Microwave heating unit, and a carbon fiber manufacturing method using the same

Abstract

According to the present invention, a microwave heating unit is provided comprising a furnace body formed by forming a fiber introduction port and a fiber exit port on the wall of a waveguide, and a microwave oscillator for introducing microwaves into the waveguide, wherein the continuous fiber to be heated is configured to travel inside the waveguide with an angle θ° with respect to the axis of the waveguide, and wherein the angle θ° is 0 < θ < 90, and the fiber exit port is formed in a part other than the end portion of the waveguide.

Description

Technology Field

[0001] The present invention relates to a microwave heating unit for heating a continuous fiber to be heated by irradiating it with microwaves, and a method for manufacturing carbon fibers using the same. Background Technology

[0002] Carbon fibers have superior specific strength and specific modulus compared to other fibers, and are widely used industrially as reinforcing fibers that are composited with resins, utilizing their lightweight properties and excellent mechanical properties.

[0003] Conventionally, carbon fibers were manufactured as follows. First, a precursor fiber is subjected to flame-retardant treatment by heating it in heated air at 230 to 260°C for 30 to 100 minutes. Through this flame-retardant treatment, a cyclization reaction of the acrylic fiber is induced, and the amount of oxygen bonded is increased to obtain a flame-retardant fiber. This flame-retardant fiber is carbonized, for example, using a calcination furnace at 300 to 800°C under a nitrogen atmosphere while applying a temperature gradient (first carbonization treatment). Subsequently, it is further carbonized using a calcination furnace at 800 to 2100°C under a nitrogen atmosphere while applying a temperature gradient (second carbonization treatment). In this way, carbon fibers are manufactured by heating the flame-retardant fiber from the outside within a heated calcination furnace.

[0004] When manufactured as described above, the temperature must be raised gradually over time to avoid insufficient carbonization within the carbonized fibers. Furthermore, in a firing furnace that heats from the outside, thermal efficiency is low because materials other than the carbonized fibers, such as the furnace body and the firing atmosphere, are also heated.

[0005] Recently, attempts have been made to manufacture carbon fibers by heating fibers to be carbonized through microwave irradiation. When a material is heated by microwaves, it is heated from the inside out. Therefore, when heating fibers to be carbonized using microwaves, it is possible to perform uniform carbonization on both the surface and inside the fiber, which is expected to reduce the manufacturing time of carbon fibers.

[0006] Conventionally, a method for manufacturing carbon fibers using microwaves is known as Patent Document 1. Patent Document 1 describes a method for manufacturing carbon fibers using microwaves.

[0007] In addition, Patent Document 2 describes a microwave heating device that suppresses heating non-uniformity of food, etc. by conveying the object to be heated at an angle relative to the heating furnace.

[0008] However, in the manufacturing process of carbon fibers, the fiber to be heated continuously changes from a dielectric to a semiconductor and then to a conductor. In particular, in the manufacturing process of carbon fibers using microwaves, the properties of the fiber to be heated change instantaneously. That is, as the dielectric constant of the fiber to be heated changes, the suitable heating conditions change instantaneously. Therefore, when heating the fiber to be heated using a conventional microwave heating unit, unstable reactions are prone to occur due to the nature of the electromagnetic energy inside the furnace, which significantly damages the fiber to be heated, thereby reducing process stability and significantly degrading the quality of the fiber obtained. Prior art literature

[0009] Japanese Patent Publication No. 6063045 Japanese Patent Publication No. 2898646 The problem to be solved

[0010] The objective of the present invention is to provide a compact microwave heating unit capable of stably heating a fiber to be heated by irradiating it with microwaves, even when the dielectric constant of the fiber to be heated changes. Additionally, an objective other than the present invention is to provide a method for manufacturing carbon fibers by carbonizing the fiber to be heated using said microwave heating unit. means of solving the problem

[0011] The inventors have discovered that the above problem can be solved by driving a continuous fiber to be heated at an angle with respect to the axis of the furnace body. Specifically, since the electromagnetic field distribution generated within the furnace body reaches a maximum electric field strength at a predetermined point of the waveguide, by driving the continuous fiber to be heated at an angle with respect to the axis of the waveguide, the continuous fiber to be heated is heated near the maximum electric field strength, and the continuous fiber to be heated, whose dielectric constant has changed due to the heating, is rapidly withdrawn from the vicinity of the maximum electric field strength. This suppresses the electric field reflection caused by the transformation of the continuous fiber to be heated into a semiconductor or conductor, thereby increasing process stability.

[0012] In addition, it was discovered that when a dielectric continuous fiber to be heated is heated after it has been transformed into a semiconductor or conductor, heating using the electric field component of microwaves is prone to causing cutting due to discharge, which leads to unstable heating and significantly degrades the quality of the continuous fiber to be heated, and that the related problems can be solved by heating using the magnetic field component.

[0013] Furthermore, the inventors conceived of arranging a conventional heat-insulating tube that transmits microwaves within a conventional furnace body, and passing a continuous fiber to be heated through it to irradiate it with microwaves. They discovered that since this heat-insulating tube absorbs microwaves and generates heat on its own at high temperatures, it is possible to maintain the continuous fiber to be heated at high temperatures and dramatically improve the carbonization rate.

[0014] Based on these findings, the present invention was completed.

[0015] The present invention, which solves the above problem, is described below.

[0016] [1] A tube body (100, 101, 201, 301, 401, 501) formed by forming fiber inlet ports (103, 203, 303) and fiber outlet ports (105, 205, 305) on the wall of a waveguide, and

[0017] A microwave heating unit (1000, 1000a, 1000b, 1000c, 1001, 1002, 1003, 1004) comprising a microwave oscillator (11) that introduces microwaves into the waveguide,

[0018] The above-mentioned heated continuous fiber (150, 250, 350, 450, 550, 251, 351, 451, 551) is configured to travel inside the waveguide with an inclination of an angle θ° with respect to the axis of the waveguide, wherein the angle θ° is 0 < θ < 90, and

[0019] A microwave heating unit characterized in that the fiber outlet is formed in a portion other than the end portion of the waveguide.

[0020] [2] A microwave heating unit described in [1] in which the angle θ° is 10 < θ < 60.

[0021] The microwave heating unit of [1] and [2] above is a microwave heating unit that uses a waveguide as a furnace body and irradiates microwaves under atmospheric pressure onto a continuous fiber to be heated traveling inside the same, and is characterized by driving the fiber to be heated at an angle with respect to the tube axis of the waveguide.

[0022] [3] A microwave heating unit described in [1], wherein the waveguide is a square waveguide and the fiber inlet and fiber outlet are formed on the short side wall of the waveguide, respectively.

