A border film and a preparation method thereof

Abstract

The present invention belongs to the field of battery frame films and relates to a frame film and a preparation method thereof. The frame film includes a skeleton layer, a transition layer attached to at least one surface of the skeleton layer, and an adhesive layer attached to the surface of the transition layer; the raw materials for forming the skeleton layer contain 50-85% of isotactic polypropylene, 5-20% of propylene copolymer, 5-20% of mineral filler, 0.1-5% of a first peroxide, and 0.1-5% of a first co-crosslinking agent; the raw materials for forming the transition layer are olefin polymers; the raw materials for forming the adhesive layer contain 75-90% of polyolefin, 5-15% of hydrogenated petroleum resin, 0.1-5% of 2-acrylamide-2-methylpropanesulfonic acid, 0.1-3% of a second peroxide, and 0.1-3% of a second co-crosslinking agent. The frame film provided by the present invention has good initial adhesion performance to the proton membrane, and still has good adhesion performance and is not prone to delamination after being boiled in high temperature water for a long time.

Description

Technical Field

[0001] The present invention belongs to the field of battery frame films, and particularly relates to a frame film and a preparation method thereof. Background Art

[0002] Data from the International Energy Agency shows that the proportion of green energy including wind, solar and nuclear is still small, and currently mainly relies on coal, oil and natural gas. The situation of hydrogen energy is still a long way to go, and it is still urgent to overcome the challenges in various technical links to achieve cost reduction and localization.

[0003] As a form of secondary energy, hydrogen needs to consume other energy sources to be produced. Therefore, the low-carbon production and efficient utilization of hydrogen become very important, including reducing the costs of storage, transportation and the construction of hydrogen refueling stations, and improving the conversion efficiency during the use of hydrogen. Ultimately, through technological innovation in each link, the utilization cost of hydrogen energy can be reduced. The production of green hydrogen, for example, by electrolyzing water using solar power generation to produce hydrogen, will be an important example of comprehensively utilizing the technical advantages of various energy sources.

[0004] As a carrier for generating hydrogen energy, the fuel cell stack is a very important component. The core material inside the fuel cell stack is the proton exchange membrane, and generally, fluorosulfonic acid type proton exchange membranes, nafion recast membranes, non-fluoropolymer materials, etc. are mainly selected for the proton exchange membrane. And the material supporting the proton exchange membrane is the frame film. The frame film should not only have a strong adhesive force to the proton exchange membrane, but also be able to withstand a long-term high-temperature water environment and an acid-resistant environment, and should not have a negative impact on the catalyst layer. Traditional frames use special engineering films such as PEN, PPS, PI, etc. as the base film and then compound various adhesive layers such as polyurethane, polyester, etc. At present, the frame film materials are mainly provided by foreign suppliers, mostly monopolized by foreign manufacturers, with high costs and difficult to obtain, and there are still deficiencies in performance under a long-term high-temperature boiling water environment, and hydrolysis is likely to occur, resulting in adhesive failure, affecting the reliability of the hydrogen fuel cell stack. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defect of poor high-temperature boiling water resistance of the existing frame film, and to provide a battery frame film that still has good adhesive performance and is not prone to delamination after long-term high-temperature boiling water, and a preparation method thereof.

[0006] Specifically, the present invention provides a border film, wherein the border film includes a skeleton layer, a transition layer attached to at least one surface of the skeleton layer, and an adhesive layer attached to the surface of the transition layer; the raw material for forming the skeleton layer contains 50-85% of isotactic polypropylene, 5-20% of propylene copolymer, 5-20% of mineral filler, 0.1-5% of a first peroxide, and 0.1-5% of a first co-crosslinking agent; the raw material for forming the transition layer is an olefin polymer; the raw material for forming the adhesive layer contains 75-90% of polyolefin, 5-15% of hydrogenated petroleum resin, 0.1-5% of 2-acrylamide-2-methylpropanesulfonic acid, 0.1-3% of a second peroxide, and 0.1-3% of a second co-crosslinking agent.

[0007] In a preferred embodiment, the number-average molecular weight of the isotactic polypropylene is 40,000-60,000.

[0008] In a preferred embodiment, the comonomer in the propylene copolymer is selected from at least one of ethylene, 1-butene, 2-butene, butadiene, and octene.

[0009] In a preferred embodiment, the mineral filler is selected from at least one of glass fiber, calcium carbonate, titanium dioxide, glass microspheres, and whiskers.

[0010] In a preferred embodiment, the olefin polymer is selected from at least one of ethylene acrylate copolymer, maleic anhydride modified polyethylene, maleic anhydride modified polypropylene, epoxy modified polyethylene, and epoxy modified polypropylene.

