JP4855707B2 - Aluminum plate for fuel cell, separator using the same, end plate and fuel cell using them. - Google Patents

Description

  The present invention relates to an aluminum plate for a fuel cell, a separator using the same, an end plate, and a fuel cell using the same, and is particularly suitable for producing a separator and an end plate for a polymer electrolyte fuel cell. The present invention relates to an aluminum plate for a fuel cell, a separator and an end plate manufactured using the same, and a fuel cell including the same.

  Fuel cells are classified into solid polymer type, phosphoric acid type, molten carbonate type, solid electrolyte type, etc., depending on the electrolyte used. Among these, polymer electrolyte fuel cells that use cation exchange membranes as electrolytes are suitable for miniaturization because of their lower operating temperature and higher output density compared to other fuel cells. Furthermore, since it has advantages such as that the components are solid and can be used for applications exposed to vibrations and shocks, it has recently been researched as an in-vehicle power source, a stationary power source and a household power source. Development has been actively conducted.

  In such a polymer electrolyte fuel cell, like other fuel cells, a plurality of unit cells each having both surfaces of an electrolyte (cation exchange membrane) sandwiched between two electrodes are stacked via a separator. In this state (solid polymer fuel cell stack), it is held in a predetermined fuel cell housing case or the like while being sandwiched by two end plates from both sides. When a hydrogen-containing gas (fuel gas) and an oxygen-containing gas (generally air) are supplied to each unit cell, an electromotive force is generated in the unit cell due to an electrochemical reaction between oxygen and hydrogen, Since the unit cells are connected in series, desired voltage and power can be obtained as the whole fuel cell.

  The separator interposed between the unit cells of the polymer electrolyte fuel cell forms a flow path for each of the hydrogen-containing gas and the oxygen-containing gas, separates these gases, and In view of the power generation efficiency of the fuel cell, the electrodes (the fuel electrode in one unit cell and the air electrode in the other unit cell) are in contact with each other to electrically connect the unit cells. It is desirable that the resistance (contact resistance) is small. In addition, the electrolyte (cation exchange membrane) in each unit cell is held in a wet state. If various ions are eluted from the separator, the ion conductivity in the electrolyte may be reduced. In addition, the acid resistance and alkali resistance are also required to be excellent. Under these circumstances, in a conventional polymer electrolyte fuel cell, a separator made of a carbon material such as a high-density fired carbon plate is widely used.

  However, since the carbon material is brittle and easily broken, for example, when a separator for a fuel cell used in an environment exposed to vibration or impact is produced using the carbon material, the thickness exceeds a predetermined value. The separator having a thickness greater than the predetermined thickness has been a factor that hinders downsizing of the fuel cell.

  In addition, the carbon material is generally expensive, and further, since the processing cost when forming a large number of grooves and flanges to be gas flow paths is also expensive, using a separator made of a carbon material, It was also a factor to raise the price of the whole fuel cell.

  Therefore, as an alternative to separators made of conventional carbon materials, research and development have recently been actively conducted on fuel cell separator materials and fuel cell separators using various metal plates. Various things have been proposed.

  For example, in Patent Document 1 (Japanese Patent Laid-Open No. 10-228914), a separator for a fuel cell made of a metal member such as stainless steel, and the contact surface with the electrode of the unit cell is directly gold-plated. In the patent document 2 (Japanese Patent Laid-Open No. 2003-193206), a predetermined carbide-based metal inclusion and boride-type inclusion having conductivity are formed on the stainless steel surface. One or more of them are dispersed and exposed, and a stainless steel for a separator of a polymer electrolyte fuel cell in which the surface roughness of the stainless steel is within a predetermined range has been proposed.

  Research is also underway on fuel cell separator materials and fuel cell separators, in which the surface of a metal as a substrate (base material) is coated with a conductive paint comprising conductive particles and a resin as an adhesive component. For example, the following has been proposed.

