JP2005273037A - Method for producing carbon fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ultra fine carbon fibers which do not have a branched structure, have a high strength / a high elastic modulus, and have a fiber diameter of 0.001μm to 2μm. <P>SOLUTION: A method for producing the carbon fibers comprises a process for forming precursor fibers from a mixture comprising a thermoplastic carbon precursor and a thermoplastic resin having an oxygen diffusion coefficient of 9.0×10<SP>-7</SP>to 1.0×10<SP>-4</SP>(cm<SP>2</SP>/sec)at 30°C, a process for subjecting the precursor fibers to a stabilization treatment to stabilize the thermoplastic carbon precursor in the precursor fibers to form the stabilized precursor fibers, a process for removing the thermoplastic resin from the stabilized precursor fibers to form the fibrous carbon precursors, and a process for carbonize or graphitize the fibrous carbon precursors. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing carbon fiber, and more specifically, from a mixture of a thermoplastic resin and a thermoplastic carbon precursor, carbon fiber is preferably ultrafine carbon fiber, specifically, fiber diameter is less than 2 μm. The present invention relates to a method for producing carbon fiber.

  Carbon fibers are used as fillers for high-performance composite materials because they have excellent properties such as high strength, high elastic modulus, high conductivity, and light weight. Its application is not limited to conventional fillers for the purpose of improving mechanical strength, but by taking advantage of the high conductivity of carbon materials, as an electromagnetic shielding material, a conductive resin filler for antistatic materials, or Use as a filler for electrostatic coatings on resins is expected. In addition, it is expected to be used as a field electron emission material such as a flat display by utilizing the characteristics of chemical stability, thermal stability and fine structure as a carbon material.

  There are two reported methods for producing carbon fibers for such high performance composite materials: (1) a method for producing carbon fibers using a vapor phase method, and (2) a method for producing from a melt spinning of a resin composition. Has been.

  As a production method using a gas phase method, for example, an organic compound such as benzene is used as a raw material, and an organic transition metal compound such as ferrocene is introduced into a high-temperature reactor as a catalyst together with a carrier gas, and is generated on a substrate (for example , See Patent Document 1), a method of generating carbon fibers by a vapor phase method in a floating state (see, for example, Patent Document 2), or a method of growing on a reaction furnace wall (see, for example, Patent Document 3). ) Etc. are disclosed. However, although the carbon fiber obtained by these methods has high strength and high elastic modulus, there are many branches, and because of the branching, the disorder of the graphite structure, that is, the grain structure is observed, and the elastic modulus and strength are reduced. There is a problem, and there is a problem that the dispersibility of the blend into the resin is lowered due to the entanglement of the carbon fibers due to branching, and the performance as a reinforcing filler is very low. In addition, there is a problem of high costs.

  On the other hand, as a method for producing carbon fibers from melt spinning of a resin composition, a method for producing ultrafine carbon fibers from a composite fiber of a phenol resin and polyethylene (for example, see Patent Document 4) is disclosed. In the case of the method, a carbon fiber having a small branched structure can be obtained, but since the phenol resin is completely amorphous, it is difficult to form an orientation and is hardly graphitized, so that the strength and elastic modulus of the obtained ultrafine carbon fiber are low. There was a problem that expression was not expected. Moreover, since it stabilized via polyethylene, there existed problems, such as taking a lot of time.

JP-A-60-27700 (page 2-3) JP 60-54998 A (page 1-2) Japanese Patent No. 2778434 (page 1-2) JP 2001-73226 A (page 3-4)

  An object of the present invention is to provide a method for producing an ultrafine carbon fiber having high strength and high elastic modulus with high productivity by shortening the stabilization treatment time.

  As a result of intensive studies in view of the above-described prior art, the present inventors have completed the present invention.

That is, the object of the present invention is to
The carbon fiber of the present invention includes (1) 100 parts by weight of a thermoplastic resin having an oxygen diffusion coefficient at 30 ° C. of 9.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁴ (cm ² / sec), and a pitch. Forming a precursor fiber from a mixture of at least one thermoplastic carbon precursor selected from the group consisting of polyacrylonitrile, polycarbodiimide, polyimide, polyetherimide, polybenzoazole, and aramids A step, (2) subjecting the precursor fiber to a stabilization treatment to stabilize the thermoplastic carbon precursor in the precursor fiber to form a stabilized precursor fiber, and (3) heat from the stabilized precursor fiber. This is achieved by removing the plastic resin to form a fibrous carbon precursor, and (4) carbonizing or graphitizing the fibrous carbon precursor.

