Adhesive composition

Abstract

This adhesive composition includes: an adhesive solution which comprises a dilution solvent and an adhesive component including one or more components selected from a silane coupling agent, an organic titanate compound, an aluminate-based coupling agent, and a zirconate-based coupling agent; and a slow-volatile solvent which is added separately from the adhesive solution, can dissolve the adhesive components therein, and has a vapor pressure at 20°C of 2.33 kPa or less. The slow-volatile solvent includes one or more components selected from methyl isobutyl ketone, ethylene glycol, diacetone alcohol, and ethyl cellosolve.

Description

Adhesive composition

[0001] The present disclosure relates to an adhesive composition, and particularly to an adhesive composition suitable for adhering a member made of metal or the like to a seal member made of a rubber material in a fuel cell, a water electrolysis device, or the like.

[0002] A fuel cell has a stack structure in which a large number of cells are stacked. The stack of cells is fastened in a compressed state by end plates arranged on both sides in the stacking direction. For example, a cell of a solid polymer fuel cell has an electrode member including a membrane electrode assembly (MEA) and a separator arranged with the electrode member interposed therebetween. A rubber seal member is arranged around the electrode member and between adjacent separators to ensure sealing properties and insulation against reaction gases and refrigerants. In order to maintain high sealing properties in the operating environment of a fuel cell, a method of integrating a seal member and a mating member using an adhesive is effective. For example, as a method of adhering a base material such as a separator and a rubber seal member, Patent Documents 1 and 2 describe a method in which an adhesive (primer) having a copolymer oligomer type silane coupling agent is applied to the surface of the base material, and then the seal member is vulcanized and adhered to the surface.

[0003] Japanese Patent Application Laid-Open No. 2014-80006 International Publication No. 2022 / 208926

[0004] As described in Patent Documents 1 and 2 above, adhesives are often used in the form of a solution in which an adhesive component such as a silane coupling agent is diluted with a volatile solvent. When such a solution-based adhesive is applied to a base material, the solvent volatilizes and dries to form a coating film. As a result of the inventor's investigation, it was found that when the drying of the solution-based adhesive application approaches the final stage, the adhesive components may aggregate, and there may be a portion where a coating film is not formed. If there is coating unevenness such as a portion where a coating film is not formed, the seal member to be adhered may peel off or the sealing properties may deteriorate.

[0005] The following is a possible explanation for the aggregation of adhesive components: In adhesives, the polymerization of silane coupling agents is sometimes advanced to increase the molecular weight in order to enhance adhesive strength. Since the polymerization of silane coupling agents is a dehydration condensation reaction between hydroxyl groups (-OH), condensation water is produced in the system. It is known that adhesives contain a small amount of water, including this condensation water. Because water does not evaporate as easily as solvents, it remains until the end of drying when most of the solvent has evaporated, forming water-rich areas. In these water-rich areas, the solubility of the adhesive components decreases, which is thought to cause aggregation of the adhesive components.

[0006] Furthermore, uneven coating can occur due to contamination on the substrate side. For example, when using metal separators such as stainless steel, the separator is pre-cleaned with an alkaline cleaning agent to remove oil and other contaminants adhering to its surface. However, alkaline cleaning does not completely remove the contaminants, so some contaminants tend to remain on the surface of the separator. Therefore, if a highly polar adhesive containing moisture is applied on top of this, it can cause repellency and lead to uneven coating.

[0007] This disclosure has been made in view of the above circumstances, and aims to provide an adhesive composition that can form an adhesive layer that is less prone to uneven coating and has excellent adhesion.

[0008] (1) In order to solve the above problems, the adhesive composition of the present disclosure is characterized by comprising an adhesive liquid having an adhesive component having one or more selected from a silane coupling agent, an organic titanate compound, an aluminate coupling agent, and a zirconate coupling agent, and a diluent, and a slow-volatile solvent added separately from the adhesive liquid, to which the adhesive component can be dissolved, and having a vapor pressure of 2.33 kPa or less at 20°C.

[0009] The adhesive composition of this disclosure contains a slow-volatile solvent in addition to a solvent for diluting the adhesive components (diluting solvent). The slow-volatile solvent can dissolve the adhesive components in the same way as the diluting solvent, but its vapor pressure at 20°C is 2.33 kPa or less, so it evaporates at the same rate as or slower than water (the vapor pressure of water at 20°C is 2.33 kPa). Therefore, in the coating of the adhesive composition of this disclosure, even if most of the diluting solvent evaporates towards the end of drying, the slow-volatile solvent tends to remain without evaporating. This allows the dissolved state of the adhesive components to be maintained even towards the end of drying, and even if the adhesive liquid contains moisture, water-rich areas are less likely to form. As a result, aggregation of adhesive components is suppressed, and coating unevenness can be suppressed. In addition, because there are fewer water-rich areas due to the remaining slow-volatile solvent, even if there is dirt on the surface of the substrate, repelling is less likely to occur, and coating unevenness can be suppressed.

