JPH0718058B2 - Carbon fiber manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a new method for producing carbon fibers.

The terms used in this specification are defined as follows.

Heavy oil: A general term for petroleum-based and carbon-based heavy oils, and examples thereof include petroleum distillation residue, naphtha pyrolysis residue, ethylene bottom oil, coal liquefied oil, coal tar and the like.

Pitch: It refers to one obtained by removing low boiling point components having a boiling point of less than 200 ° C. by distilling the above heavy oil.

Isotropic: Means to exhibit optical isotropy in a polarizing microscope.

Anisotropy: It means that it exhibits optical anisotropy in a polarizing microscope.

Carbon fiber: Includes (a) carbonized, (b) activated, and (c) carbonized and activated fibers that have been infusibilized after spinning. this house,
(B) and (c) are made porous by activation treatment.

Conventional Technology and Its Problems Conventionally, isotropic pitch is understood to mean a pitch in which the quinoline insoluble matter (QI component) is substantially 0 (for example, Shiro Otani et al., “Carbon Fiber”). "Modern Hyoronsha (1983), page 151, lines 3-4, page 2.15, N.
o. 1 to 3 physical properties, see the description on page 150, lines 17 to 18). In the case of generating a QI component in an isotropic pitch, the spinnability of the pitch is impaired, and it has been considered necessary to control the generation thereof (Japanese Patent Laid-Open Publication No. Sho.
No. 57-159885, page 2, upper right column, lines 4 to 8).

Therefore, the optically isotropic pitch as the carbon fiber material does not contain an anisotropic QI component that inhibits the spinnability at the time of spinning because it is infusible and insoluble, and the infusibilizing treatment after spinning is performed. It was common sense among those skilled in the art that it is necessary to have a high softening point in order to smoothly carry out the above.

Therefore, it has been practiced to remove the QI component from the heavy oil or pitch as a raw material by means such as filtration and then subject it to the following treatment.

1) In the method disclosed in JP-A-55-5954, a petroleum pitch is brought into contact with an inert gas under reduced pressure to remove low boiling point components and obtain a pitch having a high softening point. However, there is a problem that the softening point of the heat-treated pitch obtained by this method cannot be improved to such an extent as to completely prevent fusion of spun fibers in the infusibilizing treatment at a high temperature.

2) A method for obtaining a pitch with a high softening point by subjecting heavy oil or pitch to a heat treatment under conditions in which an anisotropic QI component and an anisotropic component are not formed has been proposed (Journal of the Japan Society for Composite Materials) Vol.8, No.3 (1982) However, even in this method, the softening point of the generated heat treatment pitch is usually about 175 ° C as long as the condition of controlling the generation of the anisotropic QI component and the anisotropic component is strictly observed. Therefore, a pitch having a high softening point of about 250 ° C. necessary for preventing fusion of spun fibers cannot be obtained.

3) There is a method of adding a softening point raising agent such as a nitro compound, quinone and polycarboxylic acid anhydride to heavy oil or pitch (JP-A-55-98914). However, the softening point of the produced pitch obtained by this method is about 165 ° C, and a pitch having a high softening point of about 250 ° C cannot be obtained.

Further, as shown below, a technique of using a raw material containing no QI component or filtering the QI component after heat treatment of the raw material has been proposed.

4) JP-B-53-12607 discloses that a hydrocarbon distillate distilled at 200 to 600 ° C. is blown with a gas containing elemental oxygen and heat-treated at 250 to 420 ° C. to obtain a softening point of 200 ° C. or less. A method of obtaining an anisotropic pitch is disclosed. However, in this document, when the polymerization reaction is carried out using oxygen, the reaction is very fast, so if the oxygen is excessive, carbon tends to precipitate, whereas if the oxygen is insufficient, Anisotropic QI
It is revealed that the component is produced. Therefore, as a raw material, a light fraction in which a QI component is hard to be produced is used, and the amount of oxygen is limited in order to reduce the production of carbon. As a result, although the QI component in the heat-treated pitch that is generated is suppressed, the softening point of the heat-treated pitch is still 200 ° C. or lower.

5) Japanese Patent Laid-Open No. 56-26009 discloses a method for producing an isotropic pitch having a high softening point.
The QI component in the pitch is adjusted to almost 0,
Its softening point is also about 200 to 250 ° C.

As described above, the conventional isotropic pitch manufacturing technique suppresses the generation of the QI component as a component that impairs the spinnability of the pitch, so that a pitch with a high softening point exceeding 250 ° C. is obtained. I couldn't.

