JPH0147564B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing carbon fibers using pituti as a raw material, and more specifically, a method for infusible pitch fibers in which pituti fibers are oxidized and converted into infusible fibers. Regarding processing method.

BACKGROUND TECHNOLOGY In recent years, a method for producing carbon fiber using pitch as a raw material has been attracting attention. This method uses inexpensive pitch as a raw material, so it is possible to produce carbon fiber at low cost.Also, when liquid crystal pitch is used as a spinning raw material, high strength can be achieved without complicated tension treatment in the firing process. It has advantages such as being able to produce highly elastic carbon fiber, and is currently being actively researched and developed.

A method for producing carbon fiber using pitch as a raw material generally begins with the preparation of a spinning pitch. Crude raw materials such as coal tar pitch or petroleum pitch are subjected to distillation, heat treatment, filtration, hydrogenation,
Treatments such as solvent fractionation are applied singly or in combination to remove components that interfere with the spinning process, such as low-boiling volatile components and insoluble solids in the pitch, and to homogenize the composition and make it moderately heavy. An optically isotropic or optically anisotropic spinning pitch is obtained. The properties of a spinning pitch can be measured using various parameters such as softening point, melt viscosity, optical structure, and solvent fractionation composition, and spinning pits with various properties can be used for spinning, but the basic It is important for the spinning pitch to contain no solids or gases under spinning conditions and to have uniform flow characteristics.

Next, the resulting spun pitch is made into fibers to produce pitch fibers, but to produce continuous long fibers, melt spinning is usually used, and cotton-like short fibers or medium fibers with intermediate lengths are pulled together. Centrifugal spinning is usually suitable for producing sliver or tow. Appropriate values can be selected for the spinning temperature, the number of discharge nozzles, the discharge amount, the centrifugal magnification, etc., depending on the purpose. The fiber diameter of spun pitch fiber is usually 5
-30 microns, and if it is too thick, it tends to impair the properties of the fiber, and if it is too thin, it becomes difficult to ensure the economic efficiency of the spinning process.

In order to convert pitch fibers into carbon fibers, prior to heating and carbonization, it is necessary to perform a so-called infusible process in which the thermoplastic pitch fibers are oxidized and converted into infusible fibers that do not melt even when heated. Normally, infusibility is achieved by adding oxygen or an oxidizing substance to the pitch fibers and crosslinking the pitch molecules, and various gases and liquids have been proposed as the oxidizing agent. In addition, since such a reaction proceeds from the fiber surface, the thinner the pitch fibers, the faster the infusibility can be expected. Pitch fibers used in the infusibility process are handled in a continuously stretched form, or in a form that is accumulated on a conveyor or basket, but the appropriate form is selected depending on the final form of the desired fiber. be able to.

Next, the infusible fibers are heated in an inert gas for about 600-3000
A carbonization process is performed in which the material is heated to about ℃ and converted into carbon fiber. (Treatment at 2000℃ or higher is sometimes called graphitization.) Through this treatment, the volatile components in the infusible fibers and the thermally unstable portions in the pitch molecules are decomposed and volatilized, and the six-membered The ring structure develops, resulting in a carbon fiber with a high carbon content, and in some cases a structure close to that of graphite crystals, resulting in carbon fibers having strength and elastic modulus.

For heating, a hot air furnace, an electric furnace using various heating elements, a plasma furnace, etc. can be used, but in either case, the high temperature consumes a large amount of energy, so it is difficult to carry out carbonization efficiently. is necessary. Furthermore, carbonization can be carried out in two or more stages, low temperature and high temperature, as required.

The obtained carbon fibers are subjected to surface treatment, oiling, unwinding, sometimes cutting, fibrillation, and other treatments as necessary, but since these are common steps, their explanations will be omitted.

Problems to be Solved by the Invention All of the above steps are important for producing carbon fibers, but the infusibility step usually takes a long time and also causes troubles that may impair the performance of carbon fibers. Because of this tendency, it is extremely important to carry out this process efficiently in order to economically produce carbon fibers.

