JPH07201673A - Manufacture of aluminum material for electrolytic capacitor electrode - Google Patents

Abstract

PURPOSE:To acquire an aluminum material for an electrolytic capacitor electrode which makes possible the increase of electrostatic capacity by removing a surface layer of an aluminum foil, by heating and oxidizing it under specified conditions thereafter and by annealing it under non-oxidizing atmosphere. CONSTITUTION:After a surface layer of an aluminum foil is removed, it is heated and oxidized under conditions of a temperature of 40 to 350 deg.C, a dew point of 0 to 80 deg.C for 30 to 1800sec. After heating and oxidation, it is annealed in non-oxidizing atmosphere. The surface layer removal of an aluminum foil is carried out for exposing a fresh surface by cleaning it using alkaline solution and acid solution. The heating and oxidation after the surface layer removal are carried out for generating a thin oxide film of high OH-group content on a foil surface. The annealing after the heating and oxidation is carried out for improving etching characteristic by making a structure of an aluminum foil an aggregate structure of much cube orientation. As for non-oxidizing atmosphere, vacuum of 10-Torr or below and inert gas atmosphere of a dew point of -30 deg.C or lower are desirable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum material for electrolytic capacitor electrodes used as an electrode foil for aluminum electrolytic capacitors.

[0002]

2. Description of the Related Art Al foil, which is generally used as an electrode material for aluminum electrolytic capacitors, usually has an electrochemical area because its effective area is enlarged to increase the capacitance per unit area. Alternatively, a chemical etching process is performed.

A foil having a better etching suitability has a larger surface expansion ratio, but it is known that an oxide film on the foil surface has a great influence on the etching suitability.

Recently, it has been found that the above oxide film often acts as a factor that inhibits etching, and it is considered desirable that the oxide film can be dissolved and removed early during the etching process. For that purpose, it is more desirable that the oxide film be thin and have a high dissolution rate in the etching solution (acidic aqueous solution).

However, in the foil manufacturing process, generally, high temperature annealing is carried out for the purpose of improving the (100) occupancy, and an oxide film of several nm is inevitably grown during this annealing. As a result of the oxide film acting in the direction of inhibiting etching, there is a limit to the increase in capacitance.

The present invention has been made in view of the above technical background, and an object of the present invention is to provide a method for producing an aluminum material for an electrolytic capacitor electrode which can increase electrostatic capacitance.

[0006]

In order to achieve the above object, the inventor, as a result of diligent research, found that an oxide film forming condition that the film thickness after annealing can be made thin and can be rapidly dissolved and removed in an etching solution. The invention was completed and the invention was completed.

That is, according to the present invention, the step of removing the surface layer of the aluminum foil and the temperature after removal: 40 to 350 ° C.
Manufacture of an aluminum material for electrolytic capacitor electrodes, which comprises performing a step of heating and oxidizing under conditions of dew point: 0 to 80 ° C. and time: 30 to 1800 seconds and a step of annealing in a non-oxidizing atmosphere after heating and oxidizing The method is the gist.

The above-mentioned aluminum foil is preferably a high-purity aluminum alloy having a purity of 99.99%, but is not limited to this and may be any aluminum foil having a purity within the range used for electrolytic capacitors.

The removal of the surface layer of the aluminum foil is carried out for the purpose of removing the non-uniform layer on the surface of the foil to expose a fresh surface. That is, oil and a heterogeneous oxide film formed by rolling exist on the aluminum foil surface after foil rolling. Also, near the surface of the aluminum foil,
There is a non-uniform contamination layer due to rolling deterioration or a roll coating during rolling. These cause non-uniformity of the oxide film in the subsequent thermal oxidation step, and hinder the formation of a uniform thin oxide film. Therefore, the non-uniform layer on the foil surface is removed. The specific means of removal is not particularly limited, and examples thereof include washing with an alkaline solution such as NaOH and an acid solution. For the purpose of removing the surface layer, it is preferable to perform it over a thickness of 1 nm or more, especially 5 nm.
The above is better.

