JP6878095B2 - Heating method and carbon fiber manufacturing method, carbonization equipment and carbon fiber manufacturing equipment - Google Patents

Description

The present invention relates to a heating method using microwaves and the like.

Carbon fibers are produced by heating precursor fibers produced from polyacrylonitrile-based fibers, rayon-based fibers, cellulosic-based fibers, pitch-based fibers and the like. For example, heating of a precursor fiber produced from polyacrylonitrile-based fiber is referred to as a fiber that has undergone a flame-resistant step and a flame-resistant step of heating in an atmosphere containing oxygen (in a flame-resistant furnace) (hereinafter, referred to as "flame-resistant fiber". ) Is heated in an inert atmosphere (carbonization furnace) through a carbonization step. The heating is performed by passing (running) the fibers through the flame-resistant furnace and the carbonization furnace. Further, the fibers here are in the form of a bundle in which a plurality of filaments are gathered.
As heating for carbonizing precursor fibers, a method using microwaves has been proposed in addition to the conventional electric heater (for example, Patent Documents 1 and 2). In the method described in Patent Document 2, a heated object traveling in the heating tube is heated by a TE mode microwave propagating in a heating tube having a pair of short side walls and a pair of long side walls and having a rectangular cross section. The object to be heated is supplied so as to cross the pair of short side walls.
The heating in Patent Document 2 is so-called electric field heating, in which the electric field is perpendicular to the object to be heated.

Patent No. 6063045 Japanese Unexamined Patent Publication No. 2016-195021

However, in the technique of Patent Document 2, since the object to be heated crosses the pair of short side walls, the heating length of the object to be heated becomes short. Therefore, in order to secure the energy to be applied, it is necessary to slow down the traveling speed of the object to be heated or to enlarge the heating tube to lengthen the short side wall, which is difficult to apply to the production machine.
Further, as described in the 80th paragraph of Patent Document 1, when the precursor fiber is heated, the reaction proceeds due to the heat storage and the precursor fiber is cut, so that the energy (electric field) applied to the object to be heated is being applied during traveling. However, it is difficult to adjust the energy by the method of Patent Document 2.
In addition to the filamentous conductive material, these problems can also occur in a film-like material or an object to be heated that is conveyed in the waveguide by a conveying means.
In view of the above problems, it is an object of the present invention to provide a heating method, a carbon fiber manufacturing method, and the like, which can lengthen the heating of the object to be heated and can adjust the energy intensity of microwaves applied during traveling. To do.

In order to achieve the above object, the heating method according to one aspect of the present invention uses a TE mode microwave electric field propagating in a heating tube having a rectangular cross section having a pair of short side walls and a pair of long side walls. In a heating method for heating an object to be heated that travels in the heating tube along the tube axis of the heating tube, the strength of the microwave electric field is determined in the cross section of the heating tube along the traveling direction of the object to be heated. It is adjusted by changing the internal area.
In order to achieve the above object, the heating method according to one aspect of the present invention uses a TE-mode microwave electric field propagating in a heating tube having a pair of short side walls and a pair of long side walls. In a heating method for heating an object to be heated that travels in a heating tube along the tube axis of the heating tube, the heating tube has a slit for introducing microwaves generated from a microwave generator in the traveling direction. The strength of the microwave electric field is adjusted by changing the dimension of the slit in the traveling direction.

In order to achieve the above object, the method for producing carbon fiber according to one aspect of the present invention is the method for producing carbon fiber by heating the precursor fiber, wherein the heating method for heating the precursor is Includes the heating methods described above.
In order to achieve the above object, the carbonization apparatus according to one aspect of the present invention heats a precursor fiber traveling along a tube axis in a heating tube having a rectangular cross section by a microwave electric field in TE mode. In the carbonization apparatus for carbonization, an adjusting means for adjusting the strength of the electric field of the microwave along the traveling direction of the precursor fiber is provided.
In order to achieve the above object, the carbonization apparatus according to one aspect of the present invention is a carbon fiber production apparatus for producing carbon fibers by heating the precursor fibers, wherein the precursor is heated and carbonized. The carbonization device includes the carbonization device described above.

The heating method and the carbon fiber manufacturing method, and the carbonization device and the carbon fiber manufacturing device according to one aspect of the present invention heat the heated object in order to heat the heated object running along the tube axis of the heating tube. It can be lengthened, and by changing the internal area in the cross section of the heating tube or changing the dimension of the slit in the traveling direction, it is possible to adjust the energy intensity of the microwave applied during the traveling.

(A) shows a conceptual diagram of the electric field strength distribution in the cross section of the heating tube through which the microwave propagates, and (b) shows the state of the microwave propagating in the heating tube. (A) is a diagram showing an introduction hole provided on a long side wall on the waveguide side of the heating tube, and (b) is a diagram showing the strength of the electric field in the heating tube provided with the introduction hole of (a). .. It is a figure explaining the heating tube which adjusts the electric field strength of a microwave, (a) is a figure which shows the state of the microwave propagating in a heating tube, (b) is the distribution of the electric field strength of a microwave. It is a figure which shows the strength of the electric field of a microwave, (c) is a figure which shows. FIG. 3A is a diagram showing the distribution of the electric field in the cross section of the heating tube at the position A shown in FIG. 3B, and FIG. 3B is a diagram showing the distribution of the electric field at the position B shown in FIG. 3B. It is a figure which shows the distribution of the electric field in the cross section, and (c) is the figure which shows the distribution of the electric field in the cross section of the heating tube at the position C shown by (b) of FIG. It is the schematic which shows the manufacturing process of carbon fiber. It is a schematic diagram of a heating device. It is a figure which shows the temperature change of the surface of the flame-resistant fiber running in a heating tube. (A) shows a step-shaped height adjusting member, and (b) shows a slope-shaped height adjusting member. It is a figure which shows the example which adjusts the electric field strength of a microwave by adjusting the interval of a pair of short side walls.

<Overview>
The heating method according to one aspect of the present invention has a heating tube having a pair of short side walls and a pair of long side walls and having a rectangular cross section, and utilizes a TE mode microwave propagating in the heating tube. It heats the object to be heated running in the pipe.
Here, TE10 will be described as an example of the TE mode, but another TE mode, for example, TE20 may be used. The object to be heated travels in a direction orthogonal to the rectangular cross section (the axial direction of the heating tube). The tube axis direction is the direction in which the tube axis of the heating tube extends.

