A glass for a magnetic recording medium substrate permitting the realization of a magnetic recording medium substrate affording good chemical durability and having an extremely flat surface, a magnetic recording medium substrate comprised of this glass, a magnetic recording medium equipped with this
A glass for a magnetic recording medium substrate permitting the realization of a magnetic recording medium substrate affording good chemical durability and having an extremely flat surface, a magnetic recording medium substrate comprised of this glass, a magnetic recording medium equipped with this substrate, and methods of manufacturing the same. The glass compositions disclosed comprise oxides of at least Si, Al, Li, Na, K, Sn and Ce, optionally Sb, but not comprising As or F. Additional oxides of Mg, Cs, Sr and Ba may be present. The oxides are presented as molar percentages, mass percentages and ratios thereof.
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1. A glass for a magnetic recording medium substrate comprised of an oxide glass comprising, as converted based on the oxide, denoted as molar percentages: SiO2 60 to 75 percent,Al2O3 1 to 15 percent,Li2O 5 to 10 percent,Na2O 8 to 15 percent,P2O5 0 percent, andK2O 0 to 5 percent,wherein a total cont
1. A glass for a magnetic recording medium substrate comprised of an oxide glass comprising, as converted based on the oxide, denoted as molar percentages: SiO2 60 to 75 percent,Al2O3 1 to 15 percent,Li2O 5 to 10 percent,Na2O 8 to 15 percent,P2O5 0 percent, andK2O 0 to 5 percent,wherein a total content of Li2O, Na2O, and K2O is 25 molar percent or lower;wherein the total amount of MgO, CaO, SrO or BaO is in a range of 0.1 to 10 molar percent,wherein a total quantity of Sn oxide and Ce oxide is in a range of 0.5 mass percent to 1.5 mass percent based on the total amount of the glass components, andwherein the ratio of the content of Sn oxide to the total content Sn oxide and Ce oxide (content of Sn oxide/(content of Sn oxide+content of Ce oxide)) is 0.45 to 0.85, an Sb oxide content is in a range of 0 to 0.1 percent, and the glass comprises no As or F. 2. The glass for a magnetic recording medium substrate according to claim 1, wherein the glass does not comprises Sb. 3. The glass for a magnetic recording medium substrate according to claim 1, wherein the glass comprises, denoted as molar percentages: MgO 0 to 10 percent,CaO 0 to 10 percent,SrO 0 to 5 percent, andBaO 0 to 5 percent. 4. The glass for a magnetic recording medium substrate according to claim 1, wherein the glass comprises 0.1 to 5 molar percent of ZrO2, TiO2, La2O3, Nb2O5, Ta2O5, and HfO2 in total. 5. The glass for a magnetic recording medium substrate according to claim 1, wherein the total content of SiO2 and Al2O3 is 65 molar percent or greater, and the glass has a viscous property such that the viscosity at 1,400° C. is 103 dPa·s or lower. 6. The glass for a magnetic recording medium substrate according to claim 1, wherein the glass comprises, denoted as molar percentages: SiO2 66 to 70 percent,Al2O3 7 to 12 percent(wherein the total content of SiO2 and Al2O3 is 75 percent or greater),Li2O 5 to 10 percent,Na2O 8 to 13 percent,K2O 0.1 to 2 percent(wherein the total content of Li2O, Na2O, and K2O is 15 to 22 percent),MgO 0.1 to 5 percent,CaO 0.1 to 5 percent,SrO and BaO in total 0 to 1 percent,ZrO2 0.1 to 2 percent,B2O3 0 to 1 percent, andZnO 0 to 1 percent. 7. The glass for a magnetic recording medium substrate according to claim 1 wherein the glass comprises, denoted as molar percentages: SiO2 66 to 70 percent,Al2O3 5 to 12 percent,Li2O 5 to 10 percent,Na2O 8 to 13 percent,K2O 0.1 to 2 percent(wherein the total content of Li2O, Na2O, and K2O is 18 to 22 percent),MgO and CaO in total 0 to 5 percent,SrO and BaO in total 0 to 5 percent,ZrO2, TiO2, La2O3, Nb2O5, Ta2O5, and HfO2 in total 0.1 to 5 percent,B2O3 0 to 3 percent,ZnO 0 to 1 percent, andP2O5 0 percent. 8. The glass for a magnetic recording medium substrate according to claim 1, wherein the glass exhibits an acid resistant property such that the etching rate when immersed in a 0.5 volume percent hydrogenfluosilicic acid aqueous solution maintained at 50° C. is 3.0 nm/minute or less and an alkali resistant property such that the etching rate when immersed in a 1 mass percent potassium hydroxide aqueous solution maintained at 50° C. is 0.1 nm/minute or less. 9. The glass for a magnetic recording medium substrate according to claim 1, wherein the glass contains 2 pieces/kg or less of residual bubbles. 10. The glass for a magnetic recording medium substrate according to claim 1, wherein the ratio of the ZrO2 content to the total content of ZrO2, TiO2, La2O3, Nb2O5, Ta2O5, and HfO2 (ZrO2/(ZrO2+TiO2+La2O3+Nb2O5+Ta2O5+HfO2)) is 0.1 to 1. 11. The glass for a magnetic recording medium substrate according to claim 1, wherein the glass has been subjected to a chemical strengthening treatment. 12. A magnetic recording medium substrate comprised of the glass according to claim 1. 13. The magnetic recording medium substrate according to claim 12, wherein roughness Ra of a main surface of the substrate is less than 0.25 nm. 14. The magnetic recording medium substrate according to claim 13, wherein the substrate exhibits a bending strength of 10 kg or greater. 15. The magnetic recording medium substrate of claim 13, wherein the substrate has a disk like shape and a thickness of 1 mm or less. 16. A magnetic recording medium having an information recording layer on the magnetic recording medium substrate according to claim 12. 17. The magnetic recording medium according to claim 16, suited to a vertical magnetic recording method. 18. The magnetic recording medium substrate according to claim 12, wherein the glass substrate does not contain residual bubbles. 19. A glass for a magnetic recording medium substrate comprised of an oxide glass comprising, as converted based on the oxide, denoted as molar percentages: SiO2 60 to 75 percent,Al2O3 1 to 15 percent,Li2O 5 to 10 percent,Na2O 8 to 15 percent,P2O5 0 percent, andK2O 0 to 5 percent,wherein a total content of Li2O, Na2O, and K2O is 25 molar percent or lower;wherein the total amount of MgO, CaO, SrO or BaO is in a range of 0.1 to 10 molar percent,wherein a total quantity of Sn oxide and Ce oxide is 0.5 mass percent to 1.5 mass percent based on the total amount of the glass components,wherein the ratio of the content of Sn oxide to the total content Sn oxide and Ce oxide (content of Sn oxide/(content of Sn oxide+content of Ce oxide)) is within a range sufficient for rendering a content of residual bubbles in the glass 2 pieces/kg or less,wherein an Sb oxide content is in a range of 0 to 0.1 percent, andwherein the glass comprises no As or F. 20. The glass for a magnetic recording medium substrate according to claim 19, wherein the ratio of the content of Sn oxide to the total content Sn oxide and Ce oxide is in a range of from about 0.45 to 0.85. 21. A magnetic recording medium substrate comprised of the glass according to claim 19. 22. The magnetic recording medium substrate according to claim 21, wherein the substrate exhibits a bending strength of 20 kg or greater.
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