JPH02229219A - Production of mesophase pitch carbon fiber and spinning nozzle - Google Patents

Abstract

PURPOSE:To provide the subject carbon fiber generating no crack and having a high strength by melt-spinning a spinning mesophase pitch through a spinning nozzle having a specific inlet opening and a circular extrusion opening communicating with the inlet opening and subjecting the melt-spun fiber to a non-fusing treatment, to a carbonization treatment and subsequently to a graphitization treatment. CONSTITUTION:A mesophase pitch for spinning is melt-spun through a spinning nozzle 1 having an inlet opening 2 and an extrusion opening 3 communicating the inlet opening 2 and having a circular cross-section, the inlet opening 2 having an irregularity degree phi of 0.1-0.9 wherein the irregularity degree is the area of a circle using the extrusion opening as the center thereof and inscribing on the inner wall surface of the inlet opening/the area of the inlet opening. The melt-spun pitch fiber is held in air in an atmosphere heated up to 200-300 deg.C for 1hr for the non-fusing treatment of the fiber, heated up to 2300 deg.C in an inert gas and held for 15min for the carbonization treatment of the fiber and further, if necessary, subjected to a graphitization treatment to provide the objective fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing mesophase pitch-based carbon tam and a spinning nozzle. This article relates to a method for stably producing mesophase pitch-based carbon m-fibers and a spinning nozzle used therein. Conventional carbon fibers are broadly classified into FA. N (polyacrylonitrile) carbon M! Carbon fibers and pitch-based carbon fibers are known. Pitch-based carbon fibers can generally have a high elastic modulus when pitch is used as a raw material and the raw pitch contains a large amount of mesophase portion. By the way, conventional mesophase pitch carbon fibers, especially when they have a high degree of graphitization and a high modulus of elasticity, often have cracks along the fiber axis, and such cracks reduce the commercial value of carbon fibers. It decreases significantly. In mesophase pitch-based carbon m-fibers, the crystallite arrangement state in a cross section perpendicular to the fiber axis (hereinafter referred to as cross-sectional structure) varies depending on the spinning conditions. In other words, basically, there are the so-called onion type in which graphite grains form crystals in the concentric direction of the fiber, the radial type in which crystals form in a radial direction from the center of the cod, or the radial type in which crystals form in arbitrary directions without showing any directionality. Although it is roughly divided into random type forms in which there is a distribution of Furthermore, defects such as vertical cracks, cracks, and voids may exist in some or all of the fibers, and if the presence or absence of defects is included, the cross-sectional structure of mesophase pitch-based carbon fibers has a wide variety of complex forms. The presence of such various defects and cross-sectional structures is one of the main factors governing the quality stability of mesophase pitch carbon fibers.

The occurrence of defects and the formation of cross-sectional structures as described above vary depending on the physical properties of the spinning pitch, but they are also greatly influenced and fluctuated by the spinning conditions. For example, JP-A-57
-100 Publication No. 186 discloses that by reducing the optically anisotropic pitch to make it isotropic and creating a pitch that becomes optically anisotropic with a slight external force, spinning can be performed under conditions with good spinnability. There is. Also, JP-A-58-18421
