JP2006164770A - Separator for fuel cell, and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a fuel cell sufficiently low in contact resistance and excellent in resistance to corrosion. <P>SOLUTION: A separator for a fuel cell is made of a resin and a conductive resin composition including a carbon material containing expanded graphite and an exposure area of the carbon material on a barrier rib upper face is 10 to 90% to a whole surface area of the upper face. The resin is a phenol resin or an epoxy resin, and the carbon material is exposed so that the upper face becomes an area ratio of 10 to 90% to the whole surface area of the upper face by at least one of blast process mechanical polishing processing, heating processing, plasma processing, and oxidant processing after forming the composition in a separator shape. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell separator and a method for manufacturing the same, and more particularly to a technique for reducing contact resistance.

  For example, as shown in a schematic perspective view in FIG. 1, the fuel cell separator 10 is formed by standing a plurality of partition walls 12 at predetermined intervals on both surfaces of a flat plate portion 11. In order to obtain a fuel cell, a large number of fuel cell separators 10 are stacked in the protruding direction of the partition wall 12 (vertical direction in the figure). And by this lamination | stacking, it has the structure which distribute | circulates reaction gas (hydrogen and oxygen) to the channel 13 formed of a pair of adjacent partition 12.

  The fuel cell separator is manufactured by molding a resin material and a conductive resin composition containing a conductive material such as graphite into the shape described above. As a molding method, a molding material containing a thermosetting resin such as a phenol resin or an epoxy resin and a conductive material is placed in a mold provided with irregularities corresponding to the partition wall 13, and this is hot pressed. It is common to use compression molding.

  In general, a fuel cell employs a structure called a fuel cell stack in which a plurality of fuel cell separators and a plurality of electrode membrane assemblies (MEAs) are stacked. At that time, the upper surface of the partition wall is used in contact with the partition wall of another fuel cell separator or the MEA diffusion layer, and current flows between the fuel cell separators or between the fuel cell separator and the MEA. Therefore, when the contact resistance between the fuel cell separators or between the fuel cell separator and the MEA is high, the power generated by the power generation is wasted due to this contact resistance, so the power generation efficiency of the fuel cell stack is low. Become.

  Therefore, in order to reduce the contact resistance, for example, it has been proposed to reduce the contact resistance by setting the surface roughness of the surface in contact with the electrode portion within a specific range (see Patent Document 1). However, when the present inventors made a further test, no correlation was observed between the surface roughness and the contact resistance, and a fuel cell separator having a low contact resistance could not be obtained. Moreover, since it processes with an acid, there also exists a problem of a wastewater treatment problem or corrosion of a manufacturing facility.

  Further, an attempt has been made to coat a conductive film made of a material having a specific resistance value smaller than the specific resistance value of the main body (see Patent Document 2). However, in order to form a conductive film, it is difficult to coat a bond carbon compound such as conductive graphite paste, gold paste, or silver paste with a uniform thickness, and a fuel cell that requires high thickness accuracy. It is an unsuitable treatment method for separators. In addition, gold paste and silver paste are expensive materials, and silver paste also has a problem of further corrosion. The conductive graphite paste is composed of a graphite material and a binder. However, in order to reduce the specific resistance value, it is necessary to increase the amount of graphite, and the fluidity of the paste is lowered, and the coating cannot be performed.

Japanese Patent Laid-Open No. 11-297338 JP 2001-196076 A

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a fuel cell separator having sufficiently low contact resistance and excellent corrosion resistance at low cost.

