JPS5988923A - Manufacture of carbon fiber - Google Patents

Abstract

PURPOSE:To obtain carbon fiber having excellent spinnability, by heat-treating hydrogenated pitch at a temperature lower than that of the conventional process, spinning the resultant specific pitch for spinning, and making infusible and carbonizing the product. CONSTITUTION:After removing solid components from hydrogenated pitch, the pitch is heat-treated at 300-450 deg.C, preferably 320-420 deg.C in nitrogen gas stream to obtain a spinning-grade pitch having a quinoline-insoluble content of 15- 75wt%, preferably 20-60wt%, benzene-insoluble content of >=75wt%, preferably >=80wt%, and a softening point of 200-300 deg.C, preferably 220-270 deg.C (measured by KOKA flow tester), containing a premeso-phase pitch, and containing a continuous phase exhibiting optical anisotropy at room temperature. The pitch is spun, made infusible, and carbonized by heating in an inert gas to obtain the objective carbon fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for producing carbon fibers, and more specifically to an improved method for efficiently producing high-strength carbon fibers using pitch as a raw material.

Carbon fiber has thermal insulation properties, heat resistance, chemical resistance,
Due to its rigidity and conductivity, it is widely used as heat insulating materials, sealing materials, electromechanical parts, structural members, friction materials, carbon electrodes, etc.

Typical methods for producing this carbon fiber include a method of firing fibers such as acrylonitrile or cellulose, and a method of spinning and carbonizing a pitch-like material.
The former has a high raw material cost and low carbonization yield, making it unsuitable for industrial implementation, while the latter has the advantage of being able to use various pitches that are inexpensive and available in large quantities as raw materials. However, it is difficult to spin.Secondly, it has the disadvantage that high-quality carbon fiber cannot be obtained.
None of these methods can be said to be satisfactory as an industrial method.

Subsequently, various studies have been conducted on methods using pitch-like materials as raw materials in order to facilitate spinning and obtain high-quality carbon fibers. 4) A method of using a pitch-like material as a raw stone (Japanese Patent Publication No. 7 I5-28013, Japanese Patent Publication No. 49-8634), a petroleum-based pitch material is first heat-treated in the presence of a Lewis acid catalyst. after,
A method in which the catalyst is removed and further heat-treated is used as a raw material (Japanese Patent Publication No. 7533/1983), in which mesoface pitch with a predetermined memphaceous content is formed under reduced pressure, and this is used as raw ore to produce carbon fibers. method (Japanese Patent Application Laid-Open No. 54-11330, Japanese Patent Publication No. 54-1810), method using membrane pitch having a specific composition and specific physical properties as a raw material (Japanese Patent Application Laid-open No. 54-55625, U.S. Patent No. 3,787,541), but these methods have not been able to sufficiently improve the spinnability, and it has not been possible to sufficiently improve spinnability, and it has been difficult to achieve physical properties comparable to that of polyacrylonitrile using poor polyacrylonitrile as a raw material. High performance grade carbon fiber has not been obtained.

In order to improve the spinnability of such pitches and the physical properties of carbon fibers, the present inventors first hydrogenated pitches with tetrahydroquinoline or the like, and then treated the hydrogenated pitches with 450% We proposed a method for manufacturing carbon fiber (%Gan Sho 56-1.17470) using as a raw material pre-mesophase pitch obtained by heat treatment at a temperature of 0.degree. C. or higher.

However, in this manufacturing method, the pinch that has been hydrogenated in the first stage is treated at a high temperature of 450°C or higher in the second stage, which causes more pitch to be thermally decomposed than necessary, reducing the yield of premenphase pitch. However, in order to produce pre-mesophase pitch having certain properties, it is not always satisfactory, as there are problems such as the necessity of selecting processing conditions strictly.

In order to solve these problems, the present inventors conducted further intensive research and found that the pitch that had been hydrogenated in the first stage was heated to 300 to 450°C, preferably 32°C, in the second stage.
It was discovered that a specific pre-mesophase pitch obtained by treatment at a temperature of 0 to 420°C has good reproducibility and excellent spinnability, and based on this knowledge, the present invention was developed. Ta.

That is, in the present invention, the hydrogenated pinch from which solids have been removed is heat-treated at 300 to 450°C in a nitrogen gas flow to reduce the quinoline insoluble content to 15 to 75% by weight and the benzene insoluble content to 7% by weight.
5% by weight or more, a softening point of 200 to 300°C by Koka flow tester, containing premesophase pitch, and having a continuous phase exhibiting optical anisotropy at room temperature, and then forming a spinning pitch. The present invention provides a method for producing carbon fiber, which is characterized by spinning, infusible treatment, and further carbonization treatment.

