Patent attributes
A polypropylene based heat shrinkable film obtained by using a propylene-ethylene block copolymer (A) which satisfies the following requirements (A-i) to (A-iv), and having heat shrinkability imparted by orientation in at least one direction:(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);(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.
