Adhesive composition for fuel cell sealing members, member for fuel cells, and method for producing member for fuel cells

Abstract

This adhesive composition for fuel cell sealing members is for bonding a thin platy base (10), which is a constituent member of a fuel cell, to a sealing member (20) produced from a rubber composition, and comprises (A) an adhesive liquid comprising a solvent and an adhesive component which comprises a silane coupling agent as a main component or comprises a silane coupling agent and an organic titanate compound as main components and (B) a dye which is compatible with the adhesive component and dissolves in the solvent. The content of the dye in the adhesive composition is 3-25 parts by mass per 100 parts by mass of the non-volatile content of the adhesive composition. The adhesive composition is colored by the dye in a color which differs from the color of the base (10) or sealing member (20).

Description

Adhesive composition for fuel cell sealing member, fuel cell member, and method for producing fuel cell member

[0001] The present disclosure relates to an adhesive composition for bonding a fuel cell component and a sealing member, a fuel cell component manufactured using the adhesive composition, and a method for manufacturing a fuel cell component.

[0002] Fuel cells have a stack structure in which many cells are stacked. The cell stack is fastened by end plates arranged on both sides in the stacking direction. For example, a cell of a polymer electrolyte fuel cell has electrode members including a membrane electrode assembly (MEA) and separators sandwiching the electrode members. Rubber seal members are arranged around the electrode members and between adjacent separators to ensure sealing and insulation against reactant gases and refrigerants. To maintain high sealing performance in the fuel cell operating environment, a method of integrating the seal member and the mating member using an adhesive is effective. For example, Patent Document 1 describes a method for bonding a rubber gasket (sealing member) to a separator, in which a silane coupling agent-based primer is applied to the surface of the rubber gasket, the primer-coated surface is brought into close contact with the separator, and the rubber gasket is heated while being pressure-bonded. Patent Document 2 describes an adhesive for bonding a seal member to a separator, the adhesive containing a copolymer oligomer-type silane coupling agent having a specific ratio of hydrophilic and hydrophobic functional groups as its main component. In Patent Document 2, an adhesive containing a silane coupling agent as a main component is applied to the surface of a separator, dried, and then a rubber composition is laminated thereon, followed by crosslinking and bonding.

[0003] JP 2017-183198 A International Publication No. 2022 / 208926 JP 2018-59630 A

[0004] Adhesives whose main component is a silane coupling agent are nearly colorless and transparent, and the coating film they form on the surface of substrates such as separators is extremely thin. For this reason, it is difficult to tell by visual inspection whether the adhesive has been properly applied to the specified area. If there are areas where the adhesive is not evenly applied or not coated, the sealing material may peel off or the sealing performance may be reduced.

[0005] One method for determining the adhesive application condition is to add a colorant to the adhesive to color the coating film. However, because the colorant does not have adhesive properties, the adhesive properties may be reduced depending on the amount added. Pigments are known as colorants, but because pigments do not dissolve in solvents, they tend to settle, making it difficult to form a uniform coating film. Furthermore, non-adhesive pigment particles are dispersed in the formed adhesive layer, which can cause the sealing material to peel off easily, or compressive forces in the lamination direction can concentrate stress near the pigment particles, potentially causing cracks in the sealing material originating from the pigment particles.

[0006] In this regard, Patent Document 3 describes coloring an adhesive that bonds an annular metal core material and an elastomer member with a dye. However, the adhesive described in Patent Document 3 is a general adhesive such as a phenolic resin or epoxy resin used in bearing parts of automobiles, wind turbines, etc., and does not use a silane coupling agent. It also describes that the dye can be either water-soluble or oil-soluble. In other words, Patent Document 3 does not anticipate the use of a silane coupling agent as an adhesive component, and does not consider the compatibility of the dye with the adhesive component.

[0007] For example, if the compatibility between the adhesive component and the dye in an adhesive is poor, the dye may precipitate or form lumps, making it difficult to form a uniform coating. In this case, the sealing member may be prone to peeling or may crack due to compressive forces in the stacking direction. Furthermore, fuel cells require thin components and high dimensional accuracy, and the thickness of the adhesive layer between the sealing member and the mating member is also extremely thin. Thus, adhesives for bonding fuel cell components and sealing members must satisfy the unique characteristics required for fuel cells, making it difficult to achieve both adhesion and distinguishability.

[0008] The present disclosure has been made in consideration of the above-described circumstances, and aims to provide an adhesive composition for fuel cell sealing members that can achieve both adhesion and identifiability, a fuel cell member manufactured using the adhesive composition, and a method for manufacturing a fuel cell member.

[0009] (1) In order to solve the above-mentioned problems, the adhesive composition for a fuel cell sealing member of the present disclosure is an adhesive composition for a fuel cell sealing member that bonds a thin plate-like substrate, which is a constituent member of a fuel cell, to a sealing member made of a rubber composition, and is characterized in that it comprises: (A) an adhesive liquid having an adhesive component whose main component is a silane coupling agent, or whose main components are a silane coupling agent and an organic titanate compound, and a solvent; and (B) a dye that is compatible with the adhesive component and dissolves in the solvent, wherein the content of the dye is 3 parts by mass or more and 25 parts by mass or less, where the non-volatile content of the adhesive composition is 100 parts by mass, and the adhesive composition is colored with the dye in a color different from the color of the substrate or the sealing member.

[0010] The adhesive composition for a fuel cell sealing member of the present disclosure (hereinafter sometimes simply referred to as the "adhesive composition") is colored with a dye. When the substrate is a base material, the adhesive composition is colored a color different from the color of the substrate, and when the substrate is a sealing member, the adhesive composition is colored a color different from the color of the sealing member. This makes the adhesive composition easier to identify on the surface of the substrate, making it easier to determine the quality of the coating state visually or using a color inspection device. As a result, uneven coating and areas that are not fully coated are less likely to occur, and peeling of the sealing member and deterioration of sealing properties can be suppressed. In the present disclosure, "color" primarily refers to the hue of the three elements of color, and refers to shades such as red, blue, green, and yellow.