As a result of intensive studies, the present inventors have greatly improved conductivity by removing the resin as the insulating material and exposing the carbon material on the surface of the partition wall of the fuel cell separator containing the resin and the carbon material. As a result, the present invention has been completed. That is, the present invention provides the following fuel cell separator and method for producing the same.
(1) It consists of a conductive resin composition containing a resin and a carbon material containing expanded graphite, and the exposed area of the carbon material on the upper surface of the partition wall is 10 to 90% with respect to the total surface area of the upper surface of the partition wall. A fuel cell separator.
(2) The fuel cell separator as described in (1) above, wherein 5 to 100% by mass of the carbon material is expanded graphite.
(3) The fuel cell separator as described in (1) or (2) above, wherein the weight ratio of the resin to the carbon material is 20:80 to 60:40.
(4) The fuel cell separator according to any one of (1) to (3), wherein the resin is a thermosetting resin.
(5) The fuel cell separator as described in (4) above, wherein the resin is a phenol resin or an epoxy resin.
(6) After molding a conductive resin composition containing a resin and a carbon material containing expanded graphite into a separator shape, the upper surface of the partition wall is subjected to blasting, mechanical grinding, heating, plasma treatment and oxidant treatment. A method for producing a fuel cell separator, wherein the carbon material is exposed so as to have an area ratio of 10 to 90% of the total surface area of the upper surface of the partition wall by at least one of the above.
(7) The method for producing a fuel cell separator as described in (6) above, wherein a dry blast treatment is performed.
(8) The method for producing a fuel cell separator as described in (6) or (7) above, wherein the particles used for the blast treatment are No. 20 to 3000 (1000 to 5 μm) defined by JIS R6001.
(9) Any one of the above (6) to (8), wherein the particles used for the blast treatment are at least one selected from metal particles, ceramic particles, glass beads, resin particles, and plant particles. The manufacturing method of the separator for fuel cells as described in a term.
(10) The method for producing a fuel cell separator as described in any one of (6) to (9) above, wherein the particles used for the blast treatment are particles having a 10-step Mohs hardness of 6 to 9.

  In the separator for a fuel cell of the present invention, the conductivity is greatly improved by removing the resin as the insulating material on the partition wall surface and exposing the carbon material at a specific area ratio. In addition, an expensive conductive paste is unnecessary, there is no problem of corrosion, and a sufficient effect can be obtained by a simple processing method, so that it is inexpensive.

  Hereinafter, the present invention will be described in detail.

  The fuel cell separator of the present invention comprises a conductive resin composition containing a resin and a carbon material containing expanded graphite.

  Normal scale-like graphite is a laminate of thin plate crystals. In contrast, expanded graphite was treated with concentrated sulfuric acid, nitric acid, hydrogen peroxide, etc., intercalated with these chemicals in the gaps between the thin plate crystals, and further heated to intercalate. When the chemical solution is vaporized, the gap between the thin plate crystals is widened. Compared with the flaky graphite or the spherical graphite, the bulk density is low, the surface area is large, and the particles are in a thin plate shape. For this reason, when mixed with resin, a conductive path can be easily formed, and a highly conductive fuel cell separator can be obtained. In addition, since expanded graphite has a thin plate shape, it is more flexible than artificial graphite and natural graphite, and a fuel cell separator using the expanded graphite is also flexible. Furthermore, since expanded graphite is oriented in the direction along the surface near the surface of the compact by using expanded graphite, the area ratio of the carbon material exposed on the surface should be increased using the method described later. Is possible. This will be described in detail later.

  For these reasons, expanded carbon is included as a carbon material in the present invention. All of the carbon material may be expanded graphite, some are expanded graphite, and the others are flaky artificial graphite, spherical artificial graphite, natural scaly graphite, carbon black, carbon fiber, carbon nanofiber, carbon nanotube, Diamond-like carbon, fullerene, carbon nanohorn or the like can be used. The proportion of expanded graphite in the carbon material is preferably 5 to 100% by mass, more preferably 20 to 80% by mass, still more preferably 30 to 70% by mass, and particularly preferably 40 to 60% by mass. When the ratio of expanded graphite is low, the contact resistance is high. In addition, since expanded graphite has a low bulk density, when the ratio of expanded graphite is high, material handling properties during kneading for compound production are poor, and there is a concern that the working environment may be contaminated.

