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

Abstract

To provide a resin composition for a fuel cell separator capable of shortening a filling time to a filling container when manufacturing the fuel cell separator, capable of restraining dispersion of a filling quantity, and capable of forming the fuel cell separator having small thickness unevenness and low contact resistance.SOLUTION: The resin composition for a fuel cell separator includes a graphite powder and an epoxy resin component containing a main agent, a curing agent and a curing accelerator, and has a compression degree of 14.0 to 40.0% obtained 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%. Compressibility (%) = 100 * (Tight bulk density of resin composition-Loose bulk density of resin composition) / Tight bulk density of resin composition SELECTED DRAWING: None

Description

[Technical Field]

[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. [Background technology]

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

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

[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 and temporarily molding the powdered raw material in the filling container, and then placing the resulting temporarily 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 a filling container with powdered raw material, to heating it, and then pouring it into a mold, is 3 to 4 minutes, which causes a problem of 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 within the raw material supply device, which can cause the problem that the specified mass cannot be filled into the filling container. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-244937 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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 is 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, wherein 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%. Compressibility (%) = 100 × (solid bulk density of resin composition - loose bulk density of resin composition) / solid 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. The resin composition for a fuel cell separator 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 a fuel cell separator 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 a fuel cell separator according to 1, wherein the curing accelerator is an imidazole compound having a phenyl group at the 2-position. 7. The resin composition for a fuel cell separator 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 filling time into the filling container is less than 120 seconds. 8. The resin composition for fuel cell separators according to 1, wherein when the resin composition is 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 of the container is less than 2.00% of the reference mass. 9. A resin composition for a fuel cell separator, which contains graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, and has a compressibility calculated by the following formula of 14.0 to 40.0% and a content of volatile components with a boiling point of 100°C or less of less than 1.00% by mass, is molded into a sheet having a thickness variation of less than 50 μm and a contact resistance of 7.00 mΩ·cm. 2 a fuel cell separator having a thickness of less than 1 / 2 mm; Compressibility (%) = 100 × (solid bulk density of resin composition - loose bulk density of resin composition) / solid 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 the surface, comprising: a method for producing a fuel cell separator, comprising: a step of introducing a resin composition for a fuel cell separator, the resin composition comprising graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, the resin composition having a compressibility calculated by the following formula of 14.0 to 40.0% and a content of volatile components having a boiling point of 100°C or less of less than 1.00% by mass, into a mold for a fuel cell separator such that the introduced mass is a volume ratio that approximates the volume ratio of the thick-walled portion to the thin-walled portion of the fuel cell separator; Compressibility (%) = 100 × (solid bulk density of resin composition - loose bulk density of resin composition) / solid bulk density of resin composition 11. A step of filling the fuel cell separator resin composition into a filling container having irregularities formed thereon that approximate the volume ratio of the thick-walled portion to the thin-walled portion of the fuel cell separator; a step of inverting the container filled with the resin composition upside down directly above a mold for a fuel cell separator and pouring the resin composition into the mold; 11. The method for producing a fuel cell separator according to claim 10, further comprising a step of compression molding the resin composition poured into the mold. to provide. [Effects of the Invention]

[0010] The resin composition for fuel cell separators of the present invention has a predetermined degree of compression, and the content of volatile components with a boiling point of 100°C or less is adjusted to a predetermined range. Therefore, the resin composition has excellent fluidity and filling 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 filling mass poured into the mold. A fuel cell separator obtained by molding the fuel cell separator composition of the present invention having such properties has small thickness variations and low contact resistance. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view showing an example of a resin composition filling device used in the production of a fuel cell separator of the present invention. [Figure 2] FIG. 2 is a schematic perspective view showing a main part of the filling device of FIG. [Figure 3] 10A and 10B are explanatory diagrams showing a molding process when a pattern is formed on a filled container. [Figure 4] 10A and 10B are explanatory diagrams showing a molding process when no pattern is formed on the filled container. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in more detail below. [Resin composition for fuel cell separator] The resin composition for fuel cell separators 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 × (solid bulk density of resin composition - loose bulk density of resin composition) / solid bulk density of resin composition

