JPH0152072B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention describes a method for powder coating metal bodies such as pipes and fittings with polyphenylene sulfide resin (hereinafter referred to as PPS resin). The present invention relates to a method for coating a thick coating film. Conventionally, in order to form a coating film of the above-mentioned PPS resin, for example, as disclosed in Japanese Patent Publication No. 56-9151,
A method has been adopted in which a coating film is formed by fusing PPS resin powder to a metal body, rapidly cooling it to solidify the resin, and then reheating it to crosslink the resin. The use of PPS resin as a rust-preventing and anti-corrosion material for metal surfaces has been rapidly increasing due to its excellent heat resistance and chemical resistance, and the resin has come to be widely used as a paint for metal surfaces. It's on. However, the resin has a low glass transition temperature (approximately 85°C);
Moreover, the coating film of this resin surprisingly has high water permeability to hot water, and becomes a relatively flexible coating film at high temperatures, so it is suitable for coatings with a thickness of 200μ or less when applied to metal surfaces such as steel surfaces. When the film is exposed to hot water for a long time, its adhesion to metals deteriorates, and furthermore, blistering occurs, which impairs its function as a coating and has poor hot water resistance. As a means of improving the hot water resistance of this resin, we have made a thick coating film (350μ or more) as a result of intensive studies.
It has been found that it is effective to increase the heating temperature after fusion bonding. However, even if such improvement measures are simply applied to the coating method disclosed in the above-mentioned Japanese Patent Publication No. 56-9151, problems may arise due to the fluidity of the PPS resin used (under heating conditions), the shape of the object to be coated, etc. Sagging occurs during heating, making it impossible to obtain a uniformly thick film.Also, when thickening a film, it is necessary to extend the heating time or raise the heating temperature to ensure heat-resistant properties, but the heating time If you extend the time, work efficiency will deteriorate,
On the other hand, when the heating temperature is raised, there is a drawback that foaming occurs on the surface or inside of the coating film, or sagging occurs, which impairs the smoothness and denseness of the coating film. In view of the above-mentioned drawbacks, it is an object of the present invention to provide a coating method capable of forming a thick coating film with excellent smoothness and density, and improved hot water resistance. The gist of the method is to form a coating film by fusing powder mainly composed of polyphenylene sulfide resin to a metal body, and then heating to crosslink the resin. The present invention relates to a method for powder coating a metal body, characterized in that heating after application is performed in two or more stages. The powder coating used in the present invention is a powder coating mainly composed of PPS resin, and what is PPS resin?