  Specifically, in Patent Document 3 (Japanese Patent Laid-Open No. 11-345618), an austenitic stainless steel whose surface is pickled is used as a base material, a mixed powder of graphite powder and carbon black as a conductive agent, and a polyolefin type A coated metal separator material for a polymer electrolyte fuel cell has been proposed, characterized in that a conductive coating composed of a resin is formed on the surface of the substrate in an amount of 3 to 20 μm. In Japanese Unexamined Patent Application Publication No. 2002-50366), the surface of a metal substrate is coated with a resin composition comprising conductive particles containing conductive ceramics and a furan resin, an epoxy resin, or a vinylidene fluoride resin. Metal separators for molecular fuel cells have been proposed. Furthermore, in Patent Document 5 (Japanese Patent Application Laid-Open No. 2004-111079), a first coating layer made of a metal-based conductive paint containing a resin is provided on a metal separator base material made of die casting such as Al, There has been proposed a metal separator for a fuel cell in which a second coating layer composed of a graphite-based conductive paint containing a resin is provided on the first coating layer.

  In each of the fuel cell separator materials or fuel cell separators proposed in each of these patent documents, since a metal such as stainless steel is used as the base material, the flow of the reaction gas is reduced. It is possible to form grooves and flanges that form the path by relatively simple and inexpensive methods such as pressing and punching. Compared with the case of using a conventional carbon material, the separator and the flange The cost can be reduced, and the size of the separator body, and hence the fuel cell can be reduced.

  However, among the fuel cell separator materials and fuel cell separators disclosed in those patent documents, those using stainless steel as proposed in Patent Document 1 and the like have a density of stainless steel. As a result, there is a problem that the weight of the obtained separator becomes heavy, and as a result, the weight of the entire fuel cell also becomes heavy. For this reason, for example, when a fuel cell using a stainless steel separator is mounted on an automobile, there is a drawback that fuel consumption deteriorates.

  Moreover, in the fuel cell separator in which the surface of the metal substrate (base material) is gold-plated as proposed in Patent Document 1, although it is excellent in terms of low electrical resistance, Since the processing (gold plating) is expensive, there is a problem in terms of economy.

  Further, as proposed in Patent Document 3 and the like, in the case of a separator material or the like in which various conductive paints are coated on the surface of a metal as a base material, the corrosion resistance (acid resistance and alkali resistance) of the separator is improved. In order to ensure, since it was necessary to make the thickness of a coating film into 3-several hundred micrometers, there existed a problem that an electrical resistance increased inevitably. In addition, a resin using furan resin, epoxy resin, phenol resin, or acrylic resin as a resin constituting the conductive paint has a long-lasting required acid resistance and alkali resistance. It is difficult to maintain it over a long period of time, and when an olefin resin or a fluororesin is used, there is a problem in adhesion between the base metal.

JP-A-10-228914 JP 2003-193206 A JP-A-11-345618 Japanese Patent Laid-Open No. 2002-50366 JP 2004-111079 A

  Here, the present invention has been made in the background of such circumstances, and the problem to be solved is that the electrical resistance (contact resistance) is low and the acid resistance and alkali resistance are also excellent. It is another object of the present invention to provide an aluminum plate for a fuel cell, a separator using such an aluminum plate, an end plate, and a fuel cell including the same.

  In order to solve such problems, the present invention provides a conductive material and an α, β-ethylenically unsaturated carboxylic acid on the surface of an aluminum plate having a thickness of 0.1 to 2.0 mm from which the oxide film has been removed. The gist is an aluminum plate for a fuel cell, in which a coating film made of a mixture containing an acid-modified polyolefin resin is formed with a thickness of 0.1 to 10 μm.

  In one preferred embodiment of the fuel cell aluminum plate according to the present invention, the conductive material is activated carbon, graphite, carbon black, vapor grown carbon fiber, gold particles, cobalt particles, gold or One or more selected from nickel particles plated with platinum, graphite or stainless steel particles, and in another preferred embodiment, the modified polyolefin resin is Polypropylene modified with maleic anhydride.

  On the other hand, the gist of the present invention is also a separator and end plate of a fuel cell using such an aluminum plate for a fuel cell, and a fuel cell using such a separator or end plate.

  Thus, in the aluminum plate for fuel cells according to the present invention, as a resin for forming a coating film while holding a conductive material on the surface of the aluminum plate as a substrate, it has excellent acid resistance and alkali resistance, and Since the polyolefin resin modified with α, β-ethylenically unsaturated carboxylic acid, which adheres strongly to the aluminum plate, is used, the thickness of the coating film is relatively thin, 0.1 to 10 μm. However, the aluminum plate for fuel cells of the present invention exhibits excellent acid resistance and alkali resistance.