[0010] Thus, the adhesive composition of this disclosure makes it possible to form a homogeneous coating film (adhesive layer) with minimal coating unevenness. As a result, excellent adhesion is achieved by the adhesive layer, and peeling of the bonded member can be suppressed.

[0011] (2) In the configuration of (1) above, the content of the slow-volatile solvent may be 0.1% by mass or more and 10% by mass or less when the total mass of the adhesive composition is 100% by mass. This configuration makes it easier to exert the effect of adding the slow-volatile solvent. This configuration is also preferable in that it does not make the concentration of the adhesive component in the adhesive composition too low, making it easier to form the adhesive layer to the desired thickness.

[0012] (3) In any of the above configurations, the water content of the adhesive liquid may be 0.5% by mass or more and 10% by mass or less. With this configuration, the influence of water in the adhesive composition can be reduced, and the effect of adding a slow-volatile solvent can be easily exerted. It is preferable that the content of the slow-volatile solvent is the same as or greater than the water content of the adhesive liquid.

[0013] (4) In any of the above configurations, the non-volatile content in the adhesive composition may be 0.1% by mass or more and 10% by mass or less. For example, when the adhesive composition consists only of an adhesive liquid and a slow-volatile solvent, the non-volatile content in the adhesive composition will be the same as the content of the adhesive component. This configuration is suitable as the concentration of the adhesive component for forming an adhesive layer with desired adhesion to a desired thickness.

[0014] (5) In any of the above configurations, the diluent solvent may be configured to have one or more selected from methanol, ethanol, methyl ethyl ketone, and toluene. These solvents can dissolve adhesive components and have a vapor pressure at 20°C that is higher than that of water. For this reason, they are more volatile than water and are suitable as diluent solvents.

[0015] (6) In any of the above configurations, the boiling point of the slow-volatile solvent may be 180°C or lower. This configuration allows for a relatively short drying time of the coating film and improves productivity.

[0016] (7) In any of the above configurations, the slow-volatile solvent may be one or more selected from methyl isobutyl ketone, diacetone alcohol, ethyl cellosolve, and n-butanol. These solvents have a vapor pressure at 20°C that is lower than 2.33 kPa, and are therefore less volatile than water. They also have a boiling point of 180°C or lower and are soluble in water.

[0017] (8) In any of the above configurations, the adhesive composition of the present disclosure may be configured to bond a thin plate-shaped substrate, which is a component of the fuel cell, to a sealing member manufactured from a rubber composition. This configuration can improve the reliability of adhesion between the substrate, such as a separator, and the sealing member. For example, if the sealing member peels off, the compression when the fuel cell is constructed may cause stress to concentrate starting from the peeling point, potentially causing cracks in the sealing member. This configuration suppresses the peeling of the sealing member, thus suppressing the occurrence of cracks.

[0018] According to the adhesive composition of this disclosure, aggregation and repulsion of adhesive components are suppressed during coating, thereby suppressing uneven coating. As a result, a homogeneous adhesive layer can be formed, excellent adhesion is achieved by the adhesive layer, and peeling of the bonded member can be suppressed.

[0019] The embodiments of the adhesive composition of this disclosure will be described below. However, the embodiments are not limited to the following forms, and can be implemented in various modified and improved forms as can be carried out by those skilled in the art.

[0020] <Adhesive Composition> The adhesive composition of the present disclosure comprises an adhesive liquid having an adhesive component having one or more selected from a silane coupling agent, an organic titanate compound, an aluminate coupling agent, and a zirconate coupling agent, and a diluent, and a slow-volatile solvent added separately from the adhesive liquid, wherein the adhesive component is soluble and has a vapor pressure of 2.33 kPa or less at 20°C.

[0021] (A) Adhesive liquid [Adhesive component] The adhesive component comprises one or more selected from silane coupling agents, organic titanate compounds, aluminate coupling agents, and zirconate coupling agents. The adhesive component may consist of one or more selected from these, but a preferred form is one in which a silane coupling agent or a silane coupling agent and an organic titanate compound are the main components. In this specification, "main component" refers to a component that accounts for 50% by mass or more when the total adhesive component is considered to be 100% by mass. In this case, the adhesive component may be in one of the following forms: a form consisting only of a silane coupling agent (content ratio 100% by mass), a form consisting only of a silane coupling agent and an organic titanate compound (content ratio 100% by mass in total for both), or a form containing a silane coupling agent and an organic titanate compound (content ratio 50% by mass or more) which is added as needed, and other components (content ratio less than 50% by mass).

