JP2007284842A - Heat-treatment furnace, flame-proofing fiber bundle and method for producing carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-treatment furnace for producing a carbon fiber having stable and high strength, a method for producing a flame-proofing fiber and a method for producing a carbon fiber. <P>SOLUTION: The heat-treatment furnace 1 is provided with a heat-treatment chamber 2 having a plurality of slit openings 3a, 3b for passing a treating object on two opposite side walls, a gas circulation path placed outside of the heat-treatment chamber, having a gas blowout port 8 positioned above the heat-treatment chamber 2 and blowing out hot gas downward and a gas sucking port 9 positioned under the heat-treatment chamber 2 and sucking hot gas, and circulating the gas from the gas sucking port 9 to the gas blowout port 8, and sealing chambers 6a, 6b placed outer side of these two side walls. The sealing chambers 6a, 6b have hot gas recovery ports 10a, 10b to recover the hot gas and placed at the upper part of the chambers and hot gas supplying ports 11a, 11b to supply the hot gas recovered from the hot gas recovery ports and placed at the lower part of the chambers. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heat treatment furnace for producing flame-resistant fibers, and a method for producing flame-resistant fibers and carbon fibers.

  Carbon fibers made from polyacrylonitrile-based fibers have excellent mechanical properties such as strength and elastic modulus, and are widely used as reinforcing materials for structural materials for various applications.

  In general, a carbon fiber using polyacrylonitrile fiber as a raw material is a precursor fiber bundle obtained by bundling thousands to tens of thousands of polyacrylonitrile polymer single fibers in an oxidizing gas such as air in a flameproofing process. It is manufactured by firing at a temperature of ˜300 ° C. to obtain a flame resistant fiber bundle, and then carbonizing the flame resistant fiber bundle at a temperature of 300 to 2000 ° C. in an inert atmosphere in a carbonization step.

  The tensile strength of carbon fibers is generally considered to be dominated by single yarn defects, and greatly depends on single yarn defects even when manufactured under the same conditions. With regard to the strength of the carbon fiber, the present inventors have noted that if there are a large amount of dust and metal components in the dust entering from the flameproof furnace atmosphere, the problem of strength reduction due to the single yarn defect is likely to occur. The present invention has been conceived.

  The flameproofing treatment method for polyacrylonitrile fiber bundles is generally performed by reciprocating a number of rollers arranged in the furnace height direction in a heat treatment furnace in which an oxidizing gas heated to 200 to 300 ° C. circulates. . A yarn is run horizontally, and a seal chamber is provided on the side surface of the horizontal heat treatment furnace turned back by a roll, and an exhaust mechanism is provided in the seal chamber to exhaust gas leaked from the heat treatment furnace. Furthermore, a horizontal heat treatment furnace has been proposed in which the pressure in the seal chamber at the bottom of the furnace is higher than that in the furnace, so that no toxic gas generated in the heat treatment chamber leaks out of the heat treatment chamber, and temperature control in the heat treatment chamber is easy. (For example, refer to Patent Document 1). In the case of this method, maintaining the state in which the pressure in the seal chamber having the exhaust mechanism is particularly high with respect to the pressure in the furnace means that the low-temperature gas in the atmosphere is actively introduced into the furnace, and temperature fluctuations in the lower part of the furnace are generated. Prone to occur. Moreover, since the temperature drop of the circulating air becomes large and enormous energy is required to heat the circulating oxidizing gas, it prevents or leaks the low temperature gas in the atmosphere as much as possible. Although it is desired to raise the atmospheric gas temperature and to reuse the leaked furnace gas, no examination has been made from this point of view.

  Moreover, the flameproofing treatment of the polyacrylonitrile fiber bundle is an oxidation exothermic reaction, and involves a large amount of heat generation. Therefore, in such a flameproofing process, a fusion phenomenon easily occurs between the fibers due to a large amount of heat generated due to the temperature during the treatment and the oxidation reaction. It deteriorates and causes fluff generation and process interruption in the subsequent carbonization process. As a result, the carbonization process is destabilized, and the quality and performance of the resulting carbon fiber is significantly reduced.

