JP2833337B2 - Manufacturing method of electrolytic chromate steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic chromate steel sheet for applying an electrolytic chromate treatment to a galvanized steel sheet to form an electrolytic chromate film having a uniform appearance without an edge overcoat on the surface of the steel sheet. And a method for producing the same.

[0002]

2. Description of the Related Art As a technique for electrolytic chromate treatment of a metal surface-treated steel sheet, Japanese Patent Application Laid-Open No. 2-145,797 proposes the following electrolytic chromate treatment method for a metal surface-treated steel sheet. The metal surface treatment steel _{sheet, CrO 3: 10~60g / l,} SiO 2:
_{1~20g / l, H 2 ZrF 6} : 0.5 ~10g / l, H 2 SO 4: 0.1 ~2
g / l, F ^- ion: 0.1 to 3 g / l and inevitable impurities, and subjected to chromate treatment in a chromate treatment solution adjusted to pH 2.0 to 3.2 while performing cathodic electrolysis (hereinafter referred to as "prior art"). 1 "). In Prior Art 1, there is one electrolytic chromate treatment tank (electrolytic chromate treatment tray), and the number of passes performed in the treatment tank is two per electrolytic chromate treatment tank. Therefore, in order to obtain a desired amount of attached chromate, it is necessary to increase the current density per pass. In addition, when an electrolytic chromate treatment is performed under the described energizing conditions without equipment such as an edge mask, there is a problem that an edge overcoat is inevitable. Further, Prior Art 1 shows an example in which the current density on the front pass side is set to の of that on the rear pass side among the two passes installed, but the edge overcoating is also performed in this range. A sufficient effect for suppression cannot be obtained.

[0003]

Conventionally, when an electrolytic chromate film is formed on the surface of a galvanized steel sheet,
Since the current used in the electrolytic chromating process in the electrolytic chromating electrode is evenly distributed to each electrode, a high current not only flows repeatedly on the surface of the galvanized steel sheet, but also the edge portion of the galvanized steel sheet. There is a problem of occurrence of a so-called edge overcoat due to an increase in the amount of coating on the edge portion due to current concentration on the edge. As described above, it has been considered that the edge overcoat generated during the electrolytic chromate treatment cannot be prevented unless equipment such as an edge mask is installed as equipment.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide an electrolytic chromate film having a uniform appearance without an edge overcoat, in which the amount of the electrolytic chromate film formed is not uneven in the width direction. An object of the present invention is to provide a method for producing an electrolytic chromate steel sheet that can be obtained.

[0005]

Means for Solving the Problems The inventor has made intensive studies to develop a method for suppressing the occurrence of edge overcoat without using an edge mask or the like. as a result,
The following findings were obtained. Provide multiple electrolytic chromate treatment tanks,
The number of electrodes is plural, and the current density at the time of electrolytic chromate treatment in each electrode is not equalized to each electrode, but the current density of the electrode up to one before the final electrode is lower than the current density of the final electrode. By controlling so as to make it possible, an electrolytic chromate film having a uniform appearance can be formed.

The present invention has been made on the basis of the above-mentioned findings, and uses an electrolytic chromate treatment liquid containing a chromate compound as a main component and contained in an electrolytic chromate treatment tank. In a method for producing an electrolytic chromate steel sheet in which an electrolytic chromate treatment is performed on a zinc electroplated steel sheet during passage to form an electrolytic chromate film on the surface of the zinc electroplated steel sheet, a plurality of electrolytic chromate treatment tanks are provided, The number is set to a plurality, and among the plurality of electrodes, the current density at the time of electrolytic chromate treatment up to the electrode immediately before the final electrode is set to a value lower than the current density at the time of electrolytic chromate treatment at the final electrode, and thus Characterized in that an electrolytic chromate film having no edge overcoat is formed on the surface of the galvanized steel sheet. A.

