JPH11128833A - Method of forming coating film and coating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a coating film with a short coating process by which a coating film having good corrosion resistance, weather resistance, chipping resistance and film appearance can be formed, and to provide a coating film having excellent corrosion resistance, weather resistance, chipping resistance and film appearance. SOLUTION: By this method, an epoxy resin powder coating material (A) is applied by electrostatic coating on a base body surface and subjected to half baking, further a polyester resin powder coating material (B) is applied by electrostatic coating. Then the unhardened films are heated at one time to form a coating film. The ratio of gelling times of the epoxy resin powder coating material (A) to the polyester resin powder coating material (B) at 180 deg.C satisfies [gelling time of the epoxy resin powder coating material (A)]/[gelling time of the polyester resin powder coating material (B)]= 1/1 to 1/5. The gelling time of the epoxy resin powder coating material (A) at 180 deg.C is 40 to 400 sec, while the gelling time of the polyester resin powder coating material (B) at 180 deg.C is <=500 sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a coating film and a coating film thereof, and more particularly, to a coating film forming method for forming a coating film having excellent corrosion resistance, weather resistance, chipping resistance, and appearance of a coating film. The present invention relates to a coating film formed by a coating film forming method.

[0002]

2. Description of the Related Art Powder coatings, which do not contain an organic solvent, are free from environmental pollution and can save resources. For this reason, fields in which powder coatings are applied in place of solvent-based coatings are expanding, and their usage is also increasing.

[0003] Powder coatings are used in the field of road materials, such as guardrails and road signs, in addition to automobile bodies and residential building materials. However, with conventional powder coatings,
It was not possible to satisfy all the required properties of corrosion resistance, weather resistance, chipping resistance, and coating film appearance required for these members used outdoors. For example, an epoxy resin-based powder coating has sufficient corrosion resistance and chipping resistance, but insufficient weather resistance. Further, polyester resin-based powder coatings and acrylic resin-based powder coatings have sufficient weather resistance, but insufficient corrosion protection and chipping resistance. Furthermore, epoxy polyester resin-based powder coatings cannot sufficiently satisfy any of these properties.

Therefore, it has been studied to improve the performance of these coating films by using two or more types of powder coating materials having different performances and forming the coating film into multiple layers. By the way, the formation of the coating film of the powder coating is usually performed by a method of curing each coating. For example, when forming a two-layer coating film, it is performed by a so-called two-coat two-bake. Is common. However, since the coating process is lengthened when the layers are formed by such a method, a so-called two-coat 1 in which two kinds of paints are applied and then simultaneously cured in consideration of time reduction and resource saving is taken into consideration.
It is desired to form a coating film into multiple layers by a baking method.

However, in the two-coat, one-bake method, the upper layer film impedes the flow property of the lower layer film, and the powder coating particles, especially coarse particles, of the lower layer film do not flow completely, and a thin film portion may be formed on the upper layer film. However, there was a problem that the powder coating of the lower layer film appeared on the surface of the upper layer film, and the appearance of the coating film could not be improved.

[0006] JP-A-6-304519 discloses a method in which a polyester resin powder coating or an acrylic resin powder coating is applied to an uncured coating film obtained by coating an epoxy resin powder coating, and the two coating films are coated. Are simultaneously cured by heating to form a multilayer coating film. In this method, chipping resistance, corrosion resistance, and weather resistance are improved by making the surface tension of the powder coating forming the upper layer coating smaller than the surface tension of the powder coating forming the lower layer coating. I can do it. However, in this method, the difference in curing rate between the lower layer film and the upper layer film causes a difference in how the internal stress is applied, so that there is a problem that the distortion or shrinkage of the coating film occurs and the appearance of the coating film is deteriorated. .

As a method for improving the appearance of a coating film when a powder coating film is formed by a two-coat one-bake method, Japanese Patent Application Laid-Open No. 6-256692 discloses a method for forming an upper layer film and a lower layer film. A method of forming a coating film by defining the heat flow property of a powder coating in a molten state and making the flow property of the powder coating forming the upper layer larger than that of the powder coating is disclosed. However, this method has a problem that the curing time of the upper layer film becomes too long, so that the curing becomes insufficient within the practical curing time, and the chipping resistance, weather resistance, and corrosion resistance deteriorate.

[0008]

SUMMARY OF THE INVENTION In view of the above, the present invention can form a coating film in which the coating step is short and all of the corrosion resistance, weather resistance, chipping resistance and coating appearance are good. It is an object of the present invention to provide a coating film forming method and a coating film excellent in corrosion resistance, weather resistance, chipping resistance and coating appearance.

[0009]

SUMMARY OF THE INVENTION The present invention provides a method for producing
The epoxy resin-based powder coating (A) is electrostatically coated, and after half-baking, the polyester resin-based powder coating (B) is further electrostatically coated, and the obtained uncured film is simultaneously heated to form a coating film. Wherein the epoxy resin-based powder coating (A) and the polyester resin-based powder coating (B) have a gelation time ratio at 180 ° C. of [epoxy resin-based powder coating. (Geling time of (A)) / [Geling time of polyester resin-based powder coating material (B)] = 1 /
1 to 1/5, and the epoxy resin-based powder coating (A)
Has a gelation time at 180 ° C. of 40 to 400 seconds, and the polyester resin-based powder coating (B) is
This is a coating film forming method in which the gel time at 180 ° C. is 500 seconds or less. Hereinafter, the present invention will be described in detail.

In the method for forming a coating film according to the present invention, an epoxy resin-based powder coating (A) is applied to the surface of a base material, subjected to a half-baking treatment, and further coated thereon with a polyester resin-based powder coating (B). Is applied, and the obtained uncured film is simultaneously heated to form a coating film.

The substrate to which the coating film forming method of the present invention is applied is not particularly limited, and examples thereof include a phosphoric acid-treated steel sheet, a galvanized steel sheet, a cold-rolled steel sheet, an aluminum sheet, a stainless steel sheet, a zinc phosphate-treated steel sheet, Metals such as a steel sheet treated with iron phosphate can be used. These may be used as they are, or may be those that have been subjected to treatments such as formation of an undercoating film by applying a rust-preventive paint or electrodeposition paint to the surface, or formation of a treated film by surface treatment. These treatments may be performed alone or in combination of two or more. However,
In the coating film forming method of the present invention, the above two types of powder coatings are electrostatically coated on the surface of the base material. preferable.

