JP2752422B2 - Method for producing aluminum material for electrolytic capacitor electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an aluminum material for an electrode of an electrolytic capacitor.

2. Description of the Related Art Aluminum foil, which is generally used as an electrode material for aluminum electrolytic capacitors, is generally subjected to electrochemical or chemical etching treatment in order to increase its effective area and increase the capacitance per unit area. Is done. However, a sufficient capacitance could not be obtained simply by etching the foil.

Further, the present applicant has previously proposed an aluminum material for an electrolytic capacitor in which a crystallized γ-Al ₂ O ₃ film having a constant thickness is formed on the surface of an aluminum foil to improve the etching performance (Japanese Patent Publication No. 58-1983). 34925). According to this material
The surface area of the foil after the etching can be increased, and the capacitance can be increased.

However, even with this material, it may not be possible to sufficiently satisfy the recent demand for higher capacitance of electrolytic capacitors.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an aluminum material for an electrolytic capacitor which is excellent in etching performance and can surely obtain a high capacitance.

Means to Solve the Problems Aluminum foil for electrolytic capacitors is generally
It is manufactured by sequentially performing the steps of casting, hot rolling, cold rolling, foil rolling, and final annealing. Of these, recrystallization occurs in the final annealing, but in order to obtain a texture having many cubic orientations, it has been conventionally performed at a high temperature of 500 ° C. or more.
The inventor of the present invention has conducted intensive studies in order to achieve the above-mentioned object. It was found that it was very important for increasing the capacitance. In other words, the positions of the pits generated by etching correspond to the cells or sub-grains of the foil which are present relatively early in the annealing. It is sufficient to reduce the size of the subgrain and increase its number, but it is not enough to become the nucleus of the formation of etching pits, and the oxide film on the foil surface at the stage where the cell or subgrain size is small is 5 to 50 mm It has been found that it is necessary that the thickness be within the range, and that the subsequently applied oxide film be as thin as possible.

The present invention has been made based on such knowledge, and it has been proposed that the thickness of the aluminum foil surface is controlled to be less than or equal to 10 μm or less on the surface of the aluminum foil before the electrochemical or chemical etching treatment is performed. 5-50Å
The above-mentioned problem can be solved by passing through a step of forming an oxide film, and a step of performing a high-temperature heat treatment within a range where the total thickness of the oxide film does not exceed 70 mm.

The aluminum foil desirably has a high purity of 99.99%, but is not limited to this. Any aluminum foil having a purity within a range used for an electrolytic capacitor may be used.

In the annealing step after the foil rolling, the oxide film initially formed on the surface of the aluminum foil is limited to 5 to 50 °, by securing the film thickness in this range, the cells on the foil surface or sub-grains This is because a nucleus of an etching pit composed of a film defect can be effectively formed at a corresponding position.
Particularly preferably, the angle is 15 to 45 °. In this oxide film forming step, the average size of the cells or sub-grains of the aluminum foil is limited to 10 μm or less because the number of cells or sub-grains is reduced by increasing the number of cells or sub-grains to improve the area expansion ratio. This is to increase the capacitance. In particular, the thickness is preferably 5 μm or less. As a specific method for forming an oxide film having a thickness of 5 to 50 ° within an average cell or subgrain size of 10 μm or less, for example, an aluminum foil having an average cell or subgrain size of 10 μm or less after foil rolling is used. And low-temperature heating in an atmosphere containing water or oxygen, an Ar atmosphere, or the like. Here, as a method for restricting the average size of the cells or sub-grains of the aluminum foil to a minute one of 10 μm or less, the temperature of the foil is reduced as much as possible by foil rolling, and for example, the temperature of the winding coil is reduced by 15 mm.
Methods such as suppressing the temperature to 0 ° C. or lower, reducing the rolling speed, and applying a large amount of rolling oil may be used. In addition, thickness 5
In the above-mentioned low-temperature heating for forming an oxide film of 50 ° C., the amount of water (H ₂ O) in the atmosphere is preferably 0.01 kg / kg or more. Is obtained. In addition, as the heating temperature at the time of low-temperature heating is lower, the size of the cell or the sub-grain can be kept small. However, since the heating time is longer, it is actually preferable to set the temperature to about 40 to 180 ° C. When the temperature exceeds 180 ° C., the size of the cell or the sub-grain becomes large, which may deviate from the requirement of an average size of 10 μm or less. The heating time is preferably about 1 hour or more in order to secure a film thickness of 5 ° or more. For example, a film thickness of about 25 ° can be obtained in about 4 hours. Such low-temperature heating may be performed in only one stage, or may be performed in two or more stages with different heating temperatures and heating times.

