PURPOSE: To prevent the fusion of fibers during the infusibilization process and improve both the flexibility and the bundlability.
CONSTITUTION: In a method for producing a carbon fiber by melt-spinning an optically anisotropic pitch, doubling the resultant pitch fibers, subsequently infusibilizing it, preliminarily carbonizing it and carbonizing or graphitizing it, a tension is applied through plural rollers to a bundle of spun pitch fibers and the resultant bundles of the spun pitch fibers are doubled through a doubling roller into a bundle of 500 to 10000 filaments while applying a heat-resistant fiber size. The resultant bundles each composed of 500 to 10000 filaments are intertwisted with each other while opening the bundle of the filaments by opening rollers. Further, a heat-resistant oily fiber size is applied thereto and the pitch fibers are bundled. The pitch fibers are subsequently infusibilized in an oxygen-containing atmosphere, then preliminarily carbonized in an inert atmosphere and subjected to carbonization or graphitization. The applied tension between open rollers to the fiber bundle is controlled to 5 to 150g/1000 filaments. The open rollers have each a cylindrical front plate shape and the curvature radius of the surface is 10 to 200mm. The pitch fibers are allowed to pass through three or more opening rollers.
TATSUMI MASAAKI
GOTO TADAAKI
