Hot melt adhesive and preparation method therefor, and fuel cell membrane electrode

Abstract

The present application relates to the technical field of adhesives, and in particular to a hot melt adhesive and a preparation method therefor, and a fuel cell membrane electrode. The hot melt adhesive comprises a first adhesive layer and a second adhesive layer. The first adhesive layer comprises a polyester resin, a styrenic thermoplastic elastomer, a graft-type toughening agent, an epoxy chain extender, and a first organic solvent. The second adhesive layer comprises an ethylene-methyl acrylate copolymer, a copolyester hot melt adhesive, an ethylene-methyl acrylate-glycidyl methacrylate terpolymer, an epoxy ring-opening accelerator, and a second organic solvent. The hot melt adhesive of the present application has a two-layer structure and can achieve good bonding to PEN and PFSA. After being immersed in an aqueous sulfuric acid solution at 95°C and pH=2 for 2,000 h or more, the hot melt adhesive does not foam or crack, can maintain good bonding performance, and forms a membrane free of crystal spots.

Description

Hot melt adhesive and its preparation method and fuel cell membrane electrode Technical Field

[0001] This application relates to the field of adhesive technology, and in particular to a hot melt adhesive, a method for preparing the same, and a membrane electrode assembly for a fuel cell. Background Technology

[0002] The membrane electrode assembly (MEA) is the site of multiphase mass transport and electrochemical reactions in a fuel cell, determining its overall performance, durability, production efficiency, and cost control. It is primarily fabricated as an integrated unit comprising a catalyst, a proton exchange membrane (PEM), a gas diffusion layer, and a frame. The PEM is a core component of the MEA assembly, possessing extremely high proton conductivity, good chemical stability, and strong hydrophilicity. It also provides support for the catalyst coating. Currently, perfluorosulfonic acid (PFSA) proton exchange membranes are widely used due to their excellent thermal and chemical stability, high mechanical strength, and high degree of industrialization.

[0003] To prevent gas leakage, improve the stability and durability of fuel cells, optimize performance, and prevent chemical corrosion, the encapsulation of the fuel cell membrane electrode assembly (MEA) is crucial. In the MEA structure, the frame membrane plays the following roles: supporting the MEA, maintaining its rigidity, encapsulating, and sealing. Materials that can be used for the frame membrane include polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), polyetherimide (PEI), polyimide (PI), polypropylene (PP), and polyethylene terephthalate (PET), among others. PEN is the most commonly used due to its high durability, high heat resistance, and cost-effectiveness. To achieve good encapsulation of the fuel cell MEA, the frame membrane and the proton exchange membrane (PFSA) must be bonded together, i.e., the PEN and PFSA must be bonded.

[0004] Currently, most adhesives used to bond PEN and PFSA are acrylic adhesives. For example, the acrylic adhesives disclosed in Chinese patent applications CN115181533A and CN116525871A exhibit good adhesion to PEN and PFSA. However, their large-scale use is limited by issues such as monomer residue, toxicity, cost, heat resistance, and weather resistance. Chinese patent application CN116814183A describes a hydrolysis-resistant hot melt adhesive layer prepared by uniformly mixing polyester resin, epoxy resin, organic solvent, anti-hydrolysis agent, leveling agent, and crosslinking agent. This layer shows good adhesion to PEN and PFSA and excellent hydrolysis resistance. However, this preparation method is difficult to control the reaction rate, resulting in numerous crystal points during film formation, making it unsuitable for practical applications in membrane electrode processes. Furthermore, this adhesive is brittle, and the brittle adhesive is prone to cracking or detachment under external force, severely affecting its performance.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] The purpose of this application is to provide a hot melt adhesive, its preparation method, and a fuel cell membrane electrode. The hot melt adhesive of this application can achieve good adhesion to PEN and PFSA. It does not bubble or crack after being soaked in sulfuric acid aqueous solution at 95°C and pH=2 for more than 2000 hours, and can maintain good adhesion performance. Moreover, the film formed is free of crystal points.

[0008] To achieve the above objectives, the first aspect of this application provides a hot melt adhesive, including a first adhesive layer and a second adhesive layer stacked together;

[0009] The first adhesive layer comprises the following components by weight: 50-80 parts polyester resin, 10-40 parts styrene-based thermoplastic elastomer, 5-20 parts grafted toughening agent, 0.1-1.5 parts epoxy chain extender, and 100-200 parts first organic solvent; the polyester resin has a melt index of ≥30 g / 10 min at 160℃ / 2.16 kg.

[0010] The second adhesive layer comprises, by weight, the following components: 40-60 parts of ethylene-methyl acrylate copolymer, 20-40 parts of copolyester hot melt adhesive, 10-30 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 0.1-2 parts of epoxy ring-opening accelerator, and 100-200 parts of a second organic solvent; wherein the content of GMA in the ethylene-methyl acrylate-glycidyl methacrylate terpolymer is 3wt%-6wt%.

[0011] In specific embodiments of this application, the styrene-based thermoplastic elastomer includes at least one of styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, and hydrogenated styrene-isoprene-styrene block copolymer.

[0012] In a specific embodiment of this application, the grafting unit of the grafted toughening agent is maleic anhydride and / or glycidyl methacrylate. Further, the grafted toughening agent is at least one of SEBS grafted with maleic anhydride and / or glycidyl methacrylate.

[0013] In a specific embodiment of this application, the grafting rate of the grafted toughening agent is ≥0.5%.

[0014] In a specific embodiment of this application, the epoxy equivalent in the epoxy chain extender is 200-600 g / mol.

[0015] In a specific embodiment of this application, the first organic solvent includes butanone and ethyl acetate. Further, the mass ratio of butanone to ethyl acetate in the first organic solvent is (1-3):1.

[0016] In a specific embodiment of this application, the methyl acrylate content in the ethylene-methyl acrylate copolymer is ≥20wt%.

[0017] In a specific embodiment of this application, the melting point of the copolyester hot melt adhesive is ≥110℃.

[0018] In specific embodiments of this application, the epoxy ring-opening accelerator includes at least one of 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, and 1-benzyl-2-methylimidazole.

