adhesive composition

Abstract

Provided is an adhesive composition that is less likely to cause coating unevenness and can form an adhesive layer with excellent adhesiveness. [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 dilution solvent, and a slowly volatile solvent that 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.

Description

[Technical Field]

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

[0002] Fuel cells have a stack structure in which many cells are stacked. The cell stack is fastened in a compressed state 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 arranged on either side of the electrode members. Rubber sealing members are arranged around the electrode members and between adjacent separators to ensure sealing and insulation against reactant gases and refrigerants. In order to maintain high sealing performance in the operating environment of a fuel cell, it is effective to integrate the sealing member and the mating member using an adhesive. For example, Patent Documents 1 and 2 describe a method for bonding a substrate such as a separator to a rubber sealing member, in which an adhesive (primer) containing a copolymer oligomer-type silane coupling agent is applied to the surface of the substrate, and then the sealing member is vulcanization-bonded to the surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-80006 [Patent Document 2] International Publication No. 2022 / 208926 Summary of the Invention [Problem to be solved by the invention]

[0004] As described in Patent Documents 1 and 2, adhesives are often used in the form of a solution in which adhesive components such as silane coupling agents are diluted with a volatile solvent. When such solution-based adhesives are applied to a substrate, the solvent evaporates and the adhesive dries to form a coating film. The inventors of the present invention have found that when a solution-based adhesive is applied and the drying process nears the end, the adhesive components aggregate, resulting in areas where a coating film is not formed. If there are coating irregularities, such as areas where a coating film is not formed, there is a risk that the sealing material to be adhered will peel off or the sealing properties will be reduced.

[0005] The cause of adhesive component aggregation is thought to be as follows: In adhesives, the molecular weight is sometimes increased by polymerizing the silane coupling agent to increase adhesive strength. The polymerization of silane coupling agents is a dehydration condensation reaction between hydroxyl groups (-OH), which results in the generation of condensed water within the system. It is known that adhesives contain small amounts of water, including this condensed water. Because water is less likely to volatilize than solvents, it remains until the end of drying when most of the solvent has evaporated, forming water-rich areas. It is thought that the solubility of adhesive components decreases in water-rich areas, causing the adhesive components to aggregate.

[0006] Furthermore, contamination on the substrate side may cause uneven coating. For example, when using a separator made of metal such as stainless steel, the separator is first cleaned with an alkaline cleaner to remove oil and other contaminants adhering to the separator surface. However, since it is difficult to completely remove the contaminants with alkaline cleaning, the contaminants tend to remain on the separator surface. Therefore, applying a highly polar adhesive containing moisture on top of the separator can cause repelling, resulting in uneven coating.

[0007] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide an adhesive composition that is less likely to cause coating unevenness and that can form an adhesive layer with 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 dilution solvent, and a slowly volatile solvent that 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.

[0009] The adhesive composition of the present disclosure contains a slow-volatility solvent in addition to a solvent (dilution solvent) that dilutes the adhesive component. The slow-volatility solvent can dissolve the adhesive component in the same way as the dilution solvent, but because its vapor pressure at 20°C is 2.33 kPa or less, it volatilizes at the same rate as or slower than water (the vapor pressure of water at 20°C is 2.33 kPa). Therefore, when applying the adhesive composition of the present disclosure, even if most of the dilution solvent volatilizes toward the end of drying, the slow-volatility solvent tends to remain. This allows the adhesive component to remain dissolved even toward the end of drying, and even if the adhesive liquid contains water, water-rich areas are unlikely to form. As a result, aggregation of the adhesive component is suppressed, and coating unevenness can be suppressed. Furthermore, because the remaining slow-volatility solvent reduces water-rich areas, even if the substrate surface is contaminated, repelling is unlikely to occur, and coating unevenness can be suppressed.

[0010] Thus, the adhesive composition of the present disclosure is able to form a uniform coating film (adhesive layer) without causing coating unevenness, resulting in excellent adhesive properties of the adhesive layer and preventing peeling of the adhered components.

