Adhesive composition

Abstract

The present invention provides an adhesive composition that is less prone to uneven coating and can form an adhesive layer with excellent adhesion. [Solution] The adhesive composition 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, which is capable of dissolving the adhesive component and has a vapor pressure of 2.33 kPa or less at 20°C.

Description

Technical Field

[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.

Background Art

[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 performance and insulation against reaction gases and cooling media. In order to maintain high sealing performance in the operating environment of a fuel cell, a method of integrating the seal member and the mating member using an adhesive is effective. For example, as a method of adhering a base material such as a separator to a rubber seal member, Patent Documents 1 and 2 describe a method in which an adhesive (primer) having a copolymerized 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.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described in the above-mentioned Patent Documents 1 and 2, adhesives are often used in the form of a solution in which the adhesive component, such as a silane coupling agent, is diluted with a volatile solvent. When such a solution-based adhesive is applied to a substrate, the solvent evaporates and it dries, forming a coating film. The inventors of this invention have found that when a solution-based adhesive is applied and nearing the end of the drying process, the adhesive component may aggregate, resulting in areas where no coating film is formed. If there are coating inconsistencies, such as areas where no coating film is formed, the sealing member to be bonded may peel off or the sealing performance may be reduced.

[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. [Means for solving the problem]

[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 which has 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 uniform 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. This configuration reduces the influence of water in the adhesive composition and makes it easier to exert the effect of adding a slow-volatile solvent. Preferably, 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 composed of 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, thereby improving 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. [Effects of the Invention]

[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. [Modes for carrying out the invention]

[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 this 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-volatility 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 has one or more selected from silane coupling agents, organic titanate compounds, aluminate coupling agents, and zirconate coupling agents. As the adhesive component, it may have one or more selected from these, but as a preferred form, there is a form mainly composed of a silane coupling agent, or a form mainly composed of a silane coupling agent and an organic titanate compound. In this specification, the "main component" is a component that occupies 50% by mass or more when the total of the adhesive component is 100% by mass. The adhesive component in this case may be in any of the forms including 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 (total content ratio 100% by mass), a silane coupling agent, and an organic titanate compound optionally blended (content ratio 50% by mass or more), and other components (content ratio less than 50% by mass).

[0022] Also, for the purpose of improving the water resistance and acid resistance of the formed adhesive layer by enhancing the adhesion to the substrate and imparting hydrophobicity, a phenolic resin, a bismaleimide resin, a vinyl resin, etc. may be added as the adhesive component. When adding these resins, it is preferably 20% by mass or less when the total of the adhesive component is 100% by mass.

[0023] The silane coupling agent may be appropriately selected from a group of compounds having one or more functional groups selected from amino groups, vinyl groups, and epoxy groups as functional groups in consideration of adhesiveness, etc. As the silane coupling agent, one kind may be used alone, or two or more kinds may be mixed and used. Alternatively, a copolymerized oligomer in which two or more silane coupling agents are copolymerized may be used. As the copolymerized oligomer, those having the following hydrophilic functional group (a) and hydrophobic functional group (b) are preferred. (a) It is 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 contains at least a silanol group or an alkoxy group. (b) At least one selected from the group consisting of a vinyl group, a (meth)acryloyl group, a maleimide group, a methyl group, an ethyl group, a styryl group, a phenyl group, and a mercapto group.

[0024] By using the specific functional groups shown in (a) and (b) as the hydrophilic functional group and the hydrophobic functional group in the silane coupling agent, the adhesiveness, water resistance, and acid resistance of the adhesive layer can be improved. Among these, the hydrophobic functional group contributes to the improvement of water resistance and acid resistance by preventing the intrusion of water into the adhesive layer by imparting hydrophobicity. The hydrophilic functional group reacts with the base material and components (such as carbon black) in the seal member to contribute to adhesiveness. For example, a silane coupling agent having the functional group of (a) and a silane coupling agent having the functional group of (b) may be subjected to an oligomerization reaction to produce a copolymer oligomer. In this specification, the (meth)acryloyl group means an acryloyl group or a methacryloyl group, and the (meth)acrylate means an acrylate or a methacrylate.

[0025] Among the silane coupling agents having hydrophilic functional groups of (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-carboxypropyltriethoxysilane, 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 diluent 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); ketone-based organic solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; and hydrocarbon-based solvents such as toluene and hexane. The diluent may be one or more types of solvents. It is desirable that the diluent is more volatile than water. In other words, it is desirable that the diluent is a solvent with a vapor pressure greater than 2.33 kPa at 20°C. For example, it is desirable to use one or more solvents selected from methanol, ethanol, methyl ethyl ketone, and toluene as the "main solvent" accounting for 80% or more by mass of the diluent.

