JPS63145419A - Production of carbon yarn - Google Patents

Abstract

PURPOSE:To obtain carbon yarn having improved tensile strength by a simple means, by subjecting pitch showing optical anisotropy to melt spinning to give undrawn yarn, making the yarn infusible while suppressing increase in orientation in a specific range and carbonizing. CONSTITUTION:Pitch showing optical anisotropy (preferably petroleum type and/or carbon type pitch having >=90% mesophase content) is subjected to melt spinning, the prepared undrawn yarn is made infusible while keeping increase in orientation degree <=2 deg. (preferably heating at <=230 deg.C in air) and then carbonized (e.g. calcining at 1,000-1,500 deg.C in an inert gas atmosphere and furthering heating at 2,000-3,000 deg.C) to give carbon yarn.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to carbon fibers, and particularly to a method for producing carbon fibers with improved tensile strength.

[Background of the invention]

Carbon fiber has excellent heat resistance and mechanical strength, and is lightweight, so it is being used in various fields.

Incidentally, it is known that the strength and elasticity of pitch-based carbon fibers depend on the orientation of the fibers. However, in the conventional field of carbon fibers, it has been thought that the orientation of fibers is solely determined by the degree of crystallinity of the spinning raw material and the melt spinning conditions.

Therefore, in order to improve the tensile strength of fibers, it is necessary to strictly control the spinning raw materials, their preparation, and melt-spinning conditions.Therefore, with conventional methods, process control becomes complicated, and the strength improvement effect is also limited. The problem is that it is not always completely satisfactory.

[Summary of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a method for obtaining carbon fibers with excellent tensile strength by relatively simple means.

In order to achieve such an object, the method for producing carbon fiber according to the present invention involves melt-spinning a pitch exhibiting optical anisotropy to obtain a raw fiber f'4, and then converting the raw fiber by infusibility. It is characterized in that the infusible fibers are infusible so that the increasing degree of orientation does not exceed 2 degrees, and then the infusible fibers that have been infusible in this way are carbonized.

Conventionally, various attempts to improve the infusibility process have been proposed (for example, Japanese Patent Application Laid-open Nos. 126323/1986 and 59-3).
No. 0915, No. 58-45277). However, all of these methods are aimed at preventing fusion between fibers and improving production efficiency. On the other hand, a method has been proposed to improve the strength of raw fibers by applying tension to the raw fibers during infusibility treatment (Japanese Patent Application Laid-open No. 59-144624). In terms of control, this is not necessarily an easy method.

In the method of the present invention, the strength of the fibers is significantly improved by a simple method of limiting the change in the degree of orientation during infusibility within a specific range.

[Detailed description of the invention]

The present invention will be explained in more detail below. In the following description, "%" representing a quantitative ratio is expressed by weight unless otherwise specified.

Spinning pitch The spinning pitch used as a raw material is made of pitch exhibiting optical anisotropy that is prepared from petroleum-based heavy oil or coal-based heavy oil. This pitch preferably has a mesophase content of 7 Ω in order to obtain good orientation and high strength fibers.
096 or more, more preferably 90% or more.

Pitch whose main component is mesophase is preferable because the molecules are oriented along the fiber axis during melt spinning, and carbonization is performed while maintaining this orientation to obtain a high-strength fiber. If it is less than 70%, the improvement in molecular orientation cannot be expected so much, and the degree of orientation of raw fibers +
Even if it is made infusible within 2 degrees, it is not preferable because the -L effect on strength is small.

Melt spinning Spinning of the above-mentioned pitch can obtain raw fibers by a conventionally known method, and the melt spinning conditions, such as spinning temperature and spinning speed, are not particularly limited and may be selected as appropriate.

Infusibility: The raw fibers obtained as described above are subjected to an infusibility treatment.

In the present invention, it is important to perform this infusibility so that the degree of orientation that increases due to infusibility does not exceed 2 degrees. If the increase in the degree of orientation exceeds 2 degrees, the mechanical properties of the fiber obtained by carbonization, especially the tensile strength and elastic modulus, will deteriorate, which is not preferable.

