Carbon fiber bundle

Details Carbon fiber bundle Carbon fiber bundle

2002-11-14

2003-05-27

Edwards, N. (Department: 1774)

Stock material or miscellaneous articles

Coated or structually defined flake, particle, cell, strand,...

C428S367000, C423S447100, C423S447200

Reexamination Certificate

active

06569523

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carbon fiber precursor fiber bundle comprising monofilaments of an acrylonitrile-based polymer that is applicable in manufacturing a carbon fiber bundle for use as reinforcing material in a fiber reinforced composite material.
This application is based on Japanese Patent Application No. 2000-190150 and Japanese Patent Application No. 2000-201535, the contents of which are incorporated herein by reference.
2. Description of Related Art
Carbon fiber, glass fiber, aramid fiber, and the like, are used in a fiber reinforced composite material. Among the aforementioned, carbon fiber is superior in relative strength, relative modulus of elasticity, thermal resistance, chemical resistance, and the like, and is used as reinforcing material in a fiber reinforced composite material for use in sporting equipment such as in golf shafts and fishing rods, as well as for general industrial purposes such as in aircraft, and the like. Such fiber reinforced composite material is manufactured, for example, according to the following method.
Initially, in the baking process (oxidizing process), a carbon fiber precursor fiber bundle comprising monofilaments of acrylonitrile-based polymers undergoes baking at 200 to 300° C. in an oxidizing gas, such as air, to yield a flame-resistant fiber bundle. Subsequently, in the carbonizing process, the flame-resistant fiber bundle is carbonized at 300 to 2000° C. under an inert atmosphere to yield a carbon fiber bundle. This carbon fiber bundle is processed, as necessary, into woven cloth, and the like, which is then impregnated by a synthetic resin and formed into a predetermined shape, to obtain a fiber reinforced composite material.
A precursor fiber bundle used in manufacturing a carbon fiber bundle is required to possess a high compactness such that, during the baking process, the monofilaments comprising a fiber bundle do not unravel and get entangled with neighboring fiber bundles, or alternatively stick to the roller. However, the resultant carbon fiber bundle obtained from a precursor fiber bundle having a high compactness possesses a problem in that it is very difficult to impregnate with resin due to its high compactness.
In addition, a carbon fiber fabric obtained by weaving carbon fiber bundles must be a fabric with as few apertures as possible, so as to avoid creating voids in the resin, at the time of impregnation by the resin. As a result, a tow spreading process is performed either during or after weaving. However, a carbon fiber bundle obtained from a precursor fiber bundle with high compactness possesses a problem in that tow spreading is extremely difficult due to its high compactness.
As a precursor fiber bundle that has a high compactness, and which can provide a carbon fiber bundle having a tow spreading ability, Japanese Patent Application, First Publication Laid Open No. 2000-144521 discloses an acrylonitrile-based fiber bundle comprising acrylonitrile-based polymers containing at least 95 wt. % of acrylonitrile, in which the total denier is at least 30,000, with 2 to 15 essentially continuous wrinkles, each of which is 0.5 to 1.0 &mgr;m in height and extends in the longitudinal direction on the surface of the fiber bundle, wherein the absorption volume of iodine per fiber weight of the fiber bundle is 0.5 to 1.5 wt. %.
This precursor fiber bundle is obtained by means of extruding a spinning solution which is a solution of an organic solvent and an acrylonitrile-based polymer to a first coagulation bath formed from an aqueous solution of an organic solvent comprising an organic solvent concentration of 50 to 70 wt. % and a temperature of 30 to 50° C. to form solid fibers. Solid fibers are then taken-up at a take-up speed no greater than 0.8 times a extrusion linear speed of the spinning solution from the first coagulation bath. Subsequently, solid fibers are placed in a second coagulation bath formed from an aqueous solution of an organic solvent comprising an organic solvent concentration of 50 to 70 wt. % and a temperature of 30 to 50° C., and drawn by 1.1 to 3.0 fold, thereby yielding the precursor fiber bundle.
However, the compactness of this precursor fiber bundle and the tow spreading ability of the carbon fiber bundle obtained from this precursor fiber bundle are inadequate. In addition, the carbon fiber woven material requires a uniform texture with few apertures, and thus a carbon fiber bundle having a high bulkiness is required.
In this manner, a carbon fiber precursor fiber bundle having a high compactness and excellent carbonizing processing ability, which is able to provide a carbon fiber bundle possessing an excellent resin impregnating ability, an excellent tow spreading ability, a high strength and high bulkiness, is required.
In addition, with respect to the cloth of carbon fiber, since a favorable external appearance and handling is also in great demand, in addition to the above-mentioned functions, it is necessary to also provide “covering ability” to the carbon fiber. In order to simultaneously provide the aforementioned resin impregnating ability, tow spreading ability, and covering ability at the time of forming a cloth, it is necessary to impart a high bulkiness to the carbon fiber bundle. Hence, in order to further improve the resin impregnating ability, tow spreading ability, and covering ability, it is necessary to further improve the bulkiness of the carbon fiber bundle.
Accordingly, it is a first object of the present invention to provide a carbon fiber precursor fiber bundle having a high compactness and excellent carbonizing processing ability, which is able to provide a carbon fiber bundle possessing an excellent resin impregnating ability and tow spreading ability, in addition to a high strength and high bulkiness.
In addition, it is a second object of the present invention to provide a carbon fiber precursor fiber bundle which is able to provide a carbon fiber bundle possessing an improved bulkiness, in addition to a superior resin impregnating ability, tow spreading ability, and covering ability at the time of forming a cloth.
SUMMARY OF THE INVENTION
The carbon fiber precursor fiber bundle according to a first embodiment of the present invention is characterized in comprising a plurality of monofilaments of acrylonitrile-based polymer, wherein the ratio of the length and width of the fiber cross section of the monofilament (length/width) is 1.05 to 1.6, and the amount of Si measured by ICP atomic emission spectrometry is in the range of 500 to 4,000 ppm.
The aforementioned carbon fiber precursor fiber bundle has a high compactness and excellent carbonizing processing ability. In addition, the carbon fiber bundle obtained therefrom possesses an excellent resin impregnating ability and tow spreading ability, in addition to a high strength and high bulkiness.
In addition, the monofilament strength within this carbon fiber precursor fiber bundle is preferably at least 5.0 cN/dtex. As a result, the generation of fluff secondary to cutting of the monofilaments during the baking process is reduced, which in turn leads to further improvement of the carbonizing processing ability.
In addition, the center line average height (Ra) of the monofilament surface of the carbon fiber precursor fiber bundle is preferably 0.01 to 0.1 &mgr;m. In this manner, it is possible to further improve the compactness and carbonizing processing ability of the carbon fiber precursor fiber bundle, and also further improve the resin impregnating ability, tow spreading ability, and strength of the carbon fiber bundle obtained therefrom.
In addition, the maximum height (Ry) of the monofilament surface of the carbon fiber precursor fiber bundle is preferably 0.1 to 0.5 &mgr;m. In this manner, it is possible to further improve the compactness and carbonizing processing ability of the carbon fiber precursor fiber bundle, and also further improve the resin impregnating ability, tow spreading ability, and strength of the carbon fiber bundle obtained t

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