Importance

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Abstract

There is provided a glass substrate which has the properties required in the use as a substrate for an information recording medium of the next generation such as a perpendicular magnetic recording system, and can be applied as a substrate for an information recording medium of the next generation particularly on the premise of using the glass substrate in a dynamic environment. More particularly, there is provided a glass substrate for an information recording medium which has sufficiently high surface hardness, has a good balance between specific gravity and mechanical strength, and has high strength to withstand high speed rotation or drop impact, and which can be produced with a high productivity adequate for a direct press method, without the occurrence of bubbles in the glass blank or reboil upon pressing even if arsenic components or antimony components are not substantially used. A glass substrate for an information recording medium, includes, as expressed in terms of percent by mass on the oxide basis: 52 to 67% of SiO₂, 3 to 15% of Al₂O₃, and 0.2 to 8% of P₂O₅, the glass substrate having a Young's modulus of 85 GPa or greater, a specific gravity of 2.60 or less, and a ratio of Young's modulus to specific gravity (Young's modulus/specific gravity) of 33.0 or greater.

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First Claim