| 摘要 |
Effective and long lasting defoamer compositions are prepared by admixing an organopolysiloxanes, a hydrophilic silica, a hydrophobic silica, optionally an organopolysiloxanes resin, and optionally a water insoluble inorganic compound, at a temperature of 50° C. to 250° C. until the viscosity of the composition has decreased to at least half its original viscosity prior to heating. |
| 主权项 |
1. A method for producing defoamer compositions comprising hydrophobic silica, comprising:
(1) providing a mixture comprising (A) organopolysiloxanes(s) having a viscosity of 500 to 20,000 mm2/s at 25° C. and 1013 hPa, and comprising units of the formula (I)
Ra(R1O)bSiO(4-a-b)/2 (I), in which R are each identical or different and denote a monovalent, optionally substituted hydrocarbon radical having 1-30 carbon atoms or a hydrogen atom, R1 are each identical or different and denote hydrogen or a monovalent hydrocarbon radical having 1-4 carbon atoms, a is 0, 1, 2 or 3, and b is 0, 1, 2 or 3, with the proviso that the sum a+b is ≦3 and in more than 50% of all the units of the formula (I) in the organopolysiloxane (A), the sum a+b is 2, and the hydroxyl content is from 30 ppm to 500 ppm by weight, the viscosity of the organopolysiloxanes (A) being determined by the number of units of the formula (I), (B) hydrophilic silica(s) having a BET surface area of 100-400 m2/g, the hydrophilic silicas being present in amounts of 1 to 10 parts by weight, based on 100 parts by weight of organopolysiloxanes (A), (C) hydrophobic silica(s) having a BET surface area of 50-200 m2/g, the hydrophobic silicas being present in amounts of 1 to 10 parts by weight, based on 100 parts by weight of organopolysiloxanes (A), (D) optionally, organopolysiloxane resin(s) comprising units of the formula
R2e(R3O)fSiO(4-e-f)/2 (II), in which R2 has the definition of R, and R3 has the definition of R1, e is 0, 1, 2 or 3, and f is 0, 1, 2 or 3, with the proviso that the sum e+f is ≦3 and in less than 50% of all the units of the formula (II) in the organopolysiloxane resin, the sum e+f is 2, and optionally (E) water-insoluble organic compound(s), (2) heating the mixture provided in (1) at a temperature of 50-250° C., until the viscosity of the mixture has a value of less than 50%, of the measured viscosity which the mixture had prior to heating, the viscosity measured using a cone/plate viscometer at a temperature of 25° C. and a shear rate of 1/s, and (3) subsequent to the in situ hydrophobization of the hydrophilic silicas carried out in (2) in the presence of the hydrophobic silicas, optionally admixing (F) organopolysiloxanes which are different from (A). |
