JP2006073470A - Manufacturing method of fuel cell separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a fuel cell separator superior in conductivity, light-weight property, mechanical strength, and impact resistance or the like, of which the manufacturing yield is improved and production efficiency is high. <P>SOLUTION: This manufacturing method of the fuel cell separator includes a molding process in which a material for the fuel cell separator containing graphite powder covered with a thermoset resin and a fine carbon fiber of which the fiber diameter is 0.5-500 nm, the fiber length is 1,000 μm or less, and the center axis has a hollow structure are pressure molded using a die, and a curing process in which the molded body molded in the molding process is cured. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a manufacturing method with high production efficiency of a separator for a fuel cell excellent in conductivity, lightness, mechanical strength, and the like.

  In recent years, from the viewpoint of environmental problems and energy problems, fuel cells have been attracting attention as clean power generators that generate hydrogen by the reverse reaction of water electrolysis using hydrogen and oxygen and have no emissions other than water. Among them, polymer electrolyte fuel cells are most promising for automobiles and consumer use because they operate at low temperatures. This fuel cell can achieve high power generation by stacking a large number of single cells composed of a polymer solid electrolyte membrane, a gas diffusion electrode, a catalyst, and a separator, for example, 400 to 800 cells for automobiles. .

  The separator used to partition this single cell usually has a groove to which fuel gas and oxidant gas are supplied, and requires high gas impermeability to completely separate these two types of gas. High conductivity is required to reduce the resistance. Furthermore, in recent years, since it is necessary to mount a fuel cell on a moving body such as an automobile, a method for manufacturing a separator having light weight, high mechanical strength, impact resistance in the event of a collision, and the like with high production efficiency. Is required.

  Fuel cell separators usually use carbon powders such as graphite and thermosetting resins such as phenolic resins, and the production methods thereof include a manufacturing method using a cold pressing process and a manufacturing method using a hot pressing process. ing.

  In the manufacturing method by the cold pressing process, first, a material in which graphite powder is coated with a thermosetting resin is filled in a normal temperature mold set in a pressurizing apparatus, and then pressed (cold pressing) at a high pressure of 100 MPa or more. In this method, the resin is molded by heating the molded body obtained by molding into a predetermined shape as a separator.

On the other hand, in the manufacturing method by the hot pressing process, carbon powder and thermosetting resin are mixed, put into a mold set in a pressurizing apparatus, and pressed while being heated (hot pressing), In this method, the resin is cured almost simultaneously with the press (see, for example, Patent Document 1).
JP 59-26907 (3rd page, FIG. 1)

  Any of the above-described conventional cold pressing steps and hot pressing methods have the following problems.

  That is, the former manufacturing method by the cold pressing process is a mechanism depending on the pressing pressure, in which a thermosetting resin is softened and melted and molded by pressing with a high pressure of 100 MPa or more using a normal temperature mold. For this reason, the thermosetting resin is often insufficiently softened or is not in a uniform softened state, and densification is often incomplete. Therefore, there is a problem that the frequency of occurrence of defective products is increased and the yield is low.

  Moreover, since the manufacturing method by a hot press process is the press by the thermosetting temperature area | region of a thermosetting resin, the thermosetting resin in a cavity starts softening melt | dissolution immediately, and it changes to hardening reaction immediately after that. However, this series of phenomena is uneven in the way heat is transmitted, and it is difficult for all of the thermosetting resins in the cavity to occur simultaneously. For this reason, the densification may be incomplete due to, for example, curing before the thermosetting resin sufficiently spreads between the graphite particles.

  In this way, the manufacturing method by the hot pressing process is not a defective product, but the densification is slightly different for each product. Therefore, the fuel cell separator is one factor that determines the performance of the fuel cell. There is also a problem that the gas permeability and the rate of defective electric resistance vary, resulting in individual differences.

  Thus, an object of the present invention is to provide a method capable of producing a stable fuel cell separator excellent in conductivity, lightness, mechanical strength, impact resistance, etc. and having no difference in performance with high yield and high production efficiency. There is.

