JPH0838999A - Method for coating metallic object with powdery resin - Google Patents

Abstract

PURPOSE:To form a uniform and thick coating film having no pin holes, by spraying a metallic object to be treated with an electrostatically charged powdery thermoplastic resin to form a molten resin thin film on the surface of the metallic object and then, spraying, thereon an uncharged powdery thermoplastic resin of the same kind as that of the former resin. CONSTITUTION:In this method, the surface of a metallic object to be treated is defatted and cleaned beforehand and then, the cleaned surface of the object is subjected to blasting treatment and thereafter, the treated surface of the metallic object is sprayed with a powdery thermoplastic resin charged by the ion bombardment through heating the metallic object beforehand or heating it from its rear surface. The charged powdery thermoplastic resin is uniformly stuck on this surface of the metallic object in an about 100mum thickness and melted by heat to form a thin film and thereby, the possibility of generating pin holes in the thin film can be minimized. Thereafter, when this molten resin thin film is sprayed with an uncharged powdery thermoplastic resin of the same kind as that of the former resin by using a spray gun provided with a powder supply device, the powdery resin particles are successively melted and stuck on the thin film and therefore, a thicker coating film can be formed on the metallic object.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for coating an object such as a metal with a resin powder.

[0002]

2. Description of the Related Art A method of coating a metal object with resin powder using an electrostatic powder spraying device or a powder spraying spraying device is a generally known method. In the electrostatic powder heating and melting method, the thermoplastic resin powder adheres to the surface of the grounded metal object, but when the discharge element of the electrostatic powder spraying device is brought close to the metal object, the resin powder is generated by corona discharge. When the discharge element is moved away from the metal object, the amount of resin powder reaching the object is reduced and it is difficult to increase the film thickness. On the other hand, in the powder spray heating and melting method, when the thermoplastic resin powder is directly sprayed onto the surface of a metal object using a spray gun, the resin powder repels on the metal surface and the amount of resin powder melted and adhered becomes uneven. Therefore, there is a problem that pinholes are likely to occur.

[0003]

In order to solve the above problems, the development of a coating method capable of forming a uniform and thick film without pinholes when coating a resin powder on the surface of a metal object has been developed. Desirable, the present invention provides such a method.

[0004]

According to the present invention, a metal object to be treated is heated in advance, or a thermoplastic resin powder charged with static electricity is applied to a metal object to be treated while being heated from the back surface of the metal object to be treated. A method for coating a surface of a metal object with a thermoplastic resin, which comprises spraying a thin molten film of the resin on the surface to form a thin molten film, and then spraying the same kind of non-statically charged thermoplastic resin powder on the molten film. Is.

The present invention is a method for coating the surface of an object such as a metal with a resin powder to form a thick film without pinholes. The object such as the flange of a steel pipe, the wall surface of a container, the wall surface of a steel pipe, etc. It is particularly suitable for, but not necessarily limited to, coating metal objects that cannot be spin coated.

The surface of the metal object is degreased / washed and then blasted, and then the metal object to be treated is heated, or the back surface of the metal to be treated is heated, and the surface of the metal object is charged by ion bombardment. Spray the thermoplastic resin powder. The electrostatically charged thermoplastic resin powder uniformly adheres to the surface of the metal object in a thickness of about 100 μm and is melted by heat to form a thin film, thereby minimizing the possibility of pinholes. The thermoplastic resin powder that can be used at this time is epoxy resin, polyethylene resin, polypropylene resin or the like. The heating method includes an electric furnace, a gas burner, and dielectric heating. If the same kind of thermoplastic resin powder that is not charged with static electricity is sprayed onto the molten film by using a spray gun equipped with a powder supply device, the resin powder will be melted and adhered one after another, so that the film can be made thicker. Becomes

[0007]

According to the present invention, it is possible to form a thick lining film without pinholes which could not be conventionally applied.

[0008]

EXAMPLES The effects of the present invention will be clarified by giving concrete examples of the present invention.

