Adhesive composition and multilayer sheet

Abstract

The present invention provides an adhesive composition comprising an acid-modified polypropylene and an unmodified polypropylene, wherein the total content of the acid-modified polypropylene and the unmodified polypropylene is 50% by mass or more relative to the total amount of the adhesive composition and the adhesive composition has a melting point of 140°C or less, and an application of the adhesive composition. This adhesive composition is used for gaskets of fuel cells.

Description

Adhesive composition and multilayer sheet

[0001] The present disclosure relates to an adhesive composition and a multilayer sheet.

[0002] In recent years, hot-melt adhesive compositions have been used as adhesive films or sheets in chemical batteries such as lithium-ion batteries and fuel cells incorporated in notebook computers, smartphones, tablets, automobiles, etc., and physical batteries such as solar cells and capacitors (condensers).

[0003] For example, Patent Document 1 describes a laminate including at least a base material layer and adhesive layers disposed on both sides of the base material layer, and the laminate has an elongation at break retention rate of 60% or more after being left standing in water at 120°C for 300 hours, a gasket member for a solid polymer fuel cell.

[0004] International Publication No. 2022 / 172983

[0005] A fuel cell obtains electric power by electrochemically reacting hydrogen and oxygen. At this time, since water and heat, which are reaction products, are generated, the fuel cell operates under high temperature and high humidity, and the adhesive layer of the fuel cell gasket is required to have heat resistance as well as water resistance.

[0006] In addition, when adhering the adhesive layer of the fuel cell gasket to other members, it is necessary to melt the adhesive layer, and the other members are required to have durability against the temperature necessary for melting the adhesive layer. If the temperature required for melting the adhesive layer can be lowered, the requirement for heat resistance to other members is relaxed, and the range of member selection is widened.

[0007] The present disclosure has been made in view of such circumstances, and the problem to be solved by one embodiment of the present disclosure is to provide an adhesive composition and a multilayer sheet that can be adhered at a lower temperature than before and have excellent hot water adhesiveness.

[0008] This disclosure includes the following embodiments: <1> An adhesive composition for use in fuel cell gaskets, comprising a polypropylene resin including acid-modified polypropylene, wherein the polypropylene resin content is 50% by mass or more of the total amount of the adhesive composition, and the melting point is 140°C or lower. <2> The adhesive composition according to <1>, further comprising at least one selected from the group consisting of a polymer containing structural units derived from α-olefins other than polypropylene resin, low-density polyethylene, and a block copolymer containing structural units derived from styrene. <3> The adhesive composition according to <2>, wherein the polymer containing structural units derived from α-olefins other than polypropylene resin is an ethylene-α-olefin copolymer, and the content of the ethylene-α-olefin copolymer is 10% by mass to 40% by mass of the total amount of the adhesive composition. <4> The adhesive composition according to any one of <1> to <3>, wherein the melting point is 100°C to 140°C. <5> The adhesive composition according to any one of <1> to <4>, wherein the content of the acid compound grafted onto the acid-modified polypropylene is 10 ppm by mass or more of the total amount of the adhesive composition. <6> The adhesive composition according to any one of <1> to <5>, wherein the polypropylene resin content is 60% to 80% by mass relative to the total amount of the adhesive composition. <7> A multilayer sheet comprising a base layer and an adhesive layer disposed on both sides of the base layer and formed by the adhesive composition according to any one of <1> to <6>. <8> The multilayer sheet according to <7>, wherein the base layer contains a resin, and the melting point of the resin is 5°C or higher than the melting point of the adhesive composition. <9> The multilayer sheet according to <7> or <8>, wherein the thickness of the base layer is 40 μm to 350 μm, and the thickness of the adhesive layer is 10 μm to 60 μm. <10> The multilayer sheet according to any one of <7> to <9> is a fuel cell gasket.

[0009] According to one embodiment of the present disclosure, an adhesive composition and a multilayer sheet are provided that can be bonded at a lower temperature than conventional methods and have excellent hot water adhesion properties.

[0010] In this specification, a numerical range indicated using "~" means a range that includes the numbers listed before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described in this specification, the upper or lower limit stated in one numerical range may be replaced with the values ​​shown in the examples.

[0011] In this specification, the amount of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In this specification, a combination of two or more preferred embodiments is a more preferred embodiment. In this specification, the term "process" is included not only in the sense of an independent process, but also in the sense of a process that cannot be clearly distinguished from other processes, as long as the intended purpose of that process is achieved.

[0012] [Adhesive Composition] The adhesive composition of this disclosure contains a polypropylene resin including acid-modified polypropylene, wherein the polypropylene resin content is 50% by mass or more of the total amount of the adhesive composition, and the melting point is 140°C or lower.

[0013] The adhesive composition disclosed herein can be bonded at a lower temperature than conventional adhesives and has excellent hot water adhesion properties, making it suitable for use in fuel cell gaskets.

