JPH11168036A - Method of manufacturing aluminum foil for electrolytic capacitor electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an aluminum foil for an electrolytic capacitor electrode the electrostatic capacitance is improved by making forming etching pits form densely uniformly on the surface to increase the surface area. SOLUTION: An aluminum foil is annealed, then is irradiated with ultrasonic wave in a processing liquid, and is etched. Preferably, the processing liquid is one in which solid particles have been diffused. The solid particles comprise one or two or more selected from among a group consisting of silicon carbide, boron carbide, diamond, and aluminum oxide, each having a mean diameter of 100 μm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an aluminum foil for an electrode of an electrolytic capacitor.

[0002] In this specification, the term "aluminum" means both aluminum and aluminum alloys.

[0003]

2. Description of the Related Art Generally, an aluminum foil used as an electrode material of an electrolytic capacitor is subjected to an electrochemical or chemical etching treatment to increase the surface area of the foil to increase the capacitance per unit area. . Therefore, in such an aluminum foil, it is necessary to generate a large number of etching pits uniformly.
Various proposals have been made to increase the area coverage.

For example, in JP-A-6-124855, the growth of etching pits is promoted by adding a trace element to a foil material, and a concentrated layer of a specific element serving as a starting point of the etching pits is formed in the surface layer. It has been proposed. Japanese Patent Application Laid-Open No. 3-122260 proposes improving the etching characteristics by controlling the metal composition and the thickness of the oxide film on the foil surface.

[0005]

However, in the above-mentioned method, there is a problem that a sufficient pit density cannot be obtained, or that pits are unevenly distributed and adjacent pits are combined to obtain a sufficient surface enlargement effect. was there.

The present invention has been made in view of such background art,
An object of the present invention is to provide a method for producing an aluminum foil for an electrolytic capacitor electrode, in which etching pits are formed with high density and uniformity to increase the surface area and obtain a high capacitance.

[0007]

The present inventors have paid attention to the fact that a minute defect generated on the foil surface becomes a starting point of etching, and the minute defect is uniformly and densely formed on the oxide film on the foil surface. It was found that if they were generated, uniform and high-density pits were formed by etching, and the present invention was completed.

[0008] That is, the basic idea of the method for producing an aluminum foil for an electrolytic capacitor electrode of the present invention is to anneal the aluminum foil, irradiate it with ultrasonic waves in a treatment solution, and then perform etching.

[0009] In the method of the present invention, the aluminum foil softened by annealing is irradiated with ultrasonic waves in a processing solution, so that an oxide film on the surface of the foil has a large number of minute defects serving as a starting point of etching uniformly. generate. Although the processing liquid can generate minute defects by ultrasonic vibration even with the liquid alone, the required minute defects can be generated in a short time by dispersing solid particles in the liquid.

As a treatment liquid in the case of using no solid particles and a dispersion medium in the case of using solid particles, any of water, an acid or alkali aqueous solution, and an organic solvent can be used. Acids include hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, etc., alkalis include caustic soda, sodium silicate, sodium carbonate, sodium phosphate, etc .; Alcohol and the like can be exemplified. In addition, the use of an acid or an alkali has the advantage that it has high solubility in an oxide film and can generate minute defects by short-time ultrasonic irradiation. However, on the other hand, since the dissolution progresses rapidly, if the dissolution proceeds too much, the oxide film may be lost, and on the contrary, good etching pits may not be obtained. Therefore, when using an acid or an alkali, it is preferable to use a low-concentration solution in order to easily manage the ultrasonic irradiation treatment. Among these treatment liquids, water or dilute acid is the cheapest, easy to handle and suitable and can be recommended.

The solid particles are fine particles having a hardness capable of causing defects in the oxide film on the foil surface in order to generate minute defects in the oxide film on the aluminum foil surface. Specifically, silicon carbide, boron carbide, diamond or aluminum oxide is suitable, and one or more of these may be used in combination. On the other hand, if the particle size is too small, the effect of generating minute defects in a short time is poor. 100 in particle size
μm or less is preferred. A particularly preferred lower limit of the average particle size is 7 μm, and an upper limit is 60 μm. The concentration of the solid particles in the treatment liquid is preferably 10 to 100 g / l.

