JPH0455237B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a spinning pitch particularly useful for producing pitch-based high-performance carbon fibers.

As is well known, when carbonaceous raw materials such as heavy oil, tar, and pitch are heated to 350 to 500°C, small particles with particle sizes ranging from several microns to several hundred microns exhibit optical anisotropy under polarized light. A sphere is generated. and,
When heated further, these small spheres grow and coalesce, and finally the whole becomes in a state exhibiting optical anisotropy. This anisotropic structure is composed of polymeric aromatic hydrocarbons produced by a thermal polycondensation reaction of carbonaceous raw materials, stacked and oriented in layers, and is considered to be a precursor of graphite crystal structure.

This heat-treated material is passed through a nozzle, melt-spun, made infusible, carbonized, and optionally graphitized to produce a raw material for pitch-based high-performance carbon fiber, which has characteristics such as high strength and high modulus. It is proposed as.

Carbon fiber is a material with high specific strength and specific modulus.
It is attracting the most attention as a filler fiber for high-performance composite materials, and among them, polyacrylonitrile-based carbon fibers have low raw material cost, high yield in the carbonization process, and high fiber elasticity. It has various advantages compared to fibers.

Although various techniques have been known for the production of spinning pitches for producing pitch-based carbon fibers, there are still many improvements to be made.

For example, after heating carbonaceous pitch as a raw material, a low boiling point organic solvent such as toluene is added to obtain the solvent-insoluble matter, which is used as raw material pitch (Japanese Unexamined Patent Publication No. 55-119).
58287), or a method in which a carbonaceous pitch is heat-treated to generate a mesophase, and then the mesophase is obtained as a sediment under stationary conditions to obtain a raw material pitch (Japanese Patent Application Laid-open No. 119984/1984). Are known. However, when the raw material carbonaceous pitch is heat-treated, especially under conditions that maximize the solvent-insoluble content of the pitch, the low-molecular components are removed as gas or oil, and at the same time radical polymerization occurs. However, because it is insoluble in the solvent or has a high specific gravity, in the above method, an undesirable component that is excessively polymerized and polymerized with an inferior carbon crystal structure is formed. , and will be mixed into the sediment.

Therefore, it is necessary to remove from the raw material in advance interfering substances such as free carbon and ash that hinder fiberization. However, since these interfering substances are suspended in the raw material as minute particles, their removal requires a heavy burden.

In addition, carbonaceous pitch is treated with aromatic light oil without any particular heat treatment to obtain its soluble content,
Furthermore, there is a method in which the soluble content obtained by treatment with an aliphatic solvent such as gasoline is heat-treated to generate a mesophase, and the mesophase is obtained as a precipitate under stationary conditions and used as a raw material pitch. 1986-78486) is known, but it is still not sufficient to obtain carbon fibers with high characteristics.

Furthermore, during heat treatment, reduced pressure or a large amount of inert gas may be blown in order to remove volatile low-molecular-weight components that impede mesophase formation, or the anisotropic phase and isotropic phase formed may be reduced. Complicated operations such as vigorous stirring are performed to improve miscibility with

The inventors of the present invention improved the problems of these conventional techniques and conducted intensive studies to provide a method for producing an optically anisotropic spinning pitch for pitch-based high-performance carbon fibers. Then, if the soluble portion obtained by contacting with a specific solvent is heat-treated and the resulting optically anisotropic portion is obtained as a precipitate and used as a raw material pitch, the desired purpose will be achieved. With this finding, we have completed the present invention.

That is, the gist of the present invention is to heat-treat a carbonaceous raw material, and then heat-treat the aromatic oil-soluble content obtained by contacting it with an aromatic oil having a boiling point or initial boiling point of 150 ° C. or higher, Production of a spinning pit for carbon fibers, characterized in that a heat-treated product containing an optically anisotropic portion is obtained, and the optically anisotropic portion is separated by sedimentation from the heat-treated product under standing conditions to obtain the precipitate. It lies in the method.

To explain the present invention below, examples of the carbonaceous raw material used in the present invention include coal-based coal tar, coal tar pitch, coal liquefied products, petroleum-based heavy oil, tar, and pitch. These carbon raw materials usually contain impurities such as free carbon, undissolved coal, and ash, but as will be described later, according to the method of the present invention, these impurities can be removed from the raw materials in advance, unlike conventional methods. It can be used advantageously without having to be specifically removed to a certain degree.

In the present invention, these carbonaceous raw materials are first heat-treated to obtain a heat-treated product (hereinafter referred to as "primary heat-treated product"). The heat treatment conditions are: temperature 350-500℃;
The time may be appropriately selected within the range of 0.5 to 20 hours and the pressure within the range of normal pressure to 10 kg/cm ² G.

Usually includes an optically anisotropic portion, preferably
A primary heat-treated product containing 10% or more, particularly preferably 30 to 95%, is obtained. Moreover, when the polycondensation reaction is carried out at a relatively high temperature for a short time, an optically isotropic primary heat-treated product can be obtained.

