Patent ID: 6609394
Filing Date: 2003-08-26
Classification: C03B,C03C

Abstract:
A method for producing a toughened glass plate comprising the steps of:carrying out air-quench toughening for quenching a glass plate heated to near a softening point thereof to thereby generate compressive stress in the surface layers of the glass plate; lowering the temperature of the toughened glass plate to ambient temperature; and elevating the temperature of the glass plate from ambient temperature to a predetermined temperature to thereby cause phase transformation of nickel sulfide (NiS) contained as a molten impurity in the glass plate from &agr;-NiS (&agr; phase) to &bgr;-NiS (&bgr; phase) concomitant with expansion of the volume thereof, resulting in compulsory breakage of the glass plate for removing defective products, characterized in that the predetermined temperature and a temperature elevation rate to the predetermined temperature satisfy any one of the following conditions: the temperature elevation rate is about 3Â° C./minute, and the predetermined temperature is in the range of 170-320Â° C.; the temperature elevation rate is about 5Â° C./minute, and the predetermined temperature is in the range of 180-320Â° C.; the temperature elevation rate is about 6Â° C./minute, and the predetermined temperature is in the range of 185-325Â° C.; the temperature elevation rate is about 20Â° C./minute, and the predetermined temperature is in the range of 235-345Â° C.; the temperature elevation rate is about 40Â° C./minute, and the predetermined temperature is in the range of 270-350Â° C.; or the temperature elevation rate is about 50Â° C./minute, and the predetermined temperature is in the range of 285-350Â° C.