Resin composition for fuel cell separator, fuel cell separator, and method for manufacturing fuel cell separator

Abstract

This resin composition for a fuel cell separator containing a graphite powder, and an epoxy resin component containing a main agent, a curing agent, and a curing accelerator, and having a compression degree of 14.0-40.0% as determined by the following formula and a content of a volatile component having a boiling point of 100°C or lower of less than 1.00 mass% can shorten a filling time to a filling container when manufacturing a fuel cell separator, can suppress variation in the filling amount, and can form a fuel cell separator having a small variation in the thickness and a low contact resistance.　Compression degree (%) = 100 × (packed bulk density of resin composition-aerated bulk density of resin composition) / packed bulk density of resin composition

Description

Resin composition for fuel cell separator, fuel cell separator, and method for manufacturing fuel cell separator

[0001] The present invention relates to a resin composition for a fuel cell separator, a fuel cell separator, and a method for producing a fuel cell separator.

[0002] Fuel cell separators provide electrical conductivity to each unit cell, ensure passage for fuel and air (oxygen) to be supplied to the unit cells, and act as a boundary wall separating them. For this reason, fuel cell separators are required to have various properties, such as high electrical conductivity, high gas impermeability, high thickness precision, chemical stability, heat resistance, and hydrophilicity.

[0003] To meet these performance requirements, early separators were formed by machining graphite plates, but this required a long processing time, which made the separators too expensive.Recently, therefore, a method has been adopted in which carbon powder and thermosetting synthetic resin powder are mixed to form a powdered raw material, which is then placed in the lower die of a press, covered with an upper die, and pressurized and heated in the press to form a shape.

[0004] For example, Patent Document 1 proposes a method for molding a fuel cell separator by filling a filling container with powdered raw material containing a conductive material and a resin, heating the powdered raw material in the filling container to form a pre-molded product, and then placing the resulting pre-molded product in a mold separate from the filling container and heating and pressurizing it.

[0005] However, in Patent Document 1, the time required for preparations, from filling the filling container with the powdered raw material, to heating it, and then pouring it into a mold, is 3 to 4 minutes, which results in low production efficiency. Furthermore, if it takes a long time to fill the filling container with the powdered raw material, the powdered raw material will aggregate inside the raw material supply device, which results in the problem that the specified mass cannot be filled into the filling container.

[0006] Japanese Patent Application Laid-Open No. 2006-244937

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a resin composition for a fuel cell separator, a fuel cell separator, and a manufacturing method thereof, which can shorten the time required to fill a filling container when manufacturing a fuel cell separator, suppress variations in the filling amount, and form a fuel cell separator with little thickness variation and low contact resistance.

[0008] As a result of extensive research into achieving the above-mentioned object, the inventors have discovered that a resin composition having a predetermined degree of compression and a predetermined range of content of volatile components having a boiling point of 100°C or less can shorten the filling time into a filling container when manufacturing a fuel cell separator, can suppress variation in the filling amount, and can form a fuel cell separator with little thickness variation and low contact resistance, thereby completing the present invention.

[0009] That is, the present invention provides: 1. A resin composition for a fuel cell separator, comprising graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, characterized in that the degree of compression calculated by the following formula is 14.0 to 40.0%, and the content of volatile components having a boiling point of 100°C or less is less than 1.00 mass%: degree of compression (%) = 100 x (packed bulk density of resin composition - loose bulk density of resin composition) / packed bulk density of resin composition 2. The resin composition for a fuel cell separator according to 1, wherein the loose bulk density of the resin composition is 0.40 to 0.90 g / cc; 3. The resin composition for a fuel cell separator according to 1, wherein the loose bulk density of the graphite powder is 0.35 to 0.70 g / cc; 4. 4. The resin composition for fuel cell separators according to 1, wherein the base resin is at least one selected from an orthocresol novolac epoxy resin having an epoxy equivalent of 194 to 215 g / eq and a biphenyl epoxy resin having an epoxy equivalent of 180 to 200 g / eq, 5. The resin composition for fuel cell separators according to 1, wherein the curing agent is a phenol novolac resin having a hydroxyl group equivalent of 103 to 106 g / eq, 6. The resin composition for fuel cell separators according to 1, wherein the curing accelerator is an imidazole compound having a phenyl group at the 2-position, 7. The resin composition for fuel cell separators according to 1, wherein the time for filling a container with the composition when filling a container to form a fuel cell separator of 300 mm x 400 mm x 1 mm is less than 120 seconds, 8. 9. A resin composition for fuel cell separators according to 1, wherein when the resin composition is filled into a filling container to form a fuel cell separator of 300 mm x 400 mm x 1 mm, the variation in the filling mass into the filling container is less than 2.00% relative to the reference mass; 10. A resin composition for fuel cell separators according to 1, wherein the resin composition contains graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, and the compression degree calculated by the following formula is 14.0 to 40.0%, and the content of volatile components having a boiling point of 100°C or less is less than 1.00 mass%, and the resin composition has a thickness variation of less than 50 μm and a contact resistance of 7.00 mΩ cm 29. A fuel cell separator having a thick portion and a thin portion for forming grooves serving as gas flow paths on at least a portion of the surface, the method comprising: introducing a fuel cell separator resin composition containing graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, the fuel cell separator resin composition having a compressibility calculated by the following formula of 14.0 to 40.0% and having a content of volatile components having a boiling point of 100°C or less of less than 1.00 mass%, into a fuel cell separator mold such that the introduced mass is a volume ratio similar to the volume ratio of the thick portion to the thin portion of the fuel cell separator, the compressibility being: Compressibility (%) = 100 x (packed bulk density of resin composition - loose bulk density of resin composition) / packed bulk density of resin composition 10. A fuel cell separator having a thick portion and a thin portion for forming grooves serving as gas flow paths on at least a portion of the surface, the method comprising: introducing a fuel cell separator resin composition containing graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, the fuel cell separator resin composition having a compressibility calculated by the following formula of 14.0 to 40.0% and having a content of volatile components having a boiling point of 100°C or less of less than 1.00 mass%, into a fuel cell separator mold such that the introduced mass is a volume ratio similar to the volume ratio of the thick portion to the thin portion of the fuel cell separator, the compressibility (%) = 100 x (packed bulk density of resin composition - loose bulk density of resin composition) / pack 11. A method for manufacturing a fuel cell separator according to claim 10, comprising the steps of: filling the resin composition for a fuel cell separator into a filling container formed with irregularities approximating the volume ratio of the thick and thin portions of the fuel cell separator; inverting the filling container filled with the resin composition upside down directly above a mold for a fuel cell separator to pour the resin composition into the mold; and compression molding the resin composition poured into the mold.

