JP4450607B2 - Method for sealing fuel cell and forming rubber packing for fuel cell - Google Patents

Description

  The present invention relates to a sealing structure for a fuel cell, particularly a polymer electrolyte fuel cell, and a method for molding a rubber packing used therefor.

  A polymer electrolyte fuel cell uses a membrane such as an ion exchange resin having ionic conductivity as a polymer electrolyte membrane, and a cathode electrode (positive electrode) and an anode electrode (negative electrode) on both sides of the polymer electrolyte membrane. By arranging both electrodes, for example, by supplying a fuel gas such as hydrogen gas on the negative electrode side and an oxidizing gas such as oxygen gas or air on the positive electrode side to cause an electrochemical reaction, the chemical energy of the fuel gas is obtained. Is converted into an amount of electricity to generate electricity.

By the way, in a polymer electrolyte fuel cell using such a polymer electrolyte membrane as an electrolyte, it must be gas-tightly sealed so that fuel gas and oxidizing gas do not leak from the peripheral edge of the polymer electrolyte membrane. A seal structure is employed in which a thin rubber packing formed by compression molding, injection molding, sheet punching, or the like is disposed on the peripheral edge of the polymer electrolyte membrane.

However, the seal structure as described above is a gas seal against the fuel gas and the oxidant gas, and the seal needs to be held strictly for a long period of time. Therefore, it is necessary to improve the accuracy and durability of the rubber packing. Has been. The above rubber packing is a very thin film-like thin film body, and when it is molded by compression molding, injection molding, etc., there is a variation in thickness and high accuracy cannot be obtained. Assembling the packing into a predetermined position of the fuel cell is difficult, and there is a problem that a reliable sealing performance cannot be ensured due to deformation or misalignment during assembly.

The following patent document 1 is a sealing material for sealing between a cell and a separator of a solid oxide fuel cell, and is softened at a temperature lower than the operating temperature of the solid oxide fuel cell, and the operating temperature A sealing material, which is a glass material that is crystallized into a crystallized glass in a solid state by crystallization is disclosed. However, such a sealing material needs to be disposed while being positioned at a predetermined position between the unit cell and the separator, and the fuel cell cannot be constructed simply and efficiently.
JP-A-10-92450

  Accordingly, an object of the present invention is to provide a fuel cell seal structure capable of securely arranging a rubber packing at a predetermined position and ensuring a tight sealing property, and a rubber packing molding method used in the seal structure. is there. Another object of the present invention is to provide a fuel cell seal structure capable of forming a rubber packing with high accuracy and high durability, and capable of incorporating a rubber packing into a fuel cell with high working efficiency even if it is thin, and the seal. An object of the present invention is to provide a method for forming a rubber packing used in the structure. Still another object of the present invention is to provide a fuel cell sealing structure that does not require a rubber packing operation and that can be reliably sealed and can be constructed with high productivity.

The present inventors have formed a vulcanized or cross-linked rubber layer as a rubber packing at the periphery of the separator of the fuel cell, so that the rubber packing is a thin layer without being disposed between the electrode and the separator. However, the present inventors have found that the rubber packing can be surely disposed at a predetermined position and a tight sealability can be secured, and the present invention has been completed.

That is, the present invention is a method for sealing between a fuel cell body comprising a polymer electrolyte membrane, a cathode electrode and an anode electrode, and a separator, which is made of a carbonaceous conductive material without using a mold. the peripheral portion of the rubber solution was applied to form an unvulcanized rubber coating layer on the surface, to form a rubber packing which is bonded and integrated to the separator by vulcanizing the unvulcanized rubber coating layer, then, the pressurized A separator in which a sulfur rubber packing is integrally formed is brought into contact with a cathode electrode and an anode electrode to assemble a single cell so that a peripheral portion of a polymer electrolyte membrane is sealed with the rubber packing. (Claim 1).
Further, the polymer electrolyte membrane is interposed between a separator and a fuel cell body comprising a polymer electrolyte membrane, a cathode electrode and an anode electrode, and the separator is brought into contact with the cathode electrode and the anode electrode to assemble a single cell. A method for forming a rubber packing integrally formed on a separator so that the peripheral edge can be sealed, and without using a mold, a rubber solution is applied to the peripheral surface of the separator to form an unvulcanized rubber coating layer. And a step of forming a rubber packing bonded and integrated with the separator by vulcanizing the unvulcanized rubber coating layer in a non-contact state with the fuel cell body, and the separator is formed of a carbonaceous conductive material. In this case, the separator is used (claim 4).

