JP2009030190A - Carbon fiber and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing carbon fibers, by which two or more mesophase pitch raw materials having different toluene-insoluble contents and having been difficult to use can effectively be used, and by which the carbon fibers can effectively be produced in stable conditions. <P>SOLUTION: This method for producing the carbon fibers includes: spinning the melted product of a pitch mixture having two mesophase pitch raw materials having different toluene insoluble contents (TI) and then obtaining the carbon fibers through an infusibilizing step and a calcination step. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a carbon fiber that can be suitably used as a heat dissipation material and a resin reinforcing material, and a method for producing the same. More specifically, it is a carbon fiber produced by a melt-blowing method, which has not been conventionally used as a raw material for carbon fiber, has an extremely high content of toluene insolubles, or an extremely low content of toluene insolubles. An object of the present invention is to provide a carbon fiber that can be suitably used as a heat dissipation material and a resin reinforcing material by effectively using raw materials.

  In recent years, the problem of heat generation due to Joule heat in CPUs and electronic circuits that have been increased in speed with the rapid development of mobile phones and PCs has been taken up. In order to solve these problems, there is a need for so-called thermal management that efficiently processes heat.

  Examples of materials having excellent thermal conductivity include metal oxides such as aluminum oxide, boron nitride, aluminum nitride, magnesium oxide, zinc oxide, silicon carbide, quartz, and aluminum hydroxide, metal nitride, metal carbide, and metal hydroxide. Etc. are known. However, metallic material-based fillers have problems such as high specific gravity and high weight when used as a composite material, or strength deterioration. As a method for solving this problem, a method using carbon black, which is a carbon-based material, has been proposed. However, there has been a problem such as powder falling off as the amount added is increased.

  As a means for solving these problems, a method using carbon fiber has been proposed. Compared with a metallic material-based filler, carbon fiber not only reduces the weight of the composite material in the same volume, but also has characteristics such as improved strength. In addition, compared with carbon black, there is also an advantage that powder is less likely to fall off due to an anchor effect peculiar to fibers. The heat dissipation characteristics of carbon fibers greatly affect their graphitization properties. For this reason, pitch-based carbon fibers that can achieve higher graphitization properties than PAN-based carbon fibers, particularly carbon fibers using mesophase pitch as a raw material are generally used (see, for example, Patent Document 1).

However, mesophase pitch raw materials generally have a problem that if the content of toluene-insoluble component (hereinafter sometimes referred to simply as “insoluble component”) exceeds 80 wt%, the spinnability is significantly reduced due to high viscosity. On the other hand, when the toluene-insoluble content is 60 wt% or less, the spinnability is good, but a long time is required for the infusibilization treatment as the next step. For this reason, there was a problem of causing a decrease in productivity. For the above reasons, in order to balance spinnability and infusibilities, there is a problem that only mesophase pitches having an appropriate toluene insoluble content can be used. In addition, if raw materials with different toluene-insoluble components are fed in a continuous process and spinning is performed under the same conditions, large fluctuations in the pressure of the die occur, which greatly affects the quality of the carbon fiber precursor and ultimately the quality of the carbon fiber. Affect. In general, it is possible to restore the die pressure by changing the spinning conditions, but the carbon fiber precursor within the restoration time until the quality is stabilized cannot be made into a product, causing a decrease in yield. There was a problem.
Japanese Patent No. 2680183

  As described above, the carbon fiber using mesophase pitch as a raw material can be suitably used as a heat dissipation material and a resin reinforcing material because of its excellent graphitization property. However, if the toluene-insoluble content is very large, the high viscosity results in a significant decrease in spinnability. On the other hand, when the toluene insoluble content is small, the spinnability is good, but a long time is required for the infusibilization treatment as the next step. For this reason, there was a problem of causing a decrease in productivity. From the above, there has been a problem that mesophase pitches having an extremely high or low toluene insoluble content cannot be used as raw materials for carbon fibers. Also, in the continuous process, if different raw materials with different toluene insoluble components are added and spinning is performed under the same conditions, a large fluctuation of the die pressure will occur, which greatly affects the quality of the carbon fiber precursor and ultimately the quality of the carbon fiber. Affect. Generally, it is possible to restore the die pressure by changing the spinning conditions, but the carbon fiber precursor within the restoration time until the quality stabilizes cannot be used as the product in the next process, resulting in a decrease in yield. There was a problem of causing.