[0022] Furthermore, to improve the water resistance and acid resistance of the formed adhesive layer by enhancing adhesion to the substrate and imparting hydrophobicity, phenolic resin, bismaleimide resin, vinyl resin, etc., may be added as adhesive components. When adding these resins, it is preferable that their amount be 20% by mass or less, based on 100% by mass of the total adhesive components.

[0023] The silane coupling agent can be appropriately selected from a group of compounds having one or more functional groups selected from amino groups, vinyl groups, and epoxy groups, taking into consideration adhesion and other factors. The silane coupling agent can be used alone or in a mixture of two or more. Alternatively, a copolymer oligomer obtained by copolymerizing two or more silane coupling agents may be used. The copolymer oligomer is preferably one having the hydrophilic functional group of (a) and the hydrophobic functional group of (b) below. (a) One or more selected from the group consisting of silanol groups, alkoxy groups, amino groups, isocyanate groups, epoxy groups, ureido groups, carboxyl groups, and hydroxyl 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.

[0024] By using specific functional groups shown in (a) and (b) for the hydrophilic and hydrophobic functional groups in the silane coupling agent, the adhesion, water resistance, and acid resistance of the adhesive layer can be improved. Of these, the hydrophobic functional group prevents water from penetrating the adhesive layer by imparting hydrophobicity, thereby contributing to improved water resistance and acid resistance. The hydrophilic functional group reacts with the substrate and components in the sealing material (such as carbon black) to contribute to adhesion. For example, a copolymer oligomer can be produced by oligomerizing a silane coupling agent having the functional group of (a) and a silane coupling agent having the functional group of (b). In this specification, (meth)acryloyl group means acryloyl group or methacryloyl group, and (meth)acrylate means acrylate or methacrylate.

[0025] Among the silane coupling agents having hydrophilic functional groups in (a), examples of silane coupling agents that also have hydrophilic functional groups other than silanol groups and alkoxy groups 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-hydroxypropyltrimethoxysilane, and 3-hydroxypropyltriethoxysilane. Among these, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, and 3-isocyanatetopropyltriethoxysilane are preferred.

[0026] Examples of silane coupling agents having the hydrophobic functional group of (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.

[0027] The oligomerization reaction begins by charging each silane coupling agent into a reactor equipped with a distillation apparatus and a stirrer, and stirring at approximately 60°C for about 1 hour. Next, approximately 0.5 to 2.0 moles of an acid such as formic acid are added within 1 hour to a total of 1 mole of the silane coupling agent having hydrophilic functional groups as shown in (a) and the silane coupling agent having hydrophobic functional groups as shown in (b). The temperature inside the reactor is maintained at approximately 65°C while the acid is being added. The mixture is stirred for a further 1 to 5 hours to allow the reaction to proceed, and at the same time, the alcohol produced by hydrolysis is distilled under reduced pressure. Distillation is stopped when only water remains in the distillate, and then the mixture is diluted to a silane concentration of 30 to 80% by mass. The copolymer oligomer obtained in this way is an oligomer soluble in alcoholic organic solvents such as methanol and ethanol. From the viewpoint of improving film-forming properties, water resistance, and acid resistance when applying adhesive compositions, copolymer oligomers of trimers or more are desirable.

[0028] When an organic titanate compound is included, acid resistance, particularly acid resistance during high-temperature and long-term use, is improved. It is desirable to use one or more organic titanate compounds selected from titanium alkoxides, titanium chelates, and titanium acylates.

[0029] Examples of titanium alkoxides include tetramethyl titanate, tetraethyl titanate, tetran-propyl titanate, tetraisopropyl titanate, tetran-butyl titanate, tetraisobutyl titanate, tetra-t-butyl titanate, tetraoctyl titanate, tetrastearyl titanate, tetra(2-ethylhexyl) titanate, and tetramethyl titanate. Among these, tetraisopropyl titanate, tetran-butyl titanate, and tetrastearyl titanate are preferred.

[0030] Examples of titanium chelates include titanium acetylacetonate, titanium octylene glycolate, titanium tetraacetylacetonate, titanium ethylacetoacetate, and titanium triethanolaluminate. Among these, titanium acetylacetonate and titanium ethylacetoacetate are preferred.

[0031] Examples of titanium acylates include titanium isostearate, tri-n-butoxytitanium monostearate, di-i-propoxytitanium distearate, titanium stearate, di-i-propoxytitanium diisostearate, and (2-n-butoxycarbonylbenzoyloxy)tributoxytitanium. Among these, titanium stearate is preferred.

