JPH04245923A - Production of pitch-based carbon fiber and graphite fiber - Google Patents

Abstract

PURPOSE:To suppress yarn breakage and fuzzing of a pitch fiber bundle in an infusibilization furnace and obtain carbon fiber improved in tensile strength, tensile elastic modulus and compressive strength. CONSTITUTION:Infusibilizing treatment of a pitch fiber bundle in an oxidizing gas atmosphere is carried out as follows. Temperature is increased at 100-5000 deg.C/min rate up to a lower temperature than the melt breaking temperature of the fiber bundle by 30-100 deg.C and drawing treatment is simultaneously performed at 5-100% draw ratio while heat-treating the fiber bundle in an ultrashort time of 1-200sec. Yarn breakage and fuzzing of the fiber bundle in the infusibilizing furnace are suppressed by the heat treatment in the short time and simultaneous drawing treatment to improve the yield in the infusibilization. Furthermore, the tensile strength, tensile elastic modulus and compressive strength of the finally obtained carbon fiber are improved.

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 pitch fiber bundles can be drawn in the process of making them infusible, it is possible to improve the tensile strength, tensile modulus, and compressive strength when they are made into carbon fibers. However, since the pitch fiber bundle to be threaded is weak at about 0.01 GPa, it has been difficult to draw the pitch fiber bundle in the past.

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

Furthermore, one pitch fiber bundle has 100 to 1
It is in the form of a fiber bundle made up of 00,000 filaments, and therefore, during infusibility, each filament tends to fuse or stick to a large extent, resulting in a loss of quality after firing as a product. A major drawback occurred in that the quality of the carbon fiber was compromised.

[0009] In the process of researching a method for manufacturing carbon fibers using a continuous firing process, the present inventors determined that infusibility in an oxidizing gas atmosphere was achieved at a temperature 30 to 100°C lower than the melting and breaking temperature of pitch fiber bundles. By heating the fiber bundle rapidly to a temperature of It was also found that the

[0010] Furthermore, it is surprising that when heat treatment under the above conditions and simultaneous stretching treatment (hereinafter referred to as stretching heat treatment as necessary) are carried out, there is also an increase in fusion and agglomeration of the fiber bundle. It was found that it was possible to suppress the breakage of fiber bundles in the furnace during processing, and to improve the yield during infusibility.

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

Therefore, an object of the present invention is to prevent yarn breakage of pitch fiber bundles in an infusibility furnace, and to effectively infusify the fiber bundles by adding stretching treatment, thereby achieving high tensile strength and high strength. 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.

[0013]

[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 includes infusible spinning and bundled pitch fiber bundles, pre-carbonizing the infusible infusible fiber bundles, then carbonizing them, and further graphitizing them as necessary. In the method for producing pitch-based carbon fibers and graphite fibers, the pitch fiber bundle is raised in an oxidizing gas atmosphere 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. Warm it up and cut the fiber bundle into 1
This method for producing pitch-based carbon fibers and graphite fibers is characterized in that fiber bundles are made infusible by heat treatment for a very short time of ~200 seconds and simultaneous stretching treatment at a stretching rate of 5 to 100%.

[0014] 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.

[0015] The temperature increase rate is a value determined from the time it takes for the pitch fiber bundle to reach the temperature of the soaking section of the furnace from the outside temperature of the furnace (usually room temperature).

In the present invention, the temperature is rapidly raised to a temperature 30 to 100° C. lower than the melt breakage temperature of the pitch fiber bundle, and a short-time stretching heat treatment is performed, which consists of heat treatment and simultaneous stretching treatment. Preferably 4
It is preferable to raise the temperature to a temperature lower than 0 to 80°C. 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, the temperature is 30 to
Since the temperature is rapidly raised to a temperature 100 degrees Celsius lower, and the infusibility treatment is performed by short-term heat treatment and stretching treatment, the physical properties of the resulting carbon fiber are dramatically improved in tensile strength and tensile modulus, Moreover, the compressive strength is also increased.

[0018]

[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.

[0021] 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.

[0022] The yarn 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.

[0023] At the time of such yarn 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.

[0025] Further, as a preferred oil agent, it is also possible to use one obtained by emulsifying 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 oils 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 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.

