GB2287034A - Silicone composition for pressure sensitive adhesives - Google Patents

Description

2287034 1 SILICONE CC24POSITIONS

CROSS REFERENCE TO RELATED APPLICATIONS Reference is made to the concurrently filed applications identified as Serial No. 08/206,497 (Attorney Docket No. 60SI-1629) and Serial No. 08/206,489 (Attorney I)ocket No. 60SI-1630).

BACKGROLTND OF THE INVF=ON The present invention relates to silicone compositions having high solids content and a method for making high solids silicone compositions. More particularly the method relates to making silicone compositions for use as addition-curable adhesives having silanol and alkenyl functionalities.

The term "pressure sensitive adhesives" (PSA) as used herein refers to adhesives that ca:n be adhered to a surface and yet can be removed from the surface without transferring more than trace quantities of adhesive to the surface, and can be readhered to the same or another surface because the adhesive retains some or all of its tack and adhesive strength.

High solids silicone compositions capable of curing to form pressure sensitive adhesive compositions are known in the art.

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 SiO1/2. units Si04/2 units and containing siiicon-bonded hydroxyl radicals ranging from 1 to 4 percent by weight of the copolymer, (b) a diorganoalkenylsiloxy endblocked polydiorganosiloxane, (c) a diorganohydrogensiloxy 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 70'C. 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 1) X_ obtaining useful pressure sensitive adhesive properties at SiH/Si-Vinyl ratios of greater than 1.25:1.

U.S. Patent No. 3,883,298 (Hahn et. al.) is directed to a composition useful 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 R3SiOi/. units and Si04/2 units, (b) from 40 to 50 parts by weight of an essentially cyclic free vinylterminated polydiorganosiloxane having a viscosity of from 20,000 to 100,000 centipoise at 25 'C, W a hydrogen-containing organopolysiloxane in an amount sufficient to provide from 1.0 to 20.0 silicon-bonded hydrogen atoms of every olefinically 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.S. Patent No. 4,774,297 (Murakami et al) is directed to a composition suitable for forming a pressure sensitive adhesives 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 25"C., (B) 70-30 parts by weight of an organopolySiloxane containing R3SiO1/2 units and Si04/2 units, (C) an organohydrogensiloxane in an amount sufficient to provide from I to 20 silicon-bonded hydrogen atoms per alkenyl group, (D) a platinum-containing cata---st, and 0 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 25"C.

U.S. Patent No. 4,988,7779 (Medford et al) discloses a composition suitable for forrning 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 25"C., from 50 to 70 parts of a benzene soluble resin copolymer containing R3SiO1/. units and Si04/2 units, an 1 3 organopolysiloxane having silicon bonded hydrogen atoms, and a platinum catalyst. The hydrogen-containing 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 olefirdcally unsaturated radical in the composition. The hydrogen-containing organopolysiloxane functions as a cross-linker and has a small structure with a=1.00 - 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 crosslinker. There is no teaching of obtaining high lap shear strength in combination with high peel and tack adhesive properties.

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 hydrogen atoms per chain. Other components in the composition include an MQ resin, an alkenyl-tern-dnated 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 silicone-bonded alkenyl groups as a crosslinker is disclosed.

U.S. Patent No. 5,292,586 (Lin et al.) discloses a composition comprising a silanol-contairdng 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 multifunctional alkenyl or multifunctional hydride silicones. 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. 07/923,111 (Lin et al.) discloses an addition cured adhesive composition having high solids content. The composition is prepared from a multifunctional vinyl-containing silicone as crosslinker, in addition to MQ resin, an alkenyl-tern-dnated silicone fluid, a 4 hydride-terminated silicone fluid and a hydrosilylation catalyst The crosslinking occurs through the external 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.

