JP2652932B2 - Flexible pitch carbon fiber with high elastic modulus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel carbon fiber having a high modulus of elasticity, using mesoface pitch obtained from coal pitch as a raw material.

2. Description of the Related Art In recent years, with the rapid growth of the aircraft, space, and missile industries, materials having extraordinary strength properties have been required. In addition, as a material for sports equipment, particularly for high-end products, materials having lighter weight and superior strength physical properties as compared with conventional materials have come to be used.

Since these materials are required to have high strength, high elastic modulus, and light weight, research on the development of these materials seems to be concentrated on composite materials.

One of the most promising materials suggested to constitute the composite material was carbon fiber with high strength and high modulus. Such carbon fibers have been incorporated into plastic and metal matrices to provide composites with very high strength and modulus, weight to weight, and other special properties. However, high-strength, high-modulus carbon fibers used as a material for such composite materials have high manufacturing costs, but despite the excellent properties of the composite materials, they are a major obstacle to widespread use. It has become.

Most currently available high strength, high modulus carbon fibers are largely derived from acrylic fibers, but are inherently expensive due to the high cost of their precursors. In addition to the starting materials being expensive, the low carbon yields (％ 45%) and complex manufacturing processes obtained from such precursors add to the cost of the final product.

In addition to the high cost, such PAN-based carbon fibers can easily obtain high strength, but it is difficult to obtain high-elastic ones, and further special processing steps are required to obtain them.

On the other hand, pitch-based carbon fibers have come into the spotlight as a carbon fiber replacing such PAN-based carbon fibers due to low raw material costs and high carbonization yield.

As the pitch-based carbon fiber, a pitch obtained from coal petroleum or the like is used as a raw material. When the pitch is a so-called mesoface pitch containing 40% or more, preferably 80% or more mesophase, the obtained carbon fiber is used. May have a high modulus of elasticity.

It is a well-known fact that the high elastic modulus of pitch-based carbon fibers can be achieved by promoting graphitization, and a typical pitch-based carbon fiber having a high elastic modulus of pitch-based fibers obtained by using this principle and The production method is disclosed in JP-A-49-19127. Such a pitch-based carbon fiber has a strength of 210k.
g ・ mm ^-2 , elasticity is 70ton ・ mm ^-2 , elongation is 0.3%,
The orientation angle (HWHM) determined by X-ray diffraction is 5 ° or less, the crystallite size (Lc ₍₀₀₂₎ ) is 100 nm or more, and the layer spacing (d ₀₀₂ ) is 0.
337 nm or less, specific resistance value of 2.5 × 10 ^-4 Ω · cm or less, separation of peaks of (100) plane and (101) plane by X-ray diffraction, (112)
This indicates that graphite crystals are developed three-dimensionally, such as the appearance of plane peaks, that is, in both the fiber axis direction and the cross-sectional direction perpendicular to the axial direction. When the graphite crystal is three-dimensionally developed, the magnetoresistance is generally positive.

However, the carbon fiber is not limited to the above-described example, and it is said that a carbon fiber having a high degree of graphitization in three dimensions and a high elastic modulus has two disadvantages.

One is that such carbon fibers become very brittle fibers instead of having a high modulus of elasticity. Here, fragility is a force other than pulling force, such as torsional force,
It refers to the fragility to stress in the direction perpendicular to the fiber.
It is considered that such fragility is partly attributable to the fact that the cleavage properties increase with the three-dimensional growth of graphite crystals.

What is important here is that, according to the analysis results of the present inventors, the elastic modulus increases with the development of graphite crystals in the fiber axis direction.
That is, the orientation angle (HWHM) determined by X-ray diffraction increases as the orientation decreases, and the graphite crystal develops also in the cross-sectional direction perpendicular to the fiber axis, forming a three-dimensional structure. As a result, the crystallite size ( Lc ₍₀₀₂₎ ) is large, the layer spacing (d ₀₀₂ ) is small, and even if the magnetoresistance is positive and large, it does not contribute to the elastic modulus at all and makes the carbon fiber brittle. is there.

