JPH09171945A - Manufacture of electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the stabilized electrode foil having excellent quality by performing the DC electrolytic etching of an aluminum foil at the front stage, performing the dipping processing of the aluminum foil at the post stage, thereafter performing AC electrolytic etching, and forming the constant initial pit, which becomes the starting point of the AC electrolytic etching at the post stage. SOLUTION: At the front stage, a DC current is made to flow through an aluminum foil in etching liquid, and the DC electrolytic etching of the aluminum foil is performed. Thereafter, the aluminum foil is dipped into the etching liquid, and the dipping processing of the aluminum foil is performed. Then, the current density of the AC electrolytic etching is gradually increased. Thereafter, the etching is performed at the constant current density of about 0.3A/cm<2> . Then, the etched etching foil undergoes formation in the aqueous solution of oxalic acid, and the electrode foil is manufactured. Thus, the electrode foil, wherein electrostatic capacitance is not lowered and the stable quality is provided, can be obtained.

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 used in various electronic devices, and more particularly to a technique for etching a low voltage anode foil.

[0002]

2. Description of the Related Art Miniaturization and high reliability of aluminum electrolytic capacitors have been promoted with the aim of downsizing electronic devices and achieving high reliability. For this purpose, it is necessary to increase the capacity and reliability of the electrode foil.

Generally, an electrode foil for an aluminum electrolytic capacitor is
The aluminum foil is electrochemically or chemically etched to increase its surface area, and an insulating oxide film is formed on the surface to manufacture. The aluminum foil is etched by alternating current electrolytic etching in which an alternating current is passed between electrodes arranged on both sides of the aluminum foil in an electrolytic solution prepared by adding phosphoric acid, sulfuric acid, nitric acid, etc. to an aqueous solution containing chlorine ions. DC electrolysis in which an aluminum foil is used as a positive electrode and electrodes on both sides of the aluminum foil are used as negative electrodes in an electrolytic solution containing phosphoric acid, sulfuric acid, nitric acid, etc. Broadly divided into etching.

Aluminum foil etched by direct current electrolytic etching has cylindrical pits formed thereon.
The pit depth, diameter, etc. can be controlled by the liquid composition, the temperature of the etching liquid, and the like. The pit diameter can be made relatively large as compared with the pits for AC electrolytic etching, and is mainly used as an intermediate foil for medium and high pressure. On the other hand, in the case of aluminum foil etched by AC electrolytic etching, the aluminum foil repeats positive and negative potentials with respect to the electrolytic solution.In the positive state, the aluminum melts starting from the weak spot of the film and is in a negative state. Then, a film is formed on the surface of aluminum. For this reason, sponge-like pits having a small diameter are formed in the aluminum foil etched by AC electrolytic etching, so that the aluminum foil is mainly used as a low voltage anode foil.

As one of the methods for producing a low voltage anode foil, the aluminum foil is dipped in an etching solution that has a function of removing a natural oxide film on the surface of the aluminum foil and a function of forming a protective film on the surface. Then, a method of gradually raising the current density of alternating current electrolytic etching to start etching is disclosed in JP-A-63-299309. This method removes the unnecessary oxide film on the surface of the aluminum foil by immersing the aluminum foil in the etching solution for a certain period of time, and forms a new film to protect the surface of the aluminum foil. Etching is started while gradually raising it, and the defect of the film is used as a starting point of pit generation, and the starting point is maintained to grow the pits inside, and etching is performed so that the surface is not dissolved as much as possible.

[0006]

However, in the above-mentioned conventional method for etching an aluminum foil, the thickness of the oxide film on the surface of the aluminum foil, the amount of rolling oil, etc. are changed depending on the annealing conditions and rolling conditions of the aluminum foil. Due to this change, the removal of the unnecessary film may not be uniform, and
The newly formed film is also non-uniform. Therefore, when AC electrolytic etching is performed, the distribution of starting points becomes non-uniform, and the pits do not progress inward and only the surface is dissolved, and as a result, the surface area does not increase and the capacitance decreases. There was a problem to do.

The present invention solves the above-mentioned conventional problems. Even if the characteristics of the original aluminum foil are changed, it is possible to form a constant initial pit that is the starting point of the AC electrolytic etching in the subsequent stage, and it is stable. It is an object of the present invention to provide a method for producing an electrode foil for an aluminum electrolytic capacitor, which is capable of producing an electrode foil having the above quality.

[0008]

In order to achieve the above object, a method for manufacturing an electrode foil for an aluminum electrolytic capacitor according to the present invention is an electrode foil for an aluminum electrolytic capacitor in which an aluminum foil is electrolytically etched in an etching solution containing chlorine ions. In the manufacturing method, the direct current electrolytic etching of the aluminum foil is performed in the first stage, and after the aluminum foil is subjected to the immersion treatment in the second stage, the current density of the alternating current electrolytic etching is gradually increased, and then the etching is performed at a constant current density. According to this manufacturing method, even if there is a change in the characteristics of the aluminum original foil, it is possible to form a constant initial pit that will be the starting point of the subsequent AC electrolytic etching, and to obtain an electrode foil with stable quality. It can be manufactured.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is a method for producing an electrode foil for an aluminum electrolytic capacitor, which comprises electrolytically etching an aluminum foil in an etching solution containing chlorine ions. De-etching is performed, and after the aluminum foil is immersed in the latter stage, the current density of alternating current electrolytic etching is gradually increased, and then etching is performed at a constant current density. , Make an appropriate number of initial pits on the surface of the aluminum foil to be the starting points for the subsequent AC electrolytic etching. Since the density, depth, diameter, etc. of the initial pits can be controlled by the conditions of DC electrolytic etching such as liquid composition and current density, the thickness of the oxide film on the surface of the aluminum original foil, the amount of rolling oil, etc. Even if it changes, a constant initial pit can always be created. In addition, it is possible to advance the pits internally from the initial pits as starting points by the subsequent AC electrolytic etching. In this case, a film is formed on the aluminum foil surface of sulfuric acid, nitric acid, oxalic acid, etc. in the etching solution. By adding a substance having properties, it is possible to prevent a new starting point from being created on the surface of the aluminum foil during AC electrolytic etching by the film formed on the surface of the aluminum foil. The pits will grow from the tips of the generated pits, and the pits will progress inward, so that surface dissolution is reduced, and thus the reduction in capacitance can be prevented.

