JP3610659B2 - Oxidation furnace and carbon fiber manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxidation treatment furnace suitable for producing high-strength carbon fibers and a method for producing carbon fibers using the furnace.
[0002]
[Prior art]
Since carbon fibers have excellent mechanical properties, they are widely used for aerospace applications, leisure applications, general industrial applications, and the like. In these fields, it is important that the specific strength and specific elastic modulus are high. In particular, it is extremely important to establish a technique that can stably obtain such characteristics.
[0003]
The elastic modulus of the carbon fiber can be controlled so as to obtain desired characteristics mainly by changing the temperature of the carbonization step or graphitization step or the drawing ratio of the yarn in such step.
[0004]
On the other hand, the tensile strength of the carbon fiber is influenced by the properties as the precursor fiber, such as the oil agent and the single fiber diameter imparted to the precursor fiber, and the temperature in the firing process such as oxidation treatment and carbonization treatment. In addition, since the tensile strength of brittle materials such as carbon fibers is likely to be dominated by defects, it is important to eliminate the retention of dust and gases that are generated or brought in during the firing process, especially with a large amount of active atmosphere such as air. In the contacting oxidation process, the cleanliness of the atmosphere is extremely important.
[0005]
Usually, in a carbon fiber oxidation treatment furnace, in order to reduce the loss of heat energy, an active gas such as air heated by a heater or the like is sent into the oxidation treatment furnace by a fan, which is extracted from the furnace and heated. It has a so-called circulation system that sends it to the machine. In such a furnace, if the operation is continued for a long period of time, for example, silica or the like caused by a silicone-based oil agent that is often applied to the precursor fiber, or dust that the precursor fiber or air brings from outside the furnace, the circulating hot air The amount of dust inside increases and eventually the tensile strength of the carbon fiber obtained decreases. Among the dusts, metal elements such as iron, aluminum, chromium, and magnesium are particularly harmful to the tensile strength of carbon fibers. However, such metal elements do not have a single element but form some bonds with the silica. It is presumed to exist with it. Therefore, it is necessary for the furnace that has been operated for a certain period of time to stop once, remove the dust in the system, and then restart the operation.
[0006]
However, even if it intends to remove the dust in the system once it has stopped, when the operation is resumed, a phenomenon occurs in which the tensile strength of the resulting carbon fiber is greatly reduced at the beginning of the operation.
[0007]
In order to further enhance the removal of dust in the system, it may take a lot of personnel and time, but this not only leads to an increase in cost, but in the case of large-scale equipment for mass production, such equipment is submicron. It was extremely difficult to effectively remove the level of dust.
[0008]
In view of such problems, the present inventors have intensively studied and found a method suitable for efficiently removing dust existing in the oxidation treatment furnace, and have completed the present invention.
[0009]
[Problems to be solved by the invention]
An object of the present invention is to solve the above-mentioned problems, that is, an apparatus and method that can easily remove dust existing in an oxidation treatment furnace after stopping and thereby stably produce high-strength carbon fibers. It is to provide.
[0010]
[Means for Solving the Problems]
The oxidation treatment furnace of the present invention has the following configuration in order to achieve the above-described problem. That is, in an oxidation treatment furnace having a circulation system in which an oxidizing gas is circulated by a fan, an exhaust port having an opening / closing mechanism capable of discharging an air volume of 13 to 100% of the suction air volume of the fan is provided on the exhaust side of the fan. Carbon fiber manufacturing comprising a switching valve that has an air supply port provided with an opening / closing mechanism on the downstream side thereof and that can block communication of a circulation duct between the exhaust port and the air supply port It is an oxidation treatment furnace. Moreover, in order to achieve the said subject, the manufacturing method of the carbon fiber of this invention has the following structure. That is, before starting the operation of the oxidation treatment furnace, after exhausting a part of the suction air volume of the fan from the exhaust port, the precursor yarn is oxidized in the oxidation treatment furnace and then carbonized. It is a manufacturing method of carbon fiber. Furthermore, the manufacturing method of the carbon fiber of this invention has the following structure in order to achieve the said subject. That is, the fan has a circulation system in which the oxidizing gas is circulated by the fan, and the vibration is applied to the oxidizing gas before the start of the operation of the oxidation treatment furnace for carbon fiber production in which the exhaust port is provided in the circulation system. A part of the suction air volume is exhausted from the exhaust port, and then the precursor yarn is oxidized in the oxidation furnace and then carbonized.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0012]
When the operation is resumed after the oxidation furnace is stopped, the tensile strength of the resulting carbon fiber decreases at the beginning of the operation, because the dust accumulated on the border of the furnace is a sudden burst at the start of the fan operation. This is thought to be due to resuspension caused by a typical circulating wind and the amount of dust in the furnace increasing. Therefore, it is necessary to remove the dust that has re-suspended after the start of operation of the fan.
