Drawn poly(ethyleneterephthalate) fiber, a tire cord, and their preparation methods

Abstract

The present invention relates to a drawn poly(ethyleneterephthalate) (PET) fiber exhibiting excellent dimensional stability and uniform properties while having high fineness of 2000 denier or more, a tire cord, and their preparation method. The drawn PET fiber includes PET 90 mol % or more, and has a crystallinity of 40 to 50%, an amorphous orientation factor (AOF) of 0.01 to 0.2, a monofilament fineness of 2.5 to 4.0 denier, a coefficient of variation (CV) of cross sectional area of 8.0% or less, and a total fineness of 2000 to 4000 denier.

What is claimed is: 
     
         1 . A drawn poly(ethyleneterephthalate) (PET) fiber, including 90 mol % or more of PET and having a crystallinity of 40 to 50%, an amorphous orientation factor (AOF) of 0.01 to 0.2, a monofilament fineness of 2.5 to 4.0 denier, a coefficient of variation (CV) of cross sectional area of 8.0% or less, and a total fineness of 2000 to 4000 denier. 
     
     
         2 . The drawn PET fiber according to  claim 1 , wherein the CV of cross sectional area is 2.5 to 7.5%. 
     
     
         3 . The drawn PET fiber according to  claim 1 , having a tensile strength of 8.0 to 9.5 g/d. 
     
     
         4 . The drawn PET fiber according to  claim 1 , having an intermediate elongation (@ 4.5 g/d load) of 4.0 to 6.5% and a breaking elongation of 12.0 to 20.0%. 
     
     
         5 . A method of preparing a drawn PET fiber, including the steps of:
 melt-spinning a polymer including 90 mol % or more of PET through a spinneret by 3-ply or 4-ply co-spinning method so as to prepare an undrawn PET fiber having a fineness of 2000 denier or more, wherein the spinning speed is 2500 to 4000 m/min; and   drawing the undrawn fiber with a drawing ratio of 1.4 to 2.0.   
     
     
         6 . The method of preparing a drawn PET fiber according to  claim 5 , wherein the melt-spinning step is carried out with a spinning tension of 0.5 to 1.2 g/d. 
     
     
         7 . The method of preparing a drawn PET fiber according to  claim 5 , wherein the undrawn fiber has a crystallinity of 10 to 30%. 
     
     
         8 . A method of preparing a PET tire cord, including the steps of:
 preparing a drawn PET fiber according to the method of  claim 5 ;   co-twisting the drawn fibers so as to prepare a twisted yarn; and   dipping the twisted yarn in an adhesive solution and heat-treating the same.   
     
     
         9 . The method of preparing a PET tire cord according to  claim 8 , wherein the heat-treating step is carried out at the temperature of 230 to 260° C. for 90 to 360 sec. 
     
     
         10 . A PET tire cord, having a total fineness of 4000 to 8000 denier, a tensile strength of 7.2 to 8.5 g/d, a dimensional stability index (E-S index) of 5.0 to 7.0%, wherein the E-S index is the sum of a dry heat shrinkage rate after heat-treatment at 177° C. for 2 min under the load of 0.01 g/d and an intermediate elongation (@ 2.25 g/d load). 
     
     
         11 . The PET tire cord according to  claim 10 , having an intermediate elongation (@ 2.25 g/d load) of 3.0 to 5.5% and a breaking elongation of 15.0% or more. 
     
     
         12 . The PET tire cord according to  claim 10 , which is used as a cord for body ply of a pneumatic tire.