In order to solve the above-mentioned problems, the present inventors diligently studied how to use a mesophase pitch raw material that cannot be suitably used as a heat dissipation material or a resin reinforcing material, and completed the present invention. That is, according to the present invention,
(A) A pitch mixture of two kinds of mesophase pitch raw materials having different contents of toluene insoluble matter (TI), and the TI of the mesophase pitch of the two kinds of raw materials is different in the range of 5 to 30 wt%, and the two kinds A step of preparing a pitch mixture having a mixing ratio of 1: 9 to 9: 1 by weight (mixture adjustment step)
(B) a step (spinning step) of obtaining a carbon fiber precursor from a melt of the pitch mixture of the previous step by a melt blow method,
(C) a step of infusifying the carbon fiber precursor of the previous step in an oxidizing atmosphere to obtain an infusible carbon fiber precursor (infusible step), and (d) an infusible carbon fiber precursor of the previous step. There is provided a carbon fiber production method comprising a step of firing to obtain carbon fibers (firing step).

In the present invention, the two raw materials to be mixed differ in the softening point (SP) of each raw material in the range of 10.1 ° C. to 50 ° C., the pitch mixture of 330 ° C., and the shear rate of 7300 s ^−1. It is also included as an aspect of the present invention that the melt viscosity in is 2.0 to 60.0 Pa · s. According to the above method, the average fiber diameter is 1 to 20 μm, the CV value obtained as a percentage of the dispersion value of the fiber diameter with respect to the average fiber diameter is in the range of 3 to 20%, and the average fiber length is in the range of 3 to 1000 mm. A certain carbon fiber can be manufactured.

  The carbon fiber of the present invention is produced using two types of mesophase pitches having different toluene-insoluble contents as raw materials. By adopting this method, it is possible not only to effectively use mesophase pitch raw materials that could not be used in the past, but also to stably produce balanced carbon fibers.

Next, embodiments of the present invention will be sequentially described.
Examples of the mesophase pitch raw material used for the production of the carbon fiber of the present invention before melt mixing include condensed polycyclic hydrocarbon compounds such as naphthalene, anthracene and phenanthrene, condensed heterocyclic compounds such as petroleum pitch and coal pitch, and the like. . Among these, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are particularly preferable. Moreover, it is preferable that the toluene insoluble content of the two kinds of mesophase pitch raw materials before melt mixing is different within a range of 5 to 30 wt%. Deviating from the above range is not preferable because the performance of the carbon fiber produced from the melt-mixed mesophase pitch may be remarkably deteriorated. The preferred range of the toluene insoluble content of each mesophase pitch raw material before melt mixing is 5 to 15 wt%. In addition, the toluene insoluble content here refers to the value evaluated according to JIS K2425.

  The softening points (SP) of the two kinds of mesophase pitch raw materials used in the present invention are preferably different within a range of 10.1 to 50.degree. If the difference between the SPs of the two mesophase pitches is less than 10.1 ° C., it is possible to spin each individual raw material alone, which is not preferable because the merit of mixing is lost. On the other hand, when it exceeds 50 ° C., a balanced carbon fiber cannot be produced, which is not preferable.

  The mesophase pitch of the mesophase pitch used in the present invention is preferably in the range of 90 to 100%. If the mesophase rate of the mesophase pitch deviates from the above range, it is not preferable because it is difficult to produce the carbon precursor fiber by the melt blow method. A more preferable range of the mesophase rate is 95 to 100%.