[0013]
An example of the oxidation treatment furnace of the present invention shown in FIG. A circulation-type oxidation treatment furnace having a fan 4 for circulating an oxidizing gas necessary for oxidizing a carbon fiber precursor fiber, and having an exhaust port 6 in a part of the circulation system duct 10 . Thereby, dust can be discharged using the wind pressure of the fan before the operation of the oxidation furnace is started. During normal operation, it is preferable to have an open / close mechanism that can close the exhaust port so that the oxidizing gas can be circulated efficiently. In order to use a circulation fan during normal operation as a dust discharge fan, it is preferable to provide an exhaust port in a circulation duct on the discharge side of the fan as shown in FIG.
[0014]
Further, as shown in FIGS. 2 and 3, if not only the exhaust port 6 but also the air supply port 7 are provided, circulation and exhaust can be repeated using the switching valves 8 and 8 'as will be described later. It is more preferable.
[0015]
The opening area of the exhaust port can be determined in consideration of the pressure loss of the circulation system and the exhaust system, and it is preferable that 13 to 100% of the suction air volume of the fan can be exhausted. The suction air volume of the fan is obtained by measuring the wind speed on the suction side of the fan with an anemometer and multiplying it by the cross-sectional area of the circulation duct. The exhaust air volume is obtained by measuring the air volume at the exhaust port with an anemometer and multiplying by the exhaust port opening area. In Examples described later, Anemo Master Model 6161 manufactured by Nippon Kanomax was used as an anemometer.
[0016]
Next, a method for producing carbon fiber using such an oxidation treatment furnace will be described.
[0017]
First, the circulation fan of the oxidation furnace once stopped is driven to exhaust gas such as air and exhaust dust from the exhaust port. Such exhaust is preferably performed before raising the temperature of the oxidizing gas for the oxidation treatment in order to reduce thermal energy loss.
[0018]
When the exhaust air volume when exhausting from the exhaust port is 13 to 100% of the suction air volume of the fan, dust can be efficiently discharged.
[0019]
In addition to the exhaust before the start of the operation of the oxidation treatment furnace, if the exhaust is performed before the furnace body at the end of the previous operation is cooled in advance, gasified tar and the like can be discharged, so that the carbon fiber It is more effective in obtaining the tensile strength stably.
[0020]
Furthermore, when evacuating, it is preferable to apply vibration to the oxidizing gas in order to promote the separation of the dust from the inner wall surface of the furnace and to discharge the dust more efficiently.
[0021]
In order to impart vibration to the oxidizing gas, it is preferable that the circulating air be disturbed by repeatedly opening and closing the exhaust port. From this point of view, as shown in FIGS. 2 and 3, if not only the exhaust port 6 but also the air supply port 7 are provided, circulation and exhaust can be repeated using the switching valves 8 and 8 ′, It is more preferable because it can disturb the wind and improve the dust discharge efficiency.
[0022]
Installing the above-mentioned switching valve in an existing oxidation treatment furnace increases the time, personnel, and cost of modification as the equipment becomes larger. In such cases, vibration is applied to the oxidizing gas. As a relatively simple method, a low-frequency sound wave generator, a gas injection device, or the like can be used. In addition, it is possible to fluctuate the rotation speed of the fan using an inverter by a programming controller and vibrate by the turbulent flow effect. In this way, the amount of dust in the oxidation treatment furnace exhausted before the start of the oxidation treatment furnace operation is 10 pieces. / Cm ³ or less is preferable. Thereby, the tensile strength of the carbon fiber at the beginning of production can be improved.
[0023]
Here, the amount of dust in the oxidation treatment furnace is a place in the oxidation treatment furnace where the circulating air is flowing stably, and particles of 0.5 to 5 microns when measured with a light scattering type automatic particle counter. Numbers. In Examples of the present invention, a particle counter KC-03 manufactured by Rion Co., Ltd. was used as a light scattering type automatic particle counter.
[0024]
In this way, the oxidizing gas is circulated through the oxidation furnace exhausted before the start of the operation of the oxidation furnace, the precursor fiber such as acrylic fiber or pitch fiber is passed through, and the oxidation treatment is performed. Carbonization treatment is performed in an inert atmosphere such as nitrogen at 1100 to 2000 ° C. Following the carbonization treatment, for example, a graphitization treatment may be performed in an inert atmosphere at 2000 to 3000 ° C.
[0025]
Thereby, not only can the tensile strength of the carbon fiber obtained immediately after the start of production be improved, but also the time from the start of production to the stabilization of the tensile strength of the carbon fiber can be shortened.
[0026]
【Example】
Hereinafter, the present invention will be described more specifically based on examples.