The powder coatings used in the coating film forming method of the present invention are an epoxy resin powder coating (A) and a polyester resin powder coating (B). The epoxy resin-based powder coating (A) and the polyester resin-based powder coating (B)
The ratio of the gel time at 180 ° C. is [the gel time of the epoxy resin-based powder coating (A)] / [the gel time of the polyester resin-based powder coating (B)] = 1/1 to 1/5. It is. The gel time is defined by JIS K 6909, and is the time required for the sol to become a gel. The gelation time of the powder resin is usually set by placing a 0.5 g sample on a steel plate at 180 ° C, spreading it in a circle with a diameter of about 3 cm with a stainless steel spatula, and repeating at a speed of about once a second. This is the time until no thread is drawn between the sample and the spatula.

The epoxy resin-based powder coating material (A) 18
If the ratio of the gelation time at 180 ° C. of the polyester resin-based powder coating material (B) to the gelation time at 0 ° C. is less than 1, large distortion occurs in the appearance of the coating film, and the chipping resistance is also low. If it is lower than 5, the film will be greatly shrunk in appearance and the chipping resistance will also be reduced, so that it is limited to the above range.

The above-mentioned epoxy resin-based powder coating material (A) comprises 1
The gel time at 80 ° C. is 40 to 400 seconds. 4
When the time is less than 0 second, the powder coating does not flow sufficiently on the appearance of the coating film, and the smoothness is poor. In this case, the curing is insufficient, and the chipping resistance, weather resistance, and corrosion resistance are inferior.

The epoxy resin-based powder coating (A) contains 9
Those having a 0% volume particle size of 70 μm or less are preferred.
When the 90% volume particle diameter exceeds 70 μm, the coarse particles do not flow completely, a thin film portion is formed on the upper layer film, or the powder coating of the lower layer film appears on the surface of the upper layer film, and the coating film appearance becomes poor. Will be enough.

Here, the 90% volume particle diameter is defined as 90% of the total particles in the particle size distribution from the side having the smaller particle diameter.
% Is the maximum particle size in a region containing particles corresponding to the percentage of particles. For example, a particle having a 90% volume particle size of x μm has particles having a particle size exceeding x μm of 10% of all particles.
% Is included. Therefore, when the 90% volume particle diameter of the epoxy resin-based powder coating material (A) is limited, the abundance of particles having a volume particle diameter equal to or larger than the size is 10% of all the particles. Particles having a large volume particle diameter contained in the resin-based powder coating material account for at most 10% of all particles, and large amounts of coarse particles that do not completely flow during heat curing are not included. In the case where the particle size distribution is a normal distribution, those having a 90% volume particle diameter of 70 μm have a volume average particle diameter of 3 μm.
This corresponds to a size of 5 to 50 μm.

The epoxy resin powder coating (A) preferably has a volume average particle diameter of 10 to 60 μm. If it is less than 10 μm, the productivity of the powder coating is very poor, and the flowability of the powder coating is poor, making it difficult to handle.
If it exceeds m, the coarse particles do not flow completely, a thin film portion is formed on the upper layer film, or the powder coating of the lower layer film appears on the surface of the upper layer film, and the appearance of the coating film becomes poor.

The epoxy resin-based powder coating (A) is a thermosetting powder coating, and contains an epoxy resin and a curing agent as coating film forming components. The epoxy resin-based powder coating (A) is prepared by mixing and kneading the epoxy resin, the curing agent, and, if necessary, a curing catalyst, a pigment, a surface conditioner, an acrylic resin, and other additives. And the like.

The epoxy resin is not particularly limited, but is preferably a compound having two or more oxirane groups in the molecule. Specifically, for example, glycidyl ester resin, glycidyl ether type resin such as condensation reaction product of bisphenol A and epichlorohydrin, alicyclic epoxy resin, flocculent aliphatic epoxy resin, brominated epoxy resin,
Phenol novolak type epoxy resin, cresol novolak type epoxy resin and the like can be mentioned.

The curing agent for the epoxy resin is not particularly limited, and examples thereof include an epoxy resin having a phenolic hydroxyl group, an amine curing agent, dicyandiamide, imidazoles, and imidazolines. Among them, an epoxy resin having a phenolic hydroxyl group is preferred.

In the present invention, the epoxy resin-based powder coating (A) obtained as described above is a phenol-curable epoxy resin-based powder coating because the chipping resistance can be further improved. Is preferred.

The curing catalyst is not particularly restricted but includes, for example, tin catalysts, imidazoles, imidazolines and the like. The pigment is not particularly limited and includes, for example, coloring pigments such as titanium dioxide, red iron oxide, iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone pigments, and azo pigments; talc, calcium carbonate, precipitated barium sulfate, An extender such as silica can be used.

The surface conditioner is not particularly limited.
For example, dimethyl silicone, methyl silicone, acrylic oligomer and the like can be mentioned. The other additives are not particularly limited, and include, for example, a curing accelerator, a plasticizer, an ultraviolet absorber, an antioxidant, and a pigment dispersant; benzoin, a derivative obtained by adding one to three kinds of functional groups to benzoin. And the like.

The polyester resin powder coating (B) used in the present invention has a gelation time at 180 ° C. of 500
Seconds or less. If it exceeds 500 seconds, the curing time of the coating film becomes too long, and the curing time becomes insufficient within the practical curing time, and the chipping resistance, weather resistance, and corrosion resistance are inferior. You.

The above-mentioned polyester resin powder coating (B)
Preferably has a volume average particle diameter of 5 to 30 μm. If it is less than 5 μm, the productivity of the powder coating decreases,
Further, the flowability of the powder coating material is poor and handling becomes inconvenient. If it exceeds 30 μm, the smoothness of the coating film is reduced, which is not preferable.

The above polyester resin powder coating (B)
Is a thermosetting powder coating material, which contains a polyester resin and a curing agent as coating film forming components. The polyester resin powder coating (B) can be produced in the same manner as the epoxy resin powder coating (A), and the polyester resin, the curing agent, and, if necessary, a curing catalyst , Pigment, surface conditioner, acrylic resin,
The polyester resin-based powder coating (B) can be obtained by mixing and kneading other additives.

The polyester resin is not particularly restricted but includes, for example, polyhydric alcohols such as ethylene glycol, propanediol, pentanediol, hexanediol, neopentyl glycol, trimethylolpropane and pentaerythritol, and maleic acid, terephthalic acid, Examples thereof include those obtained by polymerizing a carboxylic acid such as isophthalic acid, phthalic acid, succinic acid, glutanic acid, adipic acid, sebacic acid and β-oxypropionic acid by a conventional method. The curing agent for the polyester resin is not particularly limited, for example, a blocked isocyanate,
Amino resins and the like can be mentioned.

