JP2017066540A - Production method of carbon fiber and carbon fiber sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a carbon fiber and a carbon fiber sheet that can suppress a reduction in a carbon yield even when an infusibilization step is omitted in a production method of a carbon fiber sheet containing an organic fiber as a raw material of a carbon fiber.SOLUTION: The production method of a carbon fiber or a carbon fiber sheet that does not comprise an infusibilization step and comprises the following steps (a)-(c): (a) a step of preparing a mixed solution in which a water insoluble polymer compound as a raw material of a carbon fiber or a carbon fiber sheet and an organic sulfonic acid are dissolved in an organic solvent; (b) a step of obtaining a fiber or a fiber sheet by spinning the mixed solution; and (c) a step of heat treating the fiber yarn or the fiber sheet in an inert gas atmosphere at a temperature of 500°C-2600°C.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a carbon fiber and a method for producing a carbon fiber sheet using an organic sulfonic acid as a catalyst.

Carbon fiber is lightweight and has excellent strength, electrical conductivity, heat resistance, and chemical resistance, and is widely used for sports and leisure goods, aerospace and industrial applications. Even when carbon materials made of carbon fibers are used as they are, or when they are used as composite materials obtained by processing various resins on these carbon materials, the carbon materials are often used in a sheet form.
Examples of organic fibers used as a raw material for carbon fibers include PAN (polyacrylonitrile), pitch, and rayon, but PAN fibers are mainly used because of the excellent features of the obtained carbon fibers. When carbon fiber is produced from organic fiber, if the raw material fiber is carbonized as it is, the original fiber form cannot be maintained by melting the fiber, most of the fiber disappears due to thermal decomposition, or even if carbon fiber is obtained There is a problem that the carbonization yield becomes extremely low. Therefore, when organic fiber is used as a raw material for carbon fiber, an infusibilization (or flame resistance) treatment is performed before the heat treatment for the purpose of suppressing fiber melting and yield reduction.

  As a method for producing a sheet made of carbon fiber, a woven or non-woven fabric mainly composed of any one of polyacrylonitrile, rayon, and phenol-based fibers, which is a raw material of carbon fiber that has been infusibilized (flame-resistant), is used. A method of performing heat treatment at 800 to 3000 ° C. after passing through a hot roll at 150 to 350 ° C. has been proposed (Patent Document 1). Further, a sheet obtained by papermaking from a raw material mainly composed of polyacrylonitrile fiber and pulp is impregnated with an impregnating liquid containing a phenol resin and a carbonaceous powder, and then the phenol in the impregnated sheet is obtained. A method is proposed in which after the resin is cured, an infusibilization treatment (150 to 350 ° C., several tens of minutes to a hundred hours) is performed in air, and then heat treatment is performed at 800 to 1200 ° C. in an inert gas atmosphere ( Patent Document 2). When a sheet made of carbon fiber is produced by any method, a step of infusibilizing the organic fiber that is the raw material of the carbon fiber is required.

JP 2004-111341 A JP 06-60884 A

However, the infusibilization treatment complicates the production process of the carbon fiber sheet, and also contributes to an increase in production cost due to a large energy consumption.
Accordingly, the present invention provides a method for producing a carbon fiber sheet and a carbon fiber sheet that can suppress a decrease in carbon yield even if the infusibilization step is omitted in the method for producing a carbon fiber sheet containing organic fibers that are raw materials for carbon fibers. The purpose is to provide.

