JPH06275474A - Production of anode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PURPOSE:To provide a method for producing an aluminum electrolytic capacitor in which the pit formation by etching can be performed most uniformly while aluminum foils are etched and the capacitance per unit area can be made large. CONSTITUTION:As a pre-processing process in prior to etching process where a direct current is applied to the aluminum foils to etch them while they are continuously dipped in an electrolyte at a specified speed, a dipping process is added so that the aluminum foils may be dipped into a solution which contains hydrofluoric acid mainly and is mixed with at least one kind out of hydrochloric acid and nitric acid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an anode foil for an aluminum electrolytic capacitor, and more particularly to a method for producing an anode foil for an aluminum electrolytic capacitor used for medium and high voltages.

[0002]

2. Description of the Related Art In recent years, with the miniaturization and high reliability of electronic equipment, there has been a strong demand for miniaturization of users' demand for aluminum electrolytic capacitors. Therefore, the anode foil for aluminum electrolytic capacitors is also more than ever before. There is a need to increase the capacitance per unit area.

A conventional method of manufacturing an anode foil for an aluminum electrolytic capacitor will be described below. In order to reduce the size of the aluminum electrolytic capacitor, the anode foil for the aluminum electrolytic capacitor has an effective surface area enlarged by electrochemically or chemically etching the aluminum foil. Various studies have been conducted to increase the etch pit density in order to expand this effective surface area, but the most general method is to use a chloride aqueous solution containing an acid such as sulfuric acid, nitric acid, phosphoric acid, or oxalic acid. The method of electrically etching the aluminum foil is taken.

[0004]

However, in the above-mentioned conventional method, due to the influence of the nonuniform oxide film formed on the surface of the aluminum foil, the etch pit distribution becomes nonuniform in the first etching step. As the density of the etch pits is increased, the etch pits crush each other and the effective surface area of the aluminum foil is not expanded.

The present invention solves the above-mentioned conventional problems. When etching an aluminum foil, pits can be formed very uniformly by etching, and an aluminum electrolytic capacitor capable of increasing the capacitance per unit area. It is an object of the present invention to provide a method for manufacturing a positive electrode foil for use.

[0006]

In order to achieve the above object, a method for producing an anode foil for an aluminum electrolytic capacitor according to the present invention comprises a method of producing a direct current while continuously dipping an aluminum foil in an electrolytic solution at a predetermined speed. As a pretreatment step of the etching step for applying voltage to etch the aluminum foil, dipping the aluminum foil by dipping the aluminum foil in an aqueous solution mainly containing hydrofluoric acid and at least one of hydrochloric acid and nitric acid. It has a processing step.

[0007]

According to the above-mentioned method for producing an anode foil, while continuously immersing the aluminum foil in the electrolytic solution at a predetermined speed,
Hydrofluoric acid is mainly used as a pretreatment step of the etching step of applying a DC current to etch the aluminum foil.
Since the aluminum foil is provided with an immersion treatment step of immersing it in an aqueous solution in which at least one of hydrochloric acid and nitric acid is mixed, the aluminum foil is chemically treated in the immersion treatment step. It is possible to uniformly dissolve the natural oxide film formed on the surface of the aluminum oxide film and the oxide film formed during annealing, and it is also possible to remove the rolling oil and the like adhering to the surface of the aluminum foil during the rolling of the aluminum foil. In the next step, the etching step, the pit formation by the etching becomes extremely uniform, so that the anode foil for aluminum electrolytic capacitors having a high capacitance per unit area and a small variation is manufactured. Is something that can be done.

[0008]

EXAMPLES Examples of the present invention will be described below together with comparative examples.

(Comparative Example) Aluminum purity of 99.99% or more,
Aluminum foil with a thickness of 100 μm was used, and this aluminum foil was added with hydrochloric acid 7% and sulfuric acid 0.1%, and the liquid temperature was 80 ° C.
After continuous immersion in the electrolyte solution at a predetermined rate and applying a direct current with a current density of 20 A / dm ² for 900 seconds to perform the first stage etching, a solution temperature of 80 ° C. containing 5% of sodium chloride was added. The aluminum foil subjected to the first-stage etching was continuously immersed in the electrolytic solution of 1. at a predetermined speed, and the current density was 1
The second stage etching was performed by applying a direct current of 0 A / dm ² for 320 seconds.

(Example) The same aluminum foil as in the comparative example was used, and before this aluminum foil was subjected to the first-stage etching, in an aqueous solution at a liquid temperature of 45 ° C. containing 1% hydrofluoric acid and 0.1% hydrochloric acid. The aluminum foil was immersed for 60 seconds in the dipping treatment, and thereafter, the same treatment as in the comparative example, that is, the first stage etching and the second stage etching were performed.

