JPS62177222A - Production of pitch based carbon fiber - Google Patents

Abstract

PURPOSE:To obtain the titled fibers capable of freely and stably controlling the cross-sectional area without cracking along the fiber axis direction, by disturbing the flow caused when flowing in pitch just above a capillary of nozzle in melt spinning. CONSTITUTION:Mesophase-containing pitch is initially melt spun. In the process, the flow produced in flowing in the above-mentioned pitch is disturbed just above a capillary 2 of a nozzle 2. The resultant pitch fibers are subsequently infusibilized by a well-known method, e.g. air oxidation, etc. and the infusibilized fibers are heat-treated, carbonized or graphitized to provide the aimed fibers. In order to the flow of the pitch just above the capillary, an apparatus constructed to extrude the pitch 7 above the capillary 2 from the nozzle 2 while stirring with a stirring rod 8 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel method for producing pitch-based carbon fiber.

More specifically, the cross-sectional structure of carbon fiber is stabilized,
The present invention also relates to a method for producing pitch-based carbon fiber that can be freely controlled.

(Prior Art) Carbon fibers are broadly classified into PAN (polyacrylonitrile)-based carbon fibers and pitch-based carbon fibers.

In the pitch-based carbon fiber, when pitch is used as a raw material and the raw material pitch contains a mesophase portion of 40% or more, preferably 80% or more, -M can also have a high elastic modulus.

By the way, pitch-based carbon fiber has a particularly high degree of graphitization,
Conventionally, when carbon fibers have high elasticity, cracks often occur along the fiber axis direction, and such cracks significantly reduce the commercial value of carbon fibers.

It is known that this cracking along the fiber axis is caused by the carbon fiber having a so-called radial type structure in which carbon layer surfaces are arranged radially in a cross section of the carbon fiber.

This arrangement of the layer planes can be recognized by observing the cross section of the carbon fibers using a polarizing microscope or a scanning electron microscope, and FIG. 5 schematically shows this arrangement.

In order to avoid the aforementioned cracking along the fiber axis direction, we avoided the radial type cross-sectional structure and adopted the onion type cross-sectional structure schematically shown in Figure 5 or the random type cross-sectional structure shown in Figure B. Manufacturing methods have been proposed that allow carbon fibers to crack, and these methods seem to solve the problem of carbon fiber cracking.

For example, JP-A-59-53717, JP-A-59-53717,
According to the method disclosed in Japanese Patent No. 76925, carbon fibers having an onion or random type cross-sectional structure can be produced by melt spinning at a high temperature or by spinning at a high temperature and then at a low temperature. is expected to be obtained.

According to the method described in JP-A-59-168424,
Carbon fibers having a random cross-sectional structure are obtained by reducing the sliding speed when imaning the capillary during melt spinning.

According to the method described in JP-A-59-168127,
In melt spinning, a nozzle with an enlarged flow path is used at the exit of the capillary to obtain carbon fibers with an onion or random type cross-sectional structure.

According to the method described in JP-A-59-163423,
It is said that when a nozzle having a capillary with an irregular cross section is used in melt spinning, carbon fibers with a distorted radial type or random type cross-sectional structure can be obtained.

In this way, there are many proposals to overcome the problem of cracking along the fiber axis direction of pitch-based carbon fibers, but in common,
Spinning becomes unstable. ■ The cross-sectional structure can only be onion type, random type, or a combination of these. As a control method, it is more common to create multiple types of cross-sectional structures. ■Can only control the macroscopic structure of the cross section (e.g. radial type, onion type, etc.), and cannot control the cross-sectional structure at the microscopic level, that is, the degree of development of graphite crystals in the cross-sectional direction. There are problems such as:

[Problem that the invention seeks to solve]

The present invention produces carbon fibers that do not crack along the fiber axis and have various cross-sectional structures such as onion and random types, as well as other types of cross-sectional structures, without sacrificing spinning stability. The present invention provides a method for producing carbon fibers in which even the microstructure of the cross-section of carbon fibers, that is, the degree of graphitization in the cross-sectional direction, can be controlled.

