Ciba-geigy Corporation

Peter Kartschmaroff

Ewald Forster

Armin Schaffner

Prepolymers of alkali metal silicates and/or alkaline earth metal silicates and metal oxides, which can be used as molding compositions, preferably compression molding compositions, for the production of compression-molding laminates or of insulating sheets, are obtained by a method wherein a mixture of solid alkali metal silicates and/or alkaline earth metal silicates, and/or aqueous solutions of such silicates, with or without addition of water, and of divalent to tetravalent metal oxides, the ratio of metal oxide to silicate in the mixture being from 1:1 to 1:9, expressed in parts by weight of solids, and the homogenized mixture having a water content of from 10 to 50% by weight, based on the total amount of mixture, is allowed to pre-react in the temperature range of 10.degree. to 50.degree. C. until the water content of the mixture has decreased by from 0.1 to 25% by weight and a product which is sufficiently tough and dry to permit comminution is obtained, and this product is comminuted and then heated at temperatures of up to 120.degree. C. until the prepolymer obtained has a water content of from 20 to 2% by weight.

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Arlesheim, Switzerland

Peter Kartschmaroff