[0011] In the adhesive composition of the present disclosure, the dye is compatible with the adhesive components and dissolves in the solvent. This makes it difficult for the dye to precipitate and form clumps, allowing for the formation of a homogeneous coating film. As a result, peeling of the sealing member and deterioration of sealing properties can be suppressed. Furthermore, the dye content is 3 parts by mass or more and 25 parts by mass or less, assuming that the nonvolatile content of the adhesive composition is 100 parts by mass. Since coloring power is exerted with a relatively small amount of dye, even if the dye does not have adhesive properties, the adhesive properties are not likely to decrease. In this way, the adhesive composition of the present disclosure can achieve both adhesion and distinguishability.

[0012] (2) In the above-described configuration (1), the adhesive composition for a fuel cell sealing member may be applied to the substrate or the sealing member in a thickness of 0.01 μm or more and 1 μm or less. This configuration is suitable for realizing the thinning and high dimensional accuracy of components required for fuel cells.

[0013] (3) In any of the above configurations, the adhesive composition for a fuel cell sealing member may be applied to the substrate. According to this configuration, a flexible rubber sealing member (which may be an uncrosslinked rubber composition) is laminated on a thin plate-like substrate, thereby suppressing positional displacement of the sealing member and improving dimensional accuracy and workability.

[0014] (4) In the configuration of (3) above, the substrate may be a separator. With this configuration, the adhesive reliability between the separator and the seal member can be improved.

[0015] (5) In the configuration of (4) above, the separator may be silver-based, and the dye may be black-based or red-based. According to this configuration, a black-based or red-based adhesive composition is applied to a silver-based separator. This makes the presence of the adhesive composition more noticeable on the separator, making it easier to determine whether the adhesive composition is applied properly.

[0016] (6) In any of the above configurations, the dye may be a xanthene dye or an azine dye. This configuration makes it easy to select a dye that is compatible with the adhesive component, dissolves in a solvent, and can impart color in a relatively small amount.

[0017] (7) The fuel cell member of the present disclosure comprises a thin plate-shaped substrate, a sealing member made from a rubber composition, and an adhesive layer that bonds the substrate and the sealing member, and the adhesive layer is formed from the adhesive composition for a fuel cell sealing member having the configuration described in (1) above.

[0018] According to the fuel cell member of the present disclosure, the adhesive composition applied to the surface of the substrate or sealing member during the manufacturing process is easily identifiable, and the quality of the applied state can be easily determined by visual inspection, a color inspection device, etc. This makes it possible to reduce the occurrence of adhesion defects and realize a high-quality fuel cell member with excellent sealing properties.

[0019] (8) In the configuration of (7), the thickness of the adhesive layer may be 0.01 μm or more and 1 μm or less. This configuration is suitable for realizing the thinning and high dimensional accuracy of components required for fuel cells.

[0020] (9) In the configurations (7) and (8) above, the substrate may be a stainless steel separator. This configuration can improve the adhesive reliability between the separator and the seal member. Furthermore, stainless steel separators typically have a silvery color due to their metallic luster. Therefore, when contrasted with the color of the separator, various colors, such as black, red, blue, and green, can be distinguished, providing a wider range of dyes to choose from.

[0021] (10) In any of the above (7) to (9), the rubber composition may comprise one or more rubbers selected from the group consisting of ethylene-propylene rubber, ethylene-propylene-diene rubber, and ethylene-butene-diene rubber. This configuration makes it possible to realize a seal member that is excellent in sealing properties, durability, high-temperature properties, etc.

[0022] (11) The manufacturing method of a fuel cell member of the present disclosure is a manufacturing method of a fuel cell member having the configuration of (7) above, characterized by comprising: a coating step of coating the adhesive composition for a fuel cell sealing member onto the substrate; a judging step of judging the quality of the coating state based on the color of the applied adhesive composition; and, if the coating state is judged to be good, a bonding step of placing the uncrosslinked rubber composition on the adhesive composition-applied surface of the substrate to form a laminate, heating and pressurizing the laminate to crosslink the rubber composition to form the sealing member, and adhering the sealing member to the substrate.

[0023] According to the manufacturing method of the fuel cell member of the present disclosure, in the judging step, the quality of the coating state is judged based on the color of the applied adhesive composition. This makes it possible to avoid uneven coating, incomplete coating, etc. As a result, peeling of the sealing member, deterioration of sealing properties, etc. can be suppressed in the manufactured fuel cell member.

[0024] The adhesive composition for a fuel cell sealing member of the present disclosure is easily identifiable when applied to the surface of a substrate or sealing member. Therefore, the quality of the application state can be easily determined by visual inspection or a color inspection device. As a result, uneven application and incomplete application are less likely to occur, and peeling of the sealing member and deterioration of sealing properties can be suppressed. Furthermore, by using a relatively small amount of a specific dye, both adhesion and identifiability can be achieved. The fuel cell member of the present disclosure has few adhesion defects and excellent sealing properties. In the manufacturing method for a fuel cell member of the present disclosure, the quality of the application state is determined based on the color of the applied adhesive composition in the determination step. This makes it possible to avoid uneven application and incomplete application of the adhesive composition.

[0025] 1 is a cross-sectional view showing an embodiment of a fuel cell member according to the present disclosure.