The microwave A propagates in the direction orthogonal to the paper surface in (a) of FIG. 1, and the microwave A propagates in the axial direction of the heating tube 15 as shown in (b) of FIG. In FIG. 1A, the side walls 15a and 15b extending in the vertical direction are referred to as "short side walls", and the side walls 15c and 15d extending in the horizontal direction are referred to as "long side walls".

As shown in FIG. 1B, the object to be heated 1b is supplied so as to travel in the axial direction of the heating tube 15. FIG. 1 shows a precursor fiber which is an example of the object to be heated 1b, and the precursor fiber runs in parallel with a pair of long side walls 15c and 15d. The end wall 15e on the upstream side of the heating tube 15 in the tube axis direction is provided with an inlet of the object to be heated 1b, and the end wall 15f on the downstream side is provided with an outlet of the object to be heated 1b.

In consideration of productivity, a plurality of objects to be heated 1b may be supplied to the heating tube 15. In FIG. 1A, there are two. Considering the heating spots, heating efficiency, and electric field strength unevenness of the plurality of objects to be heated 1b, it is preferable to pass through a position that is line-symmetric with respect to the virtual line connecting the midpoints of the long side walls 15c and 15d (FIG. 1). (See (a)). The supplied object 1b to be heated is preferably a dielectric material.

The microwave A in the heating tube 15 may be introduced directly from the microwave oscillator provided at one end of the heating tube 15, or may be introduced into the heating tube 15 from the waveguide provided at one end of the microwave oscillator. The microwave leaked from the hole in the side wall of the waveguide may be introduced into the heating tube 15.
When the microwave leaked from the waveguide is used, the waveguide (102) is attached to the heating tube 15 and has an introduction hole (106) for leakage on the opposite side wall, as shown in FIG. 6, for example. It is configured as follows.

Depending on the object to be heated 1b, it may be preferable to adjust the microwave energy (electric field) in the tube axis direction of the heating tube 15. For example, as described in "Problems to be Solved by the Invention", the precursor fiber is cut by heat storage.
The adjustment of microwave energy will be described below.

(1) When using microwaves leaked from a waveguide This will be described mainly with reference to FIG.
When a heating tube 15 having a rectangular cross section and long in a direction orthogonal to the cross section is used and microwaves leaking from the waveguide are introduced into the inside through the introduction hole 106, the introduction hole 106 of the heating tube 15 is used. By changing the magnitude of, the strength of the microwave electric field can be adjusted. The introduction holes 106 having different sizes correspond to an example of the adjusting means in the present invention.

For example, when the strength of the electric field is increased, the introduction hole 106 may be increased, and when the strength of the electric field is weakened, the introduction hole 106 may be decreased.
A plurality (even number) of introduction holes 106 are provided at intervals along the propagation direction of the microwave A in the heating tube 15.
The pitch L of the introduction hole 106 is set, assuming that the wavelength inside the waveguide of the microwave A is λg.
L = λg / 2 × n
(N here is an integer).
The introduction holes 106 are provided as a pair. That is, a plurality of sets of introduction holes 106 are provided, with two as one set.

The introduction hole 106 is composed of, for example, a rectangular slit. The code of the slit is also set to "106". The length a, which is the dimension in the direction orthogonal to the tube axis direction of the heating tube 15 in the slit 106, is such that the spatial wavelength of the microwave in the heating tube 15 is λ. Fixed with dimensions greater than 1/2. At 1/2, there is a possibility that the cutoff frequency will be reached.
The width b, which is the dimension of the heating tube 15 in the slit 106 in the tube axis direction, may be a dimension smaller than the in-tube wavelength λg in the heating tube 15.
In FIG. 2, the length a of the plurality of slits 106 is the same, and the width b of the slits 106 of each set is the same from the upstream end in the pipe axis direction to the middle (for example, the slit 106A). After that, it is provided so as to gradually become smaller (for example, slits 106B and 106C) as it moves to the downstream side. As a result, as shown in (b) of the figure, the strength of the microwave electric field is substantially constant halfway, and becomes weaker from the middle to the downstream side.
In this way, in the plurality of sets of slits 106 formed at intervals in the pipe axis direction, the width b is reduced as the width b moves to the downstream side in each set, so that the electric field increases as the pipe axis direction moves to the downstream side. Can weaken the strength of.

(2) When using microwaves propagating in the heating tube This will be described mainly with reference to FIGS. 3 and 4.
The microwave A described here may be introduced directly from a microwave oscillator provided at one end of the heating tube 15, or may be introduced from a waveguide provided at one end of the microwave oscillator. However, microwaves leaking from the introduction hole on the side wall of the waveguide may be introduced.
The strength of the electric field of the microwave A is adjusted by changing the internal area in the cross section of the heating tube 15 along the traveling direction of the object to be heated 1b. The change in the internal area here is performed by changing the distance between the pair of facing surfaces forming a space existing between the pair of long side walls 15c and 15d facing each other in the direction parallel to the pair of short side walls 15a and 15b.
For example, when the height adjusting member 151 is arranged on at least one of the pair of long side walls 15c and 15d, the inner surface of the other long side wall 15 and the surface of the height adjusting member 151 facing the other long side wall Is a pair of facing surfaces, and by changing the height of the height adjusting member 151, the distance between the pair of facing surfaces is changed.
For example, when the heating pipes 15 are configured so that the distance between the pair of long side walls 15 is different, the inner surfaces of the long side walls 15c and 15d are a pair of facing surfaces.
The facing surfaces having different intervals correspond to an example of the adjusting means in the present invention.

The height adjusting member 151 is configured to weaken the strength of the microwave electric field in two steps on the downstream side in the tube axis direction of the heating tube 15 in the traveling direction of the object to be heated 1b.
As shown in FIGS. 3 and 4, the height adjusting member 151 heats the first height portion 151a having the first height H1 and the second height portion 151b having the second height H2. It is held along the pipe axis direction of the pipe 15. The length of the first height portion 151a is L1, and the length of the second height portion 151b is L2. Further, the length at which the height adjusting member 151 does not exist is defined as L3. If there is a member in the portion where the height adjusting member 151 does not exist, its height H3 is 0, and it can be said that it is the third height portion (151c).
For each height of the height part,
H1>H2> H3 = 0
There is a relationship.

