JPH04257322A - Production of pitch carbon fiber and graphite fiber - Google Patents

Abstract

PURPOSE:To provide a method for producing pitch carbon fibers, capable of obtaining the carbon fibers improved in the tensile strength, tensile elastic modulus and compression strength, while preventing the breakage and fuzzing of an infusible fiber strand in a preliminary carbonization oven. CONSTITUTION:Before an infusible fiber stand is preliminarily carbonized, the fiber stand is thermally treated at temperatures 30-100 deg.C lower than the melt-breaking temperature of the infusible fiber stand and raised at a rate of 100-5000 deg.C/min for a short time of 1-300 sec, and simultaneously drawn in a drawing rate of 5-100%. The thermal treatment and the simultaneous drawing treatment prevent the breakage and fuzzing of the infusible fiber stand in a preliminary carbonization oven, improve the yield of the preliminary carbonization, the tensile strength, tensile elastic modulus and compression strength of the finally obtained carbon fiber strand.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention generally relates to the production of carbon fibers (in this specification, unless otherwise specified, "carbon fibers" is used to include not only carbon fibers but also graphite fibers). The present invention relates to a method for producing carbon fibers from various carbonaceous pitches in a highly efficient manner and in large quantities.

0002

[Prior Art] Pitch-based carbon fibers manufactured from carbonaceous pitches such as petroleum-based pitch and coal-based pitch are more carbonized than rayon-based and PAN-based carbon fibers, which are currently produced in large quantities. It has attracted attention in recent years because it has the advantages of high yield, excellent physical properties such as elastic modulus, and can be manufactured at low cost.

[0003]Currently, pitch-based carbon fibers are produced by (1) preparing carbonaceous pitch suitable for carbon fiber from petroleum-based pitch, coal-based pitch, etc., heating and melting the carbonaceous pitch, and spinning it with a spinning machine. (2) The pitch fiber bundle is heated in an infusible furnace under an oxidizing atmosphere for 150 min.
(3) Then, the infusible fiber bundle was heated to ~350°C in an inert atmosphere for 30 minutes.
It is manufactured by heating to below 00°C to carbonize or graphitize.

However, with conventional techniques, pitch fibers and infusible fibers have a low tensile strength of about 0.01 GPa and are brittle, making them difficult to handle. It has been extremely difficult to stably obtain fibers in large quantities.

[0005] As one method for solving these problems, the present inventors have strengthened the strength of the fiber bundle by doubling pitch fibers obtained by spinning carbonaceous pitch and applying a straight oil. Then, they proposed a method of infusible fiber bundles by passing them continuously in a line in an oxygen-rich gas having an oxygen concentration of 30% or more (see JP-A No. 63-264917).

[0006]

[Problem to be Solved by the Invention] By the way, if the infusible fiber bundle can be drawn in the process of preliminary carbonization of the infusible fiber bundle, the tensile strength, tensile modulus, and compressive strength can be improved when the infusible fiber bundle is made into carbon fiber. Although this is a possibility, the infusible fiber bundle to be threaded is weak at about 0.01 GPa, so it has been difficult to draw the infusible fiber bundle in the past.

[0007] The infusible fiber bundle is heated at 500 to 1000°C in a chemically inert atmosphere such as argon or nitrogen gas.
When the fiber bundle is passed through a preliminary carbonization process in which the temperature is raised to 700 to 800°C, as disclosed in JP-A-59-15517, By this time, the strength of the fiber bundles had significantly decreased compared to the strength at room temperature, and the fiber bundles were likely to break in the furnace during the preliminary carbonization process, resulting in a major drawback in that they were likely to become fluffy.

The invention described in JP-A No. 63-264917 cannot fundamentally solve this problem, and breaks of the infusible fiber bundles frequently occur in the pre-carbonizing furnace. There were problems in that the yarn threading yield was low and the yarn was easily fluffed.

Furthermore, one infusible fiber bundle has 100 to 1
It is in the form of a fiber bundle composed of 00,000 filaments, and therefore, during preliminary carbonization,
A major drawback occurred in that each filament was fused or stuck to a large degree, causing a problem in the quality of the carbon fiber product after firing treatment.

[0010] In the process of researching a method for producing carbon fibers using a continuous firing process, the present inventors discovered that when performing preliminary carbonization in an inert gas atmosphere, the By rapidly raising the temperature to a low temperature of °C and simultaneously drawing the fiber bundle while heat treating it for a short time, the physical properties of the resulting carbon fibers, namely tensile strength and tensile modulus, are dramatically improved, and the compression It was found that the strength also increases.

