JPH06146121A - Production of carbon fiber - Google Patents

Abstract

(57) [Summary] [Purpose] Even if the infusible furnace is operated continuously for a long period of time,
Prevents fusion of fiber bundles due to light components emitted from the pitch fibers, and makes the pitch fibers well infusible without causing thread breakage or fluffing of the pitch fibers and cutting of the fiber bundles in the infusibilization furnace, resulting in high-quality carbon. It is possible to obtain fibers. [Configuration] The infusible furnace 1 is provided with an external circulation path 3 for gas,
Oxidizing gas drawn from the furnace 1 is passed through the circulation path 3 to the furnace 1.
A gas purifying apparatus 10 which circulates into the air and cools the oxidizing gas to a temperature of 150 ° C. or less in the middle of the circulation path 3 to condense and separate the light components of the pitch contained in the gas for purification.
Was installed. [Effect] Since the oxidizing gas purified by removing the light components of the pitch is circulated in the furnace 1 while being infusibilized, the fusion of the fiber bundles due to the light components of the pitch is prevented even if continuous operation is performed for a long period of time. It is possible to achieve the purpose.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing pitch-based carbon fibers, and more particularly to fusion of pitch fibers in an infusible furnace,
The present invention relates to a pitch-based carbon fiber manufacturing method capable of preventing yarn breakage and improving threadability. In this specification,
Unless otherwise specified, "carbon fiber" includes not only carbon fiber but also graphite fiber.

[0002]

2. Description of the Related Art Pitch-based carbon fibers produced from carbonaceous pitch such as petroleum-based pitch and coal-based pitch are carbonized in comparison with rayon-based and PAN-based carbon fibers which are currently produced in the largest amount. It has been attracting attention in recent years because it has a high yield, excellent physical properties such as elastic modulus, and has an advantage that it can be manufactured at low cost.

At present, pitch-based carbon fibers are obtained by (1) preparing meso-face pitch suitable for carbon fibers from petroleum-based pitch, coal-based pitch, etc., heating and melting the pitch, and spinning with a spinning machine. After the obtained pitch fibers are converged to form a fiber bundle, (2) the pitch fibers are heated to a maximum temperature of 250 to 350 ° C. in an infusible furnace under an oxidizing atmosphere to be infusible, and (3) ) The obtained infusible fiber is pre-carbonized by heating it to a maximum temperature of 400 to 1300 ° C. in an inert gas atmosphere in a preliminary carbonization furnace, and (4) then pre-carbonized preliminary carbonized fiber in a carbonization furnace. 3000 ℃ under an inert gas atmosphere
It is manufactured by heating to the following and carbonization (including graphitization).

Conventionally, in the above-mentioned infusibilization to carbonization process, a method of continuously infusibilizing pitch fibers formed into a fiber bundle under tension, continuously precarbonizing, and continuously carbonizing is frequently used.

The pitch fiber is formed by converging a large number of spun filaments into a single yarn, and further releasing a plurality of bobbins on which the yarn is wound at the same time to combine the filaments into a pitch. It is made into a fiber bundle, and the pitch fiber thus made into a fiber bundle is released from the bobbin and continuously passed through the infusible furnace and below.

[0006]

High-performance carbon fibers can be obtained from an optically anisotropic pitch (that is, mesophase pitch) obtained by heat-treating an optically isotropic pitch. A method in which the raw material pitch is simply heat-treated (Japanese Patent Laid-Open Nos. 49-19127 and 57-42924).
No.), a method of subjecting the optically isotropic pitch to solvent extraction and heat treatment of the insoluble matter (JP-A-54-160427, etc.), and a heat treatment while blowing an inert gas (JP-A-58). No. 1686867), a method of heat-treating after partial hydrogenation (Japanese Patent Laid-Open Nos. 57-1001816 and 58-58).
No. 18421), the thermal decomposition polycondensation is cut off in the middle, and a high-concentration anisotropic pitch is obtained by depositing or centrifuging according to the difference in specific gravity (Japanese Patent Publication No. 61-38755, 62-62).
24036) and the like have been proposed.

