JP2014234557A - Method for manufacturing carbon fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength carbon fiber suitable for a composite material requiring high composite performance.SOLUTION: The method for manufacturing a carbon fiber comprises: flameproofing a carbon fiber precursor acrylic fiber bundle at a temperature of 200-300°C in an acidified atmosphere; pre-carbonizing the obtained flameproof fiber bundle at the maximum temperature of 500-900°C in an inert atmosphere; and carbonizing the obtained pre-carbonized fiber bundle at the maximum temperature of 1200-2500°C in an inert atmosphere. The pre-carbonization introduces the flameproof fiber bundle into a pre-carbonization furnace filled with an inert atmosphere. A period of time for the flameproof fiber bundle to pass through the section of an inert atmosphere temperature of 200°C or more and less than 250°C is 6-10 seconds and a period of time for the flameproof fiber bundle to pass through the section of an inert atmosphere temperature of 250°C or more and 400°C or less is 18-36 seconds. The supply amount of inert gas supplied into the pre-carbonization furnace is 1.0-5.0 Nmto a flameproof fiber bundle of 1 kg introduced into the pre-carbonization furnace.

Description

  The present invention relates to a method for producing a high-strength carbon fiber bundle suitable for a composite material requiring high composite performance.

  In recent years, carbon fiber composite materials are used in a wide variety of fields, such as sports and leisure, industrial applications, and aerospace. Particularly in the aerospace field, there is an increasing demand for high performance (high strength, high elastic modulus). It has been found that the performance of the carbon fiber itself is more influenced by the performance of the carbon fiber composite material than the matrix resin, and the strength of the carbon fiber is required to be increased.

  In the process of carbonizing the flame resistant fiber, when tar generated from the fiber adheres to the fiber, the strength is lowered. Therefore, a preventive measure has been conventionally proposed. For example, according to Patent Document 1, there is a method of supplying an inert atmosphere at 400 ° C. or higher to a carbonization furnace, or a method of supplying a sufficient inert gas to the flame resistant fiber to be supplied.

JP 60-99010 A

  However, the performance of carbon fibers required in the recent aerospace field is very high, and sufficient performance cannot be obtained only by controlling the temperature of the inert gas supplied. Moreover, increasing the inert gas supplied to the flameproof fiber leads to an increase in cost.

  The present invention provides a method for obtaining a high-strength carbon fiber by carbonizing a flame-resistant fiber without causing the tar generated from the fiber to adhere to the fiber when heat-treated in an inert atmosphere.

  The present invention for achieving the above object is as follows.

The method for producing carbon fiber of the present invention includes a flameproofing treatment in which a carbon fiber precursor acrylic fiber bundle is passed through an acidified atmosphere at 200 ° C. to 300 ° C. to obtain a flameproof fiber bundle. Pre-carbonization treatment in which heat treatment is performed by passing through an inert atmosphere having a maximum temperature of 500 ° C. to 900 ° C., and the obtained pre-carbonized fiber bundle is passed through an inert atmosphere having a maximum temperature of 1200 ° C. to 2500 ° C. In the carbon fiber manufacturing method in which the carbonization treatment is performed in order by passing through and heat-treating, the pre-carbonization treatment introduces the flame-resistant fiber bundle into a pre-carbonization furnace filled with an inert atmosphere, and is inert. The passage time in the section where the temperature of the atmosphere is 200 ° C. or more and less than 250 ° C. is 6 seconds to 10 seconds, and the passage time in the section where the temperature of the inert atmosphere is 250 ° C. or more and 400 ° C. or less is 18 Second to 36 seconds, the front charcoal The supply amount of the inert gas supplied into the reduction furnace, a method of producing a carbon fiber which is 1.0～5.0Nm ³ against oxidized fiber bundle 1kg introduced into the front carbonization furnace.

  According to the present invention, tar adhesion to carbon fibers can be suppressed to a low level, and high-strength carbon fibers can be obtained.

It is a sectional side view which shows the outline of an example of the pre-carbonization furnace used in this invention.

The present invention will be described in detail below.
In the present invention, known carbon fiber precursor acrylic fiber bundles can be used. As the acrylonitrile-based polymer constituting the acrylic fiber bundle, an acrylonitrile homopolymer or a copolymer of acrylonitrile and another monomer can be used.