It is a compound containing the repeating unit of [Formula] and may be partially oxidized, branched or crosslinked, and the molecular weight of the PPS resin is as follows:
It is preferable that the melt flow value under the load condition of 320°C x 5 kg is in the range of 200 to 2000 g/10 minutes,
Within this range, a dense coating film with a smooth surface and no pinholes can be obtained. Further, additives such as silica powder and alumina powder may be added to the powder coating used in the present invention. In the present invention, the method of fusing the polyphenylene sulfide resin powder to the metal body includes, for example, a method of attaching the resin powder to the metal surface by electrostatic coating method and then heating and melting it at 370 to 400°C;
There are methods such as heating the metal body to 370 to 400℃ in advance and melting the resin powder by spraying, suctioning, dipping, etc., but the method is not limited to these methods, and any powder coating method can be used. can also be applied. In the present invention, the metal body is
A product made by fusing powder mainly composed of PPS resin.
The coating film is formed by crosslinking the fused PPS resin in two or more stages at a high temperature of 280°C or higher while controlling its fluidity. For example, when heating in two stages, the first stage is 288 to 370
Heat for 10 minutes or more preferably 30 minutes or more in the range of ℃,
In the second step, heating is preferably carried out at a temperature in the range of 390 to 450°C for 10 minutes or more, preferably 30 minutes or more. In the first stage, crosslinking occurs in a part of the coating film while controlling the fluidity of the PPS resin. Therefore, during heating in the second stage at a higher temperature, the coating film does not sag or pinholes occur, and crosslinking occurs. As a result, a thick coating film with no pinholes and excellent surface smoothness and improved hot water resistance can be obtained. Note that the heating described above is not limited to two stages, but can also be performed in three or more stages. Also, the above heating is PPS
After the resin is fused, the resin can be once rapidly cooled to 100° C. or below to solidify the resin, and then heated as described above to obtain a coating film. The method of the present invention is configured as described above, and after the PPS resin is fused to the metal body, heating is performed in two or more stages.
Since crosslinking progresses sufficiently without pinholes, a thick coating film with a smooth surface and no pinholes can be obtained. Therefore, it has excellent hot water resistance under high temperature conditions such as hot water. Examples of the present invention will be described below. Hot water resistance evaluation method: An elbow joint with a coating on the inside is connected to piping so that the external environment is always maintained at 65°C, and hot water at 85°C is continuously circulated inside the joint. After 150 hours of water passage, the area occupied by the pristar generated on the coating surface was determined and the hot water resistance was evaluated. Example: A powder coating mainly composed of PPS resin was applied to the inner surface of a cast iron elbow joint (nominal diameter 40 m/m) heated to 385°C using an appropriate method to a coating thickness of approximately 600 μm and melted. Immediately after arriving
A first stage heat treatment was performed by heating at 360°C for 45 minutes, followed by a second stage heat treatment at 410°C for 45 minutes, and allowed to cool to form a fully cross-linked coating of approximately 500μ on the inner surface. An elbow joint coated with a membrane was obtained. The coating on the joint was smooth and had no pinholes. The hot water resistance was also excellent, with almost no pristar formation observed. In order to clarify the effects of the method of the present invention, a comparative example will be shown below. Comparative example: After welding in the above example, 365
A painted elbow joint was obtained in the same manner as in the example except that the heat treatment was performed at ℃ for 90 minutes. The coating on the joint was smooth and free of pinholes, but
Since the heating temperature was relatively low, the crosslinking of the coating film did not progress much, so the area occupied by pristar was as high as 10% or more, and the hot water resistance was extremely poor. Comparative example: A painted elbow joint was obtained in the same manner as in the example except that it was heat-treated at 385°C for 90 minutes in the same manner as in the comparative example. The uneven thickness of the coating film was significant, and the crosslinking of the coating film was not sufficient, so the hot water resistance of the coating film was poor as the area occupied by the pristar was relatively high at 5 to 10%. Comparative Example: A painted elbow joint was obtained in the same manner as in the Example except that it was heat treated at 410° C. for 90 minutes in the same manner as in the Comparative Example. The coating film on the joint was sufficiently crosslinked and had excellent hot water resistance, but due to the high heating temperature, some sagging occurred, and the coating film also foamed during heat treatment, causing unevenness on the coating surface. However, the smoothness was extremely poor.

Claims (1)

[Scope of Claims] 1. A coating method in which a powder coating mainly composed of polyphenylene sulfide resin is fused to a metal body, and then heated to crosslink the resin to form a coating film. A powder coating method for metal bodies, characterized in that heating after fusion is performed in two or more stages. 2 After fusing, the first step is 288-370
The powder coating method for a metal object according to claim 1, wherein the powder coating is heated at 390 to 450° C. as a second step. 3 Polyphenylene sulfide resin at 320℃×
Melt flow value under 5Kg load condition is 200
~2000g/10 minutes Claim 1
Powder coating method for metal objects as described in . 4. The powder coating method for a metal body according to claim 1, 2 or 3, wherein the fusion is performed by adhering the resin to the metal by electrostatic coating and then heating and melting the resin. 5. The powder coating method for a metal body according to claim 1, 2 or 3, wherein the fusion process involves adhering the resin to the heated metal body and melting the resin.