  The resin used in the present invention is a thermosetting resin such as phenol resin, epoxy resin, diallyl phthalate resin, unsaturated polyester resin, polyimide resin, silicone resin, polyurethane resin, urea resin, melamine resin, diallyl phthalate resin; low density Polyethylene, polyethylene such as medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, chlorinated polyethylene, polyethylene terephthalate, polybutylene terephthalate, polycyclohexylene dimethylene terephthalate, liquid crystalline polyester, polyhydroxybutyrate, polycaprolactone, polyethylene adipate, Polyesters such as polylactic acid, polybutylene succinate, polybutyl adipate, polyethylene succinate, polyether ether Luketone, polytetrafluoroethylene (tetrafluoroethylene resin), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (tetrafluoroethylene / perfluoroalkoxyethylene copolymer resin), tetrafluoroethylene-hexafluoropropylene copolymer (Tetrafluoroethylene / hexafluoropropylene copolymer resin), tetrafluoroethylene-ethylene copolymer (tetrafluoroethylene / ethylene copolymer resin), polyvinylidene fluoride (vinylidene fluoride resin), polychlorotrifluoro Fluorine resins such as ethylene (ethylene trifluoride chloride resin), chlorotrifluoroethylene-ethylene copolymer (ethylene trifluoride chloride / ethylene copolymer resin), polyvinyl fluoride (vinyl fluoride resin), nylon 6, nylon 66, Iron 46, semi-aromatic nylon 6T, nylon MXD, nylon 610, nylon 612, nylon 11, nylon 12 and other polyamides, atactic polypropylene, isotactic polypropylene, syndiotactic polypropylene, polypropylene such as ethylene-propylene copolymer, Polyacetal, polyphthalamide, polyamideimide, polyetherimide, thermoplastic polyimide, polyethersulfone, atactic polystyrene, isotactic polystyrene, syndiotactic polystyrene, polyphenylene sulfide, polyphenylene ether, polyether nitrile, polyethylene oxide, Polypropylene oxide, ionomer, syndiotactic-1,2-polybutadiene, trans-1,4 Polyisoprene, polymethylpentene, polyketone, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, polyhydroxybutyrate, polyvinyl alcohol, acrylic resin, polycarbonate, Examples of the thermoplastic resin include, but are not limited to, polyethersulfone, polysulfone, polyarylate, polyvinyl acetate, polyacrylonitrile, and polyvinyl chloride. These can also be mixed and used. In particular, a thermosetting resin, particularly a phenol resin or an epoxy resin, is preferable because a fuel cell separator having high heat resistance and high strength can be obtained and, as will be described later, the contact resistance is low.

  Examples of the phenol resin include conventionally known resol type phenol resins and novolac type phenol resins, but are not limited thereto, and any phenol resin may be used. It is also possible to use a curing agent such as hexamethylenetetramine.

  As epoxy resins, bisphenol type epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins; phenol novolac type epoxy resins, cresol novolac type epoxy resins, glycidylamine type epoxy resins, biphenyl type epoxy resins are conventionally known. Examples thereof include, but are not limited to, polyfunctional epoxy resins such as resins.

  An epoxy resin produces | generates an epoxy hardened | cured material by reacting with a hardening | curing agent. Various known compounds can also be used as the curing agent. For example, aliphatic, cycloaliphatic, aromatic polyamines or carbonates thereof such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, mensendiamine, isophoronediamine, N-aminoethylpiperazine, m-xylenediamine, diaminodiphenylmethane; Phthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyl nadic anhydride, dodecyl succinic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, trimellitic anhydride, polyazeline acid anhydride, etc. Acid anhydrides; polyphenols such as phenol novolac and cresol novolac; polymercaptan; anion polymerization catalyst such as tris (dimethylaminomethyl) phenol, imidazole, ethylmethylimidazole; Cationic polymerization catalysts such as 3 and complexes thereof; more like latent curing agent that produces the compound by thermal decomposition or photolysis, but not limited thereto. A plurality of curing agents can be used in combination. Among the above, curing agents such as polyamines, carbonates thereof, acid anhydrides, polyphenols, and polymercaptans are called polyaddition type curing agents because they themselves form an epoxy cured product by a polyaddition reaction with an epoxy compound. Since excess and deficiency of the polyaddition type curing agent leads to remaining unreacted functional groups, there is an appropriate range for the amount of addition. In general, it is preferred to use 0.7 to 1.2 equivalents, particularly 0.8 to 1.1 equivalents of a polyaddition type curing agent per epoxy group of the epoxy resin precursor. On the other hand, an anionic polymerization catalyst and a cationic polymerization catalyst act as an addition polymerization catalyst for an epoxy group. Therefore, there is no appropriate addition region, and the addition amount can be determined according to the reaction rate. These catalysts are called catalyst-type curing agents or addition-type curing agents. Further, when these catalysts are used in combination with a polyaddition type curing agent, the catalyst is also called a curing accelerator because it accelerates the curing reaction by the polymerization addition type curing agent.

