Manufacturing method of carbon fiber

Abstract

To provide a manufacturing method of a carbon fiber with improved producibility.SOLUTION: The present invention relates to a manufacturing method of a carbon fiber, including: a step of producing a carbon nanotube dispersion by centrifuging a mixture containing a carbon nanotube and a polyacrylonitrile-based polymer at 2000 rpm to 20000 rpm for 1 minute to 120 minutes; a step of preparing a spinning dope by mixing the carbon nanotube dispersion and the polyacrylonitrile-based polymer; a step of obtaining a precursor fiber of the carbon fiber by spinning the spinning dope; and a step of flame-retarding and carbonizing the precursor fiber of the carbon fiber.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing carbon fibers.

Background Art

[0002] Carbon fibers are used in various applications because they have excellent physical properties such as being lightweight, having high strength, and high elastic modulus. As a method for producing carbon fibers, a method is known in which a carbon nanotube dispersion and a polyacrylonitrile-based polymer are mixed to prepare a spinning dope, which is then spun, subjected to predetermined treatments, and carbon fibers are produced (for example, Patent Documents 1 and 2).

[0003] However, in the method for producing carbon fibers disclosed in Patent Document 1, the preparation of the spinning dope includes a step of dispersing and dissolving carbon nanotubes and a polyacrylonitrile-based polymer in a specific organic solvent to prepare a carbon nanotube dispersion in order to sufficiently disperse the carbon nanotubes in the polymer, a step of concentrating this, a step of coagulating in a poor solvent, filtering, and drying, and a step of dissolving in an aqueous solution of a rhodan salt. However, the number of steps was large and the production efficiency was low.

[0004] Also, in the method for producing carbon fibers disclosed in Patent Document 2, the preparation of the spinning dope includes a step of preparing a solution of amphiphilic molecules in a specific organic solvent, a step of adding carbon nanotubes to this solution of amphiphilic molecules to disperse the carbon nanotubes and prepare a carbon nanotube dispersion, and a step of mixing this carbon nanotube dispersion and a polyacrylonitrile-based polymer to prepare a spinning dope. However, there was room to reduce the number of steps and improve the production efficiency.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, improvement in production efficiency has been demanded for the conventional method for producing carbon fibers. Therefore, an object of the present invention is to provide a method for producing carbon fibers with improved production efficiency.

Means for Solving the Problems

[0007] The present inventors have found that the production efficiency is improved by performing centrifugation under predetermined conditions when producing a carbon nanotube dispersion, and have completed the present invention.

[0008] That is, the gist of the present invention is as follows. (1) A step of producing a carbon nanotube dispersion by centrifuging a mixture containing carbon nanotubes and a polyacrylonitrile-based polymer at 2000 rpm to 20000 rpm for 1 minute to 120 minutes; A step of preparing a spinning dope by mixing the carbon nanotube dispersion and a polyacrylonitrile-based polymer; A step of spinning the spinning dope to obtain a precursor fiber of carbon fiber; A step of flameproofing and carbonizing the precursor fiber of carbon fiber A method for producing carbon fibers, comprising: (2) The method for producing carbon fibers according to (1) above, wherein the centrifugation of the mixture is performed under the conditions of 5000 rpm to 15000 rpm for 1 minute to 120 minutes. (3) The method for producing carbon fibers according to (1) or (2) above, wherein the content of the carbon nanotubes in the spinning dope is 0.3% by weight to 0.5% by weight based on the polyacrylonitrile-based polymer in the spinning dope.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a method for producing carbon fibers with improved production efficiency.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0012] The method for producing carbon fibers of the present invention includes a step of preparing a carbon nanotube dispersion (Step 1), a step of mixing the carbon nanotube dispersion and a polyacrylonitrile-based polymer to prepare a spinning dope (Step 2), a step of spinning the spinning dope to obtain a precursor fiber of carbon fiber (Step 3), and a step of rendering the precursor fiber of carbon fiber flame-resistant and carbonizing it (Step 4). In the present invention, the carbon fiber may be either a single filament or a multifilament. In the method for producing carbon fibers of the present invention, by performing centrifugation under predetermined conditions when preparing the carbon nanotube dispersion, the dispersion state of the carbon nanotubes in the dispersion is improved. By using a spinning dope obtained by adding such well-dispersed carbon nanotubes to a polyacrylonitrile-based polymer, it becomes possible to densify the stacking structure of carbon in the carbon fiber and greatly grow the crystals, and the strength and elastic modulus of the carbon fiber are improved. Further, since the method for producing carbon fibers of the present invention can prepare a spinning dope with a small number of steps, the production efficiency is improved.

