Patent ID: 6986268

Claim:
A method for preparing a plate glass by cooling a molten glass plate having a width of L cm, comprising: 1) gradually increasing the temperature gradient between a maximum temperature point set at the center part and a minimum temperature point set at 0.005 L cm away from the end part toward the center on a horizontal line across the width of the plate glass from 0 to 0.10° C./mm while the glass is in a fluid state, 2) gradually decreasing said temperature gradient from 0.10 to 0.03° C./mm while the glass changes from a fluid state into a glassy state, 3) gradually increasing said temperature gradient from 0.03 to 0.10° C./mm until the transition into a glassy state is completed, and 4) gradually decreasing said temperature gradient while the glass is in a glassy state, wherein the difference between the final temperature gradient values of steps 2) and 3) is adjusted within the range of 0.01 to 0.04° C./mm.