Method for producing a high modulus polyester yarn

Claim 1

Method for producing a high modulus yarn from a copolyester resin which yarn is heat-settable without tension comprising: a. forming filaments from a copolyester resin consisting of at least 15 to 50 mole percent of an interpolymerized randomly repeating unit having the formula: ##STR5## and from 85 to 50 percent of an interpolymerized randomly repeating unit having the formula: ##STR6## wherein n for both units is an integer of from 2 to 10, the fiber resin having an intrinsic viscosity of at least about 0.55 as determined in a 60 weight percent phenol and 40 weight percent tetrachloroethane solution at 30° C; b. combining the resulting filaments into a yarn; c. uniformly orienting the resulting yarn by drawing the yarn at a temperature of about 20° C higher than its glass transition temperature and at 75% of its break-draw ratio, and d. heat-setting the oriented yarn by passing it through a heat zone maintained about 125° to 185° C for a time ranging from 1 to 10 minutes, while in a free-to-relax condition, said heat-setting being conducted without tensioning of said yarn.