However, it is not easy to overcome such brittleness without lowering the elastic modulus of the pitch-based carbon fiber. This is because it is generally difficult to independently control the development of graphite crystals in the fiber axis direction and in the cross-sectional direction perpendicular to the axis. For example, conventionally known pitch-based carbon fibers having a tensile modulus of more than 55 ton · mm ^-2 must have graphite crystals well developed in the fiber axis direction. The orientation angle (HWHM) determined by X-ray diffraction becomes 10 ° or less, the magnetoresistance increases, the crystallite size (Lc ₍₀₀₂₎ ) increases (for example, greater than 25 nm), and the layer spacing (d
₀₀₂ ) is small (for example, less than 0.338 nm). Such fibers are very brittle as carbon fibers because graphite crystals are developed in three dimensions.

The second drawback of carbon fibers in which graphite crystals have developed three-dimensionally is that when spinning is performed by a conventional method, the cross-sectional structure perpendicular to the axis of the carbon fibers is oriented in the direction of the center of the cross-section. It is easy to be a so-called radial type, and it is easy to break vertically along the fiber axis direction as the graphite crystal develops in the cross-sectional direction. Needless to say, such carbon fibers have a markedly reduced commercial value due to cracking.

Here, the second drawback is to change either the radial type cross-sectional structure to another type of cross-sectional structure or to suppress the development of the graphite crystal in the cross-sectional direction perpendicular to the fiber axis. If you do, it will be overcome. Actually, since the former is easier to carry out, the method of producing carbon fibers having a cross-sectional structure other than the radial type has been studied without considering the latter.

For example, as disclosed in JP-A-59-76925 and JP-A-59-53717, the spinning temperature is increased to obtain a random type and an onion type sectional structure.

Since the carbon fibers manufactured by these conventional methods have a cross-sectional structure other than the radial type, they can sufficiently overcome the disadvantage of the second crack. However, it cannot overcome the disadvantage of the first fragility. Because, in order to overcome the disadvantage of the first fragility, although graphite crystal is well developed in the fiber axis direction of the carbon fiber, the graphite crystal in the cross-sectional direction perpendicular to the fiber axis is good. This is because the development must be sufficiently suppressed, and for that purpose, the molecules constituting the pitch are well oriented in the fiber axis direction at the stage of the pitch fiber, and in the cross-sectional direction, such molecules are arranged in the same direction. This is because the divided area must be subdivided. In the conventional spinning method, such a region in the cross section of the pitch fiber is not sufficiently segmented, so that the carbon fiber obtained by the heat treatment develops a three-dimensional graphite crystal. Therefore, the second cracking problem could be solved but the first brittleness problem could not be overcome.

Problems to be Solved by the Invention The object of the present invention is to overcome both of the above-mentioned two disadvantages of pitch-based carbon fiber having a high modulus of elasticity, namely, brittleness and cracking, using mesoface pitch as a raw material. Another object of the present invention is to provide a coal pitch-based carbon fiber having a high elastic modulus.

Means the present inventors for solving the problems, a high elastic modulus (55ton · mm ^-2 or more, preferably 75ton · mm ^-2 or higher), has a high tensile strength (250 kg · mm ^-2 or more), In addition, in order to be a supple carbon fiber that does not crack in the fiber axis direction, graphite crystals develop in the fiber axis direction, have a good degree of orientation, and have graphite in the cross section direction perpendicular to the fiber axis. It has been found that it is important that the development of crystals is suppressed. If this is expressed in terms of physical properties, the orientation angle (HW) determined by X-ray diffraction of carbon fibers manufactured from coal-based mesoface pitch as a raw material
HM) is small (less than 10 mm) and crystallite size (Lc ₍₀₀₂₎ )
Is small (18 nm or more and 25 nm or less), the layer spacing (d ₀₀₂ ) is large (0.338 nm or more and 0.345 nm or less), and the magnetic resistivity is low (−
2.00% or more and less than -0.40%), and in a cross section perpendicular to the axial direction of the fiber, regions in which molecules are arranged in the same direction are distributed concentrically or spirally or randomly. Carbon fiber.

The orientation angle (HWHM) of coal pitch-based carbon fiber must be 10 ° or less in order to exhibit high elastic modulus. Also,
Crystallite size and layer spacing are greater than 25nm and 0.338nm respectively
Below this, the carbon fibers become brittle.

