JPS6257929A - Infusibilization treatment of pitch fiber - Google Patents

Abstract

PURPOSE:To infusibilize a pitch fiber safely in a short time and to obtain infusibilized pitch fiber giving a high-quality carbon fiber free from welding, by carrying out the infusibilization treatment of a pitch fiber after applying talc powder to the fiber. CONSTITUTION:Talc powder (having particle diameter of preferably about 0.5-5 mu) is dispersed in water or a solvent (preferably methanol, etc.) at a concentration of preferably 5-50% and the dispersion is applied to a pitch fiber (preferably tow or strand). The fiber coated with talc is heated in an oxidizing atmosphere (preferably air, etc.) at a heating rate of 2-10 deg.C/min and a heat-treating temperature of 300-400 deg.C to effect the infusibilization of the pitch fiber. When water is used as a dispersion medium, preferably 0.05-1.0% nonionic surfactant (e.g. polyoxyethylene alkylphenol ether) is added to the water.

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. Compared to conventional methods that use PAN (polyacrylonitrile) or rayon as raw materials, this method uses cheaper pitch as a raw material, so it is possible to produce cheaper carbon fibers. The use of liquid crystal pitch in the firing process has the advantages of being able to produce 111 ft of high-density, high-elastic carbon without the need for complicated tension treatment in the firing process, and of having a high carbonization yield. Yes, and active research and development is currently underway.

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 a spinning bit to have uniform flow characteristics.

Next, the spun pitch is made into fibers to produce pitch fibers, but melt spinning is usually used to produce continuous filaments.
In addition, cotton-like short fibers or intermediate lengths of IJ&
Centrifugal spinning is usually suitable for producing lit slivers or tows. Spinning temperature, number of discharge nozzles,
Appropriate values can be selected for the discharge m, stretching ratio, etc., depending on the purpose. The fiber diameter of the spun pitch fiber is usually about 5-30μ (Mikukon), and if it is too thick, it tends to impair the characteristics of the fiber, and if it is too thin, it is necessary to ensure the economic efficiency of the spinning process. becomes difficult.

In order to convert pitch fibers into carbon fibers, it is necessary to carry out a so-called infusible process in which thermoplastic pitch fibers are oxidized and converted into infusible 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 pitch fibers and crosslinking pitch molecules, and various gases and liquids are used as oxidizing agents.
It is being proposed. In addition, since such a reaction proceeds from the fiber surface, thin pitch fibers can be rapidly rendered infusible. Pitch ili in the infusibility process! [t is handled in a continuously stretched form or in a form that is accumulated on a conveyor or basket, and an appropriate form can be selected depending on the final form of the target fiber.

Next, the infusible fibers are heated to about 600-3000℃ in an inert gas.
Carbonization treatment is performed to convert the carbon fiber into carbon fiber by heat treatment to a certain degree. (Treatment at 2000℃ or higher is sometimes called graphitization.) Through this treatment, the volatile content in the infusible fibers and the thermally unstable parts 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 similar to that of graphite crystals, resulting in carbon fibers that have 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 yA material is subjected to treatments such as surface treatment, oiling, unwinding, sometimes cutting, and fibrillation as necessary, but 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 carbon! Since troubles that impair the performance of carbon fibers are likely to 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 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 deposited in the area where the pitch fibers contact each other, resulting in pitch IJ and miscellaneous particles adhering to each other. .

Even if the fused pitch fibers are subsequently carbonized and made into carbon fibers, the fibers remain attached to each other, resulting in a lack of flexibility, which significantly impairs the value of the product, or in some cases, reduces the value of the product at all. I don't.