[0014] On the other hand, in the solid polymer fuel cell gasket member described in Patent Document 1, when the gasket member is bonded to the separator of the fuel cell, it is necessary to heat the gasket member to a high temperature of 170°C in order to melt the polyolefin resin.

[0015] <Polypropylene Resin> The adhesive composition of this disclosure contains a polypropylene resin, including acid-modified polypropylene. The polypropylene resin contained in the adhesive composition of this disclosure may be only one type or two or more types. In this disclosure, polypropylene resin means a polymer in which the proportion of constituent units derived from propylene is 70% by mass or more. That is, in this disclosure, the acid-modified polypropylene and unmodified polypropylene constituting the polypropylene resin may be a homopolymer consisting only of constituent units derived from propylene, or a copolymer containing constituent units derived from other monomers other than propylene in a range of more than 0% by mass and less than 30% by mass. Preferably, the polypropylene resin contains at least one type of unmodified polypropylene in addition to acid-modified polypropylene.

[0016] (Unmodified Polypropylene) In this disclosure, unmodified polypropylene means polypropylene in which no functional groups have been introduced.

[0017] When the unmodified polypropylene is a copolymer, other monomers include α-olefins such as ethylene, 1-butene, 1-pentene, 1-hexene, and 4-methyl-1-pentene; diene monomers such as butadiene, isoprene, chloroprene, and diene monomers; and aromatic vinyl compounds such as vinyl acetate, (meth)acrylic acid esters, and styrene. When the unmodified polypropylene is a copolymer, the content of constituent units derived from other monomers is preferably 20% by mass or less, and more preferably 15% by mass or less, based on the total amount of the unmodified polypropylene.

[0018] Known methods for producing unmodified polypropylene include those using polymerization catalysts. Examples of polymerization catalysts include Ziegler catalysts and metallocene catalysts. Examples of polymerization methods include slurry polymerization and gas-phase polymerization.

[0019] From the viewpoint of setting the melting point of the adhesive composition to 140°C or lower, the melting point of unmodified polypropylene is preferably 140°C or lower, and more preferably 135°C or lower. From the viewpoint of heat resistance, the melting point of unmodified polypropylene is preferably 80°C or higher, and more preferably 100°C or higher.

[0020] In this disclosure, the melting point is a value measured using a differential scanning calorimeter (DSC). Specifically, the melting point refers to the temperature at the peak of the endothermic peak that occurs when the temperature is raised to 180°C, held at 180°C for several minutes, cooled to 0°C, and then raised at a rate of 10°C per minute to 200°C. If there are multiple endothermic peaks, the peak of the endothermic peak with the highest temperature is taken as the melting point.

[0021] The weight-average molecular weight (Mw) of unmodified polypropylene is preferably 10,000 to 300,000, more preferably 30,000 to 250,000, and even more preferably 50,000 to 200,000.

[0022] In this disclosure, the weight-average molecular weight refers to the value obtained by converting the molecular weight measured by gel permeation chromatography (hereinafter also referred to as "GPC") to polystyrene equivalent. The weight-average molecular weight (Mw) in polystyrene equivalent can be obtained by performing gel permeation chromatography (GPC) measurement under the measurement conditions described below. Apparatus: HLC-8320 manufactured by Tosoh Corporation Column: TSKgel-SuperMultipore HZ-M (4.6 mm ID × 15 cm) × 3 tubes manufactured by Tosoh Corporation (for low molecular weight, exclusion limit molecular weight 2 million) Column temperature: 40°C Eluent: Tetrahydrofuran (0.35 ml / min) Detector: Differential refractometer (RI) Sample concentration: 0.1% by mass

[0023] From the viewpoint of heat resistance and film-forming properties, the content of unmodified polypropylene is preferably 40% by mass or more, and more preferably 50% by mass or more, based on the total amount of the adhesive composition.

[0024] From the viewpoint of stress relaxation during peeling, the content of unmodified polypropylene is preferably 80% by mass or less, and more preferably 70% by mass or less, relative to the total amount of the adhesive composition.

[0025] (Acid-modified polypropylene) The polypropylene resin contains at least one type of acid-modified polypropylene.

[0026] In this disclosure, acid-modified polypropylene is obtained by grafting unmodified polypropylene with an acid compound.

[0027] When the unmodified polypropylene before acid modification is a copolymer, other monomers include α-olefins such as ethylene, 1-butene, 1-pentene, 1-hexene, and 4-methyl-1-pentene; diene monomers such as butadiene, isoprene, chloroprene, and diene monomers; and aromatic vinyl compounds such as vinyl acetate, (meth)acrylic acid esters, and styrene.

[0028] When the unmodified polypropylene before acid modification is a copolymer, the content of constituent units derived from other monomers is preferably 30% by mass or less, and more preferably 15% by mass or less, relative to the total amount of the unmodified polypropylene.

[0029] Examples of acid compounds used to obtain acid-modified polypropylene from unmodified polypropylene include unsaturated carboxylic acids and unsaturated carboxylic acid anhydrides.