[0013] In the present invention, the compressibility of the resin composition for a fuel cell separator is 14.0 to 40.0%, and preferably 18.0 to 35.0%. If the compression rate is less than 14.0%, the time required to fill the resin composition of the present invention into a mold or filling container will be shorter, but on the other hand, the fluidity will be excessive, so that the mass when filling the resin composition into a mold or filling container will be greater than the standard value or the resin composition will overflow from the mold or filling container, making it impossible to stably fill a mass that results in a volume ratio approximating the volume ratio of the thick part (thick portion) to the thin part (thin portion) of a fuel cell separator. If the compression rate exceeds 40.0%, the fluidity of the resin composition of the present invention will be insufficient, and it will take a long time to fill it into a mold or a filling container, and the mass when filled into the mold or filling container will be less than the reference mass, making it impossible to stably fill a mass that will result in a volume ratio that approximates the volume ratio of the thick and thin portions of a 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 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 fuel cell separator resin composition of the present invention may be in any form such as granules or powder as long as it satisfies the above-mentioned compressibility and other requirements, but is preferably in powder form. 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 Microtrack Bell Co., Ltd.).

[0016] The loose bulk density of the resin composition for a fuel cell separator 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 an appropriate fluidity, so that it does not take a long time to fill the resin composition into a mold or a filling container, and the resin composition does not aggregate in the 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, and 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 filling container, and it will not be possible to stably fill a mass that will result in a volume ratio approximating the volume ratio of the thick and thin portions of a fuel cell separator. In the present invention, the amount of volatile components contained in the resin composition having a boiling point of 100°C or less is measured under conditions of holding the composition at 110°C for 10 minutes using an infrared moisture meter FD-660 manufactured by Kett Electric Laboratory Co., Ltd.

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

[0019] The loose bulk density of the graphite powder used in the present invention is preferably 0.35 to 0.75 g / cc, 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 the 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, and examples thereof include orthocresol 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, which can be used alone or in combination of two or more. Among these, orthocresol 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 in the case of an orthocresol novolac type epoxy resin, it is preferably 194 to 215 g / eq, and in the case of a biphenyl type epoxy resin, it is preferably 180 to 200 g / eq.

[0021] The hydrolyzable chlorine content of the epoxy resin base resin used in the present invention is preferably 450 ppm or less. When 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, a lower limit of 370 ppm is preferred from the standpoint of cost.

[0022] The curing agent constituting the epoxy resin component is preferably a phenolic resin. Specific examples thereof include novolac phenolic resin, cresol novolac phenolic resin, resol phenolic resin, aralkyl-modified phenolic resin, biphenyl novolac phenolic resin, and trisphenolmethane phenolic resin. These may be used alone or in combination of two or more. Among these, novolac phenolic resin is 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 the imidazole compound having an aryl group at the 2-position include 2-phenylimidazole and 2-phenyl-4-methylimidazole. 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. Specific examples include stearic acid wax, amide wax, montanic acid wax, carnauba wax, and polyethylene wax. These may be used alone or in combination of two or more.

[0025] In the resin composition of the present invention, the blending amounts of the graphite powder and epoxy resin components (main agent, curing agent, and curing accelerator) are not particularly limited, but the blending amounts of the epoxy resin components per 100 parts by mass of the graphite powder are preferably 22 to 40 parts by mass, more preferably 27 to 35 parts by mass, and even more preferably 30 to 33 parts by mass. By setting the blending amount of the epoxy resin component within this range, the fluidity of the resin composition becomes appropriate, resulting in good moldability, and it is possible to prevent a significant decrease in the gas impermeability and electrical conductivity of the resulting fuel cell separator. In this case, the curing agent is preferably blended in an amount of 0.98 to 1.08 equivalents relative to the base resin, and more preferably 0.99 to 1.05 equivalents. The amount of the curing accelerator used is not particularly limited, but is preferably 0.1 to 5 parts by mass, more preferably 0.5 to 2 parts by mass, per 100 parts by mass of the mixture of the base agent and the 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 described below, for example, when producing a fuel cell separator measuring 300 mm x 400 mm x 1 mm, the resin composition for a fuel cell separator of the present invention can be filled into a filling container of a size corresponding to the fuel cell separator (e.g., 300 mm x 400 mm x 3 mm) in less than 120 seconds. The lower limit of the filling time is not particularly limited, but is usually 20 seconds or more. The method for measuring the filling time is as described in the Examples described below. Furthermore, for example, when manufacturing a fuel cell separator of the same size as above, the variation in the filling mass relative to the reference mass when filling a container 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 usually 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 by, for example, mixing graphite powder, a base resin, a curing agent, and a curing accelerator in any order in predetermined proportions using a mixer such as a planetary mixer, ribbon blender, Loedige mixer, Henschel mixer, rocking mixer, or Nauta mixer. When an internal mold release agent is used, the order of addition is also arbitrary. Since the resin composition for fuel cell separators of the present invention is in powder form, it is preferable to use raw materials that are also in powder form, which allows the powdered resin composition to be easily prepared.

