Process of making polyester multifilament yarn
A method of producing a polyethylene terephthalate-based polyester fiber includes spinning polyethylene terephthalate based polyester to produce an undrawn yarn with an intrinsic viscosity of 0.83 or more and a density of 1338 g/cm 3 or more, multi-stage drawing the undrawn yarn, heat-setting the drawn yarn, relaxing heat-set yarn, and winding the relaxed yarn to produce the resulting drawn yarn with an intrinsic viscosity of 0.83 or more and a density of 1.38 to 1.3865 g/cm 3 , so that the thusly produced industrial polyester yarn with high modulus and low shrinkage contributes to significantly improving strength retention (tenacity of a dip cord/tenacity of a grey yarn) of the dip cord, produced by treating the polyester yarn with an adhesive (RFL) and subsequently heat-treating the RFL-treated polyester yarn, to be useful as a tire cord.
1. A method of producing a polyester multifilament yarn for rubber reinforcement, comprising;
A) melt-spinning polyester, containing 95 mole % or greater ethylene terephthalate as a repeating unit, passing the spun polyester through a hot zone (heating or non-heating zone) and a quenching zone to enable the spun polyester to be solidified to produce an undrawn yarn having an intrinsic viscosity (I.V.) of 0.83 or more and a density of 1.338 g/cm 3 or more, and oiling the undrawn yarn; and
B) multi-stage drawing the oiled undrawn yarn using a draw roller at 80° C. or less, and heat-setting a resulting yarn using a heat-set roller at 210° C. or less to produce a drawn yarn having a density from 1.38 to 1.3865 g/cm 3 and a tenacity of 7.2 g/d or more.