[0013] In Step 1, a mixture containing carbon nanotubes and a polyacrylonitrile-based polymer is centrifuged at 2000 rpm to 20000 rpm for 1 minute to 120 minutes to prepare a carbon nanotube dispersion in which the carbon nanotubes are dispersed in the polyacrylonitrile-based polymer.

[0014] As the carbon nanotubes, either single-walled or multi-walled carbon nanotubes may be used, or a mixture thereof may be used. The diameter of the carbon nanotubes is usually from 0.1 nm to 100 nm, preferably from 10 nm to 50 nm. The length of the carbon nanotubes is usually from 1 μm to 500 μm.

[0015] As the polyacrylonitrile-based polymer, a copolymer composed of polyacrylonitrile and a vinyl monomer copolymerizable with acrylonitrile can be used. The vinyl monomer copolymerizable with acrylonitrile is not particularly limited, and examples thereof include (meth)acrylic acid, (meth)acrylic acid ester, and itaconic acid. In the copolymer of acrylonitrile, the acrylonitrile component is preferably 85 mol% or more. These polymers may form salts with alkali metals or ammonia. Further, these polymers can be used alone or as a mixture of two or more.

[0016] The mixture containing carbon nanotubes and polyacrylonitrile-based polymer may contain an organic solvent. The organic solvent is not particularly limited, and examples thereof include dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0017] The mixture containing carbon nanotubes, polyacrylonitrile-based polymer and optionally an organic solvent can be obtained by mixing the components of the mixture by a commonly used method. When preparing the mixture, these components may be mixed and subjected to ultrasonic treatment.

[0018] The content of carbon nanotubes in the carbon nanotube dispersion is usually 0.01% to 10% by weight, preferably 0.1% to 1% by weight, more preferably 0.3% to 0.5% by weight, and particularly preferably about 0.4% by weight, based on the polyacrylonitrile-based polymer contained in the spinning dope prepared in the subsequent step 2. When the content of carbon nanotubes is within this range, it becomes possible to densify the carbon stacking structure and greatly grow the crystals in the resulting carbon fiber. Note that the content of carbon nanotubes in the carbon nanotube dispersion is usually 1% to 50% by weight, preferably 0.1% to 20% by weight, based on the polyacrylonitrile-based polymer in the carbon nanotube dispersion.

[0019] In step 1, a mixture containing carbon nanotubes and a polyacrylonitrile-based polymer is centrifuged at 2000 rpm to 20000 rpm for 1 minute to 120 minutes to prepare a carbon nanotube dispersion in which the carbon nanotubes are dispersed in the polyacrylonitrile-based polymer. The carbon nanotube dispersion is obtained as the supernatant after centrifugation. In the present invention, by performing centrifugation under these specific conditions, the dispersion state of the carbon nanotubes in the dispersion is improved, and by adding carbon nanotubes with a good dispersion state to the polymer, the performance of the resulting carbon fiber can be improved. The centrifugation conditions may be appropriately set for the rotation speed and time so that a carbon nanotube dispersion with a good dispersion state of carbon nanotubes is obtained. From the viewpoints of preventing contamination with impurities and the feasibility of the apparatus, the rotation speed of centrifugation is preferably 5000 rpm to 15000 rpm, more preferably 7500 rpm to 12500 rpm, particularly preferably 9000 rpm to 11000 rpm, and most preferably 10000 rpm. Also, the centrifugation time may be appropriately selected according to the rotation speed of centrifugation, preferably 5 minutes to 60 minutes, more preferably 5 minutes to 30 minutes, particularly preferably 5 minutes to 15 minutes, and most preferably 10 minutes. In one embodiment, the centrifugation conditions are 10000 rpm for 10 minutes.

[0020] As described above, in Step 1, a carbon nanotube dispersion with a good dispersion state of carbon nanotubes is obtained. In the carbon nanotube dispersion, the average particle diameter (D50) of the carbon nanotubes is usually 1 μm or less. In the present invention, the average particle diameter of the carbon nanotubes in the dispersion can be used as an index of the dispersion state of the carbon nanotubes, and the smaller the average particle diameter, the better the dispersion state. The average particle diameter of the carbon nanotubes can be determined by laser diffraction particle size distribution measurement.

