JPH01282316A - Pitch-based carbon fiber and production thereof - Google Patents

Abstract

PURPOSE:To obtain the subject high-tenacity and high elastic modulus carbon fiber having no crack by discharging a pitch with optical anisotropy through slit-shaped nozzle holes, subsequently through other nozzle holes with a circular cross section and then carrying out infusibilizing and graphitization treatment. CONSTITUTION:A pitch with optical anisotropy is initially discharged through nozzle holes 9 with a slit-shaped cross section and then through other nozzle holes 10 with a substantially circular cross section of a sectional area eta that of the above mentioned slit-shaped nozzle holes equipped in succession from the above mentioned slit-shaped nozzle holes after reducing the flow of the pitch. The resultant pitch yarn is subsequently subjected to infusibilization treatment and calcined, thus obtaining the objective carbon fiber with a circular cross section and composed of a fine structure where lamellas spread to the outside through an adjacent boundary reaching the fiber surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pitch-based carbon fiber and a method for producing the same. More specifically, this carbon fiber has achieved high strength by improving the occurrence of cracks, which are defects in pitch-based carbon fibers, and this carbon fiber is obtained by a special manufacturing method.

[Prior art] Pitch-based carbon fibers are obtained by melt-spinning pitch with optical anisotropy, but pitch-based carbon fibers discharged only from a circular cross-section spinneret have a fine structure radiating from the center of the fiber. Arrayed structure (usually called radial structure)
Because of this, cracks are likely to occur and high strength cannot be obtained.

Therefore, in order to improve this drawback, various measures have been proposed to change the cross-sectional structure of the cap hole and disturb the radial structure.

For example, JP-A-59-168126, JP-A-61-6314, Carbon Vol. 24, 47
Page 7 (19, 86>) discloses a spinning technique using a spinneret hole with a slit-like cross section. However, when a spinneret hole with an irregular cross section including a slit-like cross section is used, a circular cross-section cannot be obtained. Thread-spinning properties are improved compared to the motu nozzle.
Both operability and quality are poor, the yield is low, and it is difficult to process the die.

Furthermore, the cross section of the pitch-based carbon fibers spun through the die holes having these irregular cross sections is not circular but has an irregular cross section. Carbon fibers are used as a part of composite materials, and are usually impregnated with resin to make composite materials. However, as long as carbon fibers with irregular cross sections are used, even if the fibers have the same thickness, they will not be as close-packed as those with circular cross sections. The strength properties of the composite material are reduced due to the low strength and non-uniform distribution of fibers.

However, as described above, when optically anisotropic pitch is spun through a spinneret hole having a circular cross section, it becomes a radial structure, which results in cracks and a decrease in fiber strength. Even if conditions are adopted to prevent cracks from forming, circular cross-section fibers have lower strength than irregular cross-section fibers.

On the other hand, Japanese Patent Laid-Open No. 61-47825 discloses a technique for spinning optically anisotropic pitch using a spiral slit die to obtain fibers with a substantially circular cross section and a spiral microstructure. However, this technology is difficult to process due to the special spiral shape of the cap, low dimensional accuracy when increasing the number of holes, and troublesome cap management during production. The drawback is that it is not possible to expect a significant improvement in strength.

Roughly speaking, by spinning an optically anisotropic pitch by providing a circular or elliptical die hole downstream of a die hole having an irregular cross section and having a cross-sectional area larger than the cross-sectional area of the die hole having an irregular cross section, A method for preventing cracks in carbon fibers is disclosed in JP-A-62'-268820. Although the above method is certainly effective in preventing cracks, it expands the pitch flow formed by the irregular cross-section nozzle hole on the upstream side in the radial direction, causing cracks to occur in the nozzle hole with a circular or elliptical cross section on the downstream side. The aim is to obtain carbon fibers with a random, onion-like structure, or an intermediate structure, so it still has the problem of not being able to obtain high strength, which is a drawback of pitch-based carbon fibers. There is.

[Problems to be Solved by the Invention] In view of the above-mentioned current situation, the present invention has been completed by intensive research on the spinning method of optically anisotropic pitch.

The purpose of the present invention is to improve the above-mentioned defects of the prior art, to disturb the wi thin groove structure having a radial structure by simple means, and to
The present invention aims to provide a new pitch-based carbon fiber that is free from cracks and has high strength even though it has a substantially circular cross section, and a method for producing the same.

[Means for Solving the Problems] In order to achieve the above object, the present invention has the following configuration.

