JP2005216678A - Separator for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a fuel cell in which deterioration of battery performance caused by closure of the passage by water drop or water is suppressed and prevented, and a problem concerning durability can be eliminated. <P>SOLUTION: A plate body 1 is compression molded by a mixed forming material containing powder phenol resin, graphite, and a fluorine based compound. The average particle sizes of powder phenol resin and graphite are respectively made within 5-100 μm, and the contact angles of the both side surfaces of the plate body 1 and water are respectively set within 80°-120°. Since the contact angles of the both sides surfaces of the plate body 1 and water are in the range of 80°-120°, even if generation quantity of water drop increases, the water drop does not close the recessed part 4 that is the passage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polymer electrolyte fuel cell separator having a current collecting function, gas supply function, and drainage function from an electrode of a fuel cell.

Although not shown, the fuel cell separator is required to have high conductivity in order to collect current from the electrode of the fuel cell, and in addition to this, gas impermeability, corrosion resistance, and mechanical strength are required. The fuel cell separator is formed with a recess that is a flow path through which gas, cooling water, and reaction product water supplied to the electrodes are circulated, thereby improving the discharge performance (Patent Documents 1, 2, and 3). 4).
Japanese Patent Laid-Open No. 2003-077787 JP 2000-251903 A JP 2001-093539 A JP 11-339827 A

The conventional fuel cell separator is configured as described above. However, when the humidity becomes too high, water droplets are generated in the anode gas / cathode gas flow path due to condensation of water vapor. When the amount of generated water droplets increases, the water droplets block the flow path, and as a result, the gas does not reach the solid polymer membrane, resulting in a serious problem that the battery performance is degraded.
In particular, on the cathode side, reaction product water is generated by the cell reaction, and thus clogging of water droplets is likely to occur. For this reason, even if dew condensation occurs, various efforts are made to give the flow path a characteristic that allows quick drainage.

  In this regard, the above-described prior art document discloses a technique for hydrophilic treatment of the inner surface of the flow path, and according to this technique, water generated by condensation easily spreads on the flow path surface. Can be eliminated. Also disclosed is a method in which a water repellent treatment is performed with a silane coupling agent so that the water accompanying the condensation is made into a spherical shape that is easy to roll, and this water is drained using a gas flow.

  However, in the case of the above prior art, there is a problem that the modified film cannot be sufficiently solved because there is a problem in terms of durability of the modified film.

  The present invention has been made in view of the above, and provides a fuel cell separator that can prevent water droplets or water from blocking a flow path and thereby reducing battery performance, and can solve a problem related to durability. It is intended to provide.

In the present invention, in order to solve the above-mentioned problem, the molded body is formed of a mixed molding material containing at least a powdered phenol resin and graphite,
The contact angle between the plate body and water is in the range of 80 ° to 120 °.
In addition, the average particle diameter of a powder phenol resin and graphite can be 5-100 micrometers, respectively, and specific gravity can be 1.9 g / cm < ³ > or more.

Further, the mixed molding material can be prepared with at least a self-curing powdery phenol / formaldehyde resin, scaly graphite, and a fluororesin, and a plurality of uneven portions can be provided side by side on at least one of both surfaces of the plate.
Furthermore, it is preferable that the contact angle between at least one of both surfaces of the plate body after polishing and water is in the range of 80 ° to 120 °.

  Here, the mixed molding material in the claims only needs to contain at least powdered phenol resin and graphite, and includes other materials such as fluororesin, various coupling agents, modifiers, and fillers. May be. The plate body can be appropriately formed into a square, a rectangle, a polygon or the like in plan view, and the size and thickness are not limited. This plate may be partially thin or thick. Moreover, a several uneven | corrugated | grooved part can also be continuously provided in the plate body surface which is an exposed surface, and a board body back surface, and can also be provided in a row continuously on both the plate body front and back surfaces, respectively.

  Advantageous Effects of Invention According to the present invention, there is an effect that it is possible to suppress or prevent a drop in battery performance due to water droplets or water closing a flow path. Moreover, the problem regarding durability can be effectively solved.

Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. A fuel cell separator in the present embodiment is molded into a plate 1 by a predetermined mixed molding material as shown in FIG. The specific gravity (density) of 9 g / cm ³ or more is set, and the contact angle between the front and back surfaces of the plate 1 that is the exposed surface and water is set in the range of 80 ° to 120 °. A fuel cell separator is formed by laminating a plurality of layers.

