Patent ID: 7867930

Claim:
Process for the preparation of a lithium silicate glass ceramic wherein lithium disilicate is the main crystalline phase comprising the following components: Component wt.- % SiO 2 64.0-75.0 Li 2 O 13.0-17.0 K 2 O 2.0-5.0 Al 2 O 3 0.5-5.0 Nucleating agent 2.0-5.0 Me(II)O 0-3.0 and which comprises less than 0.1 wt. % of ZnO, with Me(II)O being selected from at least one of CaO, BaO, MgO and SrO which comprises (a) producing a starting glass containing the components of the glass ceramic, (b) subjecting the starting glass to a first heat treatment at a first temperature to give a glass product which contains nuclei suitable for forming lithium metasilicate crystals, (c) subjecting the glass product to a second heat treatment at a second temperature which is higher than the first temperature to obtain the lithium silicate glass ceramic with lithium metasilicate as the main crystalline phase, and further subjecting the lithium silicate glass ceramic of step (c) to a third heat treatment at a third temperature of 830 to 880° C. for a period of 10 to 60 minutes.