  In such a situation, the polyacrylonitrile fiber bundle is treated with a silicone oil agent to prevent fusion between single fibers in the flameproofing process, and the convergence of the fiber bundle in the process is set to a sufficient level. It has been found that it is possible to keep the fiber from breaking a single yarn, and various silicone oils have been studied.

  However, in the flame resistance of such a polyacrylonitrile fiber bundle treated with a silicone-based oil agent, white fine powder due to oxidation on the surface of the heater of the flame resistance furnace adheres to the flame resistance furnace. There was also a decrease in carbon fiber strength and a decrease with time due to the fine powder floating and adhering to the flameproof fiber.

  The main cause of strength reduction is the oxidation of silicon (SI), a silicone-based oil agent, to a fine powder that binds to metal components such as iron and aluminum and adheres to the flameproofing yarn. It is considered that it breaks down and becomes a single yarn defect.

  The metal component is also contained in the flameproofing furnace material, the polyacrylonitrile fiber bundle, and the oxidizing gas supplied to the heat treatment furnace. Oxidizing gas supplied to the heat treatment furnace is filtered with a filter, and care is taken when metal components enter.

On the other hand, in order to suppress the oxidation of the silicone component, the oxidizing gas forming the oxidizing atmosphere is heated in contact with the heating body, and at this time, the temperature of the surface of the heating body in contact with the oxidizing gas is set. Although it has been proposed that the silicone-based compound volatilized at 400 ° C. or lower does not generate a fine powder containing silicon atoms in a flameproofing furnace (see, for example, Patent Document 2), it is completely zero. It is difficult to make it, and the metal component which is the main cause of strength reduction is not described or studied. The carbonizing step is performed in a high temperature region of 1000 ° C. or higher, and metal components such as iron and aluminum are easily dissolved or reacted. For this reason, it is desired that the flameproof fiber supplied to the carbonization process has little adhesion of metal components, but no examination has been made from this viewpoint.
Japanese Patent Laid-Open No. 11-173761 JP 2003-73931 A

  An object of the present invention is to solve the above-mentioned problems of the prior art, and provides a heat treatment furnace for making a polyacrylonitrile fiber bundle flame resistant, a method for producing flame resistant fiber, and a method for producing carbon fiber. More specifically, the present invention provides a heat treatment furnace having a small amount of metal components in dust accumulated in a heat treatment furnace caused by a silicone-based oil, a method for producing flame-resistant fibers using the heat treatment furnace, and a method for producing carbon fibers. It is in. Specifically, an object of the present invention is to provide a heat treatment furnace capable of producing a carbon fiber having a stable high strength, a method for producing a flame-resistant fiber, and a method for producing a carbon fiber.

In order to achieve the above object, the present invention adopts the following configuration. That is,
(1) A heat treatment chamber having a plurality of slit-like openings on the two side walls facing each other, a gas blowout port for blowing the heated gas toward the lower position above the heat treatment chamber, and heat treatment A gas suction port that is located below the chamber and sucks the heated gas, and a gas circulation path for circulating gas from the gas suction port to the gas outlet is provided outside the heat treatment chamber, and outside the two side walls. Is a heat treatment furnace provided with a seal chamber having a plurality of slit-like openings on the outer side wall through which an object enters and exits, and the seal chamber has a heated gas recovery port at the upper portion for recovering heated gas. And a heating gas supply port for supplying the heating gas recovered from the heating gas recovery port at a lower portion.

  (2) The heat treatment furnace according to (1), further including an outside air blowing unit that blows heated outside air toward a slit-shaped opening provided on an outer side wall of the seal chamber, outside the seal chamber.

  (3) Using the heat treatment furnace described in (1) or (2), a slit-like opening having a polyacrylonitrile fiber bundle on two opposing side walls and an outer side wall of the seal chamber A flame-resistant fiber bundle that is passed through the part, folded back and passed through the heat treatment chamber a plurality of times and flame-proofed in oxidizing heating gas, and the heated gas is blown out downward from the gas blowing port, The heated gas is sucked in from the gas suction port, and the sucked heated gas is circulated to the gas blowout port via the gas circulation path, and the heated gas in the seal chamber is recovered from the heated gas recovery port and recovered. Is supplied from a heated gas supply port. A method for producing a flame resistant fiber bundle.

