JPH02454B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a method for producing carbon fibers (including graphite fibers) using pitch as a raw material, and more specifically, to a method for manufacturing carbon fibers (including graphite fibers) using pitch as a raw material. The present invention relates to a method for producing carbon fibers that prevents filament fusion and eliminates adhesion and fusion between fibers.

Conventional technology Generally, in the method of manufacturing carbon fiber using pitch as a raw material, first a spinning pitch is prepared, and then the resulting spinning pitch is turned into fibers to produce pitch fibers. Usually, melt spinning method is suitable.

In a method for manufacturing carbon fibers using pitch as a raw material, one of the important issues is handling the fragile pitch fibers without damaging them.

It is a well-known fact that individual pitch fiber filaments are extremely fragile and can be easily broken by the slightest external force, and it is industrially impossible to handle pitch fibers in the form of single fibers without breaking. It is no exaggeration to say that.

In order to handle pitch fiber filaments, which are fragile and prone to ballooning due to static electricity, in a form that does not break and is easy to handle, fiber bundles are prepared by aligning the filaments together and converging them with some kind of liquid treatment agent. It is desirable to have a shape (strand shape).

On the other hand, infusibility in the form of strands is a disadvantageous method in terms of preventing fusion.
In addition, in order to convert pitch fiber into carbon fiber,
Prior to heating and carbonization, it is necessary to perform a so-called infusible process in which thermoplastic pitch fibers are oxidized and converted into infusible fibers that do not melt even when heated.

This is because pitch fibers are bundled at high density in the strand form and have a large number of continuous contact points in the length direction. In such a state, if the pitch fibers are softened by heating for infusibility treatment, not only will fusion easily occur at each contact point, but the heat generated by the pitch oxidation reaction will accumulate inside the strands, causing partial damage. Because a high-temperature area is created in the area, pitch fibers that come into contact with each other melt and fuse together.
In addition, volatile substances generated from pitch fiber,
Alternatively, 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 causes fusion.

If the fiber bundle is only temporarily bundled, it is sufficient to attach water, solvent, etc., but after drying, such fiber bundles become hard and brittle, and require infusible treatment. The subsequent threads are also firmly adhered to each other and cannot be made into a flexible fiber bundle even after carbonization.

When an aqueous surfactant solution is used, a flexible fiber bundle can be obtained at the pitch fiber stage, but after infusibility and carbonization treatment, only so-called fused carbon fiber bundles can be obtained, which are firmly adhered to each other. I can't.

Therefore, as a surface treatment agent for handling pitch fibers and preventing fusion during the infusibility process,
Various treatment agents have been proposed to solve the above problems, but each of the conventional treatment agents has its own drawbacks.

For example, there is an example in which silicone oil having specific properties is used as a surface treatment agent for pitch fibers (Japanese Patent Laid-Open No. 88124/1983). However, if a highly volatile liquid oil such as silicone oil is used, it will evaporate and transpire during storage or during the initial stage of infusibility, and the oil itself will not be present during the firing process. If a material with low volatility is used, an oil film will be formed on the pitch fiber surface during the infusibility process, which will prevent the flow of oxidizing gas and inhibit infusibility. Therefore, it can be said that although such a liquid oil agent improves the handling of pitch fibers immediately after winding, it cannot be expected to have an effect of preventing fusion during the infusibility process.

For example, there is an example in which various solid particles are attached to the surface of pitch fibers (Japanese Patent Application No. 195400/1983). Also,
Example of combining solid particles and silicone oil (Special Publications 1986-
24681), and there is also an example of a combination of solid particles and a water-soluble oxidizing agent (Japanese Patent Application No. 249833/1983). These methods are
The presence of solid particles between the pitch fibers prevents the pitch fibers from coming into contact with each other to prevent fusion, and also promotes gas flow between the fibers. However, these methods
During manufacturing, solid particles adhering to the surface may fall off and contaminate the process, and when made into plastic composites, solid particles remaining on the fiber surface may exist at the interface between carbon fiber and resin, preventing strong adhesion between carbon fiber and resin. It has the disadvantage of being a hindrance.

There is also an example of making the surface of pitch fiber infusible by immersing it in an oxidizing agent solution (Japanese Patent Publication No. 47-21904). but,
It is difficult to complete infusibility by simply immersing the oil in an oxidizing agent solution, and usually, infusibility treatment in a heated oxidizing atmosphere is also used. Fusion cannot be prevented for the same reasons stated.

For these reasons, conventional sizing agents or surface treatment agents for pitch fibers have not been industrially satisfactory.

Problems to be Solved by the Invention The present invention is a method for producing carbon fibers that solves the drawbacks of the above-mentioned sizing agents or surface treatment agents for pitch fibers by using a special solid lubricant.

