JP2849156B2 - Method for producing hollow carbon fiber - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hollow carbon fiber, and more particularly to a high-performance hollow fiber with excellent productivity based on a pitch precursor fiber obtained by a conventionally known method. The present invention relates to a method for producing carbon fiber.

2. Description of the Related Art Carbon fiber is a material having excellent specific strength and specific elastic modulus, and has recently attracted attention as a strong and light material in the aerospace field, the automobile industry, and other industrial fields.

As a method for further reducing the weight of the carbon fiber and improving the carbon fiber to have a practically sufficient strength, a hollow carbon fiber having pores therein has been proposed.

As a manufacturing method thereof, as disclosed in JP-A-58-91826, when a pitch is melt-extruded and spun, a nozzle having a nozzle length / diameter ratio (L / D ratio) of 10 or more is used. A method has been proposed in which a hollow pitch precursor fiber is obtained by spinning and carbonization treatment is performed after infusibilizing the fiber.In this method, since a nozzle having an L / D of 10 or more is used, a method for spinning is used. Due to the high extrusion pressure, operation is difficult, or it is difficult to manufacture a nozzle having an L / D of 10 or more, and further, it is difficult to clean the nozzle hole.

Also, JP-A-62-117816 uses a nozzle having an L / D of less than 10 to obtain a hollow pitch precursor fiber by setting the melt pitch shear rate when passing through the nozzle to 400 sec ^-1 or more, There has been proposed a method of performing carbonization after infusibilization. According to the embodiment of this method, since a small amount of air is mixed in the spinning pitch for spinning, it is considered that there is a problem in stability during spinning.

As described above, in the conventional method, a hollow pitch precursor fiber is obtained, and the hollow carbon fiber is produced by infusibilizing and carbonizing the hollow pitch precursor fiber. However, the spinning stability of the hollow pitch precursor fiber and the hollow pitch precursor fiber are weak. Therefore, there was a problem in its handling.

Problems to be Solved by the Invention The present invention is a method for producing an infusible, carbonized carbon fiber having a hollow carbon fiber structure during infusibilization and carbonization from a pitch precursor fiber having excellent productivity obtained by a conventionally known method. An object of the present invention is to provide a method for producing a hollow carbon fiber having excellent productivity.

Means for Solving the Problems The present inventors focused on the swelling of the fiber during infusibilization, the shrinkage behavior of the fiber during carbonization, and as a result of repeated studies,
The present invention has been completed. That is, in the present invention, the pitch precursor fiber is reacted in a mixed gas atmosphere containing 3 to 50% by volume of chlorine and 10% by volume or more of oxygen, and the weight is 5 to 5%.
A method for producing hollow carbon fibers, characterized in that the infusible fibers are increased by 20%, and the infusible fibers are carbonized or graphitized as needed in an inert atmosphere.

 Hereinafter, the contents of the present invention will be described in detail.

The pitch of the raw material used in the present invention is a coal-tar, a lime-based pitch such as a coal-tar pitch, an ethylene tar pitch, a petroleum-based pitch such as a decant oil pitch obtained from a fluid catalytic cracking residue, or a catalyst from a naphthalene or the like. Although it includes various pitches such as synthetic pitches made using lime, in the present invention, lime-based pitch is particularly suitable because it is necessary to give a difference in the degree of reaction between the surface layer portion and the inside of the fiber during infusibilization. .

In addition, this pitch may be any of an optically isotropic pitch and an optically anisotropic mesophase pitch, but in the present invention, it is more preferable to use a mesophase pitch having a mesophase content of 40% or more. . The pitch used in the present invention has a softening point of 200 ° C. or more and 400 ° C. or less, more preferably 250 ° C. or more and 350 ° C. or less.

The pitch precursor fiber is obtained by melt-spinning the pitch by a conventionally known method. For example, the mesophase pitch has a viscosity of 100 to 20,000.
At a temperature indicating poise, 100 to 20 while extruding from a capillary with a diameter of 0.1 to 0.5 mm at a pressure of about 0.1 to 100 kg / cm ² G
Drawing is performed at a take-up speed of 00 m / min to obtain a pitch precursor fiber.

At this time, the fiber diameter of the pitch precursor fiber is 5 to 25.
μm, preferably 10 to 18 μm. If the fiber diameter is less than 5 μm, the fiber is too thin, and it is difficult to hollow the fiber by the method of the present invention. On the other hand, if the fiber diameter exceeds 25 μm, the fibers tend to fuse with each other during the carbonization treatment after the infusibilizing operation, or it becomes difficult to produce a completely hollow fiber.