[0027]
In addition, in a present Example, the physical property (strength) of carbon fiber is a physical property in the epoxy resin impregnation strand measured according to JISR-7601, and was calculated | required from the average of the frequency | count n = 10 of measurement.
[0028]
( Comparative Example 1) In the oxidation treatment furnace shown in FIG. 1 in which dust is accumulated in a long-term operation, before the operation is started and before the air is heated by the gas heater 5, the dust in the furnace is discharged by wind power from the circulation fan 4. did. At this time, 15% of the suction air volume of the fan was discharged from the exhaust port. When the amount of dust in the oxidation treatment furnace was measured after the exhaust port was closed and air was heated and circulated, it was 10 / cm ³ .
[0029]
Thereafter, an acrylic fiber composed of 12000 filaments provided with a silicone-based oil was oxidized as a precursor fiber using the oxidation furnace, and then carbonized to produce a carbon fiber. Tensile strength of carbon fibers immediately after production start is 470kgf / mm ^2, became 500 kgf / mm ² after 12 hours of operation.
[0030]
(Embodiment 1 ) In the oxidation treatment furnace shown in FIG. 2 in which dust has accumulated in a long-term operation, a part of the circulation system duct of the oxidation treatment furnace is switched before the operation is started and before the air is heated by the gas heater 5. 8 and the switching valve 8 between the exhaust port and the air supply port was opened, and the dust in the furnace was discharged by wind power from the circulation fan 4. At this time, almost 100% of the fan's suction air volume was exhausted, and almost the same amount of fresh air was introduced. Further, at this time, the switching valve was switched three times from the state of FIG. 2 and the state of FIG. 3 to discharge dust. The exhaust valve and the supply port switching valve were closed, the circulation duct switching valve 8 was opened, the air was heated and circulated, and the number of dust in the oxidation treatment furnace was measured. The result was 4 / cm ³ . .
[0031]
Thereafter, the same acrylic fiber as in Comparative Example 1 was used as a precursor fiber, oxidized using the oxidation furnace, and then carbonized to produce a carbon fiber. The tensile strength of the carbon fiber immediately after the start of production was 490 kgf / mm ² , and 510 kgf / mm ² after 6 hours of operation.
[0032]
Except to repeat (Example 2) The switching valve 30 times, it was in the same manner as in Example 1, the tensile strength of carbon fibers immediately after production start is 500 kgf / mm ^2, and 530kgf / mm ² after 6 hours became.
[0033]
( Comparative example 2 ) In the oxidation treatment furnace shown in FIG. 4 in which dust is accumulated in a long-term operation, before the operation is started and before the air is heated by the gas heater 5, the dust in the furnace is discharged by wind power from the circulation fan 4. did. At this time, 3% of the suction air volume of the fan was discharged from the exhaust port. The exhaust port was closed and air was heated and circulated, and then the number of dust in the oxidation treatment furnace was measured and found to be 100 / cm ³ .
[0034]
Thereafter, the same acrylic fiber as in Comparative Example 1 was used as a precursor fiber, oxidized using the oxidation furnace, and then carbonized to produce a carbon fiber. The tensile strength of the carbon fiber immediately after the start of production was 420 kgf / mm ² , and it became 470 kgf / mm ² after 48 hours of operation.
[0035]
(Example 3 ) In the oxidation treatment furnace shown in FIG. 4 in which dust is accumulated in a long-term operation, before the operation is started and before the air is heated by the gas heater 5, a low-frequency sound wave generator (Infraphone manufactured by Infrasonic Corp.) Then, after oxidizing gas was oscillated with a low frequency sound wave of about 20 Hz, dust in the furnace was discharged by wind power from the circulation fan 4. At this time, 15% of the suction air volume of the fan was discharged from the exhaust port.
[0036]
Thereafter, an acrylic fiber composed of 12000 filaments provided with a silicone-based oil was oxidized as a precursor fiber using the oxidation furnace, and then carbonized to produce a carbon fiber. The tensile strength of the carbon fiber immediately after the start of production was 520 kgf / mm ² , and became 560 kgf / mm ² after 6 hours of operation.
[0037]
(Example 4 ) In the oxidation treatment furnace shown in FIG. 4 in which dust is accumulated in a long-term operation, before the operation is started and before the air is heated by the gas heater 5, the gas injection device (diamond soot blow manufactured by Gadelius Co., Ltd.) The pressurized gas of ³ / hour was continuously injected to vibrate the oxidizing gas, and then dust in the furnace was discharged by wind power from the circulation fan 4. At this time, 15% of the suction air volume of the fan was discharged from the exhaust port.
[0038]
Thereafter, an acrylic fiber composed of 12000 filaments provided with a silicone-based oil was oxidized as a precursor fiber using the oxidation furnace, and then carbonized to produce a carbon fiber. Tensile strength of carbon fibers immediately after production start is 490kgf / mm ^2, became 510kgf / mm ² after 6 hours of operation.
