JPS5818421A - Preparation of carbon fiber - Google Patents

Abstract

PURPOSE:To obtain carbon fibers having improved mechanical strength, by spinning an optically isotropic carbonaceous material, etc., making the resultant fibers infusible, and carbonizing the infusible fibers to convert the optically isotropic mesophase carbonaceous material into an optically anisotropic mesophase carbonaceous material. CONSTITUTION:An optically isotropic mesophase carbonaceous material, e.g. formed by keeping coal tar pitch treated with tetrahydroquinoline at a pressure <=50mm.Hg and a temperature >=450 deg.C within 15min, is spun under such conditions as not to increase the amount of the mesophase carbonaceous material, and the resultant fibers are made infusible, e.g. by heating the fibers in an air flow at a heating rate 0.5-3 deg.C/min to 250-350 deg.C in an electric furnace, and keeping the fibers at the temperature for 5-30min, carbonized, e.g. by heating the infusible fibers in a nitrogen gas flow at a heating rate of 2-5 deg.C/min to 900-1,200 deg.C, and keeping the fibers at the temperature for 10-30min, and converted into an optically anisotropic mesophase carbonaceous material and give the aimed carbon fibers.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new method for producing carbon fibers from pitch-like materials.

More specifically, the present invention uses optically isotropic pre-mesophase carbonaceous material as a raw material, spins it, makes it infusible,
The present invention relates to a method for producing high-strength carbon fibers in high yield through carbonization treatment.

Carbon fiber is used as heat insulating materials, sealing materials, and
Widely used in electromechanical parts, structural members, friction materials, carbon electrodes, etc.

Conventionally, carbon fibers have been produced by firing fibers such as acrylonitrile or cellulose, but these raw materials are expensive and have low carbonization yields, making them less suitable for industrial mass production. It is not a good method.

On the other hand, methods have been proposed for producing carbon fibers using various pitches that can be obtained in large quantities as raw materials, but these have drawbacks such as difficulty in spinning due to softening point, viscosity, etc., and low quality of the resulting carbon fibers. There is. In order to improve these drawbacks, a method has been developed that uses a pitch-like material obtained by hydrogenating or heat treating specific condensed polycyclic aromatic compounds (Special Publications Publication No. 4).
Publication No. 5-28013, Japanese Patent Publication No. 49-8634)
, a method in which petroleum tar or pitch is subjected to a first heat treatment in the presence of a Lewis acid catalyst, and then the catalyst is removed and a second heat treatment is performed (Japanese Patent Publication No. 53-75
33 Publication), a method of forming mesoface pitch with a predetermined mesophase content under reduced pressure and producing carbon fiber using this as a raw material (Japanese Patent Application Laid-open No. 11330/1983),
Japanese Patent Publication No. 54-1810), a method using mesoface pitch having a specific composition and specific properties (Japanese Patent Publication No. 54-54)
No. 5625, U.S. Pat. No. 3,787,541), etc., but these methods are unable to obtain charcoal fibers with properties comparable to those made from acrylonitrile as a raw material. Until now, there has been no known practical method for producing high-performance grade carbon fibers from pitch-like materials.

The present inventors have conducted intensive research to develop a method for easily manufacturing carbon fibers that exhibit properties, especially mechanical strength, comparable to carbon fibers obtained from acrylonitrile using pitch-like materials as raw materials. The present inventors have discovered that the object can be achieved by using as a raw material a completely new pitch-like substance, primesophase carbonaceous material, obtained by the method described above, and have thus come to form the present invention.

According to the present invention, an optically isotropic pre-methophase carbonaceous material or a pitch-like material mainly composed of an optically isotropic pre-methophase carbonaceous material is prepared under conditions where the mesophase carbon mass does not substantially increase. Excellent quality carbon is produced by spinning the fibers, followed by infusibility treatment, and then carbonization treatment to convert substantially all of the pre-mesophase carbonaceous material into optically anisotropic memphasic carbonaceous material. Fibers can be produced.

