JPS6141271B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a steel plate with a single-sided anti-rust coating, and more particularly to a method for manufacturing a steel plate with a single-sided anti-rust coating in which no temper color occurs on the non-painted surface. In recent years, single-sided anti-corrosion coated steel plates, such as single-sided zinc-coated steel plates, have been coated with anti-rust coating on only one side.
The demand for steel sheets for automobiles, etc. used in severe corrosive environments is increasing. The above-mentioned single-sided zinc chrome-treated steel sheet is manufactured as follows. That is, after a cold-rolled steel sheet is pretreated by degreasing and surface polishing, one side of the steel sheet is undercoated with an aqueous solution containing chromic anhydride, zinc powder, etc. using a roll coater, and the coating film is heated for the first time. Baking is performed in a furnace at 150°C to 230°C, and then a topcoat is applied to the baked undercoat using a treatment solution consisting of zinc powder, epoxy resin, and organic solvent using a roll coater. It is manufactured by baking the top coat at 260°C to 280°C in a heating furnace and then cooling it. FIG. 1 shows the relationship between the baking temperature of the top coat of the single-sided zinc-treated steel sheet and the adhesion of the top coat. As is clear from FIG. 1, the higher the baking temperature is, the better the adhesion is, and the better is 270°C to 290°C. However, when manufacturing the above-mentioned steel plate, the baking of the paint film after the top coat was heated at 270℃~270℃.
If this is done in a high-temperature atmosphere of 290°C, the unpainted surface that has not been coated with anti-rust coating will be oxidized and a defect called temper color will occur. When temper color occurs, the following problems arise. In other words, it spoils the appearance of unpainted surfaces. Chemical conversion treatment properties deteriorate. Corrosion resistance after painting deteriorates. Conventionally, in order to solve the above problems,
After baking the topcoat, remove the oxide film formed on the non-painted surface, or lower the baking temperature to some extent to sacrifice the adhesion of the coating and create a temper color. Measures were taken to reduce the occurrence of However, the former method is time-consuming and almost impossible to completely remove the oxide film, while the latter method is problematic because it reduces the adhesion of the coating film. This invention has been made to solve the above problem, and includes a method for manufacturing a steel plate with one side anti-corrosion coating, in which one side of the steel plate is coated with anti-rust coating and then subjected to baking treatment. Before baking, a water-soluble flux is applied to the non-rust-preventing painted surface of the steel plate and the baking process is performed. The method is characterized in that the steel plate after baking is immediately forcedly cooled with water to completely remove the decomposition residue of the flux and prevent oxidation of the unpainted surface of the steel plate. In the method of this invention, the flux is
As mentioned above, since it only has the effect of preventing oxidation of the non-corrosive painted surface during the baking process of anti-rust coating, it is easy to apply and does not decompose during the baking process and does not remain on the coated surface. When manufacturing zinc chrome metal steel sheets, it is desirable to use potassium citrate, sodium gluconate, etc. When the baking process is completed, the flux decomposes and disappears, but remains attached to the non-painted surface as a decomposition residue. Immediately after the baking process is completed, the non-rust-preventive painted surface is still at high temperature and may be oxidized again. Therefore, in the present invention, the steel plate is forcibly cooled with water immediately after baking to prevent re-oxidation and remove the decomposition residue from the unpainted surface. The inventors of the present application investigated the relationship between the amount of oxide film and temper color on the non-rust-preventing coated surface of a steel sheet treated with zinc on one side. The results are shown in FIG. As is clear from Figure 2, the amount of oxide film is 100Å
If the temperature is exceeded, the occurrence of temper color becomes noticeable,
It can be seen that there is no problem if it is less than 80 Å. Next, embodiments of the invention will be described. After pre-treating the cold-rolled steel plate by degreasing and surface polishing, a 1% aqueous solution of potassium citrate is applied as a flux to one side of the steel plate using a roll coater, and then chromic anhydride and zinc are applied to the other side of the steel plate. An undercoat was applied with an aqueous solution containing powder, etc. using a roll coater, and then the undercoat-coated steel plate was placed in a first heating furnace and baked at about 170°C. After that, a top coat was applied to the baked undercoat using a treatment liquid consisting of zinc powder, epoxy resin, and organic solvent using a roll coater, and baking treatment was performed at 290°C in a second heating furnace. Next, the baked steel plate was forcedly cooled to room temperature by water cooling. It should be noted that it took about 1 second for the steel plate to leave the second heating furnace and start water cooling after the baking process of the top coat was completed. As a result, the flux applied to the steel plate is
It did not decompose in the heating furnace, but decomposed in the second heating furnace and disappeared by volatilization. Furthermore, the decomposition products that remained on the surface of the steel sheet without being volatilized were removed at the same time as forced water cooling, and completely disappeared from the surface of the steel sheet after water cooling was completed. When the amount of oxide film formed on the non-rust-preventing coated surface of the steel plate after exiting the second heating furnace and undergoing the water cooling described above was examined, it was found to be approximately 25 Å. Next, we used 1% each aqueous solutions of potassium citrate, sodium gluconate, and EDTA (ethylene diamine tetraacetic acid) as fluxes, and changed the baking temperature in the second heating furnace. 2
Table 1 shows the amount of oxide film formed on the non-corrosion coated surface of the steel plate that was forced to water cool immediately after leaving the heating furnace, together with the amount of oxide film when no flux was applied.