  As described above, in the present invention, the amount of the thermosetting resin is equal to the total weight of the thermosetting resin, the curing agent, and the curing accelerator. The curing rate of the thermosetting resin can be arbitrarily changed by variously selecting the type and amount of the curing agent, the type of the thermosetting resin, the type and the amount of the curing accelerator. Those skilled in the art will be able to easily determine the type and amount of thermosetting resin, curing agent and curing accelerator according to the desired curing conditions.

  In the present invention, the ratio of resin to carbon material is preferably 20:80 to 60:40 by weight. If the resin ratio is too high, the conductivity will decrease. On the other hand, if the ratio of the carbon material is too high, the strength will be low, and the fluidity of the compound will be low, so that the pressure distribution of the molding material will increase in the mold once injected into the mold, and the molding will This is a problem because the dimensional accuracy of the fuel cell separator deteriorates.

  In the present invention, a lubricant such as carnauba wax can be added to prevent sticking to a mold or a kneader during molding. As the lubricant, stearic acid, montanic acid wax, and metal salts thereof can be used. In addition, an inorganic filler such as glass fiber, silica, talc, clay, calcium carbonate, an organic filler such as wood powder, and a plasticizer can be added as long as the conductivity is not lowered.

  The conductive resin composition can be produced by various conventional methods. For example, it can be obtained by dry mixing a resin and a carbon material. Further, a carbon material or the like may be added by heating and melting the resin or dissolving it in a solvent. Also, a plurality of mixing methods may be used in combination, such as heating and melting the material that has been premixed by dry mix.

  Various mixing apparatuses can be used as an apparatus used for mixing. For example, Henschel mixer, ribbon mixer, planetary mixer, mortar mixer, cone mixer, V mixer, pressure kneader, paddle mixer, twin screw extruder, single screw extruder, Banbury mixer, two roll mill, three roll mill, etc. Although it is mentioned, it is not limited to these. Furthermore, the mixed material can be pulverized or granulated and classified as necessary.

  The conductive resin composition thus obtained is molded into a fuel cell separator according to a conventionally known method for molding a thermosetting resin molding material. As a molding method, for example, there is the following compression molding. In other words, the preheated mold is filled with the conductive resin composition, molded by heating and compression at a temperature corresponding to the thermosetting resin and the curing agent, and taken out from the mold. The mold temperature is generally about 150 ° C to 220 ° C. Moreover, you may implement secondary bridge | crosslinking as needed. In addition, although you may shape | mold by injection molding and transfer molding, a shaping | molding method is not limited to these. Moreover, it is also possible to cut after shaping | molding as needed.

  In the present invention, it is important to provide a step of exposing the carbon material on the upper surface of the partition wall after forming the fuel cell separator. As described above, since the fuel cell separator of the present invention is a molded body made of a carbon material and a resin, the carbon material can be exposed by selectively removing the resin that is an insulating material on the upper surface of the partition wall. Good.

  Examples of the method for exposing the carbon material by removing the resin include, but are not limited to, blast treatment, mechanical grinding treatment, heat treatment, plasma treatment, and oxidant treatment. These methods can be used in combination. Since the resin has a lower strength than the carbon material, it can be selectively removed by these treatments.

