Ion exchange membrane, method for preparing the same, and use thereof

Abstract

The application discloses an ion exchange membrane and a preparation method and application thereof. The preparation method of the ion exchange membrane comprises the following steps: (1) placing a perfluorosulfonic acid fluorine type resin membrane, a reinforcing membrane and the perfluorosulfonic acid fluorine type resin membrane in sequence and then performing hot pressing to obtain a composite base film; (2) performing bidirectional stretching after cooling the composite base film; and (3) performing heat treatment on the membrane after the bidirectional stretching in the step (2), and then performing alkali treatment and acid treatment in sequence to obtain the ion exchange membrane. The method of the application can increase the mechanical strength of the ion exchange membrane while ensuring the ion exchange capacity of the ion exchange membrane, the resin and the reinforcing material in the membrane are closely combined, the microporous structure is uniform, the crystallinity is high, the tensile strength is high, the proton conductivity is high, the proton exchange capacity is strong, and the ion exchange membrane can be applied to the fields of water electrolysis, fuel cells and the like.

Description

Technical Field

[0001] This invention relates to the field of ion exchange membranes, and more specifically, to an ion exchange membrane, its preparation method, and its application. Background Technology

[0002] Perfluorosulfonic acid ion exchange membranes, due to their unique perfluorinated backbone and sulfonic acid structure with ion-conducting capabilities, exhibit excellent ion conductivity while demonstrating outstanding chemical, electrochemical, and thermal stability. Therefore, they are widely used in fuel cells, water electrolysis, electrodialysis, and flow batteries. With the increasing demand for volumetric power density applications, improving the mechanical strength of perfluorosulfonic acid ion exchange membranes while reducing their thickness is a current research hotspot. However, reducing the thickness affects the membrane's lifespan; simply increasing the exchange capacity of the perfluorosulfonic acid resin improves the ion conductivity but simultaneously worsens the membrane's dimensional stability. Improving the ion conductivity of ion exchange membranes while maintaining their mechanical properties and dimensional stability is the current research direction.

[0003] Perfluorosulfonic acid resins include H-type resins with sulfonic acid groups (-SO3-) or F-type resins with sulfonyl fluoride groups (-SO2F) (also known as fluorinated perfluorosulfonic acid resins, perfluorosulfonyl fluoride resins, or fluororesins). Common production processes for perfluorosulfonic acid resins are solution casting and melt extrusion. Solution casting involves combining H-type resin with a reinforcing mesh; however, the resulting membrane has low crystallinity and significant surface swelling. Melt extrusion produces membranes with better performance than solution casting, but the reinforcing mesh cannot be used directly, as H-type resin is prone to decomposition under hot pressing. Common reinforcing materials are often inorganic particles, such as graphene oxide and silica particles; however, the reinforcing effect of inorganic nanoparticles is limited, and a large increase in particle size leads to a decrease in conductivity. Summary of the Invention

[0004] This invention is based on the inventors' discoveries and understanding of the following facts and problems: Membranes prepared by solution casting have low crystallinity and significant surface swelling. Membranes prepared by melt extrusion cannot directly use reinforcing meshes; common reinforcing materials are mostly inorganic particles, which have limited reinforcing effects, and an increase in the number of particles leads to a decrease in electrical conductivity.

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose an ion exchange membrane, its preparation method, and its applications. While increasing the mechanical strength of the ion exchange membrane, it also ensures the ion exchange capacity of the membrane. The resin and reinforcing material in the membrane are tightly integrated, resulting in a uniform microporous structure, high crystallinity, high tensile strength, high proton conductivity, and strong proton exchange capacity. It can be used in fields such as water electrolysis and fuel cells.

[0006] This invention provides a method for preparing an ion exchange membrane, comprising the following steps:

[0007] (1) The perfluorosulfonic acid fluorine resin film, the reinforcing film, and the perfluorosulfonic acid fluorine resin film are stacked in sequence and hot-pressed to obtain a composite base film.

[0008] (2) After cooling the composite base film, it is subjected to biaxial stretching;

[0009] (3) The biaxially stretched membrane in step (2) is subjected to heat treatment, followed by alkali treatment and acid treatment to obtain an ion exchange membrane.

