JPH08241832A - Method for manufacturing electrode foil for aluminum electrolytic capacitors - Google Patents

Abstract

PURPOSE: To provide a method of manufacturing an electrode foil for an aluminum electrolytic capacitor which is capable of increasing the capacitance and tanδ, and enhancing the leakage current characteristic. CONSTITUTION: An etched foil subjected to an electrochemical etching treatment carried out in an acidic solution is dechlorinated, dipped into a water solution of pH8 to 10, then thermally treated, and then subjected to a chemical conversion treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrode foil for an aluminum electrolytic capacitor for low voltage.

[0002]

2. Description of the Related Art In recent years, with the miniaturization and high reliability of sets, the needs (miniaturization, cost reduction) from users for aluminum electrolytic capacitors have been rapidly increasing. It is also required that the capacitance per unit area be increased more than before. Therefore, as the electrode foil for the anode, an aluminum foil which is electrochemically or chemically etched to have an expanded effective surface area is used. Various etching methods have been studied to expand this surface area, but in general, the aluminum foil surface area is changed by inserting the aluminum foil continuously in multiple etching tanks and changing the etching conditions in each etching tank. Is gradually expanded, subjected to final washing, and subjected to a chemical conversion treatment after applying a hydrated film.

The hydration film treatment before the chemical conversion treatment is intended to form a hydroxide film on the surface of the aluminum foil so as to improve the film quality of the anodized film during the chemical conversion process. It is carried out by immersing an aluminum foil in high temperature pure water.
The method disclosed in Japanese Patent No. 10 is performed by adding amine to high temperature pure water.

[0004]

It is said that when the hydration film treatment before chemical conversion treatment is performed at a high temperature (90 ° C. or higher), the amount of electricity used is saved and the capacitance is increased. However, when the withstand voltage is low, good results are not obtained, and it is said to be effective only when the withstand voltage is about 150 V or higher.

Further, it is said that tan δ and leakage current are improved in the case where the amine is added to the high temperature pure water, but according to the experiments of the present inventors, the tan δ and the leakage current are improved. When treated with amine added to the above, the surface of the etched aluminum foil is dissolved to lower the electrostatic capacity, or the electrostatic capacity does not increase at a withstand voltage of 150 V or less because it is processed at high temperature. all right.

Furthermore, when the chemical conversion is performed immediately after the hydration treatment, the hydration film is partially dissolved in the chemical conversion liquid and the effect is not exhibited.

In view of the above-mentioned conventional problems, the present invention can increase the electrostatic capacity with a withstand voltage of 150 V or less, and ta
It is an object of the present invention to provide a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, which can improve the characteristics of nδ and leakage current.

[0008]

In order to achieve the above object, a method for producing an electrode foil for an aluminum electrolytic capacitor according to the present invention is a method in which an etching foil subjected to electrochemical etching in an acidic solution is dechlorinated and a pH of 8 is obtained. The foil is immersed in an aqueous solution of Nos. 10 to 10, then heat-treated, and then the foil is subjected to chemical conversion treatment.

[0009]

According to the above manufacturing method, since the etching foil which has been subjected to the electrochemical etching treatment in the acidic solution is dechlorinated and is immersed in the aqueous solution of pH 8 to 10, the hydrated film is uniformly formed. While being formed, this hydrated film is fixed by the subsequent heat treatment, which can prevent dissolution of the hydrated film during chemical conversion after the heat treatment, so that the withstand voltage is 150 V or less. It is possible to increase the capacitance and also reduce tan δ and leakage current.

[0010]

Embodiments of the present invention will be described below. The aluminum foil used in the present invention is not particularly limited, but may be any aluminum foil having a purity of 99.90% or more.