If the magnetoresistance is positive, the carbon fibers will still be brittle. By setting the magnetoresistance to less than -0.40% even in the case of a negative value, cleavage between layers can be suppressed, and the flexibility of the carbon fiber can be maximized.

Effect When attempting to obtain a carbon fiber having a high elastic modulus by a conventional spinning method, graphite crystals develop not only in the fiber axis direction but also in the cross-sectional direction. Therefore, in order to increase the planarity between carbon layers and form a structure (three-dimensional structure) in which carbon layers are regularly stacked, generally speaking, Lc
Is greater than 25 nm, d ₀₀₂ is less than 0.338 nm, and the magnetoresistance becomes positive. Such carbon fibers become brittle.

If the present inventors intend to obtain a carbon fiber in which the development of the graphite crystal in the cross-sectional direction perpendicular to the fiber axis direction is suppressed, molecules are arranged in the same direction in the cross section at the stage of the pitch fiber. The present invention has been completed by conducting various technical studies based on the idea that it is necessary to subdivide the region that has been set.

That is, the present inventors first, at any stage of the spinning of the raw material pitch, the cross-sectional structure in the direction perpendicular to the fiber axis of the carbon fiber,
To examine how this was determined, the cross-sectional structure of the pitch fibers, effluent yarns and pitch directly above the capillary of the nozzle was observed with a reflection polarization microscope.

As a result of observation by the reflection polarization microscope, the present inventors have surprisingly found that the cross-sectional structures of the pitch fibers, the discharge yarn, and the pitch immediately above the capillary of the nozzle are similar to each other.

Here, the discharge yarn is obtained by allowing the raw material pitch discharged from the nozzle to fall naturally. The pitch immediately above the capillary of the nozzle is obtained by rapidly cooling and solidifying the entire spinning device with water while discharging the raw material pitch from the nozzle. The pitch fiber is obtained by stretching the discharge pitch under the nozzle to make it thinner.

The observation results of the present inventors will be described in more detail with reference to the drawings.

FIGS. 3 (A) and 3 (B) show a basic method of melt spinning of a pitch which is usually carried out. The melt pitch 1 stored in a nozzle 8 is discharged through a capillary 2 and The take-off pitch fiber 3 is manufactured at a high speed below. In this case, the cross-sectional structure in the direction perpendicular to the fiber axis of the pitch 4, the discharge yarn 5, and the pitch fiber 3 immediately above the capillary was observed with a reflection polarization microscope.
It is a radial type as shown schematically in Figure 2, and found that they corresponded similarly.

Next, the present inventors stirred the molten pitch 1 (spinning viscosity: 250 poise) in the nozzle 8 at the upper part of the capillary using the stirring rod 7 as shown in FIGS. 2 (A) and 2 (B). Disturb the flow of the molten pitch in the nozzle toward the capillary, or create a new flow (circular spiral flow at the top of the capillary), and discharge the molten pitch 1 under these conditions. By the method described above, the pitch fiber 3, the discharge yarn 5, and the pitch 4 immediately above the capillary were sampled, and their cross-sectional structures were observed with a reflection polarization microscope.

As a result, it was found that these three cross-sectional structures were all of the quagionion type as schematically shown in FIG. 1 (A), and corresponded similarly.

Here, the cross-section structure of the quasi-ionion type is a cross-section perpendicular to the axis of the fiber, in which regions in which molecules are arranged in the same direction are distributed so as to concentrically swirl. This cross-sectional structure is a novel cross-sectional structure, and when observed by reflection polarization microscopy, it is completely infusibilized and heat-treated while exhibiting a completely different aspect from the onion type known so far, and then subjected to a scanning electron microscope. When the cross-sectional structure was observed by (SEM), it was very similar to the onion type, so it was named as a quagionion (pseudo onion) type.

Further, as shown in FIGS. 2 (A) and (B), the molten pitch in the nozzle (spinning viscosity is 1000 poise) is stirred at the upper part of the capillary using a stirring rod, and the molten pitch in the nozzle is stirred. Disturb the flow toward the capillary, discharge the melted pitch under these conditions, sample the pitch fiber, discharge thread and pitch just above the capillary by the method described above, and use a reflection polarization microscope to measure their cross-sectional structure. Was observed.

