POLYPROPYLENE FILM HAVING GOOD STRETCHABILITY

摘要

PURPOSE:A PP film low in unevenness of thickness and good in stretchability, obtained by molding a specified PP into a film. CONSTITUTION:Propylene is bulk-polymerized in the presence of a catalyst system comprising a MgCl2-carrying TiCl4 catalyst, an organoaluminum compound, and ester compound, etc., and low-stereoregularity PP is removed from the product by using a low-boiling hydrocarbon to obtain PP having a limiting viscosity as determined in tetralin at 135 deg.C of 1.4-1.7dl/g, a boiling diethyl ether-soluble portion, contained in PP obtained by completely dissolving the product PP in tetralin at 160 deg.C and then cooling the solution, of 1.3-4.0wt%, and a boling n-hexane-soluble portion, contained in the boiling diethyl ether-insoluble portion, of 2.0-6.0wt%, based on the weight before extracting the boiling diethyl ether- soluble portion. A PP film obtained by melt-extruding the above PP and casting it in a cooling drum is longitudinally stretched at 120-150 deg.C and a ratio of 4- 10, laterally stretched at 130-165 deg.C and a ratio of 4-15, and then heat-treated at 80-170 deg.C while giving it a lateral relaxation of 0-25%.