JPH041091B2 - - 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. Compared to conventional methods that use PAN (polyacrylonitrile) or rayon as raw materials, this method uses inexpensive pitch as a raw material, making it possible to produce carbon fiber at low cost. Pitch has the advantages of being able to produce high-strength, high-elastic carbon fiber without complicated tension treatment during the firing process, and has a high carbonization yield, and is currently being actively used. Research and development is underway.

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 stretching ratio, etc., depending on the purpose. The fiber diameter of spun pitch fibers is usually around 5-30μ (microns), and if it is too thick, it tends to impair the characteristics of the fiber, and if it is too thin, it is difficult to ensure the economic efficiency of the spinning process. become.

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 of 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 being gradually heated to carry out an oxidation reaction. However, if the reaction is not properly controlled during this process, runaway reactions such as melting and ignition may occur, or runaway reactions may occur. Even when no reaction occurs, a phenomenon called "fusion" often occurs, 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. It is industrially extremely difficult to obtain high quality continuous carbon fibers. 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 contact points of the fibers, which acts as a type of bonding agent 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.
Japanese Patent Publication No. 48-42696, Japanese Patent Publication No. 49-75828, etc.) A method of using both together (For example, Japanese Patent Publication No. 51-88729,
JP-A No. 59-30915, etc.). However, the effect of these techniques is mainly to shorten the infusibility time, and in terms of preventing the fusion of pitch fibers in the form of tows or strands,
Both are insufficient, and hydrogen peroxide,
The use of oxidizing agents such as chromic acid is undesirable from the viewpoint of process safety.

A technique using a combination of a water-soluble oxidizing agent, a water-soluble surfactant, and a fine graphite powder has also been proposed as a method for preventing the fusion of pitch fiber strands (Japanese Patent Application Laid-Open No. 128020/1982). However, since this technique also uses an oxidizing agent, it is unfavorable from a safety standpoint as described above.

In order to solve the various problems of the prior art described above, the present inventors developed a method using molybdenum disulfide powder or tungsten disulfide powder (Japanese Patent Application No. 59-281318). However, these substances have a heavy specific gravity (MoS ₂ : 4.8, WS: 7.5), and in order to obtain a stable dispersion, it is necessary to use particles with a small particle size and use strong mechanical stirring. Ta.

Therefore, an object of the present invention is to produce pitch fibers in the form of tows or strands, which do not use peroxides that pose a safety problem and which prevent sedimentation and separation of solid particle dispersions to enable safe processing. An object of the present invention is to provide a method for making pitch fibers infusible, which has the effect of preventing fusion during the infusibility treatment of pitch fibers.

Means for Solving the Problems As a result of intensive study on the problem of preventing fusion, the present inventors have completed the present invention, which has a remarkable effect on preventing fusion as described above, unlike the prior art. did.

The method that achieves the above effects is surprisingly simple; a water or solvent dispersion of fine talc powder is processed into pitch fibers before it becomes infusible (at an appropriate time from melting prevention to infusibility). This can be achieved by heat-treating the pitch fibers in an oxidizing gas with the fine powder attached to them to make them infusible.

The fine talc powder mentioned here is a normal fine talc powder, and any fine talc powder can be used. For example, steatite from which impurities have been removed, such as limestone or marble, is pulverized and the impurities are further removed using a special cyclone, so that the particles are uniform. 0.5μ to about 5μ is preferred. Talc has advantages such as being soft (Mohs hardness: 1), not damaging the fragile pitch fibers, having a light specific gravity (2.8), and being cheaper than molybdenum disulfide. Furthermore, since the mechanism for preventing fusion is to form gaps between pitch fibers, particles that are fine to a certain extent, for example particles smaller than about 0.5μ, have a reduced fusion prevention effect. Furthermore, it is not economically advisable to use particles that are finer than necessary. The fiber diameter of Pituchi fiber is normal.
Since the particle size is about 5μ to 30μ, the particles are coarse, e.g.
If it is larger than about 5μ, it becomes difficult to penetrate uniformly between the fibers. In addition, it is difficult to maintain the stability of the dispersion with coarse particles.

The dispersion liquid referred to herein is one in which talc powder is dispersed in a suitable dispersion medium, and a physical method may be used in combination to help stabilize the dispersion.
Various solvents can be used such as hexane, heptane, methanol, ethanol, acetone, preferably methanol and ethanol.
It is also possible to use water. 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
A solvent with a temperature exceeding 200°C is undesirable because it obstructs the flow of oxidizing gas. This is because the use of a dispersion allows for easier uniform treatment and easier penetration between fibers than when spraying powder.

