Sealing material for fuel cells

Abstract

To provide a seal member for a fuel cell, which is superior in resistance against pressing crack, and low-settling resistance in a wide temperature region ranging from a low temperature to a high temperature.SOLUTION: A seal member 4a is to be used for a fuel battery sealing body. The seal member 4a comprises a cross-linked material of a rubber composition containing the following components (A) and (B): (A) at least one rubber component selected from a group consisting of an ethylene-propylene rubber, an ethylene-propylene-diene rubber and an ethylene-butene-diene rubber; and (B) carbon black of which the value of BET specific surface area (m2 / g)×DBP oil absorption (cm3 / 100 g) is 1500 to 15000. The seal member shows a modulus of repulsion elasticity of 40 to 70%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a sealing member for a fuel cell used to seal components of a fuel cell. [Background technology]

[0002] Fuel cells generate electricity through electrochemical reactions of gases, have high power generation efficiency, emit clean gases, and have minimal impact on the environment. Among these, polymer electrolyte fuel cells can be operated at relatively low temperatures and have a high power density. Therefore, polymer electrolyte fuel cells are expected to be used in a variety of applications, including power generation and as a power source for automobiles.

[0003] In a polymer electrolyte fuel cell, a cell, which is made up of a membrane electrode assembly (MEA) or the like sandwiched between separators, serves as a power generation unit. The MEA consists of a polymer membrane (electrolyte membrane) that serves as an electrolyte, and a pair of electrode catalyst layers (a fuel electrode (anode) catalyst layer and an oxygen electrode (cathode) catalyst layer) arranged on both sides of the electrolyte membrane in the thickness direction. Porous layers for diffusing gases are further arranged on the surfaces of the pair of electrode catalyst layers. A fuel gas such as hydrogen is supplied to the fuel electrode side, and an oxidant gas such as oxygen or air is supplied to the oxygen electrode side. Power is generated by an electrochemical reaction at the three-phase interface between the supplied gas, the electrolyte, and the electrode catalyst layer. A polymer electrolyte fuel cell is constructed by stacking many of the above-mentioned cells into a cell stack, which is fastened together by end plates or the like arranged on both ends in the cell stacking direction.

[0004] The separators are formed with flow paths for gases supplied to each electrode and for refrigerant to reduce heat generation during power generation. For example, mixing of the gases supplied to each electrode can cause problems such as a decrease in power generation efficiency. Furthermore, the electrolyte membrane is proton conductive when it contains water. Therefore, the electrolyte membrane must be kept wet during operation. Therefore, to prevent gas mixing and leakage of gas and refrigerant, as well as to maintain a wet state inside the cell, it is important to ensure sealing around the MEA and porous layer and between adjacent separators. As sealing materials for these components, sealing materials (rubber gaskets) made of, for example, ethylene-propylene-diene rubber or ethylene-propylene rubber have been proposed (see Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-94056 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-146781 [Patent Document 3] Patent No. 6334870 Summary of the Invention [Problem to be solved by the invention]

[0006] Since the fuel cell is constructed by stacking 200 to 300 cells and fastening them together with the sealing member (rubber gasket) under high compression, the sealing member is required to have resistance to compression cracking (resistance to compression fracture) and low settling (excellent compression set characteristics).Furthermore, it is predicted that fuel cells will be used worldwide for commercial vehicles that travel long distances, such as buses and trucks, and the sealing member is required to be able to maintain the above physical properties in both cold and hot climates. That is, the sealing member must have resistance to compression cracking and low settling properties when highly compressed over a wide temperature range from low to high temperatures.

[0007] Conventionally, a method for eliminating the low temperature resistance and compression crack resistance has been to add a large amount of a softener (plasticizer) with a low pour point to the material of the sealing member. However, since the thickness of a sealing member for a fuel cell is usually as thin as about 1 mm, the above method is susceptible to volumetric shrinkage due to the volatilization of the softener, etc., and is prone to sagging.

[0008] Furthermore, as disclosed in Patent Document 3, for example, a method of increasing resistance to compression cracking by adding a resin component to increase tensile elongation has also been considered. However, this method has the problem of a trade-off with properties such as compression set and strength, which are essential for sealing performance.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a sealing member for a fuel cell that has excellent resistance to compression cracking and low settling over a wide temperature range from low to high temperatures. [Means for solving the problem]

[0010] The present inventors conducted extensive research to solve the above-mentioned problems. During the research, they used rubber components such as ethylene-propylene rubber, ethylene-propylene-diene rubber, and ethylene-butene-diene rubber, which exhibit excellent properties as rubber components for fuel cell sealing members, and repeatedly blended and experimented with various additives to achieve both compression crack resistance and low settling properties over a wide temperature range from low to high. As a result, they found that by adding a specific carbon black and adjusting the rebound resilience of the sealing member to fall within a specific range, it was possible to achieve both compression crack resistance (compression crack resistance) and low settling properties at low to high temperatures, thereby arriving at the present invention.

