Flameproofing furnace and methods for producing flame-resistant fiber bundle and carbon fiber bundle

Abstract

The present invention suppresses an increase in the length of a heat treatment and leakage of hot wind from a heat treatment chamber in a flameproofing furnace, thereby improving the efficiency of the heat treatment and improving energy saving properties. To this end, provided is a flameproofing furnace comprising: a heat treatment chamber in which a heat treatment in an oxidizing atmosphere is performed on an aligned acrylic fiber bundle that is arranged in two or more stages the vertical direction and caused to travel in the horizontal direction, so as to obtain a flame-resistant fiber bundle; guide rollers which are disposed outside both ends of the heat treatment chamber and which are for causing the traveling acrylic fiber bundle to turn back; a hot-wind supply nozzle which supplies a hot wind of an oxidizing gas inside the heat treatment chamber; a hot-wind exhaust nozzle which is disposed inside an end part of the heat treatment chamber and above and / or below the acrylic fiber bundle traveling in the heat treatment chamber, and which discharges the hot wind to outside the heat treatment chamber; a circulation duct which is for resupplying the hot wind discharged from the hot-wind exhaust nozzle back into the heat treatment chamber from the hot-wind supply nozzle; and a heater which is provided in the circulation duct and which is for reheating the hot wind, wherein a first hot-wind exhaust port is provided to a surface of the hot-wind exhaust nozzle on the side toward the center of the heat treatment chamber, and a second hot-wind exhaust port is provided on a surface of the hot-wind exhaust nozzle facing the traveling acrylic fiber bundle.

Description

Flame-retardant furnace and method for manufacturing flame-retardant fiber bundles and carbon fiber bundles

[0001] The present invention relates to a flame-retardant furnace provided in a flame-retardant fiber bundle manufacturing apparatus, and to a method for manufacturing flame-retardant fiber bundles and carbon fiber bundles using the flame-retardant furnace. More specifically, the present invention relates to a flame-retardant furnace capable of producing high-quality flame-retardant fiber bundles while achieving both increased heat treatment capacity and energy savings, and to a method for manufacturing flame-retardant fiber bundles and carbon fiber bundles using the same.

[0002] Due to its excellent specific strength, specific modulus of elasticity, heat resistance, and chemical resistance, carbon fiber is useful as a reinforcing material for various materials and is used in a wide range of fields, including aerospace, leisure, and general industrial applications.

[0003] Generally, the following methods are known for producing carbon fiber bundles from acrylic fiber bundles: (i) A fiber bundle, consisting of several thousand to tens of thousands of single acrylic polymer fibers, is fed into a flame-retardant furnace and subjected to heat treatment (flame-retardant treatment) by being 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; (ii) The resulting flame-retardant fiber bundle is fed into a carbonization furnace and subjected to heat treatment (pre-carbonization treatment) in an inert gas atmosphere at 300 to 1,000°C; and (iii) further heat treatment (carbonization treatment) is performed in a carbonization furnace filled with an inert gas atmosphere at 1,000°C or higher.

[0004] Furthermore, the flame-retardant fiber bundles, which are intermediate materials, are widely used as materials for flame-retardant woven fabrics, taking advantage of their flame-retardant properties.

[0005] The flame-retardant treatment process is the longest-running and most energy-intensive stage in the carbon fiber bundle manufacturing process. Therefore, achieving both increased heat treatment capacity and improved energy efficiency in the flame-retardant treatment process is crucial for the successful production of carbon fiber bundles.

[0006] In the flame-retardant treatment process, to enable prolonged heat treatment, it is common practice to treat acrylic fibers by moving them back and forth horizontally many times using guide rollers installed outside the flame-retardant furnace (or the heat treatment chamber that makes up the flame-retardant furnace). The hot air supplied into the flame-retardant furnace (or the heat treatment chamber that makes up the flame-retardant furnace) from the hot air supply nozzle is then often discharged from the hot air exhaust nozzle and recirculated. This recirculation reduces the amount of heating equipment used to generate the hot air, thereby improving energy efficiency. This method of supplying hot air approximately parallel to the direction of travel of the fiber bundle is generally called the parallel flow method, and the method of supplying hot air perpendicular to the direction of travel of the fiber bundle is generally called the perpendicular flow method. Parallel flow systems include the end-to-end (ETE) hot air system, in which a hot air supply nozzle is installed at one end of the parallel flow furnace and a hot air suction nozzle (hot air exhaust nozzle) is installed at the opposite end, and the center-to-end (CTE) hot air system, in which a hot air supply nozzle is installed in the center of the parallel flow furnace and hot air suction nozzles (hot air exhaust nozzles) are installed at both ends.

[0007] To increase the heat treatment capacity in this flame-retardant process, one could consider increasing the temperature or airflow of the hot air. However, increasing the temperature of the hot air requires increased use of heaters, and increasing the airflow requires increased use of blowers, thus worsening energy efficiency. Furthermore, regarding the temperature increase, there is a concern that the increased chimney effect will lead to increased leakage of hot air outside the flame-retardant furnace and heat treatment chamber, further worsening energy efficiency. Therefore, extending the heat treatment length is a common method to increase the heat treatment capacity.

