POLYPROPYLENE BLOCK COPOLYMER AND FILM THEREFROM

摘要

PURPOSE:To provide a copolymer for films for retort foods excellent in resistance to impact, heat and blocking at low temperatures and in food sanitation. CONSTITUTION:The block copolymer can be obtained by 1st stage polymerization for the polymer portion (A-component) consisting mainly of propylene using a Ziegler-Natta catalyst virtually in the absence of inert solvent to an extent of 60-80wt.% of the overall polymerization followed by 2nd stage polymerization for the ethylene-propylene copolymer portion (B-component) 20-50wt.% in ethylene content in a vapor phase to an extent of 20-40wt.% of the overall polymerization. The intrinsic viscosity of the B-component ([eta]B) is >=2.0dl/g and the ratio of the intrinsic viscosity of the B-component to that of the A- component ([eta]B/[eta]A) is <=1.8. The other objective film can be obtained by melt blending of the above copolymer follow by extrusion.