JPH0242926B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a method for producing carbon fibers that reduces tar, fiber waste, etc. that accumulate in a carbonization furnace during production of carbon fibers, and enables continuous operation for a long time. Conventionally, carbon fibers are manufactured by subjecting acrylonitrile fibers to flame-retardant treatment to produce acrylonitrile-based flame-resistant fibers, and then carbonizing the acrylonitrile-based flame-resistant fibers. Flame-resistant fibers, which are intermediate products in this manufacturing process, are used in related fields as they are, taking advantage of their flame resistance. When carbonizing this flame-resistant fiber bundle, tar, fiber waste, and other deposits that accumulate inside the carbonization furnace make long-term continuous operation of the carbonization furnace impossible and require periodic internal cleaning. . Further, if a large amount of deposits accumulates in the carbonization furnace, even if the furnace is not clogged, the yarn path in the furnace is narrowed by the deposits, which causes the fiber bundles to be treated to become fluffy. The present invention solves these problems by reducing deposits in the furnace, suppressing fluffing of fiber bundles, and
The purpose is to obtain high-quality carbon fibers, and to achieve this purpose, carbon fibers are manufactured using acrylonitrile-based flame-resistant fibers that have undergone special treatment. The present invention is as follows. One or more water-soluble polymeric substances selected from the group of polyvinyl alcohol, polyethylene oxide, and polyacrylamide are added to acrylonitrile flame-resistant fiber bundles obtained by oxidizing acrylonitrile fibers in an oxidizing atmosphere. After applying the containing liquid, drying is performed at a temperature of 250°C or lower to deposit 0.1 to 2.0% by weight (based on the fiber bundle) of the polymeric substance, and then introduced into a carbonization furnace at 400°C or higher. Carbon fiber manufacturing method. According to the present invention, it is possible to reduce deposits in a carbonization furnace, reduce fuzz in the obtained carbon fiber bundle, and obtain high quality carbon fibers in which fibers do not stick to each other in the carbon fiber bundle. Can be done. In the present invention, an acrylonitrile-based flame-resistant fiber bundle is a fiber bundle obtained by subjecting an acrylonitrile-based fiber bundle to flame-retardant treatment using a known method. Here, an acrylonitrile fiber bundle is defined as having at least 90% acrylonitrile component in its polymer component.
It is a fiber bundle made of a polymer or copolymer containing 0 to 10% by weight of a vinyl compound commonly used for copolymerization with acrylonitrile as a copolymerization component. As a fiber bundle, one composed of 500 to 3000 filaments with a single fiber fineness of 0.5 to 1.2 deniers is usually used. The known method described in Japanese Patent Publication No. 52-39100, for example, may be employed for flame-retardant treatment of this acrylonitrile fiber bundle. The acrylonitrile flame-resistant fiber thus obtained is extremely susceptible to fuzzing due to contact with roller guides and the like during the manufacturing process. In the present invention, the water-soluble polymeric substance added to the acrylonitrile flame-resistant fiber bundle is one or more selected from the group of polyvinylalcoat, polyethylene oxide, and polyacrylamide. Polyethylene oxide here has a molecular weight of 100,000~
4.8 million, preferably 100,000 to 1.1 million. To apply these water-soluble polymer substance liquids to the acrylonitrile-based flame-resistant fiber bundles, the above-mentioned water-soluble polymer substances are made into an aqueous solution or dispersion liquid of 1 g/~20 g/, and the fiber bundles are passed through this liquid. This can be carried out arbitrarily by any method, or by spraying a liquid on the fiber bundle or bringing it into contact with a roller. After application in this manner, it is dried at a temperature of 250°C or less. If the carbon fibers are introduced into the carbonization furnace without drying, the resulting carbon fibers will stick together and have reduced strength. Furthermore, when drying at a temperature exceeding 250°C, a similar sticking phenomenon occurs and carbonization cannot be carried out smoothly. The amount of these substances attached to the flame-resistant fiber bundle is 0.1
It is necessary to set the amount to ~2.0% by weight; if the amount is less than this, there will be no effect, and if the amount is more than this, the strength of the obtained carbon fiber will decrease. A particularly preferable coating amount is 0.3 to 0.6% by weight. When acrylonitrile flame-resistant fiber bundles are carbonized in a carbonization furnace according to the present invention, the amount of deposits due to tar etc. in the carbonization furnace is reduced, long-term stable operation is possible, and the obtained carbon fibers are Quality will also improve. For example, when 450 acrylonitrile flame-resistant fiber bundles (0.9 denier, 6000 filaments) are continuously introduced into a carbonization furnace and carbonized at 1400℃ under a nitrogen stream, the amount of deposits in the carbonization furnace and the product carbon fiber The strength is shown in Table 1 below.