The fusion phenomenon is likely to occur when pitch fibers are handled in a tow or stranded state. Handling pitch fibers in the form of tow or strands is the most suitable method for producing continuous filaments. Industrially, it is 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 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 cause PIi adhesion. In addition, volatile substances generated from the pitch fibers or substances exuded from the pitch fibers are not removed from the fiber bundle 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 pitch fibers infusible. A method using an oxidizing agent solution (for example, Japanese Patent Publication No. 47-21904, Japanese Patent Publication No. 47-21905, etc.), a method using an oxidizing gas (for example, Japanese Patent Publication No. 48-48)
No. 2696, JP-A No. 49-75828, etc.) A method of using both together (e.g., JP-A No. 51-88729, JP-A-49-75828, etc.)
No. 1, 1983-30915, etc.). However, the effect of these techniques is mainly to shorten the infusibility time, and they are insufficient in terms of preventing the fusion of pitch fibers in the form of tows or strands. The use of oxidizing agents such as hydrogen and 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 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, 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 above-mentioned prior art,
The present inventors wish to develop a method using molybdenum disulfide powder or tungsten disulfide powder, and filed a patent application No. 59-2.
813181゜However, these substances have a specific gravity of < (
MoS: 4.8, WS near, 5> In order to obtain a stable dispersion, it was necessary to use particles with a small particle size and to use strong mechanical stirring in combination. Therefore, an object of the present invention is to avoid using peroxides that pose a safety problem, and to prevent sedimentation and separation of solid particle dispersions.
It is an object of the present invention to provide a method for infusible treatment of pitch fibers, which has the effect of enabling safe treatment, for example, preventing stray pitch fibers in the form of tows or strands during infusibility treatment.

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the problem of preventing fusion, and 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 dispersion of fine talc powder in water or a solvent is processed into pitch fibers before infusibility (at an appropriate time from prevention of melting to infusibility). Pitch fibers are heat-treated in an oxidizing gas to make them infusible while still having fine powder attached to them.

The fine talc powder mentioned here is a normal fine talc powder, and any fine talc powder can be used. for example,
Gravel stone from which impurities such as limestone and marble have been removed (5teat
ite) is finely pulverized, impurities are further removed using a special cyclone, and the particles are made uniform, and for the purpose of the present invention, those having an average particle diameter of about 0.5 μ to about 5 μ are preferable. Talc has advantages such as being soft (Mohs hardness 1), not damaging the fragile pitch fibers, having a light ratio tii(2,8), and being cheaper than molybdenum disulfide. In addition, since the mechanism to prevent fusion is to form gaps between pitch fibers, fine particles,
For example, particles smaller than about 0.5 μm are less effective in preventing fusion. Furthermore, it is not economically advisable to use particles that are finer than necessary. The fiber diameter of pitch fiber is usually 5μ to 30
If the particles are coarse, for example larger than about 5μ, it will be difficult to uniformly penetrate between the fibers. In addition, it is difficult to maintain the stability of the dispersion with coarse particles.

The dispersion herein refers to a dispersion of tari powder in a suitable dispersion medium, and a physical method may also be used in order to improve the stability of the dispersion.

The solvents used include hexane, heptane, methanol,
Various substances such as ethanol, acetone, preferably methanol and ethanol 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 IIMi. 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 not preferred because they impede the flow of oxidizing gases. Compared to spraying powder, using it as a dispersion makes it easier to process uniformly and
This is because it easily penetrates between W.

During the treatment, the dispersion is used as it is or after being adjusted to an appropriate concentration. The concentration of talc powder in the dispersion during treatment is preferably 5-50%. During the treatment, if it is a solvent-based treatment, there is no need to add any auxiliary agent, but if it is a water-based treatment, it is necessary to use a surfactant to improve wetting of the pitch m fibers. As the surfactant, any of cationic surfactants, anionic surfactants, and nonionic surfactants can be used, but nonionic surfactants may Examples thereof include polyoxyethylene alkyl phenol ether, polyoxyethylene alkyl ether or ester, and ethylene oxide propylene oxide block copolymer. In addition, the use of a surfactant (d) is undesirable if it is too large because it prevents the flow of oxidizing gas, and if it is too small, the wetting or dispersing effect is insufficient, and it is usually 0.05-1.0. % 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 m-fibers to immediately before the infusibility step. Various treatment methods are possible, including spraying, coating with a rotating roller, and dipping, but Pitch! The talc powder must be applied to the fibers as uniformly as possible.

The effects of the present invention can be obtained regardless of whether optically isotropic pitch or optically anisotropic pitch is used as the spinning pitch that is the raw material for pitch fibers.

The state of the pitch fibers is loosely aligned, so-called 1.
A so-called strand shape in which the fibers are closely aligned is preferably used. It is also possible to use a cotton-like material in which PEL fibers are randomly entangled, or a wool-like material (sliver) in which long fibers are separated and accumulated one by one.

However, in such a configuration, since there are originally 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 can be air, oxygen, ozone, nitrogen dioxide, sulfur dioxide, halogen, etc.
From an economic point of view, the use of air or titanium oxygen is preferred.

The temperature increase rate is suitably about 2 to 10'C/min, and the processing temperature is 300 to 400C.

