Polyester multifilament yarn for rubber reinforcement and method of producing the same
Disclosed is a method of producing a polyethylene terephthalate-based polyester fiber, including spinning polyethylene terephthalate based polyester to produce an undrawn yarn with an intrinsic viscosity of 0.83 or more and a density of 1.338 g/cm 3 or more, multi-stage drawing the undrawn yarn, heat-setting the drawn yarn, relaxing the 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 . Compared to a prior polyester yarn with high modulus and low shrinkage, produced according to conventional melt-spinning and drawing processes, an industrial polyester yarn with high modulus and low shrinkage according to the present invention 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 of the present invention with an adhesive (RFL) and subsequently heat-treating the RFL-treated polyester yarn. Therefore, the polyester multifilament yarn according to the present invention is useful as a tire cord.
1. A polyester multifilament yarn for rubber reinforcement, produced according to the method comprising:
A) melt-spinning polyester, containing 95 mole % or more ethylene terephthalate as a repeating unit, passing the spun polyester through a retarded cooling zone (heating or non-heating zone) and a cooling zone to enable the spun polyester to be solidified to produce an undrawn yarn with an intrinsic viscosity of 0.83 or more and a density of 1.338 g/cm 3 or more; and
B) multi-stage drawing the undrawn yarn such that a draw ratio is 1.5 to 2.5, and heat-setting a resulting yarn to produce a drawn yarn with a density of 1.38 to 1.3865 g/cm 3 and a tenacity of 7.2 g/d or more
and having a density of 1.38 to 1.3865 g/cm 3 , a shrinkage of 4.5% or more, an intrinsic viscosity of 0.83 or more, a tenacity of 7.2 g/d or more, and a carboxyl end group of 20 microequivalents/g or less.