JPS6328132B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high-performance carbon fibers or graphite fibers, and in particular to a method for producing high-strength, high-elastic carbon fibers or graphite fibers in a short time and with high yield using an acrylonitrile-based synthetic fiber precursor. be. As a method for producing a carbon fiber precursor using an acrylic synthetic fiber precursor, first, the fiber is elongated by applying a tension of 0.01 to 0.15 g/d to the precursor in an oxidizing atmosphere at 200 to 250°C. After pre-oxidation treatment, 250
A method of carbonization treatment in a non-oxidizing atmosphere with a temperature gradient of ~1000℃ or more was developed in the Japanese Patent Publication No. 44-
It is known as described in the specification of Japanese Patent Publication No. 21175 and Japanese Patent Publication No. 12540/1983. Among the performance of carbon fiber made by these methods,
The modulus of elasticity is considered to be uniquely determined by the heat treatment temperature of the fiber, and it is relatively easy to produce carbon fibers having a desired modulus of elasticity. However, the relationship between the strength of carbon fiber and the manufacturing method of carbon fiber has not been clarified at all, and it is simply the size of graphite crystals formed in carbon fiber, their degree of orientation, and the amount of carbon fiber present in carbon fiber. It is only assumed that there is some kind of relationship between minute cracks and strength. Conventionally, the carbon fiber manufacturing method that has been developed is to process the pre-oxidized fibers produced as described above at 250%
Carbon fibers are obtained by carbonization or graphitization treatment at temperatures of ~1000℃ or higher.
In the conventional method, it is said that the fiber length shrinks by several percent to 20% compared to the raw material fiber length during this carbonization or graphitization process, and in order to reduce this shrinkage, tension is applied to the yarn. Despite the study of methods of firing while imparting a Not only that, but also high-strength carbon fiber cannot be obtained. In view of the above-mentioned current situation, the inventors of the present invention are currently investigating the purpose of obtaining high-strength carbon fibers. 82% X-ray orientation
They found that it is possible to significantly improve the strength of carbon fibers with a certain degree of strength, and in order to make such high-strength carbon fibers, flame-resistant fibers are stretched under specific conditions and then subjected to pre-carbonization treatment. However, the present invention was completed based on the discovery that the target carbon fiber of the present invention can be obtained by subsequent complete carbonization. The gist of the present invention is that the fiber density is 1.30~
1.42g/ ^cm3 flame-retardant treated yarn in an inert atmosphere
Carbonization treatment is performed while elongating up to 25% in a temperature range of 300 to 800℃, followed by finishing the carbonization treatment while heat treatment at a temperature of 800℃ or higher, and the tensile strength is 350Kg/mm ² or higher. A method for producing high-performance carbon fiber, characterized in that the carbon fiber has an elongation of 1.5% or more. The flame-resistant treated yarn used in carrying out the present invention has a fiber density of 1.30 to 1.42 g/cm ³ and a carbon content of
Any flame-retardant treated yarn can be used as long as it has a content of about 62 to 68% by weight, but it is particularly preferable to use fibers made from polyacrylonitrile or acrylonitrile-based polymers in which the amount of polymerized acrylonitrile is 85% by weight or more. , by oxidation treatment under an oxidizing atmosphere at 200 to 250° C. while shrinking or stretching to a constant length. The fiber density of the flame-resistant treated yarn is measured by measuring a short piece of the flame-resistant treated yarn that has been dried and dehumidified using a xylol/carbon tetrachloride density gradient tube. In this measurement method, a test fiber piece is immersed in advance in the above-mentioned mixed solvent whose density is approximately equal to the fiber density, and the sample is degassed and placed in a density gradient tube.The measurement temperature is 30℃, and the measurement time after immersion is 3 hours. It was measured as follows. If the fiber density of the flame-retardant yarn used in the examples of the present invention is less than 1.30 g/cm ³ , the flame-retardant yarn may be Severe softening occurs and a flow phenomenon is observed, making it difficult to carry out the carbonization process efficiently and sufficiently.Furthermore, the fibers become hollow due to severe thermal decomposition, making it impossible to obtain high-strength carbon fibers. On the other hand, the density of flame-resistant treated yarn is 1.42g/
Flame-retardant yarns larger than cm ³ have an extremely infusible structure and cannot be elongated to a range of 25% during pre-carbonization treatment in an inert atmosphere at temperatures up to 800°C; Shrinkage may occur, and if the flame-retardant treated yarn is forcibly stretched in the pre-carbonization step, it may break or break, making it impossible to increase the degree of crystal orientation of the resulting carbon fiber. It is not possible to make high-strength carbon fiber. Therefore, it is necessary that the fiber density of the flame-retardant yarn used in carrying out the present invention is in the range of 1.30 to 1.42 g/cm ³ . The acrylonitrile polymer used to make the flame-resistant yarn is polyacrylonitrile or 85% by weight or more of acrylonitrile and other copolymerizable monomers, such as unsaturated carboxylic acid such as acrylic acid, methacrylic acid, crotonic acid, and itaconic acid. Acids, methyl, ethyl, butyl, propyl, hexyl, 2-ethylhexyl of these unsaturated carboxylic acids,
Stearyl esters, acrylic acid amide, methacrylic acid amide and methylolated products of these acid amides, N-alkoxymethylated products, diacetone acrylamide, vinyl acetate, vinyl propionate, vinyl chloride, vinyl bromide, allyl sulfonic acid, These include copolymers obtained by appropriately copolymerizing methallyl sulfonic acid, vinylbenzenesulfonic acid, sodium-p-sulfophenyl methallyl ether, and the like. The present invention uses flame-resistant treated yarn having the above-mentioned characteristics.
