Silicone-based pressure-sensitive adhesive composition and pressure-sensitive tape or sheet

A silicone-based pressure-sensitive adhesive composition comprising:

• 100 parts by weight of (A) a branched organopolysiloxane having on average at least two alkenyl groups on molecular terminals and represented by the following molecular formula (1):
• (R3SiO1/2)4-p(R1R2SiO1/2)p(R2SiO)m(RR1SiO)n(SiO4/2) (1)
• (wherein R designates a monovalent hydrocarbon group or a monovalent halogenated hydrocarbon group which is free of unsaturated aliphatic bonds and has 1 to 10 carbon atoms;
• R1 designates an alkenyl group having 2 to 10 carbon atoms;
• “p” is a number which on average is in the range of 2 to 4;
• “m” is a number which on average is in the range of 1,500 to 10,000;
• “n” is a number which on average is equal to or greater than 0;
• and m>n, and (m+n) on average is in the range of 1,500 to 10,000);
• 10 to 400 parts by weight of (B) an organopolysiloxane resin composed of R3R22SiO1/2 units (where R2 designates an alkyl group with 1 to 10 carbon atoms, R3 designates an alkyl group with 1 to 10 carbon atoms, an alkenyl group with 2 to 10 carbon atoms, an aryl group with 6 to 10 carbon atoms or a hydroxyl group) and SiO4/2 units, where the mole ratio of the R3R22SiO1/2 units to SiO4/2 units ranges from 0.6 to 1.7;
• (C) an organohydrogenpolysiloxane having in one molecule two or more silicon-bonded hydrogen atoms, which is used in an amount sufficient to provide a mole ratio of silicon-bonded hydrogen atoms of this component to alkenyl groups contained in components (A) and (B) in the range of 1.0 to 60;
• and
• (D) a catalytic quantity of a platinum-type catalyst.