[0011] In a preferred embodiment, the melting point of the polyolefin is 50-145°C.

[0012] In a preferred embodiment, the polyolefin is selected from at least one of ethylene acrylic acid copolymer, ethylene vinyl acetate copolymer, maleic anhydride modified polyethylene, maleic anhydride modified polypropylene, epoxy modified polyethylene, and epoxy modified polypropylene.

[0013] In a preferred embodiment, the first peroxide and the second peroxide are each independently selected from at least one of cumene hydroperoxide, 2,5-dimethyl-2,5-dihydroperoxyhexane, cumene hydroperoxide, and tert-butyl hydroperoxide.

[0014] In a preferred embodiment, the first co-crosslinking agent and the second co-crosslinking agent are each independently selected from at least one of triallyl isocyanurate, trimethallyl isocyanate, and trimethylolpropane triacrylate.

[0015] In a preferred embodiment, the total thickness of the border film is 20 to 200 microns; the thickness of the skeleton layer is 5 to 150 microns; the thickness of the transition layer is 1 to 10 microns; and the thickness of the adhesive layer is 5 to 25 microns.

[0016] In a preferred embodiment, a hard layer is attached to the other surface of the skeleton layer where the transition layer is not attached.

[0017] In a preferred embodiment, the raw materials for forming the hard layer contain 60 to 90% of ethoxylated bisphenol A dimethacrylate, 2 to 30% of dipropylene glycol diacrylate, 2 to 10% of trimethylolpropane trimethacrylate, and 0.3 to 1.5% of benzoyl peroxide.

[0018] In a preferred embodiment, the thickness of the hard layer is 1 to 10 microns.

[0019] The present invention also provides a method for preparing the border film. The method includes mixing the components in the skeleton layer, the transition layer, and the adhesive layer evenly respectively, then feeding them into an extruder for melt mixing and pelletizing to obtain the raw materials for forming the skeleton layer, the raw materials for forming the transition layer, and the raw materials for forming the adhesive layer respectively. Feeding the raw materials for forming the skeleton layer, the raw materials for forming the transition layer, and the raw materials for forming the adhesive layer into an extrusion casting device with a multi-layer co-extrusion structure to extrude and cast to form a composite film including the skeleton layer, the transition layer, and the adhesive layer. Optionally, it further includes mixing the components in the hard layer evenly and then coating them on the other surface of the skeleton layer, and then curing by ultraviolet light to obtain the border film.

[0020] In a preferred embodiment, the method for preparing the border film provided by the present invention further includes, after extrusion casting, aging the obtained film at 50 to 90 °C for more than 24 hours.

[0021] In a preferred embodiment, the method for preparing the border film provided by the present invention further includes, after aging, irradiating the obtained film at a voltage of 50 to 200 KV with an irradiation dose of 5 to 30 kGy.

[0022] The border film provided by the present invention has good initial adhesion performance to the proton membrane, and still has good adhesion performance and is not prone to delamination after being boiled in high temperature water for a long time. In addition, the raw materials for preparing the border film provided by the present invention are easy to obtain and have low cost, and have broad application prospects. Specific embodiments

[0023] The border film provided by the present invention comprises a skeleton layer, a transition layer, an adhesive layer and an optional hard layer. Wherein, the transition layer is attached to at least one side surface of the skeleton layer, and the adhesive layer is attached to the surface of the transition layer. When only one side surface of the skeleton layer is attached with the transition layer, a hard layer may be attached to the surface of the skeleton layer without the attached transition layer. In a specific embodiment, the border film comprises a skeleton layer, a transition layer is attached to one side surface of the skeleton layer, and an adhesive layer is attached to the surface of the transition layer. In another specific embodiment, the border film comprises a skeleton layer, transition layers are attached to both side surfaces of the skeleton layer, and an adhesive layer is attached to the surface of the transition layer. In yet another specific embodiment, the border film comprises a skeleton layer, a transition layer is attached to one side surface of the skeleton layer while a hard layer is attached to the other side surface, and an adhesive layer is attached to the outer surface of the transition layer.

