JP4281471B2 - Resin composition for molding fuel cell separator and separator for fuel cell - Google Patents

Description

  The present invention relates to a resin composition for molding a fuel cell separator and a fuel cell separator formed from the composition.

  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. Recently, solid polymer fuel cells using a solid polymer electrolyte membrane as an electrolyte have attracted attention as fuel cells that can provide high output. Has been.

  FIG. 1 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 on both left and right side surfaces. A single cell (unit cell) is formed by interposing the polymer electrolyte membrane 2 and gas diffusion electrodes (fuel electrode and oxidant electrode) 3 and 3, and several tens to several hundreds of unit cells are arranged in parallel. Thus, a battery body (cell stack) is formed. The convex portion 1a constitutes a gas supply / discharge groove 4 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 can be composed of, for example, 50 to 100 unit cells in a stationary type for home use, and can be composed of 400 to 500 unit cells for automobile loading.

In this polymer electrolyte fuel cell, hydrogen gas, which is a fluid, is supplied to a fuel electrode, and oxygen gas, which is a fluid, is supplied to an oxidizer electrode, thereby extracting current from an external circuit. In the reaction, 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 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 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.

  Among the components constituting such a fuel cell, the fuel cell separator 1 is used for supplying and discharging a plurality of gases on one side or both sides of a thin plate-like body as shown in FIGS. 1 (a) and 1 (b). It has a unique shape with a groove 4 and functions to separate the fuel gas, oxidant gas, and cooling water flowing through the fuel cell so that they do not mix, and the electric energy generated by the fuel cell is sent to the outside. It plays an important role of transferring heat or radiating heat generated in the fuel cell to the outside.

  The following demands are generally made for the fuel cell separator 1. (1) High conductivity, (2) Corrosion resistance (acid resistance) against corrosive electrolytes, (3) Airtightness to separate gases, (4) Tightening with bolts and nuts when assembling to a fuel cell It has strength to prevent cracks and cracks in the separator 1 during assembling work, etc., as well as mechanical strength, and particularly excellent vibration resistance and impact resistance when used as a moving power source for automobiles etc. Creep resistance, (5) moldability for forming complex shapes, (6) low cost, (7) swelling resistance (those that do not swell when immersed in water or aqueous sulfuric acid), (8 ) It is required to satisfy required characteristics such as heat resistance (withstand heat generation during reaction (90 to 120 ° C.)) at the same time.

  As such a polymer electrolyte fuel cell separator 1, carbon composite materials using various thermoplastic resins or thermosetting resins, which are advantageous in terms of productivity and cost, as a binder have been proposed. For example, Patent Document 1 uses a thermosetting resin such as a phenol resin, and Patent Documents 2 and 3 use a thermoplastic resin such as polypropylene or nylon as a binder. Further, in Patent Document 4, in order to obtain a carbon material suitable as the fuel cell separator 1 having a porosity of 5% or less and a ratio of the volume resistivity in the XY direction to the volume resistivity in the Z direction of 2 or less. We have proposed carbon materials containing thermosetting resin, ketjen black, and spherical graphite particles. Further, Patent Document 5 proposes a method in which a small amount of a binder is blended with a carbon material, pressure-molded, and then impregnated with an impregnating agent in order to reduce the amount of the binder and improve conductivity. Further, Patent Document 6 proposes a fuel cell separator 1 having a surface roughness in a certain range in order to obtain a fuel cell separator 1 having a low contact resistance with an electrode portion. Moreover, in patent document 7, in order to obtain the separator 1 for fuel cells with little anisotropy, it proposes using artificial graphite and natural graphite together. Further, Patent Document 8 proposes to use a specific graphite powder in order to obtain a fuel cell separator 1 member having a balance of gas impermeability, thermal conductivity, conductivity, and the like.

However, the separator 1 for a fuel cell made of a carbon composite material using a thermoplastic resin or a thermosetting resin as a binder proposed so far is a separator manufactured by machining a previously used graphite plate. It has been pointed out that although it is more excellent than 1 in terms of productivity and cost, there is a problem that does not occur when the separator 1 made of the graphite plate is used. That is, there is a problem that the electromotive force decreases as the fuel cell is used for a long time.
JP 59-26907 A JP-A-55-61752 JP-A-56-116277 Japanese Patent Laid-Open No. 8-31231 JP 59-26907 A Japanese Patent Laid-Open No. 11-297338 Japanese Unexamined Patent Publication No. 2000-40517 JP 2000-21421 A

  The present invention has been made in view of the above points, and is a resin composition used for producing a fuel cell separator made of a carbon composite material using a thermosetting resin as a binder, and the resin composition An object of the present invention is to provide a resin composition for molding a fuel cell separator capable of suppressing a decrease in electromotive force of a fuel cell using the separator formed by the above, and a fuel cell separator 1 obtained therefrom. is there.

  As a result of diligent research, the present inventors include a cause of a decrease in electromotive force of a fuel cell incorporating a fuel cell separator 1 made of a carbon composite material using a thermosetting resin as a binder. It has been found that amine compounds such as amine-based curing initiators and curing catalysts, or aminosilanes used as coupling agents, are for poisoning platinum catalysts in fuel cells, and the present invention has been completed. is there.

