GB1172643A - Composite Propylene Polymer Films. - Google Patents

Abstract

1,172,643. Composite polypropylene fibres. HERCULES Inc. 19 March, 1968 [24 March, 1967], No. 13232/68. Heading B5B. A composite film comprises an extruded layer of a first propylene polymer provided with at least one surface layer of a co-extruded different propylene polymer, each of the polymers having a density at 20‹ C. of at least 0À88. The expression " composite film " is defined as meaning a film, in the nature of a laminate, having two or more distinct polymer layers, formed by the co-extrusion of the polymeric components under such conditions that the two or more component layers come into contact with each other while they are molten. The term " propylene polymer " is defined as meaning all homopolymers of propylene and copolymers having at least 75 mole per cent propylene units in their structure. Thus the composite film can comprise a layer of a copolymer surfaced with a homopolymer, a copolymer surfaced with a copolymer of different molecular weight distribution or different molecular structure, or even a homopolymer surfaced with a homopolymer of different molecular weight distribution. A preferred form of composite film comprises a centre core of a copolymer of propylene with up to about 25 mole per cent ethylene surfaced with two layers of a homopolypropylene. The preferred composite films have a total thickness of about ¢ to 5 mils. but the thickness may be up to 20 mils. One layer can vary from about 5 to 95% of the total thickness or total mass of the film. In the example films are prepared containing core layers of a 3-block copolymer of 3 mole per cent ethylene content, the thickness of the films being 1, 2 and 3 mils and the proportions by volume of the copolymer being in each case 28, 64 and 84%. The polymers and copolymers of propylene which make up the composite films of this invention contain a substantial degree of crystallinity as indicated by the requirement that the propylene polymer must have a density of at least 0-88 at 20‹ C. copolymer of ethylene and propylene or a totally amorphous (atactic) homopolymer of polypropylene has a density of about 0-85, a totally crystalline homopolymer of propylene has a density of about 0-935 and the familiar " crystalline " polypropylene and " crystalline " block and random ethylene-propylene copolymers of commerce usually have densities of about 0-88 to about 0-91. The polypropylene homopolymer used in the composite films of the invention can be any isotactic polypropylene having a reduced specific viscosity (determined at 135‹ C. using decalin as a solvent) of about 1 to 5 and a density at 20‹ C. of at least 0À88.