Patent ID: 6906143

Claim:
A propylene-ethylene block copolymer comprising: from 60 to 85% by weight of a crystalline polypropylene portion which is a propylene homopolymer or a copolymer of propylene and up to 1 mol % of ethylene or α-olefin having 4 or more carbon atoms, and from 15 to 40% by weight of a propylene-ethylene random copolymer portion with a propylene to ethylene weight ratio (propylene/ethylene) of from 75/25 to 35/65, wherein the propylene-ethylene block copolymer satisfies requirements (1-1) and (1-2) below: Requirement (1-1): The propylene-ethylene random copolymer portion comprises two kinds of propylene-ethylene random copolymer components (EP-A) and (EP-B), wherein the copolymer component (EP-A) has an intrinsic viscosity [η] EP-A of not less than 1.5 dl/g but less than 4 dl/g and an ethylene content [(C2′) EP-A ] of not less than 20% by weight but less than 50% by weight, and wherein the copolymer component (EP-B) has an intrinsic viscosity [η] EP-B of not less than 0.5 dl/g but less than 3 dl/g and an ethylene content [(C2′) EP-B ] of not less than 50% by weight and not more than 80% by weight, Requirement (1-2): The content (EP-cont.) of the propylene-ethylene random copolymer portion, the ethylene content [(C2′) EP ] in the propylene-ethylene random copolymer portion and the volume-average equivalent circular diameter (Dv) of dispersed particles which are formed when the propylene-ethylene block copolymer is molded and which correspond to the propylene-ethylene random copolymer portion satisfy the following formula (I): Dv ≦−1.7+0.032×[( C 2′) EP ]+0.082×( EP -cont.) (I): and also satisfies requirement (2) below: Requirement (2): The propylene-ethylene block copolymer has a melt flow rate (MFR) of from 5 to 120 g/10 min.