Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2002-11-12
2003-11-04
Edwards, N. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S394000, C428S400000, C264S206000, C264S182000, C264S291000, C264S292000
Reexamination Certificate
active
06641915
ABSTRACT:
TECHNICAL FIELD
This invention relates to an acrylonitrile fiber bundle suitable for producing carbon fibers used in premium applications such as airplanes and sports or general industrial applications.
BACKGROUND ART
Demands for carbon fibers have been increased in recent years, and the carbon fibers have gained a wide application such as premium applications for airplanes and sports goods, and general industrial applications typified by civil engineering. Currently, acrylonitrile fiber bundles with an acrylonitrile filament number of 10,000 to 20,000 are wound by a filament winding method and carbonized to give carbon fibers, and several filaments of the carbon fibers are aligned for molding.
Since several carbon fibers are aligned after the carbonization in the above procedure, however, gaps tend to generate between aligned carbon fibers. This leads to molding defects of a reduced strength or elastic modulus in a molding from carbon fibers. In addition, the process of aligning multiple carbon fibers results in complexity and an increased cost in molding production.
For solving these problems, attempts have been recently made for increasing the filament number in an acrylonitrile fiber bundle as precursor for carbon fibers.
Unduly increasing the filament number of an acrylonitrile fiber bundle may, however, cause increase in tow handling or a tow volume. It may increase a load in drying step in an existing apparatus so that spinning cannot be performed with a high speed. Furthermore, an increased tow volume may cause a problem of merging between fiber bundles, leading to significant deterioration in product quality.
It has been thus needed to provide an acrylonitrile fiber bundle showing a higher total size, improved denseness, a reduced load in drying step and an improved convergence, which is suitable for the use as a precursor for a carbon fiber.
An objective of this invention is, therefore, to provide an acrylonitrile fiber bundle suitable for the use as a precursor for carbon fiber due to its higher total size, improved denseness, reduced drying load and improved convergence.
Another objective of this invention is to provide a process for easily and accurately producing an acrylonitrile fiber bundle suitable for the use as a precursor for carbon fiber due to its higher total size, improved denseness, reduced drying load and improved convergence.
DISCLOSURE OF THE INVENTION
The above problems can be solved by an acrylonitrile fiber bundle according to this invention and a production process therefor described below.
This invention provides an acrylonitrile fiber bundle for a carbon fiber precursor with a total size of 30,000 denier or more consisting of an acrylonitrile polymer comprising 95 wt % or more of an acrylonitrile unit, wherein the surface of filaments composing of the fiber bundle has 2 to 15 corrugations with a height of 0.5 to 1.0 &mgr;m which are substantially continuous in a longitudinal direction and the amount of iodine adsorbable to a fiber is 0.5 to 1.5 wt % of the fiber bundle.
A process for producing an acrylonitrile fiber bundle for a carbon fiber precursor according to this invention comprises the steps of discharging a spinning feed solution of an acrylonitrile polymer having 95 wt % or more of an acrylonitrile unit dissolved in a first organic solvent into a first coagulation bath at 30 to 50° C. consisting of an aqueous organic-solvent solution comprising 50 to 70 wt % of the second organic solvent capable of solving the acrylonitrile polymer, to prepare a coagulated fiber; drawing the coagulated fiber from the first coagulation bath at a drawing rate which is 0.8 folds or less of the linear discharge velocity of the spinning feed solution; and then stretching the coagulated fiber to 1.1 to 3.0 folds in length in a second coagulation bath at 30 to 50° C. consisting of an aqueous organic-solvent solution comprising 50 to 70 wt % of the third organic solvent capable of solving the acrylonitrile polymer.
In the process for producing an acrylonitrile fiber bundle according to this invention described above, a degree of swelling in the swollen fiber bundle before drying is preferably 70 wt % or less after 1.1 to 3.0-fold stretching in the second coagulation bath because an excessively high stretch ratio in the second coagulation bath causes reduction in a stretch ratio in post-stretching.
Another process for producing an acrylonitrile fiber bundle for a carbon fiber precursor according to this invention comprises the steps of discharging a spinning feed solution of an acrylonitrile polymer having 95 wt % or more of an acrylonitrile unit dissolved in a first organic solvent into a first coagulation bath at 30 to 50° C. consisting of an aqueous organic-solvent solution comprising 50 to 70 wt % of the second organic solvent capable of solving the acrylonitrile polymer, to prepare a coagulated fiber; drawing the coagulated fiber from the first coagulation bath at a drawing rate which is 0.8 folds or less of the linear discharge velocity of the spinning feed solution; stretching the coagulated fiber to 1.1 to 3.0 folds in length in a second coagulation bath consisting of an aqueous organic-solvent solution comprising 50 to 70 wt % of the third organic solvent capable of solving the acrylonitrile polymer at 30 to 50° C.;. and then further wet-heat stretching the resulting fiber to 4 folds or more.
In the process for producing an acrylonitrile fiber bundle according to this invention described above, a degree of swelling in the swollen fiber bundle before drying is preferably 70 wt % or less after wet-heat stretching.
In an acrylonitrile fiber bundle of this invention and a production process therefor, an acrylonitrile polymer used is a polymer containing 95 wt % or more of acrylonitrile. The acrylonitrile polymer may be also a homopolymer or copolymer of acrylonitrile or a mixture thereof.
An acrylonitrile copolymer is a copolymerization product of acrylonitrile and a monomer copolymerizable with acrylonitrile. Examples of a monomer copolymerizable with acrylonitrile include, but not limited to, (meth)acrylates such as methyl(meth)acrylate, ethyl(meth)acrylate, propyl(meth)acrylate, butyl(meth)acrylate and hexyl(meth)acrylate; halogenated vinyl compounds such as vinyl chlorides, vinyl bromide and vinylidene chloride; acids and their salts having a polymerizable double bond such as (meth)acrylic acid, itaconic acid and crotonic acid; maleimide; phenylmaleimide; (meth)acrylamide; styrene; &agr;-methyl styrene; vinyl acetate; polymerizable unsaturated monomers having a sulfonic group such as sodium styrenesulfonate, sodium allylsulfonate, sodium &bgr;-styrenesulfonate and sodium meta-allylsulfonate; and polymerizable unsaturated monomers having a pyridine group such as 2-vinylpyridine and 2-methyl-5-vinylpyridine.
Polymerization may be conducted by, but not limited to, redox polymerization in an aqueous solution, suspension polymerization in a heterogeneous system and emulsion polymerization using a dispersant.
An acrylonitrile fiber bundle for a carbon fiber precursor according to this invention has a total denier of 30,000 (33,000 dtex) or more, and the surface of filaments composing of the fiber bundle has 2 to 15 corrugation with a height of 0.5 to 1.0 &mgr;m which are substantially continuous in a longitudinal direction of the fiber. The term “corrugation ” as used herein refers to a continuous convex observed in a longitudinal direction in a 10 &mgr;m×10 &mgr;m visual field of a randomly selected fiber surface, and such corrugations are counted.
The presence of such corrugations allows an acrylonitrile fiber bundle of this invention to exhibit a good convergence and allows carbon fibers from the precursor fiber bundle to exhibit a good spreadability (spread property) when being used in pre-preg production.
An excessively tall corrugations increases the surface area of the fiber bundle, causing generation of static electricity and reduction in a convergence of the fiber bundle, while an excessively low corrugation fails to give the above improveme
Ikeda Katsuhiko
Kasabo Yukio
Edwards N.
Mitsubishi Rayon Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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