In claim 1, preferably , when an unvulcanized rubber coating layer is formed by applying a rubber solution by an ink jet method (claim 2), the rubber solution is applied by a printing method to form an unvulcanized rubber coating layer. There is a case of forming (Claim 3) , and in Claim 4, preferably, in the step of forming the unvulcanized rubber coating layer, the rubber solution is applied by an ink jet method (Claim 5) or the rubber solution is printed. (Claim 6) .

  In the present invention, the sealing material interposed between the unit cell (fuel cell main body) and the separator is previously molded and bonded and integrated as a rubber packing on the surface of the separator at a predetermined position. The rubber packing can be reliably disposed at a predetermined position without any need for deformation and displacement of the sealing material. Moreover, gas sealing between the single cell (fuel cell main body) and the separator can be performed easily and reliably, and a tight sealing property can be secured. In particular, even if it is thin, rubber packing can be incorporated into the fuel cell with high work efficiency, and a fuel cell assembly can be constructed with high productivity.

Further, in the rubber packing molding method for the seal structure of the present invention, a rubber packing having high accuracy and high durability can be formed. In particular, even a fine rubber seal can be manufactured with high accuracy and good yield. Further, when the rubber packing is subjected to radiation crosslinking, there is no possibility of damaging the separator, and further, elution of impurities from the rubber packing can be suppressed, and the performance of the fuel cell is not deteriorated.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic longitudinal sectional view of a unit cell 1 constituting a solid polymer fuel cell. Usually, a fuel cell is configured as a laminate (not shown) in which a plurality of unit cells 1 are laminated. Yes.

In FIG. 1, a unit cell 1 is composed of a unit cell (fuel cell body) and a separator that sandwiches the unit cell. The unit cell includes a polymer electrolyte membrane 2 and both sides of the polymer electrolyte membrane 2. The cathode electrode 3 and the anode electrode 4 are arranged. Further, separators 5 and 6 are provided in contact with the cathode electrode 3 and the anode electrode 4 of the unit cell (or fuel cell main body), respectively. These separators 5 and 6 are made of a conductive material (for example, carbonaceous conductive material) that is impermeable to gas and has high conductivity. That is, the separators 5 and 6 function as current collectors having gas barrier properties and conductivity. An oxidation gas supply groove 7 communicating with an oxidation gas supply pipe (not shown) is provided on the cathode electrode 3 side of the separator 5, and a fuel gas supply pipe (not shown) is connected on the anode electrode 4 side of the separator 6. The fuel gas supply groove 8 is provided.

In the unit cell 1, the fuel gas and the oxidizing gas are prevented from leaking around the unit cell (fuel cell main body) composed of the polymer electrolyte membrane 2, the cathode electrode 3 and the anode electrode 4, and the cathode electrode side In order to ensure insulation between the separator 5 and the anode electrode side separator 6, frame-like (loop-shaped) rubber packings 9, 10 are interposed between the unit cell and the separators 5, 6.

And in this invention, the said rubber packings 9 and 10 are shape | molded directly on the peripheral part surface of the separators 5 and 6 beforehand, and are united and integrated by the vulcanization process. That is, in the seal structure, the packings 9 and 10 are directly adhered and closely adhered to the peripheral edge of the separator 5 (6) (that is, closely adhered to the separator surface in the form of a loop), and vulcanized or crosslinked with a uniform thickness. It consists of a thin rubber layer.

