Fiber bundle heating method and heating device

Abstract

To provide a method capable of stably manufacturing fibers with a high property by means of electric conduction heating.SOLUTION: A heating method of a fiber bundle includes a heating step of performing Joule heating of a fiber bundle (F) which is conveyed while being in contact with at least a pair of electrodes (11, 12) and has the conductivity at least between the electrodes by means of the electric conduction to the gap between the electrodes. At least one of the electrodes has a convergence part (1511) which converges the fiber bundle while contacting the outer peripheral side of the fiber bundle. The convergence part has the groove shape or cylindrical shape having the component surface whose width becomes narrow in the depth direction. When the electrode is made of the rotor, for example, the convergence part is the open-groove which is provided on the outer peripheral side of the rotor, and has the bottom surface whose width becomes narrow toward the rotation center side. The open-groove may include a width widening part (1153) which guides the fiber bundle to the bottom surface on the outer peripheral edge side.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for heating a fiber bundle. [Background technology]

[0002] Carbon fiber composite materials, which enable both lightweight construction and high performance, are used in a variety of products, not just in the aerospace field. Carbon fiber composite materials are usually made of carbon fibers and a matrix (resin, ceramics, metal, etc.) that holds them in place. Typical carbon fibers have a carbon content of 90% or more and are obtained by sintering organic fibers. There are several types of carbon fibers depending on the raw materials used, such as PAN-based fibers obtained from polyacrylonitrile (PAN) and pitch-based fibers obtained from petroleum or coal pitch. All types of carbon fibers have in common that they are obtained by gradually heating the raw organic fibers at high temperatures.

[0003] The heating process in the manufacture of carbon fiber is generally performed by an indirect heating method in which the fiber (bundle) is heated in a furnace. However, high-temperature heating by the indirect heating method consumes a lot of energy, so a direct heating method (particularly a direct electric heating method) that can save energy has been proposed. The following document contains information related to this direct electric heating method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 61-39411 [Patent Document 2] Patent Publication 2015-214461 [Patent Document 3] U.S. Patent No. 3,313,597 [Non-patent literature]

[0005] [Non-Patent Document 1] Carbon, 146, pp.8-14, 1991 Summary of the Invention [Problem to be solved by the invention]

[0006] The direct resistance heating method applies electricity directly to the transported fiber (bundle) to joule heat the fiber itself, enabling continuous and efficient heating.

[0007] However, when the inventors tried to heat a moving fiber bundle by a conventional direct electric current heating method, the temperature fluctuated significantly depending on the position of the fiber bundle, making it impossible to heat uniformly and making it impossible to stably produce carbon fibers with high properties. However, there was no description of such problems or solutions in any of the documents.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for stably carrying out heat treatment of a fiber bundle. [Means for solving the problem]

[0009] As a result of intensive research by the inventors to solve this problem, they succeeded in uniformly heating the moving fiber bundle by applying electrical current to it by reviewing the shape of the electrodes that the fiber bundle comes into contact with. They further developed this result and completed the present invention described below.

[0010] 《Heating method》 (1) The present invention is a method for heating a fiber bundle, the method comprising: a heating step of Joule-heating a fiber bundle that is transported while in contact with at least a pair of electrodes and that has electrical conductivity at least between the electrodes by passing an electric current between the electrodes, at least one of the electrodes having a bundling portion that is in contact with an outer periphery of the fiber bundle and that aggregates the fiber bundle.

[0011] (2) According to the fiber bundle heating method of the present invention (simply referred to as the "heating method"), a fiber (bundle) with high properties can be stably obtained even by a direct electric current heating method. The mechanism behind this is currently presumed to be as follows.

[0012] The fiber bundle is concentrated by the bundling part of the electrode (the fibers constituting the fiber bundle are closely packed together). This allows the fiber bundle to maintain a stable contact state with the electrode (bundling part) over a wide area without flapping even while moving between the electrodes. As a result, not only the contact resistance between the fiber bundle and the electrode but also the contact resistance between the single fibers constituting the fiber bundle is stably reduced, which is believed to have made it possible to heat the single fibers constituting the fiber bundle approximately uniformly.

[0013] Incidentally, fibers (bundles) that are directly heated by electrical current rather than indirectly heated in a furnace are heated uniformly not only near the surface but also to the inside, and the structure (carbonized structure, etc.) can become uniform overall. For example, the orientation and crystal formation of the constituent elements (carbon, etc.) of a single fiber can be shaped along the fiber axis direction through which electrical current is passed. This can contribute to improving the properties of the fiber according to the present invention.

[0014] 《Heating device》 The present invention can also be understood as a fiber heating device. For example, the present invention may be a fiber bundle heating device that includes at least a pair of electrodes, a conveying means for moving a fiber bundle hung between the electrodes, and a power source for supplying power between the electrodes, and at least one of the electrodes has a bundling part that contacts the outer periphery of the fiber bundle and aggregates the fiber bundle.

[0015] Fiber (bundle) The present invention can also be understood as a fiber (bundle) (referred to as a "treated fiber (bundle)") that has been heat-treated using the heating method and heating device described above. The material and state of the fiber (bundle) before heating that is subjected to the heating method or heating device (referred to as an "untreated fiber (bundle)") are not important so long as they have conductivity between the electrodes that pass current. The conductivity is not important in terms of a specific electrical resistance value, etc., as long as current can pass through it.

