Glass substrate for information recording medium and method for producing the same
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 SiO 2 , 3 to 15% of Al 2 O 3 , and 0.2 to 8% of P 2 O 5 , 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.
1. A glass substrate for an information recording medium, comprising, as expressed in terms of percent by mass on an oxide basis:
52 to 67% of SiO 2 ,
3 to 14% of Al 2 O 3 ,
0.2 to 8% of P 2 O 5 ,
1.5 to 20% of MgO,
0 to 10% of CaO,
0 to 10% of ZnO,
0 to 13% of ZrO 2 ,
0 to 16% of TiO 2 ,
0 to 1% of CeO 2 ,
0 to 1% of SnO 2 ,
0 to 6% of B 2 O 3 ,
4 to 10% of Na 2 O, and
0 to 7% of K 2 O,
wherein a total amount of MgO, CaO, ZnO, ZrO 2 and TiO 2 in the glass substrate is 5 to 20% by mass on the oxide basis, and the total amount of CeO 2 and/or SnO 2 is 0.05 to 1% by mass on the oxide basis, and the total amount B 2 O 3 , Na 2 O, and/or K 2 O is 4 to 11%) by mass on the oxide basis,
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 GPa or greater.
2. The glass substrate for an information recording medium according to claim 1 , further comprising, as expressed in terms of percent by mass on the oxide basis:
2.9 to 8% Li 2 O.
3. The glass substrate for an information recording medium according to claim 1 , wherein the glass substrate does not contain As 2 O 3 component and Sb 2 O 3 component on the oxide basis, and Cl − , NO − , SO 2 − and F − components.
4. The glass substrate for an information recording medium according to claim 1 , wherein the glass substrate does not contain BaO component or SrO component on the oxide basis.
5. The glass substrate for an information recording medium according to claim 1 , wherein, when a content ratio of Li 2 O component on the oxide basis in a region inside the glass substrate for the information recording medium which extends from an end surface to a depth of 5 μm toward the center is designated as an α%, and the content ratio of the Li 2 O component n the oxide basis in the region in the glass substrate for the information recording medium which extends from beyond a depth of 5 μm from an end surface toward the center, within the region inside the glass substrate which extends from a depth of 5 μm from one main surface to a depth of 5 μm from an other main surface along the thickness direction, is designated as a β%, the ratio of α/β is 1 or less.
6. The glass substrate for an information recording medium according to claim 1 , wherein the surface roughness Ra (arithmetic mean roughness) is 2 A or less.
7. An information recording medium making use of the glass substrate for an information recording medium according to claim 1 .