[0011] The present invention, however, is summarized as follows: [1] to [7]. [1] A sealing member for a fuel cell, comprising a crosslinked product of a rubber composition containing the following components (A) and (B), and characterized in that the impact resilience of the rubber composition is 40 to 70%: (A) At least one rubber component selected from the group consisting of ethylene-propylene rubber, ethylene-propylene-diene rubber, and ethylene-butene-diene rubber. (B) BET specific surface area (m 2 / g)×DBP oil absorption (cm) 3 / 100g) value of 1500 to 15000. [2] The sealing member for a fuel cell according to [1], wherein the rubber component (A) contains an ethylene-propylene-diene rubber, the ethylene content of which is 50% by weight or less and the propylene content of which is 42% by weight or more. [3] The sealing member for a fuel cell according to [1] or [2], wherein the rubber component (A) contains an ethylene-propylene rubber, the ethylene content of which is 55% by weight or less and the propylene content of which is 45% by weight or more. [4] The sealing member for a fuel cell according to any one of [1] to [3], wherein the content of the component (B) in the rubber composition is in the range of 15 to 95 parts by weight per 100 parts by weight of the component (A). [5] The sealing member for a fuel cell according to any one of [1] to [4], wherein the rubber composition further contains the following component (C): (C) Organic peroxide. [6] A sealing member for a fuel cell according to any one of [1] to [5], wherein the content of the (C) component in the rubber composition is 1.5 to 14 parts by weight (based on the original weight) per 100 parts by weight of the (A) component. [7] The sealing member for a fuel cell according to any one of [1] to [6], wherein the rubber composition further contains the following component (D): (D) Plasticizers with a pour point of -30°C or less. [Effects of the Invention]

[0012] The sealing member for a fuel cell of the present invention can exhibit excellent performance in terms of resistance to compression cracking and low settling over a wide temperature range from low to high temperatures. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing an example of a fuel cell seal body of the present invention. [Figure 2] 1 is a cross-sectional view showing an example in which the sealing member for a fuel cell of the present invention is used. DETAILED DESCRIPTION OF THE INVENTION

[0014] Next, an embodiment of the present invention will be described in detail, but the present invention is not limited to this embodiment.

[0015] The sealing member for a fuel cell of the present invention (hereinafter sometimes simply referred to as "sealing member") is used to seal the constituent members of a fuel cell, and as described above, is made of a crosslinked product of a rubber composition containing the following components (A) and (B), and exhibits a rebound resilience in the range of 40 to 70%. (A) At least one rubber component selected from the group consisting of ethylene-propylene rubber, ethylene-propylene-diene rubber, and ethylene-butene-diene rubber. (B) BET specific surface area (m 2 / g)×DBP oil absorption (cm) 3 / 100g) value of 1500 to 15000.

[0016] Here, the "rebound resilience" refers to the resilience measured at a standard test temperature using a Lübke testing machine as described in JIS K 6255. The resilience of the crosslinked product of the rubber composition (the resilience of the sealing member) is preferably in the range of 45 to 70%, more preferably 45 to 65%. That is, if the resilience value is too small, the compression set characteristics (low settling) required in the present invention over a wide temperature range from low to high temperatures cannot be sufficiently obtained. Conversely, if the resilience value is too large, the compression cracking resistance required in the present invention (particularly, the compression cracking resistance when exposed to low and high temperature conditions alternately) cannot be sufficiently obtained.

[0017] The constituent materials of the sealing member of the present invention will be described in detail below.

[0018] <Rubber component (A)> The rubber component (A) is the main component of the rubber composition and usually accounts for 40% by weight or more of the entire rubber composition, preferably 40 to 80% by weight, more preferably 45 to 75% by weight of the entire rubber composition. As described above, ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), and ethylene-butene-diene rubber (EBT) are used as the rubber component (A), either singly or in combination. From the viewpoints of acid resistance, water resistance, and compression set in the operating environment of a fuel cell, it is preferable to use EPDM and EBT as the rubber component (A), and from the viewpoint of advantageous impact resilience, it is more preferable to use EBT as the rubber component (A).

[0019] The EPM preferably has an ethylene content (weight percentage of the ethylene component) of 55% by weight or less and a propylene content (weight percentage of the propylene component) of 45% by weight or more, from the viewpoints of reducing the crystallinity of the polymer, improving sealing performance at extremely low temperatures, and suppressing impact resilience. Furthermore, from the viewpoints of further improving low-temperature resistance and the tensile properties required for sealing members, the ethylene content is more preferably in the range of 35 to 55% by weight, even more preferably 40 to 53% by weight, and the propylene content is more preferably in the range of 45 to 65% by weight, even more preferably 47 to 60% by weight.