[0035] [others] Adhesive liquid is a liquid in which adhesive components are diluted with a diluent solvent. The concentration (content) of the adhesive components 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 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 for the content of adhesive components to be 7% by mass or less, and even more preferable to be 5% by mass or less. When the adhesive composition consists only of adhesive liquid and a slow-volatile solvent, the content of the adhesive components will be the same as the content of non-volatile components in the adhesive composition. "Non-volatile components in the adhesive composition" means the mass of residual components after the solvent (diluent solvent and slow-volatile solvent) has been removed 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(registered trademark) 5151" manufactured by Road Japan Inc. (the adhesive component is a copolymer oligomer of a silane coupling agent) may be used.

[0038] (B) Slow-volatility solvents Slow-volatility solvents are added separately from the adhesive solution, are solvents that dissolve the adhesive components, and have a vapor pressure of 2.33 kPa or less at 20°C. Examples of solvents that 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 mixtures. Slow-volatility 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-volatility solvent is 180°C or less. Of the solvents listed above, methyl isobutyl ketone, diacetone alcohol, ethyl cellosolve, and n-butanol have a boiling point of 180°C or less.

[0039] When the total mass of the adhesive composition is considered to be 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 ingredients The adhesive composition of this disclosure may contain other components such as dyes in addition to the adhesive liquid and slow-volatile solvent. 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, making it easier to determine the quality of the coating 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 solvent and slow-volatile solvent. "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 without turbidity or precipitate.

[0041] <How to use adhesive compositions> 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] <Laminate using adhesive composition> Using the adhesive composition 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, it 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 obtained in this manner is used as a component of a fuel cell or water electrolysis device, from the viewpoint of achieving a thinner component and high dimensional accuracy, it is desirable that the thickness of the adhesive layer placed between the substrate and the sealing member be 0.001 μm or more and 3 μm or less, and more specifically, 0.01 μm or more and 1 μm or less.

[0044] <Application> The adhesive composition of this disclosure can be applied to fuel cells, water electrolyzers (hydrogen production devices), and the like. Examples of fuel cells include polymer electrolyte fuel cells (PEFCs) (including direct methanol fuel cells (DMFCs)). For example, the adhesive composition of this disclosure can be used to bond a thin plate-shaped substrate, which is a component of a fuel cell, to a sealing member manufactured from a rubber composition. Examples of substrates include separators, membrane electrode assemblies (MEA) of electrode members, and gas diffusion layers (GDLs). The structure of a water electrolyzer is similar to that of a fuel cell, and therefore the adhesive composition can be applied in the same way. The substrates and sealing members that constitute fuel cells and water electrolyzers are described below.

[0045] [Base material] 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. Furthermore, 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 treatments 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 treatments such as creating irregularities to improve adhesion by increasing the wettability of the adhesive composition. The configuration of the separator, including the formed flow channels and manifold holes, is not limited, and the shape and thickness can be determined as appropriate. Considering power generation performance, the thickness of the separator should ideally be between 0.1 mm and 0.5 mm.

[0046] [Sealing material] The sealing member is manufactured by injection molding, press molding, or other methods using a rubber composition. The rubber component 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 due to their high water resistance and acid resistance at high temperatures. In addition to the rubber component, 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 preferable to use organic peroxides because they do not contain volatile components such as sulfur. Among these, dialkyl peroxides, peroxyketals, peroxyesters, ketone peroxides, diacyl peroxides, and peroxydicarbonates are particularly suitable because they can be crosslinked at relatively low temperatures. 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, subsulfate, 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). Anti-aging agents include phenols, amines, imidazoles, phosphoric acids, and waxes.

[0048] The sealing member may be arranged in a ring along the outer edge on the surface of the substrate, or it may be arranged to surround a predetermined area. The thickness of the sealing member is preferably 0.2 mm to 5 mm, and more preferably 0.5 mm to 3 mm. [Examples]

[0049] Next, the present disclosure will be described in more detail with reference to examples. Various adhesive compositions were manufactured and their coatability (drying time and presence or absence of uneven coating) when applied to a substrate was evaluated. Furthermore, evaluation samples were manufactured by bonding a substrate and a sealing member using the manufactured adhesive compositions, and their adhesiveness and the compression durability of the sealing member were evaluated.

[0050] <Coating properties of adhesive compositions> [Manufacturing of adhesive compositions] Various adhesive compositions were prepared by adding a slow-volatile solvent to the adhesive liquid and stirring, using the formulations shown in Tables 1 and 2 below.

[0051] [Adhesive liquid (A1)] A copolymer oligomer was prepared 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 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 with ethanol, the second dilution solvent, to prepare adhesive solution (A1).