Here, in the heating tube 15, if the strength of the electric field at the A position in FIG. 3 is E1, the strength of the electric field at the B position is E2, and the strength of the electric field at the C position is E3, the height adjusting member 151 is provided. As a result, the internal space area in the cross section of the heating tube 15 changes, and the strength of the electric field of the microwave A also changes. The smaller the internal area, the higher the strength of the electric field.
Therefore, the strength of the electric field of the microwave A inside the heating tube 15 is as shown in FIG. 3 (c).
E1>E2> E3
Will be.
In this way, by running the object to be heated 1b along the tube axis direction of the heating tube 15, the energy of the microwave A can be sufficiently applied. Further, by running the object to be heated 1b along the tube axis direction of the heating tube 15, one heating tube 15 can be used to adjust the strength of the electric field of the microwave A.

When the height adjusting member 151 is provided in the heating tube 15, as shown in FIG. 3B, the distribution of the electric field strength is higher in the adjusting member 151 than in the distribution at the C position. Therefore, the peak portion tends to be flat. That is, the distribution of the electric field spreads in the tube axis direction of the heating tube 15. Since the peak portion becomes flat, microwave A having strong energy can be applied to the object to be heated 1b traveling in the tube axis direction for a long time.
Further, as shown in FIG. 4, the distribution of the electric field in the cross section of the heating tube 15 tends to have a flat peak portion as the height adjusting member 151 becomes higher than the distribution at the C position. .. As a result, the distribution spreads in the width direction (the left-right direction in the drawing) in the cross section of the heating tube 15, and the number of objects to be heated 1b inserted into the heating tube 15 can be increased.

Assuming that the width which is the distance between the inner surfaces of the short side walls 15a and 15b of the heating tube 15 is W and the width of the height adjusting member 151 is s.
0.3 × W ≦ s ≦ 0.6 × W
Satisfy the relationship. When this relationship is satisfied, the strength of the electric field in the heating tube 15 can be adjusted without significantly changing the impedance in the heating tube 15. If the impedance changes significantly, the wavelength of the microwave changes, making it difficult for a standing wave to occur, or making it easier for the height adjusting member 151 to generate a reflected wave.

Assuming that the length of the nth height portion of the height adjusting member 151 is Ln (n = 2 in FIG. 3),
Ln = (λg / 4) × (2k-1)
Is preferable. Note that λg is the wavelength in the tube and k is a natural number.
Thereby, the influence of the reflected wave reflected by the microwave A on the upright surface of the height adjusting member 151 can be offset.
Further, the direction in which the height of the height adjusting member 151 decreases, that is, the direction in which the distance between the pair of facing surfaces increases is preferably the direction opposite to the traveling direction of the microwave A. This is to reduce the influence of the reflected wave. In FIG. 3, the traveling wave of the microwave A goes from the downstream side to the upstream side of the heating tube 15, and the arrow in FIG. 3 indicates the traveling direction of the object to be heated 1b.

<Embodiment>
1. 1. Overall The method for producing carbon fibers using microwave heating will be described below with reference to FIG.
Carbon fibers are produced using precursor fibers, precursor fibers. One precursor is a bundle of a plurality of filaments, for example, 24,000 filaments. In some cases, it may be a precursor fiber bundle or a carbon fiber bundle.

The precursor 1a is obtained by spinning a spinning solution obtained by polymerizing a monomer containing 90% by mass or more of acrylonitrile by a wet spinning method or a dry wet spinning method, and then washing, drying and stretching. As the monomer to be copolymerized, alkyl acrylate, alkyl methacrylate, acrylic acid, acrylamide, itaconic acid, maleic acid and the like are used.
Usually, the speed at which the precursor 1a is produced and the speed at which the precursor 1a is carbonized to produce carbon fibers are different. Therefore, the manufactured precursor 1a is once housed in a carton or wound up on a bobbin.

As shown in FIG. 5, the carbon fiber is drawn from, for example, the bobbin 30 and travels toward the downstream side, and on the way, various treatments are performed and the carbon fiber is wound up on the bobbin 39.
As shown in FIG. 3, the carbon fiber corresponds to an example of the flame-resistant step of making the precursor 1a flame-resistant and the flame-resistant fiber (hereinafter referred to as “flame-resistant fiber”, which is the “precursor fiber” of the present invention. A carbonization step of carbonizing while stretching 1b, a surface treatment step of improving the surface of the carbonized fiber (hereinafter, also referred to as "fiber after carbonization") 1d, and a surface improvement. It is produced through a sizing step of attaching a resin to the fibers 1e and a drying step of drying the fibers 1f to which the resin is attached.

1 g of the dried fiber is wound around the bobbin 39 as 1 g of carbon fiber. The fibers that have completed each step are distinguished, for example, flame-resistant fiber 1b, but "1" is used as the reference numeral when simply describing as "fiber".
Here, the treatment for making the precursor 1a flame-resistant is the flame-resistant treatment, the treatment for carbonizing the flame-resistant fiber 1b is the carbonization treatment, the treatment for improving the surface of the carbonized fiber 1d is the surface treatment, and the surface-improved fiber. The process of adhering the resin to 1e is called a sizing process, and the process of drying the fiber 1f to which the resin is attached is called a drying process. Hereinafter, the processing and the process will be described.

(1) Flame resistance process (flame resistance treatment)
The flameproofing step is performed using the flameproofing furnace 3 in which the inside of the furnace is set to an oxidizing atmosphere of 200 [° C.] to 350 [° C.]. Specifically, flame resistance is achieved by passing the precursor 1a a plurality of times in the flame resistance furnace 3 in an air atmosphere. The oxidizing atmosphere may contain oxygen, nitrogen dioxide and the like.
The precursor 1a in the flame resistance step is stretched with a predetermined tension according to the carbon fiber to be produced. The draw ratio in the flame resistance step is, for example, in the range of 0.7 to 1.3. The extension of the precursor 1a is performed by the two rollers 5 and 7 at the inlet of the flameproof furnace 3 and the three rollers 9, 11 and 13 at the outlet.

