Process for producing carbon fiber

Details Process for producing carbon fiber Process for producing carbon fiber

1987-06-04

1988-10-25

Doll, John

Chemistry of inorganic compounds

Carbon or compound thereof

Elemental carbon

4234476, 4234478, D01F 922

Patent

active

047803010

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a multistage flame-resisting treatment and carbonization of acrylic fibers in tow form, whereby it is possible to produce carbon fibers in tow form which have properties of high tenacity and high elasticity and whose monofilaments exhibit superior homogeneity said fiber having less yarn defects including nap, etc.


BACKGROUND ART

As is known generally, the usual process for producing carbon fibers is basically divided into a of flame-resisting step wherein acrylic fibers are subjected to heat treatment in an oxidizing atmosphere and a carbonization step where fibers from the flame-resisting treatment are subjected to heat treatment in an inert atmosphere. The step of imparting flame-resistance to acrylic fibers is practiced in an oxidizing atmosphere at temperatures of 200.degree. to 300.degree. C. over a period generally of 2 to 4 hours. This flame-resisting step requires 90% or more of the total time required by the process for producing carbon fibers. Accordingly it is apparent that reduction in carbon fiber production costs can be achieved by in shortening the time required for this flame-resisting reaction.
One of the methods for shortening the flame-resisting step is to raise the temperature of the treatment step as disclosed in Japanese Patent Publication No. 35938/72. However, since the flame-resisting reaction is exothermic as shown in Textile Res. J., 30, 882-896 (1960) this method when adopted may cause a vigorous uncontrollable reaction, which the inflammation of the acrylic fibers. Even if the inflammation is not induced, the acrylic fibers treated by this method will have flame-resisting structure on the peripheral portion of each filament, but will have insufficient flame-resisting structure in the inner portions thereof, thus turning into flame-resistant fibers of nonuniform flame-resisting structure. Such flame-resisting fibers in the later carbonization step will develop the undesirable phenomena known as napping and fiber break. This makes it difficult to effectively carbonize the fibers making it difficult to form high-performance carbon fibers. Japanese Patent Publication No. 25487/76 discloses a method which largely obviates these difficulties, and reduces the time for the flame-resisting treatment of the acrylic fibers to 5-30 minutes. This method comprises subjecting acrylic fibers to flame-resisting treatment under such conditions that the heat treatment time until the equilibrium moisture content of the acrylic fibers reaches 4% may be from 5 to 20 minutes, followed by carbonizing the fibers at a temperature of at least 1000.degree. C. However, the flame-resistance fibers having an equilibrium moisture content of 4%, as is evident from a number of literature references. These films exhibit an unsatisfactory flame-resistant structure and the cross section of each filament shown an outstanding double structure. Such flame-resisting fibers undergo pyrolysis in the later step of carbonization and micro-voids are formed in the resulting fibers. Hence it is difficult to convert these fibers into high-tenacity carbon fibers having a tensile strength of 400 kg/mm.sup.2 or more.
In this way, uncontrollable reactions occur during the flame resisting step and nonuniform flame-resisting reactions of acrylic fibers occur with the result that the fibers experience an increase in the number of acrylic monofilaments in a fiber a tow. Japanese Patent Application Laid-Open No. 163729/83 discloses an effective method for preparing A flame-resistance tow constructed of a large number of acrylic monofilaments. This method comprises heating acrylic tows, each constructed of 1000 to 30,000 filaments of 0.5 to 1.5 deniers in monofilament size in a flame-resisting oven at temperatures of 200.degree. to 260.degree. C. to convert the filaments into incompletely flame-resistant filaments having an oxygen content of 3 to 7%, thus preventing the filaments from fusing together during the later flame-resisting treatments of higher degrees) and treating the fila

REFERENCES:
patent: 3179605 (1965-04-01), Ohsol
patent: 3567380 (1971-03-01), Townsend
patent: 3764662 (1973-10-01), Roberts, Jr.
patent: 4609540 (1986-09-01), Izumi et al.
patent: 4610860 (1986-09-01), Mullen
patent: 4671950 (1987-06-01), Ogawa et al.

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