Method for producing gas diffusion electrode substrate

Abstract

To reduce cost and a waste in manufacture of a gas diffusion electrode base material.SOLUTION: A method for manufacturing a gas diffusion electrode base material has a compression step of heating and pressurizing a precursor fiber sheet containing a carbon fiber and a binder thermosetting resin in the state where a release sheet is brought into contact with an upper surface and / or a lower surface of the precursor fiber sheet, curing the binder thermosetting resin, and converting it into a gas diffusion electrode base material, a peeling step of peeling the release sheet from the gas diffusion electrode base material, and an attached dust removal step of removing attached dust attached to the released release sheet, in this order, wherein the release sheet through the attached dust removal step is used as a release sheet used in the compression step again.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a gas diffusion electrode substrate suitable for use in a fuel cell, particularly a polymer electrolyte fuel cell. [Background technology]

[0002] Gas diffusion electrode substrates are materials used as electrode substrates for fuel cells, and include carbon paper formed by bonding carbon fibers and a carbonized thermosetting resin, carbon fiber nonwoven fabrics formed by entangling carbon fibers, and carbon fiber woven fabrics. In the manufacture of gas diffusion electrode substrates, a compression step is often carried out in which a precursor fiber sheet, which is formed by impregnating a carbon fiber sheet made of carbon fibers with a thermosetting resin, is heated and pressurized, in order to make the thickness of the gas diffusion electrode substrate uniform and to densify the structure.

[0003] In the compression step, the precursor fiber sheet is generally pressed together with a release sheet while being heated, and the pressing method used includes an intermittent press method (Patent Document 1) in which the precursor fiber sheet is pressed while being intermittently drawn off, a belt press method (Patent Document 2), a calendar roll method, etc. In any of these methods, a release sheet coated with a release agent is used to prevent the precursor fiber sheet from coming into contact with the press surface and adhering to each other.

[0004] However, using a release sheet once and then discarding it poses problems from the viewpoints of both cost reduction and industrial waste reduction.Patent Document 3 discloses a method, different from gas diffusion electrode substrates, in which a prepreg is produced in which a resin is impregnated into reinforcing fibers by heating and pressurizing the resin, in which the release sheet is transferred to a transfer resin film while being heated and pressurized, thereby removing the residual resin and reusing the release sheet (Patent Document 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-308098 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-151568 [Patent Document 3] Japanese Patent Application Publication No. 7-258440 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the method described in Patent Document 3 is applied to the production of a gas diffusion electrode substrate, it is necessary to remove not only the resin pieces but also the carbon fiber pieces that are not softened by heating. Furthermore, the method described in Patent Document 3 requires a separate transfer resin film, and the cost reduction effect is limited.

[0007] An object of the present invention is to reduce costs and waste in the manufacture of gas diffusion electrode substrates. [Means for solving the problem]

[0008] The present invention for solving the above problems is as follows. (1) a compression step in which a precursor fiber sheet containing carbon fibers and a binder thermosetting resin is subjected to a heat and pressure treatment with a release sheet in contact with the upper and / or lower surfaces of the precursor fiber sheet to cure the binder thermosetting resin and form a gas diffusion electrode substrate; a peeling step of peeling the release sheet from the gas diffusion electrode substrate; a dust removal step for removing dust adhering to the peeled release sheet; and further, the release sheet after the dust removal step is reused as a release sheet to be used again in the compression step. (2) The method for producing a gas diffusion electrode substrate according to (1), wherein the adhering dust removing step does not involve heating the release sheet. (3) The method for producing a gas diffusion electrode substrate according to (1) or (2), wherein the adhering dust removing step is a step of adsorbing the adhering dust. (4) The method for producing a gas diffusion electrode substrate according to (3), wherein the adhering dust removing step is a step of adsorbing the adhering dust with an adhesive roll. (5) The method for producing a gas diffusion electrode substrate according to (1) or (2), wherein the adhering dust removing step is a step of spraying gas onto the release sheet. (6) The method for producing a gas diffusion electrode substrate according to (5), wherein ultrasonic air is sprayed in the adhering dust removing step. (7) The method for producing a gas diffusion electrode substrate according to any one of (1) to (6), wherein the precursor fiber sheet is a sheet obtained by impregnating a paper sheet of short carbon fibers with a thermosetting resin as a binder that can be carbonized by heat treatment. (8) The method for producing a gas diffusion electrode substrate according to any one of (1) to (7), wherein the heat and pressure treatment is an intermittent press method, a belt press method, or a calender roll method. (9) The method for producing a gas diffusion electrode substrate according to any one of (1) to (8), wherein the maximum heating temperature in the heating and pressurizing treatment is 140°C or higher and 300°C or lower. (10) The method for producing a gas diffusion electrode substrate according to any one of (1) to (9), wherein the compressing step, the peeling step, and the adhering dust removing step are carried out as continuous steps while transporting the precursor fiber sheet, the gas diffusion electrode substrate, and the release sheet. (11) The method for producing a gas diffusion electrode substrate according to any one of (1) to (10), further comprising a mechanism for winding up the release sheet into a roll after the dust removal step has been completed, and the rolled release sheet is reused as a release sheet to be used in the compression step. (12) The method for producing a gas diffusion electrode substrate according to any one of (1) to (11), wherein in the adhering dust removing step, a discharging treatment is performed to remove static electricity from the release sheet after removing the adhering dust. [Effects of the Invention]

