JPH0116927B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing high elongation carbon fiber,
More specifically, in the process of manufacturing carbon fibers using flame-resistant fibers as raw materials, carbon fibers that have been oxidized by an oxidizing agent are further heat-treated at a temperature of 1200°C to 1600°C in a specific atmosphere at least once. The present invention relates to a method for producing high elongation carbon fiber. In general, carbon fiber has excellent mechanical properties such as specific strength and specific modulus. Therefore, composite materials reinforced with carbon fiber are used in structural materials for aircraft, space development equipment, automobile parts, and sporting goods. It is becoming widely used. This composite material is
It is mainly composed of plastic reinforced with carbon fibers, and it is therefore known that the adhesiveness between the carbon fibers and the plastics has a large effect on the mechanical properties of the composite material. Conventional technology In recent years, the development of carbon fibers with high tensile elongation at break and strength, called high elongation carbon fibers, has been progressing.
Products with improved elongation of more than 50 kg/mm ² and elongation at break of nearly 2% have been developed. In order to fully utilize the effect of increasing the elongation of carbon fiber as a composite material, research into manufacturing methods to improve the adhesion between carbon fiber and plastic has increased more than ever before. It is becoming important. Conventionally, a method of oxidizing carbon fibers has been known as a technique for improving the adhesiveness between carbon fibers and plastic. Such oxidation treatment methods include a method of oxidizing the carbon fiber surface in a solution containing an oxidizing agent (liquid phase oxidation method) as described in Japanese Patent Publication No. 52-25119; As stated in No. 58-104222,
A method of oxidizing the surface of carbon fibers in an electrolytic solution by applying electricity directly to carbon fibers through an electrode roller (electrolytic oxidation method), and Japanese Patent Application Publication No. 1982-
As described in No. 40662 and No. 52-53092, there is a method in which flame-resistant fibers or carbon fibers are heat-treated in an oxidizing gas atmosphere to oxidize the surface of the fibers, and flame-resistant fibers are treated with carbon fibers. A method of oxidizing the surface at the same time as carbonization (vapor phase oxidation method) is known. Problems to be Solved by the Invention Although the oxidized fibers subjected to the above oxidation treatment have higher strength and elongation than non-oxidized fibers, the composite material produced from the oxidized fibers have been reported to have inferior properties compared to similar composites made from unoxidized fibers (K.Morita etal International
Carbon Conference Baden, Baden1976). In order to improve such oxidation treatment technology, Japanese Patent Publications No. 145696/1982, No. 59497/1982, and No. 58
−214527, etc. have been reported. However, with the recent development of carbon fiber composite materials in many fields, various types of plastics are used as matrices depending on the application, and their diversification is progressing more and more. Even though the same oxidized fibers are used, the tensile elongation at break of the composite material may be significantly reduced depending on the composition of the plastic. Means for Solving the Problems The present inventors have conducted extensive research on the mechanical fracture mechanism of carbon fiber composite materials having plastic as a matrix, and have found that the tensile fracture of carbon fiber composite materials is We obtained the knowledge that there is a close relationship with the interfacial state between matrix plastics, and based on this knowledge, we succeeded in producing high elongation carbon fiber. The method for producing high elongation carbon fibers according to the present invention includes a step of producing carbon fibers using flame-resistant fibers obtained by heat-treating acrylonitrile-based synthetic fibers in an oxidizing atmosphere. At the same time as carbonization, surface oxidation treatment is performed in the gas phase, or after carbonization, surface oxidation treatment is performed in the gas phase, and then the obtained carbon fiber is placed in an atmosphere consisting of an inert gas and/or a hydrogen halide gas. It is characterized by further heat treatment at a temperature of 1200°C to 1600°C for 1 to 80 seconds. In the present invention, high elongation carbon fibers refer to carbonaceous fibers with a tensile elongation at break of 1.5% or more and a tensile strength at break of 400 Kg/mm ^{2 or} more. In the method of the present invention, the precursor is
Synthetic acrylonitrile fibers are used, especially fibers produced by known methods from acrylonitrile polymers containing at least 90% by weight of acrylonitrile units. In particular, the single yarn fineness is 0.5 to 1.5 denier, and the number of single yarns is 1000 or more.
