Pressure-sensitive adhesive layer-forming organopolysiloxane composition, and use thereof

An organopolysiloxane composition for forming a pressure-sensitive adhesive layer, the composition comprising:

• (A) a chain or cyclic organopolysiloxane having on average more than one alkenyl group in a molecule;
• (B) an organopolysiloxane resin in which the sum of contents of hydroxyl groups and hydrolyzable groups relative to all silicon atoms in a molecule is 9 mol % or less;
• (C) an organohydrogenpolysiloxane having at least two Si—H bonds in a molecule;
• (D) an organic silicon compound having on average more than one alkenyl group in a molecule;
• and
• (E) an effective amount of a hydrosilylation reaction catalyst;
• and
• optionally, (A′) a chain organopolysiloxane not containing a reactive group containing a carbon-carbon double bond in a molecule;
• wherein an amount of component (C) is an amount such that a ratio (molar ratio) of the substance amount of SiH groups in component (C) to the total substance amount of alkenyl groups in components (A), (B) and (D) is 5.0 or more;
• wherein component (D) is different from components (A) and (B) and is at least one type of an organic silicon compound selected from a group consisting of:
• (d1) an organic silicon compound having at least one silicon atom-bonded alkenyl group and at least one silicon atom-bonded alkoxy group in a molecule;
• (d2) an organic silicon compound having at least one silicon atom-bonded alkenyl group, at least one silicon atom-bonded alkoxy group, and at least one silicon-bonded epoxy-containing monovalent organic group in a molecule;
• (d3) a reaction product of a silane or siloxane having at least one silicon atom-bonded alkoxy group in a molecule and an organosiloxane having at least one silicon atom-bonded hydroxy group and at least one silicon atom-bonded alkenyl group in a molecule;
• and
• (d4) a reaction product of an organosilane having at least one silicon atom-bonded alkoxy group and at least one silicon atom-bonded epoxy-containing monovalent organic group in a molecule, an organosiloxane having at least one silicon atom-bonded hydroxy group in a molecule, and an organosiloxane having at least one silicon atom-bonded alkenyl group in a molecule;
• and
• wherein a mass ratio of component (B) to the sum of component (A) and component (A′) is within a range of 0.9 to 3.0, and wherein a pressure-sensitive adhesive layer obtained by curing the composition has a shear storage elastic modulus G′ at 25° C. of 0.005 MPa to 20 MPa, a stress at 500% strain at 25° C. of 0.005 MPa to 3 MPa, and a pressure-sensitive adhesive force of 360 gf/inch to 4000 gf/inch as measured at a tension rate of 300 mm/min using a 180° peeling test method in accordance with JIS Z 0237 for a polymethyl methacrylate sheet having a thickness of 2 mm, when a thickness of the pressure-sensitive adhesive layer is 50 μm.