In the method for forming a coating film according to the present invention, the epoxy resin-based powder coating material (A) is electrostatically coated on the surface of a substrate,
After the half-baking treatment, the polyester resin powder coating (B) is further electrostatically coated thereon, and the obtained uncured film is simultaneously heated to form a coating film. .

The epoxy resin powder coating material (A) used in the coating film forming method of the present invention has a cured film thickness of 10 to 70 μm, especially 10 to 70 μm, from the viewpoint of corrosion resistance and chipping resistance. It is preferable to apply the coating so as to have a thickness of 50 μm. For this coating, an electrostatic coating method is used, and the coating can be performed using a known electrostatic coating machine or the like.

Next, the epoxy resin-based powder coating (A) coated on the surface of the substrate used in the method of forming a coating film of the present invention.
Is half-baked. This half bake processing is
It means a heat treatment for melting particles on the surface of the coated epoxy resin-based powder coating material (A). If the half bake treatment is not performed, the appearance of the obtained coating film will be deteriorated. Specifically, at 75 to 140 ° C., 1 to 15
The heating is preferably performed for a minute.

The polyester resin powder coating (B) used in the coating film forming method of the present invention was obtained by subjecting the epoxy resin powder coating (A) coated on the surface of the base material to electrostatic coating and half-baking. Later, it is electrostatically coated thereon. The polyester resin-based powder coating (B) is, from the viewpoint of weather resistance,
It is preferable to apply the coating so that the cured film thickness becomes 20 to 80 μm. For this coating, an electrostatic coating is used in the same manner as the epoxy resin-based powder coating (A), and can be performed using a known electrostatic coating machine or the like.

In the method for forming a coating film of the present invention, the epoxy resin-based powder coating (A) and the polyester resin-based powder coating (B) are electrostatically coated, and then the obtained uncured film is heated simultaneously. This is a film formation method. The heating is preferably performed at 130 to 220 ° C. for 10 to 60 minutes in order to sufficiently cure the epoxy resin powder coating (A) and the polyester resin powder coating (B).

The coating film forming method of the present invention can be used for a so-called PD reverse coating system. In this coating system, powder coating is first performed on a base material, and thereafter, a portion that is difficult to be coated by powder coating is coated with an electrodeposition coating material having throwing power. When the coating film forming method of the present invention is used in a PD reverse coating system, the polyester resin is coated between the electrostatic coating of the polyester resin powder coating (B) and the simultaneous heating of the obtained uncured film. The method further includes a step of half-baking a layer obtained by applying the base powder coating material (B) and electrodepositing the entire substrate.

This half baking is preferably performed under the same conditions as described for the epoxy resin powder coating (A). The electrodeposition paint used in the above-mentioned PD reverse coating system is not particularly limited. For example, a cationic electrodeposition paint obtained by combining an amino-modified epoxy resin and a blocked isocyanate as a curing agent is preferable. Further, as the electrodeposition coating conditions, those used for a normal automobile body can be applied.

In the present invention, a solid color paint, a metallic color paint, a clear paint, or the like may be further applied on the coating film formed as described above. These may be used alone to form a single-layer film.
A multilayer coating may be formed using more than one kind. The coating film formed by the coating film forming method of the present invention has good adhesion to the above-mentioned paint.

The coating film forming method of the present invention is applied to applications requiring corrosion resistance, weather resistance and chipping resistance, for example, coating of road materials such as guardrails and road signs; automobile bodies; be able to.

In the method for forming a coating film according to the present invention, since the epoxy resin powder coating (A) is applied, and half-baked, then the polyester resin powder coating (B) is applied. The coating film has excellent chipping resistance and appearance, and is composed of an epoxy resin-based coating film and a polyester resin-based coating film, so that it has excellent corrosion resistance and weather resistance. Further, in the method for forming a coating film of the present invention, the epoxy resin-based powder coating (A) is electrostatically applied, and after half-baking, the polyester resin-based powder coating (B) is further electrostatically applied. Since the coating film is formed by the so-called two-coat one-bake method in which the obtained uncured films are simultaneously heated, the work process can be shortened as compared with the conventional two-coat two-bake method, and the energy cost can be reduced. Can be reduced.

Further, the epoxy resin-based powder coating (A)
The gelling time of each of the polyester resin-based powder coatings (B) and the polyester resin-based powder coatings (B) is limited. Is [gelation time of epoxy resin-based powder coating material (A)] / [gelation time of polyester resin-based powder coating material (B)] = 1/1 to 1/5,
Even when these coating films are formed in a two-coat, one-bake method in which the coating films are formed at the same time, the appearance of the coating films can be improved without causing curing shrinkage in each of the coating films. For this reason, corrosion resistance and weather resistance can be further improved. Further, since the epoxy resin-based powder coating (A) and the polyester resin-based powder coating (B) do not contain coarse particles, the appearance of the coating film is further improved.

The coating film of the present invention is formed by the above-mentioned coating film forming method of the present invention. The coating film of the present invention is
Since it is excellent in corrosion resistance, weather resistance, chipping resistance and coating film appearance, coated materials coated with the coating film of the present invention can be used for road materials such as guardrails and road signs; building materials for houses; Suitable for applications used in

[0040]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Production Example 1Epoxy resin-based powder coating composition
Manufacturing of  Epoxy resin (Epicoat 1004F, Yuka Shell Epo)
100 parts by weight, a curing agent (Epicure 170,
30 parts by weight of Yuka Shell Epoxy Co., Ltd., curing catalyst (Cu
Azole 2MZ, manufactured by Shikoku Chemicals) 0.3 parts by weight, charcoal
5 parts by weight of calcium oxide and 20 parts by weight of titanium dioxide
About 1 minute with a paper mixer (manufactured by Nippon Spindle Manufacturing Co., Ltd.)
And mixed at about 95 ° C with a co-kneader (Bus).
Was melt-kneaded. Cool at room temperature, atomize after coarse grinding
Pulverized by Fuji Paudal Co., Ltd. and air-flow classifier DS-
Classify coarse particles with Type 2 (manufactured by Nippon Pneumatic Industries)
And the 90% volume particle diameter is 62 μm,
Epoxy resin powder coating with a gel time of 71 seconds
The composition (1) was obtained.

