JPH0250978A - Method for coating metal article with organic matter - Google Patents

Abstract

PURPOSE:To easily coat a metal article with a thermoplastic resin having a high m.p. with satisfactory adhesion by grinding the surface of the metal article heated to a high temp., cooling the article to a prescribed temp., coating it with powder of the resin, baking the powder and cooling the article. CONSTITUTION:When a metal article is coated with a thermoplastic resin having a high m.p. such as nylon or satd. polyester by powder baking, the article to be coated is heated to a temp. which is above the baking temp. of the thermoplastic resin by a prescribed temp. While the heated article is cooled to the baking temp., the surface of the article is ground with a wire brush, etc., to produce an anchoring effect by roughening as well as to remove an oxide layer on the surface. After the article is cooled to the baking temp., powder of the thermoplastic resin is blown on the article to form a coating layer and this layer is solidified and adhered by cooling the article.

Description

Detailed Description of the Invention (Industrial Application Field of the Invention) The present invention relates to an organic lining method for metal articles, and more particularly, a method for coating metal articles with a thermoplastic resin having a high melting point by a powder baking method. The present invention relates to a method for obtaining a coating layer with good adhesion.

(Prior art) As a method of coating the surface of a metal article with resin, a heated metal article is sprayed with resin powder or immersed in a fluidized resin powder bath to form a uniformly molten resin layer on the surface of the metal article. A widely used method is to form a strong coating layer by cooling the film and then cooling it.

(Problems to be Solved by the Invention) In this method, the heating temperature of the metal article is determined by the heating temperature of the metal article, taking into account cooling during the baking process of the resin powder and securing heat capacity for melting the resin. 10 from the melting point of
It is necessary to raise the temperature to about 0°C. For this reason, when trying to coat a thermoplastic resin with a high melting point such as nylon or saturated polyester, it becomes necessary to heat the article to a high temperature of about 400°C, and for articles with a large heat capacity, it is necessary to heat the article in a heating furnace for about 10 to 15 minutes. During this process, the surface of the metal article is oxidized, making it difficult for the coating layer to adhere to the metal article and easily peeling off. In particular, in zinc-plated metal articles, the oxide layer is likely to peel off, resulting in a decrease in layer adhesion.

Furthermore, the method of performing a similar treatment before the heating process, which has been adopted as a method to improve adhesion, does not produce the expected effect because the surface is exposed to high temperatures during the heating process and oxidation occurs, as mentioned above. I can't.

In addition, in the case of zinc plating, which is usually difficult to adhere to,
Methods of chemically treating the surface to improve adhesion have also been used, but these treatments are no longer effective when heated above about 300°C, and baking of high melting point resins cannot be applied to coatings.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for coating a metal article with a thermoplastic resin having a high melting point with good adhesion.

(Means for Solving the Problems) In order to achieve the above object, a metal organic lining method according to the present invention includes the following steps in a method of coating a metal article with a high melting point thermoplastic resin by powder baking. It is characterized by this.

■ Baking of the thermoplastic resin that is intended to coat the metal article is a process of heating until the temperature reaches a predetermined temperature higher than the processing temperature. A process of grinding the surface while the metal article is being cooled, ■ A process of cooling the metal article to a temperature for baking the thermoplastic resin, ■ A process of forming a coating layer of thermoplastic resin powder on the metal article, (5 ) followed by a cooling step until a strong coating layer of thermoplastic resin is formed.

In the present invention, the surface of the metal article to be coated is polished with a wire brush, sandpaper, etc. during a short period of time after the metal article to be coated is heated and while the metal article is being cooled to the processing temperature. It is characterized by removing the oxide layer on the surface and adding irregularities to the surface to obtain an anchoring effect to improve adhesion.

The biggest difference from the conventional technology is that a surface roughening process is provided after the heating process.

The present invention will be explained in more detail.

In the present invention, first, the metal article to be coated is heated to a temperature that is a predetermined temperature higher than the baking temperature of the thermoplastic resin to be coated.

The metal article to be coated is not fundamentally limited in the present invention, and metal articles conventionally used in this type of organic lining method can be effectively used.

The method according to the invention is particularly useful for metal articles that have been subjected to galvanized treatment.

The thermoplastic resin used to coat such metal articles is also not fundamentally limited in the present invention.

Although various thermoplastic resins can be used, the effects of the present invention can be significantly enjoyed especially when applied to high melting point thermoplastic resins such as nylon and saturated polyester.

In the present invention, the metal article as described above is heated to a temperature that is a predetermined temperature higher than the baking temperature. The reason why the temperature of the burn-in is set higher than the temperature is to prevent the burn-in from becoming colder than the temperature.
For this reason, the predetermined temperature is determined functionally, taking into account the time required to bake the powder, the heat capacity of the metal article, and the like.

After heating in this manner, the surface of the metal article is ground before being cooled to the baking temperature of the thermoplastic resin.

The method of grinding the metal article is not fundamentally limited in the present invention, and for example, the metal article can be ground using a sandpaper wire brush or the like. By grinding in this manner, the oxide layer on the surface of the metal article can be removed, and at the same time, it is possible to form irregularities that exhibit an anchoring effect.

Next, the metal article is cooled to the baking temperature of the thermoplastic resin by a method such as air cooling, and then a powder coating layer is formed on the metal article.

The method of forming the powder coating layer is not fundamentally limited in the present invention, and for example, the powder may be sprayed with an air can, or the powder may be immersed in a fluidized bed to form the coating layer. be able to.