[Table] Temperature indicates decomposition temperature.
As is clear from Table 1, when flux is applied to a non-corrosive painted surface, the amount of oxide film generated on the coated surface is significantly reduced compared to when no flux is applied. There is. The concentration of water-soluble flux is generally 0.1 to 10
%, preferably from 0.5 to 3.0%. In this case, if it is less than 0.1%, the purpose of the present invention as a flux cannot be achieved, while if it exceeds 10%, it is not practical from an economical point of view. The water-soluble flux in this invention is
As mentioned above, the baking temperature (i.e. maximum reached, board temperature)
It is a flux that has a decomposition temperature in the vicinity. In this case, the state of decomposition includes both the case where it volatilizes immediately and the case where it remains after decomposition. What remains after decomposition is completely removed during forced water cooling in the next step. That is, the water-soluble flux used in this invention prevents the formation of an oxide film on the non-painted surface during baking, and is decomposed and burned out by the end of baking, or is removed by water cooling. The reason why forced water cooling is performed immediately after baking in this invention is as follows. Without water cooling, the temperature of the steel plate coming out of the baking furnace is generally 250-300℃, and if left as is, the unpainted surface of the steel plate will re-oxidize.
The occurrence of temper color is encouraged. Without water cooling, it is not possible to completely remove decomposition residues that may occur when using the flux of the present invention. Generally, various operations such as oil application and roll winding performed in the final process cannot be performed smoothly. In addition to single-sided zinc-coated steel sheets, this invention
Of course, the present invention can also be applied to other single-sided rust-proof coated steel sheets. As is clear from the above description, according to the present invention, it is possible to prevent the occurrence of temper color without sacrificing the adhesion of the coating film, and furthermore, it is possible to reduce the occurrence of temper color. Various useful effects are brought about, such as being able to produce a single-sided anti-rust coated steel sheet with excellent chemical conversion treatment properties and post-painting corrosion resistance without impairing the appearance of the unpainted surface.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between baking treatment temperature and coating film adhesion, and FIG. 2 is a diagram showing the relationship between oxide film amount and temper color grade.

Claims (1)

[Claims] 1. In a method for manufacturing a steel plate with one-sided anti-rust coating, in which one side of the steel plate is coated with anti-rust coating and then subjected to baking treatment, a water-soluble flux is applied in advance to the non-rust-prevention coated surface of the steel plate before the baking treatment. Apply it and
Baking treatment is performed to prevent the flux from oxidizing the non-rust-preventing painted surface during baking, and to decompose it before the baking is completed.Then, the steel plate after baking is immediately forcedly cooled with water to remove the decomposed residue of the flux. 1. A method for manufacturing a single-sided anti-corrosion coated steel sheet, characterized by completely removing oxidation and preventing oxidation of the non-painted surface of the steel sheet.