[0020] The EPDM preferably has an ethylene content (weight percentage of the ethylene component) of 50% by weight or less and a propylene content (weight percentage of the propylene component) of 42% by weight or more, from the viewpoints of reducing the crystallinity of the polymer, improving sealing performance at extremely low temperatures, and suppressing impact resilience. Furthermore, from the viewpoints of further improving low-temperature resistance and the tensile properties required for sealing members, the ethylene content is more preferably in the range of 35 to 50% by weight, and even more preferably 40 to 50% by weight, and the propylene content is more preferably in the range of 42 to 55% by weight, and even more preferably 44 to 50% by weight.

[0021] Furthermore, it is preferable that the EBT have an ethylene content (weight percentage of the ethylene component) of 55% by weight or less and a butene content (weight percentage of the butene component) of 35% by weight or more, from the viewpoint of reducing the crystallinity of the polymer and improving sealing properties at extremely low temperatures. Furthermore, from the viewpoint of further improving low temperature resistance and the tensile properties required for sealing members, the ethylene content is more preferably in the range of 35 to 55% by weight, and even more preferably 40 to 53% by weight, and the butene content is more preferably in the range of 35 to 55% by weight, and even more preferably 38 to 50% by weight.

[0022] Furthermore, when at least one of the above EPDM and EBT is contained, the higher the diene content in the EPDM or EBT, the higher the crosslink density of the crosslinked seal member, and the further improved the compression set (low settling), which is important for sealing performance. For this reason, the diene content (mass proportion of the diene component) is preferably in the range of 1 to 20 wt%, more preferably 3 to 15 wt%.

[0023] The diene component is preferably, for example, a diene monomer having 5 to 20 carbon atoms, and specific examples thereof include 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene, 1,4-octadiene, 1,4-cyclohexadiene, cyclooctadiene, dicyclopentadiene (DCP), 5-ethylidene-2-norbornene (ENB), 5-vinyl-2-norbornene (VNB), 5-butylidene-2-norbornene, 2-methallyl-5-norbornene, and 2-isopropenyl-5-norbornene.

[0024] Carbon Black (B) As mentioned above, the carbon black (B) used in the material of the sealing member of the present invention is a carbon black having a BET specific surface area (m 2 / g)×DBP oil absorption (cm) 3 The carbon black used has a BET specific surface area (m 2 / g)×DBP oil absorption (cm) 3 / 100g) is preferably in the range of 1750 to 14000, more preferably in the range of 2000 to 13000. That is, the above-mentioned BET specific surface area (m 2 / g)×DBP oil absorption (cm) 3 If the value of (R / 100g) is too large, low settling properties cannot be obtained over a wide temperature range from low to high temperatures, and conversely, if the value is too small, the resistance to compression cracking required in the present invention (particularly, resistance to compression cracking when exposed to low temperature conditions and high temperature conditions alternately) cannot be obtained. Here, the BET specific surface area of ​​the carbon black (B) can be measured, for example, by degassing a sample at 200°C for 15 minutes and then using a mixed gas (N2: 70%, He: 30%) as an adsorption gas with a BET specific surface area measuring device (Microdata Corporation, 4232-II). The BET specific surface area is 20 to 125 m 2 / g, more preferably 25 to 120m 2 / g range. The DBP oil absorption of the carbon black (B) is a value measured in accordance with JIS K 6217-4. 3 / 100g, more preferably 70 to 175cm 3 / 100g range.

[0025] The grade of the carbon black (B) is not particularly limited, but preferred examples include SRF, SRF-HS, GPF, GPF-HS, GPF-LS, FEF, FEF-HS, FEF-LS, HAF, HAF-HS, HAF-LS, LI-HAF, N351, N339, IISAF-HS, ISAF-LS, and ISAF grades. Of these, SRF-HS, GPF, GPF-HS, GPF-LS, FEF, FEF-HS, FEF-LS, HAF, HAF-HS, HAF-LS, LI-HAF, and N351 grades are more preferred.

[0026] The amount of the carbon black (B) to be compounded is preferably 15 to 95 parts by weight per 100 parts by weight of the rubber component (A) in order to obtain the desired resistance to compression cracking and low settling properties. When the rubber component (A) is EPM or EPDM, the amount of the carbon black (B) to be compounded per 100 parts by weight of the rubber component (A) is more preferably in the range of 20 to 95 parts by weight, and even more preferably in the range of 30 to 95 parts by weight. When the rubber component (A) is EBT, the amount of the carbon black (B) to be compounded per 100 parts by weight of the rubber component (A) is more preferably in the range of 15 to 90 parts by weight, and even more preferably in the range of 25 to 90 parts by weight.

