JPH06176976A - Etching method of aluminum foil for electrolytic capacitor - Google Patents

Abstract

PURPOSE:To expand the surface area of an aluminum foil for an electrolytic capacitor by forming uniform etched pits on the aluminum foil. CONSTITUTION:The etching method of an aluminum foil for an electrolytic capacitor includes a first process in which an etching operation is performed electrochemically by a DC current in an aqueous solution which contains chlorine ions and sulfuric acid ions and, after that, a second process in which an etching operation is performed chemically in an aqueous solution which contains at least sulfuric acid ions. In the etching method, a heat treatment is executed in the halfway part of the first process.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for etching aluminum foil for electrolytic capacitors.

[0002]

2. Description of the Related Art Generally, as a means for increasing the electrostatic capacity of an electrolytic capacitor, an aluminum foil is electrically or chemically etched to increase the effective surface area of the aluminum foil.

In order to increase the expansion rate of this effective surface area,
Various researches have been carried out to increase the etching pit density, and they have been put to practical use.

As a technique for increasing the effective surface area enlargement ratio, for example, there is one disclosed in Japanese Patent Laid-Open No. 3-108711.

The technique disclosed in this publication uniformly dissolves the film on the surface of the aluminum foil by first chemically etching it in an aqueous solution containing fluorine ions, and then in a subsequent aqueous solution containing sulfate ions. The pits are uniformly and densely formed by electrical etching performed by the above and electrical or chemical etching performed in an aqueous solution containing hydrochloric acid ions.

However, according to this technique, the surface of the aluminum foil is melted as the electrochemical etching progresses, and from a certain point, the pit density is increased and the etching pits are localized in the same manner as before the homogenization. Happened,
On the contrary, the result is that there is a factor that causes a loss of capacitance.

[0007]

As described above, in the conventional method for etching an aluminum foil for an electrolytic capacitor, in order to uniformly disperse the etching pits and increase the density, an electrochemical or chemical method is used before etching. Although processing is performed, in this method, as the etching progresses, the aluminum foil surface also dissolves, and from a certain point onwards, uneven distribution of etching pits and localization of etching pits occur as in the untreated case. However, there is a problem that the electrostatic capacity is lost due to the overlapping of the etching pits, and there was a problem to be solved in practice.

The present invention has been made to solve the above problems, and its purpose is to promote uniform distribution of etching pits, thereby increasing the surface area of the surface of an aluminum foil without causing a decrease in capacitance. It is an object of the present invention to provide a method for etching an aluminum foil for electrolytic capacitors.

[0009]

The method for producing an aluminum foil for electrolytic capacitors according to the present invention comprises at least a first step of electrochemically etching with a direct current in an aqueous solution containing at least chlorine ions and sulfate ions, In the method for etching an aluminum foil for an electrolytic capacitor, which comprises a second step of chemically etching in an aqueous solution containing sulfate ions, a heat treatment is performed during the first step. .

In this case, the heat treatment is performed at a temperature of 250-4.
It is characterized in that it is carried out at 50 ° C. for 30 seconds to 3 minutes.

[0011]

According to the method of etching an aluminum foil for an electrolytic capacitor having the above-described structure, the aluminum foil is DC-etched with an aqueous solution containing hydrochloric acid and sulfuric acid in the first step. A pit is generated while suppressing the surface effect by the ion pitting effect.

Since the surface dissolution suppressing effect by sulfuric acid, which is carried out during the first step, is weak, the aluminum foil surface is gradually dissolved. However, the heat treatment carried out during the first step causes a thermal oxide film on the aluminum foil surface. Are newly formed, which suppresses the localization of pits in the latter half of the first step and brings about uniform dispersion.

Then, in the second step, the first step is performed by chemically etching in an aqueous solution containing sulfate ions.
The pits with high density and small diameter generated in the process of
It becomes thicker along the inner wall of the pit.

[0014]

EXAMPLES Examples of the present invention will be described below. That is, in the first step, a high-purity aluminum foil is
First, in an aqueous solution containing at least 2 to 9 w / v% of chlorine ions and 23 to 32 w / v% of sulfate ions, a liquid temperature of 70 to 9
^{2 at} a current density of 0.1 to 0.4 A / cm ² at 0 ° C.
Do it for 6 minutes.

Then, as an intermediate treatment of the first step, the aluminum foil is once washed with water at a half of the etching time, and then heat-treated at a temperature of 250 to 450 ° C. for a time of 30 seconds to 3 minutes. After that, as a second step, chemical etching is performed in an aqueous solution containing at least 10 to 20 w / v% of sulfuric acid at a liquid temperature of 85 to 100 ° C. for a time of 5 to 15 minutes. Is.

