JP5486276B2 - Resin composition for fuel cell separator, sheet for molding fuel cell separator, and fuel cell separator - Google Patents

Description

  The present invention relates to a resin composition for a fuel cell separator, a fuel cell separator molding sheet, and a fuel cell separator.

  In general, a fuel cell is composed of a cell stack in which several tens to several hundreds of unit cells are stacked in series, thereby obtaining a predetermined voltage.

  The most basic structure of the unit cell has a configuration of “separator / fuel electrode (anode) / electrolyte / oxidant electrode (cathode) / separator”. In this unit cell, the chemical energy of the reaction is obtained by oxidizing the fuel by electrochemical reaction by supplying fuel to the fuel electrode and supplying the oxidant to the oxidant electrode of the pair of electrodes facing each other through the electrolyte. Direct conversion to electrochemical energy.

  Such fuel cells are classified into several types depending on the type of electrolyte, but in recent years, solid polymer fuel cells using a solid polymer electrolyte membrane as an electrolyte have attracted attention as high-power fuel cells. Has been.

  FIG. 2 shows an example of a polymer electrolyte fuel cell. A solid polymer fuel cell is disposed between two fuel cell separators 1 and 1 each having a plurality of convex portions (ribs) 1a formed on both left and right side surfaces. A single cell (unit cell) is formed by interposing the molecular electrolyte membrane 4 and the gas diffusion electrodes (fuel electrode and oxidant electrode) 3 and 3, and several tens to several hundreds of unit cells are arranged in parallel. A battery body (cell stack) is configured. The convex portion 1a constitutes a gas supply / discharge groove 2 which is a flow path for hydrogen gas as a fuel and oxygen gas as an oxidant between adjacent convex portions 1a.

  Such a cell stack is composed of, for example, 50 to 100 unit cells for a stationary type for home use, 400 to 500 unit cells for mounting on a car, and 10 to 20 for mounting on a notebook computer. It is composed of unit cells.

  In this polymer electrolyte fuel cell, by supplying hydrogen gas as a fluid to the fuel electrode and oxygen gas as a fluid to the oxidizer electrode, current can be taken out from an external circuit. In each electrode, the reaction shown in the following formula occurs.

Fuel electrode reaction: H ₂ → 2H ⁺ + 2e ⁻ (1)
Oxidant electrode reaction: 2H ⁺ + 2e ⁻ + 1 / 2O ₂ → H ₂ O (2)
Overall reaction: H ₂ + 1 / 2O ₂ → H ₂ O
That is, hydrogen (H ₂ ) becomes proton (H ⁺ ) on the fuel electrode, and this proton moves through the solid polymer electrolyte membrane 4 to the oxidant electrode and reacts with oxygen (O ₂ ) on the oxidant electrode. To produce water (H ₂ O). Therefore, for the operation of the polymer electrolyte fuel cell, it is necessary to supply and discharge the reactive gas and to take out the current.

  In addition, the polymer electrolyte fuel cell is normally assumed to operate in a humid atmosphere in the range of room temperature to 120 ° C., and therefore water is often handled in a liquid state. It is necessary to manage the replenishment of liquid water and discharge the liquid water from the oxidizer electrode.

  In addition, a methanol direct fuel cell (DMFC), which is a type of solid polymer fuel cell, supplies a methanol aqueous solution instead of hydrogen as a fuel. In this case, each electrode has the following formula: A reaction is occurring. An oxygen reduction reaction (the same reaction as when hydrogen is used as fuel) occurs at the air electrode.

Fuel electrode reaction: CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1 ′)
Air electrode reaction: 3/2 O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2 ′)
Overall reaction: CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O
Comparing the overall reactions of a methanol direct fuel cell (DMFC) and a normal polymer electrolyte fuel cell, the methanol direct fuel cell generates 6 times as much water, so the liquid state from the oxidizer electrode Water discharge becomes even more important.

  Among the components constituting such a fuel cell, the separator 1 has a plurality of gas supply / discharge grooves 2 on one side or both sides of a thin plate-like body as shown in FIGS. 2 (a) and 2 (b). It has a unique shape and has the function of separating the fuel gas, oxidant gas and cooling water flowing in the fuel cell so that they do not mix, and transmits the electric energy generated by the fuel cell to the outside, It plays an important role of radiating the heat generated in the fuel cell to the outside.

  Conventionally, as a method of manufacturing the separator 1, there is known a method of molding a resin composition mainly composed of a thermosetting resin such as phenol resin or epoxy resin and graphite by compression molding, injection molding, transfer molding, or the like. (For example, refer to Patent Document 1-2). However, these methods are difficult to cope with the thinning of the separator 1.

  Therefore, in order to reduce the thickness and weight of the separator 1 and reduce the cost thereof, the resin composition is formed into a sheet shape by a roll molding method or an extrusion molding method, and further compression molding is performed on the sheet. Attempts have also been made to produce the separator 1 by hot pressing molding or the like. However, in this case, the graphite particles in the composition are subjected to a large stress during roll forming or extrusion forming for forming a sheet, so that the graphite particles are finely divided. There was a problem that the performance would be lowered. In addition, there is a problem that the mechanical strength of the separator 1 is reduced due to the thinning. For this reason, about the thinning of the separator 1 by such a method, the prospect for practical use was not found.

  Further, when the separator 1 is manufactured, the thinner the separator 1 is, the greater the influence of the thickness error on the total thickness of the separator 1 is. For example, when the total thickness of the separator 1 is 2 mm and when it is 0.5 mm, even if the thickness error is about ± 30 μm, the latter is more influenced by the thickness error. For this reason, when the separator 1 is thinned, further improvement in thickness accuracy is required for practical use. Moreover, high continuous moldability is also required for practical use.