The present invention provides the following inventions [1] to [10].
[1] A method for producing a carbon fiber or a carbon fiber sheet, which does not include an infusibilization step, including the following steps (a) to (c).
(A) a step of preparing a mixed solution in which a water-insoluble polymer compound and an organic sulfonic acid, which are raw materials for carbon fiber or carbon fiber sheet, are dissolved in an organic solvent; (b) spinning the mixed solution to obtain a fiber or fiber sheet; Step (c) A step of heat-treating the fiber or fiber sheet at a temperature of 500 ° C. to 2600 ° C. in an inert gas atmosphere.
[2] The method for producing a carbon fiber or carbon fiber sheet according to [1], further comprising the following step (d):
(D) A step of reheating the fiber or fiber sheet obtained in the step (c) at 2200 ° C. to 3200 ° C. in an inert gas atmosphere.
[3] The carbon fiber or the water-insoluble polymer compound used as a raw material of the carbon fiber has a residual carbon ratio of 5% by weight or more when treated at a heating temperature of 800 ° C. in an inert gas atmosphere. The method for producing the carbon fiber or the carbon fiber sheet according to any one of [1] to [2].
[4] The carbon according to any one of [1] to [3], wherein the water-insoluble polymer compound is polyacrylonitrile, epoxy, unsaturated polyester, phenol, polyimide, or melamine resin. Manufacturing method of fiber or carbon fiber sheet.
[5] The method for producing a carbon fiber or carbon fiber sheet according to any one of [1] to [4], wherein the organic sulfonic acid is methanesulfonic acid.
[6] The carbon fiber according to any one of [1] to [5], wherein a ratio of the organic sulfonic acid to the water-insoluble polymer compound is 0.1 wt% to 10.0 wt%. Or the manufacturing method of a carbon fiber sheet.
[7] The method for producing a carbon fiber or carbon fiber sheet according to any one of [1] to [6], wherein the mixed solution is fiberized using an electrospinning method.
[8] A woven fabric using the carbon fiber produced by the method according to any one of [1] to [7].
[9] A composite material using the carbon fiber or the carbon fiber sheet produced by the method according to any one of [1] to [7].
[10] A gas diffusion layer for a fuel cell, wherein the carbon fiber or the carbon fiber sheet produced by the method according to any one of [1] to [7] is used.

  According to the present invention, in the method for producing a carbon fiber sheet containing an organic fiber that is a raw material for carbon fiber, the carbon fiber and the method for producing the carbon fiber sheet that can suppress a decrease in carbon yield even if the infusibilization step is omitted. Can be provided.

It is an electron microscope image of the carbon fiber sheet surface of Example 1 of this invention. It is an electron microscope image of the carbon fiber sheet surface of Example 2 of this invention. It is an electron microscope image of the carbon fiber sheet surface of the comparative example 1 of this invention.

  In the method for producing carbon fiber or carbon fiber sheet of the present invention, a fiber or fiber sheet obtained using a solution containing a water-insoluble polymer compound and an organic sulfonic acid as a raw material is heated to 500 ° C to 2600 ° C in an inert gas atmosphere. It heat-processes at the temperature of. In particular, it is a major feature of the present invention that the step of infusibilizing the fiber or fiber sheet is not performed under conditions of about 200 ° C. In addition, it is also possible to reheat the obtained carbon fiber at 2200 degreeC-3200 degreeC.

(Water-insoluble polymer used as raw material for carbon fiber)
The water-insoluble polymer compound in the present invention can be used without any particular limitation as long as it is a material that is soluble in an organic solvent and insoluble in water and can be fiberized by a known spinning method. For example, polyacrylonitrile, epoxy, unsaturated polyester, phenol, polyimide, melamine resin, cellulose acetate, rayon, polymethyl methacrylate, urethane, polyvinyl chloride, polyvinylidene chloride, polystyrene, polycarbonate, polyethylene terephthalate, polybutylene terephthalate, polyether Examples include ether ketone, polyamideimide, polyetherimide, polyphenylene sulfide, nylon, polyamide, polylactic acid, polyvinylidene fluoride, acrylonitrile-butadiene-styrene, polyacetal, and the like, and copolymers of these compounds may also be used. These may be used alone or in combination of two or more.

  Among the above water-insoluble polymer compounds, polyacrylonitrile, epoxy, unsaturated polyester, phenol, polyimide, and melamine resin that can easily obtain carbon fiber by heat treatment are preferable, and polyacrylonitrile is particularly preferable.

  In addition, organic and inorganic materials may be mixed in a solution in which the water-insoluble polymer compound is dissolved as long as the fiber formation is not hindered. Materials and the like can be used as appropriate. For example, by fiberizing a solution in which an inorganic compound is dispersed as a raw material, it is possible to impart functionalities such as deodorization and antibacterial by supporting the inorganic compound in the carbon fiber after the heat treatment. By adding a surfactant or a conductive aid, the fiber forming property in the spinning process can be improved.

