JPH0797688A - Production of aluminum foil used as anode of electrolytic capacitor - Google Patents

Abstract

PURPOSE:To expand the surface area of an aluminum foil used as the anode of an electrolytic capacitor and to increase the capacity of the electrolytic capacitor. CONSTITUTION:The aluminum foil is subjected to high-temp. heat treatment and thereafter the thickness of the oxide film formed on the surface of the aluminum foil is reduced to <=4nm by the ion beam machining such as the argon sputtering, etc., and then the surface of the aluminum foil is subjected to roughening treatment. Thus, the roughening treatment is surely performed to expand the surface area of the aluminum foil and accordingly the capacity of the electrolytic capacitor can be remarkably increased.

Description

Detailed Description of the Invention

[0001]

This invention has a high electrostatic capacity,
In particular, the present invention relates to a method for manufacturing an aluminum foil for an electrolytic capacitor anode, which is suitable for an electrode foil for medium and high voltage.

[0002]

2. Description of the Related Art Aluminum foil having a purity of 99.9% or more is generally used as the electrode foil of electrolytic capacitors for medium and high voltage applications which require high capacitance. In the manufacturing process of this aluminum foil, hot rolling and cold rolling are performed by a conventional method, in which case intermediate heat treatment is carried out if necessary, and finally, for example, about 100 μm for medium-high voltage foil. The foil is rolled to a thickness of. Then, the aluminum foil is subjected to final annealing by heating to 500 to 600 ° C. Further, the aluminum foil that has undergone these steps is subjected to surface roughening treatment in order to increase the capacitance. As for the surface roughening treatment, for aluminum foil for medium and high pressure, for example, electrolytic etching is performed by direct current in a solution mainly containing hydrochloric acid, and capillary pits are grown inward from the surface of the aluminum foil to increase the surface area. To increase.

The above-mentioned final annealing is performed at 500 ° C. to 60 ° C.
The reason for the high temperature of 0 ° C. is related to the growth of the above-mentioned pits. That is, when the final annealing is performed at a low temperature, the strain of the crystal lattice is likely to remain in the material, and this strain hinders the growth of the capillary pits in the roughening step, thus increasing the surface area. It is believed to reduce. Therefore, the final annealing needs to be performed at a high temperature so that the distortion of the crystal lattice is left as little as possible. Further, it is considered that the thickness of the oxide film has a great influence on the roughening effect in etching. Therefore, the atmosphere of the final annealing is very important, and at present, to reduce the oxide film thickness after annealing as much as possible,
Inert gas atmosphere with very low oxygen content or 10 ^-4 P
Annealing is performed in a vacuum of about a. The thickness of the oxide film on the surface formed in the current process in such an atmosphere is about 50 ± 5Å.

At this time, the equation which is the basis of the thickness calculation is the following equation (1), and each factor is obtained by an X-ray photoelectron analyzer (for example, ESCA, K-1 manufactured by Shimadzu Corporation). Formula d = 23.7ln (1 / Ib) ‥‥‥‥‥‥‥‥‥‥‥‥ (1) where d: oxide film thickness (Å) Ib: peak area of photoelectron spectrum of metallic aluminum and aluminum in the aluminum oxide state Ratio of peak areas of photoelectron spectrum

[0005]

However, the aluminum foil produced by the above-mentioned conventional technique often has an unetched portion on the surface during etching in the roughening step. Since this unetched portion does not generate capillary pits, it does not contribute to the increase of the surface area and high capacitance cannot be expected. The thickness of the oxide film is considered to be the cause of this unetched portion. Therefore, a method of more strictly controlling the atmosphere of the final annealing to reduce the thickness of the oxide film can be considered. However, even if the thickness is reduced in this way,
There is no great effect in reducing the unetched portion in the surface roughening treatment, and there is a problem that it does not contribute to the improvement of the electrostatic capacitance although the cost increases due to the stricter atmosphere management.

Therefore, the present inventor has conducted various studies on the cause of the generation of the unetched portion, and has thought that the nonuniformity of the oxide film may have an effect. For example, the lubricant used in cold rolling during the production of foil adheres to the aluminum foil, which decomposes at high temperatures during annealing, which causes the oxide film of the aluminum foil to deteriorate, resulting in non-uniform quality. It is possible. It is also possible that the thickness of the oxide film is non-uniform. Therefore, the inventor of the present application has thought that the oxide film may be processed to form a uniform thin film, so that the roughening treatment in the subsequent step may be surely performed, and the capacitance may be increased. The present invention has been made in view of the above circumstances, and it is possible to secure a high electrostatic capacity by forming a uniform etched surface by suppressing the occurrence of an unetched portion in the roughening step as much as possible. The purpose is to provide a foil.