熱可塑性樹脂がポリ−４−メチルペンテン−１またはその共重合体であること、が包含される。 Further, the production method of the present invention includes a thermoplastic resin having an oxygen permeability at 30 ° C. of 9.0 × 10 ^{−10 to} 1.0 × 10 ⁻⁵ (cm ³ · cm / cm ² · sec · cmHg). Using
Forming a precursor fiber having a fiber diameter of 0.01 to 20 μm in the step (1), forming a precursor fiber having a fiber diameter of 0.05 to 10 μm in the step (1); In the step (2), the stabilization treatment is performed under a mixed gas of halogen and oxygen, iodine is used as the halogen gas, the pitch is mesophase pitch, and the thermoplastic resin is represented by the following formula (I) Using a thermoplastic resin represented by

It is included that the thermoplastic resin is poly-4-methylpentene-1 or a copolymer thereof.

  In a method for producing a carbon fiber from a mixture of a thermoplastic resin and a thermoplastic carbon precursor, an ultrafine carbon fiber having a high-strength and high-modulus carbon fiber with a small branch structure and a fiber diameter of less than 2 μm is used. It can be manufactured efficiently and inexpensively. The nonwoven fabric composed of the ultrafine carbon fiber and the carbon fiber can be used for a high-functional filter, a battery electrode substrate, and the like.

  Hereinafter, the present invention is made in the order of (A) thermoplastic resin, (B) thermoplastic carbon precursor, (C) production of a mixture comprising a thermoplastic resin and a thermoplastic carbon precursor, and (D) a method of producing carbon fiber. This will be described in detail.

(A) Thermoplastic resin The thermoplastic resin used in the present invention needs to easily incorporate oxygen and halogen gas into the thermoplastic resin by the stabilization treatment after producing the precursor fiber. Therefore, a thermoplastic resin having an oxygen diffusion coefficient at 30 ° C. of 9.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁴ (cm ² / sec) is preferably used. If the oxygen diffusion coefficient at 30 ° C. of the thermoplastic resin is lower than 9.0 × 10 ⁻⁷ cm ² / sec, it takes a long time for the stabilization treatment, which is not preferable. On the other hand, if it exceeds 1.0 × 10 ⁻⁴ cm ² / sec, the oxygen diffusion is very good, but the heat resistance of the thermoplastic resin becomes very low. As a result, it takes a lot of time for the stabilization treatment. Absent.

In general, the oxygen permeability can be evaluated by the product of the oxygen diffusion coefficient and the oxygen solubility in the thermoplastic resin. As described above, after the precursor fiber is manufactured, oxygen and halogen gas need to be easily taken into the thermoplastic resin by stabilization treatment, so that the oxygen permeability at 30 ° C. is 9.0 × 10 ^−10. It is preferable that it is -1.0 * 10 < ^-5 > (cm < ³ > * cm / cm < ² > * sec * cmHg). When the oxygen permeability of the thermoplastic resin is lower than 9.0 × 10 ⁻¹⁰ cm ³ · cm / cm ² · sec · cmHg, it takes a long time for the stabilization treatment, which is not preferable. On the other hand, if it exceeds 1.0 × 10 ⁻⁵ cm ³ · cm / cm ² · sec · cmHg, the oxygen diffusion is very good, but the heat resistance of the thermoplastic resin becomes very low, resulting in stabilization treatment. It takes a lot of time and is not preferable.

  The thermoplastic resin used in the present invention needs to be easily removed after producing the stabilized precursor fiber. For this reason, it is decomposed | disassembled to 15 wt% or less of the initial weight, more preferably 10 wt% or less, and further 5 wt% or less by hold | maintaining for 5 hours at the temperature of 350 degreeC or more and less than 600 degreeC in oxygen or an inert gas atmosphere. It is preferable to use a thermoplastic resin. As such a thermoplastic resin, a polyacrylate polymer such as polyolefin, polymethacrylate, or polymethyl methacrylate, polystyrene, polycarbonate, polyarylate, polyester carbonate, polysulfone, polyimide, polyetherimide, or the like is preferably used. Among these, for example, a polyolefin-based thermoplastic resin represented by the following formula (I) is preferably used as the thermoplastic resin that has high gas permeability and can be easily thermally decomposed.