  The mixed molding material is blended at least with a powdered phenol resin, graphite, and a fluorine compound. This mixed molding material can be used as long as the characteristics of the fuel cell separator are not lost, such as calcium carbonate, talc, kaolin, diatomaceous earth, natural or synthetic silica, wollastonite, bentonite, zeolite, mica, aluminum hydroxide, titanium oxide, Carbon type such as fillers such as glass beads, glass balloon, activated carbon, charcoal, bamboo charcoal, glass fiber, aramid fiber, metal fiber, conductive oil furnace black, acetylene black, thermal black, PAN type carbon fiber, pitch type carbon fiber, etc. Conductive fillers, metal powders such as gold, silver, copper, palladium, aluminum, and stainless steel are appropriately added. By adding these, it is possible to improve conductivity support and density, supplement gas impermeability, and adjust the contact angle.

  For powdered phenolic resin and graphite, self-curing powdery phenol / formaldehyde resin and scaly graphite are selected because the contact angle between the front and back surfaces of the plate 1 and water is set in the range of 80 ° to 120 °. And mixed in any way. The mixing method is not particularly limited, but from the viewpoint of preventing the pulverization of graphite, there is a dry mixing method using a tumbler mixer, a V blender, a nauter mixer, etc. so that a large shearing force does not act on the graphite. preferable. The reason why the pulverization of graphite is prevented is that the resistance value of the fuel cell separator increases with the pulverization, and the mechanical strength tends to decrease rapidly.

  The mixed powder obtained by mixing can be used as a mixed molding material as it is. However, in order to improve the mixing property and workability at the time of molding, it is added under conditions of normal temperature to 80 ° C. and 0.1 to 15 MPa. It is preferable that it is pressure-molded and formed into a sheet. The condition temperature of this preforming is 80 ° C. or lower. When the temperature exceeds 80 ° C., the reaction of the powdered phenol / formaldehyde resin proceeds and the resistance value of the fuel cell separator increases when the sheet is changed to the plate 1. This is because the mechanical strength sharply decreases.

  When the molding pressure is in the above range, it is difficult to form a sheet when the pressure is less than 0.1 MPa. Conversely, when the pressure exceeds 15 MPa, the powdery phenol / formaldehyde resin covers the scale-like graphite and is used for fuel cells. This is because the electrical characteristics of the separator are deteriorated.

  The powdered phenol resin is made of powdered phenol / formaldehyde resin as described above and functions as a base material. This powdery phenol / formaldehyde resin is produced, for example, by the production method described in Japanese Patent Publication No. 62-3021, and has a feature that it has fewer impurities than a resol type or novolac type phenol resin. In addition, the particle shape is spherical and has a high molecular weight, which makes it possible to increase the filling of graphite, and because the melting temperature during molding is high, the surface coating of graphite particles is small compared to other phenol resins, and the curing reaction It is ideal for manufacturing fuel cell separators.

  The powdered phenol resin is formed in a spherical shape having an average particle diameter of 5 to 100 μm. This is because when the average particle size is less than 5 μm, the powdery phenol / formaldehyde resin rises when mixed with graphite, and the working environment deteriorates. On the contrary, when the average particle size exceeds 100 μm, the mixing with the graphite becomes non-uniform, and there is a possibility that a concavo-convex pattern is formed on the fuel cell separator.

  The average molecular weight of the powdery phenol / formaldehyde resin is in the range of 3,000 to 20,000, preferably 4,000 to 15,000, more preferably 5,000 to 10,000. The average molecular weight is required to be 3,000 or more. When the average molecular weight is less than 3,000, it becomes difficult to achieve high packing with graphite, and as the melting temperature decreases, the surface coating of graphite particles increases, This is based on the reason that the characteristics deteriorate and the electrical characteristics of the fuel cell separator deteriorate.

  As described above, scaly graphite is selected as described above, but other types are appropriately used in combination. The reason why scale-like graphite is always selected is because it is scale-like at the time of molding, so that there is a high possibility that the graphites are connected to each other, and the resistance value that is a measure of conductivity is low. If spherical graphite is selected, the blending amount must be increased in order to connect the graphite to each other, and the physical properties of the molded product deteriorate when molded.

