JP5022073B2 - Flameproofing furnace and carbon fiber manufacturing method - Google Patents

Description

  The present invention relates to a flameproofing furnace and a method for producing carbon fiber.

 Since carbon fiber is excellent in specific strength, specific elastic modulus, heat resistance, and chemical resistance, it is useful as a reinforcing material for various materials and is used in a wide range of fields such as aerospace applications, leisure applications, and general industrial applications. ing. Since carbon fibers are often used in places where strength is required, it is necessary to have extremely high uniformity of properties and stability, that is, excellent quality is required.

 Generally, as a method for producing a carbon fiber bundle from a polyacrylonitrile fiber bundle, a fiber bundle obtained by bundling thousands to tens of thousands of single fibers of a polyacrylonitrile polymer (hereinafter abbreviated as a precursor fiber bundle). The heat-treated (flame-proofing treatment) was carried out by feeding into a flame-proofing furnace and exposed to hot air in an oxidizing atmosphere such as air heated to 200 to 300 ° C., and the resulting flame-resistant fiber bundle was carbonized. And then heat treatment (pre-carbonization treatment) in an inert gas atmosphere at 300 to 1000 ° C., and further heat treatment (carbonization treatment) in a carbonization furnace filled with an inert gas atmosphere at 1000 ° C. or higher. ) Is known. In addition, the flame-resistant fiber, which is an intermediate material, is widely used as a material for flame-retardant woven fabrics by taking advantage of its incombustible performance.

Among the carbon fiber manufacturing processes, the flameproofing treatment causes an oxidation reaction accompanied by heat generation of the precursor fiber bundle, so that the single fibers are likely to be fused together by a large amount of heat generated by the hot air in the flameproofing furnace or the oxidation reaction. . The flame-resistant fiber bundle in which the single fibers are fused is extremely low quality, and for example, in the subsequent carbonization treatment, fluff and thread breakage are likely to occur, and various characteristics are likely to deteriorate.
In order to avoid the fusion of flame resistant fibers, for example, a method of applying an oil agent to a precursor fiber bundle is known, and many oil agents have been studied for that purpose. Among these, silicone oils are often used because they have high heat resistance and effectively suppress fusion.

  By the way, a hot-air circulation type flameproofing furnace is widely used for the flameproofing treatment on an industrial production scale. The hot air circulation type flameproofing furnace constitutes a hot air circulation system including a heat treatment chamber for performing a flameproofing treatment on the precursor fiber bundle and a hot air circulation path for heating and circulating the hot air. Since the hot air can be repeatedly used by the hot air circulation system, the hot air circulation type flameproof furnace has an advantage that the loss of heat energy can be reduced.

However, the hot air circulation type flameproofing furnace has a disadvantage that impurities such as dust are likely to stay in the hot air in the flameproofing furnace for a long time because impurities staying in the hot air are not easily discharged outside the hot air circulation system. is there. In particular, a part of the silicone-based oil applied to the precursor fiber bundle is volatilized due to the high heat of the flameproofing treatment and tends to stay in the hot air. This volatile matter gradually solidifies into dust, accumulates in the flameproofing furnace, and adheres to the precursor fiber bundle during the flameproofing treatment. The adhesion point of the dust adhering to the precursor fiber bundle becomes a starting point of fluff generation and single yarn breakage in the subsequent carbonization treatment, and the quality of the obtained carbon fiber bundle is remarkably deteriorated.
Most of the dust staying in the flameproofing furnace is dust derived from the silicone-based oil described above, but other than that, for example, aggregates of oil component other than the silicone oil, polysilica which is a precursor fiber bundle Aggregates of tar components generated from acrylonitrile fiber bundles, dust brought into the precursor fiber bundle from the outside of the flameproofing furnace, dust contained in the outside air flowing into the flameproofing furnace, and composites thereof And the like.

 If these dusts stay in the flameproofing furnace, the perforated plate for wind speed rectification provided on the outlet surface of the hot air outlet is clogged and blocked, and the circulation of hot air is delayed. When the circulation of the hot air in the heat treatment chamber is delayed, heat removal of the precursor fiber bundle is not performed smoothly, and thread breakage of the precursor fiber bundle is induced. Thread breakage of precursor fiber bundles is further entangled with other precursor fiber bundles to induce thread breakage of precursor fiber bundles traveling in other traveling areas, and in the worst case, fire may occur. It also becomes a cause of hindering stable operation of the chemical reactor.

Therefore, the conventional flameproofing furnace is difficult to operate continuously for a long time, and it is necessary to frequently stop the operation and clean the inside of the flameproofing furnace. This has been a foothold for improving the production efficiency of the flameproof fiber bundle. In addition, the maintenance cost required for cleaning the flameproofing furnace is great, and even if a large maintenance cost is applied, it is difficult to completely remove fine dust of several μm from the inside of the flameproofing furnace by cleaning. It was.
In order to improve production efficiency and reduce maintenance in a hot air circulation type flameproofing furnace, it depends on how dust in the flameproofing furnace is reduced. In order to reduce the dust, it is conceivable to remove the generation factor of the dust or to discharge the generated dust from the hot air circulation system.