As a result, it has been found that these three cross-sectional structures are all of a tandam type as schematically shown in FIG. 1 (B), and correspond in a similar manner.

Based on the above findings, the cross-sectional structure appearing in the pitch fiber is determined by the flow in the upper part of the capillary, or the state of the pitch, and the subsequent process, that is, the flow in the capillary,
Alternatively, it was found that there was essentially no change due to the stretching after the nozzle, and only the overall structure became similar and finer.

The macroscopic or microscopic cross-sectional structure of the pitch fiber can be passed on to the carbon fiber obtained by infusibilization and heat treatment, using a reflection polarization microscope and a scanning electron microscope (SEM). Was confirmed by observation.

The carbon fiber obtained by infusibilizing and heat treating pitch fibers having such a cross-section structure of the quasi-ionion type and the random type has cracks along the fiber axis as in the conventional radial type. No.

Furthermore, the region where the molecules are arranged in a certain direction in the cross section of the pitch fiber spun while being stirred above the capillary of the nozzle is subdivided. This is because in the large cross-sectional area of the upper part of the capillary, such a region has already been subdivided by stirring,
This is because when the cross-sectional area is reduced, such a region becomes very small. The effect of the segmentation of such a region becomes large when spinning is performed with high spinning viscosity, preferably at 200 poise or more while stirring.
Such an effect cannot be obtained by the conventional method.

By the way, in the carbon fiber of the present invention, graphite crystals are well developed in the fiber axis direction.To obtain such a carbon fiber, at the stage of the pitch fiber, molecules constituting the pitch are: It must be well oriented in the fiber axis direction. The present inventors have conducted intensive studies on which process of spinning mainly contributes to the orientation of molecules in the fiber axis direction,
It has been found that the drawing process after the nozzle has an overwhelming effect as compared with the other processes of spinning, namely, the flow above the capillary of the nozzle and the flow in the capillary. Therefore, with or without agitation, the drout rate is 10
There is no difference in the degree of orientation of pitch molecules in the fiber axis direction of the pitch fiber obtained by spinning as described above.

As the raw material pitch of the present invention, any mesoface pitch obtained from coal-based pitch may be used. It may be obtained by performing heat treatment after hydrogenation treatment by various methods, or may be obtained by performing heat treatment without hydrogenation treatment. Also, when heated to a high temperature, it may be such that the mesoface portion disappears,
It may be one that does not disappear. However, those having a mesophase content of 75% or more, preferably 90% or more, are selected so that the finally obtained carbon fiber has a high elastic modulus.

By such a stirring spinning of such a raw material pitch, a region where the molecules are arranged in a certain direction in a cross section perpendicular to the fiber axis is effectively subdivided, and the molecules are satisfactorily dispersed in the fiber axis direction. The oriented pitch fiber is spun, and the pitch fiber is heated to about 250 to 350 ° C. in a gas containing oxygen to make it infusible, thereby obtaining an infusible fiber. Then, the infusibilized fiber is subjected to a heat treatment in an inert gas at a temperature referred to as a so-called graphitization treatment temperature, for example, 2000 ° C. or more, and the carbon fiber of the present invention can be obtained.

The coal pitch-based carbon fiber obtained in this way has two reasons: the development of graphite crystals in the cross-sectional direction is suppressed, and the cross-sectional structure is either a quadionion type or a random type. No cracking problem occurs.

Further, since the orientation angle (HWHM) determined by X-ray diffraction is as small as 10 ° or less, and graphite crystals are developed in the fiber axis direction, the tensile elastic modulus is 55ton · mm ^-2 or more, preferably 75ton · mm.
It is higher than ^-2 . On the other hand, crystallite size (L
c ₍₀₀₂₎ ) is as small as 18 nm or more and 25 nm or less, and the layer spacing (d ₀₀₂ )
Is large, from 0.338 nm to 0.345 nm, and the magnetoresistance is −
It is as low as 2.0% or more and less than -0.40%, indicating that the development of graphite crystals is suppressed in the cross-sectional direction perpendicular to the fiber axis.