Next, this pitch precursor fiber is reacted in a mixed gas atmosphere containing 3 to 50% by volume, preferably 5 to 25% by volume of chlorine and 10% by volume or more of oxygen to increase the weight of the fiber after infusibility. Of 5 to 20%, preferably 8 to 17%.

If the chlorine content is less than 3% by volume, swelling of the fibers during infusibility is insufficient, and the resulting carbon fibers will not be hollow fibers. On the other hand, when the chlorine concentration exceeds 50% by volume, the reaction proceeds rapidly, and the resulting fiber becomes brittle. On the other hand, if the oxygen concentration is less than 10% by volume, infusibilization does not sufficiently proceed, and fibers are fused together during carbonization.

The components of the gas other than chlorine and oxygen are preferably non-oxidizing gas such as nitrogen, but may include oxidizing gas such as oxidizing gas such as ozone, nitrogen dioxide, and sulfur dioxide. Most preferred is a mixture of air and chlorine gas.

The infusibilization temperature is 150 to 400 ° C, preferably 180 to 350
It is preferably in the range of ° C. The infusibilization time is 40
Minutes or less, preferably between 5 and 35 minutes. If the infusibilization temperature is lower than 150 ° C., the reaction will be slow and the infusibilization will be insufficient, or the reaction will take a long time to reach the center of the fiber, making it difficult to obtain a hollow fiber.
On the other hand, when the temperature exceeds 400 ° C., the reaction proceeds rapidly, and the obtained fibers tend to be brittle. If the reaction time is longer than 40 minutes, the reaction easily reaches the center of the fiber, and the obtained carbon fiber hardly becomes hollow.

If the weight increase of the fiber at the end of the infusibilization is less than 5%, the infusibilization is insufficient and the fibers are fused to each other during carbonization. If the weight increase exceeds 20%, the reaction proceeds too much, and the resulting carbon fiber does not become hollow. The weight increase is determined by the following equation, where w1 is the weight of the pitch precursor before infusibilization and w2 is the weight of the infusibilized yarn at the end of infusibilization.

By subjecting the infusibilized fiber thus obtained to a carbonization treatment by a conventionally known method, a hollow carbon fiber can be obtained.
As the carbonization conditions at this time, the heating rate between 200 ° C and 800 ° C is 10 ° C / min or more and 500 ° C / min or less, preferably 20 ° C / min.
min min and 200 ° C / min or less. When the heating rate is 10 ° C./min or less, the swollen infusible fiber shrinks during carbonization, making it difficult to obtain a hollow fiber. In addition, if the temperature rise rate is 500 ° C / min or more, rapid melting and expansion occurs in the infusibilized portion of the infusibilized yarn where the infusibilization has not proceeded sufficiently, and the internal melt jumps out to the fiber surface and the fibers are fused together. May occur.

If necessary, the obtained carbon fiber may be graphitized by a conventionally known method to obtain a hollow graphitized fiber.

Action The reason why hollow carbon fibers can be obtained by the present invention is as yet unknown, but it is considered as follows.

The infusibilizing treatment using a mixed gas of chlorine and oxygen converts the fiber surface into a hard thermosetting substance. At this time, by introducing chlorine in an amount of about 5 to 20% by weight, the fiber surface swells and the fiber diameter increases.

According to the method of the present invention, since the fiber central portion is still heat-fusible after the infusibilizing treatment, during the infusibilizing treatment or during the subsequent carbonization treatment, the molten portion at the fiber center is drawn to the swollen fiber surface layer, It is considered that continuous voids are generated in the center of the fiber.

As described above, according to the production method presented in the present invention, only the surface layer of the fiber is swollen and the reaction amount inside the fiber is slightly suppressed, whereby the hollow carbon fiber can be produced efficiently.

Examples Hereinafter, examples and comparative examples will be described to further clarify the present invention. In the present invention,
Various physical property values used to represent the characteristics of the pitch-based carbon fiber and the raw material pitch were defined as follows.

(1) Fiber diameter, tensile strength, tensile elastic modulus, fiber diameter, tensile strength, tensile elastic modulus are JIS-R-7601 (1
986). The tensile strength and the tensile modulus of the hollow fiber are based on the cross-sectional area obtained from the outer diameter of the fiber, and the hollow portion is not corrected.

(2) Viscosity and softening point The viscosity was measured using a concentric rotating double cylinder viscometer.
The softening point is the temperature at which the apparent viscosity calculated from the Hagen-Poiseuille equation using a flow tester is 20,000 poise.