[0016] "others" (1) In this specification, the term "fiber bundle" refers to an aggregate of "single fibers" (monofilaments). The number of filaments constituting a typical fiber bundle is about 10 (0.01k) to 240,000 (240k), and further 100 (0.1k) to 60,000 (60k). In this specification, the term "fiber bundle" is also referred to simply as "fiber" as appropriate. When clarifying the components of a fiber bundle, it is referred to as a single fiber or a monofilament.

[0017] (2) In conjunction with the use of the electrodes described above, for example, current flow between the electrodes may be controlled based on the temperature of the fiber bundle measured between the electrodes. Specifically, in the heating process, the power supplied between the electrodes and the current flow state between the fiber bundle and the electrodes may be controlled based on the temperature of the fiber bundle measured at least at one point between the electrodes.

[0018] (3) Unless otherwise specified, "x to y" in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the various numerical values ​​or numerical ranges described in this specification may be used as a new lower limit or upper limit value to create a new range such as "a to b". Furthermore, unless otherwise specified, "x to ymm" in this specification means xmm to ymm. The same applies to other units. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a schematic diagram showing a heating device. [Diagram 2] FIG. 1 is a cross-sectional view showing an open groove provided on the outer peripheral surface of a roller (electrode I). [Diagram 3] FIG. 11 is a cross-sectional view showing an open groove provided on the outer peripheral surface of a roller (electrode II). [Figure 4] FIG. 1 is a schematic plan view showing temperature measurement positions of a fiber bundle during electrical heating. [Diagram 5] FIG. 2 is a schematic cross-sectional view showing how fiber bundles are gathered in an open groove (gathering portion) of a roller (electrode I). [Figure 6] 13 is a flowchart showing an example of heating control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] One or more components selected arbitrarily from the items described in this specification may be added to the above-mentioned configuration of the present invention. A component related to a manufacturing method may also be a component related to a product. Which embodiment is best depends on the target, required performance, etc.

[0021] "electrode" (1) At least one of the electrodes may have a bundling section that contacts the outer periphery of the fiber bundle and aggregates the fiber bundle. The aggregation of fiber bundles refers to a state in which the individual fibers constituting the fiber bundle are densely packed or even in close contact with each other. When the fiber bundle passes through the bundling section from the upstream side to the downstream side, the cross section (a cross section formed by the envelope of the outer periphery) usually changes according to the cross section of the bundling section, and the fiber bundle shrinks according to the density of the individual fibers.

[0022] Such a focusing portion may have various shapes. For example, the focusing portion may be a groove or a cylinder having a component surface that narrows in the depth direction. The cross-sectional shape of the focusing portion may be, for example, an arc, a V-shape, a U-shape, a ring, etc. The number of focusing portions per electrode may be one or more. A plurality of grooves or cylinders may be considered as one focusing portion.

[0023] The depth (h) and width (W) of the bundled part are appropriately adjusted according to the size of the fiber bundle (single fiber diameter x number, etc.). Based on the thickness (t) from the lowest point (deepest bottom point) of the bundled part to the top surface of the fiber bundle (opposite surface of the bottom), h / t may be, for example, 1 to 10, 2 to 8, or even 3 to 5. W / t may be, for example, 0.05 to 20, 0.1 to 10, 0.2 to 8, or even 2 to 6. W is, for example, the maximum open groove width (interval between inner edges on the outer periphery) in the case of a groove-shaped bundled part, and the maximum inner periphery width in the case of a cylindrical bundled part. h is, for example, the height (shortest distance) from the measurement level of that W to the deepest bottom point. In particular, when the bottom of the bundled part has a circular arc cross section, r / t may be, for example, 0.025 to 10, 0.05 to 5, 0.1 to 4, or even 1 to 3 as the radius of curvature (r). In this case, for example, h>r or W>2r may be satisfied, or h=r (h≒r) or W=2r (W≒2r) may be satisfied.

[0024] The electrode may be a rotating body (roller, rotor, etc.) or a sliding body. The converging portion provided on the outer periphery of the rotating body may be, for example, an open groove having a bottom surface that narrows toward the center of rotation. The open groove may have a widening portion (e.g., a taper) on the outer periphery side that guides the fiber bundle to the bottom surface. The open groove may also have a side wall that continues from the bottom surface to the outer periphery side to prevent the fiber bundle from escaping.

[0025] The converging portion provided on the non-rotating body may be, for example, an open groove or a through tube. The through tube may have an enlarged diameter portion (for example, a tapered portion) on the upstream edge side thereof for guiding the fiber bundle.

[0026] The focusing portion may be present in at least one of the electrodes (particularly the upstream electrode), but may also be present in multiple electrodes with which the fiber bundle comes into contact. For example, both the upstream electrode and the downstream electrode may have focusing portions. Furthermore, a focusing portion may also be provided in the electrode between them (intermediate electrode). Also, a groove-shaped focusing portion and a cylindrical focusing portion may coexist in the path of the fiber bundle. For example, a rotating electrode having an open groove (first focusing portion) and a non-rotating electrode having a through-hole tube (second focusing portion) may coexist in the path of the fiber bundle.