That is, the first invention has a substantially circular cross section and consists of a plurality of microstructures arranged in different directions, and the microstructures have lamellae extending outward through adjacent boundaries that reach substantially the fiber surface. The second invention is a pitch-based carbon fiber characterized by having an optical anisotropy, which is discharged from a die hole having a slit-like cross section,
It is characterized in that it is discharged from a substantially circular mouthpiece hole having a cross-sectional area equal to or less than the cross-sectional area of the slit-like mouthpiece hole provided subsequent to the knot-like mouthpiece hole, and then subjected to infusibility and carbonization treatment. This method is based on the manufacturing method of pitch-based carbon fiber.

The present invention will be explained in more detail.

FIGS. 1 to 3 are schematic diagrams schematically showing cross-sectional states of carbon fibers according to the present invention.

As shown in FIGS. 1 to 3, the microstructure of the carbon fiber 1 according to the present invention has a plurality of differently arranged portions A, B, C,
..., and a boundary 2 is formed in the area where these parts are adjacent to each other.

A, B, C... parts are fine streak-like lamella 3
This lamella 3 has a tfli structure extending from the boundary 2 toward the fiber surface.

FIG. 8 is a schematic diagram showing a model cross section of a conventional pitch-based carbon fiber.

The material shown in FIG. 8 was spun using a spinneret with a circular cross section.

The fiber shown in FIG. 8 shows a typical radial structure in which the lamellae 3 extend in a substantially straight line in the radial direction from the center of the fiber.

When comparing Figures 1 to 3 as group a and Figure 8 as group 6, we find that although the lamellae in group a are partially arranged regularly and almost parallel, the fibers If you look at the entire cross-section of Bg, you will see that multiple groups are gathered together, resulting in an irregular arrangement, whereas Bg is extremely regular and the lamella arrangement is almost parallel (the radial structure is also macroscopic). There are many parts that are almost parallel). Therefore, it can be seen that cracks are likely to occur in the parallel portions of the lamella.

As described above, the microstructure of the carbon fiber according to the present invention is created by bonding a plurality of portions with relatively regular lamella arrangement, resulting in a disordered overall structure. The regularity can be considerably randomized, no cracks will occur, and the strength of the fiber itself can be increased.

Further, the pitch-based carbon fiber of the present invention is characterized in that the lamellae extend outward through adjacent boundaries 2 that reach substantially the fiber surface. Reaching substantially to the fiber surface preferably means reaching to a depth of 1μ from the surface;
．． More preferably up to 8μ. When trying to achieve 1q of high strength, it is desirable that the lamellae 3 are developed and oriented, but conventional pitch-based carbon fibers with a substantially circular cross section tend to crack at the interface when the lamella orientation is improved. There was a problem that caused

On the other hand, in the present invention, the lamellae 3 are highly oriented;
Since the structure is such that the lamella 3 spreads outward through the boundary 2 in which a plurality of microstructures arranged in different directions substantially reach the fiber surface, cracks do not occur and the fiber has high strength. In order to obtain high strength, the number of structures A, B, C, etc. having different arrangement directions is preferably 3 or more, more preferably 5 or more, and even more preferably 6 or more. The pitch-based carbon fiber obtained by the method described in JP-A No. 62-268820, which is a known example, consists of a plurality of fine structures arranged in different directions,
Although no cracks occur, since the boundary 2 does not substantially reach the surface, the lamella orientation structure in the fiber surface layer, which contributes significantly to fiber strength, is poorly developed, making it impossible to obtain high-strength carbon fibers.

The above-mentioned lamellar orientation usually develops in pitch-based carbon fibers when the firing temperature during carbonization is increased, so that the tensile strength of carbon fibers increases as the tensile modulus increases.

That is, the tensile strength T (kgf/#
2) and the tensile modulus E (kQf/M2) is:
It is preferable that T≧9.1X10-4E+310 ()
It is more preferable that T≧9.1×10 −4E+330.

Furthermore, by adopting the structure of the present invention, it can be expected that the compression characteristics of pitch-based carbon fibers, which are disadvantageous compared to PAN-based fibers, can be improved.

Next, a method for producing fibers according to the present invention will be explained.

FIG. 6 is a schematic cross-sectional view showing the main parts of the spinning pack used in the present invention.

