Method for manufacturing carbon fiber bundle

Abstract

This method for manufacturing a carbon fiber bundle comprises: a flameproofing step for subjecting an acrylic fiber bundle to a heat treatment within a range from 200°C to 300°C in an oxidizing atmosphere; a preliminary carbonizing step for performing a heat treatment within a range from 300°C to 1,000°C by using a heat treatment furnace having at least one inert gas supply opening on each of an incoming side and an outgoing side of the fiber bundle, and at least one discharge opening between the incoming-side and outgoing-side inert gas supply openings, the heat treatment being performed such that the temperature for supplying an inert gas is higher on the outgoing side than on the incoming side; and a carbonizing step for performing a heat treatment at temperatures from 1,000°C to 2,000°C in an inert gas atmosphere. In this method for manufacturing a carbon fiber bundle, from a position at which the atmosphere temperature within the heat treatment furnace is 300°C and that is located most toward the outgoing side in the machine length direction up to the inert gas supply opening on the incoming side, the flow of the inert atmosphere within the heat treatment furnace in the preliminary carbonizing step consists only of a flow in the parallel flow direction with respect to the fiber bundle travel direction in the machine length direction.　Provided is a method for manufacturing a carbon fiber bundle with which manufacturing can be performed continuously for a long time by preventing entry into a temperature zone causing deposition of gasified decomposition products, such as tar, that are produced at the time of the preliminary carbonizing treatment during manufacturing of carbon fibers and that build up within the heat treatment furnace.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a carbon fiber bundle that can be continuously manufactured for a long period of time by preventing gasified decomposition products such as tar generated during the preliminary carbonization treatment in the production of carbon fibers from flowing into the temperature zone where they are deposited in a heat treatment furnace.

Background Art

[0002] Carbon fibers have high specific strength and specific modulus compared to other reinforcing fibers, and are therefore widely used industrially as reinforcing fibers for composite materials in general industrial applications such as aerospace, sports, and general industries such as bicycles, ships, and civil engineering. Generally, as a method for manufacturing a carbon fiber bundle from an acrylic fiber bundle, it is known to use acrylonitrile-based fibers or the like as a precursor. After performing a flameproofing treatment in the range of 200°C to 300°C in an oxidizing atmosphere, preliminary carbonization is performed in the range of 300°C to 1,000°C in an inert gas atmosphere such as nitrogen gas, and carbonization treatment is performed in the range of 1,000°C or higher.

[0003] In the preliminary carbonization treatment, gasified decomposition products such as hydrogen cyanide, ammonia, nitrogen, water, carbon dioxide, and tar are generated from the fiber bundle to be treated as carbonization progresses. Therefore, it is common to provide an exhaust port in the furnace to discharge these decomposition products. Among these decomposition products, the tar component adheres to the inner wall of the heat treatment furnace, and when it accumulates above a certain amount, it falls onto the running flameproofed fiber bundle, causing a decrease in physical properties, an increase in fluff, and breakage of the yarn, resulting in a decrease in the quality and productivity of the obtained carbon fiber. In addition, this tar component deposits on the inner wall of the duct until it is sent to a device for decomposing or burning the exhaust gas from the exhaust port, causing a problem of blocking the line and shortening the continuous production period.

[0004] In order to solve these problems, Patent Document 1 describes that by defining the residence time of the fiber bundle in the range of 250°C to 400°C in the preliminary carbonization treatment, the heating rate suitable for the decomposition products containing tar components generated in the above temperature range can be achieved, and the precipitation of the generated decomposition products can be prevented.

[0005] In addition, Patent Document 2 describes that by introducing an inert gas preheated in a heat treatment furnace for the preliminary carbonization treatment in a predetermined volume, the decomposition products containing tar components can be exhausted from the exhaust port without precipitation.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, according to the findings of the present inventors, the method of Patent Document 1 only stipulates the heating rate in the low temperature range, and cannot completely prevent the precipitation of decomposition products containing tar components generated in the high temperature range.

[0008] In addition, the method of Patent Document 2 is effective in exhausting the decomposition products containing tar components while gasifying them, but since the supply temperature of the inert gas is high and the temperature range to be treated is narrow, the quality of the obtained carbon fiber is limited. In addition, the power cost for preheating the inert gas increases and the manufacturing cost is excessively high.