In response to this problem, for example, Patent Document 1 proposes a flameproof furnace in which an exhaust port is provided in a hot air circulation path. According to this flameproofing furnace, the hot air in the hot air circulation system is exhausted from the exhaust port to the outside of the hot air circulation system before restarting after cleaning the inside of the furnace, so that dust remaining in the flameproofing furnace can be reduced. Thus, it is possible to prevent deterioration in the quality of the flame-resistant fiber bundle that occurs in the initial stage after re-operation.
Japanese Patent No. 3610659

However, in Patent Document 1, although it is possible to prevent the deterioration of the quality of the flame-resistant fiber bundle that occurs in the initial stage after the restart of the flame-resistant furnace, it is not possible to suppress the generation of dust, so the frequency of cleaning the flame-resistant furnace is low. Can not be reduced.
This invention is made | formed in view of the said situation, Comprising: It aims at the flame-proofing furnace which can obtain a high quality carbon fiber, and a long-term continuous operation, and the manufacturing method of carbon fiber.

In order to achieve the above object, the present invention adopts the following configuration.
[1] A flameproof furnace having the following hot air circulation system and discharge means.
(1) Hot air circulation system It has a heat treatment chamber and a hot air circulation path,
The heat treatment chamber is flameproofed by blowing hot air on the precursor fiber bundle that travels while folding back the multi-stage traveling area,
The hot air circulation path circulates the hot air in the hot air circulation system by blowing hot air into the heat treatment chamber and discharging it out of the heat treatment chamber.
(2) Discharge means The hot air that has passed through the initial travel region of the precursor fiber bundle is discharged out of the hot air circulation system.
[2] The flameproof furnace according to [1], wherein the discharge means includes an exhaust gas combustion device and a dust collector.
[3] A method for producing carbon fiber using the flameproofing furnace according to [1] or [2].
[4] In the method for producing carbon fiber using a plurality of flameproofing furnaces, the production of carbon fiber wherein the flameproofing furnace performing at least the first flameproofing treatment is the flameproofing furnace described in [1] or [2] Method.

  According to the flameproofing furnace and carbon fiber manufacturing method of the present invention, high-quality carbon fiber can be obtained, and long-term continuous operation of the flameproofing furnace becomes possible.

The flameproofing furnace of the present invention has a hot air circulation system and discharge means. As shown in FIG. 1, the hot air circulation system includes a heat treatment chamber 2 that blows hot air on a precursor fiber bundle that travels while turning back and forth in a multi-stage traveling region, and flame-resistant treatment, and blows hot air into the heat treatment chamber 2. A hot air circulation path 8 is provided for circulating hot air in the hot air circulation system by discharging the heat treatment chamber 2 to the outside.
In the heat treatment chamber 2, hot air outlets 4 for blowing hot air disposed in each traveling region of the precursor fiber bundle 1 and hot air exhaust for discharging the hot air disposed in each traveling region to the outside of the heat treatment chamber 2. Outlets 5 and 5a are provided. Further, a heater 6 for heating the hot air and a blower 7 for controlling the wind speed of the hot air are provided in the middle of the hot air circulation path 8. Further, in order to suppress the concentration of gas such as HCN generated from the precursor fiber bundle 1 to a certain value or less, an exhaust fan 16 for exhausting hot air containing these gases out of the hot air circulation system, and gas An exhaust gas combustion device 17 for processing may be provided.

The precursor fiber bundle 1 is fed into the heat treatment chamber 2 from a slit provided on the side wall of the heat treatment chamber 2 of the flameproofing furnace 10, travels linearly in the heat treatment chamber 2, and then passes through the slit on the opposite side wall to the heat treatment chamber. 2 is once sent out, folded back by a guide roll 3 provided on a side wall outside the heat treatment chamber 2, and again fed into the heat treatment chamber 2. As described above, the precursor fiber bundle 1 is repeatedly diffracted in a plurality of directions by a plurality of guide rolls 3, so that the feeding and sending into the heat treatment chamber 2 is repeated a plurality of times, and the heat treatment chamber 2 is multi-staged as a whole. It moves from bottom to top in FIG. The number of turns of the precursor fiber bundle 1 in the heat treatment chamber 2 is not particularly limited, and is appropriately designed depending on the scale of the flameproofing furnace. The guide roll 3 may be provided inside the heat treatment chamber 2.
The precursor fiber bundle 1 is flame-resistant by hot air blown from the hot air outlet 4 while traveling in the heat treatment chamber 2 while being turned back into a flame-resistant fiber bundle or a preliminary flame-resistant fiber bundle. In addition, although not shown in figure, the precursor fiber bundle 1 has a wide sheet-like form that is aligned so that a plurality of the precursor fiber bundles 1 are parallel to each other in a direction perpendicular to the paper surface.