[0032] When an aluminate-based coupling agent is included, the strength of the coating film is improved. Examples of aluminate-based coupling agents include aluminum alkyl acetate diisopropylate, aluminum ethyl acetate diisopropylate, aluminum trisethyl acetate, aluminum isopropylate, aluminum diisopropylate monosecondary butyrate, aluminum secondary butyrate, aluminum ethylate, aluminum bisethyl acetate monoacetylacetonate, aluminum trisacetylacetonate, and aluminum monoisopropoxymonoleoxyethyl acetate. One of these can be used alone, or two or more can be used in combination. Among these, aluminum alkyl acetate diisopropylate, aluminum ethyl acetate diisopropylate, and aluminum trisethyl acetate are preferred.

[0033] When a zirconate-based coupling agent is included, the heat resistance is improved. Examples of zirconate-based coupling agents include n-propyl zirconate, n-butyl zirconate, zirconium tetraacetylacetonate, and zirconium monoacetylacetonate. Among these, n-propyl zirconate and n-butyl zirconate are preferred.

[0034] [Diluting Solvent] The diluting solvent is not particularly limited as long as it can dissolve the adhesive components. Examples include alcohol-based organic solvents such as methanol, ethanol, isopropanol, 2-ethoxyethanol (ethylene glycol monoethyl ether), and butoxyethanol (ethylene glycol monobutyl ether); ketone-based organic solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; and hydrocarbon-based solvents such as toluene and hexane. The diluting solvent may be one or more types. It is desirable that the diluting solvent be more volatile than water. In other words, it is desirable that the diluting solvent be a solvent with a vapor pressure of more than 2.33 kPa at 20°C. For example, it is desirable to use one or more selected from methanol, ethanol, methyl ethyl ketone, and toluene as the "main solvent" accounting for 80% or more by mass of the diluting solvent.

[0035] [Other] The adhesive liquid is a liquid in which the adhesive component is diluted with a diluent solvent. The concentration (content) of the adhesive component should be appropriately determined considering the adhesiveness and the thickness of the adhesive layer to be formed. For example, it is preferable to have a concentration of 0.1% to 10% by mass when the total amount of the adhesive liquid is considered to be 100% by mass. From the viewpoint of improving the stability of the adhesive liquid and making it easier to adjust the film thickness, it is more preferable that the content of the adhesive component be 7% by mass or less, and even more preferably 5% by mass or less. When the adhesive composition consists only of the adhesive liquid and a slow-volatile solvent, the content of the adhesive component will be the same as the content of the non-volatile component in the adhesive composition. "Non-volatile component in the adhesive composition" means the mass of the residual component after removing the solvent (diluent solvent and slow-volatile solvent) from the adhesive composition.

[0036] For example, adhesive liquid may contain 0.5% by mass or more of water when the total mass is considered as 100%. From the viewpoint of minimizing the influence of water in the adhesive composition, it is desirable that the water content of the adhesive liquid be 10% by mass or less. It is even more preferable that the water content of the adhesive liquid be 7% by mass or less, and more preferably 5% by mass or less.

[0037] As the adhesive liquid, commercially available products such as "CHEMLOK® 5151" manufactured by Road Japan Inc. (the adhesive component is a copolymer oligomer of a silane coupling agent) may be used.

[0038] (B) Slow-Volatile Solvents Slow-volatile solvents are added separately from the adhesive solution, are solvents that can dissolve the adhesive components, and have a vapor pressure of 2.33 kPa or less at 20°C. Examples of solvents that can dissolve the adhesive components and have a vapor pressure of 2.33 kPa or less at 20°C include methyl isobutyl ketone, ethylene glycol, diacetone alcohol, ethyl cellosolve, and n-butanol. One of these can be used alone, or two or more can be used in mixture. Slow-volatile solvents evaporate at the same rate as or slower than water. From the viewpoint of shortening the drying time of the coating film and improving productivity, it is desirable that the boiling point of the slow-volatile solvent be 180°C or less. Among the solvents listed above, those with a boiling point of 180°C or less are methyl isobutyl ketone, diacetone alcohol, ethyl cellosolve, and n-butanol.

[0039] When the total mass of the adhesive composition is taken as 100% by mass, the content of the slow-volatile solvent should preferably be 0.1% by mass or more. From the viewpoint of maximizing the effect of adding the slow-volatile solvent, it is desirable that the content of the slow-volatile solvent be equal to or greater than the water content of the adhesive liquid. It is also desirable that it be equal to or greater than the content of the adhesive component. On the other hand, from the viewpoint of not lowering the concentration of the adhesive component in the adhesive composition too much, it is desirable that the content of the slow-volatile solvent be 10% by mass or less. It is even more preferable that the content of the slow-volatile solvent be 7% by mass or less, and more preferably 5% by mass or less.

