Silicone-based antifoam compositions cross-reference to related applications

A method of preparing a silicone based antifoam in the form of an emulsion, said emulsion having a dispersed phase and a continuous phase, said dispersed phase being a secondary silicone composition and said continuous phase being a nonpolar organic medium selected from the group consisting of polyisobutylene and mineral oil, said method comprising the steps of:

• (I) preparing a primary silicone composition (A) by
• 1. reacting, at a temperature of 50.degree. C. to 300.degree. C., a mixture comprising:
• (i) 1 to 100 parts by weight of a diluent selected from the group consisting of polydiorganosiloxane, polyisobutylene and mineral oil;
• (ii) 5 to 100 parts by weight of a polyorganosiloxane having a viscosity of 200 to about 100 million mm.sup.2 /s at 25.degree. C. expressed by the general formula R.sup.1.sub.a (R.sup.2 O).sub.b SiO.sub.(4-a-b)/2 in which R.sup.1 is a monovalent hydrocarbon or halogenated hydrocarbon group having 1 to 10 carbon atoms, R.sup.2 is hydrogen or a monovalent hydrocarbon group having 1 to 10 carbon atoms, a has an average value of 1.9 to 2.2 and b has a sufficiently large value to give at least one --OR.sup.2 group in each molecule, at least one such --OR.sup.2 group being present at the end of the molecular chain;
• (iii) 0.5 to 20 parts by weight for every 100 parts by weight of the combined weight of components (i) and (ii) of at least one silicon compound selected from the group consisting of
• (a) an organosilicon compound of the general formula R.sup.3.sub.c SiX.sub.4-c in which R.sup.3 is a monovalent hydrocarbon group having 1 to 5 carbon atoms, X is selected from a halogen atom or a hydrolyzable group and c has an average value of one or less,
• (b) a partially hydrolyzed condensate of said compound (a),
• (c) a siloxane resin comprising (CH.sub.3).sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units wherein the ratio of (CH.sub.3).sub.3 SiO.sub.1/2 units to SiO.sub.4/2 units is 0.4:1 to 1.2:1, or
• (d) a condensate of said compound (c) with said compound (a) or (b);
• (iv) a catalytic amount of a first condensation catalyst;
• and
• 2. neutralizing the first condensation catalyst;
• (II) mixing, under conditions of shear, the components comprising:
• (A) about 5 to 25 weight parts of the primary silicone composition prepared in step (I);
• (B) about 10 to 50 weight parts of a polydiorganosiloxane having condensable terminal groups and a viscosity of about 10 to 50,000 mm.sup.2 /sec at 25.degree. C., in the presence of
• (C) a catalytic amount of a second condensation catalyst;
• (D) about 25 to 80 weight parts of a nonpolar organic medium selected from the group consisting of polyisobutylene and mineral oil, per 100 parts of the combined weights of (A), (B) and (D);
• said mixing step (II) causing reaction between components (A) and (B), thus forming said secondary silicone composition of said dispersed phase of said emulsion;
• said nonpolar organic medium form said continuous phase of said emulsion.