  The blasting process is a process of causing fine particles (blast particles) to collide with a fluid. When a gas such as air is used as the fluid, it is called dry blasting, and when a liquid such as water is used, it is called wet blasting. In the present invention, air dry blasting is preferably used. In wet blasting, waste liquid is generated, which may cause environmental problems. When the gas pressure of the dry blast is too high, not only the resin but also the carbon material is removed, and the contact resistance cannot be lowered. In addition, the fuel cell separator may be damaged. If the gas pressure is too low, the blasting process takes a long time. Therefore, there is a preferred range for the pressure of dry blasting. The pressure of dry blasting is preferably 0.05 to 2 MPa, more preferably 0.1 to 1 MPa, and even more preferably 0.15 to 0.5 MPa.

  As blast particles, metal particles such as iron and carbon steel, ceramic particles such as silicon carbide and alumina, glass beads, resin beads such as acrylic, and plant particles such as walnuts and corn husks can be used. Besides this, diamond and dry ice can also be used. The use of hard particles increases the grinding force, but not only the resin but also the carbon material is removed, and the contact resistance cannot be lowered. In addition, the fuel cell separator may be damaged. If the particles are too soft, blasting takes a long time. Therefore, the hardness of the particles has a preferable range. The hardness of the particles is preferably a 10-step Mohs hardness of 6-9, more preferably 8-9. Specifically, alumina having a Mohs hardness of 8 and silicon carbide having a Mohs hardness of 9 are preferably used in the present invention. The use of large particles increases the grinding force, but not only the resin but also the carbon material is removed, and the contact resistance cannot be lowered. In addition, the fuel cell separator may be damaged. If the particles are too small, the blasting process takes a long time. Therefore, the particle size is preferably 20 to 3000 (1000 μm to 5 μm) defined by JIS R6001. Ideally, only the resin is selectively removed by performing blasting for a long time using particles with low cutting force at low pressure, but depending on the assumed processing time, gas pressure and particles for blasting The hardness and particle type may be set as appropriate.

  The mechanical grinding process refers to an operation of cutting only the surface with a grinding apparatus such as machining or milling. Moreover, polishing with sandpaper and polishing with hard particles such as alumina and diamond are also included. The thickness removed by grinding by the mechanical grinding process is preferably in the range of 0.1 to 20 μm, more preferably 0.5 to 15 μm, and even more preferably 1 to 10 μm. When the thickness to be ground is less than this range, the carbon material is less exposed and the conductivity is insufficient. Moreover, when larger than this range, since grinding takes time, productivity will worsen.

  The heat treatment is a treatment in which only the surface layer resin is thermally decomposed by heating to expose the carbon material. At this time, when performed in an oxygen atmosphere, both the resin and the carbon material are thermally decomposed, but the carbon material is exposed to heat as a result because the thermal decomposition of the carbon material is slower than the thermal decomposition of the resin. . In addition, when heat treatment is performed in a nitrogen atmosphere, only the resin material is easily removed selectively, and thus the heat treatment method is preferable in the present invention. The temperature of the heat treatment is 200 to 800 ° C., preferably 300 to 750 ° C., more preferably 400 to 700 ° C. in a nitrogen atmosphere. When the temperature is higher than this range, decomposition of the carbon material may occur. Further, at a temperature lower than this range, it takes a long time to decompose the resin.

  Oxidant treatment is a process of decomposing a surface resin with a chemical substance having an oxidizing function. Substances used for this treatment include aqueous potassium permanganate solution, ozone, hydrogen peroxide, sodium hypochlorite, calcium hypochlorite, manganese dioxide, silver chloride, copper chloride and the like.

  Among the above treatments, a blast treatment which is simple but has a high resin removal effect is preferable.

  In addition, it is possible to selectively remove only the resin by blasting or mechanical grinding as compared with the case where a thermoplastic resin is used as the resin, as described above. The carbon material can be efficiently exposed in the step of exposing the carbon material. This is preferable because the thickness change of the molded body in this step can be minimized. This is because the thermosetting resin is generally harder and more brittle than the thermoplastic resin, and the surface layer resin is affected by the impact of blast particle collision during blasting or polishing by a grinding tool during mechanical grinding. Because it collapses.