[0021] In Step 2, the carbon nanotube dispersion prepared in Step 1 and a polyacrylonitrile-based polymer are mixed to prepare a spinning dope containing carbon nanotubes and a polyacrylonitrile-based polymer.

[0022] The mixing of the carbon nanotube dispersion and the polyacrylonitrile-based polymer can be carried out by a commonly used method. The polyacrylonitrile-based polymer may be used in the form of a polyacrylonitrile-based polymer solution containing the polyacrylonitrile-based polymer in an organic solvent. The organic solvent used for the polyacrylonitrile-based polymer solution is not particularly limited, and examples thereof include dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO). It is preferable that the organic solvents used for the carbon nanotube dispersion and the polyacrylonitrile-based polymer solution are the same.

[0023] The content of the carbon nanotubes in the spinning dope is usually 0.01% by weight to 10% by weight, preferably 0.1% by weight to 1% by weight, more preferably 0.3% by weight to 0.5% by weight, and particularly preferably about 0.4% by weight, based on the polyacrylonitrile-based polymer in the spinning dope. As described above, when the content of the carbon nanotubes is within this range, it is possible to densify the carbon stacking structure and greatly grow the crystals in the obtained carbon fiber.

[0024] The content of the polyacrylonitrile-based polymer in the spinning dope is usually 5% to 15% by weight, preferably 10% by weight, based on the spinning dope.

[0025] In Step 3, the spinning dope prepared in Step 2 is spun to obtain a precursor fiber of carbon fiber. The spinning is not particularly limited and can be carried out by known methods such as dry spinning method and wet spinning method. However, the wet spinning method is preferred. In the wet spinning method, for example, the spinning dope is discharged from a nozzle into a coagulating liquid of a non-solvent in the presence of a suitable solvent and solidified to form fibers.

[0026] When the carbon fiber is a single filament, the spinning by the wet spinning method can obtain a precursor fiber of carbon fiber, for example, by discharging the spinning dope into a coagulation bath using water and an organic solvent such as DMSO as a poor solvent, solidifying to obtain fibers, removing the solvent therefrom, and then subjecting it to vacuum drying.

[0027] When the carbon fiber is a multifilament, the spinning by the wet spinning method can obtain a precursor fiber of carbon fiber, for example, by discharging the spinning dope into a coagulation bath composed of a coagulation bath of water and an organic solvent such as DMSO and water, solidifying to obtain fibers, and performing washing, stretching, application of an oil agent, drying, and winding.

[0028] In Step 4, the precursor fiber of carbon fiber obtained in Step 3 is made flame-resistant and carbonized to obtain carbon fiber.

[0029] The flame resistance of the precursor fiber can be carried out, for example, at 200°C to 350°C in air.

[0030] The carbonization of the precursor fiber can be carried out, for example, at 1000°C to 2000°C in an argon (Ar) atmosphere.

[0031] The carbon fiber obtained by the production method of the present invention has a dense carbon stacking structure in the carbon fiber and large crystal growth, and is excellent in the strength and elastic modulus of the carbon fiber, so it can be suitably used for various applications.

Examples

[0032] Hereinafter, the present invention will be described in more detail with reference to examples. However, the technical scope of the present invention is not limited to these examples.

[0033] <Production of carbon fiber (single filament): Examples 1 and 2 and Comparative Examples 1 to 3> Carbon fiber (single filament) was produced by performing the following steps in order: production of carbon nanotube (CNT) dispersion, mixing with polyacrylonitrile (PAN) polymer solution, single spinning, flame resistance improvement, and carbonization.

[0034] Production of CNT dispersion 20 mg of multi-walled carbon nanotubes (MWCNT) (manufactured by TCI, C2154, 20 nm to 40 nm (diameter)), 200 mg of PAN polymer, and 20 mL of DMSO solution were mixed, and the mixture was subjected to probe sonication (125 W × 70%, 30 minutes). The mixture after sonication was centrifuged under the predetermined conditions shown in Table 3, and the supernatant was collected to obtain a CNT dispersion.

[0035] Mixing with PAN polymer solution The CNT dispersion was added to a PAN polymer solution of PAN polymer:DMSO = 10:90 (weight ratio) so that the CNT content was the predetermined addition amount shown in Table 3 with respect to the PAN polymer contained in the spinning dope, and the spinning dope was prepared. Note that no CNT dispersion was used in the preparation of the spinning dope for Comparative Example 2.