The manufacturing method of the separator for fuel cells of this invention is for solving the said subject, and has the following summary.
(1) Graphite powder coated with a thermosetting resin, a fuel containing fine carbon fibers having a fiber diameter of 0.5 to 500 nm, a fiber length of 1000 μm or less, an aspect ratio of 3 to 1000, and a central axis having a hollow structure It includes a molding step for pressure molding using a mold in a state where the battery separator material is heated to 40 to 80 ° C. and softened and melted, and a curing step for curing the molded body molded in the molding step. A method for manufacturing a fuel cell separator.
(2) A first heating process step of heating the mold and the fuel cell separator material to the required temperature with a heating device before the processing of the molding step, and a heater in the mold. And manufacturing the fuel cell separator according to the above (1), which includes any one or both of the second heating process step of heating the fuel cell separator material to the required temperature by the heater. Method.
(3) The method for producing a fuel cell separator according to (1) or (2), wherein the fine carbon fiber is graphitized at 2300 to 3500 ° C. in a non-oxidizing atmosphere.
(4) The fine carbon fiber is a thermosetting resin-coated fine carbon fiber having a surface coated with 1 to 40 parts by weight of a thermosetting resin per 100 parts by weight of the above (1) to (3). The manufacturing method of the fuel cell separator in any one.
(5) The method for producing a fuel cell separator according to any one of (1) to (4), wherein the thermosetting resin is a phenol resin and / or a furan resin.
(6) The method for producing a fuel cell separator according to any one of (1) to (5), wherein the pressurization in the molding step is performed at 15 to 100 MPa.

  According to the production method of the present invention, a graphite powder coated with a thermosetting resin and a material for a fuel cell separator including fine carbon fibers having specific physical properties are heated to a required temperature, and the thermosetting resin is softened. Since it is pressure-molded into the required shape of the separator in a short time in a molten state, there is no resin curing reaction in the molding process, and there is no variation in performance by product by curing the molded body in the curing process. A homogeneous fuel cell separator can be produced.

  In particular, the electrical resistance failure rate and the hydrogen permeation failure rate are reduced and the product yield is greatly improved as compared with the conventional one-step hot pressing.

  In addition, in the present invention, a heating process is provided before the molding process, and the mold and the fuel cell separator material in the molding process are softened and melted, thereby greatly reducing the time required for the molding process. It can be shortened and production efficiency can be increased.

  A composition comprising a graphite powder coated with a thermosetting resin, which is a material for a fuel cell separator used in the present invention, and fine carbon fibers having specific physical properties will be described.

  The graphite powder coated with a thermosetting resin in the present invention is a graphite powder coated with a thermosetting resin such as a phenol resin, a furan resin, an epoxy resin, or a mixed system thereof. The graphite powder preferably has an average particle size of 0.1 to 150 μm, particularly preferably 1 to 100 μm, and the shape of the powder may be spherical or scaly. Further, the plane spacing (d002) of the crystallites is preferably 3.354 to 3.380cm.

  As a method for coating graphite powder with a thermosetting resin, any of commonly used solution coating, spray coating, reaction coating, melt coating, and the like may be used. The coating amount of the thermosetting resin on the graphite powder is preferably 1 to 40 parts by weight, particularly preferably 5 to 25 parts by weight with respect to 100 parts by weight of the graphite powder. .

The fine carbon fiber used in the present invention has a fiber diameter of 0.5 to 500 nm or less, a fiber length of 1000 μm or less, preferably an aspect ratio of 3 to 1000, and preferably a cylinder made of a carbon hexagonal mesh surface in a concentric shape. Fine carbon fibers having a multilayer structure arranged and having a hollow structure in the central axis are used. Such fine carbon fibers are greatly different from conventional carbon fibers having a fiber diameter of 5 to 15 μm, which are obtained by heat-treating fibers such as conventional PAN, pitch, cellulose, and rayon. The fine carbon fiber used in the present invention is not only different in fiber diameter and fiber length from the conventional carbon fiber, but also significantly different in structure. As a result, it is extremely excellent in terms of physical properties such as conductivity, thermal conductivity, and slidability.