  (4) Using the heat treatment furnace described in (2), the polyacrylonitrile fiber bundle is passed through the slit-like opening provided on the two opposing side walls and the slit-like opening provided on the outer side wall of the seal chamber. , A method for producing a flame-resistant fiber bundle that is folded and passed through a heat treatment chamber a plurality of times and flame-proofing in an oxidizing heating gas, wherein the heated gas is blown out downward from the gas blowing port, from the gas suction port The heated gas is sucked in, and the sucked heated gas is circulated to the gas outlet through the gas circulation path, and the heated gas in the seal chamber is recovered from the heated gas recovery port, and the recovered heated gas is supplied to the heated gas. Flame-resistant fiber bundles, characterized in that heated outside air is blown toward the slit-shaped opening provided on the outer side wall of the seal chamber by the outside air blowing means. Manufacturing method.

  (5) The flame-resistant fiber bundle according to (4), wherein the heated outside air is purified by a filter so that the temperature is 40 to 100 ° C. and the number of dusts of 0.5 μm or more is 35 co / 10 liters or less. Manufacturing method.

  (6) The method for producing a flame resistant fiber bundle according to any one of (3) to (5), wherein a silicone-based oil agent is attached to the polyacrylonitrile fiber bundle.

  (7) A method for producing carbon fiber, comprising subjecting the flame-resistant fiber bundle obtained by the production method according to any one of (3) to (6) to carbonization in an inert atmosphere.

  According to the present invention, as described below, there are few metal components adhering to the flameproofing yarn in the flameproofing step, and there are few single yarn defects in the carbonization step, that is, high strength carbon fiber is stable for a long period of time. Can be manufactured.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the drawings.

  FIG. 1 is a schematic configuration diagram of a heat treatment furnace according to an embodiment of the present invention.

  The heat treatment furnace 1 of the present invention is positioned above the heat treatment chamber 2 and a heat treatment chamber 2 having a plurality of slit-like openings 3a and 3b on both sides 13a and 13b facing each other. It has a gas outlet 8 that blows out the heated gas downward, and a gas inlet 9 that is located below the heat treatment chamber 2 and sucks in the heated gas.

  The heat treatment furnace 1 of the present invention suppresses the ingress of outside air containing metal components such as iron, sodium, potassium, magnesium, and aluminum into the flameproofing furnace when the polyacrylonitrile fiber bundle is made flameproof, and silicon oxide It is a thing which suppresses the coupling | bonding with. As the heat treatment furnace 1, the oxidizing heating gas intersects the traveling direction of the yarn that is the object to be treated A from the gas outlet 8 provided at the upper part of the heat treatment furnace 1 through a plurality of outside-rolls 5. This is particularly effective in an apparatus for producing flame-resistant fibers, which is sprayed in the direction, preferably perpendicular direction, to obtain flame-resistant fibers.

  As described above, by disposing the roll 5 on the outside of the heat treatment furnace 1, work can be performed without entering the heat treatment furnace 1, so that it is easy to prepare for start, easy to maintain, and steady. Even when winding or yarn breakage occurs during operation, it is possible to take measures without stopping the production equipment, and the productivity is superior to the flameproofing device in which a roll is arranged in the furnace. On the other hand, from the viewpoint of hermeticity and thermal efficiency in the furnace, an opening for carrying the yarn in and out of the furnace is necessary, and since the yarn is cooled once, the furnace in which the roll is arranged in the furnace Although flame resistance efficiency is inferior to the above, long-term continuous operation, multiple yarns, and high yarn density are required, and a furnace with rolls outside the furnace is often dominant. It is done.