(2) Carbonization process (carbonization treatment)
The carbonization step is a step of heating the flame-resistant fiber 1b to cause a thermal decomposition reaction to carry out carbonization. The carbonization is performed by the flame-resistant fiber 1b passing through the first carbonization furnace 15 and the fiber 1c passing through the first carbonization furnace 15 passing through the second carbonization furnace 17. The carbonization here is carried out by passing through at least the first carbonization furnace 15 and the second carbonization furnace 17.
Here, the carbonization performed in the first carbonization furnace 15 is referred to as "first carbonization" or "first carbonization treatment", this step is referred to as the first carbonization step, and further, the first The fiber that has been carbonized (exited from the first carbonization furnace 15) is referred to as "the fiber after the first carbonization treatment".

Similarly, the carbonization performed in the second carbonization furnace 17 is referred to as "second carbonization" or "second carbonization treatment", this step is referred to as the second carbonization step, and further, the second The fibers that have been carbonized (exited from the second carbonization furnace 17) are referred to as "fibers after the second carbonization" or "fibers after the carbonization".
The plurality of carbonization furnaces are provided in a form independent of each other. Here, the first carbonization furnace 15 and the second carbonization furnace 17 are provided independently of each other, and the tension of the fiber is adjusted between the first carbonization furnace 15 and the second carbonization furnace 17. Adjustment means can be provided.

A roller 19 is located outside the first carbonization furnace 15 on the inlet side, a roller 21 is provided between the first carbonization furnace 15 and the second carbonization furnace 17, and a second carbonization furnace is provided. Rollers 23 are provided on the outside of the 17 and on the outlet side, respectively.
For carbonization in the carbon process, the first carbonization step in which the flame-resistant fiber 1b is heated in the first carbonization furnace 15 using a microwave to cause a thermal decomposition reaction, and the fiber 1c heated by the microwave are first. It includes a second carbonization step in which carbonization proceeds by rapidly uniformly heating using plasma while stretching in the carbonization furnace 17 of 2. The first carbonization furnace corresponds to an example of the carbonization apparatus of the present invention.

The first carbonization step is performed by a heating device using microwaves propagating inside a heating tube having a rectangular cross section. The flame-resistant fiber 1b runs in the heating tube 15 along the tube axis direction of the heating tube 15 and is heated. At this time, the electric field energy serving as a heating source is introduced from the waveguide through which the microwave propagates to the heating tube 15 side through the introduction hole, and the electric field is matched between the paired introduction holes. The heating device used in the first carbonization step will be described in detail later. The second carbonization step may be heated by a heating means other than plasma.

(3) Surface treatment process (surface treatment)
The surface treatment step is performed by passing the carbonized fiber 1d through the surface treatment device 25. A roller 26 is provided at the outlet of the surface treatment device 25. By surface treatment, when 1 g of carbon fiber is used as a composite material, the affinity and adhesiveness between 1 g of carbon fiber and the matrix resin are improved.
Surface treatment is generally performed by oxidizing the surface of carbon fibers. As the surface treatment, for example, there is a treatment in a liquid phase or a gas phase. Treatment in the liquid phase includes chemical oxidation by immersing the carbonized fiber 1d in an oxidizing agent, and anodic electrolytic oxidation by energizing in the electrolytic solution in which the carbonized fiber 1d is immersed. Used for.
The treatment in the gas phase can be carried out by passing the carbonized fiber 1d through an oxidizing gas or by spraying an active species generated by an electric discharge or the like.

(4) Sizing process (sizing process)
The sizing step is performed by passing the fiber 1e through the resin liquid 29. The resin liquid 29 is stored in the resin bath 27. The sizing step enhances the convergence of the surface-treated fibers 1e.
The fibers 1e in the sizing step pass through the resin liquid 29 while changing the traveling direction by a plurality of rollers 31, 33 and the like arranged inside the resin bath 27 and around the resin bath 27. As the resin liquid 29, for example, a liquid or an emulsion liquid in which an epoxy resin, a urethane resin, a phenol resin, a vinyl ester resin, an unsaturated polyester resin or the like is dissolved in a solvent is used.

(5) Drying process (drying process)
The drying step is performed by passing the fiber 1f through the drying furnace 35. The dried fiber 1 g is wound around the bobbin 39 via a roller 37 on the downstream side of the drying furnace 35 (this is a winding step).

2. Heating device (first carbonization furnace)
(1) Schematic The heating device will be described with reference to FIG.
The heating device 100 has a heating tube having a rectangular cross section. This heating tube is the first carbonization furnace 15 in FIG. The reference numeral of the heating tube will be referred to as "15", which will be described below.

The heating tube 15 has a pair of short side walls 15a and 15b and a pair of long side walls 15c and 15d. Microwave A is in TE mode. Here, it is the TE10 mode. The flame-resistant fiber 1b runs inside the heating tube 15 along the tube axis. The end walls 15e and 15f at both ends of the heating tube 15 in the tube axial direction are provided with inlets and outlets for flame-resistant fibers 1b (see FIG. 6).
The microwave A is introduced into the heating tube 15 by the waveguide 102. The waveguide 102 has a rectangular cross-sectional shape similar to that of the heating tube 15 in order to propagate the microwave B transmitted from the microwave oscillator described later in the TE mode.

The waveguide 102 is provided in a state in which the tube axis of the waveguide 102 is parallel to the tube axis of the heating tube 15 and the inside of the heating tube 15 and the inside of the waveguide 102 communicate with each other. Here, the heating tube 15 and the waveguide 102 are integrated, and the heating space (the internal space of the heating tube 15) and the waveguide space (the internal space of the waveguide 102) are integrated. It is partitioned by a partition wall 104. Here, the partition wall 104 is a long side wall (15c) on the waveguide 102 side of the heating tube 15.

