Mechanical inversion process for marking silicone oil-in-water emulsions
View Patent ↗High viscosity silicone compositions such as silicone gums, silicone rubbers, silicone elastomers, and silicone resins, are emulsified by mechanical inversion in which silicone water-in-oil (W/O) emulsions are inverted to silicone oil-in-water (O/W) emulsions. Silicone resins with a viscosity of about one billion centistoke (mm 2 /s), i.e., 1,000,000,000 centistoke (mm 2 /s) have been emulsified. These silicone O/W emulsions are useful in personal care products where they are capable of providing improved aesthetics. They are also useful in products used in the paper industry and medical industry. The silicone O/W emulsions are easier to handle than the high viscosity silicone in the emulsion, which enables the emulsions to mixed with other emulsions or other water-soluble ingredients.
1. A method of making a silicone oil-in-water emulsion comprising the steps of:
(i) forming a homogeneous oil phase containing a silicone gum, a silicone rubber, a silicone elastomer, a silicone resin, or a mixture thereof; the silicone in the homogeneous oil phase having a viscosity of at least 100,000,000 (100 million) centistoke (mm 2 /s) to 5,000,000,000 (5 billion) centistoke (mm 2 /s); (ii) mixing one or more surfactants with the homogeneous oil phase; (iii) adding water to the homogeneous oil phase to form a water-in-oil emulsion containing a continuous phase and a dispersed phase, the water being added in an amount of about 0.5-10 percent by weight based on the weight of the silicone in the homogeneous oil phase; (iv) applying high shear to the water-in-oil emulsion in a twin-screw extruder having a length to diameter L/D ratio of at least 15, to cause inversion of the water-in-oil emulsion to an oil-in-water emulsion; and (v) diluting the oil-in-water emulsion by the addition of water; the method being carried out in the absence of a solvent other than solvents present in the silicone gum, silicone rubber, silicone elastomer, or silicone resin in (i).
2. A method according to claim 1 wherein the silicone in the homogeneous oil phase has a viscosity of at least 200,000,000 (200 million) centistoke (mm 2 /s) to 2,000,000,000 (2 billion) centistoke (mm 2 /s).
3. A method according to claim 1 wherein the silicone in the homogeneous oil phase has a viscosity of at least 1,000,000,000 (1 billion) centistoke (mm 2 /s).
4. A method according to claim 1 wherein the silicone in the homogeneous oil phase is a silicone resin.
5. A method according to claim 1 wherein the amount of water added in (iii) is about 1-5 percent by weight based on the weight of the silicone in the homogeneous oil phase.
6. A method according to claim 1 wherein the L/D ratio of the twin-screw extruder is 15-60.
7. A silicone oil-in-water emulsion prepared according to the method defined in claim 1 .
8. A personal care product, medical product, coating product, household care product, or product for application to paper, containing the silicone oil-in-water emulsion prepared according to claim 7 .