JPS6163719A - Manufacture of carbon fiber - Google Patents

Abstract

PURPOSE:To obtain a carbon fiber having high strength and high modulus and free from cracking, by spinning a molten pitch having a specific meso-phase content through a spinneret wherein the cross-sectional area of the outlet of the nozzle is larger than that of the narrowest part of the channel in the nozzle, and infusibilizing and carbonizing the spun fiber. CONSTITUTION:The catalytic thermal cracking residue of a vacuum-distilled gas-oil is distilled, and the fraction having initial boiling point of >=404 deg.C is heat-treated at 420 deg.C under the flow of methane gas to effect the growth of meso-phase and obtain a meso-phase pitch having a meso-phase content of >=70%. The pitch is subjected to the melt-spinning using a spinneret wherein the cross-sectional area of the outlet of the nozzle is larger than that of the narrowest part 2 of the channel 1 in the nozzle. The spun pitch fiber is infusibilized at 300 deg.C and carbonized at 2,500 deg.C to obtain the objective carbon fiber. The melt-spinning is preferably carried out at a temperature higher than the softening point of the meso-phase pitch by 55-120 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing charcoal-J fibers. More specifically, when producing pitch-based carbon 44, the present invention involves melting pitch containing a specific electrolyte as a raw material using a spinneret having a specific shaped nozzle (discharge hole). The present invention relates to a method of spinning and producing defect-free, high-strength, high-modulus carbon fibers of excellent quality.

The mesophas used in the present invention
e]l' is one of the pitch constituents, and the cross section of the pitch block solidified near room temperature was polished and examined under crossed Nicols using a reflective polarization microscope. When observed, optical transport is observed, that is, a portion that is optically anisotropic, and a pitch in which most of the pitch consists of this "meth phase" is called a "meso-7A phase."

The mesophase content of the t&mesophase pitch is calculated from the area ratio of the optically anisotropic portion by observation using a reflective polarizing microscope.

In recent years, materials with high strength and high elasticity have been required in various fields such as the aircraft industry and automatic heavy industry, and the four requirements for carbon fiber with these characteristics are rapidly increasing. . It is a well-known fact that the precursor of currently available high-strength, high-elastic carbon fibers is mainly polyacrylonitrile fibers. However, this real acrylonitrile fiber is not only expensive, but also the carbon 4 fiber obtained from it is only about 100% low, leading to an increase in the price of the final product, carbon fiber. .

2. Description of the Related Art As a method for inexpensively constructing high-strength, high-modulus carbon fibers, a method for producing pitch containing mesophase as a technology was described in the Tokukai Sho 54-1810. It is a well-known fact that carbon fibers are excellent raw materials for high-strength, high-modulus carbon fibers.

Problems to be Solved by the Invention However, in pitch as a raw material for carbon fiber, the content of mesophase and the physical properties of mesophase have a large influence on the physical properties of carbon fiber, but the content of mesophase is high. Mesophase rights with good quality and quality,
The physical properties of the resulting charcoal and ash are improved. Also, the pitch with low menphase content 1 is carbon+44 obtained from it.
The strength 11 elasticity t of carbon fiber is rather low, and it is not suitable as a material for high-strength, high-elasticity carbon fiber. The cross section of pitch-based carbonaceous A4 cypress wood can be roughly divided into carbon arrangement: dam-like/dam-like (disorder).
, radial shape, onion shape (concentric circle shape), etc. (Reference example; for example, 12th Bi
enial Co11fereace on C
Arbon, July.

329 (1975), Pittaburg; and Ceramics 11 (1976) No. 7, 612-62.
1). These structures are highly dependent on the physical properties of the 1-Moraceae pitch. When melt-spinning is performed using two spinnerets, which are normally used in which the narrow tube part of the #1 pitch passage inside the nozzle is straight and circular in cross section, the higher the raw material pitch, the higher the Because the filament produced by melt spinning has a high degree of carbon fiber orientation, the carbon fiber becomes a pitch fiber with a radial VC orientation structure, and when this is infusible and then carbonized, the resulting carbon R fiber has a radial structure. becomes *m 4F. Carbon 4 with radial structure
Ia often has large cracks extending from the periphery toward the center of the fiber, and loses its commercial value. The present invention solves the problems of the method of manufacturing pitch-based carbon fibers according to the prior art as described above, and provides a method for stably manufacturing crack-free carbon fibers of excellent quality. This objective is achieved by the method of the present invention.

The inventor of the present application has completely eliminated the cracks in the cross section of carbon 1 cup produced using Nomen Phase Pitch as a material with a mesophase content of 70 or more. It has been found that the physical properties of the ink can be significantly improved. As a method to eliminate the carbon t & ml cross section, the mesophase pitch is set at a nozzle exit section (preferably at the nozzle exit section) which is larger than the cross section of the narrow J section inside the nozzle. I
Pj of the narrow tube g5 of the ff face record? The ratio to the area is 2
A spinneret that is more than double the size (Figures 1, 2, and 3)
40 to 14 from the softening point of the mesophase pitch (the softening point measured by Koka type flow tester).
Melt spinning at a temperature higher than 0°C, preferably 120°C higher,
By performing infusibility treatment followed by carbonization treatment using a conventional method, a method for manufacturing carbon fibers of excellent quality with no cracks was completed.