Further, a method of obtaining a mesophase pitch by polymerizing a condensed polycyclic hydrocarbon or a substance containing the same in the presence of a hydrogen fluoride or boron trifluoride catalyst (JP-A-63-146920).
No.) is also proposed.

By the way, each of these various mesophase pitches contains about 1-2% of light components generated during heat treatment and unreacted low molecular weight monomers. Since the infusibilization of the pitch fibers is carried out in an oxidizing gas atmosphere having a maximum temperature of 250 to 350 ° C., the pitch fibers emit a light fraction of pitch during the infusibilization process.

Therefore, when the infusible furnace is continuously operated for a long period of one day or more, the light components from the pitch fibers are gradually accumulated in the infusible furnace, and the fiber bundles are fused or agglomerated due to the adhesion of the light components. Was remarkable, and there was a problem that thread breakage and fuzzing occurred. When the operation is continued for a longer period of time, there is a problem that the fiber bundle is cut in the furnace.

An object of the present invention is to prevent fusion of fiber bundles due to light components emitted from the pitch fiber even when the infusible furnace is continuously operated for a long period of time, and to prevent yarn breakage of the pitch fiber in the infusible furnace. An object of the present invention is to provide a method for producing a pitch-based carbon fiber, which makes it possible to obtain a high-quality carbon fiber by satisfactorily infusibilizing the pitch fiber without causing fluffing and cutting the fiber bundle.

[0011]

The above object can be achieved by the method for producing a pitch-based carbon fiber according to the present invention. In summary, the present invention forms a fiber bundle of spun pitch fibers, and then passes it through an infusible furnace filled with a high-temperature oxidizing gas to infusibilize it, and preliminarily prepares the infusible fiber obtained. In a method for producing carbon fibers by pre-carbonizing and carbonizing in a carbonization furnace and a carbonization furnace, respectively, an external circulation path for gas is provided in the infusible furnace, and an oxidizing gas extracted from the infusible furnace is supplied. The pitch light contained in the oxidizing gas is circulated to the infusible furnace through the external circulating path, and the oxidizing gas is cooled to a temperature of 150 ° C. or lower in the middle of the external circulating path. A method for producing carbon fiber is characterized in that a refining device for condensing and separating the components and refining is installed, and the oxidizing gas passing through the external circulation path is refined by the refining device.

[0012]

EXAMPLE FIG. 1 is a configuration diagram showing an example of an infusible furnace used in the method for producing pitch-based carbon fibers of the present invention.
As shown in FIG. 1, the infusible furnace 1 has an inlet portion 1A and an outlet portion 1B of a pitch fiber F formed into a fiber bundle at both ends, and the inlet portion 1A and the outlet portion 1B are respectively provided at the end portions thereof. Furnace 1
Gas seal portions 1a and 1 for preventing invasion of air from the outside
b is provided. The inside of the furnace 1 is in an oxidizing gas atmosphere, and a gas supply path 2 for supplying a new oxidizing gas (fresh gas) into the furnace 1 is connected to the inlet portion 1A of the furnace 1.

The temperature in the infusibilizing furnace 1 is a constant temperature in the range of 150 to 350 ° C. by a heating source (not shown) in the furnace 1, or a minimum temperature of 150 to 150 from the inlet 1A to the outlet 1B of the furnace 1. Maximum temperature from 200 ℃ to 250-350 ℃
It is set to have a gradually increasing temperature gradient.

The oxidizing gas atmosphere has an oxygen concentration of 20.
~ 100% oxidizing gas is used. As this example, air, a mixed gas of air and oxygen, or oxygen gas is used.
Further, as the oxidizing gas, air containing a halogen gas such as ozone, NOx, SOx, or chlorine may be used. Alternatively, a mixed gas of air and oxygen containing ozone, NOx, SOx may be used.