[0027] (2) Since the electrodes come into contact with the fibers (bundles) that become hot, they should be made of a conductive material that is also excellent in heat resistance and abrasion resistance. Examples of such conductive materials include graphite, metals, and ceramics.

[0028] The electrode surface (including the constituent surface of the focusing portion) that comes into contact with the fibers may be smoothed to reduce contact resistance, stabilize current flow, etc. The surface roughness (Rzjis) may be, for example, 12.5 μm or less, 6.3 μm or less, or even 3.2 μm or less. The lower limit may be 0.01 μm or more, or even 0.1 μm or more.

[0029] The electrodes on the upstream side (fiber bundle delivery side) and downstream side (fiber bundle recovery side) may be of the same material or shape or may be different. Using the same electrodes makes it easier to manage parts.

[0030] At least one pair (two) of electrodes is sufficient, but three or more or two or more pairs may be used. The number of electrodes may be determined according to the number of current-carrying sections (between electrodes) installed, the wiring method, etc. When multiple current-carrying sections are provided, the current-carrying conditions (supply power, heating time, contact state, etc.) may be changed in each current-carrying section. The target temperature of the fiber bundle may be changed for each current-carrying section, or the current-carrying conditions may be optimized according to changes in the fiber bundle (changes in resistance value, shape, etc.).

[0031] "power supply" The power supply may be an AC or DC power supply. A regulated power supply facilitates control of the current and / or voltage (e.g., feedback control).

[0032] Transport The fiber bundle may be transported, for example, by driving a winding body (bobbin, roller, etc.) provided at least on the downstream side with a motor, etc., to wind up the fiber bundle. The transport means consisting of the winding body and the drive source may be provided not only on the downstream side, but also on the upstream side.

[0033] The moving speed (e.g., conveying speed) of the fiber bundle may be constant, or may be changed depending on the electrified state. If the driving source is a motor, the moving speed can be adjusted by controlling the number of revolutions. By adjusting the moving speed, it is possible to stabilize or improve the contact state (electrically energized state) between the fiber bundle and the electrode (bundling section), the contact state or rotation state between the electrode (roller, etc.) and the rotating shaft, productivity (heat treatment speed), etc. It should be noted that "movement" in this specification includes the relative movement of the fiber with respect to the electrode.

[0034] 《Distance between electrodes》 The inter-electrode distance may be constant or may be changed depending on the current flow state. For example, the inter-electrode distance may be shortened to make it easier to increase the temperature of the fiber bundle. The inter-electrode distance may be changed depending on the moving speed of the fiber bundle. By adjusting the inter-electrode distance depending on the moving speed, for example, the heating time of the fiber bundle by current flow (current flow time) may be controlled. The inter-electrode distance adjustment means may be, for example, a slider that can move at least one of the electrodes to a predetermined position. The slider is, for example, composed of a drive source (such as a servo motor), a linear guide, a ball screw, etc.

[0035] "tension" The tension of the fiber (bundle) hung between the electrodes may be constant or may be changed depending on the current flow state. The tension is adjusted, for example, by a tensioner. The tensioner applies a desired load to the fiber bundle via, for example, an idler, roller, slider, or the like that contacts the fiber bundle. The load source is, for example, electromagnetic force (motor, solenoid, etc.), hydraulic pressure, air pressure, gravity (weight), spring, etc. The roller is not particularly limited, but examples include a nip roller and a feed roller consisting of multiple rollers. The above-mentioned conveying means, etc. may also serve as a tensioner. For example, the tension of the fiber bundle may be adjusted by changing the rotation torque of a winding body provided on the downstream side and / or upstream side of the fiber bundle using a motor, etc., or the winding speed on the downstream side of the fiber bundle and the feed speed on the upstream side are adjusted to adjust the tension by the speed difference.

[0036] When there are three or more electrodes, the tension between each electrode may be adjusted collectively or individually between each electrode. By adjusting the tension, the contact state (electrical conduction state) between the fiber bundle and the electrodes can be stabilized. Naturally, the tension is adjusted within a range where the moving fiber bundle does not slacken or break.

[0037] The tension adjusting means (tensioner) is composed of, for example, a contact body (rotating body, sliding body, etc.) that contacts the fiber bundle, and a mechanism that moves it to a predetermined position and holds it there. The contact body can be made of any material, but it is preferable that it is made of a material (such as graphite) that has heat resistance and durability, just like the electrodes.

[0038] The tension applied to the fiber bundle during transportation is, for example, 0.1 to 100 (× 10 -3 N / tex), 0.2-50 and even 1-25 (×10 -3 "Tex" is an SI unit that indicates the weight (g) per 1000 m of length. For example, if a load (weight) of 100 g (0.1 kgf = 0.98 N) is added to a typical fiber bundle of 800 tex, the tension acting on the fiber bundle will be 1.225 x 10 -3 N / tex (=0.98N / 800tex).

[0039] "temperature" The temperature of the fiber (bundle) during electrical heating may be measured continuously or discretely (intermittently). The measuring means (type or type of thermometer, etc.) is not important. The temperature of the fiber (bundle) that is thin and has a small heat capacity, strength, etc. is measured with high accuracy, for example, by a non-contact thermometer (radiation thermometer, thermography, etc.).