[0023] [4] A microwave heating unit described in [1], further comprising a thermal insulation tube (107, 207, 307) that penetrates the above waveguide and connects the fiber inlet and the fiber outlet, and configured such that the continuous fiber to be heated travels through the interior of the thermal insulation tube.

[0024] [5] A microwave heating unit described in [1], wherein the material of the above-mentioned insulation tube is ceramic.

[0025] The microwave heating units of [4] and [5] above have the outer circumference of the driving section of the continuous fiber to be heated covered with a ceramic thermal insulation tube.

[0026] [6] A method for manufacturing intermediate carbon fibers or carbon fibers by heating a continuous fiber to be heated while driving it using a microwave heating unit described in [1] to [5], characterized by including a process of heating a continuous fiber to be heated with a carbon content of less than 66 mass% to obtain intermediate carbon fibers or carbon fibers.

[0027] A method for manufacturing carbon fibers as described in [7][6], wherein a continuous fiber to be heated is driven through a maximum magnetic field portion within a waveguide using a microwave heating unit as described in [1] to [5].

[0028] The carbon fiber manufacturing method described in [6] and [7] above is a method for manufacturing carbon fibers that uses a microwave heating unit described in [1] to [5] in at least part of the carbon fiber manufacturing process. Effects of the invention

[0029] In the microwave heating unit of the present invention, the continuous fiber to be heated travels at an angle with respect to the axis of the furnace body. Therefore, the continuous fiber to be heated, which has been heated in the maximum electric field region within the furnace body and has a changed property (dielectric constant), can be rapidly withdrawn from the maximum electric field region. As a result, electric field reflection by the fiber made of a semiconductor or conductor is minimized within the furnace, thereby increasing process stability.

[0030] In addition, when a square waveguide is used as the furnace body and the fiber inlet and fiber outlet are loaded on the H side of the square waveguide, the width of the furnace body can be reduced, and the device can be made compact.

[0031] In addition, when using a heat-insulating tube, the continuous fiber to be heated can be maintained at a high temperature, thereby increasing the efficiency of carbonization. Brief explanation of the drawing

[0032] FIG. 1 is an explanatory diagram showing an example configuration of a microwave heating unit of the present invention. In addition, the structure of the furnace body is illustrated in a simplified manner. FIG. 2 is an explanatory diagram showing one configuration example of a furnace body of a microwave heating unit of the present invention. FIG. 3 is an explanatory diagram showing one configuration example of a furnace body (H-plane load) of a microwave heating unit of the present invention. FIG. 4 is an explanatory diagram showing one configuration example of a furnace body (E-plane load) of a microwave heating unit of the present invention. Figure 5 is an explanatory diagram showing the electromagnetic field distribution within the furnace body of Figure 2. Figure 6 is an explanatory diagram showing the electromagnetic field distribution within the furnace body of Figure 3. Figure 7 is an explanatory diagram showing the electromagnetic field distribution within the furnace body of Figure 4. Figure 8 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (H plane field) of a microwave heating unit. Figure 9 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (E-plane field) of a microwave heating unit. Figure 10 is an explanatory diagram showing the electromagnetic field distribution within the furnace body of Figure 3. Figure 11 is an explanatory diagram showing the electromagnetic field distribution within the furnace body of Figure 4. Figure 12 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (H-plane field) of a microwave heating unit. Figure 13 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (E-plane field) of a microwave heating unit. Figure 14 is a furnace body of a microwave heating unit in the case where a metal sleeve and a thermal insulation tube are not formed. Figure 15 is a furnace body of a microwave heating unit in the case where a metal sleeve is not formed. Figure 16 is a furnace body of a microwave heating unit in the case where a thermal insulation tube is not formed. Specific details for implementing the invention

[0033] Hereinafter, the microwave heating unit of the present invention and the method for manufacturing carbon fibers using the same will be described in detail with reference to the drawings.

[0034] In addition, in the present invention, the H plane of the furnace body refers to the short side wall of the square waveguide, and the E plane refers to the long side wall of the square waveguide.

[0035] In the present invention, dielectrics, semiconductors, and conductors are not distinguished by clear numerical values, but rather mean that the state of the continuous fiber to be heated before heating is dielectric, the state of being fully heated is conductor, and the intermediate state is semiconductor. That is, when the continuous fiber to be heated is a carbon fiber precursor, it means that the carbon fiber precursor (carbon content of 66 to 72 mass%) is dielectric, the carbon fiber or graphitized fiber is conductor (carbon content of 90 mass% or more), and the intermediate state is semiconductor.

[0036] (1) Microwave heating unit

[0037] FIG. 1 is an explanatory diagram showing an example configuration of a microwave heating unit of the present invention. In FIG. 1, 11 is a microwave oscillator, and one end of a connecting waveguide (12) is connected to the microwave oscillator (11), and the other end of the connecting waveguide (12) is connected to a furnace body (100). A circulator (13) and a matching unit (15) are interposed and mounted in sequence from the side of the microwave oscillator (11) on the connecting waveguide (12). One end of a connecting waveguide (14) is connected to the circulator (13), and a dummy rod (19) is connected to the other end of the connecting waveguide (14). At this time, an iris (16), which is a mechanism for adjusting the amount of microwaves flowing into the furnace body (100) and the amount of microwaves flowing out from the furnace body (100), and a shorting plate (17) for forming a standing wave may be formed at each end of the waveguide.

[0038] (2) Noche

[0039] The furnace body (100) of the microwave heating unit of the present invention is composed of a cylindrical waveguide or a square waveguide. When microwaves are introduced into the waveguide, an electromagnetic field distribution of the TE (Transverse Electric) mode is formed within the waveguide. The TE mode refers to a transmission mode having an electric field component that is orthogonal to the direction of the microwaves transmitted within the waveguide. By generating a standing wave within the furnace body (100), a location where the electric field component is maximized and a location where the magnetic field component is maximized exist at different locations within the furnace body (100). Therefore, by driving a continuous fiber to be heated through the furnace body, heating mainly by the electric field component (hereinafter also referred to as "electric field heating") and heating mainly by the magnetic field component (hereinafter also referred to as "magnetic field heating") can be performed, respectively.

[0040] (2-1) Road body using a cylindrical waveguide

[0041] FIG. 2 is an explanatory diagram showing one configuration example of a furnace body of a microwave heating unit of the present invention.

[0042] In FIG. 2, 1000 is a microwave heating unit, and 101 is a furnace body composed of a cylindrical waveguide with at least one end closed. On the outer circumference of the furnace body (101), a fiber inlet (103) and a fiber outlet (105) are formed, respectively. In the furnace body (101), a thermal insulation tube (107) may be formed that connects the fiber inlet (103) and the fiber outlet (105) while penetrating the interior of the furnace body (101) at an angle with respect to the tube axis. The thermal insulation tube (107) is configured so that a continuous fiber (150) to be heated is conveyed inside it. A shorting plate (109) is formed at the closed inner end of the furnace body (101). In order to prevent electromagnetic leakage from the furnace body (101), metal sleeves (111 and 113) can be formed in the fiber inlet (103) and fiber outlet (105), respectively.