[0011] (2) In the above-described configuration (1), 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 taken as 100% by mass. This configuration makes it easier to achieve the effects of adding the slow-volatile solvent. This configuration is also advantageous in that it prevents the concentration of the adhesive component in the adhesive composition from being too low, making it easier to form an adhesive layer with a 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 can reduce the effect of water in the adhesive composition, making it easier to achieve the effects of adding a slowly volatile solvent. Note that the content of the slowly volatile solvent is preferably equal to or greater than the water content of the adhesive liquid.

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

[0014] (5) In any of the above configurations, the dilution solvent may be one or more selected from the group consisting of methanol, ethanol, methyl ethyl ketone, and toluene. These solvents can dissolve the adhesive component and have a vapor pressure at 20°C higher than that of water. Therefore, they are more volatile than water and are suitable as dilution solvents.

[0015] (6) In any of the above configurations, the boiling point of the slowly volatile solvent may be 180° C. or lower. This configuration allows the drying time of the coating film to be relatively short, 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 of less than 2.33 kPa at 20°C, making them less volatile than water. In addition, they have a boiling point of 180°C or less 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-like substrate, which is a component of a fuel cell, to a sealing member made from a rubber composition. This configuration can improve the adhesive reliability between a substrate such as a separator and the sealing member. For example, if peeling occurs in the sealing member, stress may concentrate at the peeling point due to compression when the fuel cell is assembled, which may cause cracks in the sealing member. This configuration can suppress peeling of the sealing member, thereby suppressing the occurrence of cracks. [Effects of the Invention]

[0018] The adhesive composition of the present disclosure suppresses aggregation and repelling of adhesive components during application, thereby suppressing coating unevenness. This allows the formation of a homogeneous adhesive layer, which exhibits excellent adhesive properties and suppresses peeling of the adhered components. DETAILED DESCRIPTION OF THE INVENTION

[0019] The following describes embodiments of the adhesive composition of the present disclosure. However, 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.

[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 dilution solvent; and a slowly volatile solvent that 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.

[0021] (A) Adhesive liquid [Adhesive component] The adhesive component contains one or more selected from the group consisting of a silane coupling agent, an organic titanate compound, an aluminate coupling agent, and a zirconate coupling agent. The adhesive component may contain one or more selected from these, but a preferred embodiment is one in which the main 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% or more by weight of the adhesive component as a whole, where the total adhesive component is 100% by weight. In this case, the adhesive component may be composed solely of a silane coupling agent (100% by weight), a silane coupling agent and an organic titanate compound (100% by weight combined), or a silane coupling agent and an optionally blended organic titanate compound (50% by weight or more) plus other components (less than 50% by weight).

[0022] Furthermore, phenolic resins, bismaleimide resins, vinyl resins, etc. may be added as adhesive components to improve adhesion to the substrate and impart hydrophobicity, thereby improving the water resistance and acid resistance of the adhesive layer that is formed. When these resins are added, the amount should be 20% by mass or less, assuming that the total adhesive components are 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, vinyl, and epoxy groups, taking into consideration adhesive properties, etc. The silane coupling agent may be used alone or in combination of two or more. Alternatively, a copolymer oligomer in which two or more silane coupling agents are copolymerized may be used. The copolymer oligomer preferably has the following hydrophilic functional group (a) and hydrophobic functional group (b): (a) One or more selected from the group consisting of a silanol group, an alkoxy group, an amino group, an isocyanate group, an epoxy group, a ureido group, a carboxy group, and a hydroxy group, and contains at least a silanol group or an alkoxy group. (b) One or more 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 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. The hydrophobic functional group imparts hydrophobic properties, preventing water penetration into the adhesive layer and contributing to improved water and acid resistance. The hydrophilic functional group reacts with the substrate or components in the sealing material (e.g., carbon black) to improve adhesion. 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.

[0025] Among the (a) silane coupling agents having a hydrophilic functional group, examples of silane coupling agents 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-dimethyl-butylidene)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-isocyanatepropyltriethoxysilane are preferred.

[0026] Examples of silane coupling agents 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.