[0028] In producing the resin composition, if necessary, for the purpose of adjusting the degree of compression to the above-mentioned range or reducing the content of volatile components with a boiling point of 100°C or less to less than a predetermined amount, the components may be mixed, and then the resulting mixture may be dried, for example, at 30 to 60°C for 1 to 3 hours, and pulverized to obtain a resin composition for fuel cell separators. Alternatively, after mixing the components, the mixture may be melted and kneaded using a pressure kneader, a twin-screw continuous kneader, an extruder, a heated roll, or the like, cooled, and then 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 a fuel cell separator, 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, preferably 49 μm or less. There is no particular lower limit, and the smaller 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 variation (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 2The lower limit is not particularly limited, but the smaller the better. 2 That's all. 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 produced, for example, by placing the fuel cell separator resin composition of the present invention described above into a predetermined mold and compression molding it. Examples of the mold that can be used include a fuel cell separator mold that can form grooves that serve as gas flow channels on at least a portion of one or both surfaces of the molded product. This produces a fuel cell separator that has thick and thin portions on at least a portion of the surface that form the grooves that serve as gas flow channels. In this case, the resin composition may be poured into the mold by any method, but it is preferable to pour it into the mold for a fuel cell separator so that the poured mass is in a volume ratio that approximates the volume ratio of the thick and thin portions of the desired fuel cell separator. The conditions for compression molding are not particularly limited, but the mold temperature is 150 to 190° C., and the molding pressure is 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, but from the viewpoint of production efficiency, a short time is preferable, specifically 40 seconds or less is preferable. After compression molding, the mixture 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 volatile components with 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. Therefore, the resin composition can be particularly suitably used in a manufacturing method such as that disclosed in Patent Document 1, which includes a step of first filling a powder raw material into a filling container and then pouring it into a mold. Therefore, the fuel cell separator of the present invention is preferably produced by a production method comprising the steps of filling a filling container with the above-mentioned resin composition, the filling container having projections and recesses formed thereon that approximate the volume ratio of the thick and thin portions of the fuel cell separator, inverting the filled container upside down directly above a mold for the fuel cell separator to pour the resin composition into the mold, and compression molding the resin composition poured into the mold. Note that in the present invention, "a filling container having projections and recesses formed thereon that approximate the volume ratio of the thick and thin portions of the fuel cell separator" refers to a filling container having recesses corresponding to the thick portions of the fuel cell separator and projections corresponding to the thin portions, the volume ratio of the recesses to the projections being approximately equal to the volume ratio of the thick and thin 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, and examples include heating at 50 to 100°C for 0.5 to 10 minutes.

[0034] Hereinafter, one embodiment of the method for manufacturing a fuel cell separator of the present invention will 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 FIG. 1 and 2, the filling device 10 is configured to include a hopper 11 that holds the 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 almost horizontally on the movable table 13, with its upper surface 12b being a nearly horizontal plane.

[0035] Moving means 14 is attached to moving table 13 via wheels 13a and rod 14a, and is placed on base 15 such as a rail. Rod 14a is also connected to a rotation mechanism (not shown), and by driving the rotation mechanism, rod 14a rotates around its axis, causing moving table 13 to rotate integrally with rod 14a. To move the movable table 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 movable table 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 poured. A narrow rectangular supply port 11b is provided at the bottom of the hopper 11. Note that this supply port 11b may be provided with an openable / closable lid 11c that can be opened and closed by sliding, for example. Supply port 11b is located a predetermined distance, for example, about 0.1 to 1 mm above upper surface 12b of filling container 12, and is configured so as to be able to scrape over upper surface 12b. If there are lumps in the resin composition A, the filled resin composition A may become uneven, so to prevent this, a mesh screen may be provided at the supply port 11b. The hopper 11 is supported by a support (not shown) and is configured to be vibrated in a horizontal plane as shown by the arrow in Fig. 1 by a vibrator (not shown) provided on the support, hopper 11, etc. The vibrator may be a rotary vibrator, a piston vibrator, or the like.