  That is, the resin composition for molding a fuel cell separator according to the present invention contains a thermosetting resin and graphite particles, the content of the graphite particles is in the range of 75 to 90% by weight, and the primary amine and the second amine. It is characterized by not containing a diamine. The fuel cell separator 1 obtained by molding this resin composition has good conductivity and high productivity, and does not poison the platinum catalyst in the fuel cell. A decrease in electromotive force when used can be suppressed.

A resin containing an epoxy resin is used as the thermosetting resin, and a curing initiator and a curing catalyst are contained . In this case, the viscosity is low and impurities are reduced, and excellent heat resistance, acid resistance, and the like can be imparted to the molded separator.
In addition, since the TOC of the molded product formed with this composition is 100 ppm or less, it is possible to suppress deterioration in characteristics as a fuel cell, and the contents of chlorine ions and sodium ions in the composition are respectively compositions. When the weight ratio is 5 ppm or less with respect to the total amount of the object, it is possible to prevent deterioration in characteristics as a fuel cell such as a decrease in starting voltage due to elution of impurities from the separator.

  Moreover, it is preferable to use the said epoxy resin whose melting | fusing point is the range of 70-90 degreeC, In this case, the handleability at the time of shaping | molding is good and preferable.

  Moreover, it is preferable to contain a phosphorus compound as the curing catalyst. In this case, the elution of impurities from the separator to be molded can be reduced.

  Moreover, it is also preferable to use what contains a phenol resin as said thermosetting resin, In this case, the acid resistance of the separator shape | molded can be improved.

  Moreover, it is also preferable to contain the resol type phenol resin whose melting | fusing point is 70-90 degreeC as said phenol resin, In this case, the handleability at the time of shaping | molding is good and preferable.

  In addition, it is preferable that the phenol resin contains a polymer that undergoes a polymerization reaction by ring-opening polymerization. In this case, generation of gas at the time of curing molding is eliminated, and generation of voids in a separator that is a molded product is suppressed. Is something that can be done.

  The graphite particles preferably include those having an average particle diameter of 1 to 150 μm. In this case, it is possible to maintain good formability and maintain good surface smoothness of the formed separator 1. .

  The fuel cell separator 1 according to the present invention is characterized by molding the resin composition for molding a fuel cell separator as described above. For this reason, this fuel cell separator 1 has good conductivity, high productivity, and does not poison the platinum catalyst in the fuel cell, and the electromotive force when the fuel cell is used for a long time. Can be suppressed.

  In the present invention, since the primary amine and the secondary amine are not contained as described above, the fuel cell separator 1 obtained by molding the resin composition for molding a fuel cell separator has good conductivity. Productivity is high, and the platinum catalyst in the fuel cell is not poisoned, so that a reduction in electromotive force when the fuel cell is used for a long time can be suppressed.

  Embodiments of the present invention will be described below.

The fuel cell separator molding resin composition according to the present invention contains a thermosetting resin and graphite particles as essential components, but does not contain a primary amine and a secondary amine. That is, this composition does not contain compounds having substituents —NH and —NH ₂ . Further, it is preferable not to contain a tertiary amine. For this reason, the fuel cell separator 1 formed from this composition does not poison the platinum catalyst in the fuel cell, and suppresses a decrease in electromotive force when the fuel cell is used for a long time. it can.

  As the thermosetting resin, appropriate ones applicable to resin molding can be used, but it is preferable to include one or both of epoxy resin and phenol resin, and these have good resin viscosity. It is suitable because it has few impurities. In particular, epoxy resins are particularly excellent because they contain few ionic impurities. Thus, when including at least one among an epoxy resin and a phenol resin as a thermosetting resin, the total amount of an epoxy resin and a phenol resin is in the range of 50 to 100 weight% with respect to the thermosetting resin whole quantity. Preferably there is.

  In addition to these resins, one or more resins selected from polyimide resins, melamine resins, unsaturated polyester resins, diallyl phthalate resins and the like can be used in combination. There is a risk of hydrolysis. Among these resins, it is particularly suitable to use a polyimide resin because it contributes to improvement of heat resistance and acid resistance. 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.

  Further, in these thermosetting resins, it is preferable that the content of chlorine ions, which are ionic impurities, and the content of sodium ions are both 5 ppm or less by weight with respect to the total amount of the thermosetting resin. In this case, the elution of impurities from the separator which is a molded product can be further reduced.

  When an epoxy resin is used as the thermosetting resin, it is preferable to use a solid resin, and it is particularly preferable to use a resin having a melting point in the range of 70 to 90 ° C. Thereby, there is little change of material and the handleability at the time of shaping | molding improves. If the melting point is less than 70 ° C., the produced molding material tends to aggregate and the handleability may be reduced.

  Such an epoxy resin is preferably contained in a proportion of 50 to 100% by weight with respect to the total amount of the thermosetting resin.

  In particular, when an epoxy resin is used, by selecting a low-viscosity resin, the moldability can be maintained and the graphite particles can be highly filled.