In Fig. 6, the base back 4 is fixed to the machine base (
(not shown), two cap plates 5 and 6 are provided at the lower end of the pack 4.
is installed. The base plate 56 is fastened to the bag 4 via a block 7. A pitch introduction hole 8 is provided in the base plate 5. A slit-shaped cap hole 9 is passed through the pitch introduction hole 8 of the cap plate 5 continuously.

On the other hand, a substantially circular base hole 10 is penetrated through the base plate 6 at a position opposite to the slit-shaped base hole 9. Therefore, the pitch introduction hole 8 and the outside world are the mouthpiece hole 9 and the mouthpiece hole 10.
communicated through. The pitch is heated and pressurized, sent to the pitch introduction hole 8, discharged to the outside through the die holes 9 and 10, and cooled to form fibers.

Since the formed fibers are fragile, they are handled with care and taken off by suitable means such as known rollers or air suckers.

The cap plate 5 shown in FIG. 6 has a slit-shaped cap hole 9.

The slit shape mentioned here may be one in which a plurality of rectangles are arranged alone, or may be one in which rectangles are appropriately crossed or joined.

For example, -1T, Y, C, F, +(x), Ha, -1≠,
Finally, there are foods such as rice. Further, the slit does not necessarily have to be rectangular, such as having a rounded tip.

FIG. 7 is a diagram showing the positional relationship between the mouthpiece hole 9 and the mouthpiece hole 10 when viewed from the pitch introduction hole 8 side.

FIG. 7 shows that the slit-shaped cap hole 9 has three slit-shaped cap holes 9a, 9b, and 9c of the same size arranged radially around the center line 11 of the pitch introduction hole 8, and a circular cap hole 1.
It is aligned with the center line of 0. In this way, when the slit-shaped cap hole 9 or the cap hole groups 9a, 9b, 9C, etc. have point symmetry or multiple symmetry axes, the point of symmetry or the intersection of the symmetry axes is the pitch introduction hole 8. It is best to place it so that it is on the center line. In the case of a cap hole 9 that does not have a point of symmetry or an axis of symmetry, the center line 1 of the pitch introduction hole 8
1 and the center of gravity of the cap hole 9 may be made to coincide with each other.

Further, in the present invention, the cross-sectional area of the cap hole 9 or 9a, 9b, 9C as a whole needs to be greater than or equal to the cross-sectional area of the cap hole 10. Therefore, between the circumscribed circle 12 of the bodies 9a, 9b, and 9C and the inner diameter 13 of the cap hole 10, a tapered portion 14 is provided on the side of the cap hole 10 facing the cap hole 9, as shown in FIG.

The cap used in the present invention is characterized in that two types having the above relationship are used. The reason for this is that the optically anisotropic pitch used in the production of the pitch-based carbon fiber of the present invention is generally called mesophase pitch, and the plate-like molecules exhibit a liquid crystal shape. Therefore, in the spinning pack shown in FIG. 6, when pitch is discharged from the circular nozzle hole of the nozzle plate 6 only, the plate-shaped molecules in the pitch flowing into the pitch introduction hole and the nozzle hole with a circular cross section are oriented, forming a circular shape. Further orientation with the cross-sectional mouth hole,
The fibers are arranged in a radial pattern and passed through to form fibers. Therefore, the carbon fiber obtained by processing this fiber naturally has a radial structure.

In the present invention, in order to disturb this radial structure and obtain the desired structure, two types of ferrules are used. First, the plate-like molecules are arranged MA structure by passing through the slit-shaped ferrules and matching the slit shape. . Then, while maintaining the arrangement structure of the plate-like molecules, the pitch flow is reduced and discharged from the mouth hole with a circular cross section, thereby forming a special lamellar structure, thereby achieving high strength.

On the other hand, the method described in JP-A No. 62-268820 requires that the cross-sectional area of the slit-like mouthpiece be smaller than the cross-sectional area of the circular mouthpiece hole to enlarge the flow formed by the slit-like mouthpiece. Therefore, the arrangement of the lamellae formed at the slit portion is disrupted by the expansion, making it impossible to obtain high strength.

This turbulence is particularly large near the surface of the fiber, and the boundary 2 is not formed at the outer periphery of the fiber, so that only carbon fibers with lower strength can be obtained than in the present invention.

