MAGNETIC RECORDING MEDIUM

摘要

PURPOSE:To narrow the relative spacing between a magnetic recording layer and magnetic head and to obtain high magnetic density by etching only the anodic oxide film layer to make the surface thereof flush with the surface of a ferromagnetic materials or lower than said surface. CONSTITUTION:An Al alloy base material is cut out to a disk shape and the surface thereof is finished to a specular surface by diamond cutting to form a disk. The disk is subjected to an alkali degreasing treatment then to an anodic oxidation treatment in a 3% oxalic acid bath to form an anodic oxide film. The material is then dipped in a phosphoric acid bath to expand the diameter of the bores formed to the oxide film and to adjust a barrier layer. The material is then subjected to AC electrolysis in a bath consisting essentially of ferrous ammonium sulfate to deposit and pack the iron into the bores. The surface of the disk is further polished to adjust the thickness of the magnetic film to 3mum and thereafter the material is dipped for 30sec at 80 deg.C in a mixed acid composed of 35ml/lH2O phosphoric acid and 20g/lH2O chromium trioxide to etch only the Al anodic oxide film layer.