[0030] Unsaturated carboxylic acids are compounds that have an ethylenic double bond and a carboxyl group within the same molecule, and include unsaturated monocarboxylic acids and unsaturated dicarboxylic acids. The acid compound may be used alone or in combination of two or more.

[0031] Examples of unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, crotonic acid, and isocrotonic acid.

[0032] Examples of unsaturated dicarboxylic acids include maleic acid, fumaric acid, itaconic acid, citraconic acid, nadic acid, and endic acid.

[0033] Unsaturated carboxylic acid anhydrides are compounds that have an ethylenic double bond and a carboxylic acid anhydride group within the same molecule, and examples include acid anhydrides of the unsaturated dicarboxylic acids mentioned above.

[0034] Examples of unsaturated dicarboxylic acid acid anhydrides include maleic anhydride, fumaric anhydride, itaconic anhydride, citraconic anhydride, nadic anhydride, and endicic anhydride.

[0035] In particular, due to its high modification effect, the acid compound is preferably maleic acid or maleic anhydride, and more preferably maleic anhydride. That is, the acid-modified polypropylene is preferably maleic acid-modified polypropylene or maleic anhydride-modified polypropylene, and more preferably maleic anhydride-modified polypropylene.

[0036] Known methods can be used for graft modification. For example, one method involves grafting an acid compound with polypropylene in a molten or solution state in the presence of a radical polymerization initiator such as an organic peroxide or an aliphatic azo compound.

[0037] The preferred temperature for the graft reaction is 80°C to 160°C when the reaction is carried out in solution, and 150°C to 300°C when the reaction is carried out in molten state. In both the solution and molten states, the reaction rate is high above the lower limit of the above reaction temperature range, and the decrease in molecular weight can be suppressed below the upper limit of the above reaction temperature range, thereby maintaining the mechanical strength of the resulting acid-modified polypropylene.

[0038] The radical polymerization initiator can be appropriately selected from commercially available organic peroxides, taking into consideration the reaction temperature and other factors.

[0039] If some of the acid compounds used for graft modification remain unreacted, it is preferable to remove the unreacted acid compounds by known methods such as reduced-pressure distillation, from the viewpoint of suppressing a decrease in adhesive strength.

[0040] The content of the acid compound grafted to the acid-modified polypropylene is preferably 10 ppm by mass or more based on the total amount of the adhesive composition. When the content of the acid compound is 10 ppm by mass or more, high adhesiveness is imparted.

[0041] From the above viewpoints, the content of the acid compound is more preferably 100 ppm by mass or more, and even more preferably 300 ppm by mass or more. Also, from the viewpoint of durability by maintaining the molecular weight of the polypropylene resin, the content of the acid compound is preferably 1% by mass or less, and more preferably 800 ppm by mass or less.

[0042] In the present disclosure, the content of the acid compound with respect to the total amount of the adhesive composition is calculated based on the acid modification degree shown below.

[0043] The acid modification degree is calculated based on the following formula. Acid modification degree (mass %) = acid value × M × 100 / (1000 × 56.1 × V) In the formula, M and V are defined by the following formula. M = (molecular weight of the acid compound) + (number of unsaturated groups in the acid compound) × 1.008 V = valence of the acid group (when including an acid anhydride group, it is the valence of the acid group when the acid anhydride group is completely hydrolyzed) The acid value indicates the number of milligrams of potassium hydroxide required to neutralize the acid contained in 1 g of the sample, and is measured according to JIS K 0070:1992.

[0044] From the viewpoint of setting the melting point of the adhesive composition to 140°C or lower, the melting point of the acid-modified polypropylene is preferably 140°C or lower, and more preferably 135°C or lower. The melting point of the acid-modified polypropylene is preferably 80°C or higher, and more preferably 100°C or higher, from the viewpoint of heat-resistant water adhesiveness.

[0045] The weight average molecular weight (Mw) of the acid-modified polypropylene is preferably from 10,000 to 300,000, more preferably from 30,000 to 250,000, and even more preferably from 50,000 to 200,000.

[0046] The content of the acid-modified polypropylene is preferably 0.1% by mass or more, more preferably 1% by mass or more, based on the total amount of the adhesive composition. The content of the acid-modified polypropylene is preferably 20% by mass or less, more preferably 10% by mass or less, based on the total amount of the adhesive composition. The content of the acid-modified polypropylene can be adjusted according to its degree of acid modification. For example, in the case of an acid-modified polypropylene with a low degree of acid modification, it may be 10% by mass or more, or may be 40% by mass or more, based on the total amount of the adhesive composition. Depending on the acid-modified polypropylene, all of the polypropylene resin may be the acid-modified polypropylene. For example, in the case of an acid-modified polypropylene with a low degree of acid modification, it may be 80% by mass or less, based on the total amount of the adhesive composition.

