Process for producing carbon fibers and the carbon fibers produced by the process

Claim 1

In a process for producing carbon fibers comprising polymerizing naphthalene at a temperature of not more than 330° C. in the presence of a Lewis acid catalyst for 0.5 to 100 hours, after removing the catalyst from reaction mixture, heating the thus obtained polymeric material under an atmospheric pressure or a reduced pressure while introducing an inert gas thereinto to remove volatile components therefrom, thereby obtaining a pitch for melt-spinning, melt-spinning pitch fibers from the thus obtained pitch, infusibilizing the thus obtained pitch fibers, carbonizing the thus infusibilized fibers by heating to a temperature of 900° C. or less in an inert atmosphere and subjecting the thus obtained carbon fibers to heat treatment at a temperature of not less than 900° C., the improvements comprising (1) heat-treating a polymeric material of naphthalene at a temperature of 330° to 440° C. for not more than 40 minutes to produce an optically isotropic pitch having a softening point of 180° to 200° C., an atomic ratio of hydrogen to carbon (H/C) of 0.6 to 0.8 and an average molecular weight of 800 to 1500, and containing 35 to 45% by weight of benzene-insoluble without containing any quinoline-insolubles and (2) melt-spinning pitch fibers from said optically isotropic pitch, and infusibilizing and carbonizing the pitch fibers, thereby obtaining carbon fibers having an apparent crystallite size (L c (002)) of 15 to 200 Å and an interlayer spacing (d 002 ) of 3.371 to 3.47 Å measured by X-ray diffractometry.