When the fiber diameter of the fine carbon fiber is smaller than 0.5 nm, the strength of the obtained composite material becomes insufficient, and when it is larger than 500 nm, mechanical strength, thermal conductivity, and the like are lowered. On the other hand, when the fiber length is larger than 1000 μm, the fine carbon fibers are difficult to disperse uniformly, so that the composition of the material becomes non-uniform and the mechanical strength of the resulting separator decreases. The fine carbon fiber used in the present invention is particularly preferably one having a fiber diameter of 10 to 200 nm, a fiber length of 3 to 300 μm, and preferably an aspect ratio of 3 to 500. In the present invention, the fiber diameter and fiber length of the fine carbon fiber can be measured with an electron microscope.

A preferred fine carbon fiber used in the present invention is a carbon nanotube. These carbon nanotubes are also called graphite whiskers, filamentous carbon, carbon fibrils, etc., and there are single-walled carbon nanotubes with a single graphite film forming the tube and multi-walled carbon nanotubes with multiple layers. Any of them can be used in the invention. However, multi-walled carbon nanotubes are preferred because they provide a high mechanical strength and are advantageous in terms of economy.

Carbon nanotubes are produced, for example, by an arc discharge method, a laser evaporation method, a thermal decomposition method, or the like as described in “Basics of Carbon Nanotube” (issued by Corona, pages 23-57, issued in 1998). The The carbon nanotube has a fiber diameter of preferably 0.5 to 500 nm, a fiber length of preferably 1 to 500 μm, and preferably an aspect ratio of 3 to 500.

Particularly preferred fine carbon fibers in the present invention are vapor grown carbon fibers having a relatively large fiber diameter and fiber length among the carbon nanotubes. Such a vapor grown carbon fiber is also called VGCF (Vapor Grown Carbon Fiber), and as described in Japanese Patent Application Laid-Open No. 2003-176327, a gas such as hydrocarbon is used in the presence of an organic transition metal catalyst. Manufactured by vapor phase pyrolysis with hydrogen gas. The vapor grown carbon fiber (VGCF) has a fiber diameter of preferably 50 to 300 nm, a fiber length of preferably 3 to 300 μm, and preferably an aspect ratio of 3 to 500. This VGCF is excellent in terms of ease of manufacture and handling.

The fine carbon fiber used in the present invention is preferably heat-treated in a non-oxidizing atmosphere at a temperature of 2300 ° C. or higher, preferably 2500 to 3500 ° C., whereby the surface thereof is graphitized, mechanical strength, Chemical stability is greatly improved, contributing to weight reduction of the resulting composite material. As the non-oxidizing atmosphere, argon, helium, and nitrogen gas are preferably used.

The fine carbon fiber used in the present invention may be used as it is, but it is preferable to use fine carbon fiber having a surface coated with the above-described thermosetting resin such as phenol resin. When fine carbon fibers coated with such a thermosetting resin are used, the dispersion state becomes uniform and a carbon fiber metal composite material having excellent characteristics can be obtained. The coating amount of the thermosetting resin on the surface of the fine carbon fibers is preferably 1 to 40 parts by weight, particularly preferably 5 to 25 parts by weight per 100 parts by weight of the fine carbon fibers. For example, when the thermosetting resin is a phenol resin, the fine carbon fiber coated with the thermosetting resin is produced by reacting phenols and aldehydes while mixing with the fine carbon fiber in the presence of a catalyst. Is done.

  The fine carbon fiber in the fuel cell separator material of the present invention is preferably used in an amount of 0.1 to 100 parts by weight, particularly preferably 0.5 to 50 parts by weight, based on 100 parts by weight of the graphite powder. When the amount of fine carbon fiber used is less than 0.1 parts by weight, there is no effect of improving conductivity, and when it exceeds 100 parts by weight, the cost increases, which is not preferable.

  The graphite powder coated with the thermosetting resin and the fine carbon fiber having specific properties are obtained by using a mixer generally used in the resin field such as a ribbon blender, a V blender, and a planetary mixer. By mixing uniformly, a fuel cell separator material can be obtained. Using this fuel cell separator material, the fuel cell separator of the present invention is produced as schematically shown in FIG.

(1) First Heating Process Step A predetermined amount of the fuel cell separator material a is put into a plurality of upper and lower pairs of molds 1 and the lower mold (inside the cavity) of the mold 1. The plurality of molds 1 are set in a heating apparatus 2 such as an oven having an industrial oven or a conveyer such as a conveyor, preferably at a temperature of about 40 to 80 ° C., particularly preferably about 50 to 80 ° C. And preheat (see FIG. 1 (a)).

