Abstract: This invention provides a sizing agent for carbon fiber which contains an isocyanate regenerating compound which is an isocyanate compound, the --NCO group of which is stabilized with a blocking agent. Further provided are carbon fiber improved in adhesion to resins and carbon fiber reinforced composite materials improved in various properties such as tensile strength, flexural strength and Izod impact strength.

Abstract: This invention provides a method for infusibilization of pitch fibers for production of carbon fibers which comprises putting pitch fibers prepared by melt spinning from a spinning pitch in containers, introducing in succession the containers containing the pitch fibers into an infusibilizing furnace divided into a plurality of sections and passing the containers therethrough from inlet to outlet wherein the containers containing the pitch fibers are intermittently moved through the infusiblizing furnace to retain each of the containers in respective sections for a given period of time, during which temperature of respective sections is independently raised from minimum controlled temperature to maximum controlled temperature and thereafter is lowered to the minimum controlled temperature and then the container is moved.

Abstract: The present invention relates to a process for the infusibilization of pitch fiber which comprises, in the production of pitch type carbon fiber, attaching a powder of solid lubricant to a pitch fiber and then subjecting the pitch fiber to an infusibilizing treatment. According to the present invention, the use of oxidant used in prior processes can be excluded, the process can be operated with a high safety, and the period of time required for the infusibilization can be shortened. Further, the infusibilized fiber obtained according to the invention can directly be introduced into the carbonization process, without any particular washing treatment and the like.