JPS61119712A - Production of carbon fiber having high strength - Google Patents

Abstract

PURPOSE:To produce the titled fiber free from fluffing, stably, by heat-treating a polyacrylonitrile fiber in air, treating the resultant flame-resistant fiber in a hot inert gas, and carbonizing the product in an inert gas containing a hydrogen halide at a high temperature under specific condition. CONSTITUTION:LA polyacrylonitrile is used as the raw material, and is heat- treated in air at 200-350 deg.C to obtain a flame-resistant fiber. The obtained flame-resistant fiber free from adhesivity is treated in an inert gas atmosphere at 300-550 deg.C under the length variation of 0-+15%, and then carbonized in an inert gas atmosphere containing 2-25vol% hydrogen halide at 600-1,600 deg.C to obtain the objective fiber. The carbonization is carried out under a length variation of -10-+10% based on the raw fiber and of >=-6% based on the flame-resistant fiber, in the inert gas supplied at an average linear velocity of 3-20m/min.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing high-strength carbon fibers, and particularly to a method for obtaining high-performance carbon fibers from polyacrylonitrile fibers.

(Prior Art) Due to its excellent strength and elastic modulus, carbon fiber is used as a reinforcing fiber for various composite materials in aerospace applications, industrial materials, sporting goods, and the like.

However, its strength is still not sufficient, and the development of high-strength carbon fibers is particularly desired as a primary structural material in the aerospace field. In the past, various proposals have been made regarding methods for improving the strength of carbon fibers, such as Japanese Patent Publication No. 47-7686 and Japanese Patent Publication No. 47-29935 regarding atmospheric gas in the carbonization process, and Japanese Patent Publication No. 47-29935 regarding the temperature increase rate. Publication No. 51-12087 and Japanese Patent Publication No. 47-29935 which carbonizes during elongation are mentioned. However, looking at the examples of these proposed fibers, the tensile strength is about 300 kg/7.2, which is low compared to the level of recent carbon fibers. Recently, an example of elongation during carbonization due to the density of flame-retardant yarn was published in JP-A-57-14.
No. 722. In other words, a flame-resistant yarn with a density in a specific range is stretched to a maximum of 25 cm at a temperature range of 300°C to 800°C, and then carbonized at 800°C or higher. This method is not necessarily satisfactory as an industrial method, as fluffing occurs and uniform stretching is difficult.

(Problems to be Solved by the Invention) Under these circumstances, the present inventors have conducted intensive studies to find an industrial method for stably obtaining high-strength carbon fibers.
We have arrived at the present invention. That is, the present invention aims to solve the problems in the prior art as described above and to provide an industrially advantageous method that can stably obtain high-strength carbon fibers.

(Another Means to Solve the Problems) The present invention provides a method for producing high-strength carbon fibers from polyacrylonitrile fibers. to obtain a flame-resistant yarn without adhesion, and then
℃~550℃ in an inert gas atmosphere with a length change of 0 to +15 degrees (first carbonization), then carbonization in an inert gas atmosphere at 600℃ to 1600℃ (second carbonization) and the length change during carbonization in this inert gas atmosphere is from -10% to +10%,
and the change in length based on the flame-retardant thread is -6- or more; the inert gas contains at least 2 to 25% by volume of atomized hydrogen gas; This is a method for producing high-strength carbon fiber, characterized in that the average linear velocity of the active gas is 3 m/min to 20 m/min.

The polyacrylonitrile fiber of the present invention has at least 90%
% or more by weight of acrylonitrile and other copolymerizable monomers, such as acrylic esters such as methyl acrylate;
Acrylic acid, methacrylic acid.

It is a long fiber obtained by a wet spinning method, a dry spinning method, a dry-wet spinning method, etc. using a (co)polymer with a carboxylic acid such as itaconic acid, and further with acrylamide, allylsulfonic acid, etc. The method for obtaining this fiber is not particularly limited as long as it is a method for obtaining fibers without adhesion, and conventionally known methods can be applied. In the present invention, this fiber is heated at 200°C to 350°C.
It is necessary to heat-treat the yarn in the air to obtain a flame-resistant yarn without adhesion. The method for obtaining this flame-resistant yarn is not particularly limited as long as it can prevent adhesion, but in general, if flame-resistant is rapidly applied at high temperatures, the fibers will fuse due to a runaway reaction and eventually break. Usually, flame resistance is achieved in several stages from the low temperature side to the high temperature side in the range of .degree. C. to 350.degree. Further, as shown in Japanese Patent Publication No. 53-38774 and Japanese Patent Publication No. 57-42729, methods of air treatment, bending treatment, etc. may be used to prevent adhesion during flame resistance. In any case, it is necessary to obtain a flame-resistant yarn without adhesion, and if it is adhered, it will be difficult to stretch during the subsequent carbonization treatment, and yarn breakage may occur, or even if there is no yarn breakage. Good physical properties were not obtained.