Silicone adhesives have been prepared from addition curable compositions. Addition curing reactions involve reacting silicon-bonded hydrides with vinyl groups in the presence of a hydrosilylation catalyst, such as one based on platinum. Generally silicone pressure sensitive adhesive compositions contain siloxane MQ resins, which almost alwavs contain silanol-functionality to provide adequate peel adhesion properties. However, previously stable high solids mixtures of relatively high viscosity vinyl-stopped polydimethylsiloxanes and silanol-co,,,aining MQ resins could not be prepared since the dispersed mixture became unstable and separated shortly after preparation. It is desirable to produce stable homogenous mixtures of alkenyl-containing diorganopolysiloxanes having relatively high viscosities and silanol-containing MQ siloxane resins having little or no organic solvent, but the instability of a high solids composition containing silanol-containing MQ resins and alkenvi-containing polydiorganosiloxane prevented the formation of these mixtures. The present invention relates to a method for preparing novel stable, homogenous silicone compositions having high solids content.

SUMMARY OF THE INVENTION

The present invention is directed to a silicone composition comprising: W from about 50 to about 90 parts by weight of a siloxane resin or resinous copolymer comprising R3SiOj A units and Si04/2 units wherein each R is independently a monovalent hydrocarbon radical having from I 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 3 )0 hydroxyl radicals; (ii) from 10 parts to 50 parts by weight of an alkenyl-containing diorganopolysiloxane having a viscosity of at least 3,000 centipoise at 25Q and optionally (iii) from 0 to about 40 % by weight of an organic solvent. Additionally, the present invention is directed to a method for making a stable, homogeneous silicone composition comprising: (A) mixing (i) a resinous siloxane solution of copolymer, substantially free of hygroscopic organic volatiles, comprising R3SiOl /4 units and Si04 / 2 units wherein R is 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, (ii) an alkenyl containing diorganopolysiloxane having a viscosity of at least 3,000 centipoise at 25C and optionally (iii) an organic solvent; (B) homogenizing the mixture at a temperature sufficient to disperse the alkenyl-containing diorganosiloxane into the siloxane resin; while stirring; and optionally (C) devolatilizing the mixture by stripping the mixture under agitation.

Although solvent can be present in the composition, the composition does not require the presence of a solvent, thus, giving a 100% solide composition. Generally solvent can be added to improve the dispensability or processibility of the composition. A key benefit of this invention, is that stable silicone compositions having high solids can be produced. DETAILED DESCRIMON OF THE INVENTION Component (i) of the composition of the present invention is an aroma tic- soluble resin or resinous organopolysiloxane copolymer. The resin or resinous copolymer (i) comprises R3SiOl/kunits (also known as 'M' units) and Si04/2 units (also known as "Q" 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 cydohexenyl; olefinic radicals, such as vinyl and allyl; and the phenyl radical. At least 95% of all R groups are alkyl groups, preferably methyl. The molar ratio of R3SiO1/2 units to Si04/2 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 1.0 to about 3.0% and most preferably from about 1.5% to about 2.5%, by weight based on the total weight of the resin or copolymer, of hydroxyl radicals. The hydroxyl radicals are bonded directly to the silicon atom of the Si04/2 units or to the silicon atom of the R3Siah units or some of the hydroxyl radicals can be bonded directly to the silicon atom of the Si04/2 units and some of the hydroxyl radicals can be bonded directly to the silicon atom of the R3SiO1h units.

Component W is present in the composition of this invention in an amount within the range of from about 50 to about 90, preferably from about 50 to about 85, and most preferably from about 50 to about 80, parts by weight.

Methods for making the resin or resinous copolymer W are known in the art. Reference is made, for example, to U.S. Patent No. 2,676,182 to Daudt et al., which is hereby incorporated by reference. In the Daudt et al. method, a silica hydrosol is reacted under acidic conditions with a source of triorganosiloxy units such as a hexaorganodisiloxane, e.g., hexamethyldisiloxane, or a hydrolyzable triorganosilane, e.g., trimethylchlorosilane, or mixtures thereof, and recovering a benzene soluble resin copolymer having M and Q units.

The resin or resinous copolymer W is 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 70% by weight solution. It is very common such resin solution contains a high level of hygroscopic organic volatiles such as alkanol, including methanol, ethanol, isopropanol, and water.