  Specific examples of the compound represented by the formula (I) include poly-4-methylpentene-1 and a copolymer of poly-4-methylpentene-1, such as poly-4-methylpentene-1. Examples thereof include a polymer obtained by copolymerizing a vinyl monomer.

  Further, from the point that the thermoplastic resin of the present invention can be easily melted and blended with a thermoplastic carbon precursor, in the case of amorphous, the glass transition temperature is 250 ° C. or less, and in the case of crystallinity, the crystal melting point is 300 ° C. or less. It is preferable that

(B) Thermoplastic carbon precursor The thermoplastic carbon precursor used in the present invention is maintained at 200 ° C. or higher and lower than 350 ° C. for 2 to 30 hours in an oxygen or oxygen / halogen mixed gas atmosphere, and then 350 ° C. or higher. It is preferable to use a thermoplastic carbon precursor in which 80 wt% or more of the initial weight remains by holding at a temperature of less than 500 ° C. for 5 hours. Under the above conditions, if the residual amount is less than 80% of the initial weight, carbon fibers cannot be obtained with a sufficient carbonization rate from the thermoplastic carbon precursor, which is not preferable. More preferably, 85% or more of the initial weight remains under the above conditions.

  Specific examples of the thermoplastic carbon precursor that satisfies the above conditions include rayon, pitch, polyacrylonitrile, poly α-chloroacrylonitrile, polycarbodiimide, polyimide, polyetherimide, polybenzoazole, and aramids. Among these, pitch, polyacrylonitrile, and polycarbodiimide are preferable, and pitch is more preferable. Of the pitches, mesophase pitches which are generally expected to have high strength and high elastic modulus are preferred. The mesophase pitch refers to a compound that can form an optically anisotropic phase (liquid crystal phase) in a molten state. As a raw material for mesophase pitch, a distillation residue of coal or petroleum may be used, or an organic compound may be used. However, aromatic hydrocarbons such as naphthalene are used because of their ease of stabilization, carbonization or graphitization. It is preferable to use a mesophase pitch using as a raw material. The thermoplastic carbon precursor may be used in an amount of 1 to 150 parts by weight, preferably 5 to 100 parts by weight, based on 100 parts by weight of the thermoplastic resin.

(C) Manufacture of the mixture which consists of a thermoplastic resin and a thermoplastic carbon precursor The mixture used by this invention is manufactured from a thermoplastic resin and a thermoplastic carbon precursor. In order to produce carbon fibers having a fiber diameter of less than 21 μm from the mixture used in the present invention, the dispersion diameter of the thermoplastic carbon precursor in the thermoplastic resin is preferably 0.01 to 50 μm.

  When the dispersion diameter of the thermoplastic carbon precursor in the thermoplastic resin deviates from the range of 0.01 to 50 μm, it may be difficult to produce carbon fibers for high performance composite materials. A more preferable range of the dispersion diameter of the thermoplastic carbon precursor is 0.01 to 30 μm.

  Moreover, it is preferable that the dispersion diameter in the thermoplastic resin of a thermoplastic carbon precursor is 0.01-50 micrometers after hold | maintaining the mixture which consists of a thermoplastic resin and a thermoplastic carbon precursor at 300 degreeC for 3 minute (s). . Generally, when a mixture obtained by melt-kneading a thermoplastic resin and a thermoplastic carbon precursor is kept in a molten state, the thermoplastic carbon precursor aggregates with time. If the dispersion diameter exceeds 50 μm due to aggregation of the thermoplastic carbon precursor, it may be difficult to produce carbon fibers for high-performance composite materials.

  The degree of aggregation rate of the thermoplastic carbon precursor varies depending on the types of the thermoplastic resin and the thermoplastic carbon precursor used, but is more preferably 300 ° C. for 5 minutes, further preferably 300 ° C. for 10 minutes or more. It is preferable to maintain a dispersion diameter of 01 to 50 μm. In the mixture, the thermoplastic carbon precursor forms an island phase and is spherical or elliptical. The dispersion diameter here means the spherical diameter of the thermoplastic carbon precursor or the major axis diameter of the ellipsoid in the mixture.