Q. Spinning by the method of the present invention-J! To describe the A degree in detail, mesophase pitch containing menphase,
The optimum spinning temperature differs slightly depending on the physical properties of Men7Aze, but as a result of experiments, it is 40° below the softening point of mesophase pitch.
If the spinning temperature is not higher than ℃, the viscosity of the menphase pitch will be too high, resulting in poor spinnability and difficulty in spinning. Due to decreased viscosity, increased staining of the spinneret, deterioration of mesophase pitch, etc., the frequency of yarn breakage increases and stable spinning becomes impossible. Therefore, the spinning temperature of mesophase pitch is 40 to 140℃, preferably 55 to 120℃, which is higher than the softening point of menphase pitch.
A temperature range higher than ℃ is suitable. (The Europeanization point of mesophase is 190 to 240'C) The raw materials for the mesophase pitch used in the present invention include atmospheric distillation residue of petroleum,
Vacuum distillation residual oil, thermal catalytic cracking residual oil of vacuum gas oil, petroleum-based heavy oil such as tar and pitch by-produced by heat treatment of these residual oils, coal-based heavy oil such as coal tar, coal tar pitch, coal liquefied products, etc. It's empty.

This raw material is heat-treated in a non-oxidizing atmosphere to generate mesophase, which is grown, and a portion that is mostly menphase is separated to produce mesophase pitch. The inventor of the present invention proposes that the mesophase pitch has a mesophase content of 70% or more, preferably 90% or more.

It has been found that carbon fibers of excellent quality can be produced at low cost by the method of the present invention. If the mesophase content of the mesophase pitch is 70% or less, even if it is spun using a normal method and subjected to infusibility treatment and carbonization treatment, the obtained carbon IJ1m has a low degree of carbon orientation, so its cross section has a radial structure. Therefore, it does not crack, but its tensile strength and modulus of elasticity are low and its commercial value is low. When mesophase pitch is used as a raw material for carbon fibers, the higher the mesophase content, the better.When melt spinning mesophase pitch containing 470% or more, preferably 90% or more, the thin tube inside the nozzle is Using a spinneret having a nozzle exit cross-sectional area larger than the final cross-sectional area, preferably with an area ratio of twice or more,
Carbon fibers with no cracks in the cross section can be produced by changing the speed of the mesophase pitch flow in the nozzle and disturbing the orientation of the carbonaceous material in the mesophase pitch.

The first example of the nozzle shape of the spinneret used in the method of the present invention is as follows.
2 and 3, the shape is not limited to this, and the cross section of the nozzle is not limited to a circular shape either, but is limited only to the conditions shown in the claims. @
Figures 1, 2, and 3 are cross-sectional views passing through the center of the nozzle. In each figure, l is the spinning solution introduction part, and 2 is the narrowest V! 3 indicates the outlet of the discharge hole.

Example 1 The initial fraction of thermal catalytic cracking residual oil of vacuum gas oil with an initial distillation temperature of 404°C or higher was heat-treated at 420°C for 2 hours while feeding methane gas, and this was further heated at 320°C for 16 hours to form a mesophase. It was grown and the part consisting mostly of mesophase was separated. The mesophase content of this menphase pitch (
The result of measurement using a reflection type optical I/I micrometer was 91°C, and the softening point (measured using a Koka type flow tester) was 215°C. Using this menphase pitch as a raw material, a spinneret having a nozzle as shown in Fig. 1 (discharge hole aioo, diameter of the spinning solution introduction part 2.5 mm, diameter of the narrowest tube part 0.15 mm, narrowest tube part Length 0.3 dragon, conical arrangement 90 that expands to the exit part
6. The diameter of the exit hole is 0.3wφ), and the spinning temperature is 300℃.
The pitch fibers were spun at a spinning speed of 210 z/min, and the pitch fibers were subjected to infusibility treatment at 300°C and carbonization treatment at 2500°C to obtain carbon fibers.

When the cross section of this carbon fiber was examined using a scanning electron microscope, it was found that the surface had a radial structure as shown in Figure 4, with no cracks occurring at all.

Moreover, this carbon fiber had a tensile strength of 278 Y/yz" and an elastic modulus of 49 W/Tsuru 2.1 and a degree of 0.57 H.

Example 2.

The menphase pitch of Example 1 was used as a raw material, and a spinneret having the nozzle shown in FIG.