  In addition, in the present invention, in addition to the coating film thickness on the surface of the fuel cell aluminum plate being thin, as the aluminum plate as the base material, the oxide film formed on the surface in the manufacturing process is once removed. As a result, the electrical resistance (contact resistance) as a whole is extremely low.

  Such an effect can be obtained by using, as a conductive material, activated carbon, graphite, carbon black, vapor grown carbon fiber, gold particles, cobalt particles, nickel particles plated with gold or platinum, graphite or stainless steel particles. By using one or two or more selected from the above, or by using polypropylene modified with maleic anhydride as a polyolefin resin modified with α, β-ethylenically unsaturated carboxylic acid, It is possible to enjoy it advantageously.

  In the separator and the end plate manufactured using the fuel cell aluminum plate according to the present invention, the polymer electrolyte fuel cell that is small and requires light weight, for example, a fuel for vehicle use. It can be used particularly advantageously in batteries.

  By the way, on the surface of a generally available aluminum plate, a relatively thick oxide film having a thickness of about 5 to 500 nm is formed by hot treatment, cold treatment, heat treatment, etc. in the production thereof. Therefore, when producing the fuel cell aluminum plate according to the present invention, it is important to first remove the oxide film covering the surface of the obtained aluminum plate according to various conventionally known methods. By forming a relatively thin coating film as described later on the surface of the aluminum plate whose conductivity has been improved by removing the oxide film, the fuel cell aluminum plate of the present invention is made of a conventional metal plate. Compared with a separator material or the like, the electrical resistance (contact resistance) is extremely low.

  The removal of the oxide film formed on the aluminum plate is appropriately performed according to a conventionally known method. For example, the surface of the obtained aluminum plate is treated with an acid such as sulfuric acid or nitric acid, or hydroxylated. A technique of washing with an alkali solution such as sodium or sodium carbonate, washing with water, and drying is advantageously used.

  In addition, if the aluminum plate after washing, washing with water and drying with such an acid or alkali is left in the atmosphere, an oxide film is formed again on its surface, which is generated by that. The oxide film to be used is relatively thin (thickness: about 0.5 to 5 nm). That is, the electrical resistance of an aluminum plate on which an oxide film is formed again after cleaning is generally lower than that on the aluminum plate before cleaning, and an aluminum plate on which such a thin oxide film is formed was used. Even in this case, it is possible to enjoy the advantageous effects of the present invention. Therefore, the aluminum plate from which the oxide film is removed in the specification and claims of the present application is only an aluminum plate in a state where the oxide film on the surface is completely removed using an acid or an alkaline aqueous solution. First, the oxide film on the surface is once removed and then left in the atmosphere, so that a relatively thin (thickness: about 0.5 to 5 nm) oxide film is formed on the surface again. Also included.

  Of the aluminum plates from which the surface oxide film has been removed, an aluminum plate having a thickness of 0.1 to 2.0 mm is used in the present invention. In a fuel cell aluminum plate using an aluminum plate having a thickness of less than 0.1 mm, when a separator is produced using the aluminum plate, the strength (rigidity) of the obtained separator is insufficient, and there is a risk that buckling is likely to occur. On the other hand, when an aluminum plate having a thickness of more than 2.0 mm is used, when the aluminum plate for a fuel cell obtained therefrom is pressed, it becomes difficult to produce uneven shapes, and hydrogen-containing gas (fuel gas) and oxygen in the separator This is because it becomes difficult to secure the flow path of the contained gas (air), and as the thickness increases, the thickness of the entire fuel cell increases and the weight also increases.

