JPH04119126A - Production of pitch-based carbon fiber and graphite fiber - Google Patents

Abstract

PURPOSE:To prevent yarn breakage in a precarbonization furnace, reduce the fusing and sticking degree of precarbonized fiber, etc., and efficiently obtain the subject fiber having a high tensile strength, tensile elongation and compressive strength by precarbonizing an infusibilized fiber bundle according to a specific method. CONSTITUTION:A spun and collected pitch fiber bundle is initially infusibilized. The resultant infusibilized fiber bundle is then heat-treated in an oxidizing gas-containing atmosphere at 500-700 deg.C, preferably 550-650 deg.C maximum temperature in a short time, preferably 50-200sec while being subjected to drawing treatment at 5-100% draw ratio and precarbonized. The aforementioned precarbonized fiber is carbonized and, as necessary, then graphitized. Furthermore, oxygen is preferred as the above-mentioned oxidizing gas and the oxygen content in the oxidizing gas-containing atmosphere is preferably 0.01-30%.

Description

Detailed Description of the Invention [l Epithelium ■ Dish 11 The present invention generally refers to carbon fibers (unless specified herein, "carbon fibers" include not only carbon fibers but also graphite fibers). The present invention relates to a method for producing carbon fibers (used in the present invention), and particularly to a method for producing carbon fibers from various carbon pitches very efficiently and in large quantities.

Pitch-based carbon fibers manufactured from carbonaceous pitches such as petroleum-based pitch and coal-based pitch have a lower carbonization yield 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 a high modulus, excellent physical properties such as elastic modulus, and can be manufactured at low cost.

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, spinning it in a spinning machine, and converging it; (2) The pitch fibers are heated to 150 to 350°C in an oxidizing atmosphere in an infusible furnace to make them infusible. (3) The infusible fibers are then carbonized. It is manufactured by heating to 3000°C or less in a furnace under an inert atmosphere to carbonize or graphitize it.

However, depending on the conventional technology, pitch fibers and infusible fibers have a low tensile strength of about 0.0 IGPa, and are brittle, making them difficult to handle. It was extremely difficult to obtain it in large quantities.

As one method to solve these problems, the present inventors have developed a method of increasing the strength of fiber bundles by doubling pitch fibers obtained by spinning carbonaceous pitch and applying a straight oil. proposed a method of infusible fiber bundles by passing them continuously in a line in an oxygen-rich gas with an oxygen concentration of 30% or more (see Japanese Patent Application Laid-open No. 264917/1983).

However, in the preliminary carbonization process in which the temperature of the infusible fibers is raised to 500 to 1000°C in an atmosphere of chemically inert argon or nitrogen gas to carry out initial carbonization, linear When passing through the fiber bundle, as disclosed in JP-A-59-15517, by the time the temperature of the fiber bundle reaches 700 to 800°C, the strength of the fiber bundle is significantly reduced from the strength at room temperature. However, there was a major drawback in that the fiber bundles were easily cut in the furnace during the preliminary carbonization process and became fluffy.

The invention described in JP-A No. 63-264917 cannot fundamentally solve this problem, and in the pre-carbonizing furnace, the infusible fibers frequently break in the furnace, and the yarn threading yield decreases. There was a problem in that it deteriorated and fuzzed easily.

Furthermore, one infusible fiber is in the form of a fiber bundle composed of 100 to 100,000 filaments, and therefore, during preliminary carbonization, each filament may fuse or stick together. This resulted in a major drawback in that the quality of the carbon fiber product after firing treatment was affected.

One way to improve the yarn breakage in the pre-carbonization furnace is to increase the degree of infusibility of the infusible fibers in the infusibility furnace, but as a result of research experiments conducted by the present inventors, According to this method, the physical properties of the carbon fiber deteriorated, and it was found that this method was not suitable.

In the process of researching a method for producing carbon fibers using a continuous firing process, the present inventors heat-treated normally infusible infusible fibers in a high-temperature oxidizing gas-containing atmosphere for a short period of time. Carbonization prevents the infusible fibers from breaking in the pre-carbonization furnace, improving threading yield, and also reduces the degree of fusion and stickiness of the pre-carbonized fibers, producing high-quality carbon fibers. I found out what can be done.