[0024] The raw materials for forming the skeleton layer contain isotactic polypropylene, propylene copolymer, mineral filler, first peroxide, and first co-crosslinking agent. The skeleton layer containing these several substances has excellent strength, enabling the border film not to shrink and deform after high-temperature boiling in water, laying a good foundation for the high-temperature boiling resistance performance. The content of the isotactic polypropylene is 50-85%, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc. The content of the propylene copolymer is 5-20%, such as 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc. The content of the mineral filler is 5-20%, such as 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc. The content of the first peroxide is 0.1-5%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. The content of the first co-crosslinking agent is 0.1-5%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. The isotactic polypropylene can provide higher strength, and its number-average molecular weight is preferably 40,000-60,000. The propylene copolymer can react better with the peroxide system. The comonomer in the propylene copolymer can specifically be selected from at least one of ethylene, 1-butene, 2-butene, butadiene, and octene. In addition, the mass ratio of the comonomer structural unit to the propylene structural unit in the propylene copolymer is preferably 1:(5-15). Specific examples of the mineral filler include, but are not limited to, at least one of glass fiber, calcium carbonate, titanium dioxide, glass microspheres, and whiskers. Specific examples of the first peroxide include, but are not limited to, at least one of diisopropylbenzene hydroperoxide, 2,5-dimethyl-2,5-dihydroperoxyhexane, cumene hydroperoxide, and tert-butyl hydroperoxide. Specific examples of the first co-crosslinking agent include, but are not limited to, at least one of triallyl isocyanurate, trimethallyl isocyanate, and trimethylolpropane triacrylate.

[0025] The forming raw material of the transition layer is an olefin polymer. The setting of the transition layer can achieve interlayer mutual solubility during the processing of the border film, reducing the risk of interlayer failure. Specific examples of the olefin polymer include, but are not limited to, at least one of ethylene acrylate copolymer, maleic anhydride modified polyethylene, maleic anhydride modified polypropylene, epoxy modified polyethylene, and epoxy modified polypropylene. Specific examples of the acrylate copolymer monomer in the ethylene acrylate copolymer include, but are not limited to, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, hexyl acrylate, isooctyl acrylate, lauryl acrylate, benzyl acrylate, cyclohexyl acrylate, perfluoroalkyl acrylate, 2-hydroxyethyl acrylate phosphate, isobornyl acrylate, tetrahydrofurfuryl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, isooctyl methacrylate, lauryl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, etc. The mass ratio of the ethylene structural unit to the acrylate structural unit in the ethylene acrylate copolymer is preferably (2-10):1. The content of maleic anhydride in the maleic anhydride modified polyethylene and maleic anhydride modified polypropylene is preferably 0.5-2%. The content of epoxy monomer in the epoxy modified polyethylene and epoxy modified polypropylene is preferably 0.5-2%.

[0026] The raw materials for forming the adhesive layer include polyolefin, hydrogenated petroleum resin, 2-acrylamido-2-methylpropanesulfonic acid, a second peroxide, and a second co-crosslinking agent. The content of the polyolefin is 75-90%, such as 75%, 78%, 80%, 82%, 85%, 88%, 90%, etc. The content of the hydrogenated petroleum resin is 5-15%, such as 5%, 8%, 10%, 12%, 15%, etc. The content of the 2-acrylamido-2-methylpropanesulfonic acid is 0.1-5%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc. The content of the second peroxide is 0.1-3%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. The content of the second co-crosslinking agent is 0.1-3%, such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. The melting point of the polyolefin is preferably 50-145°C, such as 50°C, 60°C, 70°C, 85°C, 98°C, 100°C, 102°C, 105°C, 108°C, 110°C, 112°C, 115°C, 118°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, etc. The polyolefin can be various existing polymers obtained by self-polymerization or copolymerization of α-olefins or cycloolefins. When self-polymerization is adopted, the polyolefin can be, for example, at least one of polyethylene, polypropylene, poly-1-butene, poly-1-pentene, poly-1-hexene, poly-1-octene, poly-4-methyl-1-pentene, and octene. When copolymerization is adopted, the comonomer can be, for example, an acrylic monomer, vinyl acetate, etc. Among them, specific examples of the acrylic monomer include, but are not limited to, acrylic acid, methacrylic acid, etc. In addition, the polyolefin can also be modified with various acid anhydrides or epoxies. The polyolefin is preferably selected from at least one of ethylene acrylic copolymer, ethylene vinyl acetate copolymer, maleic anhydride-modified polyethylene, maleic anhydride-modified polypropylene, epoxy-modified polyethylene, and epoxy-modified polypropylene, more preferably a mixture of ethylene acrylic copolymer and ethylene vinyl acetate copolymer, and most preferably a mixture of ethylene acrylic copolymer and ethylene vinyl acetate copolymer in a mass ratio of (75-85):10. When the polyolefin is a mixture of ethylene acrylic copolymer and ethylene vinyl acetate copolymer, it is more beneficial to improve the bonding performance of the border film. Specific examples of the second peroxide include, but are not limited to, at least one of cumene hydroperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, cumene hydroperoxide, and tert-butyl hydroperoxide. Specific examples of the second co-crosslinking agent include, but are not limited to, at least one of triallyl isocyanurate, trimethallyl isocyanate, and trimethylolpropane triacrylate.

