JPH04153326A - Production of pitch-based carbon fiber - Google Patents

Abstract

PURPOSE:To obtain the subject fiber having extremely high elastic modulus and compressive strength and useful for composite material, etc., by melt- spinning an optically anisotropic spinning pitch compounded with an optically isotropic spinning pitch, infusibilizing the spun fiber and subjecting to carbonization treatment and graphitization treatment. CONSTITUTION:The objective fiber is produced by melt-spinning an optically anisotropic spinning pitch compounded with 0.5-10wt.% (preferably 1.0-5wt.%) of an optically isotropic spinning pitch containing pitch-constituting aromatic hydrocarbon three-dimensionally crosslinked with oxygen atom and containing 0.5-2.0wt.% (preferably 1.0-1.5wt.%) of oxygen, infusibilizing the obtained fiber, carbonizing the product and graphitizing the carbonized fiber. The softening point difference between the optically isotropic spinning pitch and the optically anisotropic spinning pitch is preferably <=10 deg.C and the viscosity of the pitch in melt-spinning is preferably <=300 poise.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for producing pitch-based carbon fibers having both high elastic modulus and high compressive strength.

Conventional technology Carbon fiber is lightweight, has high strength, and has properties such as excellent heat resistance and chemical resistance, so it is used in many fields as a base material for structural composite materials and as a high-performance material, such as for space, aviation, etc. It is used in fields such as composite materials for leisure, sports, and industrial use.

Carbon fibers are broadly classified into polyacrylonitrile (PAN-based) carbon fibers and pitch-based carbon fibers, but among pitch-based carbon fibers, high-performance (HP) carbon fibers have high anisotropy and are oriented along the fiber axis. Because it is composed of graphite crystals,
Although it has a higher modulus of elasticity than the PAN type, it has the disadvantage of lower compressive strength, and improvements are needed. In particular, in the field of advanced composite materials for space and aviation applications, there is a demand for the development of pitch-based carbon fibers that have both high modulus of elasticity and high compressive strength.

The present invention was made in response to such demands and to provide a pitch-based carbon fiber that has both a sufficiently high modulus of elasticity and high compressive strength for practical use.

Means for solving the problem, that is, the present invention, is an aromatic hydrocarbon constituting pitch that contains oxygen three-dimensionally cross-linked by oxygen atoms in an amount of 0.5 to 2.
The optically isotropic spinning pitch containing 0% by weight is 0.5 to I
High compressive strength characterized by melt-spinning an optically anisotropic spinning pitch containing 0% by weight, and subjecting the obtained fiber to an infusible treatment, followed by a carbonization treatment, and then a graphitization treatment. This invention relates to a method for producing pitch-based carbon fiber that has both high elasticity and high modulus.

The optically isotropic spinning pitch used in the present invention can be prepared using petroleum-based or coal-based heavy oil or pitch as a raw material, but it can also be prepared, for example, by heat treatment while blowing air. In this case, the aeration amount is 1 to 5 M per 1 kg of heavy oil, and the heating temperature is 30
It can be carried out at 0 to 350°C.

The isotropic pitch containing oxygen as described above is usually heated at 300 to 320°C to adjust the softening point.
It is subjected to a vacuum stripping treatment under conditions of 9 l-1.0 mmHg. The softening point to be adjusted has a difference of 1 from the softening point of the optically anisotropic spinning pitch used as the base material pitch.
The temperature is within 0°C, preferably within 5°C. If the difference in softening point between the two exceeds 10oC, the optimum spinning temperature will be different between the two, resulting in a marked deterioration in spinnability.

The optically isotropic spinning pitch used in the present invention may be prepared using an oxidizing agent such as nitric acid or a mixed acid, in addition to the above-mentioned air blowing method.

The optically isotropic spinning pitch used in the present invention is thought to have a structure in which aromatic hydrocarbons constituting the pitch are three-dimensionally crosslinked by oxygen atoms.

The oxygen content of the optically isotropic spinning pitch is 0.5-2.
0% by weight, preferably 1.0 to 1.5% by weight, and 0% by weight, preferably 1.0 to 1.5% by weight.
．． If it is less than 5% by weight, as will be described later, compatibility with the anisotropic spinning pitch remains, so the effect of improving compressive strength becomes insufficient, which is not preferable. Also, 2.0
When the amount exceeds 1% by weight, the spinnability deteriorates significantly, and even a mixed pitch containing an anisotropic pitch has poor spinnability, making it impossible to perform stable spinning.

