JPS61160422A - Infusibilization of pitch fiber - Google Patents

Abstract

PURPOSE:To produce carbon fiber in a short time, preventing the fusion of the filaments, by attaching molybdenum disulfide powder or tungsten disulfide powder to a pitch fiber and infusibilizing the fiber. CONSTITUTION:Molybdenum disulfide powder or tungsten disulfide powder (preferably 5-0.3mu diameter) is applied to a pitch fiber, and the fiber is infusibilized to obtain the objective carbon fiber. The application of the powder to the pitch fiber is carried out preferably by dispersing the powder in a dispersion medium such as hexane at a concentration of 5-50% and treating the fiber with the dispersion.

Description

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

BACKGROUND OF THE INVENTION In recent years, methods for producing carbon fibers using pitch as a raw material have attracted attention. This method uses inexpensive pitch as a raw material, making it possible to produce carbon fiber at low cost.Also, by using liquid crystalline pitch 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 spinning pitch. Distillation, heat treatment, filtration, hydrogenation, solvent fractionation, and other treatments are applied to crude raw materials such as coal tar pitch or petroleum pitch, either singly or in combination, to spin the low-boiling volatile components and insoluble solids in the pitch. Optically isotropic or optically anisotropic spinning pitch is obtained by removing components that interfere with the process, homogenizing the composition, and appropriately increasing the weight. The properties of spinning pitch can be measured using various parameters such as softening point, melt viscosity, optical structure, and solvent fractionation composition, and spinning pitches with various properties can be used for spinning, but the basic Does not contain solids or gases under spinning conditions,
It is important for the spinning pitch to have uniform flow characteristics.

Next, the obtained 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 the spun pitch fiber is usually 5
If it is too thick (approximately -30 microns), 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, it is necessary to carry out a so-called infusible process in which thermoplastic pitch II fibers are oxidized and converted into unfavorable fibers that do not melt even when heated, prior to heating and carbonization. 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. Furthermore, since such a reaction proceeds from the fiber surface, it is expected that fine pitch fibers will become infusible quickly.

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 desired final form of the fiber. be able to.

Next, the infusible fibers are heated to about 600-3000℃ in an inert gas.
Carbonization treatment is carried out to convert into carbon fiber by heat treatment to a certain degree (treatment at 2000℃ or higher is sometimes called graphitization).This treatment causes the structure in the volatile matter and pitch molecules in the infusible fibers to be heated up. The physically unstable parts decompose and fail, and the six-membered ring structure in the molecule develops, resulting in a structure with a high carbon content, in some cases close to a 4-graphite crystal, which results in a carbon fiber with 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 carbonization must be carried out efficiently. It is necessary. Furthermore, carbonization can be carried out in two or more stages, low temperature and high temperature, as required.

The obtained carbon HN is subjected to treatments such as surface treatment, oiling, unwinding, sometimes cutting, and fibrillation as necessary.
Since these are common steps, their explanation 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 problems that may impair the performance of carbon fibers. Because carbon fibers easily occur, 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 thermoplastic pitch fibers to convert them into infusible fibers that do not have thermoplasticity, and to prevent melting and deformation of IIAH in the subsequent carbonization step. For this reason, pitch iim is usually heat-treated in an oxidizing gas while gradually increasing its 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 part where the pitch fibers come into contact with each other, thereby causing the pitch fibers to adhere 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. Zanai.

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 are bundled at high density in a tow or strand form 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 the pitch fibers that come into contact to melt and fuse together. In addition, continuous substances generated from the pitch fibers or substances oozing from the pitch fibers are not removed from the m-ring and accumulate at the contact points of the fibers, so this acts as a kind of binder and prevents fusion. It happens.

Various techniques have been proposed for making the pitch 1lli infusible. , a method using an oxidizing agent solution (for example, Japanese Patent Publication No. 47-21904, Japanese Patent Publication No. 47-2190)
5, etc.), methods using oxidizing gas (for example,
No. 8-42696, JP-A-49-758282, 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 fusing of tow-like or strand-like pitch fibers.

A technique using a combination of a water-soluble oxidizing agent, a water-soluble surfactant, and fine graphite powder has also been proposed as a method for preventing the fusion of pitch fiber strands (Japanese Patent Application Laid-Open No. 1986-1999).
No. 128020). However, graphite has a high temperature increase rate, that is, during infusibility treatment and carbonization treatment in a short period of time, we could not obtain the satisfactory effect of preventing X-rays.

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 above effects is surprisingly simple; a dispersion of fine molybdenum disulfide or tungsten disulfide powder is treated to a pitch of 1 mM before infusibility. This can be achieved by heat-treating the pitch IBM in an oxidizing gas while the powder remains attached to it to make it infusible.

The molybdenum disulfide fine powder referred to herein is obtained by refining and pulverizing molybdenum disulfide ore, and is usually available as a lubricant raw material. 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-purified and have a purity of 98% or more and are free of harmful impurities. Although the particle size varies depending on the degree of pulverization, for the purpose 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. Boiling point or boiling point range of 200℃
A solvent exceeding the above range is not preferable because it impedes the flow of oxidizing gas.

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 fraction solution 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. It is preferable in that it is not affected by the ionicity of other components, and examples thereof include polyoxyethylene alkyl phenol ether, polyoxyethylene alkyl ether or ester, and ethylene oxide propylene oxide block copolymer. In addition, 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, so it is usually preferable to use about 0.05-1.0%. .