The pre-mesophase carbonaceous material used as a raw material in the present invention is optically isotropic, and has the characteristic that when heated to 600° C. or higher, it changes to an optically anisotropic memphithic carbonaceous material.

Until now, isotropic pitches that change to optical anisotropy when an external force is applied, so-called dormant face pitches, have been known. However, the prime and face carbonaceous material used in the present invention is clearly different from this dormant mesoface pitch in that it does not change merely by applying an external force, but changes to isotropy only by heating.

Primesophase used as a raw material in the method of the present invention is produced in the first stage, which consists of treating the raw material pitch with tetrahydroquinoline alone, with quinoline and hydrogen in the presence of a catalyst, or with an aromatic hydrocarbon such as naphthalene and hydrogen. After the treatment, it is manufactured by performing a second stage treatment consisting of a reduced pressure heat treatment.

In this case, the raw material pitches include coal tar, coal tar pitch, coal-based heavy oils such as coal liquefied products, residual oils from atmospheric distillation of petroleum, residual oils from vacuum distillation, and tars and tars produced by heat treatment of these residual oils. Although petroleum-based heavy oils such as pitch and oil sand bitumen can be used, coal-based oils are somewhat advantageous in terms of ease of subsequent spinning.

To treat this raw material pitch with tetrahydroquinoline, for example, 30 to 100 parts by weight of tetrahydroquinoline per 10 parts by weight of raw material pitch is added and heated at 300 to 500°C, preferably 340 to 450°C. At this time, a mixture of tetrahydroquinoline and quinoline may be used instead of tetrahydroquinoline.

In addition, when treating with quinoline and hydrogen in the presence of a catalyst instead of treatment with tetrahydroquinoline, for example, 30 to 100 parts by weight of quinoline and 5 to 10 parts by weight of catalyst are added per 100 parts by weight of raw material pitch, and a hydrogen gas atmosphere is added. The process is carried out by maintaining a pressure of 50 to 200 kglcry and a temperature of 174 degrees Celsius or higher than 400 degrees Celsius for 10 minutes or more. The catalyst used in this case is cobalt-molybdenum,
Iron oxide-based materials are preferred. However, a mixture of quinoline and tetrahydroquinoline can also be used in place of the above-mentioned quinoline alone.

The product obtained by this treatment is filtered and then
Subjected to second stage processing.

Next, when processing with aromatic hydrocarbon and hydrogen gas, mix 50 parts by weight or more of aromatic hydrocarbon per 100 parts by weight of raw material pitch in a hydrogen gas atmosphere at a pressure of 50 kg/d or more and a temperature of 430°C or more. This is done by maintaining the temperature under these conditions for about 60 minutes. The aromatic hydrocarbons in this case are:
Naphthalene, anthracene, phenanthrene, pyrene and the like are preferred. In this case, it is more advantageous to use a mixture of 1 part by weight or more of quinoline per 100 parts by weight of aromatic hydrocarbon.

The raw material pitch that has been subjected to the first stage treatment as described above is then subjected to high temperature treatment under reduced pressure. This treatment is carried out at a pressure of 50 mmH.
g or less and maintained at a temperature of 450° C. or higher for 60 minutes or less. This treatment is preferably carried out at as high a temperature as possible for a short period of time, preferably within 15 minutes; if heating is carried out for too long, spinnability will be lost.

In this way, two-step processing is required to form brimesophase carbonaceous material, and the first step is to reduce the high molecular weight content in the raw material pitch, and then the second step is to reduce the high molecular weight content in the raw material pitch. It is useless to remove low molecular weight components.

The thus obtained premethophase carbonaceous material usually has a softening point of 300° C. or less, a fixed carbon content of 87% or more, and is soluble in quinoline.

However, when this pre-mesophase carbonaceous material is observed with a reflective polarization microscope under crossed nicols, the membranous phase, which is commonly used as the raw material pitch for conventional carbon fibers, becomes dark with a period of 45 degrees when the nicols are rotated. Whereas the states of color and white are repeated, this one is always dark black and does not change.

This shows that the brimesophase carbonaceous material is optically isotropic.

