JP2002190307A - Separator for fuel cell and molding method of its rubber packing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a fuel cell and a molding method of its rubber packing by which the rubber packing can be arranged securely at a prescribed position, tight sealability can be secured, assembly work of the rubber packing is eliminated, and the fuel cell assembly can be constructed with higher productivity. SOLUTION: A concave groove, formed at a part into which the rubber packing disposed in the circumferential edge portion of the separator, is filled with a printing material by screen printing and is planarized. A coating agent including rubber is coated through the screen printing on a part, where the concave groove is planarized to form a rubber layer. The rubber layer is molded through vulcanization, and a rubber packing is integrally molded at the circumferential edge portion. Then, the printing material is filled into the concave groove of the separator and planarized, using a metal mask as a screen mask.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for a fuel cell, particularly a polymer electrolyte fuel cell, and a method for molding a rubber packing thereof.

[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 placing both electrodes of the electrode (negative electrode), for example, supplying a fuel gas such as hydrogen gas to the negative electrode side and supplying 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.

[0003] Incidentally, such a polymer electrolyte fuel cell is constructed by stacking a plurality of single cells, and between adjacent single cells, a fuel gas flow path and an oxidizing gas flow path are provided between electrodes. A separator that is formed and separates the fuel gas and the oxidizing gas is provided. The space between the electrode and the separator must be gas-tightly sealed so that fuel gas and oxidizing gas do not leak from the periphery of the polymer electrolyte membrane, and are usually formed by compression molding, injection molding, sheet punching, or the like. An operation of interposing the obtained thin rubber packing when assembling the fuel cell is being performed.

[0004] Further, in some types of separators,
In order to obtain a high sealing performance with a small pressure, a concave groove is formed in a portion of the peripheral portion where a rubber packing is interposed, and an assembling operation is performed while fitting a rubber packing conforming to the shape of the concave groove.

[0005]

The above-mentioned rubber packing is a gas seal against a fuel gas and an oxidizing gas, and the seal needs to be strictly maintained for a long period of time. Materials having excellent physical properties such as heat resistance and electrical insulation are required. Also,
The above rubber packing is a very thin film-like thin film, and when molded by compression molding, injection molding, etc.,
In addition to variations in thickness, high-precision ones cannot be obtained,
It is difficult to install a thin and flexible rubber packing at a predetermined position between the electrode and the separator with a concave groove formed on the peripheral edge, and it is not possible to secure reliable sealing due to deformation or displacement during assembly. was there.

The present invention has been made to solve the above-mentioned problems, and the rubber packing can be securely disposed at a predetermined position, and a tight sealing property can be ensured. It is an object of the present invention to provide a fuel cell separator capable of constructing a fuel cell assembly with high flexibility, and a method of forming a rubber packing for sealing a fuel cell.

[0007]

According to the present invention, in order to achieve the above object, the basic means is to directly form and integrate a rubber packing into a separator in advance. A separator for sandwiching a unit cell with a rubber packing therebetween, wherein a groove formed in a peripheral portion of the separator where the rubber packing is provided is filled with a printing material by screen printing and flattened. A rubber layer is formed by coating a coating agent containing rubber by screen printing on a portion where the groove is flattened, and this rubber layer is vulcanized and formed, and a rubber packing is integrally formed on a peripheral portion. is there. Also,
According to a second aspect of the present invention, in the first aspect, the printing material is filled into the concave groove of the separator by using a metal mask as a screen mask, and is flattened.

Further, the invention according to claim 3 is a method for forming a rubber packing to be interposed between a unit cell of a fuel cell and a separator having a groove formed in a peripheral portion of the unit cell to sandwich the unit cell. A step of filling a printing material by screen printing into the concave grooves of the separator and flattening them,
By coating a coating agent containing rubber on the portion where the concave groove is flattened by screen printing to form a rubber layer, and vulcanizing or cross-linking the rubber layer and vulcanizing and bonding to the peripheral portion of the separator, Directly molding and integrating the rubber packing with the separator. According to a fourth aspect of the present invention, in the third aspect, a metal mask is used as a screen mask in screen printing for filling a printing material.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic longitudinal sectional view of a single cell 1 constituting a polymer electrolyte fuel cell, and a normal fuel cell is configured as a stacked body (not shown) in which a plurality of the single cells 1 are stacked.

