JPS58186474A - Production of steel plate coated with rust preventive paint on one side - Google Patents

Abstract

PURPOSE:To prevent the oxidation on the non-painted surface of a steel plate by coating a water soluble flux on the surface of the steel plate which is not applied with rust preventive paint and stoving the same, then cooling the surface forcibly with water right after the stoving and removing the decomposed residue of the flux thoroughly. CONSTITUTION:A cold rolled steel plate is subjected to a pretreatment of surface polishing, whereafter an aq. soln. of 1% potassium citrate is coated as a flux on one side of the steel plate, then an aq. soln. contg. chromic acid anhydride, zinc powder, etc. is coated as a primer on the other side of the steel plate by using a roll coater. The steel plate is put in the 1st heating furnace and is baked at about 170 deg.C. A treating soln. consisting of zinc powder, an epoxy resin and an org. solvent is topcoated on the backed primer paint by using a roll coater. The steel plate is further introduced into the 2nd heating furnace and is baked at 290 deg.C and is then cooled forcibly by water cooling down to a room temp.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a steel plate with one side anti-rust coating, and more particularly to a method for producing a steel plate with anti-rust coating on one side in which no temper color occurs on the non-painted surface.

In recent years, single-sided anti-rust coating steel plates have been coated with anti-rust coating on only one side, such as single-sided synchro-treated steel plates.

The demand for steel sheets for automobiles, etc. used in severe corrosive environments is increasing.

The above-mentioned single-sided synchronized steel sheet is manufactured in the following manner. That is, after pre-treating the cold-rolled steel sheet 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 is transferred to the first heating furnace. Baked at 150°C to 230°C, then zinc powder,
A top coat is applied using a roll coater with a treatment liquid consisting of an epoxy resin and an organic solvent, and then a top coat is applied at 260°C to 280°C in a second heating furnace. It is manufactured by baking it to i' and then cooling it.

FIG. 1 shows the relationship between the baking temperature of the top coat of the single-sided synchronized steel plate and the adhesion of the top coat.

As is clear from FIG. 1, the higher the processing temperature, the better the adhesion and baking, and the better is 270°C to 290°C.

However, when manufacturing the above-mentioned steel plate, the baking of the coating film after the topcoat is carried out at 270°C to 290°C (
If this is done in a high-temperature atmosphere, the unpainted surface that has not been coated with anti-rust coating will be oxidized and a defect called ``color'' will occur.If color occurs, the following problems will occur. Namely, ① spoils the appearance of the unpainted surface.

(2) Chemical conversion treatment properties deteriorate.

■ Corrosion resistance after painting deteriorates.

Conventionally, in order to solve the problems and points of ■~■ above, the baking of the top coat film was treated, and then the oxide film formed on the non-painted surface was removed (υ), or the baking was done by increasing the processing temperature. Measures have been taken to lower the coating temperature slightly and make the adhesion of the coating film chronic to some extent to reduce the occurrence of black color.

However, the former method is time-consuming and almost impossible to completely remove the oxide film, while the latter method
This is a problem 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-rust coating, in which the anti-rust coating is applied to one side of the steel plate, and then the baking process is performed. Before this process, a water-soluble flux is applied to the non-corrosion painted surface of the steel plate to prevent baking.
The flux prevents oxidation of the non-rust-preventing painted surface during baking and decomposes it before the baking is finished.Then, the steel plate is immediately forced to cool with water after the baking is finished to remove the decomposition residue of the flux. It is characterized by complete removal and complete prevention of oxidation of the non-painted surface of the steel plate.

In the method of this invention, the flux is:

As mentioned above, since the anti-rust coating has the only effect of preventing oxidation of the non-corrosive painted surface during treatment, it is easy to apply, and the anti-rust coating is decomposed at the time of treatment. It is necessary that it does not remain on the coated surface, and when manufacturing synchrometal steel sheets, it is desirable to use potassium citrate, sodium gluconate, etc.

When the baking process is completed, the flux decomposes and disappears, but the residual decomposition remains attached to the non-painted surface. Seizing is a process] There is a risk that the non-rust-proof painted surface of the beast will oxidize again. Therefore, in this invention, the steel plate is forcibly cooled with water immediately after baking is completed.