What is even more surprising is that when the heat treatment under the above conditions and the simultaneous drawing treatment (hereinafter referred to as drawing heat treatment) are carried out, the temperature of the fiber bundle inside the furnace during the treatment is It was found that it was possible to avoid yarn breakage during the process, and that the yield during preliminary carbonization could also be improved.

The present invention has been made based on this new finding.

Therefore, an object of the present invention is to prevent fiber breakage of infusible fibers in a pre-carbonization furnace and to effectively draw fiber bundles, thereby achieving high tensile strength, high tensile modulus and high compression. An object of the present invention is to provide a method for producing pitch-based carbon fibers for producing high-quality carbon fibers having strength.

[0014]

[Means for Solving the Problems] The above objects are achieved by a method for producing pitch-based carbon fibers and graphite fibers according to the present invention. In summary, the present invention comprises infusibleizing a spun and bundled pitch fiber bundle, pre-carbonizing the infusible infusible fiber bundle, then carbonizing it, and further graphitizing it if necessary. In the method for producing pitch-based carbon fibers and graphite fibers, when pre-carbonizing the infusible fiber bundle, the temperature is 30 to 10% lower than the melting and breaking temperature of the fiber bundle in an inert gas atmosphere.
By heating the fiber bundle at a rate of 100-5000°C/min to a temperature lower than 0°C and heat-treating the fiber bundle in a very short time of 1-300 seconds, the fibers are simultaneously stretched at a stretching rate of 5-100%. This is a method for producing pitch-based carbon fibers and graphite fibers, which is characterized by pre-carbonizing a bundle.

The melting and breaking temperature of the fiber bundle is determined by passing the fiber bundle through a furnace with a heating section length of 2 m maintained at a constant temperature (for example, 400° C.) in a nitrogen atmosphere at a rate of 10 m/min. (equivalent to a heating rate of 5000°C/min), which is the temperature at which the fiber bundle is cut by melting the fibers. The melting and breaking temperature of the fiber bundle is
It can be obtained as the temperature at which melting of the fibers is observed by visually observing a cut fiber bundle, but more precisely, it is determined as the temperature at which melting of the fibers is observed by observation with a scanning electron microscope.

[0016] The temperature increase rate is a value determined from the time it takes for the fiber bundle to reach the temperature at the soaking section of the furnace from the temperature at the entrance of the furnace.

In the present invention, the temperature is rapidly raised to a temperature 30 to 100° C. lower than the melt-break temperature of the fiber bundle, and a short-time drawing heat treatment is performed, which consists of heat treatment and simultaneous drawing treatment. is 40~8 higher than the melt rupture temperature.
It is preferable to raise the temperature to a temperature 0°C lower. As for the temperature increase rate, a rate of 100 to 5000°C/min is used, preferably 500 to 4000°C/min.

According to the present invention, as described above, during preliminary carbonization in an inert gas atmosphere, the temperature is rapidly raised to a temperature 30 to 100°C lower than the melting and breaking temperature of the fiber bundle, and the fiber bundle is heated for a short time. Since the heat treatment and stretching treatment are performed, the physical properties of the carbon fiber obtained are such that the tensile strength and tensile modulus are dramatically improved, and the compressive strength is also increased.

[0019]

[Examples] Examples of the present invention will be described in detail below.

First, carbonaceous pitch can be spun by methods well known to those skilled in the art. For example, by heating and melting carbonaceous pitch suitable for manufacturing carbon fiber, such as petroleum pitch, coal pitch, pitch made from aromatic hydrocarbons, etc.
000 filaments, preferably 50 to 1000 filaments are spun, and a sizing agent is applied to each filament using a commonly used oiling roller to bundle these many filaments into a single yarn. It is wound onto a bobbin.

Examples of the sizing agent include water, alcohols such as ethyl alcohol, isopropyl alcohol, n-propyl alcohol, butyl alcohol, or sizing agents with a viscosity of 5 to 5.
1000cst (25°C) dimethylpolysiloxane,
Alkylphenylpolysiloxane etc. diluted with a low boiling point silicone oil (polysiloxane) or a solvent such as paraffin oil, or dispersed in water with an emulsifier added; Similarly, graphite, polyethylene glycol or hindered esters Dispersions of surfactants; surfactants diluted with water; and other oils that do not harm pitch fibers among the various oils used for ordinary fibers, such as polyester fibers, can be used.