[0019] In a specific embodiment of this application, the second organic solvent includes ethyl acetate and acetone. Further, the mass ratio of ethyl acetate to acetone in the second solvent is (1-5):1.

[0020] In a specific embodiment of this application, the thickness of the hot melt adhesive is 10–25 μm. Further, the thicknesses of both the first adhesive layer and the second adhesive layer are ≥5 μm.

[0021] The second aspect of this application provides a method for preparing the hot melt adhesive of the first aspect of this application, comprising the following steps:

[0022] (a) Mix all components of the first adhesive layer evenly, apply and dry to obtain the first adhesive layer;

[0023] (b) Mix the components of the second adhesive layer evenly, apply the mixture to the surface of the first adhesive layer, and dry it to obtain a hot melt adhesive.

[0024] A third aspect of this application provides a fuel cell membrane electrode, including the hot melt adhesive of the first aspect of this application.

[0025] Compared with the prior art, the beneficial effects of this application are as follows:

[0026] (1) The hot melt adhesive of this application has a two-layer structure. The first adhesive layer can be used to connect PEN and the second adhesive layer can be used to connect PFSA, so that PEN and PFSA can be connected by the hot melt adhesive of this application. The hot melt adhesive has a strong adhesive effect on PEN, PFSA and the two adhesive layers of the hot melt adhesive. It does not bubble or crack after being soaked in sulfuric acid aqueous solution at 95°C and pH=2 for more than 2000 hours, and still maintains good adhesive performance.

[0027] (2) The hot melt adhesive preparation process of this application is simple, the coating film has no crystal points, and it can be continuously produced, which can be applied to the field of fuel cell membrane electrode packaging.

[0028] After reading and understanding the detailed description, other aspects can be understood. Detailed Implementation

[0029] The technical solution of this application will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of this application, not all embodiments, and are only used to illustrate this application, and should not be regarded as limiting the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0030] The hot melt adhesive provided in this application includes a first adhesive layer and a second adhesive layer that are stacked together;

[0031] The first adhesive layer comprises the following components by weight: 50-80 parts polyester resin, 10-40 parts styrene-based thermoplastic elastomer, 5-20 parts grafted toughening agent, 0.1-1.5 parts epoxy chain extender, and 100-200 parts first organic solvent; the melt index of the polyester resin at 160℃ / 2.16kg is ≥30g / 10min;

[0032] The second adhesive layer comprises the following components by weight: 40-60 parts of ethylene-methyl acrylate copolymer, 20-40 parts of copolyester hot melt adhesive, 10-30 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 0.1-2 parts of epoxy ring-opening accelerator, and 100-200 parts of a second organic solvent; in the ethylene-methyl acrylate-glycidyl methacrylate terpolymer, the content of GMA is 3wt%-6wt%.

[0033] The hot melt adhesive of this application has a two-layer structure. The first adhesive layer can be used to connect the PEN, and the second adhesive layer can be used to connect the PFSA, so that the PEN and PFSA can be connected by the hot melt adhesive of this application. The hot melt adhesive has a strong adhesive effect on the PEN, PFSA and the two adhesive layers of the hot melt adhesive. It does not bubble or crack after being soaked in sulfuric acid aqueous solution at 95°C and pH=2 for more than 2000 hours, and still maintains good adhesive performance.

[0034] The first adhesive layer can be used to bond PEN. The polyester resin in the first adhesive layer has a similar chemical structure to PEN and exhibits good adhesion to PEN. However, studies have found that PEN membranes have low surface energy and high rigidity, resulting in poor wettability of ordinary polyester resins to PEN membranes. This application uses polyester resin with a melt index ≥30 g / 10 min (160℃ / 2.16 kg) as the main material to improve its wettability to PEN membranes. For example, the melt index of the polyester resin can be within the range of 30 g / 10 min, 40 g / 10 min, 50 g / 10 min, 60 g / 10 min, 70 g / 10 min, 80 g / 10 min, or any combination thereof, thereby ensuring the wettability and adhesive strength of the first adhesive layer to PEN.

[0035] Introducing a styrene-based thermoplastic elastomer into the first adhesive layer can improve the flexibility of the polyester resin. Furthermore, during coating preparation, if the first adhesive layer is coated onto the PEN substrate, the introduction of the styrene-based thermoplastic elastomer can increase the initial adhesion of the first adhesive layer to the PEN.

[0036] Introducing an appropriate amount of grafted toughening agent into the first adhesive layer helps improve the compatibility between polyester resin and styrene-based thermoplastic elastomers. The introduction of epoxy chain extenders can further form chemical bonds in the first adhesive layer, achieving chain extension and preventing hydrolysis or thermal degradation of the polyester resin under prolonged acid cooking conditions, thereby restoring and improving mechanical and thermal properties. The first organic solvent is used to dissolve the remaining components in the first adhesive layer to ensure coating processability.

[0037] In different embodiments, the amounts of each component in the first adhesive layer, by weight, may be as follows:

[0038] The amount of polyester resin can be 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, 75 parts, 80 parts, or any combination thereof; the amount of styrene thermoplastic elastomer can be 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, or any combination thereof; the amount of grafted toughening agent can be 5 parts, 8 parts, 10 parts, 12 parts, 15 parts, 18 parts, 20 parts, or any combination thereof; the amount of epoxy chain extender can be 0.1 parts, 0.3 parts, 0.5 parts, 0.8 parts, 1 part, 1.2 parts, 1.5 parts, or any combination thereof; and the amount of the first organic solvent can be 100 parts, 120 parts, 150 parts, 180 parts, 200 parts, or any combination thereof.

