Process for producing carbon fibers

Claim 1

A process for producing carbon fibers from pitches comprising the steps of: (1) measuring pitches for their individual calorific values, ΔHs, to classify into (a) a pitch having ΔH<10 cal/g, (b) a pitch having ΔH=10 to 150 cal/g and (c) a pitch having ΔH>150 cal/g, (2) melt spinning the pitch (a) to obtain pitch fibers, partially infusibilizing the thus obtained pitch fibers at ambient temperature to 280° C. in an oxidizing atmosphere to oxidize the peripheral portion of the fibers to an extent that the thickness of the resulting oxidized peripheral portion in the form of an oxide film amounts to not larger than 5% of the radius of the original pitch fibers and then heat treating the partially infusibilized pitch fibers at 360°-450° C. in an inert atmosphere to allow the pitch fiber inner portion surrounded with said oxide film to take an optically anisotropic mesophase form thereby obtaining fixed fibers, melt spinning the pitch (b) to obtain pitch fibers, either infusibilizing the thus obtained pitch fibers at 220°-280° C. in an oxidizing atmosphere to obtain fixed fibers or partially infusibilizing the pitch fibers at ambient temperature to 280° C. in an oxidizing atmosphere to oxidize the peripheral portion of the fibers to an extent that the thickness of the resulting oxidized peripheral portion in the form of an oxide film amounts to not larger than 5% of the radius of the original pitch fibers and then heat treating the partially infusibilized pitch fibers at 360°-450° C. in an inert atmosphere to allow the pitch fiber inner portion surrounded with said oxide film to take an optically anisotropic mesophase form thereby obtaining fixed fibers, melting the pitch (c), adding a fluorine-containing surfactant to the melted pitch (c) in an amount by weight of 0.1-10% thereof and agitating the resulting mixture, melt spinning the mixture to obtain pitch fibers, either infusibilizing the thus obtained pitch fibers at 220°-280° C. in an oxidizing atmosphere to obtain fixed fibers or partially infusibilizing the pitch fibers at ambient temperature to 280° C. in an oxidizing atmosphere to oxidize the peripheral portion of the fibers to an extent that the thickness of the resulting oxidized peripheral portion in the form of an oxide film amounts to not larger than 5% of the radius of the original pitch fibers and then heat treating the partially infusibilized pitch fibers at 360°-450° C. in an inert atmosphere to allow the pitch fiber inner portion surrounded with said oxide film thereby to take an optically anisotropic mesophase form thereby obtaining fixed fibers, and (3) heat treating the fixed fibers obtained respectively from said pitches (a), (b) and (c), at 750°-1500° C. in a non-oxidizing atmosphere to obtain carbon fibers.