When viewed from the cross-sectional direction, the carbon fiber has a very fine undulating layer surface, thereby overcoming the problem of brittleness. Further, as a result, the tensile strength is improved as compared with the case where the undulation of the layer surface in the cross-sectional direction is not fine, and 250 kg · mm ⁻² or more can be easily achieved. In the case where carbon fibers are used as the composite material or in handling, the coal pitch-based carbon fibers of the present invention are particularly advantageous because tensile strength is an important factor as well as flexibility.

AABright and LSSirger (Carbon 17 , p.59, 1979
Is studying petroleum pitch-based carbon fiber.

Among them, the carbon fiber having a random structure is a calcined product at 2500 ° C., the orientation angle (HWHM) = 5 °, and the crystallite size (Lc
₍₀₀₂₎ ) = 17 nm, layer spacing (d ₀₀₂ ) = 0.3390-0.3398 nm,
The modulus of elasticity is 55 ton · mm ^-2 , and it can be said that, like the carbon fiber of the present invention, graphite crystals develop in the axial direction and are suppressed in the cross-sectional direction.

However, 200 kg · tensile strength whereas coal-pitch based carbon fiber according to the present invention is 250 kg · mm ^-2 or more
mm ^-2, and in terms of magnetoresistance, the minimum value of the transverse magnetoresistance for petroleum pitch-based carbon fiber at a magnetic field strength of 14KG and a temperature of 4.2K is -2.5%. The coal pitch-based carbon fiber of the present invention has a transverse magnetic resistivity of -2.8% or less under the same measurement conditions.

Further, when the coal pitch-based carbon fiber of the present invention is fired at 3000 ° C., the magnetic field strength is 14 KG, the transverse magnetic resistivity at a temperature of 4.2 K becomes negative, but the random structure of Bright et al. The petroleum pitch-based carbon fiber has a transverse magnetic resistivity of + 4.0% when fired at 3000 ° C. Such a difference in physical properties is naturally caused by a difference in structure.

In this sense, it can be said that the magnetoresistivity represents a structural feature of the carbon fiber that cannot be clarified by the X-ray diffraction method. The cause of such a difference is
It is considered that there are differences in raw materials and differences in spinning conditions.

However, while maintaining the elastic modulus at 55 ton · mm ^-2 or more, the layer interval (d ₀₀₂ ) is larger than 0.345 nm, and the crystallite size (L
c ₍₀₀₂₎ ) could not be reduced to less than 18 nm, and the magnetic resistivity could not be reduced to less than -2.00%. If the degree of graphitization is reduced to this point and the turbulence in the cross-sectional direction is too large, the turbulence propagates also in the fiber axis direction, and it is considered that a high elastic modulus cannot be exhibited.

As described above, the carbon fiber of the present invention is a completely new type of coal pitch-based carbon fiber having a high elastic modulus and overcoming both the problem of brittleness and the problem of cracking.

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

(1) Various physical properties and orientation angles (HWH) determined by X-ray diffraction
M), crystallite size (Lc ₍₀₀₂₎ ), layer spacing (d ₀₀₂ ) X-rays are irradiated to the fiber bundle from a direction perpendicular to the plane including the straight carbon fiber bundle. And the fiber bundle penetrates,
When the diffracted X-ray is detected by the detector, the detector is fixed in a direction in which the signal corresponding to the (002) plane is maximized.
Next, when the fiber bundle is rotated in a plane perpendicular to the incident X-ray while the directions of the incident X-ray and the detector are fixed, the signal intensity detected by the detector becomes a periodic function of the rotation angle of the fiber of 180 °. With one peak every 180 °. The half value of the half width of this peak is determined by the half width of half (Half Width of Half).
Maximum, HWHM).

According to the Gakushin method, the carbon fiber to be measured is powdered, and silicon powder is mixed with the powder to form a sample. When an X-ray diffraction pattern is obtained, the carbon calculated from the peak position corresponding to the (002) plane is obtained. The layer spacing of the fine graphite crystals of the fiber is d
_{Expressed as 002} . The lamination thickness of the fine graphite calculated from the half width of this peak is called a crystallite size and is expressed by Lc ₍₀₀₂₎ .

