Material for information recording medium substrate, information recording medium substrate, information recording medium, and method for manufacturing them

A method for manufacturing multiple pieces of a disklike glass material, a sheet thickness of said pieces of disklike glass material varying within a range, comprising:

• preparing a glass melt by heating a starting material to melt while maintaining at least one of an Fe ion content and a Cr ion content in the starting material at a constant level so that an amount of variation in at least one of the Fe ion content and the Cr ion content in the glass melt is kept to within ±50 percent;
• the successive molding of multiple pieces of disklike glass material from the glass melt,
• wherein in the course of molding multiple pieces of disklike glass material comprised of glass containing 0.1 to 100 ppm of at least one infrared radiation-absorbing ion of a metal selected from the group consisting of Fe, Cu and Cr, variation over time in the concentration of the infrared radiation-absorbing ions contained in the glass melt being molded into said pieces of disklike glass material is controlled to suppress variation in the sheet thickness of said multiple pieces of sheetlike glass material, and
• wherein the molding of the glass melt into disklike glass materials comprises the step of press molding glass melt to obtain a disklike glass material.

A method for manufacturing information recording medium-use glass substrates, comprising:

• preparing a glass melt by heating a starting material to melt while maintaining an Fe content in the starting material at a constant level so that an amount of variation in the Fe ion content in the glass melt be kept to within ±50 percent;
• manufacturing multiple pieces of a disklike glass material by the successive molding of multiple pieces of disklike glass material from the glass melt, a sheet thickness of said pieces of disklike glass material varying within a range, wherein the Fe ion content in the disklike glass material ranges from 0.1 to 100 ppm and the molding of the glass melt into disklike glass materials comprises (1) controlling variation over time in the concentration of infrared radiation-absorbing ions contained in the glass melt being molded into said pieces of disklike glass material so that the variation in the sheet thickness of said multiple pieces of disklike glass material falls within a range of ±15 percent of a reference value, said reference value being the median between the maximum value and the minimum value of the sheet thickness of 1,000 pieces of said glass material, and (2) press molding the glass melt to obtain a disklike glass material;
• forming a hole in a center of said disklike glass material;
• processing the inner and outer perimeters thereof;
• and
• grinding and/or polishing the main surfaces thereof to obtain an information recording medium-use glass substrate.

A method for manufacturing information recording medium-use glass substrates, comprising:

• preparing a glass melt by heating a starting material to melt while maintaining at least one of an Fe ion content and a Cr ion content in the starting material at a constant level so that an amount of variation in at least one of the Fe ion content and the Cr ion content in the glass melt is kept to within ±50 percent;
• manufacturing multiple pieces of a disklike glass material by the successive molding of multiple pieces of disklike glass material from the glass melt, a sheet thickness of said pieces of disklike glass material varying within a range, wherein in the course of molding multiple pieces of disklike glass material comprised of glass containing 0.1 to 100 ppm of at least one infrared radiation-absorbing ion of a metal selected from the group consisting of Fe, Cu and Cr, variation over time in the concentration of the infrared radiation-absorbing ions contained in the glass melt being molded into said pieces of disklike glass material is controlled to suppress variation in the sheet thickness of said multiple pieces of sheetlike glass material and the glass melt is press molded to obtain a disklike glass material;
• forming a hole in a center of said disklike glass material;
• processing the inner and outer perimeters thereof;
• and
• grinding and/or polishing the main surfaces thereof to obtain an information recording medium-use glass substrate.