Method for manufacturing preliminary carbon fiber bundle, method for manufacturing carbon fiber bundle, and preliminary carbonization furnace

Abstract

The present invention addresses the problem of providing: a production method and a precarbonization furnace, which are for a precarbonized fiber bundle and which enable production of a precarbonized fiber bundle continuously over a long period of time by efficiently discharging, from an entire heat treatment chamber, a tar component-containing decomposition gas that is generated during precarbonization in production of carbon fibers and resides in the heat treatment chamber. This production method for a precarbonized fiber bundle comprises: precarbonizing one or more levels of aligned flameproofed fiber bundles by vertically arranging and horizontally moving, in the heat treatment chamber, the flameproofed fiber bundles, and subjecting the flameproofed fiber bundles to a heat treatment at a maximum temperature of 300-1,000°C using an inert gas supplied from the inlet side and outlet side of the heat treatment chamber. A flow rate ratio Q2 / Q1 satisfies formula (1), where Q1 represents a gas volume flow rate of a first exhaust gas discharged out of the heat treatment chamber from a position higher than that of the flameproofed fiber bundle moving in the uppermost level, and Q2 represents a gas volume flow rate of a second exhaust gas discharged out of the heat treatment chamber from a position lower than that of the flameproofed fiber bundle moving in the uppermost level.　Formula (1): 0.01 ≤ Q2 / Q1 ≤ 0.5

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a pre-carbon fiber bundle and a pre-carbonization furnace that can be continuously manufactured for a long period by efficiently exhausting decomposition gas containing tar components staying in a heat treatment chamber when performing a pre-carbonization treatment during carbon fiber production.

Background Art

[0002] Since carbon fiber is excellent in specific strength, specific 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.

[0003] Generally, as a method for manufacturing a carbon fiber bundle from an acrylic fiber bundle, (i) a fiber bundle in which thousands to tens of thousands of single fibers of an acrylic polymer are bundled is fed into a flame-retardant furnace and exposed to hot air in an oxidizing atmosphere such as air heated to 200 to 300 °C supplied from a hot air supply nozzle installed in the furnace for heat treatment (flame-retardant treatment), and then (ii) the obtained flame-retardant fiber bundle is fed into a pre-carbonization furnace and heat-treated (pre-carbonization treatment) in an inert gas atmosphere at 300 to 1,000 °C, and then (iii) further heat-treated (carbonization treatment) in a carbonization furnace filled with an inert gas atmosphere at 1,000 °C or higher is known. Further, the flame-retardant fiber bundle as an intermediate material is also widely used as a material for flame-retardant woven fabrics by taking advantage of its flame-retardant performance.

[0004] In the pre-carbonization furnace of (ii) above, HCN, NH 3 , N 2 , H 2 , H 2, and gasified decomposition products such as tar are generated. Therefore, it is common to provide a gas outlet in the furnace to discharge these decomposition products. Among these decomposition products, especially the tar component adheres to the inner wall of the heat treatment chamber. When it accumulates beyond a certain amount, it falls onto the running flame-resistant fiber bundle, leading to a decrease in physical properties such as an increase in fluff, occurrence of thread breakage, and a decrease in the quality and productivity of the obtained carbon fiber. In addition, this tar component accumulates on the inner wall of the duct until the exhaust gas is sent to the device for decomposing or burning the exhaust gas from the exhaust port, resulting in the problem of blocking the line and shortening the continuous manufacturing period.

[0005] In order to solve these problems, Patent Document 1 describes that an exhaust port is formed on the upper wall surface of the heat treatment chamber at a position where the temperature setting in the heat treatment chamber reaches the maximum temperature, a position where the vaporized tar component does not condense in the furnace, or a temperature region where a large amount of tar component is generated from the flame-resistant fiber bundle, so that the exhaust gas can be discharged smoothly.

[0006] Also, Patent Document 2 describes that one or more exhaust ports are provided on the side wall of the heat treatment chamber, and the exhaust ports are provided in a region biased above the running height of the flame-resistant fiber bundle that runs, so that the gas containing the tar component staying in the furnace adheres and accumulates, and does not fall onto the flame-resistant fiber bundle running from the upper wall surface of the heat treatment chamber, thereby preventing the fouling of the flame-resistant fiber bundle.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, according to the findings of the present inventors, in Patent Document 1, since it is impossible to completely prevent the tar component from adhering to the vicinity of the exhaust port on the upper wall surface of the heat treatment chamber, it is necessary to frequently clean the exhaust port so that the fixed tar component does not fall onto the fiber bundle to be processed.

[0009] Further, the exhaust method described in Patent Document 2 is effective for exhausting the decomposition gas staying in a region higher than the traveling region of the flame-retardant fiber bundle, but it is expected that the exhaust efficiency of the gas staying in a region lower than the traveling region of the flame-retardant fiber bundle will be low, and it is not effective for exhausting the gas containing the tar component in the whole furnace.

[0010] Therefore, an object of the present invention is to provide a method for manufacturing a pre-carbonized fiber bundle and a pre-carbonization furnace that can be continuously manufactured for a long period by efficiently exhausting the decomposition gas containing the tar component generated during the pre-carbonization treatment in the manufacture of carbon fibers and staying in the heat treatment chamber throughout the heat treatment chamber.