[0027] The oligomerization reaction begins by placing each silane coupling agent in 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 to each mole of the silane coupling agent having a hydrophilic functional group (a) and the silane coupling agent having a hydrophobic functional group (b). The temperature inside the reactor is maintained at approximately 65°C during the acid addition. The reaction is continued for an additional 1 to 5 hours with stirring, while 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 resulting copolymerized oligomer is soluble in alcohol-based organic solvents such as methanol and ethanol. A copolymerized oligomer of trimer or higher is desirable to enhance film-forming properties, water resistance, and acid resistance when applying the adhesive composition.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The inclusion of an aluminate-based coupling agent improves coating film strength. 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 these, aluminum alkylacetoacetate diisopropylate, aluminum ethylacetoacetate diisopropylate, and aluminum trisethylacetoacetate are preferred.

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

[0034] [Dilution solvent] The dilution 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 solvents such as toluene and hexane. The dilution solvent may be one or more types. It is desirable that the dilution solvent be more volatile than water. In other words, it is desirable that the dilution solvent have a vapor pressure of greater than 2.33 kPa at 20°C. For example, it is desirable to use one or more types selected from methanol, ethanol, methyl ethyl ketone, and toluene as a "main solvent" that accounts for 80% or more by mass of the dilution solvent.

[0035] [others] The adhesive liquid is a liquid in which the adhesive component is diluted with a diluent solvent. The concentration (content) of the adhesive component can be appropriately determined taking into account factors such as the adhesive property and the thickness of the adhesive layer to be formed. For example, it is preferable to set the concentration to 0.1% by mass or more and 10% by mass or less, where the total adhesive liquid is 100% by mass. From the viewpoints of improving the stability of the adhesive liquid and making it easier to adjust the coating thickness, the content of the adhesive component is preferably 7% by mass or less, and more preferably 5% by mass or less. When the adhesive composition is composed only of the adhesive liquid and a slow-volatile solvent, the content of the adhesive component is the same as the content of the non-volatile components in the adhesive composition. The "non-volatile components in the adhesive composition" refers to the mass of the components remaining after removing the solvents (diluent solvent and slow-volatile solvent) from the adhesive composition.

[0036] For example, the adhesive liquid may contain 0.5% by mass or more of water when the total amount is taken as 100% by mass. From the viewpoint of minimizing the influence of water in the adhesive composition, the water content of the adhesive liquid is desirably 10% by mass or less. The water content of the adhesive liquid is preferably 7% by mass or less, and more desirably 5% by mass or less.

[0037] As the adhesive liquid, for example, a commercially available product such as "CHEMLOK (registered trademark) 5151" manufactured by Lord Japan Inc. (the adhesive component is a copolymerized oligomer of a silane coupling agent) may be used.

[0038] (B) Slowly volatile solvent The slow-volatility solvent is added separately from the adhesive liquid, is capable of dissolving the adhesive components, and has a vapor pressure of 2.33 kPa or less at 20°C. Examples of solvents capable of dissolving the adhesive components and having 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. These can be used alone or in combination. Slow-volatility solvents evaporate at the same rate as or slower than water. From the perspective of shortening the drying time of the coating film and improving productivity, it is desirable for the boiling point of the slow-volatility solvent to be 180°C or less. Of the solvents listed above, those with a boiling point of 180°C or less include 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 slowly volatile solvent is preferably 0.1% by mass or more. From the viewpoint of increasing the effect of adding the slowly volatile solvent, the content of the slowly volatile solvent is preferably equal to or greater than the water content of the adhesive liquid. It is also preferably equal to or greater than the content of the adhesive component. On the other hand, from the viewpoint of preventing the concentration of the adhesive component in the adhesive composition from being too low, the content of the slowly volatile solvent is preferably 10% by mass or less. The content of the slowly volatile solvent is preferably 7% by mass or less, and more preferably 5% by mass or less.