[0009] According to the present invention, it is possible to reuse the release sheet used in the compression step of the precursor fiber sheet, thereby reducing the cost and waste in the production of gas diffusion electrode substrates. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing an embodiment of a manufacturing facility for carrying out the manufacturing method of a gas diffusion electrode substrate of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] The gas diffusion electrode substrate (hereinafter, sometimes simply referred to as "substrate") produced by the production method of the present invention is a carbon fibrous structure having a structure in which carbon fibers are bound with a thermosetting resin. In particular, the production method of the present invention is suitable as a method for producing carbon paper in which short carbon fibers are bound with a carbide of a thermosetting resin.

[0012] [Precursor fiber sheet] The precursor fiber sheet is a carbon fiber sheet made of carbon fibers impregnated with a thermosetting resin as a binder that can be carbonized by heat treatment.

[0013] The carbon fibers contained in the carbon fiber sheet are obtained by heat-treating raw fiber (precursor) materials such as polyacrylonitrile (PAN) fibers, pitch fibers, rayon fibers, and phenolic fibers in an oxidizing atmosphere at a relatively low temperature of about 200 to 400°C to render them flame-resistant, and then carbonizing them in an inert atmosphere at a high temperature of 1000°C or higher. For gas diffusion electrode substrate applications, the average fiber diameter of the carbon fibers is preferably 5 to 20 μm. If the average fiber diameter is less than 5 μm, depending on the type of carbon fiber, the substrate will have low flexibility and will be difficult to form into a roll. Furthermore, if the average fiber diameter exceeds 20 μm, the substrate strength may decrease.

[0014] Thermosetting resins that bind the carbon fibers together (in this specification, the thermosetting resin that binds the carbon fibers in the precursor fiber sheet is called the "binding thermosetting resin," and the "binding thermosetting resin" becomes a resin char that binds the carbon fibers upon carbonization) include epoxy resins, unsaturated polyester resins, phenolic resins, polyimide resins, and melamine resins. Among these, it is preferable to use phenolic resins, which have a high amount of resin char after carbonization and therefore have high bending strength and high conductivity in the thickness direction.

[0015] Examples of carbon fiber sheets include carbon fiber nonwoven fabrics, carbon fiber woven fabrics, and carbon fiber paper sheets, with short carbon fiber paper sheets being preferred. A short carbon fiber paper sheet can be obtained, for example, by uniformly dispersing short carbon fibers cut to lengths of 4 to 16 mm in water, forming the paper sheet on a mesh, immersing the formed short carbon fiber sheet in an aqueous solution containing a binder such as polyvinyl alcohol, and then pulling up and drying the immersed sheet. Polyvinyl alcohol acts as a binder to bind the short carbon fibers together, producing a carbon fiber sheet in which the dispersed short carbon fibers are bound by the binder. Other binders that can be used include styrene-butadiene rubber and epoxy resin.

[0016] [Compression process] The method for producing a gas diffusion electrode substrate includes a compression step in which the precursor fiber sheet is subjected to a heat and pressure treatment. The binder thermosetting resin is cured in the compression step, thereby obtaining a gas diffusion electrode substrate from the precursor fiber sheet. That is, in this specification, the product obtained after the compression step and the binder thermosetting resin are completely cured is referred to as a "gas diffusion electrode substrate."

[0017] In the present invention, in the compression step, the precursor fiber sheet is heated and pressurized with a release sheet in contact with the upper and / or lower surfaces thereof to cure the binder thermosetting resin. The heating and pressurizing treatment is preferably a treatment in which the precursor fiber sheet is sandwiched between parallel heated plates or rolls and heated. Examples of methods that can be used for this heating and pressurizing treatment include an intermittent press method in which the precursor fiber sheet is pressed while being transported intermittently, a belt press method, and a calendar roll method.

