e.g., Styrene, vinyltoluene, α-methylstyrene, (meth) acrylonitrile, (meth) acrylamide, etc.), and functional group-containing radically polymerizable unsaturated monomers other than the above-mentioned hydroxyl group (for example, glycidyl (meth) acrylate, methylglycidyl (meth) ) Acrylate
And the like, and a hydroxyl group-containing acrylic base resin obtained by a radical copolymerization reaction with a blocked polyisocyanate crosslinking agent (for example, hexamethylene diisocyanate, trimethylene diisocyanate, isophorone diisocyanate,
An aliphatic or alicyclic polyisocyanate compound such as hydrogenated xylylene diisocyanate is blended with an isocyanate group blocked with a compound such as a phenol, lactam, alcohol, or oxime). The mixing ratio of the base resin and the crosslinking agent is such that the crosslinking agent is mixed in the range of 10 to 100 parts by weight with respect to 100 parts by weight of the base resin.

As the thermosetting polyester resin powder coating (B2), a conventionally known powder coating which is capable of electrostatic powder coating by itself and is cured by heating, for example,
Blocked isocyanate-curable polyester resin-based powder coating (c), epoxy-curable polyester resin-based powder coating (d) and the like.

Examples of the powder coating (c) include phthalic acid (anhydride), isophthalic acid, terephthalic acid, dimethyl isophthalate, dimethyl terephthalate, hexahydro (anhydride) phthalic acid, and tetrahydro (anhydrous) phthalic acid. Aromatic or alicyclic dicarboxylic acids and dihydric alcohols such as (poly) ethylene glycol, (poly) propylene glycol, butylene glycol, butylene glycol, neopentyl glycol, 1,6-hexanediol, dimethylpropionic acid, etc., if necessary To react with a monocarboxylic acid such as benzoic acid, a trivalent or more carboxylic acid such as (anhydride) trimellitic acid, and a trivalent or more alcohol such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol. Obtained hydroxyl value of about 20 to
A paint obtained by blending the above blocked polyisocyanate crosslinking agent with a hydroxyl group-containing polyester resin of 300 mgKOH / g can be used. The mixing ratio of the base resin and the curing agent is about 10 to 100 per 100 parts by weight of the base resin.
Parts by weight, preferably in the range of about 15 to 80 parts by weight, are suitable.

As the powder coating (d), for example, a coating obtained by reacting the polyester raw material described in the above powder coating (c) with an acid value of about 20 to 300 mg KOH / g and a polyepoxide is blended. Can be used.
The mixing ratio of the base resin and the curing agent is about 10 to 100 parts by weight, preferably about 15 to 8 parts by weight, per 100 parts by weight of the base resin.
A range of 0 parts by weight is preferred.

As the powder coating (B3), a conventionally known powder coating which can be electrostatic powder coated by itself and is cured by heating, for example, a block isocyanate-curable fluororesin powder coating ( e) and the like. Examples thereof include those obtained by blending the above-mentioned blocked isocyanate crosslinking agent with a hydroxyl group-containing polymer containing fluorine in the main chain or a hydroxyl group-containing polymer containing fluorine in the side chain.

Examples of the hydroxyl group-containing polymer containing a main chain fluorine include, for example, hydroxyl group-containing unsaturated monomers (for example, hydroxy (cyclo) alkyl vinyl ether,
Vinyl alcohol and the like), fluorine-containing polymerizable unsaturated monomers (for example, tetrafluoroethylene, trifluorochloroethylene, difluorodichloroethylene, fluorotrichloroethylene and the like), and other polymerizable monomers (for example, vinyl ether and allyl ether, for example, ethyl vinyl ether). n-propyl vinyl ether, isopropyl vinyl ether, butyl vinyl ether, tert
-Chain alkyl vinyl ethers such as butyl vinyl ether, pentyl vinyl ether, hexyl vinyl ether and octyl vinyl ether; cycloalkyl vinyl ethers such as cyclopentyl vinyl ether and cyclohexyl vinyl ether; aryl vinyl ethers such as phenyl vinyl ether and trivinyl phenyl ether; benzyl vinyl ether and phenethyl vinyl ether Aralkyl vinyl ethers such as; allyl ethers such as allyl glycidyl ether and allyl ethyl ether; vinyl esters and propenyl esters such as vinyl acetate, vinyl propionate, vinyl lactate, and olefinic compounds such as ethylene, propylene and butylene; And vinyl chloride).

