JPS58219727A - 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 rolled hard aluminum foil or later.

・Annealed soft aluminum foil is chemically or electrochemically etched in an aqueous solution containing chlorine ions such as sodium chloride or hydrochloric acid to measure the surface area expansion rate of the aluminum foil, and then chemical conversion treatment is applied to the surface. It is manufactured by forming an oxide film, which is a dielectric material, on the

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. Furthermore, the surface area expansion rate of the aluminum foil due to this etching 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, the mechanical strength of aluminum foil decreases with the amount of etching.
In processes such as etching and chemical 9 assembly, it is necessary to suppress the amount of etching to a level where mechanical strength does not occur such as cutting. 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 ratio 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 applying hydrostatic pressure to the aluminum foil before etching, an aluminum electrode foil with a higher surface area expansion ratio than before can be obtained. It has been accomplished.

That is, the present invention applies hydrostatic pressure to aluminum foil for electrolytic capacitors, and then chemically or electrochemically etches it in an aqueous solution containing chlorine ions.
The present invention provides an aluminum electrode foil for electrolytic capacitors that has sufficient mechanical strength and a larger surface area expansion ratio than conventional ones.

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

As mentioned above, aluminum foil for electrolytic capacitors is chemically or electrochemically etched in an aqueous solution containing chloride ions to increase its area, and is further chemically converted before use.
This surface area expansion rate is calculated by rolling and annealing aluminum foil.
It depends on many factors such as the amount of impurities in the aluminum foil, the composition of the etching agent, 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.

The surface area gradually expands, but the adsorption of chlorine ions is preferentially carried out on the weak points of the oxide film on the surface due to impurities or dislocations caused by rolling, etc., which become etch pit nuclei and further prevent etching. Proceeds along the dislocation.

It is thought that the surface area will continue to increase.

The dispersion state of dislocations in conventional aluminum foil can be seen from the state of the etch bits created by etching, and there are overcrowded and underpopulated areas. If dislocations exist locally, the etching holes will coalesce, and the effective bits will not contribute to surface area expansion, and the mechanical strength will decrease, making it impossible to perform sufficient etching. There is no choice but to suppress the expansion rate of the surface area. Therefore, by uniformly dispersing dislocations in the aluminum foil, etch bits are uniformly generated, and the surface area can be expanded.

In the present invention, applying hydrostatic pressure to the aluminum foil makes it possible to uniformize the dispersion of dislocations inside the aluminum foil, thereby improving the surface area expansion rate by etching. The lower limit of the pressure range of this hydrostatic pressure is the minimum pressure at which the effect of expanding the surface area by etching is recognized, and the upper limit is a range limited by the strength of the high-pressure cylinder of the hydrostatic pressure device, and is preferably 6° to 6°. It is in the range of 2ookg/-. Also, the time of pressurization is not a big factor, but the longer it is, the more effective it is, and usually 6 to 6
Do it in 0 seconds. The effect of this hydrostatic pressurization is greater when using hard aluminum foil than when using soft aluminum foil.

Etching after hydrostatic pressurization is carried out in an aqueous solution containing chloride ions, as in the past, and is usually carried out in an aqueous solution of hydrochloric acid or salt at a current density of 0.1-1 μm/d, 60-90 μm/d.
It is etched by a predetermined amount at a temperature of 1.5°C.The chemical conversion treatment is also carried out in the same manner as in the conventional method.

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

Both tau δ and leakage current are not significantly different from conventional ones, and only the capacitance can be increased, so it is possible to make the aluminum electrolytic capacitor 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 1 ooμ was held at a hydrostatic pressure of 0 to 2 ook/− for 1 minute. After degreasing this sample, it was heated in an aqueous solution of chloride at a concentration of 6 mol/e at a temperature of 80'C.

Etching was carried out for 3 minutes at a current density of 0.4 A/cl (etched area: 1 (71!
Chemical formation was carried out under various conditions including a C1 formation voltage of 23V.

For the obtained chemical aluminum foil, the capacitance, t
auδ was measured and shown in the following table. In addition, the measurement is Swt%
A tin foil was used as a cathode in an aqueous ammonium borate solution of 3
As is clear from the above table, the effective surface area expansion rate of the aluminum foil is improved by applying hydrostatic pressure to the aluminum foil before etching treatment, and the unit area An aluminum electrode foil for electrolytic capacitors having a large per unit capacitance and mechanical strength equivalent to conventional ones 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, an aluminum electrode foil for electrolytic capacitors having a high surface area expansion rate and sufficient mechanical strength can be obtained, and therefore its industrial value is considerable.

Claims (1)

[Claims] After applying hydrostatic pressure to the aluminum foil, it is chemically or electrochemically etched in an aqueous solution containing chlorine ions.
A method for producing an aluminum electrode foil for an electrolytic capacitor, which comprises subjecting the foil to a chemical conversion treatment.