[0009] Therefore, an object of the present invention is to provide a method for manufacturing a carbon fiber bundle that can be continuously manufactured for a long period by preventing the gasified decomposition products such as tar generated during the preliminary carbonization treatment in the production of carbon fibers from flowing into the temperature range where precipitation occurs and remaining in the heat treatment furnace.

Means for Solving the Problems

[0010] In order to solve the above problems, the method for manufacturing a carbon fiber bundle of the present invention has the following configuration. That is, A flameproofing step of heat-treating an acrylic fiber bundle in an oxidizing atmosphere in the range of 200°C to 300°C, having one or more inert gas supply ports on each of the fiber bundle inlet side and the outlet side, and using a heat treatment furnace having one or more exhaust ports between the inert gas supply ports on the inlet side and the outlet side, heat-treating in the range of 300°C to 1,000°C with the supply temperature of the inert gas on the outlet side being higher than that on the inlet side, and a carbonization step of heat-treating in an inert gas atmosphere at a temperature of 1,000°C to 2,000°C. A method for manufacturing a carbon fiber bundle, wherein from the position on the most outlet side in the machine length direction where the atmosphere temperature in the heat treatment furnace becomes 300°C to the inert gas supply port on the inlet side, the flow of the inert atmosphere in the heat treatment furnace in the pre-carbonization step is only in the co-current direction with respect to the traveling direction of the fiber bundle in the machine length direction.

[0011] In the method for manufacturing a carbon fiber bundle of the present invention, the pre-carbonization step is performed in a heat treatment furnace having three or more sections capable of temperature control in the machine length direction. With respect to the machine length direction of the heat treatment chamber, the atmosphere temperature at the fiber bundle height at the central position in the machine length direction of the section on the most inlet side is T 1 [°C], and with respect to the machine length direction of the heat treatment chamber, the atmosphere temperature at the fiber bundle height at the central position in the machine length direction of the section on the most outlet side is T 2 [°C], it is preferable that the temperature of the inert gas supplied to the heat treatment furnace satisfies the following two conditions. Inlet side inert gas supply temperature range [°C]: |T 1 -(Inlet side inert gas supply temperature)| = ΔT 1 ≤50 Outlet side inert gas supply temperature range [°C]: |T 2 -(Outlet side inert gas supply temperature)| = ΔT 2 ≤100 In the method for manufacturing a carbon fiber bundle of the present invention, the cross-sectional area in the machine length direction of the heat treatment furnace in the pre-carbonization step is substantially the same, and the flow velocity V described below1 and the flow velocity V described below 2 of the absolute value ratio (|V 1 | / |V 2 |) is preferably 0.5 ≦ |V 1 | / |V 2 | ≦ 2.0. V 1 [m / s]: The flow velocity of the inert atmosphere in the horizontal direction at the central position in the machine length direction of the section closest to the loading side with respect to the machine length direction of the heat treatment chamber V 2 [m / s]: The flow velocity of the inert atmosphere in the horizontal direction at the central position in the machine length direction of the section closest to the unloading side with respect to the machine length direction of the heat treatment chamber

Advantages of the Invention

[0012] By preventing the inflow into the temperature range where gasified decomposition products such as tar generated during the preliminary carbonization treatment in carbon fiber production and staying in the heat treatment furnace are deposited, the effect of enabling continuous production for a long period can be obtained.

Brief Description of the Drawings

[0013]

Figure 1

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Embodiments for Carrying Out the Invention

[0014] Hereinafter, the present invention will be described in detail.

[0015] In the present invention, a known acrylic fiber bundle can be used. As the acrylonitrile polymer constituting the acrylic fiber bundle, a homopolymer of acrylonitrile or a copolymer of acrylonitrile and other monomers can be used.

[0016] The acrylic fiber bundle is heat-treated in an oxidizing atmosphere at 200 to 300°C to obtain a flame-retardant fiber bundle.

[0017] The flame-retardant fiber bundle is pre-carbonized in an inert atmosphere at 300 to 1,000°C to obtain a pre-carbonized fiber bundle. As the inert gas, a known inert atmosphere such as nitrogen, argon, or helium can be adopted, but nitrogen is preferable from the viewpoint of economy. The maximum temperature of the pre-carbonization treatment is preferably 500 to 1,000°C, and more preferably 600 to 900°C.