After the removal of the foil surface layer, a heating and oxidation process is carried out by a low temperature, high dew point and short time treatment. Specifically, temperature: 40 to 350 ° C, dew point: 0 to 80 ° C, time: 30 to
The condition is 1800 seconds. By such heat oxidation treatment,
Thickness of 2.5 nm or less on the surface of the foil (Hunter hole method)
Alternatively, the thickness is 3.3 nm or less (ESCA method), and is thin.
This is carried out to form an oxide film having a high H group content. By forming such an oxide film, it is possible to suppress the growth of the oxide film in the subsequent annealing treatment, and
Even after annealing, an oxide film having a high OH group content can be obtained. It is considered that if the oxide film has a large number of OH groups, the oxide film dissolves quickly in an etching solution composed of an acidic aqueous solution. However, if the temperature, dew point, and heating time ranges deviate from the above ranges, the object cannot be achieved. Particularly preferable processing conditions are temperature: 40 to 100 ° C., dew point: 20 to
80 ° C., time: 30 to 120 seconds.

After the above thermal oxidation treatment, annealing is carried out.
The main purpose of this annealing is to improve the etching characteristics by making the texture of the aluminum foil a texture having many cubic orientations. This annealing needs to be performed in a non-oxidizing atmosphere in order to suppress the formation of a further oxide film and maintain the oxide film in a state where the content of OH groups is high. The non-oxidizing atmosphere is 10 ⁻⁴ Torr.
The following vacuum and an inert gas atmosphere with a dew point of −30 ° C. or lower can be mentioned. Other annealing conditions are not specified, but it is preferable to set the temperature to 350 to 600 ° C. and the time to 5 seconds to 24 hours. By treating under such conditions, the oxide film thickness can be made as thin as 4.0 nm or less (hunter hole method) or 4.8 nm or less (ESCA method).

The aluminum material produced as described above is
After that, it is used as an electrode material for an electrolytic capacitor after being subjected to electrochemical or chemical etching treatment using an etching solution mainly composed of an acid solution. During etching, the oxide film on the foil surface is not only extremely thin, but also contains a large amount of OH groups, which quickly dissolves in the etching solution and reduces the inconvenience of inhibiting etching. And a thick etching pit is formed.

The aluminum foil used in the present invention is not limited to the manufacturing process thereof, and may be annealed in the middle of the rolling process.

[0014]

[Function] After removing the surface of the aluminum foil, low temperature, high dew point,
Since the annealing process is performed by performing the thermal oxidation process by the short-time process, the growth of the oxide film is suppressed and the thickness becomes thin, and the film contains a large amount of OH groups. It is presumed that it rapidly dissolves in water and promotes the generation and growth of etching pits.

[0015]

Example A plurality of 100 μm thick aluminum foils made of aluminum having a purity of 99.99% were prepared.

Then, the surface of each aluminum foil is 0.0
It was washed with a 1% NaOH solution (30 ° C.). The surface removal thickness of the aluminum foil by washing is 10 n
It was m.

Next, each aluminum foil was subjected to a heat oxidation treatment under the conditions shown in Table 1, and then the dew point was -30 ° C.
The final annealing was performed in the Ar atmosphere at a temperature of 500 ° C. for a time of 6 hours. Table 1 shows the oxide film thickness by the Hunter Hall method after the heat oxidation treatment and after the final annealing.

The capacitance of each of the samples thus obtained was measured when it was converted to 250 V in a 5% boric acid solution. The results are shown in Table 1 as a relative comparison when the capacitance of Sample No. 4 is 100%.

[0019]

[Table 1]

As can be seen from the results shown in Table 1, the product of the present invention, which has been subjected to the thermal oxidation treatment under the conditions of the range of the present invention, has a larger capacitance than the comparative product which deviates from the range. This is presumably because the product of the present invention has a thin oxide film and contains many OH groups in the oxide film, so that the oxide film was rapidly dissolved during etching.

[0021]

According to the present invention, depending on the above, the step of removing the surface layer of the aluminum foil, and the temperature after removal: 40 to 40
Since it is characterized by performing a step of heating and oxidizing under conditions of 350 ° C., dew point: 0 to 80 ° C., time: 30 to 1800 seconds, and a step of annealing in a non-oxidizing atmosphere after heating and oxidizing.
It is possible to provide an electrolytic capacitor electrode material having excellent etching performance, capable of forming a large number of etching pits, and having a large surface area ratio and thus a large capacitance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isoyama Eizo 6-224, Kaiyamacho, Sakai City Showa Aluminum Co., Ltd.

Claims (1)

[Claims] 1. A step of removing the surface layer of the aluminum foil, a step of heating and oxidizing after the removal under the conditions of temperature: 40 to 350 ° C., dew point: 0 to 80 ° C., time: 30 to 1800 seconds, Then, a step of annealing in a non-oxidizing atmosphere is carried out, which is a method for manufacturing an aluminum material for electrolytic capacitor electrodes.