[0027] Here, in addition to the components (A) and (B), the rubber composition used in the sealing member of the present invention may contain various additives such as an organic peroxide (C), a plasticizer (D), a crosslinking aid, an antioxidant, a processing aid, and a reinforcing material such as silica, as described below. In addition, it is preferable that the rubber composition does not contain (is free of) adhesive components (such as silane coupling agents), pressure-sensitive adhesive components, or resin components such as thermoplastic resins, from the viewpoint of maintaining compression set (low settling), which is important for the sealing performance of the sealing member.

[0028] 《Organic peroxide (C)》 As the crosslinking agent for the rubber component (A), an organic peroxide (C) is preferred because it does not inhibit power generation in a fuel cell. Examples of the organic peroxide include peroxyketals, peroxyesters, dialkyl peroxides, ketone peroxides, diacyl peroxides, and peroxydicarbonates. These may be used alone or in combination. Among these organic peroxides, those having a one-hour half-life temperature of 160°C or less are preferred. Among these, at least one selected from the group consisting of dialkyl peroxides, peroxyketals, and peroxyesters having a one-hour half-life temperature of 100°C to 160°C is preferred because they provide excellent scorch resistance and crosslinking efficiency to the rubber composition kneaded with the crosslinking agent. At least one selected from the group consisting of dialkyl peroxides, peroxyketals, and peroxyesters having a one-hour half-life temperature of 110°C to 160°C is particularly preferred.

[0029] In the present invention, the "half-life" of the organic peroxide (C) having a one-hour half-life temperature of 160°C or less refers to the time it takes for the concentration (amount of active oxygen) of the organic peroxide to decrease to half of its initial value. Therefore, the "half-life temperature" serves as an index of the decomposition temperature of the organic peroxide. The "one-hour half-life temperature" is the temperature at which the half-life is one hour. In other words, the lower the one-hour half-life temperature, the easier the decomposition at a low temperature and the faster the reaction rate. If the one-hour half-life temperature is too low, the rubber composition is more likely to scorch and the crosslinking efficiency will decrease.

[0030] Examples of the peroxyketal include n-butyl-4,4-di(t-butylperoxy)valerate, 2,2-di(t-butylperoxy)butane, 2,2-di(4,4-di(t-butylperoxy)cyclohexyl)propane, 1,1-di(t-butylperoxy)cyclohexane, 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-hexylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-di(t-butylperoxy)-2-methylcyclohexane.

[0031] Examples of the peroxyester include t-butyl peroxybenzoate, t-butyl peroxyacetate, t-hexyl peroxybenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, t-butylperoxy-2-ethylhexyl monocarbonate, t-butyl peroxylaurate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-3,5,5-trimethylhexanoate, t-butylperoxymaleic acid, and t-hexylperoxyisopropyl monocarbonate.

[0032] Examples of the dialkyl peroxide include di(2-t-butylperoxypropyl)benzene, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylcumyl peroxide, di-t-hexyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3.

[0033] Among these, 1,1-di(t-hexylperoxy)cyclohexane, 1,1-di(t-butylperoxy)cyclohexane, n-butyl-4,4-di(t-butylperoxy)valerate, 2,2-di(t-butylperoxy)butane, t-butylperoxybenzoate, t-butylperoxy-2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, di(2-t-butylperoxypropyl)benzene, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, t-butylcumyl peroxide, di-t-hexyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 are preferred because of their high reactivity with the rubber component (A). Particularly preferred are 1,1-di(t-butylperoxy)cyclohexane, n-butyl-4,4-di(t-butylperoxy)valerate, 1,1-di(t-hexylperoxy)cyclohexane, t-hexylperoxybenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, di(2-t-butylperoxypropyl)benzene, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and t-butylcumyl peroxide.

[0034] The amount of the organic peroxide (C) (in the case of a raw material with 100% purity) is preferably in the range of 1.5 to 14 parts by weight, more preferably 1.5 to 12 parts by weight, and particularly preferably 2.0 to 10 parts by weight, per 100 parts by weight of the rubber component (A). If the amount of the organic peroxide (C) is too small, it tends to be difficult to sufficiently proceed with the crosslinking reaction, while if the amount of the organic peroxide (C) is too large, the crosslink density tends to be too high, which tends to reduce resistance to compression cracking. When a pure organic peroxide (C) is not used, it is blended so that the ratio calculated as the pure organic peroxide falls within the above range.

[0035] Plasticizer (D) Examples of the plasticizer (D) that may be added as needed to the materials for the sealing member of the present invention include petroleum-based plasticizers such as process oil, lubricating oil, paraffin, liquid paraffin, and Vaseline, fatty oil-based plasticizers such as castor oil, linseed oil, rapeseed oil, and coconut oil, waxes such as tall oil, sab, beeswax, carnauba wax, and lanolin, linoleic acid, palmitic acid, stearic acid, and lauric acid. These may be used alone or in combination of two or more.