  Moreover, when using a phenol resin as a thermosetting resin, it is preferable to use the phenol resin which a polymerization reaction advances especially by ring-opening polymerization. Examples of such phenol resins include benzoxazine resins. In this case, no gas is generated due to dehydration in the molding process, so no voids are generated in the molded product, and a decrease in gas permeability can be suppressed. When the phenol resin in which the polymerization reaction proceeds by such ring-opening polymerization is contained, the content is preferably in the range of 5 to 50% by weight with respect to the total amount of the thermosetting resin.

  In particular, when a phenol resin is used, it is also preferable to use a resol type phenol resin. At this time, for example, in 13C-NMR analysis, ortho-ortho 25-35%, ortho-para 60-70%, para-para 5 It is preferable to use a resol type phenol resin having a structure of 10%. The resol resin is usually in a liquid state, but the above-mentioned resol type phenol resin can easily adjust the softening point, and can easily obtain a resin having a melting point of 70 to 90 ° C. Thereby, there is little change of material and the handleability at the time of shaping | molding improves. If the melting point is less than 70 ° C., the produced molding material tends to aggregate and the handleability may be reduced. When such a resol type phenol resin is contained, the content thereof is preferably in the range of 10 to 70% by weight based on the total amount of the thermosetting resin.

  Further, the graphite particles are contained in order to reduce the electrical specific resistance of the molded separator 1 and improve the conductivity of the separator 1. The content of graphite particles is preferably in the range of 75 to 90% by weight with respect to the total amount of the composition. If the ratio of the graphite particles is less than 75% by weight, the conductivity required for the separator 1 may not be sufficiently obtained, and if it exceeds 90% by weight, the gas permeability and molding required for the separator 1 may be obtained. There is a risk that sufficient properties cannot be obtained.

  The graphite particles can be used without limitation as long as they exhibit high conductivity, such as graphitized carbonaceous materials such as mesocarbon microbeads, graphitized coal-based coke and petroleum-based coke. Any suitable powder 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, but natural graphite powder has the advantage of high conductivity, and artificial graphite powder is slightly inferior in conductivity to natural graphite powder. There is an advantage that there is little directivity.

  Moreover, it is preferable that the graphite particles are purified from natural graphite or artificial graphite. In this case, since the ash content and ionic impurities are low, the graphite particles are separated from the molded article separator. The elution of impurities can be suppressed.

  Here, the ash content in the graphite particles is preferably 0.05% by weight or less, and the ionic impurities in the extracted water have a sodium content of 5 ppm or less and a chlorine content of 5 ppm or less in a weight ratio with respect to the total amount of the graphite particles. It is preferable to make it. Here, the extracted water is obtained by dispersing the target component in ion-exchanged water at a rate of 100 ml of ion-exchanged water with respect to 10 g of the target component (here, graphite particles) and treating at 90 ° C. for 50 hours. Ionic impurities in the extracted water are evaluated by ion chromatography. Based on the derived amount of ionic impurities in the extracted water, the total amount of ionic impurities in the target component in the composition is converted into a weight ratio to the total amount of the target component in the composition and is derived. It is. The content of ionic impurities can be measured by the same method as above except for graphite.

  If the above ash content exceeds 0.05% by weight, there is a risk that the characteristics of the fuel cell will deteriorate. Further, when the ionic impurities in the extracted water exceed the sodium content of 5 ppm or the chlorine content exceeds 5 ppm, the characteristics of the fuel cell may deteriorate due to the elution of the impurities when the separator is molded.

  Further, graphite particles having an average particle diameter of 1 to 150 μm are preferably used, and those having an aspect ratio of 10 or less are preferable. If the average particle size is less than 1 μm, the moldability is lowered, and if it exceeds 150 μm, the surface smoothness of the molded product may be impaired. On the other hand, if the aspect ratio exceeds 10, anisotropy may occur in the molded separator 1 and warping may occur.

  Further, as the graphite particles, it is particularly preferable to use those having two or more kinds of particle size distributions, that is, those obtained by mixing two or more kinds of particle groups having different average particle diameters. In this case, it is particularly preferable that the average particle size is in the range of 1 to 50 μm and the average particle size is in the range of 50 to 100 μm. 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 50 to 100 μm is appropriately adjusted. In particular, the mixing ratio of the former to the latter is 40:60 by weight. It is preferable that it is -90: 10, especially 65: 35-85: 15.

  The composition may contain additives such as a curing initiator, a curing catalyst, a wax (release agent), and a coupling agent as necessary. At this time, since a primary amine and a secondary amine are not contained in the composition, such an amine compound is not used as these additives.

  That is, a non-amine compound is used as a curing initiator (curing agent) used when an epoxy resin is used. In the case of using an amine-based material, it is difficult to maintain the electric conductivity of the obtained separator 1 in a high state, and there is a risk of poisoning the fuel cell catalyst. Further, it is preferable not to use an acid anhydride compound as a curing initiator. An acid anhydride compound may be hydrolyzed in an acid-resistant environment such as a sulfuric acid acid environment, resulting in a decrease in electrical conductivity or an increase in impurity elution.

