Patent ID: 7213415

Claim:
A method for producing a toughened glass plate comprising the steps of: air-quench toughening a glass plate comprising α-NiS, said toughening comprising cooling the plate from a temperature near its softening point to a lower temperature to thereby generate compressive stress in the surface layers of the glass plate, said lower temperature being a temperature at which the α-NiS is stable; and cooling the plate to a predetermined temperature and maintaining it thereat for a predetermined time to thereby cause phase transformation of the α-NiS to β-NiS, resulting in drastic growth of cracks and simultaneous breakage of the glass; wherein the step of air-quench toughening and the step of cooling the plate to the predetermined temperature are performed without cooling the plate to ambient temperature therebetween and wherein the predetermined temperature is 180–280° C. and the predetermined time is 1–20 minutes.