  The usage-amount of a thermoplastic carbon precursor is 1-150 weight part with respect to 100 weight part of thermoplastic resins, Preferably it is 5-100 weight part. If the amount of the thermoplastic carbon precursor used exceeds 150 parts by weight, a thermoplastic carbon precursor having a desired dispersion diameter cannot be obtained, and if it is less than 1 part by weight, the target carbon fiber can be produced at low cost. This is not preferable because problems such as inability to occur occur.

  As a method for producing a mixture from a thermoplastic resin and a thermoplastic carbon precursor, kneading in a molten state is preferable. As the melt-kneading of the thermoplastic resin and the thermoplastic carbon precursor, known ones can be used as necessary, and examples thereof include a single screw extruder, a twin screw extruder, a mixing roll, and a Banbury mixer. Of these, the same-direction twin screw extruder is preferably used for the purpose of favorably microdispersing the thermoplastic carbon precursor in the thermoplastic resin.

  The melt kneading temperature is preferably 100 to 400 ° C. When the melt kneading temperature is less than 100 ° C., the thermoplastic carbon precursor is not in a molten state, and micro-dispersion with the thermoplastic resin is difficult, which is not preferable. On the other hand, when the temperature exceeds 400 ° C., the decomposition of the thermoplastic resin and the thermoplastic carbon precursor proceeds, which is not preferable. A more preferable range of the melt kneading temperature is 150 ° C to 350 ° C.

  The melt kneading time is 0.5 to 20 minutes, preferably 1 to 15 minutes. When the melt kneading time is less than 0.5 minutes, it is not preferable because micro dispersion of the thermoplastic carbon precursor is difficult. On the other hand, when it exceeds 20 minutes, the productivity of carbon fibers is remarkably lowered, which is not preferable.

  In the present invention, when a mixture is produced from a thermoplastic resin and a thermoplastic carbon precursor by melt-kneading, it is preferably melt-kneaded in a gas atmosphere having an oxygen gas content of less than 10%. The thermoplastic carbon precursor used in the present invention reacts with oxygen to be modified and infusible at the time of melt kneading, which may inhibit micro-dispersion in the thermoplastic resin. For this reason, it is preferable to perform melt kneading while circulating an inert gas to reduce the oxygen gas content as much as possible. The oxygen gas content during melt kneading is more preferably less than 5%, and further less than 1%. By implementing said method, a mixture can be manufactured from the thermoplastic resin and thermoplastic carbon precursor for manufacturing the nonwoven fabric which consists of carbon fibers.

(D) Method for Producing Carbon Fiber The carbon fiber of the present invention can be produced from a mixture comprising the above-mentioned thermoplastic resin and a thermoplastic carbon precursor. The carbon fiber of the present invention includes (1) a step of forming a precursor fiber from a mixture of 100 parts by weight of a thermoplastic resin and 1 to 150 parts by weight of a thermoplastic carbon precursor, and (2) a stabilization process for the precursor fiber. To stabilize the thermoplastic carbon precursor in the precursor fiber to form a stabilized precursor fiber, (3) forming a fibrous carbon precursor by removing the thermoplastic resin from the stabilized precursor fiber And (4) a fibrous carbon precursor is carbonized or graphitized. Each step will be described in detail below.

(1) Step of forming precursor fibers from a mixture comprising a thermoplastic resin and a thermoplastic carbon precursor In the present invention, a precursor is obtained from a mixture obtained by melt-kneading a thermoplastic resin and a thermoplastic carbon precursor by a melt blow method. A method for forming fibers can be exemplified. As conditions for the melt blow, a range in which the die temperature is 150 to 400 ° C. and the gas temperature is 150 to 400 ° C. is preferably used. When a mixture obtained from a thermoplastic resin and a thermoplastic carbon precursor is melt-kneaded and then melt-spun from the spinneret, the mixture is melt-kneaded and then fed into the pipe in a molten state and continuously sent to the spinneret. It is preferable to carry out liquid transfer, and the transfer time from melt-kneading to spinneret discharge is preferably within 10 minutes. The gas blowing speed of the melt blow affects the fiber diameter of the precursor fiber. The gas ejection speed is usually 2000 to 100 m / s, more preferably 1000 to 200 m / s.

