Carbon fiber bundle and method for producing the same

Abstract

The present invention provides: a carbon fiber bundle which exhibits excellent filament shape stability when forming a composite material, and a carbon fiber composite material which exhibits high tensile strength; and a method for producing the same. The provided carbon fiber bundle exhibits a tensile elasticity as a resin-impregnated strand of 265-300 GPa, a tensile strength as a resin-impregnated strand of 6.0 GPa or more, a knot strength of 820 N/mm2 or more, a filament number of 30,000 or more, and an average tear distance of 600-850 mm, wherein the rate of change in filament width is 8% or less when the carbon fiber bundle is unraveled under the conditions stipulated in the description, and there are four or fewer sections per 1,000 m which exhibit a filament width equal to or less than 75% of the average filament width when the carbon fiber bundle is unraveled under the conditions stipulated in the description.

1 . A carbon fiber bundle having a tensile modulus of resin-impregnated strands of 265 to 300 GPa, a tensile strength of resin-impregnated strands of 6.0 GPa or more, a knot strength of 820 N/mm 2  or more, a number of filaments of 30,000 or more, and an average tearable length of 600 to 850 mm,
 the carbon fiber bundle having, when unwound under conditions described in the description, a variation of fiber bundle width of 8% or less,   the carbon fiber bundle having, per 1,000 m, 4 or less sites that have a width of fiber bundle of 75% or less based on an average width of the carbon fiber bundle unwound under conditions described in the description.   
     
     
         2 . The carbon fiber bundle according to  claim 1 , having a product E×d/W of 13.0 GPa or more, and a Weibull shape parameter m in a Weibull plot of E×d/W of 12 or more, wherein d/W is a ratio of a single-fiber diameter d to a loop diameter W just before loop fracture as evaluated by a single-fiber loop test, and E is the tensile modulus of resin-impregnated strands. 
     
     
         3 . The carbon fiber bundle according to  claim 1 , having a coefficient of variation of the knot strength of 5% or less, the coefficient of variation being represented by a ratio of a standard deviation to an average of the knot strength. 
     
     
         4 . The carbon fiber bundle according to  claim 3 , having a coefficient of variation of the tensile strength of resin-impregnated strands of 4% or less, the coefficient of variation being represented by a ratio of a standard deviation to an average of the tensile strength of resin-impregnated strands. 
     
     
         5 . A method for producing the carbon fiber bundle according to  claim 1 , the method comprising:
 a gathering process of gathering, using a roller just before gathering guide and a gathering guide, precursor fiber bundles for carbon fiber entering the gathering guide at a distance between the roller just before gathering guide and the gathering guide of 12 times or more a fiber bundle pitch between the precursor fiber bundles for carbon fiber to give a polyacrylonitrile precursor fiber bundle for carbon fiber having a number of filaments of 30,000 or more and an average tearable length of 400 to 800 mm;   a first stabilization process of stabilizing the polyacrylonitrile precursor fiber bundle for carbon fiber obtained in the gathering process for 8 to 25 minutes until a ratio of a peak intensity at 1453 cm −1  to a peak intensity at 1370 cm −1  in an infrared spectrum falls within a range of 0.98 to 1.10 to give a fiber bundle;   a second stabilization process of stabilizing the fiber bundle obtained in the first stabilization process for 20 to 35 minutes until a ratio of a peak intensity at 1453 cm −1  to a peak intensity at 1370 cm −1  in an infrared spectrum falls within a range of 0.60 to 0.65 and a ratio of a peak intensity at 1254 cm −1  to a peak intensity at 1370 cm −1  in an infrared spectrum falls within a range of 0.50 to 0.65;   a pre-carbonization process of pre-carbonizing the fiber bundle obtained in the second stabilization process in an inert gas having a maximum temperature of 500 to 1200° C. at a stretch ratio of 1.00 to 1.10; and   a carbonization process of carbonizing the fiber bundle obtained in the pre-carbonization process in an inert gas having a maximum temperature of 1000 to 2000° C.   
     
     
         6 . The method according to  claim 5 , comprising a second gathering process of spraying a fluid onto the precursor fiber bundles for carbon fiber before and/or after the gathering process. 
     
     
         7 . The method according to  claim 5 , wherein the polyacrylonitrile precursor fiber bundle for carbon fiber has a coefficient of variation of a basis weight of 1 to 4%, the coefficient of variation being represented by a ratio of a standard deviation to an average of the basis weight.