The partition wall 104 has an introduction hole 106. Here, the introduction hole 106 is provided in a slit shape extending in a direction orthogonal to each tube axis of the heating tube 15 and the waveguide 102. The microwave B in the waveguide 102 leaks from the introduction hole (slit) 106 to the heating tube 15 side.
As the microwave oscillator 108, for example, a microwave electron tube such as a klystron or a magnetron, a microwave semiconductor element using a diode or the like can be used. The output of the microwave oscillator 108 can be appropriately selected depending on the number of flame-resistant fibers 1b running inside the heating tube 15, the speed, the carbon content, and the like. The frequency of the microwave transmitted from the microwave oscillator 108 is 0.3 [GHz] to 140 [GHz].

The microwave oscillator 108 is connected to one end 102a of the waveguide 102 via the connecting waveguide 110. A fixed short-circuit plate 112 is provided on the other end 102b of the waveguide 102. The fixed short-circuit plate 112 is for reflecting the microwave B propagating from one end 102a of the waveguide 102 to the other end 102b toward one end 102a, thereby being fixed inside the waveguide 102. It can cause a wave.
The standing wave (B) in the waveguide 102 leaks to the heating tube 15 through the introduction hole 106 of the partition wall 104 and propagates in the heating tube 15.

A plurality (even number) of introduction holes 106 are provided at intervals along the propagation direction of the microwave A in the partition wall 104. In the case of a normal standing wave, the size of the introduction hole 106 is the same.

A fixed short-circuit plate 114 is also provided at one end of the heating tube 15, and a variable short-circuit plate 116 is provided at the other end side via a connecting waveguide 115.
The fixed short-circuit plate 114 at one end reflects the microwave A that leaks from the introduction hole 106 and propagates toward one end toward the other end 15f. As a result, the microwave A can be effectively used. The variable short-circuit plate 116 at the other end 15f reflects the microwave A that propagates inside the heating tube 15 and reaches the other end 15f toward one end, and in the case of the device configuration of FIG. It is for making a resonance state between. As a result, as shown in FIGS. 1 and 6, a standing wave can be generated in the heating tube 15.

The connecting waveguide 110 connecting the microwave oscillator 108 and the waveguide 102 is provided with an isolator 118, a directional coupler 120, and a three-stub tuner 122 from the microwave oscillator 108 side. The isolator 118 prevents the microwave oscillator 108 from being damaged by the microwave B reflected by the other end 102b of the waveguide 102.

The directional coupler 120 measures incident (microwaves toward the other end 102b of the waveguide 102) power and reflected (microwaves reflected at the other end toward the microtransmitter) power. It is something to do. The three-way tuner 122 is for adjusting the impedance matching in the waveguide 102. This matching makes it possible to efficiently perform microwave heating.
The heating tube 15 has a plurality of temperature measuring windows 124 for measuring the temperature of the flame-resistant fiber 1b traveling in the tube along the traveling direction. The temperature measurement window 124 is provided with a lid for preventing the inflow of oxygen.

The heating tube 15 or the waveguide 102 is provided with a gas introduction port 128 for creating an inert gas atmosphere in the tube, an exhaust port 126 for exhausting gas generated when the flame-resistant fiber 1b is heated, and the like. ing. As the inert gas, for example, nitrogen can be used, or argon or the like can be used.
The heating tube 15 is connected to the variable short circuit plate 116 via a connecting waveguide 115 at the other end 15f. The connecting waveguide 115 is provided with a directional coupler 130. The directional coupler 130 propagates in the heating tube 15 toward the other end 15f, and the electric power of the microwave A not absorbed by the flame-resistant fiber 1b is reflected by the variable short-circuit plate 116 and propagates toward one end. Measure the power of microwave A.

(2) Microwave adjustment When an electric field of constant strength is applied to the flame-resistant fiber 1b, heat may be stored and cut. Therefore, the strength of the electric field of the microwave A is weakened (adjusted) as it moves from the middle of the traveling direction of the flame-resistant fiber 1b to the downstream side in the heating tube 15. Hereinafter, a method for adjusting the strength of the electric field and the means for adjusting the electric field strength will be described.

(2-1) Introduction hole A slit 106 can be used as an example of the introduction hole. Normally, the size of the slit 106 is the same. However, the strength of the electric field can be adjusted by changing the size of the slit 106.
Here, as shown in FIG. 2A, the width b of the slit 106 is reduced from the middle to the downstream side of the heating tube 15 in the tube axis direction. As a result, as shown in FIG. 2B, the strength of the electric field can be reduced from the middle to the downstream side of the heating tube 15 in the tube axis direction.

(2-2) Area of internal space By adjusting the distance between the pair of facing surfaces facing the internal space of the heating tube 15, the area of the internal space can be changed and the strength of the electric field can be adjusted. Here, as shown in FIG. 3A, the height adjusting member 151 is arranged in the heating tube 15. The distance between the height adjusting member 151 and the long side wall 15d is increased from the middle to the downstream side of the heating tube 15 in the tube axis direction. As a result, as shown in FIG. 3C, the strength of the electric field can be reduced from the middle to the downstream side of the heating tube 15 in the tube axis direction.

3. 3. Examples Hereinafter, one embodiment of the embodiment will be described.
The heating device 100 heats the supplied flame-resistant fiber 1b by microwave A.
The flame-resistant fiber 1b used has a density of 1.36 [g / cm ³ ]. Two flame-resistant fibers 1b are supplied to the heating tube 15 of the heating device 100, and the flame-resistant fibers 1b are supplied along the tube axis direction of the heating tube 15. The number of filaments of the flame-resistant fiber 1b is 24,000 [lines].
The microwave A used in the heating device 100 has a wavelength in the range of 0.705 [m] to 0.00737 [m] and a frequency in the range of 425 [MHz] to 40680 [MHz].

The width of the waveguide 102 and the heating tube 15 (the dimension between the pair of short side walls 15a and 15b) is in the range of 0.5 [m] to 16 [m]. The heights of the waveguide 102 and the heating tube 15 (dimensions between the pair of long side walls 15c and 15d) are in the range of 0.2 [m] to 10 [m].
The output of microwave A is in the range of 0.1 [kW] to 1000 [kW]. The traveling speed of the flame-resistant fiber 1b is in the range of 0.01 [m / min] to 50 [m / min]. The inside of the heating tube 15 is maintained at 91000 [Pa] to 122000 [Pa] under a nitrogen atmosphere. In the first carbonization step, the flame-resistant fiber 1b is carbonized until ^{the density becomes, for example, 1.50 [g / cm 3} ] to 1.60 [g / cm ^3].
In a heating device using a conventional electric heater, the temperature inside the furnace is 500 [° C.] to 800 [° C.], and the heating is performed by about 7 [minutes] to 10 [minutes].