Means for Solving the Problems

[0011] The method for manufacturing a pre-carbonized fiber bundle of the present invention for solving the above problems has the following configuration. That is, in the method for manufacturing a pre-carbonized fiber bundle in which a flame-retardant fiber bundle aligned along a horizontal plane is run horizontally in a heat treatment chamber in one stage or two or more stages arranged in the vertical direction, and heat-treated at a maximum temperature of 300 to 1,000 ° C. by an inert gas supplied from the loading side and the unloading side of the heat treatment chamber for pre-carbonization, the gas volume flow rate of the first exhaust exhausting to the outside of the heat treatment chamber from a position higher than the position of the flame-retardant fiber bundle running in the uppermost stage is Q1, and the gas volume flow rate of the second exhaust exhausting to the outside of the heat treatment chamber from a position lower than the position of the flame-retardant fiber bundle running in the uppermost stage is Q2. When the flow rate ratio Q2 / Q1 satisfies the following formula (1), pre-carbonization is performed. This is a method for manufacturing a pre-carbonized fiber bundle.

[0012] 0.01 ≦ Q2 / Q1 ≦ 0.5 Formula (1) Further, the method for manufacturing a carbon fiber bundle of the present invention has the following configuration. That is, it is a method for manufacturing a carbon fiber bundle in which the preliminary carbon fiber bundle obtained by the above method for manufacturing a preliminary carbon fiber bundle is carbonized at a maximum temperature of 1,000 to 2,000 °C in an inert gas.

[0013] Furthermore, the preliminary carbonization furnace of the present invention has the following configuration. That is, a heat treatment chamber for pre-carbonizing a flame-resistant fiber bundle aligned along a horizontal plane in one stage or two or more stages arranged vertically and running horizontally at a maximum temperature of 300 to 1,000 °C in an inert gas to obtain a preliminary carbon fiber bundle, a slit-shaped opening for carrying the flame-resistant fiber bundle into the heat treatment chamber and carrying the preliminary carbon fiber bundle out of the heat treatment chamber, an inert gas supply port for supplying inert gas into the heat treatment chamber provided on the carrying-in side of the flame-resistant fiber bundle and the carrying-out side of the preliminary carbon fiber bundle, respectively, a first exhaust port provided at a position higher than the position of the flame-resistant fiber bundle running on the uppermost stage, a second exhaust port provided at a position lower than the position of the flame-resistant fiber bundle running on the uppermost stage, and a mechanism for adjusting the flow rate ratio Q2 / Q1 when the gas volume flow rate discharged from the first exhaust port is Q1 and the gas volume flow rate discharged from the second exhaust port is Q2.

Advantages of the Invention

[0014] According to the present invention, by efficiently exhausting the decomposition gas containing tar components generated during the preliminary carbonization treatment during carbon fiber production and staying in the heat treatment chamber throughout the heat treatment chamber, the preliminary carbon fiber bundle can be continuously produced for a long period of time.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 to 10. The drawings are conceptual diagrams for accurately conveying the gist of the present invention and are simplified diagrams. Therefore, the preliminary carbonization furnace used in the present invention is not particularly limited to the form shown in the drawings, and for example, its dimensions and the like can be changed according to the embodiments.

[0017] The present invention is a method for producing a preliminary carbon fiber bundle by subjecting a flame-resistant fiber bundle to preliminary carbonization treatment in an inert gas at a maximum temperature of 300 to 1,000°C, which is carried out in a preliminary carbonization furnace through which an inert gas flows. As the inert gas filling the inside of the preliminary carbonization furnace, known inert gases such as nitrogen, argon, and helium can be adopted, but nitrogen is preferable from the viewpoint of economy. Further, the flame-resistant fiber bundle obtained by heat-treating an acrylic fiber bundle in an oxidizing gas is preferably used in the present invention.

[0018] First, the conventional pre-carbonization furnace will be described with reference to FIG. 8. The arrows in the drawings indicate the flow of the inert gas or exhaust gas in the heat treatment chamber. The pre-carbonization furnace 1 has a heat treatment chamber 3 for heat-treating the flame-resistant fiber bundle 2 running in the horizontal direction in an inert gas. The flame-resistant fiber bundle 2 is carried in and out through a slit-shaped opening 4 provided in the heat treatment chamber 3. Although not shown in the drawings, those having a sealing mechanism such as a labyrinth seal structure are preferably used to prevent the inflow of oxygen and the like into the heat treatment chamber. Further, the flame-resistant fiber bundle 2 has a wide sheet-like form in which a plurality of bundles are aligned in parallel in a direction perpendicular to the plane of the paper. While the flame-resistant fiber bundle 2 is running in the heat treatment chamber 3, it is heat-treated by the inert gas supplied from the inert gas supply ports 5 provided on both the carry-in side and the carry-out side of the heat treatment chamber. The supplied inert gas and the decomposition gas generated from the flame-resistant fiber bundle 2 due to carbonization are extracted from the exhaust port 6 formed in the heat treatment chamber, passed through the exhaust duct 7, and sent to the combustion or exhaust gas treatment device 8 for combustion or decomposition treatment. In the drawings, the inert gas supply port 5 is arranged on the bottom surface side of the heat treatment chamber, but it may also be on the upper surface side of the heat treatment chamber, and it may be supplied from a plurality of locations instead of one location on each of the carry-in side / carry-out side.

