| 摘要 |
PURPOSE:To obtain heat-shrinkable film excellent in not only low temp. shrinkability but also waterproof whitening and environmental destruction resistance by a method wherein a vinyl aromatic hydrocarbon copolymer block in a block copolymer is composed of both small molecular weight component and large molecular weight component in a specified ratio. CONSTITUTION:The titled film comprises a copolymer composed mainly of three or more vinyl aromatic hydrocarbon and a copolymer block composed mainly of two or more conjugated dienes. In this block copolymer, a weight ratio of the vinyl aromatic hydrocarbon to the conjugated diene is 60:40-90:10. Further, the copolymer has two kinds of vinyl aromatic hydrocarbon copolymer block groups having average molecular weights 5,000-35,000 and 5,000 or more. The block copolymer in which the weight ratio of the former to the latter is 1:1-1:6 is flattened in the film form and stretched uniaxially or biaxially to obtain heat- shrinkable film having a heat shrinking percentage 10% or more at 90 deg.C. |