In addition to preventing re-oxidation, 1-decomposition residues are peeled off and removed from non-painted surfaces.

The inventors of the present invention investigated the relationship between the amount of oxide film on the non-rust-preventing painted surface of a single-sided synchro-treated steel plate and the ten-g color. The results are shown in FIG.

As is clear from FIG. 2, when the amount of oxide film exceeds 100 mm, the occurrence of temper color becomes significant, and when it is less than soX, there is no problem.

Next (2) Examples of the present invention will be explained.

After completing all pre-treatments of degreasing and surface polishing of the G-rolled steel plate, one side of the steel plate was coated with a 1% aqueous solution of gallium citrate, and the other side of the steel plate was rolled with an aqueous solution containing chromic anhydride, zinc powder, etc. Apply an undercoat using a coater, then put the undercoated steel plate into the first heating furnace and heat it for about 1'70 minutes.
The baking process was carried out at ℃. After that, a top coat is applied on top of the baked undercoat using a treatment liquid tyrol coater consisting of zinc powder, epoxy resin, and organic solvent.
Baking was performed at 290° C. in a second heating furnace.

Next, for baking, the treated steel plate was forcibly cooled to room temperature by water cooling.

The topcoat film was baked for about 1 second after the treatment was completed until the steel plate left the second heating furnace and water cooling started.

As a result, the flux applied to the steel plate was not decomposed in the first heating furnace, but was 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 the forced water cooling, and completely disappeared from the surface of the steel sheet after the water cooling was completed.

Non-1 of the steel plate after leaving the second heating furnace and performing the water cooling described above!
7j When the amount of oxide film generated on the rust paint was investigated, it was found that F
It was 25 years ago.

Next, an aqueous solution of 1% each of potassium citrate, sodium gluconate, and EDTA (ethylene diamine tetraacetic acid) was used as a flux, and the baking in the second heating was performed by changing the processing temperature. In Table 1, Table 1 shows the non-rust-preventive coating of steel sheets that were forced to water-cool immediately after exiting the second heating furnace, the temperatures in parentheses in the valley 7 lux indicate the entire decomposition temperature.

As is clear from Table 11g1, when flux is applied to a non-rust-preventing painted surface, the amount of oxide film generated on the painted surface is significantly reduced compared to when no flux is applied. .

The concentration of the water-soluble flux used in practice is generally 0.1 to 10%, preferably 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 used in this invention is a flux that has a decomposition temperature near the baking temperature (ie, the ultimate temperature, the plate temperature), as described above. 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 bathable flux used in this invention prevents the formation of an oxide film on the non-painted surface during baking and decomposes by the time baking is completed.

It is burned out or removed by water cooling.

In this invention, the reason why forced water cooling is performed immediately after baking is completed is as follows.

(2) If water cooling is not used, the temperature of the steel plate coming out of the baking furnace is generally 250 to 300°C, and if left as it is, the unpainted surface of the steel plate will be reoxidized.

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 this invention.

■ Various operations such as oil anointing and roll springing, which are generally performed in the final process, cannot be performed smoothly.

It goes without saying that the present invention can be applied not only to single-sided synchro-treated steel plates but also to other single-sided anti-corrosion coated steel plates.

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 paint film, and furthermore, it is possible to reduce the occurrence of temper color. Various useful effects can be brought about, such as non-painting.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the baking temperature and paint adhesion, and FIG. 2 is a diagram showing the relationship between the amount of oxidation and the grade of temper color. Applicant Nippon Kokan Co., Ltd. Agent Keita Tsutsumi (1 song)

Claims (1)

[Claims] A method for manufacturing a steel plate with one side anti-rust coating, in which baking is performed after applying anti-rust coating on one side of the steel plate. Before the baking process, a water-soluble flux is applied to the non-rust-preventing painted surface of the steel plate in advance to perform the baking process, and the flux prevents oxidation of the non-rust-preventing painted surface during the baking process. At the same time, the baking is decomposed by the end of the baking process. 1) Next, the steel plate after the baking process is immediately forcedly cooled with water to completely remove the decomposition residue of the flux and to stop the oxidation of the non-painted surface of the steel plate. A method for manufacturing a steel plate coated on one side with anti-corrosion coating.