JP3513657B2 - Insoluble anode - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an insoluble anode used for plating a steel sheet with zinc, tin or the like.

[0002]

2. Description of the Related Art Conventionally, lead or a lead alloy has been used as an anode used for electroplating zinc or tin on a steel sheet. However, the eluted lead causes contamination of the plating solution and deterioration of film quality. There is a problem such as. As an alternative to this, various insoluble anodes have been proposed in which an electrode base material such as titanium is coated with an electrode catalyst layer containing an oxide of a platinum group metal, particularly iridium as an electrode active material. However, this kind of electrode is intended to be used as an anode, and there is a drawback in that electrolysis involving not only anodic polarization but also cathodic polarization has a shorter electrode life than electrolysis involving only anodic polarization.

In the conventional electroplating of a steel sheet, two anodes are used to plate both sides of the steel sheet, and a plating strip is electrolyzed by running a steel strip which serves as a cathode with a predetermined interval between them. Metal is deposited on both sides of the steel strip. Normally, as shown in FIG. 2, the width AW of the anodes 1, 1'is set to be larger than the width SW of the steel strip 2 in order to correspond to running of steel strips having various widths. Therefore, two anodes directly oppose each other at both outer edge portions 4 and 4 of the central portion 3 (the width corresponds to SW, which will be referred to as a plate path hereinafter) 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 sheet, there is a difference in potential between the two anodes.
Is known to act as a cathode intermittently. (Phenomenon of cathodic conversion of anode). Therefore, the outer edge of the anode on the low potential side is consumed before the strip path, and the life of the electrode as a whole is correspondingly shortened.

In order to extend the life of the electrode thus cathodized, Japanese Unexamined Patent Publication (Kokai) No. 5-230682 discloses two layers of a platinum layer and a metal oxide layer between an electrode substrate and an electrode active material layer. An electrode provided with the intermediate layer has been proposed. Although this electrode is recognized to have the effect of extending the life as a cathode, the life of the plate passage portion of the anode and the outer edge portion of the plate passage in electroplating of a steel sheet have not yet become the same.

Further, Japanese Patent Application Laid-Open No. 11-302892 proposes an electrode comprising an underlayer containing platinum metal on an electrode substrate, an intermediate layer containing iridium oxide as a main component, and an upper layer containing platinum as a main component. ing. The upper layer containing platinum as the main component is considered to be effective for forming a cathode, but the platinum coating amount is 7 g / m ² at the maximum, and sufficient durability is not achieved due to platinum consumption. Moreover, this electrode is formed by applying a coating solution containing a catalytic metal with a brush and then firing it. Since the adhesion between the electrode substrate and the catalyst layer is not sufficient, the catalyst amount should be further increased in order to improve durability. It cannot be increased.

Further, Japanese Patent Laid-Open No. 7-292500 proposes a method of preventing the cathodic phenomenon of the anode by improving the electroplating apparatus. In this method, the electrode potential is measured in order to reduce the potential difference between the two anodes, and the electrode gap is controlled based on this. However, in this case, there is a problem that a large amount of capital investment and an increase in operating cost are involved. Further, a conventional electrode catalyst layer containing an oxide of iridium has a drawback that the manufacturing cost is high because it has a coating and firing step of dozens to dozens of times for manufacturing.

[0007]

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 steel sheet, by prolonging the service life of the electrode accompanied by negative polarization during electrolysis. However, it is to reduce the work of repairing and replacing the electrodes.

[0008]

DISCLOSURE OF THE INVENTION The present invention is to solve the above-mentioned problems, that is, a steel strip which serves as a cathode at a predetermined interval between two insoluble anodes immersed in an electrolytic bath. In an insoluble anode used in a device for running and electroplating a steel strip, platinum is coated as an electrode active material on the electrode surface that causes negative polarization due to the potential difference between the two electrodes during electrolysis. It is an insoluble anode. In this specification, the negative polarization means a case where the potential difference between the two anodes sandwiching the steel strip is 0.5 V or more.

The invention also provides that the width of the two insoluble anodes is
The above-mentioned insoluble anode is characterized in that it is wider than the width of the steel strip running in between, and the electrode surface of the insoluble anode that causes negative polarization is the outer edge of the surface facing the steel strip.

Further, the present invention is the above insoluble anode, wherein the amount of platinum coating the electrode surface of the insoluble anode which causes the negative polarization is 100 g / m ² or more.

The present invention is also the above insoluble anode, characterized in that a platinum foil is welded to the electrode substrate in order to coat the electrode surface of the insoluble anode which causes negative polarization with platinum.