  As another method, there is a method of obtaining precursor fibers by melt spinning from a mixture obtained by melt kneading of a thermoplastic resin and a thermoplastic carbon precursor. The spinning temperature for melt spinning is 150 ° C to 400 ° C, preferably 180 ° C to 350 ° C. The spinning take-up speed is preferably 10 m / min to 2000 m / min. Deviating from the above range is not preferable because a desired fibrous precursor cannot be obtained.

(2) Step of subjecting precursor fiber to stabilization treatment to stabilize thermoplastic carbon precursor in precursor fiber to form stabilized precursor fiber In the second step of the present invention, the precursor fiber is A stabilization treatment is performed to stabilize the thermoplastic carbon precursor in the precursor fiber to form a stabilized precursor fiber. Stabilization of the thermoplastic carbon precursor is a necessary process for obtaining carbonized or graphitized carbon fibers. If the thermoplastic resin is removed as the next process without carrying out this process, the thermoplastic carbon is removed. Problems such as thermal decomposition and fusion of the precursor occur.

  As a stabilization method, a known method such as a gas flow treatment with oxygen or a solution treatment with an acidic aqueous solution can be used, but infusibilization under a gas flow is preferable from the viewpoint of productivity. As the gas component to be used, oxygen and / or from the viewpoint of permeability to the thermoplastic resin and adsorption to the thermoplastic carbon precursor and from the point that the thermoplastic carbon precursor can be rapidly infusibilized at a low temperature. A mixed gas containing a halogen gas is preferred.

  Examples of the halogen gas include fluorine gas, chlorine gas, bromine gas, and iodine gas. Among these, bromine gas, iodine gas, and particularly iodine gas are preferable. As a specific method of infusibilization under a gas stream, it is preferable to perform the treatment in a desired gas atmosphere at a temperature of 50 to 350 ° C., preferably 80 to 300 ° C., for 5 hours or less, preferably 2 hours or less. .

  Further, the softening point of the thermoplastic carbon precursor contained in the precursor fiber is remarkably increased by the infusibilization, but the softening point is preferably 400 ° C. or more for the purpose of obtaining a desired ultrafine carbon fiber, and 500 ° C. More preferably, the above is true. By carrying out the above method, it is possible to stabilize the thermoplastic carbon precursor in the precursor fiber and obtain a stabilized precursor fiber.

(3) Step of forming a fibrous carbon precursor by removing the thermoplastic resin from the stabilized precursor fiber The third step of the present invention removes the thermoplastic resin contained in the stabilized precursor fiber by pyrolysis. Specifically, the thermoplastic resin contained in the stabilized precursor fiber is removed, and only the stabilized fibrous carbon precursor is separated to form the fibrous carbon precursor. In this step, it is necessary to suppress the thermal decomposition of the fibrous carbon precursor as much as possible, to decompose and remove the thermoplastic resin, and to separate only the fibrous carbon precursor. The removal of the thermoplastic resin may be either an oxygen atmosphere or an inert gas atmosphere.

  When removing the thermoplastic resin in an oxygen atmosphere, it is necessary to remove it at a temperature of 350 ° C. or higher and lower than 600 ° C. The term “under oxygen atmosphere” as used herein refers to a gas atmosphere having an oxygen concentration of 1 to 100%. In addition to oxygen, inert gases such as carbon dioxide, nitrogen and argon, and inert gases such as iodine and bromine are used. It may contain. Among these conditions, it is particularly preferable to use air particularly from the viewpoint of cost. When the temperature at which the thermoplastic resin contained in the stabilized precursor fiber is removed is less than 350 ° C., the thermal decomposition of the fibrous carbon precursor can be suppressed, but the thermoplastic resin cannot be sufficiently decomposed, which is not preferable. . If the temperature is 600 ° C. or higher, the thermoplastic resin can be sufficiently thermally decomposed, but the fibrous carbon precursor is also thermally decomposed, resulting in carbonization of the carbon fiber obtained from the thermoplastic carbon precursor. The yield is lowered, which is not preferable.