[0036] Single spinning Spinning was performed by the wet spinning method. Specifically, the spinning dope was discharged into a coagulation bath using water and DMSO as poor solvents at a jet stretch ratio (take-up speed / discharge linear speed) of 2.0, and spinning was carried out. The spun fiber was immersed in water for one day to remove the solvent, and then vacuum dried at 140°C for one day to obtain a precursor fiber of carbon fiber.

[0037] Flame resistance improvement The precursor fiber was flame resistance improved using a small electric furnace (manufactured by Fulltech Co., Ltd.) under the conditions of an air flow rate of 5 L / min, a heating rate of 10°C / min, and a maximum temperature reached (flame resistance improvement temperature) of 300°C for 10 minutes.

[0038] Carbonization The flame-resistant precursor fibers were sandwiched between graphite plates and carbonized in an Ar atmosphere using a ceramic electric tube furnace (manufactured by Asahi Rika Kogyo Co., Ltd., ARF-80KC) under the conditions of an Ar flow rate of approximately 500 mL / min, a heating rate of 10 °C / min, a maximum temperature reached (carbonization temperature) of 1500 °C, and a holding time of 10 minutes to obtain carbon fibers.

[0039] <Production of carbon fiber (multifilament): Examples 3, 4 and Comparative Example 4> Carbon fiber (multifilament) was produced by sequentially performing the following steps: preparation of CNT dispersion, mixing with PAN polymer solution, multifilament spinning, flame resistance, and carbonization.

[0040] In the production of multifilament, the preparation of CNT dispersion and the mixing with PAN polymer solution were carried out in the same manner as these steps in the production of single filament to prepare a spinning dope. Note that no CNT dispersion was used in the preparation of the spinning dope of Comparative Example 4.

[0041] Multifilament spinning Spinning was carried out by the wet spinning method. Specifically, the spinning dope was discharged, coagulated, washed, stretched, coated with an oil agent, dried, and wound up in sequence to obtain precursor fibers of carbon fiber. A 402-hole nozzle was used at the discharge port. When the spinning dope was discharged from the die into the coagulation bath, desolvation occurred simultaneously and the spinning dope became fibers. In the coagulation process, the first to third baths with different concentrations of DMSO: water of 80:20, 50:50, and 0:100 by mass ratio were installed, and the fibers discharged into these coagulation baths were conveyed to advance desolvation. The fibers after desolvation were washed in a high-temperature water bath, an oil agent (KM-2002-T manufactured by Shin-Etsu Chemical Co., Ltd.) was applied to the washed fibers, dried through a heater, and wound up on a bobbin to obtain precursor fibers of carbon fiber. The spinning conditions are shown in Table 1 below.

[0042]

Table 1

[0043] Flame resistance Using a small electric furnace (manufactured by Denken Co., Ltd., model KDF-S90), the precursor fibers were pyrolyzed under the conditions of an air flow rate of 0.5 L / min, a heating rate of 2 °C / min, and a maximum temperature (pyrolysis temperature) of 285 °C for 180 minutes.

[0044] Carbonization Using a vertical carbonization furnace (manufactured by Tokyo Honzan Shokai Co., Ltd., model MSHTF-100250HK), the pyrolyzed precursor fibers were carbonized in an Ar atmosphere under the conditions of an Ar flow rate of 300 mL / min, a heating rate of 10 °C / min, a maximum temperature (carbonization temperature) of 1500 °C, and a holding time of 10 minutes to obtain carbon fibers.

[0045] <Evaluation> State of the CNT dispersion after centrifugation For CNT dispersions prepared under different centrifugation conditions, the dispersion state of CNTs was evaluated by laser diffraction particle size distribution measurement (SALD-7500nano, manufactured by Shimadzu Corporation). The results are shown in Table 2. Also, Figure 1 shows the particle size measurement results for CNT dispersions with different centrifugation conditions.

[0046]

Table 2

[0047] As shown in Table 2 and Figure 1, the centrifugation condition of 10000 rpm for 10 minutes had a significantly smaller particle size of the CNT dispersion and a better dispersion state of CNTs compared to the conditions without centrifugation and centrifugation at 1000 rpm for 10 minutes.

[0048] Wide-angle X-ray diffraction (WAXS) measurement For the carbon fibers of Examples 1 to 4 and Comparative Examples 1 to 4, wide-angle X-ray diffraction (WAXS) measurement was performed to measure the stacking structure of carbon in the carbon fibers.