Platinum used in the present invention is well known as a noble metal having an electrocatalytic activity. This is mainly used as an electrode for generating hydrogen gas. Further, it is well known that it also has a catalytic activity for oxygen gas generation, and it can be used as an electrode for oxygen gas generation by taking advantage of this. However, in this case, platinum is dissolved in the electrolytic solution at the same time when oxygen is generated, and the durability is poor as compared with an electrode catalyst layer containing an oxide of iridium, which is a generally well-known catalyst for oxygen gas generation, Not practical for use as an insoluble anode for plating.

As described above, the electrocatalyst layer using platinum was considered unsuitable as an insoluble anode, but in electroplating a steel sheet, the anode on the lower potential side of the two insoluble anodes became a cathodic phenomenon. It was found that an electrode having higher durability than the conventional electrode catalyst layer containing an oxide of iridium can be produced by using a sufficient amount of platinum as an electrode catalyst only in the outer edge portion of the board where It was

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION As the electrode substrate of the insoluble anode of the present invention, titanium-based alloys such as titanium metal and titanium-tantalum, titanium-tantalum-niobium and titanium-palladium are suitable, and the surface is coated with tantalum metal. You may. The shape can be a plate, a net, a rod, a perforated plate, or any other desired shape.

According to the present invention, the purity of platinum used as an electrode catalyst is not particularly limited, but a purity of 90% by weight or more is preferable. The platinum coating amount may be 100 g / m ² or more, and more preferably 200 g / m ² or more. If the platinum coating amount is less than 100 g / m ² , the durability is inferior to that of a conventional electrode catalyst layer containing an oxide of iridium. The method for producing the platinum layer coating the electrode substrate is not particularly limited, but a sufficient amount of platinum is deposited on the electrode substrate by, for example, welding a platinum foil having a predetermined thickness by a known method and adhering it to the electrode substrate. The substrate can be easily coated. However, immersing the electrode substrate in the chloroplatinic acid solution,
The method of producing a platinum layer by an electroplating method such as depositing platinum on the electrode base body tends to make the platinum layer porous, and is less durable than the method of welding the platinum foil to the electrode base body. Further, the conventional electrode catalyst layer containing an oxide of iridium has a drawback that the manufacturing cost is high because it has several tens of coating and baking steps for manufacturing, but according to the present invention, platinum foil is used as titanium. It can be attached to the substrate, and the manufacturing cost can be significantly reduced.

In the present invention, the electrode active material for covering the electrode surface which does not cause negative polarization is iridium oxide or a mixed oxide of iridium oxide and a valve metal oxide such as titanium, tantalum, niobium or tungsten. It is suitable. Representative examples include iridium-tantalum mixed oxide and iridium-titanium mixed oxide.
At this time, the iridium oxide in the mixed oxide was 6 in terms of metal.
0 to 90% by weight, particularly 60 to 95% by weight, valve metal oxides are 40 to 1% by weight, especially 40 to 5% by weight in terms of metal.
A mixed oxide consisting of is preferred. The metal conversion refers to a value calculated from the weight of only the metal element in the mixed oxide.

Of the two insoluble anodes, the anode on the high potential side, which does not cause negative polarization, may have the same electrode active material for the plate passage and its outer edge. Also, regarding the method of setting the width of the outer edge part, the width of the strip path changes depending on the width of the steel strip facing it, so in actual operation it should be set to a width that fits the smallest steel plate. You can leave it. The range of the amount of the electrode active material that covers the electrode surface that does not cause negative polarization is 15 to 100 g / m in terms of iridium metal.
² is preferred. If it is less than 15 g / m ² , the amount of the electrode active material is small and the function as the anode cannot be maintained. Also, 100
Even if it exceeds g / m ^2, the effect of extending the life of the electrode is small, which is economically disadvantageous.

[0018]

