Carbon fiber bundle and method of manufacturing same

Abstract

A carbon fiber bundle is obtained by filtering a spinning dope solution in which a polyacrylonitrile copolymer is dissolved in a solvent, at a predetermined filtration speed, using a filter medium having a predetermined particle retention and a filter basis weight, then spinning the filtered spinning dope solution to obtain a precursor fiber bundle for carbon fiber, and heat-treating the obtained precursor fiber bundle for carbon fiber at an appropriate temperature profile in an oxidizing atmosphere until reaching a predetermined density to obtain an oxidized fiber bundle, and then heat-treating the oxidized fiber bundle at a predetermined temperature in an inert atmosphere.

1 - 7 . (canceled) 
     
     
         8 . A method of manufacturing a carbon fiber bundle comprising:
 filtering a spinning dope solution in which a polyacrylonitrile copolymer is dissolved in a solvent with a filter medium having a particle retention B (μm) and a filter basis weight D (g/m 2 ), under conditions where a filtration speed A (cm/hour) satisfies equations (1) to (3),   spinning the filtered spinning dope solution to obtain a precursor fiber bundle for carbon fiber,
     D− 600/(α×β)≥0  (1)
 
   α=1−1/(1+exp(7− A ))  (2)
 
   β=1−1/(1+exp(−0.23× B ))  (3)
 
   heat-treating the obtained precursor fiber bundle for carbon fiber in an oxidizing atmosphere until a density reaches 1.32 to 1.35 g/cm 3 ,   heat-treating at 275° C. or more and 295° C. or less in an oxidizing atmosphere until a density reaches 1.46 to 1.50 g/cm 3  to obtain an oxidized fiber bundle, and   heat-treating the oxidized fiber bundle at 1200 to 1800° C. in an inert atmosphere.   
     
     
         9 . The method according to  claim 8 , wherein a tension of the oxidized fiber bundle when heat-treated at 275° C. or more and 295° C. or less in an oxidizing atmosphere until the density reaches 1.46 to 1.50 g/cm 3  is 1.6 to 4.0 mN/dtex. 
     
     
         10 . The method according to  claim 8 , further comprising heat-treating the precursor fiber bundle for carbon fiber at 210° C. or more and less than 245° C. in an oxidizing atmosphere until the density reaches 1.22 to 1.24 g/cm 3 , and subjecting to the heat treatment process in an oxidizing atmosphere until the density reaches 1.32 to 1.35 g/cm 3 , wherein the heat treatment process performed until the density reaches 1.32 to 1.35 g/cm 3  is performed at a temperature of 245° C. or more and less than 275° C. 
     
     
         11 . A carbon fiber bundle having an elastic modulus of strands of 240 to 280 GPa, a tensile strength of strands of 5.8 GPa or more, a knot strength K [MPa] of −88d+1390≤K (d: average single fiber diameter [μm]), and an average single fiber diameter of 6.5 to 8.0 μm, wherein a probability that a flaw with a size of 50 nm or more exists on a fracture surface, which is collected when a single fiber tensile test is performed with a gauge length of 10 mm, is 35% or less. 
     
     
         12 . The carbon fiber bundle according to  claim 11 , having a knot strength K of 770 MPa or more. 
     
     
         13 . The carbon fiber bundle according to  claim 11 , having a mean surface roughness Ra of 1.0 to 1.8 nm. 
     
     
         14 . The carbon fiber bundle according to  claim 11 , wherein a skin layer ratio of the single fibers of the carbon fibers is 90% or more by area.