[0007]

The electrode up to one before the final electrode is subjected to electrolytic chromate treatment at a lower current density than that of the final electrode, thereby preventing edge overcoating. By subjecting the final electrode to electrolytic chromate treatment at a higher current density than the electrodes up to one before the final electrode, a desired chromium deposition amount can be obtained.

Hereinafter, the present invention will be described in detail. The present invention uses an electrolytic chromate fluid containing a chromic acid compound as a main component, and performs electrolytic chromate treatment on a zinc electroplated steel sheet, thereby forming a zinc electroplated layer on the surface of the zinc electroplated steel sheet. When an electrolytic chromate film is formed on the surface of the electrode, a plurality of electrolytic chromate treatment tanks are provided, the number of electrodes is plural, and only the current density at the time of electrolytic chromate treatment at the final electrode (n electrode) is set high. The current density of the electrode up to the electrode {(n−1) electrode} immediately before is set lower than that of the final electrode. The provision of a plurality of electrolytic chromate treatment tanks is because the current density per electrode (one pass) in a treatment tank having only one or two electrodes (anode) per treatment tank (one pass or two passes) is set. This is to lower it. With one electrode (one pass), the current density per electrode (one pass) must be increased in order to obtain a desired amount of chromate film adhesion.

It is considered that the formation of the chromate film is carried out in parallel with both the formation of the film by electrodeposition and the chemical reaction by substitution precipitation of chromium ions and zinc on the zinc electroplated steel sheet. However, since no electrodeposition is performed in the non-energized section between the electrolytic chromate treatment tanks, the chromate film once formed is redissolved, and the amount of the film deposited by the Faraday method is not secured. That is, even in the formation of the electrolytic chromate film, the chromate film having the final target adhesion amount is formed by the composite deposition with the reaction type deposition. Therefore, in view of such a chromate film formation mechanism, a desired amount of chromate can be obtained by supplying a current at a current density capable of securing a required amount of chromate to the final electrode.

It is obvious that the concentration of the chromate film forming action on the edge of the steel sheet can be suppressed by setting the amount of current supplied to the continuous electrodes lower than the current density necessary to obtain the desired amount of the electrolytic chromate film. Matters. Therefore, in order to suppress the occurrence of the edge overcoat, the electrolytic chromate treatment may be performed at a low current density. However,
If the electrolytic chromate treatment is performed at the above-mentioned low current density in the whole process, only a chromate film having an adhesion amount lower than a desired amount can be obtained. On the other hand, even if the electrode up to one before the final electrode is subjected to electrolytic chromate treatment with the high current density necessary to obtain the desired adhesion amount, re-dissolution of the chromate film until the steel plate reaches the final electrode is suppressed. Unless this is done, it is not possible to ensure the desired amount of chromate film deposited. Therefore, in the electrodes up to one before the final electrode, the edge overcoat is suppressed by performing an electrolytic chromate treatment at a low current density at which the appearance of the edge overcoat is inconspicuous. Then, only at the final electrode, an electrolytic chromate treatment is performed at a current density that can secure a required desired amount of adhesion. By performing the electrolytic chromate treatment in this manner, a uniform appearance without an edge overcoat can be obtained, and a desired adhesion amount can be obtained.

It is preferable that the current density of the electrodes up to one before the final electrode at the time of electrolytic chromate treatment be within a range of more than 0 and less than 1/2 of the current density of the final electrode. That is, the current density of each electrode is a value obtained from the following equation (1). 0 · I _n <I ₁ = I ₂ =... = I _n-1 <1/2 I _n ─ (1) where I _{n is} the current density of the final electrode, and n is the number of electrodes. As described above, the lower limit of the current density at the time of electrolytic chromate treatment in the electrodes up to one before the final electrode is set to a small current not including 0, and the upper limit is controlled to less than 1/2 of the current density of the final electrode. Thereby, it is possible to prevent the occurrence of an edge overcoat which occurs during the formation of the chromate film, and to obtain a desired amount of adhesion. However, the control of the current density is not limited to the above numerical values.