In the present invention, two different mesophase pitches having a TI in the range of 5 to 30 wt% are melt-mixed, and the mixing ratio of the two is preferably in the range of 1: 9 to 9: 1. In this invention, it is preferable that the melt viscosity in 330 degreeC and the shear rate of 7300 s- ¹ of the pitch mixture obtained above exists in the range of 2.0-60.0 Pa.s. If the melt viscosity at a shear rate of 7300 s ⁻¹ is less than 2.0 Pa · s, the viscosity is low, so that it becomes round due to surface tension directly under spinning, which may cause a decrease in yarn quality. On the other hand, if it exceeds 60.0 Pa · s, the cross-sectional image of the carbon fiber finally obtained has a strong radial structure, and problems such as cracking of the carbon fiber occur in the step of firing the infusible carbon fiber precursor. Absent. A more preferable range of the melt viscosity at 330 ° C. and a shear rate of 7300 s ⁻¹ of the pitch mixture is 6.0 to 20.0 Pa · s.

By using the above pitch mixture, the average fiber diameter is 1 to 20 μm, the CV value obtained as a percentage of the dispersion value of the fiber diameter with respect to the average fiber diameter is 3 to 20%, and the average fiber length is 0.00. Carbon fibers in the range of 3 to 100 cm can be produced by the following methods (a) to (d).
(A) A pitch mixture of two types of mesophase pitch raw materials having different contents of toluene insoluble matter (TI), and the TI of the two types of mesophase pitch raw materials is different in the range of 5 to 30 wt%, A step of preparing a pitch mixture in which the mixing ratio is in the range of 1: 9 to 9: 1 by weight (mixture adjustment step);
(B) a step (spinning step) of obtaining a carbon fiber precursor from a melt of the pitch mixture of the previous step by a melt blow method,
(C) a step of infusifying the carbon fiber precursor of the previous step in an oxidizing atmosphere to obtain an infusible carbon fiber precursor (infusible step), and (d) an infusible carbon fiber precursor of the previous step. A process of firing to obtain carbon fibers (firing process)

Below, the process of (a)-(d) is explained in full detail in order.
(A) Mixture adjustment step In the first step of the present invention, two types of mesophase pitch raw materials having different TIs in the range of 5 to 30 wt% are melt-mixed, and the mixing ratio of the two types is 1: 9 to 9 by weight. 1 is a step of adjusting the pitch mixture in the range of 1: 1.

  When the pitch mixture is spun by the melt blow method, it is preferably a uniform molten mixture. For this reason, it is preferable to melt-knead after dry blending mesophase pitches having different TIs. Examples of the melt kneading method include a method using a commonly used kneader such as a single screw extruder, a twin screw extruder, and a kneader. The melt kneading is preferably carried out at a temperature equal to or higher than the softening point of the mesophase pitch used. Specifically, although it depends on the softening point of the mesophase pitch to be used, it is 200 ° C. or higher and 420 ° C. or lower. When the kneading temperature is lower than 200 ° C., the kneading cannot be sufficiently performed, which is not preferable. On the other hand, if it exceeds 420 ° C., the melt viscosity becomes extremely low and sufficient kneadability cannot be obtained, and the decomposition of the mesophase pitch also proceeds. A more preferable range of melt mixing is 230 ° C to 380 ° C.