[0040] (C) Other ingredients The adhesive composition of the present disclosure may contain other components, such as dyes, in addition to the adhesive liquid and the slow-volatile solvent. For example, adding a dye to the adhesive composition to a color different from that of the substrate (the member to be bonded) makes the adhesive composition easier to distinguish on the surface of the substrate, facilitating visual inspection or color inspection with a color inspection device. As a result, uneven coating and incomplete coating are less likely to occur. Here, "color" refers primarily to the hue of the three elements of color, such as red, blue, green, and yellow. A dye that is compatible with the adhesive components and soluble in the dilution solvent and slow-volatile solvent is desirable. "Compatible with the adhesive components" means that when 1.5 g of the dye is added to 100 mL of adhesive liquid containing 5% adhesive components by mass and stirred for 5 minutes, the result is visually observed to be free of turbidity and precipitates.

[0041] <Method of using the adhesive composition> The adhesive composition of the present disclosure may be applied to at least one of the objects to be bonded. The adhesive composition may be prepared by adding a slow-volatility solvent or the like to a pre-prepared adhesive liquid and stirring the mixture. Alternatively, the adhesive composition may be prepared by mixing and stirring the adhesive components of the adhesive liquid, a diluting solvent, a slow-volatility solvent, etc. 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 spray 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.

[0042] <Laminate using adhesive composition> The adhesive composition of the present disclosure can be used to produce a laminate in which, for example, a thin substrate and a sealing member made from a rubber composition are bonded together. The laminate can be produced, for example, by applying the adhesive composition to a substrate, placing an uncrosslinked rubber composition on the coated surface to form a laminate, and then heating and pressurizing the laminate to crosslink the rubber composition to form a sealing member, and then adhering the sealing member to the substrate. Alternatively, the laminate can be produced by placing a sealing member, which has been previously prepared by crosslinking a rubber composition, on the coated surface of the adhesive composition, and then heating and pressurizing as necessary.

[0043] When the laminate obtained in this manner is used as a component of a fuel cell or a water electrolysis device, from the viewpoint of realizing a thin component and high dimensional accuracy, it is desirable that the thickness of the adhesive layer disposed between the substrate and the sealing member is 0.001 μm or more and 3 μm or less, and more preferably 0.01 μm or more and 1 μm or less.

[0044] <Application> The adhesive composition of the present disclosure can be applied to fuel cells, water electrolysis devices (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 the present disclosure can be used to bond a thin-plate substrate, which is a component of a fuel cell, to a sealing member made from a rubber composition. Examples of substrates include separators, membrane electrode assemblies (MEAs) and gas diffusion layers (GDLs) that are electrode components. The structure of a water electrolysis device is similar to that of a fuel cell, and therefore can be applied in the same way. Below, the substrates and sealing members that constitute a fuel cell or a water electrolysis device are described.

[0045] [Base material] As an example of a substrate, a separator for a polymer electrolyte fuel cell will be described. 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 area of ​​the separator to which the sealing member is attached (the area 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 configuration of the separator, including the formed flow channels and manifold holes, is not limited, and the shape, thickness, etc. may be determined as appropriate. Considering power generation performance, the separator thickness should be 0.1 mm or more and 0.5 mm or less.

[0046] [Sealing material] 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.

[0047] As a crosslinking agent, organic peroxides are preferred because they do 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 particularly suitable. 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, sap, 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.

[0048] 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. [Example]

[0049] Next, the present disclosure will be described in more detail with reference to examples. Various adhesive compositions were prepared, and the coating properties (drying time and presence or absence of coating unevenness) when applied to a substrate were evaluated. In addition, the prepared adhesive compositions were used to bond a substrate and a sealing member to prepare evaluation samples, and the adhesive properties and compression durability of the sealing member were evaluated.

[0050] <Coatability of adhesive composition> [Production of adhesive composition] Various adhesive compositions were prepared by adding a slow-volatile solvent to the adhesive liquid and stirring the mixture according to the formulations shown in Tables 1 and 2 below.

[0051] [Adhesive liquid (A1)] A copolymerized oligomer was produced by copolymerizing two 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 at a rate of 1.0 mole per mole of the total mass of silane coupling agent. During the addition of formic acid, the temperature inside the reactor was maintained at approximately 65°C. The reaction was continued for an additional 3 hours with stirring, and the alcohol produced by hydrolysis was distilled under reduced pressure. The distillation was terminated when only water remained in the distillate. 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.