  More specifically, when a separator is produced using the fuel cell aluminum plate of the present invention, generally, the fuel cell aluminum plate is subjected to press working or the like, so that fuel gas and air A groove to be a flow path is formed (see FIG. 1). A plurality of unit cells comprising a fuel electrode, a solid polymer electrolyte, and an air electrode are stacked through the separator thus obtained to form a fuel cell stack (see FIGS. 2 and 3). And this fuel cell stack is hold | maintained in a predetermined fuel cell storage case in the state pressed by the end plate etc. from the both ends in the lamination direction of a unit cell (refer FIG. 4). Therefore, in aluminum plates for fuel cells using a thickness of more than 2.0 mm or a thickness of less than 0.1 mm, the separators made using them sufficiently perform the functions required as separators. There is a fear that it cannot be done.

  As the aluminum plate used in the present invention, any conventionally known aluminum plate can be used, for example, 1000 series aluminum, 3000 series aluminum alloy, and 5000 series aluminum. From the alloy plate material, considering the formability when producing the separator or end plate, the strength required for the separator, etc., the one according to the desired separator is appropriately selected, Used.

  On the other hand, together with such an aluminum plate, a conductive paint for forming a predetermined conductive coating film on the surface of the aluminum plate is prepared. In the present invention, α, β-ethylenic resin is used as the resin component. A polyolefin resin modified with an unsaturated carboxylic acid (hereinafter also referred to as a modified polyolefin resin) is used. By using such a specific modified polyolefin resin, the aluminum plate for fuel cells of the present invention exhibits excellent acid resistance and alkali resistance even though the coating film on the surface thereof is relatively thin. In addition, the thinning of the coating film and the use of the aluminum plate from which the oxide film has been removed as a base material, combined with the overall aluminum plate for fuel cells in the present invention. The electrical resistance (contact resistance) is extremely low.

  Here, as the polyolefin resin modified with α, β-ethylenically unsaturated carboxylic acid, any conventionally known resins can be used. Specific examples of the α, β-ethylenically unsaturated carboxylic acid include acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, and anhydrides thereof, and polyolefin resins. Examples thereof include polyethylene, polypropylene, ethylene-propylene copolymer, polybutene and the like. Among these, in the present invention, polypropylene modified with maleic anhydride is particularly advantageously used.

  In addition, as a conductive material blended in the conductive paint, activated carbon, graphite, carbon black, vapor grown carbon fiber, gold particles, cobalt particles, and nickel particles plated with gold or platinum, graphite and stainless steel Steel particles and the like can be mentioned, and one or more of them are selected from these as necessary, and used appropriately. In addition, since noble metal particles such as gold and cobalt, nickel particles subjected to plating treatment, etc. are expensive, activated carbon, graphite, carbon black, etc., when the conductivity of the coating film is insufficient from the viewpoint of production cost. It is desirable to use together with vapor grown carbon fiber (hereinafter also referred to as carbon-based conductive material). In addition, the size (average particle diameter or average length) of the conductive material used in the present invention is preferably not more than twice the target coating thickness in consideration of dropping of the conductive material after the coating is formed. More preferably, it is 1.5 times or less.

  A conductive coating for application to the aluminum plate surface is prepared using the modified polyolefin resin and the conductive material as described above, and such preparation is performed according to the same method as in the prior art. For example, a predetermined amount of a modified polyolefin resin and a conductive material are mixed in a predetermined organic solvent, mixed, and uniformly dispersed.

  The blending amount of the conductive material is appropriately determined in consideration of the type of the modified polyolefin resin used, the conductivity of the coating film, and further the adhesiveness to the aluminum plate, etc. Generally, if the blending amount of the conductive material is too small, the coating film may not exhibit sufficient conductivity, whereas if the blending amount is too large, the coating film may not be sufficiently formed on the aluminum plate surface. is there. Specifically, when one or more carbon-based conductive materials such as carbon black are selected and used, the carbon-based conductive material is used with respect to 100 parts by weight of the modified polyolefin resin. They are blended in a quantitative ratio so that the total amount is 50 to 150 parts by weight. In addition, in the case of using a noble metal particle such as gold or a nickel particle subjected to gold plating together with the carbon-based conductive material, the carbon-based conductive material (total amount) is 50 with respect to 100 parts by weight of the modified polyolefin resin. ˜150 parts by weight, precious metal particles and the like are each mixed in a quantitative ratio of 1 to 50 parts by weight.

  The conductive paint thus prepared is applied to the surface of the aluminum plate from which the oxide film has been removed in advance according to a conventionally known method, followed by drying or the like, whereby the aluminum plate for fuel cells according to the present invention is obtained. It is made.