(Means for Solving the Problems) The present inventors have overcome the problem of cracking along the fiber axis direction of mesophase pitch-based carbon fibers, and have solved the problem of cracking along the fiber axis direction of mesophase pitch-based carbon fibers, and have solved the problem of cracking in mesophase pitch-based carbon fibers. In order to stably produce carbon fibers with carbon fibers and control not only the macroscopic structure of the cross section but also the microscopic structure, it is necessary to It has been found that it is essentially effective to disrupt the flow that occurs when the fiber flows into the fiber, or to perform spinning while intentionally creating a new flow in the cross-sectional direction.

In conventional methods for producing carbon fibers with random, onion-type cross-sectional structures, it was not known at what stage of spinning a radial-type cross-sectional structure would develop.

The present inventors have discovered a mechanism in which a radial type cross-sectional structure is developed just above the capillary at the spinning stage when normal spinning is performed when producing carbon fiber from mesophase pitch. The present invention has been completed by solving these problems.

[For production]

The content of the present invention will be explained in detail below.

FIG. 2 shows a single-hole spinner used by the present inventors to investigate the mechanism of cross-sectional structure development. The melted mesophase pitch l is passed through the capillary 2 by nitrogen gas,
It is discharged from the nozzle 3 and wound up by the winding bobbin 4,
Becomes pitch fiber.

Here, this pitch fiber 5 and the discharge yarn 6 (the pitch discharged from the nozzle 3 is allowed to fall freely without being wound up)
Then, the pitch 7 at the top of the capillary was sampled (obtained by rapidly cooling the nozzle 3 with water while the pitch was being discharged), and its cross-sectional structure was analyzed using reflected polarized light i! Observed with a Ji microscope.

As a result, the present inventors surprisingly found that these three cross-sectional structures are all radial types and correspond to each other in a similar manner. This result shows that the same phenomenon occurs when the viscosity of mesophase pitch is 60 poise to 2300 poise, the discharge amount is 0.03 g 5in-' to 0, 1315 inch plate, and the wire diameter is 5μ to 40μm. I confirmed that.

Furthermore, as shown in FIG.
Mesophase pitch 1 was discharged at 0.065 g win-' while stirring at a rotational speed of 11, and pitch fibers 5, discharge thread 6, and pitch 7 directly above the capillary were collected by the method described above, and their transverse The surface structure was observed using a reflective polarizing microscope.

As a result, it was found that these three cross-sectional structures were all of the wadionion type as schematically shown in FIG. 5A, and corresponded to each other in a similar manner.

Here, the quadionion type cross-sectional structure is one in which regions in which molecules are arranged in the same direction are distributed in a concentric spiral manner in a cross section in a direction perpendicular to the axis of the fiber. This cross-sectional structure is a new cross-sectional structure,
When observed with a reflective polarization microscope, it appeared to have a completely different appearance from the previously known onion type; however, when the cross-sectional structure was observed with a scanning electron microscope (SEM) after being made infusible and heat treated, Because it is very similar to the onion type, it was named the Quadionion (II Onion) type.

From these findings, it is clear that the random type cross-sectional structure during normal spinning occurs just above the capillary in the nozzle, and that this structure basically does not change during the drawing process when passing through the capillary. It was found that even if the upper part has a cross-sectional structure other than the radial type, that structure is preserved as the cross-sectional structure of pitch fibers, just as in the case of the radial type.

Therefore, it is possible to produce carbon fibers with any cross-sectional structure by disrupting the pitch flow directly above the capillary or by spinning with a different flow that does not have a radial type cross-sectional structure. ′ □゛And the advantage of this method is ′ΦSince this control is performed in a relatively large place directly above the capillary, various modifications can be easily made. It is easy to create carbon fibers with various cross-sectional structures other than the random type. ■ Drawing process of molten pitch (during this process, pitch fibers tend to break)
The spinning is stable because the control is performed at spatially distant locations. ■By disrupting the flow of pitch just above the capillary, the homogeneous region of mesophase becomes smaller, and this is inherited in a similar manner during the drawing process to form pitch fibers, so that pitch molecules appear in the cross section of pitch fibers. For example, it is possible to design a region in which the particles are arranged in the same direction (in such a region, graphitization tends to proceed when heat treatment is performed after infusibility) to be smaller. 1. The degree of graphitization of the carbon fiber obtained by spinning the pitch fiber using a nozzle designed to effectively achieve (1), making it infusible and heat-treating the obtained pitch fiber will be low. However, since the degree of orientation in the fiber axis direction is mostly determined during the drawing process, the degree of orientation and elastic modulus of the obtained carbon fibers are the same as those obtained by ordinary spinning.