[0037] As shown in Figure 2, the filling container 12 has an uneven pattern 12a formed thereon that corresponds to the grooves of the fuel cell separator and that takes into account the thickness distribution and 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 mold for the fuel cell separator. However, since no pressure is applied by pressing, it is only necessary that the resin composition A does not deform when heated near its melting point and has heat resistance enough to withstand that temperature. Also, considering the transportation during heating and charging, a lightweight material is preferred. Furthermore, since heat needs to be evenly distributed to the resin composition A when heated by a heater or the like, a material with high thermal conductivity is preferred. Considering these points, for example, a dense filling container made of aluminum or the like is preferred.

[0038] The opening width w, outer width W of the filling container 12, and the length L of the supply port 11b of the hopper 11 are usually set such that w ≦ L < W. When arranging the filling container 12, the supply port 11b straddles the opening of the filling container 12. This is because if L < w, the resin composition A will not enter the filling container 12 evenly, 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, there may be cases where L < w.

[0039] When filling the resin composition A into the filling container 12, first, place the filling container 12 so that the opening end of the filling container 12 is located approximately at the center of the supply port 11b of the hopper 11, and then charge the resin composition A into the hopper 11. At that time, by vibrating the hopper 11 in the left - right direction of FIG. 2 simultaneously with a vibrator (not shown), the internal resin composition A can smoothly fall without being caught in the middle.

[0040] When the resin composition A is charged into the hopper 11, the resin composition A falls and is filled in the lower part of the supply port 11b in the filling container 12, and the resin composition A in the space 11a of the hopper accumulates on it. When the moving table 13 moves in the direction of the arrow in FIG. 2 from this state, while filling the resin composition A in the hopper 11 into the filling container 12, the excess resin composition A is scraped off at the supply port 11b of the hopper 11 to fill the resin composition A so that the upper surface is flat. A scraping plate (not shown) may be provided for the purpose of scraping at the upper surface 12b of the filling container 12. When filling container 12 has passed under supply port 11b, the resin composition A is filled into the space of filling container 12 on which concave and convex 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 heating device such as a heater 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, part of the resin contained in resin composition A melts, and the particles are lightly welded together, so that the resin does not immediately fall out even if filling container 12 is turned upside down. In the case of powder, it is difficult to pour resin composition A into a mold all at once, but pre-molding makes it possible to pour resin composition A, whose particles are lightly welded together, all at once, making it easy to pour evenly. The degree of adhesion between the particles after pre-molding may be such that some of the resin is melted and the filled container 12 is just barely prevented from falling off when it is inverted, or such that all of the resin is melted and integrated, and the particles will break if a strong stress is applied but will not break or break if a small stress is applied; however, it is preferable that the particles are just barely prevented from falling off when the filled container 12 is inverted.

[0043] Next, moving means 14 moves moving table 13, and as shown in Figure 3(b), filled container 12 filled with resin composition A is brought directly above lower molding die 21 on which pattern 21a has been formed, and is accurately positioned using a positioning pin or the like. Rod 14a is then rotated using a rotation mechanism (not shown) to turn filled container 12 upside down together with moving table 13, and resin composition A is dropped onto lower molding die 21. Even if resin composition A is only fused to the extent that it will crumble if an attempt is made to remove it from filled container 12, and it cannot be removed directly from filled container 12, this method allows it to be poured evenly into the die. Then, as shown in Figure 3(c), the upper mold 22 on which the pattern 22a 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 Figure 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 areas 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 in 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) on which no pattern is formed. As shown in FIG. 4(a), patterns 21a, 22a for forming grooves in a fuel cell separator 1' are formed on an upper mold 22 and a 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 a 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, an uneven pattern 12a is formed on the filling container 12 as shown in Fig. 2. Then, 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 set to M:N ≈ m:n. By doing this, unevenness that approximates the volume ratio of the thick portion to the thin portion of the fuel cell separator can be formed on the filling container, and the filling container can be filled with a mass that has a volume ratio that approximates the volume ratio of the thick portion to the thin portion 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 filled 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 filled container 12. If the same pattern is formed exactly, problems may occur when the filled container 12 is inserted into the mold, such that the filled container 12 is not smoothly inserted into the mold, and some of the resin composition A may remain in the filled container 12. If the pattern 1a is fine, it is possible to mold a fuel cell separator with a nearly uniform density by, for example, taking the average value of multiple irregularities.