(3) Mesophase content The mesophase in the present invention is defined as an optical anisotropy that can be determined by embedding a cooled and solidified pitch in a resin or the like, polishing the surface, and observing the surface using a reflection deflection microscope. Refers to the organization shown. The mesophase content is indicated by the area ratio of the anisotropic structure observed and observed as described above.

(4) Toluene-insoluble, quinoline-insoluble, toluene- and quinoline-insoluble are JIS-K-2425
(1978).

Examples 1 to 3 Coal tar pitch having a softening point of 80 ° C from which quinoline insolubles had been removed as a raw material was directly hydrogenated using a Co-Mo catalyst. After heat treatment of the hydrogenated pitch at 480 ° C. under normal pressure, a mesophase pitch was obtained except for a low boiling point component.
This pitch has a softening point of 300 ° C and a toluene insoluble content of 8 minutes.
The content was 5% by weight, the quinoline insoluble content was 10% by weight, and the mesophase content was 95%.

Using this pitch, using a spinning machine having a nozzle pack with a capillary diameter of 0.14 mm and a number of nozzle holes of 3000,
A hollow pitch precursor fiber having a mesophase pitch viscosity of 800 poise and a yarn diameter of 13 μm was obtained.

After drying and weighing this pitch precursor in a desiccator, 10% by volume of chlorine and the remaining gas as air were maintained at 200 ° C. for 10 minutes in a mixed gas atmosphere.
The temperature was raised to a predetermined temperature with n, and the temperature was maintained for a predetermined time to perform infusibility treatment. The obtained infusible fiber was dried in a desiccator and then weighed to determine the weight increase. This infusibilized fiber is heated from room temperature in an argon gas atmosphere at a heating rate of 40 ° C / min.
The temperature was raised to 2000 ° C. and kept for 15 minutes to perform carbonization and graphitization. Table 1 shows the physical properties and infusibility treatment conditions of the obtained graphitized fibers.

Further, scanning electron micrographs of the graphitized yarn are shown in FIGS. 1 (1) and (2) in which the hollow graphitized yarn obtained in Example 1 is shown.
FIG. 2 shows the hollow graphitized yarn obtained in Example 2. Further, as can be seen from a comparison between Example 1 and Example 2, the degree of hollowness can be controlled by changing the infusibilization conditions.

Comparative Examples 1 to 5 The pitch precursor fibers used in Example 1 were used in Comparative Example 1
Then, in Comparative Examples 2 to 5, after holding at 200 ° C. for 10 minutes in a mixed gas atmosphere of chlorine and air of a predetermined concentration in Comparative Examples 2 to 5, the temperature was raised to a predetermined temperature at a predetermined temperature rising rate, and held as it was for a predetermined time. To perform infusibilization.

The obtained infusible fiber was dried in a desiccator and then weighed to determine the weight increase. The infusible fiber was heated from room temperature to 2000 ° C. at a rate of 40 ° C./min from room temperature in an argon gas atmosphere, and kept for 15 minutes to perform carbonization and graphitization. Table 1 shows the physical properties and infusibility treatment conditions of the obtained graphitized fibers. A scanning electron micrograph of Comparative Example 1 is shown in FIG.

As is clear from the above Examples and Comparative Examples, it is understood that hollow carbon fibers can be easily produced from solid pitch precursor fibers by the method of the present invention.

Effect of the Invention According to the present invention, a high-performance hollow carbon fiber is produced from a pitch precursor fiber that is efficiently produced by a conventionally known technique without passing through a hollow pitch precursor fiber that is difficult to manufacture and difficult to handle. It becomes possible.

[Brief description of the drawings]

1 (1) and (2) are hollow carbon fibers obtained by the method of Example 1, FIG. 2 is hollow carbon fibers obtained by the method of Example 2, and FIG. 3 is a method of Comparative Example 1. 5 is a scanning electron micrograph showing the shape of each fiber of the conventional carbon fiber obtained in FIG.

──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Hirofumi Sunago 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside the 1st Technical Research Laboratory of Nippon Steel Corporation (72) Inventor Norio Tomioka 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Corporation 1st Technical Research Institute (56) References JP-A-49-75828 (JP, A) JP-A-51-75126 (JP, A) (58) Fields investigated (Int. Cl. ⁶⁾ , DB name) D01F 9/12-9/32

Claims (1)

(57) [Claims] (1) A pitch precursor fiber of 3 to 50% by volume.
In a mixed gas atmosphere containing 10% by volume or more of oxygen and chlorine to obtain an infusible fiber whose weight has been increased by 5 to 20%.
A method for producing a hollow carbon fiber, wherein the infusibilized fiber is carbonized in an inert atmosphere or graphitized as needed.