[0036] The amount of the plasticizer (D) added is usually 60 parts by weight or less, preferably in the range of 5 to 50 parts by weight, based on 100 parts by weight of the rubber component (A).

[0037] Among the plasticizers (D), those with a pour point of -30°C or less are preferred, and those with a pour point of -40°C or less are more preferred. Examples of such plasticizers include poly-α-olefin, dioctyl phthalate (DOP), dioctyl adipate (DOA), dioctyl sebacate (DOS), and dibutyl sebacate (DBS). These may be used alone or in combination of two or more. Among them, poly-α-olefins are preferred from the viewpoints of good compatibility with the rubber component (A) and resistance to bleeding. Poly-α-olefins are obtained by polymerizing α-olefins having 6 to 16 carbon atoms. The smaller the molecular weight of poly-α-olefins, the lower the viscosity and the lower the pour point.

[0038] As mentioned above, the lower the pour point of a plasticizer, the less likely it is to harden at extremely low temperatures. Therefore, the lower the pour point of a plasticizer, the greater its effect in suppressing crystallization of the rubber component at extremely low temperatures. On the other hand, if the pour point is too low, it is more likely to volatilize during operation of the fuel cell, etc. Therefore, it is desirable for the pour point of the plasticizer to be -80°C or higher. The pour point can be measured in accordance with JIS K 2269 (1987).

[0039] The kinematic viscosity of the plasticizer (D) at 40°C is preferably 8 to 500 mm 2 / s, more preferably 9 to 460 mm 2 / s range. That is, when a plasticizer having such a kinematic viscosity is used, it has good compatibility with rubber and low volatility, and therefore excellent compression set (low sag). The kinematic viscosity of the plasticizer (D) is measured in accordance with JIS K 2283.

[0040] Cross-linking aid Examples of cross-linking aids that may be added as needed to the materials for the sealing member of the present invention include maleimide compounds, triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), trimethylolpropane trimethacrylate (TMPT), bifunctional (meth)acrylates, and 1,2-polybutadiene. These may be used alone or in combination of two or more. Among these, maleimide compounds and TAIC are preferred because of their significant effect of improving cross-link density and strength.

[0041] The amount of the crosslinking aid blended is preferably 5 parts by weight or less per 100 parts by weight of the rubber component (A). If the amount of the crosslinking aid blended is too large, the crosslink density becomes too high, which tends to result in a decrease in resistance to compression cracking.

[0042] Anti-aging agent Examples of antioxidants that may be added as needed to the materials for the sealing member of the present invention include phenol-based antioxidants, amine-based antioxidants, imidazole-based antioxidants, phosphoric acid-based antioxidants, waxes, etc. These may be used alone or in combination of two or more. Among these, phenol-based antioxidants (particularly bisphenol-based antioxidants) and amine-based antioxidants are preferred from the viewpoint of their antioxidant effect. The amount of the antioxidant compounded is preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the rubber component (A).

[0043] <Production of sealing member for fuel cell> The sealing member for a fuel cell of the present invention can be produced, for example, by blending the above-mentioned components (A) and (B) and, if necessary, various other additives such as the above-mentioned components (C) and (D) to prepare a rubber composition, and then crosslinking the rubber composition. The crosslinking molding of the sealing member is usually carried out by primary crosslinking in a mold (by holding the mold at 130 to 200°C for 3 to 30 minutes), followed by demolding and secondary crosslinking in an oven (by heating at 130 to 180°C for 60 to 240 minutes). The sealing member is preferably molded into a predetermined shape according to the shape of the sealing portion. For example, if molded into a film, the sealing member can be attached to various components of a fuel cell with an adhesive and used. The sealing member of the present invention may also be used in such a way that it is disposed between various components of a fuel cell without being bonded. Furthermore, the sealing member of the present invention may be crosslinked and attached with an adhesive (post-bonding), or it may be crosslinked and molded (crosslinked-bonded) onto the adhesive-coated surface, so that the sealing member of the present invention and components of the fuel cell, such as an MEA or separator, can be integrally molded in a mold, as described below.

[0044] <Fuel cell seal body> The fuel cell seal of the present invention may be formed by bonding a fuel cell component and a seal member (fuel cell seal member of the present invention) that seals the fuel cell component to each other via an adhesive layer.

[0045] The fuel cell components sealed by the sealing member of the present invention vary depending on the type and structure of the fuel cell, but examples include separators (metal separators, etc.), gas diffusion layers (GDLs), and MEAs (electrolyte membranes, electrodes).

[0046] An example of a fuel cell seal body of the present invention is shown in Figure 1. Figure 1 mainly shows a single cell 1 in a fuel cell formed by stacking multiple cells, and cell 1 includes an MEA 2, a gas diffusion layer (GDL) 3, a seal member 4a, a separator 5, and an adhesive layer 6.

