US 7,601,446 B2
Substrate for information recording medium, information recording medium and method for manufacturing same
Mikio Ikenishi, Akishima (Japan); and Xuelu Zou, Akishima (Japan)
Assigned to Hoya Corporation, Tokyo (Japan)
Appl. No. 10/505,282
PCT Filed Oct. 29, 2003, PCT No. PCT/JP03/13846
§ 371(c)(1), (2), (4) Date Aug. 20, 2004,
PCT Pub. No. WO2004/041740, PCT Pub. Date May 21, 2004.
Claims priority of application No. 2002-323275 (JP), filed on Nov. 07, 2002.
Prior Publication US 2005/0162956 A1, Jul. 28, 2005
This patent is subject to a terminal disclaimer.
Int. Cl. G11B 5/65 (2006.01); C03C 3/17 (2006.01); C03C 3/21 (2006.01); C03C 19/00 (2006.01)
U.S. Cl. 428—846.9  [501/27; 501/102; 65/33.4] 14 Claims
 
1. A substrate for an information recording medium, which is formed of a glass containing, by mol %:
45 to 70% of SiO2, 1 to 15% of Al2O3, total content of SiO2 and Al2O3 being 57 to 85%;
2 to 25% of CaO, more than 0 but not more than 15% of BaO, 0 to 15% of MgO, 0 to 15% of SrO, 0 to 10% of ZnO, total content of MgO, CaO, SrO, BaO and ZnO being 2 to 30%;
more than 0% but not more than 15% of K2O, more than 0 but not more than 8% of Na2O, total content of K2O and Na2O being 2 to 15%;
more than 0 but not more than 12% of ZrO2, 0 to 10% of TiO2, ratio of content of CaO to the total content of MgO, CaO, SrO and BaO (CaO/(MgO+CaO+SrO+BaO)) is 0.5% or more,
the total content of SiO2, Al2O3, MgO, CaO, SrO, BaO, ZnO, K2O, Na2O, ZrO2, TiO2 components in the glass being at least 95 mol%, the glass contains no Li2O, and has a glass transition temperature (Tg) of 600° C. or higher and an etching rate of 0.1 μl/minute or less with regard to a hydrosilicofluoric acid aqueous solution maintained at a temperature of 45° C. with the hydrosilicofluoric acid concentration 1.72% by weight.