  As the curing initiator (curing agent), it is particularly preferable to use a phenol compound, and in this case, a cured product having excellent characteristics can be obtained.

  The content of such a curing initiator is appropriately set, but it is preferable that the stoichiometric equivalent ratio of the epoxy resin to the curing initiator is 1 to 0.85.

  Moreover, as a curing catalyst (curing accelerator) used when using an epoxy resin, although an appropriate thing can be contained, in order not to contain a primary amine and a secondary amine in a composition. Non-amine compounds are used. For example, amine-based diaminodiphenylmethane is not preferable because the residue may poison the fuel cell catalyst. In addition, imidazoles are not preferred because they easily release chlorine ions after curing, which may cause impurity elution.

  As a curing catalyst for the epoxy resin, a phosphorus compound is preferably used. An example thereof is triphenylphosphine. When such a phosphorus compound is contained, elution of chlorine ions from the separator which is a molded product can be suppressed.

  Also in the above-described curing initiator and curing catalyst, it is preferable that the content of chlorine ions, which are ionic impurities, and the content of sodium ions are each 5 ppm or less in weight ratio. In this case, elution of ionic impurities from the separator, which is a molded product, can be further suppressed. If each content exceeds 5 ppm, the amount of impurities elution increases, resulting in deterioration of characteristics as a fuel cell. There is a fear.

  The content of such a curing catalyst is appropriately adjusted, but is preferably in the range of 0.5 to 3 parts by weight with respect to the epoxy resin.

  Moreover, a coupling agent can be contained in the composition. As this coupling agent, an appropriate one is used, but it is preferable not to use aminosilane since the primary amine and secondary amine are not contained in the composition. When aminosilane is used, there is a risk of poisoning the fuel cell catalyst, which is not preferable. Further, it is preferable not to use mercaptosilane as a coupling agent. The use of this mercaptosilane is also not preferable because it may similarly poison the fuel cell catalyst.

  As an example of the coupling agent used, a silicon-based silane compound, titanate-based, or aluminum-based one can be used. For example, epoxy silane is suitable as a silicon-based coupling agent.

  The coupling agent is preferably attached to the surface of the graphite particles by spraying or the like in advance. The amount of addition is appropriately set, and it is necessary to consider the coating area per unit weight of the coupling agent to be used as compared with the specific surface area of the graphite particles. The total amount is in the range of 0.5 to 2 times the total surface area of the graphite particles. When this value increases, it is not preferable because it bleeds on the surface of the molded product and contaminates the mold surface.

  In addition, when a wax (release agent) is contained in the composition, an appropriate one is used, and natural carnauba wax is particularly preferably used. Further, the content of the wax is appropriately set, but it is preferably in the range of 0.1 to 2.5% by weight with respect to the total amount of the composition. If the mold release property is not obtained, and if it exceeds 2.5% by weight, sufficient wettability with water required for the separator 1 may not be obtained.

  Also in such a wax, it is preferable that the content of chlorine ions, which are ionic impurities, and the content of sodium ions are both 5 ppm or less in terms of weight. If the content of each ionic impurity exceeds 5 ppm, when the molded product is used as a fuel cell, the impurities may elute and the characteristics may deteriorate.

  In the present invention, it is preferable that the ratio of the contact resistance between the flow direction of the resin during molding and the direction orthogonal to the flow direction in the molded separator is 2 or less. When this value exceeds 2, the resistance value becomes anisotropic, and the characteristics as the fuel cell separator 1 are deteriorated.

Furthermore, compositions prepared by the present invention, you like molded article TOC formed by the composition (total organic carbon) is 100ppm or less.

Here, TOC is a numerical value measured using an aqueous solution after processing a molded article having a specific surface area of 20 cm ² / g 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 method, the concentration of carbon in the sample is quantified by measuring the CO ₂ concentration generated by burning the sample by a non-dispersive infrared gas analysis method. 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).

  If the above TOC exceeds 100 ppm, there is a risk that the characteristics of the fuel cell will deteriorate, and if it is 100 ppm or less, such characteristics deterioration can be suppressed.

  Here, in the present invention, the TOC value can be reduced and adjusted by selecting a high-purity raw material, adjusting the equivalent ratio of the resin, or performing post-curing treatment.

Further, in the overall composition, the chloride ion is water-soluble ions, the content of sodium ions, Ru der 5ppm or less in weight ratio relative to each total amount of the composition. If this value exceeds 5 ppm, the elution of impurities from the molded separator may cause a decrease in characteristics as a fuel cell such as a decrease in starting voltage. By making this value 5 ppm or less, Such characteristic deterioration can be prevented from occurring.

Based on the weight of the composition, the content of the above-mentioned chlorine ions and sodium ions is obtained by extracting water-soluble ions from a molded product obtained by molding the composition and evaluating and measuring the ions by ion chromatography. It can be derived by conversion. Extraction of water-soluble ions at this time is performed by immersing the molded product having a specific surface area of 20 cm ² / g in 100 mL of ion-exchanged water with respect to 10 g of the molded product and immersing the molded product in ion-exchanged water and treating at 90 ° C. for 50 hours. This can be done by extracting ions in ion-exchanged water.