Next, regarding the etching of the aluminum foil, since the aluminum foil of the present invention is used for a low voltage aluminum electrolytic capacitor, the surface area is enlarged by an AC etching method. The etching solution used for this is mainly an acid solution containing hydrochloric acid and at least one selected from sulfuric acid, nitric acid, phosphoric acid, and oxalic acid. The concentration of hydrochloric acid, sulfuric acid, nitric acid,
The concentration of additives such as phosphoric acid and oxalic acid varies depending on the expansion rate of the surface area and production efficiency, but is preferably in the range of 5 to 15 wt% hydrochloric acid and 0.05 to 5 wt% of additives. The etching conditions are a temperature of 20 to 50 ° C., a frequency of 10 to 60 Hz, and a current density of 0.05 to 0.5 A / cm ² , and the etching is repeated 3 to 10 times.

[0012] dechlorination treatment, Cl etching the surface ^- what is done in order to remove, may be used either sulfuric, although an aqueous solution of nitric acid is used.

Since the hydration treatment plays an important role in forming an oxide film during chemical conversion, it is necessary to form a uniform film. In the present invention, the temperature is 50 to 65 ° C.
The greatest feature is that it is immersed in an aqueous solution of H8 to 10. At a pH of 8 or less, a sufficient hydrated film is not formed, so the electrostatic capacity does not increase. On the other hand, pH 10
In the above case, the etched surface of the aluminum foil is dissolved, so that pit destruction occurs and the electrostatic capacity also decreases. Therefore, the optimum range is pH 8-10. Also,
When the temperature is 65 ° C. or higher, the dissolution of the etching surface is promoted, which is not preferable. On the other hand, when the temperature is 50 ° C. or lower, the hydrated film formation time is delayed and productivity is deteriorated. Therefore, the optimum temperature range is 50 to 65 ° C.

Aqueous solution having a pH of 8 to 10 is obtained from NaO.
It can be adjusted with H, NH ₄ OH, etc., but is not particularly limited as long as the pH can be constantly maintained.

After the above hydration treatment, heat treatment is performed. This heat treatment has a function of fixing the hydrated film on the etching surface and suppressing dissolution in the chemical conversion liquid, and the temperature of the heat treatment is preferably 250 to 400 ° C. and 1 to 3 minutes.

The chemical conversion performed after the above heat treatment is not particularly limited, but it is preferable to perform chemical conversion in an aqueous solution of ammonium adipate, boric acid, oxalic acid or the like.

Next, concrete examples of the present invention will be described together with comparative examples. (Example 1) Purity of 99.98 as an etching process
%, A high-purity aluminum foil sample (effective area 2 × 5 cm) with a thickness of 1.00 μm was placed in an etching solution having a solution temperature of 30 ° C., in which 0.5 wt% of nitric acid was added to a 10 wt% hydrochloric acid solution, and an electric current was applied. AC etching was performed at a density of 0.2 A / cm ² and a frequency of 25 Hz for 3 minutes. Next, as the dechlorination treatment, the etching foil was immersed in a 10 wt% nitric acid solution having a liquid temperature of 50 ° C. for 1 minute.

Thereafter, the temperature was 55 ° C. and the pH was 7, 8,
NaOH adjusted to 9, 10, and 11 respectively
The dechlorinated etching foil is immersed in an aqueous solution for 2 minutes to form a hydrated film, and then at 400 ° C. for 2 minutes.
Heat treatment was performed for a minute.

The formation was carried out by applying a formation voltage of 23 V in an aqueous solution of ammonium adipate of 5 wt% at a temperature of 60 ° C. for constant current formation. Capacitance at that time, tan
δ and leakage current are shown in (Table 1).

In the comparative example, an etched and dechlorinated etching foil was treated with 0.05 mol before chemical conversion.
The solution was immersed in an aqueous solution of ethylamine (1/1) (liquid temperature: 90 ° C.) for 3 minutes, and then chemical conversion was performed.

[0021]

[Table 1]

As can be seen from Table 1, Example 1 of the present invention can increase the capacitance in the range of pH 8 to 10 as compared with the comparative example, and can also reduce tan δ and leakage current. It is a thing.