The hydrotreated pitch used as a raw material in the method of the present invention is preferably one obtained by hydrogenating raw pitches using a hydrogen-donating solvent. At this time, raw material pitches include, for example, coal tar pitch, coal liquefied products, fraction iq'+ obtained by the fluid contact molecule W (method (P゛CC method)) of distillation residue crude oil of by-product tar during naphtha thermal decomposition. : Asphalt, which is the distillation residue of cool crude oil, and pitch obtained by thermal decomposition of this, etc. are used.As a hydrogen-donating solvent, as long as it can bathe the raw material pitch and hydrogenate it, it can be used. For example, hydrogenated products such as quinoline, naphthalene, anthracene, anthracene oil, creosote oil, and wash oil can be used.

In the first stage of manufacturing hydrogenated pitch, raw pitches and a hydrogen donor are mixed at a weight ratio of 1 = 0.2 to 3, placed in an autoclave, and the air inside is removed from the desired gas. After replacing with inert gas or hydrogen gas such as, 300-500℃, preferably 350-48
It may be heated in a temperature range of 0° C. for 1 to 120 minutes, preferably within 60 minutes, and then free carbon may be melted by filtration or centrifugation to remove solids such as free carbon. When the hydrogenated pinch thus obtained is observed at room temperature under polarized light magnification, it is mostly in an optically isotropic phase, with slight mesophase spherules being observed in some cases.

In the method of the present invention, the hydrogenated pitch of the first stage thus prepared is heated in a nitrogen atmosphere at a temperature of 300 to 450°C, preferably 320 to 420°C, for 10 to 10 minutes in the second stage. Heat treatment is performed for 500 minutes, preferably 15 to 300 minutes. By this heat treatment, the hydrogenated pitch undergoes polycondensation between molecules and is converted into one containing brimesophase pitch.

In the spinning pitch containing the premenphase pitch obtained in this way, the quinoline soluble content is 75% by weight,
Preferably 20 to 60% by weight, benzene-insoluble content of 75% by weight or more, 80% by weight or more of a suitable weight, softening point of 200°C by Koka type flow tester: 220 to 270°C. A carbon fiber having a continuous phase that is 1 and contains brimesophase pitch and exhibits optical anisotropy at room temperature provides a carbon fiber with excellent spinnability and high strength. In this case, an optically anisotropic continuous phase at room temperature transforms into an optically isotropic continuous phase at the spinning temperature. Such pinches are manufactured by appropriately selecting the processing conditions described in 11J.

In the method of the present invention, in order to obtain a spinning pitch containing the above-mentioned premenphase pitch having good spinnability, it is necessary that the pitch be an optically isotropic continuous phase at room temperature by hydrogenation treatment in the first step, and Contains no quinoline-soluble matter,
Alternatively, it is preferable to form a product containing less than 30% by weight, and then to subject it to the second stage of heat treatment.

In addition, the heat treatment time in the first stage hydrogenation treatment is appropriately selected from the above range depending on the type of raw material pitch, thermal history, etc., and furthermore, during the second stage heat treatment, the low point substances generated are There is also a need to remove them at the same time. Removal of these low-boiling substances can be carried out by vacuum treatment, inert gas blowing, R,
Treatment is carried out using membrane distillation equipment or in combination with high-speed stirring. The rate of removal of this low boiler has a significant influence on controlling the amount of continuous phase exhibiting optical anisotropy at room temperature in the resulting spinning pitch.

The spinning pitch containing Brimesophase pitch obtained by the method of the present invention has a continuous phase that exhibits optical anisotropy at room temperature exhibits a flow structure, in which optically isotropic portions are dotted as small spheres. There is.