Furthermore, surprisingly, during such heat treatment,
By heat-treating the infusible fibers and simultaneously applying tension to the infusible fibers and drawing them, the physical properties of the resulting carbon fibers, that is, the tensile strength and tensile modulus, are dramatically improved, and the compressive strength is also increased. I discovered that.

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

Therefore, an object of the present invention is to prevent yarn breakage of infusible fibers in a pre-carbonization furnace, improve yarn threading yield, and further reduce the degree of fusing and agglutination of pre-carbonized fibers to achieve high tensile strength and high An object of the present invention is to provide a method for producing pitch-based carbon fiber for producing high-quality carbon fiber having a tensile modulus and high compressive strength.

Another object of the present invention is to reduce the pre-carbonization time from 172 to
It is an object of the present invention to provide a method for producing pitch-based carbon fibers that can be shortened to about 1/10 and efficiently produce carbon fibers having high tensile strength, high tensile modulus, and high compressive strength.

The above object is achieved by the 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 Kurofune fibers, the infusible fiber bundle is pre-carbonized in an oxidizing gas-containing atmosphere with a maximum temperature of 500 to 700°C. This is a method for producing pitch-based carbon fibers and graphite fibers, which is characterized by carrying out a short-time heat treatment while adding a stretching treatment. Preferably, the oxidizing gas in the atmosphere is oxygen, and the oxygen content of the atmosphere is 0.01 to 3.
0%, and the heating time is 20 to 300 seconds.

According to the present invention, in the method of producing carbon fibers by a continuous firing process, the infusible fibers which have been infusible in a conventional manner are heated at a maximum temperature of 500 to 700°C, preferably 550 to 60°C.
A short period of time in an atmosphere containing oxidizing gas at 50°C, i.e.
For 20 to 300 seconds, preferably 50 to 200 seconds, tension is applied to the infusible fibers at the same time, and a stretching process of 5 to 100% is performed to perform preliminary carbonization (heat treatment). This prevents the infusible fibers from breaking in the pre-carbonization furnace and improves the threading yield. Further, according to the present invention, the degree of fusing and agglutination of the pre-carbonized fibers after the pre-carbonization treatment is reduced, and therefore the degree of fusing and agglutination of the carbon fibers after the subsequent carbonization or graphitization treatment is reduced and extremely high. You can get quality carbon fiber. At the same time, according to the present invention, since the infusible fibers are heat-treated and stretched at the same time by applying tension to the infusible fibers, the physical properties of the obtained carbon fibers are as follows:
Not only the tensile strength and tensile modulus are dramatically increased, but also the compressive strength is increased.

Furthermore, the preliminary carbonization time can be shortened to 1/2 to 1/10 of the conventional time.

Oioka l Examples of the present invention will be described in detail below.

The present inventors not only improved the yield during pre-carbonization by suppressing the cutting and fluffing of the fibers of the infusible fiber bundle in the pre-carbonization furnace (they also actively applied tension during the pre-carbonization stage). We have conducted extensive research to develop a method for producing pitch-based carbon fibers that can be stretched and stretched to produce carbon fibers with improved tensile strength, compressive strength, and elastic modulus.

As a result, if pre-carbonization of the infusible pitch fiber bundle is carried out in a short time in an atmosphere containing high temperature oxidizing gas, the surface layer of the fibers will be selectively oxidized and the surface layer will be strengthened. It is possible to advance the carbonization inside the fibers and pre-carbonize the fibers, which not only prevents the fibers from being cut or fluffed in the infusible fiber bundles in the pre-carbonization furnace, but also allows the tension to be actively applied to the infusible fiber bundles. It has been found that it is possible to carry out the stretching treatment over a period of 20 minutes, thereby not only improving the yield during preliminary carbonization but also obtaining carbon fibers with improved tensile strength, compressive strength, and elastic modulus.

The present invention has been made based on the above findings.

