Method for preparing silicone composition
A silicone composition comprising an organopolysiloxane containing at least two silicon-bonded alkenyl and/or hydroxyl groups in the molecule and a filler having a BET surface area of at least 10 m 2 /g is prepared by kneading the components in a batchwise high-shear mixer. The mixer includes a rotatable mixing pan ( 1 ), a high-speed rotation agitator ( 3 ) disposed eccentrically in the pan, and a stationary scraper ( 4 ) disposed in the pan for creating a vertical counterflow.
1. A method for preparing a silicone composition comprising an organopolysiloxane containing at least two silicon-bonded alkenyl groups and/or at least two silicon-bonded hydroxyl groups in the molecule and a filler having a BET surface area of at least 10 m 2 /g as essential components,
the method comprising the step of kneading the components in a batchwise high-shear mixer, the mixer comprising a mixing pan which itself rotates, a high-speed rotation agitator disposed eccentrically in the pan, and a stationary scraper disposed in the pan for creating a vertical counterflow.
2. The method of claim 1 wherein the kneading step includes
mixing a 30 to 100% by weight fraction of the organopolysiloxane and the entirety of the filler in the mixing pan while rotating the mixing pan at 10 to 100 rpm and the agitator at 100 to 1,000 rpm,
heat treating the mixture at 120 to 270° C. while rotating the mixing pan at 10 to 100 rpm and the agitator at 200 to 4,000 rpm, and
feeding the remainder of the organopolysiloxane, if any, to the mixture prior to and/or subsequent to the heat treatment.
3. The method of claim 2 wherein the heat treatment is under a reduced pressure of up to 300 Torr.
4. The method of claim 1 wherein a dispersant for the filler is fed during the kneading step.
5. The method of claim 4 wherein the dispersant is one or more compound selected from silazane compounds and silanol-containing compounds.
6. The method of claim 5 wherein the dispersant is 1,1,1,3,3,3-hexamethyldisilazane.
7. The method of claim 5 wherein the dispersant is a compound of HO(SiR 1 2 O) n H wherein R 1 is a monovalent hydrocarbon group of 1 to 10 carbon atoms and n is an integer of 1 to 50.
8. The method of claim 1 wherein the filler is fumed silica, precipitated silica or a mixture thereof.
9. The method of claim 8 wherein the composition comprises 100 parts by weight of the organopolysiloxane and 10 to 130 parts by weight of the silica filler.