JPS5938280A - Preparation of precursor pitch for carbon fiber - Google Patents

Abstract

PURPOSE:To produce the titled pitch excellent in thermal stability, spinnability, suitability for infusibilization etc., by removing meso phase formed by heating coal tar pitch and treating the resultant pitch not containing free carbon. CONSTITUTION:Coal tar pitch is heated to about 350-500 deg.C to form meso phase. Solvent-insoluble matters containing the meso phase are removed by extraction with an aromatic solvent and the solvent is removed. Then the resultant pitch containing no free carbon is extracted with a tar-based light oil to produce a pitch suitable as precursor for carbon fibre.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing carbon fiber precursor pitch.

Specifically, the present invention has excellent thermal stability, spinnability, and infusibility, high carbonization yield, and free carbon, petro atoms,
The present invention relates to a method for producing carbon fiber precursor pitch containing less impurities such as inorganic substances.

More specifically, the present invention has excellent thermal stability, spinnability, and infusibility, and has a softening point of 200°C or higher, L1 benzene insoluble content (hereinafter referred to as B
The present invention relates to a method for producing carbon fiber precursor pitch having a characteristic value of 45 to 60% by weight (referred to as I) and 45 to 60% by weight of quinoline soluble content (referred to as QI) or less than 0.1% by weight of ash (referred to as QI) or less.

Conventionally, the production of carbon fibers is roughly divided into two methods: methods using synthetic fibers such as acrylonitrile, and methods using petroleum pitch or coal tar pitch as raw materials. The former method has drawbacks such as expensive raw material fibers and low carbonization yield of raw material fibers. Moreover, in the latter case, there is a drawback that generally those with good spinnability are difficult to make infusible, and those with good infusibility are difficult to make spinnable. In addition, the method of adjusting carbon fiber precursor pitch using coal tar pitch as a raw material is difficult to remove minute amounts of insoluble solids (free carbon) and inorganic substances dispersed in the pitch. There is a need for improvements in spinnability and infusibility by hydrogenation at or with special hydrogen-donating solvents.

The purpose of the present invention is to eliminate such drawbacks, and to achieve excellent thermal stability, spinnability, and infusibility without hydrogenation treatment, high carbonization yield, and insolubility of ash, free carbon, etc. It is an object of the present invention to provide a method for producing carbon fiber blizzer pitch which does not have a solid content and has sufficient strength and elastic modulus as carbon fiber.

As a result of intensive research to achieve this objective, the inventors of the present invention heated the coal tar pitch of the present invention to 350 to 500°C to generate menphase, and extracted this with an aromatic system to contain menphase. Solvent-insoluble particles are removed, the solvent is removed to obtain a pitch that does not contain free carbon, and this pitch is heated to 350-500°C under reduced pressure or under conditions of inert gas blowing. The pitch is extracted with tar-based light oil, or the pitch is heated under reduced pressure or with inert gas blowing to 350~
The inventors have now invented a method for producing carbon fiber precursor pitch, which comprises heating at 500°C and washing with tar-based light oil.

That is, according to the present invention, by heat-treating coal tar pitch to generate a mesophase, the 7-ree casene in the pitch can be easily removed, and the pitch can be improved in thermal stability and spinnability without going through any particular hydrogenation treatment. In addition, it is possible to easily produce a hard pitch for carbon fibers that has excellent infusibility and a high carbonization yield.

The present invention will be explained in detail below.

The generation of mesophase when heat-treating pitch, its growth, and the progress of coalescence naturally vary slightly depending on the type of pitch, but mesophase usually begins to occur at around 350°C, and as the temperature is raised further, the amount generated increases, and at the same time it becomes larger. It grows into a sphere, and at about 470°C coalescence of menphase occurs, and furthermore, when the temperature reaches around 500°C, it becomes completely anisotropic.

In this reaction process, free carbon, which is fine particles with a diameter of 1 μm or less, and inorganic substances that become ash, which originally exist in the coal tar pitch, adhere to the periphery of the mesophase spheres, so that they can be easily removed.

