Carbon fiber and method of producing same

Abstract

A carbon fiber having a strand elastic modulus of 360 GPa or more, a strand strength of 3.5 GPa or more, and a single-fiber diameter of 6.0 μm or more, and having a residual twist count of 2 turns/m or more in a test in which one end is fixed end and another end is free end which is capable of rotation about the axis of a fiber bundle.

1 - 22 . (canceled) 
     
     
         23 . A carbon fiber having a strand elastic modulus of 360 GPa or more, a strand strength of 3.5 GPa or more, and a single-fiber diameter of 6.0 μm or more, and having a residual twist count of 2 turns/m or more in a test in which one end is fixed end and another end is free end which is capable of rotation about the axis of a fiber bundle. 
     
     
         24 . The carbon fiber as set forth in  claim 23 , meeting the relationship represented by formula (1), wherein Es (GPa) is the single-fiber elastic modulus and A (N) is the loop fracture load:
     A≥− 0.0017× Es+ 1.02  (1).
   
     
     
         25 . The carbon fiber as set forth in  claim 23 , having a single-fiber diameter of 6.0 μm or more, satisfying the relationship represented by formula (2) wherein E (GPa) is the strand elastic modulus and B (MPa) is the knot strength determined under conditions where the heat loss rate is 0.15% or less at 450° C., and having a twist count of 20 to 80 turns/m:
     B≥ 6.7×10 9   ×E   −2.85   (2).
 
 
     
     
         26 . The carbon fiber as set forth in  claim 23 , wherein the total fineness is 850 g/km. 
     
     
         27 . The carbon fiber as set forth in  claim 23 , wherein the strand elastic modulus is 440 GPa or more. 
     
     
         28 . The carbon fiber as set forth in  claim 23 , wherein the twist angle of the carbon fiber bundle surface layer is 2.0° to 30.5°. 
     
     
         29 . The carbon fiber as set forth in  claim 28 , wherein the twist angle of the carbon fiber bundle surface layer is 4.8° to 10.0°. 
     
     
         30 . The carbon fiber as set forth in  claim 23 , wherein the single-fiber diameter is 6.5 μm or more. 
     
     
         31 . The carbon fiber as set forth in  claim 23 , wherein single-fiber diameter is 7.4 μm or less. 
     
     
         32 . The carbon fiber as set forth in  claim 23 , wherein the crystallite size Lc (nm) and the orientation parameter of crystallites π 002 (%) satisfy the relationship represented by formula (3):
   π 002 ≥4.0× Lc+ 73.2  (3).
 
 
     
     
         33 . The carbon fiber as set forth in  claim 23 , wherein the crystallite size Lc is 2.2 to 3.5 nm. 
     
     
         34 . The carbon fiber as set forth in  claim 23 , wherein the strand elastic modulus E (GPa) and the crystallite size Lc (nm) satisfy the relationship represented by formula (4):
     E×Lc   −0.5 ≥200 (GPa/nm 0.5 )  (4).
   
     
     
         35 . The carbon fiber as set forth in  claim 23 , wherein the surface oxygen concentration O/C is 0.05 to 0.50. 
     
     
         36 . The carbon fiber bundle as set forth in  claim 23 , wherein the filament number is 10,000 or more. 
     
     
         37 . A carbon fiber meeting the relationship represented by formula (1) wherein Es (GPa) is the single-fiber elastic modulus and A (N) is the loop fracture load:
     A≥− 0.0017× Es+ 1.02  (1).
   
     
     
         38 . A carbon fiber having a single-fiber diameter of 6.0 μm or more, satisfying the relationship represented by formula (2) wherein E (GPa) is the strand elastic modulus and B (MPa) is the knot strength determined under conditions where the heat loss rate is 0.15% or less at 450° C., and having a twist count of 5 to 80 turns/m:
     B≥ 6.7×10 9   ×E   −2.81   (2).
 
 
     
     
         39 . The carbon fiber as set forth in  claim 37 , wherein either the single-fiber elastic modulus or the strand elastic modulus is 360 GPa or more. 
     