[0040] "control" Heating control of the fiber bundle may be performed based on the temperature of the fiber bundle measured at least at one location. The control method (feedback control, feedforward control, etc.) does not matter. For example, feedback control based on the measured temperature of the fiber bundle (simply called "actual temperature") may be performed in real time to stably converge the actual temperature of the fiber bundle to the target temperature. The temperature difference (fluctuation range) between the target temperature and the actual temperature differs depending on the type of fiber bundle, the heating purpose, the specifications of the device, etc., but is preferably within ±75°C or further ±50°C, for example.

[0041] The control objects include, for example, the amount of current passing between the electrodes (power supply), and the state of current passing between the fiber bundle and the electrodes (tension applied to the fiber bundle suspended between the electrodes, the moving speed of the fiber bundle between the electrodes, etc.) Control of the amount of current passing, which is a typical example, may be achieved by changing either the current or the voltage, or both.

[0042] The moving speed of the fiber bundle also affects the heating time. To keep the heating time within a predetermined range, the distance between the electrodes may be adjusted according to the moving speed.

[0043] "atmosphere" The fiber bundle may be heated in an atmosphere according to the purpose of the treatment. If heating is performed in an oxidizing atmosphere, the heating may be performed in the air (open state). If heating is performed in a non-oxidizing atmosphere, a chamber may be used to create the desired atmosphere for at least the fiber bundle between the electrodes.

[0044] In addition, the non-oxidizing atmosphere referred to in this specification includes an inert gas atmosphere (a rare gas atmosphere, a nitrogen gas atmosphere, etc.) as well as a vacuum atmosphere. When a part of the components of the untreated fiber is released as a gas by heating, it is preferable to perform electrical heating in an air flow atmosphere or an exhaust atmosphere.

[0045] Fiber (bundle) (1) The fiber before the electric current heating treatment (the untreated fiber) may be made of any material, such as organic fiber, inorganic fiber, metal fiber, etc., as long as it can be heated by electric current. Representative examples include flame-retardant fiber, infusible fiber, pre-carbonized fiber, carbon fiber, graphitized fiber, etc.

[0046] Organic fibers as they are spun or spun usually have a high electrical resistance and low conductivity. Such organic fibers should be pretreated to impart electrical conductivity at least before passing through the upstream electrode. For example, PAN-based organic fibers can be heated (flameproofed) at 200 to 400°C in an oxidizing atmosphere (usually in an air atmosphere) to obtain flameproof fibers, and pitch-based organic fibers can be heated (infusible) at 200 to 400°C to obtain infusible fibers. Flameproof fibers, infusible fibers, etc. increase in conductivity with increasing heating temperature, and can exhibit electrical conductivity suitable for electrical heating when heated to, for example, 250°C, preferably 300°C or higher. In addition, flameproof fibers, infusible fibers, etc. can be heated (pre-carbonized) at, for example, 400°C to 1000°C in an inert atmosphere (inert gas atmosphere, vacuum atmosphere, etc.) to obtain pre-carbonized fibers. In this specification, the term "pre-treated fibers (bundles)" includes not only pre-carbonized fibers (bundles), but also flame-retardant fibers (bundles), infusible fibers (bundles), etc. Also, organic fibers containing additives (dispersing materials) such as conductive fillers can be used as the pre-treated fibers (bundles).

[0047] Carbon fibers, graphitized fibers, etc. can be obtained by electrically heating the untreated fibers. Carbon fibers can be obtained, for example, by heating flame-retardant fibers, infusible fibers, or pre-carbonized fibers at 1000 to 2000°C in an inert atmosphere (carbonization step). Graphitized fibers can be obtained, for example, by heating carbon fibers at 2000 to 3000°C in an inert atmosphere (graphitization step).

[0048] (2) If the untreated fibers (bundles) have little fluff or twists and are well shaped, the contact state (contact resistance) with the electrode (bundle portion) can be stable. The untreated fibers may be surface-treated, such as by sizing. The treated fibers (bundles) may also be surface-treated, such as by sizing, after heating.

[0049] The organic fibers that are the raw material of the untreated fibers may be, in addition to PAN-based fibers and pitch-based fibers, for example, polyacrylamide-based fibers, phenolic resin-based fibers, polyvinyl alcohol-based fibers, polyolefin-based fibers, diene-based polymer fibers, regenerated cellulose-based fibers, lignin-based fibers, etc. The treated fibers obtained by electrically heating the untreated fibers may have a different component composition than the untreated fibers, or may have a different structure. EXAMPLES

[0050] The present invention will be described in more detail with reference to specific examples of a heating device and a heating method for a fiber bundle.

[0051] 《Heating device》 A fiber bundle heating device M1 (simply referred to as "device M1") according to one embodiment of the present invention is shown in Fig. 1. The left-right direction (horizontal direction) and the up-down direction (vertical direction) in this embodiment are the directions of the arrows shown in Fig. 1.