[0007]

In order to solve the above problems, a method for manufacturing an aluminum foil for an electrolytic capacitor anode according to the present invention is such that an oxide film formed on the surface of an aluminum foil is subjected to an ion beam treatment after the aluminum foil is subjected to a high temperature heat treatment. It is characterized in that the thickness is reduced to 4 nm or less by processing, and then the surface of the aluminum foil is roughened.

The aluminum foil used in the present invention can be exemplified by an aluminum foil having a purity of 99.9% or more, but the aluminum foil is not limited to this. Any aluminum foil may be used as the foil raw material. As the high-temperature heat treatment, generally, high-temperature annealing can be mentioned, but high-temperature heat treatment for growing an oxide film or the like may be used, and the essential point is that the high-temperature treatment is performed before the roughening treatment.

Next, as the ion beam processing, as shown in the second invention, sputtering using ions such as argon can be cited, and in addition, electron beam processing and the like can be cited. According to these ion beam processing,
Unlike the wet method such as washing with an alkaline solution, there is no risk of degrading the oxide film, and the oxide film can be processed uniformly. The surface roughening treatment can be performed by conventional electric field etching or the like.

[0010]

In other words, according to the present invention, the thickness of the oxide film of the aluminum foil after the high temperature heat treatment is reduced by ion beam processing, so that the quality of the oxide film is not deteriorated.
It is possible to process an oxide film with uniform quality and thickness. By roughening the aluminum foil having such an oxide film, the roughening treatment is performed efficiently and surely, the surface area of the aluminum foil is significantly increased, and the electrostatic capacity is effectively improved. Can be made. In addition, compared with the case where the method of ion beam processing is wet,
It can be said that this is a treatment that simply changes the thickness without changing the quality of the oxide film that was originally formed. Therefore, it is considered that the withstand voltage of the oxidized surface is lowered and the electrolytic etching is performed uniformly and uniformly.

The reason why the thickness of the oxide film after ion beam processing is limited to 4 nm or less is that if it exceeds 4 nm, many unetched portions remain and it does not contribute to the improvement of the electrostatic capacitance. An oxide film is spontaneously formed on the surface of aluminum in the air at room temperature. Since the thickness of this oxide film is about 2 nm, the thickness of the oxide film after reduction is industrially 2 nm. It is desirable to set it as above.

[0012]

EXAMPLE An example of the present invention will be described below. A roll-up aluminum foil (thickness: 100 μm) having a purity of 99.99% was manufactured by a conventional method, and this aluminum foil was annealed at 510 ° C. for 5 hours in a non-oxidizing atmosphere. Next, as an example, argon sputter was performed on a 10 cm ² area of the aluminum foil for 1 minute or 2 minutes. A sample that was not annealed with argon after annealing was used as a conventional material, and a sample that was washed with caustic soda solution after annealing was used as a comparative material.

The thickness of the oxide film after annealing and after sputtering or wet treatment of each aluminum foil was measured and calculated based on the above formula (1), and the results are shown in Table 1. Further, for each sample, as a roughening procedure, in a solution of hydrochloric acid 1 mol / liter, sulfuric acid 2.5 mol / liter, and 80 ° C.,
Electrolytic etching was carried out by applying current for 30 seconds at a current density of 0.5 A / cm ² . Then, for each sample, formation voltage 250
The electrostatic capacity was determined by volt. The results are shown in Table 1.

As a result, the invented material has much less unetched parts than the conventional material, and as shown in Table 1, the thickness of the oxide film is reduced, which causes electrostatic discharge. It is clear that the capacity has improved significantly. on the other hand,
The conventional material has a large amount of unetched portions and has a small capacitance. Further, in the comparative material which was washed with a wet alkaline solution without using the ion beam processing method to reduce the thickness of the oxide film, the oxide film thickness was as small as the invention material, but the effect of improving the capacitance was not observed. , On the contrary, it is decreasing. In this case, it is considered that the oxide film was altered. From the above points,
It was clarified that ion beam processing, especially reduction of the thickness of the oxide film by argon sputtering greatly contributes to the improvement of the capacitance.

[0015]

[Table 1]

[0016]

As described above, according to the method for producing an aluminum foil for electrolytic capacitor anodes of the present invention, after the aluminum foil is heat-treated at a high temperature, the oxide film formed on the surface of the aluminum foil is subjected to an ion beam such as argon sputtering. Since the thickness of the aluminum foil is reduced to 4 nm or less by processing and thereafter the surface of the aluminum foil is roughened, the roughening treatment is surely performed, and a capacitor having a significantly increased capacitance can be obtained.

Claims (2)

[Claims] 1. An aluminum foil is heat treated at a high temperature, an oxide film formed on the surface of the aluminum foil is reduced to a thickness of 4 nm or less by ion beam processing, and then a roughening treatment is performed on the surface of the aluminum foil. Method for manufacturing aluminum foil for electrolytic capacitor anode 2. The method for producing an aluminum foil for an electrolytic capacitor anode according to claim 1, wherein the ion beam processing is argon sputtering.