JP3480311B2 - Method for producing electrode foil for aluminum electrolytic capacitor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum electrolytic capacitor used in various electronic devices, and particularly, an electrode foil for an aluminum electrolytic capacitor which is most suitable for manufacturing an electrode foil used for a low voltage aluminum electrolytic capacitor. The present invention relates to a manufacturing method of.

[0002]

2. Description of the Related Art Conventionally, an aluminum electrolytic capacitor of this type has an oxide film as a dielectric formed by a chemical conversion process on the surface of an aluminum foil whose effective surface area has been enlarged by an etching process, and the aluminum foil as an anode. A capacitor element is constructed by winding a cathode foil and a separator interposed therebetween, and the capacitor element is impregnated with a driving electrolytic solution, and the capacitor element is sealed in a metal case. It was something that was.

The etching process of the aluminum foil in the above-mentioned aluminum electrolytic capacitor is to roughen the aluminum foil by chemically or electrochemically corroding it in a solution mainly containing a chloride solution, and nitric acid, sulfuric acid, Aluminum that has been subjected to dechlorination to remove the chlorine components attached to the aluminum foil using phosphoric acid, etc., and then formed a hydrated film on the surface of the aluminum foil, which has been roughened by etching with or without drying. Heat treatment was performed to form a thermal oxide film on the surface of the foil (see Japanese Patent Application Laid-Open No. 4-279018), and the etched aluminum foil after the heat treatment was wound and transferred to the next chemical conversion step. It was a thing. The formation of the thermal oxide film by the above heat treatment was carried out in order to promote conversion into an oxide film formed in the next chemical conversion step, and was carried out in the atmosphere.

[0004]

However, in the above-mentioned conventional manufacturing method, since the etched aluminum foil is heat-treated in the atmosphere, the oxygen concentration in the heat-treatment atmosphere has a large influence. If the oxygen concentration is too high, the unit area per unit area is increased. There was a problem that not only loss of capacitance but also increase of leakage current.

Further, the purpose of the heat treatment is to remove some of the water of crystallization remaining in the hydrated film formed on the surface of the etched aluminum foil and convert it to a thermal oxide film to form an oxide film in the chemical conversion process. It is thought that this contributes to the acceleration of the thermal oxide film, but during the conversion into the thermal oxide film, volumetric shrinkage occurs due to the removal of water of crystallization, which causes cracks in the thermal oxide film that cause leakage current after chemical conversion.

If the oxygen concentration is too high at this time, the oxidation in the atmosphere reaches the surface of the aluminum foil from the cracks, and an excessive thermal oxide film is easily generated on the surface of the aluminum foil. , The formation of an amorphous oxide film, the change to a thermal oxide film, and the generation of cracks due to volume contraction grow while repeating in sequence, so the number of cracks in the thermal oxide film increases too much and the leakage current after formation increases, There was a problem that the expected electrostatic capacitance could not be obtained sufficiently.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a method of manufacturing an electrode foil for an aluminum electrolytic capacitor, which can obtain a larger capacitance than the conventional one and can reduce the leakage current. It is what

[0008]

In order to solve this problem, in the method for manufacturing an electrode foil for an aluminum electrolytic capacitor of the present invention, the etching foil is subjected to heat treatment in an atmosphere having an oxygen concentration of 10% or less before the chemical conversion. It was done like
By this manufacturing method, it is possible to obtain an excellent electrode foil for an aluminum electrolytic capacitor, which contributes to the promotion of the oxide film in the chemical conversion step and has a large electrostatic capacity and a reduced leakage current.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the invention described in claim 1 of the present invention, the surface of an aluminum foil is roughened by etching, and then chlorine components adhering to the etched etching foil are removed. After forming the hydrated film, this etching foil is heat-treated in an atmosphere having an oxygen concentration of 1 to 10% to form an oxide film on the defective portion of the hydrated film.
The chemical conversion is carried out after that, and according to this manufacturing method, not only the extra thermal oxide film is not generated by the heat treatment , but also cracks are generated in the hydrated film when the heat treatment is performed.
Even so, it has an effect of filling the cracks generated in the hydrated film because the oxygen concentration is appropriate. As a result, a thin oxide film having a withstand voltage is formed on the surface of the etching foil by the chemical conversion step, and this electrode foil can increase the capacitance per unit area, and It has an effect that the leakage current can be reduced.

According to a second aspect of the present invention, in the first aspect of the invention, the heat treatment atmosphere is oxygen and argon.
A mixed gas of at least one or more of nitrogen, hydrogen, carbon dioxide, and carbon monoxide, which increases the amount of extra thermal oxide film on the surface of the etching foil because a gas that does not easily react with aluminum is used. It has the effect that it does not occur and a higher capacitance can be obtained.

According to a third aspect of the invention, in the invention of the first aspect, the temperature of the heat treatment is 300 to 570 ° C. and the treatment time is 0.004 to 10 hours. Some water of crystallization in the Japanese film is removed to be converted into a thermal oxide film, and this thermal oxide film contributes to promotion of the chemical conversion film, so that it has an effect that a higher capacitance can be obtained.

Hereinafter, embodiments of the present invention will be described together with a conventional example as a comparative example. (Embodiment 1) Etching process: Purity 99.98%, thickness 100 μm
Aluminum foil of 7% hydrochloric acid, 0.5% phosphoric acid, nitric acid 1
% Aqueous solution at a temperature of 30 ° C., a sinusoidal alternating current with a current density of 0.2 A / cm ² , and an electric quantity of 1
Etching was performed at 20 C / cm ² .