[0039] The second adhesive layer can be used to bond PFSA. The ethylene-methyl acrylate copolymer in the second adhesive layer has good initial adhesive strength to PFSA, therefore, ethylene-methyl acrylate copolymer is used as the main material for bonding PFSA. An appropriate amount of copolyester hot melt adhesive is introduced to increase the adhesive strength between the first and second adhesive layers. Studies have found that if the amount of copolyester hot melt adhesive is too small, it significantly affects the adhesive effect between the second and first adhesive layers; conversely, if the amount of copolyester hot melt adhesive is too large, it affects the adhesive effect between the second adhesive layer and PFSA. This application introduces an appropriate amount of copolyester hot melt adhesive into the second adhesive layer to ensure both the adhesive performance of the second adhesive layer on the first adhesive layer and the PFSA. The ethylene-methyl acrylate-glycidyl methacrylate terpolymer can improve the compatibility between the ethylene-methyl acrylate copolymer and the copolyester hot melt adhesive, as well as the flexibility of the second adhesive layer. The epoxy ring-opening accelerator can promote the opening of epoxy groups in the ethylene-methyl acrylate-glycidyl methacrylate terpolymer in the second adhesive layer. The second organic solvent is used to dissolve the remaining components in the second adhesive layer to ensure coating processability. This application further controls the GMA content in the ethylene-methyl acrylate-glycidyl methacrylate terpolymer to be 3wt% to 6wt%, for example, it can be a range of 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, or any combination thereof, thereby helping to avoid film-forming crystal point problems while sufficiently improving the compatibility of the second adhesive layer.

[0040] In a specific embodiment of this application, the styrene-based thermoplastic elastomer includes at least one of styrene-butadiene-styrene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, and hydrogenated styrene-isoprene-styrene block copolymer. It may further include at least one of hydrogenated styrene-butadiene-styrene block copolymer and hydrogenated styrene-isoprene-styrene block copolymer, thereby helping to further improve the long-term acid boiling resistance.

[0041] In a specific embodiment of this application, the grafting unit of the grafted toughening agent is maleic anhydride and / or glycidyl methacrylate. Further, the grafted toughening agent is at least one of SEBS grafted with maleic anhydride and / or glycidyl methacrylate.

[0042] In a specific embodiment of this application, the grafting rate of the grafted toughening agent is ≥0.5%, for example, it can be a range of 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any two of these.

[0043] In specific embodiments of this application, the epoxy equivalent in the epoxy chain extender is 200–600 g / mol, for example, it can be 200 g / mol, 250 g / mol, 300 g / mol, 350 g / mol, 400 g / mol, 450 g / mol, 500 g / mol, 550 g / mol, 600 g / mol, or any combination thereof, thereby achieving appropriate chain extension to ensure strength, toughness, and acid resistance. Furthermore, the epoxy chain extender includes, but is not limited to, at least one of BASF's epoxy chain extender ADR-4400 or BASF's epoxy chain extender ADR-4468.

[0044] In a specific embodiment of this application, the first organic solvent includes butanone (MEK) and ethyl acetate. Further, the mass ratio of MEK to ethyl acetate in the first organic solvent is (1-3):1, for example, it can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, or any combination thereof. Research has found that using a combination of MEK and ethyl acetate as the first organic solvent provides high solubility for the remaining components used in the first adhesive layer; it also has a suitable boiling point, ensuring drying at an appropriate drying temperature, which helps avoid the formation of crystal points; furthermore, this solvent facilitates post-processing.

[0045] In a specific embodiment of this application, the methyl acrylate content in the ethylene-methyl acrylate copolymer is ≥20wt%, for example, it can be 20wt%, 22wt%, 25wt%, 28wt%, 30wt%, or any combination thereof, thereby helping to ensure the initial bond strength to the PFSA and the bond strength to the first adhesive layer.

[0046] In a specific embodiment of this application, the melting point of the copolyester hot melt adhesive is ≥110°C, for example, it can be a range of 110°C, 120°C, 130°C, 140°C, 150°C or any combination thereof.

[0047] In specific embodiments of this application, the epoxy ring-opening accelerator includes at least one selected from 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, and 1-benzyl-2-methylimidazole. The inventors of this application discovered that, in order to further match film appearance and adhesion, the epoxy ring-opening accelerator essentially does not undergo a ring-opening reaction during film formation, but does undergo a ring-opening reaction during subsequent hot-pressing lamination of PEN and PFSA and prolonged acid boiling. At this time, the epoxy groups in the second adhesive layer will chemically react with the functional groups of the first adhesive layer, greatly increasing the adhesion reliability between the first and second adhesive layers, and simultaneously increasing the adhesion durability between the second adhesive layer and PFSA. Experiments have shown that the above-mentioned epoxy ring-opening accelerator can achieve the above-mentioned expected effects.

[0048] In a specific embodiment of this application, the second organic solvent includes ethyl acetate and acetone. Further, the mass ratio of ethyl acetate to acetone in the second solvent is (1–5):1, for example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, or any combination thereof. Studies have found that using a mixture of ethyl acetate and acetone as the second organic solvent provides high solubility for the remaining components used in the second adhesive layer; it also has a suitable boiling point, ensuring drying at an appropriate drying temperature, which helps avoid the formation of crystal points; furthermore, this solvent facilitates post-processing.

[0049] In specific embodiments of this application, the thickness of the hot melt adhesive is 10–25 μm, for example, it can be a range of 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 25 μm, or any combination thereof. Further, the thickness of both the first adhesive layer and the second adhesive layer is ≥5 μm, for example, they can each be independently a range of 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or any combination thereof.

[0050] The second aspect of this application provides a method for preparing the hot melt adhesive of the first aspect of this application, comprising the following steps:

[0051] (a) Mix all components of the first adhesive layer evenly, apply and dry to obtain the first adhesive layer;

[0052] (b) Mix the components of the second adhesive layer evenly, apply the mixture to the surface of the first adhesive layer, and dry it to obtain a hot melt adhesive.

[0053] In a specific embodiment of this application, step (a) of uniform mixing includes: mixing polyester resin, styrene thermoplastic elastomer, grafted toughening agent, epoxy chain extender and first organic solvent in a certain proportion, and stirring at 400-1000 r / min until each component is dissolved.

[0054] In a specific embodiment of this application, step (b) of uniform mixing includes: mixing ethylene-methyl acrylate copolymer, copolyester hot melt adhesive, ethylene-methyl acrylate-glycidyl methacrylate terpolymer, epoxy ring-opening accelerator, and second organic solvent in a specified ratio, and then stirring at 400-1000 r / min until each component is dissolved.

[0055] In a specific embodiment of this application, step (a) includes coating the mixture onto a PEN substrate. Further, the thickness of the PEN substrate can be 5–30 μm, but is not limited thereto.