The cross-sectional area of the slit-shaped part is
It is preferably 1.2 times or more the area of the substantially circular part, and 1.5
More preferably, it is twice or more. By making the cross-sectional area of the slit-shaped portion substantially larger than the cross-sectional area of the circular portion and reducing the pitch flow, the boundary 2 can be developed to substantially reach the fiber surface. In addition, since the spinability of pitch is extremely low compared to ordinary polymers, it is best to avoid making the cross-sectional area of the discharge hole too large, and in the case of circular holes, it is usually desirable to have a diameter of 0.4 # or less. However, as described in Japanese Patent Application Laid-Open No. 62-268820, the method of forming an irregularly shaped hole having a smaller cross-sectional area than a circular hole cannot avoid problems such as difficulty in manufacturing the cap and clogging of the cap.

In addition, the tapered part 14 between the two nozzle holes in FIG. 6 has a structure and volume that prevents the pitch from accumulating as much as possible,
Care must be taken to minimize the relaxation of the orientation of the plate-shaped molecules oriented with the slit die. Tapered part 1
The residence time at No. 4 is preferably 1 minute or less, more preferably 30 seconds or less.

The pitch used in the present invention is a synthetic pitch obtained from coal-based, petroleum-based, naphthalene, or polyvinyl chloride, and it is an optically anisotropic pitch and additives such as polymer compounds are added to the extent that the optical anisotropy is not lost. Refers to added substances.

The optically anisotropic pitch can be within a range that provides orientation of the liquid crystal component during spinning. The optically anisotropic component is preferably 60% or more, more preferably 80% or more, in view of the physical properties and spinning properties of the carbon fibers obtained.

The amount of optically anisotropic component, ie, the amount of mesophase, is measured as follows.

That is, the sample was embedded in epoxy resin and then polished by a conventional method. Polished surface with 1-eitZ 0RTHOPL
Observe by reflection polarization method using an AN microscope. The amount of the optically anisotropic component present is determined from the area ratio of the isotropic portion and the anisotropic portion observed under polarized light.

Fibers are formed using the pitch as described above and according to the method described above. The obtained fibers are made infusible by heat treatment at 250 to 450'C in air or oxygen.

There are also methods using oxidizing gases such as ozone, nitrogen oxide, sulfur oxide, etc. instead of oxygen, nitric acid hydrogen peroxide solution,
It is also possible to use oxidizing liquids such as potassium permanganate, and in some cases physical means such as electron beam crosslinking can also be used.

Furthermore, under an inert gas atmosphere such as nitrogen scum or in a vacuum, 8
Carbonize by heat treatment at 00 to 1700"C. If necessary, heat treatment at 1700"C under an inert gas atmosphere such as nitrogen gas.
Graphitize by heat treatment at temperatures above 'C.

[Examples] Example 1 Hydrogen gas was blown into coal tar in the presence of a nickel- and molybdenum-based catalyst, and the mixture was reacted at 400° C. for 120 minutes.

The obtained hydrogenated tar was filtered through a 1μ filter to remove solid matter, and then heated at 350°C to obtain hydrogenated pitch.

Then, it was heat-treated at 520'C117mmt((l) for 7 minutes to reduce the mesophase pitch to 1q.

) The resulting mesophase pitch had a softening point of 235°C, a quinoline-soluble content of 33%, a benzene-insoluble content of 89%, and a mesophase content of 85%.

The obtained pitch was spun using a spinning pack having the structure shown in FIG. The cap used must be as follows.

The cap hole 9 of the cap plate 5 has a slit width of 0.15 mm and a slit length of 0.3 nm from the center to the tip.
It is a cross section of the mold. The diameter of the cap hole 10 of the following cap plate 6 is 0.3
mm, the hole length is 0.39++++n, the diameter of the side facing the cap hole 9 is 0.6 m, and the taper angle of the tapered part 14 is 12
It is 0°.

Spinning is performed at 330'C 1600m/min with a diameter of 10μ
The pitch yarn was obtained.

The 1 q pitch yarn was heated in air from 50° C. to 340° C. at 0.5° C. 7 m1n, and held at 340° C. for 15 minutes to infusible to obtain an infusible yarn. 150% of this infusible thread
The carbon fiber fired at 0% had a strength of 335'Jf/#2, an elastic modulus of 24, and 3f/rrwn2 of 000.

On the other hand, the carbon fiber obtained by firing the above-mentioned infusible yarn at 2500'C has a strength of 410, 3f/rrun2, and an elastic modulus of 80.0.
00Kgf/m2. FIG. 4 shows a scanning electron micrograph of the cross section of the yarn fired at 2500°C.