FIG. 1 is an explanatory diagram showing one embodiment of the method for producing carbon fibers of the present invention.

In FIG. 1, reference numeral 30 denotes a preliminary carbonization furnace, in which the pitch fiber bundles obtained by spinning and doubling pitch fibers are infusible in an infusibility furnace (not shown), and the infusible fiber bundles thus obtained are Continuously, it is pre-carbonized in a pre-carbonization furnace 30, then carbonized in a carbonization furnace (not shown), graphitized if necessary,
Considered to be carbon fiber.

First, carbonaceous pitch can be spun by methods well known to those skilled in the art. For example, 1 to 2,000, preferably 50 to 1,000 filaments are produced by heating and melting carbonaceous pitch suitable for manufacturing carbon fiber, such as petroleum-based pitch, coal-based pitch, pitch made from aromatic hydrocarbons, etc. A sizing agent is applied to each filament using a commonly used oiling roller, and the large number of filaments are bundled and wound around a bobbin as a single thread.

Examples of the sizing agent include water, alcohols such as ethyl alcohol, isopropyl alcohol, n-propyl alcohol, and butyl alcohol, or alcohols with a viscosity of 5 to 1000 cs.
Dimethylpolysiloxane, alkylphenylpolysiloxane, etc. at t (25°C) diluted with a solvent such as low-boiling silicone oil (polysiloxane) or paraffin oil, or dispersed in water with an emulsifier added; the same Dispersed with graphite, polyethylene glycol, or hindered esters; surfactants diluted with water; and other oils used for ordinary fibers, such as polyester fibers, which do not harm pitch fibers. can do.

The amount of the sizing agent applied to the pitch fibers is usually 0.01 to 1% by weight, particularly preferably 0.05 to 5% by weight.

The yarn consisting of a large number of filaments once wound onto bobbins 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, the first time. By repeatedly unwinding and doubling 2 to 10 yarns, then the remaining yarn,
2 to 50 yarns are bundled (paired) and 100 to 1000
00, preferably 500 to 10,000 filaments to form a pitch fiber bundle (hereinafter simply referred to as "pitch fiber").

) is produced and wound onto another bobbin.

During 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, and the phenyl group content is 5 to 80%, preferably 10 to 50%.
In addition, the alkyl group is preferably a methyl group, ethyl group, or propyl group, and the same molecule may contain two or more types of alkyl groups. Also, the viscosity is 10 to 10 at 25°C.
00cst is used. 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.

Further, as preferred oils, each of the above oils has a boiling point of 60.
It is also possible to use an emulsified product using a surfactant having a temperature of 0° C. or lower. At this time, as the surfactant, polyoxyethylene alkyl ether, polyoxyethylene alkyl ester, polyoxyethylene modified silicone,
Polyoxyalkylene-modified silicones and the like may 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 mentioned above, by applying a heat-resistant oil to the doubled pitch fibers, the strength of the pitch fibers becomes extremely high (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.

The temperature inside the infusibility furnace can be set at a constant temperature within the range of 150 to 350°C, but it should be set so that it has a temperature gradient that gradually increases from 150°C to 350°C from the furnace inlet to the furnace outlet. You can also do it.

In addition, the inside of the infusibility furnace is made into an oxidizing atmosphere, and oxidizing gas such as air, oxygen, a mixed gas of air and oxygen, or air and nitrogen is supplied into the infusibility furnace, and a preferable gas is an oxygen concentration of 30 ~90% oxygen rich gas is used.

According to the present invention, the infusibility treatment can be carried out without applying any tension to the fiber bundle, but the slackness of the fiber bundle in the infusibility furnace causes drag scratches caused by rubbing against the furnace bottom and furnace wall. In order to prevent the occurrence of carbon fibers, improve appearance, and improve the physical properties of carbon fibers such as tensile strength and tensile modulus, it is preferable to carry out the infusibility while applying a tension of 0.00 to 0.2 g per filament.

In this way, the infusible fibers are infusible so that the oxygen concentration C becomes 7 to 12% by weight.

The infusible fiber bundle F that has been infusible in the infusible furnace is continuously introduced into the pre-carbonization furnace 30 and pre-carbonized, as described above.