[0008] For example, to solve the problem of extending the heat treatment length, Patent Document 1 describes installing an exhaust port on the outer surface of the furnace in a hot air exhaust nozzle. That is, it describes providing a hot air exhaust nozzle in which the hot air exhaust port opens toward the outer surface of the furnace. This improves heat treatment efficiency by extending the heat treatment length.

[0009] Furthermore, one method for improving energy efficiency in the flame-retardant process is to suppress the leakage of hot air outside the furnace or heat treatment chamber in order to reduce the temperature drop of the circulating gas. Patent document 2 describes a measure to suppress hot air leakage, in which capture ducts are provided at each stage to capture the hot air leaking from the heat treatment chamber.

[0010] Japanese Patent Publication No. 2013-519004, U.S. Patent No. 9217212

[0011] However, in the method described in Patent Document 1, the exhaust port of the hot air exhaust nozzle is installed to open outwards from the furnace, so the hot air blown in from the heat treatment chamber flows out of the heat treatment chamber once. As a result, the amount of leakage increases and energy efficiency deteriorates significantly. Therefore, although the method in Patent Document 1 is effective in extending the heat treatment length, it is not effective in suppressing leakage. In addition, extending the heat treatment length requires the building and the flame-resistant furnace itself to be enlarged, raising concerns about increased equipment costs.

[0012] Furthermore, Patent Document 2 describes a configuration in which capture ducts provided at each stage send hot air that could not be discharged by the hot air exhaust nozzle to a removal device. However, while Patent Document 2 has the effect of suppressing hot air leakage, it does not specifically mention an increase in the amount of heat treatment, and therefore no effect of extending the heat treatment length can be expected.

[0013] One effective way to suppress hot air leakage is to reduce the distance between multi-stage hot air exhaust nozzles and thereby reduce the gap area. However, there is a significant concern about increased thread breakage due to contact between the fiber bundle and the nozzle, making it extremely difficult to reduce the distance between nozzles to below a certain distance.

[0014] Thus, in order to increase the amount of heat treatment in the flame-retardant process while also improving energy efficiency, a new configuration is needed that can achieve both an extended heat treatment length and suppression of hot air leakage from the heat treatment chamber.

[0015] In other words, the problem that the present invention aims to solve is to provide a flame-retardant furnace that can improve energy efficiency while simultaneously extending the heat treatment length in the flame-retardant furnace and suppressing the leakage of hot air from the heat treatment chamber, and furthermore, to provide a method for manufacturing flame-retardant fiber bundles and carbon fiber bundles.

[0016] The flame-retardant furnace of the present invention for solving the above problems has one of the following configurations: (1) A flame-retardant furnace comprising: a heat treatment chamber for heat-treating aligned acrylic fiber bundles in an oxidizing atmosphere while moving them horizontally in two or more vertical rows to produce flame-retardant fiber bundles; guide rollers arranged outside both ends of the heat treatment chamber for folding back the moving acrylic fiber bundles; a hot air supply nozzle for supplying hot air of an oxidizing gas into the heat treatment chamber; a hot air exhaust nozzle located inside the end of the heat treatment chamber, above and / or below the acrylic fiber bundles moving within the heat treatment chamber, for discharging hot air to the outside of the heat treatment chamber; a circulation duct for resupplying the hot air discharged from the hot air exhaust nozzle into the heat treatment chamber from the hot air supply nozzle; and a heater installed in the circulation duct for reheating the hot air, wherein the flame-retardant furnace has a first hot air exhaust port on the heat treatment chamber side of the hot air exhaust nozzle and a second hot air exhaust port on the side facing the moving acrylic fiber bundles. (2) A flame-retardant furnace comprising: a heat treatment chamber for heat-treating aligned acrylic fiber bundles in an oxidizing atmosphere while moving them horizontally in two or more vertical rows to produce flame-retardant fiber bundles; guide rollers positioned outside both ends of the heat treatment chamber for folding back the moving acrylic fiber bundles; a hot air supply nozzle for supplying hot air of an oxidizing gas into the heat treatment chamber; a hot air exhaust nozzle positioned inside the ends of the heat treatment chamber, above and / or below the acrylic fiber bundles moving within the heat treatment chamber, for discharging hot air to the outside of the heat treatment chamber; a circulation duct for resupplying the hot air discharged from the hot air exhaust nozzle into the heat treatment chamber from the hot air supply nozzle; and a heater for reheating the hot air in the circulation duct, wherein the hot air exhaust nozzle has a first hot air exhaust port on the side of the heat treatment chamber facing the center of the heat treatment chamber and a second hot air exhaust port on the side facing the moving acrylic fiber bundles. (3) The flame-retardant furnace according to (1) or (2), wherein the second hot air exhaust port is installed from the outside of the heat treatment chamber of the hot air exhaust nozzle. (4) The flame-retardant furnace according to any one of (1) to (3), wherein the second hot air exhaust port is installed only on the upper surface of the acrylic fiber bundle. (5) The flame-retardant furnace according to any one of (1) to (4), wherein the hot air exhaust nozzles are installed at both ends of the heat treatment chamber in the direction of travel of the acrylic fiber bundle.(6) A method for manufacturing flame-resistant fiber bundles, comprising using a flame-retardant furnace as described in any of (1) to (5) above, arranging aligned acrylic fiber bundles in two or more vertical rows, moving them horizontally through a heat treatment chamber while folding them back with guide rollers, supplying hot air of an oxidizing gas with a maximum temperature of 200 to 300°C into the heat treatment chamber from a hot air supply nozzle, and heat-treating the bundles in a heat treatment chamber while discharging the hot air from a hot air exhaust nozzle, wherein the exhaust volume flow rate Q1 discharged from a first hot air exhaust port and the exhaust volume flow rate Q2 discharged from a second hot air exhaust port satisfy 0.2 ≤ Q2 / (Q1 + Q2) ≤ 0.5. (7) The method for manufacturing flame-resistant fiber bundles as described in (6) above, wherein the single fiber fineness of the acrylic fiber bundles before heat treatment is 0.05 to 0.22 tex. (8) A method for producing a carbon fiber bundle, comprising: pre-carbonizing a flame-resistant fiber bundle obtained by the method for producing a flame-resistant fiber bundle described in (6) or (7) above at a maximum temperature of 300 to 1,000°C in an inert atmosphere to produce a pre-carbonized fiber bundle; and carbonizing the pre-carbonized fiber bundle at a maximum temperature of 1,000 to 2,000°C in an inert atmosphere.

