Patent ID: 7462411
Filing Date: 2008-12-09
Classification: C03C,G11B,Y10T

Abstract:
1. A substrate for an information recording medium, which substrate is made of an alkali-metal-oxide-containing glass formed from SiO 2 , Al 2 O 3 , CaO, BaO, K 2 O, MgO, SrO, TiO 2 , ZrO 2 , Li 2 O, Na 2 O and ZnO which has no chemically strengthened layer and wherein the alkali-metal-oxide-containing glass substantially contains, by mol %, more than 50% but not more than 70% of SiO 2 , 1 to 12% of Al 2 O 3 , 2 to 25% of CaO, more than 0% but not more than 15% of BaO, 3 to 15% of K 2 O, 0 to 10% of MgO, 0 to 15% of SrO, 0 to 10% of TiO 2 , 0 to 12% of ZrO 2 , 0 to less than 1% of Li 2 O, 0 to 8% of Na 2 O and 0 to 1% of ZnO, provided that BaO is present in an amount of more than 5% by weight, the glass having a glass transition temperature (Tg) of 620° C. or higher and satisfying a requirement that the alkali ion elution amount per a unit area when the glass is immersed in water having a temperature of 80° C. for 24 hours is 0.2 μmol/cm 2 or less.