It is necessary to carry out the carbonization treatment under an inert atmosphere at a temperature in the range from 300 to 800°C, in particular from 400 to 600°C, with an elongation in the range of up to 25%, preferably up to 20%. Figure 1 shows the results of measuring the change in fiber length in a temperature range up to about 1000°C when the flame-resistant treated yarn of the present invention was heat-treated under a low load in an inert gas (nitrogen gas, etc.) atmosphere. Ta. As is clear from FIG. 1, when carrying out the present invention, flame-resistant fibers are carbonized while being heat-treated in an inert gas atmosphere, and the fiber length is elongated between 300 and 800°C, particularly up to 600°C. The most significant feature of the present invention is the discovery that the fiber length can be extended by up to 25% in this temperature range, and the degree of crystal orientation of carbon fiber obtained by such treatment can be improved. This method succeeded in increasing the carbon fiber strength compared to conventional methods, and as a result succeeded in producing high-strength carbon fiber. The elongation of fibers in the carbonization process up to 800°C in the present invention means that the flame-retardant yarn used as a raw material does not shrink, preferably elongation in the range of 0 to 20%. It is something. The elongation of the fiber in this process is 25
If the increase exceeds %, the fiber structure will be destroyed and the strength of the obtained carbon fiber will decrease.On the other hand, if a treatment that causes shrinkage is added in this process, the gain will be reduced. The degree of crystal orientation of the carbon fibers obtained cannot be substantially increased, and therefore the strength of the carbon fibers ultimately obtained cannot be increased. Further, the treatment time in this treatment step is preferably about 0.5 to 40 minutes. In the present invention, the elongated and carbonized fibers obtained as described above are treated in an inert atmosphere at a temperature of 800°C or higher so that the length does not become negative with respect to the original length of the flame-retardant yarn. It is necessary to complete carbonization. Unless this carbonization treatment is performed in an inert atmosphere at 800° C. or higher, carbon fibers with high elasticity and high strength cannot be obtained. In addition, during this process, carbon fibers exhibit shrinkage behavior as shown in Figure 1, but under conditions where the shrinkage is negative with respect to the original length of the flame-retardant yarn used as the starting material. When carbonization is completed, it is not possible to increase the degree of crystal orientation of the obtained carbon fibers, so it is not possible to obtain high-strength carbon fibers. Therefore, in the present invention, the shrinkage of the carbon fibers in this process is The length must not be negative with respect to the original length of the flame-resistant fiber used as a starting material. Preferably, the shrinkage rate of the fiber after the post-carbonization process is preferably 10% or less with respect to the fiber length after the pre-carbonization process. When carrying out the method of the present invention, a pre-carbonization step under an inert atmosphere at a temperature range of up to 800°C and a post-carbonization step under an inert atmosphere at a temperature range of 800°C or higher are performed continuously at a temperature of up to 800°C. Various methods can be used, such as a method using a continuous furnace with a gradient, a multistage furnace with a multistage temperature raising process, or a method in which the material is wound once in a pre-carbonization process and then fired in a post-carbonization process furnace. In the present invention, the flame-retardant yarn used as the starting material has a fiber density of 1.30 to 1.42 g/cm ³ and is elongated in the range of 0 to 25% in the pre-carbonization process. , and by performing the post-carbonization process under limited shrinkage, we succeeded in obtaining high-strength carbon fibers. Another feature of the present invention is that high-strength, high-elasticity carbon fibers can be obtained by The advantage is that it can be manufactured in a short time. In order to achieve this purpose, it is sufficient to set the pre-carbonization treatment time to about 0.5 to 40 minutes and the post-carbonization treatment time to about 1/1 to 1/15 of the pre-carbonization treatment time. It is possible to obtain carbon fiber with excellent performance. Compared to conventional carbon fiber manufacturing methods, the present invention specifies the flame-retardant yarn used as the starting material;
Basically, the carbonization process is divided into two parts, and in the pre-carbonization process, elongation is applied by 25%, preferably up to 20%, and in the post-carbonization process, carbonization is completed under limited contraction. The major feature of this method is that high-strength, high-elasticity carbon fibers can be produced in a short period of time. The present invention will be described in more detail with reference to Examples below. Strength, elastic modulus, X-ray orientation, and yield were determined according to the following methods. Strength, elastic modulus, and elongation Strength and elastic modulus were measured using a tensile rupture test using carbon fiber bundles impregnated with epoxy resin (Epicote 828, manufactured by Ciel Chemical Co., Ltd.) and subjected to a tensile rupture test under conditions of a sample length of 200 mm and a deformation rate of 5 mm/min. I asked. Elongation is tensile strength (Kg/mm ² )/elastic modulus (ton/mm ²
)×100. Degree of X-ray orientation In the X-ray diffraction photograph of carbon fibers aligned in one direction, we focused on the diffraction pattern having a maximum on the equator line based on the (002) reflection of graphite crystals using a diffractometer (manufactured by Rigaku Denki: - source Cu,
The half width H (degree) of the obtained intensity distribution curve in the azimuthal direction is determined by the following formula, and the degree of X-ray orientation π of the microcrystal is
(002) was found. π (002) = (180 - H) / 180 × 100 (%) Yield The weight fineness of the flame-retardant treated yarn and the carbon fiber obtained by firing the flame-retardant treated yarn is determined by the bone-dry method and is Dp. and Dc. On the other hand, the change from the flame-retardant yarn length lp to the carbon fiber length lc due to the elongation operation in the carbonization treatment and the yarn movement speed were measured and calculated using the following formula. Shrinkage = Dc/Dp x lc/lp x 100 (%) Example 1 A copolymer of acrylonitrile/methyl acrylate/methacrylic acid = 95/4/1 was made into fibers by a wet process, with a number of filaments of 3000 and a single yarn denier of 1.5. A multifilament with a tensile strength of 6.2 g/d and a breaking elongation of 15.4% was obtained. This fiber bundle is 230~250
Continuous treatment was carried out in a furnace with a temperature gradient of 0.degree. C. for a residence time of 40 minutes so that the elongation rate was as shown in Table 1. The density of this flame-retardant yarn is approximately
It was 1.36 g/cm ³ . Next, using the pre-carbonization and post-carbonization conditions shown in Table 1, carbonization treatment under nitrogen gas flow was continuously performed, and the performance of the obtained carbon fibers was evaluated. Table 1 shows the results.