  The scale-like graphite has a mean particle size of 5 to 100 μm, preferably 10 to 70 μm. This is because when the average particle size is less than 5 μm, the working environment deteriorates when mixed with the powdery phenol / formaldehyde resin. Conversely, when the average particle size exceeds 100 μm, mixing with the powdered phenol / formaldehyde resin becomes non-uniform, which may lead to a decrease in mechanical characteristics of the fuel cell separator. Other types of graphite may have the same or different average particle diameter.

The bulk density of the flake graphite, but are not particularly limited, the range of 0.1g / cm ³ ~1.0g / cm ³ are preferred. This is because if the bulk density of the flaky graphite is too small, the uniform mixing property with the powdered phenol / formaldehyde resin is lowered, and the sealing characteristics of the fuel cell separator are lowered. Conversely, when the bulk density of the flake graphite is too large, the mechanical strength and conductivity of the fuel cell separator are lowered.

  In addition, aluminate coupling agents such as acetoalkoxy aluminum diisopyropyrate, titanate coupling agents such as isopropyl triisostearoyl titanate, bis (dioctyl borophosphate), oxyacetate, isopropyl tridecylbenzenesulfonyl titanate, γ-glycol Surface modifiers such as silane coupling agents composed of Sidoxypropylmethyldiethoxysilane, β- (3,4 epoxycyclohexyl) ethyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, and the like; Or acetylene alcohol, acetylene glycol, glycerin aliphatic ester, sorbitan ester, aliphatic polyglycerin aliphatic ester, propylene glycol aliphatic ester, higher alcohol fat Graphite surface-treated with various surface active agents such as esters may be used within a range which does not impair the characteristics of the fuel cell separator.

  The compounding of the powdery phenol / formaldehyde resin and the graphite is 900 to 2,000 parts by weight of graphite with respect to 100 parts by weight of the powdery phenol / formaldehyde resin, preferably 100 parts by weight of the powdery phenol / formaldehyde resin. The graphite is preferably 1,100 to 1,900 parts by mass, more preferably 1,200 to 1,700 parts by mass with respect to 100 parts by mass of the powdered phenol / formaldehyde resin.

  This is because, when the powdered phenol / formaldehyde resin is less than 900 parts by mass of graphite with respect to 100 parts by mass of the powder, the electrical characteristics of the fuel cell separator may be hindered or the contact angle may be reduced from the optimum range due to the decrease in density. Based on the reason for losing. On the contrary, when it exceeds 2000 parts by mass of graphite with respect to 100 parts by mass of the powdery phenol / formaldehyde resin, it is based on the reason that the mechanical characteristics of a practical fuel cell separator cannot be obtained.

  Fluorine compounds include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polychlorotrifluoroethylene, and the above Fluorosurfactants such as low molecular weight compounds, fluororubber, perfluoropolyether oil, perfluoroalkylcarboxylate, carbon fluoride, etc. are applicable, and the contact angle between the both surfaces of the plate after surface polishing and water is 80 It functions to maintain in the range of ° to 120 °.

  Since the fluorine compound particles are dispersed, finer particles are preferable. Specifically, the average particle diameter is 1 to 20 μm, more preferably 3 to 10 μm. In order to avoid deterioration of physical properties, the blending amount of the fluorine-based compound needs to be an amount that does not hinder the electrical conductivity and mechanical strength and also makes the contact angle as large as possible. Specifically, it is 1 to 30%, preferably 3 to 15%, based on the powdery phenol / formaldehyde resin.

  As shown in FIG. 1, the plate body 1 is formed into a planar rectangle or square having a rib area 2 that occupies most of the plate body 1 and a flat area 6 that surrounds the rib area 2 and serves as a grip portion during operation. Then, they are stacked on another plate (not shown) with the electrolyte membrane, fuel electrode, and air electrode interposed therebetween. The plate 1 which is this molded product is not particularly limited in its production method, but has the optimum orientation of the scale-like graphite powder which determines the cost, dimensional accuracy, electrical characteristics and mechanical characteristics of the molding machine. In consideration, compression molding is preferable.

