US 11,999,652 B2
Glass for magnetic recording medium substrate or for glass spacer to be used in magnetic recording/reproducing device, magnetic recording medium substrate, magnetic recording medium, glass spacer to be used in magnetic recording/reproducing device, and magnetic recording/reproducing device
Koichi Sato, Tokyo (JP); and Kazuaki Hashimoto, Tokyo (JP)
Assigned to HOYA CORPORATION, Tokyo (JP)
Appl. No. 17/784,528
Filed by HOYA CORPORATION, Tokyo (JP)
PCT Filed Dec. 11, 2020, PCT No. PCT/JP2020/046405
§ 371(c)(1), (2) Date Jun. 10, 2022,
PCT Pub. No. WO2021/117897, PCT Pub. Date Jun. 17, 2021.
Claims priority of application No. 2019-225368 (JP), filed on Dec. 13, 2019.
Prior Publication US 2023/0192530 A1, Jun. 22, 2023
Int. Cl. G11B 5/73 (2006.01); C03C 3/087 (2006.01); C03C 3/095 (2006.01); G11B 5/235 (2006.01); G11B 5/72 (2006.01)
CPC C03C 3/095 (2013.01) [C03C 3/087 (2013.01); G11B 5/235 (2013.01); G11B 5/72 (2013.01)] 20 Claims
 
1. A glass for a magnetic recording medium substrate or for a glass spacer for a magnetic recording/reproducing apparatus,
wherein a mole ratio of the total content of Al2O3 and MgO relative to the total content of SiO2 and CaO [(A2O3+MgO)/(SiO2+CaO)] is in a range of 0.417 or more and 0.6 or less,
the total content of SiO2 and Al2O3 (SiO2+Al2O3) is in a range of 64 mol % or more and 85 mol % or less,
the total content of SiO2, Al2O3, MgO, and CaO (SiO2+Al2O3+MgO+CaO) is in a range of 87 mol % or more and 98 mol % or less,
the total content of TiO2 and ZrO2 (TiO2+ZrO2) is 0.5 mol % or more,
the glass has a glass transition temperature of 740° C. or more,
an average linear expansion coefficient of the glass at 100° C. to 300° C. is 68×10−7/° C. or less, and
the total content of Li2O, Na2O, K2O, B2O3, and ZnO (Li2O+Na2O+K2O+B2O3+ZnO) is in a range of 0 mol % or more and 3 mol % or less.