Production Example 2Epoxy resin-based powder coating composition
Manufacturing of  Epoxy resin (Epicoat 1003F, Yuka Shell Epo)
100 parts by weight, a curing agent (Epicure 170,
30 parts by weight of Yuka Shell Epoxy Co., Ltd., curing catalyst (Cu
Azole 2MZ, manufactured by Shikoku Chemicals) 0.05 parts by weight,
5 parts by weight of calcium carbonate and 20 parts by weight of titanium dioxide
About 1 with Super Mixer (manufactured by Nippon Spindle Manufacturing Co., Ltd.)
For about 95 minutes at a temperature of about 95 ° C.
It was melt-kneaded under the conditions. After cooling at room temperature,
Pulverized by Iser (made by Fuji Paudal) and air flow classifier DS
-2 type (manufactured by Nippon Pneumatic Industries) to separate coarse particles
90% volume particle diameter is 60 μm,
Epoxy resin powder having a gel time of 285 seconds
A body coating composition (2) was obtained.

Production Example 3Epoxy resin-based powder coating composition
Manufacturing of  Epoxy resin (Epicoat 1004F, Yuka Shell Epo)
100 parts by weight, a curing agent (Epicure 170,
30 parts by weight of Yuka Shell Epoxy Co., Ltd., curing catalyst (Cu
Azole C17Z, manufactured by Shikoku Chemicals) 2.4 parts by weight,
5 parts by weight of calcium carbonate and 20 parts by weight of titanium dioxide
About 1 with Super Mixer (manufactured by Nippon Spindle Manufacturing Co., Ltd.)
For about 95 minutes at a temperature of about 95 ° C.
It was melt-kneaded under the conditions. After cooling at room temperature,
Pulverized by Iser (made by Fuji Paudal) and air flow classifier DS
-2 type (manufactured by Nippon Pneumatic Industries) to separate coarse particles
90% volume particle diameter is 59 μm, 180 ° C.
Resin powder with a gel time of 43 seconds
A coating composition (3) was obtained.

Production Example 4Epoxy resin-based powder coating composition
Manufacturing of  Epoxy resin (Epicoat 1004F, Yuka Shell Epo)
100 parts by weight, a curing agent (Epicure 172,
Yuka Shell Epoxy) 30 parts by weight, calcium carbonate
5 parts by weight and 20 parts by weight of titanium dioxide are supermixed
-Mix for about 1 minute with Nippon Spindle Manufacturing Co., Ltd.
Melting and kneading with a kneader (manufactured by Bus) at about 95 ° C
did. Cool at room temperature, and after coarse pulverization
Pulverized by Udall) and air-flow classifier DS-2
Classify the coarse particles with 90%
Gelation at 180 ° C with a volume particle size of 62 μm
Epoxy resin powder coating composition having a time of 34 seconds
(4) was obtained.

Production Example 5Epoxy resin-based powder coating composition
Manufacturing of  Epoxy resin (Epicoat 1003F, Yuka Shell Epo)
100 parts by weight, a curing agent (Epicure 170,
30 parts by weight of Yuka Shell Epoxy Co., Ltd., curing catalyst (Cu
Azole C17Z, manufactured by Shikoku Chemicals) 0.2 part by weight,
5 parts by weight of calcium carbonate and 20 parts by weight of titanium dioxide
About 1 with Super Mixer (manufactured by Nippon Spindle Manufacturing Co., Ltd.)
For about 95 minutes at a temperature of about 95 ° C.
It was melt-kneaded under the conditions. After cooling at room temperature,
Pulverized by Iser (made by Fuji Paudal) and air flow classifier DS
-2 type (manufactured by Nippon Pneumatic Industries) to separate coarse particles
90% volume particle size is 55 μm, 180 ° C.
Epoxy resin powder having a gel time of 442 seconds
A body coating composition (5) was obtained.

Production Example 6Epoxy resin-based powder coating composition
Manufacturing of  Epoxy resin (Epicoat 1004F, Yuka Shell Epo)
100 parts by weight, a curing agent (Epicure 170,
23 parts by weight of Yuka Shell Epoxy Co., Ltd.
172, Yuka Shell Epoxy Co., Ltd.) 7 parts by weight, carbonic acid
5 parts by weight of calcium and 20 parts by weight of titanium dioxide
About 1 minute with a par mixer (manufactured by Nippon Spindle Manufacturing Co., Ltd.)
Mix and condition at about 95 ° C with a kneader (Bus)
Was melt-kneaded. Cool at room temperature and after coarse grinding, atomizer
-Pulverized by Fuji Paudal Co., Ltd. and air-flow classifier DS-2
Classify coarse particles with a mold (manufactured by Nippon Pneumatic Industries)
Has a 90% volume particle size of 65 μm and a temperature of 180 ° C.
Resin powder coating with gelation time of 197 seconds
The composition (6) was obtained.

Production Example 7Epoxy resin-based powder coating composition
Manufacturing of  Except that the airflow classification step was omitted, the same as in Production Example 1
And the 90% volume particle diameter is 77 μm,
Epoxy resin powder coating with a gel time of 71 seconds
A composition (7) was obtained.

Production Example 8Epoxy resin dicyandiami
Manufacture of decurable powder coating composition  Epoxy resin (Epicoat 1004F, Yuka Shell Epo)
100 parts by weight, curing agent (dicyandiamide)
4 parts by weight, curing catalyst (Curesol 2MZ, Shikoku Chemicals
0.5 parts by weight, 5 parts by weight of calcium carbonate and 2 parts by weight
15 parts by weight of titanium oxide was mixed with a super mixer (Nihon Spin
Mix for about 1 minute with a dollar manufacturer and use a kneader (Bus
Melt kneading at about 95 ° C. Cool at room temperature
And after coarse crushing with an atomizer (Fuji Paudal)
Pulverized, airflow classifier DS-2 (Nippon Pneumatic Co., Ltd.)
(Manufactured by Sangyo Co., Ltd.) to classify the coarse particles so that the 90%
7 μm, and the gel time at 180 ° C. is 92 seconds.
An epoxy resin-based powder coating composition (8) was obtained.