[0026] Hereinafter, embodiments of the adhesive composition for a fuel cell sealing member, the fuel cell member, and the method for manufacturing a fuel cell member according to the present disclosure will be described. Note that the embodiments are not limited to the following embodiments, and various modifications and improvements that can be made by those skilled in the art can be made.

[0027] <Adhesive composition for fuel cell sealing member> The adhesive composition of the present disclosure bonds a thin plate-shaped substrate, which is a constituent member of a fuel cell, to a sealing member manufactured from a rubber composition. Examples of fuel cells include polymer electrolyte fuel cells (PEFCs) (including direct methanol fuel cells (DMFCs)). The substrate varies depending on the type and configuration of the fuel cell, and in polymer electrolyte fuel cells, examples include separators, membrane electrode assemblies (MEAs) of electrode members, and gas diffusion layers (GDLs). The substrate and sealing member will be described later.

[0028] The adhesive composition of the present disclosure comprises (A) an adhesive liquid having an adhesive component whose main component is a silane coupling agent, or whose main components are a silane coupling agent and an organic titanate compound, and a solvent, and (B) a dye that is compatible with the adhesive component of the adhesive liquid and dissolves in the solvent.

[0029] (A) Adhesive Liquid [Adhesive Component] The main component of the adhesive component is a silane coupling agent or a silane coupling agent and an organic titanate compound. In this specification, the "main component" refers to a component that accounts for 50% by mass or more when the total adhesive component is 100% by mass. For example, the adhesive component may be composed of only the silane coupling agent (content ratio: 100% by mass), or may be composed of only the silane coupling agent and the organic titanate compound (content ratio: 100% by mass), or may be composed of the silane coupling agent, the organic titanate compound added as needed, and other components (content ratio: less than 50% by mass).

[0030] The silane coupling agent may be appropriately selected from a group of compounds having one or more functional groups selected from amino, vinyl, and epoxy groups, taking into consideration adhesive properties, etc. Silane coupling agents may be used singly or in combination. Alternatively, a copolymer oligomer in which two or more silane coupling agents are copolymerized may be used. Copolymer oligomers having the following (a) hydrophilic functional group and (b) hydrophobic functional group are preferred. (a) One or more selected from the group consisting of silanol groups, alkoxy groups, amino groups, isocyanate groups, epoxy groups, ureido groups, carboxy groups, and hydroxy groups, and containing at least a silanol group or an alkoxy group. (b) One or more selected from the group consisting of vinyl groups, (meth)acryloyl groups, maleimide groups, methyl groups, ethyl groups, styryl groups, phenyl groups, and mercapto groups.

[0031] By using specific functional groups (a) and (b) as the hydrophilic and hydrophobic functional groups in the silane coupling agent, the adhesive properties, water resistance, and acid resistance of the adhesive layer can be improved. Among these, the hydrophobic functional group prevents water penetration into the adhesive layer by imparting hydrophobicity, contributing to improved water resistance and acid resistance. The hydrophilic functional group reacts with the substrate or components in the sealing material (such as carbon black) to contribute to adhesive properties. For example, a copolymer oligomer can be produced by oligomerizing a silane coupling agent having the functional group (a) with a silane coupling agent having the functional group (b). In this specification, the term "(meth)acryloyl group" refers to an acryloyl group or a methacryloyl group, and the term "(meth)acrylate" refers to an acrylate or a methacrylate.

[0032] Among the silane coupling agents having a hydrophilic functional group (a), examples of the silane coupling agent having a hydrophilic functional group other than a silanol group or an alkoxy group include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, 3-isocyanatepropyltriethoxysilane, 3-ureidopropyltrialkoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-carboxypropyltrimethoxysilane, 3-carboxypropyltriethoxysilane, 3-hydroxypropyltrimethoxysilane, and 3-hydroxypropyltriethoxysilane. Of these, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and 3-isocyanatepropyltriethoxysilane are preferred.

[0033] Examples of the silane coupling agent having a hydrophobic functional group (b) include vinyltrimethoxysilane, vinyltriethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, N-(trimethoxysilylpropyl)maleimide, N-(triethoxysilylpropyl)maleimide, p-styryltrimethoxysilane, p-styryltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 3-mercaptopropylmethyltrimethoxysilane, 3-mercaptopropylmethyltriethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, and n-propyltriethoxysilane. Among these, vinyltrimethoxysilane, vinyltriethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, N-(trimethoxysilylpropyl)maleimide, and N-(triethoxysilylpropyl)maleimide are preferred.

[0034] The oligomerization reaction is carried out by first loading each silane coupling agent into a reactor equipped with a distillation apparatus and a stirrer and stirring at approximately 60°C for approximately 1 hour. Next, approximately 0.5 to 2.0 moles of an acid such as formic acid are added within 1 hour for each mole of the silane coupling agent having a hydrophilic functional group shown in (a) and the silane coupling agent having a hydrophobic functional group shown in (b). The temperature inside the reactor is maintained at approximately 65°C during the acid addition. The reaction is stirred for an additional 1 to 5 hours, during which the alcohol produced by hydrolysis is distilled under reduced pressure. The distillation is terminated when only water remains in the distillate, and the distillate is then diluted to a silane concentration of 30 to 80% by mass. The copolymerized oligomer obtained in this manner is soluble in alcohol-based organic solvents such as methanol and ethanol. A copolymerized oligomer of trimer or higher is desirable from the viewpoint of improving film-forming properties, water resistance, and acid resistance when applying the adhesive composition.

[0035] Among the adhesive components, components other than the silane coupling agent include organic titanate compounds, aluminate coupling agents, etc. When one or more selected from organic titanate compounds and aluminate coupling agents are used, the total content with the silane coupling agent should be 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or even 100% by mass. Furthermore, phenolic resins, bismaleimide resins, vinyl resins, etc. may be added to enhance adhesion to the substrate and impart hydrophobicity, thereby improving the water resistance and acid resistance of the adhesive layer formed. When these resins are added, their amount should be 20% by mass or less, based on 100% by mass of the total adhesive components.