Furthermore, not only free carbon but also high-molecular-weight components with large thermal reactivity and components with trace amounts of functional groups present in the pitch are preferentially polycondensed to form menphase, so these are removed. Pitch has a lower number of petro atoms and has excellent thermal stability.

In the present invention, it is possible to use pitch that has been heat-treated at temperatures ranging from about 350°C, the temperature at which mesophase occurs, to about 500°C, at which complete coking progresses, but if the heat treatment temperature is high, a large amount of mesophase will be generated. However, as a result, the yield of hard pitches decreases, and conversely, when the heat treatment temperature is low, highly thermally reactive components tend to remain in the hard pitches. When considering these two contradictory conditions, preferably 10~
It is desirable to generate about 30 wt%.

By adding an aromatic solvent to pitch that has been heat-treated under these conditions to generate mesophase, the mesophase can be easily separated by natural sedimentation or filtration. Separation of this mesophase by filtration is extremely easy without causing clogging, unlike free carbon filtration. After that, the solvent is removed by distillation to obtain a pitch that does not contain any free carbon, and this pitch is further heat-treated or extracted with a solvent to remove low molecular weight components from the pitch, resulting in a precursor bit suitable as a raw material pitch for carbon fibers. becomes. The characteristics of this precursor pitch include a softening point of 200°C.
Above, benzene insoluble content 45 to 65 wt%, quinoline soluble content Q, 5 wt% or less (however, free carbon is tra
ce), and the ash content is 0.1 wt% or less.

Hard pitch having a benzene insoluble content of 45 wt % or less has excellent spinnability, but is not preferred as a raw material for carbon fibers because it tends to cause phenomena such as melting and fusion of fibers during infusibility treatment. If the benzene insoluble content is 65 wt % or more, although the infusibility is improved, melt spinning becomes difficult.

There are various methods to adjust the pitch from a pitch that does not contain free carbon to a carbon fiber precursor pitch.
There is a method in which low molecular weight components in pitch are removed by heat treatment under inert gas blowing conditions. During this process, if heat treated at high temperatures for a considerable period of time, mesophase will be generated again, but it is better to have as little carbon fiber precursor pitch as possible (preferably 0.5 wt% or less. When mesophase is present in an amount of 0.5% or more, the spinnability of the precursor pitch deteriorates significantly, many knots are observed in the fibers, and the strength of the carbon fibers also decreases significantly.

When heat treatment is performed under reduced pressure or under inert gas blowing, the heat treatment conditions must be set to suppress the generation of mesophase as much as possible, but the pitch according to the present invention has excellent thermal stability. It's pitch. According to ordinary vacuum distillation or inert gas blowing, benzene insoluble matter can be reduced to 45% while sufficiently suppressing the formation of mesophase.
Precursor pitch of ~65 wt% can be produced.

A second method is to extract the pitch with benzene, toluene, or tar-based light oil to remove low molecular weight components from the pitch to obtain precursor pitch. This method removes free carbon from the pitch'! rloOMeS huhde
After pulverization to r, low molecular weight components in the pitch are extracted and removed using tar-based light oil, and the tar-based light oil is an aromatic solvent. Benzene, toluene, and tar-based light oils can be used.

Solvent ratio (solvent/pitch) 2 to 10 times the amount, preferably 3 to 10 times the amount
It is sufficient that the amount is 6 times that of the solvent, and that the extraction temperature is below the boiling point of the solvent. Unlike heat treatment, this solvent extraction method can be said to be a simple method since there is no concern that mesophase will regenerate.

The third method is a combination of heat treatment and solvent extraction. In other words, the pitch that does not include free carbon is 35
After heat treatment at 0 to 500°C under reduced pressure or under inert gas blowing conditions, low molecular weight components are removed by solvent extraction with benzene, toluene or tar-based light oil. This is a combination of the first method and the second method.

