GB831961A - Improvements in or relating to the manufacture of shaped structures such as filaments or foils from high-melting linear polyesters - Google Patents

Abstract

Extruded filaments, films and like shaped structures of linear polyesters are heated without stretching until pre-orientation, i.e. orientation imparted by the extrusion process, is substantially removed to a temperature above the second order transition point and below the lower limit of the thermoplastic temperature range of the polyester, and are thereafter stretched in at least one dimension. Preferably the heat treatment is effected at a temperature above the second order transition point and below the apparent minimum crystallization point. The heat treatment may be effected discontinuously on wound threads, so that shrinking is prevented, or on hanks, so that shrinking may proceed simultaneously. Alternatively the treatment may be a continuous treatment of a thread or cable, allowing or preventing shrinkage as desired. Hot water, hot air or steam may be used to effect the heat treatment. Specified linear polyesters are polymethylene terephthalates, e.g. polyethylene terephthalate, and polyesters of para - o - hydroxybutoxybenzoic acid and hydroxypivalic acid. Minor quantities of other bifunctional components may be incorporated with the polyesters, e.g. isophthalic acid, adipic acid, sebacic acid, diphenyl para-para-dicarboxylic acid, naphthalene - 2 : 7 - dicarboxylic acid and naphthalene - 1 : 5 - dicarboxylic acid, or the polyesters may be derived from 1 : 4-butanediol or hexamethylene glycol. In an example, polyethylene terephthalate is melt-spun into thread which is wound on a bobbin and subsequently run without tension through a water bath at 95 DEG C. The thread is thereafter oriented by cold drawing. Specification 695,567 and U.S.A. Specification 2,578,899 are referred to.