The pitch fiber F is 50 to 200 spun fibers.
A sizing agent is applied to a large number of zero filaments to focus them,
Applying an oil agent by making a single yarn and then unwinding a plurality of bobbins wound with the yarn at the same time, or by repeatedly unwinding and compounding in multiple times. Meanwhile, 2 to 50 yarns are bundled (mixed yarn), and 100 to 1
A pitch fiber bundle is manufactured from 00000 filaments, preferably 500 to 10000 filaments.

The pitch fibers F formed into a fiber bundle as described above are unwound from the bobbin and fed to the infusible furnace 1 and passed through the infusible furnace 1 at a predetermined speed, and the maximum temperature is 250. ~
It is infusibilized by heating in an oxidizing gas atmosphere at 350 ° C. This infusibilization can be performed without applying tension to the fiber F, but the occurrence of drag scratches caused by rubbing the furnace bottom and the furnace wall due to the slack of the fiber F in the infusibilization furnace 1 and the appearance are In order to improve the physical properties of the carbon fiber such as good tensile strength and tensile elasticity, it is preferable to perform infusibilization while applying a tension of 0.001 to 0.2 g per filament. In this way, the oxygen concentration of the infusible fiber is infusibilized to 7 to 12% by weight.

During the process of infusibilization in the infusibilizing furnace 1, light components are released from the pitch fibers F, and if the infusibilizing furnace 1 is continuously operated for a long period of one day or more, the pitch in the infusibilizing furnace 1 is increased. The light components from the fiber F are gradually accumulated, and the fusion and gluing of the fiber bundle due to the adhesion of the light components become remarkable, causing yarn breakage and fluffing, and further long-term operation. The problem of cutting the bundle arises.

Therefore, in the present invention, the infusible furnace 1 is replaced by the furnace 1.
A gas purification circulation line including a gas external circulation path 3 for extracting the oxidizing gas inside and returning it to the furnace 1 again, and a gas purification device 10 for purifying the oxidizing gas extracted in the middle of the circulation path 3 is installed. Then, the oxidizing gas in the furnace 1 was circulated while being purified.

According to the present embodiment, the external circulation path 3 of the gas purification circulation line has one end 3a connected to the outlet end 1B of the furnace 1 as a gas withdrawing end and the other end connected to the inlet end 1A of the furnace 1. 3b is the gas return end.

A circulating pump 4 for circulating the oxidizing gas in the infusible furnace 1 through the circulating path 3 is inserted in the middle of the circulating path 3, and the oxidizing gas in the infusible furnace 1 is pumped by the pump 4. Is drawn out from the pull-out end 3a at the exit end 1B of the furnace 1 and flows through the circulation path 3, is returned from the return end 3b to the inside of the furnace 1 at the entrance end 1A of the furnace 1, and is circulated in the furnace 1. .

A circulation pump 4 is provided to adjust the flow rate of the oxidizing gas circulated in the infusible furnace 1 through the circulation passage 3.
A gas flow rate control valve 5 and a measurement meter 6 for measuring the flow rate are installed between the hands.

Gas refining device 10 of gas refining circulation line
Is installed in the circulation path 3 by providing the gas introduction end 3c and the gas outflow end 3d between the extraction end 3a of the circulation path 3 and the pump 4. This purifier 10 has a mist separator 7 having a wire net, a porous body, etc. built in a cylinder, installed in a jacket 9 in which a cooling medium 8 such as water is flown, and a gas introduction end inserted in the separator 7 is introduced. The oxidizing gas flowing through the circulation path 3 from 3c is separated by the separator 7
It is introduced into the inside and cooled, and the light components of the pitch contained in the oxidizing gas are condensed into a fine mist, which is separated with a wire mesh of the separator 7, multiple antibodies, etc. to purify the oxidizing gas. It is supposed to do.

The above-mentioned oxidative gas needs to be cooled to 150 ° C. or less, preferably 0 ° C. to 50 ° C., in order to condense and separate the light components of pitch. By such condensation by cooling, not only the light components of the pitch but also the decomposed and deteriorated products of the sizing agent and the oil agent are removed at the same time.

Incidentally, fine mist such as light components of the pitch generated by cooling the oxidizing gas may be removed by using a filter or a cyclone.