[0043] Additionally, FIG. 14 is a furnace body (1000a) of a microwave heating unit in the case where a metal sleeve and a thermal insulation tube are not formed. FIG. 15 is a furnace body (1000b) of a microwave heating unit in the case where a metal sleeve is not formed. FIG. 16 is a furnace body (1000c) of a microwave heating unit in the case where a thermal insulation tube is not formed. Configurations identical to FIG. 2 are given the same reference numerals and their descriptions are omitted.

[0044] Next, the operation of this microwave heating unit (1000) will be described. In FIG. 2, 150 is a continuous fiber to be heated, which is continuously introduced into the furnace body (101) from the fiber introduction port (103) by passing through the interior of the thermal pipe (107) by means of a fiber conveying means not shown. The microwave generated by the microwave oscillator (11) passes through the connection waveguide (12) and further passes through the iris (16) to be introduced into the furnace body (101). The microwave that reaches the furnace body (101) is reflected by the shorting plate (109) formed at the closed inner end (terminal end) of the furnace body (101) and reaches the circulator (13) via the matching device (15). The reflected microwave (hereinafter also referred to as "reflected wave") is diverted at the circulator (13), passes through the connecting waveguide (14), and is absorbed at the dummy rod (19). At this time, a matching device (15) is used to match between the matching device (15) and the short-circuit plate (109), and a standing wave is generated within the furnace body (101). Due to this standing wave, a place where the electric field component is maximized (maximum electric field portion) and a place where the magnetic field component is maximized (maximum magnetic field portion) are formed at different locations within the furnace body (101). The continuous fiber to be heated (150) is heated by this standing wave. Furthermore, in the microwave heating unit (1000) of the present invention, the direction of travel of the continuous fiber to be heated (150) is inclined with respect to the tube axis and is neither perpendicular nor parallel. Therefore, the heated continuous fiber (150) does not travel only in the maximum electric field portion or the maximum magnetic field portion. Also, at this time, the inside of the furnace body (101) is at atmospheric pressure and is also in an inert atmosphere by an inert gas supply means not shown. The heated continuous fiber (150) passes through the fiber outlet (105) and is discharged out of the furnace body (101) by a fiber transport means not shown.The continuous fiber to be heated can be continuously heated by introducing the continuous fiber to be heated into the furnace body (101) from the fiber introduction port (103), heating the continuous fiber to be heated by irradiating it with microwaves inside the furnace body (101), and continuously discharging it from the fiber outlet (105).

[0045] The angle θ° formed by the pipe axis of the furnace body (101) and the pipe axis of the insulation pipe (107) is preferably 0 < θ < 90, 10 < θ < 60, and more preferably 15 < θ < 55. In addition, the continuous fiber to be heated (150) is configured to be discharged from the furnace body from a part other than the end portion of the furnace body. That is, the fiber outlet (105) is formed on the outer surface along the pipe axis of the furnace body (101). By intersecting the pipe axis of the furnace body (101) and the pipe axis of the insulation pipe (107) at an angle, the direction of travel of the continuous fiber to be heated is inclined with respect to the pipe axis, thereby preventing the continuous fiber to be heated from traveling only in the maximum electric field portion or the maximum magnetic field portion while traveling in the maximum electric field portion or the maximum magnetic field portion. As a result, process stability can be improved as described below. Additionally, the angle θ° formed by the pipe axis of the furnace body (101) and the continuous fiber to be heated (150) is preferably 0 < θ < 90, 10 < θ < 60, and more preferably 15 < θ < 55.

[0046] (2-2) Road body using a square waveguide

[0047] (a) H surface long

[0048] FIG. 3 is an explanatory diagram showing an example configuration of a furnace body of a microwave heating unit of the present invention. In FIG. 3, 1001 is a microwave heating unit, and 201 is a furnace body composed of a square waveguide with at least one end closed. On two H-shaped surfaces (201a, 201b) which are short-sided pipe walls of the furnace body (201), a fiber inlet (203) and a fiber outlet (205) are formed, respectively. A thermal insulation tube (207) may be formed in the furnace body (201) to connect the fiber inlet (203) and the fiber outlet (205) while penetrating the interior of the furnace body (201) at an angle. The thermal insulation tube (207) is configured so that a continuous fiber (250) to be heated is conveyed inside it. A short-circuit plate (209) is disposed and formed at the closed inner end of the furnace body (201). In order to prevent electromagnetic leakage from the furnace body (201), metal sleeves (211 and 213) may be formed in the fiber inlet (203) and fiber outlet (205), respectively. In addition, just as in the case where a cylindrical waveguide is used, the insulation tube and / or metal sleeves may be omitted even when a square waveguide is used.

[0049] Next, the operation of this microwave heating unit (1001) will be described. In FIG. 3, 250 is a continuous fiber to be heated, which is continuously introduced into the furnace body (201) from the fiber introduction port (203) by passing through the interior of the heat-insulating tube (207) by means of a fiber conveying means not shown. The microwave generated by the microwave oscillator (11) passes through the connection waveguide (12) and further passes through the iris (16) to be introduced into the furnace body (201). The microwave that reaches the furnace body (201) is reflected by the shorting plate (209) formed at the closed inner end (terminal end) of the furnace body (201) and reaches the circulator (13) via the matching device (15). The reflected wave changes direction at the circulator (13), passes through the connecting waveguide (14), and is absorbed at the dummy rod (19). At this time, a matching device (15) is used to match between the matching device (15) and the shorting plate (209), and a standing wave is generated within the furnace body (201). Due to this standing wave, a place where the electric field component is maximized (maximum electric field portion) and a place where the magnetic field component is maximized (maximum magnetic field portion) are formed at different locations within the furnace body (201). The continuous fiber to be heated (250) is heated by this standing wave. Furthermore, in the microwave heating unit (1001) of the present invention, the direction of travel of the continuous fiber to be heated (250) is inclined with respect to the tube axis and is neither perpendicular nor parallel. Therefore, the continuous fiber to be heated (250) does not travel only in the maximum electric field portion or the maximum magnetic field portion. Also, at this time, the inside of the furnace (201) is at atmospheric pressure and is also in an inert atmosphere by an inert gas supply means not shown. The heated continuous fiber (250) passes through the fiber outlet (205) by a fiber conveying means not shown and is discharged out of the furnace (201).The continuous fiber to be heated can be continuously heated by introducing the continuous fiber to be heated into the furnace (201) from the fiber introduction port (203), heating the continuous fiber to be heated by irradiating it with microwaves inside the furnace (201), and continuously discharging it from the fiber outlet (205).

