초록 ▼

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

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 SiO 2 , 2 to 45% of B 2 O 3 and/or Al 2 O 3 and 0 to 40% of R′ 2 O in which R′ is at least one member selected from the group consisting of Li, Na and K), wherein the total content of SiO 2 , B 2 O 3 , Al 2 O 3 and R′ 2 O is at least 90 mol %, and a magnetic information recording medium comprising a magnetic recording layer formed on the glass substrate.

대표청구항 ▼

1. A glass substrate for an information recording medium, comprising, by mol %, greater than 65%, as a total, of SiO 2 and at least one of B 2 O 3 and Al 2 O 3 , the content of B 2 O 3 being 1 to 25%, 0 to 20% of RO in which R is at least one member selected from the group consisting of Mg, C

1. A glass substrate for an information recording medium, comprising, by mol %, greater than 65%, as a total, of SiO 2 and at least one of B 2 O 3 and Al 2 O 3 , the content of B 2 O 3 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′ 2 O in which R′ is at least one member selected from the group consisting of Li, Na and K, 0 to 10% of TiO 2 and 0 to 10% of ZrO 2 , 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. 2. A glass substrate for an information recording medium, comprising, by mol %, greater than 65%, as a total, of SiO 2 and at least one of B 2 O 3 and Al 2 O 3 , the content of B 2 O 3 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′ 2 O in which R′ is at least one member selected from the group consisting of Li, Na and K, 0 to 10% of TiO 2 and 0 to 10% of ZrO 2 , 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 μm 1/2 or less, said glass substrate having a chemically strengthened layer. 3. A glass substrate for an information recording medium, comprising, by mol %, greater than 65%, as a total, of SiO 2 and at least one of B 2 O 3 and Al 2 O 3 , the content of B 2 O 3 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′ 2 O in which R′ is at least one member selected from the group consisting of Li, Na and K, 0 to 10% of TiO 2 and 0 to 10% of ZrO 2 , 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. 4. A glass substrate for an information recording medium, comprising, by mol %, 40 to 75% of SiO 2 , 2 to 45% of B 2 O 3 and/or Al 2 O 3 , the content of B 2 O 3 being 1 to 25%, and 0 to 40% of R′ 2 O in which R′ is at least one member selected from the group consisting of Li, Na and K, wherein the total content of SiO 2 , B 2 O 3 , Al 2 O 3 and R′ 2 O is at least 90 mol %, said glass substrate having a chemically strengthened layer. 5. The glass substrate for an information recording medium as recited in claim 4, having a fragility index value, measured in water, of 12 μm −1/2 or less. 6. The glass substrate for an information recording medium as recited in claim 4, 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. 7. The glass substrate for an information recording medium as recited in any one of claims 1 to 3, wherein the content of B 2 O 3 is 2 to 20 %. 8. The glass substrate for an information recording medium as recited in any one of claims 1 to 4, having a Young's modulus of at least 70 GPa. 9. The glass substrate for an information recording medium as recited in any one of claims 1 to 4, having a modulus of rigidity of at least 20 GPa. 10. The glass substrate for an information recording medium as recited in any one of claims 1 to 4, which is made of a glass having a region wherein the glass has a viscosity of at least 1 Pa·s, in a range of temperatures equivalent to, and higher than, a liquidus temperature of the glass. 11. The glass substrate for an information recording medium as recited in any one of claims 1 to 4, whic h is made of a glass having a thermal expansion coefficient of 60×10 −7 /° C. or greater at a temperature of from 100° C. to 300° C.