The hot air outlet 4 is preferably provided with a pressure loss by arranging a resistor such as a perforated plate and a rectifying member such as a honeycomb (both not shown) on the blowing surface. The flow of hot air blown into the heat treatment chamber 2 can be rectified by the flow regulating member, and hot air having a uniform wind speed can be blown into the heat treatment chamber 2.
As with the hot air outlet 4, the hot air outlets 5 and 5a may be provided with a pressure loss by arranging a resistor such as a perforated plate on the suction surface. To be determined as appropriate.

The hot air blown into the heat treatment chamber 2 by the hot air outlet 4 heats the precursor fiber bundle 1 while flowing in the heat treatment chamber 2 in the direction of the arrow, that is, toward the discharge port 5. The hot air reaching the downstream is discharged out of the heat treatment chamber 2 through the hot air discharge port 5 and guided to the hot air circulation path 8. And it heats to desired temperature with the heater 6 provided in the middle of the hot air circulation path 8, and after blowing the air speed by the air blower 7, it blows in the heat processing chamber 2 again from the hot air blower outlet 4. FIG. In this manner, the flameproofing furnace 10 can flow hot air at a predetermined temperature and wind speed into the heat treatment chamber 2 by the hot air circulation system including the heat treatment chamber 2 and the hot air circulation path 8.
The heater 6 used in the flameproofing furnace 10 of the present invention is not particularly limited as long as it has a desired function. For example, a known heater such as an electric heater may be used. The blower 7 is not particularly limited as long as it has a desired function. For example, a known blower such as an axial fan may be used.

The flameproofing furnace 10 of the present invention includes a discharge means for discharging the hot air that has passed through the initial travel region of the precursor fiber bundle 1 out of the hot air circulation system including the heat treatment chamber 2 and the hot air circulation path 8. It is said. The discharge means is constituted by the hot air discharge port 5 a and the discharge path 11. The hot air flowing in the initial travel region of the precursor fiber in the heat treatment chamber 2 is guided to the discharge path 11 from the hot air discharge port 5a and is discharged out of the hot air circulation system. In addition, it is preferable to provide the exhaust path 12 with the exhaust fan 12, and to assist discharge of the hot air from the hot air discharge port 5a.
Here, the initial travel region of the precursor fiber bundle 1 represents the travel region of the precursor fiber bundle 1 corresponding to the early stage of flame resistance. Specifically, up to which traveling region is set as the initial traveling region depends on the size of the flameproofing furnace, the heat treatment temperature, the type of the precursor fiber bundle 1, the progress of the flameproofing, etc. In the converter 10, the approximate range from the bottom to the second stage is the initial travel range.

Of the hot air passing through the heat treatment chamber 2, the ratio of the hot air discharged through the discharge means to the outside of the hot air circulation system varies depending on the number of hot air discharge ports 5 and hot air discharge ports 5a, etc., but is discharged from the heat treatment chamber 2. It is preferable that 2.5 to 35% of the hot air to be discharged is discharged out of the hot air circulation system through the discharge means.

The volatiles of the silicone-based oil agent from the precursor fiber bundle 1 are remarkably generated for several minutes immediately after being fed into the heat treatment chamber 2, that is, in the initial running region. For this reason, the hot air flowing through the initial travel region contains a large amount of volatile substances of silicone oil. Therefore, if the hot air that has passed through the initial travel region is discharged out of the hot air circulation system, the volatiles of the silicone-based oil that stays in the hot air circulation system can be greatly reduced. If the retention of the volatile matter can be reduced, the generation of dust generated from the volatile matter is also reduced.
As described above, the flameproofing furnace 10 provided with the hot air discharge means can reduce the retention of dust, which is a drawback of the hot air circulation method, while having the advantage of the hot air circulation method that there is little loss of thermal energy. Therefore, since the frequency of cleaning in the flameproofing furnace can be reduced, the maintenance cost can be greatly reduced as compared with the conventional flameproofing furnace. In addition, the long-term continuous operation of the flameproofing furnace becomes possible, so that the productivity of the flameproofing fiber can be improved. Furthermore, since the quality deterioration of the flame-resistant fiber due to dust can be suppressed, a high-quality flame-resistant fiber bundle can be produced uniformly and stably.

The hot air discharged out of the circulation system by the discharging means includes gas such as HCN generated when the precursor fiber bundle 1 becomes flame resistant, in addition to the volatiles of the silicone-based oil agent. Therefore, it is preferable to provide the exhaust means with an exhaust gas combustion device 13 that can oxidize the volatiles of the silicone-based oil to solid silicone oxide particles and also oxidize a gas such as HCN.
Further, since the hot air taken in by the hot air discharge port 5a contains a lot of dust, it is preferable to provide the discharge means with a dust collecting device 14 for collecting the dust.
The exhaust gas combustion device 13 used in the flameproofing furnace 10 of the present invention is not particularly limited as long as it has a desired function, and a known exhaust gas combustion device may be used. The dust collector 14 is not particularly limited as long as it has a desired function. For example, a known dust collector such as a bag filter may be used. Further, the exhaust gas combustion device 13 and the dust collection device 14 are not limited to a single number, and a plurality may be provided for the purpose of sharing functions or enhancing performance.