Examples of the polymer containing fluorine in the side chain include:
For example, hydroxyl-containing radically polymerizable unsaturated monomers and fluorine monomers described in the powder coatings (a) and (b) (for example, perfluorobutylethyl (meth) acrylate, perfluoroisononylethyl (meth) acrylate) , Perfluorooctylethyl (meth) acrylate, etc.), and radical copolymers with the hard and soft acrylic monomers described in the powder coatings (a) and (b).

The powder coating (e) is the above-mentioned hydroxyl-containing fluorine-containing copolymer (hydroxyl value: about 20 to 300 mgKOH / g).
And the above-mentioned blocked polyisocyanate crosslinking agent. The mixing ratio of the base resin and the curing agent is preferably about 10 to 100 parts by weight, and more preferably about 15 to 80 parts by weight, per 100 parts by weight of the base resin.

In the powder coating material B, paint additives such as a coloring agent, a filler, a curing catalyst, a fluidity adjusting agent, a repelling inhibitor, an ultraviolet stabilizer, and an ultraviolet absorber (benzotriazole compound, etc.) if necessary. Can be blended.

In addition to the above, the melt viscosity (Pa · s) of powder coating A measured at 130 ° C. is larger than the melt viscosity (Pa · s) of powder coating B measured at the same temperature (preferably). 1.5 or more, more than twice or more), and the melt viscosity (Pa · s) of the powder coating A is 1 to 100 (P
a · s) and the melt viscosity (Pa · s) of the powder coating B is
It is preferably 0.1 to 10 (Pa · s). As a result, the powder coating B easily spreads at the interface with the powder coating A, and the finished appearance of the coating film is improved.

In the method of the present invention, a powder coating A is applied to a substrate, and then the powder coating obtained is heated or not heated, and then the powder coating B is applied to the surface of the coating. This is a method for forming a multilayer powder coating film, which is characterized by coating and then heating. This preferred embodiment will be described below.

(1) A thermosetting powder coating A is applied to a metal or a base material (preferably a metal base) on which metal is subjected to cationic electrodeposition coating, and then a thermosetting powder coating B is applied. And then baking to cure both powder coatings, and if necessary, aqueous or organic solvent type or 1 type.
Apply a liquid paint of 00% solids.

(2) A thermosetting powder coating material A is electrostatically coated on a metal or a base material (preferably a metal base material) on which a metal is subjected to cationic electrodeposition coating. Preheating (heating to such an extent that the powder particles do not fall even when they are fused and vertical surfaces, heating to such an extent that the powder particles are fused and flow to form a coating film, but no curing occurs. Is partially cured but not completely cured, meaning that it is heated to the extent that it flows by post-heating. The same meaning is given below.)
Then, the thermosetting powder coating B is applied with electrostatic powder and then baked to cure both powder coatings, and then, if necessary, an aqueous, organic solvent type or 100% solid liquid coating is applied. I do.

(3) A thermosetting powder coating A is applied to a metal substrate by electrostatic powder coating, and the obtained powder coating is preheated (powder particles are fused and dropped even on a vertical surface). Heating to the extent not to cause the powder particles to fuse and flow to form a coating film, but to the extent that hardening does not occur, the above hardening is partially hardened but not completely hardened. Heating to the extent that it flows by heating. The same meaning applies hereinafter.) Cationic electrodeposition coating on the unpainted part, baking, then powder coating or powder coating and electrodeposition coating The surface is coated with a thermosetting powder coating material B by electrostatic powder coating and then baked to harden both powder coating films, and if necessary, an aqueous or organic solvent type or 1 type.
Apply a liquid paint of 00% solids.

[0035]

The present invention will be described below in detail with reference to examples. Parts and% indicate parts by weight and% by weight, respectively.