[0047] From the viewpoint of durability by maintaining the molecular weight, the mass ratio of the content of the unmodified polypropylene to the content of the acid-modified polypropylene (mass of acid-modified polypropylene / mass of unmodified polypropylene) is preferably 1 / 99 to 50 / 50, more preferably 2 / 98 to 10 / 90.

[0048] From the viewpoint of hot water-resistant adhesiveness, the content of the polypropylene resin is 50% by mass or more, preferably 60% to 80% by mass, based on the total amount of the adhesive composition.

[0049] <Other components> The adhesive composition of the present disclosure may contain other components other than the acid-modified polypropylene and the unmodified polypropylene.

[0050] The adhesive composition of this disclosure preferably further comprises at least one selected from the group consisting of polymers containing structural units derived from α-olefins other than polypropylene resin, low-density polyethylene, and block copolymers containing structural units derived from styrene. From the viewpoint of hot water adhesion, the total amount of polymers containing structural units derived from α-olefins other than polypropylene resin, low-density polyethylene, and block copolymers containing structural units derived from styrene is preferably 10% to 50% by mass, and more preferably 15% to 40% by mass, based on the total amount of the adhesive composition. The inclusion of these components further in the adhesive composition of this disclosure improves the hot water adhesion.

[0051] A polymer containing structural units derived from α-olefins may be a homopolymer or a copolymer. Furthermore, if the polymer containing structural units derived from α-olefins is a copolymer, it may be a random copolymer or a block copolymer.

[0052] Examples of α-olefins include ethylene, propylene, 1-butene, 1-octene, and 4-methyl-1-pentene.

[0053] In particular, polymers containing structural units derived from α-olefins are preferably ethylene-α-olefin copolymers. An ethylene-α-olefin copolymer is a copolymer containing structural units derived from ethylene and structural units derived from α-olefins other than ethylene.

[0054] In particular, from the viewpoint of hot water adhesion, the ethylene-α-olefin copolymer is preferably an ethylene-propylene copolymer. When the ethylene-α-olefin copolymer has constituent units derived from propylene, the content of constituent units derived from propylene is less than 40% by mass of the total mass of the ethylene-α-olefin copolymer, and it is distinguished from the unmodified polypropylene described above.

[0055] In the ethylene-α-olefin copolymer, the content of constituent units derived from ethylene is preferably 60% to 95% by mass, and more preferably 75% to 90% by mass, based on the total mass of the ethylene-α-olefin copolymer.

[0056] In the ethylene-α-olefin copolymer, the content of constituent units derived from α-olefin is preferably 5% to 40% by mass, and more preferably 10% to 25% by mass, based on the total mass of the ethylene-α-olefin copolymer.

[0057] The ethylene-α-olefin copolymer may be a commercially available product. Examples of ethylene-propylene random copolymers include Tuffmer P-0275, P-0375, P-0180, P-0280, P-0480, and P-0680 (manufactured by Mitsui Chemicals, Inc.). Examples of ethylene-1-butene random copolymers include Tuffmer A4070S and A1050S (manufactured by Mitsui Chemicals, Inc.).

[0058] Low-density polyethylene has a density of 910 kg / m³ according to JIS K 6922-1. ３ More than 930kg / m ３ It means less than polyethylene.

[0059] Examples of block copolymers containing styrene-derived structural units include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), polystyrene-poly(ethylene-propylene) diblock copolymer (SEP), polystyrene-poly(ethylene-propylene)-polystyrene triblock copolymer (SEPS), styrene-ethylene-butylene-styrene block copolymer (SEBS), polystyrene-poly(ethylene / ethylene-propylene)-polystyrene triblock copolymer (SEEPS), styrene-isobutylene-styrene block copolymer (SIBS), and their hydrogenated products.

[0060] In particular, the block copolymer containing styrene-derived structural units is preferably SEPS.

[0061] From the viewpoint of improving hot water adhesion, the adhesive composition of this disclosure preferably contains an ethylene-α-olefin copolymer. In this case, the content of the ethylene-α-olefin copolymer is preferably 10% to 40% by mass, and more preferably 15% to 25% by mass, based on the total amount of the adhesive composition.

[0062] Furthermore, from the viewpoint of further improving hot water adhesion, the adhesive composition of this disclosure preferably further contains an ethylene-α-olefin copolymer and low-density polyethylene. In this case, the content of the ethylene-α-olefin copolymer is preferably 10% to 40% by mass, and more preferably 15% to 25% by mass, based on the total amount of the adhesive composition. The content of the low-density polyethylene is preferably 5% to 40% by mass, and more preferably 10% to 30% by mass, based on the total amount of the adhesive composition. The total content of the ethylene-α-olefin copolymer and low-density polyethylene is preferably 10% to 50% by mass, and more preferably 15% to 40% by mass, based on the total amount of the adhesive composition.