As shown in FIGS. 2 and 3, the rubber packings 9 and 10 cover the surface of the separator 5 (6) with a mask 11 having a frame-shaped through-hole 12, and a rubber solution in which the rubber compound is dissolved by a solvent. Is applied a predetermined number of times (for example, a plurality of times) by using a screen printing method for applying from a mask, and an unvulcanized rubber coating layer 13 having a predetermined thickness matching the shape is formed through the through holes 12, After the solvent is volatilized, the unvulcanized rubber coating layer 13 is vulcanized, and a frame-like thin rubber layer 13 (rubber packing 9) is vulcanized and bonded to the peripheral edge of the separator 5 to be integrally formed. ing.

If a separator with a rubber seal bonded in advance is used, there is no need to install rubber packing, and even if the rubber seal layer is thin, the simple operation of placing the separator on both sides of the unit cell ensures reliable and accurate operation. The unit cell can be constructed by positioning well, and a sealing structure of a polymer electrolyte fuel cell can be easily formed with high assembly workability and productivity.

The electrolyte membrane constituting the unit cell of the fuel cell is not particularly limited, and is not limited to a solid polymer electrolyte membrane but may be a phosphoric acid electrolyte membrane. As a preferable electrolyte membrane, a solid electrolyte membrane, particularly a solid polymer electrolyte membrane, for example, a Nafion membrane made of a fluororesin into which a sulfonic acid group is introduced can be used.

The separator according to the present invention has a vulcanized or crosslinked rubber layer formed on the peripheral edge thereof, and is disposed on both sides of the single cell of the fuel cell to seal the peripheral edge of the single cell. The separator only needs to have gas barrier properties or gas impermeability, and is not limited to a conductive current collector, and may be nonconductive. As the separator, a current collector is usually used, and a material having high conductivity and low gas permeability, for example, a carbon material (such as a carbon graphite composite material) can be used.

The rubber forming the rubber layer may be vulcanized or crosslinkable, such as diene rubber [natural rubber (NR) or isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene rubber (SBR), nitrile. Rubber (acrylonitrile-butadiene rubber (NBR)), chloroprene rubber (CR), etc.], butyl rubber (IIR), silicone rubber (Q) (polydimethylsiloxane rubber (MQ), methyl vinyl silicone rubber (VMQ), phenyl silicone rubber ( PMQ), fluorinated silicone rubber (FVMQ), phenyl vinylmethyl silicone rubber (PVMQ), etc.), olefin rubber (ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), etc.), acrylic rubber (acrylic acid) Ethyl, butyl acrylate Of the copolymer rubber containing acrylic acid _{C 2-8} alkyl ester (ACM, etc. ANM)), fluororubber (FKM), urethane rubber (U), ethylene - vinyl acetate copolymer, ethylene - acrylic ester copolymerization Examples thereof include coalescence, polynorbornene rubber, thermoplastic elastomer (polyolefin elastomer, polyester elastomer, polyurethane elastomer, polyamide elastomer, styrene resin elastomer, etc.). As the rubber, liquid or paste-like rubber, for example, liquid polybutadiene, liquid polyisoprene, liquid polychloroprene, liquid or paste-like silicone (RTV silicone rubber, LTV silicone rubber) and the like can be used. These rubbers can be used alone or in combination of two or more. In addition, when using liquid rubber like liquid silicone rubber as a rubber solution, it can apply | coat, without melt | dissolving with a solvent. The rubber layer is preferably made of rubber that is inert to fuel gas and oxidant. Examples of such rubber include the olefin rubber and silicone rubber having excellent cushioning properties.

The rubber layer is vulcanized or crosslinked by a vulcanizing agent, a crosslinking agent, radiation irradiation or the like. As the vulcanizing agent, but sulfur-based vulcanizing agent can be used, for example, dicumyl peroxide, di-t - Buchirupa over peroxide, 2,5 - dimethyl 2,5 - di (t - butyl Bell oxy) hexane, etc. The organic peroxide is preferred. The amount of the vulcanizing agent used can be selected from the range of about 0.1 to 20 parts by weight, preferably about 1 to 10 parts by weight with respect to 100 parts by weight of rubber.