In the method of the present invention, premesophase carbonaceous material is used as the raw material pitch, but it does not necessarily have to be a single substance, and may be a mixture with memphase. In this case, it is necessary to make the viscosity of mesoface and brimesoface almost equal and to make the mixing ratio of mesoface less than 60% by weight. If the amount of mesophase is larger than this, the spinnability will decrease, and yarn breakage will be severe on a 90-weight plate, and continuous spinning will be almost impossible even at a low speed of 50 m/min, and spinning will still be difficult. Even if it were possible to do so, the resulting fibers would have extremely low strength and cannot be put to practical use.

The spinning of pre-methophase carbonaceous material in the method of the present invention is as follows:
It can be carried out according to conventionally known carbon fiber spinning methods such as melt extrusion spinning, centrifugal spinning, and blow spinning.

For example, Brimesoface carbonaceous material with a diameter of 0.1 to 0.
It is placed in a spinning machine with an 8 m+ nozzle, heated to a temperature 50 to 90°C higher than its softening point by external heating, and 0.2 to 2 Kp / using an inert gas such as nitrogen gas.
This can be carried out by extruding at a pressure of crl and winding the filament spun out from a nozzle at a winding speed of 50 to 1000 m/min.

The spinnability in this case is related to the purity of the brimesoface carbonaceous material, and if the amount of memphace in it is 60 yen, it is 1000? It is possible to wind up at a high speed of around Fl/min, but if the spinning speed is too high, continuous spinning is not possible unless the speed is slow, which often results in yarn breakage and the resulting fibers are non-uniform. . During this spinning, the amount of mesophase in the filaments produced does not substantially change before and after spinning.

Next, in the infusible treatment of the method of the present invention, the filament obtained as described above is placed in, for example, an electric furnace and heated in an air stream.
This is done by heating to 0.5-350°C and maintaining for 5-30 minutes.

The filament thus made infusible is then subjected to a carbonization treatment to convert the brimesophase carbonaceous material therein into mesophase. This carbonization treatment is carried out, for example, by heating in a stream of inert gas, such as nitrogen gas, to a temperature within the range of 2 to b°C and maintaining this temperature for 10 to 30 minutes. With this process,
Substantially all of the optically isotropic brimesophase carbonaceous material converts to optically anisotropic mesophase. In this way, the fiber diameter is 20 μ or less, the tensile strength is 150 to 32
Carbon fibers with an elongation of 1.2 to 1.6% and a yield of 88% or higher can be obtained based on the raw materials.

According to the method of the present invention, carbon fibers with strength comparable to that obtained from polyacrylonitrile can be produced at higher spinning speeds and with higher carbon conversion efficiency than conventional methods for producing carbon fibers using pitch or mesophase as raw materials. can be obtained.

Next, the present invention will be explained in more detail with reference to Examples.

The fiber diameter of the carbon fibers in each example was measured by observation using a scanning electron microscope. In addition, the tensile strength and elongation rate are
Measured according to R7601r carbon fiber test method-1.

Reference Example 1 A mixture of coal tar pitch 2002, 1.2,3.4-tetrahydroquinoline, and quinoline (tetrahydroquinoline concentration: 86.7 parts) 500 f was placed in a 21 volume autoclave, and the internal air was replaced with nitrogen gas. Thereafter, the container was sealed, heated to 450° C. at an average heating rate of 3° C./min, and held at this temperature for 10 minutes. Next, after cooling to room temperature, it was filtered under reduced pressure through a glass filter (flat 4), and the filtrate was distilled under a pressure of 10 mHg until the liquid temperature reached 200°C to remove the cytotrahydroquinoline and quinoline and produce pitch A. Obtained.

Also, instead of the heat treatment at 450°C for 10 minutes,
Pitch B was obtained by processing in exactly the same manner as above except that the processing was carried out at 0° C. for 30 minutes.

The properties of pitch A1 and pitch B thus obtained are shown in Table 1 together with those of the raw material coal tar pitch.

