CURABLE ORGANOPOLYSILOXANE COMPOSITIONS

摘要

1473371 Silicone rubbers containing treated silicas WACKER-CHEMIE GmbH 30 Aug 1974 [30 Aug 1973] 38061/74 Heading C3T A free-radical curable organopolysiloxane composition is obtained by mixing with a polydiorganosiloxane a silica which has been treated with an organosilicon compound, the silica having a surface area of at least 50 m2/g. and having its bulk density increased by mechanical treatment before or during the treatment with the organisilicon compound. Suitable densifying means include ball mills, tube mills, cone mills, vibration mills, roll mills, friction roll mills, rollers and edge runners. The original bulk density is typically 20-85 g.p.l. and is increased to 120-500 g.p.l.; after the initial treatment and before mixing with the polysiloxane the SiO 2 may be reduced in bulk density, optionally in the presence of further organosilicon compound, e.g. to 20-85 g.p.l. again. The organosilicon compound may amount to 3-25 wt. per cent of the silica and the treatment may be carried out in the presence of 0À3-3 wt. per cent (of the SiO 2 ) of water, or of a catalyst, e.g. HCl, an amine, or a metal compound. The treated silica preferably amounts to 20-65 wt. per cent of the curable composition. Suitable curing means are organic peroxy and azo compounds, and high-energy radiation. In the Examples 200 g of pyrogenic SiO 2 of 200 m2/g and bulk density 65 g.p.l. is ball milled with 15 g Me 3 SiOEt and 2 g H 2 O under HCl for 2 hours to a bulk density of 280 g.p.l.; 40 or 120 g of the product are blended with 100 g of a trimethylsilyl - terminated polydimethylsiloxane containing 0À1 mole per cent MeViSiO units, of 106 cS/25‹ C., and the composition is cured with benzoyl peroxide.