HWHM is an index indicating how well the graphite crystal is oriented along the fiber axis, and d ₀₀₂ and Lc ₍₀₀₂₎ are general indexes indicating the degree of graphitization of the fiber. as d ₀₀₂ is small, Lc ₍₀₀₂₎ represents that is progressing graphitization degree of larger fibers.

(2) Magnetoresistance The magnetoresistance is usually represented by Δρ / ρ, and is defined by the following equation. (The magnetic resistivity is a dimensionless number and is expressed as a percentage.) Δρ / ρ = (ρ () − ρ (0)) / ρ (0) where ρ () is the value of the sample. Ρ (0) is the specific resistance of the sample when no magnetic field is applied, and ρ (0) is the specific resistance of the sample when no magnetic field is applied.

The magnetic resistivity Δρ / ρ increases as the degree of graphitization of the carbon fiber increases. And the features of the magnetic resistivity are the shape of the sample,
It is independent of the size and does not depend on the presence or absence of relatively large defects, and is one of the most suitable physical property values for evaluating the degree of graphitization of a sample. Further, the magnetic resistivity is sensitive where the degree of graphitization of the carbon fiber is high, and in this region, all the physical properties obtained by X-ray diffraction become less sensitive, which is particularly useful.

The magnetoresistance shown in the description of the present application is 10 KG in the direction perpendicular to the sample in which a bundle of 40 or more carbon fibers is stretched straight at liquid nitrogen temperature unless otherwise specified.
Is the value of the magnetic resistivity when the magnetic field is applied.

(3) Tensile strength, specific elastic modulus and elongation Tensile strength properties were measured by using a resin-impregnated strand method shown in JISR7601, and elongation was measured by attaching an extensometer to a sample. The tensile strength was determined from the load at break. The modulus of elasticity was determined by drawing a tangent to the straight line portion of the load-elongation curve and calculating the ratio of the increase in load to the increase in elongation.

The elastic modulus obtained in this way is a true elastic modulus,
On the other hand, when a tensile test is performed on a single yarn, the elastic modulus is measured to be small because the apparent elongation is large. For example, using a resin-impregnated strand method, a test was performed with an extensometer attached to a sample, and when the elastic modulus was measured to be 55 ton mm- ² , the elastic modulus obtained by performing a tensile test on the same sample with a single yarn Was 40 ton · mm ^-2 .

(4) Viscosity and softening point The viscosity was calculated by a Hagen-Poiseuille equation using a flow tester. The softening point is the temperature at which the viscosity becomes 20,000 poise.

(5) Mesoface content The mesoface referred to in the present invention has 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 polarization microscope. Refers to the organization. The content of mesophase refers to the area ratio of an anisotropic structure observed and observed as described above.

Hereinafter, comparative examples and examples for describing the contents of the present invention in more detail will be described. The percentages in this component are all percentages by weight except for the magnetic resistivity and the mesophase content.

Using tetrahydroquinoline coal tar pitch having a softening point of 80 ° C. as in Example 1 material as hydrogenation solvent, 120 kg · cm ^-2
After reacting at 440 ° C. for 18 minutes under a pressure of, a solvent and a low boiling fraction were removed at 270 ° C. under reduced pressure to obtain a hydrotreated pitch. After heat-treating this at 470 ° C for 42 minutes under normal pressure,
At 80 ° C, a mesoface pitch was obtained except for the low boiling point components. This mesoface pitch has a softening point of 308 ° C, TI = 90.8%, Q
I = 19.8% and mesophase content = 100%.

Put the mesoface pitch into a spinning machine equipped with a stir bar, heat it to 355 ° C. at a heating rate of 10 ° C. min ⁻¹ , keep it for 30 minutes, and then rotate the stir bar at 27 rpm. , while stirring the molten pitch under pressure with nitrogen gas, to eject pitch melted at 0.06g · min ^-1, 500m ·
A pitch fiber was obtained by winding at a winding speed of min- ¹ .
Spinning was performed with the tip of the stirring rod approaching about 2 mm above the discharge port of the nozzle.

Observation by a reflection polarization microscope revealed that the pitch fiber thus obtained had a random cross-sectional structure.