[0036] When an organic titanate compound is contained, acid resistance, particularly acid resistance during long-term use at high temperatures, is improved. The organic titanate compound is preferably one or more selected from titanium alkoxides, titanium chelates, and titanium acylates.

[0037] Examples of titanium alkoxides include tetramethyl titanate, tetraethyl titanate, tetra-normal propyl titanate, tetraisopropyl titanate, tetra-normal butyl titanate, tetraisobutyl titanate, tetra-t-butyl titanate, tetraoctyl titanate, tetrastearyl titanate, tetra(2-ethylhexyl) titanate, tetramethyl titanate, etc. Among these, tetraisopropyl titanate, tetra-normal butyl titanate, and tetrastearyl titanate are preferred.

[0038] Examples of titanium chelates include titanium acetylacetonate, titanium octylene glycolate, titanium tetraacetylacetonate, titanium ethylacetoacetate, titanium triethanolaluminate, etc. Among these, titanium acetylacetonate and titanium ethylacetoacetate are preferred.

[0039] Examples of titanium acylate include titanium isostearate, tri-n-butoxytitanium monostearate, di-i-propoxytitanium distearate, titanium stearate, di-i-propoxytitanium diisostearate, (2-n-butoxycarbonylbenzoyloxy)tributoxytitanium, etc. Among these, titanium stearate is preferred.

[0040] When an aluminate-based coupling agent is included, the coating strength is improved. Examples of aluminate-based coupling agents include aluminum alkylacetoacetate diisopropylate, aluminum ethylacetoacetate diisopropylate, aluminum trisethylacetoacetate, aluminum isopropylate, aluminum diisopropylate mono-secondary butylate, aluminum secondary butylate, aluminum ethylate, aluminum bisethylacetoacetate monoacetylacetonate, aluminum trisacetylacetonate, and aluminum monoisopropoxymonoroxyethylacetoacetate. These can be used alone or in combination. Among them, aluminum alkylacetoacetate diisopropylate, aluminum ethylacetoacetate diisopropylate, and aluminum trisethylacetoacetate are preferred.

[0041] [Solvent] The solvent is not particularly limited as long as it can dissolve the adhesive component. Examples include alcohol-based organic solvents such as methanol, ethanol, isopropanol, 2-ethoxyethanol (ethylene glycol monoethyl ether), and butoxyethanol (ethylene glycol monobutyl ether), and ketone-based organic solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. The concentration of the adhesive component in the adhesive liquid can be determined appropriately taking into account adhesive properties and the like, and is preferably, for example, 0.5% by mass or more and 25% by mass or less.

[0042] As the adhesive liquid containing the copolymer oligomer of the silane coupling agent and the solvent, for example, commercially available products such as "CHEMLOK (registered trademark) 5151" manufactured by Lord Corporation, "MEGUM (registered trademark) 3290" manufactured by Dow Chemical Company, and "X-12-1048" and "KR-513" manufactured by Shin-Etsu Chemical Co., Ltd. may be used.

[0043] (B) Dye The dye to be used is one that is compatible with the adhesive component of the adhesive liquid and dissolves in the solvent of the adhesive liquid. Here, "compatible with the adhesive component" means that when 1.5 g of the dye is added to 100 mL of an adhesive liquid with a 5% by mass concentration of the adhesive component, the mixture is stirred for 5 minutes, and the mixture is visually observed to be free of turbidity and precipitate.

[0044] The adhesive composition of the present disclosure is colored with a dye in a color different from the color of the substrate or sealing member. When the adhesive composition is applied to a substrate, it may be colored in a color different from the color of the substrate, and when it is applied to a sealing member, it may be colored in a color different from the color of the sealing member. By making the color of the coating film different from the color of the substrate rather than being colorless and transparent, it becomes easier to determine whether the coating condition is good or bad. The color of the dye is not limited, but it is desirable to use a color that stands out against the color of the substrate. For example, when the substrate is a silver-colored separator, using a black or red-colored dye is preferable because it makes it easy to identify the presence of the adhesive composition applied to the substrate.

[0045] From the viewpoint of increasing the color intensity and enhancing the distinguishability, the dye content is set to 3 parts by mass or more, based on 100 parts by mass of the nonvolatile content of the adhesive composition. 5 parts by mass or more, and even 10 parts by mass or more, are preferred. On the other hand, from the viewpoint of ensuring the desired adhesive properties, the dye content is set to 25 parts by mass or less, based on 100 parts by mass of the nonvolatile content of the adhesive composition. 20 parts by mass or less, and even 15 parts by mass or less, are preferred. In this specification, "nonvolatile content" refers to the mass of the remaining components after removing the solvent from the adhesive composition. It is also desirable that the presence of the adhesive composition can be distinguished even when the coating film is thin. For example, it is preferable that the coloring power of the dye be exerted and the presence of the adhesive composition can be distinguished even when the coating film thickness of the adhesive composition is 0.01 μm or more and 1 μm or less.

[0046] Suitable dyes that have high coloring power even in relatively small amounts include xanthene dyes and azine dyes. Among xanthene dyes, rhodamines are preferred. Examples of red dyes include rhodamine B (CI Basic Violet 10), CI Solvent RED 49, and CI Basic RED 1:1, while examples of black dyes include CI Solvent Black 7. "CI" stands for Color Index, a database of color materials compiled by the British Society of Dyes and Colorants.