[0063] Furthermore, from the viewpoint of further improving hot water adhesion, the adhesive composition of this disclosure preferably further comprises an ethylene-α-olefin copolymer, low-density polyethylene, and a block copolymer containing structural units derived from styrene. In this case, the content of the ethylene-α-olefin copolymer is preferably 10% to 40% by mass, and more preferably 15% to 25% by mass, based on the total amount of the adhesive composition. The content of the low-density polyethylene is preferably 5% to 40% by mass, and more preferably 10% to 30% by mass, based on the total amount of the adhesive composition. The content of the block copolymer containing structural units derived from styrene is preferably 0.1% to 20% by mass, and more preferably 1% to 5% by mass, based on the total amount of the adhesive composition.

[0064] The adhesive compositions of this disclosure may further contain additives selected from the group consisting of antioxidants, ultraviolet absorbers, fillers, reinforcing fibers, mold release agents, processing aids, flame retardants, plasticizers, nucleating agents, antistatic agents, pigments, dyes, foaming agents, and combinations thereof.

[0065] The adhesive composition of this disclosure has a melting point of 140°C or lower. Because the adhesive composition has a melting point of 140°C or lower, an adhesive layer can be formed using the adhesive composition, allowing it to bond to other components at a lower temperature than conventional methods. This reduces the heat resistance requirements for other components and broadens the range of component selection.

[0066] From the viewpoint of achieving both sealing properties and heat resistance, the melting point of the adhesive composition is preferably 100°C to 140°C, and more preferably 120°C to 140°C.

[0067] [Multilayer Sheet] The multilayer sheet of this disclosure comprises a base layer and an adhesive layer disposed on at least one side of the base layer, preferably on both sides, and formed by the adhesive composition of this disclosure. Thermoplastic adhesive gaskets require rigidity and dimensional stability at high temperatures, such as during thermocompression bonding and use, from the viewpoint of preventing gas leakage and improving fluidity. The above functions can be provided by using a multilayer sheet in the gasket in which the base layer is made of a resin having high heat resistance, high rigidity, low coefficient of thermal expansion, and low thermal shrinkage. Furthermore, the rigidity of the base layer can also be used to improve the handling properties of the multilayer sheet.

[0068] <Base Layer> The base layer is preferably a layer containing resin.

[0069] From the viewpoint of hot water adhesion, the substrate layer preferably contains polyolefins such as propylene homopolymer, block polypropylene copolymer, and polymethylpentene; polyethylene naphthalate, polyphenylene sulfide, polyphenylene sulfone, polycarbonate, polyetherimide, polyimide, polyamide, polystyrene, triacetylcellulose, and polyvinyl chloride; more preferably contains at least one resin selected from the group consisting of polyolefins, polyethylene naphthalate, polyphenylene sulfide, polyphenylene sulfone, polycarbonate, polyetherimide, polyimide, and polyamide; and even more preferably consists of at least one resin selected from the group consisting of polyolefins, polycarbonate, and polyamide.

[0070] From the viewpoint of hot water adhesion, it is preferable that the melting point of the resin contained in the substrate layer is 5°C or more higher than the melting point of the adhesive composition.

[0071] The difference between the melting point of the resin contained in the base layer and the melting point of the adhesive composition is preferably 5°C or higher, and more preferably 10°C or higher. A melting point difference of 5°C to 10°C or higher prevents the base layer from melting during heat bonding, allowing it to maintain its sheet shape. On the other hand, the difference between the melting point of the resin contained in the base layer and the melting point of the adhesive composition is preferably 100°C or lower, and may be 50°C or lower.

[0072] The multilayer sheet of this disclosure contains an adhesive layer formed by the adhesive composition of this disclosure, and since the melting point of the adhesive composition is 140°C or lower, it can be bonded to other components at a lower temperature than conventional methods. Therefore, the base layer of the multilayer sheet of this disclosure can use a resin with a lower melting point than the resin conventionally used in the base layer of multilayer sheets.

[0073] The melting point of the resin contained in the base layer is preferably 100°C to 300°C, more preferably 140°C to 250°C, and may be 170°C or lower, as this allows the adhesive composition of this disclosure to bond at a lower temperature than conventional adhesives. The content of the resin with a melting point of 100°C to 300°C is preferably 50% by mass or more, more preferably 80% by mass or more, and may be 100% by mass, based on the total amount of resin contained in the base layer.

[0074] The base layer may contain inorganic fillers such as talc, silica, calcium carbonate, sepiolite, boehmite, bentonite, montmorillonite, mica, titanium oxide, zinc oxide, glass beads, and metal fibers such as aluminum, nickel, and copper, for the purpose of increasing the rigidity of the multilayer sheet of this disclosure. The inorganic filler content is preferably 5% to 50% by mass, and more preferably 15% to 30% by mass, based on the total mass of the base layer.

[0075] Polyolefins are inexpensive and offer excellent durability even in the operating environment of fuel cells. By combining polyolefins with the inorganic fillers mentioned above, the rigidity and heat resistance of the polyolefins can be improved, resulting in particularly good fuel cell gaskets.