[0018] In the intermittent press method, the precursor fiber sheet is transported intermittently while repeatedly opening and closing the press, and is heated and pressed by parallel heating plates. In this case, the effective press length in the transport direction is L P , the feed amount of the precursor fiber sheet when transporting it intermittently is L F When L F / L P is preferably 0.04 to 1.5, more preferably 0.1 to 0.98. F / L P If L is less than 0.04, the densification effect due to heating and pressurization can be more uniform, improving flatness, i.e., reducing thickness variations in the conveying direction. However, the proportion of the time required for opening and closing the press and feeding the precursor fiber sheet in the processing time increases, resulting in poor production efficiency. F / L P If the ratio exceeds 1.5, the ratio of non-densified parts to densified parts increases, resulting in increased material loss and reduced production efficiency. The effective pressurized length refers to the length of the precursor fiber sheet that comes into contact with the hot platen or mold and is heated and pressurized. The feed amount refers to the amount of precursor fiber sheet that is fed (or withdrawn) in the conveying direction per cycle when the press is opened.

[0019] The belt press method includes at least one set of rotating belts consisting of a drive roll, a driven roll, and an endless belt wound around the drive roll and the driven roll. The precursor fiber sheet is heated and pressed together with the endless belt by parallel heating plates or rolls or by a liquid to obtain a gas diffusion electrode substrate.

[0020] In the calender roll method, a precursor fiber sheet is heated and pressed between rolls arranged in parallel to each other to obtain a gas diffusion electrode substrate.

[0021] The maximum heating temperature in the heating and pressurizing treatment is preferably 140 to 300°C, more preferably 170 to 230°C. If the temperature is too low, it takes time for the thermosetting resin to harden by heating and pressurizing. If the temperature is too high, oxidation of the precursor fiber sheet in air may progress, causing problems such as a decrease in strength.

[0022] In this compression process, regardless of the pressure application method, adhesion of the binder thermosetting resin to the pressure surface is unavoidable. Therefore, adhesion of the thermosetting resin is prevented by interposing a release sheet between the precursor fiber sheet and the pressure surface, i.e., by performing a heat and pressure treatment with the release sheet in contact with the upper and / or lower surfaces of the precursor fiber sheet. Examples of release sheets that can be used include fine paper, glassine paper, kraft paper, and film. By selecting an optimal release sheet depending on the heating temperature and usage environment of the compression process, deterioration due to heat and wrinkles due to moisture absorption can be prevented. Furthermore, it is preferable to use a release sheet coated with a release agent. Examples of such release agents include silicone resins and fluororesins. The release agent coating needs to be applied to at least the surface of the release sheet that contacts the precursor fiber sheet, but it may also be applied to both sides of the release sheet.

[0023] The method for interposing a release sheet between the precursor fiber sheet and the pressure surface is not particularly limited, but it is preferable to provide an unwinding roll on the conveying line of the precursor fiber sheet and to configure the precursor fiber sheet to be supplied from the unwinding roll to between the precursor fiber sheet and the pressure surface. Furthermore, in order to prevent the release sheet from creasing during conveyance or pressure application due to shaking or sagging, and to ensure close contact between the precursor fiber sheet and the release sheet, it is also preferable to provide a free roll downstream of the unwinding roll and upstream of the pressure surface so as to press the release sheet toward the precursor fiber sheet.

[0024] [Peeling process] The peeling step is a step of peeling the release sheet used in the compression step from the precursor fiber sheet. The peeling method is not particularly limited, but a configuration is preferred in which a take-up roll is provided on the conveying line, and the release sheet that has been unwound from the unwinding roll and passed through the pressure surface as described above is wound up and peeled off from the gas diffusion electrode substrate. Furthermore, in order to prevent the release sheet from wrinkling during conveyance or pressure application due to shaking or sagging, and to reliably maintain a tight contact state between the precursor fiber sheet and the release sheet until the completion of the heating and pressure treatment, it is also preferred to provide a free roll downstream of the pressure surface and upstream of the take-up roll so as to press the release sheet toward the precursor fiber sheet.

[0025] [Dust removal process] The dust removal step is a step of removing dust that has adhered to the release sheet peeled off in the peeling step. In the compression step, carbon fiber pieces, resin pieces, and the like from the precursor fiber sheet are transferred to the release sheet and may remain on the release sheet as adhered dust. If there is adhered dust, the smoothness of the precursor fiber sheet may be impaired when the release sheet is reused in the compression step, so it is important to remove the adhered dust before reuse.