[0047] <Fuel cell member> The fuel cell member of the present disclosure comprises a thin plate-like substrate, a sealing member produced from a rubber composition, and an adhesive layer that bonds the substrate and the sealing member, and the adhesive layer is formed from the adhesive composition for a fuel cell sealing member of the present disclosure.

[0048] First, one embodiment of a fuel cell member according to the present disclosure will be described. FIG. 1 shows a cross-sectional view of the fuel cell member according to this embodiment. As shown in FIG. 1, the fuel cell member 1 includes a separator 10, a sealing member 20, and an adhesive layer 30. The separator 10 is made of stainless steel and has a silvery rectangular thin plate shape. A total of six longitudinally extending grooves 11 are recessed in the separator 10 in an area that overlaps with an electrode member (not shown) when the fuel cell is constructed. The grooves 11 serve as flow paths for refrigerants and the like. The sealing member 20 is disposed on the peripheral edge of the upper surface of the separator 10. The sealing member 20 has a frame shape when viewed from above. The sealing member 20 is made of a cross-linked rubber composition containing ethylene-butene-diene rubber. The sealing member 20 has a lip portion 21 that protrudes upward. The top of the lip portion 21 is curved. The sealing member 20 elastically contacts another separator that is stacked when a fuel cell is constructed. The adhesive layer 30 has a frame shape when viewed from above and is disposed between the separator 10 and the sealing member 20. The adhesive layer 30 is formed from the adhesive composition of the present disclosure and has a reddish color. The adhesive layer 30 bonds the separator 10 and the sealing member together.

[0049] The fuel cell member 1 is manufactured as follows. First, a rubber composition for forming the sealing member 20 is prepared. The prepared rubber composition is molded into a predetermined shape to produce an uncrosslinked rubber member. Next, an adhesive composition is applied to a predetermined position on the upper surface of the separator 10, and the state of application is confirmed. Here, the adhesive composition exhibits a reddish color, making it easy to distinguish on the upper surface of the silvery separator 10. Then, if the state of application is good, the prepared rubber member is laminated on the upper surface of the coating film, and crosslinked and bonded under predetermined conditions. In this way, a fuel cell member 1 is manufactured in which the separator 10 and the sealing member 20 are integrated via the adhesive layer 30. Next, the individual components that make up the fuel cell member of the present disclosure will be described.

[0050] [Substrate] As mentioned above, the substrate used in a fuel cell varies depending on the type and configuration of the fuel cell. In the case of a polymer electrolyte fuel cell, examples include a separator, a membrane electrode assembly of an electrode member, and a gas diffusion layer. Among these, separator materials include stainless steel, titanium, copper, magnesium, aluminum, carbon, graphite, and conductive resins (thermoplastic or thermosetting resins containing carbon, graphite, polyacrylonitrile-based carbon fiber, etc.). From the standpoints of acid resistance and cost, stainless steel (particularly austenitic) and titanium (particularly pure titanium) are desirable. Furthermore, a carbon thin film such as a diamond-like carbon film (DLC film) or a graphite film may be formed on the surface of a main body made of these materials by physical vapor deposition (PVD), chemical vapor deposition (CVD), or other processes. The separator's region to which the sealing member is bonded (the region to which the adhesive composition is applied) may be subjected to a surface treatment, such as forming irregularities, to enhance the wettability of the adhesive composition and improve adhesion. The separator's configuration, including the formed flow channels and manifold holes, is not limited, and its shape, thickness, and other properties may be determined appropriately. Considering power generation performance, the thickness of the separator is preferably 0.1 mm or more and 0.5 mm or less.

[0051] [Sealing Member] The sealing member is manufactured by subjecting a rubber composition to injection molding, press molding, or the like. The rubber component constituting the rubber composition may be liquid or solid rubber. Examples of the rubber component include ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), ethylene-butene-diene rubber (EBT), silicone rubber, fluororubber, butyl rubber (IIR), ethylene-propylene rubber (EPM), acrylonitrile-butadiene rubber (NBR), hydrogenated acrylonitrile-butadiene rubber (H-NBR), styrene-butadiene rubber (SBR), and butadiene rubber (BR). Among these, it is desirable to use one or more selected from EPM, EPDM, and EBT because of their high water resistance and acid resistance at high temperatures. In addition to the rubber component, the rubber composition may also contain a crosslinking agent, a crosslinking aid, a plasticizer, a reinforcing agent, an antioxidant, a processing aid, and the like.

[0052] As a crosslinking agent, it is desirable to use an organic peroxide because it does not contain volatile components such as sulfur. Among these, dialkyl peroxides, peroxyketals, peroxyesters, ketone peroxides, diacyl peroxides, and peroxydicarbonates, which can crosslink at relatively low temperatures, are preferred. Examples of crosslinking aids include maleimide compounds, triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), trimethylolpropane trimethacrylate (TMPT), bifunctional (meth)acrylates, and 1,2-polybutadiene. Examples of plasticizers include petroleum-based plasticizers such as process oil, lubricating oil, paraffin, liquid paraffin, and petrolatum; 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. Examples of reinforcing agents include carbon black and amorphous silica (white carbon). Examples of antioxidants include phenol-based, amine-based, imidazole-based, phosphoric acid-based, and wax-based antioxidants.

[0053] The sealing member may be disposed in a ring shape along the outer periphery of the surface of the base material, or may be disposed so as to surround a predetermined portion. The thickness of the sealing member is preferably 0.2 mm to 5 mm, more preferably 0.5 mm to 3 mm.

[0054] [Adhesive Layer] The adhesive layer that bonds the substrate and the sealing member is formed from the adhesive composition for a fuel cell sealing member of the present disclosure. From the viewpoint of achieving thinning of the component and high dimensional accuracy, the thickness of the adhesive layer is desirably 0.01 μm or more and 1 μm or less. The color of the adhesive layer is not particularly limited as long as it is different from the color of the member (substrate or sealing member) to which the adhesive composition is applied.