Therefore, the present invention is to provide a new method of producing an isotropic pitch having a high softening point, which is excellent in spinnability, infusiblity, etc. and can reduce the production cost of carbon fibers. The main purpose is.

Means for Solving the Problems The present invention is, in view of the current state of the art as described above, as a result of various studies to further increase the softening point of the isotropic pitch, a heavy oil from which the primary QI component has been removed or While blowing a gas containing oxygen or ozone into the pitch, when heat-treating it at a specific temperature, a heat-treated pitch with a softening point of 200 ° C. or higher can be obtained, and this pitch is excellent in spinnability and was obtained. It was found that the spun fiber can be infusibilized at high temperature within a short time.

That is, the present invention provides the following method for producing carbon fiber: "(1) Heavy oil or pitch obtained by removing a gas containing oxygen or ozone from the heavy oil or pitch from which the primary QI is removed is used as oxygen or ozone. Softening point 20 by heat treatment at 300-400 ℃ while blowing at a rate of 0.2-51 / min per kg.
A step of obtaining a pitch having an isotropic QI component content of 5 to 60% at 0 ° C. or higher, (2) a step of spinning the obtained heat-treated pitch, (3) a step of infusibilizing the obtained spun pitch fiber, and (4) The obtained infusible pitch fiber is (a) carbonized, (6)
A method for producing a carbon fiber, comprising a step of activating or (c) carbonizing and activating. The QI component in the heat-treated pitch obtained by the present invention is isotropic (conventionally, all QI components of isotropic pitch were considered anisotropic). The softening point of the pitch containing ~ 60% is 200 ° C or higher, such a pitch contains substantially no infusible / insoluble components, has excellent spinnability, and the obtained spun fiber is short. The fact that the infusibilizing treatment could be completed in a time was totally unexpected from the above-mentioned conventional common sense of those skilled in the art.

That is, as described above, with respect to an isotropic pitch for which the concept of “isotropic QI component” did not originally exist, the QI component is infusible and insoluble, and spinnability is impaired. For example, it is predicted that the QI component in the heat treatment pitch generated as described above will naturally be a similar impeding factor. However, according to the research by the present inventors, the isotropic QI component produced by the heat treatment performed in the presence of oxygen or ozone is a polymer having a three-dimensional structure crosslinked by oxygen molecules, and is fusible and It turned out to be melted. That is, even though these isotropic QIs are macromolecules, they have a property (compatibility) of dissolving with a component other than QI (QS component), so that they do not separate and are homogeneous. It behaves as if it were a fluid. Therefore, when heat-spinning the heat-treated pitch of the present invention, isotropic
The QI component does not hinder spinning. Moreover, since the softening point of the heat treatment pitch is high, the infusibilization of the spun fiber is easily performed.

In the present invention, from the starting heavy oil or pitch, after removing solids such as primary QI components by means such as filtration, the heavy oil or pitch is blown with a gas containing oxygen or ozone. Heat treatment at 300-400 ℃. Examples of the oxygen- or ozone-containing gas include air, oxygen-enriched air, oxygen and the like. The amount of oxygen used is
Depending on the heat treatment temperature and time, it is usually 0.2 to 51 as oxygen or ozone per kg of heavy oil or pitch.
/ Min, more preferably about 0.5 to 31 / min, and when air is used, the amount is about 4 times these values.

If the heat treatment temperature is lower than 300 ° C, the polymerization reaction rate will decrease, which is not preferable, whereas if it exceeds 400 ° C, there is a risk of ignition, explosion, etc., and excessive polymerization may occur. , Produces infusible or insoluble components.

The isotropic QI component content of the heat-treated pitch used for spinning is 5
-60% and the softening point is 200 ° C or higher. If the content of the QI component is less than 5%, the softening point of the pitch will be low, so it is necessary to lower the spinning temperature, and the time required for the infusibilizing treatment of the spun fiber will be increased, which is not preferable. . On the other hand, when the QI component exceeds 60%, a part of the pitch component is excessively polymerized and a solid content insoluble to heat is formed, which easily causes clogging of the spinning nozzle and yarn breakage. Make the spinning operation unstable. The spinning operation of the heat-treated pitch may be carried out in the same manner as in the known spinning method in which melt extrusion is carried out, and then winding on a drum, melt blown spinning method, spunbond spinning method, centrifugal spinning method and the like. For example, in the case of performing the melt extrusion spinning method, the above heat-treated pitch may be supplied to a spinning machine and extruded from a nozzle under pressure with an inert gas in a state of being heated to 300 to 400 ° C. to obtain a spinning pitch fiber. .