The content of the optically anisotropic portion of the heat-treated product (primary heat-treated product and heat-treated product described below) as used in the present invention is expressed as the area percentage of the portion exhibiting optical anisotropy in the sample of the heat-treated product under a polarizing microscope at room temperature. This is the obtained value.

Specifically, for example, a sample piece of a heat-treated product is crushed into pieces of several mm square, and the sample piece is embedded in almost the entire surface of a resin with a diameter of about 2 cm using a conventional method. Polarized light microscope (100x magnification)
It is determined by visually observing the area below and measuring the ratio of the area of the optically anisotropic portion to the total surface area of the sample.

The boiling point or initial boiling point of the above primary heat treated product is 150℃
Contact with the above aromatic oil to obtain its soluble content. Such aromatic oils include, for example, naphthalene oil, absorption oil, creosote oil, anthracene oil, the oil produced during the heat treatment of the carbonaceous raw material mentioned above, and the oil obtained by distilling the same.

Aromatic oil is based on 1 part by weight of the primary heat treated product.
It is usually used in an amount of 0.1 to 3 parts by weight, preferably 0.3 to 1.5 parts by weight.

The contact between the first heat-treated product and the aromatic oil is preferably carried out at a temperature above the temperature at which the first heat-treated product exhibits fluidity and below about 400°C, preferably from 300 to 370°C. Then, the desired aromatic oil soluble content is obtained by static sedimentation, centrifugation, filtration, or the like. Among these, static sedimentation separation is simple and convenient.

The aromatic oil soluble component thus obtained is a pitch having the following properties. That is, after substantially distilling off the aromatic oil contained in the obtained aromatic oil soluble fraction, the residual content is such that the benzene soluble (Bs) γ component is 65 to 0%, preferably 65 to 10%. So, the benzene insoluble (Bi) and quinoline soluble β component is 65-20
%, preferably 60-25%, quinoline insoluble (Qi)
The pitch is such that the α component is 30 to 0%.
In addition, the aromatic oil soluble component of the present invention exhibits an optical structure that is isotropic as a whole or contains a very small number of anisotropic spherules, and contains α and β components that are indicators of heavy components. Because it contains a large amount, it is in a state just before it can convert to an anisotropic phase (the aggregate of molecules does not have a stacked structure, but individual molecules may be affected by slight stimulation that causes molecular rearrangement). It is thought that it consists of a heavy polymerized pitch component (in an excited state that allows it to be oriented).

According to the method of the present invention, components excessively polymerized and molecularized during heat treatment of carbonaceous raw materials are separated and removed as aromatic oil-insoluble components, and free carbon, undissolved coal, and other components present in the carbonaceous raw materials are separated and removed. Ash and the like adhere to excessively polymerized components and can be easily separated and removed. Therefore, it is not particularly necessary to remove the aforementioned impurities from the raw materials in advance or to select and use raw materials that do not contain these impurities.
It is advantageous in terms of operation, and is advantageous because it does not contain low molecular weight components or excessive high molecular weight components, and the molecular composition is suitably controlled.

Next, the aromatic oil soluble content is heat-treated to obtain a heat-treated product containing usually 10 to 90%, preferably 30 to 80%, of optically anisotropic portions. The heat treatment conditions are appropriately selected within the range of temperature 350 to 500°C, time 2 minutes to 20 hours, and pressure normal pressure to 10 kg/cm ² G.

At that time, of course, stirring or blowing inert gas may be performed, but the complicated operations such as conventional vigorous stirring, blowing in a large amount of inert gas, and depressurization are not necessary. This is advantageous because almost no polymeric components polycondensed (early coking products) are formed.

Next, the above-mentioned heat-treated product is left to stand at a temperature of about 300 to 400°C for usually 0.2 to 10 hours, and the optically anisotropic part is separated from the isotropic part by the difference in specific gravity and allowed to settle, resulting in the spinning of the present invention. Get Pituchi. In the present invention,
Depending on the purpose, a precipitate containing a part of the isotropic portion may be obtained and used as a spinning pitch.

The above-mentioned static sedimentation separation can be carried out under normal pressure, but in the present invention, under pressure, usually 10 kg/
cm ² G or less, preferably 5 to 10 Kg/cm ² G.

Further, in the present invention, gentle stirring may be performed to the extent that sedimentation separation is not hindered.

According to the present invention, optically anisotropic spheres having a substantially uniform particle size are formed by heating the aromatic oil soluble content.
That is, spheres with a relatively uniform molecular weight distribution are produced. Then, since separation is performed based on the difference in specific gravity instead of immediate heat treatment that involves weighting, an increase in molecular weight does not occur and a spinning pitch with a uniform molecular weight distribution can be obtained. Therefore, the softening point decreases,
Spinnability was also improved. In addition, compared to spinning pitches obtained by conventional heat treatment, the resulting spinning pitches have a high quinoline insoluble content of 30 to 60%, but the temperature at which they reach 60 poise is approximately 300 to 300%. 350
It is characterized by a low temperature of ℃, and therefore carbon fiber can be obtained in high yield. A pitch-based carbon fiber with high properties can be produced by melt-spinning this spinning pitch according to a conventional method, making the resulting pitch fiber infusible, carbonizing it, and optionally graphitizing it.