[0010] The resin composition for fuel cell separators of the present invention has a predetermined compressibility and the content of volatile components having a boiling point of 100°C or less is adjusted to a predetermined range, so that it has excellent fluidity and packing properties as a powder, requires a short time to be poured into a mold for fuel cell separators, is highly productive, and has little variation in the packing mass poured into the mold. Fuel cell separators obtained by molding the fuel cell separator composition of the present invention having such properties have little thickness variation and low contact resistance.

[0011] 1 is a schematic cross-sectional view showing an example of a filling device for a resin composition used in the production of a fuel cell separator according to the present invention. 2 is a schematic perspective view showing a main part of the filling device of FIG. 1. 3 is an explanatory view showing a molding process when a pattern is formed on a filling container. 4 is an explanatory view showing a molding process when a pattern is not formed on a filling container.

[0012] The present invention will be described in further detail below. [Resin composition for fuel cell separator] The resin composition for fuel cell separator according to the present invention comprises graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, and is characterized in that the compressibility calculated by the following formula is 14.0 to 40.0%, and the content of volatile components having a boiling point of 100°C or less is less than 1.00 mass%. Compressibility (%) = 100 x (solid bulk density of resin composition - loose bulk density of resin composition) / solid bulk density of resin composition

[0013] In the present invention, the degree of compression of the resin composition for fuel cell separators is 14.0 to 40.0%, preferably 18.0 to 35.0%. If the degree of compression is less than 14.0%, the time required to fill the resin composition of the present invention into a mold or a filling container is shortened, but on the other hand, the fluidity becomes excessive, so that the mass of the resin composition when filled into the mold or filling container exceeds the reference value or overflows from the mold or filling container, making it impossible to stably fill a mass that achieves a volume ratio approximating the volume ratio of the thick (thick) and thin (thin) portions of the fuel cell separator. If the degree of compression exceeds 40.0%, the fluidity of the resin composition of the present invention is insufficient, so that it takes a long time to fill into the mold or filling container, and the mass when filled into the mold or filling container is less than the reference mass, making it impossible to stably fill a mass that achieves a volume ratio approximating the volume ratio of the thick (thick) and thin (thin) portions of the fuel cell separator. In the present invention, the "reference mass" refers to the filling mass required to mold the fuel cell separator to a design thickness. Furthermore, in the present invention, "filling a mass that results in a volume ratio that approximates the volume ratio of the thick and thin portions of the fuel cell separator" means that, when filling a mold or a filling container with the resin composition, the portions corresponding to the thick and thin portions of the fuel cell separator are filled thickly and thinly, respectively, so that the volume ratio of the thick and thin portions of the fuel cell separator is approximately equal to the volume ratio of the thick and thin portions of the fuel cell separator.

[0014] In the present invention, the loose bulk density (g / cc) and the compacted bulk density (g / cc) of the resin composition used to calculate the compressibility are measured using a powder tester PT-S manufactured by Hosokawa Micron Corporation. The loose bulk density is measured under the condition of a vibration time of 30 seconds, and the compacted bulk density is measured under the condition of 180 tappings.

[0015] The resin composition for fuel cell separators of the present invention can be in any form, such as granular or powdery, as long as it satisfies the above-mentioned compressibility and other requirements, but powdery is preferred. The shape of the powder is not particularly limited, and any shape can be used. The particle size is also not particularly limited, but is preferably 700 μm or less, more preferably 600 μm or less. In the present invention, the particle size is a value measured by a wet method using a particle size distribution measuring device (MT3000 manufactured by Microtrac Bell Co., Ltd.).

[0016] The loose bulk density of the resin composition for fuel cell separators of the present invention is preferably 0.40 to 0.90 g / cc, more preferably 0.45 to 0.85 g / cc. When the loose bulk density is 0.40 to 0.90 g / cc, the resin composition of the present invention has appropriate fluidity, so that it does not take a long time to fill a mold or a filling container with the resin composition, and the resin composition does not aggregate in a raw material supply device, allowing a predetermined mass to be stably filled.

[0017] The content of volatile components having a boiling point of 100°C or less contained in the resin composition for fuel cell separators of the present invention is less than 1.00% by mass, preferably 0.9% by mass or less. If the volatile components are 1.00% by mass or more, the resin composition of the present invention will adhere to the walls of the raw material supply device or aggregate within the raw material supply device, which will require a long time to fill into a mold or a filling container, making it impossible to stably fill a mass that will achieve a volume ratio approximating the volume ratio of the thick and thin portions of the fuel cell separator. In the present invention, the amount of volatile components having a boiling point of 100°C or less contained in the resin composition is measured using an infrared moisture meter FD-660 manufactured by Kett Electric Laboratory Co., Ltd., at 110°C for 10 minutes.

[0018] The graphite powder used in the present invention is not particularly limited in type, etc., as long as the range of the degree of compression of the resin composition of the present invention is satisfied, and either natural graphite or artificial graphite may be used. Examples of artificial graphite include artificial graphite obtained by calcining needle coke, artificial graphite obtained by calcining lump coke, spheroidized artificial graphite, and artificial graphite whose surface has been treated with a pitch coat or the like. On the other hand, examples of natural graphite include flake natural graphite, soil graphite, spheroidized natural graphite, and natural graphite whose surface has been treated with a pitch coat or the like. Any of these may be selected appropriately. These graphite powders may be used alone or in combination of two or more types.