  The fuel cell separator material a does not necessarily need to be put into the mold 1 and heated together with the mold 1. The mold 1 and the fuel cell separator material a (in a desired container) May be separated and heated.

  The fuel cell separator material a in the cavity begins to soften and melt as the heating proceeds, and the thermosetting resin is sufficiently distributed between the graphite powder and the fine carbon fibers.

  In place of the first heating process, a heater is installed in the mold 1 (not shown), and the mold 1 is heated by the heater to soften and melt the thermosetting resin. May be heated to a suitable temperature (second heating treatment step).

(2) Molding process When the first heating process is completed, the mold 1 is set in the press device 3 and is preferably molded at a pressure of 15 to 100 MPa, particularly preferably 20 to 80 MPa (FIG. 1). (See (b)). When the thermosetting resin is pressurized with a high pressure of approximately 100 MPa or more, the fuel cell separator material a itself in the cavity may generate heat at a temperature at which it softens and melts. Therefore, the upper limit of the pressure is 100 MPa or less. desirable. On the other hand, in order to satisfy the mechanical strength and electrical properties of the separator, the lower limit of the pressure is preferably approximately 15 MPa.

(3) Curing step When the pressure molding is completed, the mold 1 is removed from the press device 3, and the thermosetting resin starts to cure in that state, preferably 80 ° C to 250 ° C, particularly preferably 100 to 100 ° C. It is sequentially carried into a dedicated furnace 4 preheated to 230 ° C. (or the above-described heating device 2 may be shared) and thermally cured (see FIG. 1C). After a predetermined time of 5 minutes to 15 hours has elapsed, the formed fuel cell separator A that has been thermoset is removed from the mold 1 and the series of processes is completed (see FIG. 1D).

  The curing process is performed for each mold 1, but the molded body after the pressure molding is finished is removed from the mold 1, and the molded body is carried into the dedicated path 4 or the heating device 2 described above. It may be thermoset. In addition, although the molded object before the hardening process which was demolded from the mold 1 is deformed when an extreme external force is applied, the molded body already has a shape-retaining property.

  In particular, when the second heating process is employed, productivity is improved by removing the molded body from which the pressure molding has been completed from the mold 1 while the mold 1 is attached to the press device 3. It is preferable because it improves.

  Hereinafter, the method for producing the fuel cell separator of the present invention will be described more specifically with reference to examples. Examples 1 to 3 are examples of the present invention, and examples 4 to 5 are comparative examples.

Examples 1-5
In each Example, the following were used as the fuel cell separator material.
Graphite powder: 20 parts by weight of a phenol resin (thermal curing start temperature is 80 ° C.) coated by a solution coating method on 100 parts by weight of spherical or scaly graphite powder having an average particle size of 17 μm Fine carbon fiber: 100 parts by weight of fine carbon fiber graphitized by heat treatment of vapor-grown carbon fiber having a fiber diameter of 150 nm, fiber length of 15 μm, and aspect ratio of 30 in an argon gas atmosphere at a temperature of 2800 ° C. for 30 minutes On the other hand, 15 parts by weight of a phenolic resin (thermal curing start temperature is 80 ° C.) coated by a solution coating method.

  Each of the above components was stirred and mixed for 30 minutes using a ribbon blender at a weight ratio shown in Table 1 to obtain a separator material.

Using the separator material, the fuel cell separator A was manufactured through the first heating process, the molding process, and the curing process. At this time, the molding temperature (the temperature of the mold 1 and the temperature a of the fuel cell separator material a) was obtained. ) And the molding pressure (pressing pressure) were appropriately changed as shown in Table 1. The thermosetting resin was cured by holding at 150 ° C. for 1 hour. In this manner, a fuel cell separator as a sample was manufactured. In each sample number 200, the electrical resistance value failure rate (percentage of electrical resistance of 20 mΩcm or more) and the hydrogen transmission value failure rate (percentage of hydrogen transmission value of 10 ⁻¹¹ mol / m ² spa or more) were determined. The results are shown in Table 1.

