JPH11340102A - Manufacture of electrode foil for aluminum electrolytic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which such electrode foil for aluminum electrolytic capacitor that can increase the electrostatic capacity of an aluminum electrolytic capacitor per unit area, and, at the same time, can reduce the leakage current of the capacitor. SOLUTION: In a method for manufacturing electrode foil for aluminum electrolytic capacitor, etching foil is chemically processed after the foil is heat- treated in an atmosphere containing oxygen at a concentration of <=10%. As a result of the process, a thin compact oxide film having a suitable breakdown voltage is formed on the surface of the etching foil, and such electrode foil for aluminum electrolytic capacitor that can increase the electrostatic capacity of an aluminum electrolytic capacitor per unit area and can reduce the leakage current of the capacitor can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode foil for an aluminum electrolytic capacitor which is most suitable for manufacturing an electrode foil used for an aluminum electrolytic capacitor for a low voltage among aluminum electrolytic capacitors used for various electronic devices. And a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, an aluminum electrolytic capacitor of this type forms an oxide film serving as a dielectric on a surface of an aluminum foil having an effective surface area enlarged by an etching process, and forms an anode with the aluminum foil serving as an anode. A capacitor element is formed by winding a cathode foil together with a separator interposed therebetween, by impregnating the capacitor element with a driving electrolyte, and sealing the capacitor element in a metal case. Was what it was.

[0003] The etching step of the aluminum foil in the aluminum electrolytic capacitor is to roughen the aluminum foil by chemically or electrochemically corroding the aluminum foil in a solution mainly containing a chloride solution, and to make the surface roughened by nitric acid, sulfuric acid, or the like. After performing a dechlorination treatment to remove the chlorine component attached to the aluminum foil using phosphoric acid, etc., a hydrated film is formed on the surface of the aluminum foil, and this aluminum is roughened by etching after drying or without drying Heat treatment is performed to form a thermal oxide film on the surface of the foil (see Japanese Patent Application Laid-Open No. Hei 4-279018), and the aluminum foil after the heat treatment is wound up and transferred to the next chemical conversion step. Was something. The formation of the thermal oxide film by the above heat treatment was performed to promote the conversion to the oxide film generated in the next chemical conversion step, and was performed in the air.

[0004]

However, in the above conventional manufacturing method, since the etched aluminum foil is heat-treated in the air, the influence of the oxygen concentration in the heat treatment atmosphere is large. There is a problem that not only loss of capacitance but also increase of leakage current occurs.

[0005] 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 to convert it into a thermal oxide film, thereby forming an oxide film in the chemical conversion step. Is considered to contribute to the promotion of the thermal oxidation. However, when the film is converted into the thermal oxide film, volume shrinkage occurs due to the removal of water of crystallization, and as a result, a crack occurs in the thermal oxide film, which causes a leakage current after the chemical conversion.

At this time, if the oxygen concentration is too high, oxidation in the atmosphere reaches the surface of the aluminum foil from the cracks, and an excessive thermal oxide film is easily formed on the surface of the aluminum foil. Since the growth of the amorphous oxide film, the change to the thermal oxide film, and the generation of cracks due to volume shrinkage are repeated in order, the cracks in the thermal oxide film increase too much and the leakage current after chemical formation increases. There was a problem that the expected electrostatic capacity could not be sufficiently obtained.

An object of the present invention is to solve 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 capable of obtaining a larger capacitance and reducing a leakage current. It is assumed that.

[0008]

According to the present invention, there is provided a method for manufacturing an electrode foil for an aluminum electrolytic capacitor, comprising the steps of: forming an etched foil in an atmosphere having an oxygen concentration of 10% or less; It is like that,
This manufacturing method contributes to the promotion of the oxide film in the chemical conversion step, and it is possible to obtain an excellent electrode foil for an aluminum electrolytic capacitor with a large capacitance and a reduced leakage current.

[0009]

DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the present invention, the surface of an aluminum foil is roughened by etching, and then the chlorine component attached to the etched foil is removed. After the formation of the hydrated film, the etching foil is heat-treated in an atmosphere having an oxygen concentration of 10% or less, and then the chemical conversion is performed. Not only does it stop being generated, but even if cracks are generated due to the formation of the thermal oxide film, the cracks generated in the thermal oxide film can be filled because the oxidation 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, This has the effect that the leakage current can be reduced.