The purpose of the infusible step is to oxidize the thermoplastic pitch fibers to convert them into infusible fibers that do not have thermoplasticity, and to prevent the fibers from melting and deforming in the subsequent carbonization step. For this reason, pitch fibers are usually heat-treated in an oxidizing gas while gradually raising the temperature to carry out an oxidation reaction, but a phenomenon called "fusion" often occurs during this process, making this process difficult.

“Fusion” refers to a phenomenon in which adjacent pitch fibers are melted and deformed during the infusibility process, or some substance is attached to the area where the pitch fibers come into contact, and this causes the pitch fibers to stick to each other. .

Even if the fused pitch fibers are subsequently carbonized and made into carbon fibers, the fibers remain stuck to each other and lack flexibility, resulting in a significant loss of commercial value or, in some cases, no commercial value at all. I don't.

The fusion phenomenon tends to occur when pitch fibers are handled in the form of tow or strands. Handling pitch fibers in the form of tows or strands is the most suitable method for producing continuous filaments. Obtaining quality continuous carbon fibers is extremely difficult industrially. On the other hand, performing infusibility in the form of a tow or strand is a disadvantageous method in terms of preventing fusion. This is because pitch fibers in tow or strand form are bundled at high density and have a large number of continuous contact points in the length direction. In such a state, the heat generated by the oxidation reaction of the pitch accumulates inside the tow or strand, creating hot spots in some areas, causing pitch fibers that come into contact to melt and fuse together. In addition, volatile substances generated from the pitch fibers or substances oozing from the pitch fibers are not removed from the fiber bundle and accumulate at the fiber contact points, which acts as a kind of binder and prevents fusion. It happens.

Various techniques have been proposed for making pitch fibers infusible. A method using an oxidizing agent solution (for example, Japanese Patent Publication No. 47-21904, Japanese Patent Publication No. 47-21904,
21905, etc.), methods using oxidizing gases (e.g.
(Special Publication No. 48-42696, Japanese Patent Publication No. 758282, 1973, etc.)
A method of using both together (for example, Japanese Patent Application Laid-Open No. 51-88729
No., JP-A-59-30915, etc.). However, the effect of these techniques is mainly to shorten the infusibility time, and they are all insufficient in terms of preventing the fusion of tow-like or strand-like pitch fibers.

A technique using a combination of an aqueous oxidizing agent, a water-soluble surfactant, and graphite fine powder has also been proposed as a method for preventing the fusion of pitch fiber strands (Japanese Patent Application Laid-Open No. 128020/1983). However, graphite has a high temperature increase rate, that is, when it is subjected to infusibility treatment and carbonization treatment in a short period of time, it was not possible to obtain the fusion prevention effect that we were satisfied with.

Means for Solving the Problems The present inventors have conducted extensive studies on the problem of preventing fusion, and as a result, have completed the present invention, which has a remarkable effect on preventing fusion, unlike the prior art. Furthermore, since the problem of fusion has been solved, application of the present invention has made it possible to shorten the infusibility time.

The details of the present invention will be described below.

The method that achieves the effects described above is surprisingly simple; a dispersion of fine molybdenum disulfide or tungsten disulfide powder is processed into pitch fibers before being made infusible, thereby making fine powder of molybdenum disulfide or tungsten disulfide This can be achieved by heat-treating the pitch fibers in an oxidizing gas with the powder attached to them to make them infusible.

The fine molybdenum disulfide powder referred to herein is obtained by refining and pulverizing molybdenum disulfide ore, and is usually available as a raw material for lubricants. It is also well known that molybdenum disulfide as a lubricant exhibits excellent lubricating properties under a wide range of conditions.
Such powders are pre-refined, with a purity of over 98% and no harmful impurities. Although the particle size varies depending on the degree of pulverization, for the purposes of the present invention, an average particle size of about 5 microns to about 0.3 microns is preferred.

