POLYPROPYLENE/ETHYLENE POLYMER FILM HAVING EASE-OF-TEAR ON IMPACT

摘要

1398476 Composite films TOYO BOSEKI KK 11 June 1973 [9 June 1972 27 Oct 1972 27 Dec 1972] 27678/73 Heading B5B The invention comprises a composite film containing polypropylene and an ethylene polymer having (a) N y -N x of 0À006-0À025, (b) 0À5(N x +N y )-N z #0À012, e.g. down to 0À006, where N x , N y and N z are the refractive indices in machine (M.D.), transverse (T.D.) and vertical directions, (c) break elongation in M.D. of 150-180% and (d) no surface necking. The ethylene polymer may be ethylene copolymerized with propylene, vinyl acetate, an acrylate or maleic acid Zn salt. The mixture preferably contains polypropylene and polyethylene in a wt. ratio of 40 : 60-90 : 10. The polyethylene may have a density of 0À926- 0À96 gm./cm.3. Alternatively, polypropylene may be mixed with a polymerized ethylene monomer in a wt. ratio of 40 : 60-95 : 5, preferably 40 : 60-90 : 10 when the ethylene copolymer is propylene-ethylene. Propylene may also be mixed with a polypropyleneethylene copolymer and ethylene wherein the total wt. of propylene polymers to the ethylene polymer is 40 : 60-90: 10. The polyethylene may be a mixture of a polyethylene having a density of 0À926-0À945 g./cm.3 and a polyethylene having a density of 0À946 g./cm.3. The film may have a thickness of 5-200 Á. The break strength may be 200-350 kg./cm.3 in M.D. and 700-1450 kg./cm.2 in T.D. The break elongation in T.D. may be 50-750% and the impact strength 0À7-7 kg.cm./25 Á. The film may be prepared by melt extrusion, e.g. in a T-die, followed by stretching in M.D. at a draw ratio of 1À02 : 1-2À0 : 1 and then in T.D. at 4 : 1-20 : 1. During stretching the deformation rate in M.D. and T.D. may be 5000-3,000,000% min, and 200-100,000% min. respectively. The stretched film may be heated at 50-160‹ C. The unsaturated film . may have a thickness of 25-5000 Á.