[0047] Examples of the fuel cell seal body of the present invention include, as shown in FIG. 1, one in which a separator 5 and a seal member 4a are bonded together via an adhesive layer 6, one in which an MEA 2 and a seal member 4a are bonded together via an adhesive layer 6, one in which a gas diffusion layer 3 and a seal member 4a are bonded together via an adhesive layer 6, and one in which adjacent seal members 4a are bonded together via an adhesive layer 6.

[0048] Although not shown, the MEA 2 comprises an electrolyte membrane and a pair of electrodes arranged on either side of the electrolyte membrane in the stacking direction. The electrolyte membrane and the pair of electrodes are rectangular thin plates. Gas diffusion layers 3 are arranged on either side of the MEA 2 in the stacking direction. The gas diffusion layers 3 are porous layers and are rectangular thin plates.

[0049] The separator 5 is preferably made of a metal such as titanium or stainless steel (e.g., SUS304) or a conductive resin (a thermoplastic or thermosetting resin mixed with graphite, polyacrylonitrile-based carbon fiber, etc.). From the viewpoint of electrical conductivity reliability, it is more preferable for the separator surface to have a thin carbon film such as a DLC film or graphite film formed by a process such as PVD or CVD. The thickness of the thin carbon film is preferably 10 to 500 nm. The separator 5 has a rectangular thin plate shape and is provided with a total of six grooves extending in the longitudinal direction, which give the separator 5 a corrugated cross section. The separators 5 are disposed opposite each other in the stacking direction of the gas diffusion layer 3. The corrugated shape is used to define gas flow paths 7 between the gas diffusion layer 3 and the separator 5 for supplying gas to the electrodes.

[0050] The sealing member 4a has a rectangular frame shape. The sealing member 4a is adhered to the periphery of the MEA 2 and the gas diffusion layer 3 and to the separator 5 via an adhesive layer 6, thereby sealing the periphery of the MEA 2 and the gas diffusion layer 3. In the example of FIG. 1, the sealing member 4a is made up of two separate members, an upper member and a lower member, but it may also be a single sealing member combining the two.

[0051] When a fuel cell such as a polymer electrolyte fuel cell is in operation, a fuel gas and an oxidant gas are supplied through the gas flow channels 7. The periphery of the MEA 2 is sealed by a sealing member 4a via an adhesive layer 6. This prevents gas mixing and leakage.

[0052] The fuel cell seal of the present invention can be produced, for example, as follows: First, the fuel cell seal member of the present invention is produced as described above.

[0053] Next, by applying the adhesive layer forming material (adhesive) to either or both of a fuel cell component such as a metal separator and a sealing member that seals it, the fuel cell seal body of the present invention can be obtained, in which the fuel cell component such as a metal separator and the sealing member are bonded together via an adhesive layer.

[0054] Examples of the adhesive layer-forming material (adhesive) include rubber cement, a rubber composition that is liquid at room temperature (23°C), and a primer. Examples of the liquid rubber composition include a rubber composition containing a rubber component, an organic peroxide (crosslinking agent), and the like. Examples of the rubber component include liquid rubber, and specifically, liquid EPM, liquid EPDM, liquid acrylonitrile-butadiene rubber (liquid NBR), liquid hydrogenated acrylonitrile-butadiene rubber (liquid H-NBR), and the like, used alone or in combination. Examples of the primer include a primer containing a copolymer oligomer of a silane coupling agent.

[0055] The adhesive layer-forming material can be applied by, for example, spraying, dipping, roll coating, etc., and is usually applied at room temperature.

[0056] The thickness of the adhesive layer in the fuel cell seal of the present invention is usually 0.01 to 0.5 mm, preferably 0.05 to 0.3 mm, when the liquid rubber composition is used, and usually 0.01 to 25 μm, preferably 0.02 to 2 μm, when the primer is used.

[0057] Furthermore, when a fuel cell seal is manufactured by integrating a fuel cell component and a seal member by crosslinking and bonding the seal member, the manufacturing method can be as follows: A fuel cell component with an adhesive layer formed thereon is placed in a mold for molding the seal member, and a rubber composition for forming the seal member is crosslinked and molded in the mold while in contact with the fuel cell component.

[0058] Another example of use of the fuel cell sealing member of the present invention is shown in Figure 2. Figure 2 shows a member comprising a separator 5 having a rectangular thin plate shape, a total of six grooves extending in the longitudinal direction, and the aforementioned uneven cross-sectional shape, and a lip 4b having a rectangular cross-sectional convex shape provided on the periphery of the separator 5 via an adhesive layer 6. The fuel cell sealing member of the present invention is used as the lip 4b. The materials for forming the separator 5 and the adhesive layer 6 are both the same as those described above. [Example]

[0059] Next, examples will be described together with comparative examples, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.