  When preparing the resin composition for a fuel cell separator, the above components are mixed by an appropriate method, and kneading and granulation are performed as necessary. Below, the example of the preparation method of the separator 1 for fuel cells is shown.

  FIG. 2 shows an example of a mixing stirrer for preparing the composition. This is configured by arranging a stirring tool 6 (stirring blade) that drives planetary rotation in the container 5 with respect to the container 5 that opens upward. The stirrer 6 is connected to a rotation drive device 10 that rotationally drives the stirrer 6, protrudes downward from the rotation drive device 10, and rotates around a substantially vertical rotation shaft (rotation shaft 8). It is formed so as to be driven, and is configured to be driven to revolve around a substantially vertical rotation axis (revolution axis 7) eccentric from the rotation axis 8. In the illustrated example, two stirrers 6 having a common revolution shaft 7 and having rotation shafts 8 eccentric to each other are provided. As the agitator 6, an appropriate shape can be used. For example, a hook having a spiral shape as shown in the figure can be used.

  Moreover, it is preferable to form so that the contents of the container 5 can be heated. For example, the contents of the container 5 can be formed so as to be heatable by forming a hollow partition wall 5 and circulating a heating medium in the partition wall.

  Moreover, it is preferable to provide a decompression mechanism for decompressing the inside of the container 5. For example, a cover body 11 that closes the upper opening of the container 5 is provided integrally with the rotational drive device 10, and a suction port 9 is provided in the cover body 11, and the inside of the container 5 can be decompressed by suction from the suction port 9. Can be formed.

  When preparing a composition using such a mixing stirrer, the stirring tool 6 is rotated in a range of revolutions of 10 to 180 rpm and rotations of 15 to 380 rpm with the raw material of the composition being put into the container 5. It is preferable to perform stirring and mixing. By stirring and mixing at such a rotational speed, the contents can be sufficiently stirred and mixed to obtain a composition in which other components such as graphite particles are sufficiently dispersed and mixed with the thermosetting resin. In addition, the cleavage of the graphite particles in the process of stirring and mixing is suppressed, the deterioration of the fluidity of the prepared composition is prevented, and the high formability during the production of the separator 1 by this composition is maintained. It is something that can be done.

  FIG. 3 shows another example of a mixing stirrer for preparing the composition. This is provided in the container 5 with a stirring tool 6 that rotates around the rotation axis 12 in the substantially vertical direction.

  In the illustrated example, a lower blade 6 a and an upper blade 6 b that rotate about the same rotating shaft 12 are provided as a stirring tool 6 at the bottom of the container 5. The lower blade 6a is formed of two rotating arms 19 that extend radially from the rotating shaft 12 in opposite directions. The upper blade 6b supports a ring-shaped rotating wheel 17 at the tips of a plurality of support arms 16 projecting radially outward from the rotating shaft, and radially disengages the two arm portions 18 from the outer edge of the rotating wheel 17. It has a shape that protrudes in the direction.

  Moreover, it is preferable to form so that the contents of the container 5 can be heated. For example, the contents of the container 5 can be formed so as to be heatable by forming a hollow partition wall 5 and circulating a heating medium in the partition wall.

  Moreover, it is preferable to provide a decompression mechanism for decompressing the inside of the container 5. For example, the container 5 can be formed so as to be hermetically sealed, and a suction port is provided in the container 5, and the inside of the container 5 can be formed so as to be depressurized by suction from the suction port.

  FIG. 4 shows still another example of a mixing stirrer for preparing the composition. As shown in FIG. 3, the container 5 is provided with a stirrer 6 that rotates around the rotating shaft 12 in the container 5, but in the example shown, the stirrer 6 is a substantially horizontal rotating shaft. 12 is formed so as to be rotationally driven around the center.

  The agitator 6 may have an appropriate configuration, and a plurality of types of agitators 6 may be provided. In the illustrated one, a mixing arm 6 c and a chopper 6 d are provided as the stirring tool 6. The mixing arm 6c and the chopper 6d are connected to different substantially horizontal rotating shafts 12 at positions along inner walls facing each other of the container.

  The mixing arm 6c is provided with a plurality of arms 13 projecting radially outward from the base end connected to the rotating shaft 12 (12a). It is bent in a substantially horizontal direction toward the side.

  Moreover, it is preferable to provide a decompression mechanism for decompressing the inside of the container 5. For example, the container 5 can be formed so as to be hermetically sealed, and a suction port is provided in the container 5, and the inside of the container 5 can be formed so as to be depressurized by suction from the suction port.

  Two choppers 6d are provided in the illustrated example. The chopper 6d is formed so as to extend in a substantially horizontal direction from the base end connected to the rotary shaft 12 (12b) toward the opposing inner wall, and the chopper 6d It is arranged at a position surrounded by a plurality of arms 13. On the outer peripheral surface of the chopper 6d, a plurality of stirring rods 14 project radially outwardly.

  Reference numeral 15 in the figure denotes a spray nozzle that sprays liquid into the container 5 in a spray form.

