JPS6366326A - Production of high-strength carbon fiber - Google Patents

Abstract

PURPOSE:To readily obtain the titled fibers suitable as a carbon-fiber reinforced composite material which is a raw material for structural materials, etc., of aircraft, in high yield for a short treating time, by heat-treating carbon fibers in an atmosphere containing a hydrogen halide gas and hydrocarbon. CONSTITUTION:Carbon fibers are heat-treated at >=1,000 deg.C, preferably 1,300-1,400 deg.C temperature in an atmosphere containing a hydrogen halide gas, preferably hydrogen chloride gas and carbon dioxide gas to afford the aimed fibers. Furthermore, the heat-treating time is preferably 20-100sec. The carbon fibers which are a raw material are obtained by flameproofing fibers prepared from an acrylonitrile based copolymer containing >=90wt% acrylonitrile units at 240-350 deg.C and carbonizing the flameproofed fibers at 1,200-1,500 deg.C.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing high-strength carbon fiber, and more specifically, to a method for producing high-strength carbon fiber by treating carbon fiber in a special atmosphere. The present invention relates to a method for producing fibers with high yield.

In general, carbon fibers have excellent mechanical properties such as specific strength and specific modulus of elasticity. Therefore, carbon fiber reinforced composite materials (hereinafter abbreviated as "cFRPJ") using carbon fibers as reinforcement materials
is being widely used in aircraft structural materials, space development equipment, automobile parts, and sporting goods. In recent years, particularly for aircraft and space development equipment, there has been a demand for lighter weight and higher strength CFRP.

It is generally known that the strength of CFRP varies according to the composite agent. That is, the strength of CFRP is the sum of the intensities of its constituent components multiplied by their respective volume fractions. Therefore, when manufacturing CFRP, if the volume of carbon fibers contained in the CFRP is the same, the CFRP using carbon fibers with higher strength will have higher strength. Therefore, in order to obtain CFRP with even higher strength, there is an increasing demand for higher strength of the carbon fiber itself for CFRP than ever before.

[Conventional technology]

It is difficult to manufacture the above-mentioned high-strength CFRP using conventional general-purpose carbon fibers (tensile strength of 300'!g/■), so it is better to use carbon fibers with even higher strength. There is a need.

from various industrial fields including the aircraft industry.

In response to these demands, research is currently being actively conducted to increase the strength of carbon fibers, and several methods have already been proposed. Showa 59-1
According to No. 37512, by specifying the manufacturing conditions of a precursor for carbon fiber production and the firing conditions of the obtained precursor to an optimal range, the carbon fiber production can be made by approximately 2/2 to 460 to 480.
Carbon fibers having a tensile strength of fi2 have been obtained.

Furthermore, according to Japanese Patent Application Laid-Open No. 58-214527, a specific carbon fiber having a tensile strength of about 420 to 450/m is used as a raw material, and by further performing two stages of surface treatment, 490 kl? Carbon fibers having a tensile strength of /m2 or more have been obtained.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional technology, the tensile strength developed through the normal carbonization process is approximately 460 to 480 k.
g/lxm2 is the limit, and the above-mentioned Japanese Patent Application Laid-Open No. 58-214
As described in No. 527, in order to obtain carbon fibers having a tensile strength of 9As2 or more in 490, the obtained carbon fibers are heated in 68% concentrated nitric acid at 120°C for 45 minutes.
Alternatively, it requires a longer treatment time of 45 minutes in nitric acid;
Furthermore, in order to remove the nitric acid used, a water washing step must be provided, which complicates the manufacturing process and is unavoidable in terms of cost.

The inventors of the present invention have conducted extensive research into ways to increase the strength of carbon fibers, and have found that high strength, especially 500 kl? /ll112
He discovered a method for obtaining high-strength carbon fibers with tensile strength above and filed a patent application (Japanese Patent Application No. 61-68
No. 787). This method is characterized by heat-treating carbon fibers at a temperature of at least 1000° C. in an atmosphere containing hydrogen halide gas and water vapor.

[Means for solving problems]

As a result of further studies, the present inventors found that by using carbon dioxide gas in place of water vapor in the above method, high-strength carbon fibers can be produced industrially advantageously, especially in relatively high yields, as in the above method. The present invention has been completed based on the discovery that a reduced weight loss can be obtained.

That is, in the present invention, carbon fibers are heated at least 100% in an atmosphere containing hydrogen halide gas and carbon dioxide gas.
Provided is a method for producing high-strength carbon fiber, which is characterized by heat treatment at a temperature of 0° C. or higher.

The carbon fibers used in the present invention are not particularly limited, and for example, carbon fibers made by using Puricurchi as a raw material, oxidizing it to make it flame-resistant fiber, and then manufacturing it at a temperature of at least 800°C. Can be used. Especially, the tensile strength is 500! In order to produce high-strength carbon fibers with a tensile strength of 9/2 or more, it is preferable to use raw carbon fibers with a tensile strength of 400 to 450 Y/42.