[0040] (C) Other Components The adhesive composition of this disclosure may have other components in addition to the adhesive liquid and slow-volatile solvent, such as dyes. For example, by adding a dye to color the adhesive composition a different color from the object to be coated (the member to be bonded), the adhesive composition becomes easier to identify on the surface of the object to be coated, and the quality of the coating can be easily judged by visual inspection or a color inspection machine. As a result, uneven coating and missed spots are less likely to occur. Here, "color" mainly refers to the hue of the three elements of color, such as red, blue, green, and yellow. As for the dye, it is desirable that it is compatible with the adhesive component and dissolves in the diluent and slow-volatile solvents. "Compatible with the adhesive component" means that when 1.5 g of dye is added to 100 mL of adhesive liquid with an adhesive component concentration of 5% by mass and stirred for 5 minutes, the state is observed visually and there is no turbidity or precipitate.

[0041] <Method of Use of Adhesive Composition> The adhesive composition of this disclosure may be applied to at least one of the objects to be bonded. The adhesive composition may be prepared by adding a slow-volatile solvent to a pre-prepared adhesive liquid and stirring. Alternatively, it may be prepared by combining the adhesive components of the adhesive liquid, a diluent, a slow-volatile solvent, etc., and stirring. The adhesive composition may be applied by brushing, using coating machines such as dispensers, blade coaters, bar coaters, die coaters, comma coaters (registered trademark), and roll coaters, or by spraying or dipping, and then air-drying at room temperature or heating if necessary. The adhesive composition may be applied in two or more layers, but a single layer application is preferable from the viewpoint of shortening the application process time.

[0042] <Laminates using adhesive compositions> Using the adhesive compositions of this disclosure, for example, a laminate can be manufactured in which a thin plate-shaped substrate and a sealing member manufactured from a rubber composition are bonded together. The laminate can be manufactured, for example, by applying the adhesive composition to a substrate, placing an uncrosslinked rubber composition on the coated surface to form a laminate, heating and pressurizing the laminate to crosslink the rubber composition to form a sealing member, and then bonding the sealing member to the substrate. Alternatively, the laminate can be manufactured by placing a sealing member, which has been manufactured by crosslinking the rubber composition in advance, on the coated surface of the adhesive composition, and heating and pressurizing as necessary.

[0043] When the laminate thus obtained is used as a component of a fuel cell or a water electrolysis device, from the viewpoint of realizing thinning of the component and high dimensional accuracy, the thickness of the adhesive layer disposed between the base material and the seal member is desirably 0.001 μm or more and 3 μm or less, and further desirably 0.01 μm or more and 1 μm or less.

[0044] <Application> The adhesive composition of the present disclosure can be applied to a fuel cell, a water electrolysis device (hydrogen production device), and the like. Examples of the fuel cell include a solid polymer fuel cell (PEFC) (including a direct methanol fuel cell (DMFC)). For example, using the adhesive composition of the present disclosure, a thin plate-like base material, which is a component of a fuel cell, and a seal member made of a rubber composition can be adhered to each other. Examples of the base material include a separator, a membrane electrode assembly (MEA) of an electrode member, and a gas diffusion layer (GDL). Since the configuration of the water electrolysis device is similar to that of the fuel cell, it can be applied in the same manner. Hereinafter, the base material and the seal member constituting the fuel cell and the water electrolysis device will be described.

[0045] [Substrate] As an example of a substrate, a separator in a polymer electrolyte fuel cell will be described. Suitable materials for the separator include stainless steel, titanium, copper, magnesium, aluminum, carbon, graphite, and conductive resins (thermoplastic resins or thermosetting resins containing carbon, graphite, polyacrylonitrile-based carbon fibers, etc.). From the viewpoint of acid resistance and cost, stainless steel (especially austenitic) and titanium (especially pure titanium) are desirable. Alternatively, a carbon thin film such as a diamond-like carbon film (DLC film) or graphite film may be formed on the surface of the main body made of these materials by treatment such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). The area of ​​the separator to which the sealing member is bonded (the area to which the adhesive composition is applied) may be subjected to surface treatment such as forming irregularities to increase the wettability of the adhesive composition and improve adhesion. The configuration of the separator, including the formed flow channels and manifold holes, is not limited, and the shape, thickness, etc., can be determined as appropriate. Considering power generation performance, the thickness of the separator should be 0.1 mm or more and 0.5 mm or less.