The interior of the infusibility furnace is an oxidizing gas atmosphere, and an oxidizing gas such as air, oxygen, a mixed gas of air and oxygen, or air and nitrogen is supplied into the infusibility furnace. Oxygen-rich gas with an oxygen concentration of 30-90% is used. In some cases, the above gases include NOx, SOx, C
A mixed gas containing l2 or the like may also be used.

[0030] Infusibility is carried out at a temperature of 150 to 350°C, but in the present invention, the infusibility is carried out at a temperature of 100 to 50°C to a temperature 30 to 100°C lower than the melt breakage temperature of the pitch fiber bundle.
This is carried out by heating the fiber bundle at a rate of 1,000° C./min and subjecting the fiber bundle to a very short stretching heat treatment of 1 to 200 seconds.

[0031] The above-mentioned stretching heat treatment may be carried out in a constant temperature furnace, for example, at 250°C, and the temperatures from the furnace entrance to the exit are 180°C, 220°C, 250°C, 280°C,
It may be carried out in a temperature gradient furnace in which the temperature is maintained at a stepwise increase, such as 310°C.

In the present invention, the drawing heat treatment is carried out by rapidly raising the temperature to a temperature 30 to 100° C. lower than the melt breaking temperature of the fiber bundle, preferably 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.

[0033] 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 temperature increase rate is less than 100°C/min, infusibility progresses and sufficient stretching becomes difficult;
If it exceeds 00° C./min, the temperature rises too quickly and the threading speed of the fiber bundle must be increased, resulting in operational problems, which is also undesirable.

[0034] The time for the stretching heat treatment is 1 to 200 seconds, preferably a very short time of 5 to 100 seconds.

[0035] The stretching process in the stretching 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.

[0037] The heat-stretching treatment may be carried out once, but it can also be carried out in multiple steps, for example, stretching once at 250°C and then stretching at 300°C. It is preferable to divide the process into multiple times because the fibers are less damaged and can be drawn easily.

[0038] In this way, the infusible fiber bundle is infusible so that the oxygen concentration becomes 7 to 12% by weight.

As a result of the infusibility caused by such drawing heat treatment, the orientation of the fiber bundles is improved, and the physical properties of the resulting carbon fibers are improved. The infusibility by stretching heat treatment may be repeated once or multiple times to complete the infusibility, but after that, normal infusibility without stretching treatment may be performed.

The infusible fiber bundle made infusible in the infusible furnace is
It is continuously introduced into a pre-carbonization furnace and pre-carbonized.

[0041] The maximum temperature inside the preliminary carbonization furnace is 500 to 110
The furnace is heated to 0° C., and chemically inert nitrogen gas or argon gas is supplied to create an inert atmosphere inside the furnace.

The infusible fiber bundle threaded through the pre-carbonization furnace is pre-carbonized to obtain a pre-carbonized fiber bundle having a strength of about 0.2 GPa or more and an elastic modulus of about 4 GPa or more.

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 an inert gas atmosphere in a carbonization furnace 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.

Next, the method for producing carbon fiber according to the present invention will be further explained with reference to 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 convergence 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 fibers were wound up on a stainless steel bobbin with a diameter of 210 mm and a width of 200 mm that was installed 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.

[0050] As an oil agent at the time of 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 220°C is prepared. It was introduced continuously in a linear manner into a continuous infusibility furnace. The temperature increase rate from 180 to 220°C was 6°C/min.

[0052] The melt-rupture temperature of the fiber bundle infusible to 220°C was 300°C. This infusible fiber bundle
The fibers were threaded through an infusible furnace in an oxygen-rich atmosphere (oxygen/nitrogen = 60/40) at 250°C (a temperature 50°C lower than the melting failure temperature of the infusible fiber bundle) at a heating rate of 3000°C/min. Infusible treatment was performed by stretching heat treatment.

[0053] The time for this infusibility treatment was 25 seconds. A tension of 0.007 g per filament was applied to the fiber bundle. The stretching ratio was 17%.

[0054] Thereafter, the temperature was raised at a rate of 6°C/min to 29°C.
Conventional infusibility without stretching was performed in a furnace in an oxygen-rich atmosphere (oxygen/nitrogen = 60/40) up to 5°C. 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 above-mentioned infusible fiber bundle was introduced into a pre-carbonization furnace, and the temperature was raised to 1000° C. for pre-carbonization.