[0056] In a specific embodiment of this application, step (a) includes drying at 90–110°C. The drying time in step (a) is adjusted conventionally based on the evaporation of the first organic solvent in the coated layer until the first organic solvent is completely dry.

[0057] In a specific embodiment of this application, step (b) includes drying at 80–90°C. The drying time in step (b) is adjusted conventionally based on the evaporation of the second organic solvent in the coated layer until the second organic solvent is completely dry.

[0058] A third aspect of this application provides a fuel cell membrane electrode, including the hot melt adhesive of the first aspect of this application.

[0059] In a specific embodiment of this application, the fuel cell membrane electrode includes a PFSA membrane and a PEN border membrane, which are bonded together by the hot melt adhesive of this application; the first adhesive layer of the hot melt adhesive is bonded to the PEN border membrane, and the second adhesive layer is bonded to the PFSA membrane.

[0060] The hot melt adhesive of this application can be used for the encapsulation of fuel cell membrane electrodes, for example, it can be used to bond the PEN frame membrane and PFSA membrane of fuel cell membrane electrodes to achieve good encapsulation of fuel cell membrane electrodes.

[0061] Example 1

[0062] This embodiment provides a hot melt adhesive, including a first adhesive layer and a second adhesive layer stacked together, wherein the thickness of the first adhesive layer is 10 μm and the thickness of the second adhesive layer is 10 μm.

[0063] By weight, the raw materials used in the first adhesive layer include: 60 parts polyester resin, 30 parts styrene-based thermoplastic elastomer, 10 parts grafted toughening agent, 0.5 parts epoxy chain extender, and 150 parts first organic solvent. The polyester resin has a melt index (160℃ / 2.16kg) of 65g / 10min (grade 3120H, manufacturer: Guangdong Shuntian New Materials Co., Ltd.); the styrene-based thermoplastic elastomer is hydrogenated styrene-butadiene-styrene block copolymer (SEBS) (grade: Kraton G1641); the grafted toughening agent is maleic anhydride-grafted SEBS (grade: Kraton FG1901, maleic anhydride grafting rate: 1.7%); the epoxy chain extender is BASF ADR-4468; and the first organic solvent is a mixture of butanone and ethyl acetate in a mass ratio of 2:1.

[0064] By weight, the raw materials used in the second adhesive layer include: 50 parts of ethylene-methyl acrylate copolymer, 30 parts of copolyester hot melt adhesive, 20 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 0.5 parts of epoxy ring-opening accelerator, and 150 parts of a second organic solvent. Specifically, the ethylene-methyl acrylate copolymer contains 25 wt% methyl acrylate (Dow AC 1125); the copolyester hot melt adhesive has a melting point of 130℃ (HT-5130, manufactured by Wenzhou Huatai Hot Melt Adhesive Co., Ltd.); the ethylene-methyl acrylate-glycidyl methacrylate terpolymer contains 6 wt% GMA (Sumitomo BF-7M); the epoxy ring-opening accelerator is 2,4,6-tris(dimethylaminomethyl)phenol; and the second organic solvent is a mixture of ethyl acetate and acetone in a mass ratio of 2:1.

[0065] The method for preparing the hot melt adhesive in this embodiment includes the following steps:

[0066] (1) Mix the raw materials of the first adhesive layer according to the proportion at room temperature with a stirring speed of 600r / min until the materials are dissolved and mixed evenly to obtain the first adhesive layer mixture;

[0067] (2) The first adhesive layer mixture obtained in step (1) is coated on the surface of a 25μm thick PEN substrate and then placed in an oven at 100℃. After the organic solvent is dried, a PEN-first adhesive layer composite structure is obtained, and the thickness of the first adhesive layer is 10μm.

[0068] (3) Stir the raw materials of the second adhesive layer at room temperature at a stirring speed of 800 r / min according to the proportion until the materials are dissolved and mixed evenly to obtain the second adhesive layer mixture;

[0069] (4) The second adhesive layer mixture obtained in step (3) is coated on the surface of the first adhesive layer of the composite structure obtained in step (2), and then placed in an oven at a temperature of 80°C. After the organic solvent is dried, a PEN-first adhesive layer-second adhesive layer composite structure is obtained, with the thickness of the second adhesive layer being 10 μm.

[0070] Example 2

[0071] This embodiment provides a hot melt adhesive, including a first adhesive layer and a second adhesive layer stacked together, wherein the thickness of the first adhesive layer is 8 μm and the thickness of the second adhesive layer is 7 μm.

[0072] By weight, the raw materials used in the first adhesive layer include: 70 parts polyester resin, 25 parts styrene-based thermoplastic elastomer, 5 parts grafted toughening agent, 0.8 parts epoxy chain extender, and 120 parts first organic solvent. The polyester resin has a melt index (160℃ / 2.16kg) of 45g / 10min (grade 3150H, manufacturer: Guangdong Shuntian New Materials Co., Ltd.); the styrene-based thermoplastic elastomer is hydrogenated styrene-isoprene-styrene block copolymer (SEPS) (grade: Baling Petrochemical YH-4053); the grafted toughening agent is maleic anhydride-grafted SEBS (grade: Formosa Plastics 7126, maleic anhydride grafting rate: 1.6%); the epoxy chain extender is BASF ADR-4400; and the first organic solvent is a mixture of butanone and ethyl acetate in a mass ratio of 3:1.

[0073] By weight, the raw materials used in the second adhesive layer include: 40 parts of ethylene-methyl acrylate copolymer, 35 parts of copolyester hot melt adhesive, 15 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 0.3 parts of epoxy ring-opening accelerator, and 180 parts of a second organic solvent. Specifically, the methyl acrylate content of the ethylene-methyl acrylate copolymer is 29 wt% (brand name SK 29MA03T); the melting point of the copolyester hot melt adhesive is 126℃ (brand name Toyobo GM-913); the GMA content of the ethylene-methyl acrylate-glycidyl methacrylate terpolymer is 3 wt% (brand name Sumitomo BF-7L); the epoxy ring-opening accelerator is 1-benzyl-2-methylimidazolium; and the second organic solvent is a mixture of ethyl acetate and acetone in a mass ratio of 5:1.