  In this process of removing the resin on the surface and exposing the carbon material, if the carbon material is in the form of flakes, the carbon material is oriented in a plane parallel to the surface of the partition wall of the fuel cell separator. The exposed portion of the carbon material can be increased by removing the resin slightly. On the contrary, if the shape is spherical, it is necessary to remove a lot of resin in order to increase the exposed area of the carbon material. It is necessary to increase the processing time or the processing time. However, when the grinding force is increased, the carbon material is also ground together with the resin, so that it becomes difficult to expose only the carbon material, and a part of the fuel cell separator is damaged. When carbon black is used as the carbon material, the functional group present on the carbon black surface reacts with the resin to form a strong bond between the resin and carbon black. It becomes difficult to expose black. Therefore, as the carbon material, flaky expanded graphite is preferable, and other graphite materials are also preferable. This will be described with reference to the drawings. FIG. 2 is a cross-sectional view schematically showing the state in which the flaky carbon material is dispersed in the resin matrix. In this state, the carbon material is not exposed on the surface, but as shown in FIG. By removing the resin, the carbon material can be exposed over a wide area. On the other hand, FIG. 4 shows a state in which spherical carbon materials are dispersed in the resin matrix. However, as shown in FIG. 5, even if the surface layer resin is removed, the increase in the exposed area of the carbon material is slight. Yes, the exposed area of the carbon material is considerably smaller than when a flaky carbon material is used (FIG. 3). Further, as can be seen from FIG. 3, by using a flaky carbon material, the carbon material can be exposed at a rate larger than the volume ratio of the carbon material in the fuel cell separator. Although the present inventors consider a mechanism in which the ratio of the exposed area of the carbon material is increased by using the flaky carbon material as described above, the present invention is not limited to this mechanism.

  In the present invention, the carbon material is exposed to 10 to 90%, preferably 15 to 85% of the total surface area of the upper surface of the partition wall by the above treatment. If the exposed area of the carbon material is small, the contact resistance increases, which is a problem. On the other hand, if the exposed area of the carbon material is too large, the carbon material may be detached from the surface because there is less resin to hold it together.

  As a method for measuring the area of the carbon material exposed on the surface, for example, a method of image analysis of an image observed with an optical microscope is convenient and preferable. In this method, the carbon material is observed as a white part, and the resin is observed as a black part, and the contrast is clearly observed. Further, it is preferable to use a laser focus type as the optical microscope. This is because, in a normal optical microscope, when the observation surface is uneven, it is difficult to focus the entire field of view. Examples of images observed with an optical microscope are illustrated in FIGS. 6 to 8. FIG. 6 shows Example 1 (blasting treatment of resin surface containing expanded graphite with # 800 alumina particles), which will be described later, and FIG. Example 3 (resin surface containing expanded graphite is polished with # 1000 sand paper), FIG. 8 is Comparative Example 1 (no exposure treatment), and these images are binarized to obtain an area ratio of white portions. This can be determined as the exposed area of the carbon material. The binarization process is a conventionally known image processing method. Further, as a method other than the optical microscope, a method using characteristic X-rays may be used. In this method, mapping by a WDS device built in a scanning electron microscope may be performed. It is known that the characteristic X-ray changes slightly depending on the environment around the element, that is, the bonding state of the substance. Regarding carbon, it has been reported that the spectrum shape of CK characteristic X-rays generated by transition to 1s orbital is different in materials composed only of carbon such as diamond, graphite, C60, C70 (Motoyama, Hashizume: Spectroscopic studies 29 (2), 92 (1980), J. Kawai, M. Motoyama; Phys. Rev. B 47 (19), 12998 (1993)). Since the carbon bonding state is greatly different between the carbon material and the resin, the characteristic X-ray spectrum shape is also different. Accordingly, the distribution of the carbon material can be evaluated by fixing the spectral energy to the peak energy peculiar to the carbon material and examining the X-ray intensity distribution in the sample.

  Hereinafter, the present invention will be further described with reference to examples and comparative examples, but the present invention is not limited thereto.

(Preparation of molding material)
According to the formulation shown in Table 1, a total of 500 g of the material was premixed with a 10 L Henschel mixer and then kneaded with a 1 L pressure kneader at a chamber temperature of 100 ° C. for 5 minutes. This was pulverized into particles having a particle diameter of about 2 mm by a pulverizer to obtain a molding material. The unit of the formulation in Table 1 is mass%.

