GB2300861A - High solids silicone pressure sensitive adhesives - Google Patents

Description

2300861 1 HIGH SO= S=CONE PRESSURE SENSITM ADHESIVES The present invention

relates tc) silicone based pressure sensitive adhesives that are cured by a hydrosilation cure.

The present invention relates to silicone compositions suitable for forming pressure sensitive adhesive compositions. More particularly, the present invention relates to high solids, including 100% solids, silicone compositions which cure to form pressure sensitive adhesive compositions having improved lap shear strength and, in particular, improved lap shear strength at elevated temperatureL The term "pressure sensitive adhesives' (PSA) as used herein refers to adhesives that can be adhered to a surface and yet can be stripped from the surface without ferring more than trace quantities of adhesive to the surface, and can be re adhered to the same or another surface because the adhesive retains some or all of its tack and adhesive strength.

Silicone p. u sensitive adhesives have excellent adhesive strength, tack, and cohesive strength, which are generally the properties required of a pressure sensitive adhesive. Silicone PSA tapes are used in rnany high temperature and chemically harsh industrial operations, such as plater's masidng tapes, high shear splicing tapes, plasma and flame spraying, and the like. In order to be useful in these types of applications, silicone PSA's must exhibit high lap shear strength, particularly at elevated temperatures.

2 A drawback associated with currently available silicone PSA's is the lack of high solids content with improved lap strength in combination with high peel and tack, especially at high temperatures. Presently there are no silicone PSA's which can demonstrate such adhesive properties without the presence of solvents. In geographic areas in which there are stringent air quality control regulations, the use of solventi in PSA's are subject to stringent regulation which effectively prohibits their use.

ffigh solids silicone compositions capable of curing to form pressure sensitive adhesive compositions are known in the art, but these known compositions do not provide sufficient adhesive properties for demanding applications.

United States Patent No. 5,169,727 (Boardman) is directed to a pressure sensitive adhesive composition having high solids content comprising (a) a benzene soluble resinous copolymer consisting of R'R"R... SiO% units, 5i04/2 units and containing silicon-bonded hydroxyl radicals ranging from 1 to 4 percent by weight of the copolymer, (b) a diorganoyLsiloxy endblocked polydiorganositoxane, (c) a diorganohydrogensdoxy end-blocked polydiorganosiloxane, (d) a crosslinking agent and (e) a hydrosilylation catalyst Boardman requires an organosiloxane crosslinker having 1 to 15 silicone atoms. Further, the examples presented in Boardman show the pressure sensitive adhesives prepared had low to moderate tack properties. The adhesive strength ranged from poor to passing as measured by holding power at 70C There is no teaching of a PSA with improved lap shear properties, no teaching of improved lap shear properties at high temperature, and no teaching of obtaining useful pressure sensitive adhesive properties at SiH/Si-Vinyl ratios of greater than 1.25A.

U.S. Patent No. 3,883,298 (Hahn et al.) is directed to a composition as a pressure sensitive adhesive, obtained by mixing components consisting essentially of (a) from 50 to 60 parts by weight of a solid, benzene soluble resin copolymer consisting essentially of R3Si0% units and SiO4/2 units, (b) from 40 to 50 parts by weight of an essentially cyclic free vinyl-k.rminated polydiorganosiloxane having a viscosity of from 20,000 to 100,000 centipoise at 25 C, (c) a hydrogen-contLining organopolysiloxane in an amount sufficient to provide from 1.0 to 20.0 3 silicon-bonded hydrogen atoms of every olefirtically unsaturated radical in the total of (a) plus (b) and (d) a platinum catalyst It is pointed out in Hahn that compositions of the prior art containing MQ resins mixed with low viscosity polydiorganosiloxanes do not form PSA's.

U. 5. Patent No. 4,774,297 (Murakami et al) is directed to a composition suitable for forming a pressure sensitive adhesive having excellent tack and adhesive strength comprising (A) 30-70 parts by weight of a vinylterminated polydiorganosiloxane having a viscosity of at least 500,000 centipoise at 25C, (B) 70-30 parts by weight of an organopolysiloxane containing R3SiO% units and Si04/2 units, (C) an organohydrogensiloxane in an amount sufficient to provide 1-20 siliconbonded hydrogen atoms per alkenyl group, (D) a platinum-containing catalyst and (E) from 25-400 parts by weight of an organic solvent. In order to obtain a satisfactory product Murakami et al teach that it is essential that the vinyl polymer have a viscosity of at least 500,000 centipoise and preferably at least one million centipoise at 2.5C U.S. Patent No. 4,988,779 (Medford et al) discloses a composition suitable for forming a pressure sensitive adhesive, the composition having a solvent content of no more than 5-10% by weight and comprising from 30 to 50 parts of a vinyl-containing polydiorganosiloxane fluid having a viscosity of from 500 to 10,000 centipoise at 25C, from 50 to 70 parts of a benzene soluble resin copolymer containing R3SiO% units and Si04/2 units, an organopolysiloxane having silicon bonded hydrogen atoms, and a platinum catalyst. The hydrogen-contag organopolysiloxane of the formula R3aHbSiO(4-a-b)/2, is present in an amount sufficient to provide from 1.0 to 30.0 silicon-bonded hydrogen atoms for every olefinically unsaturated radical in the composition. The hydrogen-containing organopolysiloxane functions as a cross-linker and has a small structure with a-1.00 to less than 2.00, b-0.05-1.00, a+b-1.10 to less than 3.00.

There is no teaching of using higher molecular weight hydride crosslinker to give better peel and tack properties. The peel adhesion of the cured adhesive was controlled by controlling the amount of MQ resin and not by the crossliriker. There is no teaching of obtaining high lap shear strength in combination with high peel and tack adhesive properties.

4 U.S. Patent No. 5,190,827 (Lin) is directed to a composition having high solids content and having a hydrogen-containing polydiorganosiloxane containing more than 2 silicon-bonded hvdrogen atoms per chain. Other components in the composition include an MQ resin, an alkenvi-terminated silicone fluid, and a hydride-terminated silicone fluid. The cross linking that occurs is only through the hydride crosslinker which is selected from linear or resinous siloxane polymers, and no organosiloxane containing more than 2 silicon-bonded alkenyl groups as a crosslinker is disclosed.

U.S. Patent No. 5,292,586 (Lin et al.) discloses a composition comprising a silanol-containing MQ resin an alkenyl-terminated polydiorganosiloxane, a hydride-terminated organohydrogenpolysiloxane and a catalytic amount of a hydrosilylation catalyst The composition cures to form a PSA having high peel and tack adhesion properties, but does not contain any cross linker or muidhmctional alkenyl or multifunctional hydride siliconm The terminal hydride adhesive network reacts with silanol of the MQ resin to form an internally cured adhesive network.