Effect A3 and Effect When the present invention is applied, the use of the oxidizing agent used in the conventional method is eliminated and the operation is extremely safe. However, by applying the temperature increase rate mentioned above, the time required for infusibility can be appropriately selected. can. For example, the time required for infusibility is 30-1'20
It is also possible to shorten the time to just a minute. 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 fibers, 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 liquid, the filaments come together and the shape of the tow or strand becomes thinner than before wetting it. And it maintains almost the same shape even in the infusible process and the carbonization process.

Although the filaments coming together in this way generally tends to cause the filaments to fuse together during the infusibility treatment, in spite of this, according to the present invention, the talc powder dispersion 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 this excellent effect is that by uniformly applying talc powder to the pitch fibers, the talc powder will enter between the pitches bundled in a strand shape, forming fine gaps, which will cause the fusion. This eliminates the contact points between pitch fibers that cause oxidation, and allows 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.

Example 1 Using coal tar as a raw material, optically anisotropic pitch containing 35% of quinolinous content was melt-spun, and filament 1-diameter 1 was formed.
A pitch fiber strand of 3 microns and 2000 filaments was obtained. In this way, three types of strands were made, and each strand was mixed with (a) 5% by weight, (b) 10% by weight, and (c>
Each was immersed in an ethanol dispersion containing 20% by weight (the dispersion 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 system was carbonized by heat treatment to 1100° C. in an argon atmosphere to obtain carbon fibers. The obtained carbon 1Jilt was easily spread into individual filaments 1 to 1, and no fusion phenomenon was observed in each of the cases (a), (b), and (c).

Example 2 Three types of carbon fibers were produced in the same manner as in Example 1, except that the average particle size of talc was changed to 5 μm. 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 3 Two types of pitch fiber strands of Example 1 were mixed into (c) an aqueous dispersion containing 10% talc with a particle size of 1.4μ and 0.5% of a surfactant, and (d) talc with a particle size of 5μ. They were each immersed in another aqueous dispersion containing 910% surfactant and 0.5% surfactant, and then infusible and carbonized in the same manner as in Example 1. As a surfactant, alkylbenzene sulfonate,
or alkyl 1-helimethylammonium chloride,
Alternatively, polyoxyethylene alkylphenol ether was used, but carbon fibers without fusion were obtained in both cases (c) and (2) above, and in both cases of surfactants.

Comparative Example 1 While melt-spinning an optically anisotropic pitch containing 35% quinolinated content using coal tar as a raw material, water was applied to the filament l- using a rotating roller immediately below the spinning furnace.
Diameter 13 microns to filament 1, filament 1 to number 20
00 treated strands were obtained.

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 loaded and produced in the same manner as Comparative Example 1, except that water was replaced with ethanol. The @ deposition phenomenon occurred and the carbon fiber became rod-shaped.

Comparative Example 3 Carbon fibers were produced in the same manner as in 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 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 the method of JP-A-55-128020 as a comparative example of the present invention (Comparative Example 4), we found that when the temperature increase rate during infusibility was fast, there was no sufficient fusion prevention effect. I couldn't get it.

Comparative Example 4 3.6% of graphite fine particles of pitch fiber strand-shaped dot diameter of 0.7μ of Example 1, ammonium persulfate 0.8%
%, nonionic surfactant [polyoxyethylene nonylphenol ether (Kao 71-Las Co., Ltd. Emulgen 9)
10)) It was immersed in an aqueous dispersion containing 0.4%. This land is heated in an oxygen atmosphere at a heating rate of 5
°C/min (required time for infusibility: 60 minutes) and heating rate: 10
C/min (required time for infusibility: 30 minutes), and then carbonized by the method of Example 1. In both cases, FfA
S occurred, and carbon fibers that could be easily opened into individual filaments could not be obtained.

Comparative Example 5 10fflt of molybdenum disulfide with an average particle size of 1.2μ
Ethanol dispersions containing 10 μm of talc and 10% by weight of 10μ talc were prepared and subjected to particle sedimentation tests. Particles in both dispersions precipitated after 5 minutes.

Claims (2)

[Claims] (1) In the production of pitch-based carbon fibers, a method for infusible treatment of pitch fibers, which comprises applying talc powder to pitch fibers and then performing infusibility treatment. (2) The method according to item 1 above, wherein the talc powder has a particle size of about 0.5 μm to about 5 μm, and the talc is deposited by treatment with water or a solvent dispersion of talc.