[0055] <Method for manufacturing fuel cell member> One embodiment of the method for manufacturing a fuel cell member according to the present disclosure includes a coating step, a determining step, and a bonding step. Each step will be described below in order.

[0056] [Coating Step] In this step, the adhesive composition for a fuel cell sealing member of the present disclosure is coated onto a substrate. The adhesive composition may be prepared by preparing a dye solution in advance by dissolving a dye in a solvent, and then combining and stirring this dye solution with an adhesive solution. Alternatively, the adhesive composition may be prepared by adding a dye to the adhesive solution and stirring. The adhesive composition may be applied by brush coating or by a coating machine such as a dispenser, blade coater, bar coater, die coater, Comma Coater (registered trademark), or roll coater, or by a spraying method or immersion method, and then naturally dried at room temperature or, if necessary, dried by heating. The adhesive composition may be applied in two or more layers, but a single layer is preferable from the viewpoint of shortening the coating process.

[0057] [Evaluation Step] In this step, the quality of the coating state is judged based on the color of the applied adhesive composition (coating film). The judgment may be made visually, using a color inspection machine, or both.

[0058] [Bonding Process] In this process, if the adhesive composition coating condition is judged to be good, an uncrosslinked rubber composition is placed on the adhesive composition-coated surface of the substrate to form a laminate, and the laminate is heated and pressurized to crosslink the rubber composition to form a sealing member, and the sealing member is adhered to the substrate. In this process, or prior to this process, a rubber composition for forming a sealing member is first prepared. The rubber composition can be prepared by kneading the rubber component and optional components using a roll, kneader, Banbury mixer, or the like. The prepared rubber composition can be molded into a predetermined shape by injection molding, press molding, or the like (production of an uncrosslinked rubber member). This eliminates the need for complicated alignment, facilitates continuous processing, and improves productivity. Then, the rubber composition (rubber member) is laminated on the coating film formed on the substrate, and heated and pressurized. Heating and pressurization can be performed using a press, bonding machine, or the like. The heating temperature can be 130°C or higher and 200°C or lower, taking into account the crosslinking temperature of the rubber component, etc. The pressure to be applied may be appropriately set taking into consideration the adhesiveness and prevention of destruction of the sealing member, etc. The heating and pressure application time (adhesion time) may be about 3 to 30 minutes.

[0059] The above describes a form in which an uncrosslinked rubber composition is used for crosslinking and bonding in the bonding process. However, the fuel cell components of the present disclosure may also be produced by a method in which a sealing member is produced in advance by crosslinking the rubber composition, and then the sealing member is placed on the surface of the substrate to which the adhesive composition has been applied, and then heated and pressed as necessary.

[0060] Next, the present disclosure will be described in more detail with reference to examples. Various adhesive compositions were prepared and their discriminability was evaluated when applied to a substrate. Furthermore, evaluation samples were prepared by bonding a sealing member to a substrate using the prepared adhesive composition, and the adhesiveness and compression durability of the sealing member were evaluated.

[0061] <Identification of Adhesive Composition> [Adhesive Liquid (A1)] A copolymerized oligomer was produced by copolymerizing two types of silane coupling agents. First, 100 parts by mass of vinyltrimethoxysilane, 68.4 parts by mass of 3-aminopropyltrimethoxysilane, and 33.1 parts by mass of water were charged into a reactor equipped with a distillation apparatus and a stirrer, and stirred at approximately 60°C for approximately 1 hour. Next, formic acid was added within 1 hour so that the amount added was 1.0 mole per mole of the total mass of the silane coupling agent. During the addition of formic acid, the temperature inside the reactor was maintained at approximately 65°C. The mixture was stirred for an additional 3 hours to allow the reaction to proceed, while the alcohol produced by hydrolysis was distilled under reduced pressure. The distillation was terminated when only water remained in the distillate, and the distillate was then diluted to a silane concentration of 50% by mass to obtain a copolymerized oligomer. The hydrophobic functional group in the copolymerized oligomer was a vinyl group, and the hydrophilic functional groups were a silanol group, an alkoxy group, and an amino group. The produced copolymer oligomer was diluted with a mixed solvent of methanol and ethanol (mass ratio 1:1) to obtain an adhesive liquid (A1) having a concentration of the copolymer oligomer (silane coupling agent) as the adhesive component of 5 mass %.

[0062] [Adhesive liquid (A2)] 12.5 parts by mass of tetraisopropyl titanate, an organic titanate compound, was mixed with 100 parts by mass of the copolymer oligomer (silane coupling agent) used in adhesive liquid (A1) to obtain an adhesive component. This was diluted with a mixed solvent of ethanol and 2-ethoxyethanol (mass ratio 9:1) to obtain adhesive liquid (A2) with an adhesive component concentration of 5% by mass.

[0063] [Adhesive liquid (A3)] 100 parts by mass of the copolymer oligomer (silane coupling agent) used in adhesive liquid (A1) was mixed with 50 parts by mass of tetraisopropyl titanate, an organic titanate compound, to prepare an adhesive component. This was diluted with a mixed solvent of ethanol and 2-ethoxyethanol (mass ratio 9:1) to obtain adhesive liquid (A3) with an adhesive component concentration of 5 mass%.

[0064] Furthermore, commercially available adhesives containing copolymer oligomer type silane coupling agents were prepared as adhesive liquids (A4) to (A6).

[0065] [Adhesive liquid (A4)] "CHEMLOK (registered trademark) 5151" manufactured by Lord Corporation. The hydrophilic functional groups of the copolymer oligomer are silanol groups and alkoxy groups, and the hydrophobic functional group is a vinyl group. The solvent (diluent) is ethanol.