[0022] The amount of sizing agent applied to the pitch fibers is usually 0.
．． 0.01 to 10% by weight, particularly preferably 0.05 to 5% by weight.

[0023] The thread consisting of a large number of filaments once wound onto a bobbin as described above can be unwound by simultaneously unwinding a plurality of bobbins, for example 2 to 50 bobbins, or by dividing it into multiple times. For example, by unwinding and doubling 2 to 10 yarns the first time and then combing the remaining yarn, 2 to 50 yarns are bundled (paired), and 10
A pitch fiber bundle (hereinafter simply referred to as "pitch fiber") is produced from 0 to 100,000 filaments, preferably 500 to 10,000 filaments, and wound onto another bobbin.

At the time of such doubling, a heat-resistant oil agent is applied to the pitch fibers in consideration of treatments during infusibility and preliminary carbonization. As the heat-resistant oil agent, alkylphenylpolysiloxane is preferable, containing 5 to 80%, preferably 10 to 50%, of phenyl groups, and the alkyl groups include methyl groups,
Ethyl groups and propyl groups are preferred, and the same molecule may contain two or more types of alkyl groups. Further, the viscosity used is 10 to 1000 cst at 25°C. Furthermore, an antioxidant as described later can also be added.

Another preferred oil agent that can be used is dimethylpolysiloxane containing an antioxidant, and preferably has a viscosity of 5 to 1000 cst at 25°C. Examples of the antioxidant include amines, organic selenium compounds, phenols, and the like, such as phenyl-α-naphthylamine, dilauryl selenide, phenothiazine, and iron octolate. As mentioned above, these antioxidants can also be added to the alkylphenylpolysiloxane for the purpose of further increasing heat resistance.

[0026] Furthermore, as a preferable oil agent, it is also possible to use one obtained by emulsifying each of the above-mentioned oil agents using a surfactant having a boiling point of 600°C or less. At this time, as the surfactant, polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, polyoxyethylene-modified silicone, polyoxyalkylene-modified silicone, etc. can be used.

These oil agents are applied to the pitch fibers in an amount of 0.01 to 10% by weight, preferably 0.05 to 5% by weight, by roller contact, spray coating, foam coating, or the like.

As described above, by applying a heat-resistant oil agent to the pitch fibers which have been doubled, the strength of the pitch fibers becomes significantly stronger and the yarn handling properties are greatly improved.

The pitch fibers produced as described above are unwound from a bobbin and sent to an infusibility furnace.

[0030] The temperature inside the infusibility furnace can be set to a certain constant temperature within the range of 150 to 350°C, but it is possible to have a temperature gradient that gradually increases from 150°C to 350°C from the furnace inlet to the furnace outlet. It can also be set to .

The inside of the infusibility furnace is made into an oxidizing atmosphere, and an oxidizing gas such as air, oxygen, a mixed gas of air and oxygen, or air and nitrogen is supplied to the inside of the infusibility furnace. Oxygen-rich gas with an oxygen concentration of 30-90% is used.

According to the present invention, the infusibility treatment can be carried out without applying tension to the fiber bundle, but by rubbing the furnace bottom and furnace wall due to slack of the fiber bundle in the infusibility furnace, Infusibility is performed while applying a tension of 0.001 to 0.2 g per filament in order to prevent the occurrence of drag scratches, improve the appearance, and improve the physical properties of carbon fiber such as tensile strength and tensile modulus. is preferred.

[0033] In this way, the infusible fiber bundle is infusible so that the oxygen concentration becomes 7 to 12% by weight. The infusible fiber bundle that has been infusible in the infusible furnace is continuously introduced into the pre-carbonization furnace and pre-carbonized, as described above.

Preliminary carbonization is carried out under an inert gas atmosphere, with nitrogen gas and argon gas being preferably used. Pre-carbonization is carried out at a temperature of 300-1300°C, but in the present invention, during pre-carbonization, the temperature is 100-500°C lower than the melt breakage temperature of the fiber bundle.
The fiber bundle is subjected to a drawing heat treatment for a very short time of 1 to 300 seconds by increasing the temperature at a rate of 0° C./min.

[0035] The above-mentioned stretching heat treatment may be carried out in a constant temperature furnace, for example, at 400°C.
It may be carried out in a temperature gradient furnace in which the temperature is maintained at a stepwise increase, such as 1100°C.

