Patent ID: 8221840

Claim:
A method for producing a carbon fiber bundle, comprising: pre-sizing a carbon fiber bundle with an epoxy resin; treating the pre-sized carbon fiber bundle with an aqueous sizing agent solution to obtain a sized wet carbon fiber bundle; cutting the sized wet carbon fiber bundle to a prescribed length while regulating the moisture content of the pre-sized and treated carbon fiber bundle to 40 to 60 wt %; and drying the carbon fiber bundle cut to the prescribed length, wherein the carbon fiber bundle which is to be treated comprises a plurality of single fibers, which comprise a plurality of wrinkles on their surface, wherein a vertical difference between a highest portion and a lowest portion in a region defined by 2 μm of circumferential length×1 μm of fiber axial direction length of the single fibers is 40 nm or more, an amount of a sizing agent to the total weight is 1 to 5 wt %, and the aqueous sizing agent solution is obtained by dissolving or dispersing in water, a sizing agent comprising: a polymer having a main chain formed of carbon-carbon bonds which is selected from the group consisting of polypropylene, polyethylene and a copolymer of propylene and ethylene, comprising an acid group in at least a part of side chains or at least a part of main chain ends, wherein an acid value of the polymer comprising acid groups is 23 to 120 mg KOH/g as measured in accordance with ASTM D1386; and an olefin-based thermoplastic elastomer resin having a Vicat softening point of 120° C. or less as measured according to ASTM D1525-70, wherein a weight ratio of the polymer having a main chain formed of carbon-carbon bonds to the olefin-based thermoplastic elastomer resin is from 15/1 to 1/1.