[0074] The method for preparing the hot melt adhesive in this embodiment includes the following steps:

[0075] (1) Mix the raw materials of the first adhesive layer according to the proportion at room temperature with a stirring speed of 500r / min until the materials are dissolved and mixed evenly to obtain the first adhesive layer mixture;

[0076] (2) The first adhesive layer mixture obtained in step (1) is coated on the surface of a 25μm thick PEN substrate and then placed in an oven at a temperature of 90℃. After the organic solvent is dried, a PEN-first adhesive layer composite structure is obtained, and the thickness of the first adhesive layer is 8μm.

[0077] (3) Stir the raw materials of the second adhesive layer at room temperature at a stirring speed of 600r / min according to the proportion until the materials are dissolved and mixed evenly to obtain the second adhesive layer mixture;

[0078] (4) The second adhesive layer mixture obtained in step (3) is coated on the surface of the first adhesive layer of the composite structure obtained in step (2), and then placed in an oven at a temperature of 85°C. After the organic solvent is dried, a PEN-first adhesive layer-second adhesive layer composite structure is obtained, with the thickness of the second adhesive layer being 7 μm.

[0079] Example 3

[0080] This embodiment provides a hot melt adhesive, including a first adhesive layer and a second adhesive layer stacked together, wherein the thickness of the first adhesive layer is 9 μm and the thickness of the second adhesive layer is 12 μm.

[0081] By weight, the raw materials used in the first adhesive layer include: 50 parts polyester resin, 35 parts styrene-based thermoplastic elastomer, 15 parts grafted toughening agent, 1 part epoxy chain extender, and 100 parts first organic solvent. The polyester resin has a melt index (160℃ / 2.16kg) of 37g / 10min (brand name: SK EH100); the styrene-based thermoplastic elastomer is hydrogenated styrene-butadiene-styrene block copolymer (SEBS) (brand name: Kraton G1651); the grafted toughening agent is maleic anhydride-grafted SEBS (brand name: Kraton RP6670, maleic anhydride grafting rate: 1.1%); the epoxy chain extender is BASF ADR-4468; and the first organic solvent is a mixture of methyl ethyl ketone (MEK) and ethyl acetate in a mass ratio of 1:1.

[0082] By weight, the raw materials used in the second adhesive layer include: 45 parts of ethylene-methyl acrylate copolymer, 25 parts of copolyester hot melt adhesive, 30 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 0.8 parts of epoxy ring-opening accelerator, and 120 parts of a second organic solvent. Specifically, the ethylene-methyl acrylate copolymer contains 21.5 wt% methyl acrylate (ExxonMobil TC120); the copolyester hot melt adhesive has a melting point of 112℃ (Toyobo GM-900); the ethylene-methyl acrylate-glycidyl methacrylate terpolymer contains 6 wt% GMA (Sumitomo BF-7M); the epoxy ring-opening accelerator is N,N-dimethylbenzylamine; and the second organic solvent is a mixture of ethyl acetate and acetone in a mass ratio of 3:1.

[0083] The method for preparing the hot melt adhesive in this embodiment includes the following steps:

[0084] (1) Mix the raw materials of the first adhesive layer according to the proportion at room temperature with a stirring speed of 700r / min until the materials are dissolved and mixed evenly to obtain the first adhesive layer mixture;

[0085] (2) The first adhesive layer mixture obtained in step (1) is coated on the surface of a 25μm thick PEN substrate and then placed in an oven at 95℃. After the organic solvent is dried, a PEN-first adhesive layer composite structure is obtained, and the thickness of the first adhesive layer is 9μm.

[0086] (3) Stir the raw materials of the second adhesive layer at room temperature at a stirring speed of 1000r / min according to the proportion until the materials are dissolved and mixed evenly to obtain the second adhesive layer mixture;

[0087] (4) The second adhesive layer mixture obtained in step (3) is coated on the surface of the first adhesive layer of the composite structure obtained in step (2), and then placed in an oven at a temperature of 90°C. After the organic solvent is dried, a PEN-first adhesive layer-second adhesive layer composite structure is obtained, with the thickness of the second adhesive layer being 12 μm.

[0088] Example 4

[0089] This embodiment provides a hot melt adhesive, including a first adhesive layer and a second adhesive layer stacked together, wherein the thickness of the first adhesive layer is 6 μm and the thickness of the second adhesive layer is 8 μm.

[0090] By weight, the raw materials used in the first adhesive layer include: 65 parts polyester resin, 20 parts styrene-based thermoplastic elastomer, 15 parts grafted toughening agent, 1.2 parts epoxy chain extender, and 140 parts first organic solvent. The polyester resin has a melt index (160℃ / 2.16kg) of 65g / 10min (grade 3120H, manufacturer: Guangdong Shuntian New Materials Co., Ltd.); the styrene-based thermoplastic elastomer is hydrogenated styrene-isoprene-styrene block copolymer (SEPS) (grade: Baling Petrochemical YH-4051); the grafted toughening agent is glycidyl methacrylate grafted SEBS (manufacturer: Wuxi Zhiyuan Chemical Co., Ltd., glycidyl methacrylate grafting rate: 1.5%); the epoxy chain extender is BASF ADR-4400; and the first organic solvent is a mixture of butanone and ethyl acetate in a mass ratio of 5:2.

[0091] By weight, the raw materials used in the second adhesive layer include: 55 parts of ethylene-methyl acrylate copolymer, 20 parts of copolyester hot melt adhesive, 25 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 1.2 parts of epoxy ring-opening accelerator, and 100 parts of a second organic solvent. Specifically, the ethylene-methyl acrylate copolymer has a methyl acrylate content of 30 wt% (dow AC 1330); the copolyester hot melt adhesive has a melting point of 125℃ (Toyobo 30P); the ethylene-methyl acrylate-glycidyl methacrylate terpolymer has a GMA content of 3 wt% (Sumitomo BF-7L); the epoxy ring-opening accelerator is 2,4,6-tris(dimethylaminomethyl)phenol; and the second organic solvent is a mixture of ethyl acetate and acetone in a mass ratio of 1:1.