In the present invention, the temperature is rapidly raised to a temperature 30 to 100° C. lower than the melt breaking temperature of the fiber bundle, and the stretching heat treatment is preferably carried out at a temperature of 40 to 80° C. lower than the melt breaking temperature of the fiber bundle.
A lower temperature is better. The above temperature increase is 30° above the melting rupture temperature.
If the temperature is higher than a low temperature of .degree. C., it is not preferable because the fiber bundles will fuse and stick together, causing the fiber bundles to break. Furthermore, if the temperature is increased to a low temperature that is less than 100° C. lower than the melt breakage temperature, it becomes difficult to draw the fiber bundle, which is similarly undesirable.

[0037] 30 to 100°C higher than the above melt rupture temperature
The heating rate of the fiber bundle to a low temperature is 100 to 5000
A rate of 500 to 40 °C/min is used, preferably 500 to 40 °C/min.
00°C/min. If the heating rate is less than 100°C/min, the fiber structure will be fired while thermal polymerization and carbonization will partially proceed, making it difficult to draw the fibers sufficiently; Therefore, the threading speed of the fiber bundle had to be increased, which caused problems with the winding speed of the fiber bundle.
I still don't like it.

[0038] The time for the stretching heat treatment is 1 to 300 seconds, preferably a very short time of 5 to 200 seconds.

The drawing process in the drawing heat treatment is carried out by applying tension to the fiber bundle or by differentially moving two rollers, and can be achieved by either method. The tension during stretching is 0.001 to 0.2 per filament.
0g is given.

The stretching ratio of the fiber bundle is preferably 5 to 100%, preferably 10 to 80%. If the stretching ratio is less than 5%, a sufficient stretching effect cannot be obtained, and if it exceeds 100%, the fibers will be damaged by stretching, which is not preferable.

[0041] The stretching heat treatment may be carried out once, but it can also be carried out in multiple steps, for example, stretching once at 400°C and then stretching at 500°C. It is preferable to divide the process into multiple times because the fibers are less damaged and can be drawn easily.

[0042] After the above-mentioned drawing heat treatment is completed, the infusible fiber bundle may be subsequently subjected to a normal preliminary carbonization treatment without drawing treatment.

Conventionally, infusible fiber bundles are fragile, and in order to avoid cutting or fuzzing of the fibers during pre-carbonization of the infusible fiber bundles, it is necessary to apply tension to the fiber bundles only during the pre-carbonization process. If tension is not applied at all, or if tension is applied at a minimum level that does not deteriorate handling properties, it is even more difficult to apply tension to the fiber bundle during the pre-carbonization stage to draw the fiber bundle. It has been impossible to improve the tensile strength, tensile modulus, and compressive strength of.

In the present invention, the temperature is rapidly raised to a temperature 30 to 100° C. lower than the melting break temperature of the infusible fiber bundle, and the infusible fiber bundle is cut and heated for a short time. In addition to preventing the occurrence of fuzz, it is possible to perform preliminary carbonization while applying tension and stretching. During this preliminary carbonization, the stretching process that applies active tension to the infusible fiber bundle increases the alignment of the fiber structure and effectively increases the tensile strength, tensile modulus, and compressive strength of the final carbon fiber. It becomes possible to improve the

After pre-carbonizing the infusible fiber bundle as described above, the obtained pre-carbonized fiber bundle is then heated to a temperature of 1500 to 2000° C. in a carbonization furnace under an inert gas atmosphere to carbonize it. , if necessary, it may be graphitized by heating up to 3000°C. This makes it possible to obtain carbon fibers that are free from fiber breakage and fluffing and have improved tensile strength, tensile modulus, and compressive strength.

The raw material carbonaceous pitch used in the present invention is prepared from known raw materials such as various petroleum-based heavy oils, pyrolysis tar, catalytic cracking tar, heavy oil and tar obtained by carbonization of coal, etc. , mesophase pitch (optically anisotropic pitch) obtained by its thermal decomposition polycondensation,
It may be a mesoface pitch made from aromatic hydrocarbons, a pitch containing an optically anisotropic phase and an optically isotropic phase, or an optically isotropic pitch. For example, when ultra-high-strength, high-performance carbon fibers are produced from mesoface pitch obtained by pyrolysis polycondensation, mesoface pitch with a mesoface content of 70 to 100% is preferred, particularly substantially 100% mesoface pitch. Most preferred is a mesoface pitch containing.

[0047] The infusible fibers have been described as linear pitch fibers that are continuously infusible, but can-shaped fibers (pitch fibers deposited in a wire mesh container, and similar The present invention can be carried out in the same way, and the same effects can be achieved with the use of materials made infusible by using a mesh belt, pitch fibers placed on a mesh belt, or products made infusible while wound on a bobbin. obtain.

