PRODUCTION OF PRECURSOR PITCH CARBON FIBER

PURPOSE:To obtain the titled precursor pitch which is excellent in heat stability, spinnability, infusibility, etc. at low cost by adding diatomaceous earth to coal tar pitch, heat-treating the mixture to modify the pitch, extracting the modified pitch to obtain refined pitch, and heat-treating the refined pitch for finishing. CONSTITUTION:0.5-5wt% diatomaceous earth is mixed with coal tar pitch. The mixture is heated at 350-450 deg.C to modify the pitch, thereby forming 5-30wt% mesophase micropheres having a particle diameter of 1-50mum in the pitch. A solvent, such as a middle-boiling oil derived from tar or a gas oil, is added to the heat-modified pitch to effect extraction. The solvent is removed from the extract thus obtd. to obtain refined pitch free from any insoluble solid. The refined pitch is heated at 350-450 deg.C under a reduced pressure of 20mmHg or less and/or with circulation of an inert gas for finishing heat treatment to obtain carbon fiber precursor pitch exhibiting overall optical isotropy and free from mesophase.