GB866822A - Improvements in the treatment of polymers and copolymers of propylene - Google Patents

Abstract

Articles, particularly films, of polypropylene or copolymers of propylene, which have been oriented by stretching during production, are heated by means of a hot fluid and thereafter subjected, while hot, to bi-axial orientation. In a preferred process polypropylene is extruded in the form of a tube, both stretching operations are effected by gas inflation of the tube between pairs of nip rollers or other restricting means, and heating is effected by passing the tube through a hot liquid, such as propylene glycol. The propylene copolymer, which may be a graft or block copolymer, may be a copolymer of propylene with ethylene, isobutylene, amylene, butadiene or 1- or 2-butene, copolymers of propylene and ethylene containing 5% or less of propylene being excluded. Specifications 866,820 and 866,821 also are referred to.