| 摘要 |
A glass substrate of the present invention for magnetic recording media having high heat resistance and easy chemical strengthening ability at once has not been obtained, which is a glass composition essentially comprising 60 to 70 wt % SiO<SUB>2</SUB>, 5 to 20 wt % Al<SUB>2</SUB>O<SUB>3</SUB>, 0 to 1 wt % Li<SUB>2</SUB>O, 3 to 18 wt % Na<SUB>2</SUB>O, 0 to 9 wt % K<SUB>2</SUB>O, 0 to 10 wt % MgO, 1 to 15 wt % CaO, 0 to 4.5 wt % SrO, 0 to 1 wt % BaO, 0 to 1 wt % TiO<SUB>2 </SUB>and 0 to 1 wt % ZrO<SUB>2</SUB>, wherein the sum of Li<SUB>2</SUB>O, Na<SUB>2</SUB>O and K<SUB>2</SUB>O is from 5 to 25 wt %, and the sum of MgO, CaO, SrO and BaO is from 5 to 20 wt %.
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