U.S. Patent Application Ser. No. 08/150,570 (Lin et al.) disclo" an addition cured adhesive composition having high solids content The composition is prepared from a multifunctional vinyl-containing silicone as crossr, in addition to MQ resin, an alkenvi-terminated silicone fluid, a hydride-terminated sWcone fluid and a hydrosilylation caWyst The crossUnking occurs through the extemal.vinyl-crosslinker and forms the cured pressure sensitive adhesive. There is no teaching of preparing PSA's with improved lap shear strength in combination with high peel and tack adhesive properties.

It is continually desirable to provide high solids polydiorganosiloxane compositions which cure to yield silicone pressure sensitive adhesives having high solids content and improved lap shear properties, particularly at elevated temperatures. It is also desirable to have a composition which can provide these properties without the presence of any solvent Such a solvent-free composition will have great utility in areas where strict air quality control regulations are in effect In the present invention, if was found that the lap shear property of an addition-cured silicone PSA was greatly improved by using a dual crosslinker system consisting of a multi-functional hydride silicone and a multi-functional alkenyl silicone or an equivalent hybrid crosslinker 5 containing both hydrosilylation-reactive functi onali ties. SUMMARY OF THE INVENTION

The present invention is directed to an addition curable silicone pressure sensitive adhesive composition having improved lap shear strength, comprising:

(A) from about 50 to about 75 parts by weight of an aromatic soluble resin or resinous copolymer comprising R3SiChh units and SiO4/2 units wherein each R is independently a monovalent hydrocarbon radical having from 1 to about 6 carbon atoms, wherein the resinous copolymer comprises from about 0.2% to about 5.0% by weight based on the total weight of the copolymer, of hydroxyl radicals, the molar ratio of R3SiO to 5i04/2 being from about 0.6 to about 0.9 inclusive.

0 (B) a hydride terminated polydiorganosiloxane having a viscosity of 3 to about 1000 centipoise at 25Q (C) an alkenvl-terminated polydiorganosiloxane having a viscosity of from about 3 to about 1000 centipoise at 25C; (D) a mixture of two or more crossg multi-functional organosiloxane fluids or resins selected from the group consisting of.

(i) a multi-functional organosiloxane having on average two or more silicon bonded hydrogen atoms per molecule, and (ii) a multi-functional organosiloxane having on average two or more sWcon bonded alkenyl groups per molecule; wherein the weight of components (A), (B), (C), and (D) sums to 100 parts by weight and the weight of components (B), (C), and (D) ranges from about 25 to about 50 parts by weight per 100 parts by weight subject to the limitation that the molar ratio of silicon bonded hydrogen to silicon bonded alkenyl groups in the composition represented by the sum of (B), (C), and (D) ranges from about 1.00 to about 15.00; (E) a hydrosilylation catalyst; and optionally from 0 to about 40 % by weight of an organic solvent (F) may be included in the composition when 100% solids are not desired.

0 The composition of the present invention cures to form a pressure sensitive adhesive having a lap shear strength greater than 2.2 pounds per square inch @70C and preferably greater than 2-2 pounds per square inch @ 1STC. Although solvent can be present in the composition, the composition does not require the presence of a solvent to improve the workability in the uncured state, thus, permitting the composition to be described as 100% solid. A key benefit of this invention is that a PSA having improved lap strength is produced and retains this improved lap strength at elevated temperatures.

DETAILED DESCRIPTION OF THE INVENTION

Component (A) of the composition of the present invention is an aromatic-soluble resin or resinous organopolysiloxane copolymer which imparts tack to the cured pressure sensitive adhesive prepared from the composition. The resin or resinous copolymer (A) comprises R3SiO units (also known as "M" units) and SiO4/2 units (also known as WQR units) wherein each R is independently a monovalent hydrocarbon radical having from 1 to about 6 carbon atoms. Examples of radicals represented by R include alkyl radicals such as methyl, ethyl, and isopropyl; cycloaliphatic radicals such as cyclopentyl and cyclohexenyl; olefinic radicals, such as vinyl and ailvi; and the phenyl radical. At least 95% of all R groups are alkyl groups, preferably methyl, the total number of R radicals that are alkenyl radicals being 0-0.5% of all R radicals. The molar ratio of R3Si(Dh units to SiO4/2 units is from about 0.6 to about 0.9 inclusive. The resin or resinous copolymer comprises from about 0.2% to about 5% and preferably from about 0.3 to about 3.0% and most preferably from about 0.4% to about 2.5%, by weight based on the total weight of the resin or copolymer, of hydroxyl radicals. The hydroxyl radicals are be bonded directly to the silicon atom of the Si04/2 unit.

Component (A) is present in the composition of this invention in an amount within the range of from about 50 to about 75, preferably from about 50 to about 70, and most preferably from about 50 to about 62, parts by weight.

Methods for making the resin or resinous copolymer (A) are known in the art Reference is made, for example, to U.S. Patent No.

2,676,182 to Daucit et al., which is hereby incorporated by reference. In the Daucit et al. method, a silica hydrosol is reacted under acidic conditions with a source of triorganosiloxy units such as a hexaorganodisiloxane, e.g., hexamethvidisiloxane, or a hvdrolvzable triorganosilane, e.g., trimethylchlorosilane, or mixtures thereof, and 5 recovering a benzene soluble resin copolymer having M and Q units.

The resin or resinous copolymer (A) is preferably a solid, resinous material and is most often available as a solution in a solvent such as xylene or toluene, generally as a 40% to 60% by weight solution.

Component (B) of the composition of the present invention is preferably a hydride-terminated organopolysiloxane fluid having a viscosity of from about 3 to about 1000 cps at 25C and having the general formula (I) R12H5iO(R125i0)nSiHR12 wherein each R1 is independently an alkyl group having from 1 to about 10 carbon atoms or an aryl such as phenyl. The value of n is a number in the range of from about 3 to about 500, preferably from about 5 to about 400, and most preferably from about 10 to about 300. Where a solvendess composition is desired the molecular weight should be low enough to disperse component (A) without the aid of solvent, i.e., n is an integer less than about 50.

The viscosity of the hyd ride- terminated organopolysiloxane (B) ranges from about 3 to about 1000 centipoise at 25C and most preferably from about 6 to about 500 centipoise at 25C Organohydrogenpolysiloxanes and their preparation are well known in the organosilicon polymer art; some are commercially available. Briefly, the preparation of organohydrogensiloxanes can be accomplished in any suitable manner such as by hydrolyzing silanes, such as chlorosilanes, and equilibrating the resulting hydrolyzate under acid catalysis. Alternately, a mixture of suitable siloxanes, such as cyclic siloxanes and Unear siloxanes, can be copolymerized and equilibrated under acid catalysis. For example, a hydride-stopped silicone fluid suitable for use in the present invention can be prepared by reacting tetramethyldisiloxane with cyclic methyl tetramer of predetermined ratio in the presence of Filtrol-20 (an acidified clay) as a catalyst for 4-6 hours at 8 80-1001C. The Filtrol-20 catalyst is then removed by filtration and the residual reactants are removed by vacuum stripping.

