JPS60155716A - Production of carbon fiber - Google Patents

Abstract

PURPOSE:To obtain carbon fibers having improved performance with high productivity at a low cost, by using a pitchlike material, prepared by utilizing the solubility in a solvent specified by a solubility parameter, and exihibiting the solubility within a specific range. CONSTITUTION:A pitchlike material, soluble in a solvent, e.g. actone, having 9- 10.5 solubility parameter (at 20 deg.C), and insoluble in a solvent, e.g. cyclohexane, having 7.5-8.5 solubility parameter (at 25 deg.C) is used as a raw material to produce carbon fibers by the conventional method. Specifically, pitch is treated with the former solvent to remove insoluble matter, e.g. high polymers, and soluble matter is distilled to distill away the solvent. The residual material is then treated with the latter solvent to remove materials (low-molecular materials) soluble in the latter solvent, and the aimed pitchlike material consisting of components within a proper molecular weight range is preferably obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing carbon fibers, and more particularly to a method for producing high-quality carbon fibers at a relatively low cost using pitch-like materials specified by solubility parameters. It is something.

Carbon fiber has extremely excellent heat insulation, heat resistance, chemical resistance, rigidity, and electrical conductivity, so these properties can be used to make it into insulation materials, sealing materials, electromechanical parts, various structural members, friction materials, and carbon fibers. It is widely used as an electrode, etc., and its applications are expected to continue to expand in the future.

By the way, carbon fiber is conventional polyac IJ02)! J
Although good results have been obtained in terms of performance, the raw material cost is high and the carbonization yield is low, making it extremely expensive. It became.

Under these circumstances, a method for producing carbon fiber was proposed, which involved spinning, infusibility, and carbonization using pitch-like materials that could be obtained cheaply and in large quantities from the coal and oil industries, and published in Japanese Patent Publication No. 45-28013. Publication No. 49-8634, Publication No. 53-7533, Publication No. 54-1810, Publication No. 54-55625, JP 57-1598
Various improvement studies are underway, as seen in Publication No. 85 and others. However, even with these improved methods, it has not been possible to achieve performance comparable to carbon fiber made from polyacrylonitrile, especially mechanical strength, and there is no product that has been put into practical use industrially as a high-strength product. .

The present inventors have focused on these circumstances and have conducted various studies in an attempt to establish an industrially practical method for producing carbon fibers using pitch-like substances as raw materials.

As a result, if we exclude high-molecular substances that are insoluble in solvents with specific solubility parameters and low-molecular substances that are soluble in solvents with specific solubility parameters among pitch-like substances, and use only those in the specific solubility range as raw materials, it is possible to Knowing that carbon fiber with high performance can be produced with good productivity and at low cost, we completed the present invention. That is, the method for producing carbon fiber according to the present invention has a solubility parameter (value at 25°C) of 9.0 to 10.5.
is soluble in a solvent with a solubility parameter of 7.5~
The gist of this method is to manufacture carbon fiber using a pitch-like substance that is insoluble in the solvent of No. 8.5.

The raw material properties required for the production of pitch-based carbon fibers include: (1) minimal insoluble components at the spinning temperature; (2) a pitch softening point of 180°C or higher; It has also been confirmed that excellent quality carbon fibers can be obtained using pitch-like materials that are converted into optically anisotropic mesophase carbonaceous materials by melting and carbonization treatments. However, if insoluble components exist in the σ raw material, yarn breakage occurs frequently during spinning or causes clogging of the spinning nozzle, resulting in a significant decrease in operational stability and productivity, and the softening point of the σ pitch is low. This is because the heating temperature cannot be increased in the infusibility treatment step after spinning, and the infusibility takes a long time, resulting in a significant drop in productivity.

Based on this knowledge, the present inventors have conducted extensive research in an effort to establish a practical manufacturing method for pitch-based carbon fibers by clarifying the criteria for selection and purification of pitch-like substances that meet the required characteristics as described above. We have been progressing. As a result, from among ordinary pitch-like substances, solubility parameters of 9.0 to 10 were found.
．． 5 (value at 25°C: the same applies hereinafter) and a pitch-like material with a specific solubility range from which polymer components insoluble in a solvent with a solubility parameter of 7.5 to 8.5 are removed The present invention was achieved based on the knowledge that this satisfies the characteristics. Here, the solubility parameter is 9,
Examples of solvents with a molecular weight of 0 to 10.5 include acetone, toluene, benzene, chloroform, dioxane, etc., but the most common is acetone, and polymer components insoluble in this remain as insoluble substances during the spinning process. Since this causes problems such as blockage of the spinning nozzle that causes frequent yarn breakage, the above-mentioned problems can be avoided by removing this problem. Moreover, such a high-growth component has poor fluidity and significantly inhibits conversion into mesophase by heat treatment, resulting in poor quality of carbon fiber.

