Liquid crystal polyester fiber and producing method thereof

Abstract

Provided is a liquid crystal polyester fiber having high strength, high elastic modulus, high abrasion resistance, excellent processability, and little thermal deformation at high temperature, and also provided is a production method thereof. A liquid crystal polyester fiber, characterized in that the peak half-value width of the endothermic peak (Tm1) observed when measuring by differential calorimetry under rising temperature conditions starting at 50° C. and increasing 20° C./min is 15° C. or higher, the polystyrene-converted weight-average molecular weight is between 250,000 and 2,000,000 inclusive, the peak temperature of the loss tangent (tan δ) is between 100° C. and 200° C. inclusive, and the peak value of the loss tangent (tan δ) is between 0.060 and 0.090 inclusive. A mesh fabric comprising the liquid crystal polyester fiber. A production method for melt liquid crystal polyester fiber, characterized in that liquid crystal polyester fiber obtained by melt-spinning is subject to solid-phase polymerization, and subsequently heat treated at a stretch ratio of at least 0.1% and under 3.0% at a temperature at least 50° C. higher than the endothermic peak temperature (Tm1) as observed when measuring by differential calorimetry under rising temperature conditions starting at 50° C. and increasing 20° C./min.

1 . A method of producing a melt-spun liquid crystal polyester fiber, said method comprising:
 melt spinning a liquid crystal polyester fiber thereby polymerizing said fiber in a solid phase; and   heat stretching the polymer at a temperature of an endothermic peak (Tm1)+50° C. or more and at a stretch rate of 0.1% or more and less than 3.0%, wherein the endothermic peak is observed by a differential calorimetry under a temperature elevation condition of 20° C./min from 50° C.;   wherein melt-spun liquid crystal polyester has: a peak half-value width of 15° C. or more at an endothermic peak (Tm1) observed by a differential calorimetry under a temperature elevation condition of 20° C./min from 50° C.; a weight-average molecular weight in terms of polystyrene of 250,000 or more and 2,000,000 or less; a peak temperature of a loss tangent (tan δ) of 100° C. or more and 200° C. or less; and a peak value of the loss tangent (tan δ) of 0.060 or more and 0.078 or less; and   wherein the peak temperature and peak value of loss tangent (tan δ) are determined by measuring a dynamic viscoelasticity from 60° C. to 210° C. under the conditions of a frequency of 110 Hz, an initial load of 0.13 cN/dtex, and a temperature elevation rate of 3° C./m.   
     
     
         2 . The method according to  claim 1 , wherein the heated fiber is taken up under a yarn route regulation with yarn route guide in a range of 1 cm or more and 50 cm or less from an exit portion of a heating region. 
     
     
         3 . The method according to  claim 1 , wherein the liquid crystal polyester is a) a polymer of an aromatic oxycarboxylic acid component; b) a polymer of an aromatic dicarboxylic acid component, an aromatic diol component and/or an aliphatic diol component; or c) a copolymer of a) and b).