Production Example of Thermosetting Powder Coating A1 Epicoat 1004 (trade name, manufactured by Yuka Shell Co., Ltd.)
Melting and kneading a softening point of 97 to 103 ° C., an average molecular weight of about 1400, an epoxy resin, and the same meaning as described below) 1000 parts, adipic dihydrazide 500 parts, and a red stem 300 parts with a biaxial extruder, followed by cooling. The mixture was pulverized and classified to obtain a powder coating A1. The powder coating A1 has a melt viscosity at 130 ° C. of about 40 Pa · s and a particle size of about 5 to 25 μm.
5% <, and the surface tension was 31 dyne / cm.

Thermosetting powder coating material A2 Powder thermosetting powder coating material A2 was prepared in the same manner as powder coating material A1 except that 10 parts of benzyltetraphenylphosphonium chloride were used as a raw material in the production example of thermosetting powder coating material A1.

Thermosetting Powder Coatings A3, A4 The same procedure was followed as in coating A1 except that the blending amount of the petal was changed to 0 parts and 100 parts in the production example of the thermosetting powder coating A1. Body paints A3 and A4 were obtained.

Thermosetting Powder Coatings A5, A6 Powder coatings having the particle sizes shown in Table 1 were obtained by changing the classification conditions in the production examples of the thermosetting powder coatings A1.

Thermosetting powder coating material B1 Glycidyl group-containing acrylic resin (glycidyl methacrylate / styrene / methyl methacrylate / n-butyl acrylate = 40/10/20/30 "weight ratio" average molecular weight 8000, softening point 85 ° C) 800 parts by weight, 200 parts by weight of dodecanedioic acid and 80 parts by weight of titanium dioxide pigment are melt-kneaded with a twin-screw extruder, and then cooled, pulverized and classified to obtain a powder. Paint B1 was produced. The powder coating A1 has a melt viscosity at 130 ° C. of about 4 Pa · s,
96% <with a particle size of about 5 to 25 μm, surface tension 28
dyne / cm.

Thermosetting Powder Coatings B2 to B4 Manufacture in the same manner as for coating A1 except that the blending amount of titanium dioxide pigment was changed to 0, 500 and 1000 parts in the production example of thermosetting powder coating B1. And then sequentially paint B2, B
3. B4 was obtained.

Thermosetting Powder Coating B5 As a powder coating, a hydroxyl group-containing fluororesin (tetrafluoroethylene / hydroxybutyl vinyl ether / cyclohexyl vinyl ether = 40/30/30 weight ratio) /
ε-caprolactam-modified isophorone diisocyanate =
An 80/20 weight ratio was used.

Using the above powder coatings, coatings were prepared in combination as shown in Table 1.

Table 1 shows the coating film performance test results of Examples 1 to 9 and Comparative Examples 1 and 2.

[0045]

[Table 1]

In Table 1, the test was performed as follows.

Test of coating film performance Adjustment of coated plate A: Powder coating A was electrostatically powder-coated on a zinc phosphate-treated steel sheet so that the baked film thickness was about 40 μm. Was subjected to electrostatic powder coating and baked at 180 ° C. for 30 minutes.

Preparation of coated plate B: Powder coating A was electrostatically powder-coated on a zinc phosphate-treated steel plate so that the baked film thickness was about 40 μm, then pre-heated at 100 ° C. for 5 minutes, and then cooled to room temperature. After cooling, the powder coating material B was electrostatically powder-coated from the surface thereof and baked at 180 ° C. for 30 minutes.

Preparation of coated plate C: A powder coating A was electrostatically powder-coated on a zinc phosphate-treated steel plate so as to have a baked film thickness of about 40 μm, and then was cured by heating at 180 ° C. for 30 minutes and then at room temperature. Then, the powder coating material B was electrostatically powder-coated from the surface thereof and baked at 180 ° C. for 30 minutes.

