Mitsubishi Rayon Company, Limited

Hirofumi Uno

Fujio Nakao

Hajime Asai

A process for surface treatment of carbon fiber of which modulus is not lower than 30 ton/mm.sup.2, in two steps, which comprises the steps of subjecting a carbon fiber as an anode to a first electrolytic treatment in an aqueous solution of inorganic acidic electrolyte or of neutral salt electrolyte, and then subjecting the treated fiber to a second electrolytic treatment in an aqueous solution of ammonium salt of carbonic acid or of inorganic alkaline electrolyte.

Surface treatment process for carbon fibers

Disclosed are polyacrylonitrile carbon fibers excellent in substrate strength and adhesion to matrix resin wherein average nitrogen content in the whole carbon fibers which is measured by elementary analysis is 0.5-4.5% by weight and average nitrogen concentration (N/C atom number ratio) in the whole carbon fibers which is measured by elementary analysis and surface silicon concentration (Si.sub.2p /C.sub.1s atom number ratio), surface nitrogen concentration (N.sub.1s /C.sub.1s atom number ratio) and surface oxygen concentration (O.sub.1s /C.sub.1s atom number ratio) which are measured by X-ray photoelectron spectroscopy satisfy the following formulas:

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