[0017] According to the present invention, by achieving both an extended heat treatment length in a flame-retardant furnace and suppression of hot air leakage from the heat treatment chamber, it is possible to increase the amount of high-quality flame-retardant fiber bundles and carbon fiber bundles that can be heat-treated while improving energy efficiency.

[0018] This is a schematic cross-sectional view of a flame-retardant furnace used in the first embodiment of the present invention. This is a partially enlarged cross-sectional view of the area around the hot air exhaust nozzle used in the first embodiment of the present invention. This is a schematic diagram showing the airflow pattern around the hot air exhaust nozzle in the upper part of a conventional flame-retardant furnace. This is a schematic diagram showing the airflow pattern around the hot air exhaust nozzle in the lower part of a conventional flame-retardant furnace. This is a schematic diagram showing the airflow pattern around the hot air exhaust nozzle used in an embodiment of the present invention. This is a schematic cross-sectional view of a flame-retardant furnace used in the second embodiment of the present invention. This is a partially enlarged cross-sectional view of the area around the hot air exhaust nozzle used in the third embodiment of the present invention.

[0019] Embodiments of the present invention will be described in detail below with reference to Figures 1 and 2. These drawings are conceptual diagrams intended to accurately convey the essential points of the present invention, and have been simplified. Therefore, the present invention is not particularly limited by these drawings, and its dimensions and other properties can be modified according to the embodiment.

[0020] The present invention relates to a flame-retardant furnace for heat-treating acrylic fiber bundles, and more particularly to a flame-retardant furnace in which hot air flows through the interior. As shown in Figure 1, the flame-retardant furnace 1 has a heat treatment chamber 3 that blows hot air onto an acrylic fiber bundle 2 that travels through a multi-stage travel area while being folded back, thereby performing flame-retardant treatment. Guide rollers 4 for folding the acrylic fiber bundle are located outside both ends of the heat treatment chamber 3 (i.e., outside the horizontal ends of the heat treatment chamber 3), and further, there is a hot air supply nozzle 5 for supplying hot air of an oxidizing gas into the heat treatment chamber 3 and a hot air exhaust nozzle 6 for discharging the hot air to the outside of the heat treatment chamber 3. The hot air exhaust nozzle 6 is located inside the end of the heat treatment chamber 3, above and / or below the acrylic fiber bundle 2 that travels within the heat treatment chamber. In this context, "the interior of the end of the heat treatment chamber 3" refers to the interior of the heat treatment chamber 3 and its horizontal end, and "positioned at the end" means that the outer end face of the hot air exhaust nozzle 6 is positioned in the outer 10% of the horizontal length of the heat treatment chamber 3.

[0021] Furthermore, the flame-retardant furnace 1 also includes a circulation duct 10 for resupplying the hot air discharged from the hot air exhaust nozzle 6 back into the heat treatment chamber from the hot air supply nozzle 5, and a heater 7 for reheating the hot air in the circulation duct. The heater 7 is preferably installed inside the circulation duct 10, but the hot air in the circulation duct may be reheated by heating the circulation duct from the outside.

[0022] The acrylic fiber bundle 2 is composed of multiple acrylic fibers aligned together. In the flame-retardant furnace 1 described above, it is fed into the heat treatment chamber 3 through an opening (not shown) in the side wall of the heat treatment chamber 3, travels horizontally in a nearly straight line within the heat treatment chamber 3, and is then temporarily sent out of the heat treatment chamber 3 through an opening in the opposite side wall. Subsequently, the acrylic fiber bundle 2 is folded back by a guide roller 4 provided on the side wall outside the heat treatment chamber 3 and fed back into the heat treatment chamber 3 again. In this way, the acrylic fiber bundle 2 is folded back multiple times by the multiple guide rollers 4, repeating the feeding into and out of the heat treatment chamber 3 multiple times, moving vertically in multiple stages within the heat treatment chamber 3, as a whole, from top to bottom in Figure 1. The direction of movement may also be from bottom to top, and the number of times the acrylic fiber bundle 2 is folded back within the heat treatment chamber 3 is not particularly limited and is designed appropriately according to the scale of the flame-retardant furnace 1, etc.