[0046] [Sealing Members] Sealing members are manufactured by injection molding, press molding, etc., of a rubber composition. The rubber components constituting the rubber composition may be liquid rubber or solid rubber. Examples of rubber components 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). In particular, 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 rubber components, the rubber composition may also contain crosslinking agents, crosslinking aids, plasticizers, reinforcing agents, anti-aging agents, processing aids, etc.

[0047] As a crosslinking agent, it is desirable to use an organic peroxide because it does not contain volatile components such as sulfur. Among them, dialkyl peroxide, peroxyketal, peroxyester, ketone peroxide, diacyl peroxide, peroxydicarbonate, etc., which can be crosslinked at a relatively low temperature, are suitable. As crosslinking aids, maleimide compounds, triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), trimethylolpropane trimethacrylate (TMPT), bifunctional (meth)acrylate, 1,2-polybutadiene, etc. can be mentioned. As plasticizers, petroleum-based plasticizers such as process oil, lubricating oil, paraffin, liquid paraffin, petrolatum, etc., fatty oil-based plasticizers such as castor oil, linseed oil, rapeseed oil, coconut oil, etc., waxes such as tall oil, rosin, beeswax, carnauba wax, lanolin, etc., linoleic acid, palmitic acid, stearic acid, lauric acid, etc. can be mentioned. As reinforcing agents, carbon black, amorphous silica (white carbon), etc. can be mentioned. As antioxidants, phenolic, amine-based, imidazole-based, phosphate-based, wax, etc. can be mentioned.

[0048] The sealing member may be arranged annularly along the outer peripheral edge on the surface of the base material, or may be arranged so as to surround a predetermined part. The thickness of the sealing member is preferably 0.2 mm or more and 5 mm or less, more preferably 0.5 mm or more and 3 mm or less.

[0049] Next, the present disclosure will be described more specifically with reference to examples. Various adhesive compositions were manufactured, and the coating properties (drying time and presence or absence of coating unevenness) when applied to the base material were evaluated. Also, using the manufactured adhesive composition, a base material and a sealing member were adhered to manufacture an evaluation sample, and its adhesiveness and the compression durability of the sealing member were evaluated.

[0050] <Coating properties of adhesive composition> [Manufacture of adhesive composition] With the formulations shown in Tables 1 and 2 below, a slow-evaporating solvent was added to the adhesive liquid and stirred to manufacture various adhesive compositions.

[0051] [Adhesive Liquid (A1)] A copolymer 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 1 mole of the total mass of silane coupling agents. The temperature inside the reactor was maintained at approximately 65°C while the formic acid was being added. The mixture was stirred for a further 3 hours to allow the reaction to proceed, and at the same time, the alcohol produced by hydrolysis was distilled under reduced pressure. Distillation was stopped when only water remained in the distillate, and then the mixture was diluted to a silane concentration of 50% by mass to obtain the copolymer oligomer. The hydrophobic functional group in the copolymer oligomer is a vinyl group, and the hydrophilic functional groups are a silanol group, an alkoxy group, and an amino group.

[0052] The manufactured copolymer oligomer was diluted with a first dilution solvent, which was a mixture of methanol and ethanol in a mass ratio of 1:1, to prepare an adhesive stock solution with a copolymer oligomer (silane coupling agent) concentration of 5.5% by mass. This adhesive stock solution was diluted three times by adding ethanol, the second dilution solvent, to prepare adhesive solution (A1).

[0053] [Adhesive Solution (A2)] An adhesive stock solution was prepared by mixing 80 parts by mass of an adhesive stock solution with a copolymer oligomer (silane coupling agent) concentration of 5.5% by mass used in adhesive solution (A1) with 20 parts by mass of an adhesive stock solution with a tetraisopropyl titanate organic titanate concentration of 5.5% by mass (first dilution solvent is ethanol). This adhesive stock solution was diluted three times by adding ethanol as the second dilution solvent to obtain adhesive solution (A2).

[0054] [Adhesive Solution (A3)] An adhesive stock solution was prepared by mixing 60 parts by mass of an adhesive stock solution with a copolymer oligomer (silane coupling agent) concentration of 5.5% by mass used in adhesive solution (A1) with 40 parts by mass of an adhesive stock solution with a tetraisopropyl titanate organic titanate concentration of 5.5% by mass (first dilution solvent is ethanol). This adhesive stock solution was diluted three times by adding ethanol as the second dilution solvent to prepare adhesive solution (A3).

[0055] [Adhesive Solution (A4)] As a commercially available adhesive containing a copolymer oligomer type silane coupling agent, "monicas® MP3004" manufactured by Yokohama Polymer Research Institute Co., Ltd. (the hydrophilic functional groups of the copolymer oligomer are silanol groups and alkoxy groups, and the hydrophobic functional groups are vinyl groups. It contains methanol as the first dilution solvent. The adhesive component concentration is 5.0% by mass.) was prepared, and methanol as the second dilution solvent was added to this adhesive to dilute it three times to obtain adhesive solution (A4).