The pre-carbonized fiber bundle thus obtained was heated to 1500° C. in a nitrogen gas atmosphere to obtain carbon fibers. The carbon fiber yarn diameter was 9.0 μm, the tensile strength was 3.2 GPa, the tensile modulus was 320 GPa, and the compressive strength was 1.2 GPa.

[0057] Also, the carbon fibers were heated in an argon gas atmosphere for 2
The graphite carbon fiber obtained by raising the temperature to 500°C has a thread diameter of 8.
The tensile strength was 3.9 GPa, the tensile modulus was 800 GPa, and the compressive strength was 0.5 GPa.

Example 2 In Example 1, the melt-rupture temperature of the infusible fiber bundle that had been subjected to the drawing heat treatment once at 250°C was 310°C. Using this fiber bundle, it was placed in an infusible furnace in an oxygen-rich atmosphere at 260°C (a temperature 50°C lower than the melting and breaking temperature of the fiber bundle) for 30 minutes.
Threading was carried out at a temperature increase rate of 00° C./min, and the infusibility treatment by drawing heat treatment was performed 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 21%. The total stretching ratio of stretching at 250°C and stretching at 260°C was 38%.

[0060] 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.

[0061] The pre-carbonized fiber bundle obtained after pre-carbonization was heated to 1500°C in a nitrogen gas atmosphere to obtain carbon fibers. The carbon fiber thread diameter is 8.5 μm, and the tensile strength is 3.
6 GPa, and the tensile modulus was 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.
．． 4 μm, tensile strength was 4.0 GPa, and tensile modulus was 840 GPa.

As shown in Examples 1 and 2, the pitch fiber bundle was made infusible by rapidly increasing the temperature to a temperature 30 to 100° C. lower than the melting failure temperature of the fiber bundle within the range of the present invention. Since this was carried out by drawing heat treatment for several hours, the pitch fiber bundles could be infusible without breaking in the infusibility furnace, and as a result, the obtained carbon fibers and graphite fibers had little fiber fluff. Of course, there were only a few thread breaks. In addition, the above-mentioned drawing heat treatment gives an infusible fiber bundle of 5 to 100%
% of the stretching treatment, the resulting carbon fibers and graphite fibers had improved tensile strength, tensile modulus, and compressive strength.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the temperature of the infusibility furnace was 280° C. (20° C. lower than the melting and breaking temperature of the fiber bundle).

As a result, the fiber bundles were broken in the furnace, making it impossible to operate continuously.

Comparative Example 2 The same process as in Example 1 was carried out except that the temperature of the infusibility furnace was 180° C. (120° C. lower than the melting and breaking temperature of the fiber bundle). In this case, no drawing of the fiber bundle occurred.

[0067] The pre-carbonized fiber bundle obtained after pre-carbonization was heated to 15,000°C in a nitrogen gas atmosphere, and the yarn diameter of the carbon fiber obtained was 9.8 μm, and the tensile strength was 2.5 GPa.
The tensile modulus was 270 GPa, and the compressive strength was 1.0 GPa.

Furthermore, graphite carbon fiber obtained by heating carbon fiber to 2500°C in an argon gas atmosphere has a thread diameter of 9.
．． 8 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.

As in Comparative Example 2, the physical properties of the carbon fiber obtained in this case were lower than those of the stretched carbon fiber.

[0071]

As explained above, in the manufacturing method of the present invention, the pitch fiber bundle is infusible at a temperature of 100 to 100°C lower than the melting and breaking temperature of the fiber bundle in an oxidizing gas atmosphere. This is done by heating the fiber bundle at a rate of 5,000°C/min, heat-treating the fiber bundle for a very short time of 1-200 seconds, and simultaneously stretching it at a stretching rate of 5-100%. Not only can the yield during infusibility be improved by suppressing breakage and fluffing of the pitch fiber bundle, but also carbon fibers with improved tensile strength, tensile modulus, and compressive strength can 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,
The pitch fiber bundle is heated in an oxidizing gas atmosphere to a temperature 30 to 100°C lower than the melting and breaking temperature of the fiber bundle.
The fiber bundle is heated at a rate of 5000℃/min to
Stretching rate 5-10 at the same time while heat treating in a very short time of seconds
A method for producing pitch-based carbon fibers and graphite fibers, characterized in that a fiber bundle is rendered infusible by 0% stretching treatment. 2. The manufacturing method according to claim 1, wherein the heat treatment and stretching treatment to infusible the pitch fiber bundle are performed in multiple steps.