On the other hand, tungsten disulfide is rarely produced naturally and is usually synthesized industrially from metallic tungsten and sulfur. Its properties are similar to molybdenum disulfide, and its lubricity is also known to be equivalent to that of molybdenum disulfide. Since it is a synthetic product, its purity is high, and it is said that any particle size can be obtained depending on the synthesis conditions, but for the purpose of the present invention, particles with the same particle size as molybdenum disulfide are suitable.

The dispersion herein refers to a dispersion of molybdenum disulfide fine particles or tungsten disulfide fine particles dispersed in a suitable dispersion medium, and a physical method may be used in combination to help stabilize the dispersion. Various solvents such as hexane, heptane, methanol, ethanol, and acetone can be used, and water can also be used. However, strong solvents for pitch such as quinoline and chloroform are not preferred because they damage pitch fibers. The use of substances such as benzene is also restricted for the same reason. Solvents with boiling points or boiling point ranges exceeding 200°C are undesirable because they impede the flow of oxidizing gases.

During the treatment, the dispersion is used as it is or after being adjusted to an appropriate concentration. The concentration of molybdenum disulfide or tungsten disulfide in the dispersion during treatment is preferably 5-50%. During the treatment, if the treatment is solvent-based, there is no need to add any auxiliary agent, but if the treatment is water-based, it is necessary to use a surfactant to improve wetting of the pitch fibers. As the surfactant, any of cationic surfactants, anionic surfactants, and nonionic surfactants can be used, but if the nonionic surfactant is Examples thereof include polyoxyethylene alkyl phenol ether, polyoxyethylene alkyl ether or ester,
Examples include ethylene oxide propylene oxide block copolymers. Furthermore, if the amount of surfactant used is too large, it will prevent the flow of oxidizing gas, which is undesirable, and if it is too small, the wetting or dispersing effect will be insufficient, and it is usually 0.05-
About 1.0% is preferable.

The treatment of the pitch fibers with the dispersion liquid can be carried out at any appropriate time from immediately after the pitch is turned into fibers to immediately before the infusibility step. Various treatment methods are possible, including spraying, coating with a rotating roller, and dipping.
Molybdenum disulfide or tungsten disulfide must be attached to the pitch fibers as uniformly as possible.

As spinning pitch, which is the raw material for pitch fiber,
The effects of the present invention can be obtained using either an optically isotropic pitch or an optically anisotropic pitch.

The pitch fibers are preferably in a loosely aligned tow shape or tightly aligned in a so-called strand shape. It is also possible to use a cotton-like structure in which short fibers are randomly intertwined, or a wool-like structure in which long fibers are separated and accumulated one by one (sliver), but since such a form has few contact points, it is difficult to use the present invention. The effect is also small.

As the oxidizing gas used for infusibility, air, oxygen, ozone, nitrogen dioxide, sulfur dioxide, halogen, etc. can be used, but from an economical point of view, it is preferable to use air or oxygen.

Actions and Effects When the present invention is applied, the time required for infusibility is
30-120 minutes. Conventional methods cannot prevent fusion even if it takes more than 120 minutes to make the material infusible.
In order to obtain high-quality carbon fibers, a longer period of infusibility was required.

The infusible yarn according to the present invention can be directly introduced into the carbonization process without requiring any special steps such as washing.

Generally, when a tow or strand, which is a bundle of filaments, is wetted with a liquid, the filaments come together and the shape of the tow or strand becomes thinner than before wetting it. It also maintains almost the same shape during the infusibility process and carbonization process. The fact that the filaments come together in this way generally tends to cause the filaments to fuse together during the infusibility treatment, but in spite of this, according to the present invention, the dispersion of molybdenum disulfide The treated Pitschi fiber goes through an infusible process, and after a carbonization process, it is squeezed slightly.
Carbon fibers that are easily separated into individual filaments and are free from fusion can be obtained.

The reason for such an excellent effect is thought to be that fine particles of molybdenum disulfide enter between pitch fibers, eliminating contact points between pitch fibers.