[0023] As the acrylic fiber bundle 2 travels through the heat treatment chamber 3 while being folded back, it is subjected to flame-retardant treatment by hot air flowing from the hot air supply nozzle 5 towards the hot air exhaust nozzle 6, thereby becoming a flame-retardant fiber bundle.

[0024] The flame-retardant furnace 1 shown in Figure 1 is a flame-retardant furnace of the parallel-flow CTE hot air type described above. The acrylic fiber bundle 2 has a wide, sheet-like form, with multiple bundles arranged in parallel in a direction perpendicular to the plane of the drawing.

[0025] In the flame-retardant furnace 1, the running speed and tension of the acrylic fiber bundle 2 can be controlled by changing the rotation speed of each of the guide rollers 4, and this is fixed according to the required physical properties of the flame-retardant fiber bundle and the processing rate per unit time.

[0026] Furthermore, by carving grooves at predetermined intervals and in a predetermined number on the surface of the guide roller 4, or by arranging comb guides (not shown) at predetermined intervals and in a predetermined number in close proximity to the guide roller 4, the spacing and number of acrylic fiber bundles 2 running in parallel can be controlled.

[0027] The hot air flowing through the heat treatment chamber 3 can be any oxidizing gas such as air. Before entering the heat treatment chamber 3, the oxidizing gas is heated to a desired temperature by the heater 7, its airflow velocity is controlled by the blower 8, and then it is blown into the heat treatment chamber 3 from the hot air supply port 9 of the hot air supply nozzle 5.

[0028] Within the heat treatment chamber 3, the oxidizing gas flows to the hot air exhaust nozzle 6 while treating the acrylic fiber bundle 2 to make it flame-resistant, and is discharged outside the heat treatment chamber 3 from the hot air exhaust port 11 of the hot air exhaust nozzle 6 (i.e., the inlet for the discharged gas in the hot air exhaust nozzle 6). The gas discharged outside the heat treatment chamber 3 is blown back into the heat treatment chamber 3 from the hot air supply nozzle 5 through the circulation duct 10. However, it is not necessary for all of the gas to be circulated; some of the gas may be treated to remove toxic substances in an exhaust gas treatment furnace (not shown) and then released into the atmosphere, and the same amount of gas released into the atmosphere may be supplied to the circulation duct.

[0029] The heater 7 used in the flame-retardant furnace 1 is not particularly limited as long as it has the desired heating function, and a known heater such as an electric heater may be used. Similarly, the blower 8 is not particularly limited as long as it has the desired air blowing function, and a known blower such as an axial fan may be used.

[0030] To increase the heat treatment capacity, one can either raise the temperature of the hot air blown into the heat treatment chamber 3 from the hot air supply port 9 of the hot air supply nozzle 5, or increase the volume of hot air. However, as mentioned above, raising the hot air temperature requires increased use of the heater 7, and increasing the volume requires increased use of the blower 8, thus worsening energy efficiency.

[0031] Furthermore, in order to improve energy efficiency, reducing the distance H between nozzles would be a measure to suppress hot air leakage, but as mentioned above, there is a concern that contact between the acrylic fiber bundle 2 and the hot air supply nozzle 5 and the hot air exhaust nozzle 6 may increase the risk of thread breakage.

[0032] The flame-retardant furnace and method for manufacturing flame-retardant fiber bundles and carbon fiber bundles of the present invention were conceived as a result of diligent research into the above-mentioned problems, and enable the production of high-quality flame-retardant fiber bundles and carbon fiber bundles while achieving both increased heat treatment capacity and energy savings.

[0033] Next, we will explain in detail the configuration that achieves both increased heat treatment capacity and improved energy efficiency, which is the most important point of this invention.

[0034] First, in order to clarify the difference between the prior art and the present invention, the velocity vector when using a hot air exhaust nozzle 6 configured in the prior art will be explained using Figures 3 and 4. Figures 3 and 4 show a flame-retardant fiber bundle manufacturing apparatus in which aligned acrylic fiber bundles 2 are heat-treated while running through a hot air heated flame-retardant furnace 1, and the case in which hot air is discharged only from the first hot air exhaust port 11 on the inside of the furnace, which is located in a hot air exhaust nozzle 6 positioned above and / or below the acrylic fiber bundles 2 running through the flame-retardant furnace 1. Note that since hot air exhaust nozzles generally have a substantially rectangular cross-section, they are shown as such in the drawings. Also, the heat treatment chamber 3 and guide rollers 4 are omitted from the illustration in Figures 3 and 4.

[0035] Figure 3 shows the upper part of the flame-retardant furnace 1. Due to the chimney effect, the hot air passes through the fiber bundle passage 12 and leaks out of the heat treatment chamber 3, i.e., outside the furnace. Figure 4 shows the lower part of the flame-retardant furnace 1. From the fiber bundle passage 12, which is a stagnant area, outside air flows in to compensate for the hot air leakage rate at the top, causing a decrease in the temperature inside the heat treatment chamber 3. This decrease in temperature inside the heat treatment chamber 3 leads to a decrease in the amount of heat treated in the acrylic fiber bundles 2, and furthermore, increases the usage of the heater 7, resulting in a deterioration of energy efficiency. Here, "fiber bundle passage" refers to the space around the acrylic fiber bundles 2 that is formed along the direction in which the acrylic fiber bundles 2 travel within the flame-retardant furnace 1, and refers to the space between vertically adjacent hot air exhaust nozzles 6, or the space between the hot air exhaust nozzle 6 and the upper surface of the heat treatment chamber 3, or the space between the hot air exhaust nozzle 6 and the bottom surface of the heat treatment chamber 3.

