GB1115464A - Multiply film - Google Patents

Abstract

A water resistant, grease resistant, oxygen resistant, polyolefin film comprises a polyolefin film bonded to a continuous, smooth, uniform, turpentine-impermeable, water-insoluble layer of retrograded "amylose." The films may be prepared by: applying a film forming amylose composition on to a preformed self-supporting polyolefin film; applying a film-forming polyolefin composition to a preformed self suporting amylose film, or laminating a preformed, self supporting amylose film to a preformed self supporting polyolefin film. The film may be bonded to a paper base e.g. natural kraft paper. This multiply structure may be pepared by applying an amylose coating to one side of the paper and a polyolefinic coating to the other side; applying an amylose coating to the polyolefin side of a polyolefincoated paper; or applying a polyolefin coating to the amylose side of an amylose-coated layer, the coatings being applied as preformed films or as a suitable film-forming composition. The term "polyolefin" refers to polymers comprising at least 50 mole % hydrocarbon monomers such as ethylene, propylene, butene, 1, styrene. Suitable comonomers include ethyl acrylate, acrylic acid, vinyl acetate, chloride. The term "amylose" refers to the amylose resulting from the fractionation of any variety of starch into amylose and amylopectin; whole starch composed of at least 75% amylose; simulated natural starches containing at least 75% amylose e.g. mixtures of separated amylose with amylopectin, or of corn starches having less than 75% amylose mixed with separated amylose; derivatives of amylose having a maximum degree of substitution of 0.15 and are water insoluble at 40 DEG C. The amylose layer may be plasticised preferably with polyvinyl alcohol with less than 20 mole per cent of the monomeric units containing acetyl groups. A list of other suitable plasticizer is given which includes polyhydric alcohols, amino-alcohols, hydroxyalkyl amides, quarternary ammonium compounds. The amylose layer may be applied as an aqueous solution at above the gellation temperature using a roll applicator and an air knife, the amylose then being allowed to gel. The amylose retrogrades form the aqueous solution concurrently with gellation. A plurality of amylose layers may be applied. Other methods of application mentioned are coating with a doctor blade, spray applicator, wire wrapped rod, knife coating, trailing blade coater, size press. Dry amylose compositions can be extruded on to the polyolefin film or polyolefin coated paper. The polyolefin can be activated by: flame treatment; by chemicals e.g. by application of polyethylene imine, by ozone treatment; by glow discharge; by extrusion. Polyethylene may be extruded on to a preformed emylose film, paper or amylose-coated paper. Methods of preparing self supporting emylose films are described. Preformed amylose film and preformed polyolefin-film or polyolefin-coated paper may be laminated together using a polyethylene imine as a tie coat.