[0066] [Adhesive liquid (A5)] "MEGUM (registered trademark) 3290" manufactured by The Dow Chemical Company. The hydrophilic functional groups of the copolymer oligomer are silanol groups, alkoxy groups, and amino groups, and the hydrophobic functional group is a vinyl group. The solvent is ethanol.

[0067] [Adhesive liquid (A6)] "KR-513" manufactured by Shin-Etsu Chemical Co., Ltd. The hydrophilic functional groups of the copolymer oligomer are silanol groups and alkoxy groups, and the hydrophobic functional groups are acryloyl groups and methyl groups. The solvent is ethanol.

[0068] [Colorants] Five types of dyes and one pigment were prepared as colorants. The details are as follows: (i) Dyes: (B1) Rhodamine B (CI Basic Violet 10), red. (B2) CI Solvent RED 49, red. (B3) CI Basic RED 1:1, red. (B4) CI Solvent Black 7, black. (B5) CI Acid Red 27, red. (ii) Pigments: Carbon black: "Aqua-Black (registered trademark) 001" manufactured by Tokai Carbon Co., Ltd., black.

[0069] [Preparation of Adhesive Compositions] A colorant was added to a solvent and stirred to prepare a colorant liquid, and then this colorant liquid and adhesive liquid were combined and stirred to prepare various adhesive compositions. The solvent added to the colorant was the same as the solvent in the adhesive liquid to be combined. The adhesive compositions prepared were numbered 1 to 15. Tables 1 and 2 show the components of the adhesive compositions (combinations of adhesive components and colorants in the adhesive liquid, and the contents of each). In Tables 1 and 2, the units of components are parts by mass, where the non-volatile content of the adhesive composition is 100 parts by mass.

[0070]

[0071]

[0072] [Solubility of Colorants in Solvents] The colorants were added to the solvents of the adhesive liquids combined when producing the adhesive compositions, and the mixture was stirred, and the colorants were visually observed to determine whether they dissolved. As a result, all of the dyes used in adhesive compositions No. 1 to 14 were dissolved (indicated by a circle in Tables 1 and 2), but the pigment used in adhesive composition No. 15 was not dissolved (indicated by an x ​​in Table 2).

[0073] [Compatibility of Colorant with Adhesive Components] 1.5 g of colorant was added to 100 mL of adhesive liquid containing 5% by mass of adhesive components, which was used to prepare the adhesive composition. The mixture was stirred for 5 minutes and visually observed. The adhesive component concentrations of adhesive liquids (A4) to (A6) using commercially available adhesives were adjusted to 5% by mass using an appropriate solvent. The absence of turbidity or precipitate was evaluated as good compatibility, while the presence of at least one of turbidity and precipitate was evaluated as poor compatibility. The results showed that the compatibility of the dyes used in adhesive compositions No. 1 to 13 was good (indicated by a circle in Tables 1 and 2), but the compatibility of the dye used in adhesive composition No. 14 and the pigment used in adhesive composition No. 15 was poor (indicated by an x ​​in Table 2).

[0074] [Evaluation of Distinguishing Ability] The adhesive composition produced was spray-coated onto the surface of a substrate to a predetermined thickness, and after natural drying at room temperature (20°C ± 5°C), the coating film was visually observed. As the substrate, a silver-colored stainless steel plate made of SUS304 and a silver-colored titanium plate made of pure titanium were used. Both substrates were rectangular plates measuring 25 mm in width, 60 mm in length, and 1.5 mm in thickness. The adhesive composition was applied to a square area measuring 25 mm in width and 25 mm in length on the surface of the substrate. The types of substrates and the thicknesses of the coating film (adhesive layer) are summarized in Tables 1 and 2 above. In Tables 1 and 2, stainless steel plates are indicated as "SUS" and titanium plates are indicated as "Ti."

[0075] As a result, for adhesive compositions Nos. 1 to 13 and 15, the color of the coating film differed from the color of the substrate, regardless of the coating film thickness, and the coating film could be distinguished on the substrate (shown by a circle in Tables 1 and 2). However, in sample No. 13, the dye content exceeded 25 parts by mass. As a result, although distinguishability was exhibited, adhesion was reduced, as described below. On the other hand, for adhesive composition No. 14, even with a coating film thickness of 0.2 μm, the color development was faint, making it difficult to distinguish the coating film on the substrate (shown by an x ​​in Table 2). This is thought to be due to poor compatibility of the dye with the adhesive components. Note that for adhesive composition No. 15, which used a black pigment, the coating film could be distinguished on the substrate.

[0076] <Adhesion of adhesive composition and compression durability of sealing member> [Production of evaluation sample] First, a rubber composition for forming a sealing member was prepared as follows: 100 parts by mass of ethylene-butene-diene rubber (manufactured by Mitsui Chemicals, Inc., "EBT-K-9330M") as the rubber component, 1.0 part by mass of a phenolic antioxidant (manufactured by Ouchi Shinko Chemical Industry Co., Ltd., "Nocrac (registered trademark) NS-5"), 50 parts by mass of carbon black (manufactured by Tokai Carbon Co., Ltd., "Seast (registered trademark) SO") as a reinforcing agent, and 15 parts by mass of poly-α-olefin (manufactured by Nippon Steel Chemical & Material Co., Ltd., "PAO601") as a plasticizer were kneaded using a Banbury mixer at 120°C for 5 minutes. The kneaded mixture was then cooled, and 6 parts by mass of a crosslinking agent, 1,1-di(t-butylperoxy)cyclohexane ("Perhexa (registered trademark) C-80" manufactured by NOF Corporation), was added, and the mixture was kneaded using an open roll at 50°C for 10 minutes to prepare a rubber composition.