JP 2001-216976 A JP 2002-114572 A

  The present invention has been made in view of the above-described problems, and enables the fuel cell separator to be thinned and can improve the thickness accuracy and moldability of the fuel cell separator. An object of the present invention is to provide a fuel cell separator molding sheet, a fuel cell separator resin composition, and a fuel cell separator formed from the fuel cell separator molding sheet.

The resin composition for a fuel cell separator according to the present invention comprises the following component (A), the following component (B) as at least part of the epoxy resin in the thermosetting resin, and the following (C) as at least part of the curing agent: ) Component and the following component (D) as at least a part of the curing accelerator, and is in a liquid state;
(A) Graphite particles having a particle size passing through a 100 mesh sieve (mesh size 150 μm) and having an average particle size of 30 to 70 μm,
(B) An epoxy made of an ortho cresol novolac type epoxy resin or an ortho cresol novolak type epoxy resin and at least one selected from a bisphenol type epoxy resin, a biphenyl type epoxy resin, and a phenol aralkyl type epoxy resin having a biphenylene skeleton. Resin component,
(C) phenol resin, and (D) measurement start temperature 30 ° C., heating rate 10 ° C./min, holding temperature 120 ° C., holding time 30 minutes at holding temperature, weight loss 5% or less A substituted imidazole having a hydrocarbon group at the 2-position.

  For this reason, in the present invention, the substituted imidazole acts as a curing accelerator, and the substituted imidazole increases the storage stability of the liquid resin composition and decreases the volatility when forming a sheet from the resin composition. Further, the smoothness of the sheet is improved.

In the present invention, the resin composition for a fuel cell separator preferably further contains the following component (E);
(E) At least one internal mold release agent that is phase-separated with a thermosetting resin and a curing agent at 120 to 190 ° C. and is selected from polyethylene wax, carnauba wax, and long-chain fatty acid wax.

  In this case, the releasability at the time of mold forming is excellent, and the continuous moldability is excellent.

In the present invention, the resin composition for a fuel cell separator preferably further contains the following component (F);
(F) Epoxysilane coupling agent.

  In this case, the component (F) is a liquid, the dispersibility of the graphite particles in the composition is improved, the occurrence of aggregation is suppressed, and the stability of the composition is improved. Moreover, the moldability of the resin composition for a fuel cell separator is further improved by the component (F) acting as a plasticizer.

In the present invention, the fuel cell separator resin composition contains the components (A) to (F), and in the solid content, the content of the component (A) is 75 to 85% by mass,
The total content of the thermosetting resin and the curing agent is 14 to 24.1% by mass,
The content of the component (D) is 0.5 to 3% by mass with respect to the total content of the thermosetting resin and the curing agent,
The content of the component (E) is 0.1-1% by mass,
It is also preferable that the content of the component (F) is 0.5 to 1.5% by mass.

  Solid content is all the components except the solvent in a resin composition, and when not containing a solvent, it is all the components of a resin composition.

  In this case, the component (F) acts optimally as a plasticizer, and the moldability of the fuel cell separator resin composition is further improved.

  In this invention, it is preferable that the equivalent of the hydroxyl group of the said (C) component with respect to 1 equivalent of epoxy groups of the said epoxy resin is the range of 0.8-1.2.

  In this case, the moldability of the resin composition for a fuel cell separator is further improved. In particular, moldability is improved when the hydroxyl group is slightly excessive.

  In the present invention, the component (D) is preferably a substituted imidazole having 6 to 17 carbon atoms in the 2-position hydrocarbon group.

  In this case, the volatility at the time of forming a sheet from the resin composition is further reduced, thereby further stabilizing the moldability.

  In the present invention, the component (D) is preferably at least one selected from 2-undecylimidazole and 2-heptadecylimidazole.

  In this case, the volatility when forming a sheet from the resin composition is further reduced. Moreover, these (D) components are also easily available.

  The fuel cell separator molding sheet according to the present invention is characterized in that the resin composition for a fuel cell separator is molded into a sheet shape.

  The fuel cell separator according to the present invention is formed from the resin composition for a fuel cell separator.

  According to the present invention, the fuel cell separator resin composition has high storage stability, is less likely to volatilize, has high stability when molded into a sheet, and has a high thickness accuracy and a thin fuel cell separator molding sheet. And a fuel cell separator can be produced. Further, the power generation characteristics of a fuel cell produced using this fuel cell separator can be stabilized. Further, according to the present invention, the fuel cell separator can be stably manufactured.

It is sectional drawing of the fuel cell separator which shows an example of embodiment of this invention. (A) is a schematic perspective view showing a unit cell of the fuel cell, and (b) is a schematic perspective view showing a fuel cell separator in the unit cell.

  Embodiments of the present invention will be described below.

  A resin composition for a fuel cell separator (resin composition) is (A) a graphite particle having a particle size that passes through a 100 mesh sieve (aperture 150 μm) and having an average particle size of 30 to 70 μm, and (B) orthocresol. An epoxy resin component composed of a novolac type epoxy resin, or an ortho cresol novolac type epoxy resin and at least one selected from a bisphenol type epoxy resin and a phenol aralkyl type epoxy resin having a biphenylene skeleton, (C) a phenol resin, And (D) The weight loss when heated under the conditions of 30 ° C. measurement start temperature, 10 ° C./min heating rate, 120 ° C. holding temperature, and 30 min holding time at the holding temperature is 5% or less. Contains a substituted imidazole having a hydrocarbon group.

  As the graphite particles of component (A), any graphite particles can be used as long as they exhibit high conductivity. For example, graphitized carbonaceous materials such as mesocarbon microbeads, coal-based coke, and petroleum-based coke. In addition to the graphitized material, an appropriate material such as a graphite electrode, a processed powder of a special carbon material, natural graphite, quiche graphite, expanded graphite, or the like can be used. Such graphite particles can be used alone or in combination of two or more.

