Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2002-02-01
2003-10-28
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S364000, C428S375000, C428S408000
Reexamination Certificate
active
06638615
ABSTRACT:
TECHNICAL FIELD
The present invention relates to carbon fibers and a method of producing them. In more detail, the present invention relates to carbon fibers unlikely to be fluffed by abrasion, excellent in processability, excellent in adhesion properties to a matrix resin such as an unsaturated polyester resin, vinyl ester resin, phenol resin or epoxy resin, and capable of manifesting excellent bending properties and compressive properties as a composite material with the matrix resin, and also relates to a method of producing them.
BACKGROUND ART
Carbon fibers are being applied in such fields as sporting goods and aerospace components because of their excellent specific strength and specific elastic modulus, and in these fields, carbon fibers are being applied in a wider range.
On the other hand, carbon fibers are being used also as materials for forming energy related components such as CNG tanks, fly wheels, wind mills and turbine blades, as materials for reinforcing structural components of roads, bridge piers, etc. and as materials for forming or reinforcing building components such as timbers and curtain walls.
In the expansion of application fields of carbon fibers as described above, the matrix resins used for producing composite materials containing carbon fibers include a variety of resins such as epoxy resins, unsaturated polyester resins, vinyl ester resins and phenol resins. Especially unsaturated polyester resins and vinyl ester resins are used for small ships, boats, yachts, fishing boats, household waste water treatment tanks, various other tanks, etc, because of low material and molding costs. Furthermore, phenol resins are often used for interior materials of transport vehicles such as airplanes and for building members such as trusses because of their incombustibility. In these situations, carbon fibers excellent in adhesion properties to these matrix resins and good in processability are being demanded.
Especially if carbon fibers impregnated with a conventional epoxy resin sizing agent are used for fiber reinforced composite materials containing an unsaturated polyester resin or vinyl ester resin as the matrix resin, the adhesion between the carbon fibers and the unsaturated polyester resin or vinyl ester resin is lower, and especially the shear strength is lower than that between the carbon fibers and an epoxy resin, not often allowing practical application. Furthermore, these composite materials are lower in adhesion in a water absorbed state than in a dry state, and their use for fishing boats, yachts and other boats is often avoided.
Techniques for improving the adhesion between carbon fibers and unsaturated polyester resins are disclosed. For example, it is disclosed that the adhesion between carbon fibers and unsaturated polyester resins is improved by using an urethane compound with unsaturated groups (Japanese Patent Laid-Open (Kokai) Nos. Sho56-167715 or Sho63-50573) or an ester compound with unsaturated groups at the ends (Japanese Patent Laid-Open (Kokai) No. Sho63-105178) as a sizing agent also acting as a coupling agent. However, their effects are insufficient, and they do not assure excellent adhesion properties for every kind of carbon fibers. Especially carbon fibers with excellent adhesion properties even in a water absorbed state have not been obtained.
Furthermore, carbon fiber reinforced phenol resin composite materials are also low in the adhesion between carbon fibers and the matrix resin as in the case of unsaturated polyester resins and vinyl ester resins, and the excellent mechanical properties peculiar to carbon fibers are not sufficiently utilized. Accordingly, as a technique for improving the adhesion between carbon fibers and phenol resins, Japanese Patent Laid-Open (Kokai) No. Hei1-172428 discloses a method of improving adhesion by air oxidation treatment and titanate coupling agent treatment. However, the improvement is still insufficient.
Moreover, since carbon fibers are essentially stiff, brittle and poor in bindability, bending ability and abrasion resistance, they are likely to be fluffed or broken. Accordingly, they are usually impregnated with a sizing agent, but conventional sizing agents are insufficient in improving the bending ability and abrasion resistance of carbon fibers. It can happen that if such carbon fibers ace sophisticatedly processed, for example, woven into a fabric or filament-wound, they are rubbed by guide bars, rollers, etc., to be fluffed and broken, remarkably lowering working convenience and quality. At present, carbon fibers with high adhesion properties to resins and high sophisticated processability have not yet been obtained.
DISCLOSURE OF THE INVENTION
The object of the present invention is to provide carbon fibers unlikely to be fluffed and broken even when rubbed by guide bars and rollers in sophisticated processing and excellent in adhesion to matrix resins, and capable of manifesting excellent bending properties and compressive properties as composite materials, and also to provide a method of producing them.
To achieve the object of the present invention, the carbon fibers of the present invention are constituted as follows: Carbon fibers, characterized in that a polymer having polar groups and groups capable of reacting with a matrix resin is deposited on the fiber surfaces. In a preferable embodiment of the present invention, the polymer is substantially insoluble in the matrix resin and covers the fiber surfaces.
The carbon fibers of the present invention can be favorably produced by a production method, comprising the steps of heating carbon fibers, on the surfaces of which a monomer having polar groups and groups capable of reacting with the matrix resin is deposited, and polymerizing said monomer.
THE BEST EMBODIMENT OF THE INVENTION
The present invention is described below in more detail.
The carbon fibers of the present invention are characterized in that a polymer having polar groups and groups capable of reacting with the matrix resin are deposited on the fiber surfaces.
A polar group is a functional group having a polarized charge and a group capable of reacting with a matrix resin is a functional group capable of being chemically bonded to the matrix resin. In the carbon fibers, on the surfaces of which a polymer having these two kinds of functional group is deposited, since the polymer is diffused into a matrix resin at a low rate, the polar groups are strongly combined with the surfaces of carbon fibers while the groups capable of reacting with the matrix resin are chemically bonded to the matrix resin when the carbon fibers are used to mold a composite material, so, the obtained composite material can have high adhesion properties.
The mechanism by which such effects are manifested is considered to be as follows. If functional groups being polarized exist near the surfaces of carbon fibers, the basal planes or edge planes of the graphite structure on the carbon fiber surfaces adjacent to the polar groups are polarized, and electric attraction occurs between the polar groups and the carbon fiber surfaces. The adhesive strength is smaller than that of hydrogen bonds, but since the graphite structure exists over the entire carbon fiber surfaces, high adhesion can be obtained as a whole. To further enhance the adhesion in combination with hydrogen bonds, it is effective that a certain surface oxygen concentration, especially a certain amount of carboxyl groups exist on the carbon fiber surfaces. In this mechanism, it is essentially required that the compound with polar groups is localized on the carbon fiber surfaces. Therefore, it is important that the polymer having polar groups is formed as a homogeneous film on the carbon fiber surfaces, and that the polymer is not diffused into the matrix resin. Thus, the present invention is based on a quite new concept that the hitherto unheeded dipole-dipole interaction with the graphite structure of carbon fiber surfaces is used and fixed on the carbon fiber surfaces, in addition to the chemical adhesion with the matrix resin.
In
Kobayashi Masanobu
Matsuhisa Youji
Ozaki Mitsutoshi
Gray J. M.
Kelly Cynthia H.
Toray Industries Inc.
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