[0019] The pre-carbonization furnace used in the pre-carbonization treatment of the present invention is used in the temperature range of 300 to 1,000 °C, and further preferably has a temperature distribution that becomes higher in sequence from the carry-in port to the carry-out port of the flame-resistant fiber bundle 2. In this pre-carbonization furnace, with the carbonization of the flame-resistant fiber bundle 2, HCN, NH 3 , N 2 , H 2 O, CO 2and gasified decomposition products such as tar are generated. Among these decomposition products, in particular, the tar content is known to adhere to the inner wall of the heat treatment chamber. Fig. 9 shows a cross-sectional view taken along the line A-A in Fig. 8 as seen from the arrow. When discharging the decomposition gas containing tar from the exhaust port 6 provided on the upper surface of the heat treatment chamber, the tar content adheres to the periphery of the exhaust port 6 and the inner wall of the exhaust duct 7. When this accumulates above a certain amount, it falls onto the running flame-resistant fiber bundle 2, leading to a decrease in physical properties such as an increase in fluff, yarn breakage, etc., resulting in a decrease in the quality and productivity of the obtained carbon fiber. Also, since the exhaust from the upper surface of the heat treatment chamber 3, the exhaust efficiency of the gas staying in the region lower than the flame-resistant fiber bundle 2 becomes low. As a result, the tar content adheres and accumulates on the bottom surface of the heat treatment chamber 3, requiring frequent cleaning and reducing the production efficiency.

[0020] Next, another conventional pre-carbonization furnace is shown in Fig. 10. Fig. 10 is the same as the pre-carbonization furnace shown in Fig. 8 except that the exhaust port 6 is provided on the bottom surface of the heat treatment chamber. Similar to Fig. 8, the flow of the inert gas or exhaust gas is shown. When the exhaust port 6 is provided on the bottom surface of the heat treatment chamber, since the temperature of the inert gas flowing from the carry-out side of the pre-carbonization furnace is higher than the temperature of the inert gas flowing from the carry-in side, buoyancy acts due to the density difference and stays in the upper part of the furnace. The exhaust gas containing tar flowing from the carry-out side passes through the exhaust port 6 and once flows into the carry-in side, and then a flow path is formed again toward the exhaust port. At this time, the exhaust gas containing tar flowing from the carry-out side is exposed to the low-temperature part on the carry-in side, causing the tar content to adhere and accumulate on the inner wall of the heat treatment chamber 3. As a result, similar to the case where the exhaust port 6 is provided on the upper surface of the heat treatment chamber 3, the accumulated tar content falls onto the flame-resistant fiber bundle 2, not only causing a decrease in the quality and productivity of the obtained carbon fiber, but also the tar content accumulated on the inner wall of the heat treatment chamber flows into the exhaust duct 7 and accumulates on the duct inner wall, blocking the line and shortening the continuous manufacturing period.

[0021] Therefore, the inventors have found that it is difficult to completely prevent the adhesion and deposition of tar components contained in the decomposition gas by simply providing the exhaust port 6 on either the upper surface or the bottom surface of the heat treatment chamber, that is, at a position higher or lower than the traveling flame-resistant fiber bundle 2. The method for manufacturing a pre-carbon fiber bundle of the present invention has been intensively studied with respect to the above problems, and enables the continuous production of high-quality pre-carbon fiber bundles for a long period of time.

[0022] Hereinafter, the method for manufacturing a pre-carbon fiber bundle and a pre-carbonization furnace of the present invention will be described with reference to FIGS. 1 and 2. In the embodiment of the present invention shown in FIGS. 1 and 2, the aligned flame-resistant fiber bundles are arranged in one or more stages in the vertical direction and run horizontally in the heat treatment chamber, and are heat-treated at a maximum temperature of 300 to 1,000 ° C. by inert gas supplied from the loading side and the unloading side of the heat treatment chamber to be pre-carbonized. In the method for manufacturing a pre-carbon fiber bundle, when the gas volume flow rate of the first exhaust gas exhausted from outside the heat treatment chamber at a position higher than the flame-resistant fiber bundle running in the uppermost stage is Q1, and the gas volume flow rate of the second exhaust gas exhausted from outside the heat treatment chamber at a position lower than the flame-resistant fiber bundle running in the uppermost stage is Q2, the flow rate ratio Q2 / Q1 is set to satisfy the following formula (1).

[0023] 0.01 ≦ Q2 / Q1 ≦ 0.5 Formula (1) Here, the uppermost flame-resistant fiber bundle in the present invention refers to the flame-resistant fiber bundle running at the highest position in the height direction of the heat treatment chamber. In FIG. 2, since the traveling flame-resistant fiber bundle 2 is in one stage in the height direction of the heat treatment chamber, the uppermost flame-resistant fiber bundle is the flame-resistant fiber bundle 2 shown in the figure. However, for example, in the case where the flame-resistant fiber bundle is divided into a plurality of stages in the height direction (vertical direction) of the heat treatment chamber and run, the first and second exhaust ports are provided with reference to the height of the flame-resistant fiber bundle running in the uppermost stage, that is, the flame-resistant fiber bundle 2 running at the highest position in the height direction of the heat treatment chamber.

