JPS605350B2 - Powder coating method for metal objects - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for powder coating a metal body using a polyphenylene sulfide resin powder coating.

In recent years, polyphelene sulfide resin has begun to be used in the field of powder coating because of its excellent heat resistance, chemical resistance, mechanical properties, etc.

To apply the above-mentioned polyphenylene sulfide resin to the surface of a metal body, for example, the inner surface of a metal pipe joint, powder of polyphenylene sulfide resin is supplied into the inside of the pipe joint heated to 300°C or higher, and polyphenylene sulfide resin is applied to the inner surface of the pipe joint. A coating film of sulfide resin is formed, and then baked at a high temperature of 300° C. or higher, preferably 350 to 450° C.,
It is necessary to allow the curing reaction to proceed sufficiently in order to obtain a coating film with excellent performance. However, when the surface of a metal body, particularly the inner surface of a pipe joint, is exposed to such high temperatures, brittle oxidized substances are generated on the surface, reducing the adhesion of the polyphenylene sulfide resin coating to the metal surface.

Furthermore, it has become clear that when polyphenylene sulfide resin is baked at a high temperature, the surface of the metal body is altered due to the sulfur compounds contained in the resin, which adversely affects adhesion, particularly hot water resistance. Therefore, when painting with polyphenylene sulfide resin, it is important to prevent the formation of an oxide layer on the surface of the metal body during high-temperature heating, and to protect the metal base on the surface of the metal body from the sulfur components generated during late coating. Two points are important: to achieve this, we need a base treatment that has excellent adhesion and heat resistance, can prevent high-temperature oxidation of the metal surface, and is stable against sulfur compounds at high temperatures. I found out that I could do it.

However, the generally widely used organic primers such as epoxy resins lack heat resistance, so when polyphenylene sulfide resin is painted or baked, the primer layer deteriorates, reducing adhesion and causing pinholes. occurs and cannot be used.

In addition, there is Zinc Critbaint, which is an inorganic primer that has poor heat resistance and corrosion resistance, but since this paint contains more than 9% by weight of zinc in the dry coating film, polyphenylene sulfide resin The primer layer is attacked by sulfur compounds generated during baking, forming a layer with poor adhesion and hot water resistance, making it impossible to obtain a coating film with excellent performance. In addition to the above primers, chemical conversion treatments such as zinc phosphate or coating the surface with metals such as zinc are also used to achieve the same purpose as primer painting, but chemical conversion coatings are heat-resistant. Adhesion is lowered due to poor properties, and the method of coating with zinc, which is the most common metal coating, is not preferred for the same reasons as the zinc-rich veil. In addition, a solvent-based primer that overcomes the above-mentioned drawbacks is disclosed in Japanese Patent Publication No. 53-25649, but organic solvents may scatter during application and contaminate the working environment.
It has disadvantages in the process, such as sagging during coating and drying, uneven thickness, and the need for space and time for solvent drying. The purpose of the present invention is to eliminate the drawbacks of conventional polyphenylene sulfide resin powder coatings, as described above, and to provide a coated body made of polyphenylene sulfide resin that has excellent heat resistance and particularly excellent hot water resistance. The gist of this method is to form a coating by spraying aluminum on the surface of a metal body,
The present invention relates to a powder coating method for a metal body, characterized in that a polyphenylene sulfide resin powder coating is applied thereon and then glazed.

The aluminum used in the present invention may be aluminum alone or an alloy containing aluminum as a main component.

The aluminum melting process carried out in the present invention involves melting aluminum using a haze arc or high-temperature flame, blowing it away with compressed air, and spraying it onto the surface of a metal body to coat it with aluminum. Although any melting method is possible, when melting the inner surface of a metal pipe or pipe joint, a wire method is preferable in terms of equipment and economy. The polyphenylene sulfide resin powder used in the present invention is a partially oxidized, branched or cross-linked compound containing repeating units of --, and the particle size is not particularly limited, but it is suitable for spray painting. Generally, the number of particles is 150 or less, preferably 100, and additives such as steel powder and alumina powder are added as appropriate.

Aluminum is sprayed onto the surface of the metal body to form a coating as a primer layer, and polyphenylene sulfide resin powder is applied onto the coating by an appropriate coating method such as electrostatic coating. The competition is based on temperature.

The method for powder coating a metal body of the present invention is as described above, and when coating with a powder coating of polyphenylene sulfide resin, a film as a primer is formed on the surface of the metal body by spraying aluminum. Because it is a metal material, it is possible to form a coating on the entire surface of the metal body with good adhesion and no gaps, as if firmly anchored, and this coating has excellent heat resistance, rust prevention, etc., and is not damaged by sulfur compounds. Even if a polyphenylene sulfide resin powder coating is applied over this coating, the film will not be damaged by the high heat during the application of the powder coating or by the sulfur compounds generated at that time. Therefore, according to the method of the present invention, a coated metal body having excellent heat resistance, and particularly excellent hot water resistance, can be produced.

It is preferable that the surface of the metal body is grid-blasted in advance and a coating is formed thereon by spraying aluminum, since the coating will more firmly adhere to the surface of the metal body due to the anchor effect. Furthermore, when the metal body is a hollow body such as a tank, pipe, pipe joint, etc., those whose inner surfaces are coated with these materials can exhibit particularly excellent performance for water supply and damage supply. Example 1 The inner surface of a 100A threaded joint (socket) was grid-blasted, then aluminum was sprayed using a wire blasting method, heated at 350o, and polyphenylene sulfide resin powder paint was applied to the inner surface. Thereafter, firing was performed at a temperature of 38,000°C for 1 hour to obtain a coated joint with a film thickness of 400mm.

A hot water adhesion test was conducted on this painted joint, and the results shown in Table 1 were obtained. The hot water adhesion was tested by immersing the joint in 110° C. hot water for 5 times and observing the state of the coating film. As a result, the sample of Example 1 had excellent hot water resistance.

For comparison, Comparative Example 1 is the result of a test conducted in the same manner as in Example 1, except that an ethyl silicate-based zinc primer was used as a base treatment. Table 1 also shows the results of similar tests on which a polyphenylene sulfide resin powder coating was applied.

Table 1 In the table above, ◎ indicates no abnormality. 0 has floating around the cut part (below 1 willow) ) △ indicates floating around the cut part (1 to 5 column) × has peeling on the entire surface shows.

Claims (1)

[Scope of Claims] 1. Powder coating of a metal body, characterized in that aluminum is sprayed on the surface of the metal body to form a film, and polyphenylene sulfide resin powder is adhered thereon and baked. Method. 2. The powder coating method for a metal body according to claim 1, wherein the surface of the metal body is grid-blasted. 3. A powder coating method for a metal body according to claim 1 or 2, wherein the metal body is a hollow body. 4. The powder coating method for a metal body according to claim 3, wherein the hollow body is a tubular body. 5. The powder coating method for a metal body according to claim 4, wherein the tubular body is a pipe. 6. The powder coating method for a metal body according to claim 4, wherein the tubular body is a pipe joint.