  By blowing the oxidizing gas from the top of the furnace in a direction that intersects the yarn traveling direction, preferably in a direction perpendicular to it, the heat generated by the oxidation reaction can be efficiently removed compared to the method in which the gas is blown in a direction parallel to the yarn traveling direction. Since it can be heated, flameproofing treatment at high temperature and in a short time is possible. On the other hand, by blowing the oxidizing gas in a direction intersecting with the traveling direction of the yarn, preferably in a direction perpendicular to the yarn, the yarn becomes resistant, and the portion having a low resistance, that is, the slit shape of the heat treatment furnace 1 in which the object to be treated enters and exits Part of the oxidizing gas leaks into the openings 3a and 3b. Since the oxidizing gas is blown from the upper part of the furnace, a part of the oxidizing gas leaks out from the slit-shaped openings 3a and 3b through which the processed object A at the upper part of the furnace enters and exits, and the processed object at the lower part of the furnace enters and exits the slit. The outside air around the heat treatment furnace 1 is sucked from the openings 3a and 3b. From the slit-shaped openings 3a and 3b through which the object to be processed at the lower part enters and exits, the ambient temperature gas outside the furnace is sucked in, so that the temperature decrease in the lower part of the heat treatment furnace and the metal components contained in the atmospheric gas enter the furnace. And bonded to silicon oxide. Although it is necessary to make the openings 3a and 3b as narrow as possible in order to prevent leakage from the slit-like openings 3a and 3b through which the workpiece to be processed enters and exits, the leakage should be made zero. Is virtually impossible. Therefore, by collecting the oxidizing gas leaked from the slit-shaped openings 3a and 3b through which the upper workpiece is moved in and out, and supplying the oxidizing gas through the slit-shaped openings 3a and 3b through which the lower workpiece is loaded and unloaded. It is preferable to prevent the atmospheric gas outside the furnace from entering the furnace.

  Therefore, in the present invention, gas circulation paths 15a and 15b for circulating gas from the gas suction port 9 to the gas blowout port 8 are provided outside the heat treatment chamber, and the workpiece A is disposed outside the two side walls 13a and 13b. Is a heat treatment furnace provided with seal chambers 6a and 6b having a plurality of slit-like openings 4a and 4b on the outer side walls 14a and 14b, and the seal chamber has a heated gas for recovering the heated gas at the top. It has recovery ports 10a and 10b, and has heating gas supply ports 11a and 11b for supplying heated gas recovered from the heating gas recovery ports 10a and 10b in the lower part.

  As described above, in the present invention, as a method for recovering the leaked oxidizing gas, the side walls 13a and 13b having the slit-like openings 3a and 3b of the heat treatment furnace 1 and the roll 5 disposed outside the furnace are provided. There is a method in which seal chambers 6a and 6b are provided between the chambers, and the air is collected from the upper portions of the seal chambers 6a and 6b by the suction force of the fans 7a and 7b and sent to the lower seal chambers 6a and 6b by the pushing force of the fans 7a and 7b. preferable. By this method, heat loss is small and the recovery efficiency is improved. Furthermore, it is more preferable to reheat the oxidizing gas recovered by a heat source (not shown) such as a heater immediately before feeding into the lower seal chambers 6a and 6b. Since the temperature of the recovered oxidizing gas sent to the lower seal chambers 6a and 6b is lowered by heat radiation from a duct or the like and the suction of a small amount of outside air, temperature spots are generated in the heat treatment furnace, but the temperature spots are reduced. In addition, the temperature can be stably supplied by reheating with a heater or the like.

Said sealing chamber 6a, 6b can be sealed more efficiently by making it multistage. Even with one stage, there is a sealing effect, but more efficient collection is possible by using multiple stages. Two stages are more preferable in order to minimize recovery efficiency and sealability, and equipment modification. The sealing chambers 6a and 6b are for reinforcing the seal and preventing the atmosphere gas outside the furnace containing a large amount of metal components around the furnace from entering the furnace and preventing the metal components from entering. Therefore, it is important to clean the atmosphere gas. The cleanness of the atmospheric gas is preferably such that dust of 0.5 μm or more is about 35/10 liters or less. Generally, it is said that there are 10 to ³ million dusts of 0.5 μm or more per 1 m ^{3 in} a normal atmosphere such as an office. If Class 5 level comparable with defined by that classification with JIS B9920 (class JIS B9920 dust in 1 m ³⁾ over 35 co / 10 l, if such ambient air enters the furnace, oxide It is considered that the metal content in the furnace dust described later using silicon as a medium cannot satisfy the target. The degree of cleanliness of the atmospheric gas is more preferably 4 co / 10 liters or less equivalent to class 4.