[0019] The loose bulk density of the graphite powder used in the present invention is preferably 0.35 to 0.75 g / cc, and more preferably 0.35 to 0.70 g / cc. When the loose bulk density of the graphite powder is in the range of 0.35 to 0.75 g / cc, the compressibility of the resin composition can be easily adjusted to a range of 14.0 to 40.0%. The loose bulk density of the graphite powder is measured using the same apparatus and under the same conditions as the loose bulk density of the resin composition described above.

[0020] On the other hand, the base resin constituting the epoxy resin component is not particularly limited as long as it has an epoxy group. Examples include ortho-cresol novolac epoxy resins, phenol novolac epoxy resins, bisphenol A epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, biphenyl aralkyl epoxy resins, trisphenol epoxy resins, brominated epoxy resins, dicyclopentadiene epoxy resins, and biphenyl novolac epoxy resins. These may be used alone or in combination of two or more. Among these, ortho-cresol novolac epoxy resins alone, biphenyl epoxy resins alone, and mixtures thereof are preferred. The epoxy equivalent of the epoxy resin used in the present invention is not particularly limited, but is preferably 194 to 215 g / eq for ortho-cresol novolac epoxy resins, and preferably 180 to 200 g / eq for biphenyl epoxy resins.

[0021] The hydrolyzable chlorine content of the epoxy resin base resin used in the present invention is preferably 450 ppm or less. If the hydrolyzable chlorine content is 450 ppm or less, the crosslink density of the cured product increases, resulting in improved heat resistance of the resulting separator. On the other hand, the lower limit is not particularly limited, but since epoxy resins with a hydrolyzable chlorine content of less than 370 ppm are very expensive, considering the cost, the lower limit is preferably 370 ppm.

[0022] Phenol resins are preferred as curing agents constituting the epoxy resin component. Specific examples include novolac phenolic resins, cresol novolac phenolic resins, resol phenolic resins, aralkyl-modified phenolic resins, biphenyl novolac phenolic resins, and trisphenolmethane phenolic resins. These may be used alone or in combination of two or more. Among these, novolac phenolic resins are preferred. The hydroxyl group equivalent of the phenolic resin used in the present invention is not particularly limited, but is preferably 103 to 106 g / eq.

[0023] The curing accelerator constituting the epoxy resin component is not particularly limited as long as it accelerates the reaction between the epoxy group and the curing agent, and examples thereof include phosphine compounds, amine compounds, and imidazole compounds. Among these, in the present invention, it is preferable to use an imidazole compound having an aryl group at the 2-position. Specific examples of the aryl group include a phenyl group, a tolyl group, and a naphthyl group, with a phenyl group being preferred. Specific examples of imidazole compounds having an aryl group at the 2-position include 2-phenylimidazole and 2-phenyl-4-methylimidazole. Note that when an imidazole compound having a short-chain alkyl group such as 2-methylimidazole is used, the curing time may be too fast to achieve uniform molding, while when an imidazole compound having a long-chain alkyl group such as 2-undecylimidazole is used, the curing time may be too slow, resulting in a long molding time.

[0024] In addition to the above components, the composition used in the present invention may also contain optional components such as an internal mold release agent. The internal mold release agent may be appropriately selected from various internal mold release agents that have conventionally been used in molding separators, and specific examples thereof include stearic acid waxes, amide waxes, montanic acid waxes, carnauba waxes, and polyethylene waxes, which may be used alone or in combination of two or more.

[0025] In the resin composition of the present invention, the amounts of graphite powder and epoxy resin components (main agent, curing agent, and curing accelerator) are not particularly limited, but are preferably 22 to 40 parts by weight, more preferably 27 to 35 parts by weight, and even more preferably 30 to 33 parts by weight, of the epoxy resin component per 100 parts by weight of graphite powder. By incorporating the epoxy resin component in this range, the resin composition has appropriate fluidity, improving moldability, and preventing a significant decrease in the gas impermeability and electrical conductivity of the resulting fuel cell separator. In this case, the curing agent is preferably incorporated in an amount of 0.98 to 1.08 equivalents relative to the main agent, more preferably 0.99 to 1.05 equivalents. The amount of curing accelerator used is also not particularly limited, but is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 2 parts by weight, per 100 parts by weight of the mixture of main agent and curing agent. Furthermore, when an internal mold release agent is used, the amount used is not particularly limited, but is preferably 0.01 to 3.0 parts by mass, more preferably 0.05 to 1.5 parts by mass, per 100 parts by mass of graphite powder.

[0026] In the method for producing a fuel cell separator of the present invention, for example, when producing a fuel cell separator having dimensions of 300 mm × 400 mm × 1 mm, the resin composition for a fuel cell separator of the present invention can be filled into a filling container having a size corresponding to the fuel cell separator (e.g., 300 mm × 400 mm × 3 mm) in less than 120 seconds. The lower limit of the filling time is not particularly limited, but is typically 20 seconds or more. The method for measuring the filling time is as described in the Examples below. Furthermore, for example, when producing a fuel cell separator of the same dimensions as above, the variation in the filling mass of the filling container relative to the reference mass can be less than 2.00%, preferably 1.98% or less, and more preferably 1.96% or less. The lower limit of the variation is not particularly limited, but is typically 0.10% or more. The method for measuring this variation is also as described in the Examples below.

[0027] [Method for Producing a Resin Composition for a Fuel Cell Separator] The resin composition for a fuel cell separator of the present invention may be prepared, for example, by mixing graphite powder, a base material, a curing agent, and a curing accelerator in any order and in predetermined proportions. In this case, a mixer such as a planetary mixer, a ribbon blender, a Loedige mixer, a Henschel mixer, a rocking mixer, or a Nauta mixer can be used. When an internal mold release agent is used, the order of mixing the ingredients can also be arbitrary. Because the resin composition for a fuel cell separator of the present invention is in powder form, it is preferable to use powder-like raw materials, which allows for easy preparation of the powder-like resin composition.

