Silicone pressure-sensitive adhesive process and product thereof

A method of making a silicone pressure-sensitive adhesive composition possessing improved stability upon aging which comprises the steps of:

• (I) mixing
• (A) from 40 to 70 inclusive parts by weight of at least one benzene-soluble resin copolymer containing silicon-bonded hydroxyl radicals and consisting essentially of R.sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units in a mole ratio of from 0.6 to 0.9 R.sub.3 SiO.sub.1/2 units for each SiO.sub.4/2 unit present,
• (B) from 30 to 60 parts by weight of at least one polydiorganosiloxane consisting essentially of ARSiO units terminated with endblocking TRASiO.sub.1/2 units, each said polydiorganosiloxane having a viscosity of from 100 centipoise to 30,000,000 centipoise at 25.degree. C., and each T is R-- or X--,
• (C) a sufficient amount of at least one organosilicon endblocking agent capable of generating an endblocking triorganosilyl unit selected from the group consisting of ZR.sub.2 Si-- units, CH.sub.3 Z'-- units, RZ"-- units and Z"'R.sub.2 Si units to provide a 1:0.8 to 1:3 mole ratio of total silicon-bonded hydroxyl and X radicals present in said (A) and (B) to total endblocking triorganosilyl units provided by all endblocking agent present, said agent being selected from the group consisting of ZR.sub.2 SiY, (ZR.sub.2 Si).sub.q D, CH.sub.3 Z'Y, (CH.sub.3 Z').sub.2 O, RZ"Y', (RZ").sub.2 O and Z"'R.sub.2 SiY',
• (D) optionally, an additional catalytic amount of a mild silanol condensation catalyst, and
• (E) when necessary, an effective amount of an organic solvent which is inert with respect to (A), (B), (C), and (D) to reduce the viscosity of a mixture of (A), (B), (C), and (D), and
• (II) condensing the mixture of (A), (B), (C) and (D) at least until a substantial amount of the endblocking triorganosilyl units have reacted with the silicon-bonded hydroxyl radicals and X radicals of said (A) and (B),
• wherein each R is a monovalent organic radical selected from the group consisting of hydrocarbon radicals of from 1 to 6 inclusive carbon atoms, each X radical is selected from the group consisting of HO--, H-- and R'O-- radicals, each R' is an alkyl radical of from 1 to 4 inclusive carbon atoms, each Y radical is a monovalent hydrolyzable organic radical or HO--, each Y' is HO-- or a monovalent hydrolyzable organic radical free of nitrogen, each A radical is selected from the group consisting of R-- and halohydrocarbon radicals of from 1 to 6 inclusive carbon atoms, each Z radical is A-- or QR"--, each R" is a divalent alkylene radical of from 1 to 6 inclusive carbon atoms, each Q is an organofunctional monovalent radical selected from the group consisting of RCOE', RE'OC--, NC--, R'E'--, HO--, G.sub.2 N--, HO(R"O).sub.n --, and G.sub.2 NCH.sub.2 CH.sub.2 NG--, where E' is --O--, --NG-- or --S--, n has a value of from 1 to 6,
• Z' is ##STR8## Z" is ##STR9## Z"' is selected from the group consisting of HSR"--, HSCH.sub.2 CH.sub.2 NGR"-- and HOCH.sub.2 CH.sub.2 SR"-- radicals, each G is R-- or H--, D is a divalent or trivalent radical capable of being hydrolyzed to release said endblocking silyl units and q has a value of 2 when D is a divalent radical and q has a value of 3 when D is a trivalent radical.