Component (C) of the composition of the present invention is preferably an alkenvi-containing polydiorganosiloxane having a viscosity of from about 3 to about 1000 cps at 25C and having the general formula (11) R12R2SiO(R32Sio),SiR2R12 wherein each R1 is independently an alkyl group having from 1 to 10 carbon atoms cycloaliphatic group or an aryl group; R2 is an alkenyl group having from 1 to about 10 carbon atoms, each R3 is independently RI or R2 at least 99.5 % of all R3 radicals being R1, and x is a number from about 3 to about 500.

In formula (II) RI is preferably an alkyl group such as methyl, ethyl, and propyl; cycloaliphatic groups such as cyclohexyl or an aryl group such as phenyl. Preferably, at least 95 percent and most preferably 100 percent of all RI radicals are alkyl radicals having from 1 to 10 carbon atoms and most preferably methyl. R2 is preferably an alkenyl group such as vinyl, allvi, propenyl, butenyl, pentenyl, hexenyl or the like, more preferably R2 is vinyl. Each R3 is either RI or R2 with the proviso that at least 99.5%, and preferably 100%, of all R3 radicals are R1. R3 is preferably an alkyl radical having from 1 to about 10 carbon atoms, and most preferably methyl or more preferably an aryl group and most preferably a phenyl group. In formula (H), x represents a number from about 3 to about 500, preferably from about 5 to about 250, and most preferably from about 10 to about 200. When a solventless composition is desired, the molecular weight should be low enough to disperse component (A) without the aid of solvent i.e., x is an integer less than about5O.

Alkenyl-terminated polydiorganosiloxanes (C) can be prepared by any conventional methods for preparing triorganosiloxane-terminated polydiorganosiloxanes. For example, a proper ratio of the appropriate hydrolyzable silanes, e.g., vinyidimethylchlorosilane and dimethyidichlorosilane, may be co-hydrolyzed and condensed or alternately an appropriate 1,3-divinvitetraorganodisiloxane, e. g., symmetrical divinvidimethyidiphenvisiloxane o r divinyltetramethyisiloxane, which furnishes the endgroups of the 9 polydiorganosiloxane, may be equilibrated with an appropriate diorganopolysiloxane, e.g., dimethvlcvclotetrasiloxane, in the presence of an acidic or basic catalyst Regardless of the method of preparation of polydiorganosiloxane (C), there is usually co-produced a varying quantity of volatile, cyclic polydiorganosiloxanes. Volatile cyclic polydiorganosiloxanes, e.g., methyl tetramer, should be removed, since they are volatile and adversely affect pressure sensitive adhesive properties.

The viscosity of the alkenyl-terminated polydiorganosiloxane (C) ranges from 3 to about 1000, preferably from about 5 to about 400, and most preferably form about 10 to about 300, centipoise at 25C The amount used of polydiorganosiloxanes (B) and (C), their formulas (presented herein above as formulas (I) and (11% and their viscosity. for the purposes of this invention, refers to the essentially cyclic free portion of the polydiorganosiloxane. This essentially cyclic -free portion can be determined by heating a sample of the polydiorganosiloxane at 150C for up to 1 hour to yield a residue. This residue will be essentially hw of cyclic material with the exception of trace quantities of macrocyclic polydiorganosiloxanes which are non- volatile at 150C and ahnospheric pressure. Many of these polydiorganosiloxanes (B) and (C) are commercially available. Furthermore, component (B) and (C) can be homopolymers or copolymers or their several mixtures as long as they are hydride-end blocked or alkenyl-end blocked polysiloxanes of formula (I) or (I1) respectively.

(D) is a mixture of two or more ciosslinking multi-functional organosiloxane fluids or resins selected from the group consisting of:

(i) a multi-functional organosiloxane having on average two or more sWcon bonded hydrogen atoms per molecule; and (ii) a multi-functional organosiloxane having on average two or more silicon bonded alkenyl groups per molecule; wherein the weight of components (A), (B), (C), and (D) sums to 100 parts by weight and the weight of components (B), (C), and (D) ranges from about 25 to about 50 parts by weight per 100 parts by weight subject to the limitation that the molar ratio of silicon bonded hydrogen to silicon bonded alkenyl groups in the composition represented by the sum of (B), (C), and (D) ranges from about 1.00 to about 15.00; Component (D)(i) is a hydrogen-containing polyorganosiloxane containing more than 2 silicon-bonded hydrogens per chain. Examples of 5 component (D)(i) include:

(1) linear (or cyclic) hydrogen-containing polydiorganosiloxane fluids having a viscosity of from about 5 to about 12,000, preferably from about 5 to about 5000, and most preferably from about 5 to about 2500, centipoise at 25C. having the general formula H,(R4)3,Sio((R4)25io)V(HR4Sio),Si(R4)3,Hc (this formula is specffic to linear molecules), wherein each R4 is independently an alkyl radical having from about 1 to about 10 carbon atoms or an aryl radical (preferably R4 is methyl), c is 0 or 1, y is a number in the range of from about 0 to about 800, preferably form about 20 to about 400, and most preferably from about 20 to about 200 and z is a number in the range of from about 3 to about 100, preferably form about 3 to about 30, and most preferably form about 3 to about 20 and (2) resinous hydrogen-containing siloxane copolymers selected from (a) resinous hydrogen-containing siloxane copolymers comprising by weight:

(i) from about 60% to about 100% Of Si04/2 units and (R5)2HSiOl/2 units; wherein the ratio of (R5)2HSi01/2 units to SiO4/2 units is from about 0. 6A to about 2.1; and (ii)from 0 to about 40% of (R5)3Si01/2 units and (R5)2SiC)2/2 units; and (b) resinous hydrogen-containing siloxane copolymers comprising by weight (i) from about 30% to about 100% of R5Si03/2 units and (R5)2H5i01/2 units; wherein the ratio of (R5)2H5i01/2 units to R5Si03/2 units is from about 0.6A to about 11; and (ii) from 0 to about 70% of (R5)35i01/2 units and (R5)2SiO2/2 units; wherein each R5 is independently a monovalent hydrocarbon radical having from 1 to 11 about 6 carbon atoms, at least 95% of all RS groups being an alkyl group. Examples of radicals represented by R.: include alkyl radicals such as methyl, ethyl, and isopropyl; cycloaliphatic radicals such as cyclopentyl and cyclohexyl; olefinic radicals, such as vinyl and allyt; and the phenyl radical. At least 95% of all RS groups are alkyl groups, preferably methyl. The molar ratio of (R-_')2H5i01/2 units to SiO4/2 units is from about 0.6:1 to about 2A. The resinous siloxane copolymer (D)(i)(2) has a hydride content of from about 0.005% to about 3.0% by weight Component (D)(ii) is generally an alkenvi-contg organopolysiloxane having more than 2 silicon-bonded alkenyl groups per molecule, or 15 resinous siloxane copolymer having more than 2 silicon-bonded alkenyl atoms per molecule and is selected from:

