Block copolymer, block copolymer composition, hot melt pressure-sensitive adhesive composition, and pressure-sensitive adhesive composition

A hot-melt adhesive composition comprising,

• 100 parts by mass of the block copolymer composition,
• 25 to 400 parts by mass of a tackifying resin,
• 0.01 to 50 parts by mass of a free radical photo initiator, and
• 0 to 200 parts by mass of a plasticizer,
• wherein the hot-melt adhesive composition further comprises a polyfunctional unsaturated compound, and
• the block copolymer composition comprises a block copolymer A, a diblock copolymer B, and a polymer C, wherein
• a content of the block copolymer A in the block copolymer composition is 10% by mass or more, and a total content of the diblock copolymer B and the polymer C in the block copolymer composition is 60% by mass or less,
• a content of an aromatic monovinyl monomer unit in the block copolymer composition is within a range of 5 to 40% by mass,
• a weight average molecular weight (Mw) of the entire block copolymer composition is within a range of 300000 to 800000,
• a melt index measured according to ASTM D1238 of the block copolymer composition (G condition, 200° C., 5 kg load) within a range of 0.5 to 50 g/10 min,
• the block copolymer A is represented by a following general formula (I), in which a ratio ((Ar1-D1)/D2) of a mass of a branched chain represented by Ar1-D1 to a mass of a branched chain represented by D2 is 1.0/0.15 to 1.0/1.75,
• (Ar1-D1)mX(D2)n (I)
• where, in the formula (I), Ar1-D1 and D2 are each a branched chain bonded to X, Ar1 is an aromatic monovinyl polymer block, D1 and D2 are each a conjugated diene polymer block, “m” is an integer of 1 or more, “n” is an integer of 1 or more, “m”+“n” is an integer of 3 or more, and X is a residue of a polyfunctional coupling agent,
• the diblock copolymer B is a diblock copolymer represented by a following general formula (II) and having a molecular weight distribution (Mw/Mn) of 1.20 or less,
• Ar3-D3 (II)
• where, in the formula (II), Ar3 is an aromatic monovinyl polymer block, and D3 is a conjugated diene polymer block, and
• the polymer C is a conjugated diene polymer having a molecular weight distribution (Mw/Mn) of 1.20 or less.