(B) Spinning Step In the present invention, a carbon fiber precursor is produced by the melt blow method using the pitch mixture described above. At this time, the melt viscosity in the capillary is preferably in the range of 0.1 to 60.0 Pa · s, and the flow rate in the capillary is preferably in the range of 0.05 to 5.0 m / s. If the melt viscosity in the capillary is less than 0.1 Pa · s, the mesophase pitch drawn from the capillary becomes spherical due to surface tension and becomes powdery, which is not preferable. On the other hand, if the melt viscosity in the capillary exceeds 60.0 Pa · s, the cross-sectional structure of the carbon fiber becomes a strong radial structure, and the carbon fiber may be cracked in the firing process. As a result, not only the quality of the carbon fiber finally obtained is lowered, but also the mechanical strength is lowered, which is not preferable. A more preferable range of the melt viscosity in the capillary is 0.2 to 20.0 Pa · s. In the present invention, the flow rate in the capillary is also an important factor for producing the carbon fiber. That is, if the flow velocity in the capillary is less than 0.05 m / s, the pitch drawn from the capillary becomes spherical due to the surface tension and becomes a powdery material, which is not preferable. On the other hand, if it exceeds 5.0 m / s, the carbon fiber precursor can be produced satisfactorily from the mesophase pitch, but since the cross-sectional structure becomes a strong radial structure, problems as described above occur. It is not preferable. A more preferable range of the flow rate in the capillary is 0.07 to 3.0 m / s.

  The capillary shape is not particularly limited, but those having a capillary hole length / capillary diameter ratio (length / diameter) of less than 20 are preferably used, and more preferably 10 or less. .

  The temperature of the nozzle at the time of spinning is not particularly limited, but the temperature at which a stable spinning state can be continued is preferably in the range of about 250 to 400 ° C., although it depends on the softening point of the pitch mixture. It is particularly preferable to be in the range of ° C. The mesophase pitch extracted from the capillary hole is blown with a gas of 100 to 10,000 m per minute heated to 250 to 400 ° C. in the vicinity of the thinning point to be fiberized to become a carbon fiber precursor. As the gas to be blown, air, nitrogen, argon or the like can be used, but air is particularly desirable from the viewpoint of cost performance. The carbon fiber precursor is collected on a wire mesh belt and can be wound up in the form of a continuous nonwoven fabric.

(C) Infusibilization step In this step, the carbon fiber precursor obtained above is infusibilized in an oxidizing gas atmosphere to produce an infusible carbon fiber precursor. The infusibilization treatment of the carbon fiber precursor is a process necessary for obtaining carbonized or graphitized carbon fiber, and when the carbon fiber precursor is moved to the next firing step without performing this process, the carbon fiber precursor is converted into a carbon fiber precursor. Problems such as thermal decomposition or melting and fusing occur. The gas component to be used is not particularly limited as long as it is an oxidizing gas. For example, air, oxygen, halogen gas, nitrogen dioxide, ozone, etc. can be adopted. Among these, a mixed gas containing air and / or a halogen gas is preferable from the viewpoint of cost performance and insolubility at a low temperature. As the halogen gas, fluorine, iodine, bromine and the like can be taken up, and iodine is particularly preferable among these. As a specific method of infusibilization under a gas stream, treatment is performed at a temperature of 150 to 400 ° C., preferably 180 to 350 ° C., for 1 hour or less, preferably 0.5 hours or less in a desired gas atmosphere. Is preferred. Due to the infusibilization, the softening point of the carbon fiber precursor is remarkably increased and becomes an infusible carbon fiber precursor. For the purpose of obtaining a desired carbon fiber, the softening point of the infusible carbon fiber precursor is 400 ° C. or higher. It is preferable that it is 500 degreeC or more.

(D) Firing step In this step, the infusible carbon fiber precursor obtained above is carbonized or graphitized in an inert gas atmosphere to produce carbon fibers. Carbonization of the infusible carbon fiber precursor is performed in a vacuum or in an inert gas such as nitrogen, argon, krypton, etc., but it is particularly preferable to carry out the reaction at normal pressure and at low cost. The carbonization temperature is 500 to 2000 ° C, more preferably 800 to 1800 ° C. Usually, the firing of carbon fibers exceeding 2000 ° C. is called graphitization, and nitrogen gas and the like cause ionization, and therefore inert gases such as argon and krypton are used. In order to increase the thermal conductivity of the carbon fiber, graphitization is preferably performed at 2300 to 3500 ° C, and more preferably 2500 to 3200 ° C.