[0028] In producing the resin composition, if necessary, for the purpose of adjusting the degree of compression to the aforementioned range or reducing the content of volatile components with a boiling point of 100°C or less to a predetermined amount, the resulting mixture may be mixed and then dried, for example, at 30 to 60°C for 1 to 3 hours, followed by pulverization to obtain a resin composition for a fuel cell separator. Alternatively, the mixed components may be melt-kneaded using a pressure kneader, a twin-screw continuous kneader, an extruder, a heated roll, or the like, cooled, and the solidified mixture may be pulverized to a predetermined size to obtain a resin composition for a fuel cell separator. The heating temperature during melt-kneading is not particularly limited as long as it is equal to or higher than the melting point of the epoxy resin and lower than the thermosetting temperature, but is preferably 40 to 100°C, more preferably 50 to 90°C. The heating time is also not particularly limited, but is preferably 1 to 10 minutes, more preferably 1 to 5 minutes.

[0029] [Fuel Cell Separator] The fuel cell separator of the present invention is obtained by molding the above-mentioned resin composition for fuel cell separators, and has a thickness variation of less than 50 μm and a contact resistance of 7.00 mΩ·cm. 2 is less than.

[0030] The thickness unevenness of the fuel cell separator of the present invention is less than 50 μm, but preferably 49 μm or less. There is no particular lower limit, and the smaller the value, the better, but it is particularly 1 μm or more. In the present invention, the thickness unevenness is a value evaluated by measuring the thickness of the fuel cell separator at 20 points with a micrometer and using the following formula: Thickness unevenness (μm) = Maximum thickness of fuel cell separator - Minimum thickness of fuel cell separator

[0031] The contact resistance of the fuel cell separator of the present invention is 7.00 mΩ cm 2 less than 6.90 mΩ cm 2 The lower limit is not particularly limited, but the smaller the value, the better. 2 In the present invention, the contact resistance is a value calculated by the method described in the examples below.

[0032] [Method for Manufacturing Fuel Cell Separators] The fuel cell separator of the present invention can be manufactured, for example, by placing the fuel cell separator resin composition described above in a predetermined mold and compression molding it. Examples of the mold that can be used include a fuel cell separator mold capable of forming grooves serving as gas flow channels on at least a portion of one or both surfaces of the molded article. This results in a fuel cell separator having thick and thin portions on at least a portion of the surface for forming the grooves serving as gas flow channels. While any method for introducing the resin composition into the mold is possible, it is preferable to introduce the resin composition into the fuel cell separator mold so that the volume ratio of the introduced resin composition approximates the volume ratio of the thick and thin portions of the desired fuel cell separator. The compression molding conditions are not particularly limited, but include a mold temperature of 150 to 190°C and a molding pressure of 30 to 60 MPa, preferably 30 to 50 MPa. The compression molding time is not particularly limited and can be set appropriately from about 3 seconds to 1 hour. However, a short time is preferable from the viewpoint of production efficiency, specifically, 40 seconds or less. After compression molding, the composition may be further heated at 150 to 200° C. for 1 to 600 minutes to promote thermal curing.

[0033] As described above, the resin composition of the present invention has a predetermined compressibility and a predetermined range of content of volatile components having a boiling point of 100°C or less, and therefore has the properties of being able to shorten the filling time into a filling container and suppress variation in the filling amount within the filling container, and therefore can be suitably used in a manufacturing method including a step of first filling a powder raw material into a filling container and then pouring the powder raw material into a mold, as disclosed in Patent Document 1. Therefore, the fuel cell separator of the present invention is preferably manufactured by a manufacturing method including the steps of: filling the above-mentioned resin composition into a filling container formed with irregularities approximating the volume ratio of the thick-walled portion to the thin-walled portion of the fuel cell separator; inverting the filled container upside down directly above a mold for a fuel cell separator to pour the resin composition into the mold; and compression molding the resin composition poured into the mold. In the present invention, a "filled container having concaves and convexes formed thereon whose volume ratio approximates the thick-walled and thin-walled portions of a fuel cell separator" refers to a filled container having concaves corresponding to the thick-walled portions of a fuel cell separator and convex portions corresponding to the thin-walled portions, wherein the volume ratio of the concaves to the convex portions is approximately equal to the volume ratio of the thick-walled and thin-walled portions of the fuel cell separator. In this case, the filled resin composition may be pre-molded by heat treatment before the filled container is turned upside down. The heat treatment conditions are not particularly limited as long as the temperature is higher than the melting point of the epoxy resin and lower than its hardening point. For example, heating at 50 to 100°C for 0.5 to 10 minutes may be used.

[0034] An embodiment of the method for manufacturing a fuel cell separator of the present invention will now be described with reference to the drawings. The method for manufacturing a fuel cell separator of the present invention can be carried out using a filling device 10 shown in Figure 1. As shown in Figures 1 and 2, the filling device 10 is configured to include a hopper 11 that holds resin composition A, a filling container 12 installed below the hopper 11, and a movable table 13 on which the filling container 12 is placed. The filling container 12 is fitted into an opening (not shown) provided in the movable table 13 and placed approximately horizontally on the movable table 13, with its upper surface 12b being an approximately horizontal plane.

[0035] The moving platform 13 is attached with a moving means 14 via wheels 13a and a rod 14a, and is placed on a base 15 such as a rail. The rod 14a is also connected to a rotation mechanism (not shown), and by driving the rotation mechanism, the rod 14a rotates about its axis, causing the moving platform 13 to rotate integrally with the rod 14a. To move the moving platform 13, for example, the rod 14a may be used as a rack, a pinion may be provided on the moving means 14, and the pinion may be rotated in both forward and reverse directions by a motor (not shown), thereby moving the moving platform 13 in the left-right direction in FIG. 1 on the base 15. A single-axis robot or a fluid cylinder may also be used as the moving means 14.

