Glass substrate for information recording medium, process for producing the glass substrate, information recording medium, and process for producing the same

摘要

A glass substrate for an information recording medium, which has high heat resistance, has such high thermal shock resistance that it does not break when exposed to a sharp change in temperature and has high strength against scratching, and which is formed of a glass comprising SiO₂, Al₂O₃, ZrO₂, CaO, BaO, Li₂O and Na₂O as essential components and comprises, by mold %, 50 to 70% of SiO₂, 1 to 10% of Al₂O₃, over 0% but not more than 12% of ZrO₂, 2 to 24% of CaO, over 0% but not more than 15% of BaO, 0 to 10% of MgO, 0 to 15% of SrO, provided that the content of CaO+BaO+MgO+SrO is over 10% but less than 25%, over 0% but not more than 6% of Li₂O, over 0% but not more than 10% of Na₂O, 0 to 5% of K₂O, and 0 to 10% of TiO₂.