| 摘要 |
PROBLEM TO BE SOLVED: To achieve a high strength without using a chemical reinforcement method, decreasing the danger that moisture and organic components are left in a protecting film and prevent a magnetic film from being deteriorated in performance at the time of forming a magnetic disk by etching an inner circumferential end face of a doughnut-shaped glass plate and coating the inner circumferential end face with the protecting film having a specific hardness to a pencil scratch. SOLUTION: A protecting film coating an etched inner circumferential end face is set to have a pencil scratch hardness of not smaller than 5H, preferably not smaller than 6H, particularly preferably not smaller than 8H. The etching process can eliminate deep flaws present at inner and outer circumferential end faces which control a bending strength of a doughnut-shaped glass plate, particularly, deep flaws of the inner circumferential end face which more strongly controls the bending strength. A depth of the etching is preferably 15-40μm. The protecting film preferably uses a silica layer obtained by setting a coat composition including polysilazane.
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