[0018] When the maximum temperature of the pre-carbonization treatment is 500°C or higher, the expression of the strength and elastic modulus of the carbon fiber becomes better. If the maximum temperature of the pre-carbonization treatment is 1,000°C or lower, it becomes easier to reduce the cost of the heat treatment furnace, which is industrially advantageous. As the temperature distribution of the heat treatment furnace, the highest temperature is preferably on the unloading side of the furnace, and the inert atmosphere temperature is higher on the unloading side than on the loading side.

[0019] The heat treatment furnace used for preliminary carbonization treatment is not particularly limited. For example, as shown in FIG. 1, one side of the heat treatment furnace (1) has a loading port (2) and the other side has an unloading port (3). An opening is provided in the closing plates of the loading port and the unloading port, and it is preferable that the opening area is minimized. A sealing mechanism such as a labyrinth seal structure is preferably used to prevent the inflow of oxygen and the like into the heat treatment chamber (4). The loading side and the unloading side of the fiber bundle (object to be treated) (5) have inert gas supply ports (6). The cross-sectional area of the heat treatment chamber (4) in the machine length direction is preferably substantially the same, and the structure is such that the flow rate of the inert gas existing in the heat treatment chamber (4) does not change abruptly. The temperature control of the inert atmosphere is performed by the heaters (7) provided above and below the heat treatment furnace (1). In order to accurately control the temperature of the inert atmosphere, it is desirable that the heat treatment furnace has three or more temperature-controllable sections in the machine length direction. If the number of sections is less than three, it may not be possible to accurately control the temperature of the inert atmosphere. Further, an exhaust port (8) is provided to efficiently discharge the decomposition products such as gasified tar outside the furnace, and they are pyrolyzed in the exhaust gas treatment furnace (10) through the insulated exhaust duct (9).

[0020] The atmosphere temperature of the heat treatment chamber (4) used for preliminary carbonization treatment is an important factor for preventing the precipitation of decomposition products such as gasified tar. In the preliminary carbonization treatment, decomposition products such as hydrogen cyanide, ammonia, nitrogen, water, carbon dioxide, and gasified tar are generated. Among the tar components, there are compounds having melting points and boiling points near 300°C. Since most of the tar components are generated at temperatures higher than 300°C in the atmosphere, if the decomposition gas is prevented from moving from the generation location to a location where the atmosphere temperature is less than 300°C and is not discharged outside the furnace through the exhaust port (8) from a location where the atmosphere temperature is 300°C or higher, there is a risk of tar component precipitation. Since the preliminary carbonization treatment gradually raises the treatment temperature, the inert atmosphere temperature on the unloading side of the heat treatment chamber (4) is higher than that on the loading side. In order to prevent the decomposition gas generated at an atmosphere temperature of 300°C or higher from moving to the loading side where the temperature is less than 300°C, the position (P) on the outermost unloading side in the machine length direction where the atmosphere temperature in the heat treatment furnace becomes 300°C 300The flow of the in-furnace atmosphere up to [the specified point] must be only in the co-current direction with respect to the traveling direction of the fiber bundle. If there is a counter-current flow, there is a risk that the tar component will move to a location where the temperature is less than 300 °C and precipitate. The position (P where the atmospheric temperature becomes 300 °C 300 In order for the flow of the inert atmosphere up to [the specified point] to be in the co-current direction with respect to the traveling direction of the fiber bundle, it is preferable that there is a supply port (6) for the inert gas at a location where the atmospheric temperature is less than 300 °C, and an exhaust port (8) at a location where the atmospheric temperature is 300 °C or higher. It is more preferable that there is an exhaust port (8) at a location where the atmospheric temperature is 350 °C or higher. From the supply port (6) of the inert gas on the inlet side to the position (P where the atmospheric temperature becomes 300 °C 300 An example where the flow of the inert atmosphere up to [the specified point] is only in the co-current direction with respect to the traveling direction of the fiber bundle is shown in Fig. 2. From the supply port (6) of the inert gas on the inlet side to the position (P where the atmospheric temperature becomes 300 °C 300 An example where there are two directions, the co-current direction and the counter-current direction, of the flow of the inert atmosphere on the inlet side up to [the specified point] with respect to the traveling direction of the fiber bundle is shown in Fig. 3. It is more preferable that the flow of the inert atmosphere from the supply port (6) of the inert gas on the inlet side to the exhaust port (8) shown in Fig. 4 is only in the co-current direction with respect to the traveling direction of the fiber bundle.

