JP3511373B2 - Fuel cell seal structure and method of forming rubber packing - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 therein.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell uses a membrane such as an ion-exchange resin having ion conductivity as a polymer electrolyte membrane, and a cathode electrode (positive electrode) and an anode are provided on both sides of the polymer electrolyte membrane. By arranging both electrodes of the electrode (negative electrode) and supplying a fuel gas such as hydrogen gas to the negative electrode side and an oxidizing gas such as oxygen gas or air to the positive electrode side to cause an electrochemical reaction, It converts the chemical energy of gas into electricity and generates electricity.

By the way, in the polymer electrolyte fuel cell using such a polymer electrolyte membrane as an electrolyte, it is necessary to hermetically seal the fuel gas and the oxidizing gas so as not to leak from the peripheral portion of the polymer electrolyte membrane. Instead, a seal structure in which a thin rubber packing formed by compression molding, injection molding, punching of a sheet, or the like is arranged at the peripheral portion of the polymer electrolyte membrane is usually employed.

However, the seal structure as described above is a gas seal against fuel gas and oxidant gas, and since the seal must be held strictly for a long period of time, the accuracy and durability of the rubber packing are improved. Things are required. In addition, the above rubber packing is an extremely thin film-like thin film body, and when molded by compression molding, injection molding, etc., it is not possible to obtain a highly accurate one due to the variation in thickness. It is difficult to assemble the packing at a predetermined position of the fuel cell, and there is a problem that a reliable sealing property cannot be ensured due to deformation and displacement during assembly.

Japanese Unexamined Patent Publication (Kokai) No. 10-92450 discloses a sealing material for sealing between cells of a solid oxide fuel cell and a separator, which is softened at a temperature lower than the operating temperature of the solid oxide fuel cell. However, there is disclosed a sealing material which is a glass material which is crystallized at the above-mentioned operating temperature to become crystallized glass in a solid state. However, such a sealing material needs to be disposed while being positioned at a predetermined portion between the unit cell and the separator, and the fuel cell cannot be simply and efficiently constructed.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a seal structure for a fuel cell in which a rubber packing can be surely arranged at a predetermined position and a tight sealing property can be secured, and a rubber used for the seal structure. It is to provide a method of molding a packing. Another object of the present invention is to form a rubber packing with high accuracy and high durability, and to incorporate the rubber packing into a fuel cell with high work efficiency even with a thin wall, and a seal structure for the fuel cell, and the seal. It is to provide a molding method of a rubber packing used for a structure. Still another object of the present invention is to provide a fuel cell seal structure that does not require a rubber packing arranging work, can reliably seal, and can construct a fuel cell assembly with high productivity.

[0007]

Means for Solving the Problems The inventors of the present invention have formed a vulcanized or crosslinked rubber layer as a rubber packing on the peripheral portion of a separator of a fuel cell to dispose the rubber packing between the electrode and the separator. The present invention has been completed by finding that the rubber packing can be surely arranged at a predetermined position even if it is a thin layer and a tight sealing property can be ensured without providing it.

That is, the method of molding the rubber packing used in the fuel cell seal structure of the present invention is such that the mask is used as the separator.
Cover the surface of the
The process of applying from the mask and the process of removing the solvent are combined.
By repeating several times, the peripheral edge of the separator
Form a rubber coating layer with a specified thickness and
By vulcanizing or crosslinking the coating layer,
A vulcanized or crosslinked rubber layer that is directly bonded and integrated with the pallet
It is made from wood .

Further, preferably, the vulcanization or crosslinking treatment is carried out.
Is performed by irradiating radiation (Claim 2)
is there.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic vertical cross-sectional view of a unit cell 1 constituting a polymer electrolyte fuel cell. Usually, the fuel cell is constructed as a laminated body (not shown) in which a plurality of the unit cells 1 are laminated. There is.

