Pressure-sensitive adhesive sheet and pressure sensitive adhesive composition

A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of a pressure-sensitive adhesive composition, wherein

• the pressure-sensitive adhesive composition includes:
• an acrylic polymer (A) having a glass transition temperature lower than 0° C.;
• and
• a polymer (B) containing, as monomer units, both a monomer (B1) having a polyorganosiloxane skeleton and a monomer (B2) whose homopolymer has a glass transition temperature of 40° C. or higher;
• wherein the acrylic polymer (A) contains, as a monomer unit, at least one monomer selected from the group consisting of N-vinyl cyclic amides represented by the following general formula (M1);
• wherein R1 is a divalent organic group,
• wherein pressure-sensitive adhesive force to each of a stainless plate, an ABS plate, and a glass plate, occurring in an initial condition of 23° C. for 30 minutes, is smaller than 3.0 N/25 mm, and
• wherein pressure-sensitive adhesive force to each of the plates, occurring in an ordinary condition of 48 hours at 40° C., followed by 23° C. for 30 minutes, is 5.7 times or more larger than the pressure-sensitive adhesive force occurring in the initial condition.

A pressure-sensitive adhesive composition comprising:

• an acrylic polymer (A) having a glass transition temperature lower than 0° C.;
• and
• a polymer (B) containing, as monomer units, both a monomer (B1) having a polyorganosiloxane skeleton and a monomer (B2) whose homopolymer has a glass transition temperature of 40° C. or higher;
• wherein the acrylic polymer (A) contains, as a monomer unit, at least one monomer selected from the group consisting of N-vinyl cyclic amides represented by the following general formula (M1):
• wherein R1 is a divalent organic group;
• wherein a content of the monomer selected from the group consisting of N-vinyl cyclic amides is 0.01% by mass to 40% by mass, based on the total monomer components of the polymer (A),
• the total monomer components of the polymer (B) comprise:
• 15% by mass or more but 30% by mass or less of the monomer (B1), and
• 10% by mass or more but 80% by mass or less of a (meth)acrylic monomer whose homopolymer has a glass transition temperature of 80° C. or higher, as the monomer (B2),
• the monomer (B2) comprises both a (meth)acrylic monomer whose homopolymer has a glass transition temperature of 80° C. or higher and a (meth)acrylic monomer whose homopolymer has a glass transition temperature of 40° C. or higher but lower than 80° C.