JP4954024B2 - Fuel cell packing and seal structure - Google Patents

Description

The present invention relates to a packing and seal structure used in a fuel cell, particularly a polymer electrolyte fuel cell.

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 to constitute a unit cell, for example, by supplying a fuel gas such as hydrogen gas to the negative electrode side, while supplying an oxidizing gas such as oxygen gas or air to the positive electrode side to cause an electrochemical reaction, Electricity is generated by converting chemical energy of fuel gas into electricity.

Such a polymer electrolyte fuel cell is configured by laminating a plurality of single cells. Between adjacent single cells, a fuel gas channel and an oxidizing gas channel are formed between the cells and the fuel gas. And a separator for partitioning the oxidizing gas. In addition, between the electrode and the polymer electrolyte membrane and the separator, a gas seal must be hermetically sealed so that the fuel gas and the oxidizing gas do not leak from the peripheral portion of the polymer electrolyte membrane. It describes that a rubber packing is formed and integrated by radiation-crosslinking an uncrosslinked rubber thin film formed by applying a rubber solution to a predetermined position surface by screen printing.

The rubber packing described above is a gas seal against fuel gas and oxidizing gas, and the seal needs to be held strictly for a long period of time. The rubber packing mainly includes rubber having excellent heat resistance and compression set. Use as material.
JP 2001-196078 A

However, if impurities such as organic compounds are extracted from the packing formed of these rubber materials, the impurities accumulate in the stack, which may adversely affect the battery life, and rubber materials that are difficult to extract impurities are desired. It was.

The present invention solves the above-described problems, and does not require the work of incorporating a packing. The packing is securely disposed at a predetermined position to ensure complete sealing, and extraction of impurities from the packing. The purpose is to reduce the amount

As a result of intensive studies, the inventors solved the above problems by using a rubber composition containing a reactive group-containing hydrogenated isoprene rubber as a main component and an isocyanate compound as a rubber material for forming the packing. As a result, the present invention was completed.

The present invention relates to a packing interposed between a unit cell of a fuel cell and a separator sandwiching the unit cell, wherein the packing is a rubber composition mainly composed of hydrogenated isoprene rubber having a reactive group. A packing for a fuel cell comprising a composition in which an isocyanate compound is mixed with the separator and integrated by cross-linking adhesion to the peripheral edge of the separator.

The packing may be bonded and integrated with the unit cell instead of the separator (claim 2). Further, a sealing structure in which the unit cell and the separator are integrated by cross-linking and adhering with a composition in which an isocyanate compound is mixed with a rubber composition mainly composed of hydrogenated isoprene rubber having a reactive group may be used (claim) Item 3).

According to the present invention, as a sealing material for sealing between a fuel cell unit cell and a separator, a composition obtained by mixing an isocyanate compound with a rubber composition mainly composed of hydrogenated isoprene rubber having a reactive group, Since the packing formed by the sealing material is integrated by cross-linking and bonding to the peripheral part of the separator or single cell, the work of incorporating the packing is not necessary, and the packing is securely disposed at a predetermined position to ensure perfect sealing performance. And the effect of reducing the amount of impurities extracted from the packing can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic longitudinal sectional view of a single cell 1 constituting a solid polymer fuel cell, and a normal fuel cell is configured as a laminate (not shown) in which a plurality of single cells 1 are stacked.

In FIG. 1, a single cell 1 includes a fuel cell body comprising a polymer electrolyte membrane 2 and a cathode electrode 3 and an anode electrode 4 disposed on both sides of the polymer electrolyte membrane 2, and a cathode electrode 3 and an anode. The separators 5 and 6 are provided so as to be in contact with the electrodes 4 respectively. Further, an oxidizing gas supply groove 7 is provided on the electrode 3 side of the cathode electrode side separator 5, and a fuel gas supply groove 8 is provided on the electrode 4 side of the anode electrode side separator 6. The groove 8 communicates with a fuel gas supply pipe (not shown).

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-shaped (loop-shaped) packings 9, 9 are interposed between the unit cell and the separators 5, 6. In this embodiment, as shown in a partially enlarged view in FIG. 2, the packing 9 is formed directly on the peripheral surfaces of the separators 5 and 6 in advance and integrated by bonding. As shown in FIG. 2, the packing 9 can have a laminated structure of a main layer 10 having a relatively high rubber hardness and a coating layer 11 having a relatively low rubber hardness coated on the surface thereof.

In the present embodiment, the main layer 10 and the coating layer 11 are composed of a composition obtained by mixing an isocyanate compound with a rubber composition mainly composed of a hydrogenated isoprene rubber having a reactive group and crosslinking the rubber composition.

