The present invention relates to silicone compositions suitable for forming pressure sensitive adhesive compositions. More particularly, the present invention relates to free radical curable fluorosilicone compositions which cure to form pressure sensitive adhesive compositions having excellent fuel and solvent resistance, while maintaining good tack and peel adhesion properties.
The term "pressure sensitive adhesive" (PSA), as used herein, refers to adhesives that can 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 adhesive strength. In other words, an adhesive whose cohesive strength is higher or better than its adhesive strength is referred to as a pressure sensitive adhesive.
Silicone PSAs have excellent cohesive strength, tack and peel adhesion strength, which are properties generally required of pressure sensitive adhesives. In addition, they also have heat resistance, cold resistance, electrical properties, and the like, characteristic of silicones, and so are widely used for electrical-insulating tape which must be highly reliable, and for various pressure-sensitive products which must be resistant to hot and cold environments.
A drawback associated with the use of silicone PSAs is that when exposed to organic solvents such as toluene, cured silicone pressure sensitive adhesives swell and loose desirable peel and tack properties in the swollen state. Solvent-sensitivity can limit applications where frequent or even occasional exposure to harsh environments occurs.
Silicone compositions containing resinous siloxane copolymers (so-called MQ resins) and polyorganosiloxanes capable of curing to form pressure sensitive adhesive compositions are known in the art. It is also known that in such Compositions a relatively large proportion by weight of resinous siloxane copolymers is required to achieve satisfactory adhesive properties. However, these resinous copolymers are a particularly solvent-sensitive species in the compositions.
It is known that fluoro-containing polymers and fluoro-organo polymers are solvent resistant, but do not mix readily with siloxanes and tend to separate from non-fluoro compounds such as MQ resins. These materials have not been generally used for PSAs. Further, few organic solvents are available to prepare solutions containing both fluorosilicone polymers and resinous siloxanes.
U.S. Pat. No. 4,980,443 (Kendziorski et al.) is directed to a curable organo hydrogen polysiloxane compound and a fluorosilicone polymer mixed therein to provide coating compositions useful for a release liner to protect silicone pressure sensitive adhesives. Kendziorski et al. does not disclose a pressure sensitive adhesive employing an MQ resin and a fluorosilicone.
U.S. Pat. No. 4,972,037 (Garbe et al.) is directed to various compositions including adhesives, surface modifying compositions, sealing compositions and topical binders formed of copolymers having a vinyl polymeric backbone with grafted pendant siloxane polymeric moieties. In the patent, pressure sensitivity of the adhesive is varied. The non-pressure sensitive compounds include fluoro compositions.
U.S. Pat. No. 4,465,805 (Blizzard et al.) is directed to curable, hydrocarbon liquid resistant fluorosilicones which include the reaction product of an MQ resin, and a polydiorganosiloxane, a vinyl or hydroxyl fluorosilicone and a catalyst. The material may be formed into elastomers and coatings for various substrates.
European Patent Application No. 0355991 (Boardman) is directed to a pressure sensitive adhesive composition containing (A) a benzene soluble resinous copolymer (an MQ resin); (B) a diorganoalkenylsiloxy end blocked polydiorganosiloxane; (C) a polydiorganohydrogensiloxy endblocked polydiorganosiloxane, (B) and (C) having 0 to 1,000 repeating units, (D) a cross-linking agent, and (E) a hydrosilation catalyst. Boardman shows a relatively high MQ resin content and does not disclose or suggest that fluorosilicone components would provide useful properties.
U.S. Pat. No. 3,983,298 (Hahn et al.) is directed to a composition suitable for use as a pressure sensitive adhesive containing 50 to 60 parts of an MQ resin and relatively high viscosity polyorganosiloxanes.
U.S. Pat. No. 4,774,297 (Murakami et al.) is directed to the preparation of pressure sensitive adhesives using vinyl functional polysiloxanes and 70-30 parts by weight of an organopolysiloxane containing M and Q units.
European Patent Application No. 0269454 (Murakami et al.) discloses a composition suitable for forming pressure sensitive adhesives including an alkenyl group-containing silicone polymer, a tackifying silicone resin and a organohydrogensiloxane, and a platinum containing catalyst. The patent does not disclose pressure sensitive adhesives using solvent resistant fluorosilicones.
U.S. Pat. No. 4,988,779 (Medford et al.) discloses a composition suitable for forming a pressure sensitive adhesive employing an MQ resin (50-70 parts) and organopolyoxanes.
It is desirable to provide solvent resistant fluoro-containing polyorganosiloxane compositions which cure to yield silicone pressure sensitive adhesives having desirable properties. In the present invention, it was found that a free radical curable silicone composition having a high weight percent of fluorosilicone polymers, a reduced amount of silanol containing MQ resins and compatible diorganosiloxane polymers can be cured to form solvent resistant, pressure sensitive adhesives with good tack and peel adhesion.