[0049] When the carbon fiber is a single filament, the WAXS measurement was performed by the transmission method using a CuKα ray (beam diameter 0.3 mm) monochromatized with an X-ray diffractometer (manufactured by Rigaku Corporation, FR-E), an imaging plate (manufactured by Rigaku Corporation, R-AXIS-IV), and a Ni filter. The distance between the sample and the detector was set to 165 mm. Also, from the diffraction profile of the (002) plane, the interplanar spacing d002 of the carbon network plane and the stacking thickness Lc as crystallite parameters were calculated according to Bragg's equation and Scherrer's equation, respectively.

[0050] When the carbon fiber is a multifilament, the WAXS measurement was performed using an X-ray diffractometer (manufactured by Shimadzu Corporation, LabX XRD-6100). The sample was prepared by arranging bundles of carbon fibers in a strip shape and pasting them on a mount. From the diffraction profile of the (002) plane, the interplanar spacing d002 of the carbon network plane and the stacking thickness Lc as crystallite parameters were calculated according to Bragg's equation and Scherrer's equation, respectively. Also, from the diffraction profile of the (10) plane in the equatorial direction, the spread La of the carbon network plane in the direction perpendicular to the fiber axis ⊥ and from the diffraction profile of the (10) plane in the meridian direction, the spread La of the carbon network plane in the direction parallel to the fiber axis / / were calculated according to Scherrer's equation.

[0051] Table 3 shows the measurement results of the stacking structure of carbon in the carbon fibers of Examples 1 to 4 and Comparative Examples 1 to 4. Note that for the interplanar spacing d002 of the carbon network plane, the smaller the value, the better. On the other hand, for the stacking thickness Lc of the carbon network plane, the spread La of the carbon network plane in the direction perpendicular to the fiber axis ⊥ and the spread La of the carbon network plane in the direction parallel to the fiber axis / / the larger the value, the better. Also, Fig. 2 shows a schematic diagram of the stacking structure of carbon in the carbon fiber measured by wide-angle X-ray diffraction (WAXS).

[0052]

Table 3

[0053] As shown in Table 3, when the carbon fiber is a single filament, when the centrifugation conditions during the preparation of the CNT dispersion are 10,000 rpm for 10 minutes (Examples 1 and 2), compared with the case without centrifugation (Comparative Example 1), the case without using the CNT dispersion (Comparative Example 2), and the case where the centrifugation conditions are 1,000 rpm for 10 minutes (Comparative Example 3), the value of d002 was equal to or less, and the value of Lc was significantly larger, the carbon stacking structure of the carbon fiber was dense, and the crystal had grown large. Also, when the centrifugation conditions were 10,000 rpm for 10 minutes, when the CNT addition amount was 0.4 wt%, compared with the case where it was 0.1 wt%, the carbon stacking structure of the carbon fiber was denser, and the crystal had grown large.

[0054] Also, as shown in Table 3, when the carbon fiber is a multifilament, when the centrifugation conditions during the preparation of the CNT dispersion are 10,000 rpm for 10 minutes (Examples 3 and 4), compared with the case without using the CNT dispersion (Comparative Example 4), La / / was significantly larger, and the spread of the carbon network plane was larger. Also, when the centrifugation conditions were 10,000 rpm for 10 minutes, when the CNT addition amount was 0.4 wt%, compared with the case where it was 0.1 wt%, La / / and La ⊥ were larger, and the spread of the carbon network plane was larger.

Explanation of symbols

[0055] d002: Interplanar spacing of the carbon network plane, La: Spread of the carbon network plane, Lc: Stacking thickness of the carbon network plane

Claims

1. A step of centrifuging a mixture containing carbon nanotubes and a polyacrylonitrile-based polymer at 2000 rpm to 20000 rpm for 1 minute to 120 minutes to prepare a carbon nanotube dispersion; A step of mixing the carbon nanotube dispersion and a polyacrylonitrile-based polymer to prepare a spinning dope; A step of spinning the spinning dope to obtain a precursor fiber of carbon fiber; A step of flame-retarding and carbonizing the precursor fiber of carbon fiber A method for producing carbon fiber, comprising:

2. The method for producing carbon fiber according to claim 1, wherein the centrifugation of the mixture is carried out under the conditions of 5000 rpm to 15000 rpm for 1 minute to 120 minutes.

3. The method for producing carbon fiber according to claim 1 or 2, wherein the content of the carbon nanotubes in the spinning dope is 0.3% by weight to 0.5% by weight based on the polyacrylonitrile-based polymer in the spinning dope.

Images