JPH06256970A - Production of organic film-treated steel sheet - Google Patents

Abstract

PURPOSE:To prevent the coating work from being disturbed by the gelling of the processing soln. resin on the surface of a roll and to secure the surface quality of the org. film-treated steel sheet at the time of treating a chromated steel sheet with an org. resin film by roll coating and using a water-dispersing org. resin emulsion as its processing soln. CONSTITUTION:A steel sheet is chromated and then allowed to stand for at least 8 hr or the chromated steel sheet is heat-treated at >=100 deg.C (for >= about 3 sec), and then an org. film processing soln. is applied. Since chromium(VI) is not eluted into the org. emulsion coating film from the chromating film, the coating work is not disturbed, and a high quality is secured.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an organic film-treated steel sheet for forming an organic resin film on a surface of a chromate film of a steel plate which has been chromate-treated by roll coating, using a water-dispersible organic resin emulsion as a treatment liquid. Manufacturing method.

[0002]

2. Description of the Related Art Chromic anhydride (CrO ₃ , NaCr ₂ O ₇ .2H ₂ O, etc.) is used as a surface treatment for improving the corrosion resistance of zinc plated steel sheets, aluminum plated steel sheets and other plated steel sheets.
And a chromate treatment solution prepared mainly from inorganic acids (sulfuric acid, etc.) is applied to the surface of the plated steel plate to form a film of insoluble hydrated oxide containing hexavalent chromium and trivalent chromium (chromate film). Chromate-treated steel sheets laminated on the coated surface are widely used in automobiles, home appliances, and various other applications requiring high corrosion resistance. In addition, in order to improve the formability of the chromate-treated steel sheet when it is pressed into a desired shape to prevent scratches, peeling, and galling of the coating film due to friction between the forming die and the steel sheet surface. As the surface treatment of (1), an organic resin emulsion such as a polyurethane resin is applied by a roll coating method, a spray method or the like, and the chromate film is coated with a lubricating organic resin film. As a treatment liquid for forming the organic resin film, resin particles that are film components,
A resin emulsion suspended in an organic dispersion medium such as thinner has been used in the past, but due to pollution of the work environment due to the evaporative gas of the organic solvent and difficult problems such as pollution control, the Instead of the organic solvent dispersion system as the treatment liquid,
Water-dispersible organic emulsions have been developed and are commercially available.

[0003]

However, when a water-dispersible emulsion is used as the organic film treatment liquid and this is applied to the surface of the chromate film by the roll coating method, the treatment liquid does not gel on the roll surface. A solidified residue is generated and adhered, which hinders the coating work on the surface of the steel sheet, and the rough surface of the roll is transferred to the surface of the steel sheet, so that a sound treated steel sheet cannot be obtained. The formation of gelled or solidified residue of the treatment liquid on the surface of the coating roll and the resulting deterioration of the surface quality of the steel sheet are phenomena that are not seen when conventional organic dispersion treatment liquids are used. The present invention solves the above-mentioned problems in the organic film treatment performed using a water-dispersible resin emulsion, prevents the formation of residue from gelation or solidification of the treatment liquid on the roll surface, and improves the soundness of organic matter on the surface of the chromate film. It is possible to form a film.

[0004]

The present invention provides a method for forming an organic film by applying chromate treatment to a plated steel sheet and then applying a water-dispersible organic emulsion as a treatment liquid on the surface of the chromate film by roll coating. The first method is characterized in that the water-dispersible organic coating treatment liquid is applied after at least 8 hours have elapsed from the formation of the chromate coating, and the second method is that the chromate-treated steel sheet is treated at a temperature of 100 ° C. It is characterized in that the coating liquid for water-dispersible organic coating is applied after heating to above ℃ and cooling.

[0005]

[Function] Unlike the case of using an emulsion using an organic solvent as a dispersion medium, a water-dispersible emulsion is applied as a treatment liquid to the surface of a chromate film by a roll coating method. The formation and adhesion of residue due to gelation or solidification of the liquid causes the hexavalent chromium contained in the chromate film (which is water-soluble) to elute in the organic film treatment liquid applied to the surface. It is due to that.
That is, when a resin emulsion having an organic solvent as a dispersion medium is used, hexavalent chromium is hardly eluted from the chromate film into the resin emulsion, so that the treatment liquid on the surface of the coating roll does not gel or solidify. On the other hand, when a water-dispersed resin emulsion is applied, hexavalent chromium elutes, and since this is extremely reactive, a chemical reaction with the anion (emulsifier) on the particle surface of the resin in the emulsion Occurs, the emulsifier is decomposed, the uniform emulsified state is destroyed, and a solidified or gelled state occurs. According to the first method of the present invention, after the chromate treatment, wait 8 hours and then apply the water-dispersible resin emulsion, or by the second method,
When the water-dispersible resin emulsion is applied after heating the chromate film to 100 ° C. or higher, since the hexavalent chromium in the chromate film is stably fixed in the film by the dehydration condensation reaction, Even if a water-dispersible resin emulsion is applied to the film surface, the elution of hexavalent chromium is substantially prevented and prevented, and the treatment liquid on the roll surface does not gel or solidify.