Preparation of coated plate D: A powder coating A was electrostatically powder-coated on a part of the steel plate treated with zinc phosphate to a baked film thickness of about 40 μm, and then preheated at 100 ° C. for 5 minutes. After cooling to room temperature, an epoxy resin-based cationic electrodeposition paint (Electron 9600 gray, manufactured by Kansai Paint Co., Ltd., trade name) was applied by cationic electrodeposition to 20 μm.
After forming an electrodeposition coating and baking at 140 ° C for 30 minutes,
After cooling, the powder coating B was electrostatically powder-coated from the surface of the coating and baked at 180 ° C. for 30 minutes.

Preparation of coated plate E: A powder coating A or B was applied to a zinc phosphate treated steel plate by electrostatic powder coating and baked at 180 ° C. for 30 minutes.

In Table 1, the finish of the coating film and the coating film performance were tested by the following methods.

Coating appearance: The coating surface was visually observed and evaluated. ◎ indicates that there is no abnormality such as smoothness, shrinkage, etc., ○ indicates that the smoothness, shrinkage, etc. are slightly inferior, Δ indicates that abnormality such as smoothness, shrinkage, etc. is recognized, and X indicates that abnormality such as smoothness, shrinkage, etc. is observed. Significantly recognized.

Specular reflectance: 60 according to JIS K-5400
The degree of specular gloss was measured.

Accelerated weather resistance: Using a sunshine weatherometer, the gloss retention after the test for 500 hours was examined.
Appearance of coating film (◎ is good with little change compared to the initial stage, ○ is slightly glossy compared to the initial stage, Δ is glossy compared to the initial stage, ×
Glossiness is remarkable compared to the initial stage), gloss retention
[(Gloss after test (60 degrees) / initial gloss (60 degrees))
× 100] Anticorrosion: The coated plate was cut into 150 × 70 mm, and the coated film was cross-cut so as to reach the substrate, and then placed in a salt spray test apparatus. Three weeks later, the sample was taken out, and the rust generation width on one side from the cut portion was measured. ◎ indicates 0 to less than 1 mm, ○ indicates 1 to
Less than 2 mm, Δ indicates less than 2 to 6 mm, and X indicates 6 mm or more.

[0056]

According to the present invention, it is possible to form a multilayer powder coating film having excellent finishability and performance due to having the above-described configuration.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI C09D 163/00 C09D 163/00

Claims (12)

[Claims] An undercoat powder coating is applied to a substrate, and after heating the obtained undercoat powder coating or without heating, an overcoat powder coating is applied to the coating film surface, A method for forming a multilayer powder coating film, comprising heating. 2. The method according to claim 1, wherein the substrate is a metal. 3. The method according to claim 1, wherein the substrate is an electrodeposition coating film. 4. The method according to claim 1, wherein the substrate is a vehicle or a part thereof. 5. The method according to claim 1, wherein the undercoat powder coating is substantially incompatible with the overcoat powder coating. 6. The method according to claim 1, wherein the undercoat powder coating has a surface tension equal to or higher than that of the overcoat powder coating. 7. The method according to claim 1, wherein the undercoat powder coating is a thermosetting epoxy resin powder coating. 8. The thermosetting acrylic resin-based powder coating, the thermosetting polyester resin-based powder coating, and the thermosetting fluororesin-based powder coating, wherein the top-coating powder coating is at least one thermosetting type. The method for forming a multilayer powder coating film according to claim 1, wherein the method is a powder coating. 9. The method according to claim 1, wherein the undercoat powder coating has a softening temperature equal to or higher than that of the topcoat powder coating. 10. The multilayer powder coating film according to claim 1, wherein the proportion of particles having a particle diameter of 45 μm or less in the undercoat powder coating or the top coating powder coating is 90% by weight or more. Formation method. 11. The method according to claim 1, wherein the undercoat powder coating contains an onium salt compound. 12. An undercoat thermosetting powder coating is applied to a base material, and then the obtained undercoat thermosetting powder coating is baked to form an uncured powder coating, and then uncoated coating Apply a cationic electrodeposition coating to the part to form an electrodeposition coating, and then apply a top coating powder coating on the uncured powder coating surface or the uncured powder coating surface and the electrodeposition coating surface A method for forming a multilayer powder coating film, characterized by the following.