Therefore, the low degree of graphitization of this carbon fiber is due to poor graphite layer surface development in the cross-sectional direction. In fact, when observing the development of graphite crystals in the cross-sectional direction of this carbon fiber using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), it was found that the carbon layer plane The radius of curvature of the waviness is small. That is, it was confirmed that the flatness of the graphite layer surface was poor in the cross-sectional direction of the fiber.

In the present invention, it has been found that when the elastic modulus is the same, the lower the degree of development of the graphite layer plane in the cross-sectional direction, the higher the strength.

Above, we have described the new principle discovered in the present invention and the features of the carbon fiber manufacturing method that controls the cross-sectional structure of carbon fiber using the new principle.Next, we will discuss the manufacturing method of the present invention and its effects. Explain in detail.

The manufacturing method of the present invention is characterized in that the pitch flow of the nozzle directly above the capillary is controlled in the spinning stage. Specific methods include a method using a static stirrer and a method using dynamic stirring.

When using a static stirrer, a new cross-sectional structure can be created simply by installing a spiral object 9 on top of the capillary, as shown in FIG. 3(A), for example. This cross-sectional structure is very sensitive to the viscosity, flow, or condition of the pitch at the top of the capillary.

For example, softening point 308℃, TM-90.8%, Q I
Using a mesophase pitch with a mesophase content of -19.8% and a mesophase content of -100%, spinning was performed using a nozzle as shown in Figure 3 (A), and the viscosity of the mesophase pitch was adjusted to a range of 60 poise to 1000 poise. Discharge amount 0.011
By adjusting within the range of 5 in-' to 0.1 g win-', three types of cross-sectional structures schematically shown in Fig. 5 (B), (D), and (F) can be obtained. can.

Further, the nozzle shown in FIG. 3(B) was used for spinning, and the viscosity of the membrane pitch was 400 voids, and the discharge amount was 0.
02 g win-', the cross-sectional structure was as schematically shown in FIG. 5(E).

Further, spinning was performed using the nozzle shown in FIG. 3(C), and the viscosity of mesophase pitch was 250 poise, and the discharge amount was 0.
061 When set to win-', Figure 5 (B) and (
An intermediate cross-sectional structure of D) was obtained.

Next, there is a method of dynamic stirring, for example, as shown in Fig. 4 (
When spinning using a nozzle as shown in A) or (B) while rotating the stirring rod, the viscosity of mesophase pitch is 60 poise to 700 poise, and the discharge amount is 0.03 g■
In the range of 0.1315 in-' to 0.1315 in-', the type shown schematically in FIG. 5(A) or (A
) and (D) can be obtained with an intermediate type of cross-sectional structure.

Furthermore, when spinning is performed using a nozzle as shown in FIG. 4(C) while rotating the stirring bar, the viscosity of mesophase pitch is 100 poise to 600 poise, and the discharge rate is 0.031 poise.
In the range of m1n-' to 0.065 g 5in-', the cross-sectional structure of FIG. 5 (B), (D), or intermediate between (B) and (D) was obtained.

Furthermore, when spinning is performed using a nozzle as shown in FIG. 4(D) while rotating the stirring rod, the viscosity of mesophase pitch is 400 voids, and the discharge amount is 0.065 g 5in-'
In this case, a cross-sectional structure as schematically shown in FIG. 5 (A) or (G) (weak radial) was obtained.

If the cross-sectional structure can be freely controlled in this way, it becomes possible to control the surface properties of carbon fibers, thereby optimizing the properties of the interface with the matrix when used as a composite material.

Among these methods, although it is effective to use a static stirrer to control the cross-sectional structure of carbon fibers at a microscopic level, dynamic stirring of the mesophase pitch directly above the capillary is particularly effective. .