[0026] In order to reuse the release sheet that has undergone the dust removal process in the compression process, it is important to maintain the releasability of the release sheet in the dust removal process and not cause damage to the release sheet, such as wrinkles or cracks. In addition, in order to maintain the releasability, it is necessary to prevent deterioration of the release agent, and since many release agents are sensitive to heat, it is preferable that the dust removal process does not involve heating the release sheet. Such a dust removal process preferably includes a step of adhering, wiping, or decomposing and removing dust from the release sheet, or a step of spraying gas onto the release sheet, and specific examples include adhesive roll cleaning, liquid wiping, air cleaning, plasma cleaning, and film transfer cleaning.

[0027] Adhesive roll cleaning is a mechanism in which the release sheet and rubber roll rotate in unison while pressing the rubber roll or the like against the release sheet, thereby adhering the dust attached to the release sheet. In such a mechanism, it is preferable to further press the adhesive roll against the rubber roll to which the dust has been attached, ultimately accumulating the dust on the adhesive roll. The adhesive roll is preferably structured so that a new adhesive surface is exposed by peeling off the surface layer, which is expected to restore the dust accumulation effect and reduce waste. Liquid wiping is a technique in which a cleaning liquid is sprayed onto the release sheet and the dust is wiped off with a cloth or the like. Air cleaning is a mechanism in which dust is removed by simultaneously spraying air onto the release sheet surface without contact and suctioning it. In air cleaning, ultrasonic air spraying can more effectively remove dust. Plasma cleaning is a mechanism in which plasma is applied to the release sheet surface to decompose and remove dust attached to the release sheet surface. Film transfer cleaning is a mechanism in which the film and release sheet are simultaneously heated and pressurized to transfer dust attached to the release sheet to the film. Among these, in order to prevent damage such as wrinkles on the release sheet, adhesive roll cleaning and air cleaning are particularly preferred, as they do not cause wrinkles or surface deterioration due to wetting of the release sheet.

[0028] If static electricity is generated in the dust removal step, the release sheet may become charged, which may cause it to stick to the roll or attract floating foreign matter. Therefore, in the dust removal step, it is preferable to further perform a static elimination treatment to remove static electricity from the release sheet after the dust has been removed. For the static elimination treatment, it is preferable to use a static eliminator that neutralizes the charged release sheet by emitting positive and negative ions to the release sheet.

[0029] In the dust removal step, it is sufficient to remove dust from at least the side of the release sheet that has been in contact with the precursor fiber sheet. However, particularly when the release sheet is wound into a roll, there is a possibility that dust from the side that has been in contact with the precursor fiber sheet will be transferred to the opposite side. Therefore, it is preferable to have a mechanism that removes dust from both sides of the release sheet.

[0030] In order to improve production efficiency, the compression step, peeling step, and dust removal step are preferably continuous steps in which each step is performed consecutively. A continuous step refers to performing the compression step, peeling step, and dust removal step not as separate steps, but rather performing the heating and pressurizing of the precursor fiber sheet, peeling of the release sheet, and dust removal from the release sheet continuously and in parallel while transporting the precursor fiber sheet, gas diffusion electrode substrate, and release sheet. By incorporating a mechanism for peeling the release sheet after heating and pressurizing the precursor fiber sheet and removing the dust before recovering the release sheet, a gas diffusion electrode substrate in which the binder thermosetting resin has cured and a release sheet that has undergone the dust removal step can be obtained simultaneously.

[0031] It is also preferable to have a mechanism for winding up the release sheet after the dust removal process into a roll. By winding up the release sheet after dust removal into a roll, it becomes easy to reuse it as a release sheet to be used again in the compression process. [Example]

[0032] The present invention will be described below with reference to the drawings to facilitate understanding, but the present invention is not limited to these drawings. Furthermore, the description of the specific embodiments shown in the drawings can also be understood as a description of the manufacturing method of the present invention as a general concept.

[0033] FIG. 1 is a schematic diagram showing one embodiment of a manufacturing facility for carrying out the method for manufacturing a gas diffusion electrode substrate of the present invention. Before being fed to a hot press 8, a precursor fiber sheet 1 unwound from a precursor fiber sheet unwinding roll 2 is sandwiched between two release sheets 7 unwound from release sheet unwinding rolls 4 installed above and below a free roll 6 arranged to sandwich the precursor fiber sheet 1, so that the release sheets contact the upper and lower surfaces of the precursor fiber sheet. As mentioned above, a release sheet may be placed on only one of the upper and lower surfaces of the precursor fiber sheet. The precursor fiber sheet sandwiched between the release sheets is then fed to a hot press 8. In the hot press 8, the precursor fiber sheet is intermittently transported by repeatedly opening and closing the press, and is heated and pressurized by parallel heating plates 9. By passing through the hot press 8, the thermosetting resin in the precursor fiber sheet hardens, and the precursor fiber sheet becomes a gas diffusion electrode substrate (compression process). The gas diffusion electrode substrate from which the release sheets 7 have been peeled off is taken up by a take-up roll 3.