In the present invention, the non-adhesive flame resistant yarn is heated to 300°C.
It is necessary to process in an inert gas atmosphere at ~550°C with a length change of 0 to 15 inches. In this process, if the elongation is less than 0%, it is difficult to obtain high-strength carbon fibers, and if the elongation exceeds 15 inches, stretching unevenness and fluffing occur.
In some cases, thread breakage occurs, making it impossible to stably obtain high-strength carbon fibers. Further, the heat treatment temperature in this step is 300°C to 550°C. If it is lower than 300°C, the carbonization reaction is slow and takes a long time, which is disadvantageous for industrial implementation.
．． If the temperature exceeds 550°C, the yarn will be heated rapidly and the fiber structure will change too much, making it impossible to obtain high-strength carbon fibers, making it difficult to stretch, and causing yarn breakage.

In the method of the present invention, the heat-treated yarn is heated to 600°C.
When further carbonizing in an inert gas atmosphere at a temperature of 1600°C or less, the change in length is -10 inches to 10%, and the change in length is -6 inches or more with respect to the flame-resistant yarn; It is necessary to contain 2 to 25 volumes of hydrogen halide gas in the inert gas, and the average linear velocity of the inert gas must be 3 to 20 m/min. High strength carbon fiber can be obtained. The length change in this process is 110 inches or +1
0%, the length change must be -6 inches or more based on the flame-resistant yarn. If this length change is too small, high-strength carbon fibers cannot be obtained, and if it is too large, problems such as fluffing and yarn breakage occur. In addition, in this process,
It is necessary to contain 2 to 25 volumes of hydrogen halide in the inert gas. Hydrogen halide is necessary to reduce fuzz generation and obtain high-strength carbon fibers, and if its concentration is too low, the above effects will be small, and even if it is contained in excess of 25%, there will be no commensurate effect. It is industrially disadvantageous because it cannot be obtained and a lot of cost is incurred for processing the used exhaust gas. As the hydrogen halide, hydrogen chloride, hydrogen bromide, hydrogen iodide, etc. are used. Also,
The average gas linear velocity of the inert gas should be 3 to 20 m/min. If it is too low, tar, etc. generated in the carbonization furnace will adhere to the yarn and cause defects. Moreover, if the speed is too high, the threads will be disturbed at the sealing part, etc., and this will cause fuzz.

As mentioned above, the feature of the method of the present invention is that firstly, a flame-resistant yarn without adhesion is obtained, and then carbonized in two steps, in which stretching, gas conditions, etc. are carried out within a specific range. Furthermore, the industrial significance of the present invention is extremely great because it is possible to stably produce high-strength carbon fibers without the generation of fuzz for the first time under the conditions of the present invention.

(Examples) The present invention will be further explained below with reference to Examples, but these examples do not limit the present invention.

Example 1 Acrylonitrile/methacrylic acid = 98.0/2.0
A copolymer of 6,000 filaments and a single yarn denier of 1. O
A precursor of d was obtained. This fiber bundle was heated at 235°C for 20
minutes, and then flame resistant at 255° C. for 40 minutes. There was no adhesion of this flame-resistant yarn, and the specific gravity was 1.38 J; l/CC. Using this flame-resistant yarn, carbonization was carried out under various carbonization conditions as shown in Table 1.

The first carbonization was carried out in nitrogen with a temperature gradient of 350-460°C, and the second carbonization was carried out at a maximum temperature of 1350°C. Further, the flame-retardant yarn with adhesion in Experiment No. 15 was made flame-retardant in air at 260° C. for 30 minutes using the same glue cursor. In addition, the strand strength of carbon fiber is J
The test was carried out using the resin-impregnated strand test method specified in ISR7601, and the resin formulation used was Explanation Example 2.

The following margin experiment numbers 2, 3, 6, 7, 10. , it can be seen that high-strength carbon fibers can be obtained only within the range specified by the present invention.

Example 2 Using the same polymer as in Example 1, a precursor with 6,000 filaments and a single filament denier of 0.83 d was obtained using a wet spinning method, and the same flame resistance as in Example 1 was obtained by opening the precursor with air at the entrance. The experimental Al of Example 1
Carbonization was performed under the same carbonization conditions as in Example 1, and the strand strength was measured to be 548 kg/threshold.

Claims (1)

[Claims] 1. 20 polyacrylonitrile fibers as raw material fibers
In a method for producing carbon fiber by heat-treating in air at 0°C to 350°C to obtain flame-resistant fibers, (1) length change of unbonded flame-resistant fibers in an inert gas atmosphere at 300°C to 550°C; 0 to +15%, and then (2) carbonizing in an inert gas atmosphere at 600°C to 1600°C, during carbonization in this inert gas atmosphere, (a) length (b) 2% to 25% by volume of hydrogen halide in the inert gas; (c) The average linear velocity of the inert gas is 3 m/min to 20 m/min.
A method for producing high-strength carbon fiber, characterized in that: /min.