[0024] In addition, the preliminary carbonization furnace used in the preliminary carbonization treatment of the present invention is used in the range of a maximum temperature of 300 to 1,000 °C, and further, it preferably has a temperature distribution that becomes higher in temperature sequentially from the inlet to the outlet of the refractory fiber bundle 2.

[0025] According to the study by the present inventors, as will be clear from the following examples, by setting the flow rate ratio of the volume flow rates Q1 and Q2 of the discharged gas within the above range, the adhesion and deposition of the tar content contained in the cracked gas, which was a problem in the prior art, can be made extremely small throughout the heat treatment chamber, and it becomes possible to continuously produce a high-quality preliminary carbon fiber bundle for a long period of time.

[0026] Furthermore, in order to enable continuous operation for a long time, it is preferable that the flow rate ratio Q2 / Q1 of the gas volume flow rate Q1 of the first exhaust and the gas volume flow rate Q2 of the second exhaust satisfies the following formula (2).

[0027] 0.01 ≦ Q2 / Q1 ≦ 0.3 Formula (2) Thereby, the adhesion and deposition of the tar content can be minimized, and the production efficiency is improved.

[0028] Here, as a method for adjusting the volume flow rates Q1 and Q2 of the gas discharged from each discharge port, the pressure loss may be changed and adjusted by changing the length of each exhaust duct or by providing an orifice plate or the like to change the cross-sectional area. However, more simply, it is preferable to install an adjustment valve 11 such as a damper and adjust it as appropriate. Also, regarding the volume flow rate of the gas discharged from each discharge port, a measurement hole may be provided in the exhaust duct connected to each discharge port, an anemometer may be inserted, and the gas volume flow rate may be calculated from the obtained measured value of the wind speed and the cross-sectional area of the exhaust duct. Regarding the position of the measurement hole provided in the exhaust duct 7, it is preferably provided immediately after each exhaust port. However, when heat insulation measures are taken such as providing a heat insulating material in the exhaust duct and the temperature change from the temperature of the gas at the exhaust port is substantially zero, the volume flow rate may be obtained by providing the measurement hole at a position downstream from the exhaust port.

[0029] Furthermore, in order to minimize the adhesion and deposition of tar components, the first exhaust and the second exhaust are preferably performed at a position where the temperature inside the heat treatment chamber is 350 to 550 °C, that is, the first and second exhaust ports are provided at positions where the temperature inside the heat treatment chamber is 350 to 500 °C in the longitudinal direction of the heat treatment chamber. Since the thermal decomposition of the flame-resistant fiber bundle 2 proceeds rapidly in the above temperature range and it is a region where the generation of decomposition gas containing tar components is significant, it is possible to discharge to the outside of the heat treatment chamber 3 in the immediate vicinity of the location where the tar components are generated, and it is possible to reduce the adhesion of tar components into the heat treatment chamber 3 more effectively.

[0030] At this time, for the temperature measurement inside the heat treatment chamber, for example, a non-combustible wire such as a wire with a temperature sensor such as a sheathed thermocouple attached inside the heat treatment chamber can be stretched, and the position of the exhaust port can be adjusted so that it is within the above temperature range.

[0031] Next, another embodiment of the present invention is shown in FIG. 3. In FIG. 3, the first exhaust port 9 is configured to be provided at two locations on the upper surface of the heat treatment chamber 3 in the non-running region 13 of the flame-resistant fiber bundle. The non-running region of the flame-resistant fiber bundle means a region in the heat treatment chamber 3 where the flame-resistant fiber bundle is not running. That is, when the heat treatment chamber is viewed from the upper surface to the lower surface, it is a region inside the heat treatment chamber where the flame-resistant fiber bundle cannot be observed from the upper surface to the lower surface. For example, as shown in FIG. 3, in the width direction inside the heat treatment chamber 3, it refers to the region surrounded between one end of the running flame-resistant fiber bundle 2 and the side wall of the heat treatment chamber 3, and in the height direction, between the bottom surface and the upper surface of the heat treatment chamber 3. By adopting such a configuration, even when tar components adhere and deposit on the inner walls of the first exhaust port 9 and each exhaust duct, it is possible to prevent troubles such as an increase in fluff, yarn breakage, and a decrease in physical properties without falling onto the running flame-resistant fiber bundle 2.

[0032] Also, the first discharge port 9 and the second discharge port 10 do not necessarily have to be provided on the upper surface and the bottom surface of the heat treatment chamber 3 respectively. As long as they are provided at positions higher and lower than the uppermost heat-resistant fiber bundle 2 respectively, for example, as shown in FIG. 4, either the first discharge port 9 or the second discharge port 10 may be provided on the side surface of the heat treatment chamber 3, and even if both of them are provided on the side surface of the heat treatment chamber 3, the effects of the present invention will not change at all.