[0021] Since the flow of the inert atmosphere in the heat treatment furnace changes with temperature, if there is a temperature difference in the vertical direction in the atmosphere of the heat treatment chamber (4), the hot atmosphere will stay at the upper part due to buoyancy, and the colder atmosphere will stay at the lower part. At that time, there is a risk that the decomposition products such as tar gasified will stay in the heat treatment chamber (4) without reaching the exhaust port (8), and the flow of the inert atmosphere will move in the counter-current direction with respect to the traveling direction of the fiber bundle and the tar component will precipitate. Therefore, it is desirable that there is no large deviation between the atmospheric temperature in the heat treatment chamber (4) and the supply temperature of the inert gas introduced into the furnace. In the longitudinal direction of the heat treatment chamber (4), the atmospheric temperature at the fiber bundle height at the central position (13) in the longitudinal direction of the section closest to the inlet side is T 1 [°C], and in the longitudinal direction of the heat treatment chamber (4), the atmospheric temperature at the fiber bundle height at the central position (14) in the longitudinal direction of the section closest to the outlet side is T 2When [°C], it is preferable that the temperature of the inert gas supplied to the heat treatment furnace satisfies the following two conditions. Inert gas supply temperature range at the inlet side [°C]: |T 1 -(Inlet side inert gas supply temperature)| = ΔT 1 ≤ 50 °C. Inert gas supply temperature range at the outlet side [°C]: |T 2 -(Outlet side inert gas supply temperature)| = ΔT 2 ≤ 100 The ambient temperature at the central position (13) is appropriate as the ambient temperature of the heat treatment chamber (4) for comparing with the inlet side inert gas supply temperature. Also, similarly, the supply temperature of the inert gas at the outlet side is appropriate as the ambient temperature at the central position (14).

[0022] Furthermore, for the flow of the inert atmosphere in the heat treatment furnace, the flow rate balance of the inert gas at the inlet side and the outlet side is important. The absolute value ratio (|V 1 | / |V 2 |) of the horizontal flow rate of the inert atmosphere at the inlet side and the outlet side is preferably 0.5 or more and 2.0 or less (0.5 ≤ |V 1 | / |V 2 | ≤ 2.0). When the absolute value ratio |V 1 | / |V 2 | of the horizontal flow rate of the inert atmosphere at the inlet side (V1) and the outlet side (V2) is within the above preferable range, the inert gas supplied from the outlet side is exhausted to the exhaust port without flowing back to the inlet side, and there is no risk of the tar component flowing into the inlet side. When the flow of the inert gas is in the same direction as the running direction of the yarn, the values of V 1 and V 2 become positive values, and when it is in the opposite direction to the running direction of the yarn, V 1Also, assume that the values of V1 and V2 are negative. The flow velocity ratio is preferably the actual flow velocity. The positions serving as the flow velocity reference on the loading side and the unloading side are preferably the central position (13) in the machine length direction of the section closest to the loading side on the loading side, and the central position (14) in the machine length direction of the section closest to the unloading side on the unloading side. The flow velocity of the inert atmosphere in the horizontal direction at the positions (13 and 14) is preferably calculated from the flow rate of the supplied inert gas and the wind speed at the openings of the loading port (2) and the unloading port (3) of the heat treatment furnace.

[0023] The pre-carbonized fiber bundle is carbonized in an inert atmosphere at 1,000°C to 2,000°C to obtain a carbonized fiber bundle.

[0024] The carbon fiber bundle may be subjected to electrolytic oxidation treatment or oxidation treatment as needed for the purpose of improving the affinity and adhesiveness with the fiber-reinforced composite material matrix resin.

Example

[0025] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. The various measurement methods used in the examples are as follows.

[0026] <Dynamic pressure measurement> A straight-type Pitot tube (manufactured by Okano Seisakusho, product name: two-hole Pitot tube, made-to-order product, outer diameter: Φ10 mm) connected to a digital differential pressure gauge (manufactured by testo, product name: testo512-3, measurement range: 0 Pa to 200 Pa) was inserted into the furnace from the opening (11) of the loading port, and pressure measurements were taken at five measurement points (three points in the machine width direction and three points in the height direction) (12) on the cross-section of the furnace in the machine length direction shown in FIG. 5 by moving the tip of the Pitot tube parallel to the machine length direction. The total pressure was measured at the tip of the Pitot tube and the static pressure was measured on the side surface, and the presence or absence of dynamic pressure was determined from the pressure difference. When no dynamic pressure was detected up to the position (P 300 ) where the ambient temperature was 300°C, it was assumed that the flow of the inert atmosphere was only in the co-current direction with respect to the traveling direction of the fiber bundle. When dynamic pressure was detected, it was determined that there were two directions, the co-current direction and the counter-current direction, in the flow of the inert atmosphere with respect to the traveling direction of the fiber bundle.