Such spinning pinches have a softening point of 200 to 300°C, preferably 220 to 270°C, as measured by a Koka type flow tester.
It is within the temperature range of ℃. This softening point increases]
, (indicated by the inflection point drawn on the graph as measured by a flow tester. The brimesophase contained in the spinning pitch in the present invention is soluble in quinoline, optically isotropic and stable at room temperature. , and changes to anisotropy after carbonization. Spinning in the present invention may include melt spinning, extrusion spinning,
Any blow spinning method may be used. When melt spinning, the pitch is placed in a spinner with a nozzle diameter of 0.1 to 0.7 nm, and the pitch is 50 to 18 nm below the softening point of the pitch.
It is heated to a temperature lower than about 0℃, /I00℃, and spun with more pressure than pitch p4 (at this time, the spinning temperature is /
If the temperature exceeds 100℃, the pinch will deteriorate and become unfavorable.
In addition, high-speed spinning is preferable from the viewpoint of productivity, and in order to maintain the strength of the carbon 4 fibers (fM), the pitch fibers have a center spacing to reduce the diameter of the fibers. The spinning speed, that is, the winding speed is 300 to 2000 m/
It is suitable that the diameter of the pitch fibers is 10 μm or less.

The fibrous pinch spun in this way is heated to 0.5 to 200 to 400°C in air to undergo oxidation and infusibility treatment, and then placed in an inert gas at a temperature rate of 3 to 1000°C. Carbonize by heating to ~1500°C, and further heat to 2000~300°C in an argon atmosphere as desired.
The carbon-11 fiber obtained by the method of the present invention, which is heated to 0° C. and graphitized, becomes optically anisotropic throughout the fiber by such carbonization treatment.

According to the carbon fiber manufacturing method of the present invention, the hydrogenated pinch obtained in the first step is heat-treated in the second step at a temperature lower than that of conventional methods, thereby achieving good reproducibility and spinnability. It is possible to obtain a spinning pitch containing a purinone phase pitch that is delayed in a high yield, and high-strength carbon fibers can be produced industrially and efficiently from this spinning pitch.

Next, the present invention will be explained in more detail with reference to Examples.

Note that the percentages in the examples are based on weight.

Example 1 A pinch of coal having a quinoline dissolved content of 8% and a softening point of 89° C. was melted and filtered under pressure through a bronze filter having a pore size of 1511 m to remove free carbon.

This pinch 3507 and tetrahydroquinoline 350f were charged into an autoclave, and after the autoclave was purged with nitrogen, the temperature was raised to 430°C and held for 30 minutes. This solution was filtered through a 2504 glass filter and then distilled under reduced pressure at 250°C for 30 minutes to remove tetrahydroquinoline. The residue was used as hydrotreated pitch. FIG. 1 shows a polarizing microscope photograph of the hydrogenated pitch at room temperature with a magnification of 320 times. The hydrogenated pitch had a quinoline soluble content of 0%, a benzene insoluble content of 75%, and a softening point of 51°C using a Koka type flow tester.

M Hydrogenation Treatment Four pieces of Pinch 3002 were placed in a Lough flask, and heated under nitrogen bubbles with stirring for 60 minutes at 380°C. After reducing the pressure at 1.0 + an Hg to remove low boiling point substances, the mixture was further heated at the same temperature for 180 minutes. A spinning pitch containing pre-mesophase pitch was obtained by heat treatment at normal pressure with nitrogen bubbles (yield: 37%). This had a quinoline soluble content of 41%, a benzene insoluble content of 91%, and a softening point of 245°C using a Koka type flow tester. FIG. 2 shows a polarizing microscope photograph taken at room temperature of 320 particles of spinning pitch including premen phase. The continuous phase in the figure is optically anisotropic, and the scattered round black dots are isotropic.

The spinning pitch containing this pre-mesophase pitch and having optical anisotropy as a continuous phase was put into a melt spinning machine having a nozzle with a diameter of 0.3 mm and spun at a temperature of 360°C. Winding speed 8
00 m Steady winding in 7 minutes, fiber diameter is 9.5
It was μm. This pitch fiber was heated to 300° C. at a rate of 2° C./min in air and held for 30 minutes. Further, the temperature was raised to 1400°C at a rate of 5°C/min in a nitrogen stream and held for 15 minutes to obtain carbon fibers. This carbon fiber had a tensile strength of 3081<y/mA, an elongation of 1.5%, an elastic modulus of 2 J, ot/-, and a fiber diameter of 6.5 μm.

