JP6657712B2 - Method for producing carbon fiber and carbon fiber sheet - Google Patents

Description

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

  Since carbon fiber has excellent specific strength and specific elastic modulus, it is being widely used from sports and leisure goods to aerospace applications. When carbon fiber is used as such a structural material, a method is used in which a prepreg obtained by impregnating a thermosetting resin into a woven fabric obtained by weaving a carbon fiber tow is used as a cured carbon fiber reinforced plastic. General.

  Various carbon fibers using a water-soluble polymer compound such as polyvinyl alcohol (PVA) have been studied. PVA has a melting point around 230 ° C., and part or all of the resin melts under the temperature conditions necessary for carbonization, and it is difficult to maintain its form. 1) a step of spinning PVA to obtain fibers, 2) a step of making the fibers infusible at about 200 ° C., and 3) a step of carbonizing at about 500 ° C. to 2600 ° C. I have. In addition, in order to produce a carbon fiber having a higher elastic modulus, a reheating treatment at 2200 ° C. to 3200 ° C. may be included.

  That is, in the production of conventional PVA-based carbon fibers, various studies have been made on the premise that the infusibilization treatment is indispensable. In Patent Documents 1 and 2, the thermal stability in the carbonization process is improved. In order to improve the carbonization yield, a method has been proposed in which a PVA-based resin is subjected to a halogen treatment such as an iodine treatment to perform an infusibilization treatment. Patent Document 3 proposes a technique capable of shortening the processing time by coexisting at least one metal salt selected from an alkali metal salt and an alkaline earth metal salt in addition to the halogen treatment. Further, Patent Document 4 proposes a technique for improving a carbonization yield by adding a crosslinking agent to an aqueous solution in which polyvinyl alcohol is dissolved.

JP-A-2003-128407 JP-A-2004-396627 JP 2009-249238 A JP-A-2012-067432

  However, this infusibilization treatment complicates the production process of carbon fibers, and also contributes to an increase in production costs due to a large energy consumption.

  Therefore, the present invention provides a method for producing a carbon fiber or a carbon fiber sheet by heating a fiber or a fiber sheet containing an organic fiber which is a raw material of the carbon fiber, even if the infusibilization step is omitted. -To provide a manufacturing method capable of suppressing fusion.

The present invention provides the following inventions [1] to [8].
[1] A method for producing a carbon fiber or a carbon fiber sheet which does not include the infusibilizing step, which comprises the following steps (a) to (c).
(A) a step of preparing an aqueous solution in which a water-soluble polymer compound and a raw material of a carbon fiber or a carbon fiber sheet are dissolved and an organic sulfonic acid; (b) a step of spinning the aqueous solution to obtain a fiber or a fiber sheet; A step of heat-treating the fiber or the 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 carbon fiber according to any one of [1] to [2], wherein the water-soluble polymer is polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyacrylic acid, or polyvinylpyrrolidone. Sheet manufacturing method.
[4] The method for producing a carbon fiber or a carbon fiber sheet according to any one of [1] to [3], wherein the organic sulfonic acid is methanesulfonic acid.
[5] The carbon fiber according to any one of [1] to [4], wherein a ratio of the organic sulfonic acid to the water-soluble polymer compound is 0.1 wt% to 10.0 wt%. A method for producing a carbon fiber sheet.
[6] The method for producing a carbon fiber or a carbon fiber sheet according to any one of [1] to [5], wherein the fiber or the fiber sheet is obtained by an electrospinning method.
[7] A woven fabric using the carbon fiber produced by the method according to any one of [1] to [6].
[8] A composite material using a carbon fiber or a carbon fiber sheet produced by the method according to any one of [1] to [7].
[9] A gas diffusion layer for a fuel cell, comprising a carbon fiber or a carbon fiber sheet produced by the method according to any one of [1] to [7].

  According to the present invention, in a method for producing a carbon fiber or a carbon fiber sheet obtained by heat-treating a fiber or a fiber sheet containing an organic fiber serving as a raw material of a carbon fiber, even if the infusibilization step is omitted, the carbon fiber It is possible to provide a production method capable of suppressing melting and fusion.

It is an electron microscope image of the carbon fiber sheet surface of Example 1 of the present invention. 4 is an electron microscope image of the surface of a carbon fiber sheet of Comparative Example 1 of the present invention. It is an electron microscope image of the carbon fiber sheet surface of Comparative Example 3 of the present invention.

  The method for producing a carbon fiber or a carbon fiber sheet of the present invention comprises the steps of: producing a fiber or a fiber sheet obtained from a solution containing a water-soluble polymer compound and an organic sulfonic acid in an inert gas atmosphere at 500 ° C. to 2600 ° C. The heat treatment is performed at a temperature. In particular, a major feature of the present invention is that a step of infusifying a fiber or a fiber sheet at about 200 ° C. is not performed. In addition, it is also possible to reheat the obtained carbon fiber or carbon fiber sheet at 2200 ° C. to 3200 ° C.

(Water-soluble polymer)
The water-soluble polymer compound in the present invention is not particularly limited as long as it is a material capable of forming fibers, and examples thereof include polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl acetate, collagen, starch, and carboxy. Examples thereof include methylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose. These may be used alone or as a mixture of two or more kinds, and may be modified as long as water solubility is not impaired.

