Polybenzazole fiber and article comprising the same

Abstract

The present invention relates to polybenzazole fibers which can still have high durability against atmospheres of high temperatures and high humidity even after yarns made thereof have had kink bands therein due to the damages in the course of post-processing for making woven fabrics, knitted fabrics, braids, ropes and cords. The invention also relates to articles comprising the polybenzazole fibers, particularly spun yarns, rubber-reinforcing materials, fiber-reinforced composite materials, woven or knitted fabrics, knife-proof materials or bullet-proof vests, ropes and sail cloths.

1 . A polybenzazole fiber having a strength retention (%) of 80% or more, which is determined by the equation: (a/b)×100, provided that the notations a and b are defined as follows: 
 the notation a indicates the strength of a yarn [cN/dtex] measured as follows: polybenzazole filaments are S-wise twisted so that the twist coefficient can be 30, to thereby make a yarn, which is then left to stand alone for 30 seconds, and the yarn is S-wise untwisted until the twist coefficient is decreased to 6, and the untwisted yarn is exposed to an atmosphere of 80° C. and 80 RH % for 240 hours and taken out at room temperature to measure the strength of the yarn; and    the notation b indicates the strength of a yarn [cN/dtex] measured as follows: polybenzazole filaments are S-wise twisted so that the twist coefficient can be 30, to thereby make a yarn, which is then left to stand alone for 30 seconds, and the yarn is S-wise untwisted until the twist coefficient is decreased to 6, and the strength of the untwisted yarn is measured.    
   
   
       2 . A polybenzazole fiber according to  claim 1 , wherein the average strength of a single polybenzazole fiber with an average diameter d of 5 to 22 μm and a length of 100 mm is 4.5 GPa or more.  
   
   
       3 . A polybenzazole fiber according to  claim 1 , wherein the coefficient of variation CV (a standard deviation/an average value) of the diameters of a single filament, measured at 10 mm intervals over 500 mm length of the filament is 0.08 or less.  
   
   
       4 . A polybenzazole fiber according to  claim 1 , wherein the stoichiometric ratio of an inorganic base to a mineral acid remaining in the fiber is 0.8 to 1.4:1.  
   
   
       5 . A polybenzazole fiber according to  claim 1 , which contains an organic pigment having a thermal decomposition temperature of 200° C. or higher and is soluble in a mineral acid.  
   
   
       6 . A polybenzazole fiber according to  claim 5 , wherein the content of the organic pigment is 2 to 8 mass %.  
   
   
       7 . A spun yarn comprising a polybenzazole fiber according to  claim 1 , as at least one component.  
   
   
       8 . A cord for reinforcing rubber, comprising a polybenzazole fiber according to  claim 1 , as at least one component.  
   
   
       9 . A composite material comprising a polybenzazole fiber according to  claim 1 , as at least one component.  
   
   
       10 . A woven or knitted fabric comprising a polybenzazole fiber according to  claim 1 , as at least one component.  
   
   
       11 . A knife-proof material comprising a polybenzazole fiber according to  claim 1 , as at least one component.  
   
   
       12 . A bullet-proof vest comprising a polybenzazole fiber according to  claim 1 , as at least one component.  
   
   
       13 . A high strength fiber rope comprising a polybenzazole fiber according to  claim 1 , as at least one. component.  
   
   
       14 . A sail cloth comprising a polybenzazole fiber according to  claim 1 , as at least one component.