Method of Rendering Translucent Silicone Rubber Articles Transparent

摘要

1,189,270. Coated rubber. DOW CORNING CORP. 1 Oct., 1968 [30 Oct., 1967], No. 46493/68. Heading B2E. [Also in Division C3] Articles of cured silicone rubber rendered translucent by surface imperfections have their transparency restored by coating with a mixture of (1) a polysiloxane of formula: (in which each R and R1 is a phenyl or methyl radical, at least 80 mole percent of the R1 groups being methyl; n has a value such that the viscosity is at least 500 cs. at 25‹C., (2) 5 to 50% by weight based on the total weight of (1) and (2) of a copolymer of SiO 2 , (CH 3 ) 3 SiO 0.5 and (CH 3 ) 2 CH 2 =CHSiO 0.5 siloxane units, in which copolymer there is 1.5-3.5 percent by weight vinyl groups based on the weight of (2) and the ratio of total (CH 3 ) 3 SiO 0.5 and (CH 3 ) 2 =CHSiO 0 . 5 to SiO 2 units is in the range 0.6:1 to 1:1, (3) a compound compatible with (1) and (2) which is a siloxane containing 0.1-0.7 percent by weight siliconbonded hydrogen atoms, the remaining valences of the silicon atoms in (3) being satisfied by phenyl or methyl radicals, there being at least 2 silicon-bonded hydrogen atoms per molecule, and in (3) any hydrocarbon radicals attached to SiH silicon being essentially all methyl radicals, the amount of (3) being such that there is 0.7 moles-2.5 moles of SiH per mole of vinyl radicals in (1) and (2), and (4) a curing catalyst for the coating composition, and thereafter curing the coating composition on the silicone rubber. The catalyst may be a platinum catalyst, e.g. finely divided platinum, chloroplatinic acid, platinum chloride, complexes of platinum with organic compounds such as olefins. The coating composition can be applied by dipping, spraying or brushing. The resulting transparent articles can be used as face masks, eye pieces for masks and for gaskets for automobiles, decorative purposes. The coating composition can also contain additional vinyl-containing siloxanes, ultra-violet absorbers.