(solvent)
In the present invention, a mixed solution in which the above-mentioned water-insoluble polymer and organic sulfonic acid are dissolved in an organic solvent is prepared. The organic solvent is not particularly limited as long as it can dissolve the water-insoluble polymer, and can be appropriately selected according to the water-insoluble polymer to be used. Specifically, ethanol, methanol, butanol, isobutyl alcohol, isopropyl alcohol, isopentyl alcohol, ethylene glycol, ethyl ether, ethyl acetate, normal-butyl acetate, normal-propyl acetate, methyl acetate, 1,4-dioxane, chloroform, Dichloromethane, benzene, xylene, cyclohexane, acetonitrile, toluene, normal hexane, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, tetrahydrofuran, 1,1,1,3 3,3, -hexafluoro-2-propanol, hexafluoroacetic acid, methyl ethyl ketone, acetone, butyl acetate, cyclohexane, etc. Ku, may be used as a mixture of two or more.
In order to obtain a uniform carbon fiber or carbon fiber sheet, it is important that the water-insoluble polymer, solvent, and organic sulfonic acid are uniformly mixed. It is preferable to select each by paying attention to. The solubility parameter (SP value) of the organic sulfonic acid and miscible solvent described later is in the range of 9.0 to 27.0. For example, when polyacrylonitrile is selected as the water-insoluble polymer, N, N-dimethylformamide (SP value = 24.8), N, N-dimethylacetamide (SP value = 22.1) or the like is used as the organic solvent. By using it, a mixed solution (hereinafter referred to as “spinning solution”) in which an organic sulfonic acid is dissolved in an organic solvent and a water-insoluble polymer compound that is a raw material for carbon fiber in which polyacrylonitrile and organic sulfonic acid are completely dissolved. Can be obtained).

(Organic sulfonic acid)
The organic sulfonic acid used in the present invention may be any organic compound in which a sulfo group (one or more) is bonded to the carbon skeleton. Although various compounds having various sulfo groups in the family are available, a low molecular weight is preferable from the viewpoint of handling.

  Specific examples of the organic sulfonic acid include, for example, R—SO 3 H (wherein R is a linear / branched alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 3 to 20 carbon atoms, or 6 carbon atoms). To 20 aryl groups, and the alkyl group, cycloalkyl group, and aryl group may be substituted with an alkyl group, a hydroxyl group, or a halogen group, respectively. For example, methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 1-hexanesulfonic acid, vinylsulfonic acid, cyclohexanesulfonic acid, p-toluenesulfonic acid, p-phenolsulfonic acid, naphthalenesulfonic acid, benzenesulfonic acid, camphor Examples thereof include sulfonic acid. Of these, methanesulfonic acid is preferably selected. Moreover, organic sulfonic acid may be used individually by 1 type, and may use 2 or more types together.

  In the present invention, it is not clear why the infusibilization treatment becomes unnecessary by mixing the organic sulfonic acid, but the fiber structure spun from the solution in which the water-insoluble polymer compound and the organic sulfonic acid are mixed is heat-treated. As a result, it acts as a dehydration catalyst for compounds with hydroxyl groups, promotes dehydration reactions such as hydroxyl groups within and between molecules, and contributes to improving the heat resistance of compounds and suppressing thermal decomposition reactions other than dehydration reactions. As a result, it is considered that the carbonization yield is improved. Since the PAN-based polymer compound has little or no hydroxyl group, it is unlikely that the yield improvement by the organic sulfonic acid is mainly based on the action as a dehydration catalyst. Therefore, for PAN-based polymer compounds, organic sulfonic acid is presumed to be involved in reactions other than dehydration, but the details are not clear. However, regardless of the presence or absence of hydroxyl groups, there is almost no generation of hydrocarbon gases due to normal thermal decomposition, and the loss of the carbon component in the water-soluble polymer compound is suppressed, so the final carbon material The effect which can prevent the fall of the quantity can be expected.

  In the method for producing a carbon fiber sheet of the present invention, the amount of the organic sulfonic acid added is preferably 0.1 wt% to 10.0 wt% with respect to 100 parts by weight of the water-insoluble polymer compound, % To 5.0 wt% is more preferable.