[0036] The hopper 11 has an internal space 11a, which is open at the top and through which the resin composition A of the present invention is introduced. A narrow rectangular supply port 11b is provided at the bottom of the hopper 11. This supply port 11b may be provided with an openable / closable lid 11c that can be opened and closed by sliding, for example. The supply port 11b is located a predetermined distance, for example, approximately 0.1 to 1 mm above the upper surface 12b of the filling container 12, and is configured to scrape off the upper surface 12b. Since lumps in the resin composition A can cause unevenness in the filled resin composition A, a mesh screen may be provided at the supply port 11b to prevent this. The hopper 11 is supported by a support (not shown) and is configured to be vibrated in a horizontal plane by a vibrator (not shown) attached to the support, the hopper 11, or the like, as indicated by the arrow in FIG. 1 . Examples of vibrators that can be used include rotary vibrators and piston vibrators.

[0037] As shown in FIG. 2 , the filling container 12 has a concave-convex pattern 12a formed thereon, which corresponds to the grooves of the fuel cell separator and, taking into account the thickness distribution, approximates the volume ratio of the thick and thin portions of the fuel cell separator. The material of the filling container 12 may be the same as that of the fuel cell separator mold. However, since no pressure is applied by pressing, the filling container 12 only needs to be heat-resistant enough to withstand the temperatures and not deform when the resin composition A is heated near its melting point. Furthermore, a lightweight material is preferred in consideration of transportation during heating and injection. Furthermore, a material with high thermal conductivity is preferred to distribute heat evenly throughout the resin composition A when heated with a heater or the like. Considering these points, a dense filling container made of, for example, aluminum is preferred.

[0038] The opening width w and outer width W of the filling container 12 and the length L of the supply port 11b of the hopper 11 are usually set so that w≦L<W, and when the filling container 12 is arranged, the supply port 11b straddles the opening of the filling container 12. This is because if L<w, the resin composition A will not be evenly distributed inside the filling container 12, and if W<L, the resin composition A will spill outside the filling container 12, resulting in a lot of waste. However, depending on various process conditions, L<w may be set.

[0039] When filling the filling container 12 with the resin composition A, first, the filling container 12 is placed so that the open end of the filling container 12 is positioned approximately in the center of the supply port 11b of the hopper 11, and the resin composition A is poured into the hopper 11. At the same time, the hopper 11 can be vibrated in the left-right direction in Figure 2 using a vibrator (not shown) to allow the resin composition A inside to fall smoothly without getting caught along the way.

[0040] When resin composition A is poured into the hopper 11, it drops and fills the bottom of the supply port 11b in the filling container 12, with the resin composition A in the hopper space 11a piling up on top of it. When the moving platform 13 moves from this state in the direction of the arrow in FIG. 1, the resin composition A in the hopper 11 fills the filling container 12, scraping off excess resin composition A at the supply port 11b of the hopper 11, filling the filling container 12 so that the top surface is flat. A scraping plate (not shown) may be provided to scrape off the top surface 12b of the filling container 12. When the filling container 12 has passed under the supply port 11b, the resin composition A is filled into the space of the filling container 12, where the uneven pattern 12a is formed, as shown in FIG. 3(a).

[0041] Thereafter, if necessary, the filled container 12 may be placed on a heating table (not shown), and the resin composition A may be heated with a heater or other heating device to a temperature higher than the melting point of the epoxy resin but lower than its hardening point, and maintained in this state to form a pre-molded shape. If the heating temperature is too low, the resin will not melt and pre-molding will not be possible, while if the heating temperature is too high, hardening will begin, causing uneven molding (such as sparseness). The heating temperature is preferably Tm to Tm + 50°C, and more preferably Tm to Tm + 20°C, where Tm is the melting point.

[0042] After pre-molding, the resin contained in the resin composition A is partially melted, causing the particles to lightly weld together, so that they will not fall out immediately even if the filled container 12 is turned upside down. In the case of a powder, it is difficult to pour the resin composition A into a mold all at once, but by performing pre-molding, it is possible to pour the resin composition A, whose particles are lightly welded together, into a mold all at once, facilitating uniform pouring. The degree of particle welding after pre-molding may be such that only a portion of the resin is melted, so that the particles will barely not fall out even if the filled container 12 is turned over, or such that all of the resin is melted and integrated, so that the particles will break if a strong stress is applied but will not break or break if a small stress is applied. However, a degree of bonding that barely prevents the particles from falling out even if the filled container 12 is turned over is preferred.

[0043] Next, the moving means 14 moves the moving table 13, and as shown in FIG. 3( b), the filled container 12 filled with the resin composition A is brought directly above the lower mold 21 on which the pattern 21 a is formed. The container is accurately positioned using a positioning pin or the like. The rod 14 a is rotated by a rotation mechanism (not shown) to turn the filled container 12 upside down together with the moving table 13, and the resin composition A is dropped onto the lower mold 21. Even if the resin composition A is only fused to the extent that it crumbles when attempting to remove it from the filled container 12, and it cannot be removed directly from the filled container 12, this method allows it to be uniformly poured into the mold. Thereafter, as shown in FIG. 3( c), the upper mold 22 on which the pattern 22 a is formed is lowered, and pressure and heat are applied under the compression molding conditions described above to compress it to a thickness that is a fraction of its original thickness, resulting in the fuel cell separator 1 shown in FIG. 3( d).

[0044] The fuel cell separator 1 thus obtained has a pattern 1a that forms the grooves, and has two thicknesses: thick and thin. The thin portions correspond to the bottoms of the grooves, and the thick portions are the portions between the grooves. In this case, it is preferable that the thick and thin portions of the fuel cell separator 1 have the same density.

[0045] Next, the relationship between the depth of the pattern formed on the filling container 12 and the thickness of the fuel cell separator 1 will be described. FIG. 4 is a diagram illustrating the use of a filling container (not shown) without a pattern. As shown in FIG. 4(a), patterns 21a, 22a for forming grooves in the fuel cell separator 1' are formed on the upper mold 22 and the lower mold 21. When no pattern is formed on the filling container, as shown in FIG. 4(a), a resin composition A having a certain thickness is placed between the upper mold 22 and the lower mold 21, and pressure and heat are applied to produce the fuel cell separator 1'. In this case, as shown in FIG. 4(b), the density of the thin-walled portions becomes high and the density of the thick-walled portions becomes low.