Means for Solving the Problems As a result of our research aimed at making it possible to easily handle spun fibers without damaging them, and improving the drawbacks of the conventional surface treatment agents mentioned above, we have developed the present invention. They reached the following conclusions.

(1) By attaching a liquid component to the pitch fibers, they are given binding properties, and the pitch fibers are handled in a bundled form. The liquid component should preferably be one that does not damage the pitch fibers and evaporates at 150°C or lower.

(2) Particulate solids are attached to pitch fibers to prevent fusion during the infusibility process. This particulate solid is usually treated with pitch fibers in the form of a dispersion liquid, but by being dissolved in the dispersion liquid or softened and melted during the infusibility process, it forms a continuous film on the pitch fibers, allowing gas to escape. Anything that impedes distribution is not appropriate. In addition, in order to give smoothness to the pitch fiber bundle, the particulate solid must have smoothness or lubricity, and in order to penetrate uniformly between the pitch fibers, it must have a fine particle size, specifically, the average It is preferable that the particle size is about 3 μm or less.

(3) By using a substance that does not change during the infusible process and disappears during the carbonization process as a particulate solid, it is possible to obtain carbon fibers with a clean surface without adding processes such as washing after carbonization. can.

And specifically, MCA (Melamine
It has been found that a water or solvent dispersion of a substance called cyanuric acid adduct (melamine-cyanuric acid adduct) is a surface treatment composition that satisfies the above requirements. MCA can be obtained commercially as a white fine powder solid lubricant with an average particle size of 1 to 2 μm. Almost insoluble in water and organic solvents,
Regardless of which dispersion medium is selected, pitch fibers can be treated as a solid dispersion. MCA
To obtain an aqueous dispersion of
% of surfactant is added and dispersed in water. As the surfactant, a nonionic surfactant such as a block copolymer of ethylene glycol or propylene glycol can be used.

When an organic solvent is used, a dispersion liquid is usually obtained only by mechanical dispersion. As the organic solvent for the dispersion medium, for example, methanol, ethanol, acetone, silicone oil (low boiling point), etc. can be used.

The concentration of MCA in the dispersion is 2 to 30% by weight.
% is appropriate. If the concentration is low, the desired effect cannot be obtained, and if the concentration is high, it is economically disadvantageous.

Any method can be used to treat the pitch fibers with the dispersion, such as spraying, applying with a touch roller, or dipping, but it is practical to treat the pitch with a spray or touch roller immediately after the pitch is turned into fibers. It is.

Pitch fibers coated with MCA particles can be rendered infusible by heat treatment in an oxidizing gas (usually air). Infusibility is achieved by gradually raising the temperature from about 150°C to about 350°C. For infusibility, the oxidizing gas must be sufficiently supplied to the pitch fibers, and the heat generated by the reaction between the pitch fibers and the oxidizing gas, as well as the volatile matter from the pitch fibers, must be appropriately removed. is necessary.

Carbonization is carried out by heating the infusible fibers in an inert gas such as argon or nitrogen at a temperature of 800 to 1500°C, higher if necessary, for example to about 3000°C. Most of the elements other than carbon in the infusible fibers are released by carbonization, and carbon fibers can be obtained.

Effects In the above process, MCA exhibits the following effects.

(1) Since it is insoluble in water and solvents, it can be treated as a particle dispersion.

(2) The specific gravity is light (1.52) and the stability of the dispersion is good.

(3) Because it is white, it does not pollute the environment.

(4) Since it has lubricity, it gives smoothness to the collected pitch fiber bundles.

(5) Since it is powder-like, it prevents the pitch fibers from coming into contact with each other and preventing fusion.

(6) As understood from the thermogravimetric analysis curve of MCA in Figure 1, it disappears through sublimation or decomposition during the carbonization process (at temperatures above 430°C). Therefore, it does not remain on the surface of the carbon fiber after carbonization (the heat loss curve of MCA is shown).

As previously mentioned, water or solvent dispersions of MCA are
Shows excellent effects as a surface treated product for pitch fibers.

Hereinafter, the present invention will be explained using specific examples, and its effects will be shown.

