Patent ID: 8168313

Claim:
Glass for an information recording medium substrate, which comprises, as represented by mol % based on the following oxides, from 61 to 72% of SiO 2 , from 3 to 11% of Al 2 O 3 , from 0 to 14.3% of Li 2 O, from 0 to 22% of Na 2 O, from 0 to 22% of K 2 O, from 4 to 13% of MgO, from 0 to 6% of TiO 2 and from 0 to 5% of ZrO 2 , provided that the total content of Li 2 O, Na 2 O and K 2 O (R 2 O) is from 10 to 22%, and (a) the ratio of the content of Li 2 O to R 2 O (Li 2 O/R 2 O) is at most 0.52, (b) the ratio of the content of Na 2 O to R 2 O (Na 2 O/R 2 O) is at least 0.35, or (c) the ratio of the content of K 2 O to R 2 O (K 2 O/R 2 O) is at least 0.45.