EXAMPLES 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) was subjected to grit blast treatment using alumina grit at a pressure of 0.4 MPa. Using this titanium plate as a substrate, a platinum foil (purity: 99.99% by weight) having a thickness of 5 μm was attached to the outer edges (4 and 4 shown in FIG. 1) by welding.
A solution having the following liquid composition was applied to the central portion (3 shown in FIG. 1) of the base. TaCl ₅ 800 mg H ₂ Ir ₂ Cl ₆ . 6H ₂ O 2600 mg 35% HCl 1 ml n-C 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, an electrode catalyst layer containing a desired amount of iridium as iridium oxide was obtained. As a test anode, the amount of iridium contained in the electrode active material (electrode catalyst layer) 5 covering the central portion 3 (plate path, width 50 mm) shown in FIG. 1 was 50 g.
/ ^{M 2,} the electrode active material (electrode catalyst layer) that covers the outer edge 4, 4 a (each width 20mm) 5 ', 5' was prepared an electrode 1-A is a platinum 107 g / ^{m 2.} In addition, as a second anode (hereinafter referred to as an auxiliary anode) having an auxiliary role in the test shown below, the amount of iridium contained in the electrode catalyst layer covering the central portion and the outer edge portion with the same size as the test anode is used. An electrode having a weight of 50 g / m ² was produced. The test anode and the auxiliary anode are arranged as insoluble anodes 1 and 1'shown in FIG.
mm, thickness 1.5 mm) is arranged as 2 shown in FIG. 2 (distance between electrodes is 7 mm), and a sulfuric acid bath (sodium sulfate concentration 100 g / l, pH = 1.2, 60 ° C.) is used as an electrolytic bath. Then, an electrolytic test was performed.

At this time, a pulse current is repeatedly applied to the side of the insoluble anode (test anode) 1 at a current of 15 A for 10 minutes and 45 A alternately for 10 minutes, and a constant current of 45 A is applied to the side of the insoluble anode (auxiliary anode) 1 '. An electric current was passed. Therefore, when the current on the side of the test anode 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 and 4 of the test anode. In this electrolysis test, the electrode life was defined as the time until the cell voltage at the time of 45 A energization increased by 5 V compared to the initial stage of electrolysis. The results are shown in Table 1.

Example 2 By the same method as in Example 1, the amount of iridium contained in the central electrode catalyst layer was 50 g / m ² , and the electrolytic catalyst layer at the outer edge portion had a thickness of 10 μm. The amount of iridium contained in the test anode, which is .99% by weight, and is 214 g / m ² when converted to the amount of platinum), and the amount of iridium contained in the electrode catalyst layers that respectively cover the central portion and the outer edge portion is 50 g / m ² . An auxiliary anode was produced. Table 1 shows the results of an electrolytic test using the two anodes under the same conditions as in Example 1.

Example 3 A titanium plate subjected to the same grit blast treatment as in Example 1 was used as a substrate, and the outer edge portion of this substrate was chloroplatinic acid (H ₂ Pt).
Cl _6. 6H ₂ O) 10 wt% aqueous solution and the end was connected to the terminal of the rectifier. On the other hand, a platinum plate was dipped in the same aqueous solution, and another terminal of the rectifier was connected to this.
By applying an electric current to the rectifier for a certain period of time, the surface of the substrate was plated with platinum. The platinum plating amount was calculated by measuring the weight before and after plating, and the measurement result was 120 g.
It was confirmed that platinum of / m ² was plated. Test electrodes and auxiliary electrodes were produced in the same manner as in Example 1 except that this electrode was used as the outer edge portions 4 and 4 (each width 20 mm) shown in FIG. Table 1 shows the results of an electrolytic test using the two anodes under the same conditions as in Example 1.

Comparative Example 1 By the same method as in Example 1, the test anode in which the amount of iridium contained in the electrode catalyst layer covering the central portion and the outer edge portion were both 50 g / m ² and the electrode catalyst layer An auxiliary anode having an amount of iridium contained therein of 50 g / m ² was produced. An electrolytic test was conducted under the same conditions as in Example 1 using these two anodes. The results are shown in Table 1.

Comparative Example 2 By the same method as in Example 1, the amount of iridium contained in the central electrode catalyst layer was 50 g / m ² , and the amount of iridium contained in the outer electrode catalyst layer was 150 g / m ² . m ²
And the auxiliary anode in which the amount of iridium contained in the electrode catalyst layer was 50 g / m ² . An electrolytic test was conducted under the same conditions as in Example 1 using these two anodes. The results are shown in Table 1.

Reference Example 1 Two anodes similar to Comparative Example 1 were prepared, and both anodes were subjected to an electrolytic test at a constant current of 45A. The results are shown in Table 1.

Reference Example 2 Two electrodes similar to those in Example 1 were prepared, and both anodes were subjected to an electrolytic test at a constant current of 45A. The results are shown in Table 1.