In the first step, the chlorine ion and the sulfate ion in the aqueous solution are added in the above ranges, and the solution temperature, current density and etching conditions of the aqueous solution are set as described above. 2w / v% as ion addition amount
If it is less than the above value, the pits are not formed normally because the dissolution locally progresses. If it exceeds 9 w / v%, the dissolution of the surface progresses simultaneously with the formation of the pits and the capacity is reduced. If the added amount is less than 23 w / v%, the pits will penetrate and deteriorate the strength of the aluminum foil. If it exceeds 32 w / v%, the pit length will be shortened and a high capacity cannot be obtained. When the liquid temperature is lower than 70 ° C, the pits penetrate and the strength of the aluminum foil is lowered, and when the liquid temperature is higher than 90 ° C, the pits do not grow in the length direction and a high capacity cannot be obtained. Is.

Further, the heat treatment is performed under the above-mentioned conditions. If the above conditions are not satisfied, a sufficient thermal oxide film cannot be obtained. This is due to the fact that the pit formation in the next etching becomes difficult and the formation of pits in the next etching is hindered.

Further, in the second step, the amount of sulfuric acid added to the aqueous solution is set within the above range, and the solution temperature and the etching time of the aqueous solution are set to the above ranges when the added amount of sulfuric acid is 1
When it is less than 0 w / v%, the dissolution for thickening the pit diameter is not sufficiently performed, and when it exceeds 20 w / v%, the dissolution for thickening the pit diameter progresses rapidly and it is difficult to control the pit diameter. It is based on.

According to the method for etching an aluminum foil for an electrolytic capacitor having the above-mentioned structure, the pits are formed while suppressing the surface dissolution of the aluminum foil due to the film forming action of sulfuric acid and the pitting action of chlorine ions in the first step. However, this surface suppression effect is not so strong,
As the surface is gradually dissolved, a new thermal oxide film is formed on the surface by the heat treatment performed in the middle of the first step. As a result, localization of the pits in the latter half of the first step is suppressed and the pits are uniformly formed. It results in dispersion, resulting in dense pits.

However, although the pit obtained in the first step has a small diameter, a thick pit is obtained along the inner wall of the pit in the second step, and a surface area increasing effect suitable for the aluminum foil for electrolytic capacitors can be obtained. At the same time, it greatly contributes to the formation of aluminum foil for electrolytic capacitors, which has high mechanical strength.

Next, an etching method of the aluminum foil for electrolytic capacitors of the present invention will be described in comparison with a conventional example.

(Example) Thickness of 104 μm, O material, 4N,
An aluminum foil having a (100) plane occupancy rate of 90% was subjected to direct current etching for 0.2 seconds at 0.2 A / cm ² in an aqueous solution containing 3 w / v% of chlorine ions and 26 w / v% of sulfate ions, and then immediately washed with water to give 300 Heat treatment at ℃ 2 minutes, then again chlorine ion 3w / v%, sulfate ion 26w / v
% In an aqueous solution containing 0.2% A / cm ² for 120 seconds, and then chemically etched in an aqueous solution containing 16 w / v% of sulfate ions at 95 ° C. for 8 minutes.

(Conventional example) Thickness 104 μm, O material, 4N,
Aluminum foil having a (100) plane occupancy of 90% was subjected to direct current etching at 0.2 A / cm ² for 240 seconds in an aqueous solution containing chlorine ions w / v 3% and sulfate ions 26 w / v%, and then sulfate ions 16 w / v Chemical etching is carried out for 8 minutes at 95.degree.

Then, the aluminum foils etched in the above-mentioned examples and the conventional examples were subjected to 330 V chemical conversion in an ammonium adipate solution, and their electrostatic capacity and bending strength were measured. The results are shown in Table 1. .

[0025]

[Table 1]

As is clear from Table 1, the examples are superior in capacitance and bending strength as compared with the conventional examples, demonstrating the excellent effect of the present invention.

[0027]

According to the present invention, a method for etching an aluminum foil for an electrolytic capacitor, in which pits having a large diameter are uniformly dispersed, which greatly contributes to the expansion of the surface area and the formation of an aluminum foil for an electrolytic capacitor having high mechanical strength, is provided. Obtainable.

Claims (2)

[Claims] 1. A second step of electrochemically etching in an aqueous solution containing at least sulfate ions after a first step of electrochemically etching with a direct current in an aqueous solution containing chlorine ions and sulfate ions. In the method for etching an aluminum foil for an electrolytic capacitor, the heat treatment is performed during the first step in the method for etching an aluminum foil for an electrolytic capacitor. 2. The method for etching an aluminum foil for an electrolytic capacitor according to claim 1, wherein the heat treatment is performed at a temperature of 250 to 450 ° C. for a time of 30 seconds to 3 minutes.