[0036] In contrast to these, the embodiment of the present invention (first embodiment) uses a hot air exhaust nozzle 6 having a second hot air exhaust port 13 in addition to a first hot air exhaust port 11, as shown in Figure 2. In the present invention, the first hot air exhaust port 11 is provided on the surface of the hot air exhaust nozzle 6 facing the center of the heat treatment chamber (i.e., the surface facing the center of the heat treatment chamber in the horizontal direction in a substantially rectangular hot air exhaust nozzle 6), and the second hot air exhaust port is provided on the surface facing the moving acrylic fiber bundle 2 (i.e., the upper or lower surface in the vertical direction in a substantially rectangular hot air exhaust nozzle 6). Note that the heat treatment chamber 3 and guide roller 4 are omitted from the illustration in Figure 2.

[0037] In a flame-retardant furnace using such a hot air exhaust nozzle 6, the aligned acrylic fiber bundles 2 are heat-treated while being folded back by guide rollers 4 installed at both ends outside the hot air heating flame-retardant furnace 1. At this time, the hot air supplied into the heat treatment chamber 3 from the hot air supply port 9 is discharged from the hot air exhaust nozzle 6, which is located above the acrylic fiber bundles 2 on the surface facing the acrylic fiber bundles 2 running inside the flame-retardant furnace 1 at the end of the heat treatment chamber 3, and then led to the circulation duct 10, where it is reheated by the heater 7 in the circulation duct 10 and resupplied into the heat treatment chamber 3. In this way, a hot air circulation line is formed in the flame-retardant furnace 1.

[0038] The velocity vector of the hot air when using the hot air exhaust nozzle 6 having the first hot air exhaust port 11 and the second hot air exhaust port 13 is shown in FIG. 5. Different from the prior art shown in FIGS. 3 and 4, by adding the second hot air exhaust port 13, it becomes possible to rectify the fiber bundle passage flow path 12 where the air flow is likely to stagnate. And in this case, it becomes possible to simultaneously suppress the leakage at the upper part and the inflow of outside air at the lower part in the flame-resistant furnace, which has been a problem in the prior art, and the energy saving property can be improved. Further, by rectifying the fiber bundle passage flow path 12, heat treatment can be substantially performed even in the fiber bundle passage flow path 12, and the heat treatment length can be extended. In particular, in the CTE hot air method, since the hot air exhaust nozzles 6 are arranged at both ends of the flame-resistant furnace 1, the heat treatment length can be extended at both ends. That is, in the flame-resistant furnace 1 of the present invention, it is extremely important to provide the first hot air exhaust port 11 in the hot air exhaust nozzle 6 which was not considered at all in the prior art, and the second hot air exhaust port 13 on the surface facing the acrylic fiber bundle 2.

[0039] Next, a second embodiment of the flame-resistant furnace of the present invention is shown in FIG. 6. As shown in the second embodiment, in the present invention, an ETE hot air method in which a hot air supply nozzle 5 is installed at one end of the flame-resistant furnace 1 may be adopted. In this case, compared with the CTE hot air method, since the hot air exhaust nozzle 6 is arranged only at one end of the flame-resistant furnace 1, the effect of extending the heat treatment length becomes small, but when the length of the hot air exhaust nozzle 6 itself is large, the effect of the present invention becomes more remarkable.

[0040] Next, a third embodiment of the flame-resistant furnace of the present invention will be described with reference to FIG. 7. The second hot air exhaust port 13 may be disposed either above or below the acrylic fiber bundle 2, or may be disposed both above and below. Further, the second hot air exhaust port 13 may be formed on a part or the entire surface of the surface of the hot air exhaust nozzle 6 facing the acrylic fiber bundle 2. When the second hot air exhaust port 13 is provided only on a part of the surface facing the acrylic fiber bundle 2, it is preferable to provide the second hot air exhaust port 13 from the outside of the heat treatment chamber 3 in order to increase the amount of heat treatment further. That is, in the hot air exhaust nozzle 6, it is preferable to provide the second hot air exhaust port 13 in a partial region including the end on the side opposite to the center side of the heat treatment chamber (outer side) in the horizontal direction among the surfaces facing the acrylic fiber bundle 2 that is traveling. By doing so, the distance for rectification in the fiber bundle passage 12 becomes larger, and an increase in the effect of extending the effective length can be expected.

[0041] Furthermore, from the viewpoint of suppressing hot air leakage, since the hot air in the flame-resistant furnace 1 generally has a lower density than the outside air and is likely to rise, it is more preferable that the second hot air exhaust port 13 is disposed only above the acrylic fiber bundle 2.

[0042] Note that the preferable aspects regarding the second hot air exhaust port 13 as described above can be implemented in combination in any of the first embodiment and the second embodiment described above.