The purified oxidizing gas flows out into the circulation path 3 from the gas outflow end 3d inserted in the separator 7,
As described above, it is returned to the inside of the infusible furnace 1 from the return end 3b through the circulation path 3.

The external circulation path 3 of the gas purification circulation line
Connects the gas outlet end 3a to the outlet end 1B of the furnace 1,
Although the gas return end 3b has been described as being connected to the inlet end 1A of the furnace 1, conversely, the gas outlet end 3a is connected to the inlet end 1A of the furnace 1 and the gas return end 3b is connected to the outlet end 1B of the furnace 1. There is no problem in doing so. Further, the infusibilizing furnace 1 may have an inlet end or an outlet end located at a place where a heating element is present, such as the center of the furnace.

The amount of the purified oxidizing gas circulated into the furnace 1 (which is also the amount of the oxidizing gas withdrawn from the furnace 1),
The total amount of new oxidizing gas (fresh gas) supplied from the gas supply passage 2 into the furnace 1 is 10 m ³ / hr or more per 1 kg of pitch fiber, and preferably 2
It is 0 to 100 m ³ / hr. The ratio of the circulating amount of purified oxidizing gas and the supply amount of fresh gas is as follows:
Purified gas = 1: 1 to 1:50.

If the total amount of the purified gas circulated and the amount of the fresh gas supplied is less than 10 m ³ / hr per 1 kg of pitch fiber, it is not preferable because it is affected by light components.
When it exceeds 00 m ³ / hr, it is not economically preferable. Further, when the ratio of the fresh gas supply amount and the purified gas circulation amount is 1: 1 or less, the effect is small, and when the ratio is 1:50 or more, it is not economical and both are not preferable.

In order to preheat the purified oxidizing gas, a heat exchanger is provided between the inlet side and outlet side of the refining device 10 of the circulation path 3 so that the heat of the gas is exchanged between them. be able to. Further, a means for removing CO ₂ and H ₂ O contained in the oxidizing gas can be attached in the middle of the circulation path 3.

The infusibilized fiber obtained by infusibilizing the pitch fiber as described above is then fed to the preliminary carbonization furnace, and the maximum temperature is 400 to 1100 ° C. in an inert gas atmosphere such as nitrogen or argon. To be heated.

The pre-carbonized fiber obtained by pre-carbonization is then fed to a carbonization furnace, where it is heated to 3000 ° C. in an inert gas atmosphere to obtain carbon fiber and further graphite fiber.

As described above, according to the present invention, the light pitch components emitted from the pitch fibers contained in the oxidizing gas in the infusible furnace 1 are condensed, separated and purified, and the purified oxidation is carried out. Since the pitch fibers are infusibilized while circulating the fusible gas through the infusibilization furnace, even if the infusibilization furnace is continuously operated for a long period of time, the fusion of the fiber bundle due to the light components from the pitch fibers is prevented. The pitch fibers can be satisfactorily infusibilized without causing thread breakage or fluffing of the pitch fibers or cutting of the fiber bundle in the infusibilizing furnace. Therefore, it is possible to obtain a high-quality pitch-based carbon fiber while preventing the deterioration of quality due to infusibilization.

Specific examples of the embodiments of the present invention will be described.

Example 1 Pitch for carbon fiber having a softening point of 280 ° C. and consisting of 98% of an optically anisotropic phase obtained by thermal decomposition polycondensation from catalytic cracking tar as a raw material was melt-spun with a spinneret having 500 holes. It was passed through a machine (nozzle hole: diameter 0.3 mm), extruded at 330 ° C. and spun.

The 500 spun filaments were substantially converged by an air sucker and led to an oil ring roller, and a converging oil agent was supplied at a ratio of about 0.1% by weight to the yarn,
A pitch fiber yarn consisting of 500 filaments was formed.

As an oil agent, the viscosity at 25 ° C. is 13 c
st methylphenyl polysiloxane xane was used.

The above pitch fiber was wound on a bobbin rotating at a high speed provided at the lower part of the nozzle and spun at a winding speed of about 500 m / min for 10 minutes.