Comparative Example 1 Coal pitch with a quinoline dissolved content of 12% and a softening point of 102° C. was melted and filtered through a 25G4 glass filter to remove free carbon. This coal pitch of 2.000 iF and hydrogenated anthracene oil of 1500 r were charged into an autoclave, and after purging with nitrogen, the temperature was raised to 450° C. and held for 60 minutes. This solution was filtered through a 2504 glass filter, then transferred to a four-hole flask, and while stirring, the pressure was reduced in a nitrogen atmosphere to distill off the hydrogenated am]-helical oil to prepare a hydrogenated pitch. Next, the pressure was brought to normal, and the temperature was raised from 300°C to 440°C at a rate of 3°C/min while constantly distilling off low-boiling substances using nitrogen bubbles. When it reaches 440℃, stop heating and cool it down to 300℃ in about 8 minutes.
℃ and Toshida. The obtained spinning pitch containing the prime phase has a quinoline soluble content of 1168% and a benzene insoluble content of 62%.
The softening point was 144°C using a Koka type flow tester. Figure 3 shows a polarized light microscope at room temperature that is 320 times the pitch.
Show photos. In the figure, the continuous phase is isotropic and the globules are optically anisotropic.

Using this pitch, spinning, infusibility, and carbonization were performed in the same manner as in Example 1. However, although we tried spinning at a spinning temperature of 200 to 320°C, the highest winding speed was 1.50 m/min at 260°C.
The fiber diameter also varied from 15 to 38 μm, and the tensile strength of the obtained carbon fibers was less than 112 Kq/mA and varied widely.

Example 2 Hydrogenated pinch 1002 prepared in Comparative Example 1 was placed in a stainless steel four-loop flask, and heated at 400° C. for 2 hours while stirring and removing low-boiling substances by nitrogen bubbles. Thereafter, it was cooled for 3 minutes to reach 300°C.

Next, spinning, infusibility and carbonization were carried out in the same manner as in Example 1. This operation was repeated four more times to obtain carbon fibers. The results are shown in Table 1.

Comparative Example 2 Hydrotreated pitch 1.007 prepared according to Comparative Example 1 was charged into a stainless steel neck flask, and 4.
The mixture was placed in a salt bath adjusted to 70°C and heated under nitrogen bubbles for 20 minutes while stirring. Then cool for 5 minutes and
The temperature was 0°C. Next, spinning, infusibility and carbonization were carried out in Example 1.
I did the same thing. This operation was repeated four more times to obtain carbon fibers. The results are shown in Table 2.

As is clear from Tables 1 and 2, the method of the present invention has good reproducibility and can obtain spinning pitch with excellent spinnability at a relatively high yield compared to the comparative method. High-strength carbon fibers can be stably produced from this pitch.

Example 3 Carbon fibers were obtained in the same manner as in Example 2, except that the heating temperature and time of the hydrogenated pitch were changed to 420° C. and 1.5 hours, respectively.

The properties of the spinning pitch produced during the process and the carbon fiber finally obtained are shown below.

Properties of pitch for spinning Quinoline soluble content 48.3% Benzene insoluble content 97.3% Softening point 261 °C Yield 35.8% Carbon fiber properties Fiber diameter 7.9 μm Tensile strength 280 Kq/yU elongation
1.5% bounce rate 19. Ot/4 Comparative Example 3 In Comparative Example 2, the heating time of the hydrogenation treatment pinch was set to 40
A pitch for spinning was obtained in the same manner as in Comparative Example 2, except that the pitch was replaced with 100 ml, and an attempt was made to spin this to produce carbon fibers, but spinning was not possible because the softening point of this pitch was high.

The properties of the spinning pitch are shown below.

Properties of spinning pitch Quinoline insoluble content 79.7% Benzene insoluble content 98.1% Softening point 330℃ or more

[Brief explanation of drawings]

Figure 1 shows the hydrogenated pitch in Example 1, Figure 2 shows the spinning pitch in Example 1, and Figure 3 shows the ratio +lWI+
lJ] of the spinning pitch at room temperature, respectively.
This is a microscopic photograph. '(~11nI ・"T 2 +゛1 ・("+ 3 f'1 Continuation of page 1 @ Inventor Kiyoshi Shinbo 2-11-12-04 Kamezawa, Sumida-ku, Tokyo Q and applicant Dainippon Ink Chemical Industry Co., Ltd. 3-35-58 Sakashita, Itabashi-ku, Tokyo

Claims (1)

[Claims] 1 Hydrogenated pitch from which infusible or insoluble solids have been removed is heat-treated at a temperature of 300 to 450°C in a monoxide gas stream to obtain a quinoline soluble content of 15 to 75% by weight and a benzene insoluble content of 75% by weight. In addition, after forming a spinning pitch having a softening point of 200 to 300°C using a Koka type flow tester, containing Brimesophase pitch, and having a continuous phase exhibiting optical anisotropy at room temperature, and then spinning, A method for producing carbon fiber, characterized by carrying out an infusible treatment and then a carbonization treatment.