In addition, the measuring method of the electrical resistance value in an Example processed the separator for fuel cells into a 200 mm long and 1 mm square test piece, and measured by the 4 terminal method using this test piece. Also, the measurement method of hydrogen permeation value is JIS
The test was carried out in accordance with the A method (differential pressure method) of K7126, under the conditions of sample humidity control: 23 ° C., 48 Hr or higher at 50% relative humidity, measurement temperature: 23 ° C., gas type used: hydrogen gas.

Example 1
In Example 1, spherical graphite powder was used, the molding temperature was 65 ° C., and the molding pressure was 50 MPa. As a result, the electrical resistance failure rate was 0.3% and the hydrogen permeation failure rate was 0.5%, and it was confirmed that the produced fuel cell separator had a very low incidence of defective products.

Example 2
In Example 2, spherical graphite powder was used, the molding temperature was 70 ° C., and the molding pressure was 30 MPa. As a result, the electrical resistance failure rate was 0.5%, the hydrogen permeation failure rate was 0.5%, and it was confirmed that the produced fuel cell separator had a very low incidence of defective products.

Example 3
In Example 3, scaly graphite powder was used, the molding temperature was 65 ° C., and the molding pressure was 50 MPa. As a result, the electrical resistance failure rate was 0.5%, the hydrogen permeation failure rate was 0.5%, and it was confirmed that the produced fuel cell separator had a very low incidence of defective products.

Example 4
Spherical graphite powder was used, the molding temperature was 25 ° C., and the molding pressure was 20 MPa. As a result, the failure rate of electrical resistance was 8%, the failure rate of hydrogen permeation was 11%, and it was confirmed that the manufactured fuel cell separator had an extremely high incidence of defective products.

Example 5
This is a conventional hot pressing process, using spherical graphite powder, a molding temperature of 150 ° C., and a molding pressure of 20 MPa. As a result, the electrical resistance failure rate is 0.5% and the hydrogen permeation failure rate is 6%. The manufactured fuel cell separator has a hydrogen permeation failure rate exceeding 10% and the occurrence rate of defective products is extremely high. It was confirmed.

Example 6
Spherical graphite powder was used, the molding temperature was 65 ° C., and the molding pressure was 5 MPa. As a result, the electrical resistance failure rate was 15% and the hydrogen permeation failure rate was 13%. The manufactured fuel cell separator exceeded 10% in both the electrical resistance failure rate and the hydrogen permeation failure rate. Was found to be extremely high.

FIG. 5 is a production process diagram illustrating an outline of a method for producing a fuel cell separator according to an embodiment of the present invention.

Explanation of symbols

a Fuel cell separator material A Fuel cell separator
1 Mold 2 Heating device 3 Press device 4 Dedicated path

Claims (6)

  A graphite powder coated with a thermosetting resin, a fiber diameter of 0.5 to 500 nm, a fiber length of 1000 μm or less, and a fuel cell separator material containing fine carbon fibers having a central axis having a hollow structure at 40 to 80 ° C. Manufacturing of a fuel cell separator, comprising: a molding step for pressure molding using a mold in a heated and softened state; and a curing step for curing the molded body molded in the molding step Method.   Prior to the processing of the molding step, a first heating processing step of heating the mold and the fuel cell separator material to the required temperature with a heating device, and a heater in the mold, the heater 2. The method for producing a fuel cell separator according to claim 1, comprising: one or both of a second heat treatment step of heating the fuel cell separator material to the required temperature by the second heat treatment step.   The method for producing a fuel cell separator according to claim 1 or 2, wherein the fine carbon fibers are graphitized at 2300 to 3500 ° C in a non-oxidizing atmosphere.   The fuel according to any one of claims 1 to 3, wherein the fine carbon fiber is a thermosetting resin-coated fine carbon fiber whose surface is coated with 1 to 40 parts by weight of a thermosetting resin per 100 parts by weight of the fine carbon fiber. A method for producing a battery separator.   The method for producing a fuel cell separator according to any one of claims 1 to 4, wherein the thermosetting resin is a phenol resin and / or a furan resin.   The method for producing a fuel cell separator according to any one of claims 1 to 5, wherein pressurization in the molding step is performed at 15 to 100 MPa.

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