Patent ID: 6121368
Filing Date: 2000-09-19
Classification: C08G,C08L,C09J

Abstract:
A silicone composition for preparing a silicone pressure sensitive adhesive, the composition comprising:(A) 20 to 55 parts by weight of a polydiorganosiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule;(B) 45 to 80 parts by weight of an organopolysiloxane resin comprising R.sup.3.sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units wherein each R.sup.3 is independently selected from the group consisting of monovalent hydrocarbon and monovalent halogenated hydrocarbon groups, the mole ratio of R.sup.3.sub.3 SiO.sub.1/2 units to SiO.sub.4/2 units is from 0.6:1 to 1.5:1, the resin contains less than about 2 mole percent of alkenyl groups, and the total amount of components (A) and (B) is 100 parts by weight;(C) an organohydrogenpolysiloxane having an average of at least two silicon-bonded hydrogen atoms per molecule in an amount sufficient to cure the composition;(D) a thixotropic agent in an amount sufficient to impart thixotropy to the composition, wherein the agent is selected from the group consisting of(1) at least one silica filler having an average surface area of from 50 to 400 m.sup.2 /g; and(2) a mixture comprising(a) at least one silica filler having an average surface area of from 0.5 to 400 m.sup.2 /g; and(b) an additive selected from the group consisting of (i) at least one organopolysiloxane containing an average of at least two silicon-bonded hydroxyl groups and from about 4 to about 40 silicon atoms per molecule, (ii) a reaction product of at least one organopolysiloxane containing an average of at least two silicon-bonded hydroxyl groups and from about 4 to about 40 silicon atoms per molecule, and at least one silane containing at least one silicon-bonded alkoxy group and at least one silicon-bonded epoxy-containing organic group per molecule, (iii) at least one polyether, (iv) at least one poly(vinyl alcohol), (v) at least one polysaccharide, (vi) at least one triester of glycerol, (vii) at least one hydrocarbon free of aliphatic unsaturation, and (viii) a mixture comprising at least two of the aforementioned additives, provided that when the additive is (vii), the composition contains an effective amount of at least one silica filler having a surface area of from 50 to 400 m.sup.2 /g; and(E) a catalytic amount of a hydrosilylation catalyst; wherein the sum of the average number of silicon-bonded alkenyl groups per molecule in component (A) and the average number of silicon-bonded hydrogen atoms per molecule in component (C) is greater than 4.