Polypropylene based heat shrinkable film

摘要

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´) 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.