  The graphite particles may be either artificial graphite powder or natural graphite powder. Natural graphite powder has the advantage of high conductivity, and artificial graphite powder has the advantage of low anisotropy, although the conductivity is somewhat inferior to that of natural graphite powder.

  Further, it is preferable that the graphite particles are purified in both cases of natural graphite powder and artificial graphite powder. In this case, since the ash content and ionic impurities are low, the fuel which is a molded product The elution of impurities from the battery separator 1 (separator 1) can be suppressed.

  Here, the ash content in the graphite particles is preferably 0.05% by mass or less, and if the ash content exceeds 0.05% by mass, the characteristics of the fuel cell may be deteriorated.

  The average particle size of the graphite particles is in the range of 30 to 70 μm. When the average particle size is 30 μm or more, the moldability of the resin composition becomes excellent, and when it is 70 μm or less, the surface smoothness of the separator 1 is improved.

  Further, if the graphite particles contain particles that do not pass through a 100 mesh sieve, graphite particles having a large particle size are mixed in the resin composition, and the resin composition is particularly formed into a thin sheet. The formability at the time will fall.

  Further, the aspect ratio of the graphite particles is preferably 10 or less. In this case, it is possible to prevent the separator 1 from being anisotropic and to prevent deformation such as warpage.

  Regarding the reduction of the anisotropy of the separator 1, the ratio of the contact resistance between the flow direction of the resin composition during molding in the separator 1 and the direction orthogonal to the flow direction is 2 or less. Is preferred.

  Further, as the graphite particles, those having two or more types of particle size distribution, that is, those obtained by mixing two or more types of particles having different average particle diameters are also preferably used. In this case, the total average particle size may be in the range of 30 to 70 μm by mixing the average particle size of 1 to 50 μm and the average particle size of 30 to 100 μm. preferable. When graphite particles having such a particle size distribution are used, particles having a large particle size have a small surface area, so that it is expected that kneading is possible even with a small amount of resin. It is expected that the strength of the molded product will be increased while improving the contact property of the separator, thereby improving the performance such as improvement of the bulk density of the separator 1, improvement of conductivity, improvement of gas impermeability, improvement of strength, etc. Can be achieved. At this time, the mixing ratio of the particles having an average particle diameter of 1 to 50 μm and the particles having an average particle diameter of 30 to 100 μm is appropriately adjusted. In particular, the mixing ratio of the former to the latter is 40:60 by mass ratio. It is preferable that it is -90: 10, especially 65: 35-85: 15.

  The average particle size of the graphite particles is a volume average particle size measured by a laser diffraction / scattering method with a laser diffraction / scattering particle size analyzer (such as Microtrack MT3000II series manufactured by Nikkiso Co., Ltd.).

  The graphite particles are used to reduce the electrical specific resistance of the separator 1 and improve the conductivity of the separator 1. The content of the graphite particles of the component (A) in the solid content of the resin composition is preferably in the range of 75 to 85% by mass with respect to the total amount of the resin composition. Thus, when the ratio of the graphite particles is 75% by mass or more, sufficiently excellent conductivity is imparted to the separator 1, and when it is 85% by mass or less, the resin composition has sufficiently excellent moldability. As well as sufficiently good gas permeability to the separator 1.

  The epoxy resin component (B) is composed only of an ortho cresol novolac type epoxy resin, or selected from an ortho cresol novolac type epoxy resin, a bisphenol type epoxy resin, a biphenyl type epoxy resin, and a phenol aralkyl type epoxy resin having a biphenylene skeleton. Made up of at least one kind. This ortho-cresol novolac type epoxy resin, bisphenol type epoxy resin, and phenol aralkyl type epoxy resin having a biphenylene skeleton are excellent in that they have a good melt viscosity and a small amount of impurities, and in particular, a small amount of ionic impurities.

  In particular, since the ortho-cresol novolak type epoxy resin is an essential component in the component (B), the resin composition is excellent in moldability and the separator 1 is excellent in heat resistance. In addition, the manufacturing cost can be reduced. The proportion of the ortho-cresol novolak type epoxy resin in the component is preferably in the range of 50 to 100% by mass, particularly from the viewpoint of improving the moldability, improving the heat resistance of the separator 1 and reducing the manufacturing cost. It is preferable to be in the range of -70% by mass.

  In addition, in order to further reduce the melt viscosity and improve the toughness of the thin separator 1, a bisphenol type epoxy resin, a biphenyl type epoxy resin, and a phenol aralkyl type epoxy resin having a biphenylene skeleton are used together with an orthocresol novolac type epoxy resin. It is also preferable to do.

  In particular, when a bisphenol F type epoxy resin is used, the viscosity of the resin composition can be reduced, and a resin composition having particularly high moldability can be obtained. In this case, the content of the bisphenol F type epoxy resin in the component (B) is preferably in the range of 30 to 50% by mass.

  In addition, when a biphenyl type epoxy resin is used, the biphenyl type resin has a low melt viscosity, can significantly improve the fluidity of the resin composition, and the thin moldability is particularly improved. In this case, the content of the biphenyl type epoxy resin in the component (B) is preferably in the range of 30 to 50% by mass.

Moreover, when the phenol aralkyl type epoxy resin having a biphenylene skeleton is used, the strength and toughness of the separator 1 can be improved, and the hygroscopicity of the separator 1 can be reduced. For this reason, the mechanical properties, conductivity, and stability of the properties during long-term use of the separator 1 are excellent. Biphenyl type epoxy resin in component (B) in this case,
The ratio of the phenol aralkyl type epoxy resin having a biphenylene skeleton is preferably in the range of 30 to 50% by mass.

  Moreover, it is preferable that content of the (B) component with respect to the thermosetting resin whole quantity in a resin composition exists in the range of 50-100 mass%.