  In the case of a copolymer, the content of a structural unit derived from acrylonitrile is preferably 90% by mass or more among all the structural units constituting the copolymer for the purpose of good carbonization. The mass% or more is more preferable. Although there is no restriction | limiting in particular as another monomer copolymerizable with acrylonitrile, For example, the following are mentioned. Acrylic acid esters represented by methyl acrylate, ethyl acrylate, etc .; Methacrylic acid esters represented by methyl methacrylate, ethyl methacrylate, etc .; Acrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamide, styrene, Unsaturated monomers typified by vinyl toluene; methallyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, and alkali metal salts thereof. These may be one kind or a combination of two or more kinds. A carbon fiber precursor acrylic fiber bundle can be produced by dry-wet spinning or wet-spinning a spinning stock solution in which an acrylonitrile-based polymer is dissolved in a solvent.

  An oil agent is attached to the carbon fiber precursor acrylic fiber bundle for fusion spinning in flameproofing treatment. The oil agent may be either silicone-based or non-silicone-based, but is preferably a silicone-based material having high anti-fusing performance.

  Silicone may be modified silicone or unmodified silicone, but modified silicone is preferred. Among the modified silicones, epoxy-modified silicone, ethylene oxide-modified silicone, polysiloxane, and amino-modified silicone are preferable, and amino-modified silicone is particularly preferable.

The amino-modified silicone preferably has a kinematic viscosity at 25 ° C. of 50 to 300 mm ² / sec. If the kinematic viscosity is too small, the heat resistance is lowered, and a large amount of oil is scattered in the flameproofing process, so that the original function of preventing fusion cannot be performed. On the other hand, if the kinematic viscosity is too large, the amount of oil scattered in the carbonization process increases, causing problems such as blockage of the exhaust pipe.

  The carbon fiber precursor acrylic fiber bundle is heated in an oxidizing atmosphere at 200 to 300 ° C. to be flameproofed to obtain a flameproof fiber bundle. As the oxidizing atmosphere, known oxidizing atmospheres such as air, oxygen and nitrogen dioxide can be adopted, but air is preferable from the viewpoint of economy. The flameproofing treatment time is preferably 30 to 120 minutes from the viewpoint of improving the productivity and performance of the carbon fiber. By setting the flameproofing treatment time to 30 minutes or more, the flameproofing reaction becomes sufficient, and it becomes difficult to produce spots, and it becomes difficult to cause fluff and bundle breakage in the subsequent carbonization process, resulting in improved productivity. To do. On the other hand, by setting the flameproofing treatment time to 120 minutes or less, it is not necessary to increase the size of the flameproofing device or reduce the flameproofing treatment speed, thereby improving productivity.

  The maximum temperature in the pre-carbonization treatment is preferably 500 to 900 ° C, and more preferably 600 to 800 ° C. When the temperature is 500 ° C. or higher, the strength and elastic modulus of the carbon fiber are improved. If it is 900 degrees C or less, it will become easy to reduce the cost of a pre-carbonization processing furnace, and it is industrially advantageous. The treatment time in the pre-carbonization treatment is preferably 0.5 to 2.0 minutes. If it is 0.5 minutes or more, the process passability is good and sufficient physical properties are easily obtained, and if it is 2.0 minutes or less, the pre-carbonization furnace can be prevented from being enlarged, which is industrially advantageous.

  The maximum temperature of carbonization treatment is in the range of 1200 to 2500 ° C., and the maximum temperature is determined by the elastic modulus of the carbon fiber to be obtained. The treatment time in the carbonization treatment is preferably 0.5 to 2.0 minutes. If it is 0.5 minutes or longer, sufficient physical properties can be easily obtained, and if it is 2.0 minutes or less, the carbonization furnace can be prevented from becoming large.

  Both the pre-carbonization treatment and the carbonization treatment are performed in an inert atmosphere. Examples of the inert gas include nitrogen, argon, and helium, but nitrogen is preferable from the viewpoint of economy.

  Although the furnace used for the pre-carbonization process is not particularly limited, for example, a furnace as shown in FIG. An inert gas inlet is provided on the entry side and the exit side of the fiber bundle (object to be treated) to prevent oxygen from entering the furnace. Heaters are provided above and below the processing chamber, and a plurality of thermocouples are installed on the wall of the processing chamber to control the temperature of the inert atmosphere. In addition, an exhaust port is provided to remove product substances such as cyan and tar.

  In the pre-carbonization treatment, when the generated tar is reattached to the yarn, the yarn is stuck, which becomes a defect point and reduces the strength of the carbon fiber. For this reason, it is important that the generated tar is not reattached to the yarn.