A fiber bundle of 12,000 fibers is preferred, and a fiber bundle with few impurities and defects, a dense structure, and a highly oriented fiber bundle is more preferred. In the method of the present invention, the flame-resistant fibers are prepared by heating the precursor as described above at 200 to 400°C, preferably 240 to 350°C, using a hot air circulation furnace or/and heating roller in an oxidizing atmosphere represented by air. It can be obtained by heat treatment for a predetermined period of time. In the process of producing carbon fibers according to the method of the present invention, the method of subjecting the fibers to surface oxidation treatment includes heating the flame-retardant fibers in a non-oxidizing atmosphere at
A method of carbonizing at a temperature of 1450°C, preferably 1300 to 1400°C, and then oxidizing in a gas phase; There is a method in which the fiber surface is simultaneously carbonized, preferably at a temperature of 1300 to 1400°C, and oxidized in a vapor phase. On the other hand, the oxidizing agents used in the surface oxidation treatment of the method of the present invention include oxygen, ozone, nitrogen oxide,
Examples include sulfur oxide and carbon oxide, but oxygen is preferred in practice. The composition of the oxidizing gas atmosphere containing these oxidizing agents varies depending on the type of oxidizing agent, but generally the oxidizing agent concentration is 500 ppm to 40% by volume.
A mixed gas with an inert gas is used. Generally, in the case of oxidation treatment in the gas phase after carbonization, heating may be performed at about 600 to 1400° C. for about 5 to 120 seconds in an oxidizing gas atmosphere. Moreover, when carrying out surface oxidation treatment at the same time as carbonization, heating may be performed at 1200 to 1450° C. for about 5 to 60 seconds in an oxidizing gas atmosphere as described above. The above-mentioned oxidizing agent is capable of introducing oxygen-containing functional groups onto the fiber surface and/or etching the fiber surface. As in the method of the present invention, the fiber to be oxidized which has undergone surface oxidation treatment after carbonization or simultaneously with carbonization is heat treated in an atmosphere consisting of an inert gas and/or hydrogen halide gas. As the hydrogen halide, hydrogen fluoride, hydrogen chloride, hydrogen bromide, etc. can be used, but it is practically preferable to use hydrogen chloride. Further, as the inert gas, helium, argon, nitrogen, etc. can be used, but nitrogen is advantageous in terms of cost. In this case, it is possible to use an inert gas alone, but the presence of hydrogen halide is more effective in improving the surface of the fiber to be oxidized.
For this reason, it is preferable to use a mixed gas of an inert gas and hydrogen halide as the atmosphere used. In this case, it is more preferable to use a mixed gas of hydrogen halide and an inert gas containing 0.1% by volume or more of hydrogen halide. The upper limit of the content of hydrogen halide in the mixed gas is not particularly limited, but
It is better not to be too expensive from a cost standpoint. In addition, the heat treatment conditions were 1200℃ to 1600℃.
~80 seconds, at 1200-1400°C, with seconds being particularly preferred. If the temperature is less than 1200°C or the time is less than 1 second, the surface of the oxidized fibers will not be improved, so the oxidized fibers will not be blended into a plastic matrix to form a composite material. In some cases, the high elongation properties of the oxidized fibers are not fully exhibited for certain types of plastics. Furthermore, at temperatures exceeding 1600°C, the structure of the main body of the fiber to be oxidized begins to change, fine pores are generated inside the fiber, and as a result, the physical properties of the fiber begin to deteriorate, which is undesirable. . In addition, 80
When the time exceeds seconds, the tensile elongation at break and the strength of the composite material using the oxidized fibers show high values, but the The shear strength (ILSS) is drastically reduced, and therefore a high-performance composite material cannot be obtained. Effects of the Invention The composite material using high elongation carbon fiber obtained by the method of the present invention has tensile elongation at break and strength of
It exhibits a high value regardless of the type of plastic that makes up the matrix, and also maintains a sufficient value for interlaminar shear strength (ILSS) to withstand practical use. In addition, the oxygen concentration O _1S /C _1S determined by X-ray photoelectron spectroscopy (ESCA) was slightly reduced for oxidized fibers by heating above 1200°C, but compared to non-oxidized fibers, A considerable amount of oxygen remains, which suggests that sufficient surface functional groups are uniformly present on the fiber surface to form a high-performance composite material. In addition, as a result of BET specific surface area measurement using krypton gas, the surface area of the fibers heat-treated at a temperature of 1000°C or higher was smaller than that of the fibers subjected to oxidation treatment. This is thought to be due to the fact that the number of fine pores that appeared on the surface decreased. EXAMPLES Hereinafter, the present invention will be specifically described with reference to the following examples. Example 1 Acrylonitrile synthetic fiber (single denier
1.3d, 6000 filaments) was heated in air at 240°C for 40 minutes and then at 260°C for 20 minutes to obtain flame-resistant fibers, and then carbonized in a non-oxidizing atmosphere at a maximum treatment temperature of 1300°C to obtain non-oxidized fibers. I got it. Using this unoxidized fiber, oxidation treatment was performed in the gas phase at 1000°C for 40 seconds in an atmosphere consisting of 1.0% by volume of hydrogen chloride gas, 0.5% by volume of oxygen gas, and 98.5% by volume of nitrogen gas. . The obtained oxidized fibers were treated with 1.0% by volume of hydrogen chloride gas and 1.0% by volume of nitrogen gas.