Dechlorination treatment: 7% nitric acid aqueous solution, liquid temperature 60
Dechlorination treatment was carried out by immersing the substrate in ° C for 1 minute.

Hydration treatment: Hydration treatment was performed by immersing in pure water at a liquid temperature of 70 ° C. for 3 minutes. Drying: Drying was performed in the air at 200 ° C. for 8 minutes.

Heat treatment was carried out at 350 ° C. for 0.5 hours in a mixed gas in which the oxygen concentrations in the argon gas were 5, 7, 10, 13, 15, 18, and 21%, respectively.

The etching foil obtained in the first embodiment and the etching foils obtained in the first to third embodiments as comparative examples were subjected to a constant current formation of 45 V in a 5% aqueous solution of aluminium adipate in a liquid temperature of 70 ° C. Then, the results of measuring the capacitance per unit area and the leakage current are shown in (Table 1).

[0017]

[Table 1]

As is clear from (Table 1), by setting the oxygen concentration to 10% or less, the electrostatic capacity can be increased and the leakage current can be reduced as compared with the comparative example.

(Embodiment 2) Etching process: Same as in the first embodiment.

Dechlorination treatment: Same as in the first embodiment. Hydration process: Same as in the first embodiment.

Drying: Same as the first embodiment. The heat treatment was performed at 400 ° C. for 1 hour in a mixed gas containing oxygen and at least one of argon, nitrogen, hydrogen, carbon dioxide, and carbon monoxide.

The etching foil obtained in the above-mentioned Embodiment 2 and the etching foils obtained in the Embodiments 2 to 5 as a comparative example are treated with a 5% ammonium adipate aqueous solution at a liquid temperature of 7
A constant current of 45 V was formed at 0 ° C, and the capacitance per unit area and the leakage current were measured (Table 2).
Shown in.

[0023]

[Table 2]

As is clear from (Table 2), if the heat treatment atmosphere is a mixed gas of oxygen and at least one of argon, nitrogen, hydrogen, carbon dioxide, and carbon monoxide, a comparative example is obtained. In comparison, the capacitance can be increased and the leakage current can be reduced.

(Third Embodiment) Etching process: Same as in the first embodiment.

Dechlorination treatment: Same as in the first embodiment. Hydration process: Same as in the first embodiment.

Drying: Same as the first embodiment. Treatment time 0, 0.004, 0.1, 1, 1 in a mixed gas of nitrogen concentration 96%, hydrogen concentration 3% and oxygen concentration 1%
Heat treatment was performed at 400 ° C. for 0,15 hours.

The etching foil obtained in the above Embodiment 3 was subjected to constant current formation of 45 V in a 5% ammonium adipate aqueous solution at a liquid temperature of 70 ° C., and the capacitance per unit area and the leakage current thereof were measured. The results obtained are shown in (Table 3).

[0029]

[Table 3]

As is clear from Table 3, if the heat treatment time is 0.004 to 10 hours, the capacitance can be increased and the leakage current can be reduced as compared with the comparative example.

(Embodiment 4) Etching process: Same as in the first embodiment.

Dechlorination treatment: Same as in the first embodiment. Hydration process: Same as in the first embodiment.

Drying: Same as the first embodiment. Heat treatment was performed at 100, 200, 300, 400, and 570 ° C. for 0.5 hours in a mixed gas having an oxygen monoxide concentration of 95% and an oxygen concentration of 5%.

The etching foil obtained in the above-mentioned Embodiment 4 and the etching foils obtained in the Embodiments 4 to 4 as a comparative example were subjected to constant current formation of 45 V in a 5% ammonium adipate aqueous solution at a liquid temperature of 70 ° C. Then, the results of measuring the capacitance per unit area and the leakage current are shown in (Table 4).

[0035]

[Table 4]

As is clear from (Table 4), if the treatment temperature of the heat treatment is less than 300 ° C., there is no effect, and if the treatment temperature is 570 ° C. or higher, aluminum is dissolved.
If so, the capacitance can be increased and the leakage current can be reduced as compared with the comparative example.

[0037]

As described above, according to the method for producing an electrode foil for an aluminum electrolytic capacitor of the present invention, the etching foil is heat-treated in an atmosphere having an oxygen concentration of 1 to 10 % before the chemical conversion. As a result, not only does the excessive thermal oxide film not be generated by the heat treatment , but
Even if cracks occur in the hydrated film, it has an effect of filling the cracks generated in the hydrated film because the oxygen concentration is appropriate. As a result, a thin oxide film having a withstand voltage will be formed on the surface of the etching foil by the chemical conversion treatment, and this electrode foil can increase the capacitance per unit area, and The leakage current can be reduced.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI C22F 1/00 691 C22F 1/00 691B 691C (58) Fields investigated (Int.Cl. ⁷ , DB name) H01G 9/04 301 H01G 9/04 304

Claims (3)

(57) [Claims] 1. A surface of an aluminum foil is roughened by etching, chlorine components adhering to the etched etching foil are subsequently removed, and a hydrated film is further formed on the surface. Is 1-10%
And heat-treated in an atmosphere oxidizing skin to the defective portion of the hydrated film
A method for producing an electrode foil for an aluminum electrolytic capacitor, which comprises forming a film and then performing chemical conversion. 2. A heat treatment atmosphere is oxygen and argon, nitrogen, method of manufacturing electrode foil for aluminum electrolytic capacitor according to claim 1 is at least one or more of the mixed gas of hydrogen. 3. The heat treatment temperature is set to 300 to 570 ° C.,
The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the treatment time is 0.004 to 10 hours.