In FIG. 1, a single cell 1 comprises a fuel cell main body comprising a polymer electrolyte membrane 2 and cathode electrodes 3 and anode electrodes 4 disposed on both sides of the polymer electrolyte membrane 2, and a cathode electrode. 3 and separators 5 provided so as to be in contact with the anode electrode 4 respectively. Also, the cathode electrode side separator 5
A groove 7 for supplying an oxidizing gas is provided on the electrode 3 side, a groove 8 for supplying a fuel gas is provided on the electrode 4 side of the separator 5 on the anode electrode side, and the groove 7 is provided in an oxidizing gas supply pipe (not shown). The grooves 8 communicate with fuel gas supply pipes (not shown). The single cell 1 prevents fuel gas and oxidizing gas from leaking around a fuel cell body composed of a polymer electrolyte membrane 2, a cathode electrode 3, and an anode electrode 4. Frame-shaped rubber packings 9, 9 for ensuring insulation between the separators 5 are interposed between the separators 5, 5.

According to the present invention, a groove 6 is formed in the periphery of the separator 5 at a position where the rubber packing 9 is interposed. First, in a first step, a printing material 10 is formed in the groove 6 by screen printing. Have been filled and cured. That is, as shown in FIG. 2, a screen mask, preferably a metal mask 14 is provided on the surface of the separator 5 in which the concave grooves 6 are formed, and the metal mask 14 is formed using a squeegee 15.
The recesses 6 are filled with a printing material 10 such as a paste, liquid rubber, or a rubber solution through the through-holes, and the printing material 10 is heated and cured at room temperature or as needed to form a flat surface 16. . As a preferable example of the printing material 10, a rubber solution in which a rubber compound is dissolved by a solvent is used to form an unvulcanized rubber layer 10 filled in the concave groove 6 through the through hole, and the solvent is volatilized. Then, the unvulcanized rubber layer 10 is vulcanized, and the rubber layer 10 is vulcanized and bonded in the concave groove 6 of the separator 5 to be integrally formed.
In preparing the rubber solution, for example, a commercially available ethylene-propylene terpolymer rubber is used as a raw rubber.
100 parts by weight of (EPT), 3 parts by weight of peroxide dicumyl peroxide (DCP / 100) as a cross-linking agent, 1.0 part by weight of stearic acid, and other desired compounding agents are mixed and kneaded with a mixing roll. Then, an unvulcanized rubber was prepared. The unvulcanized rubber is cut into pieces of about 1 cm square, and the obtained pieces are put into a stirrer equipped with a vacuum defoaming device together with toluene, stirred under atmospheric pressure for 10 hours, dissolved, and then the vacuum defoaming device is driven. Then, the mixture was degassed by stirring under vacuum for another 15 minutes. 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 23/70.
At 5 ° C., the pressure was adjusted to 5 Pa · S. Then, after filling by screen printing, it was dried in a hot air drier (80 ° C.) for 5 minutes to evaporate the solvent and form an unvulcanized rubber layer in the groove 6. Thereafter, the rubber layer was cross-linked or heated and vulcanized by electron beam irradiation to form a rubber layer bonded and integrated with the concave groove 6.

Next, as a second step, as shown in FIGS. 3 and 4, the concave groove 6 is filled with the rubber layer 10 to form the flat surface 1.
6, the surface of the separator 5 formed in the frame-shaped through-hole 1
Covering with a screen mask 11 (which may be either a screen mesh or a metal mask) having 2 and applying a rubber solution obtained by dissolving a rubber compound with a solvent from above the mask for a predetermined number of times.
(E.g., a plurality of times) is applied, and the unvulcanized rubber coating layer 13 having a predetermined thickness conforming to the shape of the unvulcanized rubber 13
After the solvent is volatilized, 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 periphery of the separator 5. It is formed integrally. The thin rubber layer 13 is also bonded and integrated with the rubber layer 10 previously filled in the groove 6.

The use of a separator in which a rubber packing is bonded and integrated in advance makes it unnecessary to provide the rubber packing. Even if the rubber seal layer is thin, the separator can be provided on both sides of the unit cell by a simple operation. , While reliably and accurately positioning and constructing the unit cell,
A seal structure of a polymer electrolyte fuel cell can be easily formed with high assembly workability and productivity.

[0014] Even in the case of a separator having a groove formed in the peripheral portion, paste or the like can be easily filled in the groove by using screen printing, similarly to the formation of the rubber packing.
At this time, it is preferable to use a metal mask having a through hole as the screen mask because the filling operation is more reliable.