The preliminary carbonization furnace 30 is set so that the maximum temperature is 500 to 700°C. For example, the temperature is 400°C and 500°C from the inlet to the outlet. The temperature is maintained at a maximum temperature of 500 to 700°C, increasing stepwise to 600°C.

According to the present invention, in order to pre-carbonize the infusible fiber bundle F while selectively oxidizing the surface layer of the fibers by short-time heating at a maximum temperature of 500 to 700°C, the pre-carbonization furnace 30 By supplying an inert gas mixed with a small amount of oxidizing gas, an atmosphere containing a low concentration of oxidizing gas is maintained.

Nitrogen gas or argon gas is used as the inert gas.

Oxidizing gases contained in inert gas include oxygen,
Oxidizing gases such as air, a mixture of air and oxygen, NOx, SOx, water vapor, carbon dioxide gas, halogen gas, strong acid vapor, or a mixture of two or more of these gases are used, but are preferably used. oxygen or air is used.

The oxygen content in the above low concentration oxygen-containing atmosphere is
It is set at 0.01 to 30%. If the oxygen content of the low-concentration oxygen-containing atmosphere is less than 0.01%, it is too small and the surface layer of the infusible fiber cannot be effectively oxidized by short-time heating during preliminary carbonization, and on the contrary, the oxygen content is less than 30%. It's too much if it exceeds
Even with short-time heat treatment, only the surface layer of the infusible fiber cannot be selectively oxidized, causing the disadvantage that oxidation progresses to the inside of the fiber. Therefore, the oxygen content of the low-concentration oxygen-containing atmosphere is set to o.oi to 30%, more preferably 0.0%.
05-10%.

The heat treatment time during preliminary carbonization of the infusible fiber in an atmosphere containing a low concentration of oxidizing gas is too short if it is less than 20 seconds.
Even if the oxidizing gas content of the atmosphere is increased, the surface layer of the infusible fiber cannot be effectively oxidized, and conversely, if it exceeds 300 seconds, it is too long, so even if the oxidizing gas content of the atmosphere is decreased, the surface layer of the infusible fiber cannot be effectively oxidized. Oxidation inevitably occurs inside the infusible fibers. Therefore, the heating time during preliminary carbonization is 20 to 300 seconds, more preferably 50 to 200 seconds.

Furthermore, according to the present invention, the tensioning means 3 is provided before the preliminary carbonization furnace 30.
2 is provided, and tension means 32 applies tension to the infusible fiber bundle F threaded into the pre-carbonization furnace 30, thereby performing a stretching process during pre-carbonization of the infusible fibers.

Usually, the tension applied to the infusible fiber is 0.006 to 0.33 g per filament. Stretching may be set by adjusting the magnitude of tension, or may be adjusted by differential movement of two or more rolls.

Conventionally, infusible fibers are fragile, and in order to avoid cutting or fuzzing of the fibers during pre-carbonization of the infusible fibers, it is necessary to apply no or no tension to the fibers during the pre-carbonization process. However, it is necessary to use the minimum tension that does not deteriorate handling properties, and by actively applying tension during the pre-carbonization stage to draw the fibers, the bow tensile strength, compressive strength, and elastic modulus of the fibers can be improved. It was impossible to improve this.

In the present invention, by heating the infusible fiber for a short time in an atmosphere containing low concentration of oxygen, the surface layer of the fiber is selectively oxidized to strengthen the surface layer and pre-carbonize the fiber, so the infusible fiber In addition to preventing cutting and fuzzing, it is also possible to perform preliminary carbonization while applying tension and stretching at the same time.

In the above-mentioned stretching treatment during preliminary carbonization of the infusible fibers, it is preferable to stretch the infusible fibers by about 5 to 100%. If the amount of stretching of the infusible fibers is less than 5%, it is too small and the alignment of the fiber structure cannot be improved, making it difficult to effectively improve the tensile strength, compressive strength, and elastic modulus of the carbon fibers finally obtained. cannot improve. On the other hand, if the amount of stretching exceeds 100%, it is too large and causes problems such as fiber cutting during preliminary carbonization.