In FIG. 1, a unit cell 1 is composed of a unit cell (fuel cell main body) and a separator sandwiching the unit cell. The unit cell comprises a polymer electrolyte membrane 2 and this polymer electrolyte membrane. It is composed of a cathode electrode 3 and an anode electrode 4 arranged on both sides of 2. 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 gas impermeable and are formed of a conductive material having high conductivity (for example, a carbonaceous conductive material). That is, the separators 5 and 6 function as a current collector having gas barrier properties and conductivity. On the cathode electrode 3 side of the separator 5, an oxidizing gas supply groove 7 communicating with an oxidizing gas supply pipe not shown is provided, and on the anode electrode 4 side of the separator 6 communicating with a fuel gas supply pipe not shown. The groove 8 for supplying the fuel gas is provided.

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

In the present invention, the rubber packings 9 and 10 are directly molded on the peripheral surface of the separators 5 and 6 in advance, and are bonded and integrated in a vulcanization process. That is, in the seal structure, the packings 9 and 10 are directly adhered and closely adhered to the peripheral edge portion of the separator 5 (6) (that is, adhered to the surface of the separator in the form of a loop), and thus vulcanized or crosslinked with a uniform thickness. It is composed 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 dissolve the rubber compound with a solvent. The rubber solution is applied on the mask by a screen printing method a predetermined number of times (for example, a plurality of times) to form an unvulcanized rubber coating layer 13 having a predetermined thickness conforming to the shape through the through holes 12. After forming and volatilizing the solvent, the unvulcanized rubber coating layer 13 is vulcanized, and the frame-shaped thin rubber layer 13 (rubber packing 9) is vulcanized and adhered to the peripheral portion of the separator 5 to be integrated. Is formed in.

When a separator having a rubber seal integrally bonded is used in advance, the work of disposing the rubber packing is unnecessary,
Even if the rubber seal layer is thin, the unit cell can be reliably and accurately positioned to construct the unit cell by a simple operation of arranging the separators on both sides of the unit cell, and at the same time, it can be easily assembled with high assembly workability and productivity. A seal structure for a polymer fuel cell can be formed.

The electrolyte membrane constituting the unit cell of the fuel cell is not particularly limited and is not limited to the solid polymer electrolyte membrane.
It may be a phosphoric acid type electrolyte membrane or the like. As a preferable electrolyte membrane, a solid electrolyte membrane, particularly a solid polymer electrolyte membrane, for example, a Nafion membrane composed of a fluororesin having a sulfonic acid group introduced therein can be used.

The separator according to the present invention has a vulcanized or crosslinked rubber layer formed on the periphery thereof, and is disposed on both sides of the unit cell of the fuel cell to seal the periphery of the unit cell. The separator is not limited to a conductive collector and may be non-conductive as long as it has gas barrier properties or gas impermeability. As the separator, a current collector is usually used, and a material having high conductivity and low gas permeability, for example, a carbon material (carbon graphite composite material) or the like can be used.

The rubber forming the rubber layer may be vulcanizable or crosslinkable. For example, a diene rubber [natural rubber (N
R) or isoprene rubber (IR), butadiene rubber (B
R), styrene-butadiene rubber (SBR), nitrile rubber (acrylonitrile-butadiene rubber (NB
R)), chloroprene rubber (CR), etc.], butyl rubber (IIR), silicone rubber (Q) (polydimethylsiloxane rubber (MQ), methyl vinyl silicone rubber (V
MQ), phenyl silicone rubber (PMQ), fluorinated silicone rubber (FVMQ), phenyl vinyl methyl silicone rubber (PVMQ), etc., olefin rubber (ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), etc. ), Acrylic rubber (copolymer rubber containing C _2-8 alkyl acrylate such as ethyl acrylate and butyl acrylate (AC
M, ANM, etc.)), fluororubber (FKM), urethane rubber (U), ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, polynorbornene rubber, thermoplastic elastomer (polyolefin elastomer, polyester type) Examples thereof include elastomers, polyurethane-based elastomers, polyamide-based elastomers, styrene-based resin elastomers, etc. As the rubber, liquid or pasty rubber, for example, liquid polybutadiene, liquid polyisoprene, liquid polychloroprene, liquid or pasty silicone (RTV silicone rubber,
LTV silicone rubber) and the like can also be used. These rubbers can be used alone or in combination of two or more. When a liquid rubber such as liquid silicone rubber is used as the rubber solution, it can be applied without being dissolved in a solvent. The rubber layer is preferably composed of rubber that is inert to the fuel gas and the oxidant. Examples of such rubber include the above-mentioned olefin rubber and silicone rubber having excellent cushioning properties.

