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AssigneeHoya Corporation
InventorsMikio Ikenishi, Atsuko Morita, Xuelu Zou
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Disclosed are a glass substrate for an information recording medium, having excellent scratch resistance and a light weight and having high fracture toughness, the glass substrate having a fragility index value, measured in water, of 12 μm−1/2 or less or having a fragility index value, measured in an atmosphere having a dew point of −5° C. or lower, of 7 μm−1/2 or less, or the glass substrate comprising, by mol %, 40 to 75% of SiO2, 2 to 45% of B2O3 and/or Al2O3 and 0 to 40% of R′2O in which R′ is at least one member selected from the group consisting of Li, Na and K), wherein the total content of SiO2, B2O3, Al2O3 and R′2O is at least 90 mol %, and a magnetic information recording medium comprising a magnetic recording layer formed on the glass substrate.
A glass substrate for an information recording medium, comprising, by mol %, greater than 65%, as a total, of SiO2 and at least one of B2O3 and Al2O3, the content of B2O3 being 1 to 25%, 0 to 20% of RO in which R is at least one member selected from the group consisting of Mg, Ca, Zn, Sr and Ba, 0 to 28% of R′2O in which R′ is at least one member selected from the group consisting of Li, Na and K, 0 to 10% of TiO2 and 0 to 10% of ZrO2, the total content of said components being at least 95 mol %, and having a fragility index value, measured in water, of 12 μm−1/2 or less, said glass substrate having a chemically strengthened layer.
A glass substrate for an information recording medium, comprising, by mol %, greater than 65%, as a total, of SiO2 and at least one of B2O3 and Al2O3, the content of B2O3 being 1 to 25%, 0 to 20% of RO in which R is at least one member selected from the group consisting of Mg, Ca, Zn, Sr and Ba, 0 to 28% of R′2O in which R′ is at least one member selected from the group consisting of Li, Na and K, 0 to 10% of TiO2 and 0 to 10% of ZrO2, the total content of said components being at least 95 mol %, and having a fragility index value, measured in an atmosphere having a dew point of −5° C. or lower, of 7 μm1/2 or less, said glass substrate having a chemically strengthened layer.
A glass substrate for an information recording medium, comprising, by mol %, greater than 65%, as a total, of SiO2 and at least one of B2O3 and Al2O3, the content of B2O3 being 1 to 25%, 0 to 20% of RO in which R is at least one member selected from the group consisting of Mg, Ca, Zn, Sr and Ba, 0 to 28% of R′2O in which R′ is at least one member selected from the group consisting of Li, Na and K, 0 to 10% of TiO2 and 0 to 10% of ZrO2, the total content of said components being at least 95 mol %, and having a fragility index value, measured in water, of 12 μm−1/2 or less and having a fragility index value, measured in an atmosphere having a dew point of −5° C. or lower, of 7 μm−1/2 or less, said glass substrate having a chemically strengthened layer.
A glass substrate for an information recording medium, comprising, by mol %, 40 to 75% of SiO2, 2 to 45% of B2O3 and/or Al2O3, the content of B2O3 being 1 to 25%, and 0 to 40% of R′2O in which R′ is at least one member selected from the group consisting of Li, Na and K, wherein the total content of SiO2, B2O3, Al2O3 and R′2O is at least 90 mol %, said glass substrate having a chemically strengthened layer.
Dependencies are inferred from the claim text.