Wholly aromatic polyamide fiber and process for producing the same

Abstract

A wholly aromatic polyamide fiber which has excellent mechanical properties (toughness factor) and can be produced while attaining a satisfactory operation stability in the fiber formation step. The fiber comprises 100 parts by mass of a wholly aromatic polyamide and 0.05 to 20 parts by mass of particles of a lamellar clay mineral, e.g., hectorite, saponite, stevensite, beidellite, montmorillonite, or swelling mica.

1 . Drawn and oriented wholly aromatic polyamide fibers comprising a resin composition comprising a matrix composed of a wholly aromatic polyamide resin and layer-structured clay mineral particles dispersed and distributed in an amount of 0.05 to 20 parts by mass, based on 100 parts by mass of the matrix, in the matrix.  
   
   
       2 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein a plurality of regions, in which the layer-structured clay mineral particles are distributed in a relatively high distribution density, are scatteringly distributed in the wholly aromatic polyamide matrix.  
   
   
       3 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein when the wholly aromatic polyamide fibers are cross-cut along the fiber axes, the resultant cross-sectional profiles are observed with an electronic microscope at a magnification of 100,000, and in each cross-sectional profile, a total area S 1  of a plurality of regions in which regions a change in conditions of the fiber cross-sectional profile due to an influence of the layer-structured clay mineral particles distributed in the observation area S 2  of 25 μm 2  is found, is measured, the degree of dispersion Y of the layer-structured clay mineral particles in each fiber, defined by the equation (1): 
         Y (%)=( S 1/ S 2)×100  (1) 
     is in the range of from 0.1 to 40.  
   
   
       4 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein the layer-structured clay mineral comprises at least one selected from hectorite, saponite, stevensite, beidellite, montmorillonite and swelling mica.  
   
   
       5 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein the layer-structured clay mineral particles are ones treated with an intercalating agent.  
   
   
       6 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein the layer-structured clay mineral particles have an average layer thickness of 10 to 500 nm.  
   
   
       7 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein the layer-structured clay mineral particles have a degree of orientation A of 50% or more, determined in accordance with the equation (2): 
         A (%)=[(180 −w )/180]×100  (2) In equation (2), w represents a half value width of an intensity distribution determined, in an X-ray analysis of the layer-structured clay mineral particles, along a Debye ring of a reflection peak in a (001) plane of the layer-structured clay mineral particles.    
   
   
       8 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein a ratio (T/To) of a tensile strength (T) of the wholly aromatic polyamide fibers to a tensile strength (To) of comparative wholly aromatic polyamide fibers identical to the wholly aromatic polyamide fibers except that the layer-structured clay mineral particles are not contained therein, is 1.1 or more.  
   
   
       9 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein a ratio (E/Eo) of an ultimate elongation (E) of the wholly aromatic polyamide fibers to an ultimate elongation (Eo) of comparative wholly aromatic polyamide fibers identical to the wholly aromatic polyamide fibers except that the layer-structured clay mineral particles are not contained therein, is 1.1 or more.  
   
   
       10 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein the toughness factor (TF) of the wholly aromatic polyamide fibers defined by the equation (3): 
         TF=T′×E′   1/2    (3) In which equation (3), T′ represents a numeral value of the tensile strength in unit of g/1.1 dtex of the wholly aromatic polyamide fibers and E′ represents a numeral value of the ultimate elongation in unit of % of the wholly aromatic polyamide fibers, is 30 or more.    
   
   
       11 . The wholly aromatic polyamide fibers as claimed in  claim 10 , wherein the ratio (TF/TFo) of the tenacity factor (TF) of the wholly aromatic polyamide fibers to the tenacity factor (TFo) of comparative wholly aromatic polyamide fibers identical to the wholly aromatic polyamide fibers except that the layer-structured clay mineral particles are not contained therein, is 1.1 or more.  
   
   
       12 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein the layer-structured clay mineral particles contain organic onium ions located between layers thereof.  
   
   
       13 . The wholly aromatic polyamide fibers as claimed in  claim 1 , wherein the wholly aromatic polyamide resin is selected from meta-wholly aromatic polyamide resins.  
   
   
       14 . A process for producing drawn and oriented wholly aromatic polyamide fibers comprising extracting a spinning liquid comprising a solvent and a wholly aromatic polyamide resin and layer-structured clay mineral particles in an amount of 0.05 to 20 parts by mass per 100 parts by mass of the wholly aromatic polyamide resin through a spinneret to form filamentary streams of the spinning liquid; 
 Introducing the filamentary streams of the spinning liquid into an aqueous coagulation bath to coagulate the filamentary streams of the spinning liquid; 
 drawing the resultant undrawn filaments in a wetted atmosphere; and  
 dry-heat treating the resultant drawn filaments.  
   
   
   
       15 . The process for producing wholly aromatic polyamide fibers as claimed in  claim 14 , wherein the spinning liquid is prepared by mixing a solution A comprising a portion of the solvent, a portion of the wholly aromatic polyamide resin and layer-structured clay mineral particles in an amount of 30 to 300 parts by mass per 100 parts by mass of the wholly aromatic polyamide resin with a solution B comprising the remaining portion of the solvent, the remaining portion of the wholly aromatic polyamide resin, and satisfies the requirements (1) and (2): 
 (1) the viscosity of the solution (A) at a shear rate of 0.1 second −1  is 15 to 80 times the viscosity thereof at a shear rate of 10 second −1 , and    (2) the viscosity of the solution (A) at a shear rate of 0.1 second −1  is 40 to 20 times the viscosity of the solution (B) at a shear rate of 0.1 second −1 .    
   
   
       16 . The process for producing wholly aromatic polyamide fibers as claimed in  claim 14 , wherein the concentration of the wholly aromatic polyamide resin in the spinning solution is 0.1 to 30% by mass.  
   
   
       17 . The process for producing wholly aromatic polyamide fibers as claimed in  claim 14 , wherein the draw ratio of the undrawn filaments in the wetted atmosphere is in the range of 0.3 to 0.6 times the maximum draw ratio of the undrawn filaments.  
   
   
       18 . The process for producing wholly aromatic polyamide fibers as claimed in  claim 14 , wherein the solvent is selected from polar amide solvents.  
   
   
       19 . The process for producing wholly aromatic polyamide fibers as claimed in  claim 14 , wherein the wholly aromatic polyamide resin is selected from meta-wholly aromatic polyamide resins.  
   
   
       20 . The wholly aromatic polyamide fibers as claimed in  claim 2 , wherein when the wholly aromatic polyamide fibers are cross-cut along the fiber axes, the resultant cross-sectional profiles are observed with an electronic microscope at a magnification of 100,000, and in each cross-sectional profile, a total area S 1  of a plurality of regions in which regions a change in conditions of the fiber cross-sectional profile due to an influence of the layer-structured clay mineral particles distributed in the observation area S 2  of 25 μm 2  is found, is measured, the degree of dispersion Y of the layer-structured clay mineral particles in each fiber, defined by the equation (1): 
         Y (%)=( S 1/ S 2)×100  (1) 
     is in the range of from 0.1 to 40.