JPS6456546A - Polypropylene heat-shrinkable film - Google Patents

Abstract

PURPOSE:To improve processability in stretching, sliding properties and productivity and widen an appropriate temperature range for heat shrinkage and packaging, by a method wherein the title film is constituted of both outer layers comprised of specific crystalline polypropylene resin and an intermediate layer comprised of a copolymer of specific propylene and alpha-olefin. CONSTITUTION:This film is constituted so that both outside layers are comprised of crystalline polypropylene resin whose melting point is 135-150 deg.C, an intermediate layer is comprised of copolymer of propylene whose Vicat softening point is 70-110 deg.C and 2-8C alpha-olefin and, moreover, a thickness of the said intermediate layer becomes 30-80% of the whole thickness. When the melting point of the crystalline polypropylene resin exceeds 150 deg.C, processability in stretching at a low temperature becomes difficult, and when the same is lower than 135 deg.C the title film is inferior to heat resistance. When the Vicat softening point exceeds 110 deg.C, processability in stretching at the low temperature becomes difficult and when the same is lower than 70 deg.C, heat shrinkage at the low temperature can't be displayed sufficiently. When a thickness ratio of the intermediate layer is less than 30%, the processability in stretching at the low temperature is not improved and when the same exceeds 80%, the title film is inferior to heat resistance.