The publication describes a material that can be spun under conditions with good spinnability using a pitch that does not become optically anisotropic even with a slight external force just before it becomes optically anisotropic, and that has carbonization characteristics that are not much different from optically anisotropic pitches. It discloses that it can be made. Regarding spinning conditions, it is known that random type and onion type appear when the spinning temperature is higher than the bending point that appears in the relationship between the logarithm of the pitch viscosity and the reciprocal of the absolute temperature, and the radial type appears when the spinning temperature is lower. Abstracts of the 10th Annual Meeting of the Society, 2
2 pages). On the other hand, spinning nozzles have been proposed that create an onion-type or random-type cross-sectional structure to avoid cracking along the fiber axis. For example, JP-A-58-188
The spinning nozzle described in Japanese Patent Publication No. 127 expands the flow path at the exit of the cavity and then contracts the expanded flow path again. The nozzle has a cavity with an irregular cross-section, and by spinning with this nozzle, carbon fibers with a distorted radial or random cross-sectional structure can be obtained. Another method, US Pat. No. 4,378,747, discloses filling the spinning holes with a filter material. As yet another method, Japanese Patent Application Laid-Open No. 80-259809 proposes a method in which a molded body is inserted into the introduction part of a spinning hole. Furthermore, JP-A-81-258024 proposes a method of providing a mesh layer upstream of a spinning nozzle. JP-A-82-104!327 and JP-A-82-104 regarding carbon fibers with suppressed degree of graphitization in the cross-sectional direction of the fibers and methods for producing the same
Japanese Patent No. 177222 discloses a method in which spinning pitch is mechanically stirred directly above a cavity to make mesophase pitch fine and randomly oriented. Regarding the spinning nozzle structure, Japanese Patent Application Laid-Open No. 63-2113
No. 25 discloses a spinning nozzle in which two or more discharge holes are installed within one introduction hole. This is done by providing two or more discharge holes close to the bottom of the introduction hole to make the beach flow turbulent and prevent cracking in the fiber axis direction. As explained above, many proposals have been disclosed to prevent cracking of mesophase pitch-based carbon W1 and improve its quality. the difficulty of inserting into the
There are problems such as the difficulty of ensuring uniform heat transfer due to the installation of large voids in the spinning nozzle, and this method satisfies all aspects such as spinning stability, physical strength, spinning nozzle cost, and ease of recycling the spinning nozzle. There isn't.

Problems to be Solved by the Invention The present invention provides that when mesophase pitch is melt-spun, the mesophase pitch fiber cross-sectional structure becomes radial in the conventional spinning method, and during carbonization and graphitization, shrinkage stress in the circumferential direction causes the fiber axial direction to change. The aim is to solve the problem of cracks occurring in carbon fibers and to improve the strength of 2-carbon fibers. Another object of the present invention is to provide a method for producing mesophase bee 7,000 series carbon fibers and a spinning nozzle that ensure spinning stability and facilitate cleaning and regeneration of the spinning nozzle. Means for Solving the Problems The present inventors have repeatedly investigated the mechanism by which the cross-sectional structure of mesophase pitch-based carbon fibers is developed. As a result, the fiber cross-sectional structure ), it was found that the degree of asymmetry of the flow process to the circular cross-sectional discharge hole (cabillary), that is, the degree of irregularity φ defined in the present invention, and the ratio of the cross-sectional areas of both flow paths varied variously, Based on these findings, we have arrived at the present invention. The above-mentioned purpose is to solve the problem of melt-spinning spinning pitch from a spinning nozzle by changing the shape of the introduction hole cross-sectional shape of the spinning nozzle and the discharge hole having a circular cross-sectional shape leading thereto.