Next, the bobbin 6 wound with pitch fibers
The individual pieces were unwound, and combined with an oil ring roller while applying a heat resistant oil to form a pitch fiber bundle of 3000 filaments, which was wound on another bobbin.

Methylphenylpolysiloxane (35 mol% of phenyl groups) having a viscosity of 30 cst at 25 ° C. was used as an oil agent at the time of splicing. The applied amount was 0.5% based on the yarn.

While releasing the bobbin-wound pitch fiber bundle thus obtained from the bobbin, the furnace inlet temperature is 190 ° C. and the maximum temperature is 300 ° C. in an oxygen-rich atmosphere of oxygen / nitrogen = 60/40 as an oxidizing gas atmosphere. The pitch fiber was made infusible by continuously feeding it linearly to the infusibilizing furnace 1 shown in FIG. The infusibilization time was 18 minutes. When infusibilized, pitch fiber is 0.007 per filament
g tension was applied.

At the time of this infusibilization, a new oxygen-rich gas (fresh gas) is supplied from the gas supply passage 2 into the infusibilizing furnace 1 at a flow rate of 2 m ³ / hr per kg of pitch fiber, as shown in FIG.
The oxygen-rich gas purified by condensing and removing the pitch light components of the gas in the furnace 1 by the gas purification circulation line consisting of the gas external circulation path 3 and the gas purification device 10 in the furnace 1 is 8 m ³
/ Hr was circulated and supplied. The refining device 10 was used by passing tap water as the cooling medium 8.

As a result, the threadability was good even after the infusible furnace was continuously operated for 23 hours.

The infusible fiber thus obtained has a fusion degree of 5%.
The number of yarn breaks was 5 in a fiber bundle having a length of 5 cm. Further, when the light components attached to the infusibilized fiber bundle were measured by the acetone method, they were hardly recognized.

The above-mentioned infusible fiber was introduced into a pre-carbonization furnace, pre-carbonized at a maximum temperature of 1000 ° C., and the obtained pre-carbonized fiber was heated to 2000 ° C. in a nitrogen gas atmosphere to obtain carbon fiber. It was

The carbon fiber obtained from the infusible fiber after 23 hours of operation of the infusibilizing furnace had a yarn diameter of 9.8 μm, a tensile strength of 3.0 GPa and a tensile elastic modulus of 450 GPa. The fusion degree of this carbon fiber was 35%, and the number of yarn breakages in the fiber bundle having a length of 5 cm was 6.

24 hours after the operation of the infusible furnace, the infusible furnace 1
All of the purified oxygen-rich gas circulated at a circulation rate of 8 m ³ / kg · hr was switched to fresh gas, and the operation was continued for another 23 hours, but there was no change in yarn breakage or fusion degree at the time of infusibilization. The carbon fiber after carbonization at 2000 ° C. showed no change in the degree of fusion and the yarn breakage.

In the present specification, the adhered light component of the infusibilized fiber bundle is measured by removing the sizing agent from the fiber bundle and then treating the fiber bundle with 15 times the amount of acetone for 15 seconds to extract the adhered light component. Was obtained by doing.

Regarding the degree of fusion (%), a fiber bundle consisting of 3000 filaments was cut into a width of 3 mm, immersed in ethanol, blown with air for 30 seconds, and then fused under a microscope at a magnification of 20 times. The total number (N) of the filaments present was counted, and the degree of fusion was calculated by the formula: (N / 3000) × 100 (%).

Example 2 Example 1 was repeated except that the purified gas circulation rate to the infusible furnace 1 was 48 m ³ / hr per 1 kg of pitch fiber, and the total amount of the fresh gas and purified gas circulation rate was 50 m ³ / hr. The same process was carried out.

As a result, even when the infusible furnace was continuously operated for 23 hours, the threadability was good, the degree of fusion of the infusibilized fiber obtained was 0%, and the yarn breakage was 5 cm long. There was almost no fiber bundle in the fiber bundle.