[0052] (1) Overview The device M1 includes a pair of rollers 11, 12, a power source 2, a control unit 3 (control means) consisting of a computer, a radiation thermometer 4, a delivery bobbin 51 for the untreated fiber bundle F1 and a winding bobbin 52 for the treated fiber bundle F2 (conveying means), tensioners 61, 62, idlers 71, 72 (idling bodies / idler wheels) that respectively guide and support the untreated fiber bundle F1 on the delivery side and the treated fiber bundle F2 on the winding side, and a chamber 8 that creates a predetermined atmosphere around the energized fiber bundle Fh.

[0053] Rollers 11, 12 (collectively referred to as "roller 1") each consist of a graphite cylinder 111, 121 (electrode) pivoted on a graphite rotating shaft 112, 122. A power source 2 is connected to terminals 113, 123 provided on each end of the rotating shafts 112, 122. Electricity is supplied to the cylinders 111, 121 from the terminals 113, 123 via the rotating shafts 112, 122. The space between cylinder 111 and cylinder 121 (between the electrodes) will be referred to as "between the cylinders" or "between the rollers" as appropriate.

[0054] The gap (distance between electrodes) between roller 11 (cylinder 111) and roller 12 (cylinder 121) can be adjusted by a slider (not shown / distance adjustment means). The slider is composed of, for example, a linear guide, a ball screw, a servo motor, etc. The ball screw is driven by a servo motor controlled by control unit 3 to move at least one of rollers 11, 12 along a linear guide extending in the left-right direction and stop it at a desired position. In this way, the gap between rollers 11 and 12 can be adjusted.

[0055] The power supply 2 is a DC stabilized power supply, and the output (voltage and / or current) is controlled by the control unit 3. This adjusts the amount of current (supplied power) between the cylinders.

[0056] The delivery bobbin 51 and the take-up bobbin 52 (collectively referred to simply as "bobbin 5") are each driven by a motor (not shown). Each motor is controlled (e.g., synchronized) by the control unit 3 to adjust the moving speed of the untreated fiber bundle F1, the energized fiber bundle Fh, and the treated fiber bundle F2 (collectively referred to as "fiber bundle F").

[0057] The tensioners 61, 62 (collectively referred to as "tensioner 6") are provided on the delivery side (upstream side) and the take-up side (downstream side), respectively, and apply tension to the electric fiber bundle Fh hung between the cylinders 111 and 121. The tensioners 61, 62 are each driven by a motor (not shown) and can move up and down. The motors are synchronously controlled by the control unit 3, and change the downward pressing force of the unprocessed fiber bundle F1 and the downward pressing force of the processed fiber bundle F2. In this way, the tension of the electric fiber bundle Fh is adjusted by the tensioner 6.

[0058] The chamber 8 is a vessel equipped with a gas inlet and outlet, and the interior can be made into a desired atmosphere. For example, an inert gas (e.g., nitrogen gas) is introduced from the inlet on the upstream side and exhausted from the outlet on the downstream side. This keeps the interior of the chamber 8 in a stable inert gas atmosphere even if gas is generated from the heated, current-carrying fiber bundle Fh.

[0059] It is also possible to add another roller between the rollers 11 and 12 to provide multiple current-carrying sections (between the electrodes). In this case, heating conditions may be set individually for each current-carrying section. For example, the fiber bundle may be heated in stages by changing the target temperature or the supplied power in each current-carrying section.

[0060] (2) Roller (electrode) Grooves 115, 125 were formed on the outer periphery of cylindrical bodies 111, 121 of rollers 11, 12 constituting the electrodes. Rollers 11, 12 and grooves 115, 125 had the same shape. Here, groove 115 of roller 11 will be described in detail.

[0061] 2, groove 115 is a narrow annular open groove formed near the center of the outer circumferential surface of cylinder 111. Groove 115 has bottom 1151 (converging portion) with a semicircular cross section located on the rotation center side of roller 11, wall portions 1152 extending parallel to the radial direction of roller 11 from both end edges of bottom portion 1151, and guide portions 1153 (widening portions) tapering from both ends of wall portion 1152 to outer circumferential surface 114 of roller 11.

[0062] In this embodiment, the radius of curvature of the bottom 1151 is r, the groove width which is the wall spacing of the wall 1152 is W (=2r), and an electrode (roller) having such a groove shape is referred to as "electrode I."

[0063] For comparison, rollers 11 and 12 were also prepared, which had grooves 117 and 127 that were different in shape from grooves 115 and 125. Since grooves 117 and 127 had the same shape, only groove 117 will be described.

[0064] 3, groove 117 is a wide, annular open groove formed near the center of the outer circumferential surface of cylinder 111. Groove 117 has bottom 1171 (converging portion) with a rectangular (flat) cross section located toward the rotation center of roller 11, and wall portions 1172 extending parallel to the radial direction of roller 11 from both end edges of bottom 1171. Bottom 1171 and wall portions 1172 are connected by corner portions 1174.

[0065] In this embodiment, the wall portion 11 7 The groove width Wc, which is the distance between the walls of the fiber bundle 1172 and the corner 1174, is set to be Wc, and the radius of curvature of the corner 1174 is set to be rc. An electrode (roller) having a groove shape in which the groove width Wc is sufficiently larger than the outer diameter of the untreated fiber bundle F1 and the treated fiber bundle F2 is referred to as “electrode II.”

