GLASS SUBSTRATE FOR RECORDING MEDIUM, MAGNETIC RECORDING MEDIUM USING THE SAME AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To improve heat resistance, flatness and strength by using oxynitride glass as a substrate material. SOLUTION: A mixture of SiO2 with an oxide such as Na2 O, CaO, Nd2 O3 or Al2 O3 and other metal oxide or metal oxynitride is melted by heating at 1,400-1,900 deg.C for 3-10hr in an inert gaseous atmosphere and the resultant oxynitride glass is molded in a plate shape to obtain a substrate material. This substrate material is lapped and polished to obtain the objective glass substrate 2 for a magnetic recording medium having 3-8Åsurface roughness Ra. A ruggedness controlling layer 3 of a metal or alloy having 50-300Åsurface roughness Rmax, an underlayer 4, a magnetic layer 5 and a protective layer 6 are successively formed on the glass substrate 2, heat treatment is carried out at a temp. (300-1,000 deg.C) below the glass transition temp. and a lubricative layer 7 is formed by coating with a liq. lubricant to obtain the objective magnetic recording medium.