An embodiment of the present invention will be described below in comparison with a conventional method. 20 lots of aluminum foil having different annealing conditions were etched by the method of the present invention and the conventional method. (1) Method of the present invention (DC electrolytic etching + AC electrolytic etching) (A) Etching conditions DC electrolytic etching Aluminum concentration 9 g / L Hydrochloric acid concentration 7% Sulfuric acid concentration 20% Liquid temperature 80 ° C. Current density 0.4 A / cm ² AC Electrolytic etching Aluminum concentration 7g / L Hydrochloric acid concentration 15% Liquid temperature 30 ° C Immersion time 100 seconds Initial startup time 15 seconds Current density 0.3A / cm ² (B) Chemical conversion in oxalic acid aqueous solution 22V (2) Conventional method (AC electrolysis Etching) (A) Etching conditions AC electrolytic etching Aluminum concentration 7g / L Hydrochloric acid concentration 15% Liquid temperature 30 ° C Immersion time 100 seconds Initial start-up time 15 seconds Current density 0.3A / cm ² (B) Chemical conversion in oxalic acid aqueous solution 22V The method of the invention comprises an aluminum concentration of 9 g / L,
An aqueous solution of hydrochloric acid concentration 7% and sulfuric acid concentration 20% and a current density of 0.4 on an aluminum foil in an etching solution with a liquid temperature of 80 ° C.
A direct current of A / cm ² is applied to perform direct current electrolytic etching of aluminum foil, and then aluminum concentration is 7 g /
L, an aqueous solution of hydrochloric acid concentration of 15%, and the aluminum foil is immersed in an etching solution having a liquid temperature of 30 ° C. for 100 seconds to immerse the aluminum foil. The temperature is gradually raised in 15 seconds, and then etching is performed at a constant current density of 0.3 A / cm ² .

The etching foil etched as described above was subjected to 22 V chemical conversion in an oxalic acid aqueous solution to produce an electrode foil.

According to the conventional method, the aluminum concentration is 7 g /
After the aluminum foil is immersed in an etching solution having an L content and a hydrochloric acid concentration of 15% and the solution temperature is 30 ° C. for 100 seconds to dip the aluminum foil, the current density of AC electrolytic etching is initially set up for 15 seconds. Etching is performed while gradually increasing during a second.

The etching foil etched as described above was subjected to 22 V chemical conversion in an oxalic acid aqueous solution to produce an electrode foil.

An electrode foil produced by the method of the present invention,
The result of measuring the capacitance of the electrode foil manufactured by the conventional method is shown in Table 1 as a relation between the capacitance range and the number of lots.

[0015]

[Table 1]

As is clear from Table 1, according to the method of the present invention, the thickness of the oxide film on the surface of the aluminum original foil changes depending on the characteristics of the aluminum original foil, that is, the annealing conditions and rolling conditions of the aluminum original foil. However, even if there is a change in the characteristics such as the amount of rolling oil, it is possible to form a certain initial pit on the surface of the aluminum foil by the direct current electrolytic etching in the first stage, which is the starting point of the subsequent alternating current electrolytic etching. As compared with the conventional method, it is possible to obtain the electrode foil having a stable quality with a high capacitance in 20 lots.

[0017]

As described above, according to the method for producing an electrode foil for an aluminum electrolytic capacitor of the present invention, in the method for producing an electrode foil for an aluminum electrolytic capacitor in which an aluminum foil is electrolytically etched in an etching solution containing chlorine ions, Since the aluminum foil is subjected to direct current electrolytic etching in the first stage, the aluminum foil is immersed in the latter stage, the current density of the alternating current electrolytic etching is gradually increased, and then the aluminum foil is etched at a constant current density. Even if there is a change in the characteristics of the original foil, that is, the thickness of the oxide film on the surface of the original aluminum foil, the amount of rolling oil, etc. changes depending on the annealing and rolling conditions of the original aluminum foil, the direct current electrolytic etching in the previous stage , It is possible to form a certain initial pit on the surface of the aluminum foil, which is the starting point of the subsequent AC electrolytic etching, which reduces the capacitance. In which it is possible to obtain an electrode foil having a free stable quality Rukoto.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Koichi Kojima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A method of manufacturing an electrode foil for an aluminum electrolytic capacitor, comprising electrolytically etching an aluminum foil in an etching solution containing chlorine ions, wherein direct current electrolytic etching of the aluminum foil is performed in a first stage, and dipping treatment of the aluminum foil is performed in a second stage. After that, gradually increase the current density of AC electrolytic etching,
Then, a method of manufacturing an electrode foil for an aluminum electrolytic capacitor, which is so etched as to have a constant current density.