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

The effects of the present invention can be obtained by using either an optically isotropic pitch or an optically anisotropic pitch as the spinning pitch that is the raw material for the pitch m fiber.

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 iINs 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 originally has few contact points, it is difficult to apply 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.

Action and Effect When the present invention is applied, the time required for infusibility is 30-1
It is 20 minutes. In the conventional method, fusion cannot be prevented even if it takes 120 minutes or more for infusibility, and in order to obtain high-quality carbon fibers, it is necessary to infusibility for a long time.

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 more prickly 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 is generally a cause of easy fusion of the filaments during the infusibility treatment, but in spite of this, according to the present invention, the dispersion of molybdenum disulfide The pitch fibers treated with the above process are subjected to an infusible process, and after a carbonization process, by being slightly squeezed, 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 pitches 17AM and eliminate 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 Using coal tar as a raw material, optically anisotropic pitch containing 35% quinolinous content was melt-spun, and the filament diameter was 13.
A pitch fiber strand with a micron diameter and 2000 filaments was obtained. 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 thread was heated to 1100°C in an argon atmosphere.
The carbon fibers were obtained by heat treatment until carbonization. The obtained carbon fibers were easily opened into individual filaments, and no fusion phenomenon was observed.

Example 2 The dispersion medium of molybdenum disulfide dispersion was changed to ethyl alcohol (
Carbon!
! manufactured miscellaneous goods. 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 with different particle diameters (average particle diameters of 0.5 microns, 0.7 microns, 1.2 microns, and 5 microns) were each dispersed in acetone, and four types of acetone dispersions were prepared. made.

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 20.1° and 5.2.5% by weight. Content 20.1
At 0%, no fusion phenomenon occurred, but at 5%, a slight fusion phenomenon occurred, and at 2.5%, due to the fusion phenomenon, carbon mt
A strand has become rod-shaped.

Example 6 The pitch fiber strands of Example 1 were immersed in an acetone dispersion containing 20% molybdenum disulfide particles with a particle size of 0.5 microns. This strand was heated in an oxygen atmosphere for 10
It was heat-treated at a heating rate of °C/min to make it 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 Using coal tar as a raw material, an optically isotropic pitch containing 1% of quinolinated content and 70% of benzene insoluble content was melt-spun, and the filament diameter was 14 microns and the number of filaments was 2.
000 pitch fiber strands were obtained. 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 thread was heated for 1 hour in an argon atmosphere.
Carbonization was performed by heat treatment to 100° C. to obtain carbon fibers. The obtained carbon fibers can be easily opened into individual filaments,
No fusion phenomenon was observed.

Example 8 Coal tar was used as a raw material, and 10% by weight of molybdenum disulfide with a particle size of 0.5 microns was melt-spun directly under the spinning furnace while optically anisotropic pitch containing 35% quinolinous content was melt-spun.
An aqueous dispersion containing the above was applied to the filaments using a rotating roller to obtain a treated strand 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, carbon fibers without any fusion phenomenon were obtained.

Example 9 A molybdenum disulfide dispersion was spray applied to the pitch fiber strand of Example 1 using a commercially available molybdenum disulfide dispersion spray (trade name: ThreeBond 1910). 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 immersed in an aqueous dispersion containing 20% molybdenum disulfide with a particle size of 0.5 microns and 0.5% surfactant, and then treated in the same manner as in Example 1. It became infusible and carbonized.

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 was used as a raw material, and optically anisotropic pitch containing 35% quinolinous content was melt-spun, and the filament diameter was 13.
A pitch fiber strand with a micron diameter and 2000 filaments was obtained. 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 is treated in an oxygen atmosphere.
Heat treatment was performed at a heating rate of 5° C./min to 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 uA miscellaneous was 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 mixed with 20% by weight of tungsten disulfide and 0.5% polyoxyethylene nonylphenol ether (surfactant).
When the same operation as in the above example was carried out except for using an aqueous dispersion containing .

Comparative Example 1 Water, ethyl alcohol, or silicone oil (boiling point range 150-200°C) was rotated directly under the spinning furnace while melt-spinning an optically anisotropic pitch made from coal tar and containing 35% quinolinous content. It was applied to filaments using a roller to obtain a treated strand 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 infusibility, 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 mixed with 3.6% graphite fine particles with a particle size of 0.7 microns, 0.8% ammonium persulfate, and a nonionic surfactant [polyoxyethylene nonylphenol ether (Emulgen, manufactured by Kao Atlas Co., Ltd.). 910)) was immersed in an aqueous dispersion containing 0.4%.

This strand was heated in an oxygen atmosphere at a temperature increase rate of 5°C/min (required time for infusibility: 60 minutes) and a temperature increase rate of 10°C/min.
C/min (required infusibility time: 30 min) and then carbonized by the method of Example 1. In both cases, fusion occurred and charcoal S fibers that were easily spread into individual filaments were obtained. I couldn't.

Claims (1)

[Claims] 1. A method for making pitch fibers infusible, which comprises applying molybdenum disulfide powder or tungsten disulfide powder to pitch fibers and then subjecting them to infusibility treatment, in the production of pitch-based carbon fibers.