[0049] In this way, in the above embodiment, for example, by using a dense filling container, resin composition A is simply heated and pre-molded without being pressurized, which eliminates 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 direct manual manipulation is not required, concerns about the inclusion of impurities or reduced yield due to damage to the pre-molded product can be eliminated. Furthermore, the resin composition A can be evenly poured into the filling container 12, and there is no unevenness in density in the fuel cell separator 1, so the finished fuel cell separator 1 does not warp and has little unevenness in thickness.

[0050] Furthermore, fuel cell separators without uneven density can also be produced 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 above compression molding may be subjected to a surface roughening treatment for the purposes of removing the skin layer and adjusting the surface roughness. The roughening treatment method is not particularly limited and may be appropriately selected from various conventionally known roughening methods such as blasting and polishing. 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 process is not particularly limited, and examples thereof include alumina, silicon carbide, zirconia, glass, nylon, and stainless steel, which may be used alone or in combination of two or more. The discharge pressure during wet blasting cannot be generally defined because it varies depending on the particle size of the abrasive grains, but is preferably 0.1 to 1 MPa, more preferably 0.15 to 0.5 MPa. [Example]

[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. Note that 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 the carbon powder, and the loose bulk density, compacted bulk density and compressibility of the resin composition were measured using a powder tester PT-S manufactured by Hosokawa Micron Corporation. (2) Measurement of the amount of volatile matter in a resin composition with a boiling point of 100°C or less The volatile content of the resin composition having a boiling point of 100°C or less was measured by an infrared moisture meter FD-660 manufactured by Kett Electric Laboratory Co., Ltd. under conditions of holding the temperature 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 and solidified, and pulverized to form a molding resin composition, and the average particle size of the pulverized resin composition was measured in a wet manner using a particle size distribution measuring device (MT3000 manufactured by Microtrack Bell Co., Ltd.). (4) Measurement of filling time of resin composition Using the filling device shown in FIG. 1, the time required for the resin composition to be filled into a filling container measuring 300 mm in length, 400 mm in width, and 3 mm in depth was measured. The time 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, a filling container measuring 300 mm in length, 400 mm in width, and 3 mm in depth was filled with the resin composition, and the filling mass was measured. After 100 repetitions, the filling mass variation was evaluated using the following formula. The reference mass was set to 200 g. Filling mass variation (%) = (maximum filling mass - minimum filling mass) / reference mass (6) Evaluation of thickness unevenness in fuel cell separators 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 variation (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 on top of each other, and carbon paper (TGP-H060, manufactured by Toray Industries, Inc.) was placed on the top and bottom of them. Copper electrodes were then placed on the top and bottom of those, 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 the 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) Contact resistance calculation method The voltage drop between the separator sample and the carbon paper was determined from the voltage values ​​determined 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] Production of a resin composition for a fuel cell separator [Example 1-1] An epoxy resin component consisting of 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 group equivalent 103 g / eq), and 0.25 parts by mass of 2-phenylimidazole was charged into a Henschel mixer and mixed at 800 rpm for 3 minutes to prepare a mixture. 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.)), and the kneaded mixture was then pulverized to 500 μm or less using a pulverizer (Power Mill, manufactured by Dalton Co., Ltd.) to produce a resin composition for fuel cell separators.

[0055] [Example 1-2] A resin composition for a fuel cell separator was produced 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] [Examples 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 crushed to 500 μm or less to prepare a resin composition for a fuel cell separator.

[0057] [Examples 1-4] A resin composition for a fuel cell separator was produced 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] [Examples 1-5] A resin composition for a fuel cell separator was produced 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] [Examples 1-6] A resin composition for a fuel cell separator was produced 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] [Examples 1-7] A resin composition for a fuel cell separator was produced 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] [Examples 1-8] A resin composition for a fuel cell separator was produced 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] [Examples 1-9] A resin composition for a fuel cell separator was produced 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] [Examples 1-10] A mixture was prepared in the same manner as in Example 1-1 using graphite 8 (loose bulk density 0.73 g / cc) instead of graphite 1, and a resin composition for fuel cell separators was produced without subjecting the mixture to granulation such as kneading (melt kneading and pulverization).

[0064] [Examples 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 then the kneaded product was 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 produced 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 mixture was melt-kneaded at 70° C. for 3 minutes using the same pressure kneader as in Example 1-1 instead of the twin-screw continuous kneader.