The rubber layer is vulcanized or cross-linked by a vulcanizing agent, a cross-linking agent, irradiation with radiation or the like. As the vulcanizing agent, a sulfur-based vulcanizing agent can be used, and examples thereof include dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane and the like. Are preferred. The amount of vulcanizing agent used is 10
0.1 to 20 parts by weight, preferably 1 to 0 parts by weight
It can be selected from the range of about 10 parts by weight.

The preferred rubber layer is vulcanized or crosslinked by peroxide or radiation irradiation. In radiation crosslinking,
If necessary, a photopolymerization initiator (benzophenone compound, benzoin compound, ketones such as xanthone compound, etc.) may be contained in the rubber layer. The amount of the photopolymerization initiator used is, for example, 1 to 10 with respect to 100 parts by weight of the polymerizable monomer (the polyfunctional monomer or monofunctional monomer).
It can be selected from the range of about parts by weight. In particular, the rubber layer is preferably substantially free from a vulcanizing agent (crosslinking agent) and a vulcanization aid (crosslinking aid) and is formed by radiation crosslinking. When a rubber layer (rubber thin film layer) is formed by radiation crosslinking, a C—C bond is directly formed between rubber molecular chains, and it is necessary to blend a vulcanizing agent such as sulfur or peroxide or a vulcanization aid into the rubber layer. Therefore, the performance of the fuel cell is not impaired. Further, 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. Note that the rubber layer may not contain a photopolymerization initiator in order to reduce the possibility that the battery performance will decrease.

Further, the rubber layer may contain reinforcing carbon black. As carbon black,
Furnace carbon black, acetylene carbon black, channel carbon black, lamp carbon black, Ketjen carbon black, thermal carbon black and the like can be exemplified. These carbon blacks can be used alone or in combination of two or more.

A preferred carbon black is a carbon black having a small amount of impurities, especially a thermal carbon black. This thermal carbon black is a carbon black produced by thermal (pyrolysis) method, that is, natural gas is introduced into a furnace heated by burning fuel to a temperature higher than the pyrolysis temperature, and the thermal decomposition of natural gas is performed. Compared to other oil furnace carbon blacks and acetylene carbon blacks, it is a carbon black that has a large particle size and low structure and a very small specific surface area. It has excellent electrical insulation performance, and due to the complete combustion method, ash, sulfur, etc. It has the feature that the impurity content of is extremely low. Therefore, the rubber packing containing this thermal carbon black contains almost no impurities that adversely affect the power generation of the fuel cell, and can be preferably used as a fuel cell separator unit.

The average particle size of thermal carbon black which is a preferred carbon black is usually 100 to 50.
The thickness is 0 nm, preferably 120 to 500 nm, more preferably 150 to 400 nm, and particularly 200 to 350 nm (for example, 240 to 310 nm). The nitrogen adsorption specific surface area of the thermal carbon black is, for example, 5 to 2
0 m ² / g, preferably 7~15m ² / g (e.g. 9
9.5 m ² / g), dibutyl phthalate (DBP) oil absorption, for example, 10 to 50 cm ^3/100 g, preferably 20~45cm ³ / 100g, more preferably 25 to
45cm ³ / 100g (for example 34~40cm ^3/100
It is about g).

