JPS58144124A - Preparation of carbon fiber using pitch - Google Patents

Abstract

PURPOSE:To otain carbon fibers having improved strenth, modulus of elasticity, etc., by oxidizing fibers obtained from a reduced pitch, treating the oxidized pitch to give a specific content of free acid groups, and carbonizing and graphitizing the treated fibers. CONSTITUTION:Fibers obtained from a pitch reduced with tetrahydroquinoline are oxidized at a temperature 50 deg.C lower than the softenining point thereof in air, passed through a reducing liquid or an inert gas having <=100ppm content of oxygen or treated under reduced pressure to give <100ppm content of free acid groups in the fibers. The treated fibers are then carbonized at 800-1,500 deg.C in an inert gas with <100ppm content of oxygen and if necessary graphitized at 1,500-3,000 deg.C.

Description

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

In the production of carbon fibers, IAM made of pitches that have been reduced by tetrahydroquinoline has the characteristic that the infusibility treatment process due to oxidation is short, but the carbonization treatment that follows the infusibility treatment is performed in an inert gas atmosphere. Nevertheless, 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 authors have decided to pass fibers obtained from oxidized pitch through a reducing liquid and/or to improve 1100PP.
By passing through an inert gas containing less than 1,000 PP of oxygen and replacing under reduced pressure, and then carbonizing in an inert gas with an oxygen content of less than 1,100 PP, carbon fibers with no decrease in strength were obtained, and the present invention was achieved. It was.

That is, the present invention oxidizes fibers obtained from pitches that have been reduced with tetrahydroquinoline, then treats the oxidized fibers so that the free oxygen content is less than 1100 PP, and then Provided is a method for producing carbon-based fibers using pitches, which is characterized by carbonization treatment in an inert gas having an amount of less than 1100 PP and, if necessary, graphitization treatment.

The pitches used in the present invention are, for example, petroleum pitch, coal tar pitch, natural asphalt, and pitch-like substances produced as by-products during industrial production, and are reduced with tetrahydroquinoline. Tetrahydroquinoline used to reduce pitches also acts as a solvent for pitches. This reduced tetrahydroquinoline pitch is produced by mixing equal weights of coal tar pitch with a softening point of 60 to 150°C and tetrahydroquinoline, dissolving it, filtering out insoluble matter, and then heat-treating it at 350 to 530°C to remove tetrahydroquinoline. It is heated under reduced pressure at 400-530°C to adjust its softening point to 200-320°C. This pitch is heated to a temperature 20 to 50 degrees Celsius higher than its softening point, using a nozzle diameter of 0.5 to 0.15 m and a spinning speed of 200 to 10 m.
When spinning at 00 m/min, fibers of 50-15 microns are obtained. This fiber is oxidized in air at a temperature about 50°C lower than its softening point, for example, 260°C, about 15 to 60°C.
The surface is oxidized and becomes infusible in a short period of minutes.

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

Therefore, in the present invention, the oxidized fibers are passed through a reducing liquid, passed through an inert gas having an oxygen content of 1100 PP or less, or subjected to reduced pressure treatment to eliminate the content contained in the fibers. The amount of free oxygen is 110
Keep it below 0PP.

In order to reduce the free oxygen content in the oxidized fiber to 1100 PP, a compound having two or more hydroxyl groups in the oxidation treatment can be used.

The reducing liquid in step 11 is preferably one in which IIIH is adjusted to 9 or more with an alkali, and may be diluted with alcohol, acetone, or the like.

Also, an easy way to reduce the amount of oxygen in fibers is to use nitrogen,
There is also a method in which fibers that have been oxidized in an inert gas such as argon are placed in a container and replaced under reduced pressure. Note that after the treatment with the reducing liquid, performing a vacuum displacement treatment with an inert gas is more effective in controlling the free oxygen in the fibers to less than 1100 PP.

The fibers treated as described above are carbonized and optionally graphitized in an oxygen-containing inert gas of less than 1100 PP, such as nitrogen, helium, or argon, without exposing them to an oxygen atmosphere of 1100 PP or more.

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

The carbon fiber obtained by the method of the present invention has excellent physical properties such as strength and elastic modulus. The present invention will be further explained below with reference to Examples. In addition, parts are parts by weight.

Example 1 Softening point 290°C after reduction treatment with tetrahydroquinolin
18 micron fibers spun from a pitch of
Oxidation treatment was performed at 60°C for 20 minutes. The fibers were immersed for 15 minutes in a reducing liquid consisting of 12 parts of sodium thiosulfate, 0.5 parts of resorcinol, 100 parts of water, and 5 parts of sodium hydroxide, and then washed with water. In fact, this immersion tank is purged with nitrogen gas containing 50 PPM of oxygen. After washing with water, remove the fibers by 10
The pressure was reduced to Tsuru Hg.

The at,* content of this fiber was 20 PPM. Then dried in a 220°C oven purged with nitrogen gas,
In the same furnace, the temperature was raised to 1500°C at a rate of 50°C/min and heated for 30 minutes to obtain carbon fibers. The strength of this carbon fiber was 295 mm/-1, and the elastic modulus was 26 t/w.

For comparison, immediately after the oxidation treatment, the temperature was 1500°C at 50°C/min in a nitrogen gas atmosphere containing 150 PPM oxygen.
The strength of carbon fiber obtained by heating for 30 minutes at a temperature of 15
5kg/-1 elastic modulus was x2t/l:.

Example 2 A 21 micron yarn spun from pitch with a softening point of 250°C that had been reduced with tetrahydroquinoline was used, and a dipping bath containing 3 parts of hydroquinone and 100 parts of water as the reducing liquid was used, but in the same manner as in Example 1. Carbon fiber was obtained. The strength of this fiber was 208 kg/j, and the elastic modulus was 12 t/-.

For comparison, the strength of carbon fiber that was immediately carbonized in nitrogen gas containing 150 PPM oxygen after oxidation treatment was 16.
8-/-1 elastic modulus was 9.81/-.

Patent applicant Dainippon Ink and Chemicals Foundation
Materials Physics and Chemistry Research Institute 5-

Claims (1)

[Claims] After oxidizing fibers obtained from pitches that have been reduced with tetrahydroquinoline, the oxidized fibers are treated so that the free oxygen content of the oxidized fibers is less than 1100 PP, and then the fibers are treated with non-oxidized fibers having an oxygen content of less than 1100 PP. A method for producing carbon-based fibers using pitches, which comprises carbonizing in an active gas and graphitizing if necessary.