Component (ii) of the composition of the present invention is an alkenyl-containing diorganopolysiloxane having a viscosity of at least 3, 000 cps at 25'C and having the general formula R12R2SiO(Rl2SiO)x(RlR3SiO) y SiR2R12 7 wherein each RI is independently an alkyl group having from 1 to 10 carbon atoms such as methyl, ethyl, and propyl; or an aryl group such as phenyl; R2 is an alkenyl group having from 1 to about 10 carbon atoms including cx alkenyls such as vinyl, allyl, propenyl, butenyl, pentenyl, hexenyl or the like; R3 is either R1 or R2. The sum of x any y is at least about 520 to give a viscosity of about 3,000 cps at 25"C. Preferably the alkenyl group is vinyl.

The viscosity of the aikenyl-containing polydiorganosiloxane (B) is at least 3,000 cps or greater, and preferably from 10,000 centipoise at 25"C.

The alkenyl-containing diorganopolysiloxanes of the present invention is preferably a vinyl-containing diorganopolysiloxane. Preferably the diorganopolysiloxane contains from about 0.005% by weight of vinyl groups based on the total weight of the alkenyl-containing diorganopolysiloxanes.

The amount used of diorganopolysiloxane (ii) is generally from about parts to about 50 parts by weight, preferably from about 15 parts to about 50 parts and still more preferably from about 20 parts to about 50 parts, based upon the total weight of the composition.

Component (iii) of the composition of the present invention is an organic solvent. The compositions of the present invention comprise 0 to about 40, preferably from about 0 to about 20, percent by weight of Component(iii). Suitable organic solvents include any of the solvents conventionally used with organosiloxanes and having a boiling point below approximately 250C., such as aromat--- hydrocarbons, e.g., toluene, and xylene; aliphatic hydrocarbons such as hexane, heptane, and petroleum hydrocarbon distillates; normal and iso-paraffins; cycloaliphatic hydrocarbons such as cyclohexane; halogenated hydrocarbon solvents such as trichloroethane and chloroform; 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., tetrahydrofuran and the dimethylether of ethylene glycol; ketones such as methyl isobutyl ketone and esters such as ethyl acetate and the like. Nfixture of organic solvents can also be used.

8 In an embodiment of the present invention, the components of the compositions of this invention can prepared by the following method: Step (A) effecting devolitalization of a resinous siloxane solution of Component W soluble resin copolymer of R3SiO1/. units and Si04/2 units 5 until substantially all of the organic hygroscopic species are removed. Typical organic hygroscopic species include species such as alkanol such as methanol, ethanol, isopropanol, water, volatile light-end hydrolyzate of organosilane derivatives, and the like. Substantial removal generally means the devolatilized resinous solution contains less than 2% by weight of the organic hygroscopic species and preierablv contains less than 1% by weight, per total resin solution. This results in a resin concentrate. Step(B) Mixing Compoient UD an alkenyl-containing diorganopolysiloxane having a viscosity of at least 3,000 cps or higher @ 25C with the resin concentrate formed in Step (A).

In another embodiment of the present invention, an optional dry diluent solvent can be added to the mixture to facilitate the dispersing process. Specific examples of dry diluent solvents include toluene, paraffin or iso-paraffin aliphatic hydrocarbon solvent and the like. Step(C) homogenizing the mixture at a temperature sufficiently high to disperse the mixture from step (B) generally this temperature is at least 80'C or higher, and preferably at least 100"C or higher while stirring. This stirring can be accomplished by any mechanical mixer or stirrer known to the art. Preferably a shear n-Lixer is used. The nuxing continues until a homogeneous, uniform mixture is obtained.

0 tionally step (D) devolatilizing the mixture to give a particular solids p I content by any conventional means known to the art. Specific examples of devolatilizing include vacuum stripped under continuous, uniform, mechanical stirring or the like may be used.

In another embodiment of the present invention, the components of 3 the present compositions of this invention can be prepared separately bef ore they are mixed together. For example, a substantially organic hy I. groscopic species free (or having less than 2% by weight) can be prepared during the 9 12 5 siloxane resin or resinous copolymer manufacturing or devolatized substantially solid. This substantially organic-hygroscopic-species-free resin then can be mixed with component (ii) alkenyl-containing organopolysiloxane with or without aid of any organic solvent.

In still another embodiment of the present invention, the homogeneously dispersed mixture composition of alkenyl-containing organopolysiloxane and component (i) silanol-containing MQ siloxane resin can be further condensed using a base catalyst such as NaOH to form a reaction mixture. A high solids mixture can be derived from the reaction mixture with further devolatilizing.