  (B) It is preferable that a component is solid at normal temperature, and it is preferable that the melting | fusing point is the range of 70-90 degreeC especially. In this case, aggregation of the components in the resin composition is suppressed, and the change of the material is reduced, so that the handleability during molding is improved. If a resin having a low melt viscosity is selected as the component (B), the resin composition and the separator 1 can be highly filled with graphite particles while maintaining the moldability of the resin composition. In addition, a part of (B) component may be liquid within the range in which the said effect | action is exhibited.

  The component (B) is contained in the resin composition as at least a part of the epoxy resin in the thermosetting resin. When other thermosetting resins are used in addition to the component (B), for example, epoxy resins other than the component (B), thermosetting phenol resins, vinyl ester resins, polyimide resins, unsaturated polyester resins, diallyl phthalate resins. One or more kinds of resins selected from the above can be used. However, it is desirable not to use a resin containing an ester bond because it may hydrolyze in an acid resistant environment.

  Moreover, it is also suitable to use a polyimide resin as a thermosetting resin at the point which contributes to the improvement of the heat resistance and acid resistance of the separator 1. As such a polyimide resin, it is particularly preferable to use a bismaleimide resin, for example, 4,4-diaminodiphenyl bismaleimide. By using this together, the heat resistance of the molded product can be further increased.

  The (C) component phenolic resin is a curing agent for epoxy resin (component (B)). Examples of the phenol resin include novolac type phenol resins, cresol novolac type phenol resins, polyfunctional phenol resins, and aralkyl-modified phenol resins.

  Component (C) is contained in the resin composition as at least a part of the curing agent. The content of the phenol resin relative to the total amount of the curing agent is determined depending on the amount of the epoxy resin used. Further, it is particularly preferable that the curing agent is only a phenol resin.

  The total content of the thermosetting resin and the curing agent in the solid content of the resin composition is preferably in the range of 14 to 24.1% by mass.

  Moreover, it is preferable that the equivalent of the hydroxyl group of the phenol resin of (C) component with respect to 1 equivalent of epoxy groups of the epoxy resin in a resin composition is the range of 0.8-1.2.

  The component (D) has a weight loss of 5% or less when heated under conditions of a measurement start temperature of 30 ° C., a heating rate of 10 ° C./min, a holding temperature of 120 ° C., and a holding time of 30 minutes at The substituted imidazole having a hydrocarbon group at the position acts as a curing catalyst (curing accelerator) for the epoxy resin. When such a substituted imidazole is used as a curing accelerator, the storage stability of the liquid (varnish or slurry) resin composition, the volatility when forming a sheet from the resin composition, the smoothness of the sheet, etc. It becomes good. As this substituted imidazole, it is particularly preferable to use a substituted imidazole having 6 to 17 carbon atoms in the 2-position hydrocarbon group.

  Specific examples of the substituted imidazole having a hydrocarbon group at the 2-position include 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 1-benzyl-2-phenylimidazole and the like. Of these, 2-undecylimidazole and 2-heptadecylimidazole are preferred. These compounds are used alone or in combination of two or more.

  In addition to the substituted imidazole having a hydrocarbon group at the 2-position, other compounds such as other imidazole compounds and phosphorus compounds such as triphenylphosphine can be used in combination as a curing accelerator. When a phosphorus compound is used, elution of chlorine ions from the separator 1 which is a molded product can be suppressed.

  The content of such component (D) is appropriately adjusted, and thereby the molding and curing time can be adjusted. The content of the component (D) is preferably in the range of 0.5 to 3% by mass with respect to the total amount of the thermosetting resin and the curing agent in the resin composition.

  Further, the resin composition may contain additives such as wax (internal mold release agent) and coupling agent as necessary.

  As the internal mold release agent, an appropriate one is used. Particularly, the internal component that is phase-separated without being compatible with the thermosetting resin and the curing agent in the resin composition at 120 to 190 ° C., which is the component (E). It is preferable to use at least one type of release agent selected from polyethylene wax, carnauba wax, and long-chain fatty acid wax.

  When the component (E) is phase-separated from the thermosetting resin and the curing agent in the resin composition at 120 to 190 ° C. as described above, the thermosetting resin and the curing agent and the component (E) are formed in the molding process of the resin composition. Therefore, the effect of improving the releasability by the component (E) is exhibited well in the molding process of the resin composition.

  In addition, the content of the internal mold release agent of the component (E) is appropriately set according to the complexity of the shape of the separator 1, the groove depth, the ease of releasability from the mold surface such as the draft angle, and the like. However, it is preferable that the content in the solid content of the resin composition is in the range of 0.1 to 1% by mass. In addition, when the content is 1% by mass or less, the hydrophilicity of the separator 1 is sufficiently suppressed by the internal mold release agent.

  Examples of coupling agents used include silicon-based silane compounds, titanate-based, and aluminum-based coupling agents. Particularly, among the silicon-based coupling agents, the epoxy silane coupling agent which is the component (F) is suitable. The coupling agent may be previously attached to the surface of the graphite particles by spraying or the like.

  As for the usage-amount of the epoxysilane coupling agent of this (F) component, it is preferable that content in the solid content of a resin composition is the range of 0.5-1.5 mass%. In this range, bleeding of the coupling agent on the surface of the separator 1 can be sufficiently suppressed.

  Moreover, it is preferable to prepare this resin composition in a liquid form (including varnish form and slurry form) by containing a solvent in the resin composition. As the solvent, it is preferable to use a polar solvent such as methyl ethyl ketone, methoxypropanol, N, N-dimethylformamide, dimethyl sulfoxide or the like. Moreover, a solvent may use only 1 type and may use 2 or more types together. The amount of the solvent used is appropriately set in consideration of moldability when producing a molding sheet from the resin composition, but the amount used is preferably such that the viscosity of the resin composition is in the range of 1000 to 5000 cps. Is set.