[Table] According to the results in Table 1, it can be seen that in the present invention, the amount of deposits in the carbonization furnace during the carbonization process is small, and the strength of the carbon fibers is high. This deposit is mainly tar-like substances and short fibers such as carbon fibers. In the case of a comparative example in which flame-resistant fibers that had not been dried were carbonized, the fiber bundles stuck together during the carbonization process, resulting in many single fibers being cut and short fibers falling off due to one-sided splitting, resulting in a large amount of deposits. The deposits clogged the yarn path, promoted fiber breakage, and also reduced the strength of the resulting carbon fibers. Next, Table 2 shows the influence of the amount of polyacrylamide attached to the flame-resistant fibers.

[Table] 〓Note〓 *: Comparative example From the results in Table 2, it can be seen that a deposition amount of less than 0.1% by weight has no effect on reducing the amount of deposits, and 2.% by weight
If the amount of deposits exceeds 0.1 to 2.0% by weight, the strength of the obtained carbon fiber will decrease, but only in the case of the amount of deposits falling within the range of 0.1 to 2.0% by weight, the amount of deposits will be noticeably small and the strength of the product carbon fiber will decrease. It can be seen that the level is maintained at a high level. A method of applying a water-soluble polymeric substance to an acrylonitrile flame-resistant fiber and then carbonizing the fiber in an inert atmosphere is known, for example, from JP-A-55-122021. In the method described herein, polyethylene glycol, polypropylene glycol, or an alkyl derivative thereof is applied as a water-soluble polymer substance to flame-resistant fibers, and then the fibers are subjected to a carbonization step. Specific examples include polyethylene glycol (molecular weight 400 to 10,000), polypropylene glycol (molecular weight 600 to 20,000), and the like. Polyethylene oxide, which is a type of water-soluble polymer substance added to the acrylonitrile flame-resistant fiber bundle in the present invention, has the same repeating chemical structure as the polyethylene glycol described in the above-mentioned publication in terms of its basic skeleton. Particularly high molecular weight, usually
This substance had a molecular weight of over 70,000.
It is distinguished as a substance (compound) from polyethylene glycol, which has a low molecular weight, and has different properties. For example, polyethylene glycol with a low molecular weight is liquid or waxy, whereas polyethylene oxide with a high molecular weight used in the present invention is crystalline (solid) and has excellent smoothing properties (Encyclopedia of Polymer Science and
Technology.No.6 p117-145, Makromol
chem., Vol. 73, No. 109 (1964), “Water-soluble polymers”
(pages 117, 119, and 125) published by Kagaku Kogyo Co., Ltd., and "Water-soluble thermoplastic resin" (page 11) published by Polymer Division of Seitetsu Kagaku Kogyo Co., Ltd.). In the next step, the acrylonitrile-based flame-resistant fiber bundle is carbonized in a high-temperature furnace in an inert atmosphere. Therefore, even if the aqueous solution or dispersion of the water-soluble polymeric substance applied to the acrylonitrile-based flame-resistant fiber bundle is dried in a high-temperature oven, the water-soluble polymeric substance is carbonized. However, when water-soluble polymer substances such as polyvinyl alcohol, polyethylene oxide, and polyacrylamide are applied to acrylonitrile-based flame-resistant fiber bundles, the temperature at 250°C prior to this carbonization process is
It is necessary to dry at the following temperature from the viewpoint of improving fiber strength and reducing deposits in the furnace. The present invention provides acrylonitrile-based flame-resistant fiber bundles with water-soluble polymeric substances such as polyvinyl alcohol, polyethylene oxide, and polyacrylamide;