As the hydrogenated isoprene rubber, hydrogenated isoprene rubber having a reactive group capable of reacting with an isocyanate group of an isocyanate compound described later can be used. For example, Epole (trade name) manufactured by Idemitsu Kosan Co., Ltd. can be exemplified. For the purpose of improving the properties of rubber, a rubber composition to which other rubber is added can also be used. The rubber components that can be added are silicone rubber, fluorosilicone rubber, ethylene propylene rubber, fluorine rubber, butyl rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, styrene isoprene rubber, acrylic rubber, ethylene acrylic rubber, fluoroacrylic rubber, styrene series Examples thereof include rubbers such as rubber and rubbers obtained by hydrogenating these rubbers. In addition, you may use hydrogenated isoprene rubber single-piece | unit, without adding another rubber component.

As isocyanate compounds that can be used in the present invention, tolylene diisocyanate (TDI), diphenylmethane-4,4′-diisocyanate (MDI), polymeric MDI, hexamethylene diisocyanate (HDI), xylylene diisocyanate (XDI), 1,3 bis (Isocyanatomethyl) cyclohexane (H6XDI) can be exemplified, and TMP adduct modified products, isocyanurate modified products, burette modified products and allophanate modified products of these isocyanate compounds can also be used in the present invention. In particular, hexamethylene diisocyanate (HDI) and a modified product thereof are preferable. The isocyanate compound is preferably added in an amount of 6 to 26 parts by weight, more preferably 16 to 21 parts by weight, based on 100 parts by weight of the rubber composition containing hydrogenated isoprene rubber as a main component.

When an isocyanate compound is added, the isocyanate compound does not decompose at the time of crosslinking, and the isocyanate group is bonded to the reactive group of the hydrogenated isoprene rubber, so that a decomposed product in the rubber composition after crosslinking or an unbonded compound is removed. It is possible to reduce the amount of decomposition products and unbound compounds as impurities.

Further, in order to form the packing of the present invention by screen printing, it is preferable to further blend carbon black (particularly MT carbon) and polysiloxane (particularly polydimethylsiloxane).

Hereinafter, the manufacturing method of the packing of the said embodiment is demonstrated. First, as shown in FIGS. 3 and 4, the main layer 10 is loaded with a first mask 12 having a frame-shaped through-hole 13 on the surface of the separator 5 (6), and then a liquid reactive group is formed from above the mask. A non-vulcanized rubber thin film (packing precursor) that conforms to the shape of the through-hole 13 by performing screen printing a predetermined number of times to apply the liquid rubber composition in which the hydrogenated isoprene rubber composition and isocyanate compound are mixed. Then, the rubber thin film is crosslinked. This cross-linking is performed by heat treatment such as hot air or infrared irradiation, and the frame-shaped main layer 10 is bonded and integrated to the peripheral portion of the separator 5. Further, when screen printing is repeated, crosslinking may be performed each time.

Next, as shown in FIG. 5 and FIG. 6, a second mask 14 having a frame-shaped through hole 15 having a size slightly larger than the through hole 13 is loaded on the surface of the formed main layer 10. Screen printing for applying a liquid rubber composition in which a hydrogenated isoprene rubber composition having a liquid reactive group and an isocyanate compound are mixed a predetermined number of times to form a coating layer 11 matching the shape through the through holes 15; The coating layer 11 is crosslinked. This cross-linking can also be performed by heat treatment, and the coating layer 11 can be bonded and integrated to the surface of the main layer 10. It is preferable from the viewpoint of improving airtightness that the rubber composition constituting the coating layer 11 is lower in hardness than the rubber composition constituting the main layer.

Thus, the separators 5 and 6 in which the packing 9 is integrated are stacked and assembled on a single cell, and a fuel cell in which the separator peripheral portion is sealed by the packing 9 is obtained.

In the above embodiment, the packing 9 having a laminated structure composed of the main layer 10 and the covering layer 11 is formed of a rubber composition in which a hydrogenated isoprene rubber composition having a reactive group and an isocyanate compound are mixed, and the packing is used to form a fuel cell. Although the sealing of the peripheral portion of the single cell has been described, the present invention is not limited to the packing having a laminated structure, and the packing 9 may be a single-layer packing. In that case, if crosslinking is performed after completion of the coating process shown in FIGS. 3 and 4, packing integration into the separator can be completed, and the processes from FIG.

Further, even in the case of a packing having a laminated structure, it is not always necessary to provide the main layer and the covering layer, and it is relatively small (narrow) on a relatively large (wide) base material layer. It is good also as packing of the structure which laminated | stacked the formed upper layer.

Furthermore, in the packing 9 having the above-mentioned laminated structure, only the coating layer 11 is composed of a composition obtained by mixing an isocyanate compound with a rubber composition mainly composed of hydrogenated isoprene rubber, and the main layer 10 is made of silicone rubber or Alternatively, other rubber materials may be used. Since the coating layer according to the present invention has a low extractability, the extraction of impurities from the packing can be reduced even if it is used as a coating layer for a packing made of other rubber. In the case where only the coating layer 11 is constituted by a composition obtained by mixing an isocyanate compound with a rubber composition mainly composed of a hydrogenated isoprene rubber having a reactive group, a main component as shown in FIG. It is preferable to adjust the size so that the through hole 15 of the second mask is larger than the through hole 13 of the first mask so that the side surface of the layer 10 is covered with the covering layer 11.