Table 1 shows an example of the physical properties of carbon fibers obtained by a conventional spinning method and a spinning method according to the present invention, which involves dynamic stirring.
Shown in 1.

Among the spinning methods of the present invention, the carbon fibers obtained by spinning with particularly dynamic stirring have a low degree of graphitization, but there is no change in the orientation angle, no decrease in the elastic modulus, and the strength is low. You can see that it has been improved.

Table 1 Comparison of physical properties of carbon fibers
The pitch may be any mesophase pitch. For example, it may be petroleum-based pitch or coal-based pitch, or it may be hydrogenated by various methods and then heat treated. The mesophase portion may or may not disappear when heated to high temperatures. It may be something like this.

However, since the present invention is to control the cross-sectional structure of carbon fibers, carbon fibers with a large amount of mesophase, such as 5
The effect is particularly great when using 0% or more, preferably 90% or more.

Furthermore, when carrying out the spinning method of the present invention, the viscosity of the mesophase pitch, the discharge amount, the wire diameter of the pitch fiber, etc. may be selected in any way as long as spinning is possible.For example, the viscosity of the mesophase pitch Since the discharge amount varies depending on the spinning temperature and the wire diameter, it may be selected as appropriate in the range of about 50 to 2000 voids.

Practically speaking, it would be best to select the wire diameter of the pitch fiber from a range of about 5 μl to 50 μl. However, when carrying out the spinning method of the present invention, the viscosity and discharge rate of the mesophase pitch may vary as described above. affects the cross-sectional structure, so
These spinning conditions should be determined by considering the desired cross-sectional structure.

The obtained pitch fibers are made into infusible fibers by a known method such as air oxidation, and the infusible fibers are heated to 100% in an inert gas.
Carbon fibers are obtained by heat treatment at a suitable heat treatment temperature of 0 to 2000°C, or subsequently 2000°C or higher, and carbonization or graphitization. The carbon fiber thus obtained has a macroscopic and microscopic cross-sectional structure imparted by the spinning method of the present invention.

As described above, the manufacturing method of the present invention has excellent spinning stability, and can freely control not only onion and random cross-sectional structures, but also the micro-level structure of the cross-section. This is a new manufacturing method that overcomes the problems of conventional spinning methods.

Next, in the present invention, various physical property values used to express the characteristics of pitch-based carbon fibers and raw material pitch will be described.

(1) Physical properties determined by X-ray diffraction, orientation angle (HWH
M), crystallite size (Lc(..8〉), layer spacing (d
O. e) Irradiate the fiber bundle with xm from a direction perpendicular to the plane containing the straight carbon fiber bundle. When the detector detects XvA transmitted through and diffracted through the fiber bundle, the detector is fixed in the direction where the signal corresponding to the 002 plane is maximized. ' Next, when the fiber bundle is rotated in a plane perpendicular to the incident X-rays while keeping the directions of the incident X-rays and the detector fixed, the signal intensity detected by the detector is equal to the period of 180° of the rotation angle of the fibers. It is a function with one peak every 180°. The half value of this peak is determined as the orientation angle (Half Wi
dthof Half Maximum, HWHM).

In addition, in accordance with the Gakushin Law, the carbon fiber to be measured is powdered,
A sample was obtained by mixing silicon powder with this, and when an X-ray diffraction pattern was obtained, the interlayer spacing of the carbon fiber micro graphite crystals calculated from the peak position corresponding to the (002) plane was d,
. 2, and the stacking thickness of micrographite calculated from the half-width of this peak is called the crystallite size.
. 2).

HW HM is an indicator of how well graphite crystals are oriented along the fiber axis, d. 2.LC. .

2. is a general index expressing the degree of graphitization of fibers. d
o. The smaller 2 is, the LCT. . 2. The larger the value, the more advanced the degree of graphitization of the fibers.

(2) Magnetoresistivity Magnetoresistivity is usually expressed as Δρ/ρ and is defined by the following formula (0) (Magnetoresistivity is a dimensionless number and is expressed as a percentage).

△ρ/=(ρ(Ilt)−ρ(0))/ρ<o>...
(2) Here, ρ (sweet) is the specific resistance of the sample when a magnetic field of magnetic flux density is applied to the sample, and ρ (0) is the specific resistance of the sample when no magnetic field is applied.

