Pressure-sensitive adhesive composition and pressure-sensitive adhesive sheets

Pressure-sensitive adhesive sheets comprising a substrate having formed on one or both sides thereof an adhesive layer comprising an adhesive composition comprising

• a reactive mixture of an acrylic prepolymer having highly reactive hydroxyl groups in the molecule thereof and a weight average molecular weight of 5,000 to 300,000 which is obtained by copolymerizing
• (a) 75 to 99.95% by weight of an acrylate monomer represented by formula (I):
• CH.sub.2 .dbd.CH(R.sub.1)COOR.sub.2 (I)
• wherein
• R.sub.1 represents a hydrogen atom or a methyl group;
• and
• R.sub.2 represents an alkyl group having 2 to 14 carbon atoms, and
• (b) 0.05 to 25% by weight of an acrylate monomer represented by formula (II):
• CH.sub.2 .dbd.CH(R.sub.1)COOR.sub.3 (II)
• wherein
• R.sub.1 represents a hydrogen atom or a methyl group;
• and
• R.sub.3 represents an alkyl group having 3 to 14 carbon atoms and at least one hydroxyl group,
• provided that a positional number n of the carbon atom farthest from the ester bond in formula (I) and a positional number m of the farthest carbon atom from the ester bond that has a hydroxyl group bonded thereto in formula (II) satisfy the relationship:
• m.gtoreq.n-1, and
• a polyfunctional isocyanate mainly acting as a bifunctional chain extender.

A pressure-sensitive adhesive composition comprising

• (1) a reactive mixture of
• (A) an acrylic prepolymer having highly reactive hydroxyl groups in the molecule thereof and a weight average molecular weight of 2,000 to 300,000 which is obtained by copolymerizing
• (a) 75 to 99.95% by weight of an acrylic monomer represented by formula (I):
• CH.sub.2 .dbd.CH(R.sub.1)COOR.sub.2 (I)
• wherein
• R.sub.1 represents a hydrogen atom or a methyl group;
• and
• R.sub.2 represents an alkyl group having 2 to 14 carbon atoms, and
• (b) 0.05 to 25% by weight of an acrylic monomer represented by formula (II):
• CH.sub.2 .dbd.CH(R.sub.1)COOR.sub.3 (II)
• wherein
• R.sub.1 represents a hydrogen atom or a methyl group;
• and
• R.sub.3 represents an alkyl group having 3 to 14 carbon atoms and at least one hydroxyl group,
• provided that a positional number n of the carbon atom farthest from the ester bond in formula (I) and a positional number m of the farthest carbon atom from the ester bond that has a hydroxyl group bonded thereto in formula (II) satisfy the relationship:
• m.gtoreq.n-1, and
• (B) a polyfunctional isocyanate mainly acting as a bifunctional chain extender, and
• (2) a relatively high molecular weight polymer component having a glass transition temperature of -10.degree. C. or lower and a weight average molecular weight of 200,000 to 1,500,000.

Pressure-sensitive adhesive sheets comprising a substrate having formed on one or both sides thereof an adhesive layer comprising an adhesive composition comprising

• (1) a reactive mixture of
• (A) an acrylic prepolymer having highly reactive hydroxyl groups in the molecule thereof and a weight average molecular weight of 2,000 to 300,000 which is obtained by copolymerizing
• (a) 75 to 99.95% by weight of an acrylic monomer represented by formula (I):
• CH.sub.2 .dbd.CH(R.sub.1)COOR.sub.2 (I)
• wherein
• R.sub.1 represents a hydrogen atom or a methyl group;
• and
• R.sub.2 represents an alkyl group having 2 to 14 carbon atoms, and
• (b) 0.05 to 25% by weight of an acrylate monomer represented by formula (II):
• CH.sub.2 .dbd.CH(R.sub.1)COOR.sub.3 (II)
• wherein
• R.sub.1 represents a hydrogen atom or a methyl group;
• and
• R.sub.3 represents an alkyl group having 3 to 14 carbon atoms and at least one hydroxyl group,
• provided that a positional number n of the carbon atom farthest from the ester bond in formula (I) and a positional number m of the farthest carbon atom from the ester bond that has a hydroxyl group bonded thereto in formula (II) satisfy the relationship:
• m.gtoreq.n-1, and
• (B) a polyfunctional isocyanate mainly acting as a bifunctional chain extender, and
• (2) a relatively high molecular polymer component having a glass transition temperature of -10.degree. C. or lower and a weight average molecular weight of 200,000 to 1,500,000.