[0050] The angle θ° formed by the pipe axis of the furnace body (201) and the pipe axis of the insulation pipe (207) is preferably 0 < θ < 90, 10 < θ < 60, and more preferably 15 < θ < 55. In addition, the continuous fiber to be heated (250) is configured to be discharged from the furnace body from a part other than the end portion of the furnace body. That is, the fiber outlet (205) is formed on the H surface (201b) of the furnace body (201). By intersecting the pipe axis of the furnace body (201) and the pipe axis of the insulation pipe (207) at an angle, the direction of travel of the continuous fiber to be heated is inclined with respect to the pipe axis, thereby preventing the continuous fiber to be heated from traveling only in the maximum electric field portion or the maximum magnetic field portion while traveling in the maximum electric field portion or the maximum magnetic field portion. As a result, process stability can be improved as described below. Additionally, the angle θ° formed by the pipe axis of the furnace body (201) and the continuous fiber to be heated (250) is preferably 0 < θ < 90, 10 < θ < 60, and more preferably 15 < θ < 55.

[0051] In the present invention, it is preferable to have an H-plane furnace capable of reducing the width and tow pitch.

[0052] (b) E surface, Jangha-ro

[0053] FIG. 4 is an explanatory diagram showing another configuration example of the furnace body of the microwave heating unit of the present invention. In FIG. 4, 1002 is a microwave heating unit, and 301 is a furnace body composed of a square waveguide with at least one end closed. On two E-sides (301a, 301b), which are the long side walls of the furnace body (301), a fiber inlet (303) and a fiber outlet (305) are formed, respectively. In the furnace body (301), a thermal insulation tube (307) is formed that connects the fiber inlet (303) and the fiber outlet (305) while penetrating the interior of the furnace body (301) at an angle. The thermal insulation tube (307) is configured so that a continuous fiber (350) to be heated is conveyed inside it. A shorting plate (309) is disposed and formed at the closed inner end of the furnace body (301). In order to prevent electromagnetic leakage from the furnace body (301), metal sleeves (311 and 313) may be formed in the fiber inlet (303) and fiber outlet (305), respectively.

[0054] The operation of this microwave heating unit (1002) is omitted because it is the same as the aforementioned microwave heating unit (1001).

[0055] (3) Electric field heating

[0056] Below, the composition of a furnace body that heats a dielectric carbon fiber precursor by electric field heating is described.

[0057] FIG. 5 is an explanatory diagram showing an example of the electromagnetic field distribution within the furnace body (101) of the microwave heating unit of FIG. 2. This furnace body (101) is configured to include a maximum electric field portion in the running portion of the continuous fiber (150) (carbon fiber precursor) to be heated. In FIG. 5, the electric field distribution within the furnace body (101) is schematically depicted as a solid line, and the magnetic field distribution as a dashed line. In this furnace body (101), an electric field component orthogonal to the continuous fiber (150) (carbon fiber precursor) to be heated running within the furnace body (101) is formed, thereby heating the continuous fiber (150) (carbon fiber precursor). At this time, since the travel direction of the continuous fiber (150) (carbon fiber precursor) to be heated intersects the pipe axis of the furnace body (101) at an angle, it passes not only through the maximum electric field portion within the furnace body (101) but also through the weak electric field portion. That is, the continuous fiber (150) (carbon fiber precursor) to be heated, introduced into the furnace body (101) from the fiber introduction port (103), passes sequentially through the weak electric field portion, the maximum electric field portion, and the weak electric field portion within the furnace body (101), and is configured to be discharged from the furnace body (101) through the fiber outlet (105). After the carbon fiber precursor is transformed into a semiconductor or conductor by being heated in the maximum electric field portion, the fiber to be heated is quickly discharged from the maximum electric field portion. Therefore, the microwave irradiation state within the furnace body can be stabilized. In addition, at this time, it is preferable to form a fiber introduction port on the upper side of the furnace body (101) so that heat generated from the furnace body is discharged to the upper side of the furnace body, thereby preheating the continuous fiber (150) (carbon fiber precursor) to be heated.

[0058] FIG. 6 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (201) of the microwave heating unit of FIG. 3. The furnace body (201) is an H-plane furnace. This H-plane furnace is configured to include a maximum electric field portion in the running portion of the continuous fiber (250) (carbon fiber precursor) to be heated. In FIG. 6, the electric field distribution within the furnace body (201) is schematically depicted as a solid line, and the magnetic field distribution as a dashed line. In this furnace body, an electric field component orthogonal to the continuous fiber (250) (carbon fiber precursor) to be heated running within the furnace body (201) is formed, thereby heating the continuous fiber (250) (carbon fiber precursor). At this time, since the travel direction of the continuous fiber (250) (carbon fiber precursor) to be heated intersects the pipe axis of the furnace body (201) at an angle, it passes not only through the maximum electric field portion within the furnace body (201) but also through the weak electric field portion. That is, the continuous fiber (250) (carbon fiber precursor) to be heated, introduced into the furnace body (201) from the fiber introduction port (203), passes sequentially through the weak electric field portion, the maximum electric field portion, and the weak electric field portion within the furnace body (201), and is configured to be discharged from the furnace body (201) through the fiber outlet (205). After the carbon fiber precursor is transformed into a semiconductor or conductor by being heated in the maximum electric field portion, the fiber to be heated is quickly withdrawn from the maximum electric field portion. Therefore, the microwave irradiation state within the furnace body can be stabilized. In addition, at this time, it is preferable to form a fiber introduction port on the upper side of the furnace body (201) so that heat generated from the furnace body is directed toward the upper side of the furnace body, thereby preheating the continuous fiber (250) (carbon fiber precursor) to be heated.

[0059] FIG. 7 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (301) of the microwave heating unit of FIG. 4. The furnace body (301) is an E-plane furnace. This E-plane furnace is configured to include a maximum electric field portion in the running portion of the continuous fiber (350) (carbon fiber precursor) to be heated. In FIG. 7, the electric field distribution within the furnace body (301) is schematically depicted as a solid line, and the magnetic field distribution as a dashed line. In this furnace body, a portion of the electric field component is formed along the length direction of the continuous fiber (350) (carbon fiber precursor) to be heated running within the furnace body (301), thereby efficiently heating the continuous fiber (350) (carbon fiber precursor). At this time, since the travel direction of the continuous fiber to be heated (350) (carbon fiber precursor) intersects at an angle with respect to the pipe axis of the furnace body (301), it passes not only through the maximum electric field portion within the furnace body (301) but also through the weak electric field portion. That is, the continuous fiber to be heated (350) (carbon fiber precursor) introduced into the furnace body (301) from the fiber introduction port (303) is configured to sequentially pass through the weak electric field portion, the maximum electric field portion, and the weak electric field portion within the furnace body (301) and be discharged out of the furnace body (301) through the fiber outlet (305). After the carbon fiber precursor is heated in the maximum electric field portion containing the electric field component in the longitudinal direction of the continuous fiber to be heated (350) (carbon fiber precursor) and is transformed into a semiconductor or conductor, the fiber to be heated is quickly discharged from the maximum electric field portion. Therefore, the microwave irradiation state inside the furnace can be stabilized.