As a precursor, acrylonitrile synthetic fiber,
Those commonly used in the production of carbon fibers, such as fC fibers obtained from petroleum/coal-based pitches, cellulose fibers such as rayon, and phenol resin fibers, can be used.

Among these, fibers produced by known methods from acrylonitrile copolymers containing at least 90% by weight of acrylonitrile units are preferred. In particular, single yarn fineness 0
．． 5-1.5 denier, number of single threads 1,000-30,0
00 fiber bundles are preferred. Fiber bundles with few impurities and defects, a dense structure, and a high degree of orientation are particularly preferred.

The flame-resistant fibers are prepared by heating the precursor in an oxidizing atmosphere such as air in a hot air circulation furnace or in a Vi/
It can be obtained by heat treatment using a heating roller at 200 to 400°C, preferably 240 to 350°C for a predetermined time.

The carbon fibers used in the present invention can be obtained, for example, by carbonizing the flame-resistant fibers described above in a non-oxidizing atmosphere at a temperature of 800 to 1800°C, preferably 1200 to 1500°C. Furthermore, carbon fibers obtained by carrying out the carbonization process of the flame-resistant fibers in an atmosphere containing an oxidizing gas, and carbon fibers whose fiber surfaces have been oxidized in a vapor phase, and unoxidized carbon fibers that have undergone a carbonization process Carbon fibers whose surface has been oxidized by gas-phase oxidation in an oxidizing gas, electrolytic oxidation using an electrolysis reaction, or liquid-phase oxidation using a solution containing an oxidizing agent can also be used. good. Further, it is also possible to use vapor-grown carbon fibers produced in the vapor phase using hydrocarbon gas as a raw material.

The heat treatment temperature in the present invention is 1000°C or higher, preferably 1300°C to 1400°C.

The improvement in strength that is the objective of the present invention occurs at a heat treatment temperature of 1000°C or higher, and in particular at 1300°C to 1400°C, the carbonaceous composition inside the raw material carbon fiber does not change in quality and a homogeneous carbon fiber is produced. can get. Further, the treatment time at the above-mentioned heating temperature is preferably 10 seconds or more, particularly 20 to 1
00 seconds is preferred. When the heating time is 10 seconds or more, a sufficient effect of improving the tensile strength is observed, and when the heating time is 100 seconds or less, the weight loss of the raw material carbon fiber is very small and the highest tensile strength is obtained.

The hydrogen halide gas used as the atmospheric gas is hydrogen halide gas exclusively for hydrogen fluoride gas, hydrogen chloride gas, hydrogen bromide gas, or the aforementioned hydrogen halide gas by thermal decomposition at the heat treatment temperature of carbon fibers. Hydrogen halide generated by adding a halogen compound that produces 2 to the heat treatment system may be used, but from a practical standpoint, it is preferable to use hydrogen chloride gas.

The carbon dioxide gas may be a commercially available carbon dioxide gas, or a carbonic acid compound that generates carbon dioxide by thermal decomposition at the heat treatment temperature of carbon fibers may be heat-treated. Although it is possible to use carbon dioxide generated by adding it to the system, it is preferable to use carbon dioxide gas itself because the operation becomes more stable.

Further, in the atmospheric gas, in addition to hydrogen halide gas and carbon dioxide gas, other gases can be used as diluents. The diluent is preferably an inert gas such as nitrogen gas or alcohol.

As for the amount of carbon dioxide gas, it is preferable that the concentration of carbon dioxide gas in the atmosphere is 1.0 by volume or more, and particularly preferably 4 to 40 by volume. When the carbon dioxide gas concentration is 4 volumes or more, the effect of increasing the strength, which is the objective of the present invention, is well exhibited, and when it is 40 volumes or less, the high strength carbon fiber, which is the objective of the present invention, is well exhibited. , especially in high yields.

Further, as for the ratio of carbon dioxide gas to hydrogen halide gas, it is preferable that the volume ratio of hydrogen halide gas to carbon dioxide gas is 0.001 or more, and more preferably the volume ratio is 0.05 to 0.25. It is more preferable if

When the capacity ratio is 0.001 or more, the objective of the present invention, which is to increase the strength, is particularly sufficiently achieved.

〔Effect of the invention〕

The tensile strength of the carbon fibers obtained by the method of the present invention has been significantly improved compared to the raw material carbon fibers obtained before the method of the present invention. Two or more high strength carbon fibers can be obtained. Furthermore, in the method of the present invention, the effect of improving tensile strength is achieved relatively easily and in a short time, and the weight loss rate is also quite small.