The magnetoresistivity Δρ/ρ increases as the degree of graphitization of the carbon fiber increases. The advantage of magnetoresistivity is that it is not affected by the shape or size of the sample, nor does it depend on the presence or absence of relatively large defects, and is one of the most commonly used physical property values for evaluating the degree of graphitization of a sample. It is one. Furthermore, magnetoresistive properties are particularly sensitive in areas where the degree of graphitization of carbon fibers is high, and all physical property values determined from X-ray diffraction become insensitive in this area, which is particularly useful.

The magnetic resistivity shown in the explanation of this application is the magnetic resistivity when a magnetic field of 10 KG is applied in the perpendicular direction to a sample made of a bundle of 40 or more carbon fibers stretched straight at liquid nitrogen temperature. It is a value.

(3) Tensile strength, tensile modulus, and elongation tensile strength physical properties were measured according to the method shown in JISR7601.

(4) Viscosity and softening point viscosity were calculated using the Hagen-Boiseuille formula using a flow tester. The softening point is the temperature at which the viscosity becomes 20,000 voids.

(5) Mesophase content The mesophase referred to in the present invention exhibits optical anisotropy, which can be determined by embedding cooled and solidified pitch in resin, polishing the surface, and observing it using a reflective polarization microscope. Refers to an organization. Further, the mesophase content refers to the area ratio of the anisotropic structure observed as described above.

Comparative Examples and Examples are shown below to explain the content of the present invention in more detail. Note that all percentages in the text are percentages by weight except for magnetoresistivity and mesophase content.

Example 1 Coal tar pitch with a softening point of 80° C. was used as a raw material, and tetrahydroquinoline was used as a hydrogenation solvent, and 120 k
After reacting at 440°C for 18 minutes under the pressure of ``g am-'', the solvent and low boiling point fractions were removed at 270°C under reduced pressure to obtain a hydrogenated pitch.This was heat treated at 470°C for 42 minutes under normal pressure. After that, low boiling point components were removed at 480°C under reduced pressure to obtain mesophase pitch.
Softening point is 308°C, T I = 90.8%, Q I
= 19.8%, mesophase content = 100%.

The fourth mesophase pitch is equipped with a stirring bar.
Put it in a nozzle like the one shown in figure (C) and heat it for 5 inches at 10℃.
-' heating rate to 355°C and keep for 30 minutes,
After that, while stirring the molten pitch by rotating the stirring rod at 27 rps+, pressure was applied with nitrogen gas to reduce the pitch to 0.06
Discharge the molten pitch with g mic', and
The pitch fiber was wound up at a winding speed of ml1 in-'.

The tip of the stirring rod was brought close to about 21 cm above the discharge port of the nozzle for spinning. During this period, the spinning condition was good and stable.

As a result of observation using a reflective polarizing microscope, the pitch fiber thus obtained was found to have a random cross-sectional structure as schematically shown in FIG. 5(B).

The pitch fibers obtained in this way were heated at 200℃ in air for 3
The temperature was raised to 00°C at a rate of 0.5°C mic', and the infusibility treatment was continued for 1 hour. Thereafter, the temperature was increased to 2500°C in argon gas at a heating rate of 50°Cff1 in-'.
The temperature was raised to .degree. C., and heat treatment was performed for 15 minutes to obtain carbon fibers.

The cross-sectional structure of the carbon fiber thus obtained in the direction perpendicular to the fiber axis was observed using a reflective polarizing microscope and a scanning electron microscope, and was found to be of a random type as schematically shown in Figure 5 (B). there were.

Orientation angle (HWHM) determined by X-ray diffraction of this carbon fiber
) is 8.4°, crystallite size (Lc+oon) is 20n
I11. The interlayer spacing (doo,) is 0.339 mm, the magnetic resistivity (Δρ/ρ) is -0,401%, the tensile strength is 263 kg am-'', and the tensile modulus is 49 t.
on Tsuru-2, the elongation was 0.54%.

