JPH10287998A - Insoluble anode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the consumption of two sheets of insoluble anodes and to prolong the service life of these anodes by changing the amt. of the electrode active substances according to the potential difference to be impressed on the electrodes at the time of applying the electroplating on both surfaces of a steel sheet in different amts. by using two sheets of the insoluble anodes. SOLUTION: At the time of allowing the steel sheet to travel between two sheets of the insoluble anodes in the plating liquid and applying the electroplating of the different amts. on both surfaces thereof, the width of the insoluble anodes is set larger than the width of the steel sheet to be plated and both surfaces of the steel sheet are plated by giving a difference in the potential of the anodes by a difference in the plating amts. The insoluble anodes are formed by coating the surfaces of titanium substrates with iridium oxide or a compound oxide of iridium-tantalum, iridium- titanium, etc., as the electrode active substances. The coating material, of the electrode active substance on the anode surface where cathode polarization is induced by the difference in the potential between the two anodes is set at 60 g/m<2> and the coating amt. of the electrode active substance of the anode where the cathode polarization does not arise is set at 15 to 60 g/m<2> . As a result, the consumption of the electrode active substance by the cathode polarization of the anodes is decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insoluble anode used for electroplating zinc, tin or the like on a steel sheet.

[0002]

2. Description of the Related Art Conventionally, lead or a lead alloy has been used as an anode used for electroplating zinc, tin, etc. on a steel sheet. However, contamination of the plating solution by the eluted lead and deterioration of the film quality have been used. There are problems such as. As an alternative anode, a platinum group metal as an electrode active material on a conductive substrate such as titanium,
In particular, various insoluble anodes coated with an electrode active layer containing iridium oxide have been proposed. However, this type of electrode is intended to be used as an anode, and there is a disadvantage that electrolysis involving not only positive polarization but also negative polarization has a shorter electrode life than electrolysis using only positive polarization.

In conventional electroplating of a steel sheet, two anodes are used to plate both sides of the steel sheet, and a plating bath is electrolyzed while running a steel strip serving as a cathode at a predetermined interval between the two anodes. Metal is deposited on both sides of the steel strip. Usually, as shown in FIG. 2, the width AW of the anodes 1 and 1 'is set to be larger than the width SW of the steel strip 2 in order to cope with running of the steel strip having various widths. Therefore, two anodes are directly opposed to each other at the outer edges 4, 4 of the central portion 3 (the width is equivalent to SW, hereinafter referred to as a plate path) of the anode surface facing the running surface of the steel strip. When the metal plates having different thicknesses are applied to the respective surfaces of the steel plate, there is a difference between the potentials of the two anodes.
Is known to act as a cathode intermittently (cathodic phenomenon of anode). Therefore, the outer edge of the anode on the low potential side is consumed before the plate path, so that the life of the entire electrode is correspondingly shortened.

In order to extend the life of the electrode which has been made into a cathode as described above, Japanese Patent Application Laid-Open No. 5-230682 discloses that a platinum layer and a metal oxide layer are provided between an electrode substrate and an electrode active material layer. An electrode provided with two intermediate layers has been proposed. Although this electrode has an effect of extending the life as a cathode, the life of the plate path and the outer edge of the plate path in the electroplating of the steel sheet has not reached the same level.

Further, Japanese Patent Application Laid-Open No. 7-292500 proposes a method for preventing the cathodic phenomenon of an anode by improving an electroplating apparatus. In this method, the electrode potential is measured to reduce the potential difference between two anodes, and the gap is controlled based on the measured potential. However, in this case, there is a problem that a lot of capital investment and operation cost increase.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to extend the service life of an electrode, such as an insoluble anode used for double-sided plating of a steel sheet, by extending the life of the electrode with negative polarization during electrolysis. It is another object of the present invention to reduce the work of repairing and replacing electrodes.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, that is, a steel strip serving as a cathode is provided at a predetermined interval between two insoluble anodes immersed in an electrolytic bath. In the insoluble anode used in an apparatus for electroplating a steel strip, the amount of the electrode active material on the electrode surface that causes negative polarization due to the potential difference between the two electrodes during electrolysis is determined by the electrode that does not generate negative polarization. This is an insoluble anode characterized by being larger than the surface coverage.

The present invention also provides that the width of the two insoluble anodes is
The insoluble anode as described above, characterized in that the electrode surface, which is larger than the width of the steel strip running between the steel strips and causes negative polarization of the insoluble anode, is the outer edge of the surface facing the steel strip.

