Glass substrate for information recording medium, process for producing the glass substrate, information recording medium, and process for producing the same
A glass substrate for an information recording medium, which has high heat resistance, has such high thermal shock resistance that it does not break when exposed to a sharp change in temperature and has high strength against scratching, and which is formed of a glass comprising SiO 2 , Al 2 O 3 , ZrO 2 , CaO, BaO, Li 2 O and Na 2 O as essential components and comprises, by mole %, 50 to 70% of SiO 2 , 1 to 10% of Al 2 O 3 , over 0% but not more than 12% of ZrO 2 , 2 to 24% of CaO, over 0% but not more than 15% of BaO, 0 to 10% of MgO, 0 to 15% of SrO, provided that the content of CaO+BaO+MgO+SrO is over 10% but less than 25%, over 0% but not more than 6% of Li 2 O, over 0% but not more than 10% of Na 2 O, 0 to 5% of K 2 O, and 0 to 10% of TiO 2 .
1. A glass substrate for an information recording medium, which is formed of a glass comprising SiO 2 , Al 2 O 3 , ZrO 2 , CaO, BaO, Li 2 O and Na 2 O as essential components and comprising, by mol %,
50 to 70% of SiO 2 ,
1 to 10% of Al 2 O 3 ,
over 0% but not more than 12% of ZrO 2 ,
2 to 24% of CaO,
over 0% but not more than 15% of BaO,
0 to 2% of MgO,
0 to 15% of SrO,
provided that the content of CaO+BaO+MgO+SrO is over 10% but less than 25%,
over 0% but not more than 6% of Li 2 O,
over 0% but not more than 10% of Na 2 O,
0 to 5% of K 2 O, and
0 to 10% of TiO 2 ,
wherein the glass has a glass transition temperature of 560° C. or higher.
2. The glass substrate for an information recording medium as recited in claim 1 , which has such thermal shock resistance that it does not break when rapidly cooled in a manner in which it is introduced into water maintained at 20° C. from a heating state under heat at 170° C. and immersed in the water.
3. The glass substrate for an information recording medium as recited in claim 1 , wherein the glass has an average linear expansion coefficient of 70×10 −7 /K or more at 100 to 300° C.
4. The glass substrate for an information recording medium as recited in claim 1 , wherein the glass is a chemically strengthened glass.
5. The glass substrate for an information recording medium as recited in claim 1 , which is a substrate for an information perpendicular-recording medium.
6. A process for producing a glass substrate for an information recording medium, which comprises the step of shaping a molten glass into a plate-shaped glass, the molten glass containing SiO 2 , Al 2 O 3 , ZrO 2 , CaO, BaO, Li 2 O and Na 2 O as essential components and comprising, by mol %,
50 to 70% of SiO 2 ,
1 to 10% of Al 2 O 3 ,
over 0% but not more than 12% of ZrO 2 ,
2 to 24% of CaO,
over 0% but not more than 15% of BaO,
0 to 2% of MgO,
0 to 15% of SrO,
provided that the content of CaO+BaO+MgO+SrO is over 10 but less than 25%,
over 0% but not more than 6% of Li 2 O,
over 0% but not more than 10% of Na 2 O,
0 to 5% of K 2 O, and
0 to 10% of TiO 2 ,
wherein the glass has a glass transition temperature of 560° C. or higher.
7. An information recording medium comprising the glass substrate for an information recording medium recited in claim 1 and at least an information recording layer formed on said glass substrate.
8. A process for producing an information recording medium, which comprises the step of forming an information recording layer on the glass substrate from an information recording medium recited in claim 1 .