Carbon fiber bundle that develops high mechanical performance

Abstract

Provided is a carbon fiber bundle for obtaining a fiber-reinforced resin having high mechanical characteristics. A carbon fiber bundle formed of single carbon fibers, each of which has no uneven surface structure of 0.6 μm or more in length extending in the longitudinal direction of the single fiber; which has an uneven structure having a difference in height (Rp−v) of 5 to 25 nm between the highest portion and the lowest portion of the surface of the single fiber and having an average roughness Ra of 2 to 6 nm; and which has a ratio of the major axis to the minor axis (major axis/minor axis) of a cross-section of the single fiber of 1.00 to 1.01, wherein a mass of the single fiber per unit length falls within the range of 0.030 to 0.042 mg/m; a strand strength is 5900 MPa or more; a strand elastic modulus measured by the ASTM method is 250 to 380 GPa; and a knot tenacity is 900 N/mm 2 or more.

1 . A carbon fiber bundle formed of the single carbon fiber: each single carbon fiber having has no uneven surface structure that has a length of 0.6 μm or more and that extends in the longitudinal direction of the single fiber, each single carbon fiber having an uneven structure in which the difference in height (Rp−v) between a highest portion and a lowest portion of the surface of the single fiber is 5 to 25 nm, and in which an average roughness Ra is 2 to 6 nm, and each of which has a ratio of 1.00 to 1.01 of a major axis to a minor axis (major axis/minor axis) of a cross-section of the single fiber; wherein a mass of the single fiber per unit length falls within the range of 0.030 to 0.042 mg/m; a strand strength is 5900 MPa or more; a strand elastic modulus measured by the ASTM method is 250 to 380 GPa; and a knot tenacity is 900 N/mm 2  or more. 
     
     
         2 . A carbon fiber bundle formed of the single carbon fiber: each single carbon fiber having no uneven surface structure that has a length of 0.6 μm or more and that extends in the longitudinal direction of the single fiber, each single carbon fiber having an uneven structure that has a length of 300 nm or less in which the difference in height (Rp−v) between a highest portion and a lowest portion of the surface of the single fiber is 5 to 25 nm, and in which an average roughness Ra is 2 to 6 nm, and each of which has a ratio of 1.00 to 1.01 of a major axis to a minor axis (major axis/minor axis) of a cross-section of the single fiber; wherein a mass of the single fiber per unit length falls within the range of 0.030 to 0.042 mg/m; a strand strength is 5900 MPa or more; a strand elastic modulus measured by the ASTM method is 250 to 380 GPa; and a knot tenacity is 900 N/mm 2  or more. 
     
     
         3 . The carbon fiber bundle according to  claim 1 , wherein a hemispherical defect having a size within a predetermined range is formed on a single fiber surface by a laser, the fiber is broken at the hemispherical defective site by a tensile test, and “surface energy of surface formed by fracture” obtained from breaking strength of the fiber and the size of the hemispherical defect in accordance with the Griffith Equation (1) is 30 N/m or more, wherein σ is a breaking strength; E is an ultrasonic elastic modulus of a carbon fiber bundle; and C is a size of a hemispherical defect.
   σ=(2 E/πC ) 1/2 ×(surface energy of surface formed by fracture) 1/2   (1)
 
 
     
     
         4 . The carbon fiber bundle according to  claim 1 , wherein an ipa value obtained by an electrochemical measuring method (cyclic voltammetry) is 0.05 to 0.25 μA/cm 2 , and an amount of an oxygen-containing functional group (O1S/C1S) in a carbon fiber surface obtained by X-ray photoelectron spectroscopy falls within the range of 0.05 to 0.15. 
     
     
         5 . The carbon fiber bundle according to  claim 1 , wherein a Si amount measured by ICP emission spectrometry is 200 ppm or less. 
     
     
         6 . The carbon fiber bundle according to  claim 1 , sized by a sizing agent composition comprising a urethane modified epoxy resin, which is a reaction product of (a) an epoxy resin having a hydroxy group, (b) a polyhydroxy compound and (c) a diisocyanate containing an aromatic ring, or sized by a sizing agent composition comprising a mixture of the urethane modified epoxy resin and (a) an epoxy resin having a hydroxy group and/or (d) an epoxy resin having no hydroxy group. 
     
     
         7 . The carbon fiber bundle according to  claim 6 , wherein (a) the epoxy resin having a hydroxy group is a bisphenol type epoxy resin. 
     
     
         8 . The carbon fiber bundle according to  claim 6 , wherein (b) the polyhydroxy compound is any one from among an adduct of a bisphenol-A with an alkylene oxide, an aliphatic polyhydroxy compound and a polyhydroxy monocarboxy compound or a mixture thereof. 
     
     
         9 . The carbon fiber bundle according to  claim 6 , wherein (c) the diisocyanate containing an aromatic ring is toluene diisocyanate or xylene diisocyanate. 
     
     
         10 . The carbon fiber bundle according to  claim 1 , wherein a total content of metals including an alkaline metal, an alkaline earth metal, zinc, iron and aluminum is 50 ppm or less.