(Production of molded body)
A mold having a shape of 100 × 100 × 2 mm was preheated to 170 ° C., filled therein with about 35 g of a molding material, and hot compression molded at 170 ° C. for 10 minutes with a hot press. In addition, a 100 × 100 × 4 mm-shaped mold was heated in advance to 170 ° C., filled with about 70 g of a molding material, and hot compression molded at 170 ° C. for 10 minutes with a hot press. All the molds used were mirror-finished with a surface roughness Ra = 0.1. Then, the obtained molded body was cut into a predetermined shape, and further subjected to blasting or mechanical grinding as shown below to obtain a specimen.

Example 1
The molded body was subjected to blasting using # 800 alumina particles (Mohs hardness 8) under conditions of pressure 0.2 MPa and processing time 0.1 sec / cm ² .
(Example 2)
The molded body was subjected to blasting using # 800 alumina particles (Mohs hardness 8) under conditions of pressure 0.2 MPa and processing time 0.1 sec / cm ² .
(Example 3)
The molded body was polished with # 1000 sand paper at a time of 60 sec / cm ² .
Example 4
The molded body was subjected to blasting using # 800 silicon carbide particles (Mohs hardness 9) under the conditions of pressure 0.2 MPa and processing time 0.1 sec / cm ² .
(Example 5)
Blasting was performed on the compact that was hot compression molded by the above-described method using # 1000 alumina particles (Mohs hardness 8) under the conditions of a pressure of 0.2 MPa and a processing time of 0.1 sec / cm ² .
(Example 6)
The molded body was subjected to blasting using # 300 alumina particles (Mohs hardness 8) under the conditions of pressure 0.2 MPa and processing time 0.1 sec / cm ² .
(Comparative Example 1)
The molded body was used as it was as a test body without being subjected to blasting or mechanical grinding.
(Comparative Example 2)
The molded body was subjected to blasting using # 800 alumina particles (Mohs hardness 8) under conditions of pressure 0.2 MPa and processing time 0.1 sec / cm ² .

(Measurement of exposed area and surface roughness of carbon material)
An image observed from the upper surface of the specimen is acquired with a laser microscope manufactured by Lasertec, and binarized using the image analysis software ImageProPlus of Media Cybernetic to determine the area ratio of the white part, The exposed area ratio of the material was used. The laser microscope image according to Example 1 is shown in FIG. 6, the laser microscope image according to Example 3 is shown in FIG. 7, and the laser microscope image according to Comparative Example 1 is shown in FIG. The length of one side of the image is about 1.5 mm, the white part is graphite and the black part is resin. Further, the surface roughness Ra of the specimen was also measured simultaneously with a laser microscope. The results are shown in Table 2.

(Measurement of contact resistance)
As shown in FIG. 9, a sample 81 cut out from a specimen is set on an electrode 83 through a carbon paper 82, and a current (measured with an ammeter 84) passed between the electrodes and a voltage (voltmeter) between the carbon papers. The electrical resistance was calculated from (measured at 85) and multiplied by the sample area to obtain the resistivity in the penetration direction. Measurements were made on both 2mm and 4mm thick samples. The horizontal axis represents the thickness, the vertical axis plotted the penetration direction resistivity, and the vertical axis intercept of the obtained straight line divided by 2 was defined as the contact resistance. . The slope of the plotted straight line is the electric resistance resistance resulting from the volume resistance. The straight intercept is the penetration direction resistivity when the thickness of the sample 81 becomes 0 mm, and is caused only by the contact resistance between the carbon paper 82 and the sample 81 since the influence of the volume resistance is excluded. Further, since the contact resistance is generated on each of the upper and lower surfaces of the sample 81, the value obtained by dividing the section by 2 is the contact resistance per surface of the contact portion between the sample 81 and the carbon paper 82. The results are shown in Table 2.