The pitch fiber obtained in this way is heated from 200 ° C to 300 ° C in air.
The temperature was raised to 0.5 ° C. at a rate of 0.5 ° C. min ⁻¹ , and the infusibilization treatment was performed for 1 hour. Then, in argon gas 50
The temperature was raised to 2500 ° C. at a temperature-increasing rate of ° C. · min ⁻¹ and heat-treated for 15 minutes to obtain carbon fibers.

The cross-sectional structure of the carbon fiber thus obtained in a direction perpendicular to the fiber axis was a random type as a result of observation with a reflection polarization microscope and a scanning electron microscope.

Orientation angle (HWHM) of this carbon fiber determined by X-ray diffraction
Is 8.4 mm, crystallite size (Lc ₍₀₀₂₎ ) is 20 nm, and layer spacing (d
₀₀₂ ) is 0.339 nm, and the magnetic resistivity (△ ρ / ρ) is -0.401%
And the fiber was supple.

The tensile strength is 270kg ・ mm ^-2 and the tensile modulus is 67ton ・
mm ^-2 , the elongation was 0.40%.

Example 2 The raw material pitch used in Example 1 was placed in a spinning machine equipped with the same stirring rod as in Example 1 and heated at a heating rate of 10 ° C. · min ⁻¹ to 3
Heat to 55 ° C, hold for 30 minutes, then stir bar for 17.8
While rotating at rpm, apply pressure with nitrogen gas to 0.06 g
The raw material pitch melted at min ⁻¹ was discharged and wound at a winding speed of 500 m · min ^{−1 to} form pitch fibers. The tip of the stirring rod was set at a height of about 7 mm from the discharge port of the nozzle.

The pitch fiber thus obtained had a cross-sectional structure of a quadionion type.

This pitch fiber was infusibilized and heat-treated in the same manner as in Example 1 to obtain a carbon fiber.

The cross-sectional structure of the carbon fiber in a direction perpendicular to the fiber axis was a quarionion type as a result of observation with a reflection microscope and a scanning electron microscope.

Orientation angle (HWHM) of this carbon fiber determined by X-ray diffraction
Is 8.3 mm, crystallite size (Lc ₍₀₀₂₎ ) is 19 nm, and layer spacing (d
₀₀₂ ) is 0.339 nm, and the magnetic resistivity (△ ρ / ρ) is -0.432%
And the fiber was supple.

The tensile strength is 265kg · mm ^-2 and the tensile modulus is 62ton
・ Mm ^-2 , elongation was 0.43%.

Using tetrahydroquinoline coal tar pitch having a softening point of 80 ° C. Example 3 feedstock as hydrogenation solvent, 120 kg · cm ^-2
After the reaction at 450 ° C. for 18 minutes under the pressure of, the solvent and the low-boiling fraction were removed at a reduced pressure of 270 ° C. to obtain a hydrotreated pitch. After heat-treating this at 460 ° C for 60 minutes under normal pressure,
At 80 ° C, a mesoface pitch was obtained except for the low boiling point components. This mesoface pitch has a softening point of 318 ° C, TI = 92.1%, Q
I = 10.5%, mesophase content = 98%. The pitch was placed in a spinning machine equipped with the same stir bar as in Example 1, heated to 358 ° C. at a heating rate of 10 ° C. min ⁻¹ and kept for 30 minutes, after which the stir bar was turned at 9.8 rpm. While rotating
By applying pressure with nitrogen gas, the raw material pitch was discharged at 0.065 g · min ⁻¹ and wound at a winding speed of 500 m · min ⁻¹ to obtain pitch fibers. The tip of the stirring rod was set at a height of about 10 mm from the discharge port of the nozzle.

The pitch fiber thus obtained was observed with a reflection polarization microscope, and as a result, its cross-sectional structure was a quadionion type.

This pitch fiber was infusibilized and heat-treated in the same manner as in Example 1 to obtain a carbon fiber.

The cross-sectional structure of the obtained carbon fiber was a quasi-ionion type as a result of observation with a reflection polarization microscope and a scanning electron microscope.

Orientation angle (HWHM) of this carbon fiber determined by X-ray diffraction
Is 7.5 mm, the crystallite thickness (Lc ₍₀₀₂₎ ) is 23 nm, the layer spacing (d ₀₀₂ ) is 0.339 nm, and the magnetoresistance (△ ρ / ρ) is −0.415.
%, And the fiber was supple.

