| 摘要 |
Powder mixt. (I) for preparing an opaquing agent contains: (a) one or more feldspar frits consisting of several feldspar frits of differing chemical compsn. and having different physical properties; (b) CeO2 as opacifier, opt. other opacifiers; and (c) opt. pigments. Also claimed is a mixt. in paste form contg. at least one (I) and also one or more liquids for imparting a pasty consistency, and opt. auxiliaries. Also claimed is a mixt. in paste form, where the mixing ratio of liquid(s) to (I) is 1:4-1:1. The feldspar frit(s) has a max. grain size below 20 mu m, a d50 of 3-6 mu m and a d90 of 12-16 mu m. The opacifiers are metal oxides, such as SnO2, TiO2 and/or ZrO2. The pigments are coloured metal oxides. The powder mixt. contains, as main components, (by wt.%): 30-65 SiO2, 2-6 Na2O, 3-15 K2O, 5-15 Al2O3, 0.5-10 CaO, 0.5-10 B2O3 and 0.5-50 CeO2. The mixt. also contains up to 50 wt.% TiO2, 9 wt.% ZrO2, and 50 wt.% SnO2. The liquids are water, modelling liquids, dihydric alcohols, glycerin, polyethylene glycols and/or silicone oils. Substances preventing the separation of powder mixt. and liq. (stabilisers) and/or preservatives are added as auxiliaries. The stabilisers are: (a) surface-active metal oxide powders with grain sizes in the nanometre range (5 to 40 nm), e.g. SiO2, aerosils, TiO2-P25, pyrogenic ZrO2, aluminium oxide C; (b) small amounts of organic substances as thickeners in 0-5 wt.%, pref. 0.05-1 wt.%, e.g. cellulose, methyl cellulose and their derivs., gelatine and/or alginates; and/or (c) complexing and/or chelating agents e.g. citric acid, Tween 20, etc.. |