  According to the method of the present invention, carbon fibers can be obtained in the form of a non-woven fabric by the steps (a) to (d), but if necessary, the non-woven form after the (c) infusibilization step or (d) firing step. The fiber precursor or carbon fiber may be pulverized into a short fiber form. This crushing means will be described later. The pulverization is preferably performed after (d) the firing step.

  Thus, according to the present invention, not only can the mesophase pitch raw materials that could not be used conventionally be effectively used under stable conditions, but also balanced carbon fibers can be produced.

  Another object of the present invention is to provide a well-balanced carbon fiber excellent in mechanical characteristics, heat dissipation characteristics and the like using a pitch mixture as a raw material. That is, the carbon fiber of the present invention has an average fiber diameter of 1 to 20 μm, a CV value obtained as a percentage of the dispersion value of the fiber diameter with respect to the average fiber diameter is in the range of 3 to 20%, and the average fiber length is 3 to 3. Carbon fiber in the range of 1000 mm, radial structure, onion structure, random structure, outer layer onion inner layer radial structure, outer layer onion inner layer random structure, radial wedge structure, outlet, where these structures are combined in at least part of the cross-sectional structure It is preferable to have one of the lick structures. Among these, from the viewpoint of mechanical characteristics and heat dissipation characteristics, it is preferable that at least a part of the cross-sectional structure has a radical structure. However, as described above, the complete radial structure may cause cracks in the fiber cross-sectional direction, not only reducing the quality of the carbon fiber finally obtained, but also causing a decrease in mechanical strength. It is preferable that a part has a radial structure. In addition, the cross-sectional structure | tissue of carbon fiber can be confirmed from the cross-sectional microscope observation of the carbon fiber normally baked at 1300 degreeC or more.

  The average fiber diameter of the carbon fiber of the present invention is preferably in the range of 1 to 20 μm. When the average fiber diameter is less than 1 μm, the shape of the nonwoven fabric cannot be maintained when the carbon fiber precursor is produced by the melt-blowing method, which may cause a reduction in handling. On the other hand, if it exceeds 20 μm, infusibilization unevenness in the infusibilization process becomes large, and partial fusion may occur. As a result, the quality of the carbon fiber and further the quality of the finally obtained carbon fiber may be deteriorated, which is not preferable. A more preferable range of the average fiber diameter is 3 to 18 μm, and further preferably 5 to 15 μm. The CV value obtained as a percentage of the dispersion value of the yarn diameter with respect to the average value of the yarn diameter is desirably 3 to 20%. When the CV value exceeds 20%, carbon fiber precursors having an average fiber diameter exceeding 20 μm, which easily causes trouble in the infusibilization process, increase, which is not desirable from the viewpoint of productivity. Further, if the CV value is less than 3%, it is not preferable because high filling into the resin becomes difficult. More desirably, it is 3 to 17%. The average length of the carbon fiber is 3 to 1000 mm. If the thickness is less than 3 mm, handling as a fiber becomes difficult, and when the carbon fiber precursor is produced by the melt blow method, the shape of the mat cannot be maintained, which causes a reduction in handling. On the other hand, if it exceeds 1000 mm, the entanglement of the fibers is remarkably increased, the bulk of the mat is increased, and the handling becomes difficult. A more preferable range of the average fiber length is 5 to 800 mm, and more preferably 10 to 500 mm.

  The carbon fiber of the present invention preferably has a tensile modulus of 100 to 1000 GPa, a tensile strength of 1 to 10 GPa, and an elongation of 0.1 to 2%. If the tensile modulus, tensile strength, and elongation deviate from the above ranges, it is not preferable because not only the reinforcing effect when mixed with the resin is remarkably reduced, but also the heat dissipation characteristics are lowered. As a more preferable range of the tensile elastic modulus, tensile strength, and elongation, the tensile elastic modulus is 500 to 1000 GPa, the tensile strength is 3 to 10 GPa, and the elongation is 0.1 to 1.5%.