[0056] [Adhesive Solution (A5)] As a commercially available adhesive containing a copolymer oligomer type silane coupling agent, "IMB1030TF" manufactured by Rhode Japan Inc. was prepared (the hydrophilic functional groups of the copolymer oligomer are silanol groups and alkoxy groups, and the hydrophobic functional groups are vinyl groups. It contains methanol, methyl ethyl ketone (MEK), and ethanol as the first dilution solvent. The adhesive component concentration is 3.0% by mass). This adhesive was diluted three times by adding methanol as the second dilution solvent to obtain adhesive solution (A5).

[0057] [Moisture content of adhesive solution] The moisture content of the manufactured adhesive solution was measured using the CA-310 moisture measuring device manufactured by Nitto Seikou Analytech Co., Ltd.

[0058] [Slow-Volatile Solvents] Five types of solvents were prepared as slow-volatile solvents. Details are as follows: (B1) Methyl isobutyl ketone (MIBK) Vapor pressure at 20°C: 2.07 kPa, boiling point: 116°C. (B2) Diacetone alcohol (DAA) Vapor pressure at 20°C: Less than 0.13 kPa, boiling point: 168°C. (B3) Ethyl cellosolve Vapor pressure at 20°C: 0.51 kPa, boiling point: 135°C. (B4) n-butanol Vapor pressure at 20°C: 0.67 kPa, boiling point: 118°C. (B5) Ethylene glycol Vapor pressure at 20°C: 0.01 kPa, boiling point: 197°C.

[0059] The manufactured adhesive compositions were numbered Examples 1 to 9. For comparison, adhesive compositions made by using the adhesive liquid without adding a slow-volatile solvent were numbered Comparative Examples 1 to 4. Tables 1 and 2 show the components of the adhesive compositions. Tables 1 and 2 also show the water content of the adhesive liquid, the content of the slow-volatile solvent and non-volatile components (adhesive components) when the total mass of the adhesive composition is taken as 100% by mass, and the evaluation results described later.

[0060]

[0061]

[0062] [Evaluation of Coatability] The adhesive composition was spray-applied to the surface of the substrate to a film thickness of 1 μm, and then placed on a hot plate heated to 50°C. The time it took for the coating to dry was measured. After drying, the coating was visually inspected to check for any chipping (uncoated areas). The drying time and the presence or absence of chipping were evaluated according to the following criteria (1) and (2). The substrate was a stainless steel plate that had been cleaned with an alkaline cleaning agent, and was a rectangular plate with a width of 25 mm, a length of 60 mm, and a thickness of 0.1 mm. (1) Criteria for Judging Drying Time From the viewpoint of productivity, if the drying time of the coating was 60 seconds or less, it was evaluated as good drying performance (indicated by ○ in Tables 1 and 2), and if it exceeded 60 seconds, it was evaluated as insufficient drying performance (indicated by △ in the same tables). (2) Criteria for determining whether or not there are chips in the coating If the coating is formed on the entire surface, or if there are areas where the coating has not been formed but the maximum length of those areas is less than 0.5 mm, then there are no chips and no uneven coating (indicated by ○ in Tables 1 and 2). If there are areas where the coating has not been formed but the maximum length is 0.5 mm or more, then there are chips and uneven coating (indicated by × in the same tables).

[0063] As shown in Table 1, no uneven coating occurred in any of the sample examples where adhesive compositions using slow-volatile solvents were applied. However, in the sample of Example 9, a slow-volatile solvent (ethylene glycol) with a boiling point exceeding 180°C was used, resulting in a longer drying time and inferior productivity compared to the other examples. On the other hand, as shown in Table 2, uneven coating occurred in all of the comparative example samples that did not use slow-volatile solvents.

[0064] <Adhesion of the adhesive composition and compression durability of the sealing member> [Preparation of evaluation samples] First, a rubber composition for forming the sealing member was prepared as follows: 100 parts by mass of ethylene-butene-diene rubber (EBT-K-9330M, manufactured by Mitsui Chemicals, Inc.), 1.0 part by mass of a phenolic antioxidant (Nocrac® NS-5, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.), 50 parts by mass of carbon black (Seast® SO, manufactured by Tokai Carbon Co., Ltd.) as a reinforcing agent, and 15 parts by mass of poly-α-olefin (PAO601, manufactured by Nippon Steel Chemical & Material Co., Ltd.) as a plasticizer were kneaded at 120°C for 5 minutes using a Banbury mixer. The mixture was then cooled, and 6 parts by mass of the crosslinking agent 1,1-di(t-butylperoxy)cyclohexane ("Perhexa® C-80" manufactured by NOF Corporation) was added. The mixture was then kneaded at 50°C for 10 minutes using an open roll to prepare the rubber composition.