Next, the method for manufacturing carbon fiber according to the present invention will be further explained based on specific examples.

Example 1 Carbon fiber pitch consisting of 98% optically anisotropic phase was
It was passed through a melt spinning machine (nozzle hole diameter: 0.3 mm in diameter) having a spinneret with 00 holes, and extruded and spun at 355° C. under a nitrogen gas pressure of 200 mmHg.

The 500 spun filaments were approximately converged by an air sucker and guided to an oiling roller, and a converging oil was supplied at a ratio of about 0.2% by weight to the yarn.
A pitch fiber consisting of 0 filaments was formed. As the oil agent, methylphenylpolysiloxane having a viscosity of 14 cst at 25° C. was used.

The pitch fiber was wound onto a stainless steel bobbin with a diameter of 210 mm and a width of 200 mm that was provided at the bottom of the nozzle and rotated at high speed, and spun for 10 minutes at a winding speed of about 500 m/min.

Next, the bobbin 6 wound with pitch fibers is
The fibers were unwound, and the fibers were combined using an oiling roller while applying a heat-resistant oil to form a pitch fiber (bundle) consisting of 3,000 filaments, which was wound onto another stainless steel bobbin.

[0053] As an oil agent during yarn doubling, use 40cst at 25°C.
of methylphenylpolysiloxane (phenyl group content 4
5 mol%) was used. The amount applied was 0.5% based on the yarn.

While unwinding the bobbin-wound pitch fiber thus obtained from the bobbin, an oxygen-rich atmosphere (oxygen/nitrogen = 60/40) having a temperature gradient of a furnace inlet temperature of 180°C and a maximum temperature of 295°C is prepared. It was introduced continuously in a linear manner into a continuous infusibility furnace. The temperature increase rate was 6° C./min, and the infusibility time was 19 minutes. The tension applied to the fiber bundle was 0.007 g per filament (20 g for a fiber bundle of 3000 filaments). The oxygen concentration of the infusible fiber after infusibility was 9.5% by weight.

During the infusibility, the pitch fibers were smoothly unwound from the bobbin, and the infusibility treatment could be carried out smoothly without any breakage of the fiber bundle in the infusibility furnace. The melting failure temperature of the infusible fiber bundle made infusible in this way in a nitrogen atmosphere is 45
It was 0°C.

[0056] This infusible fiber bundle is passed through a pre-carbonization furnace in a nitrogen atmosphere at 400°C (a temperature 50°C lower than the melting failure temperature of the infusible fiber bundle) at a heating rate of 3000°C/min. Stretching heat treatment was performed in which heat treatment and stretching treatment were performed simultaneously.

[0057] The stretching heat treatment time was 25 seconds. A tension of 0.007 g per filament was applied to the fiber bundle. The stretching ratio was 21%. Although the continuous treatment was carried out for one hour, no breakage of the fiber bundle occurred in the furnace during that time.

Next, the fiber bundle treated as described above was further heated to 1000° C. at a rate of 100° C./min and subjected to normal preliminary carbonization without applying tension.

The pre-carbonized fiber thus obtained was heated to 1500° C. in a nitrogen gas atmosphere to obtain carbon fiber. The carbon fiber thread diameter is 8.9 μm, and the tensile strength is 3
．． 3GPa, tensile modulus is 330GPa, compressive strength is 1
．． It was 2GPa.

[0060] Also, the carbon fiber was exposed to 2
The graphite carbon fiber obtained by raising the temperature to 500°C has a thread diameter of 8.
8 μm, tensile strength was 4.0 GPa, tensile modulus was 810 GPa, and compressive strength was 0.5 GPa.

Example 2 In Example 1, the fiber bundle subjected to the drawing heat treatment once at 400°C had a melting and breaking temperature of 550°C. This fiber bundle was heated at 500°C (50°C higher than the melting and breaking temperature of the fiber bundle).
3000℃ in a pre-carbonization furnace with nitrogen atmosphere (temperature 0℃ lower)
The yarn was threaded at a temperature increase rate of /min and subjected to drawing heat treatment again.

The treatment time was 25 seconds, and a tension of 20 g per filament was applied to the fiber bundle. The stretching ratio at this time was 25%. The total stretching ratio of stretching at 400°C and stretching at 500°C was 46%.

[0063] Except for the above, the process was carried out in the same manner as in Example 1. 1
Although the process was carried out continuously for several hours, there was no yarn breakage in the furnace during that time.