  In the initial stage where tar is generated, the yarn temperature may not be sufficiently increased. If the temperature of the yarn is not sufficiently increased, the generated tar will condense on the yarn, causing sticking and strength reduction. Therefore, it is necessary to quickly raise the yarn temperature in the initial stage where tar is generated. That is, it is necessary to increase the rate of temperature increase in the initial stage where tar is generated.

  There are two types of tars: tars produced by scattering of the oil applied to the precursor fibers and tars produced by the decomposition reaction of the flame resistant fibers themselves. Therefore, it is necessary to set a temperature increase rate suitable for each of the two types of tar generation regions.

  In order to suppress tar content condensation derived from the oil agent, it is necessary to set the passage time in the temperature range of 200 ° C. or more and less than 250 ° C. to 6 seconds or more and 10 seconds or less, and more preferably 7 seconds or more and 9 seconds or less.

  If the passage time is 6 seconds or more, a rapid increase in the temperature of the fiber bundle can be suppressed, and it becomes difficult to impair the densification of the fibers. Moreover, if it is 10 seconds or less, it will become easy to suppress the condensation of the tar part derived from an oil agent.

  In order to make it easy to suppress the condensation of the tar component derived from the oil agent, the temperature increase rate at any point of the fiber bundle in the temperature region of 200 ° C. or higher and lower than 250 ° C. is preferably 300 ° C./min or higher.

  Since the temperature of the inert atmosphere and the temperature of the fiber bundle are almost the same, the temperature increase rate of the fiber bundle can be obtained by arithmetic operation from the atmosphere temperature and the passage time.

  In order to suppress tar condensation from the flame resistant fiber, it is necessary to set the passage time in the temperature range of 250 ° C. or more and 400 ° C. or less to 18 seconds or more and 36 seconds or less, more preferably 21 seconds or more and 35 seconds or less. More preferably, it is at least 34 seconds.

  If the passage time is 18 seconds or more, a rapid increase in the temperature of the fiber bundle can be suppressed, and it becomes difficult to impair the densification of the fibers. Moreover, if it is 36 seconds or less, it will become easy to suppress the condensation of the tar part derived from a flame-resistant fiber.

  In order to make it easy to suppress the condensation of tar components derived from flame-resistant fibers, it is preferable that the rate of temperature increase at any point of the fiber bundle in the temperature range of 250 ° C. or more and 400 ° C. or less is 250 ° C./min or more.

  In addition, it is known that excessively increasing the temperature raising rate in the pre-carbonization treatment impairs the denseness of the fibers and causes a decrease in physical properties. The heating rate at any point of the fiber bundle in the temperature range of 250 ° C. or more and 400 ° C. or less is preferably 500 ° C./min or less, more preferably 450 ° C./min or less, and further preferably 400 ° C./min or less.

In this invention, the supply amount of the inert gas in the pre-carbonization furnace with respect to 1 kg of flameproofing fibers introduce | transduced in a pre-carbonization furnace is 1.0-5.0 Nm < ³ > / kg. Lowering the tar concentration in the furnace is also important in order not to condense the tar. In order to reduce the tar concentration in the furnace, it is necessary to increase the input amount of the inert gas with respect to the input amount of the flameproof fiber. The supply amount of the inert gas from the viewpoint of reducing the tar concentration is required to be 1.0 Nm ³ / kg or more, is preferably 2.0 Nm ³ / kg or more. Meanwhile, since the increase in the input amount of the inert gas lead to manufacturing cost, it is necessary that at most 5.0 nm ³ / kg, preferably at most 4.0 nm ³ / kg.

  Moreover, in order not to reduce the temperature in the furnace, the temperature of the inert gas supplied is preferably 100 ° C. or higher and 200 ° C. or lower.

  The fiber bundle treated in the pre-carbonization process is carbonized in an inert atmosphere having a maximum temperature of 1200 to 2500 ° C. in the carbonization process to produce carbon fibers.

[1. Strength of carbon fiber bundle]
The strength of the carbon fiber bundle is determined by the method described in Japanese Industrial Standard (JIS) -R-7601 (Revised March 1, 1986) “Resin-impregnated strand test method”. However, the resin-impregnated strand of carbon fiber to be measured is obtained by impregnating a carbon fiber bundle with a mixed solution of “BAKELITE” ERL 4221 (100 parts by mass) / 3 boron trifluoride monoethylamine (3 parts by mass) / acetone (4 parts by mass). And cured at 130 ° C. for 30 minutes. In addition, the number of strands to be measured is 6, and the average value of each measurement result is the strength of the carbon fiber bundle.