  Here, when the conductive paint is applied to the surface of the aluminum plate, the amount of the solidified product (coating film) of the conductive paint formed on the surface is 0.1 to 10 μm. A conductive paint is applied. If the coating film thickness is less than 0.1 μm, the resulting aluminum plate for fuel cells may not exhibit sufficient acid resistance and alkali resistance, while on the other hand, even if a coating film having a thickness of 10 μm or more is formed, It is economically unfavorable because it only reduces the conductivity of the aluminum plate for fuel cells. In other words, the aluminum plate for fuel cells of the present invention has excellent acid resistance and alkali resistance (corrosion resistance) even if the thickness of the coating film formed on the surface thereof is relatively thin, 0.1 to 10 μm. Demonstrate.

  In addition, as a method for applying the conductive paint to the surface of the aluminum plate as the base material, for example, the conductive paint is continuously applied to both surfaces of the aluminum plate drawn out from the aluminum plate coil by a roll coating method or the like. Then, after heating at a temperature equal to or higher than the softening temperature of the modified polyolefin resin contained in the conductive coating, volatilizing the organic solvent sufficiently, cooling, and rewinding into a coil shape, It is possible to continuously process a series of processes from the application of the conductive paint to the formation of the coating film, and it is possible to produce the aluminum plate for a fuel cell of the present invention at a lower cost.

  The coil-shaped aluminum plate for a fuel cell thus obtained is cut into a desired separator size, and the cut product is subjected to a pressing process or the like by a press molding machine. A separator having a groove or a flange serving as a gas flow path is obtained. Thus, when producing a separator using the aluminum plate for fuel cells of the present invention, there is no need for the advanced cutting work, etc. that were required when producing a separator using a conventional carbon material. In addition, a fuel cell separator having excellent corrosion resistance and low electrical resistance can be manufactured at an extremely low cost.

  Further, among the aluminum plates for a fuel cell according to the present invention, a relatively thick one (thickness: about 1.5 mm) is subjected to pressing or the like, thereby comprising a plurality of unit cells and a plurality of separators. An end plate is advantageously manufactured that clamps the fuel cell stack from both sides.

  Hereinafter, a separator and an end plate obtained using an aluminum plate for a fuel cell according to the present invention, and a polymer electrolyte fuel cell including them will be described with reference to the drawings.

  First, FIG. 1 is a perspective view showing an example of a separator manufactured by subjecting an aluminum plate for a fuel cell according to the present invention to a predetermined pressing process. The separator 10 shown there has a concavo-convex shape formed by press working, and has a plurality of groove portions 12 on both sides of the concavo-convex shape. Although not shown in FIG. 1, the separator 10 is a coating film made of a mixture of a conductive material and a polyolefin resin modified with α, β-ethylenically unsaturated carboxylic acid on both surfaces of the aluminum substrate (30). (28) is formed with a relatively thin thickness (0.1 to 10 μm).

  2 and 3 show a polymer electrolyte fuel cell stack 14 using the separator 10 shown in FIG. 1, and FIG. 2 is a front view thereof. 3 is a partial cross-sectional view in the vertical direction. As is clear from FIGS. 2 and 3, the polymer electrolyte fuel cell stack 14 includes a plurality of (seven) unit cells 18 via two separators 10 (10a, 10b). Laminated and configured. It is apparent from FIGS. 1 and 2 that the separators 10a and 10b have the same shape.

  Further, in FIG. 4, as an example of actually using the polymer electrolyte fuel cell stack 14 shown in FIGS. 2 and 3, the polymer electrolyte fuel cell stack 14 includes four legs 17. A state of being accommodated in a fuel cell accommodating case 16 having one (not shown) is shown. Therein, the polymer electrolyte fuel cell stack 14 having a laminated structure is sandwiched from both sides by end plates 20a and 20b manufactured using the aluminum plate for fuel cells of the present invention. They are held in the fuel cell housing case 16 while being pressed toward the opposite end plates 20b, 20a by the pressurizing mechanisms (bolts) 21 provided on 20a, 20b, respectively.