(Manufacture of fibers and fiber sheets: spinning process)
The fiber in the present invention includes a single yarn composed of one filament and a twisted yarn obtained by twisting a plurality of single yarns. The twisted yarn includes a spun yarn formed by twisting short fibers and a filament yarn formed by twisting long fibers. The method for producing the fiber in the present invention is not particularly limited, and a known spinning method using a solution as a raw material can be appropriately selected. Specifically, the solution is ejected from a spinneret and the solvent is removed with hot air. It is possible to use a dry spinning method and a wet spinning method in which a solution is introduced into a coagulating liquid from a spinning nozzle and converted into a fiber. The obtained fiber may be processed by cutting or the like and cut into an arbitrary length.

The fiber sheet in the present invention refers to a material obtained by processing a large number of fibers into a thin and wide plate shape, and includes woven fabrics, knitted fabrics, and nonwoven fabrics. The method for producing the nonwoven fabric is not particularly limited, but a method of obtaining a fiber sheet using the above-mentioned fibers cut into an appropriate length as a raw material using a dry method or a wet method, or directly from a solution using an electrospinning method or the like. The method of obtaining a fiber sheet can be illustrated. Furthermore, after the nonwoven fabric is obtained, treatment with resin bond, thermal bond, spunlace, needle punch, or the like may be added for the purpose of bonding the fibers together.
In particular, in the electrospinning method having a fiber diameter on the order of submicron, the diameter of the fiber constituting the fiber sheet is extremely thin, so that the fiber is likely to be broken or burnt off by heat treatment. As a result, a carbon fiber sheet in which the shape of the fiber and the sheet is maintained before and after the heat treatment can be produced.

  The electrospinning method can be performed by well-known means. Specifically, the spinning solution is discharged from the nozzle in a state where a voltage is applied between the nozzle filled with the spinning solution and the substrate (also referred to as a collector). Collect the fibers on the substrate.

  As the substrate on which the spinning solution is discharged from the nozzle, an electrode collector such as a metal plate may be used as it is. However, a non-conductive material such as paper may be placed between the nozzle and the collector to form a substrate. Such a substrate is not particularly limited, and the shape thereof is not particularly limited, but a flexible sheet is preferable. By having flexibility, when a target is covered with a fiber composite composed of a substrate and a fiber structure formed on the substrate, the fiber composite may adhere to the target along the unevenness of the target. It becomes possible. In the present invention, paper, nonwoven fabric, plastic film or the like is preferably used as such a substrate.

  The conditions for performing the electrospinning method are not particularly limited, and may be appropriately adjusted according to the type of spinning solution and the use of the obtained nanofibers. As general conditions in the method of the present invention, for example, the applied voltage is 5 to 30 kV, the discharge speed is 0.01 to 1.00 mL / min, and the vertical distance between the nozzle and the substrate is 100 to 200 mm. A nozzle having a diameter of 15 to 25 G can be used. The spinning environment need not be strictly controlled, but it is preferable that the relative humidity is 10 to 50% and the temperature is 10 to 25 ° C.

  By this method, fibers having a diameter of 5 nm to 50 μm can be obtained. Further, nanofibers having an average length of 200 to 300 nm can be obtained by setting and adjusting the spinning conditions.

(Carbonization treatment)
In the present invention, a fiber or fiber sheet spun from a mixed solution in which a water-insoluble polymer compound and an organic sulfonic acid are dissolved in an organic solvent is heat-treated (carbonized). Carbonization is performed in an inert gas atmosphere. Examples of the inert gas include argon and nitrogen.

  In the present invention, it is preferable and more preferable to heat-treat a fiber or sheet spun from a mixed aqueous solution of a water-insoluble polymer compound and an organic sulfonic acid in an inert gas atmosphere at a temperature of 500 ° C. to 2600 ° C. Is 500 ° C to 1000 ° C. By setting it as this heat processing condition, the carbon fiber fabric by which the fiber form was maintained can be obtained. When the heat treatment temperature is less than 500 ° C., the carbon content of the carbon fiber is 80% or less and the carbonization is insufficient. On the other hand, when the temperature exceeds 2600 ° C., the carbonization state almost no longer changes. Further, the carbonization treatment may be performed continuously or in a batch state.