By drying before carbonization in an inert atmosphere, a solid film is formed between the single fibers that make up the fiber bundle subjected to the carbonization process, increasing the slipperiness between the single fibers. As a result, as described above, long-term continuous operation in the carbonization process and high mechanical properties of carbon fibers are obtained, and such a method has not been known in the past. According to the present invention, there is no clogging in the carbonization furnace, allowing continuous operation over a long period of time, and improving operability. According to the present invention, there is no clogging in the carbonization furnace, allowing continuous operation over a long period of time, and improving operability. The present invention will be explained below using examples. Example 1 450 acrylonitrile fiber bundles (specific gravity 1.4) consisting of 0.9 denier 6000 filaments were flame-retardant treated in an oxidizing atmosphere at a temperature of 250°C at a speed of 140 m/hour, and the resulting flame-resistant fiber bundle was After being immersed in a polyvinyl alcohol aqueous solution, it was dried at a temperature of approximately 100°C (adhesion amount: 0.4% by weight) and introduced into a carbonization furnace. Carbonization was carried out in a carbonization furnace at 1400℃ in a nitrogen stream. After 300 hours of operation, an investigation revealed that the amount of sediment, including fluff, was 2.4 kg, and there was no problem in continuing the operation. The resulting carbon fiber has a strength of 420
Kg/mm ² , elastic modulus 24.6 Tmm ² , and elongation 1.7%. Comparative Example 1 (Example in which no deposition was performed) When operation was performed for 300 hours under the same operating conditions as in Example 1 without depositing a water-soluble polymer substance, the amount of deposits after operation reached as much as 5.1 kg. The obtained carbon fiber has a lot of fuzz, and this carbon fiber has a strength of 405 kg/
mm ² , elastic modulus 24.5T/mm ² , and elongation 1.7%. Example 2 A flame-resistant fiber bundle was immersed in an aqueous solution of 2 g of polyethylene oxide (molecular weight: 700,000) (adhesion amount: 0.4% by weight) under the same operating conditions as in Example 1.
After 300 hours of operation, the amount of deposits in the carbonization furnace after operation was 2.5 kg. The obtained carbon fiber has a strength of 410 Kg/mm ² and an elastic modulus of
The elongation was 24.2T/mm ² and 1.69%. Example 3 Operation was performed for 300 hours under the same operating conditions as in Example 1, except that the flame-resistant fiber bundle was immersed in a 2 g polyacrylamide aqueous solution (coating amount: 0.4% by weight). The amount of material was 2.0Kg. The obtained carbon fiber has a strength of 406 Kg/mm ² and an elastic modulus of
The elongation was 24.1T/ ^mm2 and 1.68%. Comparative Example 2 (example without drying) A flame-resistant fiber bundle was immersed in a 2 g/aqueous polyvinyl alcohol solution (adhesion amount: 0.4% by weight) and then dried under the same operating conditions as in Example 1, except that it was not dried. As a result, the inside of the furnace became clogged with deposits and became inoperable before reaching 300 hours. The obtained carbon fiber has a strength of 250Kg/mm ² and an elastic modulus of 24.0T/
mm ² and elongation was 1.1. Comparative Example 3 (Example where the drying temperature is outside the range of the present invention) A flame-resistant fiber bundle was immersed in a 2 g/aqueous polyvinyl alcohol solution (adhesion amount: 0.2% by weight), and then heated at 300°C.
As a result of carrying out the operation under the same operating conditions as in Example 1 except that drying was carried out, the inside of the furnace was clogged with deposits and operation became impossible before reaching 300 hours. The obtained carbon fiber has a strength of 240Kg/mm ² and an elastic modulus of 24.0T/
mm ² and elongation was 1.0%. Comparative Example 4 (example in which no adhesion was applied to flame-resistant fiber bundles) 450 0.9-denier, 6000-filament acrylonitrile fiber bundles were attached with 0.4% by weight of polyethylene oxide with a molecular weight of 1 million, and after flame-retardation, polyethylene oxide was attached. When the system was operated for 300 hours under the same operating conditions as in Example 1, the amount of bulk material after operation was 6.1 kg. The obtained carbon fibers were sticky and had a lot of fuzz. Further, the strength was 240 Kg/mm ² , the elastic modulus was 23 T/mm ² , and the elongation was 1.0%.

Claims (1)

[Claims] 1 One or more water-soluble polymeric substances selected from the group of polyvinyl alcohol, polyethylene oxide, and polyacrylamide are added to the acrylonitrile flame-resistant fiber bundle obtained by oxidizing acrylonitrile fibers in an oxidizing atmosphere. After applying a liquid containing the above, drying at a temperature of 250°C or lower to deposit 0.1 to 2.0% by weight (based on the fiber bundle) of the polymeric substance,
A method for manufacturing carbon fiber, which is characterized by introducing the carbon fiber into a carbonization furnace at a temperature of 400℃ or higher.