The following ultrasonic conditions are preferable in order to generate minute defects with high density and uniformity. The oscillation frequency of the ultrasonic wave is preferably from 28 to 100 kHz, particularly 45 kHz.
kHz or less is preferable. The output is preferably 100 to 600 W. The irradiation time is preferably 1 to 50 minutes, particularly 3 to 30 minutes.
Minutes are preferred.

The type and composition of the aluminum foil used in the method of the present invention and the annealing conditions are not particularly limited.

According to the method of the present invention, microscopic defects are uniformly and densely formed in the oxide film on the foil surface by the ultrasonic irradiation performed before the etching, and the defects serve as a starting point of the etching to form pits. Therefore, high-density and uniform etching pits are formed.

[0015]

Next, an embodiment of the method for producing an aluminum foil for an electrolytic capacitor electrode according to the present invention will be described.

First, aluminum having a purity of 99.99% was formed to a thickness of 100 μm by a conventional method by foil rolling. This foil was washed in a 0.1% aqueous solution of caustic soda at 35 ° C. to remove the rolling oil, and then washed in nitrogen gas at 500 ° C.
Annealed for 4 hours.

With respect to the thus produced annealed foil,
Each example was immersed in a treatment solution shown in Table 1 below and irradiated with ultrasonic waves. The treatment liquid was only water without using solid particles in Example 1, and in Examples 2 to 18, solid particles having an average particle diameter shown in Table 1 were added to water or 0.1% hydrochloric acid at a ratio of 50 g / l. Was used. Also,
No ultrasonic irradiation was performed for the comparative example.

Each of the aluminum foils subjected to the above treatment was subjected to two-stage etching under the following conditions, and further subjected to a chemical conversion treatment.

(First Stage of Etching) Etching was performed for 2 minutes at a current density of 20 A / dm ² in a 5% hydrochloric acid + 30% sulfuric acid bath at 78 ° C.

(Second Stage of Etching) Chemical etching was performed in a 5% hydrochloric acid + 0.1% oxalic acid bath at 85 ° C. for 12 minutes.

(Chemical conversion treatment) Chemical conversion treatment was performed at 270 V in a bath of 100 g / l boric acid + 0.9 g / l ammonium borate at 90 ° C.

The capacitance of these aluminum foils was measured. Table 1 also shows relative values when the capacitance of the comparative example is set to 100.

[0023]

[Table 1]

From the results shown in Table 1, it was confirmed that a high electrostatic capacitance was obtained in the examples in which the ultrasonic irradiation was performed.

[0025]

As described above, according to the method for producing an aluminum foil for an electrolytic capacitor electrode of the present invention, the aluminum foil is annealed, irradiated with ultrasonic waves in a processing solution, and then subjected to etching. In addition, fine defects uniformly and densely generated in the oxide film on the foil surface serve as a starting point of etching, so that high-density and uniform etching pits are formed. As a result, the enlargement ratio is increased, a high capacitance is achieved, and the miniaturization of the capacitor can be realized.

Further, by dispersing the solid particles in the treatment liquid, necessary minute defects can be generated in a short time. In addition, ultrasonic irradiation can be performed at low cost by using water or a dilute acid as the treatment liquid or a dispersion medium of the treatment liquid. In addition, by using one or more of silicon carbide, boron carbide, diamond and aluminum oxide having an average particle diameter of 100 μm or less as the solid particles, the most efficient and efficient generation of minute defects is achieved. Can be done.

Claims (4)

[Claims] 1. A method of manufacturing an aluminum foil for an electrolytic capacitor electrode, comprising: irradiating an ultrasonic wave in a treatment liquid after heat-treating or annealing the aluminum foil, and then performing an etching treatment. 2. The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the treatment liquid is obtained by dispersing solid particles in a liquid. 3. The method for producing an aluminum foil for an electrolytic capacitor electrode according to claim 1, wherein the treatment liquid or the dispersion medium of the treatment liquid is water or a dilute acid. 4. The aluminum for an electrolytic capacitor electrode according to claim 2, wherein the solid particles are one or more of silicon carbide, boron carbide, diamond and aluminum oxide having an average particle size of 100 μm or less. Method of manufacturing foil.