[0060] FIG. 8 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (401) of a microwave heating unit (1003). This furnace body (401) is an H-plane furnace. In this H-plane furnace, the continuous fiber (450) (carbon fiber precursor) to be heated is configured to travel through the maximum electric field portion. In FIG. 8, the electric field distribution within the furnace body (401) is schematically depicted as a dashed line, and the magnetic field distribution as a solid line. In this furnace body, an electric field component perpendicular to the long side wall of the furnace body (401) is formed, thereby heating the continuous fiber (450) (carbon fiber precursor). That is, the continuous fiber (450) (carbon fiber precursor) to be heated, which is introduced into the furnace body (401) from the fiber introduction port, passes through the maximum electric field portion within the furnace body (401) and is configured to be discharged out of the furnace body (401) from the fiber outlet.

[0061] FIG. 9 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (501) of a microwave heating unit (1004). This furnace body (501) is an E-plane furnace. In this E-plane furnace, the continuous fiber (550) (carbon fiber precursor) to be heated is configured to travel through the maximum electric field portion. In FIG. 9, the electric field distribution within the furnace body (501) is schematically depicted as a dashed line, and the magnetic field distribution as a solid line. In this furnace body, an electric field component is formed that is parallel to the long side wall of the furnace body (501) and also parallel to the traveling continuous fiber (550) (carbon fiber precursor), thereby heating the continuous fiber (550) (carbon fiber precursor). That is, the continuous fiber (550) (carbon fiber precursor) to be heated, which is introduced into the furnace body (501) from the fiber introduction port, is configured to pass through the maximum electric field portion within the furnace body (501) and be discharged out of the furnace body (501) from the fiber outlet.

[0062] (4) Magnetic field heating

[0063] Below, the configuration of a furnace body that heats a continuous fiber to be heated, which is a semiconductor or a conductor, by magnetic field heating is described.

[0064] FIG. 10 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (201) of the microwave heating unit of FIG. 3. This furnace body (201) is an H-plane furnace. This H-plane furnace is configured to include a maximum magnetic field generating portion in the running portion of the continuous fiber (251) to be heated. In FIG. 10, the electric field distribution within the furnace body (201) is schematically depicted as a dashed line, and the magnetic field distribution is schematically depicted as a solid line. In this furnace body, a magnetic field component parallel to the long side pipe wall of the furnace body (201) is formed, thereby heating the continuous fiber (251) to be heated. At this time, since the running direction of the continuous fiber (251) to be heated intersects at an angle with respect to the pipe axis of the furnace body (201), it passes not only through the maximum magnetic field portion within the furnace body (201) but also through the weak magnetic field portion. That is, the continuous fiber to be heated (251) introduced into the furnace body (201) from the fiber introduction port (203) is configured to sequentially pass through the weak magnetic field portion, the maximum magnetic field portion, and the weak magnetic field portion within the furnace body (201), and then be discharged out of the furnace body (201) through the fiber exit port (205). By being heated in the maximum magnetic field portion and avoiding the maximum electric field portion, the microwave irradiation state within the furnace body can be stabilized. Since it passes through the weak magnetic field portion, the maximum magnetic field portion, and the weak magnetic field portion sequentially, the temperature of the continuous fiber to be heated is prone to dropping. Therefore, it is preferable to use the thermal insulation tube described later.

[0065] FIG. 11 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (301) of the microwave heating unit of FIG. 4. This furnace body (301) is an E-plane furnace. This E-plane furnace is configured to include a maximum magnetic field portion in the running portion of the continuous fiber (351) to be heated. In FIG. 11, the electric field distribution within the furnace body (301) is schematically depicted as a dashed line, and the magnetic field distribution as a solid line. In this furnace body, a magnetic field component parallel to the long side wall of the furnace body (301) is formed, thereby heating the continuous fiber (351) to be heated. At this time, since the running direction of the continuous fiber (351) to be heated intersects at an angle with respect to the pipe axis of the furnace body (301), it passes not only through the maximum magnetic field portion within the furnace body (301) but also through the weak magnetic field portion. That is, the continuous fiber to be heated (351) introduced into the furnace body (301) from the fiber introduction port (303) is configured to sequentially pass through the weak magnetic field portion, the maximum magnetic field portion, and the weak magnetic field portion within the furnace body (301), and then be discharged from the furnace body (301) through the fiber outlet port (305). By heating in the maximum magnetic field portion and avoiding the maximum electric field portion, the microwave irradiation state within the furnace body can be stabilized. Since it passes through the weak magnetic field portion, the maximum magnetic field portion, and the weak magnetic field portion sequentially, the temperature of the continuous fiber to be heated is prone to dropping. Therefore, it is preferable to use the thermal insulation tube described later.

[0066] FIG. 12 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (401) of a microwave heating unit (1003). This furnace body (401) is an H-plane furnace. In this H-plane furnace, the continuous fiber to be heated is configured to travel through the maximum magnetic field portion. In FIG. 12, the electric field distribution within the furnace body (401) is schematically depicted as a dashed line, and the magnetic field distribution as a solid line. In this furnace body, a magnetic field component parallel to the long side wall of the furnace body (401) is formed, thereby heating the continuous fiber (451) to be heated. That is, the continuous fiber (451) to be heated, introduced into the furnace body (401) from the fiber introduction port, is configured to pass through the maximum magnetic field portion while avoiding the maximum electric field portion within the furnace body (401), and to be discharged out of the furnace body (401) through the fiber outlet.

[0067] FIG. 13 is an explanatory diagram showing the electromagnetic field distribution within the furnace body (501) of a microwave heating unit (1004). This furnace body (501) is an E-plane furnace. In this E-plane furnace, the continuous fiber to be heated is configured to travel through a maximum magnetic field portion. In FIG. 13, the electric field distribution within the furnace body (501) is schematically depicted as a dashed line, and the magnetic field distribution as a solid line. In this furnace body, a magnetic field component is formed that is parallel to the long side wall of the furnace body (501) and is also orthogonal to the traveling continuous fiber to be heated, thereby heating the continuous fiber to be heated (551). That is, the carbon fiber precursor (551) introduced into the furnace body (501) from the fiber introduction port is configured to pass through the maximum magnetic field portion while avoiding the maximum electric field portion within the furnace body (501) and to be discharged out of the furnace body (501) from the fiber exit port.