The tensile strength is 333kg ・ mm ^-2 and the tensile modulus is 87ton ・
mm ^-2 and elongation was 0.38%.

Comparative Example The raw material pitch used in Example 1 was placed in a conventional spinning machine, heated to 355 ° C. at a temperature rising rate of 10 ° C. · min ⁻¹ , kept for 30 minutes, and then pressurized with nitrogen gas. the molten raw material pitch discharged at 0.06 g · min ^-1 from the nozzle, 500 meters this
-It was wound at a winding speed of min- ¹ to obtain a pitch fiber.

As a result of observation by a reflection polarization microscope, the cross-sectional structure of the pitch fiber thus obtained was a radial type.

This pitch fiber was infusibilized and heat-treated in the same manner as in Example 1 to obtain a carbon fiber.

The cross-sectional structure of the carbon fiber obtained in this manner was of a radial type as a result of observation with a reflection polarization microscope and a scanning electron microscope, and a number of cracks were found along the fiber axis direction. The carbon fiber was brittle and could be easily broken by handling. The orientation angle (HWHM) of the obtained carbon fiber determined by X-ray diffraction was 9.
6 ゜, crystallite size (Lc ₍₀₀₂₎ ) 32 nm, layer spacing (d ₀₀₂ )
Is 0.337 nm and the magnetic resistivity (率 ρ / ρ) is + 0.455%
Met.

The tensile strength is 190kg ・ mm ^-2 and the tensile modulus is 69t
on · mm ^-2 , elongation was 0.28%.

Effect of the Invention The carbon fiber of the present invention, which is manufactured using a mesoface pitch obtained from a petroleum pitch as a raw material, has a high elastic modulus, is supple, and does not crack in the fiber axis direction.
It is easy to handle, has good workability, and contributes to improvement of production efficiency.

When the carbon fiber of the present invention is used for a composite material, the composite material obtained can be expected to improve the impact strength, and can be applied to various uses.

[Brief description of the drawings]

1 (A), 1 (B) and 1 (C) are schematic views of a cross-sectional structure in a direction perpendicular to a fiber axis of a pitch fiber, a carbon fiber or the like, and FIG. 1 (A) is a quasi-ion type, FIG. 1B shows a random type, and FIG. 1C shows a radial type. 2 (A) and 2 (B) are elevation views of a stirring spinner, and FIG.
Figures (A) and (B) are elevational views of a conventional spinning device of the conventional method. Reference numeral 1 denotes a molten pitch at an upper portion of a nozzle, 2 denotes a capillary, 3 denotes a pitch fiber, 4 denotes a molten pitch just above a capillary, 5 denotes a discharge thread, 6 denotes a drum, 7 denotes a stirring rod, 8 ……nozzle.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasunori Sanao 1618 Ida, Nakahara-ku, Kawasaki City Nippon Steel Corporation First Technical Research Institute (72) Inventor Takuhiko Nishida 1618 Ida, Nakahara-ku, Kawasaki City New Japan (72) Inventor Mitsuaki Matsumoto 1618 Ida, Nakahara-ku, Kawasaki City Nippon Steel Corporation 1st Research Laboratory (56) References JP-A-61-186520 (JP, A) JP-A-61-167022 (JP, A) JP-A-61-258024 (JP, A)

Claims (1)

(57) [Claims] 1. A coal fiber produced from a coal-based mesoface pitch, having an orientation angle (HWHM) determined by X-ray diffraction of 10 ° or less and a crystallite size (Lc ₍₀₀₂₎ ) of 18n.
m to 25 nm, layer spacing (d ₀₀₂ ) 0.338 nm to 0.345 nm
It has the following microstructure, and the magnetic resistivity measured by applying a magnetic field of 10KG perpendicular to the fiber axis at liquid nitrogen temperature is -2.00%
Less than -0.40% and tensile modulus of elasticity is 55ton · mm ^-2
As described above, the tensile strength is 250 kgmm- ² or more, and in the cross section perpendicular to the axial direction of the fiber, the region where the molecules are arranged in the same direction is distributed like concentric swirling or random. Coal pitch-based carbon fiber characterized by being distributed in a shape.