In the present invention, preliminary carbonization is performed on the infusible fiber bundle F in the preliminary carbonization furnace 30 under the above conditions. According to this, preliminary carbonization of the infusible fiber bundle F is carried out by heating the infusible fiber bundle F for a short time in an atmosphere containing oxidizing gas at a predetermined temperature, so that the surface layer of the fibers is selectively oxidized to harden the surface layer and , the fibers can be pre-carbonized by advancing the carbonization inside the fibers, and therefore the infusible fiber bundle will not be cut or fluffed in the pre-carbonization furnace. During the preliminary carbonization, the infusible fiber bundle F is stretched by actively applying tension, so the arrangement of the fiber structure is improved, and the tensile strength and compressive strength of the final carbon fibers are increased. And it becomes possible to effectively improve the elastic modulus.

According to the present invention, as described above, the preliminary carbonization time is 1/2 to 1/2 compared to the preliminary carbonization time according to the conventional manufacturing method.
It was found that the time can be shortened to about /10.

After pre-carbonizing the infusible fiber bundle F as described above, the obtained pre-carbonized fiber bundle F is then heated in a carbonization furnace (not shown) at a temperature of 1500 to 2000°C under an inert gas atmosphere.
What is necessary is just to heat it to 3000 degreeC and carbonize it, and to graphitize it by heating it to 3000 degreeC as needed. This makes it possible to obtain carbon fibers that are free from fiber breakage and fluffing and have improved tensile strength, compressive strength, and elastic modulus.

The raw material carbonaceous pitch used in the present invention is made 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. Menface pitch (optically anisotropic pitch) obtained by decomposition polycondensation, menface pitch made from aromatic hydrocarbons, pitch or optical pitch containing an optically anisotropic phase and an optically isotropic phase It may be an isotropic pitch. For example, when producing ultra-high-strength, high-performance carbon fiber from mesoface pitch obtained by pyrolysis polycondensation, the mesoface content is 70 to 10
A mesoface pitch of 0% is preferred, especially substantially 1
Most preferred is a membrane pitch containing 0.00% membrane.

Incidentally, the infusible fibers have been explained as linear pitch fibers that are continuously infusible, but can-shaped fibers (pitch fibers placed in a wire mesh container and deposited, or similar) The present invention can be carried out in the same manner, and the same effects can be achieved with the following methods: those made infusible by placing pitch fibers on a mesh belt, or made infusible while still being wound on a bobbin.

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

Example 1 In producing pitch fiber, an optically anisotropic phase of about 55%
% and a softening point of 232° C. was used as the precursor pitch. This precursor pitch was centrifuged to successively separate pitches containing many optically anisotropic phases and pitches containing many optically isotropic phases, and each was extracted.

The obtained pitch containing a large amount of optically anisotropic phase contained 98% of the optically anisotropic phase, had a softening point of 270° C., and had a quinoline solubility of 30.0%. The pitch for carbon fiber is 500
Melt spinning machine with hole spinneret (nozzle hole diameter: diameter 0
．． 3 mm) and was extruded and spun at 355° C. under a nitrogen gas pressure of 200 mmHg.

The 500 spun filaments are roughly converged by an air sucker and guided to an oiling roller, with a ratio of about 0.2 to the yarn.
A focusing oil was supplied in a proportion of 500% by weight to form a pitch fiber consisting of 500 filaments. As an oil agent, 25
A methylphenylpolysiloxane having a viscosity of 14 cst at °C was used.

The pitch fibers were 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. The pitch of the traverse per revolution of the bobbin was 10 mm/rotation. No yarn breakage occurred during spinning.

Next, the six bobbins wound with pitch fibers were unwound,
Then, 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 around another stainless steel bobbin.

Methylphenylpolysiloxane (phenyl group content: 45 mol %) of 40 cst at 25° C. was used as an oil agent during yarn doubling. The amount applied was 0.15% to the yarn.