The infusibilizing treatment of the spun pitch fiber can be performed according to a conventional method. That is, for example, at a temperature of 20 in an oxidizing atmosphere.
The conditions of about 0 to 400 ° C. and the holding time of about 1 to 3 hours are generally used, but other conditions can also be adopted. Examples of the oxidizing atmosphere include oxygen, oxygen-enriched air, air, etc., and when measures are taken to prevent deterioration of the work environment and corrosion of equipment, chlorine gas, NO gas, NO ₂ You may add gas etc. The pressure of the oxidizing atmosphere 0.2kg / cm ² · G or more, more preferably by a more pressurized 1.0kg / cm ² · G, it is possible to greatly shorten the infusibilized time. In this case, although it depends on the properties of the heat treated pitch, the thickness of the spun pitch fiber, etc., under the optimum conditions, for example, 1
It is also possible to complete the infusibilizing treatment within an extremely short time such as about a minute.

The infusibilized pitch fiber obtained is (a) carbonized, (b)
It is subjected to activation treatment or (c) carbonization treatment and activation treatment.

When carrying out the carbonization treatment, in accordance with a conventional method, the infusible pitch fiber in the presence of an inert gas such as nitrogen gas 20 ~
The temperature may be raised to about 900 to 1200 ° C. at a rate of about 50 ° C./minute and kept at the same temperature for about 10 to 30 minutes. In this case,
Carbon fiber in a narrow sense can be obtained.

When carrying out the activation treatment, according to a conventional method, the infusible pitch fiber is, for example, in the air at 400 to 700 ° C., preferably 50.
Hold at 0-600 ℃ for 3-10 minutes, or steam at 600-1000 ℃, preferably 700-900 ℃.
Hold it for ~ 120 minutes. In this case, 500-20
A porous pitch fiber having a specific surface area of about 00 m ² / g is obtained.

When carbonizing and activating, the infusible pitch fiber may be carbonized according to a conventional method under the same conditions as above, and then activated. In this case, a porous carbon fiber having a specific surface area of about 500 to 2000 m ² / g can be obtained.

EFFECTS OF THE INVENTION According to the present invention, by carrying out heat treatment while blowing a gas containing oxygen or ozone into an optically isotropic heavy oil or pitch, a peculiarity of containing a fusible QI component After obtaining the isotropic pitch, it is spun and infusibilized. Therefore, nozzle clogging and yarn breakage during spinning can be prevented, and the infusibilizing treatment of the spun pitch fiber can be performed at a high temperature in a short time without causing fusion, which is extremely economical. Is.

Examples Examples will be shown below to further clarify the characteristics of the present invention. In the following, "%" means "% by weight".

Example 1 (1) Coal tar was heated to 150 ° C., pressure filtration was performed using filter paper to remove the primary QI component in the coal tar, and then the purified tar was distilled under reduced pressure (normal pressure conversion: 500). C.) to remove low boiling components. The properties of the obtained pitch are
Softening point (Mettler method) = 125 ° C., QI component = 0%, BI component = 27.5%, fixed carbon = 51.3%.

Then, 500 g of the pitch obtained above was charged into an 11 autoclave, and heat-treated for 2 hours at 350 ° C. with stirring while blowing air at 51 / min. The properties of the heat-treated pitch obtained are as follows: softening point (Mettler method) = 296.3 ° C, QI component = 38.4%, BI component = 7
It was 9.6%. Moreover, the QI component was confirmed to be isotropic by observation with a polarization microscope at room temperature.

(2) 150 g of the heat-treated pitch obtained above and 350 g of tetrahydroquinoline were charged into an 11 autoclave, and 20 kg / cm ² · G
After heating for 10 minutes at 450 ℃ in a nitrogen atmosphere, the pitch is hydrotreated, the treated product is transferred to a distillation flask, the liquid temperature in the flask 205 ℃, to remove the terahydroquinoline at a reduced pressure of 10 mmHg, A hydrogenated pitch having a softening point (Mettler method) = 131.0 ° C., a QI component = 0.2%, and a BI component = 30.8% was obtained.

From this result, in the heat treatment pitch obtained in the above (1),
It was confirmed that the QI component is not a solid content such as free carbon but a polymer substance having a three-dimensional structure due to cross-linking and easily hydrogenated.

(3) Also, using a 5-layer metal filter having a mesh of 2 μm, 5 g of the heat-treated pitch obtained in (1) above was subjected to pressure filtration at 370 ° C. in a nitrogen atmosphere, and then 500 ml of quinoline was added. The quinoline-soluble matter adhering to the filter was dissolved and removed by pouring onto a metal filter. Then, the quinoline adhering to the metal filter was washed away with acetone, the filter was dried and then weighed, and the residue on the filter was only 0.6% of the initially heat-treated pitch weight (5 g).