4. Heating test A heating test was performed using the heating device 100.
(1) Test 1
In the first embodiment, the traveling speed of the flame resistant fiber 1b is 0.3 [m / min]. In this case, the residence time of the flame-resistant fiber 1b inside the heating tube 15 is about 8 [minutes]. The output of microwave A is 1.0 [kW].
The width b of the slit 106 is 14 [mm], 10 [mm], 8 [mm], and 6 [mm], and is provided at an interval of 37 [mm] in the traveling direction of the flame-resistant fiber 1b. A pair of slits 106 having the same width are provided adjacent to each other, and there are a total of eight slits 106. Here, the slit existing at the "i" th slit (where "i" is a natural number from 1 to 8) from the upstream side in the traveling direction of the flame resistant fiber 1b is defined as the i-th slit, and this "i" is used. Is the slit number.
The temperature change on the surface of the flame-resistant fiber 1b running in the heating tube 15 is shown by the solid line in FIG. A radiation thermometer is used to measure the surface temperature of the flame-resistant fiber 1b.

In the first embodiment, the energy (electric field strength) of the microwave A is weakened along the traveling direction of the flame-resistant fiber 1b by reducing the slit width b along the traveling direction of the flame-resistant fiber 1b.
The temperature of the flame-resistant fiber 1b rises (heats) due to the energy of the microwave A, and the flame-resistant fiber 1b is carbonized. At this time, as shown by the solid line in FIG. 7, the temperature of the flame-resistant fiber 1b peaks at the fourth slit position after entering the heating tube 15, and gradually decreases thereafter.
Since the strength of the electric field of the microwave A is weakened along with the progress of carbonization of the flame-resistant fiber 1b, the amount of heat stored in the flame-resistant fiber 1b is reduced, and troubles such as cutting into the flame-resistant fiber 1b during traveling are reduced. Did not occur.

(2) Experiment 2
The height adjusting member 151 is arranged inside by using the heating tube 15 provided with the slit 106 having the slit width b described in the first embodiment. The output of microwave A is 0.75 [W].
The height adjusting member 151 adjusts the distance (height of the space) between the pair of facing surfaces of the heating tube 15. The intervals (height) are 11 [mm], 16 [mm], and 21 [mm] from the upstream side. The interval (height) here is obtained by subtracting the height of the height adjusting member 151 shown in FIG. 3A from the distance between the long side walls 15c and 15d.

The temperature change on the surface of the flame-resistant fiber 1b running in the heating tube 15 is shown by the alternate long and short dash line in FIG.
In the second embodiment, the electric field energy of the microwave A is weakened along the traveling direction of the flame-resistant fiber 1b by widening the distance between the facing surfaces (the height of the space between the long side walls) along the traveling direction of the flame-resistant fiber 1b. (Including the effect of slit 106).
As shown by the alternate long and short dash line in FIG. 7, the temperature of the flame-resistant fiber 1b in the heating tube 15 gradually increases as it travels (moves to the downstream side). This is because the output of the microwave A is lower than that of the first embodiment, but the height of the space between the long side walls 15c and 15d is narrowed, so that the energy (density) of the microwave A is increased.
After that, the energy of the microwave A is weakened while widening the distance between the facing surfaces (height of the space). As a result, the temperature of the flame-resistant fiber 1b gradually rises, the runaway reaction of the flame-resistant fiber 1b can be suppressed, and the flame-resistant fiber 1b does not cut during traveling.

(3) Comparative Example For comparison, heating was performed by microwave A using a heating tube 15 having a constant slit width b. The traveling speed, the number of the flame-resistant fibers 1b, and the output of the microwave are the same as those in the first embodiment. The slit width b in the comparative example is 10 [mm], and 4 sets (8 pieces) are provided in the tube axis direction of the heating tube. The pitch L of the slit 106 is the same as that of the first embodiment.

The temperature change on the surface of the flame-resistant fiber 1b running in the heating tube 15 is shown by the broken line in FIG.
As shown by the broken line in FIG. 7, the temperature of the flame-resistant fiber 1b in the heating tube 15 is lower than the temperatures of Examples 1 and 2 up to the fifth slit position after entering the heating tube 15. It has become. This is because, in Examples 1 and 2, the energy of the microwave A is higher on the upstream side of the heating tube 15 than on the downstream side, but in the comparative example, the energy is not adjusted, so that it is on the upstream side. This is because the energy is low.
The temperature of the flame-resistant fiber 1b of the comparative example enters the heating tube 15 and the temperature gradient becomes higher from about the third slit position, and the temperature becomes higher than that of Examples 1 and 2 at about the sixth slit position. ing. This is because the runaway reaction was started by the heat storage of the flame-resistant fiber 1b, and the flame-resistant fiber 1b may be cut during the running.

(4) Summary As described above, the adjustment by changing the slit width b (Example 1) and the adjustment by changing the distance (height of space) between the pair of facing surfaces (Example 2) are the energies of the microwave A. The strength of the flame-resistant fiber 1b can be adjusted, and for example, the carbonization step of the flame-resistant fiber 1b can be performed stably (without cutting).
Further, as shown in the second embodiment, even if the low output microwave A is used, the energy equivalent to that of the high output microwave A can be given by increasing the energy on the upstream side in the traveling direction.

<Modification example>
As described above, the present invention is not limited to the embodiment. For example, any of the embodiments and modifications described below may be appropriately combined, or a plurality of modified examples may be appropriately combined.

