JPH0329891B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical Field The present invention relates to a method for producing high-performance carbon fibers having high strength and high modulus of elasticity from acrylonitrile-based synthetic fibers. (b) Prior art Generally, when producing carbon fiber from acrylonitrile synthetic fiber, the flame-resistant fiber obtained by heat treatment in an oxidizing atmosphere at 200 to 300°C is carbonized at a higher temperature in an inert atmosphere. There are known ways to treat it. To date, much research has been carried out to obtain carbon fibers with higher performance, and some results have been achieved. Strength and high modulus of elasticity are required. However, it is difficult to obtain carbon fibers with high strength and high elastic modulus. As is generally known, the highest strength of carbon fiber is obtained through carbonization treatment at a maximum temperature of 1000 to 1500℃.
This is because the elastic modulus increases as the carbonization temperature increases, although it decreases above this temperature. It is known that applying an appropriate heating rate and elongation operation under specific conditions during carbonization treatment contributes to improving the performance of carbon fibers. Furthermore, although the decompression operation is disclosed in Japanese Patent Laid-Open No. 147222/1983, it has not yet achieved a sufficient effect. In addition, methods using hydrogen halide gas as the carbonization treatment atmosphere are shown in Japanese Patent Publications No. 47-7686, Japanese Patent Publication No. 47-40575, etc., but these methods are not yet sufficiently effective. Not yet. (c) Object of the invention In view of the above-mentioned current situation, the object of the invention is to provide a high-performance carbon fiber having higher strength and higher modulus of elasticity. (d) Structure of the Invention The method for producing high-performance carbon fibers according to the present invention includes carbonizing acrylonitrile-based synthetic fibers at a maximum temperature of 1000°C or higher after flame-retardant treatment in an oxidizing atmosphere. The temperature increase rate in the temperature range below ℃ is 900℃/min or more and 3000℃/min or less,
The carbonization treatment is performed under elongation of up to 25%, and the carbonization treatment is performed in an oxidizing atmosphere containing hydrogen halide gas. (e) Embodiment The acrylonitrile synthetic fiber used in the present invention is a fiber made of a polymer containing 90% by weight or more of acrylonitrile. If it is less than 10% by weight,
Conventionally known monomers copolymerizable with acrylonitrile, such as unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and itaconic acid, esters of these acids, vinyl chloride, vinyl acetate, styrene, acrylamide, diacetone acrylamide, Methacrylamide, α-chloroacrylonitrile, allylsulfonic acid, etc. can be advantageously used as a partner component to be copolymerized with acrylonitrile. Conventionally known methods are used for the flame-retardant treatment in the present invention, but generally the acrylonitrile synthetic fiber is heat treated at 200 to 300°C in an oxidizing atmosphere. At this time, it is more preferable to perform an appropriate elongation operation. In the carbonization treatment in the present invention, the maximum temperature is 1000
For carbonization treatment at temperatures above 300°C
Temperature increase rate of 200℃ in temperature range below 1000℃
℃/min or more 3000℃/preferably 900℃/min or more 300
It is necessary to keep the temperature below ℃/min. If the heating rate is less than 200℃/min, defects will easily occur inside the fiber, making it impossible to obtain high-performance carbon fiber.
If the heating rate exceeds .degree. C./min, troubles such as fiber bundle breakage will occur due to rapid thermal decomposition reactions. In addition, carbonization treatment can shrink up to 4% or 25%
It is necessary to carry out the process under elongation of up to 25% (excluding constant length), preferably up to 25% elongation. 4%
If the shrinkage exceeds 25%, high-performance carbon fibers will not be obtained because the internal orientation of the fibers will not improve, and if the elongation exceeds 25%, fiber bundle breakage will occur. Through the above operations in carbonization treatment,
Although there is an improvement in strength and elastic modulus compared to the untreated one, the strength and elastic modulus contemplated by the present invention cannot be achieved. In the present invention, in addition to the operations described above, it is necessary to carry out the carbonization treatment in an oxidizing atmosphere containing hydrogen halide gas. An oxidizing atmosphere containing hydrogen halide gas can be used even if it is diluted with an inert gas, but hydrogen halide gas should be 0.1% by volume or more,
It is preferable that the amount is 0.05 to 5% by volume, and the rest is inert gas. However, it is not particularly limited to this. Examples of hydrogen halide gas include hydrogen chloride,
Hydrogen fluoride, hydrogen bromide, etc. can be used, oxygen, air, carbon dioxide, water vapor, etc. can be used as the oxidizing gas, and nitrogen, argon, helium, hydrogen, etc. can be used as the inert gas.
From the viewpoint of operability and economy, it is preferable to use a combination of hydrogen chloride, oxygen and nitrogen. Conventionally, carbonization treatment is performed in an atmosphere containing as little oxidizing gas as possible, such as oxygen, and it has been thought that the presence of oxygen reduces the performance of carbon fibers. However, in the present invention, the carbonization treatment after the flameproofing treatment is
It is characterized by being carried out in an oxidizing atmosphere containing hydrogen halide gas, and producing high-performance carbon fibers with much higher strength and higher modulus than conventional methods. All carbonization treatments in the method of the present invention can be performed in a single furnace, which is advantageous from the viewpoint of operability and economy. However, when adding a furnace to further improve productivity or introduce graphitization treatment to achieve higher elastic modulus,
For the additional furnace, an atmosphere different from the atmosphere in the present invention may be used. (f) Effects of the invention As described above, in the present invention, in carbonization treatment in which individual operations such as heating rate and elongation operation or a combination thereof alone cannot produce sufficient effects,
By using the above-mentioned special atmosphere, it has become possible to produce high-performance carbon fibers with much higher strength and modulus of elasticity than ever before. Furthermore, in the present invention, by using an oxidizing gas in the carbonization treatment, interlaminar shear strength, which is an important element when using carbon fibers as a reinforcing material for composite materials, is improved. This means that the present invention also has the excellent effect of simultaneously performing surface treatment on carbon fibers. (G) Examples The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto. The strength and elastic modulus of carbon fiber in the following examples are
Measured using the strand test method specified in JIS R7601. Example 1 A fiber bundle of acrylonitrile polymer consisting of a single fiber fineness of 1.3 denier and 6000 filaments was
Heat treatment was performed in air at 250° C. for 1 hour while giving an elongation rate of 12% to obtain a flame-resistant fiber. This flame-resistant fiber is heated to a maximum temperature of 1350℃ at an elongation rate of 13%,
Carbonization treatment was performed at 1350°C for 2 minutes. At this time, carbonization treatment is performed using hydrogen halide gas.
The experiment was carried out in an atmosphere of 2.7% by volume, 0.3% by volume of oxygen gas, and 97.0% by volume of nitrogen gas. Table 1 shows the strength and elastic modulus of the carbon fibers obtained by carbonizing the carbon fibers under the same conditions and with the heating rate in the temperature range of 300°C to 1000°C set to the values listed in Table 1. Shown below. From these results, the heating rate is 200℃/min or more.
It can be seen that high-performance carbon fibers having high strength and high modulus of elasticity can be obtained in the range of 3000° C./min or less.