[0046] Therefore, in this embodiment, a pattern 12a of protrusions and recesses is formed on the filling container 12 as shown in Fig. 2. As shown in Fig. 3(d), the thickness of the thick portion of the resulting fuel cell separator 1 is m, the thickness of the thin portion is n, and as shown in Fig. 3(a), the depth of the deep portion of the pattern 12a of the filling container 12 is M, and the depth of the shallow portion is N. The relationship between M, N, m, and n is M:N ≈ m:n. This allows the filling container to be formed with protrusions and recesses that approximate the volume ratio of the thick and thin portions of the fuel cell separator, and allows the filling container to be filled with a mass that achieves a volume ratio that approximates the volume ratio of the thick and thin portions of the fuel cell separator.

[0047] In this embodiment, the uneven pattern 12a of the filling container 12 is formed based on this idea, so that the completed fuel cell separator 1 does not have uneven density, and a uniform molded body can be obtained.

[0048] The pattern 1a of the fuel cell separator 1 and the pattern 12a of the filling container 12 may be the same, but if the pattern 1a is fine, it is not necessary to form the same pattern as the pattern 1a on the filling container 12. If the same pattern is formed exactly, problems may occur when the filling container 12 is inserted into the mold, such that the filling container 12 is not smoothly inserted into the mold, and some of the resin composition A may remain in the filling container 12. If the pattern 1a is fine, it is possible to mold a fuel cell separator with a substantially uniform density by, for example, taking the average value of multiple irregularities.

[0049] In this manner, in the above embodiment, for example, by using a dense filling container, resin composition A is simply heated and pre-molded without pressure, eliminating the need for large-scale equipment for pressing resin composition A, thereby reducing the manufacturing cost of fuel cell separators and improving production efficiency. Furthermore, since no direct manual manipulation is required, concerns about reduced yield due to the inclusion of impurities or damage to the pre-molded product are eliminated. Furthermore, resin composition A can be evenly poured into filling container 12, and there is no unevenness in density in fuel cell separator 1, so the completed fuel cell separator 1 does not warp and has minimal thickness unevenness.

[0050] Furthermore, fuel cell separators without uneven density can also be manufactured by pouring the resin composition into a mold for a fuel cell separator so that the mass of the resin composition is in a volume ratio that approximates the volume ratio of the thick and thin portions of the fuel cell separator, without using a filling container.

[0051] In the present invention, the fuel cell separator (molded body) obtained by the compression molding may be subjected to a surface roughening treatment for the purpose of removing a skin layer, adjusting surface roughness, etc. The surface roughening method is not particularly limited and may be appropriately selected from various surface roughening methods known in the art, such as blasting and polishing, but air blasting, wet blasting, barrel polishing, and brush polishing are preferred, blasting using abrasive grains is more preferred, and wet blasting is even more preferred.

[0052] In this case, the average particle size (d=50) of the abrasive grains used in the blasting treatment is preferably 3 to 30 μm, more preferably 4 to 25 μm, and even more preferably 5 to 20 μm. The material of the abrasive grains used in the blasting treatment is not particularly limited, and for example, alumina, silicon carbide, zirconia, glass, nylon, stainless steel, etc. can be used, each of which can be used alone or in combination of two or more. The discharge pressure during the wet blasting treatment cannot be generally specified because it varies depending on the particle size of the abrasive grains, etc., but is preferably 0.1 to 1 MPa, more preferably 0.15 to 0.5 MPa.

[0053] The present invention will be described in more detail below with reference to examples, comparative examples, and test examples, but the present invention is not limited to the following examples. The physical properties in the following examples were measured by the following methods. (1) Measurement of loose bulk density of carbon powder, loose bulk density, compacted bulk density, and compressibility of resin composition: The loose bulk density of carbon powder, and the loose bulk density, compacted bulk density, and compactibility of resin composition were measured using a powder tester PT-S manufactured by Hosokawa Micron Corporation. (2) Measurement of the amount of volatile matter having a boiling point of 100°C or less in resin composition: The amount of volatile matter having a boiling point of 100°C or less contained in the resin composition was measured using an infrared moisture meter FD-660 manufactured by Kett Electric Laboratory Co., Ltd., by holding the resin composition at 110°C for 10 minutes. (3) Measurement of particle size of molding resin composition: The resin composition for fuel cell separators was melt-kneaded, cooled, solidified, and pulverized. The average particle size of the molding resin composition was measured wet using a particle size distribution analyzer (MT3000, manufactured by Microtrac-Bell Co., Ltd.). (4) Measurement of filling time of resin composition: Using the filling device shown in Figure 1, the time it took for the resin composition to fill a filling container measuring 300 mm long, 400 mm wide, and 3 mm deep was measured. The measurement started when the resin composition in the hopper began to fill the filling container, and ended when the resin composition filled the space in the filling container. (5) Evaluation of variation in filling mass of resin composition: Using the filling device shown in Figure 1, the filling mass of a filling container measuring 300 mm long, 400 mm wide, and 3 mm deep was measured, and the variation in filling mass after 100 repetitions was evaluated using the following formula. The reference mass was 200 g. Filling mass variation (%) = (maximum filling mass - minimum filling mass) / reference mass (6) Evaluation of thickness unevenness of fuel cell separator The thickness of the fuel cell separator was measured at 20 points with a micrometer, and the thickness unevenness was evaluated using the following formula.Thickness Unevenness (μm) = Maximum Thickness of Fuel Cell Separator - Minimum Thickness of Fuel Cell Separator (7) Evaluation of Contact Resistance of Fuel Cell Separators (i) Carbon Paper + Separator Sample Two of the prepared fuel cell separators were stacked together, and carbon paper (TGP-H060, manufactured by Toray Industries, Inc.) was placed on top and bottom of them. Copper electrodes were then placed on top and bottom of these, and a surface pressure of 1 MPa was applied in the vertical direction, and the voltage was measured using the four-terminal method. (ii) Carbon Paper Copper electrodes were placed on top and bottom of the carbon paper, and a surface pressure of 1 MPa was applied in the vertical direction, and the voltage was measured using the four-terminal method. (iii) Method for Calculating Contact Resistance The voltage drop between the separator sample and the carbon paper was calculated from the voltage values ​​obtained in (i) and (ii) above, and the contact resistance was calculated using the following formula. Contact resistance (mΩ cm). 2 ) = (voltage drop x contact area) / current