  The solvent may be used as needed. If the resin composition can be prepared in a liquid state without using a solvent, such as when a liquid resin is added to the resin composition, the solvent is used. It does not have to be.

  Moreover, it is preferable that the content of the ionic impurities in the separator 1 is such that the sodium content is 5 ppm or less and the chlorine content is 5 ppm or less by mass ratio. For this purpose, the resin composition is contained in the resin composition. It is preferable that the content of the ionic impurities is adjusted so that the sodium content is 5 ppm or less and the chlorine content is 5 ppm or less by mass ratio with respect to the total solid content of the resin composition. In this case, elution of ionic impurities from the separator 1 can be suppressed, and deterioration of characteristics such as a decrease in starting voltage of the fuel cell due to elution of impurities can be suppressed.

  In order to reduce the content of ionic impurities in the separator 1 and the resin composition as described above, as components such as a thermosetting resin, a curing agent, graphite, and other additives constituting the resin composition, It is preferable to use a component in which the content of ionic impurities is a sodium content of 5 ppm or less and a chlorine content of 5 ppm or less with respect to each component.

  Here, the content of the ionic impurities is derived based on the amount of the ionic impurities in the extraction water of the object. The extracted water can be obtained by putting the object into ion-exchanged water at a rate of 100 ml of ion-exchanged water with respect to 10 g of the object and treating it at 90 ° C. for 50 hours. In addition, ionic impurities in the extracted water are evaluated by ion chromatography. Then, based on the amount of ionic impurities in the extracted water, the amount of ionic impurities in the target is converted into a mass ratio with respect to the target and is derived.

  In addition, the resin composition is preferably prepared such that the TOC (total organic carbon) of the separator 1 formed from this resin composition is 100 ppm or less.

  Here, TOC is a numerical value measured using an aqueous solution after the separator 1 is charged into ion-exchanged water at a rate of 100 ml of ion-exchanged water with respect to 10 g of the mass of the separator 1 and treated at 90 ° C. for 50 hours. . Such a TOC can be measured by, for example, Shimadzu total organic carbon analyzer “TOC-50” in accordance with JIS K0102. In the measurement, the CO2 concentration generated by burning the sample is measured by a non-dispersive infrared gas analysis method, and the carbon concentration in the sample is quantified. By measuring the carbon concentration, the concentration of organic substances contained indirectly can be measured, the inorganic carbon (IC) and total carbon (TC) in the sample are measured, and the difference between the total carbon and inorganic carbon (TC− IC) to measure total organic carbon (TOC).

  When the TOC is 100 ppm or less, it is possible to further suppress the deterioration of characteristics as a fuel cell.

  The value of TOC can be reduced by selecting a high-purity component as each component constituting the resin composition, further adjusting the equivalent ratio of the resin, or performing post-curing treatment during molding.

  The resin composition is prepared by mixing the components as described above. The resin composition can be molded to produce the separator 1. For example, as shown in FIG. 1, the separator 1 is formed with a plurality of convex portions (ribs) 1a on both the left and right side surfaces, so that hydrogen gas as a fuel and an oxidizing agent are formed between the adjacent convex portions 1a. A gas supply / discharge groove 2 which is an oxygen gas flow path is formed.

  In producing the separator 1, first, the resin composition is molded into a sheet shape to obtain a fuel cell separator molding sheet (molding sheet). The resin composition is formed into a sheet shape by, for example, casting (progressive) molding. In this case, a plurality of types of film thickness adjusting means can be used. Such a casting method using a plurality of types of film thickness adjusting means can be realized, for example, by using a multi-coater that has already been put into practical use. As a film thickness adjusting means for casting, it is preferable to use a slit knife and at least one of a doctor knife and a wire bar, that is, either one or both. Thus, the thickness of the molding sheet formed from the resin composition is preferably 0.05 mm or more, and more preferably 0.1 mm or more. The thickness is preferably 0.5 mm or less, and more preferably 0.3 mm or less. Thus, by making the thickness of the molding sheet 0.5 mm or less, the separator 1 can be made thinner and lighter, and the cost thereof can be reduced. In particular, if the thickness is 0.3 mm or less. When the solvent is used, the remaining solvent in the molding sheet can be effectively suppressed. In addition, when the thickness is less than 0.05 mm, the advantage of manufacturing the separator 1 is low, and when considering the formability, it is preferably 0.1 mm or more.

  The molding sheet is made into a semi-cured (B stage) state by drying along with casting, and this is compressed and thermoset to form a plurality of convex portions (ribs) 1a on both sides and the convex portions. (Rib) A gas supply / discharge groove 2 can be formed between the ribs 1a to form the separator 1. At this time, when the separator 1 is formed in a corrugated plate shape as shown in FIG. 1 so that the gas supply / discharge groove 2 on the other side is formed on the back side of the convex portion 1a on the one side, the separator 1 is thin. A separator 1 having a plurality of projections (ribs) 1a on both sides and a gas supply / discharge groove 2 between the projections (ribs) 1a can be obtained.

  At the time of compression / thermosetting molding of the molding sheet, first, the molding sheet is cut (cut) or punched into a predetermined plane dimension as necessary, and is thermally cured in a mold by a compression molding machine. The compression and thermosetting molding conditions depend on the composition of the resin composition, the type of conductive base material, the molding thickness, etc., but the heating temperature is in the range of 120 to 190 ° C. and the compression pressure is in the range of 1 to 40 MPa. It is preferable to set.

  In manufacturing the separator 1, the separator 1 may be manufactured by molding a single molding sheet, or the separator 1 may be manufactured by stacking a plurality of molding sheets.

  By forming the molding sheet in this manner, a thin separator 1, particularly a separator 1 having a thickness in the range of 0.2 to 1.0 mm can be manufactured. Thus, by using the molding sheet at the time of manufacturing the separator 1, it becomes easy to form and arrange the molding material thinly and uniformly even when manufacturing the thin separator 1, and the moldability and thickness accuracy are high. Become.