Heat treatment was performed at 1200° C. for 7 seconds in an atmosphere consisting of 99.0% by volume to obtain high elongation carbon fibers. From the obtained high elongation carbon fiber, JIS-R-7601-
Strands were prepared according to the method described in 1980-5.3.2, and the tensile strength and elongation at break were measured. Two types of strands were produced. That is, epoxy resin (Epicoat manufactured by Yuka Ciel Epoxy Co., Ltd.)
828) The fibers were impregnated in a mixture of 100 parts by weight, 90 parts by weight of methylnadic anhydride, and 2 parts by weight of benzyldimethylamine dissolved in methyl ethyl ketone (hereinafter referred to as "MEK"), and cured at 150°C for 1 hour. (hereinafter referred to as "Strand A"), 100 parts by weight of the epoxy resin, and 3 parts by weight of boron trifluoride monoethylamine were similarly impregnated in a mixed solution in MEK, and heated at 130°C for 1 hour. ,
The strand was further cured at 180°C for 2 hours (hereinafter referred to as ``Strand B''). ). As a result of the measurement, strand A had a tensile elongation at break (hereinafter referred to as "elongation") of 1.78% and tensile strength at break (hereinafter referred to as "strength") of 435 Kg/mm ² , and strand B had a tensile elongation at break of 1.72%. The strength was 421Kg/ ^mm2 . In addition, the high elongation carbon fiber was coated with epoxy resin (Araldide MY720 manufactured by Ciba Geigy) 100%
Parts by weight, 4,4'-diaminodiphenylsulfone 20
A prepreg is prepared by impregnating a mixture of MEK with 1.5 parts by weight of boron trifluoride monoethylamine, which is then laminated and cured by heating to create a flat plate-like molded product. When the shear strength (ILSS) was measured, it was 12.7Kg/ ^mm2 . Further, O _1S /C _1S by ESCA was 0.15, and BET specific surface area by krypton was 0.34 m ² /g. On the other hand, Table 1 shows the results for strands and plate-shaped molded products made using unoxidized fibers that were never oxidized when producing carbon fibers using flame-resistant fibers as raw materials. Example 2 The same treatment as in Example 1 was carried out except that the atmosphere in which the fibers to be oxidized were heat treated was 100% nitrogen by volume, and the heat treatment temperature and time were 1350°C and 15 seconds, respectively. A strand and a molded article were produced. As a result of physical property measurements, strand A has an elongation of 1.79% and a strength of 440 kg/ ^mm2 .
Strand B has an elongation of 1.64 and a strength of 403 Kg/mm ² .
ILSS was 12.3Kg/ ^mm2 . Example 3 In Example 1, the atmosphere in which the fibers to be oxidized were heat treated was hydrogen chloride gas 3.0% by volume and nitrogen gas.