  Moreover, in order to supplement the hot air discharged from the discharge means, the outside air intake 15 may be provided, and the outside air (oxidizing atmosphere) may be supplemented therefrom. The installation location of the outside air inlet 15 is not particularly limited as long as it can perform a desired function, but is preferably disposed in the circulation furnace 8 on the upstream side of the flow of the atmosphere of the heater 6. Thereby, the taken-out outside air can be sent into the heat treatment chamber 2 after being heated by the heater 6. The outside air inlet 15 is preferably provided with a filter (not shown) in order to remove dust and the like mixed in the outside air. For taking in the outside air from the outside air inlet 15, the intake amount may be controlled using a blower fan, a regulating valve (both not shown) or the like, but passively according to the discharge of hot air from the discharge means. May be included.

  Further, the waste heat recovery device (not shown) provided in the discharge means recovers waste heat from the hot air passing through the discharge path 11 and uses the recovered waste heat for heating the outside air taken in from the outside air inlet 15. You can also. Thereby, the external air heated previously can be sent in into the flame-proofing furnace 10, and the burden of the heater 6 can be reduced. Note that a waste heat recovery device can be incorporated into the exhaust gas combustion device.

  In the flameproofing furnace of the present invention, a partition plate 9 may be provided between the initial traveling area and the late traveling area, for example, as in the flameproofing furnace 20 shown in FIG. By providing the partition plate 9, the inside of the heat treatment chamber 2 can be divided into a heat treatment section 2a corresponding to the initial traveling area and a heat treatment section 2b corresponding to the latter traveling area, and the hot air flowing through the initial traveling area can be efficiently discharged into the hot air outlet. 5a. The partition plate 9 may completely partition between the heat treatment compartment 2a and the heat treatment compartment 2b, or may only partly partition. For the reference numerals of the flameproofing furnace 20 in FIG. 2, the same reference numerals as those in FIG.

In the above description, a so-called horizontal flameproofing furnace has been described. However, a vertical flameproofing furnace in which the heat treatment chamber 2 extends in the vertical direction can be configured in exactly the same manner.
Moreover, you may use multiple flameproofing furnaces 10 and 20 of this invention in the manufacturing process of carbon fiber. Furthermore, you may use in combination with the conventional flameproofing furnace 30 shown in FIG. Since most of the volatiles derived from the silicone oil are generated at the beginning of the flameproofing treatment, in the production of carbon fiber using a plurality of flameproofing furnaces, at least the first flameproofing furnace that performs the flameproofing treatment, It is preferable to use the flameproofing furnaces 10 and 20 of the present invention. Thereby, the volatile matter from the precursor fiber bundle 1 can be efficiently removed from the heat treatment chamber 2, and generation of dust in the entire production line can be suppressed. Therefore, if the flameproofing furnaces 10 and 20 of the present invention are used, a plurality of flameproofing furnaces can be operated continuously for a long time even when a plurality of flameproofing furnaces are used.
The flameproofing furnaces 10 and 20 of the present invention are preferably used mainly for the flameproofing treatment of the precursor fiber bundle 1 for obtaining carbon fibers, but various other types such as yarns, films, sheets, etc. Can also be used for heat treatment. In addition, in the code | symbol of each structure attached | subjected to the flameproofing furnace 30 of FIG. 3, the code | symbol same as each structure of the flameproofing furnace 10 of FIG. 1 is attached | subjected, and description is abbreviate | omitted.

Next, the manufacturing method of the carbon fiber using the flameproofing furnaces 10 and 20 of this invention is demonstrated. Examples of the precursor fiber used in the carbon fiber production method of the present invention include known precursor fibers such as polyacrylonitrile fiber bundles, pitch fibers, and phenol fibers, but from the balance of cost and performance. A polyacrylonitrile system is preferably used.
The polyacrylonitrile fiber bundle is prepared by dissolving an acrylonitrile polymer in an organic solvent or an inorganic solvent and spinning by a commonly used method, but there are no particular restrictions on the spinning method and spinning conditions.

Although there is no restriction | limiting in particular as a ratio of the component of an acrylonitrile type polymer, The polymer containing 85 weight% or more of acrylonitrile, More preferably, 90 weight% or more is used. As the acrylonitrile-based polymer, an acrylonitrile homopolymer, an acrylonitrile copolymer, or a mixed polymer of these polymers is preferably used.
The acrylonitrile copolymer is a copolymerized product of a monomer that can be copolymerized with acrylonitrile and acrylonitrile. Monomers that can be copolymerized with acrylonitrile include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth) acrylate. (Meth) acrylic acid esters such as vinyl chloride, vinyl halides such as vinyl chloride, vinyl bromide, vinylidene chloride, acids such as (meth) acrylic acid, itaconic acid, crotonic acid and their salts and maleic imides, Phenylmaleimide, (meth) acrylamide, styrene, α-methylstyrene, vinyl acetate, styrene sulfonic acid soda, allyl sulfonic acid soda, β-styrene sulfonic acid soda, methallyl sulfonic acid soda A polymerizable unsaturated monomer containing a sulfone group such as 2-vinylpyridine, 2-methyl-5-vinylpyridine and the like Examples thereof include, but are not limited to, polymerizable unsaturated monomers containing an amine group.

