FEUILLE ORIENTEE BIAXIALEMENT EN POLYPROPYLENE, EN COPOLYMERE OU EN MELANGES DE POLYPROPYLENE ET DE POLYETHYLENE ET PROCEDE DE FABRICATION DE CELLE-CI

摘要

1373965 Isotropic polypropylene films KALLE AG 13 Dec 1971 [14 Dec 1970] 57780/71 Heading B5B [Also in Division B2] A substantially isotropic film is made from polypropylene or a copolymer or blend of polypropylene with from 1 to 10% by weight of polyethylene. The film has the following properties:-(a) the modulus of elasticity is greater than 230 kg./mm.2 preferably greater than 250 kg./mm.2 in all directions of the film; (b) the ratio of the elastic moduli; in the longitudinal direction to the transverse direction is from 0À75 to 1À25, preferably between 0À85 to 1À15; (c) the tensile strengths in all directions of the film plane are above 20 kg./mm.2, preferably above 22 kg./mm2.; (d) the ratio of the tensile strengths in the longitudinal and transverse directions is 0À75 to 1À25, preferably from 0À85 to 1À15; (e) the elongation at break in all directions of the film plane are less than 90%, preferably less than 85%; (f) the shrinkage at 120% is more than 10%, preferably more than 12%, in all directions of the film plane; (g) the shrinkage ratios in the longitudinal and transverse directions are 0À70 to 1À30, preferably from 0À80 to 1À20. The film is made by extruding at 200 to 300‹C. from a slit die and then treating in the following fashion:-(i) cooling to a temperature of 15 to 80‹ C., preferably 20‹ C. to 40‹ C.; (ii) the film is heated to a temperature from 60 to 10‹ C., preferably 50 to 20‹ C. below the crystallite melting point of the polypropylene; (iii) the film is stretched longitudinally at a ratio of 6 : 1 to 8 : 1, preferably 6À5 : 1 to 7À5 : 1; (iv) the film is cooled to a temperature of 140 to 60‹ C. below the c.m.p., preferably 120 to 50‹ C. below; (v) the film is heated to a temperature of 50 to 5‹ C., preferably 35 to 15‹ C. below the c.m.p.; (vi) the film is then transversely stretched at a ratio of 6 : 1 to 8 : 1, preferably 6À5 : 1 to 7À5 : 1; (vii) the film is cooled under tension to a temperature below 50‹ C., preferably below 30‹ C., no diminution of width being permitted preferably the width being increased.