[0043] Furthermore, when manufacturing flame-resistant fiber bundles from acrylic fiber bundles using the flame-resistant furnace of the present invention, it is more preferable that the exhaust volume flow rate Q1 from the first hot air exhaust port and the exhaust volume flow rate Q2 from the second hot air exhaust port satisfy 0.2 ≤ Q2 / (Q1 + Q2) ≤ 0.5. If the exhaust volume flow rate Q1 from the first hot air exhaust port is too large, the exhaust volume flow rate Q2 from the second hot air exhaust port becomes relatively small, reducing the effect of straightening the fiber bundle passage and decreasing the effect of suppressing hot air leakage from the top of the flame-resistant furnace and outside air inflow from the bottom of the flame-resistant furnace. On the other hand, if the exhaust volume flow rate Q1 from the first hot air exhaust port is too small, the flow rate of hot air passing through the fiber bundle passage increases, making it difficult to adequately discharge from the second hot air exhaust port and reducing the effect of suppressing hot air leakage from the bottom of the heat treatment chamber. For this reason, it is preferable to keep Q2 / (Q1 + Q2) within the above range in order to minimize hot air leakage.

[0044] Methods for controlling the ratio of Q2 / (Q1+Q2) to within the above range include, for example, installing a damper at the hot air exhaust port or adding a pressure-reducing member.

[0045] Furthermore, in the method for producing flame-resistant fiber bundles of the present invention, the single fiber fineness of the acrylic fiber bundle is preferably 0.05 to 0.22 tex, and more preferably 0.05 to 0.17 tex. By setting it within this preferred range, single fibers are less likely to entangle when adjacent fiber bundles come into contact, effectively preventing intermingling between fiber bundles. At the same time, heat can be sufficiently distributed to the inner layer of the single fibers in the flame-retardant furnace, reducing fuzzing of the fiber bundles and effectively preventing large-scale intermingling, thus providing superior quality and operability of the flame-resistant fiber bundles.

[0046] The flame-retardant fiber bundles produced by the method described above are then pre-carbonized in an inert atmosphere at a maximum temperature of 300 to 1,000°C to become pre-carbonized fiber bundles. These pre-carbonized fiber bundles are then further carbonized in an inert atmosphere at a maximum temperature of 1,000 to 2,000°C to become carbon fiber bundles. In this way, carbon fiber bundles are produced from acrylic fiber bundles.

[0047] The maximum temperature of the inert atmosphere in the pre-carbonization treatment is preferably 550 to 800°C. While known inert atmospheres such as nitrogen, argon, and helium can be used to fill the pre-carbonization furnace, nitrogen is preferred from an economic standpoint.

[0048] The pre-carbonized fibers obtained by the pre-carbonization treatment are then fed into a carbonization furnace for further carbonization. To improve the mechanical properties of the carbon fibers, it is preferable to perform the carbonization treatment at a maximum temperature of 1,200 to 2,000°C in an inert atmosphere. While known inert atmospheres such as nitrogen, argon, and helium can be used to fill the carbonization furnace, nitrogen is preferred from an economic standpoint.

[0049] Furthermore, the maximum temperature range for the inert atmosphere means that the maximum temperature of the inert atmosphere in both the pre-carbonization process and the carbonization process must fall within that temperature range.

[0050] The carbon fiber bundles obtained in this manner may be treated with a sizing agent to improve their handling properties and affinity with the matrix resin. The type of sizing agent is not particularly limited as long as the desired properties can be obtained, but examples include sizing agents mainly composed of epoxy resin, polyether resin, epoxy-modified polyurethane resin, and polyester resin. Known methods can be used to apply the sizing agent.

[0051] Furthermore, the carbon fiber bundles may be subjected to electrolytic oxidation treatment or oxidation treatment as needed, in order to improve their affinity and adhesion to the fiber-reinforced composite material matrix resin.

[0052] In the method for producing flame-resistant fiber bundles of the present invention, the acrylic fiber bundle used as the heat-treated fiber bundle is preferably composed of 100% acrylonitrile acrylic fiber or acrylic copolymer fiber containing 90 mol% or more of acrylonitrile. 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., but the chemical properties, physical properties, dimensions, etc., of the acrylic fiber bundle are not particularly limited.

[0053] The present invention will be described in more detail below with reference to the drawings, but the present invention is not limited thereto. The effective length of the heat treatment and the amount of hot air leakage in each example and comparative example were measured by the method described below.

[0054] (1) Method for measuring the effective length Using an Anemomaster high-temperature anemometer Model 6162 manufactured by Nippon Kanomax Co., Ltd., the effective length of the heat treatment was measured by inserting a measuring probe through a measuring hole (not shown) on the side of the heat treatment chamber 3. Specifically, in the fiber bundle passage channel 12, the average temperature T ａｖｅ The effective length was defined as the range where the temperature is within -1°C of the temperature of the hot air supply port 9, and the total length for each stage was calculated. Here, the average temperature T ａｖｅ This value was calculated as the average of three points, including the center, in the width direction of the fiber bundle.

[0055] (2) Method for measuring leakage amount An Anemomaster high-temperature anemometer Model 6162 manufactured by Nippon Kanomax Co., Ltd. was used to measure the amount of hot air leakage by inserting a measuring probe through a measuring hole (not shown) on the side of the flame-retardant furnace 1. Specifically, at the outermost end of the fiber bundle passage 12 (outside both horizontal ends of the heat treatment chamber), the average velocity V in the direction outward of the furnace was measured. ａｖｅ The average velocity V was measured, and the total leakage amount for each stage was calculated. ａｖｅ This value was calculated as the average of three points, including the center, in the width direction of the fiber bundle.

