Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2000-03-09
2001-04-24
Edwards, N. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C423S447100
Reexamination Certificate
active
06221490
ABSTRACT:
TECHNICAL FIELD
The invention relates to carbon fibers, acrylic fibers (precursor fibers) used for producing the carbon fibers, and a process for producing the acrylic fibers. In more detail, the invention relates to carbon fibers satisfying specific relations not satisfied by the conventionally known carbon fibers, expressed as a relation between tensile strength of a resin impregnated strand of the carbon fibers and the average diameter of single filaments constituting the carbon fibers and as a value of the difference between the inner and outer layers of each single filament in crystallinity obtained by RAMAN, and also relates to acrylic fibers (precursor fibers) used for producing the carbon fibers, and further relates to a process for producing the acrylic fibers.
BACKGROUND ARTS
Carbon fibers have been applied for sporting goods and aerospace materials because of their excellent specific strength and specific modulus, and are being used in wider ranges in these fields.
On the other hand, carbon fibers are also used for forming energy related apparatuses such as CNG tanks, fly wheels, wind mills and turbine blades, as materials for reinforcing structural members of roads, bridge piers, etc., and also for forming or reinforcing architectural members such as timber and curtain walls.
Since that carbon fibers are being applied in wider fields, they are demanded to have higher tensile strength when expressed as a resin impregnated strand than before. Further expanding applicable fields, the carbon fibers are demanded to be produced at lower cost.
The conventional techniques for improving tensile strength of carbon fibers as a resin impregnated strand have been concerned with decrease of macro-defects, for example, for decreasing impurities existing inside single filaments constituting the carbon fibers, or for inhibiting the production of macro-voids formed inside the single filaments, and for reducing defects generated on the surfaces of the single filaments.
To decrease the inner impurities and macro-voids of single filaments, techniques to intensify the filtration of monomer or polymer dope are proposed in Japanese Patent Laid-Open (Kokai) No. 59-88924 and Japanese Patent Publication (Kokoku) No. 4-12882. Furthermore, techniques to inhibit the production of surface defects by controlling the shape of fiber guides used in the production process of precursor fibers or controlling the tension of fibers in contact with a guide are proposed in Japanese Patent Publication (Kokoku) No. 3-41561.
Although they were effective in improving strength in the past, when the tensile strength level of carbon fibers as a resin impregnated strand was low, the techniques have already achieved their intended effects of strength improvement, as impurities and macro-voids have been almost perfectly removed. In other words, these techniques cannot be expected to improve the strength further.
Furthermore, when precursor fibers are stabilized and carbonized at a high temperature to produce carbon fibers, coalescence between single filaments is likely to occur, and the coalescence between single filaments and marks that remain after their separation cause surface defects, and lower fiber strength.
To inhibit coalescence between single filaments, techniques for impregnating precursor fibers with fine particles of graphite in the production process of precursor fibers are proposed in Japanese Patent Laid-Open (Kokai) No. 49-102930 and Japanese Patent Publication (Kokoku) No. 6-37724, and a technique for impregnating precursor fibers with fine particles of potassium permanganate is proposed in Japanese Patent Publication (Kokoku) No. 52-39455.
The addition of these fine particles was effective in improving strength in the past when the coalescence between filaments occurred frequently and the tensile strength of carbon fibers as a resin impregnated strand was at a low level. However, today when the coalescence between filaments has been decreased to improve the strength level due to the application of the above techniques, these hard inorganic fine particles impregnated onto soft swelling fibers during production cause surface defects and lower the tensile strength of the carbon fibers when assembled as a resin impregnated strand.
Furthermore, to inhibit coalescence between single filaments, techniques are proposed to improve process oil as applied to precursor fibers. Techniques for applying silicone oils, which are excellent in lubricity and smoothness, instead of conventional non-silicone oils made from higher alcohols are proposed in Japanese Patent Publication (Kokoku) Nos. 60-18334 and 53-10175 and Japanese Patent Laid-Open (Kokai) Nos. 60-99011 and 58-214517.
Moreover, techniques for improving heat resistance of silicone oils are proposed in Japanese Patent Publication (Kokoku) Nos. 4-33862 and 58-5287, and Japanese Patent Laid-Open (Kokai) No. 60-146076. Particularly epoxy-modified silicone oils are proposed in Japanese Patent Publication (Kokoku) Nos. 4-29766 and 60-18334. The use of a mixture of amino-modified silicone and epoxy-modified silicone is proposed in Japanese Patent Publication (Kokoku) Nos. 4-33892 and 5-83642. The use of a mixture of an amino-modified silicone, epoxy-modified silicone and alkyleneoxide-modified silicone in combination is proposed in Japanese Patent Publication (Kokoku) No. 3-40152. However, even if these oils are applied, the coalescence between single filaments was not perfectly inhibited, in other words effect of inhibiting the coalescence between single filaments was not sufficient.
On the other hand, if these oils are improved in heat resistance, the deposition of oil gels (hereinafter called gum-ups) on the heating rollers, etc. existing downstream of the oiling process, increases problem s greatly in achieving stable production. Therefore, the equipment has to be stopped very frequently to remove the gum, or expensive gum removers must be installed which cause increased production cost.
Techniques to remove the surface defects generated in the precursor fiber production process, carbonization process or any subsequent processes are proposed. Techniques for heating carbon fibers in a dense inorganic acid are proposed in Japanese Patent Laid-Open (Kokai) No. 54-59497 and Japanese Patent Publication (Kokoku) No. 52-35796, and a technique for electrolyzing in inorganic acid at high temperature is proposed in Japanese Patent Publication (Kokoku) No. 5-4463. These techniques remove the generated surface defects by etching.
However, these techniques require inerting treatment of surface chemical functions excessively produced as a result of the etching treatment, to improve the strength of the composite material produced with these carbon fibers. The equipment, therefore, becomes complicated and it provides another cause for increase of production cost.
In addition to the macro-defects mentioned above, the strength is also affected by presence of micro-voids or micro-defects. Techniques are proposed to inhibit their generation. Techniques to densify precursor fibers for inhibiting the their generation are proposed. A technique to densify undrawn fibers by optimizing the conditions of the coagulating bath is disclosed in Japanese Patent Laid-Open (Kokai) No. 59-82420, and a technique to densify drawn fibers by keeping the drawing temperature in a bath as high as possible is disclosed in Japanese Patent Publication (Kokoku) No. 615722. However, since the techniques for achieving densification tend to lower oxygen permeability into the fibers in a stabilization process, the improvement in tensile strength expressed as a resin impregnated strand of the obtained carbon fibers, tends to be depreciated.
Therefore, the tensile strength of carbon fibers as a resin impregnated strand can be improved by these techniques only when precursor fibers are 0.8 denier or less in fineness of each single filament, or only when the carbon fibers are 6 &mgr;m or less in the diameter of a single filament. For carbon fibers thicker than 6 &mgr;m in diameter of a single filament, the im
Kibayashi Makoto
Matsuhisa Yoji
Okuda Akira
Yamasaki Katsumi
Edwards N.
Miller Austin R.
Toray Industries Inc.
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