  In preparing the composition using such a mixing stirrer shown in FIGS. 3 and 4, the peripheral speed of the outermost edge portion of the stirring tool 6 is kept in a state in which the raw material of the composition is put in the container 5. It is preferable to rotate so that it may become 15 m / sec or less. By stirring and mixing under such conditions, the contents can be sufficiently stirred and mixed to obtain a composition in which other components such as graphite particles are sufficiently dispersed and mixed with the thermosetting resin. In addition, the cleavage of the graphite particles in the process of stirring and mixing is suppressed, the deterioration of the fluidity of the prepared composition is prevented, and the high formability at the time of producing the separator 1 by this composition is maintained. It is something that can be done. Here, the lower limit of the peripheral speed of the outermost edge portion of the agitator 6 is not particularly limited, but it is preferable to set the peripheral speed to 5 m / second or more in order to mix uniformly.

  A more specific example of a method for preparing a composition using a mixing stirrer as shown in FIGS. 2 to 4 will be described.

  For example, first, a mixture of components constituting the composition is put into the container 5, and the agitator 6 is rotationally driven and mixed under predetermined conditions. At this time, it is preferable to heat the contents of the container 5 to a temperature equal to or higher than the melting start temperature of the thermosetting resin in the composition by heating the container 5. Although the heating temperature of this container 5 is suitably set according to the kind of thermosetting resin which comprises a composition, Preferably the upper limit of this heating temperature shall be 120 degreeC. Moreover, it is preferable that the stirring time at this time shall be 5 to 30 minutes. Thus, by mixing the thermosetting resin in a molten state, the thermosetting resin and other components such as graphite particles can be mixed uniformly.

  Next, a solvent in which the thermosetting resin is dissolved is added into the container 5, and the stirring tool 6 is further rotated under predetermined conditions to continue mixing. The stirring time at this time is preferably 5 to 30 minutes. Thereby, the thermosetting resin and other components such as graphite particles can be further uniformly mixed. At the same time, by heating the container 5 in the same manner as described above, if the contents are heated to a temperature equal to or higher than the melting start temperature of the thermosetting resin in the composition, further uniform mixing is possible. Can do.

  Although said solvent is suitably selected according to the kind etc. of thermosetting resin, isopropyl alcohol can be mentioned, for example. The amount of the solvent used is adjusted to an appropriate amount so that all the thermosetting resin can be dissolved. Preferably, the amount of the solvent used is 50% by weight based on the total solid content of the composition raw material. %, And if the amount of the solvent used exceeds this range, the time required for the solvent to evaporate becomes longer and the productivity decreases. The amount used is more preferably 25% by weight or less.

An appropriate method can be adopted when adding the solvent, but it is preferable to drop or spray the solvent into the container 5. Especially when added by spraying, the resin component and graphite particles can be mixed while blending, and it becomes possible to obtain a fine granular composition by preventing the formation of large lumps in the composition. A composition having excellent moldability can be obtained. The solvent injection conditions are preferably a spray pressure of 0.05 to 0.3 MPa, an amount of spray air of 5 to 50 ml / min, and a fluid pressure of 0.05 to 0.5 MPa. Next, the composition is granulated by further rotating the stirring tool 6 under predetermined conditions and volatilizing the solvent. The stirring time at this time is preferably 5 to 30 minutes.
Volatilization of the solvent can be performed by heating the inside of the container 5 or reducing the pressure inside the container 5. For example, the solvent can be volatilized by heating the inside of the container 5 and reducing the pressure. At this time, for example, the inside of the container 5 is heated to a temperature higher than the temperature at which the thermosetting resin dissolves, and the inside of the container 5 is set to 0. The pressure can be reduced to a pressure range of 1 MPa to 0.01 MPa. When stirring and mixing are continued in such a state, the solvent is volatilized, the viscosity of the contents is increased, granulation is performed, and a granular composition is prepared. If the solvent remains, voids may be generated in the molded product and gas permeability may be reduced.

  Moreover, the obtained composition can be further pulverized with a granulator or the like to be formed into a smaller particle size, for example, a particle size of 500 μm or less.

  Another example of the method for preparing the composition using the above mixing stirrer will be described.

  In this example, out of the components constituting the composition, the one excluding the thermosetting resin is first put into the container 5, and the stirrer 6 is rotationally driven to be mixed. The stirring time at this time is preferably 5 to 30 minutes.

  Next, the thermosetting resin is added to the container 5 in a state dissolved in a solvent, and stirring and mixing are continued. The solvent is appropriately selected according to the type of thermosetting resin, and examples thereof include isopropyl alcohol. The amount of the solvent used is adjusted to an appropriate amount so that all the thermosetting resin can be dissolved. Preferably, the amount of the solvent used is 50% by weight based on the total solid content of the composition raw material. %, And if the amount of the solvent used exceeds this range, the time required for the solvent to evaporate becomes longer and the productivity decreases. The amount used is more preferably 25% by weight or less.