Example 2 The mesophase pitch used in Example 1 was put into a nozzle equipped with a stirring bar as schematically shown in FIG. Heat,
Hold for 30 minutes, then pressurize with nitrogen gas while rotating the stirring bar at 17.8 rpm to remove 0.06 g.
+m1n-' to discharge the melted raw material pitch, 50
It was wound up at a winding speed of 0 m·in-' to form a pitch fiber.

The tip of the stirring rod was placed at a height of about 7 fins from the nozzle outlet.

The pitch fiber obtained in this way has a cross-sectional structure of 5
It was of the wadionion type as schematically shown in Figure (A). Moreover, the spinning was stable.

This pitch fiber was made infusible and heat treated in the same manner as in Example 1 to obtain carbon fiber.

The cross-sectional structure of this carbon fiber in the direction perpendicular to the fiber axis was determined by observation using a reflection = pm mirror and a scanning electron microscope.
It was of the wadionion type as schematically shown in Figure (A).

Orientation angle (HWHM) determined by X-ray diffraction of this carbon fiber
) is 8.3°, and the crystallite size (L c (aot+ )
was 19 mm, the interlayer spacing (dtot) was 0.339 mm, and the magnetoresistive rate (Δρ/ρ) was −0,432%.

Further, the tensile strength was 260 kgm-'', the tensile modulus was 45 ton m-'', and the elongation was 0.58%.

Example 3 The same mesophase pitch used in Example 1 was placed in a nozzle equipped with a stirring bar as schematically shown in Figure 4(A), and a 10'''e*in-' rise was applied. 35 at temperature speed
Heating it to 5°C, keeping it for 30 minutes, then applying pressure with nitrogen gas while rotating the stirring bar at 9.8 rpm, discharging the raw material pitch at 0.05g 5in-',
It was wound up at a winding speed of 500 m@1n-1 to obtain a pitch fiber.

The tip of the stirring rod was placed at a height of approximately 10 mm from the discharge port of the nozzle.

The pitch fibers obtained in this way reflect polarized light s! As a result of observation with a J-hui mirror, the cross-sectional structure was a wadionion type as schematically shown in FIG. 5(A). Moreover, the spinning was stable.

This pitch fiber was made infusible and heat treated in the same manner as in Example 1 to obtain carbon fiber.

The cross-sectional structure of the obtained carbon fiber, as a result of observation using a reflective polarized GL microscope and a scanning electron microscope, was of a wadionion type as schematically shown in FIG. 5(A).

Orientation angle (HWHM) determined by X-ray diffraction of this carbon fiber
) is 8.1°, crystallite thickness Lc(..2)) is 21m
m, the layer spacing (doo2) was 0.339 mm, and the magnetoresistive rate (Δρ/ρ) was −0,323%.

The tensile strength was 268 kg M-'', the tensile modulus was 50 tons Tsuru-1, and the elongation was 0.54%.

Example 4 The raw material pitch used in Example 1 was put into a nozzle equipped with a drill-shaped fitting as schematically shown in Fig. 3(A), and heated at a heating rate of 10°C-1. Heat to 3.45℃,
Hold for 30 minutes, then apply pressure with nitrogen gas and reduce to 0.
．． 051 +m1n-' to discharge the melted raw material pitch, and wind it up at a winding speed of 400m-5in-'.
Made with pitch fiber.

The pitch fiber thus obtained had an onion-type cross-sectional structure as schematically shown in FIG. 5(D). Moreover, the spinning was stable.

This pitch fiber was made infusible and heat treated in the same manner as in Example 1 to obtain carbon fiber.

The cross-sectional structure of this carbon fiber in the direction perpendicular to the fiber axis is shown in Figure 5 as a result of observation using a reflection microscope and a scanning electron microscope.
It was an onion type as schematically shown in D).

Orientation angle (HWHM) determined by X-ray diffraction of this carbon fiber
) is 8.2°, crystallite size (Lc+oon) is 29n
m, the layer spacing (does) was 0.338 mm, and the magnetoresistive rate (Δρ/ρ) was +0.15%.

Further, the tensile strength was 240 kg■-2, the tensile modulus was 50 ton m-'', and the elongation was 0.48%.

