Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Patent
1987-08-07
1989-05-23
Doll, John
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
4234471, 4234474, 4234476, 264 292, D01F 912
Patent
active
048329320
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to carbon fibers effective for producing carbon-fiber composite materials which are excellent in mechanical properties, particularly in compressive strength after impact. Composite materials from the present carbon fibers can be used extensively for aircraft in the first place, and automobiles and general industrial purposes.
BACKGROUND ART
Conventional carbon fibers for use in carbon-fiber composite materials, when a polyacrylonitrile-based precursor is used as starting fibers, are commonly produced by subjecting first the precursor to flame-resisting treatment in an oxidizing atmosphere at temperatures of 200.degree. to 300.degree. C., then carbonizing the treated fibers in an inert atmosphere, and generally subjecting the carbonized fibers to gas-phase or liquid-phase oxidation to enhance the adhesion of the carbon fibers to the matrix, followed by treating the fibers with a suitable sizing agent for the purpose of inhibiting the fiber breaking and fuzzing which may take place during handling of the fiber. However, the composite materials containing these carbon fibers are still insufficient in the adhesion of the fibers to the matrix. In particular, the compressive strength after impact (CAI) is generally on a level of 193.2.times.10.sup.3 KPa (19.7 kg/mm.sup.2) when the impact force is 68.1 kg/cm (1500 lb in/in), as shown in Eur. Patent Application Laid-Open No. 132853, Table IV, Example 35. Thus, it is the present situation that the CAI is extremely difficult to improve by using a matrix having such a high heat resistance as shown in Example 35 mentioned above.
While an average CAI of 45.3 ksi (31.8 kg/mm.sup.2) is obtained in Eur. Patent Application Laid-Open No. 133280, Examples 6, 7, and 8, which aimed at improving the CAI, this type of composite has a tough layer called an interlief between prepreg layers and this inserted layer hinders the raise of the fiber content by volume, gives two different faces to the prepreg, and makes the handleness inferior.
On the other hand, it is required in the aircraft industry to improve the CAI to 27 kg/mm.sup.2 or more in order to reduce the weight of plane bodies and it is desired to develop a composite material containing no special layer for the purpose of satisfying this requirement.
DISCLOSURE OF INVENTION
In view of such problems as noted above, the present inventors made intensive studies. As a result, it has been found that the compressive strength after impact, in spite of using the same kind of matrix resin, can be improved markedly by using carbon fibers subjected to oxidizing treatment which satisfy such specific conditions as stated below, and the present invention has been accomplished.
The substance of the invention is that the compressive strength of carbon-fiber reinforced composites after impact, in spite of using the same kind of matrix resin, can be improved markedly by using carbon fibers having the oxygen concentration (O.sub.1S /C.sub.1S atom number ratio) in the surface part of carbon fiber is from 0.05 to 0.30 as measured by X-ray photoelectron spectroscopy, a coefficient of water-extractable fraction as is defined later is up to 2.0, preferably up to 0.5, a coefficient of tow spread as is defined later is at least 1.times.10.sup.-3 mm/denier, and the amount of a sizing agent on the fiber is up to 0.1% by weight.
BRIEF DESCRIPTION OF DRAWINGS
The drawings referred to in the description of the invention are explained below.
FIG. 1 illustrates the method applied to measure the coefficient of tow spread. The arrow indicates the direction of tow movement.
1: weight; 2, 3, and 4: 50-mm.phi. Rolls;
5: carbon fibers in tow form
FIGS. 2 and 3 are electron microscopic photographs (each magnification factor: 900) showing cross sections of test pieces preaared in Example 1 and Comparative Example 1, respectively.
In each of FIGS. 2 and 3, a white part on the lower left side indicates a length of 10 .mu..
BEST MODE FOR CARRYING OUT THE INVENTION
The term "coefficient of water-extractable f
REFERENCES:
patent: 3723607 (1973-03-01), Kalnin
patent: 3754957 (1973-08-01), Druin et al.
patent: 3772429 (1973-11-01), Basche et al.
patent: 3894884 (1975-07-01), Druin et al.
patent: 3989802 (1976-11-01), Joe et al.
patent: 4600572 (1986-07-01), Hiramatsu et al.
patent: 4609540 (1986-09-01), Izumi et al.
Search Report for European Application 87 90 0270.
Agata Akira
Kashiyama Setuo
Murata Takashi
Saruta Masahiro
Tada Hisashi
Doll John
Kunemund Robert M.
Mitsubishi Rayon Co. Ltd.
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