(1) linear (or cyclic) alkenvl-containing organopolysiloxane fluids having the general formula R2R3 2SiO(R3 2SiO),,,(R2R3SiO)aSiR 3 2R2 (this formula is specific to linear molecules)where each R3 is independently an alkyl radical having from about 1 to about 10 carbon atoms or an aryl radical; R2 is either R3 or an alkenyl radical having from about 2 to about 10 carbon atoms such as vinyl, allyl, propenyl or hexenvi; the sum of m+a is at least about 20, preferably is at least about 100, and most preferably is at least about 250; (The weight % of alkenyl groups is defined by the weight % of alkenyl units to the total weight of the organopolysiloxane. This ranges from about 0.1% to about 40.0% by weight preferably from about 0.1 to about 30.0% by weight and most preferably from about 0.3 to about 20.0% by weight of the total weight of organopolysiloxane) or (2) resinous alkenyl-containing siloxane copolymers, wherein said silicon bonded alkenyl group is a combination of (R1 p R2 q 5i01/2)(!.e. M) or R1. R2.Si02/2ffi.e. D), R3Si03/20.e. 1) and/or Si04/2 (i.e. Q) containing resinous copolymer where each R1 is independently an alkyl radical having form about 1 to about carbon atoms or an aryl radical; each R2 is independently an alkenyl radical having from about 2 to about 10 carbon atoms such as vinyl, allyl, propenyl or hexenvi; p is 0, 1, 2, or 3; q is 0, 1, 2, or 3; r is 0, 1, or 2; s is 0, 1, or 2; p + q=3; and r+s-2. The weight % of alkenyl groups is defined by the weight % of alkenyl units to the total weight of the organopolysiloxane. This ranges from about 0.1 to about 40.0% by weight preferably from about 0.1 to about 30.0% by weight and most preferably from about 0.3 to about 20.0% by weight of the total weight of organopolysiloxane. Component D(ii) is preferably a vinyl-containing poly(dimethyl-co-methylvinvl) siloxane.

When selected from the list of preferred crosslinker compositions the following are preferred: D(i)(2) is preferably a methythydrogencontaining resin. Component (D)(ii)(1) is preferably a vinyl-containing copolymer crosslinker. Component (D)(ii)(2) is preferably a dimethylvinylcontaining resinous copolymer crosslinker or a methylvinyl-containing resinous copolymer crosslinker.

Component (D)(i) is preferably a multi-functional hydrogencontaining organosiloxane fluid having more than 2 silicon-bonded hydrogens per molecule of Formula IM provided that the number molecular weight is in the range of from about 300 to about 5,000 grams/mole, more preferably from about 500 to about 3000 grams/mole, and most preferably from about 800 to about 2000 grams/ mole, or a cyclic or branched multi- functional hydrogen-containing organosiloxane fluid having a viscosity in the range of from about 1 centipoise to about 30 centipoise and a number molecular weight of from about 100 to about 3000.

Component (D)(i) may also be a multi-functional hydrogencontaining organosiloxane MQ resin having more than 2 silicon-bonded hydrogens per molecule having an M/Q ratio of from about 0.3/1 to about 1/1, more preferably from about 0A/1 to about 0.8/1 and most preferably from about 03/1 to about 0.7/1. The MQ resin may optionally contain D and T units provided to M/Q ratio is within the foregoing ratio range.

Component (D)(ii) may also be a multi-functional alkenyl group containing organosiloxane fluid having more than 2 silicon-bonded alkenyl groups per molecule of Formula IV, provided that the number molecule weight is in the range of from about 300 to about 5,000 grams/mole, more preferably from about 500 to about 3000 grams/mole, and more preferably from about 800 to about 2000 grams/mole, or a cyclic or branched multi-functional alkenyl group-containing organosiloxane fluid having a viscosity in the range of from about 1 centipoise to about 30 centipoise and a number molecular weight of from about 100 to about 3000.

Component (D)(ii) may further also be a multi-functional alkenyl group-containing organosiloxane MQ resin having more than 2 silicon bonded alkenvi-groups per molecule having an M/Q ratio of from about 3/1 to about 1/1, more preferably from about 0A/1 to about 0.8/1 and most preferably from about 03/1 to about 0.7/1. The MQ resin may optionally contain D and T units provided the M/Q ratio is within the foregoing ratio range.

The sets of silicone crosslinkers, at least one from (D)(i) and (D)(ii), at least two from(D)(i), or at least two from D(H) can be either added separately or as a blend to the adhesive mixture. It is also possible to prepare a dual-functional silicone, having both hydrogen and alkenyl functionality, to act as component (D), the crosslinker, instead of the separate components, (D)(i) and (D)(ii).

The amount of (D) present in the composition is to provide generally from about 3 mole percent to about 60 mole percent and preferably from about 5 mole percent to about 50 mole percent of the total hydrosilylation reactive groups in the composition as either silicon bonded hydrogens or alkenyl groups and the ratio of the total silicon bonded hydride of both (B) and (D)(i) to total silicon-bonded alkenyl groups of both (C) and (D)(ii) being from about 1.00 to about 15, preferably 1.05 to about 15.

Component (E) of the composition of the present invention is a catalyst which promotes the hydrosilation reaction. Useful catalysts for facilitating the hydrosilation curing reaction include precious metal catalysts such as those which use ruthenium, rhodium, palladium, 14 is osmium, iridium, and platinum, and complexes of these metals. Examples of suitable hydrosilation catalysts for use in the present invention are disclosed, for example, in U.S. Pat Nos. 3,159,601 and 3,159,662 (Ashbv) 3,220,970 (Lamoreax); 3,814,730 (Karstedt); 3,516,946 (Modic), and 4,029, 629 (jeram); all of the foregoing patents being hereby incorporated by reference herein.

Preferably, the hvdrosilation catalyst used in the present invention is a platinum-containing catalyst Suitable platinum-containing hydrosilation catalysts include any of the well known forms of platinum that are effective for catalyzing the reaction of silicon-bonded hydrogen atoms with silicon-bonded vinyl groups, such as finely divided metallicplatinum, platinum on a finely divided carrier such as alumina, compounds of platinum such as chloroplatinic acid and complexes of platinum compounds.

Other suitable platinum -containing hydrosilation catalysts for use in the present invention include the platinum hydrocarbon complexes dbed in U.S. Pat Nos. 3,159,601 and 3,159,662 to Ashby, and the platinum alcoholate catalysts described in U.S. Pat No. 3,220,970 to Lamoreax, as well as the platinum catalysts of U.S. Pat No. 4,510,094 to Drahnak. All of the U. S. Patents cited in the instant paragraph are incorporated by reference into the present disclosure.

The hydrosilation catalyst (E) is present in the composition of this invention m an amount sufficient to proved at least 0.1 part by weight metal for one million parts by weight of the combined weight of (A), (B), (C), and (D). Frequently, such small amounts of the catalyst are poisoned by trace amounts of impurities in the composition, so it is advantageous to use the catalyst in such quantities to provide at least 1.0 part per million (ppm). The amount of catalyst is not critical as long as it is an amount sufficient to facilitate the hydrosilation curing reaction. There may also be an acetylenic, maleate or other known hydrosilation catalyst inhibitor included in the composition to extend the pot-life of the compositions. Such inhibitors are well-known to the skilled artisan and described in the patent literature.