Infusibility can be achieved, for example, by heating in air. The heating temperature at this time is 250°C or lower, preferably 230°C or lower.

If the heating temperature exceeds 250° C., it becomes difficult to control the degree of orientation of the infusible fibers to within the degree of orientation of the raw fibers plus 2 degrees, and the tensile strength after carbonization decreases, which is not preferable. Furthermore, the infusibility treatment time is also selected to suit the above-mentioned orientation degree conditions. In order to control the increase in the degree of orientation within the above range, the above infusible conditions can be set so that the quinoline soluble content of the infusible fibers does not exceed 70%.

The degree of orientation, which is the basis of the degree of orientation in the present invention, can be determined by M1 from a diffraction intensity distribution curve along the Debye ring by wide-angle X-ray diffraction according to a known method. A specific method for measuring the degree of orientation is disclosed in Chapter 12 of "Carbon Fiber" published by Kindai Editorial Company.

Conventionally, it has been generally thought that the orientation of carbon fibers and the tensile strength resulting from this orientation depend on the degree of crystallinity of the spinning raw material pitch and the melt spinning conditions. In the present invention, it is possible to obtain a carbon material with superior mechanical strength compared to conventional materials by a relatively simple method of controlling the orientation of fibers under the above-mentioned specific conditions during infusibility.

Carbon fibers are obtained by carbonizing the carbonized and infusible fibers and, if necessary, graphitizing them.

The carbonization treatment can be carried out by firing at 1000 to 1500° C. in an inert gas atmosphere such as N2 gas according to a conventional method. Then further 2000-3000°
It can be graphitized by heating to C.

Hereinafter, the present invention will be explained based on Examples, but the present invention is not limited to the description of these Examples.

EXAMPLE A petroleum-based spinning pitch having an optically anisotropic phase of 100% and a softening point of 238° C. was melt-spun to obtain a raw fiber having an average yarn diameter of 11 μm, a quinoline solubility of 23%, and an orientation degree of 22 degrees.

Next, this raw fiber was heated at 2°C/min at 200°C in an air atmosphere.
The fiber after heating up to ℃ and infusibility treatment at 200℃ for 6 hours has a quinoline dissolved content of 44% by weight? 6. The degree of orientation was 23 degrees. The fibers thus obtained after infusibility were
The physical properties of carbon fiber after being carbonized at 1000°C for 1 hour in a two-gas atmosphere are tensile strength 300 kg/si and elastic modulus 2.
It was 0TON/In1j1.

Comparative Example The raw fiber obtained in the above example was heated at 2°C/min for 2 hours in an air atmosphere.
After heating up to 90°C and infusible treatment at 290°C for 30 minutes, the fiber has a quinoline melting content of 83% by weight and an orientation degree of 26%.
It was degree. Furthermore, the binary value of oxygen element hexa in the thus obtained infusible fiber was the same as that of the infusible fiber obtained in the example.

This infusible fiber was carbonized under the same conditions as in the example.
17 The physical properties of the carbon fiber are tensile strength of 240 kg/i
, the elastic modulus was 16 TON/mA.

i'1lll constant standard In the above 6 examples, the quinolinated content is JIS-K-
M1 was determined according to the method of 2425.

In addition, the degree of orientation is "carbon fiber" (published by Kindai Editorial Co., Ltd., Showa Fiber).
WJ was determined according to the method described on pages 644 to 646L''f of the 1958 revised edition).

Claims (1)

[Claims] 1. After obtaining a raw fiber by melt-spinning a pitch exhibiting optical anisotropy, the raw fiber is infusible so that the degree of orientation that increases due to infusibility does not exceed 2 degrees. and then carbonizing the infusible fibers that have been made infusible in this way. 2. The method according to claim 1, wherein the pitch is petroleum-based or/and carbon-based pitch with a mesophase content of 70% or more.