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Abstract

A method and apparatus for manufacturing a film suitable for use in lamination under heat and pressure. A plurality of resins is co-extruded into concentric annuli, the inner annulus being a polyester type resin, and at least one of the outer annuli consisting of a polyolefin based resin. The co-extrusion is carried out as the extruding die is rotated about its axis. After quenching to form a multi-layer seamless tube, the tube is collapsed and heated to a temperature suitable for biaxial orientation. An air bubble is introduced into the heated tube to expand the diameter thereof and simultaneously orient the tube biaxially by molecular orientation. The biaxially oriented tube is cooled sufficiently to retain its molecular orientation, and is then collapsed. The tube is then heated to a shrinking temperature while under controlled restraint to achieve a predetermined dimension in amount of shrinkage in the film. Finally, the edges of the shrunk tube are slit to form a pair of flat films. Additional improvements are achieved by including irradiation of the films by ultraviolet light, and by treating one of the film surfaces with a corona discharge.

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First Claim