Table 1 Approximately 1002 of this pitch A or pitch B is converted into an internal volume of 30
Place it in a 0-Pyrox container and add 500~
It was connected to a vacuum pump immersed in a salt bath heated to 530°C, and the pressure was gradually reduced to a final pressure of 10°C. After holding under these conditions for the time shown in Table 2, the mixture was cooled to room temperature to produce a brimethophase carbonaceous material. The retention time in the table is the time from when the container was immersed in the bath. Furthermore, the actual temperature of the pitch was about 20°C lower than the salt bath temperature.

The yield and properties of the primesophase carbonaceous material thus obtained are shown in Table 2.

Reference Example 2 Vacuum distillation residue of Kafji crude oil was heated at 420°C in a nitrogen gas stream.
The sample was heat-treated for 60 minutes. The yield of residual pitch is 58
It contained 6.8% by weight of Ashi and Quinoline solubles.

Next, this residual pitch was dissolved in quinoline, filtered to remove insoluble matter, and P solution was distilled to remove quinoline to obtain pitch.

Put this pitch 2001 into an autoclave.
Add 50 (l) of a mixture of tetrahydroquinoline and quinoline (tetrahydroquinoline concentration 87.6%) and reduce the hydrogen pressure to 5
o Kg/crl (gauge pressure) and a temperature of 450° C. for 3 hours. Next, after removing tetrahydroquinoline and quinoline by vacuum distillation, the mixture was treated in the same manner as in Reference Example 1 at 490°C for 10 minutes under a pressure of 10 mm Hg to obtain brimesophase carbonaceous material with a yield of 45.2%. Obtained.

This brimesophase carbonaceous material had a softening point of 341°C, a quinoline soluble content of 64.3%, and a fixed carbon content of 87.6%.

Reference example 3 Add naphthatal pitch 3502 to 2!・The mixture of tetrahydroquinoline and quinoline collected in Reference Example 2 was placed in a crepe (tetrahydroquinoline concentration 38.1
%) After adding 350f and adding red mud 352 as a catalyst, the hydrogen pressure was 75 and 9/ci.

Heat treatment was performed at a temperature of 450° C. for 60 minutes. Next, this treated product was filtered to remove red mud, and the P liquid was distilled under reduced pressure to remove tetrahydroquinoline and quinoline.

In this way, the obtained pitch is set as in Reference Example 1, and l
By treating the mixture at 480° C. for 10 minutes under a pressure of ommHg, brimesophase carbonaceous material was obtained with a yield of 38.9%.

This brimesophase carbonaceous material had a softening point of 341°C, a quinoline soluble content of 53.6%, and a fixed carbon content of 88.6%.

Example 1 Various Brimesoface carbonaceous materials 209 obtained in Reference Example 1 were prepared using a nozzle with an inner diameter of 20 mm and a length of 15 mm.
Place each pitch in a zero-throttle brass spinning machine, heat each pitch by external heating to a temperature approximately 70°C higher than its softening point, and heat it with nitrogen gas to a temperature of 1 to 1/CI (gauge pressure).
The filament was extruded under pressure and the filament spun from the nozzle was wound up at 10,100°.

The filament trained in this way is placed in an electric furnace and heated at a rate of 1°C/min to 260°C or 300°C while passing air at a rate of approximately 200 d/min, and maintained at this temperature for 15 minutes. Infusibility treatment was carried out by holding it.

Next, the treated filament thus obtained was heated to 1000° C. at a temperature increase rate of 5° C./min in a nitrogen gas stream and held for 15 minutes to perform carbonization.

The preparation conditions and physical properties of the carbon fiber obtained in this way were described in the third section.
Shown in the table.

Note that the pitcher in the table is the same as the pitcher in Reference Example 1.

Comparative Example 1 The raw material coal tar pitch used in Reference Example 1 was dissolved in quinoline, and free carbon was removed by filtration. Reference example 1 is the pitch that does not contain free carbon obtained in this way.
When it was heat-treated at 500° C. for 15 minutes under reduced pressure in the same manner as above, the entire product was caulked and could not be softened or melted even by heating.