Production Example 9Polyester resin-based powder coating
Manufacture of products  Polyester resin (Fine Dick M8024, Dainichi
50 parts by weight of a hardener (Adduct)
B-1540, manufactured by Huls Co.) 30 parts by weight, calcium carbonate
6 parts by weight of aluminum, 35 parts by weight of titanium dioxide and a surface conditioner
(CF-1056, manufactured by Toshiba Silicone Co., Ltd.) 0.6 parts by weight
With a super mixer (manufactured by Nippon Spindle Manufacturing Co., Ltd.)
Mix for 2 minutes and use a kneader (made by Buss Corp.)
It was melt-kneaded under the condition of ° C. Cool at room temperature,
Grind with Tomizer (Fuji Paudal)
Gelation time at 180 ° C. with a particle size of 23 μm
Resin-based powder coating composition having a length of 259 seconds
(1) was obtained.

Production Example 10Polyester resin powder coating
Production of the composition  Polyester resin (Fine Dick M8020, Dainichi
60 parts by weight of the Ink Chemical Industry Co., Ltd., curing agent (Adduct)
B-1530, manufactured by Huls) 10 parts by weight, curing catalyst
(Neostan U-100, manufactured by Nitto Kasei) 0.4 weight
Parts, 5 parts by weight of calcium carbonate, 30 parts by weight of titanium dioxide
And surface conditioner (CF-1056, Toshiba Silicone Co., Ltd.)
0.5 parts by weight of Super Mixer (Nippon Spindle)
Mix for about 2 minutes with a kneader (Bus
Was melt-kneaded under the conditions of about 100 ° C. Cool at room temperature
And after coarse crushing with an atomizer (Fuji Paudal)
After pulverization, the volume average particle size is 25 μm,
Polyester resin having a gel time of 195 seconds
A powder coating composition (2) was obtained.

Production Example 11Polyester resin powder coating
Production of the composition  Polyester resin (Fine Dick M8020, Dainichi
60 parts by weight of the Ink Chemical Industry Co., Ltd., curing agent (Adduct)
B-1530, manufactured by Huls) 10 parts by weight, curing catalyst
(Neostan U-100, manufactured by Nitto Kasei) 0.5 weight
Parts, 5 parts by weight of calcium carbonate, 30 parts by weight of titanium dioxide
And surface conditioner (CF-1056, Toshiba Silicone Co., Ltd.)
0.5 parts by weight of Super Mixer (Nippon Spindle)
Mix for about 2 minutes with a kneader (Bus
Was melt-kneaded under the conditions of about 100 ° C. Cool at room temperature
And after coarse crushing with an atomizer (Fuji Paudal)
After pulverization, the volume average particle size is 25 μm,
Polyester resin having a gelation time of 150 seconds in
A powder coating composition (3) was obtained.

Production Example 12Polyester resin powder coating
Production of the composition  Polyester resin (Fine Dick M8020, Dainichi
60 parts by weight of this ink manufactured by Ink Chemical Industry Co., Ltd.
B-1530, manufactured by Huls) 10 parts by weight, curing catalyst
(Neostan U-100, manufactured by Nitto Kasei) 0.15 weight
Parts, 5 parts by weight of calcium carbonate, 30 parts by weight of titanium dioxide
And surface conditioner (CF-1056, Toshiba Silicone Co., Ltd.)
0.5 parts by weight of Super Mixer (Nippon Spindle)
Mix for about 2 minutes with a kneader (Bus
Was melt-kneaded under the conditions of about 100 ° C. Cool at room temperature
And after coarse crushing with an atomizer (Fuji Paudal)
After pulverization, the volume average particle diameter is 21 μm,
Polyester resin having a gel time of 490 seconds
A powder coating composition (4) was obtained.

Production Example 13Polyester resin powder coating
Production of the composition  The crusher is a centrifugal crusher ZM-1000 (Nippon Seiki Seisakusho)
90) in the same manner as in Production Example 9 except that
% Volume particle diameter is 39 μm, gel at 180 ° C.
Polyester resin powder coating set with 259 seconds
The product (5) was obtained.

Production Example 14Polyester resin powder coating
Production of the composition  Polyester resin (Fine Dick M8020, Dainichi
60 parts by weight of the Ink Chemical Industry Co., Ltd., curing agent (Adduct)
B-1530, manufactured by Huls) 10 parts by weight, curing catalyst
(Neostan U-100, manufactured by Nitto Kasei) 0.10 weight
Parts, 5 parts by weight of calcium carbonate, 30 parts by weight of titanium dioxide
And surface conditioner (CF-1056, Toshiba Silicone Co., Ltd.)
0.5 parts by weight of Super Mixer (Nippon Spindle)
Mix for about 2 minutes with a kneader (Bus
Was melt-kneaded under the conditions of about 100 ° C. Cool at room temperature
And after coarse crushing with an atomizer (Fuji Paudal)
After pulverization, the volume average particle size is 22 μm,
Polyester resin having a gel time of 560 seconds
A powder coating composition (6) was obtained.

Production Example 15Epoxy resin powder coating composition
Manufacture of goods  Epoxy resin (Epicoat 1004F, Yuka Shell Epo)
100 parts by weight, a curing agent (Epicure 170,
23 parts by weight of Yuka Shell Epoxy Co., Ltd.
172, Yuka Shell Epoxy Co., Ltd.) 7 parts by weight, carbonic acid
5 parts by weight of calcium and 20 parts by weight of titanium dioxide
About 1 minute with a par mixer (manufactured by Nippon Spindle Manufacturing Co., Ltd.)
Mix and condition at about 95 ° C with a kneader (Bus)
Was melt-kneaded. Cool at room temperature and after coarse grinding, atomizer
-(Made by Fuji Paudal Co., Ltd.)
25 μm and a gel time at 180 ° C. of 197
Second, an epoxy resin-based powder coating composition (9) was obtained.

Production Example 16Polyester resin powder coating
Production of the composition  Polyester resin (Fine Dick M8020, Dainichi
60 parts by weight of the Ink Chemical Industry Co., Ltd., curing agent (Adduct)
B-1530, manufactured by Huls) 10 parts by weight, curing catalyst
(Neostan U-100, manufactured by Nitto Kasei) 0.4 weight
Parts, 5 parts by weight of calcium carbonate, 30 parts by weight of titanium dioxide
And surface conditioner (CF-1056, Toshiba Silicone Co., Ltd.)
0.5 parts by weight of Super Mixer (Nippon Spindle)
Mix for about 2 minutes with a kneader (Bus
Was melt-kneaded under the conditions of about 100 ° C. Cool at room temperature
And after coarse crushing with an atomizer (Fuji Paudal)
Pulverized, airflow classifier DS-2 (Nippon Pneumatic Co., Ltd.)
(Manufactured by Sangyo Co., Ltd.) to classify the coarse particles to have a 90% volume particle diameter of 6%.
4 μm, gel time at 180 ° C. 195 seconds
Polyester resin powder coating composition (7)
Was.