Spinning was performed at a spinning temperature of 307° C. and a spinning speed of 2 soom/min, using a conical angle 11c45' widening to the exit section, a diameter of 0.2 φ) at a spinning temperature of 307° C., and a spinning speed of 2 soom/min. Example 1
Carbon vlIm was obtained by the same treatment. When the cross-section of this addictive substance was observed using a scanning electronic microscope, it had an onion-like cross-sectional structure, as shown in Figure 5, and one crack was not observed.

Example 3 Using the mesophase pitch of Example 1, a spinneret having a nozzle as shown in Fig. 2 (number of discharge holes: 100, diameter of the spinning solution introduction part: 2.5flφ, diameter of the narrow tube portion: 0.1wφ1.Narrowest rope) '
Using an IsF wire with a length of 0.1 mm and a hemispherical outlet diameter of 0.25 φ), the spinning temperature was 280°C.
The typical broken thi structure of the carbon fiber obtained by spinning at a spinning speed of 180@/min and performing the same operation as in Example 1 is a mixture of radial, onion, and random shapes, as shown in Figure 6. There were no cracks in the structure.

Example 4 A 1004 mesophase pitch with a softening point of 235° C. was obtained by carrying out the same procedure as in Example 1, except that a longer time was spent separating the mesophase pitch.

This pitch? '# Using the spinneret used in Selection Example 27,
Spinning temperature 304℃, yarn speed 1! Spun at Son/min.

Carbon NII Usui was obtained by the same treatment as in Example 1. A typical cross-sectional structure, as shown in Figure 7, has a structure in which radial shapes and random shapes are abundant, and there are no 1% cracks.

Comparative Example 1 The meso-7Aze pitch f raw material used in Example 1 had a straight tube shape with a narrow +1fI31S inside the discharge hole and a cross-section with a thickness of 0.
．． 31φ, the length of the thin tube part is 0.3 flag, and the outlet part 4 is also 0.3
Carbon gt fibers were produced under the same spinning conditions, infusibility conditions, and carbonization conditions as in Example 1 using a spinneret having a discharge hole of mφ. When the cross-section of this carbon pheasant was restored at a cross-section, the structure of the cross-section was found to be radial and bent at an angle of about 4, as shown in Figure 8. This carbon fiber has a tensile strength of 157 kg/*m'' and an elasticity of 1/-1 elongation of 0.41 degrees.

Comparative Example 2 The 1004 meso-7Azebitch used in Example 4 was used as a raw material, and the thin tube inside the discharge hole was straight, with a cross-sectional diameter of 0.
．． Using a spinneret with a discharge hole having a diameter of 1flφ, a length of the thin tube part of 0.1wa, and a diameter of the outlet part of 0.1wφ,
Carbon 4! under the same spinning conditions, infusibility conditions, and carbonization conditions as in Example 4! # was made W. This carbon fiber had the same radial cross-sectional structure as Comparative Example 1 and had cracks.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view passing through the center of one type of nozzle of the present invention. FIG. 2 is also an N& sectional view passing through the center of a nozzle having another shape according to the present invention. Figure 3 is also a vertical sectional view passing through the center of the nozzle having the shape of the example of the present invention. Figures 4 to 7 show cross-sections 4 of a 9R elementary jet i4 produced using the nozzle of the present invention, observed with a scanning type seiko microscope. Figure @8 is a cross-sectional photograph of carbon fiber produced using the nozzle of the comparative example, observed with a scanning electron microscope 41-.

Claims (1)

[Claims] 1. Melt-spinning pitch containing mesophase, making it infusible, and carbonizing it to produce carbon fiber, using mesophase pitch with a mesophase content of 70% or more as a raw material, and using it as a nozzle. 1. A method for producing carbon fibers, which comprises performing melt spinning using a spinneret in which the cross-sectional area of the outlet of the nozzle is larger than the cross-sectional area of the narrowest part of the internal thin tube part. 2. The method for producing carbon fibers according to claim 1, which comprises melt spinning at a temperature 55 to 120° C. higher than the softening point of mesophase pitch. 3. In producing carbon fibers by melt-spinning pitch containing mesophase, making it infusible, and carbonizing it, mesophase pitch having a mesophase content of 100% is used as a raw material, claim 1. The method for manufacturing carbon fiber described below. 4. In manufacturing carbon fiber by melt-spinning pitch containing mesophase, making it infusible, and carbonizing it, a patent claim that uses mesophase pitch with a mesophase content of 70% or more, which does not reach 100%, is used as a raw material. A method for producing carbon fiber according to scope 1. 5. The method for producing carbon fibers according to claim 1, wherein the carbon fibers have a radial cross-sectional structure. 6. The method for producing carbon fibers according to claim 1, wherein the carbon fibers have a random cross-sectional structure. 7. The method for producing carbon fibers according to claim 1, wherein the carbon fibers have an onion-like cross-sectional structure. 8. The method for producing carbon fibers according to claim 1, wherein the cross-sectional structure of the carbon fibers is partially radial, partially random, partially onion-like, or a mixture of these structures.