[Table] Example 2 Strength and elastic modulus of carbon fiber obtained by performing all the same treatments except that in No. 3 in Table 1 of Example 1, the carbonization elongation rate was changed to the value listed in Table 2. the second
Shown in the table. These results show that high-performance carbon fibers with high strength and high modulus can be obtained if carbonization is performed under contraction of up to 4% or elongation of up to 25% (excluding constant length).

[Table] Example 3 The carbon fiber bundle obtained in No. 4 in Table 2 of Example 2 was impregnated with epoxy resin (Epicote 828) to create a prepreg, which was laminated and cured by heating to form a composite material. created something. The interlaminar shear strength of the resulting composite material molded product was measured and was 9.1Kg/
It was warm in ^mm2 . This value is comparable to that of commercially available surface-treated carbon fibers. Reference example: A fiber bundle of acrylonitrile polymer consisting of 6000 filaments with a single filament fineness of 1.3 denier,
Heat treatment was performed in air at 250° C. for 1 hour while giving an elongation rate of 12% to obtain a flame-resistant fiber. This flame-resistant fiber is heated to a maximum temperature of 1350℃ with an elongation rate of 0%,
Carbonization treatment was performed at 1350°C for 2 minutes. At this time, the temperature increase rate in the temperature range from 300°C to 1000°C was 900°C/min. Table 3 shows the strength and elastic modulus of carbon fibers obtained by carbonization under the same conditions as above and using the proportions of hydrogen halide gas, oxygen gas, and nitrogen gas as the volume % values listed in Table 3. . These results show that high-performance carbon fibers having high strength and high elastic modulus can be obtained by performing carbonization treatment in an oxidizing atmosphere containing hydrogen halide gas.

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Claims (1)

[Claims] 1 When acrylonitrile synthetic fibers are flame-resistant treated in an oxidizing atmosphere and then carbonized at a maximum temperature of 1000°C or higher, the temperature increase rate in the temperature range of 300°C or higher and 1000°C or lower is set at 900°C/min or higher and 3000°C/min.
1. A method for producing high-performance carbon fiber, characterized in that the carbonization treatment is carried out under an elongation of up to 25%, and the carbonization treatment is carried out in an oxidizing atmosphere containing hydrogen halide gas.