Hydrophobic pyrogenically prepared silica prepn. - by treating the silica with an organo-silicon cpd. as hydrophobicising agent, useful as filler for elastomers

摘要

Pyrogenically prepd. silicic acid is rendered hydrophobic by stirring the silicic acid into a soln. of a hydrophobing agent in an organic solvent; homogenising the mixt.; admixing further pyrogenically prepd. silicic acid; tempering the mixt.; and post-treating the tempered product in a ball mill. Used as reinforcing filler material for compsns., curable to elastomers, based on diorganopolysiloxanes, in amts. of 5-50, pref. 5-40%, w.r.t. the curable compsn. the filler is partic. advantageous in two-component mixtures vulcanisable at room temp. by the cross-linking of polydiorganosiloxanes contg. terminal silanol gps. with polyfunctional cross-linking agents. There is no thickening of the liquid when the filler is used in high proportions.