  More specifically, the structure of the polymer electrolyte fuel cell stack 14 will be described. As is apparent from FIGS. 2 and 3, the unit cells 18 constituting the fuel cell stack 14 together with the separators 10 (10a, 10b) The solid polymer electrolyte 22, the fuel electrode 24, and the air electrode 26, the fuel electrode 24 is disposed on one side surface of the solid polymer electrolyte 22, and the air electrode 26 is disposed on the other side surface. ing. Here, although not shown, the fuel electrode 24 and the air electrode 26 have a catalyst layer on the side surface in contact with the solid polymer electrolyte 22 and the side in contact with the separator 10 (10a, 10b). A gas diffusion layer is provided on each side surface.

  Further, as shown in FIG. 3, separators 10 a and 10 b made of an aluminum base material 30 whose surface is covered with a coating film 28 are opposed to the groove portions 12 on both sides of the unit battery 18. With such a separator arrangement, a hydrogen-containing gas (fuel gas) flow path 32 is provided between the fuel electrode 24 and the separator 10a on the fuel electrode 24 side of the unit cell 18. On the other hand, on the air electrode 26 side of the unit cell 18, oxygen-containing gas (air) flow paths 34 are advantageously formed between the air electrode 26 and the separator 10b.

  The polymer electrolyte fuel cell stack 14 having the above-described structure is held in the housing case 16 as shown in FIG. 4 or the polymer electrolyte fuel cell stack 14 is left as it is. In a stationary fuel cell system equipped with a fuel gas supply device, an air supply device, and other various devices, an in-vehicle fuel cell system, and the like. In these fuel cell systems, fuel gas is supplied to the hydrogen-containing gas flow path 32 and air is supplied to the oxygen-containing gas flow path 34 in the fuel cell stack 14, whereby each unit cell 18. In FIG. 1, an electromotive force is generated by an electrochemical reaction, and each unit cell 18 is electrically connected in series via a conductive separator 10, so that a solid polymer fuel is used. The desired voltage and power can be obtained as the entire battery stack 14.

  In the separator 10 (10a, 10b) constituting the solid polymer fuel cell stack 14, the thickness of the coating film 28 covering the surface of the separator 10 is a separator using a conventional metal substrate. In comparison with the thickness of the coating film, the oxide film on the surface of the aluminum base 30 is removed in advance before the coating film 28 is formed. In the fuel cell stack 14 using the separator 10 (10a, 10b), the electrical resistance (contact resistance) in the separator 10 (10a, 10b) is remarkably low, and as a result, the power generation efficiency is very excellent. ing. Therefore, by using the separator 10 (10a, 10b) according to the present invention, the solid polymer fuel cell stack 14 can be advantageously downsized.

  Further, since the separator 10 (10a, 10b) and the end plates 20a, 20b are made of light aluminum, the polymer electrolyte fuel cell stack 14 using them is conventionally known. Compared to the solid polymer fuel cell, it is lightweight.

  Therefore, the separator and the end plate according to the present invention can be used extremely advantageously in an in-vehicle fuel cell in which miniaturization and weight reduction of the entire fuel cell are particularly required.

  Some examples of the present invention will be shown below to clarify the present invention more specifically. However, the present invention is not limited by the description of such examples. Needless to say. In addition to the following examples, the present invention includes various changes and modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention, in addition to the specific description described above. It should be understood that improvements and the like can be added.

  While preparing three types (A1050-H24, A3104-H24, A5052-H32) of aluminum alloy plates having a thickness of 3 mm, maleic anhydride-modified polypropylene was prepared as follows.

  Specifically, with respect to 100 parts by weight of polypropylene (MFR: 10 g / 10 min, 230 ° C.), 15 parts by weight of maleic anhydride and 400 parts by weight of xylene were added and heated to 130 ° C., respectively. While stirring in a nitrogen gas atmosphere, a 1% xylene solution of benzoyl peroxide was added dropwise over 2 hours. After the dropping, the solution was further stirred for 60 minutes while being kept at 130 ° C., and then allowed to cool to room temperature. The suspension thus obtained was filtered, and the filtrate was washed with methyl ethyl ketone to obtain polypropylene modified with maleic anhydride.

