Carbon fiber strand

Abstract

A sizing agent for carbon fiber consisting of a reaction products containing an unsaturated urethane compound as the principal component obtained by reacting an unsaturated alcohol with an isocyanate compound is disclosed in claim 1.

1 . A carbon fiber strand obtained by impregnating a carbon fiber with a sizing agent composition containing a sizing agent comprising at least two kinds of epoxy resins, wherein the sizing agent composition is such that, when it is mixed with a given curing agent at proportions of 100 parts by mass (the sizing agent composition) and 30 parts by mass (the curing agent) to make a composition for estimation, the composition for estimation is heat-treated at 130° C. for 2 hours, and the resulting cured material for estimation is measured for dynamic viscoelasticity to obtain its tan  6  of a relaxation peak and its tan δ of β relaxation peak, their product α tan δ  β tan δ  is 0.07 to 0.2.  
   
   
       2 . A carbon fiber strand according to  claim 1 , wherein the sizing agent composition has a Viscosity of 100 to 10,000 poises at 30° C.  
   
   
       3 . A carbon fiber strand according to  claim 1 , wherein the sizing agent contained in the sizing agent composition contains a PO/EO block copolymer in an amount of less than 30% by mass relative to the epoxy resins.  
   
   
       4 . A carbon fiber strand according to  claim 1 , wherein the content of the sizing agent composition is 0.3 to 5.0% by mass.  
   
   
       5 . A carbon fiber strand according to  claim 1 , which is constituted by 1,000 to 50,000 single fibers.  
   
   
       6 . A carbon fiber strand according to  claim 1 , wherein the carbon fibers constituting the carbon fiber strand show a surface oxygen concentration ratio O/C of 0.05 to 0.3 when measured by X-ray photoelectron spectroscopy.