[0068] [Comparative Example 1-4] A resin composition for a fuel cell separator was produced 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] An epoxy resin component consisting of 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 group equivalent 103 g / eq), and 0.25 parts by mass of 2-phenylimidazole, and 150 parts by mass of methyl ethyl ketone was added to 100 parts by mass of graphite 4 (loose bulk density 0.52 g / cc) in 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 the kneaded product was pulverized to 500 μm or less to prepare a resin composition for a fuel cell separator.

[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 produced 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] [Table 1]

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

[0075] [2] Manufacturing of fuel cell separator molded bodies [Example 2-1] The fuel cell separator resin composition obtained in Example 1-1 was used to obtain a fuel cell separator molded article by the following method. 1) Using the filling device shown in Figure 1, the mixture was filled into a dense filling container measuring 300 mm in length, 400 mm in width, and 3 mm in depth, with irregularities that approximate the volume ratio of the thick and thin parts of a fuel cell separator. 2) Next, the container containing the resin composition is heated at 75°C for 1 minute, 3) Next, the container filled with the resin composition is turned upside down directly above the fuel cell separator mold to pour the resin composition into the mold; 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 molded body (a molded body for fuel cell separators, length 300 mm x width 400 mm x thickness 1 mm). The entire surface of the obtained fuel cell separator molded body was roughened by wet blasting using an alumina abrasive (average particle size: d50 = 6 μm) at a discharge pressure of 0.25 MPa and a conveying speed of 1.5 m / min to obtain a fuel cell separator.

[0076] [Examples 2-2 to 2-11, Comparative Examples 2-1 to 2-7] The resin compositions for fuel cell separators 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] [Table 2]

[0079] It is clear that the fuel cell separators obtained in Examples 2-1 to 2-11 had thickness variations of less than 50 μm and low contact resistance.

[0080] [Test Example 1-1] The resin composition for fuel cell separator obtained in Example 1-1 was directly poured into a mold for fuel cell separator, and then compression molded under the 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 molded body for fuel cell separator. 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 methods described above, and the results are shown in Table 2 together with the results of Example 2-1.

[0082] [Table 3]

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

[0084] 1. Fuel cell separator 10 Filling equipment 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 separators

Claims

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, wherein 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%. Compressibility (%)=100×(solid bulk density of resin composition−loose bulk density of resin composition) / solid bulk density of resin composition

2. 2. The resin composition for fuel cell separators according to claim 1, wherein the resin composition has a loose bulk density of 0.40 to 0.90 g / cc.

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

4. 2. The resin composition for fuel cell separators according to claim 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. 2. The resin composition for a fuel cell separator 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. 2. 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. 2. The resin composition for a fuel cell separator according to claim 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 filling time into the filling container is less than 120 seconds.

8. 2. The resin composition for fuel cell separators according to claim 1, wherein when the resin composition is 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. The resin composition for a fuel cell separator is molded from a resin composition containing graphite powder and an epoxy resin component containing a base resin, a curing agent, and a curing accelerator, and has a compressibility of 14.0 to 40.0% as determined by the following formula, and a content of volatile components having a boiling point of 100°C or less of less than 1.00% by mass, and has a thickness variation of less than 50 μm and a contact resistance of 7.00 mΩ cm 2 A fuel cell separator characterized in that: Compressibility (%)=100×(solid bulk density of resin composition−loose bulk density of resin composition) / solid 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 the surface, comprising: A method for manufacturing a fuel cell separator, comprising: a step of pouring a resin composition for a fuel cell separator, the resin composition comprising graphite powder and an epoxy resin component including a base resin, a curing agent, and a curing accelerator, the resin composition having a compressibility calculated by the following formula of 14.0 to 40.0% and a content of volatile components having a boiling point of 100°C or less of less than 1.00 mass%, into a mold for a fuel cell separator such that the poured mass is a volume ratio that approximates the volume ratio of the thick-walled portion to the thin-walled portion of the fuel cell separator. Compressibility (%)=100×(solid bulk density of resin composition−loose bulk density of resin composition) / solid bulk density of resin composition

11. a step of filling the resin composition for a fuel cell separator into a filling container having irregularities formed thereon that approximate the volume ratio of the thick-walled portion to the thin-walled portion of the fuel cell separator; a step of inverting the container filled with the resin composition upside down directly above a mold for a fuel cell separator and pouring the resin composition into the mold; The method for manufacturing a fuel cell separator according to claim 10, further comprising the step of compression molding the resin composition poured into the mold.

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