Although the number of dust has never been small, if it is equivalent to the class 5 level, the metal components in the dust in the furnace described later can achieve the target.
In addition, such a cleanliness degree should just have the atmosphere gas of the range from the outer walls 14a and 14b of the seal chambers 6a and 6b to the outer roll 5.

  As a method of cleaning the atmospheric gas, it is possible to reduce the number of dusts to 35/10 liters or less by filtering the outside air with a filter. By using a HEPA filter (High Efficiency Particulate Air) or a ULPA filter (Ultra Low Penetration Air) as the type of filter, it is possible to reduce the number of dusts to a target or less. If it is set to the same level as class 5, it is preferable to use a HEPA filter from the viewpoint of cost, life and durability. The number of dusts can be measured by using a particle counter with ambient gas at room temperature.

  In order to make the atmospheric gas have such a cleanliness, in the present invention, it is preferable to blow heated outside air toward the slit-shaped opening provided on the outer side wall of the seal chamber by the outside air blowing means. In particular, it is preferable to spray heated outside air through a filter as described above. Next, as an example of the outside air blowing means, an outside air blowing device will be described.

  FIG. 2 is an enlarged partial cross-sectional view of the heat treatment furnace provided with the outside air spraying device 12.

  Although the blowing direction is not particularly limited, the outside air blowing device 12 preferably has an elevation angle of 0 ° to 80 ° with respect to the furnace opening. More preferably, it is the range of 10 degrees-60 degrees. Moreover, it is preferable to use the heated gas heated at 40 to 100 degreeC. The temperature around the furnace rises to about 30 to 100 ° C. as the yarn is carried in and out. The atmospheric gas at room temperature cools the yarn to be carried more than necessary, and causes flameproofing spots. Moreover, since atmospheric temperature will raise and work environment will deteriorate when too high, More preferably, it is the range of 50-70 degreeC.

  As a method of blowing heated outside air, a gas blowing device 12 such as a nozzle having a slit in the machine width direction is provided between the furnace opening and the roll, and directed toward the slit-like openings 3a and 3b of the seal chambers 6a and 6b. A method of spraying with a supply device such as a fan is preferred. If it is too far from the furnace side, a large amount of air flow is required to reduce the target number of dusts or less, and the efficiency is deteriorated. Therefore, it is desirable to be close to the openings 3a and 3b. It is desirable to install in consideration of the characteristics As the number of stages to be blown, it is preferable to blow all the openings, but since the atmosphere on the furnace side is an updraft and there is a flow of wind upward, the heated outside air is blown from the bottom opening to the middle stage in the height direction. The target number of dust can be satisfied. As a result, the number of stages can be reduced, and the equipment cost can be reduced without a large-scale equipment modification. Although there is no particular limitation on the amount of blowing air, ascending airflow is generated around the heat treatment furnace due to the heat radiation of the furnace body and the object to be processed, and the wind is moving upward. Although depending on conditions and circumstances, a wind of about 1 m / sec is flowing, and it is important to supply a higher air volume for sealing. It is preferable that the mechanism be able to confirm the flow of the wind and adjust the air volume accordingly. The time for measuring the number of dust is not particularly limited, but before starting to manufacture the flame-resistant fiber bundle, spray clean ambient air at room temperature, measure the number of dust in the atmosphere gas, and make it within the above range Is preferred. In the present invention, the polyacrylonitrile fiber bundle is preferably formed by adhering a silicone oil. The silicone oil agent is an oil agent containing at least 0.1% by weight of silicone, and may be in the form of a solution using silicone alone or an organic solvent. From the viewpoint of properties, an aqueous emulsion is preferably used.