  The temperature at which the thermoplastic resin contained in the stabilized precursor fiber is decomposed is preferably treated in an oxygen atmosphere at a temperature of 380 to 500 ° C., more preferably 400 to 450 ° C., for 0.5 to 10 hours. By performing the above-mentioned treatment, it is decomposed to 15 wt% or less of the initial weight of the used thermoplastic resin. Moreover, 80 wt% or more of the initial weight of the used thermoplastic carbon precursor remains as a fibrous carbon precursor. When removing the thermoplastic resin in an inert gas atmosphere, it is necessary to remove it at a temperature of 350 ° C. or higher and lower than 600 ° C. The term “inert gas atmosphere” as used herein refers to a gas such as carbon dioxide, nitrogen, or argon having an oxygen concentration of 30 ppm or less, more preferably 20 ppm or less, but may contain a halogen gas such as iodine or bromine. . In addition, as an inert gas used at this process, a carbon dioxide and nitrogen are good from the relationship of cost, and nitrogen is especially preferable.

  When the temperature at which the thermoplastic resin contained in the nonwoven fabric composed of the stabilized precursor fibers is removed is less than 350 ° C., the thermal decomposition of the fibrous carbon precursor can be suppressed, but the thermoplastic resin can be sufficiently decomposed. Not preferable. Further, when the temperature is 600 ° C. or higher, the thermoplastic resin can be sufficiently thermally decomposed, but the fibrous carbon precursor is also thermally decomposed. As a result, the thermoplastic resin is made of carbon fibers obtained from the thermoplastic carbon precursor. Since the carbonization yield of a nonwoven fabric is reduced, it is not preferable. The temperature for decomposing the thermoplastic resin contained in the stabilized precursor fiber is preferably 380 to 550 ° C., more preferably 400 to 530 ° C. in an inert gas atmosphere, and 0.5 to 10 hours. .

  By performing the above-mentioned treatment, it is decomposed to 15 wt% or less of the initial weight of the used thermoplastic resin. Moreover, 80 wt% or more of the initial weight of the used thermoplastic carbon precursor remains as a fibrous carbon precursor.

(4) Step of carbonizing or graphitizing the fibrous carbon precursor In the fourth step of the present invention, the fibrous carbon precursor obtained by removing the thermoplastic resin to 15 wt% or less of the initial weight is in an inert gas atmosphere. Carbonized or graphitized to produce carbon fiber. In the present invention, the fibrous carbon precursor is carbonized or graphitized by high-temperature treatment in an inert gas atmosphere to form a desired carbon fiber. The fiber diameter of the obtained carbon fiber is preferably 0.001 μm to 2 μm.

  Carbonization or graphitization of the fibrous carbon precursor can be performed by a known method. Examples of the inert gas used include nitrogen and argon, and the temperature is 500 ° C to 3500 ° C, preferably 800 ° C to 3000 ° C. Note that the oxygen concentration during carbonization or graphitization is preferably 20 ppm or less, and more preferably 10 ppm or less. By carrying out the above method, carbon fibers can be produced.

(5) Non-woven fabric made of carbon fiber By carrying out this method, a non-woven fabric made of carbon fiber having a fiber diameter of less than 2 μm may be produced. In addition, the nonwoven fabric said by this invention points out the planar form of thickness 1-100,000 micrometers which the fiber of 0.001-20 micrometers of fiber diameters made intricately entangled.

  The nonwoven fabric made of carbon fiber obtained by this method is composed of carbon fibers having a fiber diameter of 0.001 to 2 μm. The nonwoven fabric made of carbon fibers obtained by this method maintains the nonwoven fabric form by intricately intertwining the carbon fibers, but in order to make the form retention stronger, it is partly fused between the fibers. May be happening.

  The nonwoven fabric made of carbon fiber of the present invention may be made of a single felt or mat by stacking several nonwoven fabrics made of carbon fiber. In addition, by stacking a plurality of nonwoven fabrics made of carbon fiber precursors, nonwoven fabrics made of precursor fibers, stabilized precursor fibers, and nonwoven fabrics made of fibrous carbon precursors, the following steps are followed. A felt or mat made of a piece of carbon fiber may be produced.

  Examples of the present invention will be described below. In addition, this invention is not limited by the content described below. The precursor fiber diameter and carbon fiber diameter were measured with a scanning electron microscope S-2400 (Hitachi). The oxygen permeability and oxygen diffusion coefficient of the thermoplastic resin were calculated by the unsteady step method. The test method of the unsteady step method is described below.