[0076] The heat resistance can be further improved by using block polypropylene copolymer as the polyolefin. The block polypropylene copolymer is preferably an ethylene-propylene copolymer resin. Specifically, the block polypropylene copolymer may be a resin having a sea-island structure in which polyethylene and / or ethylene-propylene rubber are dispersed in homopolypropylene, with homopolypropylene as the sea portion (continuous phase) and polyethylene and / or ethylene-propylene rubber as the island portion (dispersed phase). In particular, the block polypropylene copolymer is preferably a resin having a homopolypropylene (crystalline polypropylene) homopolymer portion obtained by the homopolymerization of propylene and an ethylene-propylene-random copolymer portion.

[0077] The base layer may further contain additives selected from the group consisting of antioxidants, ultraviolet absorbers, fillers, reinforcing fibers, mold release agents, processing aids, flame retardants, plasticizers, nucleating agents, antistatic agents, pigments, dyes, foaming agents, and combinations thereof.

[0078] The thickness of the substrate layer is preferably 40 μm to 350 μm, and more preferably 100 μm to 200 μm.

[0079] In this disclosure, the thickness of each layer constituting the multilayer sheet is the arithmetic mean of the thicknesses at three locations obtained by preparing a section having a cross-section perpendicular to the main surface of the multilayer sheet and measuring it using a digital microscope VHX-8000 (manufactured by Keyence Corporation).

[0080] The coefficient of linear expansion of the multilayer sheet in the MD direction or TD direction is preferably 200 ppm / K or less, more preferably 180 ppm / K or less, and particularly preferably 170 ppm / K or less.

[0081] <Adhesive Layer> In the multilayer sheet of the present disclosure, the adhesive layer is disposed on at least one side of the substrate layer, preferably on both sides. The adhesive layer is a layer formed by the adhesive composition of the present disclosure.

[0082] The thickness of the adhesive layer is preferably 10 μm to 60 μm, and more preferably 15 μm to 50 μm.

[0083] <Method for manufacturing a multilayer sheet> The multilayer sheet of this disclosure can be obtained, for example, by pelletizing an adhesive composition for forming an adhesive layer and a base layer composition for forming a base layer, and then forming each pellet into a sheet using a co-extrusion multilayer film manufacturing machine.

[0084] The adhesive composition and the base layer composition can be pelletized by melt-kneading them in an extruder or the like, cooling the strands extruded from the extruder, and cutting them into pellets.

[0085] In the melt kneading of the base layer composition, the temperature is preferably 150°C to 320°C, more preferably 180°C to 300°C. The time is usually 0.5 minutes to 20 minutes, preferably 1 minute to 15 minutes.

[0086] In the melt kneading of the adhesive composition, the temperature is preferably 150°C to 270°C, more preferably 170°C to 250°C. The time is usually 0.5 minutes to 20 minutes, preferably 1 minute to 15 minutes.

[0087] The multilayer sheet of this disclosure is preferably a gasket for a fuel cell.

[0088] Fuel cell gaskets can be bonded to adherends made of various materials such as metal, glass, ceramics, and plastic. This allows for the creation of a joint including the fuel cell gasket and the adherend.

[0089] The metal used as the adherend may be a commonly known metal sheet, metal plate, or metal foil, and can be iron, copper, aluminum, lead, zinc, titanium, chromium, stainless steel, etc. Among these, iron, aluminum, titanium, or stainless steel are particularly preferred.

[0090] Various thermoplastic or thermosetting resins can be used as the adherend. Composite materials may also be used, which are resins compounded with inorganic materials such as glass or ceramics, or with fillers or fibers such as metal or carbon.

[0091] The multilayer sheet of this disclosure is suitably used as a gasket placed between the electrolyte membrane and the separator of a fuel cell. For example, in the multilayer sheet of this disclosure having adhesive layers on both sides, one adhesive layer is placed on the electrolyte membrane side and the other adhesive layer is placed on the separator side.

[0092] The present disclosure will be explained in more detail below with reference to examples and comparative examples, but this disclosure is not limited thereto.

[0093] [Preparation of Adhesive Compositions] The components listed in Tables 1 and 2 were mixed in the amounts (parts by mass) listed in Tables 1 and 2, and melt-kneaded using a twin-screw extruder. The extruded material was cooled and cut to obtain pellet-shaped adhesive compositions 1 to 15 and 1A to 3A.

[0094] The melting point of an adhesive composition depends on the melting point of the component with the highest melting point among the components constituting the adhesive composition. In Tables 1 and 2, the melting points of adhesive compositions 1 to 15 and 1A are listed as the melting points of the component with the highest melting point among the components constituting each adhesive composition. The melting points of adhesive compositions 2A and 3A are measured values.