  When making such an aqueous emulsion, an appropriate emulsifier can be added to the silicone, and from the viewpoint of long-term stability, an antioxidant or the like can be added, but a silicone that does not inhibit the crosslinking reaction of the silicone is selected. It is preferable.

  Examples of silicone modifying groups used in the silicone fluid of the present invention are amino groups, epoxy groups, and alkylene oxide groups. Among these, those that cause a crosslinking reaction upon heating are preferably used. A silicone having a plurality of such modifying groups may be used as long as it is mainly composed of these three types of silicones of amino group, epoxy group and alkylene oxide group. In addition to these, silicones having other different modifying groups may be mixed. It may be used. The silicone component of the silicone-based oil agent is oxidized on the surface of the heater that volatilizes in the flameproofing furnace and becomes silicon oxide. In the case of a method for making an oxidizing gas flame resistant in a circulation type heat treatment furnace, silicon oxide stays and scatters in the furnace and becomes a medium on which metal components adhere.

  In the present invention, the seal chamber is provided and circulated to improve the sealing performance. Preferably, the atmosphere gas from the outside of the furnace is cleaned to suppress the entry of metal components into the furnace. The total content of iron, sodium, potassium, magnesium, and aluminum is 1000 mass ppm or less as measured by inductively coupled high-frequency plasma emission spectrometry (hereinafter referred to as ICP emission spectrometry) in the dust collected from the inside. Can be.

  Deterioration in quality, especially in tensile strength, is thought to be due to increased defects due to adhesion of metal components, and when pure silicon oxide such as a reagent is forcibly adhered to a flame resistant yarn, The strength reduction is 5% or less, and almost no strength reduction occurs. However, when dust collected from the furnace in which the metal component exceeds 1000 mass ppm is adhered, it becomes a defect in the carbonization process and causes a significant decrease in strength. The metal component is preferably as small as possible. However, when the amount exceeds 1000 mass ppm, a decrease in strength appears remarkably as 10% or more. Therefore, the metal component in the dust in the furnace is preferably 1000 mass ppm or less, more preferably. It is good to set it as 800 mass ppm or less. The lower limit is not particularly limited, but it is difficult to make it less than 300 ppm by mass because it is impossible to completely block the carry-in from the object to be processed (precursor) and the entry of outside air.

  The dust in the furnace in this case is a fine powder mainly composed of silicon oxide deposited on the upper part of the furnace, and is dust that may adhere to the flameproof yarn. Such dust can be collected at the top of the furnace with a stainless steel saucer, which can be collected during non-production after production is finished. The collected dust is ashed and the remainder is heated in a solvent such as hydrochloric acid or aqua regia. When the dissolved and cooled solution is measured by ICP emission spectrometry, the total content of the metal components described above can be determined.

  Hereinafter, the present invention will be described more specifically with reference to examples.

Each measured value in the examples was determined by the following method.
[Total content of metal elements in dust]
Measurement was performed by ICP emission spectrometry according to the following procedure. An SPS4000 manufactured by Seiko Instruments Inc. was used as an ICP emission analysis apparatus.
(A) Dust in the flameproofing furnace was dry ashed with a low-temperature ashing device, and the residue was removed and dissolved in dilute nitric acid.
(B) The residue was filtered and ashed, dissolved by heating with hydrochloric acid, and mixed with the solution dissolved in (a) to prepare a constant solution.
(C) The fixed solution was cooled, diluted with pure water by a predetermined amount, and then analyzed by ICP emission spectrometry.
[Dust count]
Measure 10 liters of ambient gas at room temperature using a particle counter to determine the number of dust. In this example, a particle counter KC03A1 manufactured by RION was used as the particle counter.
[Strand strength of carbon fiber bundle]
Measured in accordance with JIS R 7601 test method. The measurement was performed with 20 strand test pieces, and the average value was obtained.