[0092] The method for preparing the hot melt adhesive in this embodiment includes the following steps:

[0093] (1) Mix the raw materials of the first adhesive layer according to the proportion at room temperature with a stirring speed of 800r / min until the materials are dissolved and mixed evenly to obtain the first adhesive layer mixture;

[0094] (2) The first adhesive layer mixture obtained in step (1) is coated on the surface of a 25μm thick PEN substrate and then placed in an oven at 105℃. After the organic solvent is dried, a PEN-first adhesive layer composite structure is obtained, and the thickness of the first adhesive layer is 6μm.

[0095] (3) Stir the raw materials of the second adhesive layer at room temperature at a stirring speed of 500r / min according to the proportion until the materials are dissolved and mixed evenly to obtain the second adhesive layer mixture;

[0096] (4) The second adhesive layer mixture obtained in step (3) is coated on the surface of the first adhesive layer of the composite structure obtained in step (2), and then placed in an oven at a temperature of 80°C. After the organic solvent is dried, a PEN-first adhesive layer-second adhesive layer composite structure is obtained, with the thickness of the second adhesive layer being 8 μm.

[0097] Example 5

[0098] This embodiment provides a hot melt adhesive, including a first adhesive layer and a second adhesive layer stacked together, wherein the thickness of the first adhesive layer is 12 μm and the thickness of the second adhesive layer is 6 μm.

[0099] By weight, the raw materials used in the first adhesive layer include: 80 parts polyester resin, 10 parts styrene-based thermoplastic elastomer, 10 parts grafted toughening agent, 0.3 parts epoxy chain extender, and 180 parts first organic solvent. The polyester resin has a melt index (160℃ / 2.16kg) of 45g / 10min (grade 3150H, manufacturer: Guangdong Shuntian New Materials Co., Ltd.); the styrene-based thermoplastic elastomer is hydrogenated styrene-butadiene-styrene block copolymer (SEBS) (grade: Kraton G1642, USA); the grafted toughening agent is maleic anhydride-grafted SEBS (grade: Formosa Plastics 7131, Taiwan, with a maleic anhydride grafting rate of 1.3%); the epoxy chain extender is BASF ADR-4468, Germany; and the first organic solvent is a mixture of methyl ethyl ketone (MEK) and ethyl acetate in a mass ratio of 7:2.

[0100] By weight, the raw materials used in the second adhesive layer include: 60 parts of ethylene-methyl acrylate copolymer, 25 parts of copolyester hot melt adhesive, 15 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 1.5 parts of epoxy ring-opening accelerator, and 200 parts of a second organic solvent. Specifically, the ethylene-methyl acrylate copolymer has a methyl acrylate content of 24 wt% (Dow AC 1224); the copolyester hot melt adhesive has a melting point of 122℃ (SK EH400); the ethylene-methyl acrylate-glycidyl methacrylate terpolymer has a GMA content of 6 wt% (Sumitomo BF-7M); the epoxy ring-opening accelerator is 1-benzyl-2-methylimidazole; and the second organic solvent is a mixture of ethyl acetate and acetone in a mass ratio of 4:1.

[0101] The method for preparing the hot melt adhesive in this embodiment includes the following steps:

[0102] (1) Mix the raw materials of the first adhesive layer according to the proportion at room temperature with a stirring speed of 900r / min until the materials are dissolved and mixed evenly to obtain the first adhesive layer mixture;

[0103] (2) The first adhesive layer mixture obtained in step (1) is coated on the surface of a 25μm thick PEN substrate and then placed in an oven at 110℃. After the organic solvent is dried, a PEN-first adhesive layer composite structure is obtained, with the thickness of the first adhesive layer being 12μm.

[0104] (3) Stir the raw materials of the second adhesive layer at room temperature at a stirring speed of 700r / min according to the proportion until the materials are dissolved and mixed evenly to obtain the second adhesive layer mixture;

[0105] (4) The second adhesive layer mixture obtained in step (3) is coated on the surface of the first adhesive layer of the composite structure obtained in step (2), and then placed in an oven at a temperature of 85°C. After the organic solvent is dried, a PEN-first adhesive layer-second adhesive layer composite structure is obtained, with the thickness of the second adhesive layer being 6 μm.

[0106] Example 6

[0107] This embodiment provides a hot melt adhesive, including a first adhesive layer and a second adhesive layer stacked together, wherein the thickness of the first adhesive layer is 7 μm and the thickness of the second adhesive layer is 15 μm.

[0108] By weight, the raw materials used in the first adhesive layer include: 55 parts polyester resin, 25 parts styrene-based thermoplastic elastomer, 20 parts grafted toughening agent, 0.6 parts epoxy chain extender, and 200 parts first organic solvent. The polyester resin has a melt index (160℃ / 2.16kg) of 37g / 10min (brand name: SK EH100); the styrene-based thermoplastic elastomer is hydrogenated styrene-isoprene-styrene block copolymer (SEPS) (brand name: Baling Petrochemical YH-4052); the grafted toughening agent is glycidyl methacrylate grafted SEBS (manufacturer: Wuxi Zhiyuan Chemical Co., Ltd., glycidyl methacrylate grafting rate: 1.5%); the epoxy chain extender is BASF ADR-4400; and the first organic solvent is a mixture of butanone and ethyl acetate in a mass ratio of 7:3.

[0109] By weight, the raw materials used in the second adhesive layer include: 52 parts of ethylene-methyl acrylate copolymer, 26 parts of copolyester hot melt adhesive, 22 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 1.8 parts of epoxy ring-opening accelerator, and 140 parts of a second organic solvent. Specifically, the ethylene-methyl acrylate copolymer has a methyl acrylate content of 24 wt% (Dow AC 1224); the copolyester hot melt adhesive has a melting point of 143℃ (Toyobo GM-400); the ethylene-methyl acrylate-glycidyl methacrylate terpolymer has a GMA content of 3 wt% (Sumitomo BF-7L); the epoxy ring-opening accelerator is N,N-dimethylbenzylamine; and the second organic solvent is a mixture of ethyl acetate and acetone in a mass ratio of 5:2.