Mesophase pitch using a spinning nozzle with a value of irregularity (φ = area of a circle centered on the discharge hole and inscribed on the wall surface of the introduction hole/area of the introduction hole) obtained from Section I is 0.1 or more and 0.9 or less. This can be achieved by the method for producing carbon fibers and the above-mentioned spinning nozzle. Hereinafter, the method for producing mesophase pitch carbon fiber, the spinning nozzle, and its effects of the present invention will be explained in detail. The spinning pitch used in wood invention is not particularly limited as long as it has molecular species that are easily oriented and provides an optically anisotropic pitch, and various mesophase pitches can be used. It can be done. Examples of carbonaceous raw materials for obtaining these spinning pitches include coal-based coal tar pitch, petroleum-based heavy oil, and pitch. In the present invention, the carbonaceous raw material or hydrogenated carbon material is usually 350 to 500%
℃, preferably 380 to 470℃ for 2 minutes to 10 hours,
70% or more, preferably obtained by continuously supplying in an inert gas atmosphere such as nitrogen or argon for 5 minutes to 5 hours, or under blowing, and then removing volatile components under reduced pressure after heat treatment. Pitch containing 90% or more of optically anisotropic structure, so-called mesophase, can be suitably used as pitch for spinning. The present inventors examined how mesophase pitch flows in a spinning nozzle and forms a cross-sectional structure by visualizing the state of flow of mesophase pitch in a spinning nozzle. The visualization method is to install a filter directly above the introduction hole of the spinning nozzle, and use a polarizing microscope to observe changes in the filter pattern that remains on the pitch fiber cross section as the mesophase pitch flows in from the introduction hole until it passes through the discharge hole. This was done by observing. The filter used was a 400 mesh stainless steel plain weave type. Figures 3 and 4 show the filter pattern remaining on the cross section of the peach and chi fibers. FIG. 3 is a pitch aS cross section obtained using the spinning nozzle of the Moki invention, in which the introduction hole cross-sectional shape is a rectangular cross-section, and the discharge hole cross-sectional shape is a circular cross-section. The discharge hole position is at the midpoint of the rectangular cross-section introduction hole, and the degree of irregularity φ is 0.449 (Fig. 1(a)). Here, the midpoint defined in the present invention means the inner center of a triangle and the center of gravity of a polygon. The filter pattern on the cross section of this bitch MII fiber is a very curved radial type or a random type, which shows a flow state in which the rectangular cross section of the inlet hole shape is reduced and projected onto the circular cross section of the discharge hole. It has a filter pattern. Even more surprisingly, when using a spinning nozzle (irregularity φ of 0.25) in which both the introduction hole and the discharge hole shown in FIG. However, the cross-sectional structure of the obtained pitch m#I was either a very curved radial type or a random type. On the other hand, Fig. 4 shows a pitch fiber cross section obtained using the most common conventional spinning nozzle, and the cross-sectional shape of both the introduction hole and the discharge hole of the spinning nozzle is circular, and the degree of irregularity φ is 1.0.
It is. In this case, the pitch fiber cross-sectional filter pattern has no curved flow and the cross-sectional structure forms a clean radial shape5, which is similar to that disclosed in US Pat. No. 4,818,812. The difference between the two is
In order to form the cross-sectional structure of mesophase pitch fibers, even if the discharge hole has a circular cross-section, the introduction hole must be made into an irregular cross-section, or the position of the discharge hole may be shifted from the midpoint of the introduction hole cross-section. This shows that it is possible to obtain pitch fibers with a sliding radial type or random type cross-sectional structure that does not cause cracks in any direction. This indicates that the cross-sectional shape of the introduction hole and the position of the discharge hole are closely related to the control of the cross-sectional structure of mesophase pitch fibers. The degree of irregularity φ of the introduction hole defined in the present invention is a measure representing the asymmetry of the flow when the pitch flow in the introduction hole flows into the discharge hole, and the cross-sectional shape of the introduction hole is reduced to the cross-sectional shape of the discharge hole. It was defined as a scale for projection. The degree of irregularity φ is defined as the cross-sectional area of the introduction hole and a circle inscribed in the wall surface of the introduction hole centered on the discharge hole drilled at the bottom of the introduction hole, that is, the radius is the shortest distance between the center of the discharge hole and the inner wall of the introduction hole, and the center is the discharge hole. It is expressed as the ratio of the area of the circle and is defined by the following formula. Furthermore, a concrete example of the definition is shown in Figure 2. Degree of irregularity φ=Area of a circle centered on the discharge hole and inscribed in the wall surface of the introduction hole/Area of the introduction hole In the present invention, a scale indicating the degree of irregularity is important, and the value of the degree of irregularity φ is 0.1 to 0.3, More preferably 0.1
It is important that the value is 0.8 or less. Anomaly degree φ is 0
．． If it exceeds 9, the asymmetric effect of the pitch flow process will be weakened, which is not desirable. Furthermore, if the degree of irregularity φ is less than 0.1, it is not clear whether the asymmetric effect is strengthened or the flow process is not properly reflected, but the strength actually decreases, which is undesirable. In determining the degree of irregularity Φ, the placement of the discharge hole in the cross section of the inlet hole as well as the cross-sectional shape of the inlet hole are important. In the present invention, circularity is introduced as a measure to express the cross-sectional shape of the introduction hole. The concept of circularity is (Powder and Granule Engineering, p. 73, 1
Published by Asakura Shoten in 1972). This is W
It was introduced by Idell (1933) and is also called the perimeter ratio. Circularity (Dc) is the circumference (LC) of a circle with the same area as the projected area of the particle, and the length of the contour of the particle projection (LP).