[0027] <Measurement of Inert Atmosphere Temperature inside Heat Treatment Furnace> A sheathed thermocouple (manufactured by Fukuden, outer diameter: Φ1.6 mm, material: SUS316) was attached to a wire stretched across the opening (11) from the loading port to the unloading port, and at five measurement points (12) in the cross-section of the heat treatment furnace in the machine length direction shown in Fig. 5, the tip of the thermocouple at the measurement site was moved in the machine length direction to measure the atmosphere temperature (measurement interval was every 100 mm). Also, when measuring the atmosphere temperature at the height of the fiber bundle, the wire to which the thermocouple was attached was set to the height of the fiber bundle, and the tip of the thermocouple was aligned with the measurement point to measure three points in the machine width direction shown in Fig. 6. Weights were attached to the tip of the wire to apply tension so that the wire and thermocouple would not sag.

[0028] <Flow Velocity (V 1 and V 2 ) Calculation Method of Horizontal Inert Atmosphere inside Heat Treatment Furnace> The wind speed in the immediate vicinity of the opening (11) of the loading port (2) was measured at three measurement points (12) in the machine width direction shown in Fig. 6 using a high-temperature anemometer (manufactured by Nippon Kanomax, product number: 6162, heat-resistant temperature: 500 °C). The average value of the measurement results for 15 seconds was taken as the wind speed (V out ) of the inert atmosphere flowing out of the opening (11) to the outside of the furnace. From the measured wind speed (V out ) and the area of the opening, the flow rate of the inert atmosphere per unit time flowing out of the opening (11) to the outside of the furnace was obtained, and from the difference in the flow rate of the inert atmosphere per unit time from the inert gas supply port on the loading side, the flow rate per unit time in the traveling direction of the fiber bundle inside the heat treatment furnace was calculated. From the flow rate and the cross-sectional area in the machine length direction of the heat treatment furnace (1), the flow velocity (V 1 ) of the horizontal inert atmosphere on the loading side was calculated. The flow velocity (V 2 ) of the horizontal inert atmosphere on the unloading side was also calculated in the same manner.

[0029] <Carbon Fiber Bundle Fuzz Quality Standard> The criteria for judging the quality in the examples and comparative examples were as follows respectively. Excellent: The number of flyings of 10 mm or more on the fiber bundle that can be visually confirmed after the preliminary carbonization process is five or less per meter on average, and the flying quality is at a level that does not affect the process throughput or the high-order processability of the product at all. Good: The number of flyings of 10 mm or more on the fiber bundle that can be visually confirmed after the preliminary carbonization process is more than five per meter on average and less than ten per meter on average, and the flying quality is at a level that hardly affects the process throughput or the high-order processability of the product. Poor: The number of flyings of 10 mm or more on the fiber bundle that can be visually confirmed after the preliminary carbonization process is ten or more per meter on average, and the flying quality is at a level that adversely affects the process throughput or the high-order processability of the product.

[0030] <Environmental Standards for Heat Treatment Furnace Interior and Exhaust Duct> The judgment criteria for the environment of the heat treatment furnace interior and exhaust duct in the examples and comparative examples were as follows, respectively. Excellent: There is no trace of tar component solidifying and adhering in the heat treatment furnace interior or exhaust duct, and it is at a level that does not affect the operation at all. Good: There is a small amount of trace of tar component solidifying and adhering in the heat treatment furnace interior or exhaust duct, and it is at a level that hardly affects the operation. Poor: There is a large amount of trace of tar component solidifying and adhering in the heat treatment furnace interior or exhaust duct, and blockage of the furnace interior and duct occurs, causing problems in the operation.