[0027] In the present invention, the peroxide contained in the skeleton layer is referred to as "the first peroxide", and the co-crosslinking agent contained therein is referred to as "the first co-crosslinking agent"; the peroxide contained in the adhesive layer is referred to as "the second peroxide", and the co-crosslinking agent contained therein is referred to as "the second co-crosslinking agent". The terms "first" and "second" are only for the convenience of distinction and description and have no other special meanings.

[0028] The raw materials for forming the hard layer include ethoxylated bisphenol A dimethacrylate, dipropylene glycol diacrylate, trimethylolpropane trimethacrylate, and benzoyl peroxide. The content of the ethoxylated bisphenol A dimethacrylate is 60-90%, such as 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc. The content of the dipropylene glycol diacrylate is 2-30%, such as 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, etc. The content of the trimethylolpropane trimethacrylate is 2-10%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. The content of the benzoyl peroxide is 0.3-1.5%, such as 0.3%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, etc.

[0029] In the present invention, the total thickness of the border film is generally 20-200 microns, such as 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 microns, etc. In addition, in order to achieve a more perfect fit between layers, the thickness of the skeleton layer is preferably 5-150 microns, such as 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150 microns, etc.; the thickness of the transition layer is preferably 1-10 microns, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 microns, etc.; the thickness of the adhesive layer is preferably 5-25 microns, such as 5, 8, 10, 12, 15, 18, 20, 22, 25 microns, etc. In addition, the thickness of the hard layer is preferably 1-10 microns, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 microns, etc.

[0030] The preparation method of the border film provided by the present invention includes uniformly mixing the components in the skeleton layer, the transition layer and the adhesive layer respectively, and then feeding them into an extruder for melting, mixing and pelletizing respectively to obtain the raw materials for forming the skeleton layer, the raw materials for forming the transition layer and the raw materials for forming the adhesive layer. The raw materials for forming the skeleton layer, the raw materials for forming the transition layer and the raw materials for forming the adhesive layer are fed into an extrusion casting device with a multi-layer co-extrusion structure for extrusion casting to form a composite film including the skeleton layer, the transition layer and the adhesive layer. Optionally, it further includes uniformly mixing the components in the hard layer and then coating them on the other surface of the skeleton layer, and then curing and forming by ultraviolet light to obtain the border film. Among them, the equipment for mixing the raw materials can be, for example, a mixer, a kneader, an open mill, a Banbury mixer, etc. The mixing conditions are based on being able to fully mix the raw materials, and there are no special limitations. The melting, mixing and pelletizing are carried out, for example, in a single-screw extruder or a twin-screw extruder. In addition, it should be noted that the extrusion casting device usually includes multiple extruders. Different materials can be heated in the multiple extruders, and the materials heated by different extruders can be extruded and cast through the same composite die head including a multi-layer distributor, so as to obtain a border film including multiple layers; among them, the materials in each extruder are extruded from one layer of the composite die head. Therefore, it should be easily understood by those skilled in the art that when a border film with a transition layer attached to both surfaces of the skeleton layer and an adhesive layer attached to the surface of the transition layer (a total of five layers, in sequence: the first adhesive layer, the first transition layer, the skeleton layer, the second transition layer, the second adhesive layer) is required, multiple different extruders are used to melt the raw materials for forming the first adhesive layer, the first transition layer, the skeleton layer, the second transition layer, and the second adhesive layer, and the molten products are simultaneously extruded and cast into a film through the same die head including a five-layer distributor. The five film layers are stacked together during the extrusion process to obtain the five-layer structure border film of the present invention; when a border film with a transition layer and a hard layer attached to both surfaces of the skeleton layer respectively and an adhesive layer attached to the surface of the transition layer (a total of four layers, in sequence: the adhesive layer, the transition layer, the skeleton layer, the hard layer) is required, first, three different extruders are used to melt the raw materials for forming the adhesive layer, the transition layer, and the skeleton layer, and the molten products are simultaneously extruded and cast into a film through the same die head including a three-layer distributor. Then, the hard layer raw materials are uniformly mixed in proportion and coated on the skeleton layer by means of roll coating, and cured and formed by ultraviolet light to obtain the four-layer structure border film of the present invention; when a border film with a transition layer attached to one surface of the skeleton layer and an adhesive layer attached to the surface of the transition layer (a total of three layers, in sequence: the skeleton layer, the transition layer, and the adhesive layer) is required, three different extruders are used to melt the raw materials for forming the skeleton layer, the transition layer, and the adhesive layer, and the molten products are simultaneously extruded and cast into a film through the same die head including a three-layer distributor. The three film layers are stacked together during the extrusion process to obtain the border film of the present invention.In addition, the extrusion temperature generally does not exceed 250°C, preferably 180 - 200°C.