Example 1
A polyacrylonitrile (PAN) polymer was spun using dimethyl sulfoxide (DMSO) as a solvent to obtain a polyacrylonitrile fiber bundle (precursor) provided with a silicone oil.
Next, in FIG. 1, using a heat treatment furnace having 20 outside rolls, an oxidizing heating gas was circulated at 250 ° C. and sprayed at right angles to the yarn from the top, and 300 precursors of 12,000 filaments were applied for 40 minutes. It was run continuously. The oxidation heating gas leaked from the flame-resistant upper part is recovered from the upper part of the seal chamber, and the recovered gas reheated to 250 ° C. with a heater is circulated and supplied at 8000 Nm ³ / hr using a fan in the furnace lower seal chamber. Got a bunch. The obtained flame-resistant fiber bundle was treated at 300 to 800 ° C. in an inert atmosphere, and further carbonized at 800 to 1500 ° C. in an inert atmosphere to obtain carbon fibers. Table 1 shows the physical properties of the obtained carbon fibers.
When the physical properties of the obtained carbon fibers were compared for 30 days, the strength was good without any significant decrease in strength. In addition, when the metal component was measured by ICP emission analysis for the dust inside the flameproofing furnace deposited on the upper and lower parts in the flameproofing furnace after 30 days of operation, it was as shown in Table 1 and was below the target metal component content. confirmed. The strength target of the carbon fiber in this example is in the range of 5,100 MPa / mm ^{2 to} 5,500 MPa / mm ² .

Example 2
The atmosphere outside the furnace was purified with a HEPA filter so that the number of dust of 0.5 μm or more was 30/10 liters, and the heated outside air heated to 70 ° C. was blown to the furnace opening at an elevation angle of 30 ° and 4000 m ³ / hr. A carbon fiber was obtained in the same manner as in Example 1 except that the carbon fiber was sprayed. Table 1 shows the physical properties of the obtained carbon fibers. When the physical properties of the obtained carbon fibers were compared for 30 days in the same manner as in Example 1, the strength was good without any significant decrease in strength. In addition, when the metal component was measured by ICP emission analysis for the dust inside the flameproofing furnace deposited on the upper and lower parts in the flameproofing furnace after 30 days of operation, it was as shown in Table 1 and was below the target metal component content. confirmed.

Comparative Example 1
Carbon fibers were obtained in the same manner as in Example 1 except that the heated gas leaked from the upper part of the heat treatment furnace was exhausted from the upper part of the seal chamber. When the internal pressure of the furnace at the lower part of the heat treatment chamber was negative with respect to the outside of the furnace and the atmospheric gas was sucked in, the physical properties of the obtained carbon fibers were compared. As a result, the strength was lowered and the target could not be satisfied. In addition, when metal components were measured by ICP emission analysis for dust in the flameproofing furnace deposited on the upper and lower parts of the flameproofing furnace after 30 days of operation, it was as shown in Table 1 and could satisfy the target metal component content. could not.

Comparative Example 2
The atmosphere outside the furnace was purified with a HEPA filter so that the number of dust of 0.5 μm or more was 30/10 liters, and the heated outside air heated to 70 ° C. was blown to the furnace opening at an elevation angle of 30 ° and 4000 m ³ / hr. A carbon fiber was obtained in the same manner as in Comparative Example 1, except that the carbon fiber was sprayed. Table 1 shows the physical properties of the obtained carbon fibers. When continuously operating for 30 days in the same manner as in Example 1 and comparing the physical properties of the obtained carbon fibers, the strength was lowered and the target could not be satisfied. In addition, when metal components were measured by ICP emission analysis for dust in the flameproofing furnace deposited on the upper and lower parts of the flameproofing furnace after 30 days of operation, it was as shown in Table 1 and could satisfy the target metal component content. could not.

  As described above, the present invention is particularly suitable as a heat treatment furnace and a flame resistance method for making a precursor to which a silicone oil agent is applied flame resistant, and collects oxidizing gas leaked from the heat treatment furnace and supplies it from below. This prevents dust in the atmosphere outside the heat treatment furnace from entering the heat treatment furnace, and by cleaning the atmosphere outside the furnace with a filter, the entry of metal components into the heat treatment furnace can be suppressed. A carbon fiber suitable for use in a heat treatment furnace and a flameproofing method with improved fiber strength stability can be provided.

