JPS6132406B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing carbon fibers using so-called pitches.

During the production of carbon fibers, fibers made from pitts treated with tetrahydroquinoline have a short time for infusibility by oxidation, but the carbonization treatment following infusibility is performed in an inert gas atmosphere. Despite this, the strength decreases due to the influence of trace amounts of oxygen contained in the fiber bundle.

As a result of intensive studies to improve these drawbacks, the present inventors decided to pass the fibers obtained from oxidized pitch through a cyclic liquid and/or to pass an inert gas containing less than 100 PPM of oxygen. The oxygen content is then
Obtaining carbon fibers whose strength does not decrease by carbonization treatment in an inert gas having a concentration of less than 100 PPM,
We have arrived at the present invention.

That is, the present invention oxidizes fibers obtained from pitches treated with tetrahydroquinoline and then reduces the free oxygen content of the oxidized fibers.
Provided is a method for producing carbon fibers using pits, which comprises treating the fibers so that the oxygen content is less than 100 PPM, followed by carbonization in an inert gas having an oxygen content of less than 100 PPM, and graphitization if necessary. do.

The pitches used in the present invention include, for example, petroleum pitch, coal tar pitch, natural asphalt, and pitch-like substances produced as by-products during industrial production, and are subjected to ring treatment with tetrahydroquinoline. Tetrahydroquinoline, which is used for the ring treatment of pitches, also acts as a solvent for pitches. This tetrahydroquinoline ring element pitch has a softening point of 60, for example.
Coal tar pitch at ~150°C and tetrahydroquinoline are contained in equal weights, dissolved, and the insoluble matter is filtered, followed by heat treatment at 350~530°C, followed by removal of tetrahydroquinoline, and then at 400~530°C. Heat treated under reduced pressure to adjust the softening point to 200-320°C. This pitch is heated to a temperature 20~50℃ higher than the softening point, with a nozzle diameter of 0.5~0.15mm, and a spinning speed of 200~200mm.
Spinning at 1000 m/min yields 50-15 micron fibers. This fiber is oxidized in air at a temperature approximately 50°C below its softening point, e.g. 260°C, approximately 15°C.
The surface is oxidized and becomes infusible in a short period of ~60 minutes.

Such oxidized fibers contain free oxygen, which causes deterioration of the carbon fibers during the next step of carbonization treatment, and is inefficient because it is necessary to slow down the temperature rise during carbonization.

Therefore, the present invention aims at passing such oxidized fibers through a cyclic liquid or reducing the oxygen content.
The amount of free oxygen contained in the fiber is reduced to 100 PPM or less by passing it through an inert gas of 100 PPM or less, or by treating it under reduced pressure.

Examples of cyclic liquids that can be used to reduce the free oxygen content in oxidized fibers to 100 PPM include thiosulfate, sulfite, sulfinic acid, sulfenic acid; catechol,
Examples include compounds having two or more hydroxyl groups on an aromatic group such as hydroquinone and resorcinol. This cyclic liquid is preferably one whose pH is adjusted to 9 or more with an alkali, and may be diluted with alcohol, acetone, or the like. An easy method for reducing the amount of oxygen in the fibers is to place the fibers that have been oxidized in an inert gas such as nitrogen or argon into a container and carry out displacement under reduced pressure. Incidentally, after the treatment with the above-mentioned cyclic liquid, performing a vacuum displacement treatment with an inert gas is more effective in controlling the free oxygen in the fibers to less than 100 PPM.

Without exposing the fibers treated as above to an oxygen atmosphere of 100 PPM or more, an oxygen-containing inert gas of less than 100 PPM, such as nitrogen, helium, etc.
Carbonized in argon and graphitized if necessary.

At this time, carbonization is usually carried out at approximately 800 to 1500°C in a metal furnace or refractory brick furnace under an inert gas atmosphere.
It is carried out under conditions of 5 to 60 minutes. Furthermore, if necessary, graphitization is usually performed in a graphite furnace under an atmosphere of argon or helium at about 1500 to 3000°C for 5 to 50 minutes.
It is carried out under the conditions of 60 minutes.

The carbon fiber obtained by the method of the present invention has excellent physical properties such as strength and elastic modulus. below,
The invention will be further illustrated by examples. In addition, parts represent parts by weight.

Example 1 Softening point after ring treatment with tetrahydroquinoline
18 micron fibers spun from pitch at 290°C were oxidized in air at 260°C for 20 minutes. This fiber was mixed with 12 parts of sodium thiosulfate, 0.5 part of resorcinol,
It was immersed in a cyclic liquid consisting of 100 parts of water and 5 parts of sodium hydroxide for 15 minutes, and then washed with water. Note that this immersion bath was replaced with nitrogen gas containing 50 PPM of oxygen. After washing with water, the fibers were vacuumed to 10 mmHg. The oxygen content of this fiber was 20 PPM. Next, it was dried in a 220° C. furnace purged with nitrogen gas, and heated in the same furnace at a rate of 50° C./min to 1500° C. for 30 minutes to obtain carbon fibers. The strength of this carbon fiber is
295Kg/mm ² , and the elastic modulus was 26t/mm ² .

For comparison, immediately after oxidation treatment, the test was carried out at 50℃/min in a nitrogen gas atmosphere containing 150PPM oxygen.
The carbon fiber obtained by heating it to 1500°C for 30 minutes had a strength of 155 Kg/mm ² and an elastic modulus of 12 t/mm ² .

Example 2 Softening point after ring treatment with tetrahydroquinoline
Using 21 micron thread spun from pitch at 250℃, 3 parts of hydroquinone and water are used as the cyclic liquid.
Carbon fibers were obtained in the same manner as in Example 1 except that a 100 parts dipping bath was used. The strength of this fiber is 208Kg/
mm ² and elastic modulus of 12t/mm ² .

For comparison, a carbon fiber carbonized in nitrogen gas containing 150 PPM of oxygen immediately after the oxidation treatment had a strength of 168 Kg/mm ² and an elastic modulus of 9.8 t/mm ² .

Claims (1)

[Claims] 1. After oxidizing fibers obtained from pitches treated with tetrahydroquinoline, the fibers are treated so that the free oxygen content of the oxidized fibers is less than 100 PPM, and then the oxygen content is
A method for producing carbon-based fibers using pitches, characterized by carbonization treatment in an inert gas of less than 100 PPM, and graphitization treatment if necessary.