[0010] The advantages and technical effects of the ion exchange membrane preparation method of this invention are as follows: A method for reinforcing a fluorinated resin membrane is provided, in which a reinforcing membrane and a perfluorosulfonic acid fluorinated resin membrane are hot-pressed together, and then the membrane is subjected to bi-stretching to form slit-like micropores. Heat treatment is then performed to further promote the composite of the reinforcing membrane and the perfluorosulfonic acid fluorinated resin membrane, eliminating residual stress from the bi-stretching process. This reduces or even eliminates the pores caused by bi-stretching on the perfluorosulfonic acid fluorinated resin layer, forming a porous intermediate layer. Finally, alkali and acid treatments are performed to obtain a reinforced ion exchange membrane with perfluorosulfonic acid resin layers on both sides and an intermediate layer. Currently, methods for preparing ion exchange membranes by directly hot-pressing reinforcing meshes typically suffer from large pore sizes in existing reinforcing meshes. Even when using smaller pore sizes, the meshes cannot effectively bond tightly with the perfluorosulfonic acid fluorinated resin membrane through hot pressing, thus failing to produce composite ion exchange membranes. However, the method of this invention directly uses reinforcing membrane materials and employs a bistretching process to form a porous intermediate layer, preparing a multilayer composite ion exchange membrane. The micropores formed by bistretching are even smaller, resulting in a tighter bonding between the fluorinated resin and the reinforcing material, and a uniform microporous structure. This method increases the mechanical strength of the ion exchange membrane while maintaining its ion exchange capacity. The membrane exhibits a tight bonding between the resin and the reinforcing material, a uniform microporous structure, high crystallinity, high tensile strength, high proton conductivity, and strong proton exchange capacity, making it suitable for applications such as water electrolysis and fuel cells.

[0011] In some embodiments, in step (1), the perfluorosulfonic acid fluorine resin membrane is obtained by melt extrusion of perfluorosulfonic acid fluorine resin;

[0012] And / or, the ion exchange capacity of the perfluorosulfonic acid fluorinated resin membrane is 500-20000 g / mol;

[0013] And / or, the thickness of the perfluorosulfonic acid fluorinated resin film is 50-200 μm.

[0014] In some embodiments, in step (1), the reinforcing film includes at least one of polyetheretherketone, sulfonated polyetheretherketone, soluble polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, and polyethersulfone.

[0015] In some embodiments, in step (1), the reinforcing film is obtained by melt extrusion;

[0016] And / or, the thickness of the reinforcing film is 1-20 μm.

[0017] In some embodiments, in step (1), the temperature of the hot pressing is 200-500°C;

[0018] And / or, the pressure of the hot pressing is 2-10 MPa;

[0019] And / or, the hot pressing time is 5-30 min.

[0020] In some embodiments, in step (2), the temperature of the biaxial stretching is 200-420°C;

[0021] And / or, the biaxial stretching rate is 2-9 m / min;

[0022] And / or, the bidirectional stretching includes longitudinal stretching and transverse stretching, wherein the longitudinal stretching multiple is 1.5-10 times; and the transverse stretching multiple is 1.5-10 times.

[0023] In some embodiments, in step (3), the temperature of the heat treatment is 180-350°C;

[0024] And / or, the heat treatment time is not less than 10 minutes.

[0025] This invention provides an ion exchange membrane prepared using the method described in this invention. This invention possesses the corresponding advantages of the ion exchange membrane preparation method, which will not be elaborated further here.

[0026] In some embodiments, the thickness of the ion exchange membrane is 10-300 μm;

[0027] And / or, the pore size of the intermediate layer of the ion exchange membrane is 5-20 μm.

[0028] This invention provides an application of an ion exchange membrane for water electrolysis, batteries, or electrodialysis. In this embodiment, the ion exchange membrane can be used in fields such as water electrolysis and batteries, for example, in water electrolysis hydrogen production devices and proton exchange membranes. Detailed Implementation

[0029] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0030] An embodiment of the present invention provides a method for preparing an ion exchange membrane, comprising the following steps:

[0031] (1) The perfluorosulfonic acid fluorine resin film, the reinforcing film, and the perfluorosulfonic acid fluorine resin film are stacked in sequence and hot-pressed to obtain a composite base film.