Further, the present invention provides the above-mentioned insoluble anode, wherein the amount of the electrode active material covering the electrode surface that causes the negative polarization of the insoluble anode is 60 g / m ² or more.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The electrode substrate of the insoluble anode of the present invention is preferably a titanium-based alloy such as titanium metal or titanium-tantalum, titanium-tantalum-niobium, or titanium-palladium. Any desired shape such as a net shape, a rod shape, and a perforated plate shape can be obtained. As the electrode active material for coating the base, iridium oxide or a mixed oxide thereof with a valve metal oxide such as titanium, tantalum, niobium, tungsten, and zirconium is preferable. Representative examples include iridium-tantalum mixed oxide, iridium-
And titanium mixed oxide. At this time, the iridium oxide in the mixed oxide is 60 to 99% by weight, particularly 60 to 95% by weight in terms of metal, and the valve metal oxide is 4 to 4% in terms of metal.
A mixed oxide composed of 0 to 1% by weight, particularly 40 to 5% by weight is excellent in durability.

When this type of insoluble anode is used only for positive polarization, a phenomenon that the electrode active layer becomes brittle at the end of electrolysis and the peeling becomes severe is observed. Therefore, the life of the electrode is determined by the rate of embrittlement of the electrode active layer rather than the consumption of the electrode active material. This tendency is remarkable in an electrode containing iridium oxide as an electrode active material. Therefore, even if the amount of the electrode active material is increased beyond 60 g / m ² , the effect of extending the life of the electrode is small, which is economically disadvantageous.

On the other hand, when the insoluble anode is used not only for the positive polarization but also for the electrolysis accompanied by the negative polarization as described above, the consumption of the electrode active material is much faster than when the insoluble anode is used only for the positive polarization. It was found that the amount of the electrode active material was consumed before the electrode active layer became brittle, and the life was shortened.

Therefore, in the present invention, the amount of the electrode active material covering the electrode surface which causes negative polarization is 60 g / m ² or more, preferably 80 to 500 g / m ² , particularly preferably 100 to ² g / m ^2.
By setting it to 50 g / m ² , it is possible to prevent the electrode life from being shortened due to consumption of the electrode active material. Specifically, in the insoluble anode for electroplating of a steel plate, an electrode surface that causes negative polarization due to a potential difference between the two anodes (outer edge of the plate path)
By making the coating amount of the electrode active material in (1) larger than the coating amount of the electrode surface (plate road) that does not cause negative polarization, the electrode life of the plate road portion and the other portions can be made the same. In this case, of the two insoluble anodes, the amount of the electrode active material at the outer edge of the plate path needs to be larger than that at the plate path part only at the lower potential side anode. The amount of the electrode active material may be the same as that of the outer edge. Further, since the width of the sheet path varies depending on the width of the steel strip opposed thereto, the width may be set to a width suitable for the steel sheet having the smallest width in actual operation. The range of the amount of the electrode active material covering the electrode surface that does not cause negative polarization is 15 g.
/ M ² or more and less than 60 g / m ² . 15g / m
^If it is less than ² , the amount of the electrode active material is too small to maintain the function as an anode.

[0014]

The effects of the insoluble anode of the present invention will be described below with reference to examples. Example 1 Commercially available titanium plate (length 30 mm, width 90 mm, thickness 1.5
mm) using alumina grit at a pressure of 4 kgf / cm ²
Was subjected to grit blasting. A solution having the following composition was applied to the substrate. TaCl ₅ 800 mg H ₂ Ir ₂ Cl ₆ . 6H ₂ O 2600 mg 35% HCl 1 ml nC ₄ H ₉ OH 10 ml This was dried at 120 ° C. for 10 minutes, and then calcined in an electric furnace kept at 500 ° C. for 20 minutes. By repeating this operation, a desired amount of the electrode active layer was obtained. As the test anode, the amount of the electrode active material 5 covering the central portion 3 (plate path, width 50 mm) shown in FIG. 1 was 30 g / m ² , and the outer edges 4 and 4 were used.
An electrode 1-A in which the amount of the electrode active materials 5 ′, 5 ′ covering each (20 mm in width) was 100 g / m ² was prepared. Further, as a second anode having an auxiliary role in the following test (hereinafter referred to as an auxiliary anode), the amount of the electrode active material covering the center portion and the outer edge portion of the same size as the test anode is 5
An electrode of 0 g / m ² was produced. The test anode and the auxiliary anode are arranged as insoluble anodes 1 and 1 ′ shown in FIG.
Further, a steel plate (length: 30 mm, width: 50 mm, thickness: 1.5 mm) serving as a cathode is arranged as shown in FIG. (pH = 1.2, 60 ° C.), and an electrolysis test was performed.

At this time, a pulse current of 15 A is alternately applied to the insoluble anode (test anode) 1 for 10 minutes and 45 A alternately for 10 minutes, and a constant current of 45 A is applied to the insoluble anode (auxiliary anode) 1 '. Electric current was applied. Therefore, when the current on the test anode side is 15 A, the potential of the test anode becomes lower than the potential of the auxiliary anode, so that negative polarization occurs at the outer edges 4, 4 of the test anode. In this electrolysis test, the time required for the cell voltage to rise by 5 V as compared with the initial stage of electrolysis when 45 A was supplied was defined as the electrode life. Table 1 shows the results.

