JPS62201992A - Production of precursor pitch for carbon fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a novel method for producing precursor pitch for producing general-purpose carbon fibers.

(Prior art) There are two methods for producing carbon fiber: one is to sinter synthetic fibers such as polyacryloni-1-lyl and cellulose, and the other is to spin, infusible, and carbonize petroleum and coal-based tar pitch-like materials as raw materials. It can be broadly divided into

Among these, the former has the drawbacks of high amount of raw material (1) and low yield when carbonized.

On the other hand, according to the latter method, the raw material pitch is a by-product of the coal and petroleum industries, so it is readily available and has the advantage of being low cost. A step is required to adjust the precursor Briker servidge. In addition, this precursor pitch is classified into optically isotropic and anisotropic mesophase pitch depending on the characteristics of the target carbon fiber, but regarding the second precursor pitch, In order to reduce the viscosity in order to smoothly carry out spinning in the subsequent process, it was discovered in Japanese Patent Publication No. 1973-1 that mesophase bits with low viscosity and good spinnability could be obtained by hydrogenating the raw material pitch.
28013, JP 49-8634, JP 58-184219, and JP 60-2352.
It is proposed in the Publication No. However, the former problem, optically isotropic blender pitch, has not yet been resolved. This is because if pitch is made with a low viscosity with emphasis on spinnability, its infusibility will be poor, and if it is made with a high viscosity pitch with advanced polycondensation, with emphasis on infusibility, the pitch will decrease due to the upper limit of the spinning temperature. This is because there remains a contradictory problem in that spinning becomes difficult due to deterioration of quality and the like.

(Problems to be Solved by the Invention) The present invention advantageously solves the above-mentioned problems by removing pitch impurities together with mesophases generated during the first heat treatment. Piddy binding with excellent thermal stability. By heating this pitch rapidly in the second heat treatment and treating it at a relatively high temperature for 7 hours, it can be spun with a low viscosity without special treatment such as hydrogenation. The purpose of this invention is to produce an optically isotropic blizzer pidge for general-purpose carbon fibers that has excellent properties and infusibility.

(Means for Solving the Problems) The present invention takes advantage of the fact that free carbon present in tar pitch adheres to the periphery of the mesh spheres produced by heat treatment of the pitch, thereby reducing the solid content insoluble in the solvent. The pitch purified in this way is thermally stable (9) and does not easily generate mesophase even when treated at high temperatures, and the pitch can be heated in a high-temperature bed by rapid heating and can be heated in a short period of time. The present invention was achieved based on the new finding that homogeneous, low-viscosity, isotropic pitch can be produced by processing.

That is, in the present invention, tar pitch soft pitch or medium pitch is heat-treated at 350 to 500°C to generate mesophase, solvent-insoluble components including mesophase are removed by solvent fractionation, and the solvent is removed to produce quinoline-insoluble The method is characterized in that a pitch is obtained with the smallest trace amount, and then the iqed pitch is heat-treated.

Generally, tar pitches contain solid content such as free carbon and inorganic substances that are insoluble in solvents. If such solid content remains in the carbon fiber precursor pitch, it will cause clogging of the nozzle during the spinning process, and furthermore, even if it is fired after spinning to form a canvas, it will cause a decrease in strength. This is well known. Therefore, it goes without saying that this kind of solid content should be removed by 2 tons,
Free carbon alone has the problem of being difficult to settle and clogging when filtered. In the present invention, it is noted that this solid content adheres to the periphery of mesophase spherules generated when pitch is heat-treated, and the solid content is efficiently separated and removed together with the mesophase by sedimentation or filtration. At this time, the mesophase generation Φ is 10~
30% by weight is preferred. In other words, if more mesophase is produced, the separation efficiency and the yield of purified pitch will decrease.

Furthermore, when pitch is heat-treated, mesophase, which is represented by quinoline-insoluble components, is generated as the temperature increases. This mesophase is secondarily generated by the heat treatment of pitch, and is one of the causes of spinning inhibition, like the above-mentioned solid content such as free carbon. Therefore, the raw material pitch for general-purpose carbon fiber precursor pitch must be a bit with excellent thermal stability so that it does not generate J: Rimesof process during heat treatment. When removing the component, the highly reactive polymer component in the pitch is grown into a mesophase and separated and removed, so it has greater thermal stability at high temperatures than regular pitch, and can be removed by reheating. It is characterized by the high production humidity of menphase.

Furthermore, in order to produce a low-viscosity homogeneous precursor pitch according to the present invention, it is important to use the raw material pitch treated as described above and to select the heat treatment conditions for the raw material pitch. .

In other words, when raw material pitch is heat-treated at a low temperature increase rate (5°C/min or less) for a long time, polymerization of the pitch is promoted due to excessive polycondensation reaction, and the infusibility of the pitch is improved.
The viscosity significantly increases, and as a result, the spinning temperature becomes high, and the pitch during spinning tends to change in quality, making it difficult to perform smooth spinning.

However, pitch treated for a short time at a high temperature increase rate (5°C/min or more) by the method of the present invention has a benzene insoluble content (BI) of 50m% (preferably 5%), which is a characteristic value of pitch.
If the temperature is increased to 5% by weight or more, the infusibility is good, and the same level of BI can be obtained by low heating rate and long-time treatment.
It can be said that this pitch has a low viscosity and is suitable for spinning when compared with pitches having a high value.

