GB695567A - Super-stretching polyester filaments, yarns, films, and similar structures - Google Patents

Abstract

Filaments, yarns, films or like articles are formed of a substantially amorphous synthetic linear polyester and stretched in at least one dimension 10-75 times the original dimension at a temperature which is 20-60 DEG C. above the apparent minimum crystallization temperature of the amorphous polyester. Such a treatment results in stretched products which are free from molecular orientation. If desired, these products may be submitted to a subsequent drawing operation to produce molecular orientation. This subsequent drawing may be effected at a temperature which is lower than that of the previous stretching operation and which is between the second order transition temperature (Tg) for the polyester and a temperature 30 DEG C. above the apparent minimum crystallization temperature (T1). The temperature T1 is the lowest temperature at which a marked density change, known to occur simultaneously with crystallization, takes place within six hours. The temperature Tg is the temperature at which a discontinuity occurs in the curve of a first derivative thermodynamic quantity with temperature, i.e. in the first portion of the curve showing the relation to temperature of a physical property which is a linear function of the temperature. It can be observed by plotting density, specific volume, specific heat, sonic modulus, or index of refraction against temperature. The subsequent drawing operation may be carried out in two stages if desired. The drawing operation is accompanied by molecular crystallization. If desired, crystallization may be effected by a heat treatment without the subsequent drawing operation, and the yarn or film may be allowed to shrink. The initial stretching should be carried out under dry heating conditions, e.g. the yarn or film may be heated in air, glycol, silicone oils or mineral oils. The polymer is preferably a polymethylene terephthalate, e.g. it may be a polymerized ester of ethylene glycol and terephthalic acid with, if desired, other copolymerizable substances such as diethylene glycol, tetra- or hexa-methylene glycol, hydroterephthalic acid, adipic acid, a naphthalic acid or bis-p-carboxyphenoxyethane. A polyester having an intrinsic viscosity of at least 0.3 is preferred. The amorphous state of the polymer is obtained by melt spinning and rapidly chilling the yarn or film as soon as it is formed. In an example, an amorphous polyethylene terephthalate yarn (Tg=67 DEG C., T1= 99 DEG C.) is run through oil at 127 DEG C. and on emerging is passed round a roll which stretches it 13 times. From this roll the yarn is passed round a pin which is heated to 94 DEG C., and then to another roll which draws the initially stretched yarn to 4 times its length, giving a total length of 52 times the original. In another example, monofils are stretched and drawn while in the form of a warp sheet, and in another example yarn is heated and stretched while passing through a tube through which hot air travels in counter-current. Specification 578,079 is referred to.