JPS62110924A - Production of high performance carbon fiber - Google Patents

Abstract

PURPOSE:To provide a high performance carbon fiber having high strength and elastic modulus, by dividing a temperature region in a carbonization step and controlling the rate of temperature increase in a specific temperature range. CONSTITUTION:An acrylonitrile-based synthetic fiber is subjected to flame- retardant treatment in an oxidizing atmosphere and heat-treated in an inert atmosphere at 300-500 deg.C under tension while controlling the decomposition reaction by keeping the rate of temperature increase to 50-300 deg.C/min. The subsequent heat-treatment is carried out in an inert atmosphere at 400-800 deg.C under tension. The treatment time is adjusted to 0.1-1min to control the condensation cyclization reaction. The formation of fluffs, etc., in the treatment at >=800 deg.C can be suppressed without hindering the reaction at >=800 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing high performance carbon fibers by heat treating an acrylonitrile fiber precursor.

[Traffic technology]

Carbon fiber has high specific strength and specific modulus, and is widely used as a reinforcing material for various composite materials for aerospace, leisure goods, industrial materials, and the like.

However, its performance is still not sufficient, and there is a desire to develop high-performance carbon fibers with even higher strength and elasticity.

In order to produce such high-performance carbon fibers, for example, flame-resistant yarn made of acrylonitrile-based synthetic fibers is heat-treated under tension at 500 to 500°C in an inert atmosphere.
A method has been proposed in which heat treatment is performed by applying tension in an inert atmosphere at a temperature of 0 to 800°C, and then heat treatment is performed in an inert atmosphere at a temperature of 800°C or higher (JP-A-59-1501).
Publication No. 16). By optimizing the temperature profile in each temperature range, this method can be expected to have greater performance effects.

On the other hand, methods for controlling the temperature increase rate in a constant temperature range in the heat treatment process have been studied, for example,
No. 4529, JP-A-59-106522, JP-A-60
Although improved methods have been proposed in various publications, it cannot be said that they are fully effective.

[Problem that the invention seeks to solve]

In manufacturing carbon fiber by heat-treating acrylonitrile yarn synthetic fiber gold, the inventors disclosed
- A method of dividing the temperature range in the carbonization process as proposed in JP-A-150116, JP-A-60-11
The inventors conducted studies aimed at obtaining sufficient effects in the method of controlling the temperature increase rate in a specific temperature range, as proposed in Japanese Patent No. 0925, etc., and as a result, the present invention was achieved.

[The tth way to solve the problem]

The gist of the present invention is to subject acrylonitrile synthetic fibers to flame resistance treatment in an oxidizing atmosphere, and then to
After heat treatment under tension at ~500℃, 400~80℃
When heat treatment is performed while applying tension in an inert atmosphere at 0°C, and further heat treatment is performed in an inert atmosphere at 800°C or higher, the temperature increase rate tl-50 to 300°C/min in the temperature range of 300 to 500°C. This is a method for producing high-performance carbon fiber, characterized in that the processing time in the temperature range of 400 to 800° C. is set to α1 to 1 minute.

The present invention will be explained below with reference to FIG.

FIG. 1 shows the dependence of the expansion and contraction behavior of the yarn on the temperature increase rate when the flame-retardant treatment system used in the example was heat-treated in an inert gas under a constant load.

The vertical axis shows the change in yarn length, and the horizontal axis shows the heat treatment temperature.

In the range of 300 to 500°C, elongation due to decomposition reaction is observed, and in the range of 400 to 800°C, yield due to combinatorial cyclization reaction is observed.

Furthermore, when the temperature increase rate is reduced, the elongation accompanying the decomposition reaction in the 300 to 500°C region becomes smaller. 30
As shown in FIG. 1, the temperature range of 0 to 500° C. is a region where decomposition reactions are dominant, and the decomposition reactions can be suppressed by lowering the rate of temperature rise. The decomposition reaction in the temperature range of C generates defects such as minute voids and cracks on the fiber surface, and also causes relaxation of orientation, thereby causing deterioration in carbon fiber performance. Therefore, in order to produce high-performance carbon fibers, it is necessary to control the decomposition reaction by controlling the heating rate. However, in reality, as shown in the examples, the effect reaches a plateau at a heating rate of less than 50° C./min, and a significant decline in performance begins at a heating rate exceeding 300° C./min.

On the other hand, the temperature range of 400 to 800°C, as shown in Figure 1, is the region in which condensation and cyclization reactions are dominant, and the condensation and cyclization reactions are not affected by the temperature increase rate in this temperature range. It is thought that if the treatment time is prolonged, the condensation and cyclization reaction will proceed too much, thereby hindering the reaction at a temperature of 800° C. or higher, which ultimately determines the performance of the carbon fiber. In fact, as shown in the example, a sudden drop in performance was observed when the processing time exceeded 1 minute.
Ru. However, this 400~8o.

If the processing time in the temperature range of ℃ is too short.

When treated at a temperature of 800° C. or higher, residual decomposed bottom matter will be generated, which is unfavorable from the viewpoint of process passability such as generation of fuzz. When a flame-resistant acrylonitrile synthetic fiber yarn is treated once at 300 to SOO℃ in an inert atmosphere, and then treated again at 800℃ in an inert atmosphere, the N amount decreases by 9% in approximately 11 minutes. It showed a tendency to saturate.

From this, it is considered that the preferable treatment time in the temperature range of 400 to 800°C is 0.1 minute.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples. In addition, the strand strength and elastic modulus are JISR-7601-198.
Measured by 0.

Example 1 Acrylonitrile/methacrylic acid (98/2) copolymer was made into fibers using a semi-dry wet process to produce 120 filaments.
Obtained 00 pieces of multifilament with a single yarn denier of 1.5d. This fiber bundle was subjected to flame-retardant treatment for about 45 minutes while being stretched by a total of 20 degrees in air with a temperature gradient of 230 to 270°C, resulting in a density of 1.35 to 1.36 t/cc.
You can get flame-retardant yarn from.

The above flame-retardant yarn was treated in an inert atmosphere with a linearly increasing temperature profile of 300-500°C, with 8 inches of elongation, and then subjected to a temperature profile with a maximum temperature of 80°C. The performance of the carbon fibers obtained by processing in an inert atmosphere under 4 inch stretching and then processing in an inert atmosphere with a temperature profile with a maximum temperature of 1600 °C is shown in Table 1 together with the experimental conditions. 1st table graves 1 and 6 are comparative examples in which the temperature rise rate in the temperature range of 500 to 500 °C is high;
This is a comparative example with different processing times.

[Brief explanation of drawings]

FIG. 1 shows the relationship between the expansion/contraction behavior of yarn and the rate of temperature increase when the flame-retardant treatment system used in the examples was heat-treated.

Claims (1)

[Claims] Acrylonitrile synthetic fibers are flame-resistant treated in an oxidizing atmosphere, then heat treated under tension at 300-500°C in an inert atmosphere, and then heat-treated under tension at 400-800°C in an inert atmosphere. and further heated to 800℃
When performing heat treatment under the above inert atmosphere, 300~
Temperature increase rate in the temperature range of 500℃ to 50 to 300℃
1. A method for producing high-performance carbon fiber, characterized in that the processing time is 0.1 to 1 minute in a temperature range of 400 to 800°C.