[0054] [1] Preparation of a Resin Composition for Fuel Cell Separators [Example 1-1] 100 parts by mass of graphite 1 (loose bulk density 0.36 g / cc) was mixed with 20.4 parts by mass of an epoxy resin (ortho-cresol novolac epoxy resin, epoxy equivalent 198 g / eq), 10.7 parts by mass of a phenolic resin (novolac phenolic resin, hydroxyl equivalent 103 g / eq), and 0.25 parts by mass of 2-phenylimidazole in a Henschel mixer. The resulting mixture was melt-kneaded at 70°C for 3 minutes using a pressure kneader (MS-type small pressure kneader, manufactured by Nippon Spindle Manufacturing Co., Ltd. (formerly Moriyama Co., Ltd.)). The resulting mixture was then pulverized to 500 μm or less using a power mill (manufactured by Dalton Co., Ltd.) to prepare a resin composition for fuel cell separators.

[0055] Example 1-2 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-1, except that the mixture was melt-kneaded using a twin-screw continuous kneader (S1KRC kneader, manufactured by Kurimoto, Ltd.) instead of a pressure kneader.

[0056] [Example 1-3] The same graphite 1 and epoxy resin component as in Example 1-1, and 150 parts by mass of methyl ethyl ketone were charged into a Henschel mixer and mixed at 800 rpm for 3 minutes to prepare a mixture. The resulting mixture was dried at 40°C for 2 hours and then pulverized to 500 μm or less to prepare a resin composition for a fuel cell separator.

[0057] Example 1-4 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-1, except that graphite 2 (loose bulk density: 0.40 g / cc) was used instead of graphite 1.

[0058] Example 1-5 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-1, except that graphite 3 (loose bulk density: 0.48 g / cc) was used instead of graphite 1.

[0059] Example 1-6 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-1, except that graphite 4 (loose bulk density: 0.52 g / cc) was used instead of graphite 1.

[0060] Example 1-7 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-1, except that graphite 5 (loose bulk density: 0.60 g / cc) was used instead of graphite 1.

[0061] Example 1-8 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-1, except that graphite 6 (loose bulk density: 0.70 g / cc) was used instead of graphite 1.

[0062] Example 1-9 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-8, except that the mixture was melt-kneaded in the same twin-screw continuous kneader as in Example 1-2 instead of the pressure kneader.

[0063] Example 1-10 A mixture was prepared in the same manner as in Example 1-1, except that graphite 8 (loose bulk density 0.73 g / cc) was used instead of graphite 1, and a resin composition for a fuel cell separator was produced without subjecting the mixture to granulation such as kneading (melt-kneading and pulverization).

[0064] Example 1-11 The mixture of Example 1-10 was melt-kneaded at 70° C. using the same twin-screw continuous kneader as in Example 1-2, and the kneaded product was then pulverized to 500 μm or less to prepare a resin composition for a fuel cell separator.

[0065] Comparative Example 1-1 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-1, except that graphite 7 (loose bulk density: 0.33 g / cc) was used instead of graphite 1.

[0066] Comparative Example 1-2 A resin composition for a fuel cell separator was prepared in the same manner as in Comparative Example 1-1, except that melt-kneading was carried out at 70° C. using the same twin-screw continuous kneader as in Example 1-2 instead of the pressure kneader.

[0067] Comparative Example 1-3 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-11, except that the same pressure kneader as in Example 1-1 was used instead of the twin-screw continuous kneader to perform melt kneading at 70° C. for 3 minutes.

[0068] Comparative Example 1-4 A resin composition for a fuel cell separator was prepared in the same manner as in Comparative Example 1-2, except that graphite 7 in Comparative Example 1-2 was changed to graphite 9 (loose bulk density 0.82 g / cc).

[0069] Comparative Example 1-5: 100 parts by mass of graphite 4 (loose bulk density 0.52 g / cc) was mixed with 20.4 parts by mass of epoxy resin (ortho-cresol novolac epoxy resin, epoxy equivalent 198 g / eq), 10.7 parts by mass of phenolic resin (novolac phenolic resin, hydroxyl equivalent 103 g / eq), and 0.25 parts by mass of 2-phenylimidazole, along with 150 parts by mass of methyl ethyl ketone, in a Henschel mixer. The mixture was dried at 40°C for 2 hours and then pulverized to a particle size of 500 μm or less to prepare a resin composition for fuel cell separators.

[0070] Comparative Example 1-6 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-1, except that a roller compactor (roller compactor FT105, manufactured by Freund Corporation) was used instead of the pressure kneader.

[0071] Comparative Example 1-7 A resin composition for a fuel cell separator was prepared in the same manner as in Example 1-1, except that the mixture was not kneaded in a pressure kneader.

[0072] Table 1 shows a summary of the above examples and comparative examples.

[0073]

[0074] The resin compositions for fuel cell separators produced in Examples 1-1 to 1-11 had a compression ratio of 14.0 to 40.0%, and the content of volatile components having a boiling point of 100°C or less was adjusted to less than 1.00 mass%. Therefore, compared with the resin compositions for fuel cell separators for molding produced in Comparative Examples 1-1 to 1-2 and 1-4 to 1-7, the filling time into a filling container was shorter, and the variation in filling mass was also smaller compared with Comparative Examples 1-1 to 1-7.