[0032] Specifically, the perfluorosulfonic acid fluorine resin film, the reinforcing film, and the perfluorosulfonic acid fluorine resin film are stacked sequentially along the film thickness direction and then hot-pressed along the film thickness direction to obtain a composite base film.

[0033] (2) After cooling the composite base film, it is subjected to biaxial stretching; optionally, the cooling is natural cooling.

[0034] (3) The biaxially stretched membrane in step (2) is subjected to heat treatment, followed by alkali treatment and acid treatment to obtain an ion exchange membrane.

[0035] The method for preparing an ion exchange membrane according to an embodiment of the present invention provides a method for reinforcing a fluorinated resin membrane. The reinforcing membrane and a perfluorosulfonic acid fluorinated resin membrane are hot-pressed together. Then, the membrane is subjected to bistretching to create pores, forming slit-like micropores. Further heat treatment promotes the composite of the reinforcing membrane and the perfluorosulfonic acid fluorinated resin membrane, eliminating residual stress from the bistretching process. This reduces or even eliminates the pores on the perfluorosulfonic acid fluorinated resin layer caused by bistretching, forming a porous intermediate layer. Finally, alkali and acid treatments are performed to obtain a reinforced ion exchange membrane with perfluorosulfonic acid resin layers on both sides and an intermediate layer. Currently, methods for preparing ion exchange membranes by directly hot-pressing reinforcing meshes typically suffer from large pore sizes in existing reinforcing meshes. Even when using smaller pore sizes, the meshes cannot effectively bond tightly with the perfluorosulfonic acid fluorinated resin membrane through hot pressing, thus failing to produce composite ion exchange membranes. However, the method of this invention directly uses reinforcing membrane materials and employs a bistretching process to form a porous intermediate layer, preparing a multilayer composite ion exchange membrane. The micropores formed by bistretching are even smaller, resulting in a tighter bonding between the fluorinated resin and the reinforcing material, and a uniform microporous structure. This method increases the mechanical strength of the ion exchange membrane while maintaining its ion exchange capacity. The membrane exhibits a tight bonding between the resin and the reinforcing material, a uniform microporous structure, high crystallinity, high tensile strength, high proton conductivity, and strong proton exchange capacity, making it suitable for applications such as water electrolysis and fuel cells.

[0036] In some embodiments, in step (1), the perfluorosulfonic acid fluorinated resin film is obtained by melt extrusion of the perfluorosulfonic acid fluorinated resin; preferably, the melt extrusion temperature is 300-400℃, specifically, for example, 300℃, 320℃, 340℃, 360℃, 380℃, 400℃; the temperature of the melt extrusion die is 300-350℃, specifically, for example, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃. In this embodiment of the invention, the perfluorosulfonic acid fluorinated resin film is obtained by melt extrusion. After melt extrusion, the perfluorosulfonic acid fluorinated resin molecules undergo high-temperature stretching, resulting in a more regular molecular orientation.

[0037] In some embodiments, the perfluorosulfonic acid fluoride-type resin membrane is a perfluorosulfonic acid resin F-type resin having sulfonyl fluoride groups (-SO2F), i.e., perfluorosulfonyl fluoride resin; the ion exchange capacity of the perfluorosulfonic acid fluoride-type resin membrane is 500-20000 g / mol, specifically, for example, 500 g / mol, 1000 g / mol, 5000 g / mol, 10000 g / mol, 15000 g / mol, 20000 g / mol; and / or, the thickness of the perfluorosulfonic acid fluoride-type resin membrane is 50-200 μm, specifically, for example, 50 μm, 70 μm, 100 μm, 150 μm, 200 μm. In these embodiments of the invention, by optimizing the ion exchange capacity of the perfluorosulfonic acid fluoride-type resin membrane, better ion exchange is achieved.

[0038] In some embodiments, in step (1), the reinforcing membrane includes at least one of polyetheretherketone, sulfonated polyetheretherketone, soluble polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, and polyethersulfone. In these embodiments, by selecting the appropriate type of reinforcing membrane, it is beneficial to achieve a tighter composite between the fluororesin and the reinforcing membrane material, further increasing the mechanical strength of the subsequently produced ion exchange membrane. This results in a more uniform microporous structure, higher tensile strength, and superior overall performance of the ion exchange membrane.

