Process for producing carbon fibers having excellent properties

Claim 1

A process for producing a carbon fiber which comprises (a) impregnating a water-swollen acrylonitrile fiber containing at least 85 mol % acrylonitrile with 0.05 - 5%, based on the dry weight of the fiber, of at least one compound represented by the following general formula (I) or (II): r.sub.1 -nh.sub.2 (i) ##STR3## wherein R.sub.1 is a hydrocarbon group containing 7 - 16 carbon atoms; R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are each a hydrocarbon group containing 1 - 16 carbon atoms, with at least one of R.sub.2, R.sub.3, R.sub.4 and R.sub.5 being a hydrocarbon group containing 7 - 16 carbon atoms; and X is a monovalent anion; (b) heat treating the fiber at a temperature of at least 150° C. for 0.1 second to 30 minutes so as to render the fiber to have 20 - 80 weight percent undissolved matter upon being immersed in a 60% aqueous sodium thiocyanate solution at 80° C. for 20 minutes; (c) thermally stabilizing the fiber by heating under tension in an oxidizing atmosphere at a temperature of from 150° C. to 400° C. and thereafter (d) carbonizing or carbonizing and then graphitizing under tension in a non-oxidizing atmosphere at a temperature above 800° C.