Patent ID: 7871948

Claim:
Process for the preparation of a lithium silicate glass ceramic wherein lithium metasilicate 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 ZrO 2 0.1-4.0 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, and (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.