Example 5 The mesophase pitch used in Example 1 is shown in Figure 3 (A).
The sample was placed in a nozzle equipped with a drill-shaped metal fitting as schematically shown in , and heated to 355°C at a temperature increase rate of 10°C-1n-', maintained for 30 minutes, and then pressurized with nitrogen gas. , 0.02 g win''l was discharged and wound up at a winding speed of 170 m-ain-' to form a pitch fiber.

The pitch fiber thus obtained had a random cross-sectional structure as schematically shown in FIG. 5(B). Moreover, the spinning was stable.

This pitch fiber was made infusible and heat treated in the same manner as in Example 1 to obtain carbon fiber.

The cross-sectional structure of this carbon fiber in the direction perpendicular to the fiber axis is shown in Figure 5 as a result of observation using a reflection microscope and a scanning electron microscope.
It was a random type as schematically shown in B).

Orientation angle (HWHM) determined by X-ray diffraction of this carbon fiber
) is 9.0%, crystallite size (L Ctooz, ) is 2
6nm, layer spacing (dooz) is 0.338nm, +1
The 1st resistivity (Δρ/ρ) was +0.08%.

Further, the tensile strength was 245 kg tm-'', the tensile modulus was 50 ton mn-'', and the elongation was 0.49%.

Example 6 The raw material pitch used in Example 1 was put into a nozzle equipped with a flat metal fitting as schematically shown in Fig. 3(B), and heated at a heating rate of 10°C m1n-'. Heat to 350℃,
Hold for 30 minutes, then apply pressure with nitrogen gas and reduce to 0.
．． Discharge the melted raw material pitch at 02 g m1n-' and wind it up at a winding speed of 170 m-Ilin-'.
Made with pitch fiber. The spinning situation was stable.

The pitch fiber thus obtained had a cross-sectional structure as schematically shown in FIG. 5(E).

This pitch fiber was made infusible and heat treated in the same manner as in Example 1 to obtain carbon fiber.

The cross-sectional structure of this carbon fiber in the direction perpendicular to the fiber axis is shown in Figure 5-1 as a result of observation using a reflection microscope and a scanning electron microscope.
) The structure was schematically shown in .

Orientation angle (f(WH
M) is 7.9°, crystallite size (lc(.ot,) is 3
0ns, layer spacing (doo,) is 0.337nm, 53
The resistivity (Δρ/ρ) was +0.25%.

Further, the tensile strength was 235 kg va-'', the tensile modulus was 49 ton am-'', and the elongation was 0.48%.

Example 7 The raw material pitch used in Example 1 was put into a nozzle equipped with a spiral metal fitting as schematically shown in FIG. ℃, kept for 30 minutes, then applied pressure with nitrogen gas, discharged 0.02 g sin of molten raw material pitch, and wound it at a winding speed of 170 m-m1n-'.
Made with pitch fiber.

The pitch fiber thus obtained had a cross-sectional structure intermediate between those shown in FIGS. 5(B) and 5(D). Moreover, the spinning was stable.

This pitch fiber was made infusible and heat treated in the same manner as in Example 1 to obtain carbon fiber.

The cross-sectional structure of this carbon fiber in the direction perpendicular to the fiber axis is shown in Figure 5 as a result of observation using a reflection microscope and a scanning electron microscope.
It was an intermediate type between B) and (D).

The orientation angle (HW H
M) is 8.3°, crystallite size (LC<a□,) is 28
n-1 layer spacing (does) is 0.338n+i, fa
The magnetoresistivity Δρ/ρ) was -0.06%.

Further, the tensile strength was 250 kg +18-'', the tensile modulus was 45 ton fin-'', and the elongation was 0.55%.

Comparative Example The raw material pitch used in Example 1 was put into a conventional type nozzle as shown in Fig. 2, heated to 355°C at a heating rate of 10'C5in-', kept for 30 minutes, and then Pressure was applied with nitrogen gas, and the molten raw material pitch was discharged from the nozzle at a rate of 0.06 g n+in-'.
The pitch fiber was wound up at a winding speed of Q m-5 in-'.

As a result of observation using a reflective polarizing microscope, the pitch fiber thus obtained was found to have a radial cross-sectional structure as schematically shown in FIG. 5(C).

This pitch fiber was made infusible and heat treated in the same manner as in Example 1 to obtain carbon fiber.