Next, heat treatment under reduced pressure is performed at 5001? , for 5 minutes, the quinoline dissolved content (menface) was 72.0.
A pitch containing % by weight was obtained. The yield at this time was 53.0% by weight, and the softening point of pitch was 370°C. An attempt was made to spin this pitch at a spinning temperature of 430°C, but no filaments could be obtained.

Comparative Example 2 Pitch A shown in Reference Example 1 was treated at 450'C for 10 minutes, and the product was treated at 500C for 60 minutes without reducing the pressure. In this way, pitch was obtained with a yield of 58.2% by weight, a softening point of 379° C., and an insoluble content of Kinori 7 of 72.9% by weight.

An attempt was made to spin this pitch at about 430°C, but almost no filaments were obtained. Next, under the condition that the above pitch was reduced to I Ot#MHg, 42
By heat treatment at 0℃ for 18 hours, the softening point is 323℃.
, quinoline solubility 73.2% by weight, fixed carbon amount 82.9
Weight% pitch. Attempts were made to spin this product at a spinning temperature in the range of 380 to 420°C, but only a small amount of fiber was spun from the nozzle at the beginning of spinning, and it was not possible to form filaments at all.

Example 2 The premethophase carbonaceous substance obtained in Reference Example 2 was spun at about 410° C. in the same manner as in Example 1.

Next, the obtained filament was heated to 300°C at a heating rate of 1°C/min in an electric furnace while blowing air.
It was kept at this temperature for 30 minutes to make it infusible. The weight increase rate at this time was 3.5%.

Next, this infusible filament is heated at an average heating rate of 3
．． It was heated to 1000°C at a rate of 3°C/min and maintained at this temperature for 15 minutes to carbonize, thereby obtaining carbon fibers.

The yield at this time was 87
．． It was 4%. In addition, the tensile strength of the obtained carbon fiber was 186, the elongation rate was 1.2%, and the fiber diameter was 18 μm.
Met.

Example 3 The premethophase carbonaceous material obtained in Reference Example 3 was spun at a spinning temperature of 400 to 420'C in the same manner as in Example 1, and then subjected to infusibility treatment in air at 260C for 15 minutes.

Next, the infusible filament was heated in a nitrogen gas flow at a heating rate of 2°C/min to 1000'C, and held at this temperature for 15 minutes to carbonize, resulting in a yield of 87.3%. , tensile strength 216KLi/-1 elongation rate 1.1%,
Carbon fibers with a fiber diameter of 16 μm were obtained.

Reference Example 4 The optically isotropic quinoline soluble content in the spinning pitch is optically isotropic during spinning and its infusibility treatment, and by carbonizing the spun fiber, it is completely converted into mesophase. The conversion was proved by the following experiment.

After treating coal tar pitch and tetrahydroquinoline in a closed container at 450°C for 10 minutes, free carbon in the coal tar pitch was removed by centrifugal sedimentation,
Then, vacuum distillation was performed to remove tetrahydroquinoline and quinoline. The obtained pitch 10cI was placed in a 300-cm polymerization flask and placed in a salt bath preheated to 500°C.

Immediately after charging, it was connected to a pressure reduction system, and the distilled oil was guided to the trap while gradually reducing the pressure. The temperature of the pitch reached 480°C approximately 4 minutes after the addition, and was maintained at this temperature for 5 minutes. Note that the final reduced pressure is 1°tHRHg. Immediately after the time elapsed, the flask was removed from the salt bath and cooled to room temperature.

The spinning pitch obtained as flask residue was 36.82. The softening point of this pitch is 171℃, and the amount of fixed carbon is 8
6.6%, and the quinoline dissolved content was 0.8%.

When the structure was observed using a reflective polarizing microscope, it was found that mesophase spherules with a diameter of about 1 μm were scattered, and the rest of the structure was optically isotropic.

Pitch was put into a spinning machine equipped with a nozzle with a hole diameter of 0.5 fi, heated to about 250°C, and then heated with nitrogen gas.
Spinning was carried out under pressure of about 0.5 Kp/m. Spinning was quite easy, and the yarn could be wound for several minutes at a winding speed of about 300 m/- without any breakage.

