Method for producing glass substrate for information recording medium

1. A method of producing a glass substrate for an information recording medium, comprising:

a rough polishing step of performing a rough polishing on a glass material containing 0.01 to 2 mass % of cerium oxide;

a washing step of washing the glass material after the rough polishing step, so that the cerium content of the glass material surface becomes 0.125 ng/cm 2 or less; and

a precision polishing step of performing precision polishing on the glass material after the washing step by cyclically using a volume of a slurry of a polishing material containing colloidal silica, wherein

after the washing step, a machining allowance of the glass material in the precision polishing step is 0.2 to 2 μm, and

when the volume of the slurry of the polishing material in the precision polishing step is (a) liters, the number of the glass materials to be polished by cyclically using the volume of the slurry of the polishing material is (b), cerium oxide content of the glass material is (X) mass %, and the machining allowance is (Y) μm, and

Z=Y ×substrate area (cm 2 )×substrate density (g/cm 3 )  (1)

the precision polishing step cyclically uses the volume of the slurry of the polishing material so as to satisfy the following formula:

( X×Z )× b/a< 3 (μg/l)  (2).

2. The method of producing a glass substrate for an information recording medium according to claim 1 ,

wherein the rough polishing step uses cerium oxide as the polishing material.

3. The method of producing a glass substrate for an information recording medium according to claim 1 , wherein the glass material has following composition:

55 mass % to 75 mass % of SiO 2

5 mass % to 18 mass % of Al 2 O 3

1 mass % to 10 mass % of Li 2 O

3 mass % to 15 mass % of Na 2 O

0.1 mass % to 5 mass % of K 2 O,

where a total amount of Li 2 O+Na 2 O+K 2 O is 10 mass % to 25 mass %,

0.1 mass % to 5 mass % of MgO

0.1 mass % to 5 mass % of CaO

0 mass % to 8 mass % of ZrO 2 , and

0.10≦(MgO+CaO)/(Li 2 O+Na 2 O+K 2 O)≦0.80.

4. The method of producing a glass substrate for an information recording medium according to claim 1 , wherein

the glass material is a glass material that contains:

65 mass % to 90 mass % in a total amount of SiO 2 +Al 2 O 3 +B 2 O 2

wherein

45 mass % to 75 mass % of SiO 2

1 mass % to 20 mass % of Al 2 O 3 ,

0 mass % to 8 mass % of B 2 O 3 ,

7 mass % to 20 mass % in a total amount of R 2 O,

wherein R═Li, Na, K,

0.1 mass % to 12 mass % in a total amount of R′O,

wherein R′═Mg, Ca, Sr, Ba, Zn,

0.5 mass % to 10 mass % in a total amount of TiO 2 +ZrO 2 , and wherein

the glass material contains at least one type of polyvalent element selected from a group of V, Mn, Ni, Mo, Sn, Ce and Bi, and

when oxides of the polyvalent elements are respectively V 2 O 5 , MnO 2 , Ni 2 O 3 , MoO 3 , SnO 2 , CeO 2 , and Bi 2 O 3 , a molar ratio of a total amount of oxides of the polyvalent elements relative to a total amount of TiO 2 +ZrO 2 (total amount of oxides of the polyvalent element/(total amount of TiO 2 +ZrO 2 )) is within a range of 0.05 to 0.50.