By blending various conductive materials listed below into the maleic anhydride-modified polypropylene thus obtained, and mixing and dispersing uniformly, four types of conductive paints (conductive paints 1 to 4) were obtained. Prepared. In this preparation, maleic anhydride-modified polypropylene was used in a state of being dispersed in toluene.
<Conductive paint 1>
100 parts by weight of carbon black (manufactured by Mitsubishi Chemical Corporation, # 980, average particle size: 16 nm) was blended with 100 parts by weight of maleic anhydride-modified polypropylene, mixed, and dispersed uniformly.
<Conductive paint 2>
20 parts by weight of graphite powder (ASP, average size: 0.5 μm, scaly) made by 100 parts by weight of maleic anhydride-modified polypropylene, carbon black (Mitsubishi Chemical Corporation, # 8030 parts by weight of 3030B and average particle size: 55 nm) were mixed, mixed, and uniformly dispersed.
<Conductive paint 3>
70 parts by weight of carbon black (manufactured by Ketjen Black International Co., Ltd., Ketjen Black EC600JD, average particle size: 34 nm), 100% by weight of maleic anhydride-modified polypropylene, vapor grown carbon fiber (Showa Denko Co., Ltd.) 20 parts by weight of VGCF manufactured by company, average diameter: 150 nm, average length: 10 to 20 μm, fibrous) were mixed, mixed and uniformly dispersed.
<Conductive paint 4>
100 parts by weight of maleic anhydride-modified polypropylene, 100 parts by weight of carbon black (manufactured by Mitsubishi Chemical Corporation), # 980, average particle size: 16 nm, gold-coated Ni powder (manufactured by Nikko Rica Corporation, 8087- 10 parts by weight (10A, average particle diameter: 5 μm) were mixed, mixed and uniformly dispersed.

The previously prepared aluminum alloy plate was first cleaned by any one of the following cleaning methods, and after such cleaning, a conductive paint was applied to the surface of the aluminum alloy plate by a bar coating method. The number of bars was appropriately selected so that the film thickness after drying would be a predetermined value. The aluminum alloy plate coated with the conductive paint was heated in an electric furnace at 180 ° C. for 1 minute, then taken out of the electric furnace and allowed to cool. After the cooling, the same operation was repeated on the surface opposite to the surface on which the conductive paint was previously applied. Thirty kinds of conductive coating films formed on the surface by performing such operations while appropriately changing the type of aluminum alloy plate, the cleaning method thereof, the type of conductive paint, and the thickness of the coating film to be formed. Of pre-coated aluminum alloy plates (Samples 1 to 30). Table 1 below shows the aluminum alloy plate used for producing each pre-coated aluminum alloy plate, the cleaning method and the type of conductive paint, and the thickness of the formed coating film.
<Cleaning method 1 of aluminum alloy plate>
The aluminum alloy plate was immersed in 1% by mass sulfuric acid at 65 ° C. for 30 seconds, then washed with water and dried.
<Washing method 2 of aluminum alloy plate>
The aluminum alloy plate was immersed in a 10% aqueous sodium hydroxide solution at 60 ° C. for 20 seconds, washed with water, and further immersed in 10% nitric acid at room temperature for 15 seconds. Thereafter, it was washed with water and dried.
<Washing method 3 of aluminum alloy plate>
Normal hexane (30 ° C.) was placed in an ultrasonic cleaning device, and after immersing the aluminum alloy plate in it for 3 minutes, the aluminum alloy plate was taken out of the device, wiped with clean normal hexane, and then dried. .

  And about 30 types of obtained precoat aluminum alloy plates, according to the following method, contact resistance was measured and the evaluation by an acid-proof and alkali-proof test was performed.

<Measurement of contact resistance>
A sample for measurement having a size of 10 cm square was cut out from the pre-coated aluminum alloy plate, and as shown in FIG. 5, the measurement sample was a platinum plate having a thickness of 0.5 mm and a thickness of 0.6 mm. The carbon plate (Showa Denko Co., Ltd., SG3) was sandwiched from above and below, and the resistance between both platinum plates was measured by the 4-terminal method. The pressing force (weight) of the measurement sample was 1 MPa. The measurement results are also shown in Table 1 below.