The present invention will be described in detail below. The plated steel plate to be treated in the present invention is a zinc plated steel plate,
Regardless of the type of metal used for plating, such as aluminum plated steel plate, tin plated steel plate, etc., the plating may be performed by any of melt plating, electric plating, vapor deposition plating and the like. The chromate treatment on the plated surface of the plated steel sheet is performed by applying a known chromate treatment method such as a reactive chromate treatment, an electrolytic chromate treatment, and a coating chromate treatment. For the coating type chromate treatment and the reactive type chromate treatment, a dipping method, a roll coating method, a spray method and the like are appropriately adopted. The chromate treatment liquid contains chromic acid (CrO ₃ ) and an inorganic acid (sulfuric acid, etc.) as main components, and reduces chromic acid by adding hypophosphorous acid, phosphorous acid, or an organic reducing agent (eg sucrose, alcohol), etc. Then, the desired ratio of hexavalent chromium and trivalent chromium, for example, the ratio (molar ratio) of Cr ⁺³ / total chromium (Cr ⁺³ + Cr ⁺⁶ ) is 0 to 0.6.
Other appropriate additives, for example, boric acid,
For the purpose of improving malonic acid, corrosion resistance, etc., water-dispersible silica (silica gel, colloidal silica), alumina sol, inorganic colloidal, inorganic powder, etc. may be prepared by mixing them in appropriate amounts according to a conventional method. The amount of the chromate film adhered may be appropriately determined according to the chromate treatment method, the application of the steel sheet, required characteristics such as corrosion resistance, and the like. The amount of adhesion is, for example, 10 to 150 mg / m in total chromium amount.
^{Is 2} .

After the above chromate film treatment, an organic film treatment by roll coating is performed on the surface of the chromate film using a water-dispersible organic resin emulsion as a treatment liquid.
In the first method of the present invention, the organic film treatment is performed after waiting for at least 8 hours after the chromate treatment.
As a result, hexavalent chromium in the chromate film is fixed in the film and is prevented from being eluted into the water-dispersible organic emulsion. That is, in the chromate-treated coating film, the dehydration condensation reaction of the coating film composition proceeds with the passage of time, and Cr ions are fixed. The waiting time before starting the application of the organic film treatment liquid was set to 8 hours or more, whereby the dehydration condensation reaction of hexavalent chromium proceeded sufficiently, and the elution into the water-dispersible organic resin emulsion and This is because it is possible to substantially completely avoid gelation and solidification of the treatment liquid on the roll surface, which is caused by this.

In the second method of the present invention, the chromate-treated steel sheet is heated and held at a temperature of 100 ° C. or higher and then cooled to apply the organic resin emulsion to the surface of the chromate film. This heat treatment is intended to accelerate the dehydration condensation reaction of the chromate coating film so that hexavalent chromium is not eluted in a short time. The heating temperature is set to 100 ° C. or higher because at lower temperatures, the effect of promoting the dehydration condensation reaction of the chromate film is small. As the heating temperature is raised, the time required to complete the reaction is shortened. In the heat treatment, a reduction reaction of a part of hexavalent chromium to trivalent chromium also occurs. However, excessively high temperature heating causes cracks in the chromate film and causes subsequent deterioration of corrosion resistance. Therefore, it is preferable to set the upper limit to about 250 ° C. Although the heat treatment time depends on the heating temperature and the thickness of the chromate film, it may be about 3 to 5 seconds.

The organic film treatment in which a water-dispersible organic resin emulsion is applied as a treatment liquid to the chromate film by roll coating should be carried out smoothly under the same processing conditions as in the case of using a resin emulsion of an organic dispersion medium. You can The water-dispersible organic resin emulsion is prepared by adding resin particles as a film component (eg, polyurethane resin, polyethyleneimine resin, polyacrylic acid resin, etc.) and an emulsifier to a dispersion medium (water) and suspending them. Various additives to be blended, for example, those prepared by blending a wax, a curing agent, an antifoaming agent, etc. for enhancing the lubricity of the film are appropriately used. The organic coating solution is
Various products are commercially available.

The coating operation of the above water-dispersible organic resin emulsion may be carried out according to a conventional method. Following the coating of the treatment liquid, a post-treatment is appropriately heat-treated in accordance with the film composition to form a resin film. Complete. The film thickness of the organic resin film is
Although it depends on the type of resin and the desired coating film performance, if the film thickness is too thin, the film lacks uniformity and it is difficult to obtain a stable lubrication effect. However, it is appropriate that the thickness is approximately 0.5 to 5 μm, since it has little effect on the economy and impairs the economical efficiency.

