Mold for glass substrate molding, method for producing glass substrate, method for producing glass substrate for information recording medium, and method for producing information recording medium
Disclosed is a mold for glass substrate molding, which enables to produce a glass substrate having high flatness by a method for producing a glass substrate through press molding of molten glass. Also disclosed is a method for producing a glass substrate by using such a mold. Specifically disclosed is a mold comprising a lower mold having a first molding surface for pressing a molten glass supplied thereto, and an upper mold having a second molding surface for pressing the molten glass against the first molding surface. In the first molding surface, the surface roughness Ra of the peripheral portion which is in contact with the molten glass after pressing is higher than the surface roughness Ra of the central portion which is in contact with the molten glass before pressing.
1. A method of producing a glass substrate by press-shaping molten glass, the method comprising:
supplying molten glass to a first shaping surface formed on a lower mold;
cooling the molten glass supplied onto the first shaping surface while pressing the molten glass between the first shaping surface and a second shaping surface formed on an upper mold so that the molten glass is shaped into a glass substrate;
wherein the first shaping surface includes a central section adapted to contact the molten glass before the molten glass is pressed, and includes a peripheral section adapted to contact the molten glass after the molten glass has been pressed; and
wherein a surface roughness of a peripheral section is greater than a surface roughness of the central section and the molten glass in contact with the greater surface roughness of the peripheral section has a cooling rate faster than the molten glass in contact with the central section, such that the solidification timing of the molten glass in the central and peripheral sections is equalized.
2. The method described in claim 1 , wherein the surface roughness of the central section is 0.05 to 3.00 μm and the surface roughness of the peripheral section is 0.07 to 10.00 μm.
3. The method described in claim 1 , wherein the surface roughness of the peripheral section is 1.5 to 20 times of the surface roughness of the central section.
4. The method described in claim 1 , wherein the glass substrate is a glass substrate for producing a glass substrate for an information recording medium.
5. The method of claim 1 , wherein each of the first shaping surface and the second shaping surface is a flat surface.
6. A method of producing a glass substrate for an information recording medium, comprising:
polishing the glass substrate produced by the method described in claim 1 .
7. A method of producing an information recording medium, comprising:
forming a recording layer on the glass substrate produced by the method described in claim 6 .
8. The method of claim 1 , wherein the surface roughness of the peripheral section is determined such that the glass substrate has a flatness of 20 μm or less.
9. The producing method described in claim 8 , wherein the flatness is 10 μm or less.