[0068] (5) Insulation tube

[0069] The microwave heating unit of the present invention preferably has a heat-retaining tube. The heat-retaining tube is inserted into the furnace body to connect the fiber inlet and the fiber outlet while penetrating the furnace body, and is configured to allow a continuous fiber to be heated to travel inside. The heat-retaining tube blocks radiant heat generated from the heating of the continuous fiber to be heated, thereby suppressing heat dissipation and maintaining the inside of the heat-retaining tube at a high temperature. The inside of the heat-retaining tube is at atmospheric pressure and is also maintained in an inert atmosphere by an inert gas supply means (not shown).

[0070] The thermal insulation tube (107, 207, 307) is preferably cylindrical. The inner diameter of the thermal insulation tube (107, 207, 307) is not particularly limited, but is generally 8 to 55 mm. The outer diameter of the thermal insulation tube (107, 207, 307) is not particularly limited, but is generally 10 to 60 mm. The length of the thermal insulation tube (107, 207, 307) is not particularly limited, but is generally 100 to 2500 mm. In addition, the material of the thermal insulation tube (107, 207, 307) must be a material that transmits microwaves, and the microwave transmittance is preferably 90 to 100% at room temperature (25°C), and more preferably 95 to 100%. Examples of such materials include ceramics such as quartz or alumina. The microwave transmittance of these materials is 100% for quartz and 99.9% for alumina. The microwave transmittance of ceramics varies depending on the composition; for a composition of 41% silica to 55% alumina, it is 99.9%, but the composition is not limited to this combination as long as the microwave transmittance is within the above range. As for the ceramic, it may contain metal oxides such as alumina, silica-alumina, titania, zirconia, magnesia, and calcia, metal nitrides such as silicon nitride, aluminum nitride, and titanium nitride, or other compounds. In particular, alumina or silica-alumina is preferred because it functions as a susceptor that partially absorbs microwaves and generates heat at high temperatures. At both ends of the insulation tube (107, 207, 307), a microwave-absorbing material may be placed to prevent microwave leakage.

[0071] The shape of the waveguide used as the core is not particularly limited as long as it can form an electromagnetic field distribution of TE mode within the waveguide. Generally, the length of the waveguide is preferably 500 to 1500 mm. In addition, the opening of the cross-section perpendicular to the axis of the square waveguide is preferably 105 to 115 mm in length and 50 to 60 mm in width. The material of the waveguide is not particularly limited, but is generally made of metal such as stainless steel, iron, copper, or aluminum.

[0072] The frequency of the microwave is not particularly limited, but generally 915 MHz, 2.45 GHz, or 5.8 GHz is used. The output of the microwave oscillator is not particularly limited, but 300 to 2400 W is suitable, and 500 to 2000 W is more suitable.

[0073] The conveying speed of the fiber to be carbonized in the carbonization furnace is preferably 0.05 to 10 m / min, more preferably 0.1 to 5.0 m / min, and particularly preferably 0.2 to 2.0 m / min.

[0074] The carbon fiber obtained in this way preferably has a carbon content of 90 mass% or more, and more preferably 91 mass% or more.

[0075] (6) Method for manufacturing carbon fiber

[0076] When manufacturing carbon fibers using the microwave heating unit of the present invention, multiple microwave heating units of the present invention may be connected in series to perform heating. Additionally, the device may be configured to include a microwave heating unit other than the present invention, or a heating device other than a microwave heating unit.

[0077] Examples

[0078] The present invention will be explained in more detail below through examples. The present invention is not limited to these examples.

[0079] In the following examples, the carbon fiber precursor fiber refers to a PAN-based flame-retardant fiber with a carbon content of 60 mass%, and the intermediate carbon fiber refers to a PAN-based intermediate carbon fiber with a carbon content of 66 mass% unless otherwise specified. In addition, the evaluation of "process passability" was marked as ◎ when continuous carbonization (continuous operation) is possible without the individual fibers being cut, as ○ when continuous operation is possible even though some individual fibers are cut, as △ when the cut individual fibers are likely to get entangled in a conveying device such as a roll and cause interference with continuous operation, and as × when the entire fiber bundle is cut and cannot be removed from the furnace. The evaluation of "fiber quality" was marked as ◎ when the fibers are not cut at all during carbonization, as ○ when extremely fine lint is generated on the fibers during carbonization, as △ when a large amount of lint is generated, and as × when the fibers are completely cut.

[0080] (Example 1)

[0081] A microwave heating unit (microwave oscillator frequency: 2.45 GHz) as described in Fig. 1 was constructed. For the furnace body, a square waveguide with an opening of 110 × 55 mm in cross-section perpendicular to the tube axis and a length of 500 mm was used, and the configuration as shown in Fig. 3 was established. The fiber inlet and outlet were formed on the H-side (short axial wall) of the furnace body. The angle θ between the axis of the furnace body and the fiber travel direction was set to 37°. At this time, the length of the fiber accommodated within the furnace body (i.e., the length of the line segment connecting the center of the fiber inlet and the center of the outlet; the same applies hereinafter) was 183 mm. For the insulation tube, a cylindrical silica alumina tube (microwave transmittance = 99.9%) with an inner diameter of 15 mm, an outer diameter of 17 mm, and a length of 300 mm was used. Microwaves were introduced into a furnace body under a nitrogen gas atmosphere to form an electromagnetic field distribution in the TE mode. The output of the microwave oscillator was set to 300 W. Carbon fibers were obtained by carbonizing a carbon fiber precursor while driving it at 0.3 m / min so that the region of maximum electric field within the furnace body intersected the dielectric carbon fiber precursor at the axis of the furnace body. The carbon content of the obtained carbon fibers was 93 mass%, and no fiber breakage was observed, indicating very good process passability. The evaluation results are shown in Table 1.

[0082] (Example 2)

[0083] Intermediate carbon fibers were obtained by heating in the same manner as in Example 1, except that the angle between the furnace body axis and the fiber travel direction was changed to 54°. At this time, the length of the fibers accommodated in the furnace body was 136 mm. During the process, breakage was observed in some single filaments, but the process passability was good. The evaluation results are shown in Table 1.

[0084] (Example 3)

[0085] Intermediate carbon fibers were obtained by heating in the same manner as in Example 1, except that the angle between the furnace body's axis and the fiber's travel direction was set to 17° and the length of the insulation tube was changed to 500 mm. At this time, the length of the fibers accommodated in the furnace body was 376 mm. Although the furnace temperature rose, it did not reach a temperature sufficient for the carbonization reaction of the fibers during the process, so intermediate carbon fibers and carbon fibers could not be obtained. The evaluation results are shown in Table 1.