  The heat treatment furnace and flameproofing method according to the present invention are particularly suitable for applications that require flameproofing, and are particularly suitable for use in carbon fiber production processes.

It is a schematic block diagram of the heat processing furnace which concerns on one embodiment of this invention. It is an expanded partial sectional view of a heat treatment furnace provided with an outside air spraying device.

Explanation of symbols

A: Object to be treated 1: Heat treatment furnace 2: Heat treatment chamber 3a, 3b: Slit opening 4a, 4b of heat treatment furnace 5: Roll slit 6a, 6b: Seal chamber 7a, 7b: Heated gas recovery fan 8: Gas outlet 9: Gas suction port 10a, 10b: Heated gas recovery port 11a, 11b: Heated gas supply port 12: Outside air spraying device 13a, 13b: Side walls 14a, 14b of heat treatment furnace Outer side walls 15a, 15b: gas circulation path

Claims (7)

A heat treatment chamber having a plurality of slit-like openings on two side walls facing each other, a gas outlet that is located above the heat treatment chamber and blows heated gas downward, and below the heat treatment chamber And a gas circulation path for circulating gas from the gas suction port to the gas blowout port is provided outside the heat treatment chamber, and outside the two side walls, A heat treatment furnace provided with a seal chamber having a plurality of slit-like openings on the outer side wall through which processed objects come and go, wherein the seal chamber has a heated gas recovery port for recovering heated gas at the upper part, and a lower part And a heating gas supply port for supplying the heating gas recovered from the heating gas recovery port. 2. The heat treatment furnace according to claim 1, further comprising an outside air blowing unit that blows heated outside air toward a slit-shaped opening provided on an outer side wall of the seal chamber, outside the seal chamber. Using the heat treatment furnace according to claim 1 or 2, the polyacrylonitrile fiber bundle is allowed to pass through a slit-like opening provided on two opposing side walls and a slit-like opening provided on the outer side wall of the seal chamber, A method for producing a flame-resistant fiber bundle that is folded and passed through a heat treatment chamber a plurality of times and flame-proofing in an oxidizing heating gas, wherein the heated gas is blown downward from the gas blowing port and heated from the gas suction port. Gas is sucked in and the sucked heated gas is circulated to the gas outlet through the gas circulation path, and the heated gas in the seal chamber is recovered from the heated gas recovery port, and the recovered heated gas is supplied to the heated gas supply port. A method for producing a flame-resistant fiber bundle, characterized by being supplied from Using the heat treatment furnace according to claim 2, the polyacrylonitrile fiber bundle is passed through the slit-like opening provided on the two opposing side walls and the slit-like opening provided on the outer side wall of the seal chamber, and folded. A method of manufacturing a flame-resistant fiber bundle that passes through a heat treatment chamber a plurality of times and flame-proofs in an oxidizing heating gas, and blows the heating gas downward from the gas blowing port, and the heating gas from the gas suction port. Inhale and circulate the sucked heated gas to the gas outlet through the gas circulation path, collect the heated gas in the seal chamber from the heated gas recovery port, and supply the recovered heated gas from the heated gas supply port And heated outside air is sprayed toward the slit-shaped opening on the outer side wall of the seal chamber by the outside air blowing means. Method. The method for producing a flame-resistant fiber bundle according to claim 4, wherein the heated outside air is purified by a filter so that the temperature is 40 to 100 ° C and the number of dust of 0.5 µm or more is 35 co / 10 liters or less. . The method for producing a flame-resistant fiber bundle according to any one of claims 3 to 5, wherein a silicone-based oil agent is attached to the polyacrylonitrile fiber bundle. A method for producing carbon fiber, comprising subjecting the flame-resistant fiber bundle obtained by the production method according to claim 3 to carbonization in an inert atmosphere.

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