The content of carbon black in the rubber layer is
For example, with respect to 100 parts by weight of rubber, 10 to 100 parts by weight of carbon black (particularly thermal carbon black), preferably 20 to 80 parts by weight, and more preferably 3 parts by weight.
It is about 0 to 70 parts by weight. The rubber layer is, if necessary, a conventional compounding agent, for example, a vulcanization accelerator, an activator, a vulcanization retarder, a stabilizer (an antioxidant, an ultraviolet absorber,
Heat stabilizer, anti-aging agent, etc.), plasticizer, filler (white carbon, talc, calcium carbonate, etc.), softener,
Lubricants, tackifiers, colorants, curing agents, reinforcing agents, etc. 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 it with an additive such as a vulcanizing agent and a crosslinking agent. As the solvent of the coating agent, various solvents capable of dissolving or dispersing rubber, for example, hydrocarbons (hexane,
Aliphatic hydrocarbons such as octane, alicyclic hydrocarbons such as cyclohexane, aromatic hydrocarbons such as toluene), halogenated hydrocarbons, alcohols (aliphatic alcohols such as ethanol and isopropanol),
Ketones (acetone, methyl ethyl ketone, methyl isoptyl ketone, etc.), esters (ethyl acetate, butyl acetate, etc.), ethers (diethyl ether, dioxane, tetrahydrofuran, etc.) and the like can be used. These solvents may be used as a mixed solvent. When the rubber is in the form of emulsion or the like, the solvent may be water or a water-soluble solvent (alcohols, cellosolves, etc.).

23 ° C. of rubber coating agent (rubber solution)
The viscosity in is, for example, 0.1 to 40 Pa · S, preferably 0.5 to 30 Pa · S, more preferably 1 to 1
It is about 5 Pa · S. If the viscosity is less than 0.1 Pa · S, the number of coatings must be increased until the unvulcanized rubber coating layer formed is thin and has a predetermined thickness.
When it exceeds 40 Pa · S, the fluidity is poor, it is difficult to pass through the mask, and the unevenness of the coating layer becomes large.

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

The rubber layer containing the vulcanizing agent or the crosslinking agent may be hot-pressed to be vulcanized or crosslinked. Vulcanization or cross-linking can be performed by a conventional method, for example, by heating and pressurizing (hot pressing) at a temperature of about 100 to 200 ° C.
In the radiation cross-linking, the rubber layer may be cross-linked by UV irradiation, but it is preferable that the rubber layer is cross-linked by high energy actinic rays such as electron beam, X-ray and γ-ray. If radiation crosslinking is used, in the same way as above, in the process of constructing a fuel cell by stacking a large number of separator units that are required to be made smaller, the work of incorporating rubber packing becomes unnecessary, and hot pressing is performed. The rubber packing can be cross-linked without any molding. Therefore, as compared with the above-mentioned heat vulcanization or cross-linking, there is no risk of degrading the quality of the separator without causing any damage to the separator formed of carbon graphite or the like. In consideration of the heat resistance and strength physical properties of the rubber packing, the irradiation method and irradiation conditions can be optimized for crosslinking by irradiation with radiation. Further, the rubber layer may be crosslinked by combining the crosslinking methods. For example, not only complete cross-linking of rubber by radiation cross-linking but also radiation cross-linking can be used as pre-crosslinking, and heat treatment or post-crosslinking by microwave can be performed.

[0029]

According to the present invention, the sealing material interposed between the unit cell (fuel cell main body) and the separator is preliminarily formed as a rubber packing on the surface of a predetermined position of the separator and is bonded and integrated. The work of assembling a single unit is not necessary, and the rubber packing can be reliably arranged at a predetermined position without causing deformation or displacement of the sealing material. Moreover, gas sealing between the unit cell (fuel cell body) and the separator can be performed easily and reliably, and a tight sealing property can be secured. In particular, the rubber packing can be incorporated into the fuel cell with high work efficiency even if it is thin, and the fuel cell assembly can be constructed with high productivity.

Further, according to the method of molding the rubber packing for the seal structure of the present invention, it is possible to form the rubber packing with high accuracy and high durability. In particular, even a rubber seal having a fine thickness can be manufactured with high accuracy and high yield. Further, when the rubber packing is radiation-crosslinked, there is no risk 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.