[0065] Next, the rubber composition was placed on the surface of the substrate used for the coating property evaluation, overlapping the coating film of the adhesive composition to form a laminate. This laminate was then placed in a mold and heated and pressurized at 170°C for 10 minutes. In this way, an evaluation sample was produced in which a sealing member (2.0 mm thick), which is a crosslinked rubber composition, and the substrate were bonded together via the adhesive layer. Hereafter, the numbers of the evaluation samples correspond to the numbers of the adhesive compositions used.

[0066] [Evaluation of Adhesion] A peel test was performed on the evaluation samples to assess the adhesion between the substrate and the sealing member. In the peel test, a gripping portion was created by making an incision in the end of the sealing member that was not adhered to the substrate, and the gripping portion was pulled perpendicular to the substrate at a speed of 10 mm / second to peel off the sealing member. The condition of the peeled surface was then visually observed, and if material fracture (cutting of the sealing member) occurred, it was evaluated as good adhesion (indicated by ○ in Tables 1 and 2), and if interface fracture occurred, it was evaluated as poor adhesion (indicated by × in the same tables).

[0067] As a result, as shown in Table 1, the samples in the examples coated with adhesive compositions using slow-volatile solvents all exhibited good adhesion. On the other hand, as shown in Table 2, the samples in the comparative examples that did not use slow-volatile solvents all exhibited poor adhesion.

[0068] [Evaluation of Compression Durability] The durability of the sealing material was evaluated by performing a compression test on the evaluation sample. The compression test was performed as follows: First, the evaluation sample was placed in a press machine and fixed in a state where the sealing material was compressed to 60% 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 machine. The sealing material of the removed evaluation sample was cut in the thickness direction and the cross-section was visually observed. If there were no cracks, the compression durability was evaluated as good (indicated by ○ in Tables 1 and 2), and if there were cracks, the compression durability was evaluated as poor (indicated by × in the same tables).

[0069] As a result, as shown in Table 1, none of the samples in the example where the adhesive composition using a slow-volatile solvent was applied showed cracks, and the compressive durability was good. On the other hand, as shown in Table 2, none of the samples in the comparative example where a slow-volatile solvent was used showed cracks, and the compressive durability was poor.

[0070] Based on the above, it has been confirmed that the adhesive composition of this disclosure can form an adhesive layer that is less prone to uneven coating and has excellent adhesion.

[0071] The adhesive composition of this disclosure is suitable for bonding components in fuel cells, water electrolysis devices, and the like.

Claims

1. An adhesive composition comprising: an adhesive liquid having an adhesive component having one or more selected from silane coupling agents, organic titanate compounds, aluminate coupling agents, and zirconate coupling agents, and a diluent; and a slow-volatile solvent added separately from the adhesive liquid, to which the adhesive component can be dissolved, and having a vapor pressure of 2.33 kPa or less at 20°C, wherein the water content of the adhesive liquid is 0.5% by mass or more and 10% by mass or less, and the slow-volatile solvent is one or more selected from methyl isobutyl ketone, ethylene glycol, diacetone alcohol, and ethyl cellosolve.

2. An adhesive composition comprising: an adhesive liquid having an adhesive component having one or more selected from a silane coupling agent, an organic titanate compound, an aluminate coupling agent, and a zirconate coupling agent, and a diluent; and a slow-volatile solvent added separately from the adhesive liquid, to which the adhesive component can be dissolved, and having a vapor pressure of 2.33 kPa or less at 20°C, wherein the slow-volatile solvent has one or more selected from methyl isobutyl ketone, ethylene glycol, diacetone alcohol, and ethyl cellosolve, and the non-volatile content is 0.1% by mass or more and 10% by mass or less.

3. An adhesive liquid comprising an adhesive component having one or more selected from silane coupling agents, organic titanate compounds, aluminate coupling agents, and zirconate coupling agents, and a diluent solvent, and a slow-volatile solvent added separately from the adhesive liquid, wherein the adhesive component is soluble in the slow-volatile solvent and has a vapor pressure of 2.33 kPa or less at 20°C, wherein the slow-volatile solvent is one or more selected from methyl isobutyl ketone, ethylene glycol, diacetone alcohol, and ethyl cellosolve, and characterized in that it adheres a thin plate-shaped substrate which is a component of a fuel cell to a sealing member manufactured from a rubber composition.

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