Component (F) of the composition of the present invention is an organic solvent The compositions of the present invention comprise 0 to 1 about 40, preferably from about 0 to about 20, and most preferabi.,,, 0, percent by weight of (F). Suitable organic solvents include any of the solvents conventionally used with organosiloxanes and having a boiling point below approximately 250'C, such as aromatic hydrocarbons, e.g., benzene, toluene, and xylene; aliphatic hydrocarbons containing from 2 to 18 carbon atoms such as hexane, heptane, cyclohexane, paraffins, isoparaffins, or the light ends of petroleum distillates; halogenated hydrocarbon solvents; naphthas such as petroleum ether, VM and P Naphtha and refined naphthas such as Naphthalite 66/3 and oxygenated solvents such as hydrocarbon ethers, e.g., tetrahvdrofuran and the dimethylether of ethylene glycol; ketones such as methyl isobutyl ketone and esters such as ethyl acetate and the like. Mixtures of organic solvents can also be used.

The components of the compositions of this invention can be mixed in any manner such as in bulk or in organic solvent Since the resin or resinous copolymer (A) is generally a solid, and is conveniently prepared and handled in an organic solvent the preparation of the composition of this invention preferably uses an organic solvent The organic solvent can be any of the solvents recited above in connection with component (E).

The mixing of the components can be accomplished by any of the techniques known in the art such as millin& blendin& stirring, and the like, either in batch or in continuous process. The components may also be prepared, with or without the aid of solvent by simply mixing (A), (B), (C), (D)and (E). The order of mixing is not critical. Wherever there are restrictions on the use of volatile organic compounds, it is preferable to simply mix (A), (B), (C), (D) and (E) without solvent and prepare the composition as a 100% solids composition. Such a 100% solids composition can provide a PSA cured on a 1 mil Kaptong polvimide film in a thickness 13-2 mil with the following adhesive properties:

Tack Strength greater than 500g/cm2 Peel Adhesion greater than 20 oz/ in Lap Shear greater than 24 h with a 1 kg weight at 150'C.

Small amounts of additional ingredients may be added to the composition of this invention if desired. For example, antioxidants, pigments, stabilizers, fillers, and the like, may be added as long as they 16 do not materially reduce the pressure sensitive adhesive properties of these compositions. Volatile additives are preferably added after any solvent removal operations have been completed.

The compositions of this invention are useful as pressure sensitive adhesives and will readily stick to a solid support, whether flexible or rigid. The composition is simply applied to the surface of the support or substrate by any suitable coating means such as rolling, spreadin& spraying and the like; then cured. The curing of the composition of the present invention proceeds by the addition reaction of the silicon-bonded alkenyl groups in (C) and (D)(ii) with the hydride groups in (B) and (D)(i) in the presence of catalyst (E). Cure adhesive with improved lap shear properties in combination with high peel and tack adhesion properties is provided to the cured pressure sensitive adhesive by adjusting the total alkenyl and hydride groups in the present composition available for crosslinking as well as the amount and ratio of the multifunctional component (D).

The surface of the support and the substrate to which the PSA may be applied may be any known solid material such as metals, porous materials, leather, and fabrics, organic polymeric materials, fluorocarbon polymers, silicone elastomers, silicone resins, polystyrene, polvamides, Polvimides, polyesters and acrylic polymers, painted surfaces, siliceous materials and glass, and the like.

Useful articles which can be prepared with the PSA's of this invention include PSA tapes, labels, emblems, and other decorative or informative sigw, and the like. An especially useful article is one comprising a support, flexible or rigid, that can withstand extreme temperatures, hot and/or cold and carrying at least one surface thereof, the PSA's of this invention. A preferred article is a pressure sensitive adhesive applied to a plastic film substrate such as a polyolefin, polyvinyl chloride, polyester, polyimide, poltrafluoroethylene, aluminum foil impregnated glass cloth, and treated paper.

All U. 5. patents referenced herein are herewith specifically incorporated by reference.

17 EXPERIMENTAL In order that those skilled in the art may better understand the present invention, the following examples are given to illustrate but not to limit the invention which is fully delineated by the appended claims.

EXAMPLE 1 Preparation of High Solids Component Mixtures The preparation of the silicone adhesive compositions was 5 facilitated by preparing two high solids mixtures designated as Component 1A and 1B.

Component 1A: About a 95% solids in toluene by weight mixture of 58% by weight MQ resin and 42% by weight vinyl-stopped silicone fluid was prepared by mixing 279 grams of MQ resin (M0.7Q 60% solids in toluene), 121 g of vinyl fluid (227 cps at 25'C, ".D127.8mvl, about 0.56 wt% vinyl), and 0.40 gram of Karstedt Pt-catalyst (5% active Pt), then vacuum stripping to about 95 wt% solids. Component 1B: About a 95% solids in toluene by weight mixture having a 58% by weight MQ resin and 42% by weight hydride-stopped silicone fluid was prepared by mixing 193 grams of MQ resin (M0.7Q 60% solids in toluene) and 84 g of a hydride-stopped silicone fluid (139 cps at 25'C, MHD94.9MH, about 0.0279 wt% H),then vacuum stripping to about 95 wt% solids, with a trace amount of dimethvl maleate, added as stabilizer.

EXAMPLES 2 and 3 Hydride Silicone Crosslinker Cured PSA A linear hydride silicone fluid a, (MD20DH3M, 0.16 wt% H) was used as the crosslinker in the high solids composition of Example 2- A different linear hydride silicone fluid b,(MD582DH29.5M; 0.064 wt'. F1) was used in the high solids composition of Example 3.

The Example 2 composition was prepared by mixing together the following ingredients:

20.8 g of Component 1A, 20.0 g of Component 1B, both made in accordance with Example 1; 0.5 g of the hydride silicone a (@ 0.16 wt % H). The resulting mixture had a SiH to Si-vinyl ration of 1.22 and a crosslinker hydride concentration to total (hvdride and vinyl) functionalities of 17 percent is Ihe high solids composition of Example 3 was prepared by incorporating 1. 25 g of linear hydride silicone b into 20.8 g of Component IA and 20.0 g of Component IB of Example 1. The resulted mixture represented a SiH to Si-vinyl ratio 1.22 and a crosslinker hydride concentration to total (hvdride and vinvi) functionalities of 17 percent The mixtures were coated over 1 mil polvimide film to give a dry adhesive thickness from about 1.5 mil to about 2.0 mil, then cured for 3 minutes in an oven @ ISO'C. the peel adhesion against a clean steel plate @ 180 degree was measured according to ASTM D-1000, at a 12 inch/minute rate. The probe tack adhesion was measured on a Polyken Probe Tack tester. The lap shear strength of an adhesive was measured by placing an I" x V' adhesive against a clean steel plate (or otherwise indicated) under 1 Kg deadweight at the temperature specified. This gives a static lap shear of about 2.2 lbs per square inch (PSI) testing conditions. If the adhesive failed to pass a specified time test, the time the adhesive slipped off the steel plate was reported. As shown in the following. The hydride-containing crosslinker alone cured P5As do not have high temperature lap shear properties.