[0031] The method for preparing the edge frame film provided by the present invention preferably further includes, after extrusion casting, curing the obtained film at 50 - 90°C for more than 24 hours to further increase the crosslinking density and thereby improve the film strength.

[0032] The method for preparing the edge frame film provided by the present invention preferably further includes, after curing, irradiating the obtained film at a voltage of 50 - 200 KV with an irradiation dose of 5 - 30 kGy to further enhance the stiffness of the film and control the hot pressing fluidity.

[0033] The present invention will be described in detail below through examples.

[0034] Example 1

[0035] The raw materials and their proportions of the skeleton layer are shown in Table 1. After weighing all the raw materials in Table 1 according to the proportions, they are put into a high-speed mixer and stirred for 30 minutes, and then melt blended and pelletized at 200°C through a twin-screw extruder to obtain the raw materials for preparing the skeleton layer for standby use.

[0036] Table 1

[0037] Number Manufacturer Product Name Brand Ratio (by mass fraction) 1 Borealis Isotactic PP GE300 82.70％ 2 Hanwha Total Copolymerized PP RJ580Z 12.00％ 3 China National Bluestar Chopped Glass Fiber 910 5.00％ 4 Arkema Dicumyl Peroxide LUPEROX DH 0.20％ 5 Hunan Yixiang Technology Triallyl Isocyanate TMAIC 0.10％

[0038] The raw materials and their proportions of the transition layer are shown in Table 2. After weighing all the raw materials in Table 2 according to the proportions, they are put into a high-speed mixer and stirred for 15 minutes, and then melt blended and pelletized at 180°C through a twin-screw extruder to obtain the raw materials for preparing the transition layer for standby use.

[0039] Table 2

[0040] Number Manufacturer Product Name Brand Ratio (by mass fraction) 1 Sumitomo Chemical Ethylene Methacrylate Copolymer WD301-F 50％ 2 Dow Maleic Anhydride Modified Polypropylene BYNEL 50E803 50％

[0041] The raw materials and their proportions of the adhesive layer are shown in Table 3. After weighing all the raw materials in Table 3 according to the proportions, they are put into a high-speed mixer and stirred for 30 minutes, and then melt blended and pelletized at 150°C through a twin-screw extruder to obtain the raw materials for preparing the adhesive layer for standby use.

[0042] Table 3

[0043] Number Manufacturer Product Name Brand Ratio (by mass fraction) 1 INEOS Ethylene Methacrylic Acid Copolymer M28N430 79.70％ 2 Mitsui Ethylene Vinyl Acetate 45X 10.00％ 3 Guangxi Huangchuan Hydrogenated Petroleum Resin P-90 7.00％ 4 Merck Chemicals 2-Acrylamide-2-Methylpropanesulfonic Acid AMPS 3.00％ 5 Arkema Dicumyl Peroxide LUPEROX DH 0.20％ 6 Hunan Yixiang Technology Triallyl Isocyanate TMAIC 0.10％

[0044] Put the raw materials for preparing the skeleton layer, the raw materials for preparing the transition layer, and the raw materials for preparing the adhesive layer into three extruders respectively. Set the extrusion temperatures of the three extruders at 230 °C, 190 °C, and 180 °C respectively. Set the temperature at the connection between the flange and the mold at 220 °C, and the mold temperature at 220 °C. Cast and form with a skeleton layer of 25 microns, a transition layer of 3 microns, and an adhesive layer of 12 microns. Then place the obtained film in a curing oven at 60 °C for 24 hours. After that, perform electron beam irradiation on the obtained film, set the voltage at 80 KV, and the irradiation dose at 20 kGy to obtain a border film successively including a skeleton layer, a transition layer, and an adhesive layer, denoted as BM-1.

[0045] Example 2

[0046] The raw materials and their proportions of the skeleton layer are shown in Table 4. Weigh all the raw materials in Table 4 according to the proportions and put them into a high-speed mixer and stir for 30 minutes. Then, through a twin-screw extruder, carry out blending and granulation at 200 °C to obtain the raw materials for preparing the skeleton layer for standby use.