Example 2 In the same manner as in Example 1, the amount of the electrode active material at the center was 30 g / m ² and the amount of the electrode active material at the outer edge was 60 g / m ^2.
, And an auxiliary anode having an electrode active material amount of 50 g / m ² at both the center and the outer edge. This 2
Table 1 shows the results of an electrolytic test performed under the same conditions as in Example 1 using one anode.

COMPARATIVE EXAMPLE In the same manner as in Example 1, a test anode in which the amounts of the electrode active materials at the center and the outer edge were both 30 g / m ² ,
g / m ² . Using these two anodes, an electrolytic test was performed under the same conditions as in Example 1. Table 1 shows the results.

Reference Example Two anodes were prepared as in the comparative example.
The electrolysis test was performed at a constant current of 5A. Table 1 shows the results.

[0019]

[Table 1]

As shown in Table 1, in Example 1 in which the amount of the electrode active material covering the outer edge of the test anode causing the negative polarization was the largest, the life of the test anode was very long and the distance between the two anodes was large. Since there is no potential difference, an electrode life almost equivalent to that of the reference example in which no negative polarization occurs is obtained. In Example 2, although the amount of the electrode active material at the outer edge portion was larger than that at the center portion, it was smaller than that in Example 1, so that the life of the test anode was slightly shortened. That is, the amount of the electrode active material at the outer edge portion is determined by the use conditions of the electrode, and it is most effective that the amount is approximately equal to the electrolysis time at the central portion where no negative polarization occurs. The comparative example is a conventional method, in which the amounts of the electrode active materials in the central portion and the outer edge are the same, and the negative electrode polarization occurs at the outer edge due to a change in current, so that the life of the electrode is clearly shorter than that of the example. ing.

[0021]

According to the insoluble anode of the present invention, when electroplating a steel sheet, excessive consumption of the electrode active material due to the cathodic phenomenon is compensated for by increasing the amount of the electrode active material.
It enables the use period of the electrode to be extended. In particular, since deterioration in electrolysis due to negative polarization of an insoluble anode containing iridium oxide as an electrode active material is not a problem of embrittlement but of wear, the effect of extending the electrode life by increasing the amount of the electrode active material is remarkable. The amount of the electrode active material in the portion where the negative polarization occurs is
What is necessary is just to determine by the conditions which use the electrode. Therefore, when the insoluble anode of the present invention is used for electroplating of a steel sheet, the amount of the electrode active material covering the outer edge of the electrode causing negative polarization is adjusted so that the anode strip faces the steel strip and the outer edge. It is possible to make the electrolysis possible time with the part equal and to prolong the life of the electrode as a whole as much as possible. With this, it is possible to contribute to reduction of work such as repair and replacement of the electrode.

[Brief description of the drawings]

FIG. 1 is a plan view (a) of a test anode used in Example 1,
It is sectional drawing (b) of a width direction.

FIG. 2 is an explanatory view showing the arrangement of electrodes when performing electroplating on both surfaces of a steel plate.

[Explanation of symbols]

 1,1 ′ Insoluble anode 1-A Test anode 2 Steel plate (cathode) 3 Central portion of anode surface facing steel plate 4,4 Outer edge of anode surface 5 Electrode active material at center 5 ′, 5 ′ Electrode active at outer edge Material AW Anode width SW Steel plate width

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hirokatsu Shimizu 19-4 Sakaibashi-cho, Neyagawa-shi, Osaka (72) Inventor Hiroshi Kitaike 1 Fuji-cho, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Hirohata Inside the steelworks (72) Inventor Akihiro Kasuya 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division

Claims (5)

[Claims] A steel strip as a cathode runs at a predetermined interval between two insoluble anodes immersed in an electrolytic bath, and the insoluble anode used in an apparatus for electroplating a steel strip comprises:
An insoluble anode characterized in that the coating amount of the electrode active material on the electrode surface that causes negative polarization due to the potential difference between the two anodes during electrolysis is larger than the coating amount on the electrode surface that does not generate negative polarization. 2. The method according to claim 1, wherein the width of the two insoluble anodes is larger than the width of the steel strip running between them, and the electrode surface of the insoluble anode that causes negative polarization is the outer edge of the surface facing the steel strip. Item 1
4. The insoluble anode according to 1. 3. The insoluble anode according to claim 1, wherein the amount of the electrode active material covering the electrode surface that causes negative polarization of the insoluble anode is 60 g / m ² or more. 4. The amount of the electrode active material covering the electrode surface of the insoluble anode that does not cause negative polarization is 15 g / m ² or more and 60 g / m ^2.
The insoluble anode according to claim 1, wherein the anode is less than m ² . 5. An electrode active material comprising at least one selected from the group consisting of iridium oxide or iridium oxide and titanium, tantalum, niobium, tungsten or zirconium.
A mixed oxide with an oxide of a kind of metal.
5. The insoluble anode according to 3 or 4.