Ex. No. Peel, orlin Tack, gcm2 Lap Shear ( @ 105'C), minutes 2 20 563 12 3 16 472 27 EXAMPLE 4

Vinyl silicone crosslinker Cured PSA A resinous vinyl siloxane, vinyl siloxane a, (MDv'Q. -2.7 wt% vinvi) was prepared at 60 weight percent solids in toluene. A second vinyl siloxane, vinyl siloxane b, (MMviO, -2.7 wt% vinyl) was prepared at 60 weight percent solids in xylene.

A high solids formulation was prepared as follows:

30.0 g Component IA, 23.52 g of Component IB (both prepared as in Example 1), 5 g of MQ resin solution (@ 60% solids) and 1.60 g of linear hydride silicone a of Example 2 were mixed thoroughly. The resulting mixture had a total SiH to Si-vinyl ration of 2.10, the crosslinker hydride to the total hyd ride and vinyl functionalities being 34 percent and the total MQ resin level dt 58.2 wt %.

19 A 2 mil thick cured adhesive over 1 mil polvimide film was prepared after curing for 3 minutes @ 1SO'C. It showed that vinyl crosslinker cured P5As did not pass the 2.2 Ibs/ in2 lap shear test@ lOYC.

Ex. No. Peel, ozlin 4 20 EXAMPLES 5-6 Dual Crosslinkers Cured PSA's A set of dual crosslinkers: linear hydride silicone a (MD20DH 3m; 0.16 wt% H) and resinous vinyl silicone b (MMviQ structure; -2.7 wt% vinyl; @60 solids in xylene) were incorporated in high solids compositions as described below.

The composition of Example 5 contained the following:

23.43 g of Component 1A, 20.09 g of Component IB (m-ade in accordance with Example 1), 0.937 g of the linear hydride silicone a and 1.66 g of resinous vinyl silicone b. The composition of Example 6 was prepared by adding additional 2-09 g of a MQ resin to the mixture in Example 5 to increase the weight content of MQ resin in the mixture.

The overall SiH/Si-vinyl ratio, (silicon-bonded hydride to siliconbonded vinyl in the mixture), % crosslinkers (ratio in percentage of crosslinkers functionalities to the total functionalities in the mixture), ratio of hydride crosslinker concentration to vinyl crosslinker concentration, and the weight percent of MQ resin in the composition on solids base for these examples are indicated in the following table.

Ex. No. (Sil-VSi- % Crosslinkers (SilVSi- Wt% MQ vinyl) total vinyl) of crosslinker 1.27 38 1.50 55.3 6 1.27 38 1.50 57.0 The adhesion properties were as follows:

Ex. No. Peel, ozlin Tack, Lap Shear, Lap Shear, gIcm2 minutes minutes (12 lbWin2, steel, 1SO'C) 669 Tack, g/cxn2 Lap Shear (a 105"C), minutes 74 (2.2 lbs./in2, polyimide film 150-C) 19 43 (polyester) 6 22 668 passed 2400 passed 1200 872 N/A N/A 620 passed 2400 passed 1200 47 (polyester) 775 N/A N/A The reported times on tap shear tests were the times when the tests were terminated due to passing the time frame of practical interest The peel adhesion property of a PSA typically is a function of the of film substrate. A peel adhesion of 15 oz/in or above on 1 mil polyimide film is considered of practical value. For reference, these two adhesives above were coated over a 2 mil polyester film and their adhesive properties are shown.

EXAMPLES 7-10 Various Dual Crosslinkers Cured PSA's Example 7: 20.0 g of Component 1A, 18,67 g of Component 1B, 2.11 g of linear hydride silicone b, 1.80 g of resinous vinyl silicone, and 5.0 g of a MQ resin (@78,4% solids) to give a composition of 57 wt% MQ resin, and total SiH/Si-vinyl ratio of 1.25.

Example 8: 20.0 g of Component IA, 18.67 g of Component 1B, 0.844 g of linear hydride silicone a, 1.80 g of resinous vinyl silicone a, and 5.0 g of a MQ resin (@ 78.4% solids). The mixture had about 57 wt% MQ resin, and a total SiH/Si-vinyl ratio of 1.25.

Example 9: 23.43 g of Component 1A, 20.09g of Component IB, 2.34 g of linear hydride silicone b, 1.66 g of vinyl silicone b, and 5.0 g of a MQ resin (@ 78.4% solids). The mixture had about 57 wt% MQ resin, and a total SiH/Si-vinA ratio of 1.27.

Example 10: 23.43 g of Component 1A, 20.09 g of Component 1B, 2.34 g of hydride crosslinker b, and 1.66 g of vinyl crosslinker b. The mixture had about 55.3 wt% MQ resin, and a total SiH/Si-vinyl ratio of 1.27.

The choice of dual crosslinker system can effect the extent of lap shear strength improvement including high temperature affinity to certain substrates. While singular crosslinker cured PSA's generally do not sustain themselves at temperatures greater than 100C the lap shear tests were performed on the dual crosslinker cured PSA's at 150'C against different substrates to illustrate the improvement 21 Ex No. Hydride Virtyl Crosslinker (SiH/Si- /0 Crosalinker Crosslinker Type Type vinyl) Crosslinker 7 Lu-tear hydnde b Resm vLnyl a 1-25 40 8 Linear hvclnde a Resin vinyl a 1.7-1 40 9 linear hydride b Resui vinyl b 1.30 38 Linear hycb-ide b Resin vinyl b 1.30 38 The adhesive properties are shown below:

Exp. No. Peel, oz/ in Tack, g/an2 lap shear Lap shear minutes, minutes, (2.2 Ibs/inZ (2.2 Ibs/inZ 1500c) 150.q steel polvinude 7 19 570 PASSED 1620 PASSED 2897 8 33 540 PASSED 1350 3.4 9 21 534 PASSED 1350 12 694 PASSED 1350 In the following examples and elsewhere in the following abbreviations are used:

vi = vinyl, Me = methyl, PASSED 1768 PASSED 2899 specification the

PDMS = polydimethylsiloxane, MW = molecular weight D4 = octamethyltetrasiloxane, CH3 CH-CH2 H f 1 1 D or D unit 0- Si DVI U- bt DH - O-Si 1 1 t CH3 CH3 -M3 Q or Q unit= 0- SI- U CH3 CH3 'iH3 1 1 1 M or M unit = CH3 Si Mv1 - CH2 - CH - Si MH - H- S, 1 1 1 CH3 CH3 LP1-X _Y) C H3 T unit = 0 - si - 0 1 U Note: It may be necessary to uisert an oxygen atom for structural completeness.