The cross-sectional structure of the carbon fiber thus obtained was observed using a reflective polarizing microscope and a scanning electron microscope, as shown in Figure 5 (C
), and many cracks were observed along the fiber axis direction.

The orientation angle (HW
) (M) is 9.6°, crystallite size (Lc <5tun
) is 32n-, layer spacing (doom) is 0.337nm
The magnetic resistivity (Δρ/ρ) was +0.455%. In addition, the tensile strength is 170 kg.
Tensile modulus is 49 tons llIn-”, elongation is 0
．． It was 35%.

〔Effect of the invention〕

The manufacturing method of the present invention, which is capable of controlling the cross-sectional structure of carbon fibers, has excellent spinning stability, and therefore has good production efficiency in the carbon fiber manufacturing process.

This makes it possible to easily produce carbon fibers having cross-sectional structures other than the radial type without increasing costs.

Furthermore, when carbon fibers are used as a material for composite materials, the surface condition of the carbon fibers is an important factor when considering the interface between the matrix and the carbon fibers, but according to the manufacturing method of the present invention, the surface condition of the carbon fibers is an important factor. Since cross-sectional structures other than , onion, and random types can be controlled and manufactured as desired, the optimal surface condition for the composite material can be freely selected.

Furthermore, since the method of the present invention can control not only the macro structure of the cross section but also the micro structure, it is possible to greatly change the physical properties of carbon fibers, which reduces the impact when made into a composite material. Improvements in strength, etc. can be expected.

Furthermore, it is well known that carbon fibers with a low degree of graphitization are easier to handle than carbon fibers with a high degree of graphitization. Therefore, by using the manufacturing method of the present invention, troubles such as handling and yarn breakage during yarn feeding can be reduced in the carbon fiber manufacturing process, and high quality carbon fibers can be stably manufactured at lower costs.

[Brief explanation of drawings]

FIGS. 1 (1) and (2) are schematic elevational views showing an example of the spinning method of the present invention. FIGS. 2(1) and 2(2) are schematic elevational views of a single-hole spinning machine showing a normal spinning method. FIGS. 3(A), 3(B), and 3(C) are explanatory elevational views showing examples of installation of nozzles used in the spinning method of the present invention. (A)
(B) shows a plate-shaped member, and (C) shows a spiral-shaped metal fitting placed on top of a capillary. FIGS. 4(A), CB), (C), and (D) are also explanatory elevational views showing examples of installation of nozzles used in the spinning method of the present invention. (
A), (B), (C), and (D) each show a diagram in which the shape of the stirring bar is different. FIG. 5 (A), (B), (C), (D). (E), (F), CG) are cross-sectional views schematically showing various types of cross-sectional structures such as carbon fibers. (A
) is Quadionion type, (B) is random type,
(C) is radial type, CD) is onion type, (
E) is Prolux Taylor type, (F) is (C) and (
D) is a combination type, and (G) is a diagram showing a weak radial type. l... molten membrane pitch, 2... capillary, 3... nozzle, 4... fist/winding bobbin, 5... pitch fiber, 6... discharge thread, 7... pitch, 8・・−
[Stirring rod, 9ψ... spiral-shaped object, 10... plate-shaped object,
It... spiral metal fittings.

Claims (3)

[Claims] (1) When pitch fibers obtained by melt-spinning mesophase-containing pitch are infusible and further heat-treated to produce pitch-based carbon fibers, mesophase-containing pitch is formed directly above the capillary of the nozzle during the melt-spinning stage. A pitch system characterized by controlling the cross-sectional structure of the resulting carbon fiber by disturbing the flow that occurs when it flows into the fiber, or by performing spinning with a new flow intentionally created in the cross-sectional direction. Carbon fiber manufacturing method. (2) In the melt-spinning step, the cross-sectional structure of the resulting carbon fiber is controlled by performing spinning with a static stirrer placed above the capillary of the nozzle. 1) The method for producing pitch-based carbon fiber as described in item 1). (3) In the melt-spinning step, the cross-sectional structure of the resulting carbon fiber is controlled by performing spinning while dynamically stirring the molten pitch above the capillary of the nozzle. The method for producing pitch-based carbon fiber according to item (1).