Biaxially-oriented polypropylene films
AssigneeQpf, Llg
InventorsAlan M. Davis, Thomas M. Krigas
Life of this patent
Estimating the term…
Abstract
A biaxially-oriented polypropylene (BOPP) film with improved barrier properties, and a method of making the film are provided. The MVTR of a multi-layer BOPP film is improved by blending wax in the core layer resin, and providing a polyolefin cap layer on each side of the core layer. Significant additional improvements are seen when the film is heated at a temperature below the melting point of the core layer resin, below the distortion temperature of the film, and above the melting point of the wax for a time generally extending from at least five minutes to several hours or more in length, depending on the temperature.
Claims32
A method of making a multilayer thermoplastic film having improved barrier and haze properties, comprising the steps of:
- (a) forming a blend of a polypropylene resin selected from the group consisting of isotactic homopolymers of propylene, copolymers of propylene with ethylene or butene, terpolymers of propylene with ethylene and butene and mixtures thereof, and 0.25 to 15 wt. % of a crystalline, incompatible wax having an average molecular weight of 300 to 1000;
- (b) extruding and casting the blend to form a core layer of a film;
- (c) orienting the Core layer in biaxial directions;
- and,
- (d) then providing on each side of the oriented core layer a polyolefin cap layer to provide a multilayer film, whereby loss of wax from said film is avoided.
A method of making a multilayer thermoplastic film having improved barrier and haze properties, comprising the steps of:
- (a) forming a blend of a polypropylene resin selected from the group consisting of isotactic homopolymers of propylene, copolymers of propylene with ethylene or butene, terpolymers of propylene with ethylene and butene and mixtures thereof, and an 0.25 to 15 wt. % of a crystalline, incompatible wax having an average molecular weight of 300 to 1000;
- (b) extruding and casting the blend to form a core layer of a film;
- (c) orienting the core layer in a first direction;
- (d) then providing on each side of the oriented core layer a polyolefin cap layer to provide a multilayer film, whereby loss of wax from said film is avoided;
- and
- (e) orienting the film of step (d) in a second direction transverse to the first direction.
Dependencies are inferred from the claim text.