From the results shown in (1), (2) and (3) above, the QI component in the obtained heat-treated pitch is an isotropic and fusible polymer substance, which is infusible. It was confirmed that it was not a solid content.

Example 2 The heat treatment pitch obtained in the same manner as in (1) of Example 1 above was wound up at a melting temperature of 360 ° C. from a nozzle having a diameter of 0.3 mm.
Continuous spinning was performed at 600 m / min to obtain pitch fibers.

The pitch fiber was heated in air at a rate of 3 ° C./minute to 300 ° C., and then held at the same temperature for 2 hours for infusibilization treatment. The oxygen content of the obtained infusible pitch fiber was 8.2%.

The infusible pitch fiber obtained above was heated in a nitrogen atmosphere at 50 ° C /
The temperature was raised at a minute rate, and the temperature was maintained at 1200 ° C. for 3 minutes to obtain carbon fibers.

The time required for the infusibilizing treatment in this example was 212 minutes, the time required for the carbonization treatment was 21 minutes, and the total was 23 minutes.
It was 3 minutes.

The average values of various properties measured for the 15 obtained carbon fibers were as follows.

Diameter: 10 μm, tensile strength: 134 kg / mm ² , elastic modulus: 5.2 ton / mm ² ,
Elongation: 2.6%.

Example 3 Coal tar was heated to 300 ° C. and pressure-filtered using a filter paper to remove the primary QI component in the coal tar.
500 g of the mixture was charged into an 11 autoclave, and heat-treated for 1 hour and 30 minutes at 300 ° C. with stirring while blowing 51 / min of air.
The properties of the obtained heat-treated pitch have a softening point (Mettler method)
= 273.2 ° C, QI component = 28.6%, BI component = 66.8%.

The heat-treated pitch thus obtained was subjected to the spinning, infusibilization and carbonization steps in the same manner as in Example 2 to obtain carbon fibers.

In the present example, the time required for the infusibilization treatment was 212 minutes, the time required for the carbonization treatment was 21 minutes, and the total thereof was 233 minutes.

The average values of various properties measured for the 15 obtained carbon fibers were as follows.

Diameter: 11 μm, tensile strength: 127 kg / mm ² , elastic modulus: 5.3 ton / mm ² ,
Elongation: 2.4%.

Example 4 The pitch fiber obtained in the same manner as in Example 2 was heated to 300 ° C. at a rate of 3 ° C./min in air, and then held at the same temperature for 4 hours to be infusibilized. The oxygen content of the obtained infusible pitch fiber was 12.3%.

Then, the obtained infusible pitch fiber was carbonized in the same manner as in Example 2 to form carbon fiber, which was then heated to 800 with steam.
Activation treatment was performed at 0 ° C. for 1 hour to obtain a porous carbon fiber. At this time, the time required for carbon treatment was 21 minutes, the time required for activation treatment was 60 minutes, and the total thereof was 81 minutes.

The specific surface area of the obtained porous carbon fiber is 1230 m ² / g,
The tensile strength was 52 kg / mm ² .

Example 5 The infusible pitch fiber obtained in the same manner as in Example 4 was activated with steam at 800 ° C. for 1 hour to obtain a porous pitch fiber.

The specific surface area of the obtained porous pitch fiber was 1480 m ² / g, and the tensile strength was 28 kg / mm ² .

Example 6 Ethylene bottom oil having the properties shown in Table 1 was heat-treated at 410 ° C. for 6 hours in a nitrogen atmosphere of 20 kg / cm ² , and then filtered using filter paper to obtain a solid content mainly containing a secondary QI component. 0.9% was removed. Then, the heat-treated product after filtration is distilled to 350 ° C.
The following low boiling point components were removed to obtain a heat-treated pitch having the properties shown in Table 2.

Table 1 QI (%) Trace BI (%) Trace Fixed carbon (%) 12.1 Specific gravity (15 ℃ / 4 ℃) 1.070 Table 2 Softening point (℃ / Mettler method) 129.2 QI (%) 0.0 BI (%) 18.1 Fixed carbon (%) 53.0 Next, heat-treated pitch 500g having the properties shown in Table 2 was charged into an 11 autoclave and heat-treated for 2 hours at 350 ° C under stirring while blowing air at 51 / min, and the properties shown in Table 3 were obtained. The heat treatment pitch of was obtained.