[0066] <Sample Preparation> Using the above-mentioned heating device, a treated fiber bundle was actually produced by heat-treating the untreated fiber bundle, and the properties of the treated fiber bundle were evaluated.

[0067] [Fiber bundle before processing] As the fiber bundle before treatment, a pre-carbonized fiber bundle prepared as follows was used.

[0068] (1) As the raw fiber bundle, a polyacrylonitrile fiber bundle (number of fibers: 3,000 / bundle, fiber bundle fineness: 360 tex / bundle, single fiber fineness: 0.12 tex / fiber, single fiber diameter: approximately 11 μm) was prepared.

[0069] This raw fiber bundle was moved under an air flow in a heating furnace with a temperature gradient (temperature rise) from 200°C to 300°C for 48 minutes (flame retardation treatment process). In this way, a flame retardant fiber bundle (number of fibers: 3000 / bundle, fiber bundle fineness: 330 tex / bundle, single fiber fineness: 0.11 tex / bundle, single fiber diameter: approximately 10 μm) was produced.

[0070] This flame-retardant fiber bundle was moved under a nitrogen gas flow in a heating furnace with a temperature gradient (temperature rise) from 300°C to 1000°C for 3 minutes (pre-carbonization process). In this way, a pre-carbonized fiber bundle (number of fibers: 3000 / bundle, fiber bundle fineness: 180 tex / bundle, single fiber fineness: 0.06 tex / bundle, single fiber diameter: approximately 7 μm) was produced. This pre-carbonized fiber bundle (fiber bundle width: approximately 2 mm) is referred to as "pre-treatment fiber bundle α."

[0071] (2) The above-mentioned flame-retardant fiber bundle was also moved under a nitrogen flow for 3 minutes in a heating furnace with a temperature gradient (temperature rise) from 300°C to 800°C. This resulted in a pre-carbonized fiber bundle (number of fibers: 3000 / bundle, fiber bundle fineness: 220 tex / bundle, single fiber fineness: 0.07 tex / bundle, single fiber diameter: approximately 8 μm). This pre-carbonized fiber bundle (fiber bundle width: approximately 2 mm) is referred to as "pre-treatment fiber bundle β."

[0072] [Electric heating] Each untreated fiber bundle (preliminary carbonized fiber bundle) was electrically heated using the device M1 to produce a treated fiber bundle. Specifically, the process is as follows.

[0073] (1) Conditions Nitrogen was introduced into the chamber 8 to create an inert atmosphere with an oxygen concentration of less than 10 ppm inside the chamber 8. The conveying speed of the fiber bundle F: 12 mm / min, the tension of the fiber bundle F: 191 gf (7.8×10 -3 N / tex), distance between electrodes for energizing: 35 mm (time to pass between rollers 11 and 12: 2 minutes 55 seconds), energization time: 10 minutes. At this time, the heating temperature of fiber bundle F was set to 1400°C (target temperature), and fiber bundle F was heated by constant current control with a current value of 5 A (constant).

[0074] (2) Processing Using device M1 equipped with electrode I (r=0.5mm, W=1mm) or electrode II (rc=0.5mm, Wc=6mm), the untreated fiber bundle α or the untreated fiber bundle β was heated by applying electricity. As a result, treated fiber bundle F2 (carbon fiber bundle) of samples 1, 2, and C1 shown in Table 1 was obtained. The depth from the outer peripheral surface 114 of electrode I to the deepest part was 1.5 mm, and the depth from the outer peripheral surface 114 of electrode II to the bottom 1171 was 1.5 mm.

[0075] (3) Measurement During the electrical heating, the resistance between the electrodes (between rollers 11 and 12) and the surface temperature of the electrical fiber bundle Fh were measured. The resistance was calculated by dividing the voltage measured by the power supply by the current. The temperature was measured from above the electrical fiber bundle Fh using a radiation thermometer 4. The measurement was performed at three locations in the width direction of the electrical fiber bundle Fh (center: P0, one end: P1, the other end: P2) approximately in the center between the electrodes, as shown in FIG. 4.

[0076] The resistance and surface temperature measured for each sample while it was being heated with electricity are also shown in Table 1. The average values ​​shown in the table are the arithmetic mean values ​​(N=5) of the values ​​measured every 0.5 milliseconds. The fluctuation range is the error (variation) from the average value of each measurement. The surface temperatures of the ends P1 and P2 shown in Table 1 are the error (variation) of the average values ​​of the ends P1 and P2 from the average value of the center P0.

[0077] [Furnace heating] For comparison, the above-mentioned pre-carbonized fiber bundle was also heated in a conventional carbonization furnace (electric furnace) to produce a treated fiber bundle.

[0078] The atmosphere in the furnace and the tension of the fiber bundle F were the same as those in the case of electrical heating, and the untreated fiber bundle α or the untreated fiber bundle β was heated in the furnace at 1400°C for 3 minutes. In this way, the treated fiber bundle F2 (carbon fiber bundle) of samples D1 and D2 shown in Table 1 was obtained.

