Carbon fiber bundle and production method therefor

Abstract

According to the present invention, a carbon fiber composite material, which has excellent energy absorption and is composed of a carbon fiber having high strength and high elongation, is provided by a production method yielding an excellent production amount. This carbon fiber bundle having a plurality of single fibers has a strand elastic modulus of 260-350 GPa, a strength of 6.5-8.5 GPa, an elongation of at least 1.8%, a filament number of 1,000-9,000, and a total fineness of 0.15-0.35 g/m, wherein the average value of major axis/minor axis ratios in single fiber cross sections is 1.01-1.08, the coefficient of variation is 1-4%, and the skewness is 0.3-1.2.

1 . A carbon fiber bundle comprising a plurality of filaments characterized by having a strand elastic modulus of 260 to 350 GPa, a strand strength of 6.0 to 8.5 GPa, an elongation percentage of 1.8% or more, a filament count of 1,000 to 9,000, an overall fineness of 0.15 to 0.35 g/m, wherein the filament cross sections have an average long diameter to short diameter ratio of 1.01 to 1.08, a coefficient of variation of 1% to 4%, and a skewness of 0.3 to 1.2. 
     
     
         2 . A carbon fiber bundle as set forth in  claim 1 , wherein the cross section of the carbon fiber bundle has an area ratio 0.50 to 0.70. 
     
     
         3 . A carbon fiber bundle as set forth in either  claim 1 , wherein the elongation percentage is 2.0% or more. 
     
     
         4 . A carbon fiber bundle as set forth in  claim 1 , wherein the elongation percentage is 2.2% or more. 
     
     
         5 . A carbon fiber bundle as set forth in  claim 1 , wherein the proportion of filaments with long diameter to short diameter ratios of 1.04 to 1.10 is in the range of 10% to 40%. 
     
     
         6 . A carbon fiber bundle as set forth in  claim 1 , wherein the proportion of filaments with long diameter to short diameter ratios of 1.00 to 1.03 is in the range of 30% to 90%. 
     
     
         7 . A production method for carbon fiber bundles, comprising:
 a first flame resistant treatment step for subjecting polyacrylonitrile based carbon fiber precursor fiber bundles to flame resistant treatment performed for 8 to 25 minutes until the ratio of the peak intensity at 1,453 cm −1  to the peak intensity at 1,370 cm −1  in the infrared spectrum comes into the range of 0.98 to 1.10,   a second flame resistant treatment step for performing additional flame resistant treatment performed for 5 to 20 minutes until the ratio of the peak intensity at 1,453 cm −1  to the peak intensity at 1,370 cm −1  in the infrared spectrum comes into the range of 0.70 to 0.75 while at the same time the ratio of the peak intensity at 1,254 cm −1  to the peak intensity at 1,370 cm −1  in the infrared spectrum comes into the range of 0.50 to 0.65, wherein the twist angle of the fiber bundles is maintained at 0.2° or more during the flame resistant treatment while maintaining the tension on the fiber bundles at 0.7 to 1.5 mN/dtex during the flame resistant treatment, and feeding a plurality of fiber bundles to each of the grooves on the rollers,   a preliminary carbonization step for subjecting the fiber bundles resulting from the first and second flame resistant treatment steps to preliminary carbonization performed in an inactive atmosphere at a maximum temperature of 500° C. to 1,200° C. and a stretching ratio of 1.00 to 1.20,   a carbonization step for subjecting the fiber bundles resulting from the preliminary carbonization step to carbonization performed in an inactive atmosphere at a maximum temperature of 1,000° C. to 1,500° C., and   a step for subjecting the fiber bundles resulting from the carbonization step to electrolytic surface treatment to produce carbon fiber bundles.   
     
     
         8 . A production method for carbon fiber bundles as set forth in  claim 7 , wherein in the carbonization step, treatment at the maximum temperature is continued for 20 to 60 seconds and the heating rate is 0.40° C./sec to 1.10° C./sec.