[0039]
(Embodiment 5 ) In the oxidation treatment furnace shown in FIG. 4 in which dust is accumulated in a long-term operation, before the operation is started and before the air is heated by the gas heater 5, the rotation speed of the fan is intermittently set using a programming controller. After fluctuating and vibrating the oxidizing gas, dust in the furnace was discharged by wind power from the circulation fan 4. At this time, 15% of the suction air volume of the fan was discharged from the exhaust port.
[0040]
Thereafter, an acrylic fiber composed of 12000 filaments provided with a silicone-based oil was oxidized as a precursor fiber using the oxidation furnace, and then carbonized to produce a carbon fiber. The tensile strength of the carbon fiber immediately after the start of production was 490 kgf / mm ² , and became 530 kgf / mm ² after 6 hours of operation.
[0041]
(Comparative Example 3 ) In the oxidation treatment furnace shown in FIG. 7 in which dust accumulated in a long-term operation, the number of dust in the oxidation treatment furnace was measured after heating and circulating the air without discharging any air before the start of operation. 400 pieces / cm ³ .
[0042]
Thereafter, the same acrylic fiber as in Comparative Example 1 was used as a precursor fiber, oxidized using the oxidation furnace, and then carbonized to produce a carbon fiber. The tensile strength of the carbon fiber immediately after the start of production was 400 kgf / mm ² , and it became 460 kgf / mm ² after 96 hours of operation.
[0043]
【The invention's effect】
The oxidation furnace of the present invention is capable of efficiently exhausting and removing dust in the furnace and purifying the carbon fiber obtained immediately after the start of production by producing carbon fiber using such an oxidation furnace. The tensile strength of the carbon fiber can be made good, and the time until the tensile strength of the obtained carbon fiber reaches a stable level can be shortened.
[Brief description of the drawings]
FIG. 1 is a schematic side view showing a conventional oxidation treatment furnace.
FIG. 2 is a schematic side view showing an oxidation treatment furnace according to an embodiment of the present invention in an exhaust state.
FIG. 3 is a schematic side view showing an oxidation treatment furnace according to an embodiment of the present invention in a circulating state.
FIG. 4 is a schematic side view showing a conventional oxidation treatment furnace.
5 is a conceptual diagram of a system configuration of a fan rotation speed control device used in Embodiment 7. FIG.
FIG. 6 is a control pattern of a programming controller used in the seventh embodiment.
FIG. 7 is a schematic side view showing a conventional oxidation treatment furnace.
[Explanation of symbols]
1: Oxidation furnace 2: Roller 3: Yarn 4: Circulation fan 5: Gas heater 6: Exhaust port 7: Air supply port 8: Exhaust port, air supply port switching valve 8 ': Switching of circulation system duct Valve 9: Gas flow 10: Circulation system duct 11: Fan motor 12: Inverter 13: Programming controller

Claims (8)

In an oxidation processing furnace having a circulation system in which an oxidizing gas is circulated by a fan, an exhaust port having an opening / closing mechanism capable of discharging an air volume of 13 to 100% of the suction air volume of the fan is provided on the exhaust side of the fan. An oxidation for carbon fiber production comprising an air supply port provided with an opening / closing mechanism on the downstream side thereof, and a switching valve capable of blocking communication of the circulation duct between the exhaust port and the air supply port Processing furnace. A carbon fiber, wherein a part of the suction air flow of a fan is exhausted from an exhaust port before starting the operation of the oxidation treatment furnace according to claim 1, and then the precursor yarn is oxidized in the oxidation treatment furnace and then carbonized. Manufacturing method. The method for producing carbon fiber according to claim 2, wherein an air volume of 13 to 100% of a suction air volume of the fan is exhausted from an exhaust port. A part of the fan's suction air volume is exhausted from the exhaust port, thereby reducing the amount of dust in the oxidation furnace to 10 pieces / cm ^Three The method for producing a carbon fiber according to claim 2 or 3, wherein: Before starting the operation of the oxidation treatment furnace for carbon fiber production, which has a circulation system that circulates an oxidizing gas by a fan and has an exhaust port in the circulation system, suction of the fan while applying vibration to the oxidizing gas A method for producing carbon fiber in which a part of the air volume is exhausted from an exhaust port, and then the precursor yarn is oxidized in the oxidation furnace and then carbonized. The method for producing carbon fiber according to claim 5, wherein vibration is imparted to the oxidizing gas by low-frequency sound waves. The method for producing carbon fiber according to claim 5, wherein a gas is injected to impart vibration to the oxidizing gas. The method for producing carbon fiber according to claim 5, wherein vibration is imparted to the oxidizing gas by changing the rotational speed of the fan.

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