Glass substrate for information recording medium and method for manufacturing the same, and magnetic recording medium

1. A method for manufacturing a glass substrate for information recording medium, said method comprising: a lapping step of lapping a circular glass plate made of an alkali aluminosilicate glass; and a subsequent cerium oxide polishing step of polishing the circular glass plate with a slurry containing a cerium oxide abrasive,

wherein a difference (SiO 2 −Al 2 O 3 ) obtained by subtracting an Al 2 O 3 content from an SiO 2 content in the alkali aluminosilicate glass is 62% by mole or less;

and wherein said method further comprises:

subsequently to the cerium oxide polishing step, a detergent rinsing step, and

subsequently to the detergent rinsing step, a cleaning step of cleaning the circular glass plate with a cleaning liquid having a sulfuric acid concentration of 50% by mass or more and 80% by mass or less and a hydrogen peroxide concentration of 3% by mass or more and 10% by mass or less at a liquid temperature of 50° C. or higher and 100° C. or lower, and

after the cleaning step, a finish polishing step of polishing a main surface of the circular glass plate with a slurry containing a colloidal silica abrasive.

2. The method for manufacturing a glass substrate for information recording medium according to claim 1 , wherein the alkali aluminosilicate glass has a composition of from 55 to 75% by mole of SiO 2 , from 5 to 17% by mole of Al 2 O 3 , from 4 to 27% by mole of Li 2 O+Na 2 O+K 2 O, from 0 to 20% by mole of MgO+CaO+SrO+BaO, provided that SiO 2 +Al 2 O 3 +Li 2 O+Na 2 O+K 2 O+MgO+CaO+SrO+BaO is 90% by mole or more.

3. The method for manufacturing a glass substrate for information recording medium according to claim 2 , wherein in the composition of the alkali aluminosilicate glass, SiO 2 is 63% by mole or more, Li 2 O+Na 2 O+K 2 O is 16% by mole or more, and MgO+CaO+SrO+BaO is from 0 to 10% by mole.

4. The method for manufacturing a glass substrate for information recording medium according to claim 1 , wherein the colloidal silica abrasive has an average particle size of 10 nm or more and 50 nm or less.

5. The method for manufacturing a glass substrate for information recording medium according to claim 4 , wherein the slurry containing a colloidal silica abrasive has a pH of 1 or more and 6 or less.

6. The method for manufacturing a glass substrate for information recording medium according to claim 1 , wherein the difference (SiO 2 −Al 2 O 3 ) obtained by subtracting an Al 2 O 3 content from an SiO 2 content in the alkali aluminosilicate glass is 50% by mole or more and 62% by mole or less.

7. The method for manufacturing a glass substrate for information recording medium according to claim 6 , wherein the alkali aluminosilicate glass has a composition of from 63 to 71% by mole of SiO 2 , from 7 to 12.5% by mole of Al 2 O 3 , from 16 to 24% by mole of Li 2 O+Na 2 O+K 2 O, from 0 to 10% by mole of MgO+CaO+SrO+BaO, provided that SiO 2 +Al 2 O 3 +Li 2 O+Na 2 O+K 2 O+MgO+CaO+SrO+BaO is 90% by mole or more.

8. The method for manufacturing a glass substrate for information recording medium according to claim 1 , wherein a repolishing step of polishing the main surface of the circular glass plate with a slurry containing a cerium oxide abrasive and using a polishing pad having a foamed resin layer having a Shore A hardness of 60° or less is included between the cleaning step and the finish polishing step.

9. The method for manufacturing a glass substrate for information recording medium according to claim 4 , wherein a step of polishing the main surface of the circular glass plate with a slurry containing a colloidal silica abrasive having an average particle size of more than 50 nm and 100 nm or less and having a pH of 8 or more and 12 or less is included between the cleaning step and the finish polishing step.

10. The method for manufacturing a glass substrate for information recording medium according to claim 8 , wherein the difference (SiO 2 −Al 2 O 3 ) obtained by subtracting an Al 2 O 3 content from an SiO 2 content in the alkali aluminosilicate glass is 45% by mole or more and less than 50% by mole.

11. The method for manufacturing a glass substrate for information recording medium according to claim 10 , wherein the alkali aluminosilicate glass has a composition of from 60% by mole or more and less than 63% by mole of SiO 2 , from 12.5 to 15% by mole of Al 2 O 3 , from 18 to 22% by mole of Li 2 O+Na 2 O+K 2 O, from 0 to 6% by mole of MgO+CaO+SrO+BaO, provided that SiO 2 +Al 2 O 3 +Li 2 O+Na 2 O+K 2 O+MgO+CaO+SrO+BaO is 90% by mole or more.

12. The method for manufacturing a glass substrate for information recording medium according to claim 1 , wherein in the cleaning step, the circular glass plate is dipped in the cleaning liquid at 500° C. or higher and lower than 600° C. for 25 minutes or more and 30 minutes or less, the cleaning liquid at 600° C. or higher and lower than 700° C. for 15 minutes or more and 30 minutes or less, or the cleaning liquid at 700° C. or higher and 1000° C. or lower for 5 minutes or more and 30 minutes or less.

13. The method for manufacturing a glass substrate for information recording medium according to claim 1 , wherein in the finish polishing step, a root mean square roughness (Rms) of the main surface of the circular glass plate is regulated to 0.15 nm or less.

14. The method for manufacturing a glass substrate for information recording medium according to claim 1 , wherein a cleaning step of cleaning the circular glass plate with an alkaline detergent having a pH of 10 or more is included after the finish polishing step.

15. The method for manufacturing a glass substrate for information recording medium according to claim 1 , wherein the detergent rinsing step comprises rinsing with an alkaline detergent.

16. The method for manufacturing a glass substrate for information recording medium according to claim 1 , wherein the detergent rinsing step comprises rinsing with an acidic detergent.