[0033] Next, FIG. 5 shows another embodiment of the present invention. In FIG. 5, in the longitudinal direction of the heat treatment chamber 3, an additional inert gas supply port 12 for vertically upward supplying inert gas is provided on the bottom surface of the heat treatment chamber between the inert gas supply port 5 on the loading side and the first and second exhaust ports. In FIG. 5, the first and second exhaust ports are provided at the same position in the longitudinal direction of the heat treatment chamber 3. However, when the first and second exhaust ports are provided at different positions in the longitudinal direction, the additional inert gas supply port 12 is provided at a position between the inert gas supply port 5 on the loading side and the exhaust port closest to the loading side among the first and second exhaust ports. FIG. 6 shows a cross-sectional view taken along the line C-C of FIG. 5. The additional inert gas supply port 12 is provided at the center of the bottom surface of the heat treatment chamber 3. Further, since the heat-resistant fiber bundle 2 is configured to travel avoiding directly above the additional inert gas supply port 12, a circulation flow path in the cross-section as shown by the arrow in the drawing is formed in the cross-section. By this circulation flow path, it is possible to prevent the exhaust gas containing the tar component flowing from the unloading side from passing through the discharge port 6 and flowing into the loading side where the temperature is low, and suppress the adhesion of the tar component. The method of forming such a circulation flow path in the cross-section is not limited to the configuration shown in FIG. 6. As shown in FIG. 7, the additional inert gas supply port 12 may be provided on the side surface or the upper surface of the heat treatment chamber 3. However, in order to prevent the adhered and deposited tar component from falling onto the heat-resistant fiber bundle 2, it is preferable to provide it on the bottom surface or the side surface of the heat treatment chamber 3 to supply additional inert gas.

[0034] Also, it is more preferable to satisfy the following formula (3), where S is the cross-sectional area of the heat treatment chamber 3 at the position where the additional inert gas supply port 12 exists, which is a plane parallel to the plane orthogonal to the traveling direction of the flame-resistant fiber bundle 2, and V is the volume flow rate of the inert gas supplied from the additional inert gas supply port 12.

[0035] 0.1 ≦ V / S ≦ 0.4 [m / s] Formula (3).

[0036] When V / S is less than 0.1, a sufficient circulation flow path is not formed to prevent the exhaust gas containing tar components flowing in from the unloading side. When V / S exceeds 0.4, the shaking of the flame-resistant fiber bundle 2 occurs due to the flow of the circulation flow, and the contact frequency between adjacent fiber bundles increases, so there is a risk of fiber bundle blending or single filament breakage. The volume flow rate V of the inert gas supplied from the additional inert gas supply port 12 can be calculated, for example, from the measured wind speed in the duct with an anemometer through a measurement hole provided in the duct connected to the additional inert gas supply port 12, and the cross-sectional area of the duct. When the cross-section of the heat treatment chamber 3 is rectangular as shown in FIG. 5, with the height of the heat treatment chamber 3 being h and the width being b, the cross-sectional area S is h×b. In other cases of different shapes, it can be calculated as appropriate. Regarding the position of the measurement hole provided in the duct connected to the additional inert gas supply port 12, it is preferably provided immediately before the additional inert gas supply port 12. However, if heat insulation measures are taken such as providing a heat insulating material in the duct, and the temperature change from the gas temperature at the additional inert gas supply port 12 is substantially negligible, the volume flow rate may be obtained by providing a measurement hole at a position upstream from the additional inert gas supply port 12.

[0037] The above-mentioned production method and the pre-carbonized fiber bundle produced in the pre-carbonization furnace are carbonized at the highest temperature of 1,000 to 2,000 °C in an inert gas to produce a carbon fiber bundle. At this time, in order to improve the mechanical properties of the carbon fiber bundle, it is preferable to perform carbonization treatment at the highest temperature of 1,200 to 2,000 °C in an inert gas. As the inert gas filling the carbonization furnace, known inert gases such as nitrogen, argon, and helium can be adopted, but nitrogen is preferable from the perspective of economy.

[0038] For the carbon fiber bundle thus obtained, a sizing agent may be applied in order to improve handleability and affinity with the matrix resin. The type of the sizing agent is not particularly limited as long as desired properties can be obtained. Examples thereof include sizing agents mainly composed of epoxy resin, polyether resin, epoxy-modified polyurethane resin, and polyester resin. Known methods can be used for applying the sizing agent.

[0039] Furthermore, the carbon fiber bundle may be subjected to electrolytic oxidation treatment or oxidation treatment for the purpose of improving affinity and adhesiveness with the fiber-reinforced composite material matrix resin, if necessary.

[0040] The acrylic fiber bundle preferably used as the flame-resistant fiber bundle which is the fiber bundle to be heat-treated in the present invention is preferably composed of acrylic fiber of 100 mol% of acrylonitrile or acrylic copolymer fiber containing 90 mol% or more of acrylonitrile. The fineness of the single fiber constituting the fiber bundle to be heat-treated is not particularly limited, but is preferably 0.05 to 0.22 tex, more preferably 0.05 to 0.17 tex. Preferred copolymer components in the acrylic copolymer fiber include acrylic acid, methacrylic acid, itaconic acid, and their alkali metal salts, ammonium metal salts, acrylamide, methyl acrylate, etc. However, the chemical properties, physical properties, dimensions, etc. of the acrylic fiber bundle are not particularly limited.

Examples

[0041] Hereinafter, the present invention will be described more specifically with reference to the drawings by way of examples, but the present invention is not limited thereto.

[0042] The evaluation of the gas volume flow rate Q1 of the first exhaust and the gas volume flow rate Q2 of the second gas was as follows.