The base catalvst can be anv base catalyst known to the art. Specific examples include NaOH, KOH, silylated hydroxides and the like.

Small amounts of additional ingredients may be added to the composition of this invention if desired. For example, hydrosilylation catalyst, antioxidants, inhibitors, pigments, stabilizers, fillers, and the like, may be added as long as they do not materially reduce the stability of the mixture or composition, or 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 base mixtures and/ or additives for preparing pressure sensitive adhesives.

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

Vinyl Polymers and Siloxane Resins Two vinyl-containing polydimethylsiloxanes were selected for the preparation of silicone compositions of the following Examples.

Vinyl Silicone A: a dimethylvinylsiloxy stopped polydimethylsiloxane having a viscosity of about 82,000 cps @ 25'C and about 0.064 wt.% vinyl content.

Vinyl Silicone B: A dimethylvinylsiloxy stopped copolymer gum having a general structure MviD_7000DV114MvI and about 0.08 wt.% vinyl content.

Three siloxane resins were selected for use in the following Examples.

Siloxane Resin A: an MQ resin having an approximate structure Of M-0-60Q about 2% by weight of silanol groups and a viscosity of 13.0 cps at 61 wt. % solids in toluene and 3650 cps at 80.1 wt.% solids.

Siloxane Resin B: an MQ resin having an approximate structure of M_0.64Q about 2% by weight of silanol groups and a viscosity of 12 cps at about 61 wt.% solids in toluene and 2225 cps at 79.5 wt.% solids @ 25'C.

Siloxane Resin C: an MQ resin having an approximate structure Of M-0.67Q, about 2% by weight of silanol groups and a viscosity of 15 cps at about 60.5 wt.% solids in toluene and 4800 cps 0 80 wt.% solids.

EXAMPLE-2

Hot Blended and Refluxed Silicone Composition To a reactor equipped with heating and mechanical stirring was charged the following ingredients: 920 g of Siloxane Resin C and 400g of Vinyl Silicone A. After mixing for about 20 minutes, the mixture was heated to reflux, about 170'C, and held at reflux for about 2 hours. Af ter cooling, 2.06 g of dimethyl maleate (DMM) inhibitor was dispersed into the mixture.

The resulting silicone composition had a solids content of 83.4 wt.% and appeared hazy. This mixture exhibited a "waxy, wavy" texture on the container surface. Within a few davs, an oilv laver developed on the mixture.

The mixture was coated over a I mil polyimide film substrate and cured for 3 minutes @ 1701C and the cured adhesive film had a non-uniform, wavy texture. No meaningful adhesive properties could be measured due to a nonuniform adhesive surface.

EXAMPLE 3 Cold Blended, Vacuum Stripped Silicone Mixture This example is prepared according to the method outlined in US Patent No. 4,988,779 (Medford et. al.). A mixture containing the same amounts and components as in Example 2 was mechanically mixed until a 1 11 homogenous mixture was formed at room temperature, and followed by vacuum stripping to yield a mixture having a solids content of about 92 wt.%.

The resulting mixture was very hazy and thick with a heavy "grainy" texture on the mixture surface. The mixture separated into two-layers after approximately 1 week.

The cured adhesive derived from this mixture had an unacceptable grainy texture. No meaningful adhesive properties could be measured due to a nonuniform adhesive surface.

EXAMPLE 4

High Viscosity Silicone Composition Prepared by Reflux Mixing To a reactor equipped with heating and stirring was charged 400 g of Vinvi Silicone B, and 920 g of Siloxane Resin C. After mixing for 30 minutes, the mixture was heated to reflux and held for 2 hours at the reflux temperature. Excess solvents and volatiles were drained and the mixture was cooled to ambient temperature.

The resulting mixture was 80 Wt.% solids and developed "particulates." The bulk mixture had a "waxy and wavy" texture and hazy appearance. No meaningful adhesive properties could be measured due to a non-uniform adhesive surface.