In addition, when the method of the present invention is carried out on carbon fibers whose surface has not been oxidized, the specific surface area is improved, and measurements of the ratio of constituent atoms on the surface using a photoelectron spectrometer (JCA) show that the high-strength carbon fibers It was observed that the number of oxygen atoms on the surface was increased compared to the number of oxygen atoms on the surface of the raw carbon fiber.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to Examples.

Example l Acrylonitrile □-based synthetic fiber (single yarn denier 1.3 d
, 6000 filaments) was heated in air at 240°C for 40 minutes and then at 260°C for 20 minutes to obtain a flame-resistant fiber, which was then carbonized in a non-oxidizing atmosphere at a maximum processing temperature of 1300°C to have a tensile strength of 434. 9/m2.
TEX 420vl 000m.

Next, carbon fibers with a laminar shear strength of 9.7 and bleaching-2 in CFRP were obtained. Note: 0/C of carbon fiber surface by ESCA
The value was 0.07.

Using this carbon fiber, the concentration of carbon dioxide gas was 1.9 volumes, hydrogen chloride gas was 2.0 volumes, and nitrogen gas was 96.1 volumes.
A heat treatment was performed for 38 seconds at 1,300 tl in an atmosphere consisting of a capacitance of 1,000 liters to obtain high-strength carbon fibers.

Using the obtained high strength carbon fiber, JIS-R-7601
Strands were produced according to the method described in -5.3.2, and the tensile strength and TEX were measured. The results are shown in Table 1. Also, the interlaminar shear strength of the high-strength carbon fiber was 11.
8kl? /m2, KSCA K Yoru0/C value is 0.1
It was 5.

Example 2 In Example 1, the carbon dioxide gas concentration was set to 20 volumes,
1.0 volume of hydrogen chloride gas, 79 volume it% of nitrogen gas
A strand was produced in the same manner, except for binding. The results of physical property measurements are shown in Table 1.

Comparative Example 1 The same treatment as in Example 1 was performed except that only nitrogen was used as the atmospheric gas, and the physical properties of the strands were measured. The results are shown in Table 1.

Comparative Example 2 In Example 1, the atmospheric gas was changed to a carbon dioxide gas concentration of 2.
The same treatment was performed except that the volume of nitrogen gas was 0 and the volume of nitrogen gas was 80, and the strand strength was measured in the same manner. The results are shown in Table 1.

Comparative Example 3 All the same treatments as in Example 1 were carried out except that the atmospheric gases were hydrogen chloride gas of 1.0 volume and nitrogen gas of 99.0 volume, and the physical properties of the strands were measured in the same manner. Ta. The results are shown in Table 1.

Example 3 In Example 1, the atmospheric gases were carbon dioxide gas concentration of 20 volumes, hydrogen bromide gas of 1.0 volumes, and nitrogen gas of 79 volumes.
All of the strands were treated in the same manner except that the capacity was changed to 1, and the physical properties of the strands were measured in the same manner. The results are shown in Table 1.

Example 4 Flame-resistant fiber obtained from acrylonitrile synthetic fiber was carbonized at the maximum treatment temperature of 1350°C in an oxidizing atmosphere, and the fiber surface was simultaneously oxidized to have a tensile strength of 460 and 9/m.
, TEX406. F/1000-carbon fiber was obtained. A strand was produced in the same manner as in Example 1, except that this carbon fiber was used and the heat treatment temperature was 1350°C. The results of measuring the physical properties of the strands are shown in Table 1.

Example 5 In Example 4, the atmospheric gas was carbon dioxide gas 40
The strand physical properties were measured in the same manner except that the volume was 1.0 vol., the hydrogen chloride gas was 1.0 vol., and the nitrogen gas was 59 vol.

The results are shown in the first light.

Example 6 Flame-resistant fibers obtained from acrylonitrile synthetic fibers were carbonized in an inert atmosphere at a maximum temperature of 1250°C, and then the carbon fibers were used as anodes and energized in an electrolytic solution to undergo surface oxidation treatment. After applying it, the tensile strength is 467IK! 9/m, T
EX316J/1000m carbon fiber was obtained. Using this carbon fiber, the atmospheric gas was set to 20 volumes of carbon dioxide gas, 1.0 volumes of hydrogen chloride gas, and 79 volumes of nitrogen gas.
Heat treatment was performed at a treatment temperature of 1200° C. for 38 seconds. Table 1 shows the physical properties of the obtained carbon fiber.

Remaining days below

Claims (2)

[Claims] (1) A method for producing high-strength carbon fibers, which comprises heat-treating carbon fibers at a temperature of at least 1000° C. in an atmosphere containing hydrogen halide gas and carbon dioxide gas. (2) The high strength according to claim 1, wherein the carbon dioxide gas concentration in the atmosphere is 1.0% by volume or more, and the volume ratio of hydrogen halide gas to carbon dioxide gas is 0.001 or more. Carbon fiber manufacturing method.