1. 1. In the precursor fiber embodiment, the flame-resistant fiber having 24,000 filaments has been described, but other fibers such as 3,000, 6,000, 12,000, and 36,000 filaments have been described. It can also be applied to flame-resistant fibers.
In the embodiment, the method for producing the carbon fiber including the carbonization step has been described, but for example, the graphitization treatment may be further performed before the surface treatment step. That is, in the embodiment, in the production of carbon fibers having a general-purpose product (elastic modulus 240 [GPa], the heating method or the like of the present invention was used for the first carbonization, but the present heating method or the like is a highly elastic product or medium. It can also be used for the first carbonization of the precursor fiber for carbon fiber of a high-performance product such as an elastic high-strength product.

2. Heating by microwave (1) In the temperature test, the surface temperature of the fiber was heated to 400 [° C] to 800 [° C], but it may be set to a temperature suitable for carbonization. The temperature can be adjusted, for example, by adjusting the output of the microwave, adjusting the traveling speed of the precursor fiber, changing the dimensions of the heating tube, changing the TE mode of the microwave, and the like.

(2) TE mode In the embodiment, the microwave mode is TE10, but other modes may be used. Other modes include TE20 mode and TE30 mode. That is, if the microwave mode is the TEm0 mode in which the strength of the electric field on the short side wall becomes 0 (lowers) (“m” is a natural number and “0” is a number zero). Good.
When "m" is 2 or more, in the heating tube, two regions (two regions in which the strength of the electric field is positive and negative) sandwiching the virtual surface connecting the centers of the pair of short side walls are formed. , The traveling region of the precursor fiber can be set, and the number of supplied precursor fibers can be doubled as compared with the TE10 mode in which the traveling region of the precursor fiber is one. However, when the microwave output is the same, the electric field strength in the TE20 mode is half the electric field strength in the TE10 mode.

(3) Traveling wave, standing wave Although the microwave A of the embodiment is mainly described as a standing wave, it may be a traveling wave. In this case, when arranging the height adjusting member in the heating tube, it is preferable to arrange it in a direction that reduces the influence of the reflected wave.
For example, in the case of the height adjusting member 151 as shown in FIG. 3A, it is preferable to introduce microwaves from the upstream side. On the contrary, when the height adjusting member (151) as shown in FIG. 3A is arranged in the center of the heating pipe 15, the height portion proceeds from the lower side (downstream side of the heating pipe). It is preferable to introduce waves.

(4) Electric field / magnetic field The heating in the embodiment uses the electric field component of the microwave, but for example, the object to be heated may be heated by using the magnetic field component, or the electric field component and the magnetic field component may be heated. Both components may be used to heat the object to be heated.

3. 3. Heating tube The cross-sectional shape of the heating tube of the embodiment is rectangular, but other shapes may be used. Examples of other shapes include a circular shape and an elliptical shape. In the case of these shapes, the microwave propagation mode is a TM mode such as TM01.
In the embodiment, the height adjusting member 151 is arranged in the heating tube 15, but for example, a heating tube having a shape having an internal space when the height adjusting member 151 is arranged may be used.

4. Height adjusting member The height adjusting member of the embodiment has a stepped shape as shown in FIG. 8A. However, the height adjusting member may have a slope shape as shown in FIG. 8 (b), as long as the distance between the height adjusting member and the facing surface of the heating tube can be adjusted. The upper surface (the surface facing the heating tube) constituting the slope may be linear or curved in the vertical cross section.

5. Intensity adjustment In an example of the embodiment, the strength of the microwave electric field is adjusted by a height adjusting member. However, for example, in the case of a heating tube having a rectangular cross section, the distance between the pair of short side walls may be adjusted as shown in FIG.
In FIG. 9, the distance between the pair of short side walls 15Aa and 15Ab of the heating tube 15A is gradually widened, and the adjusting member 151A is arranged inside the heating tube 15A. The adjusting member 151A has a first height portion 151Aa and a second height portion 151Ab. The first height portion 151Aa is higher than the second height portion 151Ab. The width of the adjusting member 151A gradually increases corresponding to the pair of short side walls 15Aa and 15Ab.
In this case as well, the energy density of the microwave can be changed to adjust the intensity of the microwave energy in the heating tube.
In the embodiment, the height adjusting member is used to adjust the space area of the heating tube, but as described above, the shape of the heating tube may be adjusted to match the height adjusting member. That is, for the strength adjustment, an adjusting member may be used, or the heating tube may be freely provided with an adjusting function.

1 Fiber 1a Precursor 1b Flame resistant fiber 1c First carbonized fiber 15 First carbonized furnace (heating tube)
15a, 15b Short side wall 15c, 15d Long side wall 151 Height adjustment member

Claims (9)