  The carbon fiber of the present invention is suitably used as a heat dissipation material. The heat conduction is mainly borne by phonons, and it is necessary to be connected by strong bonds without defects. In the case of carbon fibers, it is known that heat conducts in the growth direction of the hexagonal network surface rather than in the thickness direction of the crystal in the crystal forming graphite. For this reason, the crystallite size derived from the growth direction of the hexagonal network surface plays a large role. The crystallite size derived from the growth direction of the hexagonal network surface can be determined by a known method, and can be determined by diffraction lines from the (110) plane of the carbon crystal obtained by the X-ray diffraction method. In the carbon fiber of the present invention, the crystallite size derived from the growth direction of the hexagonal network surface is desirably 5 nm or more, more desirably 10 nm, and further desirably 20 nm or more.

  Since the carbon fiber of the present invention is manufactured by the melt blow method, it can be obtained in the form of a nonwoven fabric. As described above, the carbon fiber of the present invention may be pulverized by pulverizing a nonwoven fabric. The method for pulverizing the nonwoven fabric is not particularly limited, but in the dry method, for example, a ball mill pulverization method using a ball mill, or a nail-like shape in which the raw material sent to the pulverization chamber is attached to an impact claw (pin) and a lid. As a result of rotation with the stator (fixed platen), a method of pulverizing by impact, shearing action (impact mill) shearing grinding method, hammer type grinding method, rod mill method, mutual collision of powder with compressed air, grinding by mutual friction Examples include a method (jet mill), a collision pulverization method, a friction pulverization method, and a centrifugal pulverization method. On the other hand, as the wet method, for example, a method of charging together with zirconia balls or the like in water or an organic solvent such as N-methylpyrrolidone or dimethylacetamide, and pulverizing by collision or shearing can be exemplified. The carbon fiber of the present invention may be a carbon fiber filler which is a pulverized product having an average fiber diameter of 1 to 20 μm and an average fiber length of 0.01 to 2 mm by the above-described pulverization.

Examples of the present invention will be described below. In addition, this invention is not limited by the content described below.
The toluene-insoluble content of mesophase pitch was evaluated according to JIS K2425. The softening point of the mesophase pitch before and after the melt kneading was measured using a FP083HT manufactured by MDTTLDR TOLDDO at a heating rate of 2 ° C./min. The viscosity characteristics of the mesophase pitch were evaluated using a capillary rheometer CAPILOGRAP 1D (Toyo Seiki Seisakusho Co., Ltd.). The average fiber diameter of the carbon fiber and the cross-sectional structure thereof were confirmed by observing the fracture surface of the baked carbon fiber with a scanning electron microscope S-2400 (manufactured by Hitachi, Ltd.). The crystallite size of the carbon fiber was determined by the Gakushin method by measuring reflection from the (110) plane appearing in X-ray diffraction. Moreover, the mechanical measurement of carbon fiber measured using RTC-1225A made from ORIDNTDC. Moreover, the measurement of the average fiber length of the carbon fiber after grinding | pulverization evaluated by measuring 1000 fiber length with an electron microscope, and taking the average.

[Example 1]
Two mesophase pitches each having a mesophase pitch having a toluene insoluble content of 72.3 wt% and a softening point of 285.7 ° C. and a mesophase pitch having a toluene insoluble content of 93.0 wt% and a softening point of 325.4 ° C. The parts by weight were dry blended (weight fraction: 0.5: 0.5). The dry blended mesophase pitch was melt kneaded at 335 ° C. using a Kurimoto steel kneader KRC kneader S1. The melt-mixed mesophase pitch had a toluene insoluble content of 82.8 wt%. The melt viscosity of the melt-mixed mesophase pitch mixture at 330 ° C. and a shear rate of 7300 s ⁻¹ was 32.8 Pa · s. The mesophase ratio of this mixture was 100%.