  Note that when the separator 1 is manufactured, a molding sheet and an appropriate conductive base material may be laminated and molded. When a conductive substrate is used, the mechanical strength of the separator 1 can be improved. When a conductive substrate is used, compression / thermosetting can be performed in a state in which molding sheets (including a laminate of a plurality of molding sheets) are laminated on both sides of the conductive substrate, or Compression / thermosetting can be performed in a state where conductive substrates are laminated on both sides of a molding sheet (including a laminate of a plurality of molding sheets).

  Examples of the conductive substrate include carbon paper, carbon prepreg, carbon felt and the like. Moreover, these electroconductive base materials may contain base material components, such as glass and resin, in the range which does not impair electroconductivity. The thickness of the conductive substrate is preferably in the range of 0.03 to 0.5 mm, and more preferably in the range of 0.05 to 0.2 mm.

  Further, this resin composition is used not only for producing the thin separator 1 through the production of the molding sheet as described above, but also through the production of the molding sheet by an appropriate technique such as injection molding or compression molding. It is also useful for manufacturing the separator 1. Thereby, the storage stability and moldability of the resin composition are excellent. In this case, the thickness of the separator 1 is preferably in the range of 0.5 to 2.5 mm, and more preferably in the range of 0.8 to 2.5 mm.

  Hereinafter, the present invention will be described in detail based on examples.

(Examples 1-28, Comparative Examples 1-5)
<1> Resin Composition for Molding Fuel Cell Separator For each Example and Comparative Example, the components shown in Tables 1 and 2 and the solvent (methyl ethyl ketone) were added to a stirring mixer ("5XDMV-rr type" manufactured by Dalton). The mixture was stirred and mixed so that the composition shown in 2 was obtained, and a slurry-like resin composition having a viscosity in the range of 1000 to 5000 cps was obtained.

  In addition, unless otherwise indicated, the compounding quantity of each component in Tables 1 and 2 is the compounding quantity based on all components (solid content) excluding the solvent.

<2> Production of Fuel Cell Separator Forming Sheet A molding sheet was produced from the resin composition using a multicoater (manufactured by Hirano Techseed Co., Ltd., product number M-400) as an apparatus for sheet production. In this apparatus, casting with a doctor knife and a wire bar and film thickness adjustment in two stages are performed together with a slit die. After film thickness adjustment at each stage, drying overheating is performed at 93 ° C. for 10 minutes (first drying zone), 128 ° C. for 10 minutes (second drying zone) in the drying zone.

<3> Manufacture and Evaluation of Fuel Cell Separator Two 0.1 mm thick molding sheets, one 0.2 mm thick molding sheet, and 0.3 mm thick molding sheet produced in <2> above, Using two molding sheets having a thickness of 0.3 mm, the sheet was thermally cured by a compression molding machine under the following conditions: 170 ° C., 20 MPa, 5 minutes. The obtained molded product was subjected to surface blasting to adjust the surface roughness. Thus, a separator 1 having a size in plan view of 100 mm × 100 mm (100 ports) and thicknesses of 0.2 mm, 0.2 mm, 0.3 mm, and 0.6 mm was obtained.

(Varnish stability)
After preparing the resin composition obtained by each Example and the comparative example, after storing for 240 hours at 25 degreeC, this resin composition was observed visually. As a result, the case where no precipitation of graphite particles was observed was evaluated as “◯”, and the case where precipitation was observed was evaluated as “x”.

(Sheet manufacturing stability)
The surface of the molding sheet obtained in each example and comparative example was observed, and the case where no streak or unevenness was observed was evaluated as “◯”, and the case where a streak or unevenness was observed was evaluated as “x”.

(Thin formability)
Twenty separators 1 having a thickness of 0.5 mm were produced using a molding sheet having a thickness of 0.1 mm in each example and comparative example. This separator 1 was visually observed, and the thin moldability was evaluated by the number of separators 1 in which 20 of the separators 1 were found to be faint and unfilled.

(Thickness accuracy)
The thickness of the separator 1 obtained in each example and comparative example was measured with a micrometer at 12 different positions for each separator 1. Measurement was performed on 20 samples for each example and comparative example, and the thickness accuracy was evaluated with the number of samples having a thickness variation exceeding ± 15 μm. Tables 1 and 2 show that each example has good thin formability and good thickness accuracy.

(Flexibility)
In each example and comparative example, a separator 1 having a thickness of 0.5 mm was prepared using a molding sheet having a thickness of 0.1 mm, and the flexibility of the separator 1 was determined using a bending tester in accordance with JIS K5400. Measured. As a result, 30 ° bend is repeated twice, “を” indicates that no crack is generated even after the second bend, and “◯” indicates that crack is generated after the second bend but no crack is generated in the first bend. The case where a crack was generated by the first bending was evaluated as “x”.

(Volume resistivity)
In each example and comparative example, a separator 1 having a thickness of 0.5 mm was prepared using a molding sheet having a thickness of 0.1 mm, and the volume resistivity of the separator 1 was evaluated according to JIS K7194. Tables 1 and 2 show that each example is excellent in conductivity.

(Contact resistance evaluation)
In each of Examples and Comparative Examples, a separator 1 having a thickness of 0.5 mm was prepared using a molding sheet having a thickness of 0.1 mm. Carbon paper was disposed above and below the separator 1, copper plates were disposed above and below it, and a surface pressure of 1 MPa was applied in the vertical direction. The voltage between the two carbon papers was measured with a voltmeter and the current between the two copper plates was measured with an ammeter, and the resistance (average value) was calculated from the result. The carbon paper used is TGP-HM series (090M: thickness 0.28 mm, 120M: thickness 0.38 mm) manufactured by Toray.