[0043] First, using a Kanomax Anemometer Master high-temperature anemometer Model 6162, probes were inserted through the wind speed holes installed 0.5 m downstream from the first and second exhaust ports in the first exhaust duct and the second exhaust duct to measure the wind speed of the exhaust gas. The measurement points were taken at seven points including the center of the duct. At each measurement point, the average value of 30 measured values per second was calculated and used as the wind speed (m / s) of the gas in the first exhaust and the gas in the second exhaust. Also, the cross-sectional areas (m 2 ) of the first exhaust duct and the second exhaust duct were measured. The value obtained by multiplying the measured wind speed by the cross-sectional area of the exhaust duct was taken as the exhaust gas volume flow rate (m 3 / s). The exhaust gas volume flow rate of the first exhaust was designated as Q1, and the volume flow rate of the second gas was designated as Q2. Note that the first exhaust duct and the second exhaust duct are equipped with heat insulation materials to ensure that there is no temperature change in the gas discharged from the first and second exhaust ports. V / S was determined as follows.

[0044] First, using a Kanomax Anemometer Master high-temperature anemometer Model 6162, probes were inserted through the wind speed holes installed 0.5 m upstream from the additional inert gas supply port 12 in the duct connected to the additional inert gas supply port 12 to measure the wind speed of the supplied gas. The measurement points were taken at seven points including the center of the duct. At each measurement point, the average value of 30 measured values per second was calculated and used as the wind speed (m / s) of the gas supplied from the additional inert gas supply port 12. Also, the cross-sectional area (m 2 ) of the duct connected to the additional inert gas supply port 12 was measured. The value obtained by multiplying the measured wind speed by the cross-sectional area of the duct was taken as the volume flow rate V (m 3 / s) of the inert gas supplied from the additional inert gas supply port 12. Note that the duct connected to the additional inert gas supply port 12 is equipped with heat insulation materials to ensure that there is no temperature change in the gas supplied from the additional inert gas supply port 12. The volume flow rate V of the inert gas supplied from the obtained additional inert gas supply port 12 was divided by the cross-sectional area S of the heat treatment chamber 3 to obtain V / S.

[0045] The quality judgment criteria for the examples and comparative examples were as follows respectively.

[0046] A: After passing through the preliminary carbonization process, the average number of flyings of 10 mm or more on the fiber bundle that can be visually confirmed is less than 5 pieces / m, and the flying quality level has no influence on the process passability and the high-order processability of the product at all.

[0047] B: After passing through the preliminary carbonization process, the average number of flyings of 10 mm or more on the fiber bundle that can be visually confirmed is 5 pieces / m or more and 10 pieces / m or less, and the flying quality level has almost no influence on the process passability and the high-order processability of the product.

[0048] C: After passing through the preliminary carbonization process, the average number of flyings of 10 mm or more on the fiber bundle that can be visually confirmed is greater than 10 pieces / m, and the flying quality level has an adverse effect on the process passability and the high-order processability of the product.

[0049] [Example 1] Align 100 acrylic fiber bundles, each consisting of 20,000 single fibers with a single fiber fineness of 0.11 tex, and heat-treat them at 240 - 280 °C in air. Pass the flame-retardant fiber bundles with an effective heat-treatment length of 4 m in the shape shown in Figure 1 continuously through a pre-carbonization furnace maintained at a maximum temperature of 700 °C at a thread speed of 1.0 m / min to obtain pre-carbonized fiber bundles. Nitrogen, an inert gas filling the heat-treatment chamber 3, is supplied from the inert gas supply ports 5 provided on each of the inlet and outlet sides, and the first exhaust port 9 and the second exhaust port 10 are provided at positions where the furnace temperature is around 450 °C for exhaust. For measuring the temperature inside the furnace, a wire with a sheathed thermocouple (OKAZAKI “AEROPAK (registered trademark)”, sheath outer diameter 1.6 mm) attached is stretched inside the furnace, and the position of the exhaust port is adjusted so that the temperature is as described above. As shown in Figure 2, the first exhaust port 9 is provided on the upper surface of the heat-treatment chamber 3, and the second exhaust port 10 is provided on the bottom surface of the heat-treatment chamber 3. An adjustment valve 11 (damper) for adjusting the exhaust flow rate is provided in the exhaust duct 7 connected to each exhaust port. For measuring the exhaust flow rate, an anemometer for high temperatures, Kanomax Anemomaster Model 6162, is used, and a probe is inserted through the wind speed holes provided in each exhaust duct for measurement. The measurement points are seven points including the center of the duct. At each measurement point, the average value of 30 measured values per second is calculated, and this is used as the wind speed. Then, the exhaust flow rate is calculated from the measured value of the obtained wind speed and the cross-sectional area of the exhaust duct.

[0050] Subsequently, the obtained pre-carbonized fiber bundles are fired in a carbonization furnace at a maximum temperature of 1,400 °C, and a sizing agent is applied after electrolytic surface treatment to obtain carbon fiber bundles.

[0051] At this time, the damper opening degree of each exhaust duct was adjusted so that the flow rate ratio Q2 / Q1 of the gas volume flow rate Q1 discharged from the first exhaust port 9 and the gas volume flow rate Q2 discharged from the second exhaust port 10 became 0.5. After operating continuously for 10 days under the above conditions, no thread breakage of the flame-resistant fiber bundle 2 or blockage in the exhaust duct occurred, and continuous operation was possible. After the operation was completed, when the inside of the furnace was visually inspected, a small amount of tar was found to be adhered to the inner wall of the heat treatment chamber, but it was confirmed that this was at a level that did not cause problems in the operation. Also, as a result of visually inspecting the obtained preliminary carbon fiber bundle and carbon fiber bundle, they were of good quality with few flyings and the like.