[0047] Table 4

[0048] Number Manufacturer Product Name Brand Ratio (by mass fraction) 1 Borealis Isotactic PP GE300 50.00％ 2 Hanwha Total Copolymerized PP RJ580Z 20.00％ 3 China National Bluestar Chopped Glass Fiber 910 20.00％ 4 Arkema Dicumyl Peroxide LUPEROX DH 5.00％ 5 Hunan Yixiang Technology Triallyl Isocyanate TMAIC 5.00％

[0049] The raw materials and their proportions of the first transition layer and the second transition layer are shown in Table 5. Weigh all the raw materials in Table 5 according to the proportions and put them into a high-speed mixer and stir for 15 minutes. Then, through a twin-screw extruder, carry out blending and granulation at 180 °C to obtain the raw materials for preparing the first transition layer and the second transition layer for standby use.

[0050] Table 5

[0051] Number Manufacturer Product Name Brand Ratio (by mass fraction) 1 Sumitomo Chemical Ethylene Methacrylate Copolymer WD301-F 50％ 2 Dow Maleic Anhydride Modified Polypropylene BYNEL 50E803 50％

[0052] The raw materials and their proportions of the first adhesive layer and the second adhesive layer are shown in Table 6. Weigh all the raw materials in Table 6 according to the proportions and put them into a high-speed mixer and stir for 30 minutes. Then, through a twin-screw extruder, carry out blending and granulation at 150 °C to obtain the raw materials for preparing the first adhesive layer and the second adhesive layer for standby use.

[0053] Table 6

[0054] Number Manufacturer Product Name Brand Ratio (by mass fraction) 1 INEOS Ethylene Methacrylic Acid Copolymer M28N430 79.70％ 2 Mitsui Ethylene Vinyl Acetate 45X 10.00％ 3 Guangxi Huangchuan Hydrogenated Petroleum Resin P-90 7.00％ 4 Merck Chemicals 2-Acrylamide-2-Methylpropanesulfonic Acid AMPS 3.00％ 5 Arkema Dicumyl Peroxide LUPEROX DH 0.20％ 6 Hunan Yixiang Technology Triallyl Isocyanate TMAIC 0.10％

[0055] The raw materials for preparing the first adhesive layer, the first transition layer, the skeleton layer, the second transition layer, and the second adhesive layer are respectively fed into five extruders. The extrusion temperatures of the five extruders are respectively set at 180°C, 190°C, 220°C, 190°C, and 180°C. The temperature at the connection between the flange and the mold is set at 220°C, and the mold temperature is set at 220°C. Casting and forming are carried out according to 12 microns for the first adhesive layer, 3 microns for the first transition layer, 25 microns for the skeleton layer, 3 microns for the second transition layer, and 12 microns for the second adhesive layer. Then, the obtained film is placed in an oven at 60°C for 24 hours of curing. After that, the obtained film is subjected to electron beam irradiation, with the voltage set at 80 KV and the irradiation dose set at 20 kGy, to obtain a border film successively including the first adhesive layer, the first transition layer, the skeleton layer, the second transition layer, and the second adhesive layer, denoted as BM-2.

[0056] Example 3

[0057] The raw materials and their proportions of the skeleton layer are shown in Table 7. All the raw materials in Table 7 are weighed according to the proportions and then fed into a high-speed mixer and stirred for 30 minutes, and then compounded and granulated by a twin-screw extruder at 200°C to obtain the raw materials for preparing the skeleton layer for standby use.

[0058] Table 7

[0059]

[0060]

[0061] The raw materials and their proportions of the transition layer are shown in Table 8. All the raw materials in Table 8 are weighed according to the proportions and then fed into a high-speed mixer and stirred for 15 minutes, and then compounded and granulated by a twin-screw extruder at 180°C to obtain the raw materials for preparing the transition layer for standby use.

[0062] Table 8

[0063] Number Manufacturer Product Name Brand Ratio (by mass fraction) 1 Sumitomo Chemical Ethylene Methacrylate Copolymer WD301-F 50％ 2 Dow Maleic Anhydride Modified Polypropylene BYNEL 50E803 50％

[0064] The raw materials and their proportions of the adhesive layer are shown in Table 9. All the raw materials in Table 9 are weighed according to the proportions and then fed into a high-speed mixer and stirred for 30 minutes, and then compounded and granulated by a twin-screw extruder at 150°C to obtain the raw materials for preparing the adhesive layer for standby use.