As the polymerization method of the acrylonitrile copolymer, conventionally known solution polymerization, suspension polymerization, emulsion polymerization and the like can be applied. As the solvent used for preparing the acrylonitrile copolymer solution, known solvents such as dimethyl sulfoxide, dimethylacetamide, dimethylformamide, zinc chloride aqueous solution, nitric acid and the like can be used. It should be noted that known spinning methods such as a wet spinning method, a dry wet spinning method, and a dry spinning method can be applied to the spinning method of the acrylonitrile copolymer.
The coagulated yarn thus obtained is then primarily drawn. As a method for primary stretching, a known method can be used, but stretching in a bath is preferably used. Stretching in a bath is a stretching method in which a coagulated yarn of about 50 to 98 ° C. is stretched in a coagulation bath or in a stretching bath. The drawing in the bath is performed once or twice or more on the coagulated yarn. In addition to this, a plurality of stretching methods such as partially stretching in the air and then stretching in the bath may be combined. Moreover, you may perform the washing process by a well-known method before and after primary extending | stretching, or simultaneously with primary extending | stretching.

The precursor fiber bundle 1 composed of the polyacrylonitrile fiber thus obtained is then subjected to a spinning process oil treatment and further subjected to a secondary stretching treatment. In addition, the oil agent treatment of the precursor fiber bundle 1 is performed twice in total, that is, the spinning step oil agent treatment and the oil agent treatment (flame resistance step oil agent treatment) immediately before the flame resistance treatment to be performed later. At this time, it is preferable to use an oil containing a silicone compound (silicone oil) in at least one of the oil agent treatments. That is, the following three are mentioned as a combination of the oil agent provided by the spinning process and the flameproofing process oil agent treatment.
1) Spinning process oil: silicone-based oil, flameproofing process oil: silicone-based oil 2) Spinning process oil: silicone-based oil, flameproofing process oil: non-silicone-based oil 3) Spinning process oil: non-silicone-based oil, flameproofing Process oil: Silicone oil

The spinning process oil treatment improves the convergence, flexibility, smoothness, process stability, and antistatic properties of the precursor fiber bundle 1 in the spinning process. Furthermore, in the flame resistance treatment and the carbonization treatment, passability, convergence, and anti-fusing properties are improved.
In particular, the silicone-based oil agent can give excellent convergence and process stability to the precursor fiber bundle 1, and can also obtain excellent passability in flameproofing treatment and carbonization treatment, particularly carbon. Demonstrates remarkable effect in preventing fusion in the heat treatment.
An amino-modified silicone is preferably used as the silicone compound contained in the silicone oil. Among amino-modified silicones, side-chain primary amino-modified silicone, side-chain 1, secondary amino-modified silicone, or both-end amino-modified silicone is particularly preferably used.

The spinning process oil agent treatment is preferably performed on the precursor fiber bundle 1 in a water-swollen state after stretching in the bath or after washing in order to uniformly apply the precursor fiber bundle 1 to the precursor fiber bundle 1.
There is no particular limitation on the method of applying the spinning process oil to the precursor fiber bundle 1, but generally, the precursor fiber bundle 1 is immersed in an oil treatment tank containing a treatment liquid containing an oil and water, and the oil is attached. It is preferable from the industrial viewpoint.
As for the adhesion amount of the oil agent of the precursor fiber bundle 1 by a spinning process oil agent process, 0.1-3.0 mass% is preferable with respect to the dried precursor fiber bundle 1. FIG. As a method of adjusting the adhesion amount of the oil agent, for example, the oil agent concentration in the treatment liquid can be adjusted, or the treatment liquid immersed in the precursor fiber bundle 1 can be adjusted by squeezing with a nip roll or the like.

The precursor fiber bundle 1 that has finished the first oil agent treatment, that is, the spinning step oil agent treatment, is then subjected to a drying densification treatment and a post-stretching treatment by a known method, and then a second oil agent treatment, that is, flame resistance. Process oil treatment is performed. The purpose of performing the flameproofing process oil treatment is the same as that of the spinning process oil treatment, but is performed in order to make the adhesion of the oil more reliable.
Although there is no restriction | limiting in particular about the provision method of the flameproofing process oil agent in a flameproofing process oil agent process, The method similar to the said spinning process oil agent process can be used. Further, the adhesion amount of the flameproofing process oil agent to the precursor fiber bundle 1 and the method for adjusting the adhesion amount can also follow the spinning process oil agent treatment.
In addition, if the precursor fiber bundle 1 that has undergone the oil agent treatment is subjected to flame resistance treatment in a state of containing a large amount of moisture, the generation amount of dust derived from the silicone oil agent increases. Although the causal relationship between the amount of dust generated from the silicone-based oil and the moisture contained in the precursor fiber bundle 1 is not clear, it is important that the precursor fiber bundle 1 be sufficiently dried before performing the flame resistance treatment. is there.