After forming the coating in this way, it is cooled to form a strong coating layer.

The above-mentioned cooling method is not fundamentally limited in the present invention, and may be performed by, for example, water cooling, air cooling, or the like.

Next, examples of the present invention will be described.

(Example 1) FIG. 1 is a diagram illustrating a process of baking and coating a saturated polyester resin in a hatch type on a hot-dip galvanized steel article as a first example of the present invention. 1 is a heating furnace, 2 is a surface roughening device using an electric wire brush, 3 is a fluidized immersion tank for saturated polyester resin powder, and 4 is a water tank for cooling.

The hot-dip galvanized article to be coated is held in the heating furnace 1 and heated to about 380°C, then taken out from the heating furnace 1, wire brushed for about 1 minute in the surface roughening device 2, and oxidized. Remove debris and roughen the surface. When this step is completed, the temperature of the article is air-cooled to 320 to 350° C., which is the optimum processing temperature for saturated polyester resin, so the article is immediately transferred to the fluidized dipping bath 3 and immersed for about 5 seconds while shaking the article. After that, it is air-cooled for about 5 minutes, and then immersed in a water tank 4 to be cooled to room temperature. In this way, a saturated polyester coating with a thickness of approximately 300 μm is completed.

Since the resin is baked immediately after wire brushing, there is little surface oxidation and the surface is uneven, resulting in a very tight coating.

FIG. 2 is a diagram comparing the adhesion of the coating obtained by the method of this example with that obtained by the conventional method.

The test pieces used were steel plates measuring 50 x 100 x 2 tmm that were hot-dip galvanized to a thickness of about 70 μm, left indoors for about one month, and then coated with a 300 μm thick saturated polyester resin using various methods. Adhesion was determined by gluing one end of a steel cylinder with a diameter of 20 mm to the test piece, making a cut along the outer periphery of the coating that reached the galvanized layer, fixing the test piece in a tensile testing machine, and using the cylinder as the adhesive surface. This was done by pulling in the vertical direction and measuring the load at which the coating peeled off.

In FIG. 2, sample number A is a sample obtained by the method of this embodiment, B is a sample obtained by wire brushing according to the method of this embodiment before the heating process as in the conventional technique, and C is a sample obtained by the conventional technique before the heating process. A chemical conversion treatment was performed, and the wire brushing after heating was not performed, and the material was air-cooled until it reached the treatment temperature, and the baking in this example was performed after the treatment step. In both B and C, the heating temperature, treatment temperature, immersion time in the fluidized immersion tank, air cooling/cooling step, and other treatment conditions are the same as the method of this example. Sample A obtained by the method of this example, B and C obtained by the conventional technique
The adhesion force is significantly greater than that of .

As is clear from these results, the method of the present invention significantly improves the adhesion of the coating compared to the prior art.

(Example 2) FIG. 3 is a diagram illustrating the process of continuously baking and coating a saturated polyester resin on a hot-dip galvanized steel pipe as a second example of the present invention. An induction heating furnace, 6 a surface roughening device using an electric wire flan, 7 a tank for spraying saturated polyester resin powder with a spray gun, 8 a cooling tank for water spray, and 9 rollers for moving the steel pipe.

A series of coating treatments can be completed while moving the steel pipe at a speed of approximately 5 m/min. The capacity of the heating furnace, the length of each device/tank, and the mutual distance are appropriately selected depending on the desired coating thickness.

By simply adding the surface roughening device 6 to the prior art coating device for continuous baking of steel pipes, a coating exhibiting excellent adhesion almost the same as the value shown in FIG. 2 can be achieved.

(Effects of the Invention) As explained above, according to the present invention, it becomes possible to coat a metal article with a thermoplastic resin having a high melting point with good adhesion, and the range of selection of coating resin is significantly expanded.

In particular, although it is very promising as a coating resin due to its excellent weather resistance and coating strength, the heating temperature for baking is as high as 380℃, so it is very difficult to treat it on zinc plating. It is now possible to coat saturated polyester, which had been difficult, with ease, and is expected to have a great industrial effect.

[Brief explanation of the drawing]

Figure 1 is a diagram illustrating the first embodiment of the present invention, which is a process of baking and coating a saturated polyester resin on a hot-dip galvanized steel article in a batch process. Fig. 3 shows a comparison of the adhesion of the coating obtained by the method of the embodiment with that of the conventional technique, and Fig. 3 shows the second embodiment of the present invention in which a saturated polyester resin is continuously baked and coated on a hot-dip galvanized steel pipe. It is a figure explaining the processing process to do. 3. Fluidized immersion tank for saturated polyester resin powder, 4. Water tank for cooling, 5.
Induction heating furnace, 6... Surface roughening device using an electric wire brush, 7... Tank for spraying saturated polyester resin powder with a spray gun, 8... Cooling tank using water spray, 9... Steel pipe roller to move the.

Claims (1)

[Scope of Claims] 1. A method for organic lining a metal article, the method comprising a method of coating a metal article with a high melting point thermoplastic resin by powder baking, the method comprising the following steps. (1) A step of heating the metal article to be coated until the temperature reaches a predetermined temperature higher than the baking temperature of the thermoplastic resin to be coated; (2) After heating, the metal article undergoes the baking treatment of the thermoplastic resin. (3) a step of grinding the surface until it is cooled to temperature;
(4) Forming a coating layer of thermoplastic resin powder on the metal article; (5) After that, a strong coating layer of thermoplastic resin is formed. The process of cooling until