Adhesive composition and adhesive sheet

1 . An adhesive composition comprising:

a (meth)acrylic polymer (A) which is a polymer of monomer components comprising 69.9 to 99 mass % of at least one (meth)acrylic acid ester consisting of an alkyl (meth)acrylate ester having an alkyl group having 4 to 12 carbon atoms, 0.5 to 15 mass % of a crosslinkable functional group-containing monomer other than an amino group-containing monomer, and 0.01 to 5 mass % of an amino group-containing monomer;

an acid-modified polyolefin (B);

at least one tackifier resin (C) selected from a rosin tackifier resin (C1) and a terpene phenol tackifier resin (C2), wherein the tackifier resin (C) has a weight average molecular weight of 500 to 4500 and a hydroxyl value of 15 to 150 mgKOH/g; and

a crosslinking agent (D),

the adhesive composition satisfying the following requirements (I) to (III):

(I) a value of a ball tack test performed by a J. Dow method using an adhesive layer having a thickness of 50 μm obtained from the adhesive composition is 5 or less,

(II) an adhesive force in measurement after an adhesive surface of an adhesive layer having a thickness of 50 μm obtained from the adhesive composition is bonded to a polypropylene plate and left to stand for 20 minutes in an environment at 80° C. is 10.0 N/25 mm or more, and

(III) when a test piece in which an adhesive surface of an adhesive layer having a thickness of 50 μm obtained from the adhesive composition is bonded to a polypropylene plate in an area of 50 mm×20 mm is left to stand for 20 minutes in an environment at 80° C. and then a load of 200 g is applied to an end portion on one end side in a longitudinal direction of the test piece in an environment at 80° C., a peeling amount of the adhesive layer after 1 hour from the start of application of a load is 30 mm or less.

2 . The adhesive composition according to claim 1 , wherein the amino group of the amino group-containing monomer is a tertiary amino group.

3 . The adhesive composition according to claim 1 , wherein the (meth)acrylic polymer (A) is a polymer of monomer components comprising 69.9 to 94 mass % of the alkyl (meth)acrylate ester having an alkyl group having 4 to 12 carbon atoms, 0.5 to 15 mass % of the crosslinkable functional group-containing monomer other than the amino group-containing monomer, 0.01 to 5 mass % of the amino group-containing monomer, and 5 to 25 mass % of an alkyl (meth)acrylate ester having an alkyl group having 1 to 3 carbon atoms.

4 . The adhesive composition according to claim 1 , wherein the crosslinkable functional group-containing monomer other than the amino group-containing monomer is (meth)acrylic acid.

5 . The adhesive composition according to claim 1 , wherein the adhesive composition comprises 5 to 20 parts by mass of the acid-modified polyolefin (B) and 5 to 50 parts by mass of the tackifier resin (C) with respect to 100 parts by mass of the (meth)acrylic polymer (A).

6 . The adhesive composition according to claim 1 , wherein a haze of an adhesive layer having a thickness of 50 μm obtained from the adhesive composition is less than 35%.

7 . The adhesive composition according to claim 1 , wherein the (meth)acrylic polymer (A) is a polymer of monomer components comprising 74.9 to 99 mass % of the alkyl (meth)acrylate ester having an alkyl group having 4 to 12 carbon atoms, 0.5 to 15 mass % of the crosslinkable functional group-containing monomer other than the amino group-containing monomer, and 0.01 to 5 mass % of the amino group-containing monomer.

8 . An adhesive sheet comprising:

a substrate; and

an adhesive layer provided on the substrate, the adhesive layer being obtained from the adhesive composition according to claim 1 .