  For each example and comparative example, the relationship between the surface roughness and the contact resistance is shown in FIG. 10, and the relationship between the exposed area ratio of the carbon material and the contact resistance is shown in FIG.

As shown in each measurement result above, the specimen of each example contains expanded graphite as a carbon material, and since the exposed area ratio of the carbon material is as large as 10% or more, the contact resistance is 3.8 to 5.6 mΩcm ² . It shows a very low value and can be said to be an ideal molded article as a fuel cell separator. It can also be seen from FIGS. 6 and 7 that the exposed area of the carbon material is large. On the other hand, in the comparative example 1, since the process which exposes a carbon material is not performed, since the exposed area of a carbon material is less than 10%, contact resistance is high. It can be seen from FIG. 8 that the exposed area of the carbon material of Comparative Example 1 is small. Further, the specimen of Comparative Example 2 is subjected to the same blasting treatment as that of Example 1, and since it does not contain expanded graphite, the exposed area of the carbon material is less than 10%, and the contact resistance is high. .

  Further, it can be seen from FIG. 10 that there is no correlation between the surface roughness and the contact resistance. On the other hand, FIG. 11 shows that there is a strong correlation between the exposed area ratio of the carbon material and the contact resistance, and the larger the exposed area ratio of the carbon material, the lower the contact resistance. In particular, when the exposed area ratio of the carbon material is less than 10%, the contact resistance increases rapidly.

It is a schematic perspective view which shows an example of the separator for fuel cells. It is a schematic diagram which shows the state before exposing expanded graphite in the separator for fuel cells using expanded graphite as a carbon material. FIG. 3 is a schematic view showing a state in which expanded graphite is exposed in a fuel cell separator using expanded graphite as a carbon material. It is a schematic diagram which shows the state before exposing expanded graphite in the separator for fuel cells using spherical graphite as a carbon material. It is a schematic diagram showing a state in which expanded graphite is exposed in a fuel cell separator using spherical graphite as a carbon material. 2 is a laser microscope image of the specimen of Example 1. 2 is a laser microscope image of a specimen of Example 3. 2 is a laser microscope image of a specimen of Comparative Example 1. It is a schematic diagram which shows the measuring method of penetration direction resistivity. It is a graph which shows the relationship between surface roughness and contact resistance. It is a graph which shows the relationship between the exposure area ratio of carbon material, and contact resistance.

Explanation of symbols

10 Fuel Cell Separator 11 Flat Plate 12 Bulkhead 13 Channel

Claims (10)

  The conductive resin composition comprising a resin and a carbon material containing expanded graphite, wherein the exposed area of the carbon material on the upper surface of the partition wall is 10 to 90% with respect to the total surface area of the upper surface of the partition wall Fuel cell separator.   The fuel cell separator according to claim 1, wherein 5 to 100% by mass of the carbon material is expanded graphite.   The fuel cell separator according to claim 1 or 2, wherein the ratio of the resin to the carbon material is 20:80 to 60:40 by weight.   The fuel cell separator according to any one of claims 1 to 3, wherein the resin is a thermosetting resin.   The fuel cell separator according to claim 4, wherein the resin is a phenol resin or an epoxy resin.   After forming a conductive resin composition containing a resin and a carbon material containing expanded graphite into a separator shape, the upper surface of the partition wall is at least one of blast treatment, mechanical grinding treatment, heat treatment, plasma treatment, and oxidant treatment. Thus, the carbon material is exposed so that the area ratio is 10 to 90% of the total surface area of the upper surface of the partition wall.   The method for producing a separator for a fuel cell according to claim 6, wherein dry blasting is performed.   8. The method for producing a fuel cell separator according to claim 6 or 7, wherein the particles used for the blasting treatment are No. 20 to 3000 (1000 to 5 [mu] m) defined by JIS R6001.   The fuel cell according to any one of claims 6 to 8, wherein the particles used for the blasting are at least one selected from metal particles, ceramic particles, glass beads, resin particles, and plant particles. Manufacturing method for the separator. The method for producing a separator for a fuel cell according to any one of claims 6 to 9, wherein the particles used for the blast treatment are particles having a 10-step Mohs hardness of 6 to 9.