Silicone-based pressure-sensitive adhesives are characterized by excellent electrical-insulating properties, resistance to heat, adhesive strength, and other useful properties, and therefore they find wide application in situations that require reliability.
In particular, in order to improve heat-resistant properties of silicone-based pressure-sensitive adhesives, it has been proposed to combine them with cerium-containing compounds (see Japanese Patent Publication No. Hei 6-96698), substances that contain organosilicon compounds with B—O—Si bonds (see Japanese Patent Application Laid-Open No. Hei 7-11228), or phenol-based oxidation inhibitors (see Japanese Patent Application Laid-Open No. 2003-96429, corresponding to U.S. Pat. No. 6,815,076).
However, the use of adhesive tapes that utilize silicone-based pressure-sensitive adhesives with cerium-containing compounds or with substances that contain organosilicon compounds having B—O—Si bonds is associated with a problem. This problem is that peeling of these adhesive tapes from their substrates after expose to high temperatures leaves a part of the pressure-sensitive adhesive layer on the substrate. As compared to the adhesives of the aforementioned type, the adhesives with phenol-based oxidation inhibitors are subject to the above problem to a lesser degree, but they still leave a part of the pressure-sensitive adhesive layer on a substrate if exposed to high temperatures over a long time. Therefore, when the adhesive tapes based on the use of the aforementioned pressure-sensitive adhesives are used as masking tapes, e.g., in solder reflow processes on printed-circuit boards, the residual pressure-sensitive adhesive layer left on the surface of the heat-treated substrate after removal of the tape creates problems for subsequent processing of the product.
It is an object of the present invention to provide a silicone-based pressure-sensitive adhesive capable of forming a pressure-sensitive adhesive layer that maintains good removability after being exposed to high temperatures. It is another object to provide an adhesive tape that preserves good removability after being exposed to high temperatures.