[2. Number of stalemates]
In order to investigate fiber sticking, the following measurements are made.
A carbon fiber bundle is cut into a length of 3 mm, placed in a 500 ml beaker containing 200 ml of water, stirred for 10 minutes with a stirrer, and observed with an optical microscope at a magnification of 20 times. Is counted as the number of stalemates.

[Example 1]
The acrylonitrile copolymer was dry and wet spun (12,000 nozzles), and an oil agent having the following composition was adhered to obtain a carbon fiber precursor acrylic fiber bundle.
(1) Amino-modified silicone; KF-865 (manufactured by Shin-Etsu Chemical Co., Ltd., primary side chain type, viscosity 110 cSt (25 ° C., amino equivalent 5,000 g / mol), 85% by mass,
(2) Emulsifier: NIKKOL BL-9EX (manufactured by Nikko Chemicals, POE (9) lauryl ether), 15% by mass.

  The precursor fiber bundle was passed through an air atmosphere having an initial temperature of 230 ° C. to a final temperature of 250 ° C. to obtain a flame resistant fiber bundle. A hot air circulation type furnace was used as the flameproofing furnace, and the flameproofing treatment time was 60 minutes.

In the pre-carbonization treatment, the inside of the pre-carbonization furnace is a nitrogen atmosphere, the passing time in the temperature range of 200 ° C. or higher and lower than 250 ° C. is 8 seconds, the passing time in the temperature range of 250 ° C. or higher and 400 ° C. or lower is 33 seconds, The treatment was performed at a temperature of 700 ° C. The passing time of the entire pre-carbonization furnace was 1.0 minute. Further, nitrogen at a temperature of 150 ° C. was supplied to the pre-carbonization furnace at a rate of 2.9 Nm ³ / kg with respect to the input amount of the flameproof fiber bundle. A pre-carbonization furnace having the structure shown in FIG. 1 was used.

  The carbonization treatment was performed at 1000 to 1500 ° C. for 2 minutes in a nitrogen atmosphere. The strength of the 12K (12,000 filaments) carbon fiber bundles thus obtained and the number of carbon fibers stuck were measured. The evaluation results are shown in Table 1.

[Example 2, Comparative Examples 1-3]
Carbon fiber in the same manner as in Example 1 except that the passage time in the temperature range of 200 ° C. or more and less than 250 ° C. and the passage time in the temperature region of 250 ° C. or more and 400 ° C. or less in the pre-carbonization treatment was changed as shown in Table 1. Were manufactured and evaluated.

[Comparative Example 4]
Carbon fibers were produced and evaluated in the same manner as in Example 1 except that the amount of nitrogen input relative to the amount of flameproofed fiber bundle was changed as shown in Table 1.

1 Fiber bundle 2 Inert gas inlet (inlet side)
3 Inert gas inlet (exit side)
4 Exhaust port 5 Heater 1 for heating
6 Heating heater 2
7 Heating heater 3
8 Heater 4
9 Furnace body

Claims (1)

Flameproofing treatment for obtaining a flameproofed fiber bundle by passing the carbon fiber precursor acrylic fiber bundle through an acidified atmosphere at 200 ° C to 300 ° C. A pre-carbonization treatment in which heat treatment is performed by passing through an active atmosphere, and a carbonization treatment in which the obtained pre-carbonization fiber bundle is heat-treated by passing through an inert atmosphere having a maximum temperature of 1200 ° C. to 2500 ° C. are sequentially performed. In the carbon fiber manufacturing method to be performed,
The pre-carbonization treatment introduces the flame-resistant fiber bundle into a pre-carbonization furnace filled with an inert atmosphere, and passes through a section in a temperature range where the temperature of the inert atmosphere is 200 ° C. or more and less than 250 ° C. The inert gas supplied into the pre-carbonization furnace has a passage time of 18 seconds to 36 seconds in a time range of 6 seconds to 10 seconds and a temperature range of the inert atmosphere of 250 ° C. to 400 ° C. The manufacturing method of the carbon fiber whose supply amount of gas is 1.0-5.0Nm < ³ > with respect to 1 kg of flame-resistant fiber bundles introduce | transduced in this pre-carbonization furnace.

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