[0052] [Example 2] The same procedure as in Example 1 was carried out except that Q2 / Q1 was set to 0.3. After operating continuously for 10 days under the above conditions, no thread breakage of the flame-resistant fiber bundle 2 or blockage in the exhaust duct occurred, and continuous operation was possible. After the operation was completed, the inside of the furnace was visually inspected, but no adhesion of tar was observed, and it was confirmed that operation for 10 days or more was possible. Also, as a result of visually inspecting the obtained preliminary carbon fiber bundle and carbon fiber bundle, they were of extremely good quality with no flyings and the like.

[0053] [Example 3] The same procedure as in Example 1 was carried out except that Q2 / Q1 was set to 0.4. After operating continuously for 10 days under the above conditions, no thread breakage of the flame-resistant fiber bundle 2 or blockage in the exhaust duct occurred, and continuous operation was possible. After the operation was completed, when the inside of the furnace was visually inspected, a small amount of tar was found to be adhered to the inner wall of the heat treatment chamber, but it was confirmed that this was at a level that did not cause problems in the operation. Also, as a result of visually inspecting the obtained preliminary carbon fiber bundle and carbon fiber bundle, they were of good quality with few flyings and the like.

[0054] [Example 4] As shown in FIGS. 5 and 6, an additional inert gas supply port 12 was provided at the center of the bottom surface of the heat treatment chamber 3 between the inert gas supply port 5 on the loading side and the exhaust port, and nitrogen was supplied. Further, except that V / S was set to 0.2 m / s where S is the cross-sectional area of the heat treatment chamber in the running direction of the flame-resistant fiber bundle 2 and V is the volume flow rate of the additional inert gas, it was the same as in Example 1. After operating continuously for 10 days under the above conditions, there was no breakage of the flame-resistant fiber bundle 2 or clogging in the exhaust duct, and continuous operation was possible. Then, after the operation was completed, the inside of the furnace was visually inspected, but no tar deposit was found, and it was confirmed that operation for 10 days or more was possible. Also, as a result of visually inspecting the obtained pre-carbon fiber bundle and carbon fiber bundle, they were of extremely good quality with no fluff or the like.

[0055] [Example 5] It was the same as in Example 1 except that Q2 / Q1 was set to 0.01. After operating continuously for 10 days under the above conditions, there was no breakage of the flame-resistant fiber bundle 2 or clogging in the exhaust duct, and continuous operation was possible. Then, after the operation was completed, the inside of the furnace was visually inspected, but no tar deposit was found, and it was confirmed that operation for 10 days or more was possible. Also, as a result of visually inspecting the obtained pre-carbon fiber bundle and carbon fiber bundle, they were of extremely good quality with no fluff or the like.

[0056] [Example 6] It was the same as in Example 4 except that V / S was set to 0.6 m / s. After operating continuously for 10 days under the above conditions, there was no breakage of the flame-resistant fiber bundle 2 or clogging in the exhaust duct, and continuous operation was possible. Then, after the operation was completed, the inside of the furnace was visually inspected, but no tar deposit was found, and it was confirmed that operation for 10 days or more was possible. Also, as a result of visually inspecting the obtained pre-carbon fiber bundle and carbon fiber bundle, they were of good quality with few fluff or the like.

[0057] [Example 7] Except for setting V / S to 0.03 m / s, the same procedure as in Example 4 was followed. After operating continuously for 10 days under the above conditions, no thread breakage of the flame-retardant fiber bundle 2 or clogging in the exhaust duct occurred, and continuous operation was possible. After the operation was completed, visual inspection of the furnace interior showed that a small amount of tar was adhered to the inner wall of the heat treatment chamber, but it was confirmed that this was at a level that did not pose a problem for the operation. Also, as a result of visually inspecting the obtained pre-carbon fiber bundle and carbon fiber bundle, they were of good quality with few flyings and the like.

[0058] [Comparative Example 1] Except for setting Q2 / Q1 to 0.6, the same procedure as in Example 1 was followed. Clogging of the exhaust duct occurred approximately 5 hours after the start of fiber bundle passage under the above conditions, making continuous operation impossible. After the operation was completed, visual inspection of the furnace interior confirmed that a large amount of tar was adhered and deposited on the inner wall of the heat treatment chamber. Also, as a result of visually inspecting the obtained pre-carbon fiber bundle and carbon fiber bundle, they were of poor quality with many flyings and the like.

[0059] [Comparative Example 2] Except for setting Q2 / Q1 to 0, that is, only exhausting from the upper surface of the heat treatment chamber 3, the same procedure as in Example 1 was followed. Thread breakage of the flame-retardant fiber bundle 2 occurred frequently from the second day after the start of fiber bundle passage under the above conditions, so the operation was stopped. After the operation was stopped, visual inspection of the furnace interior showed that a large amount of tar was adhered to the inner wall of the heat treatment chamber, and it was in a state that required cleaning. Also, as a result of visually inspecting the obtained pre-carbon fiber bundle and carbon fiber bundle, they were of poor quality with many flyings and the like.

