Process for the Preparation of a Silicone Pressure-Sensitive Adhesive
Silicone pressure sensitive adhesive (PSA) compositions and methods for their preparation are provided. In one embodiment, PSAs are formed from a silicone polymer mixture by condensation polymerization of low viscosity polyorganosiloxanes in inert solvents and/or silicone fluids, and optionally adding a silicone resin (MQ) during polymerization. The silicone polymer mixture formed may also be mixed with a silicone resin (MQ) and bodying catalyst, and bodying is allowed to continue until the desired reaction product is formed.
1 . A silicone pressure-sensitive adhesive composition obtained by a method comprising the sequential steps of:
(I) forming a polymer mixture comprising:
(A) a silicone polymer formed by condensation polymerization of at least one polyorganosiloxane in the presence of at least one hydrocarbon solvent or silicone fluid;
wherein the polyorganosiloxane has an average solution viscosity of from about 1 mm 2 /s to about 200 mm 2 /s at 25° C. and at least one hydroxyl group capable of undergoing condensation polymerization;
wherein polymerization is facilitated by addition of at least one condensation catalyst and occurs at a temperature of from about 30° C. to about 110° C.;
wherein the silicone polymer formed has a solution viscosity of from about 10,000 mm 2 /s to about 5,000,000 mm 2 /s at 25° C.;
(B) optionally, a silicone resin that has at least one hydroxyl group capable of undergoing condensation polymerization and that is soluble in at least one hydrocarbon solvent or silicone fluid;
wherein the resin has a hydroxyl group content of from about 0.5% to about 2.5% (by weight based on resin solids content);
wherein the resin comprises R 3 SiO 1/2 units and SiO 4/2 units in a molar ratio of from about 0.6 to about 1.5 (R 3 SiO 1/2 units:SiO 4/2 units);
wherein R is independently selected from a monovalent hydrocarbon or a halohydrocarbon radical having from 1 to 20 carbon atoms, an alkenyl radical, or a hydroxyl radical; and
(C) optionally, a neutralizing agent; wherein the neutralizing agent is added in an amount sufficient to neutralize the condensation catalyst;
(II) mixing with the polymer mixture of (I), at least one bodying catalyst and a silicone resin that has at least one hydroxyl group capable of undergoing bodying; and then allowing a bodying reaction to occur at a temperature of from about 40° C. to about 145° C. to form the silicone pressure-sensitive adhesive composition;
wherein the resin is soluble in at least one hydrocarbon solvent or silicone fluid;
wherein the resin has a hydroxyl group content of from about 0.5% to about 2.5% (by weight based on resin solids content);
wherein the resin comprises R 3 SiO 1/2 units and SiO 4/2 units in a molar ratio of from about 0.6 to about 1.5 (R 3 SiO 1/2 units:SiO 4/2 units);
wherein R is independently selected from a monovalent hydrocarbon or a halohydrocarbon radical having from 1 to 20 carbon atoms, an alkenyl radical, or a hydroxyl radical; and
(III) optionally, adding to the silicone pressure-sensitive adhesive composition of (II) from about 0.5% to about 3.5% (by weight) of an organic peroxide.
2 . A composition according to claim 1 , wherein the polyorganosiloxane is generally characterized by the formula
R 1 O[R 2 R 3 SiO] x H
wherein R 1 , R 2 , and R 3 are independently selected from methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, iso-butyl, tert-butyl, perfluorobutylethyl, phenyl ethyl, chlorpropyl, fluoropropyl, vinyl, and phenyl; and wherein x is an integer with a value of at least 2.
3 . A composition according to claim 2 , wherein the polyorganosiloxane is polydimethylsiloxane.
4 . A composition according to claim 1 , wherein the polyorganosiloxane has a solution viscosity of from about 10 mm 2 /s to about 100 mm 2 /s at 25° C.
5 . A composition according to claim 1 , wherein the at least one hydrocarbon solvent or silicone fluid is selected from xylene, heptane, benzene, toluene, naptha, mineral spirits, polydimethylsiloxane, isododecane, hexane, and decane.
6 . A composition according to claim 1 , wherein the condensation catalyst is selected from [PCl 3 ═N—PCl 2 ═N—PCl 3 ] + PCl 6 − .
7 . A composition according to claim 1 , wherein the silicone polymer has an average viscosity of from about 80,000 mm 2 /s to about 750,000 mm 2 /s at 25° C.
8 . A composition according to claim 7 , wherein the pressure-sensitive adhesive has from about 20% to about 60% (by weight) of a silicone polymer.
9 . A composition according to claim 1 , wherein the silicone resin of step (I)(B) undergoes condensation polymerization with the silicone polymer prior to addition of the neutralizing agent.
10 . A composition according to claim 9 , wherein the silicone resin of step (I)(B) is the same as the silicone resin of step (II).
11 . A composition according to claim 9 , wherein the silicone resin of step (I)(B) is different from the silicone resin of step (II).
12 . A composition according to claim 1 , wherein the pressure-sensitive adhesive has from about 40% to about 80% (by weight) of silicone resins.
13 . A composition according to claim 1 , wherein the optional organic peroxide is selected from benzoyl peroxide and dichlorobenzoyl peroxide.
14 . A composition according to claim 1 , wherein the pressure-sensitive adhesive has less than 0.1 wt % octamethylcyclotetrasiloxanes or decamethylcyclopentasiloxanes.
15 . A composition according to claim 1 , wherein the silicone polymer of step (I)(A) comprises branched polyorganosiloxanes.
16 . A composition according to claim 15 , wherein the silicone polymer is formed by condensation polymerization in the presence of trialkoxyphenylsilanes, tetraalkoxysilanes, or combinations thereof.
17 . A composition according to claim 16 , wherein the silicone polymer is formed by condensation polymerization in the presence of trimethoxyphenylsilane, tetraethoxysilane, or combinations thereof.