In Production Examples 1 to 16, the volume average particle diameter and the 90% volume particle diameter of the powder coating composition were measured using the following particle size distribution analyzer under the following conditions. Particle size analyzer: Nikkiso Microtrac HRA X-
100 analysis software: MICROTRAC D. H. S. X10
0 Data Handling System SD
-9300PRO-100 Measurement conditions: Particle Transparenc
y is reflected Sample dispersion conditions: 0.5 g of a sample is put in 50 g of a 0.1% aqueous solution of a surfactant, and an ultrasonic cleaner (SILENTSONI) is used.
(CUT-105, manufactured by Sharp Corporation) for 3 minutes was used as a measurement sample.

In Production Examples 1 to 16, the gel time was
The measurement was performed at 180 ° C. using a gelling tester (manufactured by Nissin Kagaku).

Example 1 The epoxy resin powder coating composition (1) obtained in Production Example 1 as a first layer on a 0.8 mm thick zinc phosphate treated steel sheet
Was subjected to electrostatic coating so as to have a cured film thickness of 30 ± 5 μm, followed by half-baking at 100 ° C. for 5 minutes and cooling at room temperature. Further, the polyester resin-based powder coating composition (1) obtained in Production Example 9 was electrostatically coated thereon as a second layer so as to have a cured film thickness of 50 ± 5 μm.
The coating was formed by heating in a hot-air drying furnace for 5 minutes to prepare a test plate.

Example 2 Except that the epoxy resin-based powder coating composition (6) obtained in Production Example 6 was used instead of the epoxy resin-based powder coating composition (1) obtained in Production Example 1. Formed a coating film in the same manner as in Example 1 to produce a test plate.

Example 3 A production example using the epoxy resin-based powder coating composition (3) obtained in Production Example 3 in place of the epoxy resin-based powder coating composition (1) obtained in Production Example 1. Production Example 1 in place of the polyester resin powder coating composition (1) obtained in Example 9
Polyester resin-based powder coating composition obtained in (0)
A coating film was formed in the same manner as in Example 1, except for using, to prepare a test plate.

Example 4 Except that the epoxy resin-based powder coating composition (7) obtained in Production Example 7 was used instead of the epoxy resin-based powder coating composition (1) obtained in Production Example 1. Formed a coating film in the same manner as in Example 1 to produce a test plate.

Example 5 Except that the polyester resin-based powder coating composition (5) obtained in Production Example 13 was used instead of the polyester resin-based powder coating composition (1) obtained in Production Example 9. Formed a coating film in the same manner as in Example 1 to produce a test plate.

Example 6 Except that the epoxy resin-based powder coating composition (8) obtained in Production Example 8 was used instead of the epoxy resin-based powder coating composition (1) obtained in Production Example 1. Formed a coating film in the same manner as in Example 1 to produce a test plate.

Comparative Example 1 Except that the epoxy resin-based powder coating composition (2) obtained in Production Example 2 was used instead of the epoxy resin-based powder coating composition (1) obtained in Production Example 1. Formed a coating film in the same manner as in Example 1 to produce a test plate.

Comparative Example 2 Except that the epoxy resin-based powder coating composition (3) obtained in Production Example 3 was used instead of the epoxy resin-based powder coating composition (1) obtained in Production Example 1. Formed a coating film in the same manner as in Example 1 to produce a test plate.

COMPARATIVE EXAMPLE 3 An epoxy resin-based powder coating composition (4) obtained in Production Example 4 was used in place of the epoxy resin-based powder coating composition (1) obtained in Production Example 1, and Production Example 1 in place of the polyester resin powder coating composition (1) obtained in Example 9
Polyester resin-based powder coating composition obtained in 1 (3)
A coating film was formed in the same manner as in Example 1, except for using, to prepare a test plate.

COMPARATIVE EXAMPLE 4 A production example using the epoxy resin-based powder coating composition (5) obtained in Production Example 5 instead of the epoxy resin-based powder coating composition (1) obtained in Production Example 1. Production Example 1 in place of the polyester resin powder coating composition (1) obtained in Example 9
Polyester resin powder coating composition obtained in 2 (4)
A coating film was formed in the same manner as in Example 1, except for using, to prepare a test plate.

COMPARATIVE EXAMPLE 5 An epoxy resin-based powder coating composition (2) obtained in Production Example 2 was used instead of the epoxy resin-based powder coating composition (1) obtained in Production Example 1, and Production Example 1 in place of the polyester resin powder coating composition (1) obtained in Example 9
Polyester resin-based powder coating composition obtained in 4 (6)
A coating film was formed in the same manner as in Example 1, except for using, to prepare a test plate.

Comparative Example 6 Except that the epoxy resin-based powder coating composition (9) obtained in Production Example 15 was used instead of the polyester resin-based powder coating composition (1) obtained in Production Example 9. Formed a coating film in the same manner as in Example 1 to produce a test plate.

COMPARATIVE EXAMPLE 7 Except that the polyester resin powder coating composition (7) obtained in Production Example 16 was used instead of the epoxy resin powder coating composition (1) obtained in Production Example 1. Formed a coating film in the same manner as in Example 1 to produce a test plate.

Comparative Example 8 Example 1 was repeated except that the half bake treatment was not performed.
A coating film was formed in the same manner as described above to obtain a test plate.

Production Example 17JP-A-6-304519
Of Epoxy Resin Powder Coating Compositions  Epoxy resin (Epicoat 1004F, Yuka Shell Epo)
100 parts by weight, curing agent (dihydradipic acid)
6 parts by weight, 50 parts by weight of titanium dioxide, carbon
1 part by weight of rack and 0.5 parts by weight of benzoin super
Mix for about 1 minute with a mixer (manufactured by Nippon Spindle Manufacturing Co., Ltd.)
And melted with a co-kneader (Bus) at about 95 ° C.
Melted and kneaded. Cool at room temperature, atomize after coarse grinding
(Made by Fuji Paudal Co., Ltd.) and airflow classifier DS-2
(Nippon Pneumatic Industries Ltd.) to classify coarse particles
Thus, the 90% volume particle diameter is 60 μm,
Resin coating composition with 210 seconds gel time
The product (A-1) was obtained.

