Pan-based carbon fiber and production method therefor

Abstract

A polyacrylonitrile (PAN)-based carbon fiber includes three or more phases different in crystal size.

1 .- 12 . (canceled) 
     
     
         13 . A polyacrylonitrile (PAN)-based carbon fiber comprising three or more phases different in crystal size. 
     
     
         14 . The PAN-based carbon fiber according to  claim 13 , wherein respective phases are layered. 
     
     
         15 . The PAN-based carbon fiber according to  claim 14 , wherein said carbon fiber has a sheath-core structure having three or more layers, and satisfies conditions A to D:
 A: in a sectional area in a direction perpendicular to a fiber axis, an area occupied by a core occupies 10 to 70% of the whole of said sectional area,   B: a thickness of a sheath is 100 nm to 10,000 nm,   C: a thickness of an intermediate layer is more than 0 and 5,000 nm or less, and   D: a diameter in said direction perpendicular to said fiber axis is 2 μm or more.   
     
     
         16 . The PAN-based carbon fiber according to  claim 14 , wherein said carbon fiber has a sheath-core structure having three or more layers, and satisfies conditions E to H:
 wherein a crystal size of a core is Lc1, a crystal size of a sheath is Lc2, and a crystal size of an intermediate layer is Lc3.   E: Lc1/Lc3≧1.05,   F: Lc1/Lc2≧1.05,   G: 1.0≦Lc1≦7.0 nm, and   H: Lc2≠Lc3.   
     
     
         17 . The PAN-based carbon fiber according to  claim 15 , wherein an orientation degree f of a crystal of a core is 0.7 or less. 
     
     
         18 . The PAN-based carbon fiber according to  claim 15 , wherein said carbon fiber has a sheath-core structure having three or more layers, and satisfies conditions E to H:
 wherein a crystal size of a core is Lc1, a crystal size of a sheath is Lc2, and a crystal size of an intermediate layer is Lc3.   E: Lc1/Lc3≧1.05,   F: Lc1/Lc2≧1.05,   G: 1.0≦Lc1≦7.0 nm, and   H: Lc2≠Lc3.   
     
     
         19 . The PAN-based carbon fiber according to  claim 16 , wherein an orientation degree f of a crystal of a core is 0.7 or less. 
     
     
         20 . A method of producing a PAN-based carbon fiber according to  claim 13  comprising:
 spinning a solution of a polymer prepared by modifying PAN with an amine-base compound and oxidizing it with a nitro compound to prepare a spun fiber; 
 performing stabilization of said spun fiber in air at 280° C. or higher and 400° C. or lower for 10 seconds or more and 15 minutes or less; and thereafter, 
 performing carbonization.