JPH046236B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a novel method for producing low-viscosity isotropic precursor pitch, which is a raw material for producing carbon fibers. <Prior art and its problems> Carbon fiber manufacturing methods include a method of firing synthetic fibers such as polyacrylonitrile and cellulose;
It can be roughly divided into methods of spinning, infusible, and carbonizing using petroleum and coal-based tar pitch-like materials as raw materials. The former of these two methods has the drawbacks of high raw material cost and low carbonization yield. On the other hand, according to the latter method, various pitches used as raw materials are by-products of the coal and oil industries, so they can be obtained in large quantities and have the advantage of being low cost. A process for preparing a precursor pitch is required, and many problems still remain before it can be implemented industrially. On the other hand, precursor pitches are classified into optically isotropic ones and anisotropic mesophase pitches depending on the characteristics of the target carbon fiber. 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. 45-28013 that the desired low-viscosity mesophase pitch could be obtained by hydrogenation treatment.
However, the former isotropic precursor pitch has not yet been solved. A low-viscosity, isotropic precursor pitch for producing carbon fiber with excellent spinnability has a benzene-insoluble content of about 50-65% by weight, a trace amount of quinoline-insoluble content, a softening point of about 200-240°C, and mesophase. Preferably, it has the property that it does not exist. <Objective of the Invention> The present invention advantageously solves the above-mentioned problems, and provides a general-purpose yarn with low viscosity and excellent spinnability by heat-treating pitches at a relatively high temperature for a short period of time by rapid heating. It is an object of the present invention to provide a method for manufacturing an isotropic precursor pitch for carbon fiber. <Structure of the Invention> The present invention uses tar or tar pitch in which highly thermally reactive high molecular weight components present in tar pitch have been separated and removed by solvent extraction, is heated to a high temperature by rapid heating, and is treated at this temperature for a short period of time. This is based on the new knowledge that by doing so, it is possible to produce a precursor pitch with low viscosity and excellent spinnability even in an isotropic pitch. That is, in the present invention, the benzene insoluble content is 50 to
60wt%, trace amount of quinoline insoluble matter, softening point 200
When producing precursor pitch for carbon fiber at ~240°C and substantially free of mesophase, tar or tar pitch is dissolved in a solvent, quinoline-insoluble matter is removed to a trace amount, and pyridine-insoluble matter is removed at the same time. A pitch was obtained from which the water content was removed to 5% by weight or less, and then the temperature was raised at a rate of 7°C/min or more while passing an inert gas under a reduced pressure of 20 mmHg or less.
The present invention provides a method for producing precursor pitch for carbon fibers, characterized in that heat treatment is performed at a maximum treatment temperature of 350 to 480°C. The present invention will be explained in detail below. The raw material used in the present invention is tar or tar pitch (hereinafter referred to as pitch). This is first extracted with a suitable solvent such as relatively light aromatic solvents such as coal-based tar oil or light oil, and then the quinoline-insoluble matter, which is mainly composed of free carbon present in the pitch, becomes the solvent-insoluble matter. Inorganic substances are substantially separated, and pyridine-insoluble components, which are high molecular weight components, are removed to 5% by weight or less. The reason why the quinoline insoluble matter is substantially separated and removed to a trace amount is that the quinoline insoluble matter does not dissolve during melt spinning and exists as a solid content, which causes nozzle clogging, and furthermore, it is added to the fiber after firing. This is because if it remains, it becomes a foreign substance and causes a decrease in strength. The reason why the pyridine-insoluble content is removed to 5% by weight is that the pyridine-insoluble content is highly thermally reactive and easily generates mesophases through heat treatment, and this mesophase acts as a secondary QI that inhibits spinning. Because it will be. That is, the present invention removes the thermally unstable and highly reactive high molecular weight components in the raw material pitch, so that when the raw material pitch is heat-treated to produce a precursor pitch, quinoline remains even when treated at high temperatures. It is possible to suppress the production of mesophase, which becomes an insoluble content, and to increase the benzene insoluble content to a desired range. Originally, when pitch is heat-treated, the higher the treatment temperature, the more likely it is that mesophase will be generated. However, in order to produce a low-viscosity precursor pitch, which is the objective of the present invention, it is necessary to process at a high temperature for a short time rather than at a low temperature for a long time. Remove the components before heat treatment,
It is necessary to use a raw material pitch with excellent thermal stability. If the above-mentioned mesophases exist in the precursor pitch, the pitch will become inhomogeneous, and when melt spinning is performed, it will cause nozzle blockage and bead-like bulges on the fibers.