[0056] [Example 1] Figure 1 is a schematic diagram showing an example of using the heat treatment furnace of the present invention as a flame-retardant furnace for carbon fiber production. Flame-retardant fiber bundles were obtained by heat-treating acrylic fiber bundles 2 using this flame-retardant furnace 1.

[0057] In this case, the acrylic fiber bundle 2 traveling inside the flame-retardant furnace 1 was made by aligning 100 fiber bundles, each consisting of 20,000 single fibers with a single fiber fineness of 0.11 tex.

[0058] Furthermore, hot air exhaust nozzles 6, each having a first hot air exhaust port 11 and a second hot air exhaust port 13, were installed above and below the acrylic fiber bundle 2 that travels inside the flame-retardant furnace 1 (the horizontal ends inside the heat treatment chamber 3). Here, the hot air exhaust nozzle 6 was configured such that the first hot air exhaust port 11 could be provided on the furnace-side surface (the surface of the hot air exhaust nozzle 6 facing the center of the heat treatment chamber), and the second hot air exhaust port 13 could be provided on the surface facing the traveling acrylic fiber bundle 2 (above or below the acrylic fiber bundle 2). The length of the hot air exhaust nozzle 6 itself in the yarn transport direction was 1 m. In addition, perforated plates with an opening ratio of 30% were provided at the first hot air exhaust port 11 and the second hot air exhaust port 13 to ensure uniform air velocity in the width direction.

[0059] Furthermore, the horizontal distance between the guide rollers 4 located on both sides of the heat treatment chamber 3 was set to 15 m, the guide rollers 4 were grooved rollers, and the groove pitch was set to 8 mm.

[0060] The gas temperature supplied from the hot air supply nozzle 5 was set to 250°C, and the horizontal airflow velocity of the gas inside the flame-retardant furnace 1 was set to 6 m / s. The running speed of the acrylic fiber bundle 2 was adjusted within the range of 1 to 15 m / min to allow sufficient time for flame-retardant treatment, and the process tension was adjusted within the range of 0.5 to 2.5 g / tex.

[0061] The obtained flame-resistant fiber bundles were then fired in a pre-carbonization furnace at a maximum temperature of 700°C, followed by firing in a carbonization furnace at a maximum temperature of 1,400°C. After electrolytic surface treatment, a sizing agent was applied to obtain carbon fiber bundles.

[0062] During the operation described above, the average temperature and average speed of each stage of the flame-retardant furnace 1 were measured. The detailed conditions and results are shown in Table 1.

[0063] When the second hot air exhaust port 13 is installed above the acrylic fiber bundle 2 and in a region 30 cm in length from the outer end (the end of the hot air exhaust nozzle 6 opposite to the center of the heat treatment chamber), and the relationship between the exhaust volume flow rate Q1 from the first hot air exhaust port and the exhaust volume flow rate Q2 from the second hot air exhaust port is Q2 / (Q1+Q2) = 0.2, the effective length is 112.5 m and the leakage volume is 335 m ３ It was / h.

[0064] [Example 2] The same procedure as in Example 1 was carried out, except that the second hot air exhaust port 13 was installed above the acrylic fiber bundle 2 and in a region having a length of 30 cm from the inner end (the end on the central side of the heat treatment chamber in the hot air exhaust nozzle 6). At this time, the effective length was 106.5 m, and the leakage amount was 469 m ３ / h.

[0065] [Example 3] The same procedure as in Example 1 was carried out, except that the second hot air exhaust port 13 was installed over the entire upper part of the acrylic fiber bundle 2. At this time, the effective length was 111.0 m, and the leakage amount was 581 m ３ / h.

[0066] [Example 4] The same procedure as in Example 1 was carried out, except that the second hot air exhaust port 13 was installed below the acrylic fiber bundle 2. At this time, the effective length was 114.0 m, and the leakage amount was 447 m ３ / h.

[0067] [Example 5] The same procedure as in Example 1 was carried out, except that the second hot air exhaust port 13 was installed both above and below the acrylic fiber bundle 2. At this time, the effective length was 114.0 m, and the leakage amount was 782 m ３ / h.

[0068] [Example 6] The same procedure as in Example 1 was carried out, except that the relationship between the exhaust gas volume flow rate Q1 from the first hot air exhaust port and the exhaust gas volume flow rate Q2 from the second hot air exhaust port was set to Q2 / (Q1 + Q2) = 0.1. At this time, the effective length was 112.5 m, and the leakage amount was 536 m ３ / h.

[0069] [Example 7] The same procedure as in Example 1 was carried out, except that the relationship between the exhaust gas volume flow rate Q1 from the first hot air exhaust port and the exhaust gas volume flow rate Q2 from the second hot air exhaust port was set to Q2 / (Q1 + Q2) = 0.5. At this time, the effective length was 113.7 m, and the leakage amount was 313 m ３ / h.

[0070] [Example 8] The same procedure as in Example 1 was carried out, except that the relationship between the exhaust gas volume flow rate Q1 from the first hot air exhaust port and the exhaust gas volume flow rate Q2 from the second hot air exhaust port was set to Q2 / (Q1 + Q2) = 0.8. At this time, the effective length was 114.3 m, and the leakage amount was 447 m ３It was / h.