The blending amount of the above oxygen-containing optically isotropic spinning pitch is 0.
5 to 10% by weight, preferably 1.0 to 5% by weight,
If the amount is less than 0.5% by weight, the compressive strength cannot be sufficiently improved, and if it is more than 10% by weight, the modulus of elasticity will decrease, which is not preferable.

The optically anisotropic spinning pitch used in the present invention may be prepared from petroleum-based or coal-based heavy oil or pitch by any conventionally known manufacturing method, and the manufacturing method is not particularly limited. However, the ratio of optically anisotropic components is 9
It may be adjusted to 0% or more, preferably 95% or more. The softening point of such optically anisotropic spinning pitch is usually 200-280°C, and the toluene-insoluble content and quinoline-soluble content are usually 50-90% and 0-40%, respectively.
It is.

The above-mentioned optically isotropic spinning pitch and optically anisotropic spinning pitch are, for example, 300 to
By melting and stirring and mixing at a temperature of 360° C., a mixed spinning pitch is obtained in which the former is uniformly dispersed in the latter.

The obtained mixed spinning pitch is subjected to a melt spinning process. Melt spinning conditions are not particularly limited, but the melt spinning is carried out, for example, under the following conditions.

Nozzle hole diameter: 0.05~0,5 mm Spinning temperature =
300 to 350°C Spinning viscosity = 100 to 300 poise Spinning speed: 100 to 500 m/min The spinning conditions in the present invention are such that the viscosity of the mixed spinning pitch is 30
Spinning is carried out at a temperature of 0 poise or less, preferably 150 to 200 poise. If the spinning viscosity is higher than 300 poise, as will be described later, fibrillation due to isotropic pitch spinning deformation becomes insufficient and the elastic modulus and tensile strength of the fiber decrease, which is not preferable.

By subjecting the fiber obtained by the above melt-spinning process to an infusible treatment, a carbonization treatment, and a graphitization treatment in accordance with a conventional method, the present invention achieves both high elastic modulus and high compressive strength. Pitch-based carbon fibers are obtained.

The conditions for the infusibility treatment, carbonization treatment, and graphitization treatment are, for example, as follows.

Infusibility treatment temperature: 270-300°C Treatment time: 10-30 minutes Atmosphere: Air Carbonization treatment temperature: 800-1000°C Temperature rising rate: 1-5°C/min Treatment time: 30-90 minutes Atmosphere Nitrogen gas Graphitization treatment under airflow Treatment temperature: 2500-2800°C Temperature increase rate: 1O ~ 50°C/min Treatment time: 1-10 minutes Atmosphere: Optically isotropic spinning pipe used in the present invention under argon gas flow・Sochi is thought to have a structure in which aromatic hydrocarbons, which are the constituent components of pitch, are three-dimensionally cross-linked by oxygen atoms, so it does not take on a graphite structure even after graphitization, and is an optical material used as a base pitch. It shows no compatibility with anisotropic spinning pitch. Therefore, when both are melted and mixed, the former will be about 1 to 5
It becomes optically isotropic small spheres of about μ size and disperses in the latter.

It is impossible with conventional technology to mix and spin such incompatible pitches, but in the present invention, by approximating the softening points of both pitches, the temperatures at which the optimum spinning viscosity is achieved are brought close to each other, improving spinnability. It becomes possible to perform mixed spinning without damage.

The reason why carbon fibers having both high elastic modulus and high compressive strength can be obtained by spinning a mixed pitch having such characteristics is not necessarily clear, but it can be inferred as follows. In other words, the optically isotropic spinning pitch becomes extremely thin needle-like bodies due to the deformation stress during spinning and is dispersed in the fiber like fibrils, which makes it possible to reinforce the strength of the fiber in the compression direction. can improve the compressive strength of Regarding the elastic modulus, the fiber diameter of the optically isotropic spun pitch dispersed in the form of fibrils in the fiber is small, and the proportion of the fiber cross section is also small. Since it becomes possible to maintain the elastic modulus of the fiber without much loss, it is presumed that carbon fibers having both high elastic modulus and high compressive strength can be obtained.