Ten etching foils were prepared for each of the comparative example and the example of the present invention, and after forming 370 V of these in an aqueous solution of boric acid, the capacitance and bending strength ( 1.0 mmR, 20
(Table 1) shows the results of measurement under a condition of 0 g load and a bending angle of 90 degrees for one reciprocation.

[0012]

[Table 1]

As is clear from this (Table 1), in the embodiment of the present invention, the liquid temperature 4 in which 1% hydrofluoric acid and 0.1% hydrochloric acid were mixed was used.
Since the aluminum foil is soaked in an aqueous solution at 5 ° C for 60 seconds, a natural oxide film formed on the surface of the aluminum foil and an oxide film formed during annealing can be uniformly dissolved. It is also possible to remove rolling oil that adheres to the surface of the aluminum foil during rolling of the aluminum foil, and as a result, etch pits are formed uniformly on the surface of the aluminum foil when the next etching is performed. Therefore, the capacitance can be increased by about 5% as compared with the comparative example, and the variation in capacitance between lots of aluminum foil can be reduced to about 1/3.

In the embodiment of the present invention, the aqueous solution for dipping the aluminum foil was an aqueous solution containing 1% hydrofluoric acid and 0.1% hydrochloric acid. However, the aqueous solution is not limited to this. Alternatively, an aqueous solution containing nitric acid other than hydrochloric acid may be used. The point is that an aqueous solution mainly containing hydrofluoric acid and at least one of hydrochloric acid and nitric acid is used to carry out the above-described embodiment of the present invention. The same effect as the example is achieved.

Further, in the embodiment of the present invention, the liquid temperature of the aqueous solution for dipping the aluminum foil is set to 45 ° C., but the liquid temperature is preferably in the range of 10 ° C. to 60 ° C., and particularly preferably 20. It is in the range of 50 ° C to 50 ° C. That is, when the liquid temperature is lower than 10 ° C., the effect of dissolving the oxide film formed on the surface of the aluminum foil is small, while when the liquid temperature exceeds 60 ° C., the oxide film formed on the surface of the aluminum foil is excessively dissolved and the next etching is performed. This is because the starting point of the generation of the etch pits is reduced when the above is performed.

In the embodiment of the present invention, the dipping treatment time of the aluminum foil was set to 60 seconds, but the dipping treatment time is preferably in the range of 20 seconds to 120 seconds, and particularly preferably 30 seconds to 90 seconds. Within the range of seconds. That is, when the immersion treatment time is less than 20 seconds, the effect of dissolving the oxide film formed on the surface of the aluminum foil is small, while
This is because if it exceeds 0 seconds, the oxide film formed on the surface of the aluminum foil will be excessively dissolved.

[0017]

As described above, according to the method for producing an anode foil for an aluminum electrolytic capacitor of the present invention, a direct current is applied to the aluminum foil while the aluminum foil is continuously dipped in the electrolytic solution at a predetermined speed. As a pre-treatment step of the etching step for performing the etching, a dipping treatment step of dipping the aluminum foil in an aqueous solution mainly containing hydrofluoric acid and at least one of hydrochloric acid and nitric acid is provided. Therefore, the chemical treatment of the aqueous solution in this dipping treatment step can evenly dissolve the natural oxide film formed on the surface of the aluminum foil and the oxide film formed during annealing, and the aluminum foil can be rolled at the time of rolling. Rolling oil, etc. that adheres to the surface of the can also be removed, so that in the next step, the etching step, the etching oil is removed. Since so pit formation by ring are very uniformly performed, high capacitance per unit area, and is capable of producing a small anode foil for aluminum electrolytic capacitors variations.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Sonoda 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Katsunori Suzuki, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co. 72) Inventor Takaomi Izumii 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. Hydrofluoric acid is mainly added to hydrochloric acid as a pretreatment step for etching the aluminum foil by applying a direct current while continuously immersing the aluminum foil in an electrolytic solution at a predetermined rate. A method for manufacturing an anode foil for an aluminum electrolytic capacitor, comprising an immersion treatment step of immersing an aluminum foil in an aqueous solution containing at least one kind of nitric acid. 2. The method for producing an anode foil for an aluminum electrolytic capacitor according to claim 1, wherein the liquid temperature of the aqueous solution in which the aluminum foil is immersed is 10 ° C. to 60 ° C. 3. The method for producing an anode foil for an aluminum electrolytic capacitor according to claim 1, wherein the dipping treatment time of the aluminum foil is 20 seconds to 120 seconds.