| 摘要 |
PROBLEM TO BE SOLVED: To suppress the migration of alkali and to prevent an information recording medium on a substrate from being adversely affected by chemically strengthening the lapped glass substrate, removing a part of the strengthened layer by polishing and then dealkalizing the substrate. SOLUTION: A discoid glass substrate of specified size is lapped to a specified thickness and then chemically strengthened to form a strengthened layer having >=20μm thickness. The strengthened layer on the principal plane is then polished off by >=10μm, and the strengthened layer on the principal plane is left by >=10μm. The polished substrate is dealkalized to remove the alkali metal component from the substrate principal plane and a surface layer part at the end, and a glass substrate not adversely affecting an information recording medium is obtained. The dealkalizing is performed by the dipping in hot water or the treatment with an aq. acidic soln. such as sulfuric acid or with the acidic vapor such as sulfur dioxide.
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