METHOD OF MANUFACTURING GLASS BLANK FOR MAGNETIC RECORDING MEDIUM GLASS SUBSTRATE,METHOD OF MANUFACTURING MAGNETIC RECORDING MEDIUM GLASS SUBSTRATE,AND METHOD OF MANUFACTURING MAGNETIC RECORDING MEDIUM

摘要

IN ORDER TO OBTAIN A GLASS BLANK BEING ABLE TO BE FORMED INTO A MAGNETIC RECORDING MEDIUM GLASS SUBSTRATE HAVING EXCELLENT HEAT RESISTANCE BY CARRYING OUT POST—PROCESSING, BEING EXCELLENT IN THICKNESS DEVIATION AND FLATNESS, AND HAVING LITTLE CRACK DEFECT, PROVIDED IS A METHOD OF MANUFACTURING A GLASS BLANK FOR A MAGNETIC RECORDING MEDIUM GLASS SUBSTRATE, INCLUDING: MANUFACTURING A GLASS BLANK BY AT LEAST PRESS MOLDING A FALLING MOLTEN GLASS GOB WITH A PAIR OF PRESS MOLDS BOTH SO AS TO FACE EACH OTHER IN A DIRECTION PERPENDICULAR TO A DIRECTION IN WHICH THE MOLTEN GLASS GOB FALLS, IN WHICH: THE MOLTEN GLASS GOB IS FORMED OF A GLASS MATERIAL HAVING A GLASS TRANSITION TEMPERATURE OF 600°C OR MORE; AND WHEN THE PRESS MOLDING IS CARRIED OUT SO THAT THE MOLTEN GLASS GOB IS COMPLETELY EXTENDED BY PRESSURE AND MOLDED INTO A FLAT GLASS BETWEEN PRESS-MOLDING SURFACES OF THE PAIR OF PRESS MOLDS, AT LEAST A REGION IN CONTACT WITH THE FLAT GLASS IN EACH OF THE PRESS—MOLDING SURFACES OF THE PAIR OF PRESS MOLDS FORMS A SUBSTANTIALLY FLAT SURFACE. ALSO PROVIDED ARE A METHOD OF MANUFACTURING A MAGNETIC RECORDING MEDIUM GLASS SUBSTRATE AND A METHOD OF MANUFACTURING A MAGNETIC RECORDING MEDIUM EACH USING THE METHOD OF MANUFACTURING A GLASS BLANK FOR A MAGNETIC RECORDING MEDIUM GLASS SUBSTRATE.