[0079] [measurement] Tensile tests were conducted on five single fibers randomly taken from the treated fiber bundle F2 of each sample, and the tensile strength and tensile modulus were measured. The arithmetic mean values ​​(N=5) of the measured values ​​are also shown in Table 1. Note that for sample C1, the upper limit was indicated using an inequality sign (<) because the measured values ​​varied widely.

[0080] The tensile test was carried out at room temperature using a micro strength evaluation tester (Micro Autograph MST-I manufactured by Shimadzu Corporation) in accordance with JIS R 7606. In this case, the gauge length was 25 mm and the tensile speed was 1 mm / min.

[0081] The size of the single fibers (referred to as "fiber diameter") was measured using a microscope (Keyence Corporation's digital microscope VHX-1000). Specifically, the fiber width was measured at four randomly selected points for each of 10 single fibers randomly extracted from the fiber bundle F of each sample. The arithmetic average of these values ​​was taken as the fiber diameter of the single fiber for each sample. The cross section of each single fiber was made into a circular shape with the fiber diameter as its diameter.

[0082] "evaluation" (1) As is clear from Table 1, in the case of Samples 1 and 2 in which the raw fiber bundle F1 was electrically heated using rollers 11 and 12 (electrode I) having grooves 115, carbon fibers with high strength and high rigidity were stably obtained. In addition, in the case of Samples 1 and 2, the electrical current state (change in resistance value) during electrical heating and the surface temperature of the electrical fiber bundle Fh were also stable. This is thought to be because the grooves 115 allowed the raw fiber bundle F1 to be electrically heated in a dense state.

[0083] On the other hand, in the case of sample C1 in which the untreated fiber bundle F1 was electrically heated using rollers 11 and 12 (electrode II) with grooves 117, the strength and rigidity of the carbon fiber were insufficient, as shown in Table 1. In addition, in the case of sample C1, the electrical current state (change in resistance value) during electrical heating and the surface temperature of the electrically-heated fiber bundle Fh also varied greatly. This is thought to be because the fiber bundle F was not gathered in the grooves 117, but moved within the bottom 1171 in a flat, spread-out state.

[0084] (2) Samples 1 and 2, which were heated by applying current through electrode I, produced carbon fibers (bundles) with higher properties than samples D1 and D2, which were conventionally heated in a furnace. On the other hand, sample C1, which was heated by applying current through electrode II, produced carbon fibers (bundles) with lower properties than samples D1 and D2.

[0085] (3) The state in which the fiber bundle F moves inside the groove 115 (electrode I) is shown diagrammatically in Fig. 5. The bottom 1151 of the groove 115 has a constituent surface with an arc-shaped cross section that narrows as it becomes deeper. For this reason, the fiber bundle F is gathered along the bottom 1151, and the single fibers that make up the fiber bundle F are densely packed.

[0086] By the way, in the case of samples 1 and 2, the cross-sectional area A of the fiber bundle F1 before treatment is 0.12 mm 2 , Cross-sectional area of ​​bottom 1151 (semicircular part: W = 1 mm, r = 0.5 mm): 0.39 mm 2 The thickness t of the untreated fiber bundle F1 from its deepest position is 0.21 mm. In this case, r / t=2.38 and W / t=4.76.

[0087] As described above, according to the present invention, uniform heating is possible even with the electric current heating method, and fibers (bundles) with high properties can be stably obtained.

[0088] "supplement" An example of a process (procedure / steps) for heat-treating the untreated fiber bundle F1 using the above-mentioned device M1 is shown in Fig. 6. In addition to the electrical heating using an electrode having a focusing portion, the following steps may be performed.

[0089] Process S 0The conditions required for the heat treatment of the raw fiber bundle F1 are initially set. The setting items include, for example, the target temperature (To) of the current-carrying fiber bundle Fh during current heating, the tolerance (ΔT = |T-To|) of the actual temperature (T) relative to the target temperature, the heating time of the current-carrying fiber bundle Fh (tm: time to pass between the rollers), the distance between the rollers (L: distance between the electrodes), the conveying speed of the fiber bundle F (V: moving speed), the tension (S) of the current-carrying fiber bundle Fh, the amount of current between the rollers (voltage (E)·current (I) or power (Q)), etc. The initial value of each setting item (variable) is indicated with the suffix "o" appropriately.

[0090] The heating time (tm) is calculated from the distance (L) between the rollers and the conveying speed (V) of the fiber bundle F (tm = L / V). If the heating time is kept roughly constant and electrical current heating is performed, it is advisable to change L and V in concert. If there is a positive correlation between the actual temperature (T) of the electrical current fiber bundle Fh and the amount of electrical current (Q = E·I), it becomes easy to set the initial voltage (Eo) and initial current (Io) or initial power (Wo) according to the target temperature (To).

[0091] In step S1, the control unit 3 operates or sets the bobbin 5, the slider of the roller 1, the tensioner 6, etc. based on the initially set Vo, Lo, So, etc., and starts (or continues) the conveyance of the fiber bundle F.

[0092] In step S2, the control unit 3 starts (or continues) the energization of the roller 1 from the power source 2 based on the initially set Qo (=Eo·Io), and starts (or continues) Joule heating of the energized fiber bundle Fh between the rollers. Note that steps S1 and S2 may be started in reverse order or approximately simultaneously.