When the fibers treated in this way were subjected to the next pre-carbonization treatment, there was no breakage in the pre-carbonization furnace during continuous operation for 24 hours, and the obtained pre-carbonized fiber bundles did not have any fluff. There wasn't much.

[0065] This pre-carbonized fiber bundle was heated to 1500°C in a nitrogen gas atmosphere to obtain carbon fibers. The carbon fiber had a thread diameter of 8.3 μm, a tensile strength of 3.6 GPa, and a tensile modulus of 340 GPa.

Furthermore, graphite carbon fiber obtained by heating carbon fiber to 2500°C in an argon gas atmosphere has a thread diameter of 8.
．． 2 μm, tensile strength was 4.2 GPa, and tensile modulus was 850 GPa.

As shown in Examples 1 and 2, during pre-carbonization, the melting and breaking temperature of the fiber bundle within the range of the present invention was lowered by 3.
Since the temperature was rapidly raised to a temperature lower than 0 to 100 degrees Celsius and the drawing heat treatment was performed for a short time, it was possible to pre-carbonize the infusible fiber bundle without causing yarn breakage in the pre-carbonization furnace. The carbon fibers and graphite fibers obtained had not only little fiber fuzz but also slight yarn breakage. In addition, during preliminary carbonization, the above-mentioned stretching heat treatment is applied to the fiber bundle by 5 to 100%.
Since the stretching treatment was added, the obtained carbon fibers and graphite fibers had improved tensile strength, tensile modulus, and compressive strength.

Comparative Example 1 In Example 1, except that the temperature of the preliminary carbonization furnace was 430°C (20°C lower than the melting and breaking temperature of the fiber bundle),
It was treated in the same manner as in Example 1.

As a result, the fiber bundles were broken in the furnace, making continuous operation impossible.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the temperature of the preliminary carbonization furnace was 330° C. (120° C. lower than the melting and breaking temperature of the fiber bundle). In this case, no drawing of the fiber bundle occurred.

As a result, there was no yarn breakage in the preliminary carbonization furnace, and continuous operation for one hour was possible. However, the carbon fiber obtained by heating this pre-carbonized fiber to 1500°C in a nitrogen gas atmosphere has a thread diameter of 9.8 μm and a tensile strength of 2.
6GPa, tensile modulus is 270GPa, and compressive strength is 1.
It was 0 GPa.

Furthermore, graphite carbon fiber obtained by heating carbon fiber to 2500°C in an argon gas atmosphere has a thread diameter of 9.
．． 7 μm, tensile strength was 3.2 GPa, tensile modulus was 690 GPa, and compressive strength was 0.4 GPa.

Comparative Example 3 The same procedure as in Example 1 was carried out except that the temperature increase rate was 50° C./min. In this case, no drawing of the fiber bundle occurred.

Similar to Comparative Example 2, the physical properties of the carbon fiber obtained in this case were lower than that of the stretched carbon fiber.

[0075]

As explained above, in the manufacturing method of the present invention, when pre-carbonizing the infusible fiber bundle obtained by infusible pitch fiber bundle, the temperature is 30 to 100% lower than the melting and breaking temperature of the fiber bundle.
The temperature is raised to a low temperature at a rate of 100 to 5000 degrees C/min, and the fiber bundle is heat treated for a very short time of 1 to 300 seconds while simultaneously being stretched at a stretching rate of 5 to 100%. This not only improves the yield during pre-carbonization by suppressing breakage and fluffing of the infusible fiber bundles in the process, but also allows carbon fibers with improved fiber tensile strength, tensile modulus, and compressive strength to be obtained. .

Claims (2)

[Claims] 1. Pitch, which is made by infusibleizing a spun and bundled pitch fiber bundle, pre-carbonizing the infusible infusible fiber bundle, followed by carbonization, and further graphitization if necessary. In the method for producing carbon fiber and graphite fiber,
When pre-carbonizing the infusible fiber bundle, the fiber bundle is heated at a rate of 100 to 5000°C/min to a temperature 30 to 100°C lower than the melting and breaking temperature of the fiber bundle in an inert gas atmosphere. A method for producing pitch-based carbon fibers and graphite fibers, which comprises pre-carbonizing a fiber bundle by heat treatment for a very short time of 1 to 300 seconds and simultaneously stretching at a stretching rate of 5 to 100%. 2. The manufacturing method according to claim 1, wherein the heat treatment and stretching treatment of the infusible fiber bundle are performed in multiple steps.