Example 1 Coal tar pitch was used as a raw material, mixed with twice the amount of tetralin, and heated in an autoclave for 450 min.
After heating at ℃ for 10 minutes, it was filtered and distilled to obtain hydrogenated pitch. This hydrogenation pitch was heated at 470°C under reduced pressure for 10
Heat treated for minutes, QI content (quinoline insoluble content) 35%,
A mesophase pitch with a softening point of 285°C and an optical anisotropy of 95% was obtained. This mesophace pitch,
The mixture was put into a spinning furnace having a spinneret with a nozzle diameter of 0.2 mm and a number of holes of 400, and was spun at a spinning temperature of 345° C. and at a winding speed of 800 m/min to obtain pitch fibers with a fiber diameter of 13 μm.
The pitch discharged from the nozzle is stretched and cooled.
Immediately after solidifying into pitch fibers and before being collected into fiber bundles using a ceramic focusing guide, the fibers were treated with an MCA water dispersion stream using a spray method. The MCA dispersion has an average particle size of 1 to 2μ.
It was prepared by stirring 15 parts of MCA powder, 0.5 parts of polyoxyethylene nonyphenol ether, and 84.5 parts of water using a homogenizer. The pitch fiber bundles treated with the MCA dispersion were wound into plastic tubes and then unwound and stacked on stainless steel mesh baskets while wet. The pitch fiber bundles collected on this stainless steel basket were put into a hot air heating furnace (air atmosphere), and
Infusibility was achieved by raising the temperature from °C to 330 °C over 3 hours. The obtained infusible fiber is
There was no fusion and it was easily defibrated. Next, this infusible fiber was placed in a heating furnace in a nitrogen atmosphere, and the temperature was gradually raised to perform a carbonization treatment at 1100° C. for 10 minutes. After cooling, the obtained carbon fiber has no fusion, has a tensile strength of 255 Kg/mm ² , and a tensile modulus of 16.2 ton/mm ²
showed that. Furthermore, when the obtained carbon fibers were strongly squeezed with fingertips, no substance that would contaminate the fingertips was observed. As shown in FIG. 2, there is very little deposit on the fiber surface.

Example 2 In the method of Example 1, an aqueous dispersion of MCA was
Ethyl alcohol dispersion of MCA (15 parts of MCA and 85 parts of ethanol stirred with a homogenizer)
Carbon fibers were produced in the same manner as in Example 1 except that the treatment method was changed from the spray method to the application method using a rotating roller. The obtained carbon fibers had no fusion, had a tensile strength of 246 Kg/mm ² , a tensile modulus of elasticity of 15.9 ton/mm ² , and had no contaminants attached to them.

Example 3 Using a method similar to that used in Example 1, substituting deionized water for the MCA dispersion as the surface treatment, the focused pitch fibers were wound onto a plastic bobbin. While the resulting pitch fiber was still wet, it was rewound and cut into 30 cm lengths, and immersed in a 5% dispersion of MCA (15% MCA dispersion of Example 1 diluted 3 times with water). After pulling it up, it was collected in a stainless steel mesh basket. Next, infusibility and carbonization were performed in the same manner as in Example 1 to obtain carbon fibers. The obtained carbon fiber had no fusion, a tensile strength of 252 Kg/mm ² , and a tensile modulus of 16.5 ton/mm ² .
Moreover, the presence of any substance contaminating the surface was not observed.

Comparative Example In the method of Example 3, an ethanol dispersion of MCA was mixed with an aqueous graphite dispersion (10 parts of natural graphite powder with an average particle size of 1 μm, 0.5 parts of sodium alkylbenzenesulfonate, and 89.5 parts of water) using a propeller-type stirrer. Carbon fibers were produced in the same manner as in Example 3, except that the carbon fibers were replaced with The obtained carbon fiber was free from fusion, had a tensile strength of 242 Kg/mm ² , and a tensile modulus of elasticity of 242 Kg/mm 2
It was 15.1ton/ ^mm2 . When this carbon fiber was strongly squeezed with a fingertip, the remaining graphite powder rose up in the form of dust, and also stained the fingertip black. As shown in FIG. 3, the amount of deposits on the carbon fiber surface was extremely large and dispersed over the entire surface of the fiber.

[Brief explanation of drawings]

FIG. 1 shows a thermogravimetric analysis curve (TGA) and a differential thermal analysis curve of the melamine-cyanuric acid adduct (MCA) used in the present invention (experimental conditions: in air, heating rate 10° C./min). FIG. 2 is an enlarged view (1000x magnification) of carbon fiber using MCA according to the present invention. FIG. 3 is an enlarged view (1000x magnification) of carbon fiber using fine particulate graphite as a treatment agent.

Claims (1)

[Scope of Claims] 1. In a method for producing carbon fiber in which pitch fibers are infusible and then carbonized, the pitch fibers contain particulates that are solid during the infusibility treatment and sublimate and decompose during the carbonization treatment. A method for producing carbon fibers, which comprises applying a solid lubricant and then performing an infusibility treatment. 2. The carbon fiber manufacturing method according to claim 1, wherein the particulate solid lubricant is a melamine-cyanuric acid adduct.