FREMGANGSMAADE OG APPARAT TIL FREMSTILLING AF ET ARK- ELLER BANEFORMET PLASTMATERIALE MED STOR STYRKE

摘要

A method of preparing a high strength sheet material comprising (a) forming a laminate comprising at least two layers of a thermoplastic polymer material, each layer having a fibrillar grain structure providing a predominant direction of splittability in each said layer, and wherein the layers are bonded to one another with the said predominant directions of splittability transverse to each other, (b) biaxially orienting the molecules of said layers by stretching the layers in substantially uniaxial steps, the transverse streching being effected by applying pressure to the surface of the laminate along lines extending substantially in the longitudinal direction of the laminate to impart thereto a waved configuration, and (c) subjecting the biaxially oriented laminate to a heat treatment while allowing at least 7% shrinkage of the laminate to take place in at least its transverse direction.