EXAMPLE 11

Preparation of Vinyl-Terminated Fluid A ViMe2Si-terminated PDMS silicone fluid having a VW of 953 g/mole (ViMe2Si(OSiMe2)10.40SiMe2Vi) was prepared by acid catalyzed equilibration of D4 and ViMe2SiOSiMe2Vi. An HMe2Si-terminated PDM5 silicone fluid having a MW of 1032 g/mole (HMe2Si(C)SiMe2)12.10SiMe2H) was similarly prepared by acid catalyzed equilibration of D4 and HMe2SiOSIMe2H. Volatiles from both fluids were removed by vacuum distillation.

Each of these fluids (500g) was mixed with MQ resin in xviene (816g dry weight), and the solvent was removed from the mixtures to form the following solventless PSA components:

Part A: 62% MQ resin 38% ViMe2Si-terminated fluid 62% MQ resin 38% HMe2Si-terminated fluid The MQ resin used in these components had an M/Q ratio of 0.64, an OH content of 0.6% (dry weight), and a Mn of about 4,000 g/mole. Part A had a viscosity of 18,000 cps and Part B 12,000 cps.

EXAMPLE 12

Preparation of Silicone PSA's Six silicone PSA's were prepared using the PSA components prepared above, and also containing one of three crosslinkers or mixtures of these crosslinkers. The crosslinkers used in these example were DVi4, an MDxDH y M fluid having an SiH content of 0.058% H and a viscosity of 800 centipoise, and an MMViQ resin having an SiVi content of 2.4% Vi and contained 50% by weight of Q groups. These PSA's had the following compositions:

PSA 12A COMPARATIVE Part B:

7.92g Part A - 6.31 mmol SiVi 10g Part B - 7.36 mmol SiH 0.061 g DVi4 - 0. 70 mmol SiVi 23 PSA 12B COMPARATIVE PSA 12C 10 COMPARATIVE ppm Pt in the form of Karstedt's catalvst (US Patent No. 3,814,730) 0.06g dimethyimaleate (DMM) inhibitor 10g Part A - 7.97 mmol SiVi 12.23g Part B - 7.53 mmol SiH 1.44g MDXDHVM fluid - 0.84 mmol SiH ppm Pt (Karstedt) 0.06g - DMM 7.92g Part A - 6.31 mmol SiVi 10g Part B -7.36 mmol SiH 0.79g MMViQ resin - 0.70 mmol SiVi ppm Pt (Karstedt) 0.06g - DMM PSA 12D 7.92g Part A - 6.31 mmol SiVi 10g Part B - 7.36 mmol SiH 0.030g DV4 - 0.35 mmol SiVi 0.39g MMViQ resin - 0.35 mmol SiVi ppm Pt (Karstedt) 0.06g - DMM PSA 12E 8.77g Part A - 6.99 mmol SiVi 10g Part B - 7.36 mmol SiH 0.63g MDDH,M fluid - 0.37 mmol SiH 0.41g MMViQ'resin - 0.37 mmol SiVi ppm Pt (Karstedt) 0.06g - DMM PSA 12F 7.92g Part A - 6.31 mmol SiVi 10.51g Part B - 7.74 mmol SiH 0.60g MMViQ resin - 0.53 mmol SiVi 0.046g DV'4 - 0.53 mmol SiVi ppm Pt (Karstedt) 0.06g - DMM All of these PSA's had an SiH/SiVi molar ratio of 1.05 and also had the same molar quantities of hydrosilation active crosslink sites relative to chain extension sites. The PSA's were prepared by first combining the 5Xl 24 functional components, Pt, and DMNI. After mixing, the SIF1 functional components were added, followed by additional mixing.

The PSA's were each coated onto 1 mil Kapton (trademark of DuPont) polyimide film. The thickness of each adhesive was 1.8-2.0 mil. The tapes were then cured for 4 minutes at 140'C. The adhesive properties of each tape were then measured and are listed in the table below. Tack was determined using a Polyken Probe Tack tester at 1 cm/sec, 1 kg weight and a 1 sec. dwell time. Peel adhesion was measured against a clean steel plate using ASTM D1000 (12 in./min./180 pull). Adhesion was measured with a Scott Tensile Tester. Lap shear was determined by adhering a 1 in. by 1 in. portion of PSA tape to a clean steel plate. A 1 kg weight was then attached to the tape with use of a jig. The tape and the weight were then suspended in an oven heated to 150C. The tap shear test was judged as a pass if the PSA adhesive did not fail in 24 h. at 150-C.

PSA Crosslinker Type Tack Peel Adhesion Lap Shear (g/cm2) (0ym) (niin. to failure) 12A SiVi fluid 628 19 < 10 12B SiH fluid 521 12 <10 12C SiVi resin 524 22 <10 12D SiVi Fluid + SiVi resin 544 20 passed 12E SiH fluid + SiVi resin 529 is passed I2F SiVi fluid + 5M resin 510 22 passed is These results clearly show that good high temperature lap shear properties are obtained only when the PSA contains a mixture of crosslinkers, one of which is a silicone resin and the other a silicone fluid. It does not matter whether or not the crosslinkers contain the same or different hydrosilation reactive SiH or SiVi group. EXAMPLE 13 Preparation of PSA with SiH Resin Containing 1.5 SiH Groups per Molecule COMPARATIVE EXAMPLE The following PSA was prepared in the same manner as Example 12.

7.5g MViD20.5MV'- 8.81 mmol SiVifflW = 1702 g/mole Viscosity = 20 centipoise) 0.19g DV'4 - 2.20 mmol SiVi ppm Pt (Karstedt) 0.04 dimethyimaleate inhibitor 9.07g MHD20.5 MH - 11.0 mmol SiH (NfW = 1648 g/moie Viscosity = 20 centipoise 6.65g(M0.71 MHO. 05Q30 Resin -2.75 mmol SiH (1.5 SiH groups per molecule) 18.64g M0.65Q resin This gave a PSA with an SiH/SM ratio of 1.25/1 and 60% bv weight resin.

This uncured PSA was coated onto 1 mil unprimed Kapton polvimide with an adhesive thickness of 1.75 mil. The PSA was then cured at 150C for 10 min. The following adhesive properties were then measured: tack = 1006 g/cm2, peel adhesion = 18.6 oz/in, and lap shear failed after 5 min. at 150C with a 1 kg weight load and Px1" overlap onto a steel test panel.

This example demonstrates that inferior lap shear properties are obtained when using a functionalized resin containing less than 2 reactive groups per molecule.

26

Claims (26)

1. An addition curable silicone pressure sensitive adhesive composition comprising:

(A) from about 50 to about 75 parts by weight of an aromatic soluble, resin or resinous copolymer comprising R3SiO/

2 units and SiO4/2 units wherein each R is independently a monovalent hydrocarbon radical having from 1 to about 6 carbon atoms, wherein the resinous copolymer comprises from about 0.2% to about 5.0% by weight based on the total weight of the copolymer, of hydroxyl radicals, the molar ratio of R3Si01/2 to Si04/2 being from about 0.6 to about 0.9 inclusive; (B) a hyd ride- term ina ted. polvdiorganosiloxane having a viscosity of

3 to about 1,000 centipoise at 25Q (C) an alkenvi-terminated polydiorganosiloxane having a viscosity of from about 3 to about 1000 centipoise at 250c; (D) a mixture of two or more crosslg multi-functional organosiloxane fluids or resins selected from the group consisting of---.

