High tenacity polyethylene-2, 6-naphthalate fibers

Abstract

The present invention relates to a high strength polyethylene-2,6-naphthalate fiber produced by a method comprising controlling the stress-strain curve and fine structure of an undrawn yarn such that the drawability of the undrawn yarn in a drawing step is improved. The industrial polyethylene-2,6-naphthalate fiber with high strength according to the present invention shows high strength and low shrinkage, and a treated cord formed from this fiber has improved dimensional stability and high strength, such that it can be advantageously employed as a fibrous reinforcement material of rubber products such as tires.

1 - 10 . (canceled)  
   
   
       11 . A process for producing polyethylene naphthalate fiber comprising the steps of: 
 (a) extruding a polymer containing more than 85 mol % of ethylene 2,6-naphthalate units and having an intrinsic viscosity of 0.80-1.2, through a spinneret at a spinning draft ratio from 20 to 200 at a temperature of 290-330° C. to form a molten spun yarn;    (b) passing the molten spun yarn through a retarded cooling zone and then quenching and solidifying the spun yarn;    (c) withdrawing the solidified yarn at a speed that the undrawn yarn has a birefringence of 0.001-0.015 and shows a stress-strain curve in which the yarn is elongated by less than 10% and has an initial modulus of 10-50 g/d, when subjected to an initial stress of 0.3 g/d, and it is elongated by at least 200% when subjected to a stress greater than the initial stress but smaller than 1.0 g/d; and    (d) subjecting the withdrawn yarn to multi-stage drawing to a total draw ratio of at least 4.0.    
   
   
       12 . The process of  claim 11 , wherein the polymer used in the step (a) is a solid state-polymerized polyethylene-2,6-naphthalate chip containing 30-70 ppm of manganese metal and 150-300 ppm of antimony metal.  
   
   
       13 . The process of  claim 12 , wherein the chip further comprises a phosphorus component in an amount such that the manganese/phosphorus weight ratio is 2.0 or below.  
   
   
       14 . The process of  claim 11 , wherein the solidification zone in step (b) comprises a heating zone having a length of 200 to 700 mm and is maintained at a temperature of 300 to 400° C., and a cooling zone disposed just below the heating zone.  
   
   
       15 . A polyethylene naphthalate fiber obtained by the process according to  claim 11 , wherein the polyethylene naphthalate fiber has (1) an intrinsic viscosity of 0.6 to 0.9, (2) a tenacity of at least 8.5 g/d, (3) an elongation of at least 6%, (4) a birefringence of at least 0.35, (5) a density of 1.355 to 1.375, and (5) a shrinkage of 1 to 4%.