[0095] The details of each component listed in Table 1 are as follows:

[0096] (Unmodified Polypropylene (Unmodified PP)) • Polymer A1: Product name "Wintec WFW4M", manufactured by Nippon Polypropylene Co., Ltd., melting point 135°C • Polymer A2: Product name "Wintec WFX6", manufactured by Nippon Polypropylene Co., Ltd., melting point 125°C • Polymer A3: Product name "Novatec PP BC3HF", manufactured by Nippon Polypropylene Co., Ltd., melting point 160°C

[0097] (Acid-modified polypropylene (acid-modified PP)) ・Polymer B1: Product name "Hardlen PMA-F2", manufactured by Toyobo MC Co., Ltd., melting point 125°C ・Polymer B2: Produced by grafting maleic anhydride onto polymer A1, melting point 135°C ・Polymer B3: Product name "Lyosen M1070", manufactured by Toyochem Co., Ltd., melting point 155°C

[0098] (Ethylene-α-olefin copolymer) Product name: "Tafmer P-0280S", manufactured by Mitsui Chemicals, Inc., melting point: 50°C

[0099] (Low-density polyethylene (LDPE)) • Product name: Novatec LD LC522, manufactured by Nippon Polypropylene Co., Ltd., melting point: 111°C

[0100] (Polystyrene-poly(ethylene-propylene)-polystyrene triblock copolymer (SEPS); a block copolymer containing styrene-derived structural units) • Product name: "Septon 2002", manufactured by Kuraray Co., Ltd., melting point: 100°C

[0101] The content of the acid compound grafted onto the acid-modified polypropylene relative to the total amount of the adhesive composition was calculated based on the degree of acid modification shown below. Degree of acid modification (mass ppm) = Acid value × M × 100 / (1000 × 56.1 × V) In the formula, M and V are defined by the following equations: M = (Molecular weight of the acid compound) + (Number of unsaturated groups in the acid compound) × 1.008 V = Valence of the acid group (However, if an acid anhydride group is included, it is the valence of the acid group when the acid anhydride group is completely hydrolyzed) The acid value indicates the number of milligrams of potassium hydroxide required to neutralize the acid contained in 1 g of the sample, and was measured in accordance with JIS K 0070:1992.

[0102] [Preparation of the composition for the base layer] The following resin and inorganic filler were prepared as the composition for the base layer.

[0103] - Propylene homopolymer (PP-1): Product name "Sun Allomer PC600A", manufactured by Sun Allomer Co., Ltd., melting point 166°C - Block polypropylene copolymer (PP-2): Product name "Novatec PP BC6CB", manufactured by Nippon Polypropylene Co., Ltd., melting point 160°C - Polyamide (PA): Product name "Grilamid L25", manufactured by M-Scheme Japan Co., Ltd., melting point 178°C - Ethylene-α-olefin copolymer (PO): Product name "ENGAGE 8200", manufactured by Dow, melting point 59°C - Talc: Product name "Micro Ace RA-3", manufactured by Nippon Talc Co., Ltd., average particle size 5 μm

[0104] [Preparation of single-layer sheets] In Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-3, adhesive compositions 1-15 and 1A-3A were melted in a single-layer film forming machine to obtain single-layer sheets with a thickness of 100 μm.

[0105] [Preparation of Multilayer Sheets] In Examples 2-1 to 2-8, the adhesive compositions and substrate layer compositions described in Table 3 were melted in a co-extrusion multilayer film manufacturing machine to obtain multilayer sheets consisting of an adhesive layer / substrate layer / adhesive layer. The thickness of each adhesive layer was 30 μm, and the thickness of the substrate layer was 120 μm. Adhesive composition 2, adhesive composition 4, and adhesive composition 7 are the adhesive compositions prepared in Examples 1-2, 1-4, and 1-7, respectively.

[0106] In Examples 3-1 to 3-7, the adhesive composition and the substrate layer composition were used to melt the materials in a co-extrusion multilayer film manufacturing machine so that the thickness of each adhesive layer and the thickness of the substrate layer were as shown in Table 4, thereby obtaining a multilayer sheet consisting of an adhesive layer / substrate layer / adhesive layer. Adhesive composition 2 was used as the adhesive composition, and PA was used as the substrate layer composition.

[0107] The single-layer and multi-layer sheets obtained were used to evaluate their adhesion at 135°C and their resistance to hot water adhesion. In addition, the coefficient of linear thermal expansion was measured for the multi-layer sheets of Examples 3-1 to 3-7.

[0108] <Adhesion at 135°C> A SUS304 plate with a thickness of 0.1 mm was used as the adherend. A single-layer or multi-layer sheet was sandwiched between two SUS304 plates and heat-pressed using a precision press (temperature: 135°C, time: 60 seconds, pressure: 0.3 MPa) to create a bonded body. This bonded body was cut into strips with a width of 10 mm to make test pieces. The bonded portion of the test piece was 10 mm wide and 10 mm long. An IMADA Corporation MX2-1000N measuring stand was fitted with an IMADA Corporation IMADA Corporation load cell eDPU-50N, and a hot water bath with a hook attached to the bottom was filled with 95°C hot water. The above test pieces were immersed for 1 minute for isothermal treatment. During isothermal treatment, it was visually observed whether or not delamination occurred. The evaluation criteria are as follows: In case A, it can be said that the adhesion is excellent in heat-pressure bonding at 135°C. A: No delamination occurred. B: It peeled off.

