| 摘要 |
The tendency of a silica or alumina filler to induce structure especially in curable organopolysiloxane compositions, is reduced by injecting 5 - 50 parts of volatile lower alkyl or alkenylpolysiloxane (as defined) having a boiling point less than 250 DEG C. into 100 parts of a bulk mass of filler, and allowing the filler and polysiloxane to remain in intimate contact in a sealed container until the polysiloxane is intimately dispersed through the bulk mass. The filler may be fume, precipitated, or aerogel silica, alkoxy-modified silica, or gamma alumina. The siloxane may be injected into the filler in bags through one or more small diameter perforated tubes, or through a single spray head on one or more tubes. The tubes may be slowly withdrawn from the bags, which are resealed and stored for at least 4 days at 25 DEG - 35 DEG C. to produce a polysiloxane coating on the filler. Alternatively, the filler may be sprayed with the polysiloxane during manufacture and then sealed in containers. The polysiloxane has alkyl groups containing 1 or 2 C atoms, and a vapour pressure at 27 DEG C. at least 0,1 mm., and may be chosen from hexamethylcyclotri-, octamethyl cyclotetra-, hexamethyldi-, octamethyltri-, decamethyltetra- and hexaethyltrisiloxanes, methyl hydrogen polysiloxanes of formula (CH3SiOH)p where p is 3 - 5, alkenyl polysiloxanes of formula [(CH2 = CH)CH3SiO]q where q is 3 or 4, and mixtures of methyl polysiloxanes of formula <FORM:0904548/III/1> where r is 0 - 10. Specification 806,563 is referred to.ALSO:Curable organopolysiloxane compositions contain say 10-200% structure-inducing silica or alumina filler which has been coated with a volatile lower alkyl- or alkenylpolysiloxane (see Group III). The curable siloxanes should contain 1,98-2,1 organic groups per Si, which groups may be monovalent hydrocarbon, hydrogenated aryl, and phenyl alkyl radicals, e.g. ethyl-, or methylvinyl-, polysiloxanes. Curing may be effected by heat or high energy electrons, and the composition may include a curing agent, e.g. benzoyl peroxide, bis-(2,4-dichlorobenzoyl)-peroxide, tetiary butyl perbenzoate, say 0,1-8%, a diphenylsilanediol structure additive, and other fillers, e.g. TiO2, lithopone, ZnO, zirconium silicate, iron oxide, diatomaceous earth, sand, or CaCO3. Specification 806,563 is referred to.
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