The high-temperature heating performed after the formation of the initial oxide film having a thickness of 5 to 50 ° is mainly intended to improve the etching characteristics by making the structure of the aluminum foil a texture having many cubic orientations. Thus, in this high-temperature heat treatment, if the thickness of the oxide film further formed on the initial oxide film is too thick, the defective portion of the initial oxide film is erased, and sufficient etching pits are formed during etching. Can not do. For this reason, the high-temperature heat treatment needs to be performed within a range where the total thickness of the oxide film including the initial oxide film is 70 mm or less. Preferably, it is better to regulate to 50 ° or less. In order to reduce the total thickness of the oxide film to 70 mm or less, it is desirable to heat in an atmosphere from which moisture and oxygen have been removed as much as possible, specifically, in an inert gas such as Ar gas or 10 ^-3 To
It is preferable to heat in a vacuum of about rr or less. The heating temperature is preferably about 460 ° C. or more, and the heating time is preferably about 1 to 5 hours.

The aluminum material produced as described above is then used as an electrode material for an electrolytic capacitor after being subjected to an electrochemical or chemical etching treatment.

The manufacturing process of the aluminum foil used in the present invention is not limited, and may be intermediately annealed during the rolling process.

Since the present invention is dependent on the above, it is possible to form a large number of etching pits with excellent etching performance, and to reliably and stably provide an electrolytic capacitor electrode material having a large surface area and a large capacitance. .

Example (Example 1) When manufacturing an aluminum foil having a purity of 99.99% and having a thickness of 100 μm, the foil temperature, the rolling speed, and the amount of rolling oil in the foil rolling were adjusted, and the cells as shown in Table 1 were obtained. In addition, various aluminum foils having an average subgrain size were manufactured.

Next, the aluminum foil was heated at a low temperature in an atmosphere containing H ₂ O content as shown in Table 1 by changing the heating temperature and the heating time to various values, so that the thickness shown in Table 1 on the foil surface was obtained. An initial oxide film was formed. The thickness of the oxide film was measured by the Hunter Hall method according to the following conditions. Measurement solution: 30 g / l aqueous ammonium tartrate solution Temperature: 30 ° C. Counter electrode: carbon Measurement electrode: sample to be measured A voltage was applied to the sample to be measured under the conditions of a DC voltage application speed: 5 V / sec. The current / voltage characteristics as shown were measured. Then, the voltage difference χ shown in the figure was measured, and the film thickness was measured by converting the film thickness into an equation of 膜厚 × 14Å / V.

When the average size of the cells or sub-grains of the aluminum foil at the end of the heating was examined, it was found to be as shown in Table 1.

Next, for each of the above aluminum foils, in a vacuum of 10 ^-4 Torr
After performing a high-temperature heat treatment at 520 ° C. × 1 hour, the total thickness of the oxide film on the foil surface was measured by the Hunter Hall method in the same manner as described above.

Each aluminum material obtained as described above was subjected to electrolytic etching in a 3% hydrochloric acid aqueous solution (85 ° C.) at a current density of 10 A / dm ² for 3 minutes, and then to chemical etching in the same solution for 10 minutes. And then 35% in a 5% boric acid bath
After the chemical conversion treatment to 0 V, the capacitance of each material was measured.
Table 1 also shows the results.

(Example 2) A 100 μm-thick aluminum foil having a purity of 99.99% and an average cell or subgrain size of 4 μm was used.
The aluminum foil was placed in an atmosphere containing H ₂ O: 0.015 kg / kg for 1 hour.
The substrate was heated at a low temperature of 00 ° C. × 10 hours to form an initial oxide film having a thickness of 32 ° on the surface. The average size of the cells or sub-grains on the foil surface after low-temperature heating was 7 μm, and the average size was maintained at 10 μm or less throughout the low-temperature heating step.

Next, the aluminum foil was heated at a heating temperature of 520 ° C. while changing the heating time and the degree of vacuum (10 ⁻¹ to 10 ⁻⁵ Torr) at a high temperature. Table 2 shows the total thickness of the oxide film after high-temperature heating measured by the Hunter Hall method.

Next, the aluminum material was subjected to an etching treatment and a chemical conversion treatment under the same conditions as in Example 1, and the capacitance of the obtained material was measured. Table 2 shows the results.

As can be seen from Tables 1 and 2, the product of the present invention is:
Since a large number of etching pits were formed and the etching state was high in density, a large capacitance could be reliably obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a current-voltage characteristic diagram for explaining a method of measuring the thickness of an oxide film by a Hunter Hall method performed in an example.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kiyoshi Tada 6,224, Kaiyamacho, Sakai City, Osaka Prefecture Inside Showa Aluminum Co., Ltd. (72) Inventor Shozo Umezu 6,224, Kaiyamacho, Sakai City, Osaka Prefecture Showa Aluminum Incorporated (72) Inventor Takashi Tamura 6,224 Umiyamacho, Sakai-shi, Osaka Showa Aluminum Co., Ltd.

Claims (1)

(57) [Claims] 1. A step of forming an oxide film having a thickness of 5 to 50 ° on an aluminum foil surface in an average cell or subgrain size of 10 μm or less before performing an electrochemical or chemical etching treatment. And a step of subjecting the oxide film to a high-temperature heat treatment so that the total thickness of the oxide film does not exceed 70 mm.