[0110] The method for preparing the hot melt adhesive in this embodiment includes the following steps:

[0111] (1) Mix the raw materials of the first adhesive layer according to the proportion at room temperature with a stirring speed of 1000r / min until the materials are dissolved and mixed evenly to obtain the first adhesive layer mixture;

[0112] (2) The first adhesive layer mixture obtained in step (1) is coated on the surface of a 25μm thick PEN substrate and then placed in an oven at a temperature of 95℃. After the organic solvent is dried, a PEN-first adhesive layer composite structure is obtained, and the thickness of the first adhesive layer is 7μm.

[0113] (3) Stir the raw materials of the second adhesive layer at room temperature at a stirring speed of 900 r / min according to the proportion until the materials are dissolved and mixed evenly to obtain the second adhesive layer mixture;

[0114] (4) The second adhesive layer mixture obtained in step (3) is coated on the surface of the first adhesive layer of the composite structure obtained in step (2), and then placed in an oven at a temperature of 90°C. After the organic solvent is dried, a PEN-first adhesive layer-second adhesive layer composite structure is obtained, with the thickness of the second adhesive layer being 15 μm.

[0115] Comparative Example 1

[0116] Comparative Example 1 refers to the hot melt adhesive and its preparation method in Example 1, except that the raw materials used in the first adhesive layer do not contain styrene-based thermoplastic elastomers or grafted toughening agents, while the rest are the same as in Example 1.

[0117] By weight, the raw materials used in the first adhesive layer of Comparative Example 1 include: 100 parts polyester resin, 0.5 parts epoxy chain extender, and 150 parts first organic solvent.

[0118] Comparative Example 2

[0119] Comparative Example 2 refers to the hot melt adhesive and its preparation method of Example 1, except that the raw materials used in the first adhesive layer do not contain grafted toughening agents, while the rest are the same as in Example 1.

[0120] By weight, the raw materials used in the first adhesive layer of Comparative Example 2 include: 70 parts polyester resin, 30 parts styrene thermoplastic elastomer, 0.5 parts epoxy chain extender, and 150 parts first organic solvent.

[0121] Comparative Example 3

[0122] Comparative Example 3 refers to the hot melt adhesive and its preparation method in Example 1, except that the raw materials used in the first adhesive layer do not contain epoxy chain extenders, while the rest are the same as in Example 1.

[0123] By weight, the raw materials used in the first adhesive layer of Comparative Example 3 include: 60 parts polyester resin, 30 parts styrene thermoplastic elastomer, 10 parts grafted toughening agent, and 150 parts first organic solvent.

[0124] Comparative Example 4

[0125] Comparative Example 4 refers to the hot melt adhesive and its preparation method in Example 1, except that the raw materials used in the second adhesive layer do not contain copolyester hot melt adhesive, ethylene-methyl acrylate-glycidyl methacrylate terpolymer and epoxy ring-opening accelerator, but are otherwise the same as in Example 1.

[0126] By weight, the raw materials used in the second adhesive layer of Comparative Example 4 include: 100 parts of ethylene-methyl acrylate copolymer and 150 parts of a second organic solvent.

[0127] Comparative Example 5

[0128] Comparative Example 5 refers to the hot melt adhesive and its preparation method of Example 1, except that the raw materials used in the second adhesive layer do not contain copolyester hot melt adhesive, and the rest are the same as in Example 1.

[0129] By weight, the raw materials used in the second adhesive layer of Comparative Example 5 include: 80 parts of ethylene-methyl acrylate copolymer, 20 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 0.5 parts of epoxy ring-opening accelerator, and 150 parts of second organic solvent.

[0130] Comparative Example 6

[0131] Comparative Example 6 refers to the hot melt adhesive and its preparation method in Example 1, except that the raw materials used in the second adhesive layer do not contain ethylene-methyl acrylate-glycidyl methacrylate terpolymer, while the rest are the same as in Example 1.

[0132] By weight, the raw materials used in the second adhesive layer of Comparative Example 6 include: 70 parts ethylene-methyl acrylate copolymer, 30 parts copolyester hot melt adhesive, 0.5 parts epoxy ring-opening accelerator, and 150 parts second organic solvent.

[0133] Comparative Example 7

[0134] Comparative Example 7 refers to the hot melt adhesive and its preparation method in Example 1, except that the type of ethylene-methyl acrylate-glycidyl methacrylate terpolymer used in the second adhesive layer is different, while the rest is the same as in Example 1.

[0135] The second adhesive layer of Comparative Example 7 uses an ethylene-methyl acrylate-glycidyl methacrylate terpolymer with a GMA content of 8 wt% (brand name: Arkema AX 8900, France).

[0136] Comparative Example 8

[0137] Comparative Example 8 refers to the hot melt adhesive and its preparation method of Example 1, except that the raw materials used in the second adhesive layer do not contain epoxy ring-opening accelerators, and the rest are the same as in Example 1.

[0138] By weight, the raw materials used in the second adhesive layer of Comparative Example 8 include: 50 parts of ethylene-methyl acrylate copolymer, 30 parts of copolyester hot melt adhesive, 20 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, and 150 parts of the second organic solvent.

[0139] Comparative Example 9

[0140] Comparative Example 9 refers to the hot melt adhesive and its preparation method of Example 1, except that the type of polyester resin used in the first adhesive layer is different, while the rest is the same as in Example 1.

[0141] The melt index (160℃ / 2.16kg) of the polyester resin used in the first adhesive layer of Comparative Example 9 was 15g / 10min (brand name: HT-5120-C, manufacturer: Wenzhou Huatai Hot Melt Adhesive Co., Ltd.).

[0142] Experimental Example

[0143] The hot melt adhesives obtained from each embodiment and comparative example were respectively made into the following composite structure samples:

[0144] PEN / hot melt adhesive / hot melt adhesive / PEN(PEN / first adhesive layer / second adhesive layer / second adhesive layer / first adhesive layer / PEN), PEN / hot melt adhesive / PFSA(PEN / first adhesive layer / second adhesive layer / PFSA), PEN / hot melt adhesive / PFSA / hot melt adhesive / PEN(PEN / first adhesive layer / second adhesive layer / PFSA / second adhesive layer / first adhesive layer / PEN); wherein, the thickness of PEN is 25μm and the thickness of PFSA is 15μm; the composite structure sample was prepared by bonding at a bonding temperature of 135℃ and a bonding pressure of 0.6MPa for 10s.