[0031] <Example 1> A fiber bundle composed of 20,000 single fibers with a single fiber fineness of 0.11 tex was aligned with 100 fibers, and a flame-retardant fiber bundle heat-treated at 240°C to 280°C in air was continuously passed through a heat treatment furnace with an effective heat treatment length of 4 m in the shape shown in Fig. 1 at a yarn speed of 1.0 m / min while maintaining the maximum temperature at 700°C to obtain a preliminary carbon fiber bundle. Nitrogen was used as the inert gas filling the heat treatment furnace, and it was preheated on both the inlet side and the outlet side and supplied from the inert gas supply ports provided respectively, and the ambient temperature at the exhaust port position was set at 500°C. The obtained preliminary carbon fiber bundle was then heat-treated at a maximum temperature of 1,500°C in a carbonization furnace, and sizing agent was applied after electrolytic surface treatment to obtain a carbon fiber bundle.

[0032] At this time, based on the dynamic pressure measurement results, the position (P 300 ) on the outermost side in the machine length direction where the ambient temperature in the heat treatment furnace becomes 300 °C 1 ) to the inert gas supply port on the inlet side, it was determined that the flow of the inert atmosphere was only in the co-current direction with respect to the traveling direction of the fiber bundle. Also, the difference (ΔT 1 ) between the ambient temperature (T 2 ) at the height of the fiber bundle at the center position in the machine length direction of the section on the outermost inlet side and the supply temperature of nitrogen on the inlet side was 150 °C, and the difference (ΔT 2 ) between the ambient temperature (T 1 ) at the height of the fiber bundle at the center position in the machine length direction of the section on the outermost outlet side and the supply temperature of nitrogen on the outlet side was 150 °C. The absolute value ratio (|V 2 | / |V

[0033] <Example 2> The nitrogen preheating temperature was set so that the difference (ΔT 1 ) between the ambient temperature (T 1 ) at the height of the fiber bundle at the center position in the machine length direction of the section on the outermost inlet side and the supply temperature of nitrogen on the inlet side became 40 °C, and the nitrogen supply temperature was set so that the difference (ΔT 2 ) between the ambient temperature (T 2 ) at the height of the fiber bundle at the center position in the machine length direction of the section on the outermost outlet side and the supply temperature of nitrogen on the outlet side became 80 °C, and otherwise it was the same as in Example 1. Under the above conditions, no major problems occurred during production, and continuous operation was carried out for 10 days. Also, as a result of visually checking the obtained pre-carbon fiber bundle and carbon fiber bundle, the hairiness quality of the carbon fiber bundle was good according to the above judgment criteria, the environment in the furnace and the exhaust duct was good, and the exhaust duct was not blocked.

[0034] <Example 3> The absolute value ratio (|V 1 | / |V2 Except that the flow rate of nitrogen on the inlet side was set to 1.5, the procedure was the same as in Example 2. During production under the above conditions, no serious problems occurred, and continuous operation was carried out for 10 days. Further, as a result of visually inspecting the obtained preliminary carbon fiber bundle and carbon fiber bundle, the hairiness quality of the carbon fiber bundle was excellent according to the above criteria, the environment in the furnace and the exhaust duct was also excellent, and there was no deposit in the exhaust duct.

[0035] <Example 4> The ambient temperature (T 1 ) of the height of the fiber bundle at the center position in the machine length direction in the section closest to the inlet side and the difference (ΔT 1 ) between the supply temperature of nitrogen on the inlet side were set to 150 °C. Except for this, the procedure was the same as in Example 3. During production under the above conditions, no serious problems occurred, and continuous operation was carried out for 10 days. Further, as a result of visually inspecting the obtained preliminary carbon fiber bundle and carbon fiber bundle, the hairiness quality of the carbon fiber bundle was excellent according to the above criteria, the environment in the furnace and the exhaust duct was good, and the exhaust duct was not blocked.

[0036] <Comparative Example 1> When the absolute value ratio (|V 1 | / |V 2 ) of the flow velocity of the inert atmosphere in the horizontal direction between the inlet side and the outlet side was set to 0.5 by setting the flow rate of nitrogen on the inlet side, according to the dynamic pressure measurement results, it was determined that there were two directions of the flow of the inert atmosphere from the position (P 300 ) closest to the outlet side in the machine length direction where the ambient temperature in the heat treatment furnace was 300 °C to the inert gas supply port on the inlet side, namely, the forward flow direction and the countercurrent direction to the traveling direction of the fiber bundle. Except for the above, the procedure was the same as in Example 3. However, under the above conditions, during production, the pressure inside the heat treatment furnace for performing the preliminary carbonization treatment constantly increased, and decomposition products such as tar gasified from the openings of the inlet and outlet ports spurted out, and it was determined that operation was impossible, so the machine was stopped. As a result of visually inspecting the obtained preliminary carbon fiber bundle and carbon fiber bundle, the hairiness quality of the carbon fiber bundle was poor according to the above criteria, the environment in the furnace and the exhaust duct was also poor, and the exhaust duct was blocked.