[Table] Nos. 1 to 10 in Table 1 indicate the conditions for carrying out the method of the present invention and the performance and yield of carbon fibers obtained by the method of the present invention. 1 shows a conventional carbon fiber manufacturing method and the performance of the obtained carbon fiber. The carbon fiber obtained by the method of the present invention has a higher degree of X-ray orientation than that of the comparative example,
As a result, it can be seen that the strength of the carbon fibers is significantly improved. Furthermore, the yield is improved compared to that of the conventional method, and although the carbonization treatment time can be shortened, carbon fibers with sufficiently excellent performance are obtained. Example 2 The acrylonitrile-based synthetic fiber multifilament used in Example 1 was placed in a flameproofing treatment furnace with a temperature gradient of 230 to 250°C by varying the residence time to produce four types of fibers having the fiber densities shown in Table 2. A flame-resistant treated yarn was prepared. These four kinds of flame-resistant treated yarns were carbonized using the pre-carbonization conditions and post-carbonization conditions shown in Table 2, and the performance of the obtained carbon fibers is shown in Table 2. From the results shown in Table 2, it is clear that the fiber density of the flame-resistant treated yarn must be within the range specified by the present invention.

【table】 [Brief explanation of the drawing]

Figure 1 shows the change in yarn length when the flame-resistant treated yarn used in the present invention is heat-treated, with the vertical axis representing the heat treatment temperature, and the horizontal axis representing the heat treatment temperature. This shows the change in length.

Claims (1)

[Claims] 1. A flame-retardant treated yarn with a fiber density of 1.30 to 1.42 g/ ^cm3 is carbonized in an inert atmosphere at a temperature range of 300 to 800°C while being stretched up to 25%, and then A method for producing high-performance carbon fiber, which is characterized by completing carbonization at a temperature of 800°C or higher, producing carbon fiber with a tensile strength of 350 kg/mm ² or higher and an elongation of 1.5% or higher. 2. The method for producing high-performance carbon fiber according to claim 1, wherein the flame-resistant treated yarn is made of acrylonitrile synthetic fiber. 3. The carbonization treatment according to claim 1 or 2, characterized in that the carbonization treatment is carried out so that the length of the carbonized carbon fibers is not negative with respect to the original length of the flame-resistant treated yarn. Production method of performance carbon fiber.