Example 1 A carbon steel plate having a length of 70 mm, a width of 200 mm, and a thickness of 5 mm was degreased, shot-blasted, and fixed in a vertical direction with a clamp. Preheat the surface of the carbon steel plate with a gas burner to a surface temperature of 270 ° C.
It was sprayed using an electrostatic powder spraying device kept at KV. The resin powder charged with static electricity was uniformly attached to the surface of the carbon steel sheet with a thickness of about 100 μm. Next, when a polypropylene resin powder that was not charged with static electricity was sprayed onto this molten film, the heat retained by the metal melted and adhered to the molten film one after another to form a film. The lining film thus prepared had a thickness of 2.0 mm, and the film surface was uniform. As a result of measuring the pinhole of the film using a pinhole tester, there was no problem at all.

(Example 2) The same experiment as in Example 1 was conducted using polyethylene powder for metal coating. However, the surface temperature of the carbon steel sheet was 240 ° C. The film thickness after solidification was 1.8 mm, and the film surface was uniform. As a result of measuring the pinhole of the film using a pinhole tester, there was no problem at all.

Example 3 The same experiment as in Example 1 was conducted using an epoxy resin for metal coating. However, the surface temperature of the carbon steel sheet was 200 ° C. The film thickness after solidification is 2.
It was 1 mm and the coating surface was uniform. As a result of measuring the pinhole of the film using a pinhole tester, there was no problem at all.

Example 4 A carbon steel plate having a length of 70 mm, a width of 200 mm, and a thickness of 5 mm was degreased, shot-blasted, and fixed in a vertical direction with a clamp. While heating with a gas burner from the back side of the carbon steel sheet, the surface temperature was set to 250 ° C., and the polypropylene resin powder for metal coating was sprayed using an electrostatic powder spraying device kept at 20 KV. The resin powder charged with static electricity was uniformly attached to the surface of the carbon steel sheet with a thickness of about 100 μm. When the powder which was not charged with static electricity was sprayed while continuing to be heated, it was melted and adhered to the molten film one after another by heat. The film thickness after solidification was 1.7 mm, and the film surface was uniform.
As a result of measuring the pinhole of the film using a pinhole tester, there was no problem at all.

Example 5 The same experiment as in Example 4 was conducted using polyethylene powder for metal coating. However, the surface temperature of the carbon steel sheet was set to 220 ° C. The film thickness after solidification was 1.8 mm, and the film surface was uniform. As a result of measuring the pinhole of the film using a pinhole tester, there was no problem at all.

Example 6 The same experiment as in Example 4 was conducted using an epoxy resin for metal coating. However, the surface temperature of the carbon steel sheet was set to 180 ° C. The film thickness after solidification was 1.9 mm, and the film surface was uniform. As a result of measuring the pinhole of the film using a pinhole tester, there was no problem at all.

(Comparative Example 1) 70 mm long × 200 mm wide ×
A 5 mm-thick carbon steel plate was degreased, shot-blasted, and then fixed vertically using a clamp. It was previously heated from the back side of the carbon steel sheet using a gas burner so that the surface temperature was 270 ° C., and the polypropylene resin powder for metal coating was sprayed using a spray gun. Since the polypropylene resin powder repelled on the metal surface and was hard to adhere, the film formation was non-uniform and the film thickness varied. As a result of measuring the film using a pinhole tester, some pinholes were confirmed.

(Comparative Example 2) 70 mm long × 200 mm wide ×
A 5 mm-thick carbon steel plate was degreased, shot-blasted, and then fixed vertically using a clamp. The surface temperature is 250 ° C when heated from the back side of the carbon steel sheet using a gas burner.
Then, the polypropylene resin powder for metal coating was sprayed using an electrostatic powder spraying device kept at 20 KV. The polypropylene resin powder was continuously supplied to thicken the film, but the powder adhering due to corona discharge was repelled and the film became non-uniform and the film thickness varied. As a result of measuring the film using a pinhole tester, some pinholes were confirmed.

[0017]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a thick resin powder and a uniform coating free from pinholes, which has not been successful in the past. Therefore, its industrial and economical effects are great.

Claims (1)

[Claims] 1. A metal object to be treated is heated in advance, or
Alternatively, a thermoplastic resin powder charged with static electricity is sprayed onto the surface of the metal object to be treated while being heated from the back surface of the metal object to be processed to form a thin molten film of the resin, and then static electricity is applied on the molten film. A method for coating the surface of a metal object with a thermoplastic resin, which comprises spraying the same type of thermoplastic resin powder.