It is quite difficult to make the spun fibers infusible due to the low softening point of pitch, and complete infusibility cannot be achieved by air oxidation alone. Particularly, the thick fibers of about 20 μm seemed to be melted by the infusibility treatment, and although they retained their fiber shape, they were hard and brittle.

The fibers after the infusibility treatment were heated to 1,000° C. at a temperature increase rate of 5° C. and 7 ml in a nitrogen gas flow and held for 15 minutes to carbonize.

The carbonized fibers, spun, and infusible fibers were embedded in resin and polished, and then their structures were observed under crossed Nicols using a reflective polarization microscope. A photograph of the structure is shown in Figure 1. Figure 1a.

b is a spun fiber, and C2d in the figure is a carbonized fiber. In a and C, the fiber axes are parallel or perpendicular (not perpendicular Nicols) to the vibration direction of the polarizing plate, and b and d are diagonal at 45°. The spun fiber of a is dark black, and several shining small spheres (spherical diameter approximately 1 μm) are present within it. This state does not change even if this is rotated 45 degrees to the right and placed in a diagonal position (b). In addition, when observing the gypsum test plate (large plate) in person, it is observed that the color of the small sphere changes when rotated 45 degrees to the right.
Dark black is red and does not change. In other words, a small number of small spheres present in the fiber are optically anisotropic, and most of the other particles are optically isotropic and not membranous. This condition was the same as that of the spinning pitch containing memphis spherules, and was also the same with the infusible treated fibers.

However, the carbonized fibers are dark black at C, but at 45°
When rotated to the right (C diagonal position), the entire fiber shines white. 4 more
Rotate 5 degrees to the right (rotate 90 degrees in total) to darken the black color, and then turn 45
Rotate by 9 degrees (total rotation of 135 degrees) to turn white, and every 45 degrees to turn dark black and white. Furthermore, when observing the gypsum test plate in this way, the color C is red and the color d is blue. The direction of this blue flow coincides with the fiber axis direction. From this observation result, it can be seen that the carbon layer surface within the carbonized fiber almost coincides with the fiber axis direction.

As mentioned above, spinning pitch is optically isotropic when it is simply formed into fibers, but it is understood that it can be converted into optically anisotropic (Q-no-face) only by carbonization treatment. If pitch for spinning is heated as it is without forming it into fibers, the entire pitch will of course be converted to membrane face. However, it is well known that the production and growth of membranes does not proceed smoothly within a very narrow fiber of about 10 to 20 μm. This is because carbonization of fibers is not a liquid phase reaction but rather a solid phase reaction.

Therefore, in the past, it was thought that optically anisotropic carbon fiber could only be obtained unless a pitch containing mesophase was spun. It should be said that it was completely unexpected that carbon fibers with anisotropic properties were obtained.

[Brief explanation of the drawing]

Figures 1 a) and b) are polarized light micrographs of spun brimesophase carbonaceous material, and Figure 1 C) and d) are polarized light micrographs of the spun carbonaceous substance. Patent applicant: Makoto Ishizaka, Director of the Agency of Industrial Science and Technology - Engraving of drawings (no changes in content) a,) b) c)
a) Procedural rectification letter (
Method) 2. Name of the invention Method for manufacturing carbon fiber 3. Relationship with the amended person's case Patent applicant Makoto Ishizaka, Director of the Agency of Industrial Science and Technology, 1-3-1 Kasumigaseki, Chiyoda-ku, Tokyo (114) - 1981
May 5th (Delivery date: January 26, 1980) 6. Number of inventions increased by amendment 07. Subject of amendment Drawing 8. Contents of amendment The amendments are made as shown in the attached drawing.

Claims (1)

[Claims] 1. Spinning an optically isotropic pre-mesophase carbonaceous material or a pitch-like material mainly composed of an optically isotropic pre-mesophase carbonaceous material under conditions where the mesophase carbon mass does not substantially increase, 1. A method for producing carbon fibers, characterized in that the fibers are then subjected to an infusibility treatment and then a carbonization treatment to convert substantially all of the pre-mesophase carbonaceous material into optically anisotropic memphasic carbonaceous material.