[0065] Table 9

[0066] Number Manufacturer Product Name Brand Ratio (by mass fraction) 1 INEOS Ethylene Methacrylic Acid Copolymer M28N430 79.70％ 2 Mitsui Ethylene Vinyl Acetate 45X 10.00％ 3 Guangxi Huangchuan Hydrogenated Petroleum Resin P-90 7.00％ 4 Merck Chemicals 2-Acrylamide-2-Methylpropanesulfonic Acid AMPS 3.00％ 5 Arkema Dicumyl Peroxide LUPEROX DH 0.20％ 6 Hunan Yixiang Technology Triallyl Isocyanate TMAIC 0.10％

[0067] The raw materials and their proportions of the hard layer are shown in Table 10. All the raw materials in Table 10 are weighed according to the proportions and then stirred in a high-speed mixer for 30 minutes, and then stored in the dark for standby use.

[0068] Table 10

[0069] Number Manufacturer Product Name Brand Ratio (by mass fraction) 1 Changxing Chemical Ethoxylated Bisphenol A Dimethacrylate EM3260 80.00％ 2 Guangdong Sanqi Tripropylene Glycol Diacrylate L-61025 10.00％ 3 Sartomer Trimethylolpropane Trimethacrylate SR350 9.00％ 4 I.G.M Benzoyl Peroxide BPO 1.00％

[0070] First, the raw materials for preparing the skeleton layer, the transition layer, and the adhesive layer are respectively put into three extruders. The extrusion temperatures of the three extruders are set at 220°C, 190°C, and 180°C respectively. The temperature at the connection between the flange and the mold is set at 220°C, and the mold temperature is set at 220°C. Casting and forming are carried out according to 25 microns for the skeleton layer, 3 microns for the transition layer, and 12 microns for the adhesive layer. Then, the obtained film is placed in a curing oven at 60°C for 24 hours. After that, the obtained film is subjected to electron beam irradiation. The voltage is set at 80 KV, and the irradiation dose is set at 20 kGy, obtaining a border film successively including a skeleton layer, a transition layer, and an adhesive layer.

[0071] The raw materials of the hard layer in Table 10 are mixed evenly and then coated on the skeleton layer by roll coating. The coating thickness is controlled at 3 microns, and then a hard layer is obtained through ultraviolet curing. Among them, the ultraviolet lamp is an H+ light source, and the irradiation energy is 1200 J / cm 2 , and finally the border film of the present invention is obtained, denoted as BM-3.

[0072] Comparative Example 1

[0073] A border film is prepared according to the method of Example 1. The difference is that the isotactic PP in the skeleton layer is replaced with the same weight part of copolymerized PP, and the other conditions are the same as those in Example 1, obtaining a reference border film, denoted as DBM-1.

[0074] Comparative Example 2

[0075] A border film is prepared according to the method of Example 1. The difference is that the copolymerized PP in the skeleton layer is replaced with the same weight part of isotactic PP, and the other conditions are the same as those in Example 1, obtaining a reference border film, denoted as DBM-2.

[0076] Comparative Example 3

[0077] A border film is prepared according to the method of Example 1. The difference is that it does not include a transition layer. That is, in the process of preparing the border film, only the raw materials for preparing the skeleton layer and the transition layer are extruded and formed, and the other conditions are the same as those in Example 1, obtaining a reference border film, denoted as DBM-3.

[0078] Comparative Example 4

[0079] A border film is prepared according to the method of Example 1. The difference is that both the ethylene methacrylic acid copolymer and ethylene vinyl acetate in the adhesive layer are replaced with the same weight part of hydrogenated petroleum resin, and the other conditions are the same as those in Example 1, obtaining a reference border film, denoted as DBM-4.

[0080] Comparative Example 5

[0081] The border film was prepared according to the method of Example 1, except that the hydrogenated petroleum resin in the adhesive layer was replaced with ethylene vinyl acetate in the same weight parts, and the other conditions were the same as those in Example 1, obtaining a reference border film, denoted as DBM-5.

[0082] Test Example

[0083] (1) Initial adhesion performance: The border films and proton exchange membranes (PEMs) obtained in the above examples and comparative examples were subjected to reciprocating hot roll lamination three times on a hot roll with a preset temperature of 170 °C and a pressure of 0.6 MPa. Then, they were cut into a width of 1 cm, cooled to room temperature, and subjected to 180° peeling according to the method specified in ASTM D903, with a peeling speed of 50 mm / min. The obtained results are shown in Table 1.

[0084] (2) High-temperature water environment performance: The border films obtained in the above examples and comparative examples were boiled in hot water at 95 °C for 1000 hours, and then the adhesion strength was tested according to the method specified in ASTM D903. The obtained results are shown in Table 1.