MMPLE 5 Silicone Compositions Siloxane Resin A, having 80.1 wt.% solids and a viscosity of 3650 cps @ 25"C, was devolatilized under reduced vacuum (about 18 mm of mercurv @ 50"C). The devolatilized resin concentrate was further diluted with an isoparaffin hydrocarbon solvent to about 61.2 wt.% solids level. A gas chromatographic analysis was performed to determine the content of hygroscopic organic species. It was found that there was about 2.4% by weight in siloxane resin A before vacuum devolatilization and only about 3 0 0.72% by weight of hygroscopic alcohol in the devolatilized resin solution.

To a reactor was added 350 g of Vinyl Silicone A mixed with 789.2 g of the siloxane resin solution. The mixture was heated to about 100C and held 12 for about 4 hours, while mechanically mixing. The mixture was then stripped under reduced pressure (about 15 nun of mercury) at about 1001C. About 2.07 g of dimethyl maleate and a catalytic amount of Pt catalyst were added to the mixture after cooling.

The resulting silicone mixture had about 89.0 wt.% solids. The mixture appeared homogeneous and remained stable after four months of storage.

EXAMPLE 6

Additional Stable Silicone Composition Siloxane Resin B was processed according to the procedure described in Example 5. The siloxane resin B contains about 2.7% by -weight of hygroscopic organics such as isopropyl alcohol, water and the like, before vacuum devolatilization and its content of these hygroscopic organics was reduced to below 1.0% by weight after devolatilization The siloxane resin concentrate was about 80 wt.% solids. The concentrate was then diluted with Isopar E@ hydrocarbon solvent (an iso-paraffin made by Exxon Chemicals) to about 60.1 wt.% solids.

A silicone composition was prepared according to the procedure described in Example 5 having 304.6 g of Vinyl Silicone A mixed with 700.0 g of the diluted siloxane resin prepared above. The resulting mixture had a solids content of 90.9 % by weight.

The resulting mixture was clear and homogeneous, having a viscositv of about 28,000 cps @ 25'C. The resulting composition remained stable and homogeneous after four months of storage.

EXAMPLES 7 and 8 Stable Reaction Mixtures of Adhesive Compositions Example 7:

The product of a base catalyzed reaction mixture containing 30 parts by weight of a vinyl-containing polydimethylsiloxane gum (approximate )0 structure MD-7/000DV114M; -0.083 wt.% vinyl) and 70 parts by weight of a devolatilized silanol-bearing MQ resin. The devolatilized MQ siloxane resin solution is prepared according to the procedure described in Example 5. The 13 mixture contained 700g devolatilized MQ resin at 60% solids in toluene, 180 g vinyl gum, 120 g toluene was catalyzed with 0.25 g of 10% NaOH. The mixture was heated to reflux temperature and held for 3 hours. The mixture was then deactivated with phosphoric acid to a slightly acidic level; the mixture was then stabilized with a trace amount of rare earth octoate and adjusted to about 73.3 wt.% solids.

Example 8:

The product of a base catalyzed reaction mixture containing 20 parts by weight of a vinyl-containing polydimethylsiloxane gum (approximate structure MD-700ODvil4M; -0-083 wt.% vinyl) and 80 parts by weight of a devolatilized silanol-bearing MQ resin. The devolatilized MQ siloxane resin solution is prepared according to the procedure described in Example 5. The mixture contained 8OOg cievolatilized MQ resin at 60% solids in toluene, 120 g vinyl gum, 80 g toluene was catalyzed with 0.24 g of 10% NaOH. The mixture was heated to reflux temperature and held for 3 hours. The mixture was then deactivated with phosphoric acid to a slightly acidic level; the mixture was then stabilized with a trace amount of rare earth octoate and adjusted to about 72 wt.% solids having a viscosity of about 2900 cps at 25'C.

EXAMPLE 9

Silicone Adhesive Composition Curable silicone compositions for pressure sensitive adhesives were prepared from the following formulation:

30-62 g of the silicone composition prepared in Example 5, 2.20 g of a linear hvdride silicone fluid, 1.30 g of a vinvi siloxane resin (60% solids in toluene solution, MMviQ structure, 2.7 wt.% vinyl), 2.71 g of a siloxane resin- rich reinforcer solution (72.,4% solids, 2840 cps @ 25"0 and a catalytic amount of Pt.

