Patent ID: 7601446

Claim:
A substrate for an information recording medium, which is formed of a glass containing, by mol %: 45 to 70% of SiO 2 , 1 to 15% of Al 2 O 3 , total content of SiO 2 and Al 2 O 3 being 57 to 85%; 2 to 25% of CaO, more than 0 but not more than 15% of BaO, 0 to 15% of MgO, 0 to 15% of SrO, 0 to 10% of ZnO, total content of MgO, CaO, SrO, BaO and ZnO being 2 to 30%; more than 0% but not more than 15% of K 2 O, more than 0 but not more than 8% of Na 2 O, total content of K 2 O and Na 2 O being 2 to 15%; more than 0 but not more than 12% of ZrO 2 , 0 to 10% of TiO 2 , ratio of content of CaO to the total content of MgO, CaO, SrO and BaO (CaO/(MgO+CaO+SrO+BaO)) is 0.5% or more, the total content of SiO 2 , Al 2 O 3 , MgO, CaO, SrO, BaO, ZnO, K 2 O, Na 2 O, ZrO 2 , TiO 2 components in the glass being at least 95 mol%, the glass contains no Li 2 O, and has a glass transition temperature (Tg) of 600° C. or higher and an etching rate of 0.1 μl/minute or less with regard to a hydrosilicofluoric acid aqueous solution maintained at a temperature of 45° C. with the hydrosilicofluoric acid concentration 1.72% by weight.