<Evaluation by acid / alkali resistance test>
A hard vinyl chloride ring (inner diameter: 30 mm, height: 30 mm) was brought into close contact with petrolatum on the coating of a precoated aluminum alloy plate cut out to a predetermined size, and the outer periphery of the ring was sufficiently sealed. . On the coating film surrounded by the ring, 5 mL of 2% sulfuric acid or 1% aqueous sodium hydroxide solution was dropped, covered with a glass plate, and held at 20 ° C. for 168 hours. After such holding, the ring was removed, and the part surrounded by the ring was washed with water and left in the room for 1 hour. And the corrosion condition of the precoat aluminum alloy plate was evaluated visually. The evaluation results are also shown in Table 1 below.

  As is clear from the results in Table 1, the precoated aluminum alloy plates (samples 17, 22, 24, and 30) on which a thick coating film exceeding 10 μm was formed were found to have high contact resistance, It was recognized that acid resistance and / or alkali resistance was not sufficient in the case where a thin coating film of less than 0.1 μm was formed (Samples 23 and 29). Moreover, even if it is the precoat aluminum alloy plate by which the thickness of the formed coating film was made into the range of 0.1-10 micrometers, what used the aluminum alloy plate wash | cleaned according to the washing | cleaning method 3, ie, normal hexane In the pre-coated aluminum alloy plates (samples 18 to 21 and 25 to 28) obtained by using the aluminum alloy plates washed in the above, it was confirmed that they had high contact resistance. It is presumed that the oxide film on the surface of the aluminum alloy plate could not be sufficiently removed by cleaning.

  On the other hand, as in the present invention, the surface of the aluminum alloy plate from which the oxide film has been removed by previously cleaning the surface with an acid or alkaline aqueous solution is used, and the surface of the aluminum alloy plate from which the oxide film has been removed is used. In the pre-coated aluminum alloy plate (samples 1 to 16) formed with a conductive coating having a thickness of 0.1 to 10 μm, the contact resistance is low, and excellent acid resistance and alkali resistance are exhibited. That was confirmed.

It is a perspective explanatory view showing an example of a separator of a fuel cell according to the present invention. It is front explanatory drawing which shows an example of the polymer electrolyte fuel cell stack using the separator shown by FIG. FIG. 3 is a partial cross-sectional explanatory view in the vertical direction of the polymer electrolyte fuel cell stack shown in FIG. 2. FIG. 3 is a partially cutaway explanatory view showing a state in which the polymer electrolyte fuel cell stack shown in FIG. 2 is held in a fuel cell housing case. It is explanatory drawing which showed roughly the method of measuring the contact resistance of the precoat aluminum alloy plate performed in the present Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 10a, 10b Separator 12 Groove part 14 Solid polymer fuel cell stack 16 Fuel-electron storage case 17 Leg part 18 Unit cell 20a, 20b End plate 21 Pressurization mechanism 22 Solid polymer electrolyte 24 Fuel electrode 26 Air electrode 28 Coating film 30 Aluminum substrate 32 Hydrogen-containing gas flow path 34 Oxygen-containing gas flow path

Claims (7)

Removal treatment of the oxide film is formed by applied include the surface of the aluminum plate having a thickness of 0.1 to 2.0 mm, a conductive material, alpha, and a polyolefin resin modified with β- ethylenically unsaturated carboxylic acid A fuel cell separator or an end plate aluminum plate excellent in acid resistance and alkali resistance , wherein a coating film made of a mixture is formed with a thickness of 0.1 to 10 μm. The conductive material is selected from activated carbon, graphite, carbon black, vapor grown carbon fiber, gold particles, cobalt particles, nickel particles plated with gold or platinum, graphite or stainless steel particles or a aluminum plate according to claim 1, characterized in that two or more. The modified polyolefin resin is, A aluminum plate according to claim 1 or claim 2 characterized in that it is a polypropylene modified by maleic anhydride.   A fuel cell separator obtained by using the aluminum plate according to any one of claims 1 to 3.   An end plate of a fuel cell obtained by using the aluminum plate according to any one of claims 1 to 3.   A fuel cell comprising the separator according to claim 4. A fuel cell comprising the end plate according to claim 5.

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