A 1.5 to 2.0 mil thick adhesive was prepared by coating the catalyzed adhesive mixture onto a I mil thick polyiMide film, then cured for 3 minutes @ 170'C. The resulting adhesive had a smooth and uniform finish, and excellent adhesion properties. The 180' Peel adhesion against steel plate was measured according to ASTM D-1000 using a Polyken Probe Tack Tester A 14 equipped with a 0.5 cm probe, 1 second dwell time, a contact pressure of 1000 g per cm2 and a rate of 1 cm/sec. was 25.5 Win, probe tack was 532 g/ cm2, and the adhesive passed a 500T, 1 kg dead-weight, 24 hour lap shear test.

k 1

Claims (1)

1. A silicone composition comprising:

   (i) from about 50 to about 90 parts by weight of a siloxane resin or resinous copolymer comprising R3Si01/4 units and Si04/2 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; (ii) from 10 parts to 50 parts by weight of an alkenyl-containing diorganopolysiloxane having a viscosity of at least 3,000 centipoise at 25'C; and optionally (iii) from 0 to about 40 parts by weight of an organic solvent.

   A method for preparing a stable, homogeneous silicone composition comprising:

   (A) mixing (i) a substantially free of hygroscopic organic volatiles resinous siloxane solution of copolymer comprising R3SiOl /4 units and Si04 /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, (ii) an alkenyl cQntaining diorganopolysiloxane having a viscosity of at least 3,000 centipoise at 25'C and optionally (iii) an organic solvent; (B) homogenizing the mixture at a temperature sufficient to homogeneously disperse the mixture while stirring; and optionally (C) devolatilizing the mixture by stripping the mixture under agitation at reduced pressure.

   1 0. A method'for preparing a stable, homogeneous silicone composition as in Claim 2 further comprising the step of reacting said mixture in the presence of a base catalyst.

   16 4. A method for preparing a stable, homogeneous silicone composition as in Claim 2 further comprising the step of adding a dry diluent solvent to said mixture. 5. A method of preparing a stable, homogeneous silicone composition comprising the steps of. (A) preparing a substantially organic hygroscopic species free siloxane resin or resinous copolymer; (B) mixing said organic hygroscopic species resin or resinous copolymer with an alkenyl-containing organopolysiloxane; (C) homogenizing the mixture at a temperature sufficient to homogeneously disperse the mixture while stirring; and optionally (D) adding an organic solvent. 6. A method of preparing a stable, homogeneous silicone composition as in Claim 5 further comprising the step of condensing said mixture using a base catalyst. 7. A composition as in Claim 1 wherein component (A) is a resinous copolymer and wherein R is a methyl group. 8. A composition as in Claim 1 wherein component (B) is an alkenylcontaining organopolvsfloxane having a viscosity of at least 10,000 centipoise 9250C. 9. A composition as in Claim 1 wherein component (B) is a vinylcontaining polydiorganosiloxane polymer. 10. A composition as in Claim 1 wherein component (B) is a alkenylcontaining polydimethylsiloxane. 11. A composition as in Claim 1 wherein component (B) is an alkenylcontaining poly(dimethyl-co-diphenyl)siloxane or an alkenyl- containing poly(dimethyl-co-methylphenyl)siloxane. 12. A method for preparing a stable, homogeneous silicone composition as in Claim 3 wherein the base catalyst is selected from sodium hydroxide, potassium hydroxide or silylated salts of these bases. 13. A composition as in Claim 1 wherein the optional organic solvent W1) is a non-aromatic solvent selected from aliphatic hydrocarbons having 1 to 20 7 t i Z 17 carbons, normal and isoparaffins having boiling points below 250C, and cycloaliphic hydrocarbons. 14. A composition as in Claim 1 where it contains optionally from 0 to about 20% by weight of an organic solvent. 15. A composition as in Claim 6 wherein the base catalyst for preparing reaction mixture is selected from sodium hydroxide, potassium hydroxide, or their silylated salts. 16. A composition as in Claim I wherein the content of hygroscopic organic volatile is preferably less than about 2% by weight of the composition. 17. A composition as in Claim I further comprising a thermal stabilizer. 18. A composition as in Claim 17, wherein said thermal stabilizer is a carboxylic acid salt of rare earth metal.