PURPOSE: To produce the aluminum foil for electrolytic capacitors with which excellent etching performance and the high electrostatic capacity are obtainable and which is free from the fluctuation in the electrostatic capacity in a transverse direction.
CONSTITUTION: An aluminum slab having ≥99.9% purity is used and before the slab is subjected to final finish rolling after hot rolling, the aluminum foil base is subjected to at least one pass of washing for removing the surface layers, by which the flaw-like recessed parts and inclusions, such as Al oxides and carbon, on the foil surfaces are removed. As a result, the generation of the coarse etching pits by the unavoidable local concn. of these recessed parts and inclusions is obviated and the uniform etching pits are formed. In addition, the aluminum foil is subjected to a low-temp. heating treatment in an atmosphere of ≤0.05kg/kg moisture content prior to final annealing after foil rolling and, therefore, the thickness in the transverse direction of the oxide films formed on the surfaces of the aluminum foil is previously uniformalized and the fluctuation in the electrostatic capacity is prevented prior to final annealing.
KATO YUTAKA
ISOYAMA EIZO
GOSHIYONA KENJI