(i) a multi-functional organosiloxane having on average two or more silicon bonded hydrogen atoms per molecule; and (ii) a multi-functional organosiloxane having on average two or more silicon bonded alkenyl groups per molecule; wherein the weight of components (A), (B), (C), and (D) sums to 100 parts by weight and the weight of components (B), (C), and (D) ranges from about 25 to about 50 parts by weight per 100 parts by weight subject to the limitation that the molar ratio of silicon bonded hydrogen to silicon bonded alkenyl groups in the composition represented by the sum of (B), (C), and (D) ranges from about 1.00 to about 15.00; and (E) a hydrosilylation catalyst 2. A composition as in Claim 1 wherein component (B) is represented by the general formula:

R12H5iO(R12SiO)nSiHR12 wherein each R1 is independently an alkyl group having from 1 to about 10 carbon atoms or an aryl such as phenyl, and n is a number in the range of from about 3 to about 500.

27 3. A composition as in Claim 1 wherein component (C) has a viscosity of from about 5 to about 500 cps. at 25'C.

4. A composition as in Claim 1 wherein the hydrogen-containing polydiorganosiloxane fluid of component (D) is linear and has the viscosity of from about

5 to about 12,000 centipoise at 25C. - 5. A composition as in Claim 1 the wherein the hydrogen containing siloxane copolymers of component (D) are resins.

6. A composition as in Claim 1 wherein the alkenvl-contairting organopolysiloxane fluid of component (D) has the general formula R2R32SiO(R32Sio)m(R2R3SiO)nSiR3 2R2 wherein each R3 is independently an alkyl radical having from about 1 to about 10 carbon atoms or an aryl radical; R2 is R3 or an alkenyl radical having from about 2 to about 10 carbon atoms; the sum of m+n is at least about20.

7. A composition as in Claim 1 wherein the alkenvl-containing siloxane copolymer of component (D) is a resinous copolymer selected from the group of resinous copolymers containing (R1P R2 q Sio, / 2), (5i04/2), (RI.R2.5i0212), and (R3SiO3/2) groups wherein each RI is independently an alkyl radical having from about 2 to about 10 carbon atoms or an aryl radical; each R2 is independently an alkenyl radical having from about 1 to about 10 carbon atoms; p is 00 1, 2, or 3; q is 0, 1, 2, or 3; r is 0, 1, or Z. s is 0, 1, or 2, p + q-3; and r+s-2.

8. A composition as in Claim 1 wherein the alkenvi-containing resinous copolymer of component (D) is selected from dimethylvinvicontaining or a methylvinyi-containing resinous copolymer.

9. A composition as in Claim 1 wherein the silicon-bonded hydrogen content of component (D)(i) is present in an amount such that component (D) has a silicon-bonded hydrogen content of from about 0.005% to about 3. 0% by weight

10. A composition according to Claim 5 wherein component (D) contains from 0.1% to about 40.0% by weight of alkenyl groups based upon the total weight of the alkenvl-containing organosiloxane.

11. A composition as in Claim 8 wherein component (D) is present in an amount of from about 3 mole percent to about 60 mole percent of the total hydrosilviation reactive groups.

28 11 A composition according to Claim 1 wherein the molar ratio of silicon- bonded hvdrogen atoms in (B) and (D) to alkenvl groups in (C) and (D) is in the range of from about 1.00 to about 15.0.

13. A composition according to Claim 1 wherein component (A) has a silanol content of from about 0.2 to about 5.0 % by weight

14. A composition as in Claim 1 wherein component (C) is an alkenviterminated polydimethylsilicone fluid.

15. A composition as in Claim 13 wherein component (C) is an alkenvlterminated polydimethvldiphenyisiloxane or an alkeny kerm ina ted poly(dimethyi-co-methylphenvl) siloxane.

16. A composition according to Claim 1 wherein the total amount of (B), (C), and (D) is from about 30 to about 50 parts by weight

17. A cured silicone pressure sensitive adhesive comprising:

(A) from about 50 to about 75 parts by weight of an aromatic soluble, resin or resinous copolymer comprising R35i0% units and SiO4/2 units wherein each R is independently a monovalent hydrocarbon radical having from 1 to about 6 carbon atoms, wherein the resinous copolymer comprises from about 0.2% to about 5.0% by weight based on the total weight of the copolymer, of hydroxyl radicals, the molar ratio of R3Si0% to SiO4/2 being from about 0.6 to about 0.9 inclusive, (B) a hydride-terminated polydiorganosiloxane having a viscosity of 3 to about 1,000 centipoise at 25Q (C) an alkenyl-berminated polydiorganosiloxane having a viscosity of from about 3 to about 1000 centipoise at 25Q (D) a mixture of two or more crosslinking multi-functional organosiloxane fluids or resins selected from the group consisting of.

(i) a multi-functional organosiloxane having on average two or more silicon bonded hydrogen atoms per molecule; and (ii) a multi-functional organosiloxane having on average two or more sihcon bonded alkenyl groups per molecule; wherein the weight of components (A), (B), (C), and (D) sums to 100 parts by weight and the weight of components (B), (C), and (D) ranges from about 25 to about 50 parts by weight per 100 parts by weight subject to the limitation that the molar ratio of silicon bonded hydrogen to silicon 0 29 bonded alkenyl groups in the composition represented by the sum of (13), (C), and (D) ranges from about 1.00 to about 15.00; and (E) a hydrosilation catalyst

18. The composition of Claim 17 wherein the composition additionally comprises up to about 40% by weight of an organic solvent (F).

19. A composition according to Claim 1 further comprising an inhibitor for the hydrosilation catalyst

20. A composition according to Claim 19 wherein the inhibitor is a dialkylmaleate.

21. A composition according to Claim 20 wherein the dialkylmaleate is dimethyimaleate.

22- A pressure sensitive adhesive tape comprising a flexible support curing on at least one surface thereof the curable composition of Claim 1.

23. A pressure sensitive adhesive tape comprising a flexible support curing on at least one surface thereof the cured composition of Claim 17.

24. The composition of Claim 1 wherein the crosslinkers (D) are a multifunctional hydrogen-containing organosiloxane having more than 2 siliconbonded hydrogens per molecule; and a multi-functional alkenyl containing organosiloxane having more than 2 silicon-bonded alkenyl 5 groups per molecule.

25. The composition of Claim 1 wherein the crosslinkers (D) are a multifunctional hydrogen-.containing organosiloxane fluid having more than 2 silicon-bonded hydrogens per molecule, and a multi-functional alkenvicontaining organosiloxane resin having more than 2 silicon5 bonded alkenyl groups per molecule.

26. The composition of Claim 1 wherein the crosslinkers (D) are a multifunctional alkenvi-containing organosiloxane fluid having more than two silicon-bonded alkenyl groups per molecule, and a multifunctional alkenylcontaining organosiloxane resin having more than two s silicon-bonded alkenyl groups per molecule.