Manufacturing method of fuel cell separator

Abstract

To provide a manufacturing method of a fuel cell separator, which can manufacture a fuel cell separator that does not have a multilayer structure while having sufficient gas impermeability and electrical conductivity, in a short molding time.SOLUTION: A manufacturing method of a fuel cell separator includes the steps of: mixing a thermoplastic resin, spherical graphite, and carbon fiber to prepare a mixture, the mixture including a thermoplastic resin in an amount of 37 vol.% or more and less than 45 vol.% based on the total volume of the mixture; heating the mixture to soften it; and cooling the softened mixture while pressing it to obtain a molded body.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a separator for a fuel cell. [Background technology]

[0002] In a fuel cell, the separator provides electrical conductivity to each unit cell and also functions as a boundary wall separating the fuel and air (oxygen) while ensuring passage of the fuel and air supplied to the unit cell. Therefore, the separator for a fuel cell is required to be gas impermeable and electrically conductive.

[0003] Patent Document 1 describes the production of a fuel cell separator by compression molding a multilayer precursor sheet for a fuel cell separator, the precursor sheet comprising a conductive substrate sheet, a first dense layer containing graphite particles and a resin, and a second conductive layer containing graphite particles and a resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-091104 Summary of the Invention [Problem to be solved by the invention]

[0005] The precursor sheet for a fuel cell separator described in Patent Document 1 has a multilayer structure, which makes the manufacturing process complicated and tends to result in low production efficiency. Therefore, the present disclosure provides a manufacturing method for a fuel cell separator that can manufacture a fuel cell separator that does not have a multilayer structure but has sufficient gas impermeability and conductivity in a short molding time. [Means for solving the problem]

[0006] Aspects of the present disclosure include the following. [Aspect 1] A method for manufacturing a separator for a fuel cell, comprising: A step of preparing a mixture by mixing a thermoplastic resin, spherical graphite, and carbon fibers, wherein the mixture contains the thermoplastic resin in an amount of 37% by volume or more and less than 45% by volume based on the total volume of the mixture; heating the mixture to soften it; a step of cooling the softened mixture while pressing to obtain a molded body; A method comprising: [Aspect 2] 2. The method of embodiment 1, further comprising removing the resin layer on the surface of the molded body. [Aspect 3] 3. The method according to claim 1, wherein the mixture is cooled while being pressed for 10 to 20 seconds. [Aspect 4] A method according to any one of aspects 1 to 3, wherein the thermoplastic resin is polyethersulfone. [Aspect 5] A method according to any one of aspects 1 to 4, wherein the mixed material produced by mixing the thermoplastic resin, the spherical graphite, and the carbon fibers has a sheet-like shape. [Effects of the Invention]

[0007] The manufacturing method of the fuel cell separator of the present disclosure makes it possible to manufacture a fuel cell separator that does not have a multilayer structure but has sufficient gas impermeability and conductivity in a short molding time. DETAILED DESCRIPTION OF THE INVENTION

[0008] In this application, unless otherwise specified, numerical ranges expressed using the symbol "~" include the numerical values ​​written before and after the symbol "~" as the lower and upper limits, respectively. The upper and lower limits described in this application can be used alone or in any combination.

[0009] In this application, unless otherwise specified, "comprising" means that additional components or elements may be included, and includes "consisting essentially of" and "consisting of." "Consisting essentially of" means that additional components or elements may be included that do not have a substantial adverse effect. "Consisting of" means that the material or element is included only, but does not exclude the further inclusion of unavoidable impurities.

[0010] A manufacturing method for a fuel cell separator according to an embodiment includes a step of mixing a thermoplastic resin, spherical graphite, and carbon fiber to prepare a mixture, the mixture containing the thermoplastic resin in an amount of 37% by volume or more and less than 45% by volume based on the total volume of the mixture (mixture preparation step), a step of heating and softening the mixture (softening step), and a step of cooling the softened mixture while pressing it to obtain a molded body (molding step).

[0011] (1) Mixture preparation process A mixture is prepared by mixing a thermoplastic resin, spherical graphite, and carbon fiber. The mixture may be prepared by melting a thermoplastic resin and mixing it with spherical graphite and carbon fiber, and then molding the resulting mixture into a desired shape such as a sheet (i.e., a flat plate). Alternatively, a mixture having a shape such as a sheet may be prepared by mixing a thermoplastic resin, spherical graphite, and carbon fiber in a solvent, and then coating and drying the resulting mixture. The prepared mixture may consist of a mixture containing a thermoplastic resin, spherical graphite, and carbon fiber. The prepared mixture may be densified by heating and pressurizing.

[0012] The prepared mixture contains 37% by volume or more and less than 45% by volume of thermoplastic resin, based on the total volume of the mixture. When the mixture contains 37% by volume or more of thermoplastic resin, the separator produced can have sufficient gas impermeability. When the mixture contains less than 45% by volume of thermoplastic resin, press molding can be performed in a short time of 10 to 20 seconds in the subsequent molding process. If the proportion of thermoplastic resin is 45% by volume or more, the thermoplastic resin may penetrate between the spherical graphite and carbon fibers during press molding, hindering the formation of conductive paths and resulting in insufficient conductivity of the separator produced. The penetration of the thermoplastic resin can be prevented or reduced by lowering the heating temperature in the softening process to reduce the fluidity of the thermoplastic resin, but this requires a longer press time, making it difficult to produce the separator in a short molding time.

[0013] Examples of thermoplastic resins that can be used include polyethersulfone (PES) and polypropylene (PP). The spherical graphite may have an average particle size of 20 to 40 μm. In this application, the average particle size refers to the particle size at a cumulative degree of 50% on a cumulative particle size distribution curve obtained using a laser diffraction / scattering particle size distribution analyzer LMS-350 (manufactured by Seishin Enterprise Co., Ltd.). Examples of solvents that can be used include N-methyl-2-pyrrolidone (NMP).