[0026]

[Table 1]

As shown in Table 1, by coating a sufficient amount of platinum on the outer edge of the test anode which causes negative polarization, the electrode was compared with Comparative Example 1 using a catalyst layer containing ordinary iridium. Improved durability is recognized. Further, compared with Comparative Example 2 in which the amount of the catalyst containing iridium is larger than that, it is recognized that the electrode durability is improved. In Example 2 in which the amount of platinum coated was the largest, the life of the test anode was very long, and there was no potential difference between the two anodes, so an electrode life almost the same as in Reference Example 1 in which no negative polarization was generated was obtained. ing. Further, in Reference Example 2 in which no negative polarization was generated and the electrode whose outer edge portion was coated with platinum was used, the platinum coating amount was sufficiently larger than that of iridium contained in the central electrode catalyst layer. It can be seen that the durability is inferior to that of Reference Example 1 using the catalyst layer containing iridium. That is, the durability of the electrode is improved only when the outer edge of the test anode which causes negative polarization is coated with platinum. Further, the platinum coating amount is determined by the use conditions of the electrode, and it is most effective to make it approximately equal to the electrolyzable time of the central portion where negative polarization does not occur. The comparative example is a conventional method, in which the electrode active material in the central portion and the outer edge portion are the same, and the negative polarization occurs in the outer edge portion due to the change in the current, so that the life of the electrode is clearly shorter than that in the embodiment There is.

[0028]

INDUSTRIAL APPLICABILITY In the insoluble anode of the present invention, when electroplating a steel sheet, the electrode surface of the outer edge portion which causes negative polarization is coated with a sufficient amount of platinum, thereby making it possible to extend the period of use. Further, the amount of platinum coated on the portion that causes negative polarization may be determined depending on the conditions under which the electrode is used.
Therefore, when the insoluble anode of the present invention is used for electroplating a steel sheet, the steel strip facing surface (plate path) and the outer edge portion of the anode are adjusted by adjusting the amount of platinum coating the outer edge portion of the electrode that causes negative polarization. It is possible to make the electrolyzable time equal to that of the above and to prolong the life of the electrode as a whole as much as possible. Along with this, it can contribute to the reduction of the work such as the repair and replacement of the electrodes. Further, since the manufacturing process can be simplified as compared with the conventional electrode catalyst layer containing an oxide of iridium, the manufacturing cost can be reduced.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing an arrangement of electrodes when electroplating both surfaces of a steel plate.

[Explanation of symbols]

1,1 'insoluble anode 1-A test anode 2 Steel plate, steel strip (cathode) 3 Central part of the anode surface facing the steel plate 4,4 Outer edge of anode surface 5 Electrode active material in the center 5 ', 5' Electrode active material on outer edge (platinum) AW anode width SW steel plate width

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ryuichi Otogawa 1-10-8 Edobori, Nishi-ku, Osaka City, Osaka Prefecture Daiso Co., Ltd. (72) Hirokatsu Shimizu 1-10-8 Edobori, Nishi-ku, Osaka City, Osaka Prefecture No. Daiso Co., Ltd. (72) Inventor Shinji Idoko, 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Co., Ltd. Kimitsu Steel Co., Ltd. (72) Inventor, Katsuhiro Hamaguchi 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corp. In-house Kimitsu Works (72) Inventor Akira Takayasu 5-1 Hotta-dori, Mizuho-ku, Nagoya, Aichi Prefecture Showa Lead Tetsunai Co., Ltd. (56) References JP-A-10-287998 (JP, A) (58) ) Fields surveyed (Int.Cl. ⁷ , DB name) C25D 17/10 101 C25D 17/12

Claims (6)

(57) [Claims] 1. An insoluble anode used in an apparatus for electroplating a steel strip, wherein a steel strip serving as a cathode runs at a predetermined interval between two insoluble anodes immersed in an electrolytic bath.
An insoluble anode characterized in that an electrode surface which undergoes negative polarization due to a potential difference between two anodes during electrolysis is coated with platinum as an electrode active material. 2. 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 which causes negative polarization is the outer edge of the surface facing the steel strip. Item 1
The insoluble anode according to 1. 3. The insoluble anode according to claim 1, wherein the amount of platinum coating the electrode surface of the insoluble anode that causes negative polarization is 100 g / m ² or more. 4. The insoluble anode according to claim 1, 2 or 3, characterized in that a platinum foil is welded to the electrode substrate in order to coat the electrode surface of the insoluble anode which causes negative polarization with platinum. 5. An iridium oxide or iridium oxide as an electrode active material and at least one metal selected from the group consisting of titanium, tantalum, niobium, tungsten and zirconium on the electrode surface of the insoluble anode which does not cause negative polarization. The insoluble anode according to claim 1 or 2, which is coated with a mixed oxide with an oxide. 6. The amount of the electrode active material covering the electrode surface of the insoluble anode that does not cause negative polarization is 15 to 15 in terms of iridium metal.
The insoluble anode according to claim 5, which is 100 g / m ² .