Natural oxidic or silicate filler modified on the surface, a process for its production

Claim 1

A process of preparing a surface modified natural oxidic or silicate filler which comprises (a) emulsifying in a water insoluble organosilicon compound of the formula [R.sup.1.sub.n (RO).sub.3-n Si-(Alk).sub.m -(AR).sub.p ].sub.2 [S].sub.x (I) where R is an alkyl group having 1 to 4 carbon atoms, or is a C 1 -C 4 -alkyl-C 1 -C 4 alkoxy group or a phenyl group and R 1 is an alkyl group having 1 to 4 carbon atoms or the phenyl group, n is 0, 1, or 2, Alk is a divalent straight or branched hydrocarbon group having 1 to 6 carbon atoms, m is 0 or 1, Ar is an arylene group having 6 to 12 carbon atoms in the rings, p is 0 or 1 with the proviso that p and m cannot simultaneously be zero, and x is a number from 2 to 8, (b) with stirring mixing this emulsion with an aqueous suspension of a finely divided oxidic or silicate filler or a mixture of such fillers at a temperature of 10° to 50° C., (c) heating the mixture to a temperature of 50° to 100° C., and (d) after 10 to 120 minutes, filtering off the modified filler and drying the suspension at a temperature of 100° to 150° C., or spray drying the suspension.