[0071] [Comparative Example 1] In Comparative Example 1, the second hot air exhaust port 13 was blocked, and the relationship between the exhaust volume flow rate Q1 from the first hot air exhaust port and the exhaust volume flow rate Q2 from the second hot air exhaust port was set to Q2 / (Q1+Q2)=0.0, except that the procedure was the same as in Example 1. In this case, the effective length was 105.0 m and the leakage volume was 849 m ３ It was / h.

[0072]

[0073] The flame-retardant furnace of the present invention can be used in the apparatus and method for manufacturing flame-retardant fiber bundles. Flame-retardant fiber bundles and carbon fiber bundles manufactured using such a flame-retardant furnace can be applied to aircraft applications, industrial applications such as pressure vessels and wind turbines, and sports applications such as golf shafts, but the scope of application is not limited to these.

[0074] 1. Flame-retardant furnace 2. Acrylic fiber bundle 3. Heat treatment chamber 4. Guide roller 5. Hot air supply nozzle 6. Hot air exhaust nozzle 7. Heater 8. Blower 9. Hot air supply port 10. Circulation duct 11. First hot air exhaust port 12. Fiber bundle passage path 13. Second hot air exhaust port H. Distance between nozzles

Claims

1. A flame-retardant furnace comprising: a heat treatment chamber for heat-treating aligned acrylic fiber bundles in an oxidizing atmosphere while moving them horizontally in two or more vertical rows to produce flame-retardant fiber bundles; guide rollers positioned outside both ends of the heat treatment chamber for folding back the moving acrylic fiber bundles; a hot air supply nozzle for supplying hot air of an oxidizing gas into the heat treatment chamber; a hot air exhaust nozzle positioned inside the ends of the heat treatment chamber, above and / or below the acrylic fiber bundles moving within the heat treatment chamber, for discharging hot air to the outside of the heat treatment chamber; a circulation duct for resupplying the hot air discharged from the hot air exhaust nozzle back into the heat treatment chamber from the hot air supply nozzle; and a heater installed in the circulation duct for reheating the hot air, wherein the flame-retardant furnace has a first hot air exhaust port on the heat treatment chamber side of the hot air exhaust nozzle and a second hot air exhaust port on the side facing the moving acrylic fiber bundles.

2. A flame-retardant furnace comprising: a heat treatment chamber for heat-treating aligned acrylic fiber bundles in an oxidizing atmosphere while moving them horizontally in two or more vertical rows to produce flame-retardant fiber bundles; guide rollers positioned outside both ends of the heat treatment chamber for folding back the moving acrylic fiber bundles; a hot air supply nozzle for supplying hot air of an oxidizing gas into the heat treatment chamber; a hot air exhaust nozzle positioned inside the ends of the heat treatment chamber, above and / or below the acrylic fiber bundles moving within the heat treatment chamber, for discharging hot air to the outside of the heat treatment chamber; a circulation duct for resupplying the hot air discharged from the hot air exhaust nozzles back into the heat treatment chamber from the hot air supply nozzles; and a heater for reheating the hot air in the circulation duct, wherein the hot air exhaust nozzle has a first hot air exhaust port on the side of the heat treatment chamber facing the center of the heat treatment chamber and a second hot air exhaust port on the side facing the moving acrylic fiber bundles.

3. The flame-retardant furnace according to claim 1 or 2, wherein the second hot air exhaust port is installed on the outside of the heat treatment chamber of the hot air exhaust nozzle.

4. The flame-retardant furnace according to claim 1 or 2, wherein the second hot air exhaust port is installed only on the upper surface of the acrylic fiber bundle.

5. The flame-retardant furnace according to claim 1 or 2, wherein hot air exhaust nozzles are installed at both ends of the heat treatment chamber in the direction of travel of the acrylic fiber bundle.

6. A method for manufacturing flame-resistant fiber bundles, comprising using the flame-retardant furnace described in claim 1 or 2, arranging aligned acrylic fiber bundles in two or more vertical rows, moving them horizontally through a heat treatment chamber while folding them back with guide rollers, supplying hot air of an oxidizing gas with a maximum temperature of 200 to 300°C into the heat treatment chamber from a hot air supply nozzle, and heat-treating the bundles in a heat treatment chamber while discharging the hot air from a hot air exhaust nozzle, wherein the exhaust volume flow rate Q1 discharged from a first hot air exhaust port and the exhaust volume flow rate Q2 discharged from a second hot air exhaust port satisfy 0.2 ≤ Q2 / (Q1 + Q2) ≤ 0.

5.

7. The method for producing a flame-resistant fiber bundle according to claim 6, wherein the single fiber fineness of the acrylic fiber bundle before heat treatment is 0.05 to 0.22 tex.

8. A method for producing a carbon fiber bundle, comprising: pre-carbonizing a flame-resistant fiber bundle obtained by the method for producing a flame-resistant fiber bundle described in claim 6 at a maximum temperature of 300 to 1,000°C in an inert atmosphere to obtain a pre-carbonized fiber bundle; and carbonizing the pre-carbonized fiber bundle at a maximum temperature of 1,000 to 2,000°C in an inert atmosphere.

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