Flame proofing process After the precursor fiber bundle 1 treated with the oil is sufficiently dried, it is then fed into the flame proofing furnace 10 or 20 of the present invention and flame proofed.
As the flameproofing conditions of the precursor fiber bundle 1, the density of the flameproofed fiber after the flameproofing treatment is preferably 1.30 g / cm ^{3 to} 1.40 g in hot air at 200 to 300 ° C. under tension or stretching conditions. It is preferable to carry out the flameproofing treatment until it becomes / cm ³ . If it is less than 1.30 g / cm ³ , the degree of progress of flame resistance is insufficient, and the carbon fiber obtained is likely to cause fusion between single yarns during pre-carbonization treatment and carbonization treatment performed after the flame resistance treatment. The quality of the bundle is reduced. Further, when the density of the flame resistant fiber exceeds 1.40 g / cm ³ , oxygen is excessively introduced into the flame resistant fiber bundle during the pre-carbonization treatment and the carbonization treatment, and the final internal structure of the carbon fiber is obtained. Does not become dense, and the quality of the obtained carbon fiber bundle is deteriorated.

On the other hand, when a heat-resistant product such as a flame-retardant woven fabric is produced by firing the flame-resistant fiber bundle, the density of the flame-resistant fiber bundle used therefor may exceed 1.40 g / cm ³ . However, if it exceeds 1.50 g / cm ³ , the time for firing the flameproof fiber bundle becomes longer, which is not economically preferable.

 The hot air (oxidizing atmosphere) that fills the heat treatment chamber 2 of the flameproofing furnace 10 or 20 of the present invention is not particularly limited as long as it is a gas containing oxygen, but from the viewpoint of industrial production, it is economical to use air. It is particularly excellent in terms of safety and safety. Further, the oxygen concentration in the hot air can be changed for the purpose of adjusting the oxidation ability.

The flame-resistant fiber bundle obtained by the flame resistance treatment is then fed into a carbonization furnace and pre-carbonized. The maximum temperature in the pre-carbonization treatment is preferably 550 to 800 ° C.
In the temperature range of 300 to 500 ° C., it is preferable to perform the pre-carbonization treatment at a heating rate of 500 ° C./min or less in order to improve the mechanical properties of the carbon fiber. More preferably, it is 300 degrees C / min or less.
As the inert atmosphere that fills the carbonization furnace, a known inert atmosphere such as nitrogen, argon, or helium can be adopted, but nitrogen is preferable from the viewpoint of economy.

The pre-carbonized fiber bundle obtained by the pre-carbonization treatment is then fed into a carbonization furnace and carbonized. In order to improve the mechanical properties of the carbon fiber, it is preferable to perform carbonization treatment at a temperature increase rate of 500 ° C./min or less in a temperature range of 1000 to 1200 ° C. in an inert atmosphere of 1200 to 3000 ° C.
As the inert atmosphere, a known inert atmosphere such as nitrogen, argon, helium or the like can be adopted, but nitrogen is preferable from the viewpoint of economy.

The carbon fiber bundle obtained in this manner may be provided with a sizing agent as necessary in order to improve the handleability of the carbon fiber bundle and the affinity with the matrix resin. The type of the sizing agent is not particularly limited as long as desired characteristics can be obtained, and examples thereof include a sizing agent mainly composed of an epoxy resin, a polyether resin, an epoxy-modified polyurethane resin, and a polyester resin. A known method can be used to apply the sizing agent.
Further, the carbon fiber bundle may be subjected to electrolytic oxidation treatment or oxidation treatment for the purpose of improving the affinity and adhesiveness with the fiber reinforced composite material matrix resin as necessary.

