Fast ultraviolet radiation curing silicone composition

Claim 1

A composition having a stable viscosity, which increases to less than two fold, after the composition has been heated at 100°C for 24 hours and being curable by ultraviolet radiation comprising a mixture of (A) alkenyl functional, linear triorganosiloxy endblocked polydiorganosiloxane having a degree of polymerization of 30 to 1,000 where each silicon-bonded organic radical is selected from vinyl, methyl, phenyl, 3,3,3,-trifluoropropyl, ethyl, cyclohexenyl, allyl, and silacyclopentenyl, and having per molecule at least two silicon-bonded organic radicals selected from vinyl, cyclohexenyl, allyl, and silacyclopentenyl, (B) mercapto functional crosslinker which is at least one material selected from mercapto functional polyorganosiloxanes and mercapto organic compounds, said mercapto functional polyorganosiloxanes are represented by the general formula wherein each R is selected from mercaptoalkyl radicals having from 2 to 6 carbon atoms per radical; each R' is selected from methyl, phenyl, 3,3,3-trifluoropropyl, and ethyl; and each R" is selected from the radicals of R and R'; and each R'" is selected from methyl and phenyl, on the average there being per molecule at least two mercaptoalkyl radicals, x is 0 or greater, y is 0 or greater, and the amount and kind of organic radicals represented by R, R', R", and R'" being of such a nature as to make (A) and (B) compatible, and said mercapto organic compounds have at least two mercapto groups per molecule, consisting of atoms of sulfur, carbon, and hydrogen, and optionally oxygen, having a molecular weight less than 1,000, and being of such a nature as to make (A) and (B) compatible, and there being in said composition from 0.5 to 1.5 total alkenyl radicals per mercapto group, (C) photosensitizer, (D) an amine as storage stabilizer in an amount of from 0.01 to 1.5 weight percent based on the weight of the composition.