(TOC evaluation)
In each of Examples and Comparative Examples, a separator 1 having a thickness of 0.5 mm was prepared using a molding sheet having a thickness of 0.1 mm. In accordance with JIS K0551-4.3, the separator 1 was washed with methanol for 1 minute and then washed with ion-exchanged water for 1 minute. Next, the separator 1 and ion-exchanged water were placed in a glass container so that the amount of ion-exchanged water was 100 ml with respect to 10 g of the separator 1 and treated at 90 ° C. for 50 hours. After adjusting the pH to 2 or less by adding phosphoric acid to the ion-exchanged water after the treatment, the amount of organic carbonic acid is measured using a wet oxidation-infrared TOC measurement method (using “Toray Stro TOC Automatic Analyzer MODEL 1800” manufactured by Toray Engineering Co., Ltd.). Was measured.

(Surface roughness measurement)
In each of Examples and Comparative Examples, a separator 1 having a thickness of 0.5 mm was prepared using a molding sheet having a thickness of 0.1 mm. The arithmetic surface roughness Ra of the separator 1 was measured using a surface roughness meter having a probe tip diameter of 5 μm.

(Water-soluble ion analysis)
In each of Examples and Comparative Examples, a separator 1 having a thickness of 0.5 mm was prepared using a molding sheet having a thickness of 0.1 mm. This separator 1 was washed with methanol for 1 minute and then washed with ion-exchanged water for 1 minute. Next, the separator 1 and ion-exchanged water were put in a polyethylene container so that the amount of ion-exchanged water was 100 ml with respect to 10 g of the mass of the separator 1 and treated at 90 ° C. for 50 hours. The ion-exchanged water (extracted water) after the treatment was measured by ion chromatography (“CDD-6A” manufactured by Shimadzu Corporation).

(Electrical conductivity evaluation)
In each of Examples and Comparative Examples, a separator 1 having a thickness of 0.5 mm was prepared using a molding sheet having a thickness of 0.1 mm. This separator 1 was washed with methanol for 1 minute and then washed with ion-exchanged water for 1 minute. Next, the separator 1 and ion-exchanged water were put in a polyethylene container so that the amount of ion-exchanged water was 100 ml with respect to 10 g of the mass of the separator 1 and treated at 90 ° C. for 50 hours. The ion-exchanged water (extracted water) after the treatment was measured with a conductivity meter.

(Evaluation of fuel cell electromotive voltage fluctuation)
In each of Examples and Comparative Examples, a separator 1 having a thickness of 0.5 mm was prepared using a molding sheet having a thickness of 0.1 mm. Both surfaces of the separator 1 were subjected to blasting with alumina particles using a blasting machine, thereby removing the surface skin layer and adjusting the arithmetic average roughness Ra of the surface to 0.6 μm. A fuel cell having the structure shown in FIG. 1 was produced by interposing the solid polymer electrolyte membrane 4 and the gas diffusion electrodes (fuel electrode and oxidant electrode) 3 and 3 between the separators 1 and 1. Then, these fuel cells 1 were continuously operated for 1000 hours in a state where an external circuit was connected, and the state of fluctuation of the electromotive voltage (V) with time was investigated. The results were expressed as a value of (E1 / E0) × 100 (%), where the percentage of the electromotive force after the fluctuation was a percentage of the initial value, that is, the electromotive voltage after the fluctuation was E1, and the initial electromotive voltage was E0.

Details of each component in the table are as follows.
Epoxy resin A: orthocresol novolak type epoxy resin (“EOCN-1020-75” manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent 199, melting point 75 ° C.)
-Epoxy resin B: Bisphenol F type epoxy resin ("830CRP" manufactured by Dainippon Ink & Chemicals, Inc., epoxy equivalent 171, liquid at 25 ° C)
Epoxy resin C: biphenyl type epoxy resin (E-2: manufactured by Japan Epoxy Resin Co., Ltd., YX-4000, epoxy equivalent 190, melting point 105 ° C.)
Epoxy resin D: phenol aralkyl type epoxy resin having a biphenylene skeleton (E-3: Nippon Kayaku Co., Ltd., NC3000, softening point 58 ° C., epoxy equivalent 274)
Curing agent A: Novolac type phenolic resin ("PSM6200" manufactured by Gunei Chemical Co., OH equivalent 105)
Curing agent B: polyfunctional phenol resin (Maywa Kasei Co., Ltd. "MEH-7500", OH equivalent 100)
Curing agent C: Phenol aralkyl resin (H-2: manufactured by Mitsui Chemicals, XLC-4L, softening point 62 ° C., hydroxyl group equivalent 168)
Curing agent D: phenol aralkyl resin having a biphenylene skeleton (H-3: Meiwa Kasei Co., Ltd., MEH-7851SS, softening point 65 ° C., hydroxyl group equivalent 203)
Curing accelerator A: 2-heptadecyl imidazole (Shikoku Chemicals), weight loss 3.1%
Curing accelerator B: 2-undecylimidazole (Shikoku Chemicals), weight loss 3.2%
Curing accelerator C: 2-ethyl-4methylimidazole (Shikoku Chemicals), weight loss 11.6%
Curing accelerator D: 2-methylimidazole (Shikoku Chemicals), weight loss 15.6%
Natural graphite A: classified product obtained by applying “WR30A” manufactured by Chuetsu Graphite Industries Co., Ltd. to a 100 mesh sieve (mesh size 150 μm), average particle size 30 μm, ash content 0.05%, sodium ion 4 ppm, chloride Ion 2ppm
Natural graphite B: classified product obtained by applying “WR50A” manufactured by Chuetsu Graphite Industries Co., Ltd. to a 100 mesh sieve (mesh size 150 μm), average particle size 50 μm, ash content 0.05%, sodium ion 4 ppm, chloride Ion 2ppm
・ Natural graphite C: classified product obtained by adjusting the particle size of natural graphite B with a classifier, average particle size 70 μm, 100 mesh sieve (mesh 150 μm) pass product • artificial graphite A: artificial graphite (“SGP100”, manufactured by ESC Corporation, A graded product with an average particle size of 100 μm, an ash content of 0.05%, sodium ions of 3 ppm, and a chloride ion of 1 ppm) adjusted by a classifier, an average particle size of 30 μm and a 100 mesh sieve (mesh size of 150 μm) passed. B: A classified product obtained by adjusting the particle size of artificial graphite (“SGP100”, average particle size 100 μm, ash content 0.05%, sodium ion 3 ppm, chloride ion 1 ppm) manufactured by ESC, 100 mesh with an average particle size of 70 μm Passed through sieve (mesh 150 μm) ・ Natural graphite D: classified product obtained by adjusting particle size of natural graphite B with classifier, average particle size 20 μm, 100 mesh sieve (mesh opening 150 μm) pass product / natural graphite E: natural graphite B particle size adjusted with a classifier, average particle size 80 μm, 100 mesh sieve (mesh opening 150 μm) pass product / natural graphite F : Natural graphite containing particles that do not pass through a 100 mesh sieve (mesh opening 150 μm), “WR50A” manufactured by Chuetsu Graphite Industries Co., Ltd., average particle size 50 μm, ash content 0.05%, sodium ion 4 ppm, chloride ion 2 ppm
Coupling agent: Epoxy silane (“A187” manufactured by Nihon Unicar)
Wax A: natural carnauba wax (“H1-100” manufactured by Dainichi Chemical Co., Ltd., melting point: 83 ° C.)
Wax B: Montanic acid bisamide (“J-900” manufactured by Dainichi Chemical Co., Ltd., melting point: 123 ° C.)
The weight loss in the curing accelerators A to D is determined by heating each curing accelerator under the conditions of a measurement start temperature of 30 ° C., a temperature increase rate of 10 ° C./min, a holding temperature of 120 ° C., and a holding temperature of 30 minutes. This is a weight loss from the start. The measurement was performed in the air using a differential thermothermal gravimetric simultaneous measurement apparatus (TG / DTA; TG / DTA7000 series manufactured by Seiko Instruments Inc.).