  According to the present invention, dust existing in the hot air circulation system can be efficiently removed, so that the flameproof furnace 10 can be continuously operated for a long time. Thereby, the maintenance cost required for dust removal can be reduced, and the productivity of the flameproof fiber can be improved. Moreover, since the accumulation of dust in the heat treatment chamber 2 is reduced, flameproof fibers without yarn breakage can be obtained, and as a result, high-quality carbon fibers can be produced.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, the evaluation method of the Example was based on the following method.
<Measurement of contained silicone amount (Si remaining amount)>
After the precursor fiber bundle 1 and the flame-resistant fiber bundle measurement sample made of a polyacrylonitrile-based precursor fiber bundle are uniformly wound in a lateral direction on an acrylic resin plate having a length of 2 cm, a width of 4 cm, and a width of 0.5 cm without gaps. Then, the fluorescent X-ray intensity was measured by an ordinary fluorescent X-ray analysis method, and the amount of silicone contained, that is, the Si residual amount (fluorescent X-ray intensity, unit: cps) was determined. Note that the measurement sample was carefully wound so that all the measurement samples had the same winding length. A fluorescent X-ray analyzer (model: ZSX100e, manufactured by Rigaku Corporation) was used as a measuring device for fluorescent X-ray intensity.
Taking into account the adhesion spots of the oil agent to the precursor fiber bundle 1 and the flameproof fiber bundle, or measurement errors, the number of samples measured per measurement time was set to n = 10, and the average value was obtained as the Si residual amount. .
The amount of Si remaining in the precursor fiber bundle 1 obtained by the measurement was A1, and the amount of Si remaining in the flame-resistant fiber bundle obtained by the measurement was A2. The value was made into Si residual rate.
Si residual ratio (%) = A2 / A1 × 100 (1)

Example 1
The acrylonitrile copolymer was dissolved in dimethylacetamide so that the copolymer concentration was 21% by mass to obtain a spinning dope. This spinning dope was discharged into a dimethylacetamide aqueous solution having a concentration of 70% by mass and a temperature of 35 ° C. using a 12,000-hole nozzle to perform wet spinning. Next, the coagulated fiber was stretched 1.5 times by air stretching, and further stretched in a bath in boiling water to stretch 3 times, and at the same time, washing and solvent removal were performed.
Thereafter, the coagulated yarn is immersed in an oil agent treatment tank containing an aqueous dispersion of the spinning process oil agent, and 1.0 mass% of the oil agent in the spinning process is attached, and then dried and densified with a heating roller at 140 ° C. The polyacrylonitrile fiber bundle having a single fiber fineness of 1.2 dtex was obtained.
The aqueous dispersion of the spinning process oil used above was prepared using the following raw materials and methods. First, an oil-based main agent is an amino-modified silicone at both ends (viscosity 450 cSt at 25 ° C., amino equivalent 5700), and an oil-based emulsion is a nonionic emulsifier (polyoxyethylene stearyl ether [ethylene oxide: 12 mol, HLB: 13.9]. ]), Ion-exchanged water is added to these mixtures, emulsified with a homomixer, and further adjusted by performing secondary emulsification by adjusting the pressure with a high-pressure homogenizer so that the emulsion particle size becomes 0.3 μm, An aqueous dispersion of the spinning process oil was obtained.

 Next, this polyacrylonitrile fiber bundle was immersed in an oil agent treatment tank containing an aqueous dispersion of the same oil agent as that in the spinning process, and subjected to a flame resistance process oil agent treatment to deposit 0.1% by mass of the oil agent. Then, the precursor fiber bundle 1 which consists of a polyacrylonitrile fiber bundle was obtained by restrict | squeezing the water | moisture content of a polyacrylonitrile fiber bundle with a nip roller, and adjusting Si residual amount. The water content of the fiber bundle after being squeezed by the nip roller was 36.8%, and the residual amount of Si in the polyacrylonitrile fiber bundle was 5659 cps.

The precursor fiber bundle 1 that had been subjected to the oil treatment immediately before the flameproofing process was continuously fed into four flameproofing furnaces, and the flameproofing process was divided into four times.
First, the flameproofing furnace 20 of the present invention shown in FIG. 2 was used as the first flameproofing process, that is, the preliminary flameproofing process. The temperature in the heat treatment chamber 2 was set to 231 ° C., and the precursor fiber bundle 1 was flameproofed under tension over 15 minutes. The traveling time in the heat treatment section 2a corresponding to the initial traveling region of the precursor fiber bundle 1 was 225 seconds.

The precursor fiber bundle 1 subjected to the preliminary flameproofing treatment in the first flameproofing treatment is then prepared, and three conventional flameproofing furnaces 30 having the structure shown in FIG. The fourth flameproofing treatment was performed. In the heat treatment chambers 2 of the three flameproofing furnaces 30, the set temperatures were 236 ° C., 243 ° C., and 252 ° C., respectively, and the precursor fiber bundle 1 was flameproofed under tension for 15 minutes each. In this way, the flame-resistant fiber bundle obtained by the four times flame-proofing treatment had a flame-resistant density of 1.35 g / cm ³ .