  Further, a fiber or fiber sheet spun from a mixed solution obtained by dissolving a water-insoluble polymer compound and an organic sulfonic acid in an organic solvent is further inactivated after heat treatment at a temperature of 500 ° C. to 2600 ° C. in an inert gas atmosphere. Reheating treatment (graphitization step) can be performed at 2200 ° C. to 3200 ° C. in a gas atmosphere. When the reheating treatment temperature is less than 2200 ° C., the progress of graphitization (crystallization) hardly occurs. On the other hand, when it exceeds 3200 ° C., the degree of graphitization hardly changes.

  The specific carbonization method is described below.

  First, the fiber or fiber sheet formed through the spinning process is heat-treated at 500 ° C. to 2600 ° C. in a nitrogen or argon atmosphere using an electric furnace while maintaining the form. At this time, the heat treatment time is preferably 0.5 to 1 hour, although it depends on the heat treatment temperature. The temperature raising time from room temperature to the predetermined heat treatment temperature is preferably 3 to 8 ° C./min. In the heat treatment process, a high-temperature furnace in an inert gas atmosphere such as a tubular furnace or an electric furnace can be used. In this case, the inert gas exhaust pipe is filled with an adsorbent such as activated carbon and is generated from sulfonic acid. It is preferable to desulfurize a small amount of sulfur-based gas.

  As the reheating treatment step (graphitization step), the fiber or fiber sheet heat-treated in the above step is preferably returned to room temperature and then reheated at a temperature of 2200 ° C. to 3200 ° C. in an inert gas atmosphere. Thereby, the sheet | seat which consists of carbon fiber or carbon fiber graphitized in the state in which the initial form was maintained can be obtained. In the present invention, in the reheating treatment, the graphite crystals can be efficiently oriented by stretching by applying tension in the axial direction of the fibers, so that the strength of the carbon fibers is improved.

Next, the present invention will be described in more detail than Examples and Comparative Examples, but the present invention is not limited thereto.

[Example 1]
(Spinning process)
92 g of N, N-dimethylformamide was collected in a 200 ml glass beaker, 8 g of commercially available polyacrylonitrile (PAN) (manufactured by Aldrich, reagent) was added as a water-insoluble polymer, and the mixture was stirred at room temperature for 24 hours using a stirrer. As a result, 100 g of a solution in which PAN was completely dissolved was prepared. 0.08 g of commercially available methanesulfonic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was added to the solution and stirred for 1 hour at room temperature using a stirrer to prepare a spinning solution.

  5 ml of the spinning solution was collected using a 10 ml syringe equipped with an 18 G non-bevel syringe needle at the tip, and an electrospinning device (manufactured by Kato Tech, NEU nanofiber electrospinning unit) was used. A fiber sheet was produced by spinning for 2 hours under the conditions of an applied voltage of 10 kV, a solution feed speed of 15 μl / min, and a drum rotation speed of 10 rpm. The temperature in the apparatus during spinning was 25 ° C., and the humidity was 40% RH.

(Measurement of residual coal rate)
The fiber sheet obtained in the above spinning process is peeled off from the drum of the electrospinning device, 5 mg of the fiber sheet is collected in a platinum pan, and is placed on a thermobalance of a thermal analyzer (manufactured by Rigaku Corporation, ThermoPlus 2 TG-8120). The heat treatment was carried out by heating up to 800 ° C. at 20 ° C./min in a nitrogen gas atmosphere, and the weight after the heat treatment was measured. After the weight measurement, the weight was also measured after the temperature was continuously raised to 1300 ° C. and the heat treatment was performed. The residual carbon ratio was calculated from the weight before and after the heat treatment using the following formula.
Residual carbon ratio (%) = (weight after heat treatment (g)) / (weight before heat treatment (g))
As a result, the residual carbon ratio after the heat treatment was 39.4% by weight at 800 ° C. and 29.4% by weight at 1300 ° C.