At the time of treatment, the dispersion is used as it is or after adjusting to an appropriate concentration. The concentration of talc powder in the dispersion during processing 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, and ethylene oxide propylene oxide block copolymer. In addition, if the amount of surfactant used is too large, it may prevent the flow of oxidizing gas, which is undesirable.
If the amount 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 turned into fibers to immediately before the infusibility step. Various treatment methods are possible, including spraying, coating with a rotating roller, and dipping.
The talc powder must be applied 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 can also be applied in the form of cotton, in which short fibers are randomly intertwined, or in the form of a woom (sliver), in which long fibers are separated and accumulated one by one. However, in such a configuration, of course, since there are few contact points, the effect of the present invention is also small.

The infusibility treatment after depositing the talc powder is carried out by applying heat treatment while increasing the temperature in an oxidizing gas. The oxidizing gas used for infusibility is air,
Oxygen, ozone, nitrogen dioxide, sulfur dioxide, halogen, etc. can be used, but from an economic point of view, it is preferable to use air or oxygen. The heating rate is 2 to 10
Approximately ℃/min is appropriate, and the maximum processing temperature is 300℃.
℃~400℃.

Actions and Effects When the present invention is applied, the use of the oxidizing agent used in the conventional method is eliminated and operation is extremely safe, but the time required for infusibility can also be appropriately selected by applying the temperature increase rate mentioned above. . For example, the time required for infusibility can be shortened to 30 to 120 minutes. In addition, in the conventional method using an oxidizing agent, it is not possible to prevent fusion even if it takes more than 120 minutes for infusibility, and in order to obtain high-quality carbon fiber, it is necessary to infusibility for an even longer time. Ta.

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 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 talc powder The treated pituti fiber goes through an infusible process,
After the carbonization step, by slight squeezing, carbon fibers that are easily separated into individual filaments and are free from fusion can be obtained.

The reason for this excellent effect is that by uniformly applying talc powder to the pitch fibers, the talc powder can enter between the pitch fibers bundled into strands, forming fine gaps, which can lead to fusion bonding. This eliminates the contact points between the pitch fibers that cause oxidation, and allows the oxidizing gas to flow between the fibers, allowing the oxidation reaction to proceed uniformly and reducing the volatilization generated from the pitch fibers during infusibility. This is because sexual substances can be quickly removed.

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.

Reference 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. In this way, three types of strands were made, and each of the strands was treated with ethanol containing (a) 5% by weight, (b) 10% by weight, and (c) 20% by weight of talc with an average particle size of 1.4μ. Each was immersed in a dispersion (which was stable for 1 hour). Each of these treated strands was heat treated in an oxygen atmosphere at a heating 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 in each of the cases (a), (b), and (c).

Reference Example 2 Three types of carbon fibers were produced in the same manner as in Reference Example 1, except that the average particle size of talc was changed to 5μ. The three types of carbon fibers obtained were easily opened into individual filaments, and no fusion phenomenon was observed. Note that the dispersion used was stable for 30 minutes.

Example Two types of pitch fiber strands of Reference Example 1 were (c)
Immersion treatment in an aqueous dispersion containing 10% talc with a particle size of 1.4μ and 0.5% surfactant, and (d) another aqueous dispersion containing 10% talc with a particle size of 5μ and 0.5% surfactant, respectively. Thereafter, they were made infusible and carbonized in the same manner as in Example 1. As the surfactant, alkylbenzene sulfonate, alkyltrimethylammonium chloride, or polyoxyethylene alkylphenol ether was used.
Carbon fibers free from fusion were obtained in both cases (c) and (d) and in all cases of surfactants.

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 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 Reference Example 1, it became rod-shaped carbon fibers due to the fusion phenomenon.

Comparative Example 2 Carbon fibers were produced in the same manner as in Comparative Example 1, except that water was replaced with ethanol. A fusion phenomenon occurs,
It turned into a rod-shaped carbon fiber.

Comparative Example 3 Carbon fibers were produced in the same manner as in Reference Example 1, except that the dispersion medium for talc 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 4),
When the rate of temperature increase during infusibility was high, a sufficient effect of preventing fusion could not be obtained.

Comparative Example 4 Pitch fiber strands of Reference Example 1 were used with a particle size of 0.7μ.
The sample was immersed in an aqueous dispersion containing 3.6% of graphite fine 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 is placed in an oxygen atmosphere.
Temperature increase rate during infusibility: 5°C/min (time required for infusibility: 60
min) and heating rate 10°C/min (required time for infusibility 30°C)
When the carbon fibers were made infusible by the method described in Reference Example 1, fusion occurred in both cases, and carbon fibers that could be easily spread into individual filaments could not be obtained.

Comparative Example 5 10% by weight of molybdenum disulfide with an average particle size of 1.2μ
of ethanol dispersion, and 10μ of talc.
An ethanol dispersion containing 10% by weight was prepared and a particle sedimentation test was conducted. Particles in both dispersions precipitated after 5 minutes.

Claims (1)

[Claims] 1. In the production of pitch-based carbon fibers, pitch fibers are soaked in water containing a surfactant with an average particle size of 0.5 to 5μ.
1. A method for infusible treatment of pitch fibers, which comprises applying a dispersion of 5 to 50% by weight of talc powder and then infusibility treatment.