FIGS. 4 and 5 show the Si residual amount and Si residual rate of the precursor fiber bundle 1 over time when the preliminary flameproofing treatment is performed in the flameproofing furnace 20. The remaining amount of Si adhering to the precursor fiber bundle 1 rapidly decreases in 30 seconds after being fed into the flameproofing furnace 20, and the Si remaining rate after 30 seconds is 86.5%, after 120 seconds. Was 83.0%, and after 600 seconds, it was 80.0%. In addition, after 600 seconds, the change of Si residual amount was hardly recognized, and the Si residual rate of the flame-resistant fiber bundle was 79.9%. Therefore, it was confirmed that most of the volatiles from the silicone-based oil were generated in less than 3 minutes after being fed into the flameproofing furnace. Since the residence time of the heat treatment chamber 2a of the flameproofing furnace 20 in this example was 233 seconds, it was assumed that most of the volatiles were discharged out of the hot air circulation system by the discharge means.
Although the above flameproofing treatment was continued for 2 weeks, clogging of the perforated plate did not occur in the flameproofing furnace 20 and the conventional flameproofing furnace 30.
(Comparative Example 1)
Except for using the conventional flameproofing furnace 30 of FIG. 3 for the first flameproofing treatment, that is, except that the precursor fiber bundle 1 was continuously fed into four flameproofing furnaces 30, the same conditions as in Example 1 were used. Thus, a flame-resistant fiber bundle having a density of 1.35 g / cm ³ was obtained. Further, the Si residual ratio of the obtained flame-resistant fiber bundle was 79.9%.
In this state, the flameproofing treatment was continued, but in the conventional flameproofing furnace 30 used for the first flameproofing treatment in the first week of operation, yarn breakage of the precursor fiber bundle 1 occurred frequently. . When the operation was stopped and the inside of the conventional flameproofing furnace 30 was observed, clogging due to dust occurred in the porous plate provided in the hot air outlet 4, and the hot air outlet 4 was almost closed.

 According to Example 1 and Comparative Example 1 described above, the flameproofing furnace 20 of the present invention is more than the conventional flameproofing furnace 30 because most of the volatiles from the silicone-based oil are discharged out of the hot air circulation system. Thus, the generation of dust in the heat treatment chamber 2 can be suppressed, and it has been evaluated that long-term continuous operation of the flameproofing furnace is possible.

According to the flameproofing furnace and the carbon fiber manufacturing method of the present invention, it is possible to reduce dust retention, which is a disadvantage of the hot air circulation system, while having the advantage of the hot air circulation system that there is little loss of thermal energy. Therefore, the maintenance cost accompanying the cleaning of the flameproofing furnace can be reduced, and the flameproofing furnace can be operated continuously for a long time, so that the production efficiency of the flameproofing fiber bundle can be improved.
Moreover, since the flameproofing furnace of the present invention can reduce the accumulation of dust in the hot air circulation system, the hot air outlet is not easily blocked. Therefore, according to the carbon fiber manufacturing method using the flameproofing furnace of the present invention, hot air is circulated stably over a long period of time, so that yarn breakage of the precursor fiber bundle can be reduced. Moreover, since dust is reduced, adhesion of dust to the precursor fiber bundle is also reduced. Therefore, a high quality carbon fiber can be obtained.
In the production of carbon fibers using a plurality of flameproofing furnaces, if the flameproofing furnace of the present invention is used in at least the first flameproofing furnace, the volatile matter generated from the precursor fiber bundle is removed from the hot air circulation system. Since it can discharge outside, yarn breakage and ignition in the first flameproofing furnace and the subsequent flameproofing furnaces can be reduced. Thereby, a high-quality flameproof fiber can be obtained, and thus a high-quality carbon fiber can be produced.

The schematic side view which shows the flameproofing furnace of this invention. The schematic side view which shows the flameproofing furnace of another form of this invention. The schematic side view which shows the conventional flameproofing furnace. The figure which showed the relationship between Si residual amount of a precursor fiber bundle, and flameproofing processing time. The figure which showed the relationship between Si residual rate of a precursor fiber bundle, and flame-proofing processing time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Precursor fiber bundle 2 Heat processing chamber 2a, 2b Heat processing section 3 Guide roll 4 Hot-air outlet 5, 5a Hot-air outlet 6 Heater 7 Blower 8 Hot-air circulation path 9 Partition plate 10, 20 Flame-resistant furnace 11 Exhaust path 12, 16 Exhaust fans 13, 17 Exhaust gas combustion device 14 Dust collector 15 Outside air intake 30 Conventional flameproofing furnace

Claims (4)

A flameproof furnace having the following hot air circulation system and discharge means.
(1) Hot air circulation system It has a heat treatment chamber and a hot air circulation path,
The heat treatment chamber is flameproofed by blowing hot air on the precursor fiber bundle that travels while folding back the multi-stage traveling area,
The hot air circulation path circulates the hot air in the hot air circulation system by blowing hot air into the heat treatment chamber and discharging the hot air from outside the initial travel region of the precursor fiber bundle in the heat treatment chamber.
(2) Discharge means The hot air that has passed through the initial travel region of the precursor fiber bundle is discharged out of the hot air circulation system.   The flameproof furnace according to claim 1, wherein the discharge means includes an exhaust gas combustion device and a dust collector.   A carbon fiber production method using the flameproofing furnace according to claim 1 or 2.   The carbon fiber manufacturing method using a plurality of flameproofing furnaces, wherein the flameproofing furnace performing at least the first flameproofing process is the flameproofing furnace according to claim 1 or 2.

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