[0109] <Hot Water Adhesion Resistance> The test specimen was immersed for 1 minute and subjected to isothermal treatment, similar to the method described in "Adhesion at 135°C" above. The SUS304 plate was peeled off at a tensile speed of 30 mm / min from the isothermal state, and the peeling force in the stable region was defined as the peel strength. This result was defined as the hot water peel strength (N / mm). A higher hot water peel strength indicates superior hot water adhesion resistance.

[0110] <Linear Expansion Coefficient> Using a thermomechanical device (TMA: Q400) manufactured by TA Instruments, a multilayer sheet cut to a width of 5 mm was set and heated to 100°C under conditions of a load of 0.05 N and a heating rate of 5°C / min. After holding for several minutes, it was cooled to 20°C. The linear expansion coefficient was calculated by dividing the slope of the sample length change from 80°C to 30°C during the cooling process by the original sample length. The linear expansion coefficient was calculated in both the MD and TD directions.

[0111]

[0112]

[0113]

[0114]

[0115] As shown in Tables 1 and 2, it was found that Examples 1-1 to 1-15 could be bonded at a relatively low temperature of 135°C and exhibited excellent resistance to hot water adhesion.

[0116] On the other hand, in Comparative Example 1-1, acid-modified polypropylene was not included, and it was found to have poor adhesion at 135°C. In Comparative Example 1-2, the melting point of the adhesive composition was above 140°C, and it was found to have poor hot water adhesion. In Comparative Example 1-3, the melting point of the adhesive composition was above 140°C, and it was found to have poor adhesion at 135°C and poor hot water adhesion.

[0117] As shown in Table 3, the multilayer sheets in Examples 2-1 to 2-5 were found to have excellent adhesion at 135°C, similar to the single-layer sheets. Furthermore, the multilayer sheets in Examples 2-6 to 2-8 were found to have excellent adhesion at 135°C, similar to the single-layer sheets, even when the substrate layer contained inorganic fillers or elastomer components.

[0118] As shown in Table 4, it was found that the coefficient of thermal expansion can be reduced by controlling the thickness of the adhesive layer and the substrate layer. Furthermore, as shown in Example 3-3, it was found that even when the thickness of the adhesive layer is as thin as 10 μm, it exhibits excellent hot water adhesion.

[0119] The adhesive compositions and multilayer sheets of this disclosure are useful for bonding and sealing metals and other materials, and can be suitably used in applications where the bonded structure may be in continuous or intermittent contact with moisture, such as fuel cells. In particular, because they can seal at relatively low temperatures, they are useful as components of batteries, contributing to a reduction in the number of battery components and costs, and a significant improvement in productivity.

[0120] Furthermore, the disclosure of Japanese Patent Application No. 2024-226619, filed on December 23, 2024, is incorporated herein by reference in its entirety. In addition, all documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated as being incorporated by reference.

Claims

1. An adhesive composition for use in fuel cell gaskets, comprising a polypropylene resin including acid-modified polypropylene, wherein the content of the polypropylene resin is 50% by mass or more of the total amount of the adhesive composition, and the melting point is 140°C or lower.

2. The adhesive composition according to claim 1, further comprising at least one selected from the group consisting of a polymer containing structural units derived from α-olefins other than the polypropylene resin, low-density polyethylene, and a block copolymer containing structural units derived from styrene.

3. The adhesive composition according to claim 2, wherein the polymer containing structural units derived from α-olefins other than the polypropylene resin is an ethylene-α-olefin copolymer, and the content of the ethylene-α-olefin copolymer is 10% by mass to 40% by mass with respect to the total amount of the adhesive composition.

4. The adhesive composition according to claim 1, wherein the melting point is 100°C to 140°C.

5. The adhesive composition according to claim 1, wherein the content of the acid compound grafted onto the acid-modified polypropylene is 10 ppm by mass or more, relative to the total amount of the adhesive composition.

6. The adhesive composition according to claim 1, wherein the content of the polypropylene resin is 60% by mass to 80% by mass based on the total amount of the adhesive composition.

7. A multilayer sheet comprising a base layer and an adhesive layer disposed on both sides of the base layer and formed by the adhesive composition described in any one of claims 1 to 6.

8. The multilayer sheet according to claim 7, wherein the base layer contains a resin, and the melting point of the resin is 5°C or higher than the melting point of the adhesive composition.

9. The multilayer sheet according to claim 7, wherein the thickness of the substrate layer is 40 μm to 350 μm, and the thickness of the adhesive layer is 10 μm to 60 μm.

10. A multilayer sheet according to claim 7, which is a gasket for a fuel cell.

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