The same treatment was carried out except that a mixed gas consisting of 97.0% by volume was used, and the heat treatment temperature and time were 1400°C and 10 seconds, and strands and
A molded article was produced. As a result of physical property measurements, strand A has an elongation of 1.77% and a strength of 433 Kg/mm ² , strand B has an elongation of 1.76% and a strength of 430 Kg/mm ² , and ILSS is
It was 12.1Kg/ ^mm2 . Example 4 In Example 1, flame-resistant fibers were used as raw materials in an atmosphere consisting of 5% by volume of hydrogen chloride gas, 2.0% by volume of oxygen gas, and 93.0% by volume of nitrogen gas at the maximum treatment temperature.
Carbonize at 1300℃ to produce oxidized fibers,
The obtained oxidized fibers were heated at 1,400 °C in an atmosphere containing 1.0% by volume of hydrogen chloride gas and 99.0% by volume of nitrogen gas.
Strands and molded products were produced in the same manner, except that the heat treatment was performed at ℃ for 10 seconds. As a result of physical property measurements, in strand A,
Strand B has an elongation of 1.78% and a strength of 436Kg/ ^mm2 .
Elongation 1.73%, strength 425Kg/mm ² , ILSS 12.1Kg/
It was warm in ^mm2 . Comparative Example 1 In Example 1, except that the oxidized fibers were not heat-treated, all the same treatments were performed. Strand A had an elongation of 1.75% and a strength of 428 Kg/mm 2 , and Strand B had an elongation of 1.75% and a strength of 428 Kg/mm ² . The elongation was 1.20%, the strength was 295 Kg/mm ² , and the ILSS was 12.7 Kg/mm ² . Comparative Example 2 The same treatment as in Example 1 was carried out except that the fibers to be oxidized were heat-treated at 500°C for 30 seconds in an atmosphere consisting of 1.0% by volume of hydrogen chloride gas and 99.0% by volume of nitrogen gas. However, strand A
Strand B has an elongation of 1.78%, a strength of 435 Kg/mm ² , and an elongation of strand B of 1.23%, a strength of 302 Kg/mm ² , and an ILSS of 12.6.
It was Kg/ ^mm2 . Comparative Example 3 In Example 4, for the oxidized fiber,
When all the same treatments were performed except that no heat treatment was performed, Strand A had an elongation of 1.79% and a strength of 439 Kg/mm ² , and Strand B had an elongation of 1.22 and a strength of 439 Kg/mm 2
298Kg/mm ² and ILSS was 12.8Kg/mm ² . Comparative Example 4 Carbon fibers were produced in the same manner as in Example 1, and two types of strands A and B were produced from these carbon fibers in the same manner. However, the heat treatment of the fibers to be oxidized is carried out in an atmosphere consisting of 1.0% by volume of hydrogen chloride, 0.5% by volume of oxygen, and 98.5% by volume of nitrogen.
Similar treatment methods and conditions were used except that the treatment was carried out at 1350°C for 15 seconds. Strand A has elongation
Strand B has an elongation of 1.25% and a strength of 305Kg/mm ² , and ^the ILSS has a
It was 12.6Kg/ ^mm2 .

【table】

[Table] Example 5 and Comparative Example 5 The oxidized fibers obtained in the same manner as in Example 4 were heat treated in an atmosphere containing 1.0% by volume of hydrogen chloride gas and 99.0% by volume of nitrogen gas. The heat treatment temperature is
The temperature was 1000°C (Comparative Example 6) and 1200°C (Example 6), and the heat treatment times were 5, 10, and 20 seconds. The results of measuring the tensile strength of the obtained fiber strand B are shown in FIG.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the heat treatment conditions in Example 5 and Comparative Example 5 and the tensile strength of the obtained fiber strand B.

Claims (1)

[Claims] 1. In the process of manufacturing carbon fiber using flame-resistant fiber obtained by heat-treating acrylonitrile-based synthetic fiber in an oxidizing atmosphere as a raw material, surface oxidation treatment is carried out in the gas phase at the same time as carbonization, or After carbonization, surface oxidation treatment is performed in the gas phase, and then the obtained carbon fiber is heated at a temperature of 1200°C to 1600°C for 1 to 80°C in an atmosphere consisting of an inert gas and/or hydrogen halide gas. A method for producing high elongation carbon fiber, characterized by further heat treatment for seconds.