The carbon fiber obtained from the infusible fiber after the infusible furnace had been operated for 23 hours, had a tensile strength of 3.1 GPa and a tensile modulus of 460 GPa. The degree of fusion of this carbon fiber was 17%, and the number of yarn breakages in the fiber bundle having a length of 5 cm was 1 or less.

Comparative Example 1 Example 1 was repeated except that the gas refining and circulation line was not used, and the fresh gas supply amount of oxygen-rich gas to the infusible furnace 1 was 2 m ³ / hr per 1 kg of pitch fiber. Was processed in the same manner as. In this case, although the initial threadability was good, fluffing gradually began to stand out from the 5th hour of operation of the infusibilizing furnace, and after 23 hours, the fiber bundle was broken in the furnace.

The fusion degree of the obtained infusible fiber is 59%.
The number of yarn breaks in the fiber bundle length of 5 cm was 250. When the light adhered content was measured, it was 0.3%.

The carbon fiber obtained from the infusible fiber cut in 23 hours in the infusible furnace has a yarn diameter of 9.8 μm, a tensile strength of 2.8 GPa and a tensile elastic modulus of 440 G.
It was Pa. The fusion degree of this carbon fiber is 85%,
The number of yarn breakages was 250 in a fiber bundle having a length of 5 cm.

Comparative Example 2 The supply amount of fresh oxygen-rich gas to the infusible furnace 1 was set to 2 m ³ / hr per kg of pitch fiber, and the amount of purified circulation gas was set to 8
When the infusible furnace was continuously operated for 23 hours at m ³ / hr, and then the circulation amount was kept as it was to prevent light components in the pitch from being condensed and trapped, and then continuously operated. After 25 hours, the fiber bundle was broken in the furnace.

The fusion degree of the obtained infusible fiber was 55%, and 240 yarn breaks were observed in a fiber bundle length of 5 cm.

The tensile strength of the obtained carbon fiber is 2.8 G.
Pa and the tensile elastic modulus were 430 GPa. The degree of fusion of this carbon fiber was 91%, and the number of yarn breaks in a fiber bundle length of 5 cm was 243.

[0058]

As described above, in the manufacturing method of the present invention, the infusible furnace is provided with an external circulation path for gas, and a gas refining device is installed in the middle of the circulation path so that By cooling the oxidizing gas to a temperature of 150 ° C. or less, the light components of pitch contained in the gas are condensed, separated, and purified, and the purified oxidizing gas is circulated to the infusible furnace to produce pitch fibers. Since infusibilization is performed, even if a long-term continuous operation of infusibilization is performed, it prevents fusion of the fiber bundle due to the light components coming out of the pitch fiber, and the thread is fluffed or fluffed in the infusibilization furnace. The pitch fibers can be satisfactorily infusibilized without cutting the bundle. Therefore, it is possible to obtain a high-quality pitch-based carbon fiber while preventing the deterioration of quality due to infusibilization.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an example of an infusible furnace used in a method for producing a pitch-based carbon fiber of the present invention.

[Explanation of symbols]

 1 infusible furnace 1A inlet part 1B outlet part 2 gas supply furnace 3 gas external circulation path 4 circulation pump 7 mist separator 10 gas purification device F pitch fiber

Claims (1)

[Claims] 1. After forming spun pitch fibers into a fiber bundle, the spun pitch fibers are passed through an infusible furnace filled with a high-temperature oxidizing gas to infusibilize the obtained infusible fibers, and the resulting infusible fibers are pre-carbonized. And a method for producing carbon fiber, which obtains carbon fiber by pre-carbonizing and carbonizing in a carbonization furnace, respectively, wherein an external gas circulation path is provided in the infusible furnace, and the oxidizing gas drawn from the infusible furnace is circulated. While circulating through the passage to the infusible furnace, the oxidizing gas is cooled to a temperature of 150 ° C. or lower in the middle of the external circulation passage to condense the light components of the pitch contained in the oxidizing gas. A method for producing carbon fiber, wherein a refining device for separating and refining is installed, and the refining device purifies the oxidizing gas passing through the external circulation path.