JPH07118434B2 - Aluminum alloy foil for electrolytic capacitor electrodes - Google Patents

Description

TECHNICAL FIELD The present invention relates to an aluminum alloy foil for electrolytic capacitor electrodes, particularly for anodes.

2. Description of the Related Art Aluminum electrode foils for electrolytic capacitors are generally subjected to electrical or chemical etching treatment in order to increase their effective surface area and increase the capacitance per unit volume. Thus, as a preferable aluminum foil material used for such an application, a surface expansion ratio as large as possible can be obtained by etching, so that the capacitance can be made large and the relative relationship with the surface expansion ratio can be obtained. Therefore, it is desired that the corrosion weight loss is small and that the excellent mechanical strength can be retained.

Based on such requirements, various improvements have been attempted in the past regarding the aluminum foil for electrolytic capacitor electrodes in terms of both the material composition and the manufacturing process of the foil.

As the main means of improvement from the material aspect, a small amount of additional element is added to high-purity aluminum to improve the etching density during etching.As such an additional element, Ag, In, The effectiveness of Cd, Pb, Bi, Sr, Zr, Th, etc. has already been reported (for example, Japanese Patent Publication No. 42-1428).
9, JP-B-44-29577, JP-A-54-43563, JP-A-5
7-66617, JP-A-57-66618, JP-A-57-66619
issue).

Against the background described above, as a result of various experiments and studies for the purpose of improving the material composition in the same manner as described above, still other types of additive elements effective for improving the capacitance and their addition It could be completed by finding the range of appropriate content.

(Means for Achieving the Purpose) The aluminum foil for electrolytic capacitor electrodes according to the present invention has aluminum purity of 99.9% or more, and Ca
Is contained in the range of 5 to 30 ppm.

The additive element Ca contributes to the improvement of the surface expansion ratio by etching of the aluminum alloy due to its small addition, and if the content is less than 5 ppm (0.0005 wt%), there is no effect of increasing the capacitance. . On the contrary, 30ppm (0.03wt%)
When not less than, not only the gradual decrease in the capacitance tends to be exhibited, but with the increase in the local dissolution amount of the foil during etching, the corrosion weight loss increases and the mechanical strength decreases, which is more disadvantageous, which is preferable. Absent.

The reason why the capacitance of the foil is increased by containing Ca is considered to be as follows. That is, the magnitude of the capacitance is
Although it depends on the expansion efficiency of the effective surface area of the foil by etching as described above, the foil containing Ca has a significantly higher number of etching holes per unit area than a normal high-purity aluminum foil containing no Ca. It is thought that this is because the number increases and the density increases. However, its content is 30ppm
If it exceeds, the density of the etching holes will be high, but the surface of the foil will also be melted, and as a result, the capacitance will tend to decrease and the mechanical strength will be poor.

On the other hand, it is well known that aluminum purity of 99.9% or more is required for aluminum foil for electrolytic capacitor electrodes, especially as foil for anodes. Needless to say, it is 99.99%.
The above is preferable.

(Example) Next, the example of this invention is shown in comparison with a comparative example.

Aluminum purity is 99.99%, and various aluminum alloy foils with different addition contents of Ca, and aluminum foil to which the elemental Ca is not added are used as test materials,
Current density of these foils in a 3% hydrochloric acid solution with a bath temperature of 75 ° C
Etching for 8 minutes with a direct current of 15 A / dm ²
The capacitance when formed to 50 V was measured. Further, the mechanical strength of the foil after etching was measured and compared. The results are shown in the table below.

In the table below, the tensile strength indicates the breaking load per unit length of a 10 mm width etching foil subjected to a tensile test.

As is clear from the results in the above table, according to the high-purity aluminum alloy foil containing Ca in the range of 5 to 30 ppm, the high-purity aluminum alloy foil contains less than that of Ca containing less than or exceeding the above range. A clear increase effect of the electric capacity was recognized.

Also, in both cases, corrosion weight loss can be suppressed to a relatively small range,
It was confirmed that the foil after etching was also excellent in mechanical strength.

(Effects of the Invention) According to the present invention, as described above, the surface expansion rate by etching is increased, and while having a large electrostatic capacity, it retains the required mechanical strength even after etching, and is difficult to handle. It is possible to provide a high-performance aluminum alloy foil for electrolytic capacitor electrodes, which does not cause

Claims (1)

[Claims] 1. The purity of aluminum is 99.9% or more,
Also, an aluminum alloy foil for electrolytic capacitor electrodes containing Ca in the range of 5 to 30 ppm.