Example 2 Etching and dechlorination were carried out in the same manner as in Example 1, and the hydrated film was treated with NH ₄ O adjusted to a liquid temperature of 55 ° C. and a pH of 8.5.
The etching foil subjected to the dechlorination treatment was immersed in the H 2 aqueous solution for 2 minutes to form a hydrated film, and then heat-treated at 400 ° C. for 2 minutes. On the other hand, for comparison, a prototype without heat treatment was made, and thereafter, a formation voltage of 23% in an aqueous solution of ammonium adipate of 5 wt% at a temperature of 60 ° C.
V was applied to perform constant current formation. Capacitance at that time,
Tan δ and leakage current are shown in (Table 2).

[0024]

[Table 2]

As is clear from (Table 2), in Example 2 of the present invention, since the heat treatment was performed, the capacitance can be increased as compared with the case where the heat treatment was not performed, and t
It is also possible to reduce an δ and leakage current.

(Embodiment 3) Instead of nitric acid which is an additive for the etching solution in Embodiment 1, 0.5 wt% of sulfuric acid, 2 wt% of oxalic acid, 1 wt% of phosphoric acid and 0.5 wt% of nitric acid are added as additives. Using the respective etching solutions containing 1 wt% of sulfuric acid and sulfuric acid, AC etching was performed under the conditions shown in Example 1 to obtain an etching foil. Next, as the dechlorination treatment, the etching foil was immersed in a 10 wt% nitric acid solution having a liquid temperature of 50 ° C. for 1 minute.

Thereafter, the dechlorinated etching foil was immersed for 2 minutes in a KOH and NH ₄ OH aqueous solution adjusted to a temperature of 55 ° C. and a pH of 8.5 to form a hydrated film, and Then, heat treatment was performed at 400 ° C. for 2 minutes.

The formation was carried out by applying a formation voltage of 23 V in a 5 wt% aqueous solution of ammonium adipate at a temperature of 60 ° C. to form a constant current. Capacitance at that time, tan
δ and leakage current are shown in (Table 3).

[0029]

[Table 3]

As can be seen from Table 3, even when sulfuric acid, oxalic acid, phosphoric acid, or nitric acid + phosphoric acid was used as the additive for the etching solution, nitric acid, which is the additive for the etching solution shown in Example 1, was used. Similarly to the above, the capacitance can be increased, and tan δ and leakage current can be reduced.

[0031]

As described above, according to the method of manufacturing the electrode foil for an aluminum electrolytic capacitor of the present invention, the etching foil which has been subjected to the electrochemical etching treatment in an acidic solution is dechlorinated, and p
It was soaked in an aqueous solution of H8 to 10 and then subjected to heat treatment, and thereafter, this foil was subjected to chemical conversion treatment. The etching foil subjected to electrochemical etching treatment in an acidic solution was dechlorinated, and By immersing in an aqueous solution having a pH of 8 to 10, a hydrated film is formed uniformly, and this hydrated film is fixed by the subsequent heat treatment, which results in hydration during chemical conversion after heat treatment. Since the film can be prevented from melting, the withstand voltage is 15
Capacitance of 0 V or less can be increased, and t
It is also possible to reduce an δ and leakage current.

Claims (3)

[Claims] 1. An etching foil subjected to electrochemical etching treatment in an acidic solution is dechlorinated and immersed in an aqueous solution having a pH of 8 to 10, followed by heat treatment, and then chemical conversion treatment of this foil. Of manufacturing method of electrode foil for aluminum electrolytic capacitor. 2. The temperature of an aqueous solution having a pH of 8 to 10 is 50 to 6
It is 5 degreeC, The manufacturing method of the electrode foil for aluminum electrolytic capacitors of Claim 1. 3. The aluminum electrolytic capacitor according to claim 1, wherein the acidic solution is composed mainly of hydrochloric acid, and at least one selected from sulfuric acid, nitric acid, phosphoric acid and oxalic acid is added to this hydrochloric acid. Method for manufacturing electrode foil.