While unwinding the bobbin-wound pitch fiber thus obtained from the bobbin, the furnace inlet temperature was 180°C, and the maximum temperature was 295°C.
Oxygen-rich atmosphere with a temperature gradient of (oxygen/nitrogen = 60/4
0) was continuously introduced in a linear manner into the 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 is 0.007g 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 process, the pitch fibers were unraveled from the bobbin smoothly, and the infusibility treatment was carried out smoothly without any breakage of the fiber bundle in the infusibility furnace.

The infusible fiber bundle F thus infusible was continuously fed to the preliminary carbonization furnace 30.

According to this embodiment, the temperature inside the preliminary carbonization furnace 30 is 400°C, 500°C, and 600°C from the inlet to the outlet.
Heating was maintained so that the temperature rose in stages.

According to the present invention, nitrogen gas and a small amount of oxygen gas are supplied into the pre-carbonization furnace 30 to create an oxidizing gas-containing atmosphere with an oxygen concentration of 5%, and the infusible fiber bundle F is heat-treated for a short time. Preliminary carbonization was carried out.

The oxygen concentration in the oxidizing gas atmosphere was 5%.

A tension of 0.017 g per filament was applied to the fiber bundle. Preliminary carbonization time was 100 seconds. The stretching ratio of the yarn in this preliminary carbonization treatment was 19%.

Preliminary carbonization treatment was carried out continuously for 24 hours, but during this period, no yarn breakage or yarn breakage occurred at all in Class 30.

This pre-carbonized fiber was heated to 1500° C. in a nitrogen gas atmosphere to obtain carbon fiber. Carbon fiber thread diameter is 8.9μm
The tensile strength is 3.2GPa1 and the tensile modulus is 330
GPa, compressive strength is l.

It was 2GPa. Also, the degree of fusion and adhesion of this carbon fiber is 8%.
Met.

In addition, graphite carbon fiber obtained by heating carbon fiber to 2500°C in an argon gas atmosphere has a thread diameter of 8.8 μm, a tensile strength of 3.9 GPa, and a bowing modulus of 810 GPa.
, the compressive strength was 0.5 GPa. Further, the degree of fusion and adhesion of this graphite fiber was 12%.

In this specification, the degree of fusion adhesion (%) is determined by cutting a fiber bundle consisting of 3000 filaments to a width of 3 mm, immersing it in ethanol, blowing air for 30 seconds, and then melting it under a microscope at 20x magnification. It is determined by the following formula by counting the total number (N) of stuck filaments.

Fusion degree: (N/3000)X100 (%) Example 2 In Example 1, when pre-carbonizing the infusible fibers,
The process was carried out in the same manner as in Example 1, except that a tension of 0.04 g was applied per filament. The stretching ratio at this time was 39
%Met.

When this fiber was subjected to the next pre-carbonization treatment, there was no yarn breakage in the pre-carbonization furnace during 24 hours of continuous operation, and the obtained pre-carbonized fiber had almost no fuzz.

This pre-carbonized fiber was heated to 1500° C. in a nitrogen gas atmosphere to obtain carbon fiber. Carbon fiber thread diameter is 8.4μm
The tensile strength is 3.6 GPa and the tensile modulus is 340.
It was GPa. Further, the degree of fusion and adhesion of this carbon fiber was 9%.

Furthermore, graphite carbon fiber obtained by heating carbon fiber to 2500°C in an argon gas atmosphere has a thread diameter of 8.3 μm, a tensile strength of 4.0 GPa, and a bow tensile modulus of 850 GPa.
It was a. Further, the degree of fusion and adhesion of this graphite fiber was 15%.

As shown in Examples 1 and 2, the atmosphere during preliminary carbonization was an atmosphere containing low oxygen concentration within the range of 0.01 to 30% of the present invention, and the heat treatment time was within the range of 20 to 300 seconds of the present invention. Since the infusible fibers were pre-carbonized as described above, the infusible fibers could be pre-carbonized in the pre-carbonization furnace 30 without being cut or fluffed, and as a result, the graphite fibers obtained had no fiber fuzz. Of course, there were only a few cuts. Furthermore, since the infusible fibers were subjected to a stretching treatment of 5 to 100% within the scope of the present invention during preliminary carbonization, the resulting graphite fibers had improved tensile strength, compressive strength, and elastic modulus.