Preferred rubber layers are vulcanized or crosslinked by peroxide or radiation. In the radiation crosslinking, if necessary, a photopolymerization initiator (a ketone such as a benzophenone compound, a benzoin compound, or a xanthone compound) may be contained in the rubber layer. The usage-amount of a photoinitiator can be selected from the range of about 1-10 weight part with respect to 100 weight part of polymeric monomers (the said polyfunctional monomer, monofunctional monomer), for example.
In particular, the rubber layer is preferably substantially free of a vulcanizing agent (crosslinking agent) and a vulcanization auxiliary agent (crosslinking auxiliary agent) and formed by radiation crosslinking. When a rubber layer (rubber thin film layer) is formed by radiation crosslinking, a C—C bond is formed directly between the rubber molecular chains, and it is necessary to add a vulcanizing agent such as sulfur or peroxide, or a vulcanization aid to the rubber layer. The fuel cell performance is not hindered. Furthermore, cationic impurities (for example, metal oxides such as zinc oxide and magnesium oxide) that hinder the performance of the fuel cell are not eluted from the rubber material. In addition, in order to reduce possibility that battery performance will fall, the rubber layer does not need to contain the photoinitiator.

Furthermore, the rubber layer may contain reinforcing carbon black. Examples of the carbon black include furnace carbon black, acetylene carbon black, channel carbon black, lamp carbon black, ketjen carbon black, and thermal carbon black. These carbon blacks can be used alone or in combination of two or more.

The preferred carbon black is carbon black with few impurities, especially thermal carbon black. This thermal carbon black is a carbon black produced by the thermal (pyrolysis) method, that is, natural gas is introduced into a furnace heated to a temperature equal to or higher than the pyrolysis temperature by burning fuel, Compared to oil furnace carbon black, acetylene carbon black, etc., it is a carbon black with a large particle size and a very small specific surface area of low structur. It has the feature of extremely low impurity content. Therefore, the rubber packing blended with the thermal carbon black hardly contains impurities that adversely affect the power generation of the fuel cell, and can be suitably used as a fuel cell separator unit.

The average particle size of thermal carbon black, which is preferable carbon black, is usually about 100 to 500 nm, preferably 120 to 500 nm, more preferably 150 to 400 nm, and particularly 200 to 350 nm (for example, 240 to 310 nm). Moreover, the nitrogen adsorption specific surface area of thermal carbon black is, for example, 5 to ²⁰ m ² / g, preferably 7 to 15 m ² / g (for example, 9 to 9.5 m ² / g), and dibutyl phthalate (DBP) oil absorption is, for example, It is about 10-50 cm < ³ > / 100g, Preferably it is 20-45 cm < ³ > / 100g, More preferably, it is about 25-45 cm < ³ > / 100g (for example, 34-40 cm < ³ > / 100g).

The content of carbon black in the rubber layer is, for example, 10 to 100 parts by weight, preferably 20 to 80 parts by weight, more preferably 30 to 70 parts by weight with respect to 100 parts by weight of rubber. Degree.
The rubber layer may contain a conventional compounding agent such as a vulcanization accelerator, an activator, a vulcanization retarder, a stabilizer (an antioxidant, an ultraviolet absorber, a heat stabilizer, an anti-aging agent, if necessary. Etc.), plasticizers, fillers (white carbon, talc, calcium carbonate, etc.), softeners, lubricants, tackifiers, colorants, curing agents, reinforcing agents and the like may be added. As these additives, it is preferable to select components that do not adversely affect the characteristics of the fuel cell.

As described above, the rubber may be contained in the coating agent as a rubber compound composition by combining with an additive such as a vulcanizing agent or a crosslinking agent. Examples of the solvent for the coating agent include various solvents that can dissolve or disperse rubber, for example, hydrocarbons (aliphatic hydrocarbons such as hexane and octane, alicyclic hydrocarbons such as cyclohexane, and aromatics such as toluene. Hydrocarbons), halogenated hydrocarbons, alcohols (such as aliphatic alcohols such as ethanol and isopropanol), ketones (such as acetone, methyl ethyl ketone, and methyl isoptyl ketone), esters (such as ethyl acetate and butyl acetate), Ethers (diethyl ether, dioxane, tetrahydrofuran, etc.) can be used. These solvents may be used as a mixed solvent. When the rubber is in the form of an emulsion or the like, the solvent may be water or a water-soluble solvent (alcohols, cellosolves, etc.).