Production Example 18JP-A-6-304519
Of the polyester resin powder coating composition described in the report  Polyester resin (ER6570, manufactured by Nippon Ester)
60 parts by weight, curing agent (Adduct B-1530, Hüls
12 parts by weight, titanium dioxide 30 parts by weight, dibutyl
0.6 parts by weight of tin dilaurate, a surface preparation agent (Modaflow
-, Manufactured by Mitsubishi Monsanto Kasei Co., Ltd.) 0.6 parts by weight and benzo
0.3 parts by weight of Super Mixer (Nippon Spindle
Mix for about 1 minute with a manufacturer (Bus)
Was melt-kneaded under the conditions of about 95 ° C. Cool at room temperature
And after coarse crushing, powder with an atomizer (Fuji Paudal)
Crushed and has a volume average particle size of 24 μm at 180 ° C.
Polyester resin powder coating composition with gelation time of 50 seconds
A product (B-1) was obtained.

Comparative Example 9 Instead of the epoxy resin powder coating composition (1) obtained in Production Example 1, the epoxy resin powder coating composition (A-1) obtained in Production Example 17 was used. Further, except that the polyester resin-based powder coating composition (B-1) obtained in Production Example 18 was used instead of the polyester resin-based powder coating composition (1) obtained in Production Example 9, A coating film was formed in the same manner as in Example 1 to obtain a test plate.

Production Example 19JP-A-6-256692
Of Epoxy Resin Powder Coating Compositions  Epoxy resin (Epicoat 1004F, Yuka Shell Epo)
100 parts by weight, a curing agent (Epicure 108)
FF, Yuka Shell Epoxy) 7 parts by weight, titanium dioxide
20 parts by weight, magnesium silicate 40 parts by weight and surface
1 part by weight of a regulator (Acronal 4F, manufactured by BASF)
About 1 with Super Mixer (manufactured by Nippon Spindle Manufacturing Co., Ltd.)
For about 95 minutes at a temperature of about 95 ° C.
It was melt-kneaded under the conditions. After cooling at room temperature,
Pulverized by Iser (made by Fuji Paudal) and air flow classifier DS
-2 type (manufactured by Nippon Pneumatic Industries) to separate coarse particles
By classifying, the 90% volume particle diameter is 65 μm and 180%
Epoxy resin powder with gel time of 175 seconds at ℃
A coating composition (A-2) was obtained.

Production Example 20JP-A-6-256692
Of the polyester resin powder coating composition described in the report  Polyester resin (Fine Dick M8010, Dainichi
60 parts by weight of the Ink Chemical Industry Co., Ltd., curing agent (Adduct)
B-1530, manufactured by Huls) 18 parts by weight, titanium dioxide
18 parts by weight and a surface preparation agent (Acronal 4F, BA
0.6 parts by weight of Super Mixer (manufactured by SF Company)
Mix for about 1 minute with a kneader
Melt kneading at about 95 ° C. At room temperature
After cooling and coarse grinding, atomizer (Fuji Paudal)
At a volume average particle diameter of 26 μm and at 180 ° C.
Polyester resin powder coating with gelling time of 820 seconds
The composition (B-2) was obtained.

Comparative Example 10 Instead of the epoxy resin powder coating composition (1) obtained in Production Example 1, the epoxy resin powder coating composition (A-2) obtained in Production Example 19 was used. Further, except that the polyester resin-based powder coating composition (B-2) obtained in Production Example 20 was used instead of the polyester resin-based powder coating composition (1) obtained in Production Example 9, A coating film was formed in the same manner as in Example 1 to obtain a test plate.

In Production Examples 17 to 20, the volume average particle diameter, the 90% volume particle diameter, and the gelation time of the powder coating composition were measured in the same manner as in Production Examples 1 to 16.

With respect to the test plates obtained in Examples 1 to 6 and Comparative Examples 1 to 10, the appearance of the coating film was evaluated by visual inspection for bumps, distortion, shrinkage, and surface roughness, and chipping resistance, corrosion resistance and weather resistance were evaluated. Was evaluated.

[0081]Evaluation of appearance of coating film  Visual inspection of bumps, distortion and shrinkage of coating film according to the following evaluation criteria
Was evaluated. The results are shown in Table 1. In addition, the rough surface of the coating film
Is measured using a surface roughness profile measuring instrument and evaluated by Ra value.
did.

(I) Criteria for evaluation of bumps ○: There are no bumps and smooth Δ: There are some bumps, but there is no practical problem ×: There are many bumps and there is a practical problem (ii) Evaluation criteria of distortion ：: Smooth without distortion Δ: Slight slight distortion but no practical problem ×: Many large distortions and practical problem (iii) Judgment criteria for shrinkage ○: Smooth without shrinkage Δ: slight shrinkage, but no problem in practical use ×: many shrinkage, problem in practical use

(Iv) Evaluation of Surface Roughness The Ra value was measured using a surface roughness shape measuring instrument (Surfcom 470A, manufactured by Tokyo Seimitsu Co., Ltd.). The measurement of the Ra value was performed at a cutoff value of 0.8 mm and a scanning speed of 0.3 mm / sec. The measured values are shown in Table 1. In addition, Ra value is 0-0.5.
μm, the coating film appearance is good, and the Ra value is 0.5 μm.
Those having a length of more than m and not more than 0.8 μm have no practical problem.

[0084]Evaluation of chipping resistance  Test of Examples 1 to 6 and Comparative Examples 1 to 10 kept at 0 ° C
50g of No. 7 crushed stone on the plate from the direction perpendicular to the test plate
4kg / cm^Two Spray with the air pressure of
Peeling was evaluated according to the following criteria [chipping resistance
(1)]. In addition, trials of Examples 1 to 6 and Comparative Examples 1 to 10
In addition to the solvent type color coat paint (Sue
Parrack M-100 Black, Nippon Paint Co., Ltd.)
Is applied to a dry film thickness of 15 ± 5 μm.
Leave the setting for 0 minutes, and then
Paint (Super Rack O-100 Clear, Nippon Paint)
(Manufactured by Int Co.) so that the dry film thickness becomes 30 ± 5 μm
After setting at room temperature for 10 minutes,
Bake at 20 ° C for 20 minutes to form a composite coating
In the same way, the chipping resistance was similarly evaluated.
[Chip resistance (2)]. Table 1 shows the results.
did. ：: No peeling reaching the substrate △: Size of peeling reaching the substrate is about 2 mm square or less
×: The size of the peeling reaching the substrate is about 2 mm square or less.
Of three or more places or peeling
Some are about 2mm square or larger

[0085]Evaluation of corrosion resistance  Using the test plates of Examples 1 to 6 and Comparative Examples 1 to 10, J
500 hours with the equipment and conditions of IS K 5400 9.1
Between tests. The evaluation results are
The rust progress distance (mm) from the cut portion was expressed. Table of results
1 is shown. In addition, the thing whose traveling distance of rust is 1 mm or less
Passed level.

