JPS6257089B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aluminum alloy foil for electrodes of electrolytic capacitors. Aluminum electrode foils for electrolytic capacitors are generally subjected to electrical or chemical etching treatment in order to expand their effective surface area and increase capacitance per unit volume. Therefore, as a preferable aluminum foil material used for such purposes, etching can obtain as large an area expansion ratio as possible, thereby increasing capacitance and increasing the area expansion ratio. In this regard, it is desired that the corrosion loss is small and that the material has excellent mechanical strength. An object of the present invention is to provide an aluminum alloy foil for electrolytic capacitor electrodes that can satisfy the above requirements. The aluminum alloy foil for electrolytic capacitor electrodes according to the present invention is characterized by having an aluminum purity of 99.9% or more and containing 0.05 to 30 ppm of thorium. Thorium content in foil is 0.05ppm
(0.000005wt%), the effect of increasing capacitance is small; conversely, if it exceeds 30ppm (0.003wt%), corrosion loss increases, mechanical strength decreases, and capacitance also decreases due to surface dissolution. do. Therefore, the thorium content should be selected within the range of 0.05 to 30 ppm, particularly preferably 0.5 to 5.0 ppm. The reason why the capacitance of the foil is increased by the inclusion of thorium is considered to be as follows. In other words, the amount of capacitance depends on the efficiency of enlarging the effective surface area of the foil by etching, as mentioned above.
This is thought to be because the foil containing thorium has a significantly greater number of etching holes per unit area and a higher density than ordinary high-purity aluminum foil that does not contain thorium. However, if the content exceeds 30 ppm, the etching hole density increases, but the surface of the foil also dissolves.
As a result, the capacitance decreases and the strength decreases. On the other hand, it goes without saying that aluminum foil for electrolytic capacitor electrodes requires an aluminum purity of 99.9% or higher.
99.99% or higher is preferable. Next, examples of the present invention will be shown together with comparative examples. Various aluminum alloy foils with an aluminum purity of 99.99% and varying thorium content and aluminum foil without thorium were used as test samples. These foils were placed in a 3% aqueous hydrochloric acid solution at a bath temperature of 75°C. When etching was carried out for 8 minutes using a direct current with a current density of 15 A/dm ² and the electrostatic capacity was converted to 350 V, the capacitance was as shown in the table below.

[Table] As is clear from the results in the above table, the capacitance of the high-purity aluminum alloy foil containing a predetermined amount of thorium was clearly increased compared to the foil that did not contain thorium. Further, in all cases, the corrosion weight loss hardly increased compared to the control example, and the mechanical strength was also excellent.

Claims (1)

[Claims] 1. An aluminum alloy foil for electrolytic capacitor electrodes having an aluminum purity of 99.9% or more and containing 0.05 to 30 ppm of thorium.