Patent ID: 7858708

Claim:
A propylene-ethylene-butene block copolymer comprising from 60 to 85% by weight, based on the whole amount of the propylene-ethylene-butene block copolymer, of a polypropylene portion which is a propylene homopolymer or a copolymer of propylene with 1 mol % or less of at least one comonomer selected from the group consisting of ethylene and α-olefins having 4 or more carbon atoms, and from 15 to 40% by weight, based on the whole amount of the propylene-ethylene-butene block copolymer, of a propylene-ethylene-butene random copolymer portion having a weight ratio of propylene units to ethylene units is from 35/65 to 75/25, wherein the propylene-ethylene-butene block copolymer satisfies the requirements (1) and (2) provided below: requirement (1): the propylene-ethylene-butene random copolymer portion comprises a propylene-ethylene random copolymer component (EP) and a propylene-ethylene-butene random copolymer component (EPB), the copolymer component (EP) having an intrinsic viscosity [η] EP of from 1.5 to 8 dl/g and an ethylene unit content [(C2′) EP ] of from 20 to 50% by weight, and the copolymer component (EPB) having an intrinsic viscosity [η] EPB of from 0.5 to 8 dl/g, an ethylene unit content [(C2′) EPB ] of from 47 to 77% by weight, a butene unit component [(C′4) EPB ] of from 3 to 33% by weight, and a total of the ethylene unit content [(C′2) EPB ] and the butene unit content [(C4′) EPB ] being from 50 to 80% by weight; requirement (2): the propylene-ethylene-butene block copolymer has a melt flow rate of from 5 to 120 g/10 min.