The softening point obtained in this way is 200°C or higher, the benzene insoluble content is 45 to 65 wt%, and the quinoline soluble content is 20.5 wt%.
% or less, however, free carbon is trace, ash content is 0, 1
Precursor pitch of less than wt % is a carbon fiber precursor pitch that has excellent thermal stability, melt spinnability, and infusibility, and has a high carbonization yield.

It is an impurity in the precursor pitch that causes ash separation, the generation of voids in carbon fibers, and a decrease in strength.It is preferable to have as little as possible, but the precursor pitch according to the present invention has an ash content of 0 to 1. It is extremely clean with a content of less than wt%, and is excellent as a carbon fiber precursor pitch. /This precursor pitch is spun at a temperature 40 to 50° C. higher than the softening point using a normal melt spinning method.

The spun fibers can be infusible by air oxidation without pretreatment with ozone oxidation or oxidizing agents such as sulfuric acid. After this infusibility treatment, the temperature is raised to about 1000° C. in an inert gas atmosphere such as Ar N2, and the fiber is fired and carbonized to obtain Eri carbon fiber.

Next, the present invention will be specifically explained using examples.

Example 1 Coal tar soft pitch was heat treated at 460° C. for 60 minutes to produce about 30 inches of mesophase, which was extracted with tar oil and high molecular weight components mainly consisting of mesophase were separated. The solvent of the P solution was recovered by vacuum distillation to obtain a pitch with a softening point of 100° C. and a benzene insoluble content of 15 traces of chiquinoline insoluble content. This pitch'r430℃, degree of vacuum 20mmH
Vacuum distillation was carried out at F.A.M. to obtain a precursor pitch having a softening point of 270°C, a benzene insoluble content of 503%, and a quinoline soluble content of 0.02%. This precursor pitch was melt-spun at 300°C, air oxidized at 300°C for 2 hours, and then carbonized at 1000°C in argon to obtain carbon fibers. This fiber has a fiber diameter of 10-12μ and a tensile strength of 105
ky/mm2. Elastic modulus6. It was Ot/mm2.

Example 2 The pitch of Example 1 having a softening point of 100° C. was vacuum distilled at 400° C. and a vacuum degree of 20 mmH abs to obtain a pitch with a benzene insoluble content of 42.5 wt % and a quinoline soluble content of nidrace. This pitch was ground to 100 mesh under, extracted with 4 times the amount of toluene at -40°C to remove low molecular weight components, softening point: 320°C, benzene insoluble content:
A precursor pitch of 59.7 wt % of quinoline-soluble nidolase was obtained. This precursor pitch is heated to 345°C.
After melt spinning at 300° C. for 2 hours and air oxidation, carbonization treatment was performed at 100° C. in argon to obtain carbon fibers. This fiber has a fiber diameter of 10 to 12μ and a tensile strength of 148.6kp/mm2. Elastic modulus6. Ot/mm
It was 2.

Claims (3)

[Claims] (1) Coal tar pitch f: Heat to 350 to 500°C to generate mesophase, extract this with an aromatic solvent to remove solvent-insoluble components including mesophase, and remove the solvent to generate free carbon. 1. A method for producing carbon fiber precursor pitch, which comprises obtaining carbon fiber precursor pitch and heating this pitch to 350 to 500° C. under reduced pressure or under conditions of inert gas blowing. (2) heating coal tar pitch to 350 to 500°C to generate mesophase, extracting this with an aromatic solvent to remove solvent-insoluble components including mesophase;
Remove the solvent to obtain a pitch free of free carbon,
A method for producing carbon fiber precursor pitch, which comprises extracting this pitch with tar-based light oil. (3) heating coal tar pitch to 350 to 500°C to generate mesophase, extracting this with an aromatic solvent to remove solvent-insoluble components including mesophase;
Remove the solvent to obtain a pitch free of free carbon,
A method for producing carbon fiber precursor pitch, which comprises heating the pitch to 350 to 500°C under reduced pressure or blowing inert gas, and then washing it with tar-based light oil.