  A plurality of concavo-convex portions 3 extending in the depth direction of FIG. 1 are continuously arranged on both surfaces of the rib region 2, and the plurality of concavo-convex portions 3 are arranged at different pitches on the front surface and the back surface of the plate body 1. The back surface convex portion 5 is positioned below the front surface concave portion 4, and the back surface concave portion 4 is positioned below the front surface convex portion 5. The plurality of concavo-convex portions 3 have conductivity and electrical conductivity, and function to form flow paths of gas, cooling water, and reaction product water as the plate bodies 1 are stacked. The concave portion 4 of the concave-convex portion 3 is formed with a flow hole (not shown) through which hydrogen gas, oxygen gas, and cooling water are circulated, and is partitioned into a pair of adjacent convex portions 5 to form a flow path.

  The flat region 6 is basically formed flat so that gas and water do not leak, and a plurality of communication holes 7 communicating with the flow holes of the recess 4 are formed in the thickness direction. The plate body 1 communicates with the communication hole 7 to form a long hole, and this long hole allows hydrogen gas, oxygen gas, and cooling water to flow therethrough. Through-holes for mounting and fixing are appropriately drilled in both sides of the flat region 6 and the four corners of the periphery, and bolts (not shown) are inserted into the through-holes.

The specific gravity of the fuel cell separator is not particularly limited, but the specific gravity of the rib region 2 and the flat region 6 is 1.9 g / cm ³ or more, preferably 1.95 g / cm ³ or more. This is because if the specific gravity is set to 1.9 g / cm ³ or more, sufficient airtightness can be secured, and gas impermeability and water repellent effect are increased.

  The contact angle between the front and back surfaces of the plate 1 and water is set in the range of 80 ° to 120 °, preferably in the range of 90 ° to 110 °. This is because when the contact angle is less than 80 °, there is a problem in water repellency between the convex portion 5 and water, so that water droplets or cooling water is likely to intervene in the concave portion 4, making it difficult to ensure a stable flow path. Because it becomes. As a method of securing the flow path, a method of forcibly removing water by increasing the gas pressure is conceivable. In this case, however, the gas sealability, mechanical strength, and the gas seal performance of the entire fuel cell are improved. Improvement is necessary, which is not preferable.

  Further, when the contact angle exceeds 120 °, the cost is increased, and it is difficult to manufacture a fuel cell separator.

  In the above, when producing a fuel cell separator having a contact angle with water in the range of 80 ° to 120 °, first, powdered phenol / formaldehyde resin, scaly graphite, and fluorine compound are mixed at a predetermined blending ratio. To prepare a mixed molding material, preform the mixed molding material under a predetermined condition to form a sheet, and set the intermediate sheet in a preheated mold for compression molding . Thus, if the plate body 1 is compression-molded, and the uneven portion 3 of the plate body 1 taken out is appropriately processed as necessary, a fuel cell separator having a contact angle with water in the range of 80 ° to 120 ° is manufactured. Can do.

  Then, if the manufactured separators for multiple fuel cells are stacked with the electrolyte membrane, fuel electrode, and air electrode overlapped, and these are firmly fixed with bolts, etc., battery characteristics, moldability, drainage, drainage durability A fuel cell excellent in gas impermeability, electrical characteristics, and mechanical characteristics can be obtained.

  According to the above configuration, since the contact angle between the front and back surfaces of the plate body 1 including the concavo-convex portion 3 and water is in the range of 80 ° to 120 °, even if the amount of generated water droplets increases, the water droplets are flow paths. The recess 4 is not blocked. Therefore, it is possible to effectively solve the problem that the gas does not reach the solid polymer film and the battery performance is deteriorated.

Moreover, since it mixes and shape | molds powdered phenol resin, graphite, and a fluorine-type compound, durability can be improved. Further, since the specific gravity of the fuel cell separator is set to 1.9 g / cm ³ or more and the fluorine-based compound is added, the contact angle is increased, and an improvement in the water repellency effect can be expected. Furthermore, the contact angle between the both surfaces of the plate and the water after the surface polishing can be maintained in the range of 80 ° to 120 ° by adding the fluorine-based compound.

Next, FIG. 2 shows another embodiment of the present invention. In this case, a plurality of concavo-convex portions 3 are arranged at the same pitch on the front surface and the back surface of the plate 1, and the concave portions 4 on the front surface are arranged. The back surface concave portion 4 is positioned below the front surface, and the back surface convex portion 5 is positioned below the front surface convex portion 5. The other parts are the same as those in the above embodiment, and the description thereof is omitted.
In the present embodiment, it is obvious that the same effects as those of the above embodiment can be expected, and the pattern of the uneven portion 3 can be diversified.