Hereinafter, the present invention will be explained by examples.

Example 1 Petroleum pitch obtained from heavy oil produced by catalytic cracking of petroleum was heat treated under reduced pressure (400-450'c/l O
~30 mmHg) to prepare a pitch containing mesophase microspheres, and the mesophase pitch was
Optically anisotropic spinning pitch A (anisotropy ratio: 99
%, Softening point: 235° C. 1 Torr, insoluble matter: 5%, quinoline soluble matter: 25%) were separated.

In addition, 1 kg of residual oil obtained by distilling heavy oil produced by catalytic cracking of petroleum at 430°C was subjected to heat treatment (320°C for 112 hours) while blowing air at a rate of 4Q/min, and then heated to 300°C for 112 hours. Optically isotropic spinning pitch (oxygen content = 0
．． 9% by weight, softening point: 235°O,) Luene insoluble content = 5
3%, quinoline solubility 20%).

Optically anisotropic spinning pitch A9 prepared as above
8 parts by weight and 2 parts by weight of optically isotropic spinning pitch were melt-stirred and mixed (melting temperature = 330°C), and the mixed pitch was
, through a 3 mm nozzle hole (spinning temperature = 333°C, 1-spinning viscosity: 170 poise). in this case,
Thread stringability was good, and no thread breakage occurred for more than 1 hour.

After subjecting this fiber to infusibility treatment (in air, 280°C) and then carbonization treatment (in N2 stream, 1000°C),
A pitch-based carbon fiber (2) was obtained by subjecting it to graphitization treatment (in an Ar air flow, at 2800°C).

The physical properties of the obtained pitch-based carbon fiber I are shown in Table 1 below.

Example 2 Pitch-based carbon fiber (2) was prepared in the same manner as in Example 1, except that 90 parts by weight of optically anisotropic spinning pitch A and 10 parts by weight of optically isotropic spinning pitch were melted and stirred.

The physical properties of the pitch-based carbon fiber (2) obtained are shown in Table 1 below.

Comparative Example) A pitch-based carbon fiber fabric was produced in the same manner as in Example 1, except that the optically anisotropic spinning pitch A prepared by the method described in Example 1 was used alone as the raw material spinning pitch. .

The physical properties of the obtained pitch-based carbon fiber I' are shown in Table 1 below.

Comparative Example 2 Based on the procedure for preparing anisotropic spinning pitch A described in Example 1, optically anisotropic spinning pitch B (anisotropic ratio: 100%
, softening point = 260°O, l-luene insoluble content: 8%, quinoline soluble content: 28%) were separated.

98 parts by weight of optically anisotropic spinning pitch B and 2 parts by weight of optically isotropic spinning pitch prepared by the method described in Example 1 were melted and stirred, and the mixed pitch was subjected to the same spinning treatment as in Example 1. However, thread breakage occurred frequently and fibers could not be obtained.

Comparative Example 3 Pitch-based carbon fibers were produced in the same manner as in Example 1, except that the optically isotropic spinning pitch prepared by the method described in Example 1 was used alone as the raw material spinning pitch.

The physical properties of the obtained pitch-based carbon fibers are shown in Table 1 below.

I (1) Effect of the invention on compressive strength of the fiber itself using the loop method According to the present invention, pitch-based carbon fibers having both high elastic modulus and high compressive strength, which could not be produced using conventional methods, can be produced using a simple method. Can be manufactured at low cost.

Claims (1)

[Scope of Claims] 1. An optically isotropic spinning pitch containing 0.5 to 2.0% by weight of oxygen in which the aromatic hydrocarbon constituting the pitch is three-dimensionally cross-linked with oxygen atoms. It is characterized by melt spinning an optically anisotropic spinning pitch containing 5 to 10% by weight, and subjecting the obtained fiber to an infusible treatment, followed by a carbonization treatment, and then a graphitization treatment. A method for producing pitch-based carbon fiber that has both high compressive strength and high modulus. 2. The method according to claim 1, wherein the softening point difference between the optically isotropic spinning pitch and the optically anisotropic spinning pitch is 10° C. or less. 3. The method according to claim 1, wherein the viscosity during melt spinning is 300 poise or less. 4. A pitch-based carbon fiber produced by the method according to any one of claims 1 to 3.