SUBSTRATE FOR OPTICAL DISK

摘要

PURPOSE:To stabilize a protective film as the free fluoride therein reacts with a rear earth metal by subjecting the protective film which is formed on a resin substrate and consists of a fluoride and rear earth metal to a heating treatment. CONSTITUTION:The protective film 2 consisting of the fluoride (e.g.: MgF2) and the rear earth metal (e.g.: Tb) is formed by vapor deposition or sputtering on the resin substrate 1 which consists of an acrylic plate or the like and is provided with guide grooves preferably at the ratio of the film formation speeds of the fluoride and rear earth metal adjusted to 0.3-0.6. The film 2 is subjected to the heating treatment preferably at 45 deg.C up to the permissible temp. of the substrate 1. A magnetic recording medium film 3 and surface protective film 4 are formed on such film 2. The free fluorine and rear earth metal atoms react with each other to form the stable fluoride if the film 2 is subjected to the heating treatment. The diffusion of the free fluorine into the film and the deterioration of the film are thereby suppressed.