). It is desirable that the cross-sectional shape of the introduction hole used in the wood invention has a circularity (Dc) of 0.30 or less, more preferably 0.88 or less. If the circularity (DC) exceeds 0.9, the dissimilarity between the shapes of the inlet hole and the discharge hole becomes small, and the asymmetric effect of pitch flow regression becomes undesirable. Next, we will specifically explain the shape and positional relationship of the introduction hole and discharge hole that satisfy the degree of irregularity φ defined in the present invention. (l
) If the cross-sectional shape of the introduction hole is a non-circular shape, if the cross-sectional shape of the discharge hole is circular and the discharge hole position is at the midpoint of the irregular-shaped cross-sectional shape of the introduction hole, (2) If the cross-sectional shape of the introduction hole is non-circular, Deformity,
If the cross-sectional shape of the discharge hole is circular and the discharge hole position is shifted from the midpoint of the irregular cross-section introduction hole, (3) the cross-sectional shape of the introduction hole is circular, the cross-sectional shape of the discharge hole is circular, and the discharge This is a case where the hole position is shifted from the center point of the circular cross section introduction hole. The relationship between the number of introduction holes and the number of discharge holes of the spinning nozzle of the present invention will be described. In the spinning nozzle of the present invention, the number of introduction holes and the number of discharge holes are 1:1. This is important in ensuring uniformity of the fiber cross-sectional structure, spinning stability, uniform heat transfer on the nozzle surface, nozzle pressure resistance, etc. Furthermore, the larger the ratio (Sea/Sep) of the cross-sectional area of the introduction hole (Sca) to the cross-sectional area of the discharge hole (Sep), the more effective it is. In the present invention, the larger this ratio is, the more the radial or random cross-sectional structure is formed. As a result, cracking in the fiber axis direction after graphitization is prevented. These are important findings that were first concretely understood by visualizing the flow process of mesophase pitch from the introduction hole to the discharge hole. In order to obtain pitch fibers with a more complementary radial cross-sectional structure, the value of Sce/Sep should be 50 or more2.
500 or less, more preferably 100 or more2
500 or less, Sce/Sep value is 2500
If this value is exceeded, the number of introduction holes that can be machined within the mouth surface will be restricted, or the diameter of the discharge hole will become too small, making it difficult to process.
Furthermore, the pressure resistance of the spinning nozzle is not sufficiently maintained, making it unfavorable. Also, if the value of Scs/Sep is less than 50, 5W
The i-bending effect is insufficient and undesirable. Next, regarding the shape of the part from the introduction hole to the discharge hole, a normal spinning nozzle has a 45- to 90-degree abutment, but the existence of this approach promotes the formation of a regular radial cross-sectional structure. I'm letting you do it. In the spinning nozzle of the present invention, the approach angle from the introduction hole wall surface to the discharge hole is 170 degrees or more and 190 degrees.
