Patent ID: 8232351

Claim:
A heat-shrinkable polystyrene film formed in an elongated shape with a constant width from a polystyrene resin, a main shrinkage direction thereof being in a longitudinal direction, the heat-shrinkable polystyrene film meeting the following requirements (1) to (4): (1) the hot-water heat shrinkage ratio in the longitudinal direction is 25% or more and 80% or less when the film is treated in hot water at 90° C. for 10 seconds; (2) the hot-water heat shrinkage ratio in a width direction orthogonal to the longitudinal direction is −5% or more and 10% or less when the film is treated in hot water at 90° C. for 10 seconds; (3) the right angle tear strength in the width direction per unit thickness after the film is shrunk by 10% in the longitudinal direction in hot water at 80° C. is 50 N/mm or more and 200 N/mm or less; and (4) each of the breaking energies in the longitudinal direction and the width direction is 1,000 MPa·% or more and 10,000 MPa·% or less when the film is kept at 30° C. for 2 weeks or longer and then a tensile test is performed at 23° C.