The viscosity at 23 ° C. of the rubber coating agent (rubber solution) is, for example, about 0.1 to 40 Pa · S, preferably about 0.5 to 30 Pa · S, and more preferably about 1 to 15 Pa · S. When the viscosity is less than 0.1 Pa · S, the number of coatings must be increased until the unvulcanized rubber coating layer to be formed is thin and has a predetermined thickness. It is bad, it is difficult to pass through the mask, and the unevenness of the coating layer increases.

The rubber layer may be formed by using an ink jet method or the like, but it is advantageous to form the rubber layer by a conventional printing method such as screen printing from the viewpoint of productivity. In the screen printing, for example, the surface of the separator is covered with a mask, and a rubber coating layer having a predetermined thickness is formed on the peripheral edge of the separator (for example, in a loop) through the mask. In particular, it can be performed by using a mask or a screen having a through hole in a region corresponding to the shape of the rubber layer. The coating agent may be coated or printed multiple times to form a rubber layer with a predetermined thickness. By coating, a rubber layer is usually formed in the form of a closed loop corresponding to the planar shape of the packing. The separator may be pretreated to improve adhesion with the rubber layer. A thin rubber layer bonded and integrated with the separator can be formed by directly coating the surface of the separator with a coating agent, removing the solvent, drying, and performing vulcanization or crosslinking treatment. The thickness of the thin rubber layer is not particularly limited as long as the sealing property can be secured, and can be appropriately selected from the range of, for example, 30 μm to 1 mm, preferably 50 μm to 0.8 mm, and more preferably about 100 μm to 500 μm.

The rubber layer containing the vulcanizing agent or the crosslinking agent may be vulcanized or crosslinked by heating and pressing. Vulcanization or crosslinking can be performed by a conventional method, for example, by heating and pressing (hot pressing) at a temperature of about 100 to 200 ° C. In the radiation cross-linking, the rubber layer may be cross-linked by ultraviolet irradiation, but is preferably cross-linked by a high energy active ray such as an electron beam, X-ray or γ ray. When radiation crosslinking is used, in the same way as described above, in the process of constructing a fuel cell by stacking a large number of separator units that require further miniaturization, the operation of incorporating a rubber packing becomes unnecessary, and heat pressing is performed. The rubber packing can be cross-linked without forming. Therefore, compared to the heat vulcanization or cross-linking, the separator formed of carbon graphite or the like is not damaged and there is no possibility of degrading the quality of the separator.
In view of the heat resistance and strength properties of the rubber packing, the irradiation method and irradiation conditions can be optimized for the crosslinking by radiation irradiation. Further, the rubber layer may be crosslinked by combining crosslinking methods. For example, not only complete crosslinking of rubber by radiation crosslinking but also radiation crosslinking can be used as pre-crosslinking, and post-crosslinking by heat treatment or microwave can be performed.

3 parts by weight of peroxide dicumyl peroxide (DCP / 100) as a crosslinking agent, 1.0 part by weight of stearic acid, 100 parts by weight of commercially available ethylene-propylene terpolymer rubber (EPT) as raw rubber The unvulcanized rubber was prepared by blending with the above compounding agents and kneading with a mixing roll. The unvulcanized rubber is cut into pieces of about 1 cm square, and the obtained pieces are put together with toluene into a stirrer equipped with a vacuum deaerator, stirred for 10 hours under atmospheric pressure and dissolved, and then the vacuum deaerator is driven. Then, the mixture was degassed by stirring for 15 minutes under vacuum. The ratio of the unvulcanized rubber and toluene was the former / the latter (weight ratio) = 30/70, and the viscosity of the resulting rubber solution was 5 Pa · S at 23 ° C.

