FLUXING AGENT MODIFIED PIGMENTARY COMPOSITIONS

摘要

1475721 Pigmentary compositions T H FERRIGNO 17 May 1974 [5 July 1973] 22140/74 Heading C4A A pigmentary composition comprises calcined agglomerated particles, the agglomerates comprising: (a) from 30 to 98À5% by weight of anhydrous silicate having an average particle size of less than 100 microns, (b) from 1 to 10% by weight of an inorganic binder selected from one or more of a soluble silicate, a sodium polyphosphate and an expanding lattice montmorillonite, and (c) from 0À5 to 10% by weight of a fluxing agent which is a metal oxide or metal oxide complex which melts at a temperature below the melting point of the anhydrous silicate, and the agglomerates having a specific gravity at least 5% below that of constituents (a), (b) and (c). The term "soluble silicate" means an alkali metal silicate wherein the mole ratio of SiO 2 to M 2 O, where M is the alkali metal, is from 1À65 : 1 to 3À88 : 1. The pigmentary composition may be prepared by mixing the anhydrous silicate, 0 to 40% by weight of a hydrous silicate, both silicates being in the form of particles having an average size in the range of 2 to 20 microns, the fluxing agent and the inorganic binder, forming the materials into agglomerates each containing a plurality of mineral particles and having a size ranging from 20 microns to 1 centimetre, drying the agglomerates to reduce the free water content thereof to 0 to 10% by weight of the agglomerates, and thereafter calcining the agglomerates below the melting points of both the hydrous and the anhydrous silicates. Suitable fluxing agents are boric oxide or a compound thereof, e.g. borax, lead oxide, barium oxide or a metal oxide complex which is a glass or frit. In the examples, the compositions are prepared from feldspar, silica, borax glass, boric acid, bentonite, a glassy polyphosphate, a water-fractionated kaolinite of the phyllosilicates and zirconium silicate.