Moreover, in the said embodiment, although the method of forming the packing 9 on a separator by screen printing was demonstrated, the formation method of the packing 9 is not limited to screen printing, It depends on other application | coating methods and shaping | molding methods. be able to. For example, it is possible to crosslink after applying by a dispenser, or to form a packing by a liquid rubber injection molding method (LIMS).

Further, the packing 9 may be provided integrally with the polymer electrolyte membrane instead of the separator side.

In the above embodiment, the fuel cell is configured by cross-linking and integrating the packing to the separator or the unit cell, and stacking and assembling them, and the second embodiment of the present invention described below will be described. As described above, the unit cell and the separator may be bonded and integrated with each other so that their peripheral portions are sealed. That is, in the second embodiment, an isocyanate compound is mixed with a rubber composition containing hydrogenated isoprene rubber as a main component so that the periphery is sealed between the separators 5 and 6 and the polymer electrolyte membrane 2. The liquid rubber composition is applied in a predetermined pattern by a dispenser, and then the separators 5 and 6 and the polymer electrolyte membrane 2 are laminated to each other and crosslinked in a laminated state to form a packing 9. The separators 5 and 6 and the polymer electrolyte membrane 2 are bonded and integrated with each other, and the peripheral edge thereof is sealed.

In the second embodiment, the separator and the single cell (polymer electrolyte membrane) are bonded and integrated with each other and can no longer be disassembled, but the reliability of the seal can be further improved.

After mixing 100 parts by weight of hydrogenated isoprene rubber having a reactive group (trade name Epol, manufactured by Idemitsu Kosan Co., Ltd.), 20 parts by weight of carbon black (MT carbon), and 0.5 parts by weight of polydimethylsiloxane, Then, 18.1 parts by weight of a modified product of hexamethylene diisocyanate was added and mixed to obtain an uncrosslinked liquid rubber composition. Example 1

Screen printing is performed using the liquid rubber composition to form a rubber thin film as a frame-shaped uncrosslinked packing precursor on the separator, and the separator is heated with HAV at 120 ° C. for 10 minutes together with the formed packing precursor. The rubber composition was crosslinked and bonded and integrated with the separator. This process was repeated three times to obtain a 0.5 mm-thick packing bonded and integrated with the separator.

As Comparative Example 1, 2.5 parts by weight of a peroxide crosslinking agent was added to a rubber solution in which 100 parts by weight of EPDM was dissolved in xylene to adjust the viscosity, thereby obtaining an uncrosslinked liquid rubber composition.

Using the rubber compositions of Example 1 and Comparative Example 1, a thin plate-like cross-linked test piece was prepared, and an organic compound extractability test was performed. As a result, in Example 1 of the present invention, it was confirmed that the extraction amount (TOC) of the organic compound was smaller than that in Comparative Example 1.

According to the present invention, the sealing material interposed between the fuel cell main body and the separator is made of a material excellent in low extractability of impurities, and the sealing material is previously cross-linked to a predetermined position surface of the separator or single cell. Since the bonded and integrated packing is configured, the work of incorporating the packing becomes unnecessary, and the gas seal between the fuel cell body and the separator can be easily and reliably performed without causing deformation or displacement of the packing. It is possible to prevent the life of the fuel cell from being shortened by the extracted impurities.

The schematic longitudinal cross-sectional view of the single cell which comprises a polymer electrolyte fuel cell. The partially expanded sectional view of FIG. The figure which shows a part of shaping | molding process of a main body layer. The figure which shows the state by which the main body layer was integrally molded by the separator. The figure which shows a part of shaping | molding process of a coating layer. The figure which shows the state by which the coating layer was coat | covered by the main body layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single 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, 9 Packing 10 Main layer 11 Covering layer 12 First mask 13 Through-hole 14 Second Mask 15 through hole

Claims (3)

A packing interposed between a unit cell of a fuel cell and a separator sandwiching the unit cell, wherein the packing contains an isocyanate compound in a rubber composition mainly composed of hydrogenated isoprene rubber having a reactive group. A fuel cell packing comprising a mixed composition and integrated by cross-linking adhesion to a peripheral portion of a separator. A packing interposed between a unit cell of a fuel cell and a separator sandwiching the unit cell, wherein the packing contains an isocyanate compound in a rubber composition mainly composed of hydrogenated isoprene rubber having a reactive group. A fuel cell packing comprising a mixed composition and integrated by cross-linking adhesion to a peripheral portion of a unit cell. A sealing structure that seals between a unit cell of a fuel cell and a separator that sandwiches the unit cell, and is a composition in which an isocyanate compound is mixed with a rubber composition mainly composed of a hydrogenated isoprene rubber having a reactive group A fuel cell sealing structure characterized in that the peripheral edge of the unit cell and the peripheral edge of the separator are integrated by cross-linking.

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