Examples of solvents with a solubility parameter of 7.5 to 8.5 include cyclohexane, cyclopentane, octane, and butyl acetate, but the most common is cyclohexane, and the low molecular weight components soluble in it are pitch. Since it lowers the softening point of the carbon fiber, it inhibits its infusibility by heating, and it also volatilizes during melt spinning, creating bubbles in the raw material pitch, leading to a decrease in spinnability and significantly deteriorating the quality of the carbon fiber. However, if such low-molecular components are removed, all of the above-mentioned problems can be avoided, and high-quality carbon fibers can be manufactured with good productivity.

Next, a specific method for obtaining the above-mentioned pitch-like material will be explained.

First, pitch raw materials are not limited to pitch separated by coal-based or petroleum-based rectification, but can also be recovered as a residue after gas and low-molecular components are recovered after hydrocracking coal or petroleum. Alternatively, hydrogen cracking may be performed under mild conditions from the beginning in order to increase the yield of the pitch-like material. In the present invention, such a pitch raw material is added to a solvent having a solubility parameter of 9.0 to 10.5, dissolved and dispersed, and insoluble matter is removed. Next, the soluble content is distilled at a temperature of, for example, 450 to 550°C to remove the solvent (although it is possible to distill off the solvent at a lower temperature by employing vacuum distillation), the residue is distilled off at a solubility parameter of 7. Treat with .5 to 8.5 solvent to remove solubles. The resulting pitch-like material has the above-mentioned high-molecular components and low-molecular components removed to have only the appropriate molecular weight, and almost all of it is converted into mesophase by heat treatment. Therefore, high-quality carbon fibers can be obtained by melt-spinning, infusibility, and carbonization treatment according to conventional methods.

In addition, components (ash and ultra-high molecular components) that are insoluble in high solubility parameter solvents (pyridine, etc.) are removed from the primary hydrogenation product of coal (including low-rank coal such as lignite), and the solubility parameter is 9. The carbonaceous pitch containing components insoluble in solvents (benzene, etc.) of .
℃ or less) to remove 80% of the insoluble components.
After converting more than % to soluble content, the solvent is distilled off, and the soluble content is further eluted and removed with a solvent with a solubility parameter of 7.5 to 8.5. It has excellent suitability as a raw material for manufacturing fibers.

As described above, the pitch-like substance used as a raw material in the present invention is
Basically, it removes both high-molecular components and low-molecular components based on their solubility in a solvent with a specified solubility parameter, and limits them to only those components in an appropriate molecular weight range that exhibits a specific range of solubility. Although it is best that 100% of the material is in the above appropriate molecular weight range, a small amount of a high molecular component or a low molecular component may be mixed as long as the above-mentioned problems do not occur.

The manufacturing method of carbon fiber using such a pitch-like substance as a raw material is not particularly special, and is based on the conventional manufacturing method of pitch-based carbon fiber, which involves melt spinning, heat infusibility, carbonization (and graphitization). ) can be performed sequentially to obtain high-performance carbon fiber. In this case, the pitch-like material specified in the present invention has the polymer components that cause thread breakage and spinning nozzle clogging during spinning as described above removed, and also has a property that lowers the softening point and prevents air bubbles from being mixed in due to evaporation. Low-molecular components that cause the problem have been removed, and almost all of them have the property of converting into mesophase by heat treatment, so spinning - infusibility - carbonization (and graphitization) is possible.
A series of steps can be carried out efficiently and with high productivity.

The present invention is configured as described above, and by clarifying the selection or purification criteria for pitch-like substances, it is possible to obtain good pitch-based carbon fibers.

Next, examples and comparative examples will be shown.

Example 1 After hydrogenating 1 kg of Australian Morwell coal under the conditions shown in Table 1, it was treated with acetone to remove insoluble matter. Then, it was distilled to recover acetone, further distilled to remove components with low boiling points below 530°C (normal pressure), and cyclohexane was added to the residue to extract and remove the soluble components to obtain about 350 g of pitch-like material. . 10 g of the pitch was sampled and the softening point was measured. After further heat treatment at 400°C for 4 hours in a N2 stream, the structure was observed with a polarizing microscope and the yield was measured.

Table 1: As a result, the yield was 86%, the softening point was 180°C, and the structure after heat treatment became a mesophase with a flow structure as shown in reference photo 1, making it an excellent raw material for carbon fibers. It was confirmed that it was.

In fact, when carbon fibers were manufactured using this pitch-like material under the conditions described below, no particular problems occurred during the manufacturing process, and the physical properties of the obtained carbon fibers were also excellent.

[Carbon fiber manufacturing conditions]

Melt spinning: Temperature: 300°C Nozzle diameter: 0.5 mmφ Winding speed: 350 m/miR Infusibility treatment: After treatment in air flow at 150°C for 4 hours, heating carbonization at 250°C for 1 hour Treatment: Heating at 1200°C x 20 g in N2 stream [Physical properties of carbon fiber] Wire diameter: 8 to 11 μm Tensile strength: 125 kg/mm2 Tensile modulus: 8,400 kg/mm”Example 2 Hydrogenation under the same conditions as Example 1 Chloroform is added to the pitch obtained to remove insoluble materials, and then distilled to recover chloroform, followed by further heating to remove the fraction with a low boiling point below 450°C. Octane is added to the residue to remove the soluble matter. was extracted and removed to obtain about 330 g of pitch-like material.Hereafter, heat treatment was carried out in the same manner as in Example 1, and the structure was observed under a microscope.
When the yield and softening point of the pitch-like material were measured, the yield was 80°C and the softening point was 160°C), and the structure was a mesophase with a flow structure as shown in Reference Photo 2, and the carbon fiber It was confirmed that it is an excellent raw material for industrial use.