The inlet of one end in the tube axis direction in which the tube axis of the heating tube extends in the heating tube by the electric field of the TE mode microwave propagating in the heating tube having a pair of short side walls and a pair of long side walls. In a heating method for heating an object to be heated running along the pipe axis from the to the outlet at the other end.
The intensity of the electric field of the microwave, the along the running direction of the object to be heated, by changing the internal area of the cross section of the heating tube, is adjusted,
The change in the internal area in the cross section of the heating tube is performed by the change in the distance between the facing surfaces facing each other in the direction parallel to the pair of short side walls.
The change in the interval is performed by arranging a height adjusting member on one of the long side walls.
When the distance between the inner surfaces of the pair of short side walls is "W" and the dimension of the height adjusting member in the opposite direction of the pair of short side walls is "S".
0.3 × W ≦ S ≦ 0.6 × W
A heating method that satisfies the relationship. The inlet of one end in the tube axis direction in which the tube axis of the heating tube extends in the heating tube by the electric field of the TE mode microwave propagating in the heating tube having a pair of short side walls and a pair of long side walls. In a heating method for heating an object to be heated running along the pipe axis from the to the outlet at the other end.
The strength of the electric field of the microwave is adjusted by changing the internal area in the cross section of the heating tube along the traveling direction of the object to be heated.
The change in the internal area in the cross section of the heating tube is performed by the change in the distance between the facing surfaces facing each other in the direction parallel to the pair of short side walls.
The change in the interval is performed by arranging a height adjusting member on one of the long side walls.
The traveling direction of the microwave is opposite to the traveling direction of the object to be heated.
The height adjusting member has n different heights (n is a natural number of 2 or more), and the height becomes lower in a stepped manner toward the outlet at the other end.
When the height closest to the entrance is the first and the height closest to the exit is the nth.
Assuming that the length of the portion having the nth height in the tube axis direction is "Ln" and the wavelength in the tube of the heating tube is "λg", it is assumed.
Ln = (λg / 4) × (2k-1)
(However, k is a natural number)
Heating method. The inlet of one end in the tube axis direction in which the tube axis of the heating tube extends in the heating tube by the electric field of the TE mode microwave propagating in the heating tube having a pair of short side walls and a pair of long side walls. In a heating method for heating an object to be heated running along the pipe axis from the to the outlet at the other end.
The strength of the electric field of the microwave is adjusted by changing the internal area in the cross section of the heating tube along the traveling direction of the object to be heated.
The change in the internal area in the cross section of the heating tube is performed by the change in the distance between the facing surfaces facing each other in the direction parallel to the pair of short side walls.
The change in the interval is performed by arranging a height adjusting member on one of the long side walls.
When the distance between the inner surfaces of the pair of short side walls is "W" and the dimension of the height adjusting member in the opposite direction of the pair of short side walls is "S".
0.3 × W ≦ S ≦ 0.6 × W
Meet the relationship,
The traveling direction of the microwave is opposite to the traveling direction of the object to be heated.
The height adjusting member has n different heights (n is a natural number of 2 or more), and the height becomes lower in a stepped manner toward the outlet at the other end.
When the height closest to the entrance is the first and the height closest to the exit is the nth.
Assuming that the length of the portion having the nth height in the tube axis direction is "Ln" and the wavelength in the tube of the heating tube is "λg", it is assumed.
Ln = (λg / 4) × (2k-1)
(However, k is a natural number)
Heating method. Before SL heating tube, a slit for introducing the microwaves generated from the microwave generator has a plurality at intervals in the traveling direction,
The strength of the microwave electric field is adjusted by changing the dimension of the slit in the traveling direction.
The heating method according to any one of claims 1 to 3. In the method for producing carbon fiber, which produces carbon fiber by heating the precursor fiber,
The heating method for heating the precursor fiber is a method for producing carbon fiber, which comprises the heating method according to any one of claims 1 to 4. A microwave electric field in TE mode is used to drive precursor fibers running along the tube axis from the inlet at one end in the direction of the tube axis extending in the heating tube having a rectangular cross section to the outlet at the other end. In a carbonization device that is heated and carbonized by
An adjusting means for adjusting the strength of the electric field of the microwave along the traveling direction of the precursor fiber is provided .
The strength of the microwave electric field is adjusted by changing the internal area in the cross section of the heating tube along the traveling direction of the precursor fiber.
The change in the internal area in the cross section of the heating tube is performed by the change in the distance between the facing surfaces facing each other in the direction parallel to the pair of short side walls of the heating tube.
The adjusting means includes a height adjusting member arranged on one long side wall of the heating tube in order to change the interval.
When the distance between the inner surfaces of the pair of short side walls of the height adjusting member is "W" and the dimension of the pair of short side walls in the opposite direction of the height adjusting member is "S",
0.3 × W ≦ S ≦ 0.6 × W
Carbonation equipment that satisfies the relationship. A microwave electric field in TE mode is used to drive precursor fibers running along the tube axis from the inlet at one end in the direction of the tube axis extending in the heating tube having a rectangular cross section to the outlet at the other end. In a carbonization device that is heated and carbonized by
An adjusting means for adjusting the strength of the electric field of the microwave along the traveling direction of the precursor fiber is provided.
The strength of the microwave electric field is adjusted by changing the internal area in the cross section of the heating tube along the traveling direction of the precursor fiber.
The change in the internal area in the cross section of the heating tube is performed by the change in the distance between the facing surfaces facing each other in the direction parallel to the pair of short side walls of the heating tube.
The adjusting means includes a height adjusting member arranged on one long side wall of the heating tube in order to change the interval.
The traveling direction of the microwave is opposite to the traveling direction of the precursor fiber.
The height adjusting member has n different heights (n is a natural number of 2 or more), and the height becomes lower in a stepped manner toward the outlet at the other end.
When the height closest to the entrance is the first and the height closest to the exit is the nth.
Assuming that the length of the portion having the nth height in the tube axis direction is "Ln" and the wavelength in the tube of the heating tube is "λg", it is assumed.
Ln = (λg / 4) × (2k-1)
(However, k is a natural number)
Carbonization equipment. A microwave electric field in TE mode is used to drive precursor fibers running along the tube axis from the inlet at one end in the direction of the tube axis extending in the heating tube having a rectangular cross section to the outlet at the other end. In a carbonization device that is heated and carbonized by
An adjusting means for adjusting the strength of the electric field of the microwave along the traveling direction of the precursor fiber is provided.
The strength of the microwave electric field is adjusted by changing the internal area in the cross section of the heating tube along the traveling direction of the precursor fiber.
The change in the internal area in the cross section of the heating tube is performed by the change in the distance between the facing surfaces facing each other in the direction parallel to the pair of short side walls of the heating tube.
The adjusting means includes a height adjusting member arranged on one long side wall of the heating tube in order to change the interval.
When the distance between the inner surfaces of the pair of short side walls of the height adjusting member is "W" and the dimension of the pair of short side walls in the opposite direction of the height adjusting member is "S",
0.3 × W ≦ S ≦ 0.6 × W
Meet the relationship,
The traveling direction of the microwave is opposite to the traveling direction of the precursor fiber.
The height adjusting member has n different heights (n is a natural number of 2 or more), and the height becomes lower in a stepped manner toward the outlet at the other end.
When the height closest to the entrance is the first and the height closest to the exit is the nth.
Assuming that the length of the portion having the nth height in the tube axis direction is "Ln" and the wavelength in the tube of the heating tube is "λg", it is assumed.
Ln = (λg / 4) × (2k-1)
(However, k is a natural number)
Carbonization equipment. In a carbon fiber manufacturing apparatus that heats precursor fibers to produce carbon fibers,
A carbon fiber manufacturing apparatus including the carbonization apparatus according to any one of claims 6 to 8, as a carbonization apparatus for heating and carbonizing the precursor fiber.

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