[0086]Evaluation of weather resistance  Using the test plates of Examples 1 to 6 and Comparative Examples 1 to 10, J
50 with the equipment and conditions of IS K 5400 9.8.1
A 0 hour test was performed. The evaluation result is 60 ° gloss.
It was expressed as retention. The results are shown in Table 1. In addition, 60 degrees
Those having a loss retention of 70% or more were regarded as acceptable levels.

[0087]

[Table 1]

From the above, it was found that both of the two coating films consisted of an epoxy resin-based powder coating (Comparative Example 6) and 2
It was found that when all the coating films of the layers were made of a polyester resin-based powder coating (Comparative Example 7), the weather resistance and the corrosion resistance were insufficient. Further, even if the first layer is made of an epoxy resin-based powder coating and the second layer is made of a polyester resin-based powder coating, the gel of the powder coating forming the first layer as in Comparative Example 4 is used. When the gelation time exceeds 400 seconds or when the gel time of the powder coating forming the second layer exceeds 500 seconds as in Comparative Examples 5 and 10, both the chipping resistance, corrosion resistance and weather resistance are reduced. It turned out to be inadequate.

In Comparative Example 8, since the second layer was coated without performing the half-bake treatment after the first layer was applied, the powder paint of the second layer was applied during the coating of the second layer. It was found that a phenomenon of infiltration into the film occurred, and the Ra of the coating film decreased.

The first, second and ninth comparative examples correspond to the first
Since the ratio (A) / (B) of the gel time of the powder coating material forming the layer and the second layer is out of the range of 1/1 to 1/5,
It was found that the coating film had irregularities and shrinkage, resulting in poor appearance of the coating film and insufficient chipping resistance. In Comparative Example 3, the gelation time ratio (A) /
Although (B) was within the above range, the gel time of the powder coating material forming the first layer was less than 40 seconds, so that the surface of the coating film was rough and not practical.

In Examples 1 to 6 in which the appearance of the coating film, the corrosion resistance, the weather resistance and the chipping resistance were all good, the test plate was further coated with a color coat paint, and then coated with a clear coat paint. When heat-cured to form a composite coating, the chipping resistance was also good, so the adhesion to these paints was good, and it was also practical as a primer having chipping resistance It turned out that it was something.

Example 7 An epoxy resin-based powder coating composition (1) obtained in Production Example 1 as a first layer after masking a part of a 0.8 mm thick zinc phosphate treated steel sheet with a masking tape The cured film thickness 3
Electrostatic coating was performed to a thickness of 0 ± 5 μm, half-baked at 100 ° C. for 5 minutes, and cooled at room temperature. Further, the polyester resin-based powder coating composition (1) obtained in Production Example 9 was electrostatically coated thereon as a second layer so as to have a cured film thickness of 50 ± 5 μm, and half-baked at 100 ° C. for 5 minutes. After the treatment, it was cooled again at room temperature. Subsequently, the masking tape was peeled off, and the cationic electrodeposition paint (Power Top V-5) was removed.
(Nippon Paint Co., Ltd.) in an electrodeposition bath set at 28 ° C., and the entire substrate was electrodeposited at a coating voltage of 230 V for 3 minutes and washed with water. The steel sheet coated with the two kinds of powder paint and the electrodeposition paint obtained in this manner was heated at 180 ° C. for 25 minutes.
The coating was formed by heating in a hot-air drying oven for a minute to prepare a test plate.

In the obtained test plate, the portions other than the portions coated with powder, for example, the masked portion and the back surface of the powder coated surface are subjected to electrodeposition coating. The appearance was satisfactory without any visual inspection.

[0094]

Since the coating film forming method of the present invention has the above-mentioned structure, the coating process can be shortened, and the energy cost can be reduced. A coating film excellent in chipping resistance and coating appearance can be formed, and can be suitably used as a primer, a top coating material, and the like in coating a metal material or the like. Further, since the coating film of the present invention is excellent in corrosion resistance, weather resistance, chipping resistance and coating film appearance, it is used outdoors such as road materials such as guardrails and road signs, housing materials, automobile bodies and the like. Suitable for use.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI B32B 27/38 B32B 27/38

Claims (7)

[Claims] An epoxy resin-based powder coating (A) is electrostatically coated on the surface of a base material, and after a half-baking treatment, a polyester resin-based powder coating (B) is further electrostatically coated. A coating film forming method for forming a coating film by simultaneously heating a cured film, wherein the epoxy resin-based powder coating material (A)
And the polyester resin-based powder coating (B) is 180
The gelation time ratio at ° C is [gelation time of epoxy resin-based powder coating material (A)] / [gelation time of polyester resin-based powder coating material (B)] = 1/1 to 1/5, The epoxy resin-based powder coating material (A) has a gel time at 180 ° C. of 40 to 400 seconds, and the polyester resin-based powder coating material (B) has a gel time at 180 ° C. of 500 seconds or less. A method for forming a coating film, characterized in that: 2. The coating film forming method according to claim 1, wherein the half bake treatment is heating at 75 to 140 ° C. for 1 to 15 minutes. 3. The epoxy resin-based powder coating (A) has a content of 90%.
The coating film forming method according to claim 1 or 2, wherein the% volume particle size is 70 µm or less. 4. The polyester resin powder coating (B) comprises:
4. The method for forming a coating film according to claim 1, wherein the volume average particle diameter is 5 to 30 [mu] m. 5. The epoxy resin-based powder coating (A) is a phenol-curable epoxy resin-based powder coating.
5. The method for forming a coating film according to 2, 3, or 4. 6. The polyester resin powder coating (B) obtained by electrostatic coating between the electrostatic coating of the polyester resin powder coating (B) and the simultaneous heating of the uncured film. The coating film forming method according to claim 1, further comprising a step of subjecting the entire substrate to electrodeposition coating after the layer is half-baked. 7. A coating film formed by the method for forming a coating film according to claim 1, 2, 3, 4, 5, or 6.