  Examples of the fuel cell separator according to the present invention will be described below together with comparative examples.

Example 1
First, flaky graphite having an average molecular weight of 10,000 and an average particle size of 20 μm, phenol / formaldehyde resin (manufactured by Kanebo Co., Ltd .: trade name Belpearl S890), 100 parts by mass, an average particle size of 50 μm, and a bulk specific gravity of 0.3 g / cm ^3. [Made by Chuetsu Graphite Industry Co., Ltd .: trade name HG-50A] 1,500 parts by mass, fluorine resin [Daikin Kogyo Co., Ltd .: trade name Lubron L-5] 10 parts by weight are dry blended for 30 minutes with a tumbler mixer, A mixed molding material was prepared.

  Next, the mixed molding material was preformed under the conditions of a molding temperature of 30 ° C., a molding pressure of 0.15 MPa, and a pressurization time of 10 sec, thereby molding an intermediate product composed of a flat sheet. After the intermediate product is molded in this way, it is inserted into a mold heated to a temperature of 180 ° C., and molded under conditions of a molding pressure of 7 MPa and a heating and pressing time of 20 minutes to obtain a fuel cell separator shown in FIG. It was.

Example 2
First, 100 parts by mass of phenol / formaldehyde resin having an average particle size of 20 μm (manufactured by Kanebo Co., Ltd .: trade name Belpearl S99W), an average particle size of 50 μm and a bulk specific gravity of 0.3 g / cm ³ (Product name: HG-50A) 1,500 parts by mass was dry blended with a tumbler mixer for 30 minutes to prepare a mixed molding material.

  Next, the mixed molding material is preformed in the same manner as in Example 1 to form an intermediate product made of a flat sheet, and this intermediate product is finally molded in the same manner as in Example 1 to produce the fuel cell shown in FIG. A separator was obtained.

Comparative Example 100 parts by mass of phenol-formaldehyde resin similar to Example 2 and 250 parts by mass of flaky graphite were dry blended for 30 minutes with a tumbler mixer to prepare a mixed molding material. The fuel cell separator shown in FIG. 1 was obtained by molding by transfer molding under the conditions of ℃ and material temperature of 180 ℃.

Measurement of contact angle The contact angles with water before and after polishing of the fuel cell separators obtained in Examples 1 and 2 and Comparative Example were measured. Specifically, it measured using ion-exchange water and a contact angle measuring device [Kyowa Interface Science Co., Ltd. make: brand name CA-X type], and summarized in Table 1.

Since the fuel cell separators of Examples 1 and 2 have a contact angle with water in the range of 80 ° to 120 °, the release property is good, and even if the surface is polished, there is little change in the contact angle and the durability is excellent. The effect was obtained.
In contrast, the fuel cell separator of the comparative example has a large contact angle with water due to the release agent, but the contact angle changes greatly due to surface polishing, so drainage and cooling properties are used for a long time. There is a risk that the output will be reduced.

It is explanatory drawing which shows embodiment of the separator for fuel cells which concerns on this invention. It is explanatory drawing which shows other embodiment of the separator for fuel cells which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plate body 2 Rib area | region 3 Uneven part 4 Concave part 5 Convex part 6 Flat area

Claims (4)

A fuel cell separator formed into a plate body by a mixed molding material containing at least a powdered phenol resin and graphite,
A separator for a fuel cell, wherein the contact angle of the plate with water is in the range of 80 ° to 120 °. 2. The fuel cell separator according to claim 1, wherein the average particle diameter of the powdered phenol resin and graphite is 5 to 100 μm, and the specific gravity is 1.9 g / cm ³ or more.   3. The mixed molding material is prepared from at least a self-curing powdery phenol / formaldehyde resin, scaly graphite, and a fluororesin, and a plurality of concave and convex portions are provided side by side on at least one of both surfaces of the plate. The fuel cell separator as described.   The fuel cell separator according to claim 3, wherein a contact angle between at least one of both surfaces of the plate body after polishing and water is in the range of 80 ° to 120 °.

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