EXAMPLES The present invention will be further explained in detail by giving examples below.

Example 1 Coal tar pitch (Bi6.0%, Qi0%) was heat-treated at 440° C. for 4 hours at normal pressure in a nitrogen atmosphere to obtain a first heat-treated product with an anisotropy ratio of 80%. 0.5 parts by weight of anthracene oil was added to 1 part by weight of this heat-treated product, and the mixture was allowed to stand at 350°C for 30 minutes, and the supernatant liquid was obtained by decantation. This supernatant is γ62
%, β 32.2%, and α 5.8%, and when observed under a polarizing microscope, the entire surface was isotropic.

This supernatant liquid was heated at 420°C for 1 hour at normal pressure in a nitrogen atmosphere to contain approximately 40% optically anisotropic spheres.
A heat-treated product with a Qi of 29.8% was obtained. Next, this heat-treated product was allowed to stand at 370° C. and normal pressure for 2 hours to precipitate optically anisotropic spheres.

By cooling the heat-treated product after standing for 2 hours and observing its cross section with a polarizing microscope, it was found that the heat-treated product was
It was confirmed that it was separated into layers.

The lower layer was anisotropic throughout and had a Qi of 42.0%.
Moreover, the temperature showing 60 poise was 339°C.

This lower layer was spun at a temperature of 348°C using a spinning machine with a nozzle of 0.3 mm in diameter. The obtained pitch fibers were subjected to infusibility treatment at 310°C for 30 minutes in an oxygen atmosphere, and then carbonized at 1400°C for 0.5 hours in a nitrogen atmosphere to obtain carbon fibers.

The tensile strength of this carbon fiber is 34t/ ^cm2 , and
The tensile modulus was 2300t/ ^cm2 .

Comparative Example 1 Coal tar pitch (Bi6.0%, Qi0%) was heat-treated at 420°C for 2 hours in a nitrogen atmosphere to obtain a heat-treated product. This heat-treated product is anisotropic throughout and has a Qi of 65.5%.
Also, the temperature that showed 60 poise was 416°C.

This heat-treated product was spun in the same manner as in Example 1, but yarn breakage occurred and fibers could not be obtained.

Example 2 Coal tar pitch (Bi 10.5%, Qi 0.7%) was heat-treated at 440° C. for 4 hours at normal pressure in a nitrogen atmosphere to obtain a primary heat-treated product with an anisotropy ratio of 90%. 0.5 parts by weight of anthracene oil was added to 1 part by weight of this heat-treated product, and the mixture was allowed to stand at 350°C for 30 minutes, and the supernatant liquid was obtained by decantation. This supernatant liquid is γ59.7
%β35%α5.3%, and when observed under a polarizing microscope, the entire surface was isotropic.

This supernatant liquid was heat-treated at 420°C for 5 minutes at normal pressure in a nitrogen atmosphere to contain 50% of optically anisotropic spheres.
A heat-treated product with Qi of 21.0% was obtained. Next, this heat-treated product was allowed to stand at 360° C. and normal pressure for 3 hours to precipitate optically anisotropic spheres.

Thereafter, the heat-treated product was cooled and its cross section was observed with a polarizing microscope, and it was confirmed that the heat-treated product was separated into two layers.

The lower layer was anisotropic throughout, with a Qi of 35.7% and a temperature of 60 poise at 333°C.

This lower layer was spun at 339°C using a spinning machine with a nozzle having a diameter of 0.2 mm, and then carbonized and graphitized at 2800°C in the same manner as in Example 1 to obtain carbon fibers. This carbon fiber had a tensile strength of 27 t/cm ² and a tensile modulus of 2800 t/cm ² .

Claims (1)

[Scope of Claims] 1. A carbonaceous raw material is heat-treated, and then the aromatic oil-soluble content obtained by contacting it with an aromatic oil having a boiling point or initial boiling point of 150°C or higher is heat-treated to obtain optical properties. A method for producing a spinning pit for carbon fibers, which comprises obtaining a heat-treated product containing an optically anisotropic portion, and separating the optically anisotropic portion from the heat-treated product by sedimentation under standing conditions to obtain the precipitate. . 2. The method according to claim 1, wherein the aromatic oil is naphthalene oil, absorption oil, creosote oil or anthracene oil. 3. The method according to claim 1, wherein the aromatic oil is an oil produced by heat treatment of carbonaceous raw materials. 4. The method according to claim 1, wherein the sedimentation separation is carried out at a temperature of 300 to 400°C.