[0085] (3) Failure mode: The border films obtained in the above examples and comparative examples were boiled in hot water at 95 °C for 1000 hours, and then the adhesion strength was tested according to the method specified in ASTM D903. During the test of the adhesion strength, the adhesion failure mode was visually observed simultaneously and recorded as follows: one, the base film was damaged; two, the interface was damaged; three, the adhesion failed.

[0086] The obtained results are shown in Table 1.

[0087] Table 1

[0088]

[0089] It can be seen from the results in Table 1 that the border film provided by the present invention has good initial adhesion performance to the proton exchange membrane, and still has good adhesion performance and is not prone to delamination after long-term high-temperature boiling.

[0090] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principles and purposes of the present invention.

Claims

1. A border film, characterized in that, the border film comprises a skeleton layer, a transition layer attached to at least one surface of the skeleton layer, and an adhesive layer attached to the surface of the transition layer; the raw material for forming the skeleton layer contains 50-85% of isotactic polypropylene, 5-20% of propylene copolymer, 5-20% of mineral filler, 0.1-5% of a first peroxide and 0.1-5% of a first co-crosslinking agent; the raw material for forming the transition layer is an olefin polymer; the raw material for forming the adhesive layer contains 75-90% of polyolefin, 5-15% of hydrogenated petroleum resin, 0.1-5% of 2-acrylamido-2-methylpropanesulfonic acid, 0.1-3% of a second peroxide and 0.1-3% of a second co-crosslinking agent; the mineral filler is selected from at least one of glass fiber, calcium carbonate, titanium dioxide, glass microspheres and whiskers; the olefin polymer is selected from at least one of ethylene acrylate copolymer, maleic anhydride modified polyethylene, maleic anhydride modified polypropylene, epoxy modified polyethylene and epoxy modified polypropylene; the melting point of the polyolefin is 50-145°C; the polyolefin is selected from at least one of ethylene acrylic acid copolymer, ethylene vinyl acetate copolymer, maleic anhydride modified polyethylene, maleic anhydride modified polypropylene, epoxy modified polyethylene and epoxy modified polypropylene; the first peroxide and the second peroxide are each independently selected from at least one of cumene hydroperoxide, 2,5-dimethyl-2,5-dihydroperoxyhexane, cumene hydroperoxide and tert-butyl hydroperoxide.

2. The border film according to claim 1, characterized in that, the number average molecular weight of the isotactic polypropylene is 40,000-60,000.

3. The border film according to claim 1, characterized in that, the comonomer in the propylene copolymer is selected from at least one of ethylene, 1-butene, 2-butene, butadiene and octene.

4. The border film according to claim 1, characterized in that, the first co-crosslinking agent and the second co-crosslinking agent are each independently selected from at least one of triallyl isocyanurate, trimethallyl isocyanate and trimethylolpropane triacrylate.

5. The border film according to claim 1, characterized in that, the total thickness of the border film is 20-200 microns; the thickness of the skeleton layer is 5-150 microns; the thickness of the transition layer is 1-10 microns; the thickness of the adhesive layer is 5-25 microns.

6. The border film according to claim 1, characterized in that, a hard layer is attached to the other surface of the skeleton layer where the transition layer is not attached; the raw material for forming the hard layer contains 60-90% of ethoxylated bisphenol A dimethacrylate, 2-30% of dipropylene glycol diacrylate, 2-10% of trimethylolpropane trimethacrylate and 0.3-1.5% of benzoyl peroxide; the thickness of the hard layer is 1-10 microns.

7. The preparation method of the border film according to any one of claims 1-6, characterized in that, The method includes separately feeding each component in the skeleton layer, transition layer, and adhesive layer into an extruder after mixing them evenly, melting and kneading them, and then extruding and pelletizing them to obtain the raw materials for forming the skeleton layer, the raw materials for forming the transition layer, and the raw materials for forming the adhesive layer. Feeding the raw materials for forming the skeleton layer, the raw materials for forming the transition layer, and the raw materials for forming the adhesive layer into an extrusion casting device with a multi-layer co-extrusion structure to extrude and cast a composite film including the skeleton layer, the transition layer, and the adhesive layer. Optionally, it further includes mixing each component in the hard layer evenly and coating it on the other surface of the skeleton layer, and then curing it by ultraviolet light to obtain a border film.

8. The method for preparing the border film according to claim 7, characterized in that, the method further includes, after extrusion casting, curing the obtained film at 50-90 °C for more than 24 hours.

9. The method for preparing the border film according to claim 8, characterized in that, the method further includes, after curing, irradiating the obtained film at a voltage of 50-200 KV and an irradiation dose of 5-30 kGy.

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