[0086] (Comparative Example 1)

[0087] A microwave heating unit (microwave oscillator frequency: 2.45 GHz) as described in Fig. 1 was constructed. For the furnace body, a square waveguide with an opening of 110 × 55 mm in a cross-section perpendicular to the tube axis and a length of 500 mm was used. The fiber inlet was formed on the microwave introduction surface of the furnace body, and the fiber outlet was formed at the end of the furnace body. The angle between the furnace body axis and the fiber travel direction was set to 0°. At this time, the length of the fiber accommodated within the furnace body was 500 mm. For the insulation tube, a cylindrical silica-alumina tube (microwave transmittance = 99.9%) with an inner diameter of 15 mm, an outer diameter of 17 mm, and a length of 600 mm was used. Microwaves were introduced into the furnace body under a nitrogen gas atmosphere to form an electromagnetic field distribution in the TE mode. The output of the microwave oscillator was set to 300 W. Carbon fiber precursors were carbonized while driving at 0.3 m / min to pass through the furnace. At this time, since regions of maximum electric and magnetic fields alternately exist within the furnace, the electromagnetic field to which the fibers are exposed undergoes repeated transitions between the regions of maximum electric and magnetic fields. During the process, the fibers were cut, and due to very poor process passability, intermediate carbon fibers and carbon fibers could not be obtained. The evaluation results are shown in Table 1.

[0088] (Comparative Example 2)

[0089] A microwave heating unit (microwave oscillator frequency: 2.45 GHz) as described in Fig. 1 was constructed. For the furnace body, a square waveguide with an opening of 110 × 55 mm in cross-section perpendicular to the tube axis and a length of 500 mm was used, as shown in Fig. 8. The fiber inlet and outlet were formed on the H-side (short axial wall) of the furnace body. The angle between the axis of the furnace body and the fiber travel direction was set to 90°. At this time, the length of the fiber accommodated within the furnace body was 110 mm. For the insulation tube, a cylindrical silica-alumina tube (microwave transmittance = 99.9%) with an inner diameter of 15 mm, an outer diameter of 17 mm, and a length of 300 mm was used. Microwaves were introduced into the furnace body under a nitrogen gas atmosphere to form an electromagnetic field distribution of the TE mode. The output of the microwave oscillator was set to 300 W. Carbonation was performed by driving the carbon fiber precursor at 0.3 m / min so that it passed only through the maximum electric field portion within the furnace body. During the process, the fibers were cut, and due to very poor process passability, intermediate carbon fibers and carbon fibers could not be obtained. The evaluation results are shown in Table 1.

[0090] (Example 4)

[0091] Carbon fibers were obtained by heating in the same manner as in Example 1, except that the maximum magnetic field portion within the furnace body and the carbon fiber precursor were modified to intersect the axis of the furnace body. At this time, the length of the fibers accommodated within the furnace body was 183 mm. The carbon content of the obtained carbon fibers was 93 mass%, and no fiber breakage was observed, indicating very good processability. The evaluation results are shown in Table 1.

[0092] (Example 5)

[0093] Intermediate carbon fibers were obtained by heating in the same manner as in Example 4, except that the angle between the axial center of the furnace and the fiber travel direction was changed to 54°. At this time, the length of the fibers accommodated in the furnace was 136 mm. The carbon content of the obtained intermediate carbon fibers was 70 mass%, and although some single filaments showed breakage during the process, the process passability was good. The evaluation results are shown in Table 1.

[0094] (Example 6)

[0095] Intermediate carbon fibers were obtained by heating in the same manner as in Example 4, except that the angle between the furnace body's axis and the fiber's travel direction was set to 17° and the length of the insulation tube was changed to 500 mm. At this time, the length of the fibers accommodated in the furnace body was 376 mm. Although the furnace temperature rose, it did not reach a temperature rise sufficient for the carbonization reaction of the fibers during the process, so intermediate carbon fibers and carbon fibers could not be obtained. The evaluation results are shown in Table 1.

[0096] (Comparative Example 3)

[0097] Heating was performed in the same manner as in Comparative Example 2, except that the maximum magnetic field portion within the furnace body and the carbon fiber precursor were modified so that they intersected with the axis of the furnace body (i.e., the configuration of Fig. 12). At this time, the length of the fiber accommodated within the furnace body was 110 mm. During the process, no temperature rise of the fiber was observed, so intermediate carbon fibers and carbon fibers could not be obtained. The evaluation results are shown in Table 1.

[0098] (Example 7)

[0099] Intermediate carbon fibers were obtained by heating in the same manner as in Example 1, except that the fiber inlet and fiber outlet were positioned on the E-plane of the furnace body (i.e., the configuration of Fig. 4), and the position where the carbon fiber precursor and the axis of the furnace body intersect was changed from the maximum electric field portion to the maximum magnetic field portion. At this time, the length of the fibers accommodated in the furnace body was 91 mm. The carbon content of the obtained intermediate carbon fibers was 74 mass%, and no fiber breakage was observed, indicating very good process passability. The evaluation results are shown in Table 1.

[0100] (Example 8)

[0101] Intermediate carbon fibers were obtained by heating in the same manner as in Example 7, except that the angle between the axis of the furnace body and the fiber travel direction was changed to 54°. At this time, the length of the fibers accommodated in the furnace body was 68 mm. The carbon content of the obtained intermediate carbon fibers was 72 mass%, some single filaments showed breakage, and the fibers after heating were easily wound onto a conveyor roll. The evaluation results are shown in Table 1.

[0102] (Example 9)

[0103] Intermediate carbon fibers were obtained by heating in the same manner as in Example 7, except that the angle between the furnace body axis and the fiber travel direction was changed to 17°. At this time, the length of the fibers accommodated in the furnace body was 188 mm. No fiber breakage was observed, indicating very good process passability. The evaluation results are shown in Table 1.

[0104] (Comparative Example 4)

[0105] The configuration described in FIG. 13 was used, and heating was performed in the same manner as in Comparative Example 3, except that the fiber inlet and outlet were formed on the E side (long axis pipe wall) of the furnace body. At this time, the length of the fiber received in the furnace body was 55 mm. During the process, no temperature rise of the fiber was observed, so intermediate carbon fibers and carbon fibers could not be obtained. The evaluation results are shown in Table 1.

[0106] (Example 10)

[0107] Intermediate carbon fibers were obtained by heating in the same manner as in Example 7, except that the maximum electric field portion within the furnace body and the carbon fiber precursor intersected with the axis of the furnace body. At this time, the length of the fibers accommodated within the furnace body was 91 mm. The carbon content of the obtained intermediate carbon fibers was 72%, and no fiber breakage was observed, indicating very good process passability. The evaluation results are shown in Table 1.