[0031]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 100 parts by weight of a commercially available ethylene-propylene terpolymer rubber (EPT) as a raw material rubber, and a peroxide dicumyl peroxide (DCP /) as a crosslinking agent.
3) 100 parts by weight, 1.0 part by weight of stearic acid, and other desired compounding ingredients were mixed and kneaded with a mixing roll to prepare an unvulcanized rubber. About 1c of this unvulcanized rubber
It is made into m-square pieces, and the obtained pieces are put into a stirrer with a vacuum degassing device together with toluene, stirred for 10 hours at atmospheric pressure and dissolved, and then the vacuum defoaming device is driven to further vacuum for 15 minutes. The mixture was degassed with stirring. The ratio of the unvulcanized rubber and toluene was set to the former / the latter (weight ratio) = 30/70, and the viscosity of the obtained rubber solution was set to 5 Pa · S at 23 ° C.

Then, the above-mentioned dissolved and defoamed EPT rubber solution is applied to the predetermined surface of a carbon graphite current collector by screen printing, and then dried by a hot air dryer (80 ° C.) for 5 minutes to volatilize the solvent. It was This coating and drying treatment was repeated 7 times to form an unvulcanized rubber coating layer having a thickness of 300 μm on the peripheral surface of the current collector. After that, the rubber layer on the current collector was crosslinked by electron beam irradiation to form a rubber seal integrally bonded and integrated.

(Example 2) EPD commercially available as a raw material rubber
To 100 parts by weight of M, 40 parts by weight of thermal black (manufactured by Cancarb Co., Ltd., MT carbon N990 Ultra Pure) was added and blended, and kneaded with a mixing roll to prepare an unvulcanized rubber. About 1c of this unvulcanized rubber
It is made into m-square pieces, and the obtained pieces are put into a stirrer with a vacuum degassing device together with toluene, stirred for 10 hours at atmospheric pressure and dissolved, and then the vacuum defoaming device is driven to further vacuum for 15 minutes. The mixture was degassed with stirring.

Then, the above-mentioned dissolved and defoamed EPDM rubber solution is applied by screen printing on a predetermined surface of a carbon graphite separator, and then a hot air drier (80
(° C) for 5 minutes to evaporate the solvent. This coating and drying treatment was repeated 7 times to form an uncrosslinked rubber thin film having a thickness of 300 μm on the peripheral surface of the separator. After that, the rubber thin film on the separator was introduced into an electron beam irradiation device and the irradiation dose was 15 to 80 Mr in a nitrogen atmosphere.
By irradiating with an electron beam of ad to crosslink, a rubber packing was directly molded to obtain a fuel cell separator integrally bonded.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a unit cell constituting a polymer electrolyte fuel cell.

FIG. 2 is a schematic cross-sectional view showing a part of the molding process of the rubber packing.

FIG. 3 is a schematic sectional view showing a separator integrally formed with a rubber packing.

[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 masks 12 through holes 13 Rubber coating layer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-55813 (JP, A) JP-A-8-185875 (JP, A) JP-A-9-147890 (JP, A) JP-A-3- 101058 (JP, A) JP 8-148171 (JP, A) JP 8-69806 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 8/02 H01M 8 /Ten

Claims (2)

(57) [Claims] 1. A mask covering the surface of the separator,
Apply the rubber solution on the mask by the lean printing method.
Repeating the process of removing the solvent and the process of removing the solvent multiple times
Allows the rubber coating of a predetermined thickness to be applied to the peripheral portion of the separator.
Coating layer and vulcanize or coat this rubber coating layer.
Is directly bonded to the separator by cross-linking
Fuel cell with integrated vulcanized or crosslinked rubber layer as sealing material
Molding method for rubber packing for ponds . 2. Vulcanization or crosslinking treatment by irradiation with radiation
The method for molding the rubber packing according to claim 1, wherein the rubber packing is formed .