[0077] Next, a rubber composition was placed on the surface of the substrate used in the evaluation of discriminability so as to overlap the coating film of the adhesive composition to form a laminate, and this laminate was placed in a mold and heated and pressed at 170°C for 10 minutes. In this way, an evaluation sample was produced in which a sealing member (thickness 2.0 mm) that was a cross-linked product of the rubber composition and the substrate were bonded via an adhesive layer. Hereinafter, the numbers of the evaluation samples correspond to the numbers of the adhesive compositions used.

[0078] [Evaluation of Adhesion] A peel test was performed on the evaluation sample to evaluate the adhesion between the substrate and the sealing member. In the peel test, a notch was made in the end of the sealing member that was not adhered to the substrate to make a gripping portion, and the gripping portion was pulled perpendicular to the substrate at a speed of 10 mm / sec to peel the sealing member. Then, the state of the peeled surface was visually observed, and if there was material failure (cutting of the sealing member), the adhesion was evaluated as good, and if there was interfacial failure, the adhesion was evaluated as poor.

[0079] The peel test was performed on two types of samples: "initial" and "after immersion in acidic water." The "initial" sample was left at room temperature after production, while the "after immersion in acidic water" sample was a produced sample that was immersed in a sulfuric acid aqueous solution (pH 3.0) at 90°C for 368 hours, then removed and left at room temperature. The test results for the sample after immersion in acidic water serve as an index for determining the quality of acid-resistant adhesion at high temperatures.

[0080] As a result, samples No. 1 to 12 had good adhesion both initially and after immersion in acidic water (shown by a circle in Table 1 above). In contrast, sample No. 13, which had a high dye content, had poor initial adhesion (shown by an x ​​in Table 2 above). Sample No. 13 had poor initial adhesion, so acid resistance was not evaluated. For samples No. 14 and 15, the compatibility of the colorant with the adhesive components was poor, resulting in precipitation of the colorant in the adhesive composition, so the adhesive properties were not evaluated.

[0081] [Evaluation of Compression Durability] A compression test was performed on the evaluation sample to evaluate the durability of the sealing member. The compression test was performed as follows. First, the evaluation sample was placed in a press and fixed in a state where the sealing member was compressed by 40% in the thickness direction. In this state, the temperature was raised to 100°C and held for 10 minutes. After that, it was cooled to room temperature, and the evaluation sample was removed from the press. The removed sealing member of the evaluation sample was cut in the thickness direction, and the cross section was visually observed. If there were no cracks, it was evaluated as having good compression durability, and if there were cracks, it was evaluated as having poor compression durability.

[0082] As a result, no cracks were observed in any of Samples No. 1 to 13, and the compression durability was good (shown by a circle in Tables 1 and 2 above). On the other hand, cracks were observed in Samples No. 14 and 15, which used colorants with poor compatibility with the adhesive component, and the compression durability was poor (shown by an x ​​in Table 2 above).

[0083] From the above, it was confirmed that the adhesive compositions Nos. 1 to 12 could provide distinguishability while ensuring adhesiveness, and that it was possible to easily determine whether the coating state was good or bad.

[0084] 1: fuel cell member, 10: separator, 11: groove portion, 20: sealing member, 21: lip portion, 30: adhesive layer.

Claims

1. An adhesive composition for a fuel cell sealing member, which bonds a thin-plate substrate, which is a constituent member of a fuel cell, to a sealing member made from a rubber composition, comprising: (A) an adhesive liquid having an adhesive component whose main component is a silane coupling agent, or whose main components are a silane coupling agent and an organic titanate compound, and a solvent; and (B) a dye that is compatible with the adhesive component and dissolves in the solvent, wherein the content of the dye is 3 parts by mass or more and 25 parts by mass or less when the non-volatile content of the adhesive composition is 100 parts by mass, and the adhesive composition is colored with the dye in a color different from the color of the substrate or the sealing member.

2. The adhesive composition for a fuel cell sealing member according to claim 1, which is applied to the substrate or the sealing member in a thickness of 0.01 μm or more and 1 μm or less.

3. The adhesive composition for a fuel cell sealing member according to claim 1, which is applied to the substrate.

4. The adhesive composition for a fuel cell sealing member according to claim 3, wherein the substrate is a separator.

5. The adhesive composition for a fuel cell sealing member according to claim 4, wherein the separator is silver-based in color, and the dye is black-based or red-based in color.

6. The adhesive composition for a fuel cell sealing member according to claim 1, wherein the dye is a xanthene dye or an azine dye.

7. A fuel cell member comprising a thin plate-like substrate, a sealing member made from a rubber composition, and an adhesive layer for bonding the substrate and the sealing member, the adhesive layer being formed from the adhesive composition for fuel cell sealing members as defined in claim 1.

8. The fuel cell member according to claim 7, wherein the thickness of the adhesive layer is from 0.01 μm to 1 μm.

9. The fuel cell member according to claim 7, wherein the substrate is a separator made of stainless steel.

10. The fuel cell member according to claim 7, wherein the rubber composition comprises at least one rubber selected from the group consisting of ethylene-propylene rubber, ethylene-propylene-diene rubber, and ethylene-butene-diene rubber.

11. A method for producing a fuel cell member as described in claim 7, comprising: a coating step of coating the adhesive composition for a fuel cell sealing member onto the substrate; a judging step of judging whether the coating state is good or bad based on the color of the applied adhesive composition; and if the coating state is judged to be good, a bonding step of arranging the uncrosslinked rubber composition on the applied surface of the substrate to which the adhesive composition has been applied to form a laminate, heating and pressurizing the laminate to crosslink the rubber composition to form the sealing member, and bonding the sealing member to the substrate.

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