[0011]

Example 1 (method of the first invention) After chromate treatment, an organic film treatment is carried out after a certain period of time. [1] Steel plate to be treated, hot dip galvanized steel plate, weight per unit area: 45 g / m ² ·
One side [2] Chromate film treatment A coating type chromate treatment liquid having the following composition is applied to the plating surface by roll coating, and then the temperature is adjusted to 18
Baking amount is 50mg / m after baking at 0 ℃
² (per surface) chromate film is formed. Treatment liquid composition Cr ⁺³ / total chromium (molar ratio): 0.
4. Total chromium amount: 15 g / l, colloidal silica: 50 g / l: [3] Organic film treatment After the above chromate film treatment, a water-dispersible organic emulsion (film component resin: polyurethane) as shown below is waited for a certain period of time. Resin, heating residue 25%) is used as a treatment liquid, and it is applied to the chromate film surface by roll coating, and then heat treatment (treatment temperature: 200 ° C, treatment time: 20 seconds).
Was added to form an organic film. Thickness of organic film: 1 μm
・ One side.

[4] Results (i) Elapsed time from the chromate film treatment to the organic film treatment and the elution amount of hexavalent chromium in the organic film treatment liquid coating film applied to the surface of the chromate film ( The relationship between the chemical analysis values) is shown in FIG. (ii) The quality of the surface of the product steel sheet was visually evaluated to obtain the results shown in Table 1 below. In the table, x mark: The roll surface becomes uneven due to the gelation of the resin of the treatment liquid, and the product steel plate surface becomes rough. ○ mark: The resin of the treatment liquid on the coating roll surface does not gel, and the product surface is sound. It has a smooth surface. As shown in Table 1, by performing the organic film treatment 8 hours after the chromate treatment, gelation of the treatment liquid on the roll surface does not occur, and a normal roll surface state is maintained, and a sound surface is obtained. It can be seen that a product steel sheet having quality is obtained.

[0013]

[Table 1] Elapsed time (Hr) 0 8 20 Cr ⁺⁶ Elution amount (%) 88 21 10 Product surface quality × ○ ○

Example 2 (Method of the Second Invention) After the chromate treatment, the steel sheet is heat treated and then an organic film treatment is performed. [1] Plated steel plate Same as in Example 1. [2] Chromate film treatment Same as in Example 1. [3] Organic film treatment After the chromate treatment, the steel sheet is heated and held at a constant temperature, and then the treatment liquid is applied by a coating roll. The heat treatment time was 5 seconds in all cases. The composition of the treatment liquid and the heat treatment conditions after coating the treatment liquid were the same as in Example 1. [4] Results The quality of the surface of the product steel sheet thus obtained was visually determined to obtain the results shown in Table 2 below. “X” and “◯” in the table have the same meanings as described above. As shown in Table 2, the chromate treatment is followed by a short-time heat treatment at a treatment temperature of 100 ° C. or higher, whereby the treatment liquid on the roll surface does not gel and a normal roll surface condition is obtained. It can be seen that a product steel sheet having a sound surface quality can be obtained while maintaining the above.

[00015]

[Table 2] Heating temperature (° C) 50 100 150 Product surface quality × ○ ○

[0016]

According to the present invention, a water-dispersible resin emulsion is used as the organic coating treatment liquid on the surface of the chromate coating of the plated steel sheet, and the treatment liquid gels or solidifies on the surface of the coating roll. It is possible to perform a smooth organic film treatment without producing irregularities on the roll surface due to the above, and to manufacture an organic film-treated steel sheet having a sound surface quality.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between an elapsed time from a chromate treatment to an organic film treatment and an elution amount of hexavalent chromium in an organic resin film laminated on the chromate film.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location B05D 7/24 301 F 8720-4D B32B 15/08 G C23C 2/06 (72) Inventor Yasushi Araya Sakai Osaka Prefecture No.5, Ishizu Nishimachi, Ichi, Japan Sakai Works, Nisshin Steel Co., Ltd.

Claims (2)

[Claims] 1. A method of laminating an organic film by applying a water-dispersible resin emulsion as a treatment liquid to a chromate film after the chromate treatment on a plated steel plate to form an organic film in a laminated form. A method for producing an organic coating-treated steel sheet, characterized in that the coating treatment liquid is applied at least 8 hours after the formation of the chromate coating. 2. A method of forming a laminated organic film by applying a water-dispersible resin emulsion as a treatment liquid on a plated steel plate, followed by roll coating to form an organic film in a laminated manner. Is heated to a temperature of 100 ° C. or higher, and after cooling, a water-dispersible organic film treatment liquid is applied, and a method for producing an organic film-treated steel sheet.