It is preferable that the angle is 180 degrees or less, more preferably 180 degrees (plane). The approach angle defined in this invention refers to the angle formed by the surrounding wall surface leading to the discharge hole. Figures 1 and 5 show examples of the cross-sectional shape of the introduction hole, the position of the discharge hole, and the spinning nozzle used in the wood invention. 2 is the introduction hole entrance, and 3 is the discharge hole. Here, it is preferable to use a straight pipe-shaped discharge hole that satisfies the condition of having a circular cross section. Next, in the present invention, various physical property values used to express the characteristics of mesophase pitch carbon fiber and raw material pitch will be described. (1) Tensile strength, tensile modulus, tensile strength physical properties were measured according to the method shown in JISR7601. (2) 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. (3) Mesophase content In the present invention, mesophase refers to a structure that exhibits optical anisotropy, which can be determined by embedding pitch that has been cooled and solidified in resin, polishing the surface, and observing it using a polarizing microscope. In addition, mesophase content refers to the area percentage of anisotropic structure observed as described above. Examples Examples and comparative examples are shown to explain the content of the present invention in more detail. Note that the percentages in the text are area % for mesophase content, and weight % for others. Examples 1 to 7 Coal tar pitch with a softening point of 22°C was heat-treated at 200°C to obtain pitch from which insoluble quinoline was removed. Next, using a fixed bed Go-No hydrogenation catalyst, the hydrogenation conditions were L}ISV=1.7, reaction temperature 350°C, and reaction pressure 1.
Direct hydrogenation was carried out at 20 atm. Furthermore, light components were distilled off to obtain a pitch with a softening point of 90° C., a toluene-insoluble content of 4%, and quinoline-insoluble portion traces. After heat-treating this at 470°C under normal pressure, mesophase pitch was obtained by removing low boiling point components. This mesophase pitch has a softening point of 300°C, TI = 85%,
QI = 14%, mesophase content = 35%.
Using a spinning nozzle with an introduction hole having a degree of irregularity φ within the range of the present invention and a circular cross-sectional discharge hole of 100 holes as shown in FIGS. The Beech 2 discharge amount was set to 0.05 g/min. ho
! It was melt spun as e. Irregularity φ of the spinning nozzle used
Table 1 shows the circularity (De) of the introduction hole and the area ratio of the introduction hole to the discharge hole (Sea/Scp). In both cases, spinnability is determined by increasing the yarn winding speed to 34°C at the optimum temperature.
At 0 m/sin, pitch fibers with a thread diameter of 12 JLm could be stably obtained over a long period of time. The pitch fiber thus obtained was heated in air from 200°C to 300°C at 0.5°C.
The temperature was increased at a temperature increase rate of °C/sin, and the temperature was maintained for 1 hour to perform an infusibility treatment. Then in argon gas at 50°C.
The carbon fiber was heated to 2300° C. at a heating rate of /sin and heat treated for 15 minutes to obtain carbon fiber, and the tensile strength and tensile modulus of this carbon fiber were measured. The results are shown in Table 1.
The cross-sectional structure of the carbon fiber thus obtained was observed using a polarizing microscope and a scanning electron microscope, and the results are shown in Table 1. Comparative Examples 1 to Comparative Examples 3 The mesophase pitch used in Example 1 was changed to normal type discharge in which the pitch introduction hole leading to the discharge hole shown in FIG. 6 had a circular cross section and the degree of irregularity φ was 1.0. Melt spinning was performed using a spinning nozzle with 100 holes and different discharge hole diameters.
The spinning temperature range and pitch discharge rate were the same as in Example 1. The introduction hole diameter of this spinning nozzle is 3.0 m, and the depth is 10 m.
mm, and the angle of the approach section 4 is 90 degrees. Melt spinning was also carried out using the mesophase pitch used in Example 1 using a circular introduction hole type spinning nozzle with a degree of irregularity φ of 0.0031. In each case, pitch fibers with a yarn diameter of 12 lm could be stably obtained over a long period of time at the optimum temperature and at a yarn winding speed of 340+s/inch. The thus obtained pitch fibers were made infusible and heat treated under the same conditions as in Example 1 to obtain carbon fibers. Table 1 shows the results of observing the tensile strength, tensile modulus, and cross-sectional structure of the obtained carbon fibers using a polarizing microscope and a scanning electron microscope. The carbon fiber produced by the method of the present invention has high strength, the fiber cross-sectional structure shows a curved radial or random structure, and no cracks in the fiber axis direction are observed, while the degree of irregularity φ is 1.