  Among these materials, polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyacrylic acid, and polyvinylpyrrolidone, which are relatively easy to spin from an aqueous solution, are preferable, and polyvinyl alcohol is more preferable.

  Further, an organic / inorganic material may be mixed in an aqueous solution in which the water-soluble polymer compound is dissolved within a range that does not inhibit the fiber formation, and the form may be a granular material, a fibrous solid material or a material that is miscible in the aqueous solution. Etc. can be used as appropriate. For example, by fibrillating an aqueous solution in which an inorganic compound is dispersed as a raw material, it is possible to support the inorganic compound in the carbon fiber after the heat treatment and to impart functionality such as deodorization or antibacterial, and also to the aqueous solution. By adding a surfactant or a conductive auxiliary, the fiber forming property in the spinning step can be improved.

(Organic sulfonic acid)
In the present invention, the organic sulfonic acid to be mixed with the aqueous solution of the water-soluble polymer compound may be any organic compound having a carbon skeleton to which a sulfo group (which may be one or more) is bonded. May be used, and compounds having various aliphatic or aromatic sulfo groups can be used, but from the viewpoint of handling, it is preferable that the compound has a low molecular weight.

  Specific examples of the organic sulfonic acid include, for example, R-SO3H (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). And alkyl groups, cycloalkyl groups, and aryl groups, each of which may be substituted with an alkyl group, a hydroxyl group, or a halogen group. 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 Sulfonic acid and the like. Of these, methanesulfonic acid is preferably selected. Further, one type of organic sulfonic acid may be used alone, or two or more types may be used in combination.

  In the present invention, it is not clear why the infusibilization treatment is not required by mixing the organic sulfonic acid, but the heat treatment of the fiber sheet spun from a solution in which the water-soluble polymer compound and the organic sulfonic acid are mixed is performed. Thus, the organic sulfonic acid acts as a dehydration catalyst, promotes the dehydration reaction of hydroxyl groups and the like in the molecule and between the molecules, and contributes to improvement of the heat resistance of the compound and suppression of a thermal decomposition reaction other than the dehydration reaction. For this reason, it is presumed that the generation of hydrocarbon-based gas and the reduction of the carbon component in the water-soluble polymer compound due to ordinary thermal decomposition are suppressed.

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

(Manufacture of fiber and fiber sheet: 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. A dry spinning method and a wet spinning method in which a solution is introduced into a coagulating liquid from a spinneret and formed into fibers can be used. The obtained fiber may be subjected to a treatment such as cutting and cut into an arbitrary length for use.

  The fiber sheet in the present invention refers to a sheet obtained by processing a large number of fibers into a thin and wide plate shape, and includes a woven fabric, a knitted fabric, and a nonwoven fabric. The method for producing the nonwoven fabric is not particularly limited, but a method of obtaining a fiber sheet using a dry method or a wet method using the above-described fibers cut to an appropriate length as a raw material, or directly from a solution using an electrospinning method or the like. A method for obtaining a fiber sheet can be exemplified. Further, after the nonwoven fabric is obtained, a treatment such as resin bond, thermal bond, spunlace, or needle punch may be added for the purpose of bonding the fibers.

  In particular, in the electrospinning method having a fiber diameter of a submicron order, the diameter of the fiber constituting the fiber sheet is extremely small, so that the fiber is likely to be broken or burned out by heat treatment. Can be kept large, and 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 a known means. Specifically, in a state where a voltage is applied between a nozzle filled with a spinning solution and a substrate (also called a collector), the spinning solution is discharged from the nozzle. Collect the fibers on the substrate.

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

  Conditions for performing the electrospinning method are not particularly limited, and may be appropriately adjusted according to the type of the spinning solution, the use of the obtained nanofiber, and the like. As general conditions in the method of the present invention, for example, the applied voltage is 5 to 30 kV, the ejection speed is 0.01 to 1.00 mL / min, and the vertical distance between the nozzle and the substrate is 100 to 200 mm. It is possible to use a nozzle having a diameter of 15 to 25 G. The spinning environment does not need to 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, by setting and adjusting spinning conditions, nanofibers having an average length of 200 to 300 nm can be obtained.

(Carburizing treatment)
In the present invention, a fiber or a fiber sheet spun from a mixed solution in which a water-soluble polymer compound and an organic sulfonic acid are dissolved in an organic solvent is subjected to heat treatment (carbonization). 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 preferably, to heat-treat a fiber or a fiber sheet spun from a mixed aqueous solution of a water-soluble polymer compound and an organic sulfonic acid at a temperature of 500 ° C to 2600 ° C in an inert gas atmosphere. Is 500 ° C to 1000 ° C. Under these heat treatment conditions, a carbon fiber woven fabric in which the fiber form is maintained can be obtained. If the heat treatment temperature is less than 500 ° C., the carbon content of the carbon fiber is not more than 80% and the carbonization is insufficient, while if it exceeds 2600 ° C., the carbonized state hardly changes anymore. Further, the carbonization treatment may be performed continuously or in a batch state.