A test gas is supplied at a constant pressure (high pressure side) to one side with a test piece having a known sample thickness (L) and gas permeation area (A) as a boundary, and the other is caused to have a pressure difference by evacuation ( Low pressure side). After the gas permeation reaches a steady state, the evacuation is stopped, the test gas that has permeated the test piece is stored in the measuring tube, and the time (t) is measured. Next, the test gas in the measuring tube is guided to the gas chromatograph with a carrier gas, and after the components are separated, the permeation amount of each component is quantified with a heat conduction detector, and the transmittance is calculated by the following equation.
Gas permeability = (Q × K × L) / (P × A × t)
(Where Q: test gas permeation amount (cc), K: cell constant = 2.35, L: film thickness (cm) of test piece, P: pressure difference (kgf / cm ² , A: permeation area (cm ² ), t: measurement time (sec))

In the case of the unsteady step method, the measurement of the permeation amount is started at the same time as the test gas is applied stepwise, and the transmissivity is calculated from the gradient after the permeation amount-time characteristic reaches the linear state. Further, the diffusion coefficient D is obtained by t = L ² / 6D from the intercept of the same gradient expressed by a linear expression in the gas permeation curve and the thickness of the test piece.

The measuring apparatus is a differential pressure type gas permeability measuring system manufactured by Yanagimoto Seisakusho Co., Ltd., the test gas is oxygen gas, the temperature is 30 ° C., the test gas pressure (gauge pressure) is 3.0 kgf / cm ² (low pressure side: rotary vacuum) Aspiration by pump). The gas permeation area was 15.2 cm ² , and He gas was used as the carrier gas. The measurement was carried out at n = 2 and the average value was taken. The gas volume was calculated at 23 ° C./1 atm. The oxygen permeability and oxygen diffusion coefficient were measured by preparing a 50 μm film by melt extrusion of a thermoplastic resin.

[Example 1]
100 parts by weight of poly-4-methylpentene-1 (TPX: Grade RT-18 [manufactured by Mitsui Chemicals, Inc.) as a thermoplastic resin and mesophase pitch AR-HP (manufactured by Mitsubishi Gas Chemical Co., Ltd.) as a thermoplastic carbon precursor 11.1 parts were melt-kneaded with the same direction twin screw extruder (TEX-30, manufactured by Nippon Steel Works, barrel temperature 290 ° C., under nitrogen stream) to prepare a mixture. The dispersion diameter of the thermoplastic carbon precursor obtained under these conditions in the thermoplastic resin was 0.05 to 2 μm. Further, this mixture was kept at 300 ° C. for 10 minutes, but aggregation of the thermoplastic carbon precursor was not observed, and the dispersion diameter was 0.05 to 2 μm. Poly-4-methylpentene-1 had an oxygen diffusion coefficient of 1.3 × 10 ⁻⁶ (cm ² / sec) and an oxygen permeability of 2.6 × 10 ⁻⁹ (cm ² / sec).

  The above mixture was spun from a spinneret at 330 ° C., and a non-woven fabric made of precursor fibers having a fiber diameter of 0.5 to 5 μm was created by blowing air at a temperature of 350 ° C. and 500 m / min directly under the spinning to fibers in a molten state. . Stabilized precursor fiber is prepared by charging 0.5 parts by weight of iodine into 1 liter of pressure-resistant glass in air with respect to 10 parts by weight of the nonwoven fabric composed of the precursor fiber and performing a stabilization treatment at 180 ° C. for 10 hours. A nonwoven fabric made of

  Next, the thermoplastic resin was removed by raising the temperature of the nonwoven fabric composed of the stabilized precursor fibers to 550 ° C. at 5 ° C./min in a nitrogen gas atmosphere, thereby creating a nonwoven fabric composed of the fibrous carbon precursor. The nonwoven fabric made of carbon fiber was made by raising the temperature of the nonwoven fabric made of fibrous carbon precursor from room temperature to 1000 ° C. at 10 ° C./min in a nitrogen gas atmosphere. The obtained nonwoven fabric had a carbon fiber diameter of approximately 300 to 800 nm, and no fusion between the carbon fibers was observed.

