Abstract: There is provided a silicone rubber composition comprising an organopolysiloxane having a viscosity of at least 250,000 mPa·s at 250C, treated filler, and an organic peroxide curing agent. The composition is substantially free of reinforcing silica fillers and is characterised in that the filler comprises a mixture of aluminium trihydroxide and kaolin in a ratio of from 1:3 to 4:1.

Abstract: A process for making a flowable powdered base suitable for use in the formulation of liquid silicone rubber compositions that can be cured to form silicone elastomers. The process comprises (A) fluidizing a reinforcing silica filler in a high-shear mixer, (B) maintaining the content of the mixer at a temperature below about 60.degree. C. while adding to the mixer a silylating agent, a nitrogen containing compound to facilitate the silylation reaction, and water thereby forming an essentially homogeneous mixture comprising a treated reinforcing silica filler; (C) adding a polydiorganosiloxane having a viscosity of about 0.03 to 300 Pa.s at 25.degree. C. to the mixer and forming a flowable powdered base having an average particle size of from about 1 to 1000 microns, and (D) heating the flowable powdered base under conditions sufficient to remove volatiles.

Abstract: A method for the preparation of hydrophobic fumed silicas which are useful, for example, as reinforcing fillers in rubber compositions. The method comprises two steps, where in the first step an aqueous suspension of fumed silica is contacted with an organosilicon compound in the presence of a catalytic amount of an acid to effect hydrophobing of the fumed silica. In the preferred method the first step is conducted in the presence of a water miscible organic solvent which facilitates hydrophobing of the fumed silica with the organosilicon compound and the fumed silica has a BET surface area greater than 50 m.sup.2 /g. In the second step the aqueous suspension of the fumed silica is contacted with a water-immiscible organic solvent at a solvent to silica weight ratio greater than 0.1:1 to effect separation of the hydrophobic fumed silica from the aqueous phase. In a preferred process the hydrophobic fumed silica has a surface area within a range of about 100 m.sup.2 /g to 750 m.sup.2 /g.

Abstract: A platinum curing organosiloxane composition having improved hysteresis characteristics when cured. The composition requires the presence of a diorganovinylsiloxy terminated polydiorganosiloxane having a viscosity within a range of about 20 Pa.multidot.s to 200 Pa.multidot.s at 25.degree. C. and containing essentially no ethylenically unsaturated hydrocarbon radicals bonded to non-terminal silicon atoms and a diorganovinylsiloxy terminated polydiorganosiloxane having a viscosity within a range of about 0.1 Pa.multidot.s to 200 Pa.multidot.s at 25.degree. C., where from 1 to 5 percent of the non-terminal repeating units of the siloxane comprise a vinyl radical. In addition, the present composition comprises 10 to 30 weight percent of a reinforcing silica filler that has been treated with hexamethyldisilazane and 1,1,3,3-tetramethyl-1,3-divinyldisilazane, and an organohydrogensiloxane resin crosslinker comprising greater than 5 silicon-bonded hydrogen atoms per molecule.

Abstract: A platinum group-metal curing liquid silicone rubber compositions having improved physical properties such as tear and heat-aging, especially at durometers below about 35 and above about 65. The present inventors have unexpectedly discovered that the addition of diorganohydrogensiloxy end-blocked polydiorganosiloxanes and triorganosiloxy end-blocked polydiorganosiloxanes having a viscosity greater than about 10 Pa.cndot.s at 25.degree. C. to liquid silicone rubber compositions can provide for the described improved properties.

Abstract: A method for preparing organopolysiloxane bases with high levels of fillers. The present inventors have found that by mixing the components of the base at a temperature below about 60.degree. C. for a period of time sufficient to effect essentially a homogeneous blend, a base composition is formed which can be further blended with a platinum group metal-containing catalyst, an organohydrogensiloxane, and optionally an inhibitor to form a curable liquid silicone rubber (LSR) composition. The curable LSR composition has improved flow characteristics and improved shelf life when compared to similar materials where the base is prepared at temperatures above about 60.degree. C. The improved flow characteristics allows larger quantities of fillers to be incorporated into the curable LSR composition while still maintaining acceptable flow characteristics.

Abstract: A platinum curing organosiloxane composition having improved hysteresis characteristics when cured. The composition requires the presence of a diorganovinylsiloxy terminated polydiorganosiloxane having a viscosity within a range of about 20 Pa.multidot.s to 200 Pa.multidot.s at 25.degree. C. and containing essentially no ethylenically unsaturated hydrocarbon radicals bonded to non-terminal silicon atoms and a diorganovinylsiloxy terminated polydiorganosiloxane having a viscosity within a range of about 0.1 Pa.multidot.s to 200 Pa.multidot.s at 25.degree. C., where from 1 to 5 percent of the non-terminal repeating units of the siloxane comprise a vinyl radical. In addition, the present composition comprises 10 to 30 weight percent of a reinforcing silica filler that has been treated with hexamethyldisilazane and 1,1,3,3-tetramethyl-1,3-divinyldisilazane, and an organohydrogen siloxane crosslinker comprising at least ten silicon-bonded hydrogen atoms per molecule.