There is disclosed a thermoplastic, film-forming composition comprising a blend of
A. a propylene-ethylene copolymer, the propylene content of the copolymer being from 95 to 99.75% by weight of the copolymer, and
B. a polymer of an alpha-olefin of 4 to 10 carbon atoms copolymerized with from 0 to 10% by weight of the copolymer of an alpha-olefin of 2 to 10 carbon atoms,
The alpha-olefin polymer constituting from 41 to 90% by weight of the composition.
The propylene-ethylene copolymer preferably contains from 2 to 4% by weight of ethylene, and preferably, in granular form, exhibits a Melt Flow Index of from 10 to 200 g/10 minutes, measured according to ASTM/D1238-65T (Condition N).
The alpha-olefin component of the blend is suitably a polymer, preferably a homo-polymer, of butene-1, and suitably has a Melt Flow Index, by the aforementioned test, of less than 50 g/10 minutes, preferably between 5 and 40 g/10 minutes.
To ensure the production of films having acceptable optical characteristics, the alpha-olefin component preferably comprises from 45 to 65% by weight of the composition. Additives, such as pigments, anti-static agents, and the like, conventionally employed in film production, may be included in the composition, if desired.
The composition is suitably employed for the production of self-supporting films, and is particularly useful as a heat-sealable surface layer of a coextruded, biaxially oriented, multiple-layer film having a substrate layer of a propylene homo- or co-polymer. Such films are heat-sealable at comparatively low temperatures to provide strong heat seals, and are particularly suitable for the packaging of foodstuffs, and the like.