  The wax A and the wax B are phase-separated from the epoxy resin and the phenol resin in the resin composition of each example at 120 to 190 ° C. This phase separation was confirmed as follows. First, an epoxy resin and a phenol resin used in each example were mixed at a predetermined equivalence ratio for 3 minutes at a temperature not lower than the melting point and not higher than 120 ° C., and then 1% by weight of wax A or wax B was added and further stirred for 3 minutes. . After cooling this, using a microscope equipped with a heatable stage, while heating and changing the heating temperature in the range of 120-190 ° C, observe the optical microscope at 400 times magnification to confirm the compatibility state did.

  In Example 9, an internal mold release agent was not blended in the resin composition, and instead an external mold release agent was used during compression molding of the molding sheet.

  Moreover, about Comparative Examples 1-3, 5 with poor thin moldability and thickness precision, the evaluation test after volume resistivity is not performed.

  In each of Examples 1 to 28, the sheet manufacturing stability, the thin formability, and the thickness accuracy were high, and the formability when manufacturing the thin separator 1 was high. In Examples 16, 25 and 26 in which epoxy resin C is used in particular, the surface appearance of the molding sheet is particularly excellent, and the variation in thickness accuracy is small compared to other examples, and the moldability is high. It was particularly expensive.

  1 Fuel cell separator (separator)

Claims (7)

The following (A) component, the following (B) component as at least part of the epoxy resin in the thermosetting resin, the following (C) component as at least part of the curing agent, and the following as at least part of the curing accelerator: A resin composition for a fuel cell separator, comprising a component (D) and being in a liquid state;
(A) Graphite particles having a particle size that passes through a 100 mesh sieve and having an average particle size of 30 to 70 μm,
(B) An epoxy made of an ortho cresol novolac type epoxy resin or an ortho cresol novolak type epoxy resin and at least one selected from a bisphenol type epoxy resin, a biphenyl type epoxy resin, and a phenol aralkyl type epoxy resin having a biphenylene skeleton. Resin component,
(C) a phenol resin, and (D) at least one substituted imidazole selected from 2-undecylimidazole and 2-heptadecylimidazole . The following (E) component is contained, The resin composition for fuel cell separators of Claim 1 characterized by the above-mentioned;
(E) At least one internal mold release agent that is phase-separated with a thermosetting resin and a curing agent at 120 to 190 ° C. and is selected from polyethylene wax, carnauba wax, and long-chain fatty acid wax. The following (F) component is contained, The resin composition for fuel cell separators of Claim 1 or 2 characterized by the above-mentioned;
(F) Epoxysilane coupling agent. Containing the components (A) to (F), and the content of the component (A) in the solid content is 75 to 85% by mass;
The total content of the thermosetting resin and the curing agent is 14 to 24.1% by mass,
The content of the component (D) is 0.5 to 3% by mass with respect to the total content of the thermosetting resin and the curing agent,
The content of the component (E) is 0.1-1% by mass,
4. The resin composition for a fuel cell separator according to claim 3, wherein the content of the component (F) is 0.5 to 1.5 mass%.   The equivalent of the hydroxyl group of the said (C) component with respect to 1 equivalent of epoxy groups of the said epoxy resin is the range of 0.8-1.2, The Claim 1 thru | or 4 characterized by the above-mentioned. Resin composition for fuel cell separator. A fuel cell separator molding sheet obtained by molding the resin composition for a fuel cell separator according to any one of claims 1 to 5 into a sheet shape. A fuel cell separator formed from the resin composition for a fuel cell separator according to any one of claims 1 to 5 .

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