[0052] The produced copolymerized oligomer was diluted with a first dilution solvent, which was a mixture of methanol and ethanol in a mass ratio of 1:1, to produce an adhesive stock solution with a concentration of the adhesive component copolymerized oligomer (silane coupling agent) of 5.5 mass%. This adhesive stock solution was diluted three-fold with a second dilution solvent, ethanol, to produce adhesive liquid (A1).

[0053] [Adhesive liquid (A2)] A stock adhesive solution was produced by mixing 80 parts by mass of an adhesive stock solution with a 5.5% by mass concentration of the copolymer oligomer (silane coupling agent) used in adhesive solution (A1) and 20 parts by mass of an adhesive stock solution with a 5.5% by mass concentration of the organic titanate compound tetraisopropyl titanate (first dilution solvent: ethanol). This stock adhesive solution was diluted three times with the second dilution solvent, ethanol, to produce adhesive solution (A2).

[0054] [Adhesive liquid (A3)] An adhesive stock solution was produced by mixing 60 parts by mass of an adhesive stock solution with a 5.5% by mass concentration of the copolymer oligomer (silane coupling agent) used in adhesive solution (A1) and 40 parts by mass of an adhesive stock solution with a 5.5% by mass concentration of the organic titanate compound tetraisopropyl titanate (first dilution solvent: ethanol).This adhesive stock solution was diluted three times with the addition of ethanol as a second dilution solvent to produce 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, Ltd. (The hydrophilic functional groups of the copolymer oligomer are silanol groups and alkoxy groups, and the hydrophobic functional group is a vinyl group. Methanol is contained as the first dilution solvent. The adhesive component concentration is 5.0% by mass.) was prepared, and this adhesive was diluted three times with methanol as the second dilution solvent to produce adhesive liquid (A4).

[0056] [Adhesive liquid (A5)] A commercially available adhesive containing a copolymer oligomer type silane coupling agent was prepared: "IMB1030TF" manufactured by Lord Japan Inc. (the copolymer oligomer's hydrophilic functional groups are silanol groups and alkoxy groups, and the hydrophobic functional group is a vinyl group. It contains methanol, methyl ethyl ketone (MEK), and ethanol as the first dilution solvent. The adhesive component concentration is 3.0 mass %). This adhesive was diluted three times with methanol as the second dilution solvent to create adhesive liquid (A5).

[0057] [Water content of adhesive liquid] The moisture content of the prepared adhesive liquid was measured using a moisture measuring device "CA-310" manufactured by Nitto Seiko Analytech Co., Ltd.

[0058] [Slowly volatile solvent] Five types of slow-volatile solvents were prepared, the details of which 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 adhesive compositions produced were numbered Examples 1 to 9. For comparison, adhesive compositions prepared by directly using the adhesive liquid without adding a slowly 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 slowly volatile solvent and non-volatile components (adhesive components) when the total mass of the adhesive composition is taken as 100 mass %, as well as the evaluation results described below.

[0060] [Table 1]

[0061] [Table 2]

[0062] [Coatability evaluation] The adhesive composition was sprayed onto the surface of the substrate to a coating thickness of 1 μm, and the substrate was placed on a hot plate heated to 50°C. The time until the coating dried was measured. The dried coating was then visually inspected for chips in the coating (areas where the coating was not formed). The drying time and the presence of chips in the coating were evaluated according to the following criteria (1) and (2). The substrate was a stainless steel plate that had been cleaned with an alkaline cleaner and had a rectangular shape measuring 25 mm wide, 60 mm long, and 0.1 mm thick. (1) Drying time criteria From the viewpoint of productivity, if the drying time of the coating film was within 60 seconds, the drying property was evaluated as good (indicated by a circle in Tables 1 and 2), and if it exceeded 60 seconds, the drying property was evaluated as insufficient (indicated by a triangle in the same tables). (2) Criteria for determining whether or not the coating is chipped If the coating was formed over the entire surface, or if there were areas where the coating was not formed but the maximum length of those areas was less than 0.5 mm, it was evaluated as having no chips and no coating unevenness (indicated by a circle in Tables 1 and 2), and if there were areas where the coating was not formed but the maximum length was 0.5 mm or more, it was evaluated as having chips and coating unevenness (indicated by an x ​​in the same tables).