[0060] First, prior to the Examples and Comparative Examples, the following rubber composition materials were prepared. Note that the "specific surface area x oil absorption amount" of the carbon black described below is calculated by multiplying the BET specific surface area (m 2 / g)×DBP oil absorption (cm) 3 / 100g) and the BET specific surface area (m 2 / g) is a value measured using a BET specific surface area measuring device (Microdata Corporation, 4232-II) based on the above description, and the DBP oil absorption is a value measured in accordance with JIS K 6217-4.

[0061] [Rubber (i) (Component A)] Ethylene-butene-diene rubber (Mitsui Chemicals, Inc., EBT-K9330M) with an ethylene content of 50% by weight, a butene content of 42.9% by weight, and a diene content of 7.1% by weight

[0062] [Rubber (ii) (Component A)] Ethylene-propylene-diene rubber (keltan 2650C, manufactured by ARLANXEO) with an ethylene content of 46% by weight, a propylene content of 48% by weight, and a diene content of 6.0% by weight.

[0063] [Rubber (iii) (Component A)] Ethylene-propylene rubber (Mitsui Chemicals, EPT-0045) with an ethylene content of 51% by weight and a propylene content of 49% by weight

[0064] [Anti-aging agent] Bisphenol-based antioxidant (Ouchi Shinko Chemical Industry Co., Ltd., Nocrac NS-5)

[0065] [Carbon black (i)] Tokai Carbon Co., Ltd., SEAT SO (FEF grade, BET specific surface area: 42 m 2 / g, DBP oil absorption: 115cm 3 / 100g, specific surface area x oil absorption: 4830)

[0066] [Carbon black (ii)] Tokai Carbon Co., Ltd., Seast V (GPF grade, BET specific surface area: 27m 2 / g, DBP oil absorption: 87cm 3 / 100g, specific surface area x oil absorption: 2349)

[0067] [Carbon black (iii)] Tokai Carbon Co., Ltd., Seast 6 (ISAF grade, BET specific surface area: 119 m 2 / g, DBP oil absorption: 114cm 3 / 100g, specific surface area x oil absorption: 13566)

[0068] [Carbon black (iv)] Cancarb, Thermax N990 (MT grade, BET specific surface area: 10 m 2 / g, DBP oil absorption: 44cm 3 / 100g, specific surface area x oil absorption: 440)

[0069] [Carbon black (v)] Tokai Carbon Co., Ltd., SEA ST 9 (SAF grade, BET specific surface area: 142 m 2 / g, DBP oil absorption: 115cm 3 / 100g, specific surface area x oil absorption: 16330)

[0070] [Plasticizer] Poly-α-olefin (PAO601, manufactured by Nippon Steel Chemical & Material Co., Ltd., kinematic viscosity at 40°C: 30.7 mm 2 / s, pour point (JIS K 2269): -63℃)

[0071] [Organic peroxide] 1,1-Di(t-butylperoxy)cyclohexane (Perhexa C-80, NOF Corporation, purity 80%, 1-hour half-life temperature: 111.1°C)

[0072] [Crosslinking aid] Triallyl isocyanurate (TAIC, manufactured by Mitsubishi Chemical Corporation)

[0073] [Examples 1 to 9, Comparative Examples 1 to 4] The components shown in Tables 1 and 2 below were blended in the proportions shown in the tables, and the mixture was kneaded using a Banbury mixer and an open roll to prepare rubber compositions. Next, the impact resilience of the rubber composition was measured according to the following criteria, and the results are shown in Tables 1 and 2 below.

[0074] <Rebound elasticity> The rubber composition prepared above was crosslinked by holding it in a specified mold at 170°C for 15 minutes and then demolded. After that, it was heated in an oven at 150°C for 120 minutes to cause secondary crosslinking, thereby producing a cylindrical crosslinked rubber sample with a diameter of 29 mm and a thickness of 12.5 mm. Then, the crosslinked rubber sample was measured for its impact resilience at a standard test temperature using a Lubke type testing machine as described in JIS K 6255.

[0075] Using the rubber composition, samples for evaluation of each property were prepared according to the following criteria, and the properties were measured and evaluated. The results are shown in Tables 1 and 2 below.

[0076] <High-temperature compression set, low-temperature compression set> The rubber composition prepared above was crosslinked by holding it in a specified mold at 170°C for 15 minutes and then demolded. After that, it was heated in an oven at 150°C for 120 minutes to cause secondary crosslinking, thereby producing a cylindrical crosslinked rubber sample with a diameter of 29 mm and a thickness of 12.5 mm. The crosslinked rubber samples were then measured for compression set in accordance with JIS K 6256 and evaluated according to the following criteria: The high-temperature compression set evaluation was performed by measuring and evaluating the compression set after leaving the crosslinked rubber sample to stand in a 120°C atmosphere for 240 hours, and the low-temperature compression set evaluation was performed by measuring and evaluating the compression set after leaving the crosslinked rubber sample to stand in a -40°C atmosphere for 24 hours. (High temperature compression set evaluation standard) ◎: Compression set is less than 20%. Good: Compression set is 20-25%. ×: Compression set exceeds 25%. (Low temperature compression set evaluation criteria) ◎: Compression set is less than 50%. Good: Compression set is 50-60%. ×: Compression set exceeds 60%.

