Adhesive compositions are typically comprised of a silicone resin such as an MQ resin and a polydiorganosiloxane fluid containing sufficient hydrolyzable/condensable functionality to crosslink and form a cured matrix. MQ resins which contain a significant level of Si-bonded hydroxyls, or whose surface has been rendered inert through an additional trimethylsilylation capping reaction, are useful for these types of adhesive sealants.
Adhesive systems, containing MQ resin having a significant amount of reactive --SiOH produce strong adhesive products which demonstrate the ability to provide an acceptable level of adhesive strength, not only at room temperature, but also at elevated temperatures (e.g. &gt;120.degree. C.). This is important in some applications where the laminated part has to operate at temperatures of at least 120.degree. C. In addition to providing sites for interaction with the fluid portion of the adhesive matrix, the hydroxyl content can also be a source of instability and abbreviated shelf life in the final product. Shelf life of these systems can be improved via the addition of reactive, hydrolyzable silanes. The degree of improvement in stability is dependent upon both the type and concentration of silane added to the mixture.
Capped resins can also be used to produce high-strength, moisture curable adhesives. For example, Japanese Kokai Patent Application No. Hei 4[1992]81487 to Arai et al. discloses a pressure sensitive composition containing (1) an organosiloxane polymer resin having less than 0.7 wt % hydroxylsilyl radicals (2) a hydrolyzable group containing organopolysiloxane having a viscosity of 50 to 300,000 mm.sup.2 /s and (3) a condensing catalyst.
Although the compositions produced using capped resins are stable in the absence reactive silanes, they do not retain a sufficient amount of adhesive strength for service at elevated temperatures.
It is an object of the instant invention to provide pressure sensitive adhesive compositions which can be cured in the presence of moisture and that has high adhesive strength at elevated temperatures.