Examples of the present invention will be described below. The examples described herein are intended to facilitate understanding of the method and effects of the invention, and are not intended to limit the scope of the invention.

Example 1 Coal tar is used as raw material, quinoline insoluble content is 35%
The optically anisotropic pitch fiber containing the fiber was melt-spun to obtain a pitch fiber strand with a filament diameter of 13 microns and a number of filaments of 2000. This strand was immersed in an acetone dispersion containing 10% by weight of molybdenum disulfide with an average particle size of 0.5 microns. This treated strand was heat treated in an oxygen atmosphere at a temperature increase rate of 5° C./min to make it infusible over 1 hour. This infusible yarn was carbonized by heat treatment to 1100° C. in an argon atmosphere to obtain carbon fibers. The obtained carbon fibers were easily opened into individual filaments, and no fusion phenomenon was observed.

Example 2 Carbon fibers were produced in the same manner as in Example 1, except that ethyl alcohol (99.5%) was used as the dispersion medium for the molybdenum disulfide dispersion. The obtained carbon fibers were easily opened into individual filaments, and no fusion phenomenon was observed.

Example 3 Carbon fibers were produced in the same manner as in Example 1, except that heptane was used as the dispersion medium of the molybdenum disulfide dispersion and the content of molybdenum disulfide was 20%. The obtained carbon fibers were easily opened into individual filaments, and no fusion phenomenon was observed.

Example 4 Four types of molybdenum disulfide having different particle diameters (average particle diameters of 0.5 microns, 0.7 microns, 1.2 microns, and 5 microns) were respectively dispersed in acetone to prepare four types of acetone dispersions. Using this, carbon fibers were produced in the same manner as in Example 1. A slight fusion phenomenon occurred in carbon fibers using molybdenum disulfide having a particle size of 5 microns, but no fusion phenomenon was observed in other cases.

Example 5 Carbon fibers were produced in the same manner as in Example 1 except that the content of molybdenum disulfide in the dispersion was changed to 20, 10, 5, and 2.5% by weight.
No fusion phenomenon occurred at the content of 20% and 10%, but
At 5%, a slight fusion phenomenon occurred, and at 2.5%, the carbon fiber strand became rod-shaped due to the fusion phenomenon.

Example 6 The pitch fiber strands of Example 1 were
It was immersed in an acetone dispersion containing 20% 0.5 micron molybdenum disulfide particles. This strand is heat treated in an oxygen atmosphere at a heating rate of 10°C/min.
It became infusible. This infusible fiber was carbonized in the same manner as in Example 1 to produce carbon fiber. No fusion phenomenon was observed in the obtained carbon fibers.

Example 7 Coulter was used as raw material, quinoline insoluble content was 1%,
Optically isotropic pitch containing 70% benzene insoluble matter was melt-spun to obtain pitch fiber strands with a filament diameter of 14 microns and a number of filaments of 2000. This strand was immersed in an acetone dispersion containing 10% by weight of molybdenum disulfide with a particle size of 0.5 microns. This treated strand was heat treated in air at a temperature increase rate of 2° C./min to make it infusible over 2 hours. This infusible yarn was carbonized by heat treatment to 1100° C. in an argon atmosphere to obtain carbon fibers. The obtained carbon fibers were easily opened into individual filaments, and no fusion phenomenon was observed.

Example 8 Coal tar is used as raw material, quinoline insoluble content is 35%
While melt spinning an optically anisotropic pitch containing
Directly below the spinning furnace, an aqueous dispersion containing 10% by weight of molybdenum disulfide with a particle size of 0.5 microns was applied to the filament using a rotating roller.
A treated strand with a filament count of 2000 microns was obtained. When this was made infusible and carbonized in the same manner as in Example 1, carbon fibers without any fusion phenomenon were obtained.