[0108] (Example 11)

[0109] Intermediate carbon fibers were obtained by heating in the same manner as in Example 10, except that the angle between the furnace body axis and the fiber travel direction was changed to 54°. At this time, the length of the fibers accommodated in the furnace body was 68 mm. During the process, some single filaments were observed to be broken, and the fibers after heating were easily wound onto the conveyor rolls. The evaluation results are shown in Table 1.

[0110] (Example 12)

[0111] Intermediate carbon fibers were obtained by heating in the same manner as in Example 10, except that the angle between the furnace body axis and the fiber travel direction was changed to 17°. At this time, the length of the fiber accommodated in the furnace body was 188 mm. No fiber breakage was observed, indicating very good process passability. The evaluation results are shown in Table 1.

[0112] (Comparative Example 5)

[0113] Heating was performed in the same manner as in Comparative Example 4, except that the maximum electric field portion within the furnace body and the carbon fiber precursor were modified to intersect the axis of the furnace body (i.e., the configuration of Fig. 9). At this time, the length of the fibers accommodated within the furnace body was 55 mm. During the process, a large amount of lint was generated on the fibers, and the process passability was very poor, so intermediate carbon fibers and carbon fibers could not be obtained. The evaluation results are shown in Table 1.

[0114]

[0115] (Example 13)

[0116] Carbon fibers were obtained by carbonization in the same manner as in Example 4, except that the fiber to be heated was changed from a carbon fiber precursor to an intermediate carbon fiber that is a semiconductor or conductor. The carbon content of the obtained carbon fiber was 95 mass%, and no fiber breakage was observed, indicating very good processability. The evaluation results are shown in Table 2.

[0117] (Example 14)

[0118] Carbon fibers were obtained by heating in the same manner as in Example 13, except that the angle between the axis of the furnace body and the fiber travel direction was changed to 54°. The length of the fibers accommodated in the furnace body was 136 mm. Some single filaments showed breakage, and the fibers after heating were easily wound onto a conveyor roll. The evaluation results are shown in Table 2.

[0119] (Example 15)

[0120] Carbon fibers were obtained by heating in the same manner as in Example 13, except that the angle between the furnace body axis and the fiber travel direction was changed to 17°. The length of the fibers accommodated in the furnace body was 376 mm. During the process, breakage was observed in some single filaments, but the process passability was good. The evaluation results are shown in Table 2.

[0121] (Comparative Example 6)

[0122] Carbonization was performed in the same manner as in Comparative Example 1, except that the fiber to be heated was changed from a carbon fiber precursor to an intermediate carbon fiber that is a semiconductor or conductor. During the process, the fiber was cut, and the process passability was very poor, so carbon fiber could not be obtained. The evaluation results are shown in Table 2.

[0123] (Comparative Example 7)

[0124] Carbonization was performed in the same manner as in Comparative Example 3, except that the fiber being heated was changed from a carbon fiber precursor to an intermediate carbon fiber that is a semiconductor or conductor. During the process, breakage was observed in the single fiber, and a large amount of fluff was generated. The evaluation results are shown in Table 2.

[0125] (Example 16)

[0126] Carbon fibers were obtained by carbonization in the same manner as in Example 7, except that the fiber being heated was changed from a carbon fiber precursor to an intermediate carbon fiber that is a semiconductor or conductor. The carbon content of the obtained carbon fiber was 90 mass%, and no fiber breakage was observed, indicating very good processability. The evaluation results are shown in Table 2.

[0127] (Example 17)

[0128] Carbon fibers were obtained by heating in the same manner as in Example 8, except that the fiber being heated was changed from a carbon fiber precursor to an intermediate carbon fiber that is a semiconductor or conductor. During the process, some single filaments were cut, and the fibers after heating were easily wound onto a conveyor roll. The evaluation results are shown in Table 2.

[0129] (Example 18)

[0130] Carbon fibers were obtained by heating in the same manner as in Example 9, except that the fiber being heated was changed from a carbon fiber precursor to an intermediate carbon fiber that is a semiconductor or conductor. During the process, some single fibers showed breakage, but the process passability was good. The evaluation results are shown in Table 2.

[0131] (Comparative Example 8)

[0132] Carbonization was performed in the same manner as in Comparative Example 4, except that the fiber to be heated was changed from a carbon fiber precursor to an intermediate carbon fiber that is a semiconductor or conductor. During the process, a large amount of lint was generated on the fiber, and winding onto the conveying roll occurred easily. The carbon content of the obtained carbon fiber was 90 mass%. The evaluation results are shown in Table 2.

[0133] Explanation of the symbols

[0134] 11 : Microwave oscillator 12, 14: Connecting waveguides 13 : Circulator 15 : Matching unit 16 : Iris 17, 109, 209, 309 : Paragraph board 19 : Dummy Load 100, 101, 201, 301, 401, 501 : Noche 201a, 201b: H-face of the road body 301a, 301b: Surface E of the road body 103, 203, 303: Fiber inlet 105, 205, 305: Fiber outlet 107, 207, 307: Insulation tubes 111, 113, 211, 213, 311, 313: Metal sleeve 150, 250, 350, 450, 550, 251, 351, 451, 551: Continuous fiber to be heated 1000, 1000a, 1000b, 1000c, 1001, 1002, 1003, 1004: Microwave heating unit

Claims

Claim 1 A microwave heating unit comprising a furnace body formed by forming a fiber introduction port and a fiber exit port on the wall of a waveguide, and a microwave oscillator for introducing microwaves into the waveguide, wherein a continuous fiber to be heated, which is a carbon fiber precursor, is configured to travel inside the waveguide with an angle θ° with respect to the axis of the waveguide, wherein the angle θ° is 0 < θ < 90, and the fiber exit port is formed in a part other than the end portion of the waveguide. Claim 2 A microwave heating unit according to claim 1, wherein the angle θ° is 10 < θ < 60. Claim 3 A microwave heating unit according to claim 1, wherein the waveguide is a square waveguide, and a fiber inlet and a fiber outlet are formed on the short side wall of the waveguide, respectively. Claim 4 A microwave heating unit according to claim 1, further comprising a thermal insulation tube that penetrates the waveguide and connects the fiber inlet and the fiber outlet, and configured such that the continuous fiber to be heated travels through the interior of the thermal insulation tube. Claim 5 In claim 4, a microwave heating unit in which the material of the insulation tube is alumina, silica-alumina, or ceramic. Claim 6 A method for manufacturing intermediate carbon fibers or carbon fibers, wherein a continuous fiber to be heated is heated while being driven using a microwave heating unit described in any one of claims 1 to 5, and wherein the method comprises a process of heating a continuous fiber to be heated having a carbon content of less than 66 mass% to obtain intermediate carbon fibers or carbon fibers. Claim 7 A method for manufacturing carbon fibers as described in claim 6, wherein the continuous fiber to be heated is driven by a maximum magnetic field portion within a waveguide using the microwave heating unit.

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