[0075] [2] Production of Fuel Cell Separator Molded Body [Example 2-1] A fuel cell separator molded body was obtained using the fuel cell separator resin composition obtained in Example 1-1 by the following method: 1) Using the filling device shown in Figure 1, the resin composition was filled into a dense filling container measuring 300 mm in length, 400 mm in width, and 3 mm in depth, with irregularities approximating the volume ratio of the thick and thin portions of a fuel cell separator, 2) the filling container containing the resin composition was then heated at 75°C for 1 minute, 3) the filled container was then turned upside down directly above a fuel cell separator mold to introduce the resin composition into the mold, and 4) compression molding was performed under conditions of a mold temperature of 185°C, a molding pressure of 36.6 MPa, and a molding time of 30 seconds to obtain a dense molding (a fuel cell separator molded body measuring 300 mm in length, 400 mm in width, and 1 mm in thickness). The entire surface of the obtained fuel cell separator molded body was subjected to a roughening treatment by wet blasting using an alumina abrasive (average particle size: d50 = 6 μm) under conditions of a discharge pressure of 0.25 MPa and a conveying speed of 1.5 m / min, thereby obtaining a fuel cell separator.

[0076] [Examples 2-2 to 2-11, Comparative Examples 2-1 to 2-7] The fuel cell separator resin compositions obtained in Examples 1-2 to 1-11 and Comparative Examples 1-1 to 1-7 were compression molded in the same manner as in Example 2-1, and the entire surface of the resulting fuel cell separator molded body was roughened in the same manner as in Example 2-1 to obtain a fuel cell separator.

[0077] The thickness unevenness and contact resistance of the resulting fuel cell separator were measured using the methods described above. The results are shown in Table 2.

[0078]

[0079] The fuel cell separators obtained in Examples 2-1 to 2-11 had thickness variations of less than 50 μm, and were found to have low contact resistance.

[0080] [Test Example 1-1] The fuel cell separator resin composition obtained in Example 1-1 was directly poured into a fuel cell separator mold, and then compression molded under conditions of a mold temperature of 185°C, a molding pressure of 36.6 MPa, and a molding time of 30 seconds to obtain a fuel cell separator molded article. Next, the entire surface of the obtained fuel cell separator molded article was subjected to a surface roughening treatment in the same manner as in Example 2-1 to obtain a fuel cell separator.

[0081] The thickness unevenness and contact resistance of the resulting fuel cell separator were measured by the above-mentioned methods, and the results are shown in Table 2 together with the results of Example 2-1.

[0082]

[0083] The fuel cell separator of Example 2-1 was produced by filling a fuel cell separator resin composition into a filling container and then putting it into a mold, and therefore had less unevenness in thickness and lower contact resistance than Test Example 1-1.

[0084] REFERENCE SIGNS LIST 1 fuel cell separator 10 filling device 12 filling container 21 lower mold (mold for fuel cell separator) 22 upper mold (mold for fuel cell separator) A resin composition for fuel cell separator

Claims

1. A resin composition for fuel cell separators, comprising graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, characterized in that the compressibility calculated by the following formula is 14.0 to 40.0%, and the content of volatile components having a boiling point of 100°C or less is less than 1.00 mass%: Compressibility (%) = 100 x (solid bulk density of resin composition - loose bulk density of resin composition) / solid bulk density of resin composition 2. The resin composition for fuel cell separators according to claim 1, wherein the loose bulk density of said resin composition is 0.40 to 0.90 g / cc.

3. The resin composition for fuel cell separators according to claim 1, wherein the loose bulk density of said graphite powder is 0.35 to 0.70 g / cc.

4. A resin composition for fuel cell separators according to claim 1, wherein the base resin is at least one selected from the group consisting of an orthocresol novolac epoxy resin having an epoxy equivalent of 194 to 215 g / eq and a biphenyl epoxy resin having an epoxy equivalent of 180 to 200 g / eq.

5. The resin composition for fuel cell separators according to claim 1, wherein the curing agent is a phenol novolac resin having a hydroxyl group equivalent of 103 to 106 g / eq.

6. The fuel cell separator resin composition according to claim 1, wherein the curing accelerator is an imidazole compound having a phenyl group at the 2-position.

7. The resin composition for fuel cell separators according to claim 1, which, when filled into a container to form a fuel cell separator of 300 mm x 400 mm x 1 mm, takes less than 120 seconds to fill into the container.

8. A resin composition for fuel cell separators according to claim 1, wherein when filled into a container to form a fuel cell separator of 300 mm x 400 mm x 1 mm, the variation in the filling mass into the container is less than 2.00% of the reference mass.

9. A resin composition for a fuel cell separator is molded from a resin composition containing graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, and the degree of compression calculated by the following formula is 14.0 to 40.0%, and the content of volatile components with a boiling point of 100°C or less is less than 1.00 mass%, and the thickness variation is less than 50 μm and the contact resistance is 7.00 mΩ cm 2 Compressibility (%)=100×(packed bulk density of resin composition−loose bulk density of resin composition) / packed bulk density of resin composition 10. A method for manufacturing a fuel cell separator having thick and thin portions for forming grooves that serve as gas flow paths on at least a portion of its surface, comprising the steps of: introducing a fuel cell separator resin composition containing graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, the resin composition having a compressibility of 14.0 to 40.0% as determined by the following formula, and a volatile component content of less than 1.00 mass% with a boiling point of 100°C or less, into a fuel cell separator mold so that the introduced mass approximates the volume ratio of the thick and thin portions of the fuel cell separator: Compressibility (%) = 100 x (solid bulk density of resin composition - loose bulk density of resin composition) / solid bulk density of resin composition 11. A method for manufacturing a fuel cell separator as described in claim 10, comprising the steps of: filling the resin composition for a fuel cell separator into a filling container formed with irregularities approximating the volume ratio of the thick and thin portions of the fuel cell separator; inverting the filling container filled with the resin composition upside down directly above a mold for a fuel cell separator to pour the resin composition into the mold; and compression molding the resin composition poured into the mold.

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