Furthermore, the heat treatment is carried out under reduced pressure or while passing an inert gas such as nitrogen or argon, or by using both in combination, to remove low molecular components generated by thermal decomposition during the heat treatment and low molecular weight components originally present in the raw material pitch. It is necessary to actively remove molecular components from the reaction system. That is, such low molecular components volatilize during melt spinning and form bubbles and 73
This is because it may cause thread breakage.

As described above, the precursor pitch prepared from the raw pitch according to the present invention has a benzene insoluble content of 50 to 65% by weight, a quinoline insoluble content of 1% by weight or less, and a softening point of 200 to 200% by weight.
This precursor pitch has all the characteristics of 240°C, and can be smoothly spun according to the usual melt spinning method, and the carbon fiber obtained from Kakko's pitch has sufficient characteristics as a general-purpose carbon fiber. ing.

(Effects of the Invention) As described above, in the present invention, the raw material pitch is used as a pitch with excellent thermal stability in the first heat treatment, and the material is subjected to rapid heating for a short time in the second heat treatment, thereby spinning at a low temperature. Low viscosity precursor pitch possible! From this precursor pitch, carbon fibers with low viscosity but good infusibility compared to high viscosity pitches and sufficient properties can be produced. can do.

That is, according to the present invention, it is possible to produce a precursor pitch for general-purpose carbon 1ift with low viscosity and excellent spinnability and infusibility.

(Example 1) Coal-based tarbidge (softening point = 80°C, quinoline insoluble content: 3%, benzene insoluble content: 17%) was heat treated at 450°C for 60 minutes to generate about 25% mesophase. 1st
As is clear from the polarized light micrograph showing the pitch particle structure shown in the figure, impurities such as free carbon were attached around the mesophase. This pitch was extracted with tar oil and mesophase and free carbon were filtered off. This filtrate was distilled to obtain a soft pitch having a softening point of 30° C., a trace amount of quinoline insoluble matter, and 9% benzene insoluble matter. This pitch to NZ
567℃2 under reduced pressure of 10mmHg under gas flow
The temperature was raised at a rate of 440°C, and after reaching a temperature of 440°C, it was immediately allowed to cool to obtain hard pitch A. Minutes to this pitch.

The analysis results are not shown in Table 1.

Also, the obtained soft pitch is N? Under gas flow, 10m
Under reduced pressure of mHg, the temperature was increased at a rate of 10.9°C/min, and
After reaching 15° C., hard pitch B was obtained by cooling. Further, the analysis results of this pitch B are shown in Table 1. Although these hard pitches A and B were both treated at high temperatures,
It did not contain mesophase and showed isotropy over the entire surface.

These pitches A and B are determined by the nozzle system 0.3 mm, L/
Pitch fibers were obtained by spinning at temperatures of 295° C. and 288° C. under nitrogen pressure using a monohole spinning device having D=3 nozzles.

Furthermore, these pitch II ills were heated to 310°C in air.
The fibers were made infusible and then carbonized at 1000° C. in argon gas to obtain carbon fibers. Table 2 shows the characteristics of these carbon fibers.

(Comparative Example 1) 1q of soft pitches obtained in Example 1 were heated at a rate of 1° C./min under reduced pressure under N2 gas flow and heat treated at 400° C. to obtain hard pitch C. The analytical properties of this pitch C are shown in Table 1.

Further, when this Vidge C was spun in the same manner as in Example 1, only thick fibers were obtained at a temperature of 332°C. Table 2 does not show the characteristic values of the carbon cord obtained by carbonizing this pitch fiber.

(Comparative Example 2) The tar pitch used in Example 1 was not heat-treated, but tar oil was added, extracted, filtered, and further distilled to obtain pitch (q) containing no quinoline-insoluble matter. This pitch had a softening point of 32°C. and the benzene insoluble content was 10%.

This bit was heat treated under the same conditions as hard pitch A of Example 1 to obtain hard pitch D@. An analysis of this pitch is shown in Table 1. This hard pitch D contained mesophase spheres of several μm.

Table 1 Table 2

[Brief explanation of drawings]

FIG. 1 is a polarized light micrograph showing the grain structure of pitch. Patent applicant: Kawasaki Steel Corporation Applicant: Nittobo Co., Ltd. Engraving of drawings (no change in content) No. ′:・Mi! 00 μm Procedural Amendment C Method] March 24, 1985 1. Display of the case 1985 Patent Application No. 217919 2. Name of the invention Method for manufacturing Briker servidge for carbon fiber & Person making the amendment Between the case and the case Patent applicant (125) Kawasaki Steel Corporation Nittobo Co., Ltd. 5 Date of amendment order February 24, 1988

Claims (1)

[Claims] 1. Tar pitch soft pitch or medium pitch 350 to 5
Heat treatment at 00°C to generate mesophase, remove solvent-insoluble components including mesophase by solvent fractionation, remove the solvent to obtain a pitch with trace amounts of quinoline-insoluble components, and then remove the resulting pitch. A method for producing precursor pitch for carbon fiber, characterized by heat treatment. 2. The heat treatment is performed under reduced pressure or under an inert gas flow,
The method according to claim 1, which is carried out at a temperature range of 350 to 500° C. or in combination of both of these. 3. The method according to claim 1, wherein the heating rate in the heat treatment is 5° C./min or more until the predetermined temperature is reached, and the holding time at the predetermined heat treatment temperature is 10 minutes or less. 4. The precursor pitch obtained by the heat treatment has an optically isotropic structure on the entire surface, is substantially free of mesophase, has a benzene insoluble content (BI) of 50% to 65% by weight, and has a quinoline insoluble content of 1% by weight. % or less, and the softening point is in the range of 200 to 240°C.