Method for preparing storage stable, one part curable polyorganosiloxane compositions

Claim 1

In a method for preparing a one-part, heat curable organosiloxane composition, said method comprising blending to homogeniety (A) at least one organosiloxane copolymer consisting essentially of from 80 to 96.5 mol percent of (CH 3 ) 2 SiO units, from 2.0 to 10.0 mol percent of CH 3 SiO 1 .5 units, from 1.25 to 6.0 mol percent of (CH 3 ) 3 SiO 0 .5 units and from 0.25 to 4.0 mol percent of (CH 3 ) 2 (CH 2 ═CH)SiO 0 .5 units; (B) an organohydrogensiloxane containing at least two silicon-bonded hydrogen atoms per molecule, no more than one silicon-bonded hydrogen per silicon atom and organic radicals selected from the group consisting of alkyl containing from 1 to 6 carbon atoms per radical, phenyl and 3,3,3-trifluoropropyl, said organohydrogensiloxane providing from 0.7 to 1.2 silicon-bonded hydrogen atoms per silicon-bonded vinyl radical present in said composition; (C) a platinum catalyst in an amount sufficient to promote the reaction of (A) and (B), and (D) a platinum catalyst inhibitor of the formula R 1 2 NR 3 NR 2 2 or R 4 NH 2 in an amount sufficient to impart long term storage stability at temperatures of up to 70° C., where each R 1 is individually selected from alkyl radicals containing from 1 to 4 carbon atoms, R 2 is R 1 or hydrogen, R 3 represents an alkylene radical containing from 2 to 4 carbon atoms, and R 4 represents an alkyl radical containing from 2 to 4 carbon atoms, the improvement consisting essentially of the following sequence of steps: (1) forming a homogeneous mixture of said organohydrogensiloxane, said platinum catalyst and said platinum catalyst inhibitor, (2) aging said mixture for a period of at least 14 days under ambient conditions, and (3) combining the aged mixture with said organosiloxane copolymer to form said curable composition.