[0145] All composite structure samples of PEN / hot melt adhesive / hot melt adhesive / PEN and PEN / hot melt adhesive / PFSA were left with peeling openings to examine their initial peel strength and peel strength after acid boiling for 2000 hours.

[0146] The composite structure sample of PEN / hot melt adhesive / PFSA / hot melt adhesive / PEN has no peeling opening and is a sealed structure. After acid boiling for 2000 hours, it was examined whether there were any bubbles or cracks.

[0147] Specifically, the initial peel strength refers to the peel strength tested after the prepared composite structure sample has been cooled to room temperature.

[0148] The peel strength after acid boiling for 2000 hours refers to the peel strength tested after the prepared composite structure sample is cooled to room temperature, immersed in a sulfuric acid aqueous solution at 95℃ and pH=2 for 2000 hours, removed, dried, and cooled to room temperature.

[0149] Whether there are bubbles or cracks after acid boiling for 2000 hours refers to: after the prepared composite structure sample is cooled to room temperature, it is immersed in sulfuric acid aqueous solution at 95℃ and pH=2 for 2000 hours, then removed, the acid solution is wiped dry and cooled to room temperature. The appearance of the sample is then observed in a well-lit place to check for bubbles, and the sample is bent and folded to check for cracks.

[0150] Whether the film has crystal points refers to: placing the PEN / hot melt adhesive composite structures prepared in different embodiments and comparative examples under light to detect the number of crystal points. If there are no crystal points with a diameter greater than 1 mm and a diameter between 0.5 and 1 mm, and the number is less than 5 per square meter, it means that the film has no crystal points. Otherwise, it means that the film has crystal points.

[0151] The test results are shown in Table 1. The peel strength test method refers to GB / T GB8808-88 "Peel Test Method for Flexible Composite Plastic Materials".

[0152] Table 1 Test results for each embodiment and comparative example

[0153] The test results from Examples 1 and Comparative Examples 1-9 show that styrene-based thermoplastic elastomers improve the flexibility of polyester resins without affecting their adhesion to PEN; grafted toughening agents improve the compatibility between polyester resins and styrene-based thermoplastic elastomers, preventing phase separation and performance degradation after prolonged acid boiling; epoxy chain extenders are used to restore and improve the mechanical and thermal properties of polyester resins under long-term acid boiling; an appropriate amount of copolyester hot melt adhesive effectively improves the bond strength between the second adhesive layer and the first adhesive layer; ethylene-methyl acrylate-glycidyl methacrylate terpolymer and epoxy ring-opening accelerator greatly improve the acid boiling resistance of the second adhesive layer and the first adhesive layer, and the second adhesive layer and PFSA.

[0154] The test results from Examples 1-6 show that the hot melt adhesive with a two-layer structure of this application can achieve good adhesion between PEN and PFSA. Furthermore, it does not bubble or crack after being immersed in a sulfuric acid aqueous solution at 95°C and pH=2 for more than 2000 hours, and still maintains good adhesive performance. Moreover, the preparation process of the hot melt adhesive of this application is simple; the solution is coated onto the PEN substrate to form a film without crystal points, enabling continuous production and application in the field of fuel cell membrane electrode encapsulation.

[0155] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A hot melt adhesive, comprising a first adhesive layer and a second adhesive layer stacked together; The first adhesive layer comprises the following components by weight: 50-80 parts polyester resin, 10-40 parts styrene-based thermoplastic elastomer, 5-20 parts grafted toughening agent, 0.1-1.5 parts epoxy chain extender, and 100-200 parts first organic solvent; the polyester resin has a melt index of ≥30 g / 10 min at 160℃ / 2.16 kg. The second adhesive layer comprises, by weight, the following components: 40-60 parts of ethylene-methyl acrylate copolymer, 20-40 parts of copolyester hot melt adhesive, 10-30 parts of ethylene-methyl acrylate-glycidyl methacrylate terpolymer, 0.1-2 parts of epoxy ring-opening accelerator, and 100-200 parts of a second organic solvent; wherein the content of GMA in the ethylene-methyl acrylate-glycidyl methacrylate terpolymer is 3wt%-6wt%.

2. The hot melt adhesive according to claim 1, wherein, The styrene-based thermoplastic elastomers include at least one of styrene-butadiene-styrene block copolymers, hydrogenated styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, and hydrogenated styrene-isoprene-styrene block copolymers.

3. The hot melt adhesive according to claim 1, wherein, The grafting unit of the grafted toughening agent is maleic anhydride and / or glycidyl methacrylate. In the grafted toughening agent, the grafting rate of the grafted unit is ≥0.5%.

4. The hot melt adhesive according to claim 1, wherein, In the epoxy chain extender, the epoxy equivalent is 200-600 g / mol.

5. The hot melt adhesive according to claim 1, wherein, It has at least one of the following characteristics: (1) The first organic solvent includes butanone and ethyl acetate; (2) In the ethylene-methyl acrylate copolymer, the content of methyl acrylate is ≥20wt%.

6. The hot melt adhesive according to claim 1, wherein, The epoxy ring-opening accelerator includes at least one of 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, and 1-benzyl-2-methylimidazole.

7. The hot melt adhesive according to claim 1, wherein, It has at least one of the following characteristics: (1) The melting point of the copolyester hot melt adhesive is ≥110℃; (2) The second organic solvent includes ethyl acetate and acetone.

8. The hot melt adhesive according to claim 1, wherein, The thickness of the hot melt adhesive is 10–25 μm; The thickness of both the first adhesive layer and the second adhesive layer is ≥5μm.

9. A method for preparing the hot melt adhesive according to any one of claims 1 to 8, comprising the following steps: (a) Mix all components of the first adhesive layer evenly, apply and dry to obtain the first adhesive layer; (b) Mix the components of the second adhesive layer evenly, apply the mixture to the surface of the first adhesive layer, and dry it to obtain a hot melt adhesive.

10. A fuel cell membrane electrode comprising the hot melt adhesive according to any one of claims 1 to 8 or the hot melt adhesive prepared by the preparation method according to claim 9.

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