  Further, a fiber or a fiber sheet spun from a mixed solution in which a water-soluble polymer compound and an organic sulfonic acid are dissolved in an organic solvent is heated in an inert gas atmosphere at a temperature of 500 ° C. to 2600 ° C. It is possible to perform a reheating treatment (graphitization step) at 2200 ° C. to 3200 ° C. in an atmosphere. If the reheating temperature is lower than 2200 ° C., the progress of graphitization (crystallization) hardly occurs, while if it exceeds 3200 ° C., the degree of graphitization hardly changes.

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

  In the reheating step (graphitizing step), preferably, the fiber or fiber sheet heat-treated in the above step is once returned to room temperature, and then reheated in an inert gas atmosphere at a temperature of 2200 ° C to 3200 ° C. As a result, it is possible to obtain a carbon fiber or a sheet made of carbon fiber that has been graphitized while maintaining the initial form. In the present invention, the graphite crystal can be efficiently oriented by applying tension in the axial direction of the fiber during the reheating treatment and stretching the fiber, thereby improving the strength of the carbon fiber.

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

<Example 1>
(Spinning process)
90 g of distilled water is collected in a glass beaker having a capacity of 200 ml, 10 g of commercially available PVA (manufactured by Kuraray, PVA117) is added, and the mixture is stirred for 24 hours with a stirrer while heating to 80 ° C., and the PVA solution in which PVA is completely dissolved is added. 100 g were produced. After allowing the PVA solution to stand at room temperature, 0.1 g of commercially available methanesulfonic acid (manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the mixture was stirred for 1 hour at room temperature using a stirrer to prepare a spinning solution.

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

(Carburizing process)
The fiber sheet obtained in the above spinning step was peeled from the drum and cut into a length of 11 cm and a width of 9 cm. Then, the upper and lower sides of the fiber sheet were sandwiched between two carbon plates having a length of 11 cm and a width of 9 cm and a thickness of 0.1 cm. After putting into a gas replacement furnace (manufactured by Denken Hydental, KDF-75) and reducing the pressure in the furnace to 500 Pa or less, nitrogen gas was introduced, and the temperature was raised to 800 ° C. at 5 ° C./min in a nitrogen gas atmosphere. . After holding at 800 ° C. for 1 hour, the mixture was naturally cooled in a furnace for 24 hours to obtain a carbon fiber sheet. When the carbon fiber sheet was observed with an electron microscope (Minicope TM-1000, manufactured by Hitachi High-Technologies Corporation), the fiber shape before the heat treatment was maintained. An electron microscope image is shown in FIG.

<Comparative Example 1>
A carbon fiber sheet was produced in the same manner as in Example 1 except that methanesulfonic acid was not added. The carbon fiber sheet after the carbonization step did not retain the fiber shape before the carbonization step, and some of the fibers were melted and fused to form a film. An electron microscope image is shown in FIG.

<Comparative Example 2>
A spinning solution was prepared in the same manner as in Example 1, except that 0.5 g of sulfuric acid was added to the PVA solution instead of methanesulfonic acid. Spinning was attempted in the same manner as in Example 1 using the spinning solution, but no fibers were discharged from the syringe, and a fiber sheet could not be obtained.

<Comparative Example 3>
A carbon fiber sheet was produced in the same manner as in Example 1, except that 0.1 g of sulfuric acid was added to the PVA solution instead of methanesulfonic acid. The carbon fiber sheet after the carbonization step did not retain the fiber shape before the carbonization step, and some of the fibers were melted and fused. The electron microscope image is shown in FIG.

Claims (8)

A method for producing a carbon fiber or a carbon fiber sheet that does not include the infusibilizing step, which comprises the following steps (a) to (c).
(A) A water-soluble polymer compound and an organic sulfonic acid, which are raw materials for a carbon fiber or a carbon fiber sheet , are dissolved in a ratio of 0.1 wt% to 10.0 wt% of an organic sulfonic acid to the water-soluble polymer compound . Adjusting the aqueous solution (b) spinning the aqueous solution to obtain a fiber or a fiber sheet (c) heating the fiber or the fiber sheet at a temperature of 500 ° C. to 2600 ° C. in an inert gas atmosphere The method for producing a carbon fiber or a carbon fiber sheet according to claim 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;   The method for producing a carbon fiber or a carbon fiber sheet according to any one of claims 1 to 2, wherein the water-soluble polymer is polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyacrylic acid, or polyvinylpyrrolidone.   The method for producing a carbon fiber or a carbon fiber sheet according to any one of claims 1 to 3, wherein the organic sulfonic acid is methanesulfonic acid. The method for producing a carbon fiber or a carbon fiber sheet according to any one of claims 1 to 4 , wherein the fiber or the fiber sheet is obtained by an electrospinning method. A woven fabric using carbon fibers produced by the method according to any one of claims 1 to 5 . A composite material using a carbon fiber or a carbon fiber sheet produced by the method according to any one of claims 1 to 6 . A gas diffusion layer for a fuel cell, comprising a carbon fiber or a carbon fiber sheet produced by the method according to any one of claims 1 to 6 .

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