Patent ID: 7662888

Claim:
A polypropylene based heat shrinkable film comprising a propylene-ethylene block copolymer (A), and having heat shrinkability imparted by orientation in at least one direction: wherein at least prior to melt extrusion of the propylene-ethylene block copolymer (A) into the film and the orientation in at least one direction, the propylene-ethylene block copolymer (A) satisfies the following requirements (A-i) to (A-iv) (A-i) it is a propylene-ethylene block copolymer obtained through sequential polymerization catalyzed by a metallocene catalyst which is composed of 30 to 95 wt % of a propylene homopolymer or propylene-ethylene random copolymer component (A1) having an ethylene content of at most 7 wt % produced in a first step and 70 to 5 wt % of a propylene-ethylene random copolymer component (A2) produced in a second step having an ethylene content higher by 3 to 20 wt% than that of the component (A1); wherein the sequential polymerization comprises the first step of polymerizing propylene, and optionally up to at most 7% of ethylene, in the presence of the metallocene catalyst to produce propylene homopolymer or propylene-ethylene random copolymer component (A1); followed by the second step of copolymerizing, in the presence of component (A1), propylene and ethylene in the presence of the metallocene catalyst, wherein the content of ethylene in the second step is higher than the ethylene content in the first step by an amount of 3 to 20wt %, to provide propylene-ethylene random copolymer component (A2); (A-ii) it has a melt flow rate (MFR: 2.16 kg, 230° C.) within a range of 0.1 to 30 g/10 min; (A-iii) a temperature-loss tangent (tan δ) curve obtained by dynamic mechanical analysis (DMA) has a single peak at a temperature of at most 0° C.; (A-iv) in a temperature rising elution fractionation (TREF) curve obtained as a plot of an elution amount (dwt%/dT) to a temperature by means of temperature rising elution fractionation (TREF) using an o-dichlorobenzene solvent in a temperature range of −15° C. to 140° C., a peak temperature T(A1) observed at a high temperature side is within a range of 60° C. to 88° C., a peak temperature T(A2) observed at a low temperature side is at most 40° C. or a peak temperature T(A2) is not observed, and a temperature T(A4) at which 99 wt% of the total amount of the propylene-ethylene block copolymer is eluted is less than 90° C.