Table 3 Softening point (℃ / Mettler method) 283.1 QI (%) 24.6 BI (%) 63.4 The obtained heat-treated pitch was continuously spun at a melting temperature of 350 ° C. from a nozzle having a diameter of 0.3 mm at a winding speed of 500 m / min. , Pitch fibers were obtained.

The pitch fiber was heated in air at a rate of 3 ° C./min to 300 ° C., and then held at the same temperature for 3 hours to obtain an infusible pitch fiber. The oxygen content of the obtained infusible pitch fiber is 9.4.
%Met.

The infusible pitch fiber obtained above was heated in a nitrogen atmosphere at 50 ° C /
The temperature was raised at a minute rate, and the temperature was maintained at 1200 ° C. for 3 minutes to obtain carbon fibers.

The average values of various properties measured for the 15 obtained carbon fibers were as follows.

Diameter: 13 μm, tensile strength: 116 kg / mm ² , elastic modulus 5.0 ton / mm ² ,
Elongation: 2.3%.

Comparative Example 1 Coal tar from which the primary QI component was removed was distilled in the same manner as in (1) of Example 1 to remove low-boiling components having a boiling point of 550 ° C. or lower, and pitches having the properties shown in Table 4 were obtained.

Table 4 Softening point (℃ / Mettler method) 198.2 QI (%) 3.3 BI (%) 54.1 The pitch fiber was continuously spun at a melting temperature of 240 ° C. from a nozzle having a diameter of 0.3 mm at a winding speed of 300 m / min to obtain pitch fiber. Got However, since the nozzle is heavily clogged with infusible solids,
Spinning was performed by installing a metal filter in front of the nozzle.

The pitch fiber thus obtained was heated to 300 ° C. in the air under the same conditions as in Example 2, that is, at a rate of 3 ° C./minute, and then held at the same temperature for 2 hours for infusibilization treatment. And it became a lump.

Therefore, the above-mentioned pitch fiber is used in air at a rate of 3 ° C / min for 20
After the temperature was raised to 0 ° C, the temperature was kept at the same temperature for 3 hours, further raised to 300 ° C at a rate of 3 ° C / min, and then the temperature was raised to 4 ° C.
After holding the time, the infusibilization process was finally completed.

Next, the obtained infusible pitch fiber is heated to 50 ° C. in a nitrogen atmosphere.
The temperature was raised at a rate of / min and the temperature was held at 1200 ° C. for 3 minutes to obtain carbon fibers, but partial fusion occurred, and measurement of tensile strength and the like was impossible.

Comparative Example 2 The pitch fiber obtained in the same manner as in Comparative Example 1 was heated to 200 ° C. in air at a rate of 3 ° C./minute, then kept at the same temperature for 3 hours, and further heated to 300 ° C. at a rate of 3 ° C./minute. After raising the temperature to ℃,
The temperature was maintained for 6 hours to obtain infusible pitch fibers.

Next, the obtained infusible pitch fiber is heated to 50 ° C. in a nitrogen atmosphere.
The temperature was raised at a rate of / minute and the temperature was maintained at 1200 ° C for 3 minutes to obtain carbon fibers.

The average values of various properties measured for the 15 obtained carbon fibers were as follows.

Diameter: 11 μm, tensile strength: 73 kg / mm ² , elastic modulus: 3.8 ton / mm ² ,
Elongation: 1.9%.

In this comparative example, the time required for the infusibilizing treatment of the pitch fiber was 632 minutes, and the total time until the carbon fiber was obtained from the pitch fiber reached 655 minutes. On the contrary,
In Examples 2 and 3, a similar total time is about 1 /
It was only 3.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Keiji Sakai 5-1-1, Hirano-cho, Higashi-ku, Osaka-shi, Osaka (56) References JP-A-58-142975 (JP, A) JP-A-SHO 59-26525 (JP, A) JP-B-53-12607 (JP, B2)

Claims (1)

[Claims] (1) While blowing a gas containing oxygen or ozone into heavy oil or pitch from which primary QI has been removed as oxygen or ozone at a rate of 0.2 to 51 / min per kg of heavy oil or pitch, A step of obtaining a pitch having a softening point of 200 ° C. or more and an isotropic QI component content of 5 to 60% by heat treatment at 300 to 400 ° C., (2) a step of spinning the obtained heat treated pitch, (3) obtained Infusible spun pitch fiber, and (4) carbonizing the infusibilized pitch fiber obtained, (b)
A method for producing a carbon fiber, comprising a step of activating or (c) carbonizing and activating.