     
         40 . A method of producing a carbon fiber comprising:
 a step in which a precursor fiber bundle for carbon fiber is subjected to stabilization (oxidation) treatment in an air atmosphere in the temperature range of 200° C. to 300° C.;   a step of pre-carbonization in which the resulting stabilized fiber (oxidized fiber) bundle is heat-treated in an inert atmosphere at or below a maximum temperature of 500° C. to 1,000° C. until the density reaches 1.5 to 1.8 g/cm 3 ; and   a step of carbonization in which the resulting pre-carbonized fiber bundle is heat-treated in an inert atmosphere, the precursor fiber bundle for carbon fiber having a single-fiber fineness of 0.9 dtex or more, having a tension controlled at 5 mN/dtex or more during the carbonization treatment, meeting either (c) or (d), and having a strand elastic modulus of 360 GPa or more:   
       (c) the fiber bundle to be subjected to the carbonization treatment has a twist count of 2 turns/m or more, and 
       (d) the total fineness, which is the product of the single fiber fineness (g/km) and the filament number (number), of the resulting carbon fiber is 740 g/km or more. 
     
     
         41 . The method as set forth in  claim 40 , wherein the fiber bundle to be subjected to carbonization treatment has a twist count of 16 turns/m or more. 
     
     
         42 . The method as set forth in  claim 40 , wherein the maximum temperature in the carbonization treatment step is 1,500° C. or more. 
     
     
         43 . The method as set forth in  claim 42 , wherein the maximum temperature in the carbonization treatment step is 2,300° C. or more. 
     
     
         44 . The method as set forth in  claim 40 , wherein electrolytic surface treatment with an amount of current of 2 to 100 c/g is performed after the carbonization treatment step. 
     
     
         45 . A carbon fiber having a strand elastic modulus of 360 GPa or more, a strand strength of 3.5 GPa or more, a single-fiber diameter of 6.0 μm or more, and a total fineness, which is a product of the single-fiber fineness (g/km) and the filament number (number) of the carbon fiber, of 740 g/km or more, and meeting the relationship represented by formula (1), wherein Es (Gpa) is the single-fiber elastic modulus and A (N) is the loop fracture load:
     A≥− 0.0017× Es+ 1.02  (1).
 
 
     
     
         46 . A carbon fiber having a strand elastic modulus of 360 GPa or more, a strand strength of 3.5 GPa or more, a single-fiber diameter of 6.0 μm or more, and a total fineness, which is a product of the single-fiber fineness (g/km) and the filament number (number) of the carbon fiber, of 740 g/km or more, satisfying the relationship represented by formula (2) wherein E (GPa) is the strand elastic modulus and B (MPa) is the knot strength determined under conditions where the heat loss rate is 0.15% or less at 450° C., and having a twist count of 20 to 80 turns/m:
     B≥ 6.7×10 9   ×E   −2.85   (2).
 
 
     
     
         47 . A carbon fiber having a strand elastic modulus of 360 GPa or more, a strand strength of 3.5 GPa or more, a single-fiber diameter of 6.0 μm or more, and a total fineness, which is a product of the single-fiber fineness (g/km) and the filament number (number) of the carbon fiber, of 740 g/km or more, wherein the twist angle of the carbon fiber bundle surface layer is 2.0° to 30.5°. 
     
     
         48 . A carbon fiber having a strand elastic modulus of 360 GPa or more, a strand strength of 3.5 GPa or more, a single-fiber diameter of 6.0 μm or more, and a total fineness, which is a product of the single-fiber fineness (g/km) and the filament number (number) of the carbon fiber, of 740 g/km or more, wherein the twist angle of the carbon fiber bundle surface layer is 4.8° to 10.0°. 
     
     
         49 . A carbon fiber having a strand elastic modulus of 360 GPa or more, a strand strength of 3.5 GPa or more, a single-fiber diameter of 6.0 μm or more, and a total fineness, which is a product of the single-fiber fineness (g/km) and the filament number (number) of the carbon fiber, of 740 g/km or more, wherein the crystallite size Lc (nm) and the orientation parameter of crystallites π 002 (%) satisfy the relationship represented by formula (3):
   π 002 ≥4.0× Lc+ 73.2  (3).
 
 
     
     
         50 . A carbon fiber having a strand elastic modulus of 360 GPa or more, a strand strength of 3.5 GPa or more, a single-fiber diameter of 6.0 μm or more, and a total fineness, which is a product of the single-fiber fineness (g/km) and the filament number (number) of the carbon fiber, of 740 g/km or more, wherein the crystallite size Lc is 2.2 to 3.5 nm. 
     
     
         51 . A carbon fiber having a strand elastic modulus of 360 GPa or more, a strand strength of 3.5 GPa or more, a single-fiber diameter of 6.0 μm or more, and a total fineness, which is a product of the single-fiber fineness (g/km) and the filament number (number) of the carbon fiber, of 740 g/km or more, wherein the strand elastic modulus E (GPa) and the crystallite size Lc (nm) satisfy the relationship represented by formula (4):
     E×Lc   −0.5 ≥200 (GPa/nm 0.5 )  (4).