[0037]

Table 1

Industrial Applicability

[0038] The present invention can be suitably used for the production of carbon fiber bundles. The flame-retardant fiber bundles and carbon fiber bundles obtained by the present invention can be suitably applied to aircraft applications, industrial applications such as pressure vessels and wind turbines, sports applications such as golf shafts, etc., but the scope of application is not limited to these.

Explanation of Signs

[0039] 1 Heat treatment furnace for performing pre-carbonization treatment 2 Loading port of the heat treatment furnace for performing pre-carbonization treatment 3 Unloading port of the heat treatment furnace for performing pre-carbonization treatment 4 Heat treatment chamber of the heat treatment furnace for performing pre-carbonization treatment 5 Fiber bundle 6 Inert gas supply port 7 Heater 8 Exhaust port 9 Exhaust duct 10 Exhaust gas treatment device 11 Opening of the loading port of the heat treatment furnace for performing pre-carbonization treatment 12 Measuring point for each measurement 13 Central position in the longitudinal direction of the section closest to the loading side inside the heat treatment furnace for performing pre-carbonization treatment 14 Central position in the longitudinal direction of the section closest to the unloading side inside the heat treatment furnace for performing pre-carbonization treatment P 300 Position closest to the unloading side in the longitudinal direction where the ambient temperature inside the heat treatment furnace becomes 300 °C

Claims

1. A method for producing a carbon fiber bundle, comprising: a flameproofing step of heat-treating an acrylic fiber bundle in an oxidizing atmosphere at a temperature in the range of 200°C to 300°C; a heat treatment furnace having one or more inert gas supply ports on each of the inlet side and the outlet side of the fiber bundle, and having one or more exhaust ports between the inert gas supply ports on the inlet side and the outlet side, and performing heat treatment at a temperature in the range of 300°C to 1,000°C with the supply temperature of the inert gas being higher on the outlet side than on the inlet side; and a carbonization step of heat-treating in an inert gas atmosphere at a temperature in the range of 1,000°C to 2,000°C, wherein from the position on the most outlet side in the machine length direction where the atmospheric temperature in the heat treatment furnace becomes 300°C to the inert gas supply port on the inlet side, the flow of the inert atmosphere in the heat treatment furnace in the preliminary carbonization step is only a co-current flow with respect to the traveling direction of the fiber bundle in the machine length direction.

2. The preliminary carbonization process is carried out in a heat treatment furnace having three or more temperature-controllable sections in the machine length direction, and the atmospheric temperature at the fiber bundle height at the center position in the machine length direction of the section closest to the inlet side in the machine length direction of the heat treatment chamber is set to T １ [°C], the atmospheric temperature at the fiber bundle height at the center position in the longitudinal direction of the section closest to the discharge side in the longitudinal direction of the heat treatment chamber is T ２ 2. The method for producing a carbon fiber bundle according to claim 1, wherein the temperature of the inert gas supplied to the heat treatment furnace satisfies the following two conditions when expressed in [° C.]: Inlet-side inert gas supply temperature range [°C]: |T １ − (Inlet-side inert gas supply temperature)| = ΔT １ ≤ 50 Unloading side inert gas supply temperature range [°C]: |T ２ -(Unloading side inert gas supply temperature)| = ΔT ２ ≦100

3. The cross-sectional area in the machine length direction of the heat treatment furnace in the preliminary carbonization process is substantially the same, and the flow velocity V described below １ and the flow velocity V described below ２ The absolute value ratio of (|V １ | / |V ２ |) is 0.5 ≤ |V １ | / |V ２ | ≤ 2.

0. The method for producing a carbon fiber bundle according to claim 1 or 2 V １ [m / s]: The flow velocity of the inert atmosphere in the horizontal direction at the central position in the machine length direction of the section that is the most infeed side with respect to the machine length direction of the heat treatment chamber V ２ [m / s]: The flow velocity of the inert atmosphere in the horizontal direction at the central position in the machine length direction of the section that is the most outfeed side with respect to the machine length direction of the heat treatment chamber

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