The carbon fibers obtained from the spinning nozzle No. 0 were of radial type, and many had wedge-shaped cracks along the fiber axis direction. Carbon fibers obtained from a spinning nozzle with a degree of irregularity φ of 0.0031 showed no cracks in the fiber axis direction, but a decrease in strength was observed. (The following is a blank space) Effects of the Invention According to the method for producing mesophase pitch-based carbon fiber and the spinning nozzle of the present invention, mesophase pitch flows through the introduction hole and is spun from the discharge hole with a circular cross section, in which the flow of mesophase pitch is controlled. Since the flow from the inlet of the introduction hole to the discharge hole is asymmetrical, the cross-sectional structure of the pitch fibers exhibits a curved radial shape or a random shape. By infusible treatment using oxidizing gas, carbonization in an inert gas atmosphere, and graphitization if necessary, the carbon fiber will not crack in the fiber axis direction and its strength and physical properties will be improved. Conceivable. In addition, the discharge hole of the spinning nozzle has a circular cross section, which does not impede spinning properties and allows stable spinning for long periods of time. Furthermore, since the spinning nozzle has a simple structure, cleaning and regeneration of the spinning nozzle is easy and can be done in a short time.

[Brief explanation of the drawing]

Figures 1 (a) to (i) are explanatory diagrams showing examples of the cross-sectional shape of the introduction hole and the position of the discharge hole of the spinning nozzle of the present invention, and Figure 2 is a specific example showing the degree of irregularity φ defined in the present invention. Explanatory diagram, 3rd
The figure shows the pitch flow situation when the irregularity degree φ is (1.449 (rectangular and circular)) by installing a 400 mesh filter over the inlet hole. A photograph (photo magnification: 340x) that visualizes the cross-sectional shape of a bitch ta fiber, and Figure 4 shows the pitch when the irregularity degree ◆ is 1.0 with a normal type nozzle (however, the abroach angle is 180 degrees). Figure 5 is a side view of the spinning nozzle of the present invention. Figure 5 is a side view of the spinning nozzle of the present invention. The figure is a schematic diagram showing a normal spinning nozzle. 1●●Fist spinning nozzle, 2e-φ introduction hole inlet 3...circular cross-section discharge hole, 4...φ approach part, 5...filter layer, SA●・ψCircular cross sectionArea of the circle inscribed in the wall of the introduction hole centered on the discharge hole, SB--●Area of the cross section of the introduction hole.

Claims (2)

[Claims] (1) In a method for producing mesophase pitch-based carbon fiber by melt-spinning mesophase pitch for spinning from a spinning nozzle, infusibility treatment, carbonization treatment, and further graphitization treatment as necessary, the degree of irregularity defined below is as follows: φ is 0
．． 1. A method for producing mesophase pitch-based carbon fiber, which comprises spinning using a spinning nozzle having an introduction hole of 1 or more and 0.9 or less and a discharge hole communicating therewith having a circular cross-sectional shape. Irregularity φ=Area of a circle centered on the discharge hole and inscribed on the wall of the introduction hole/Area of the introduction hole (2) A spinning nozzle for producing mesophase pitch-based carbon fibers having an introduction hole having a degree of irregularity φ defined below of 0.1 or more and 0.9 or less, and a discharge hole communicating with the introduction hole having a circular cross-sectional shape. Irregularity φ=Area of a circle centered on the discharge hole and inscribed on the wall of the introduction hole/Area of the introduction hole