This makes spinning very difficult. Furthermore, in order to produce the low viscosity isotropic precursor pitch of the present invention, it is important to use the above-mentioned raw material pitch and to select a heat treatment method for this raw material pitch. That is, the raw material pitch must be rapidly heated to a high temperature of 350 to 480°C at a rate of 70°C/min or more, and then treated at that temperature for a short period of time. That is, if the heat treatment is carried out for a long time, an excessive polycondensation reaction will occur, and the pitch will become polymerized and its viscosity will increase, making it impossible to achieve the low-viscosity precursor pitch that is the object of the present invention. If the temperature increase rate is less than 7℃/min, the heat treatment time must be lengthened, resulting in high viscosity of the pitch. This is because the residual low molecular weight components make it difficult to make the material infusible, and at high temperatures, the above-mentioned mesophase is likely to be produced. In addition, heat treatment is performed under reduced pressure of 20 mmHg or less.
It is necessary to carry out the heat treatment while circulating an inert gas such as nitrogen or argon, and to actively remove low molecular weight components generated by thermal decomposition and low molecular weight components originally present in the raw materials from the reaction system during the heat treatment. This is because if this low molecular weight component remains in the precursor pitch, it will volatilize and form bubbles during melt spinning, making it difficult to perform smooth spinning. This is because if the reduced pressure is lower than 20 mmHg, low molecular components that cause fiber fusion can be sufficiently removed in the infusibility step after spinning. The precursor pitch prepared as described above has a benzene insoluble content of 50 to 65% by weight, a trace amount of quinoline insoluble content, and a softening point of 200 to 240°C. Smooth spinning can be achieved by the melt spinning method. <Example> (Example 1) Coal tar pitch (softening point: 80°C, quinoline insoluble content: 3%, pyridine insoluble content: 7%) was extracted by adding 5 times the amount of pyridine as a solvent, and then filtered and separated to remove the solvent insoluble. After removing the components, it was distilled to obtain pitch with a softening point of 75°C, traces of insoluble quinoline, and 2% insoluble pyridine. The pitch is 10mm under nitrogen gas flow.
The temperature was raised at a rate of 9.5°C/min under reduced pressure of Hg, and after reaching 460°C, it was immediately allowed to cool. The analysis results of the pitch are shown in Table 1-A. (Example 2) A pitcher from which solvent-insoluble matter had been removed in the same manner as in Example 1 was heated to 475°C at a temperature increase rate of 10.9°C/min under nitrogen gas flow and a reduced pressure of 10 mmHg.
It was immediately left to cool. The analysis results of the pitch are shown in Table 1-
Shown in B. Even though the pitches obtained in Examples 1 and 2 were both treated at high temperatures, when observed under a polarizing microscope, no mesophase was generated and the entire surface was isotropic. These pitches A and B are set with a nozzle diameter of 0.3 mm, L/
Pitch fibers were obtained by melt spinning at temperatures of 281°C and 288°C under nitrogen pressure using a D=3 cylindrical monohole spinning device. Table 2 shows the characteristic values of the carbonized fibers obtained by infusibleizing the pitch fibers obtained from Pitch A and B at 300° C. in air and then carbonizing them at 1000° C. in argon gas. (Comparative Example 1) The same tar pitch used in Example 1 was extracted using quinoline as a solvent, filtered, and distilled to obtain a trace amount of insoluble quinoline, 7% insoluble pyridine, and a softening point of 78°C.
I got the pitch. The analysis results of pitch C obtained by treating the pitch under the same heat treatment conditions as in Example 1 are shown in Table 1-C. When observed with a polarizing microscope, the pitch C is several μm.
Mesophase spheres were observed and spinning was not possible. (Comparative Example 2) Using a pitch from which the solvent-insoluble matter had been removed in the same manner as in Example 1, it was treated at 370°C at a temperature increase rate of 1.2°C/min under nitrogen gas flow and a reduced pressure of 10 mmHg. The analysis results of the pitch are shown in Table 1-D. The pitch was then spun, infusible, and carbonized in the same manner as in Examples, and the characteristic values of the carbonized fibers obtained are shown in Table 2-D. The spinning temperature of the pitch was as high as 307°C, and only fibers with a large diameter could be obtained.

【table】

[Table] <Effects of the Invention> As is clear from the above explanation, the isotropic precursor pitch prepared by the method of the present invention has a low viscosity and can be spun at low temperatures.
Furthermore, the carbon fiber obtained from the pitch had sufficient strength compared to the fiber shown in Comparative Example 2. That is, by the method of the present invention, isotropic precursor pitches for producing general-purpose carbon fibers with lower viscosity and better spinnability can be produced.

Claims (1)

[Scope of Claims] 1. In the production of a precursor pitch for carbon fiber, which has a benzene insoluble content of 50 to 60 wt%, a trace amount of quinoline insoluble content, a softening point of 200 to 240°C, and substantially no mesophase. After dissolving the tar or tar pitch with a solvent, the quinoline insoluble matter was removed to a trace amount, and at the same time, the pyridine insoluble matter was removed to 5% by weight or less to obtain pitch, and then to this obtained pitch, Raise the temperature at 7℃/min or more while flowing inert gas under reduced pressure of 20mmHg or less.
A method for producing precursor pitch for carbon fibers, which comprises performing heat treatment at a maximum treatment temperature of 350 to 480°C.