  An appropriate method can be adopted when adding the thermosetting resin dissolved in the solvent, but it is preferable to drop or spray this into the container 5. In particular, when added by spraying, the resin component and graphite particles can be mixed while being blended, and it becomes possible to obtain a fine granular composition by preventing the formation of large lumps in the composition. A composition having excellent moldability can be obtained. The spray conditions of the thermosetting resin dissolved in the solvent are preferably a spray pressure of 0.05 to 0.3 MPa, a spray air amount of 5 to 50 ml / min, and a fluid pressure of 0.05 to 0.5 MPa. The above effects are sufficiently exhibited.

  The stirring time at this time is preferably 5 to 30 minutes. Thus, by performing stirring and mixing in a state where the thermosetting resin is dissolved in the solvent, the thermosetting resin and other components such as graphite particles are further uniformly mixed.

  Moreover, in the case of this stirring and mixing, it is preferable to heat the container 5 to a temperature equal to or higher than the melting start temperature of the thermosetting resin in the composition. Although the heating temperature of this container 5 is suitably set according to the kind of thermosetting resin which comprises a composition, it is preferable that the upper limit of heating temperature shall be 130 degreeC. Thereby, thermosetting resin and other components, such as a graphite particle, are mixed further more uniformly.

  Next, the composition is granulated by further rotating the stirrer 6 under predetermined conditions and volatilizing the solvent. The stirring time at this time is preferably 5 to 30 minutes.

  Volatilization of the solvent can be performed by heating the inside of the container 5 or reducing the pressure inside the container 5. For example, the solvent can be volatilized by heating the inside of the container 5 and reducing the pressure. At this time, for example, the inside of the container 5 is heated to a temperature equal to or higher than the temperature at which the thermosetting resin dissolves, and The pressure can be reduced to a pressure range of 1 MPa to 0.01 MPa. When stirring and mixing are continued in such a state, the solvent is volatilized, the viscosity of the contents is increased, granulation is performed, and a granular composition is prepared. If the solvent remains, voids may be generated in the molded product and gas permeability may be reduced.

  Moreover, the obtained composition can be further pulverized with a granulator or the like to be formed into a smaller particle size, for example, a particle size of 500 μm or less.

  The resin composition for molding a fuel cell separator obtained as described above is used for molding the fuel cell separator 1. As a molding method at this time, an appropriate method such as injection molding or compression molding can be employed. As described above, the separator 1 can be formed in the shape shown in FIG.

  In such a molding process, when the above-described preparation method is employed as a method for preparing the composition, the composition is less likely to cleave the graphite particles as described above during the molding process. The composition has good fluidity and excellent moldability. For this reason, also when forming in a complicated shape like the case where a plurality of fine convex parts (ribs) 1a are formed in the separator 1, the occurrence of unfilling at the time of molding is suppressed and molding defects are prevented. Can do. Moreover, when the particle size of the composition is 500 μm or less as described above, unfilling at the time of molding can be further suppressed.

  Moreover, since the separator 1 is formed from the composition which does not contain a primary amine and a secondary amine as mentioned above, when a fuel cell is produced using this separator 1 and this is operated, platinum catalyst Poisoning can be suppressed, and thereby a decrease in the output of the fuel cell can be suppressed.

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

(Examples 1 , 2, 4 to 11, reference examples, comparative examples)
As a stirring mixer, the one having the structure shown in FIG. 2 (Dalton “5XDMV-rr type”) is used. The raw materials are put into the container so as to have the composition shown in Table 1, and the container is heated to 90 ° C. with warm water. In a heated state, the stirrer 6 was planetarily rotated at the revolution number and rotation number described in the column of “Stirrer Rotation Speed” in Table 1 and stirred for 5 minutes, and then the solvent (isopropanol) was changed to Table 1. The indicated amount was added. When “spray” is listed in Table 1, the solvent is sprayed under the conditions of a spray pressure of 0.2 MPa, a spray air amount of 25 ml / min, and a liquid pressure of 0.3 MPa. Added by Stirring was continued for another 10 minutes after the addition of the solvent. Next, the solvent isopropanol was completely removed by drying under reduced pressure at 90 ° C. using a vacuum pump. The obtained kneaded material was pulverized to a particle size of 500 μm or less with a granulator.

The obtained pulverized product was molded for 20 minutes under conditions of a temperature of 175 ° C. and a pressure of 34.3 MPa (350 kg / cm ² ), and demolded to obtain a separator 1 having a shape as shown in FIG.

(Evaluation)
-TOC measurement: According to JIS K0551-4.3, the molded article was first washed with methanol for 1 minute and then washed with ion-exchanged water for 1 minute. Next, the molded product and ion-exchanged water were placed in a glass bottle so that the amount of ion-exchanged water was 100 ml with respect to 10 g of the molded product, 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 by a wet oxidation-infrared TOC measurement method (using “Toray Stro TOC Automatic Analyzer MODEL1800” manufactured by Toray Engineering Co., Ltd.). Was measured.