The above melt-mixed mesophase pitch mixture was fed at 340 ° C. using a cap having a diameter of 0.2 mmφ and a length of 2 mm at a capillary flow rate of 0.21 m / s (shear rate: 8413 s ⁻¹ ), In addition, air of 341 ° C. was blown from a slit next to the capillary at a rate of 5500 m / min, and the melt-mixed mesophase pitch was pulled to prepare a nonwoven fabric composed of carbon fiber precursors having an average diameter of 11 μm.

  The nonwoven fabric composed of the carbon fiber precursor was heated from 200 ° C. to 300 ° C. in an air atmosphere in 30 minutes to obtain a nonwoven fabric composed of an infusible carbon fiber precursor. Next, the non-woven fabric described above was fired at 3000 ° C. over 2 hours from room temperature in an argon gas atmosphere. From a cross-sectional microscopic observation of carbon fiber fired at 3000 ° C., it has a radial structure in a part of the cross-sectional structure, an average fiber diameter of 9 μm, an average fiber length of 18 cm, and a crystallite derived from the growth direction of the hexagonal mesh surface The size was 31 nm.

[Example 2]
The nonwoven fabric made of the infusible carbon fiber precursor obtained in Example 1 was fired at 800 ° C. over 1 hour from room temperature in an argon gas atmosphere. Next, the carbon fiber fired at 800 ° C. was pulverized using an AO jet mill manufactured by Seishin Enterprise Co., Ltd. The pulverized material on the left was fired at 3000 ° C. over 3 hours from room temperature under an argon gas atmosphere. From a cross-sectional microscopic observation of carbon fiber fired at 3000 ° C., a part of the cross-sectional structure has a radial structure, the average fiber diameter is 9 μm, and the CV value obtained as a percentage of the dispersion value of the fiber diameter with respect to the average fiber diameter is The average fiber length was 12% and the average fiber length was 356 μm.

[Comparative Example 1]
Using a die consisting of a capillary with a diameter of 0.2 mmφ and a length of 2 mm at a mesophase pitch having a toluene insoluble content of 93.0 wt% wt% at 360 ° C., a flow rate in the capillary of 0.078 m / s (shear rate: 3116 s ⁻¹ ) In addition, the melted and mixed mesophase pitch was pulled by blowing air at 365 ° C. at 5500 m / min from the slit next to the capillary, but countless bubbles were generated in the carbon precursor fiber due to gas generation due to decomposition of the mesophase pitch. The carbon precursor fiber could not be obtained.

Claims (5)

(A) A pitch mixture of two types of mesophase pitch raw materials having different contents of toluene insolubles (TI), and the TI of the two types of mesophase pitch raw materials is different in the range of 5 to 30 wt%, A step of preparing a pitch mixture whose mixing ratio is in the range of 1: 9 to 9: 1 by weight (mixture adjustment step)
(B) a step (spinning step) of obtaining a carbon fiber precursor from a melt of the pitch mixture of the previous step by a melt blow method,
(C) a step of infusifying the carbon fiber precursor of the previous step in an oxidizing atmosphere to obtain an infusible carbon fiber precursor (infusible step), and (d) an infusible carbon fiber precursor of the previous step. A process of firing to obtain carbon fibers (firing process)
A method for producing carbon fiber, comprising:   Furthermore, the two types of mesophase pitch raw materials differ in the softening point (SP) in the range of 10.1 degreeC-50 degreeC, The manufacturing method of the carbon fiber of Claim 1. Pitch mixture 330 ° C., and a melt viscosity at a shear rate of 7300S ^-1 is 2.0~60.0Pa · s, method of producing a carbon fiber according to claim 1, wherein.   The method for producing a carbon fiber according to claim 1, wherein the infusible carbon fiber precursor or the calcined carbon fiber is pulverized after the infusibilization step or the firing step.   The average fiber diameter is 1 to 20 µm, the CV value obtained as a percentage of the dispersion value of the fiber diameter with respect to the average fiber diameter is in the range of 3 to 20%, and the average fiber length is in the range of 3 to 1000 mm. Carbon fiber manufactured by the method of