Method of manufacturing thin-plate glass article, method of manufacturing glass substrate for information recording medium, and method of manufacturing magnetic recording medium

A method for manufacturing a thin plate-shape glass article utilizing a mold having a lower die forming face and a first and a second opposing molding surfaces, comprising the steps of:

• (a) preheating said lower die forming face and said first opposing molding surfaces to a predetermined preheat temperature;
• (b) delivering to said lower forming face die a charge of molten glass of a predetermined volume to form a glass article of desired shape and dimensions;
• (c) bringing said lower die forming face and said first opposing molding surfaces of said mold into close proximity with each other;
• (d) pressing said charge to transfer heat from said charge of molten glass to form an initial thin plate-shape glass article;
• (e) bringing said lower die forming face and said first opposing molding surfaces of said mold apart with each other when the inside of said initial plage-shape glass article maintains a temperature higher than a glass softening point temperature;
• (f) bringing said lower die forming face and either said first opposing or said second opposing surfaces of said mold into close proximity with each other;
• (g) pressing said initial thin plate-shape glass article to transfer heat from said initial thin plate-shape glass article for warp modification of said initial thin plate-shape glass article;
• (h) bringing said lower die forming face and either said first opposing or said second opposing surfaces of said mold apart with each other when the inside of said initial thin plate shape glass article maintains a temperature higher than said glass transition point temperature;
• and
• (i) removing said thin plate-shape glass article from said lower die forming face.

A method for manufacturing a glass substrate for an information recording medium, comprising the steps of:

• (a) preparing a thin plate-shape glass article with a curvature state therein obtained by pressing a charge of molten glass;
• (b) grinding a main surface of said thin plate-shape glass article;
• and
• (c) further polishing the main surface of said thin plate-shape glass article;
• said step (b) including the steps of:
• (b1) flattening said thin plate-shape glass article in such a manner that said curvature state is maintained without being deformed;
• and
• (b2) grinding the main surface of said flattened thin plate-shape glass article to remove a predetermined amount of thickness.

A method for manufacturing a glass substrate for an information recording medium, comprising the steps of:

• (a) preparing a thin plate-shape glass article with a curvature state therein manufactured by pressing at least with a pair of mold dies;
• (b) grinding a main surface of said thin plate-shape glass article;
• and
• (c) further polishing the main surface of said thin plate-shape glass article;
• said step (b) including the step of:
• flattening said thin plate-shape glass article by setting a load pressure of a lapping machine to a value enabling to maintain said curvature state without being deformed.

A method for manufacturing a thin plate-shape glass article utilizing a mold having a lower die forming face and opposing molding surfaces and a pressing die having a predetermined pattern therein, comprising the steps of:

• (a) preheating said lower die forming face and opposing molding surfaces to a predetermined heat temperature;
• (b) delivering to said lower die forming face a charge of molten glass of a predetermined volume to form a glass article of desired shape and dimensions;
• (c) bringing said lower die forming face and opposing molding surfaces of said mold into close proximity with each other;
• (d) pressing said charge to transfer heat from said charge of molten glass to form an initial thin plate-shape glass article;
• (e) bringing said lower die forming face and opposing molding surfaces of said mold apart with each other when the inside of said initial thin plate-shape glass article maintains a temperature higher than a glass transition point temperature;
• (f) bringing said lower die forming face of said mold and said pressing die into close proximity with each other;
• (g) pressing said initial thin plate-shape glass article to transfer heat from said initial thin plate-shape glass article to reduce a temperature difference between the upper and the lower surfaces of said initial thin plate-shape glass article when the inside of said initial thin plate-shape glass article maintains a temperature higher than said glass transition point temperature for warp modification of said initial thin plate-shape glass, article.