[0077] <Compression crack resistance> The rubber composition prepared above was crosslinked by holding it at 170°C for 15 minutes in a specified mold and then demolded. After that, it was heated in an oven at 150°C for 120 minutes to cause secondary crosslinking, thereby producing a circular crosslinked rubber sample with a diameter of 15 mm and a thickness of 1 mm. The crosslinked rubber sample was then compressed to a predetermined compression ratio (50% or 55%) using a tool similar to that specified in JIS K 6256, and repeatedly left to stand in a high-temperature atmosphere and a low-temperature atmosphere. Specifically, the crosslinked rubber sample was compressed at the compression ratio and then left to stand in a 110°C atmosphere for 5 minutes, followed by a -40°C atmosphere for 5 minutes (cooling and heating cycle), which was considered as one cycle. Ten such cycles were performed. After this treatment, the sample was released, and the crosslinked rubber sample was visually inspected for any cracks. The resistance to compression cracking was evaluated according to the following criteria: ⊚: No cracks were observed in appearance even at a compression rate of 55%. ◯: Appearance cracks were observed at a compression rate of 55%, but no appearance cracks were observed at a compression rate of 50%. ×: Even with a compression rate of 50%, cracks were observed in the appearance.

[0078] [Table 1]

[0079] [Table 2]

[0080] The results in Tables 1 and 2 above show that the crosslinked rubbers (sealing members) of the examples have excellent compression set characteristics (low settling) and compression cracking resistance (resistance to compression cracking associated with thermal cycling) over a wide temperature range from low to high.

[0081] In contrast, the crosslinked rubber of Comparative Example 1 used carbon black (specific surface area x oil absorption: 440) that did not satisfy the criteria of the present invention, and also had a high rebound resilience, resulting in the desired compression cracking resistance (resistance to compression cracking associated with thermal cycling). The crosslinked rubber of Comparative Example 2 used carbon black (specific surface area x oil absorption: 16,330) that did not satisfy the criteria of the present invention, resulting in poor high-temperature and low-temperature compression set. The crosslinked rubber of Comparative Example 3 used carbon black (specific surface area x oil absorption: 4,830) that met the criteria of the present invention, but its high rebound resilience resulted in the desired compression cracking resistance (resistance to compression cracking associated with thermal cycling). The crosslinked rubber of Comparative Example 4 also used carbon black (specific surface area x oil absorption: 4,830) that met the criteria of the present invention, but its low rebound resilience and poor low-temperature compression set resulted. [Industrial Applicability]

[0082] The fuel cell sealing member of the present invention is used for a fuel cell sealing body in which a fuel cell component such as a metal separator is bonded to a rubber sealing member that seals it via an adhesive layer, or for the sealing member of a fuel cell sealing body in which the above sealing members are bonded to each other via an adhesive layer. [Explanation of symbols]

[0083] 1 cell 2 MEA 3 Gas diffusion layer 4a sealing member 4b lip 5 Separator 6 Adhesive layer 7 Gas flow path

Claims

1. A sealing member for a fuel cell, comprising a crosslinked product of a rubber composition containing the following components (A), (B) and (D), and having a rebound resilience of 55 to 70%: (A) Ethylene-butene-diene rubber. (B) BET specific surface area (m 2 / g) x DBP oil absorption (cm 3 / 100g) value of 1,500 to 15,000. (D) A plasticizer having a pour point of -30°C or less.

2. 2. The sealing member for a fuel cell according to claim 1, wherein the ethylene content of said ethylene-butene-diene rubber (A) is 55% by weight or less and the butene content is 35% by weight or more.

3. 3. The sealing member for a fuel cell according to claim 1, wherein the content of said component (B) in said rubber composition is in the range of 15 to 95 parts by weight per 100 parts by weight of said component (A).

4. 3. The sealing member for a fuel cell according to claim 2, wherein the content of the component (B) in the rubber composition is in the range of 25 to 90 parts by weight per 100 parts by weight of the component (A).

5. The sealing member for a fuel cell according to any one of claims 1 to 4, wherein the rubber composition further contains the following component (C): (C) Organic peroxide.

6. 6. The sealing member for a fuel cell according to claim 5, wherein the content of the component (C) in the rubber composition is 1.5 to 14 parts by weight (based on the original weight) per 100 parts by weight of the component (A).

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