In the case where three or more electrodes (three passes) are used, the current densities of the electrodes up to one before the final electrode should be the same as in the above equation (1). Preferred, but not necessarily identical.

[0013]

EXAMPLE An electrolytic chromate treatment solution containing a chromate compound as a main component was used for an electrogalvanized steel sheet having a thickness of 0.8 mm on which a zinc electroplating layer having an adhesion amount of 20 g / m ² was formed, A continuous electrolytic chromate treatment tank containing the treatment liquid is provided, and an electrolytic chromate treatment facility having three electrodes {a first electrode, a second electrode, and a third electrode (final electrode)} provides a current within the range of the present invention. The samples were subjected to electrolytic chromate treatment at the density, and specimens of electrolytic chromate-treated steel sheets within the scope of the present invention (hereinafter, referred to as “the present invention specimens”) Nos. 1, 2 were prepared. For comparison, a test piece of an electrolytic chromate-treated steel sheet outside the scope of the present invention was subjected to electrolytic chromate treatment at a current density outside the scope of the present invention (hereinafter referred to as a “sample for comparison”).
Nos. 1 to 3 were prepared. Table 1 shows the current densities at the time of electrolytic chromate treatment of each electrode in the examples and comparative examples. Then, with respect to the test specimens Nos. 1 and 2 of the present invention and the test specimens Nos. 1 to 3 for comparison, the state of occurrence of edge overcoat of the formed chromate film was evaluated. The evaluation was carried out by visually measuring the width of the color tone, which was clearly different. The results are shown in Table 2 together with the amount of chromium formed.

[0014]

[Table 1]

[0015]

[Table 2]

As is clear from Tables 1 and 2, in each of the test samples Nos. 1 and 2 of the present invention, no edge overcoat occurred and a desired amount of chromium was obtained.

On the other hand, the test sample No. 1 has the same current density during electrolytic chromate treatment for all the electrodes, and the numerical value is too low to obtain a desired chromium adhesion amount. , It was not possible to obtain the desired amount of chromium.

In Comparative Sample No. 2, the current density during the electrolytic chromate treatment was the same for all the electrodes, and the value was a high value necessary to obtain the desired amount of adhesion. Edge overcoat occurred.

In Comparative Sample No. 3, the current density at the time of electrolytic chromate treatment was low for the first electrode, but the current density at the time of electrolytic chromate treatment of the second electrode was low to obtain a desired adhesion amount. Since the required high value was the same as the third electrode (final electrode), edge overcoat occurred.

[0020]

As described above, according to the production method of the present invention, an electrolytic chromate steel sheet having an electrolytic chromate film having a uniform appearance without an edge overcoat is formed on the surface of a zinc electroplated steel sheet. Obtained, thus providing an industrially useful effect.

Claims (2)

(57) [Claims] An electrolytic chromate treatment is performed on a zinc electroplated steel sheet passing through the electrolytic chromate treatment solution using an electrolytic chromate treatment solution containing a chromate compound as a main component and contained in an electrolytic chromate treatment tank. Thus, in the method for producing an electrolytic chromate steel sheet in which an electrolytic chromate film is formed on the surface of the zinc electroplated steel sheet, a plurality of electrolytic chromate treatment tanks are provided, the number of the electrodes is plural, and a final electrode among the plurality of electrodes is provided. The current density at the time of electrolytic chromate treatment up to the immediately preceding electrode is set to a value lower than the current density at the time of electrolytic chromate treatment at the final electrode, so that there is no edge overcoat on the surface of the galvanized steel sheet. A method for producing an electrolytic chromate steel sheet, comprising forming an electrolytic chromate film. 2. The method according to claim 1, wherein the current density of the electrode up to one before the final electrode at the time of electrolytic chromate treatment is more than 0 and less than 1/2 of the current density at the time of electrolytic chromate treatment of the final electrode.