(Carbonization process)
Further, after cutting the fiber sheet obtained in the above spinning process to 11 cm in length and 9 cm in width, the upper and lower sides of the fiber sheet are sandwiched between two carbon plates of 11 cm in length, 9 cm in width and 0.1 cm in thickness, and a tabletop vacuum Put in a gas replacement furnace (Denken Hydental, KDF-75), reduce the pressure in the furnace to 500 Pa or less, introduce nitrogen gas, and raise the temperature to 800 ° C. at a rate of 5 ° C./min in a nitrogen gas atmosphere. did. After holding at 800 ° C. for 1 hour, it was naturally cooled in a furnace for 24 hours to obtain a carbon fiber sheet. The carbon fiber sheet was taken out of the furnace and observed with an electron microscope (Miniscope TM-1000 manufactured by Hitachi High-Technologies). As a result, the fiber shape before the heat treatment was maintained, and no fiber breakage was confirmed. An electron microscope image is shown in FIG.

[Example 2]
A fiber sheet was prepared in the same manner as in Example 1 except that the amount of methanesulfonic acid added was 0.16 g, and the residual carbon ratio was measured. The residual carbon ratio after the heat treatment was 44.8% by weight at 800 ° C. and 33.1% by weight at 1300 ° C.

  Furthermore, when the carbon fiber sheet produced through the carbonization step in the same manner as in Example 1 was observed with an electron microscope, the fiber shape before the heat treatment was maintained, and no fiber breakage was confirmed. An electron microscope image is shown in FIG.

[Comparative Example 1]
A fiber sheet was prepared in the same manner as in Example 1 except that methanesulfonic acid was not added, and the residual carbon ratio was measured. The residual carbon ratio after the heat treatment was 36.0% by weight at 800 ° C. and 24.9% by weight at 1300 ° C., and the carbon yield was significantly reduced as compared with the examples.
Further, for the fiber sheet obtained in the spinning process, the carbon fiber sheet produced through the carbonization process in the same manner as in Example 1 was observed with an electron microscope. It was confirmed that the shape was not completely retained. An electron microscope image is shown in FIG.

Claims (10)

The manufacturing method of the carbon fiber or carbon fiber sheet which does not contain the infusibilization process characterized by including the process of following (a)-(c).
(A) a step of preparing a mixed solution in which a water-insoluble polymer compound and an organic sulfonic acid, which are raw materials for carbon fiber or carbon fiber sheet, are dissolved in an organic solvent; (b) spinning the mixed solution to obtain a fiber or fiber sheet; Step (c) A step of heat-treating the fiber or fiber sheet at a temperature of 500 ° C. to 2600 ° C. in an inert gas atmosphere. Furthermore, the process of the following (d) is included, The manufacturing method of the carbon fiber or carbon fiber sheet of Claim 1 characterized by the above-mentioned.
(D) A step of reheating the fiber or fiber sheet obtained in the step (c) at 2200 ° C. to 3200 ° C. in an inert gas atmosphere.   The carbon fiber or the water-insoluble polymer compound used as a raw material of the carbon fiber has a residual carbon ratio of 5% by weight or more when treated at 800 ° C. in an inert gas atmosphere. The manufacturing method of the carbon fiber or carbon fiber sheet in any one of 1-2.   The said water-insoluble polymer compound is polyacrylonitrile, epoxy, unsaturated polyester, phenol, polyimide, melamine resin, The manufacture of the carbon fiber or carbon fiber sheet in any one of Claims 1-3 characterized by the above-mentioned. Method.   The said organic sulfonic acid is methanesulfonic acid, The manufacturing method of the carbon fiber or carbon fiber sheet as described in any one of Claims 1-4 characterized by the above-mentioned.   The ratio of the organic sulfonic acid with respect to the said water-insoluble polymer compound is 0.1 wt%-10.0 wt%, The carbon fiber or carbon fiber sheet of any one of Claims 1-5 characterized by the above-mentioned. Production method.   The method for producing a carbon fiber or a carbon fiber sheet according to any one of claims 1 to 6, wherein the mixed liquid is made into a fiber using an electrospinning method.   A woven fabric using the carbon fiber produced by the method according to any one of claims 1 to 7.   The composite material characterized by using the carbon fiber or carbon fiber sheet manufactured by the method as described in any one of Claims 1-7.   A gas diffusion layer for a fuel cell, wherein the carbon fiber or the carbon fiber sheet produced by the method according to any one of claims 1 to 7 is used.

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