[0053] [Adhesive liquid (A2)] A new 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: ethanol). This adhesive stock solution was diluted threefold by adding ethanol as the second dilution solvent to prepare adhesive solution (A2).

[0054] [Adhesive liquid (A3)] A new 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: ethanol). This adhesive stock solution was diluted threefold by adding ethanol as the second dilution solvent to prepare adhesive solution (A3).

[0055] [Adhesive liquid (A4)] As a commercially available adhesive containing a copolymer oligomer-type silane coupling agent, "monicas(registered trademark) 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 diluent. The adhesive component concentration is 5.0% by mass.) was prepared, and methanol as the second diluent was added to this adhesive to dilute it three times to obtain adhesive solution (A4).

[0056] [Adhesive liquid (A5)] As a commercially available adhesive containing a copolymer oligomer-type silane coupling agent, "IMB1030TF" manufactured by Road Japan Inc. (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.) was prepared, and methanol, the second dilution solvent, was added to this adhesive to dilute it threefold to obtain adhesive solution (A5).

[0057] [Water content of adhesive liquid] The moisture content of the manufactured adhesive liquid was measured using the "CA-310" moisture meter manufactured by Nitto Seikou Analytech Co., Ltd.

[0058] [Slow-volatile solvents] Five types of slow-volatility solvents were prepared. 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: 0.67kPa, 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] [Table 1]

[0061] [Table 2]

[0062] [Evaluation of coating properties] 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 determining drying time From a productivity standpoint, drying time of 60 seconds or less was considered good drying performance (indicated by ○ in Tables 1 and 2), while drying time exceeding 60 seconds was considered insufficient drying performance (indicated by △ in the same tables). (2) Criteria for determining whether or not there are chips in the paint film If the coating was formed over the entire surface, or if there were areas without a coating but the maximum length of those areas was less than 0.5 mm, it was evaluated as having no chips and no uneven coating (indicated by ○ in Tables 1 and 2). If there were areas without a coating that were 0.5 mm or longer in maximum length, it was evaluated as having 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 properties of adhesive compositions and compression durability of sealing members> [Manufacturing of evaluation samples] First, a rubber composition for forming a 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 (Seasto® 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 kneaded mixture was then cooled, and 6 parts by mass of 1,1-di(t-butylperoxy)cyclohexane (Perhexa® C-80, manufactured by NOF Corporation) as a crosslinking agent 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 properties evaluation, overlapping the adhesive composition coating, 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. The gripping portion was then 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 the adhesion was evaluated as good (indicated by a circle in Tables 1 and 2) in the case of material failure (cutting of the sealing member), and as poor adhesion (indicated by a cross in the same tables) in the case of interface failure.

[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 endurance] The durability of the sealing material was evaluated by performing compression tests on evaluation samples. The compression tests were conducted 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 removed evaluation sample's sealing material was cut in the thickness direction and the cross-section was visually observed. If there were no cracks, the compression durability was good (indicated by a circle in Tables 1 and 2), and if there were cracks, the compression durability was poor (indicated by a cross in the same tables).

[0069] As a result, as shown in Table 1, none of the samples in the examples coated with the adhesive composition using a slow-volatile solvent showed cracks, and the compressive durability was good. On the other hand, as shown in Table 2, none of the samples in the comparative examples that did not use a slow-volatile solvent 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. [Industrial applicability]

[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 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, A slow-volatile solvent is added separately from the adhesive liquid, is capable of dissolving the adhesive component, and has a vapor pressure of 2.33 kPa or less at 20°C. An adhesive composition characterized by having the following:

2. The adhesive composition according to claim 1, wherein the content of the slow-volatile solvent is 0.1% by mass or more and 10% by mass or less when the total mass of the adhesive composition is 100% by mass.

3. The adhesive composition according to claim 1, wherein the water content of the adhesive liquid is 0.5% by mass or more and 10% by mass or less.

4. The adhesive composition according to claim 1, wherein the content of nonvolatile matter in the adhesive composition is 0.1% by mass or more and 10% by mass or less.

5. The adhesive composition according to claim 1, wherein the diluting solvent is one or more selected from methanol, ethanol, methyl ethyl ketone, and toluene.

6. The adhesive composition according to claim 1, wherein the boiling point of the slow-volatile solvent is 180°C or lower.

7. The adhesive composition according to claim 1, wherein the slow-volatile solvent is one or more selected from methyl isobutyl ketone, diacetone alcohol, ethyl cellosolve, and n-butanol.

8. The adhesive composition according to claim 1, for bonding a thin plate-shaped substrate which is a component of a fuel cell and a sealing member manufactured from a rubber composition.

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