Next, the dissolved and defoamed EPT rubber solution was applied to a predetermined surface of a carbon graphite current collector by screen printing, and then dried in a hot air dryer (80 ° C.) for 5 minutes to volatilize the solvent. This coating and drying process was repeated seven times to form an unvulcanized rubber coating layer having a thickness of 300 μm on the peripheral surface of the current collector. Thereafter, the rubber layer on the current collector was crosslinked by electron beam irradiation to form a rubber seal bonded and integrated.

To 100 parts by weight of commercially available EPDM as a raw rubber, 40 parts by weight of thermal black (manufactured by Cancarb, MT Carbon N990 Ultra Pure) was added and blended, and kneaded with a mixing roll to prepare an unvulcanized rubber. The unvulcanized rubber is cut into pieces of about 1 cm square, and the obtained pieces are put together with toluene into a stirrer equipped with a vacuum deaerator, stirred for 10 hours under atmospheric pressure and dissolved, and then the vacuum deaerator is driven. Then, the mixture was degassed by stirring for 15 minutes under vacuum.

Next, the dissolved and defoamed EPDM rubber solution was applied to a predetermined surface of a carbon graphite separator by screen printing, and then dried in a hot air dryer (80 ° C.) for 5 minutes to volatilize the solvent. This coating and drying process was repeated seven times to form an uncrosslinked rubber thin film having a thickness of 300 μm on the peripheral surface of the separator. Thereafter, the rubber thin film on the separator is introduced into an electron beam irradiation device and crosslinked by irradiating with an electron beam with an irradiation dose of 15 to 80 Mrad in a nitrogen atmosphere, so that the rubber packing is directly molded and bonded and integrated. A separator was obtained.

It is a schematic longitudinal cross-sectional view of the unit cell which comprises a polymer electrolyte fuel cell. It is a general | schematic cross-sectional view which shows a part of shaping | molding process of rubber packing. It is a schematic sectional drawing which shows the separator by which rubber packing was integrally molded.

Explanation of symbols

1 Unit cell 2 Polymer electrolyte membrane 3 Cathode electrode 4 Anode electrode 5 Cathode electrode side separator 6 Anode electrode side separator 7, 8 Groove 9, 10 Rubber packing 11 Mask 12 Through-hole 13 Rubber coating layer

Claims (6)

A method of sealing between a separator and a fuel cell body composed of a polymer electrolyte membrane, a cathode electrode and an anode electrode, and without using a mold, on the peripheral surface of the separator made of a carbonaceous conductive material The solution is applied to form an unvulcanized rubber coating layer, and this unvulcanized rubber coating layer is vulcanized to form a rubber packing that is bonded and integrated with the separator. Thereafter, the vulcanized rubber packing is A fuel cell sealing method, wherein a separator formed integrally is brought into contact with a cathode electrode and an anode electrode to assemble a single cell so that a peripheral portion of a polymer electrolyte membrane is sealed with the rubber packing. 2. The fuel cell sealing method according to claim 1, wherein the rubber solution is applied by an ink jet method to form an unvulcanized rubber coating layer. 2. The fuel cell sealing method according to claim 1, wherein the rubber solution is applied by a printing method to form an unvulcanized rubber coating layer. A polymer electrolyte membrane, a cathode electrode and an anode electrode are interposed between the fuel cell body and the separator, and the separator is brought into contact with the cathode electrode and the anode electrode to assemble the single cell so that the peripheral portion of the polymer electrolyte membrane is A method of forming a rubber packing integrally formed with a separator so as to be sealed,
Applying a rubber solution to the peripheral surface of the separator to form an unvulcanized rubber coating layer without using a mold, and vulcanizing the unvulcanized rubber coating layer in a non-contact state with the fuel cell body A process of forming a rubber packing that is bonded and integrated with the separator.
A method of forming a rubber packing for a fuel cell, wherein a separator formed of a carbonaceous conductive material is used as the separator. The method for forming a rubber packing for a fuel cell according to claim 4, wherein in the step of forming the unvulcanized rubber coating layer, the rubber solution is applied by an ink jet method. The method for forming a rubber packing for a fuel cell according to claim 4, wherein in the step of forming the unvulcanized rubber coating layer, the rubber solution is applied by a printing method.

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