When both carbon fibers were impregnated with epoxy resin, the m-male volume fraction Vf could be increased to 75%.
A value higher than 70% of the irregular cross-section yarn obtained by spinning and firing under the same conditions using only the spinneret plate 5 was obtained.

On the other hand, in the spinning pack shown in Fig. 6, which was spun under the same conditions and fired under the same conditions using only the above-described spindle plate 6, it showed a clear radial structure, but only a product with low strength was obtained due to cracks. Ta.

[Comparative Example] The cap hole 9 of the comparative cap plate 5 has a Y-shaped cross section with a slit width of 0.05 # and a slit length of 0.10 s from the center to the tip, and the cap plate 6 has a shape without the tapered portion 14. Carbon fibers were obtained in the same manner as in Example 1 except for the following. The 1500'C fired yarn has a strength of 31 ONyf/#2, an elastic modulus of 23, OO
0Kfff/mm2.2500℃ fired yarn has a strength of 350
K! If/rrvn 2, modulus of elasticity 70,000 to 9f
/mu2, and the strength was lower than that of Example 1. When the cross section of this carbon fiber was observed using a scanning electron microscope, it was found that the boundaries of the lamellae at the outer periphery of the fiber were unclear and the arrangement of the lamellae was also disordered. In addition, with the spindle of the comparative example, the spinneret was easily clogged and stable spinning for a long time was difficult.

Example 2 Carbon fibers were obtained in the same manner as in Example 1, except that the die hole 9 of the gold plate 5 had a slit width of 0.15 m and a slit length of 0.60711111 mm. The 1500'C fired yarn has a strength of 331 KFlf/rrm2 and an elastic modulus of 23. O
○○KFJf/#2.2500'C fired yarn has a strength of 38
0 to 3f/mm2, elastic modulus 75.0001 (yf/mm2
Met.

The fifth scanning electron micrograph of the cross section of the yarn fired at 2500°C is
As shown in the figure.

[Effects of the Invention] With the above configuration, the present invention provides the following excellent effects.

(1) 9 The carbon fiber according to the present invention has a plurality of microstructures arranged in different directions, and has a lamellar arrangement structure that is different from a radial structure. Therefore, it does not generate cracks and has high strength. It becomes carbon fiber.

(2) When spinning mesophase pitch, carbon fibers having the above-mentioned structure and properties are produced by first discharging the pitch from the slit-shaped die hole, and by the flow of the pitch coming out from the slit-shaped die hole. By discharging from a one-faced circular nozzle hole which has been reduced in size so as not to disturb the orientation, 1q can be obtained.

(3) By adopting a simple spinning method with a two-stage spinneret in which a sleeve-shaped spinneret hole and a circular cross-section spinneret hole are arranged in series, pitch-based carbon fibers with high strength and high elastic modulus without cracks can be produced. can get.

[Brief explanation of the drawing]

FIGS. 1 to 3 are schematic diagrams schematically showing cross-sectional states of carbon fibers according to the present invention. FIGS. 4 and 5 are scanning electron micrographs of cross sections of pitch-based carbon fibers of the present invention. FIG. 6 is a schematic cross-sectional view showing the main parts of the spinning pack used in the present invention. FIG. 7 is a diagram showing the positional relationship between the mouthpiece hole 9 and the mouthpiece hole 10 when viewed from the pitch introduction hole 8 side. FIG. 8 is a schematic diagram showing a model cross section of a conventional pitch-based carbon fiber. 1: Carbon fiber 2: Sakaikai 3: Lamella 4: Base back 5; 6: Base plate 7: Block 8: Pitch introduction hole 9 Slit-shaped base hole 10: Circular base hole 11: Center line of pitch introduction hole 12 Circumscribed circle 13 of the two-way metal hole 9: Inner diameter 14 of the mouthpiece hole 10: Part of the taber

Claims (2)

[Claims] (1) It is composed of a plurality of microstructures that have a substantially circular cross section and are arranged in different directions, and the microstructures have lamellae extending outward through adjacent boundaries that reach substantially the fiber surface. Characteristic pitch-based carbon fiber. (2) A pitch having optical anisotropy is discharged from a die hole having a slit-shaped cross section, and the pitch has a cross-sectional area equal to or less than the cross-sectional area of the slit-shaped die hole provided following the slit-shaped die hole. A method for producing pitch-based carbon fibers, which comprises discharging pitch-based carbon fibers from a die hole having a substantially circular cross section, followed by infusibility and carbonization treatment.