[Comparative Example 1]
100 parts by weight of polyarylate (polyarylate: grade U100 [manufactured by Unitika Ltd.)] as the thermoplastic resin and 11.1 parts of mesophase pitch AR-HP (manufactured by Mitsubishi Gas Chemical Co., Ltd.) as the thermoplastic carbon precursor The mixture was prepared by melt-kneading with a shaft extruder (TEX-30 manufactured by Nippon Steel Works, barrel temperature: 290 ° C., under nitrogen stream). The dispersion diameter of the thermoplastic carbon precursor obtained under these conditions in the thermoplastic resin was 0.05 to 3 μm. Further, this mixture was kept at 300 ° C. for 10 minutes, but aggregation of the thermoplastic carbon precursor was not observed, and the dispersion diameter was 0.05 to 2 μm. The polyarylate had an oxygen diffusion coefficient of 3.2 × 10 ⁻⁸ (cm ² / sec) and an oxygen permeability of 1.5 × 10 ⁻¹⁰ (cm ² / sec).

  The above mixture is spun from a spinneret at 330 ° C., and a nonwoven fabric composed of precursor fibers having a fiber diameter of 0.5 to 5 μm is blown onto the fiber in a molten state at 350 ° C. directly below the spinneret surface at 500 ° C./min. Created. Stabilized precursor fiber is prepared by charging 0.5 parts by weight of iodine into 1 liter of pressure-resistant glass in air with respect to 10 parts by weight of the nonwoven fabric composed of the precursor fiber and performing a stabilization treatment at 180 ° C. for 10 hours. A nonwoven fabric made of Next, the thermoplastic resin was removed by raising the temperature of the nonwoven fabric composed of the stabilized precursor fibers to 550 ° C. at 5 ° C./min in a nitrogen gas atmosphere, thereby creating a nonwoven fabric composed of the fibrous carbon precursor. A nonwoven fabric made of carbon fiber was created by heating the nonwoven fabric made of fibrous carbon precursor from room temperature to 1000 ° C. at a rate of 10 ° C./min in a nitrogen gas atmosphere, but extreme fusion was observed between the carbon fibers. It was.

Claims (11)

(1) 100 parts by weight of a thermoplastic resin having a diffusion coefficient of oxygen at 30 ° C. of 9.0 × 10 ^{−7 to} 1.0 × 10 ⁻⁴ (cm ² / sec), pitch, polyacrylonitrile, polycarbodiimide, Forming a precursor fiber from a mixture comprising 1 to 150 parts by weight of at least one thermoplastic carbon precursor selected from the group consisting of polyimide, polyetherimide, polybenzoazole, and aramids,
(2) subjecting the precursor fiber to a stabilization treatment to stabilize the thermoplastic carbon precursor in the precursor fiber to form a stabilized precursor fiber;
(3) a step of removing the thermoplastic resin from the stabilized precursor fiber to form a fibrous carbon precursor;
(4) a step of carbonizing or graphitizing the fibrous carbon precursor,
The manufacturing method of the carbon fiber manufactured by going through. The carbon fiber according to claim 1, wherein a thermoplastic resin having an oxygen permeability at 30 ° C. of 9.0 × 10 ^{−10 to} 1.0 × 10 ⁻⁵ (cm ³ · cm / cm ² · sec · cmHg) is used. Production method.   The method for producing carbon fibers according to claim 1, wherein in the step (1), precursor fibers are formed from a mixture of a thermoplastic resin and a thermoplastic carbon precursor by a melt blow method.   The method for producing carbon fiber according to claim 1, wherein in the step (1), a precursor fiber having a fiber diameter of 0.01 to 20 μm is formed.   The method for producing carbon fiber according to claim 1, wherein in the step (1), a precursor fiber having a fiber diameter of 0.05 to 10 µm is formed.   The method for producing a carbon fiber according to any one of claims 1 to 5, wherein in the step (2), the stabilization treatment is performed under a mixed gas of halogen and oxygen.   The method for producing carbon fiber according to claim 6, wherein iodine is used as the halogen gas.   The manufacturing method of the carbon fiber in any one of Claims 1-7 whose pitch is a mesophase pitch. The method for producing carbon fiber according to claim 1, wherein the thermoplastic resin is a thermoplastic resin represented by the following formula (I).

  The method for producing carbon fiber according to claim 9, wherein the thermoplastic resin is poly-4-methylpentene-1 or a copolymer thereof.   The nonwoven fabric which consists of carbon fiber whose fiber diameter obtained by the method in any one of Claims 1-10 is less than 1 micrometer.