[0093] In step S3, the control unit 3 measures the temperature of the current-carrying fiber bundle Fh between the rollers using the radiation thermometer 4. After the start of current-carrying in step S2, the temperature measurement may be started after a time period during which the temperature of the current-carrying fiber bundle Fh stabilizes (initial transition time). Usually, the current-carrying fiber bundle Fh rises to near the target temperature within an extremely short time period after the start of current-carrying.

[0094] In step S4, the control unit 3 determines whether the measured actual temperature of the current-carrying fiber bundle Fh is within a predetermined temperature range with respect to the target temperature (for example, |T-To|≦ΔT).

[0095] If the actual temperature is outside the temperature range, in step S5, the control unit 3 controls the power source 2, tensioner 6, or bobbin 5 to change one or more of the settings and conditions of the amount of current (E, I, or Q), tension (S), and conveying speed (V). For example, if the actual temperature of the energized fiber bundle Fh is low, the power source 2 is controlled to increase the amount of current. If the actual temperature fluctuates greatly, the tensioner 6 and / or bobbin 5 are controlled to increase or decrease the tension and / or the conveying speed. This improves the contact state between the energized fiber bundle Fh and the surface of the roller 1, the contact state between the cylindrical bodies 111, 121 and the rotating shafts 112, 122, etc., stabilizes their contact resistance, and suppresses the variation in the actual temperature. If it is necessary to keep the heating time of the energized fiber bundle Fh constant, the control unit 3 may control a slider (not shown) to shorten the distance between the rollers in response to a decrease in the conveying speed, or to extend the distance in response to an increase in the conveying speed.

[0096] If the actual temperature is within the predetermined temperature range in step S4, the control unit 3 continues the electrical heating and transport of the fiber bundle F under the same settings and conditions (step S6). This process is performed until electrical heating of a desired amount of the raw fiber bundle F1 is completed. For example, this process is performed until the raw fiber bundle F1 wound around the delivery bobbin 51 is completely wound around the take-up bobbin 52 as the treated fiber bundle F2 (step S6). Of course, when winding around the bobbin 52 is completed, the process may be continued within the desired range while switching to the next bobbin either semi-automatically or manually.

[0097] If the actual temperature fluctuates beyond a predetermined range during this process (during the circulatory processing loop: steps S6→S1→S2→S3→S4→S6) (step S4), the settings and conditions are reviewed (step S5), and the processing loop from step S1 to step S6 is repeated. In this way, feedback control based on the actual temperature of the energized fiber bundle Fh is performed in real time, and a treated fiber bundle F2 heated to the desired temperature is obtained for a desired amount of untreated fiber bundle F1.

[0098] In this way, the heat treatment of the fiber bundle F may be further stabilized. The combination and priority order of the control items to be changed in the above-mentioned step S5 may be determined according to the type of the fiber bundle F, the change in the actual temperature, and the like.

[0099] In this specification, "means" and "step" can be interpreted interchangeably. For example, "step" can be interpreted as "means" to be a constituent element of a "product" (e.g., a heating device), and conversely, "means" can be interpreted as "step" to be a constituent element of a "method" (e.g., a heating method).

[0100] [Table 1] [Explanation of symbols]

[0101] 11, 12 Roller (electrode) 115 Groove 1151 Bottom (Focusing part) 2 Power supply 3 Control unit (control means) 4 Radiation thermometer 5 Bobbin (vehicle) 6 Tensioner 7. Idler 8. Chamber M1, M2 Fiber bundle heating device F1 Untreated fiber bundle Fh Electrically conductive fiber bundle F2 treated fiber bundle

Claims

1. A heating step is provided in which a fiber bundle that is transported while being in contact with at least a pair of electrodes and has electrical conductivity at least between the electrodes is Joule-heated by passing an electric current between the electrodes, At least one of the electrodes is a rotor having an open groove on its outer periphery, the open groove having a converging portion that consolidates the fiber bundle while contacting the outer periphery of the fiber bundle, The converging portion has a bottom surface with an arc-shaped cross section that narrows toward the center of rotation.

2. 2. The fiber bundle heating method according to claim 1, wherein a thickness (t) from the deepest bottom point of the bundled portion to an upper surface of the fiber bundle and a radius of curvature (r) of the bottom satisfy r / t: 1 to 10.

3. A method for heating a fiber bundle as described in claim 1, wherein the electrodes are made of graphite.

4. The method for heating a fiber bundle according to claim 1 , wherein the groove has a guide portion for the fiber bundle, the guide portion being tapered and widened on an outer peripheral edge side.

5. 5. The method for heating a fiber bundle according to claim 1, wherein the fiber bundle is made of flame-retardant fiber, infusible fiber or pre-carbonized fiber.

6. At least one pair of electrodes; A conveying means for moving the fiber bundle hung between the electrodes; a power source for supplying power between the electrodes; At least one of the electrodes is a rotor having an open groove on its outer periphery, the open groove having a converging portion that consolidates the fiber bundle while contacting the outer periphery of the fiber bundle, The converging section is a heating device for a fiber bundle having a bottom surface with an arc-shaped cross section that narrows toward the center of rotation.

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