[0063] As shown in Table 1, none of the samples in the examples in which an adhesive composition using a slow-volatile solvent was applied exhibited coating unevenness. Of these, the sample in Example 9 used a slow-volatile solvent (ethylene glycol) with a boiling point exceeding 180°C, which resulted in a longer drying time and inferior productivity compared to the other examples. On the other hand, as shown in Table 2, all of the samples in the comparative examples in which a slow-volatile solvent was not used exhibited coating unevenness.

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

[0065] Next, a rubber composition was placed on the surface of the substrate used in the evaluation of coatability so that it overlapped 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.

[0066] [Adhesion evaluation] 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 create a gripping portion, and the gripping portion was pulled perpendicular to the substrate at a speed of 10 mm / s to peel the sealing member. The state of the peeled surface was then visually observed, and material failure (cutting of the sealing member) was evaluated as good adhesion (indicated by a circle in Tables 1 and 2), and interfacial failure was evaluated as poor adhesion (indicated by an x ​​in the same tables).

[0067] As a result, as shown in Table 1, all of the samples of the examples in which the adhesive composition using the slow-volatile solvent was applied had good adhesion. On the other hand, as shown in Table 2, all of the samples of the comparative examples in which the slow-volatile solvent was not used had poor adhesion.

[0068] [Evaluation of compression durability] A compression test was conducted on the evaluation sample to evaluate the durability of the sealing member. The compression test was conducted as follows. First, the evaluation sample was placed in a press and fixed in a state where the sealing member was compressed by 60% in the thickness direction. In this state, the temperature was raised to 100°C and maintained 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 (indicated by a circle in Tables 1 and 2), and if there were cracks, it was evaluated as having poor compression durability (indicated by an x ​​in the same tables).

[0069] As a result, as shown in Table 1, none of the samples of the example in which the adhesive composition using the slow-volatile solvent was applied showed cracks and the compression durability was good. On the other hand, as shown in Table 2, all of the samples of the comparative example in which the slow-volatile solvent was not used showed cracks and the compression durability was poor.

[0070] From the above, it was confirmed that the adhesive composition of the present disclosure is less likely to cause coating unevenness and can form an adhesive layer with excellent adhesion. [Industrial Applicability]

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

Claims

1. an adhesive liquid having an adhesive component having at least one selected from a silane coupling agent, an organic titanate compound, an aluminate-based coupling agent, and a zirconate-based coupling agent, and a dilution solvent; a slowly volatile solvent that 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; and The water content of the adhesive liquid is 0.5% by mass or more and 10% by mass or less, The adhesive composition is characterized in that the slow-volatile solvent comprises at least one selected from the group consisting of methyl isobutyl ketone, ethylene glycol, diacetone alcohol, and ethyl cellosolve.

2. an adhesive liquid having an adhesive component having at least one selected from a silane coupling agent, an organic titanate compound, an aluminate-based coupling agent, and a zirconate-based coupling agent, and a dilution solvent; a slowly volatile solvent that 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; and The slow-volatile solvent is at least one selected from the group consisting of methyl isobutyl ketone, ethylene glycol, diacetone alcohol, and ethyl cellosolve; An adhesive composition characterized in that the content of nonvolatile matter is 0.1% by mass or more and 10% by mass or less.

3. an adhesive liquid having an adhesive component having at least one selected from a silane coupling agent, an organic titanate compound, an aluminate-based coupling agent, and a zirconate-based coupling agent, and a dilution solvent; a slowly volatile solvent that 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; and The slow-volatile solvent is at least one selected from the group consisting of methyl isobutyl ketone, ethylene glycol, diacetone alcohol, and ethyl cellosolve; An adhesive composition characterized by bonding a thin plate-like substrate, which is a component of a fuel cell, to a sealing member made of a rubber composition.

Images