According to a second aspect of the present invention, in the first aspect, the atmosphere for the heat treatment is oxygen and argon,
A mixture of at least one of nitrogen, hydrogen, carbon dioxide, and carbon monoxide, which increases the excess thermal oxide film on the surface of the etching foil due to the use of a gas that does not easily react with aluminum. This has the effect that higher capacitance can be obtained.

According to a third aspect of the present invention, in the first aspect, the temperature of the heat treatment is set to 300 to 570 ° C. and the processing time is set to 0.004 to 10 hours. Some of the water of crystallization in the Japanese film is removed and converted into a thermal oxide film, and this thermal oxide film contributes to the promotion of the chemical conversion film, and thus has the effect of obtaining a higher capacitance.

Hereinafter, embodiments of the present invention will be described together with a conventional example as a comparative example. Embodiment Mode 1 Etching Step: Purity 99.98%, Thickness 100 μm
7% hydrochloric acid, 0.5% phosphoric acid, 1% nitric acid
% Of an aqueous solution containing 30% aqueous solution at a temperature of 30 ° C., a current density of 0.2 A / cm ² and a quantity of electricity of 1 with a sine AC current.
Etching at 20 C / cm ² was performed.

Dechlorination treatment: 7% nitric acid aqueous solution, liquid temperature 60
The sample was immersed in a temperature of 1 ° C. for 1 minute to perform a dechlorination treatment.

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

Heat treatment was performed at 350 ° C. for 0.5 hour in a mixed gas in which the oxygen concentration in the argon gas was 5, 7, 10, 13, 15, 18, and 21%, respectively.

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

[0017]

[Table 1]

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

(Embodiment 2) Etching step: Same as in Embodiment 1.

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

Drying: Same as in the first embodiment. The heat treatment was performed at 400 ° C. for one 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 second embodiment and the etching foil obtained in the first to third embodiments as a comparative example were combined with a 5% aqueous ammonium adipate solution at a liquid temperature of 7%.
The results of performing a constant current formation of 45 V at 0 ° C. and measuring the capacitance and the leakage current per unit area are shown in Table 2 below.
Shown in

[0023]

[Table 2]

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

(Embodiment 3) Etching step: Same as in Embodiment 1.

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

Drying: Same as in the first embodiment. Processing time 0,0.004,0.1,1,1 in a mixed gas of 96% nitrogen, 3% hydrogen and 1% oxygen
The heat treatment was performed at 400 ° C. for 0.15 hours.

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

[0029]

[Table 3]

As is clear from Table 3, if the processing time of the heat treatment 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 step: Same as in Embodiment 1.

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

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

The etching foil obtained in the fourth embodiment and the etching foil obtained in the fourth to fourth embodiments as a comparative example were subjected to a constant current conversion of 45 V in a 5% aqueous ammonium adipate solution at a liquid temperature of 70 ° C. The results of measuring the capacitance per unit area and the leakage current are shown in Table 4 below.

[0035]

[Table 4]

As is clear from Table 4, if the heat treatment temperature is lower than 300.degree. C., there is no effect, and if the heat treatment temperature is 570.degree. C. or higher, aluminum dissolution occurs.
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 manufacturing 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 10% or less, and then the chemical conversion is performed. In addition to the fact that an excess thermal oxide film is not generated due to the heat treatment, even if cracks are generated due to the thermal oxide film being formed, the cracks generated in the thermal oxide film are filled because the oxygen concentration is moderate. As a result, a thin oxide film having a withstand voltage is formed on the surface of the etching foil by the chemical conversion treatment, and this electrode foil can increase the capacitance per unit area, The leakage current can be reduced.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 691 C22F 1/00 691C

Claims (3)

[Claims] 1. The surface of an aluminum foil is roughened by etching, the chlorine component adhered to the etched foil is removed, and a hydrated film is formed on the surface of the aluminum foil. A method for producing an electrode foil for an aluminum electrolytic capacitor, wherein a heat treatment is carried out in an atmosphere of 10% or less. 2. The heat treatment atmosphere is at least one of oxygen and argon, nitrogen, hydrogen, carbon dioxide, and carbon monoxide.
2. The method for producing an electrode foil for an aluminum electrolytic capacitor according to claim 1, wherein the gaseous mixture is a mixture of at least two kinds of gases. 3. The heat treatment temperature is 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.