  Water-soluble ion analysis (ion chromatography measurement): The molded product was washed with methanol for 1 minute and then washed with ion-exchanged water for 1 minute. Next, the molded product and ion-exchanged water were placed in a polyethylene bottle so that the amount of ion-exchanged water was 100 ml with respect to 10 g of the molded product, 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: The molded product was washed with methanol for 1 minute and then washed with ion-exchanged water for 1 minute. Next, the molded product and ion-exchanged water were placed in a polyethylene bottle so that the amount of ion-exchanged water was 100 ml with respect to 10 g of the molded product, and treated at 90 ° C. for 50 hours. The ion-exchanged water (extracted water) after the treatment was measured with a conductivity meter.

  ・ Measurement method of contact resistance (area resistance): Carbon paper was placed above and below a 3 mm thick sample (separator), copper plates were further placed above and below it, and a surface pressure of 0.5 MPa was applied vertically. . The voltage between the two carbon papers was read with a voltmeter, and simultaneously the current between the two copper plates was read with an ammeter to calculate the resistance (average value). The carbon paper used is TGP-HM series (090M: thickness 0.28 mm, 120M: thickness 0.38 mm) manufactured by Toray Industries, Inc.

-Formability evaluation: For each example , reference example, and comparative example, 10 samples were molded under the same conditions, and the appearance was observed to confirm whether there was any unfilled. As the number of occurrences.

・ Evaluation of change rate of electromotive force of fuel cell: For each of Examples , Reference Examples and Comparative Examples, between the obtained separators 1 and 1, a solid polymer electrolyte membrane 2 and a gas diffusion electrode (fuel electrode and oxidation) The fuel cell having the structure shown in FIG. 1 was fabricated with the agent electrodes 3 and 3 interposed. 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 voltage value (V) of the electromotive force with time was investigated. The rate of change relative to the initial value is displayed.

The details of each component in the table are as follows: Epoxy resin A: Cresol 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)
Curing initiator: phenol novolac resin (Gunei Chemical Co., Ltd. “PSM6200”, OH equivalent 105)
Phenol resin A: resol type phenol resin (“Sample A” manufactured by Gunei Chemical Co., Ltd., melting point 75 ° C., ortho-ortho 25-35% by 13C-NMR analysis, ortho-para 60-70%, para-para 5 10%)
Phenol resin B: benzoxazine resin (“Bm” manufactured by Shikoku Kasei Kogyo Co., Ltd., melting point 80 ° C.)
Curing catalyst A: Triphenylphosphine (“TPP” manufactured by Hokuko Chemical Co., Ltd.)
Curing catalyst B: 2-phenyl-4-methyl-5-hydroxymethylimidazole (“2PHZ-PW” manufactured by Shikoku Chemicals)
Graphite particles A: artificial graphite (“SGS30A” manufactured by Chuetsu Graphite Industries Co., Ltd., average particle size 30 μm, ash content 0.05%, sodium ion 3 ppm, chloride ion 1 ppm)
Graphite particles B: artificial graphite (“SGS60” manufactured by Chuetsu Graphite Industries Co., Ltd., average particle size 60 μm, ash content 0.03%, sodium ion 2 ppm, chloride ion 1 ppm)
Graphite particles C: Natural graphite (“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)
Graphite particles D: Artificial graphite (“SGP100” manufactured by ESC Corporation, average particle size 100 μm, ash content 0.05%, sodium ion 3 ppm, chloride ion 1 ppm)
Graphite particles E: Artificial graphite (“SGP5” manufactured by ESC Corporation, average particle size 5 μm, ash content 0.05%, sodium ion 8 ppm, chloride ion 1 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.)

An example of embodiment of this invention is shown, (a) (b) is a perspective view. It is sectional drawing which shows an example of a mixing stirrer. It is sectional drawing which shows the other example of a mixing stirrer. (A) (b) is sectional drawing which shows the further another example of a mixing stirrer.

Explanation of symbols

1 Separator

Claims (8)

It contains a thermosetting resin including an epoxy resin , a curing initiator, a curing catalyst and graphite particles, the graphite particle content is in the range of 75 to 90% by weight, and the primary amine and secondary amine are contained . In addition, the molded article formed from this composition has a TOC of 100 ppm or less, and the content of chlorine ions and sodium ions in the composition is 5 ppm or less by weight with respect to the total amount of the composition. A resin composition for molding a fuel cell separator. 2. The resin composition for molding a fuel cell separator according to claim 1, wherein the epoxy resin has a melting point in the range of 70 to 90 ° C. 3. The resin composition for molding a fuel cell separator according to claim 1 or 2 , wherein the curing catalyst contains a phosphorus compound. The resin composition for molding a fuel cell separator according to any one of claims 1 to 3 , wherein the thermosetting resin contains a phenol resin. 5. The resin composition for molding a fuel cell separator according to claim 4 , wherein the phenol resin contains a resol type phenol resin having a melting point of 70 to 90 ° C. 6. As the phenolic resin, according to claim 4 or 5 fuel cell separator molding resin composition according to characterized in that it contains those polymerization reaction by ring-opening polymerization proceeds. The resin composition for molding a fuel cell separator according to any one of claims 1 to 6 , wherein the graphite particles include those having an average particle diameter of 1 to 150 µm. A fuel cell separator comprising the resin composition for molding a fuel cell separator according to any one of claims 1 to 7 .

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