[0014] (2) Softening process The mixed material is heated to soften it. The mixed material may be placed in a mold to be used in the subsequent molding step and heated. The heating temperature may be set appropriately depending on the type of thermoplastic resin, the composition of the mixed material, etc.

[0015] (3) Molding process The softened mixture is cooled while being pressed in a separator molding die. This allows the mixture to be molded into the shape of the separator. This results in a molded product having the shape of the separator. The time for cooling the mixture while being pressed may be 10 to 20 seconds.

[0016] The manufacturing method according to the embodiment may further include a step of removing a resin layer on the surface of the molded body obtained in the molding step. Here, the resin layer refers to a resin-rich layer containing a thermoplastic resin at a higher ratio than the ratio of thermoplastic resin in the entire molded body. The resin layer can be removed by polishing, for example, using sandpaper, a blast, a laser, or the like. In this way, a fuel cell separator without a multilayer structure is manufactured.

[0017] Although the embodiments of the present disclosure have been described in detail above, the present disclosure is not limited to the above embodiments, and various design modifications can be made without departing from the technical scope described in the claims. [Example]

[0018] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.

[0019] Example 1 and Comparative Example 1 Polyethersulfone (PES) (Sumitomo Chemical Co., Ltd.'s "Sumikaexcel (registered trademark) PES3600P"), spherical graphite (Ito Graphite Industries Co., Ltd.'s "SG-BL40", average particle size 40 μm), and carbon fiber (Mitsubishi Chemical Corporation's "K223HM") were mixed in N-methyl-2-pyrrolidone (NMP) at the volume ratios shown in Table 1. The mixture was coated and dried to prepare a sheet-shaped mixture. The mixture was then heated and pressed to densify it.

[0020] Next, the mixed material was placed in a mold for molding the separator, and the mixed material was heated to its softening temperature to soften it. The softened mixed material was placed together with the mold in a press heated to the same softening temperature as the mixed material or in a press at room temperature, and cooled while being pressed. Once the mixed material had cooled to a predetermined temperature, the pressing was stopped, and the molded mixed material (molded body) was removed from the mold. The cooling and pressing time was 300 seconds when a preheated press was used, and 10 seconds when a room-temperature press was used.

[0021] The resin layer formed on the surface of the molded body was removed by polishing with sandpaper, thereby obtaining a separator for a fuel cell.

[0022] A laminate was fabricated using Toray Industries, Inc.'s "TORAYCA® Carbon Paper TGP-R-0503" as the gas diffusion layer (GDL) and Kobe Steel, Ltd.'s "NC Titanium" as the fin, with the GDL / separator / fin / separator / GDL stacked in this order, and the penetration resistance of the laminate was measured using a DC four-probe method while applying a surface pressure of 1 MPa. The results are shown in Table 1.

[0023] When the pressing time was 300 seconds, Example 1 and Comparative Example 1 showed comparable, sufficiently low resistance values. When the pressing time was 10 seconds, Comparative Example 1 showed high resistance, but Example 1 showed a sufficiently low resistance value. This indicates that in Example 1, in which the amount of PES, a thermoplastic resin, was less than 45% by volume, a separator with low resistance (i.e., high conductivity) was formed by short pressing. In Comparative Example 1, when the pressing time was as short as 10 seconds, the thermoplastic resin entered between the spherical graphite and the carbon fibers, hindering the formation of conductive paths, presumably resulting in low conductivity of the separator.

[0024] [Table 1]

[0025] Examples 2-4 and Comparative Example 2 A separator was produced in the same manner as in Example 1, except that the volume ratios of PES, spherical graphite, and carbon fiber were as shown in Table 2 and the cooling and pressing times were 10 seconds.

[0026] A dye penetrant test agent (Taseto Corporation's "Color Check") was applied to one surface of the separator, and it was visually confirmed whether the dye penetrant test agent had penetrated to the opposite surface of the separator. If penetration of the dye penetrant test agent was confirmed, the separator had pores through which the dye penetrant test agent could pass, and gas could also pass through. Therefore, separators in which penetration of the dye penetrant test agent was confirmed have insufficient gas impermeability. The results are shown in Table 2, with "-" indicating cases where penetration of the dye penetrant test agent was confirmed and "+" indicating cases where penetration was not confirmed.

[0027] The separator of Comparative Example 2, in which the amount of PES, a thermoplastic resin, was 35% by volume, was confirmed to have permeation with the dye penetrant, indicating that it had insufficient gas impermeability.The separator of Example 2-4 was confirmed to have no permeation with the dye penetrant, indicating that it had sufficient gas impermeability.

[0028] [Table 2]

Claims

1. A method for manufacturing a separator for a fuel cell, comprising: A step of preparing a mixture by mixing a thermoplastic resin, spherical graphite, and carbon fibers, wherein the mixture contains the thermoplastic resin in an amount of 37% by volume or more and less than 45% by volume based on the total volume of the mixture; heating the mixture to soften it; a step of cooling the softened mixture while pressing to obtain a molded body; A method comprising:

2. The method according to claim 1 , further comprising the step of removing the resin layer on the surface of the molded body.

3. 3. The method according to claim 1, wherein the time for cooling the mixed material while pressing is 10 to 20 seconds.

4. 3. The method of claim 1 or 2, wherein the thermoplastic resin is polyethersulfone.

5. The method according to claim 1 or 2, wherein the mixture produced by mixing the thermoplastic resin, the spherical graphite, and the carbon fibers has a sheet-like shape.

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