[0060]

Table 1

Industrial Applicability

[0061] The present invention can be suitably used for producing preliminary carbon fiber bundles and carbon fiber bundles. The flame-resistant 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

[0062] 1 Preliminary carbonization furnace 2 Flame-resistant fiber bundle 3 Heat treatment chamber 4 Slit-shaped opening 5 Inert gas supply port 6 Exhaust port 7 Exhaust duct 8 Combustion or exhaust gas treatment device 9 First exhaust port 10 Second exhaust port 11 Control valve 12 Additional inert gas supply port 13 Non-running area of flame-resistant fiber bundle Q1 Gas volume flow rate discharged from the first exhaust port Q2 Gas volume flow rate discharged from the second exhaust port h Height of the heat treatment chamber b Width of the heat treatment chamber

Claims

1. In a method for manufacturing a pre-carbonized fiber bundle, flame-retardant fiber bundles aligned along a horizontal plane are arranged in one or more than two stages in the vertical direction and run horizontally in a heat treatment chamber, and are heat-treated at a maximum temperature of 300 to 1,000 °C with an inert gas supplied from the inlet side and the outlet side of the heat treatment chamber for pre-carbonization. When the gas volume flow rate of the first exhaust gas exhausted out of the heat treatment chamber from a position higher than the position of the flame-retardant fiber bundle running in the uppermost stage is Q1, and the gas volume flow rate of the second exhaust gas exhausted out of the heat treatment chamber from a position lower than the flame-retardant fiber bundle running in the uppermost stage is Q2, the pre-carbonization is performed such that the flow rate ratio Q2 / Q1 satisfies the following formula (1). 0.01 ≦ Q2 / Q1 ≦ 0.5 Formula (1)

2. The method for manufacturing a pre-carbonized fiber bundle according to Claim 1, wherein the pre-carbonization is performed such that the flow rate ratio Q2 / Q1 of the gas volume flow rate Q1 of the first exhaust gas and the gas volume flow rate Q2 of the second exhaust gas satisfies the following formula (2). 0.01 ≦ Q2 / Q1 ≦ 0.3 Formula (2)

3. The method for manufacturing a pre-carbonized fiber bundle according to Claim 1 or 2, wherein the first exhaust gas and the second exhaust gas are discharged at a position where the temperature in the heat treatment chamber is 350 to 550 °C.

4. The method for manufacturing a pre-carbonized fiber bundle according to any one of Claims 1 to 3, wherein the first exhaust gas is discharged in a non-running region of the flame-retardant fiber bundle.

5. When viewed in the longitudinal direction of the heat treatment chamber, an additional inert gas is supplied from a position on the bottom surface or side surface of the heat treatment chamber, which is a position between the supply position of the inert gas supplied from the inlet side and the position closest to the inlet side among the positions where the first exhaust gas and the second exhaust gas are discharged, according to any one of Claims 1 to 4.

6. The method for manufacturing a pre-carbonized fiber bundle according to Claim 5, when the cross-sectional area of the heat treatment chamber in the running direction of the flame-retardant fiber bundle is S and the supply volume flow rate of the additional inert gas is V, satisfies the following formula (3). 0.1 ≦ V / S ≦ 0.4 [m / s] Formula (3)

7. A method for manufacturing a carbon fiber bundle, wherein the pre-carbonized fiber bundle obtained by the method for manufacturing a pre-carbonized fiber bundle according to any one of Claims 1 to 6 is carbonized at a maximum temperature of 1,000 to 2,000 °C in an inert gas.

8. A pre-carbonization furnace for pre-carbonizing by heat-treating a flame-retardant fiber bundle aligned along a horizontal plane in one stage or two or more stages arranged vertically at a maximum temperature of 300 to 1,000 ° C in an inert gas while running horizontally to obtain a pre-carbonized fiber bundle, comprising a heat treatment chamber, a slit-shaped opening for carrying the flame-retardant fiber bundle into the heat treatment chamber and carrying the pre-carbonized fiber bundle out of the heat treatment chamber, an inert gas supply port for supplying an inert gas into the heat treatment chamber provided on the carrying-in side of the flame-retardant fiber bundle and the carrying-out side of the pre-carbonized fiber bundle, a first exhaust port provided at a position higher than the position of the flame-retardant fiber bundle running on the uppermost stage, a second exhaust port provided at a position lower than the position of the flame-retardant fiber bundle running on the uppermost stage, and a mechanism for adjusting the gas volume flow rate Q1 discharged from the first exhaust port and the gas volume flow rate Q2 discharged from the second exhaust port.

9. The pre-carbonization furnace according to claim 8, wherein the mechanism is a regulating valve for adjusting the flow rate ratio Q2 / Q1.

10. The pre-carbonization furnace according to claim 8 or 9, wherein the first exhaust port is provided in a non-running region of the flame-retardant fiber bundle.

11. In the longitudinal direction of the heat treatment chamber, at a position between the inert gas supply port on the carrying-in side of the flame-retardant fiber bundle and the exhaust port closest to the carrying-in side among the first exhaust port and the second exhaust port, and at a position on the bottom surface or side surface of the heat treatment chamber, the pre-carbonization furnace according to any one of claims 8 to 10, comprising an inert gas supply port for supplying additional inert gas.

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