JPS58219728A - Method of producing aluminum electrode foil for electrolytic condenser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an aluminum electrode foil for electrolytic capacitors having a high effective surface area expansion rate.

Generally, aluminum electrode foil for electrolytic capacitors is made by chemically or electrochemically etching rolled hard aluminum foil or annealed soft aluminum foil in an aqueous solution containing chlorine ions such as sodium chloride or hydrochloric acid. After expanding the surface area of the aluminum foil, a chemical conversion treatment is performed to form an oxide film that becomes a dielectric on the surface.

Since the capacitance of an aluminum electrode foil for an electrolytic capacitor is approximately proportional to the surface area of the aluminum foil, the larger the surface area expansion rate, the more desirable. The surface area expansion rate of the aluminum foil due to the etching described above increases in proportion to the amount of etching, but beyond a certain limit, the surface area expansion rate slows down and, on the contrary, shows a decrease. On the other hand, since the mechanical strength of the aluminum foil decreases with the amount of etching, it is necessary to suppress the amount of etching to a level where mechanical strength does not occur during etching, chemical formation assembly, and other processes. For this reason, an appropriate amount of etching is determined from the viewpoint of the surface area expansion rate and mechanical strength of the aluminum foil.

On the other hand, aluminum electrolytic capacitors are desired to be further miniaturized and have a larger capacity, and aluminum electrode foils with sufficient mechanical strength and a larger surface area expansion rate are desired. Although it is rare, a lot of research has been conducted on etching.

The present invention is based on the fact that, as a result of various studies on the etching of aluminum foil, it was discovered that by irradiating the aluminum foil before etching with radiation, an aluminum electrode foil with a higher surface area expansion ratio than before can be obtained. It was made by

That is, in the present invention, aluminum foil for electrolytic capacitors is irradiated with radiation, and then chemically or electrochemically etched in an aqueous solution containing chlorine ions, so that it has sufficient mechanical strength and a surface area expansion rate that is higher than that of conventional foils. The present invention provides a method for manufacturing a larger aluminum electrode foil for an electrolytic capacitor.

The manufacturing method of the present invention will be specifically explained below.

As mentioned above, the surface area of aluminum foil for electrolytic capacitors is expanded by chemically or electrochemically etching it in an aqueous solution containing chloride ions.
The aluminum foil is further chemically converted and used, but the surface area expansion rate depends on many factors such as the rolling process and annealing of the aluminum foil, the amount of impurities in the aluminum foil, the composition of the etching solution, and the electrolytic conditions.

Etching of aluminum in an aqueous solution containing chlorine ions begins with etch pit nuclei where chlorine ions are adsorbed on the surface, and as etching progresses, corrosion of the aluminum foil occurs internally in the form of pitting corrosion, and the surface area gradually expands. However, the adsorption of chlorine ions is preferentially carried out at weak points in the oxide film on the surface due to impurities or dislocations caused by rolling, etc., and these become etch pit nuclei, and further etching progresses along the dislocations. It is thought that the surface area will continue to expand.

In the present invention, the radiation irradiation is intended to increase the number of dislocations and to make the dislocations uniform, thereby making it possible to improve the surface area expansion rate by etching. This radiation irradiation is done with neutron beams, but the lower limit of the range of irradiation is the minimum amount that is recognized as having the effect of expanding the surface area by etching, and the upper limit is the time required for irradiation and the allowable value of residual radioactivity after irradiation. The range is limited by the time required to reach the following, preferably 1o16 to
1021n//c4. Regarding aluminum foil, the effect is large for hard foil that has been rolled, and the effect is small for soft foil that has been annealed. Furthermore, the greater the amount of impurities in the aluminum foil, the longer it takes for the radioactivity to fall below the allowable amount. Etching of aluminum foil irradiated with radiation is carried out in an aqueous solution containing chloride ions, as is the case with the conventional method. A predetermined amount of etching is performed.The chemical conversion treatment is also performed in the same manner as in the conventional method.

Therefore, the aluminum electrode foil for electrolytic capacitors obtained by the present invention has high mechanical strength.

-δ and leakage current are not much different from conventional ones, and only the capacitance can be increased, making it possible to make aluminum electrolytic capacitors smaller and larger in capacity.

Next, the present invention will be explained based on examples.

(Example) A high-purity aluminum foil sample with a purity of 99.99 and a thickness of 100μ was degreased and washed with acetone in advance, then sealed in a polyethylene capsule, and a neutron beam of 1.8
X 1015 to 7.2 X 1018n/c, j irradiated. The irradiated sample was left for 20 days or more, and after the residual radioactivity became below the allowable value, the sample was immersed in a sodium chloride aqueous solution with a concentration of 6 mo/+7/l at a temperature of 80°C and a current density of 0.4.
Etched for 3 minutes at h/c$ (etched part:
1C1rL×1CrrL). Next, coat this etching foil with boric acid 100%! ? Chemical formation was carried out in an aqueous solution of 0° C./l and a formation voltage of 2'3 V.

Capacitance about the obtained chemical aluminum foil.

−δ was measured and shown in the table below. The measurement was conducted in an ammonium borate aqueous solution of SWt at 30°C using a tin foil as a cathode.
The test was carried out at 120H2 with an AC bridge at a temperature of 120H2. The measurement sample area is 1 cr/L×1 crrL.

(L-L lower metal 1i) As is clear from the table above, by irradiating the aluminum foil with radiation before etching, the effective surface area expansion rate of the aluminum foil is improved, the capacitance per unit area is large, and the mechanical strength is increased. Also, aluminum electrode foil for electrolytic capacitors equivalent to the conventional one can be obtained. In addition, although the present invention is applied to an anode foil in the embodiment, it goes without saying that it can also be applied to a cathode foil.

As explained above, according to the present invention, a high-quality aluminum electrode foil for surface electrolytic capacitors can be obtained, which has great industrial value.

Claims (1)

[Claims] After irradiating the aluminum foil with radiation, it is chemically or electrochemically etched in a solution containing chlorine ions.
A method for producing an aluminum electrode foil for an electrolytic capacitor, the method comprising subsequently subjecting it to a chemical conversion treatment.