When carbon fiber was manufactured using this pitch-like material under the following conditions, no particular problems occurred during the manufacturing process.
Moreover, the physical properties of the obtained carbon fiber were also extremely excellent. The softening point of the pitch-like substance used in this example was 160°C, which is slightly lower than the generally considered suitable softening point (180°C), but low molecular weight substances were actively excluded. Even those with a low softening point are sufficiently practical.

[Carbon fiber manufacturing conditions]

Melt spinning: Temperature: 240℃ Nozzle diameter: o, amm Winding speed: -400m/m1fi Infusibility treatment: After treatment at 150℃ for 8 hours, heating carbonization treatment at 250℃ for 1 hour at 1200℃ in N2 air flow ×201 heating [Physical properties of charcoal fiber] Wire diameter: 6 to 8 μm Tensile strength: 140 kg/mm2 Tensile modulus: 9,000 kg/mm” Comparative Example 1 For pitch obtained by hydrogenation under the same conditions as Example 1 , high molecular components were removed using carbon tetrachloride (solubility parameter: 8.5), and low molecular components were removed using n-hexane (solubility parameter: 3), and approximately 300 g of pitch-like material was obtained. This was heat-treated in the same manner as in Example 1, and the yield and softening point of the pitch-like material were measured, and the microstructure was observed using a microscope.As shown in Reference Photo 3, most of the structure was Although it was converted to mesophase, the yield was extremely low at 28%, and the softening point was 70°C, making it unsuitable as a raw material for carbon fibers.

In fact, this pitch-like material was melt-spun under the same conditions as in Example 1, and then treated at 50°C in an oxygen stream for 48 hours, but no increase in the softening point was observed, and sufficient infusibility could not be achieved. Ta. As a result, when the fiber was heated at a heating rate of 0.5°C/min, it melted and broke at 85°C.

Comparative Example 2 Approximately 420 g of pitch-like material (softening point: 120-300°C) was prepared in the same manner as Comparative Example 1, except that pyridine (solubility parameter: 10.7) and n-hexane were used as solvents.
I got it. When this pitch-like material was heat-treated under the same conditions, a yield of 88 cm was obtained and good results were obtained, but since it contained a considerable amount of polymeric components, the structure was not sufficiently converted to menphase. As shown in Reference Photo 4, it was confirmed that part of the matrix did not exhibit sufficient fluidity.

When melt spinning was attempted using this pitch-like material at a temperature of 400° C., it hardly became thread-like, and significant nozzle clogging occurred.

Example 3 Pyridine was added to pitch obtained by hydrogenating shaped coal produced in China as shown in Table 2 to remove insoluble matter, and then distilled to remove pyridine. The residue has a solubility parameter of 9.2
The amount of insoluble matter was determined by adding 25% by weight of benzene. This residue was hydrogenated together with a coal-based solvent under the conditions shown in Table 3, the solvent was distilled off, and cyclohexane was added to remove the soluble content, resulting in a softening point of 1.
A pitch-like material at 80°C was obtained.

After heat-treating this pitch-like material in a N2 stream at 400°C for 4 hours, the yield was measured and the structure was observed using a polarizing microscope.The yield was extremely high at 88 cm, and the structure was shown in the reference photo. As shown in Figure 5, the entire structure exhibited a mesophase flow structure.

Using this pitch-like material, melt spinning, infusibility, and carbonization were performed under the same conditions as in Example 1, and the series of steps could be carried out smoothly without any problems such as yarn breakage or nozzle clogging. , and the physical properties of the obtained carbon fiber were excellent as shown below.

[Physical properties of carbon fiber]

Wire diameter: 8-11μm Tensile strength: 120kg/mm! Tensile modulus: 8,200 kg/mm" Comparative Example 3 Residue pitch obtained by removing the solvent after the first hydrogenation in Example 3 (benzene insoluble content 25 cm: softening point 100
~300℃) was used as is, and then heated to 400℃ in a N2 stream.
After treatment for 4 hours, the yield and structure were observed using a polarizing microscope. As a result, the yield was 88 cm, which was somewhat satisfactory, but the structure remained isotropic as shown in Reference Photo 6, and it lacked suitability for use in carbon fibers.

Applicant: Kobe Steel, Ltd.

Claims (1)

[Claims] The solubility parameter is 9.0 to 10.5 (it is soluble in the solvent with the value at 25°C, and the solubility parameter is 7.5
8.5 (value at 25° C.) A method for producing carbon fibers, characterized in that carbon fibers are produced using a pitch-like substance that is insoluble in a solvent.