[0034] After passing through the hot press 8, the release sheet 7 is peeled off from the gas diffusion electrode (peeling step) and passes through rubber rolls 10 that are placed so as to sandwich the release sheet 7. As the upper and lower rubber rolls 10 rotate while conveying the release sheet 7, dust adhering to the surface of the release sheet 7 is adsorbed by the rubber rolls 10 (adhered dust removal step). In addition, an adhesive roll 11 that rotates while in contact with the rubber roll 10 is disposed adjacent to the rubber roll 10. As a result, the adhering dust adsorbed to the rubber roll 10 is transferred to the adhesive roll 11, and the adhering dust is collected on the adhesive roll 11. The release sheet 7 that has been removed of the adhering dust and taken up in this way is taken up by the release sheet take-up roll 5 via the free roll 6, and then set again on the release sheet unwinding roll 4 and subjected to the hot press 8, which is the compression step, for reuse. [Explanation of symbols]

[0035] 1: Precursor fiber sheet 2: Unwinding roll 3: Winding roll 4: Release sheet unwinding roll 5: Release sheet winding roll 6: Freeroll 7: Release sheet 8:Hot press 9: Heat plate 10: Rubber roll 11: Adhesive roll

Claims

1. a compression step of subjecting a precursor fiber sheet containing carbon fibers and a binder thermosetting resin to a heat and pressure treatment in a state in which a release sheet is in contact with the upper and / or lower surfaces of the precursor fiber sheet, thereby curing the binder thermosetting resin and forming a gas diffusion electrode substrate; a peeling step of peeling the release sheet from the gas diffusion electrode substrate; a dust removal step of removing dust adhering to the peeled release sheet; and a method for producing a gas diffusion electrode substrate, the method comprising the steps of: The method for producing a gas diffusion electrode substrate, wherein the adhering dust removing step is a step of adsorbing the adhering dust.

2. a compression step of subjecting a precursor fiber sheet containing carbon fibers and a binder thermosetting resin to a heat and pressure treatment in a state in which a release sheet is in contact with the upper and / or lower surfaces of the precursor fiber sheet, thereby curing the binder thermosetting resin and forming a gas diffusion electrode substrate; a peeling step of peeling the release sheet from the gas diffusion electrode substrate; a dust removal step of removing dust adhering to the peeled release sheet; and a method for producing a gas diffusion electrode substrate, the method comprising the steps of: The method for producing a gas diffusion electrode substrate, wherein the adhering dust removing step is a step of spraying gas onto the release sheet.

3. 2. The method for producing a gas diffusion electrode substrate according to claim 1, wherein the adhering dust removing step is a step of adsorbing the adhering dust with an adhesive roll.

4. The method for producing a gas diffusion electrode substrate according to claim 2 , wherein ultrasonic air is jetted in the adhering dust removing step.

5. The method for producing a gas diffusion electrode substrate according to any one of claims 1 to 4, wherein the adhering dust removing step does not involve heating the release sheet.

6. The method for producing a gas diffusion electrode substrate according to any one of claims 1 to 5, wherein the precursor fiber sheet is a sheet obtained by impregnating a paper body of short carbon fibers with a thermosetting resin as a binder that can be carbonized by heat treatment.

7. The method for producing a gas diffusion electrode substrate according to any one of claims 1 to 6, wherein the heat and pressure treatment is carried out by an intermittent press method, a belt press method, or a calender roll method.

8. The method for producing a gas diffusion electrode substrate according to any one of claims 1 to 7, wherein the maximum heating temperature in the heating and pressurizing treatment is 140°C or higher and 300°C or lower.

9. 9. The method for producing a gas diffusion electrode substrate according to claim 1, wherein the compressing step, the peeling step, and the adhering dust removing step are performed as continuous steps while transporting the precursor fiber sheet, the gas diffusion electrode substrate, and the release sheet.

10. The method for producing a gas diffusion electrode substrate according to any one of claims 1 to 9, further comprising a mechanism for winding up the release sheet into a roll after the adhered dust removal step has been completed, and the rolled release sheet is reused as a release sheet to be used in the compression step.

11. The method for producing a gas diffusion electrode substrate according to any one of claims 1 to 10, wherein in the adhering dust removing step, a discharging treatment is performed to remove static electricity from the release sheet after removing the adhering dust.

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