Example 9 A commercially available molybdenum disulfide dispersion spray (trade name: ThreeBond 1910) was used to spray coat the pitch fiber strand of Example 1 with a molybdenum disulfide dispersion. When the obtained treated strand was made infusible and carbonized in the same manner as in Example 1, carbon fibers without any fusion phenomenon were obtained.

Example 10 The pitch fiber strands of Example 1 were
It was immersed in an aqueous dispersion containing 0.5 micron molybdenum disulfide 20% and a surfactant 0.5%, and then infusible and carbonized in the same manner as in Example 1. Although alkylbenzene sulfonate, alkyltrimethylammonium chloride, or polyoxyethylene alkylphenol ether was used as the surfactant, carbon fibers without fusion were obtained in all cases.

Example 11 Coal tar is used as raw material, quinoline insoluble content is 35%
The optically anisotropic pitch fiber containing the fiber was melt-spun to obtain a pitch fiber strand with a filament diameter of 13 microns and a number of filaments of 2000. This strand was immersed in an acetone dispersion containing 20% by weight of tungsten disulfide with an average particle size of 0.7 microns. This treated strand was heat treated in an oxygen atmosphere at a temperature increase rate of 5° C./min to make it infusible over 1 hour. This infusible yarn was heat-treated to 1100°C in an argon atmosphere to carbonize it, yielding carbon fibers. The obtained carbon fibers were easily opened into individual filaments, and no fusion phenomenon was observed.

Example 12 The 20% acetone dispersion of tungsten disulfide in the above example was replaced with an aqueous dispersion containing 20% by weight of tungsten disulfide and 0.5% polyoxyethylene nonylphenol ether (surfactant), and the rest were as above. When the same operation as in Example 1 was carried out, the obtained carbon fibers were easily opened into individual filaments, and no fusion phenomenon was observed.

Comparative example 1 Coal tar is used as raw material, quinoline insoluble content is 35%
While melt spinning an optically anisotropic pitch containing
Directly below the spinning furnace, water, ethyl alcohol or silicone oil (boiling range 150-200°C) was applied to the filaments using a rotating roller to obtain treated strands with a filament diameter of 13 microns and a number of filaments of 2000. When this was made infusible and carbonized in the same manner as in Example 1, rod-shaped carbon fibers were formed due to the fusion phenomenon in both cases.

Comparative Example 2 Carbon fibers were produced in the same manner as in Example 1, except that the molybdenum disulfide dispersion medium was replaced with quinoline, chloroform, and benzene. When quinoline was used, the pitch fibers melted during the infusible process, and no infusible fibers were obtained. In the case of chloroform and benzene, carbonization was possible, but it was extremely difficult to open the obtained carbon fibers into individual filaments due to the fusion phenomenon.

In addition, when we tried to trace the method of JP-A-55-128020 as a comparative example of the present invention (Comparative Example 3), we found that a sufficient fusion prevention effect was obtained when the temperature increase rate during infusibility was fast. The superiority of the present invention is clear.

Comparative Example 3 The pitch fiber strands of Example 1 were used with a particle size of 0.7.
It was immersed in an aqueous dispersion containing 3.6% of micron graphite particles, 0.8% of ammonium persulfate, and 0.4% of a nonionic surfactant [polyoxyethylene nonylphenol ether (Emulgen 910, manufactured by Kao Atlas Co., Ltd.)]. This strand was made infusible in an oxygen atmosphere at a temperature increase rate of 5°C/min (time required for infusibilization: 60 minutes) and a temperature increase rate of 10°C/min (time required for infusibilization 30 minutes), and then carried out. When carbonization was performed using the method of Example 1, fusion occurred in all cases.
Carbon fibers that could be easily opened into individual filaments could not be obtained.

Claims (1)

[Claims] 1. In the production of pitch-based carbon fibers, fine molybdenum disulfide powder or fine tungsten disulfide powder is added to pitch fibers in water containing a surfactant for 5 to 50 minutes.
1. A method for infusibility treatment of pitch fibers, which comprises applying a dispersion liquid dispersed in weight percent and then infusibility treatment.