Comparative Example 1 The same process as in Example 1 was carried out, except that preliminary carbonization was performed in an inert gas (nitrogen gas) instead of creating an atmosphere containing an oxidizing gas with an oxygen concentration of 5%.

In this case, the infusible fiber bundle F was cut in the pre-carbonization furnace 30, and no pre-carbonized fibers could be obtained.

Comparative Example 2 The infusible fiber bundle F was continuously and linearly introduced directly into the preliminary carbonization furnace 30 for 250 seconds (2.5 times the time of Example 1).
The fiber bundle F has a tension of 1.
0.017 g was applied per filament. Other than that, the process was the same as in Example 1.

In this case, there was no yarn breakage in the pre-carbonization furnace (one hour of continuous operation was possible. However, the obtained pre-carbonized fibers had a lot of fuzz.

This pre-carbonized fiber was heated to 1500° C. in a nitrogen gas atmosphere to obtain carbon fiber. Carbon fiber thread diameter is 9.8μm
The tensile strength is 2.5 GPa and the tensile modulus is 270.
GPa, and the compressive strength was 1°0 GPa. Further, the degree of fusion and adhesion of this carbon fiber was 17%.

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, a tensile strength of 3.2 GPa, and a bowing modulus of 690 GPa.
a. The compressive strength was 0.4 GPa. Further, the degree of fusion and adhesion of this graphite fiber was 41%.

Comparative Example 3 The process was carried out in the same manner as in Example 1, except that during preliminary carbonization, a tension of 0.003 g per filament was applied to the infusible fiber bundle F. In this case, no yarn drawing occurred during precarbonization.

This pre-carbonized fiber was heated to 1500° C. in a nitrogen gas atmosphere to obtain carbon fiber. Carbon fiber thread diameter is 9.8μm
The tensile strength is 2.8 GPa and the tensile modulus is 275.
It was GPa. Further, the degree of fusion and adhesion of this carbon fiber was 5%.

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, a tensile strength of 3°3 GPa, and a bow tensile modulus of 700 GPa.
Met. Further, the degree of fusion and adhesion of this graphite fiber was 8%.

As described above, in Comparative Examples 1 to 3, in which preliminary carbonization was performed with the atmosphere, heating time, or amount of stretching at the time of preliminary carbonization being small (all of which were outside the scope of the present invention), the infusible fibers were The resulting carbon fibers and graphite fibers had many fiber breaks and had low tensile strength, compressive strength, and elastic modulus.

As explained above, in the production method of the present invention, the infusible pitch fiber bundle is pre-carbonized in an oxidizing gas-containing atmosphere with a maximum temperature of 500 to 700°C. ~1
This is done by heating for a short time while applying 00% stretching treatment, so it not only prevents the fibers of the infusible fiber bundle from being cut and fluffed in the pre-carbonization furnace, but also improves the yield during pre-carbonization. Carbon fibers with improved tensile strength, compressive strength, and elastic modulus can be obtained.

Furthermore, the preliminary carbonization time can be shortened to about 1/2 to 1/10 of the conventional time, and carbon fibers having high tensile strength, high tensile modulus, and high compressive strength can be efficiently produced.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of the manufacturing method of the present invention. 30: Pre-carbonization furnace 32: Tensioning means F: Fiber bundle

Claims (1)

[Claims] 1) Making the spun and bundled pitch fiber bundle infusible, 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, the infusible fiber bundle is pre-carbonized in an oxidizing gas-containing atmosphere with a maximum temperature of 500 to 700°C.
A method for producing pitch-based carbon fibers and graphite fibers, characterized in that the process is carried out by heat treatment for a short time while adding % stretching treatment. 2) The method according to claim 1, wherein the oxidizing gas in the atmosphere is oxygen, and the oxygen content in the atmosphere is 0.01 to 30%. 3) The method according to claim 1 or 2, wherein the heating time is 20 to 300 seconds.