[0015]

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

[0016]

An embodiment of the second step of forming and integrating a rubber packing on the surface of the separator in which the printing material is filled and cured in the concave groove will be described in detail below. (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 / 10) as a crosslinking agent.
3), 1.0 part by weight of stearic acid, and other desired compounding agents, and kneaded with a mixing roll to prepare an unvulcanized rubber. About 1cm of this unvulcanized rubber
The resulting pieces are put into a stirrer equipped with a vacuum defoaming device together with toluene, and stirred for 10 hours under atmospheric pressure to dissolve. Then, the vacuum defoaming device is driven to stir for another 15 minutes under vacuum. Defoamed. The ratio of the unvulcanized rubber and toluene was the former / the latter (weight ratio) = 30/70, and the viscosity of the obtained rubber solution was 5 Pa · S at 23 ° C.

Then, the above-dissolved and defoamed EPT rubber solution is applied to a predetermined surface of a carbon graphite current collector by screen printing, and then the hot air drier (80 ° C.)
The solvent was evaporated by drying for a minute. This coating and drying process is repeated seven times, and a thickness of 3
A 00 μm unvulcanized rubber coating layer was formed. Thereafter, the rubber layer on the current collector was crosslinked by electron beam irradiation to form an integrated rubber seal.

Example 2 Commercially available EPDM as raw rubber
Thermal black as a reinforcing agent for 100 parts by weight
40 parts by weight (MT Carbon N990 Ultra Pure, manufactured by Can Curve Co., Ltd.) were added and mixed, and kneaded with a mixing roll to prepare an unvulcanized rubber. About 1c of this unvulcanized rubber
The obtained pieces were put into a stirrer with a vacuum defoaming device together with toluene, and stirred for 10 hours under atmospheric pressure to dissolve. After that, the vacuum defoaming device was driven and vacuuming was further performed for 15 minutes. The mixture was degassed by stirring.

Next, after applying the above-mentioned dissolved and defoamed EPDM rubber solution to a predetermined surface of a carbon graphite separator by screen printing, a hot air drier (80 ° C.)
For 5 minutes to evaporate the solvent. This coating and drying treatment was repeated seven 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 gasket is introduced into an electron beam irradiation device and irradiated with an electron beam having an irradiation dose of 15 to 80 Mrad in a nitrogen atmosphere to crosslink the rubber thin film. A separator was obtained.

[Brief description of the drawings]

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

FIG. 2 is a view showing a step of filling a concave groove of a separator.

FIG. 3 is a schematic sectional view showing a part of a molding step of a rubber packing.

FIG. 4 is a schematic sectional view showing a separator in which a rubber packing is integrally formed.

[Explanation of symbols]

 Reference Signs List 1 unit cell 2 polymer electrolyte membrane 3 cathode electrode 4 anode electrode 5 separator 6 concave groove 7,8 groove 9 rubber packing 10 printing material 11 screen mask 12 through hole 13 rubber coating layer 14 metal mask 15 squeegee 16 flat surface

Claims (4)

[Claims] 1. A separator for sandwiching a unit cell of a fuel cell via a rubber packing, wherein a groove formed in a peripheral portion of the separator where the rubber packing is provided is filled with a printing material by screen printing. A rubber layer is formed by coating a coating agent containing rubber by screen printing on a portion where the concave groove is flattened, and a rubber packing is formed on the peripheral portion by vulcanization molding. A fuel cell separator characterized by being molded and integrated. 2. The fuel cell separator according to claim 1, wherein the recess is filled with a printing material using a metal mask as a screen mask and is flattened. 3. A method of molding a rubber packing interposed between a unit cell of a fuel cell and a separator having a groove formed in a peripheral portion of the unit cell which sandwiches the unit cell. A step of filling a printing material by screen printing and flattening, and forming a rubber layer by coating a coating agent containing rubber on a portion where the concave groove is flattened by screen printing, and vulcanizing or vulcanizing the rubber layer. Forming the rubber packing directly on the separator by crosslinking and vulcanizing the rubber packing to the peripheral portion of the separator, thereby forming the rubber packing for the fuel cell. 4. The method for molding a rubber packing for a fuel cell according to claim 3, wherein a metal mask is used as a screen mask in screen printing for filling a printing material.