[0039] In some embodiments, in step (1), the reinforcing membrane has no through holes.

[0040] In some embodiments, in step (1), the reinforcing membrane is obtained by melt extrusion; the reinforcing membrane is a homogeneous membrane; preferably, the temperature of the melt extrusion is 200-450°C, specifically, for example, 200°C, 250°C, 260°C, 300°C, 350°C, 360°C, 380°C, 400°C, 420°C, 450°C; the temperature of the die for the melt extrusion is 200-400°C, specifically, for example, 200°C, 210°C, 250°C, 290°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C. In this embodiment of the invention, the reinforcing membrane is obtained by melt extrusion of the reinforcing membrane material, forming a polymer film under tensile stress during extrusion, and then further processed to form micropores using bistretching during the preparation of the ion exchange membrane.

[0041] In some embodiments, the thickness of the reinforcing film is 1-20 μm, specifically, for example, 1 μm, 2 μm, 3 μm, 4 μm, 7 μm, 10 μm, 15 μm, 20 μm.

[0042] In some embodiments, in step (1), the hot-pressing temperature is 200-500℃, specifically, for example, 200℃, 210℃, 250℃, 300℃, 350℃, 400℃, 450℃, 500℃; and / or, the hot-pressing pressure is 2-10MPa, specifically, for example, 2MPa, 4MPa, 6MPa, 8MPa, 10MPa; and / or, the hot-pressing time is 5-30min, specifically, for example, 5min, 10min, 15min, 20min, 30min; and / or, the hot-pressing is performed using a flatbed hot press. In this embodiment of the invention, by optimizing the hot-pressing temperature and other conditions, it is beneficial to achieve a tighter composite between the fluororesin and the reinforcing material, further increasing the mechanical strength and tensile strength of the ion exchange membrane, which is further beneficial to the uniformity of the microporous structure formed by subsequent biaxial stretching, resulting in better overall performance. If the hot-pressing temperature is too low or the hot-pressing pressure is too low, the materials may separate into layers, and the fluoropolymer and reinforcing material may not be tightly bonded, thus affecting the mechanical and electrochemical properties. If the hot-pressing temperature is too high, some materials may decompose. If the hot-pressing pressure is too high, it is not conducive to the removal of air bubbles between the multilayer materials.

[0043] In some embodiments, in step (1), the breathable substrate, the perfluorosulfonic acid fluorinated resin film, the reinforcing film, the perfluorosulfonic acid fluorinated resin film, and the breathable substrate are stacked sequentially and hot-pressed to obtain a composite base film. Specifically, they are stacked sequentially along the film thickness direction and hot-pressed. Optionally, the breathable substrate includes at least one of sulfuric acid paper and polytetrafluoroethylene film. After the composite base film is cooled, the breathable substrate is removed. The cooling is done by natural cooling. The breathable substrate includes 1-3 breathable substrates, specifically, 2 breathable substrates are covered on the top and bottom.

[0044] In some embodiments, in step (1), the hot pressing is performed by clamping two graphite plates together.

[0045] In some embodiments, in step (1), the extrusion casting direction is denoted as the longitudinal stretching (MD) direction, and the direction perpendicular to the MD direction is denoted as the transverse stretching (TD) direction.

[0046] In some embodiments, in step (2), the temperature of the biaxial stretching is 200-420°C, specifically, for example, 200°C, 210°C, 250°C, 300°C, 350°C, 360°C, 400°C, 420°C; and / or, the rate of the biaxial stretching is 2-9 m / min, specifically, for example, 2 m / min, 3 m / min, 4 m / min, 5 m / min, 8 m / min, 9 m / min; the biaxial stretching includes longitudinal stretching (MD) and transverse stretching (TD), the longitudinal stretching multiple is 1.5-10 times, specifically, for example, 1.5 times, 2 times, 3 times, 4 times, 6 times, 8 times, 10 times; the transverse stretching multiple is 1.5-10 times, specifically, for example, 1.5 times, 2 times, 3 times, 4 times, 6 times, 8 times, 10 times. In this embodiment of the invention, the preferred biaxial stretching process facilitates the formation of uniformly structured micropores in the interlayer material. Excessively low stretching temperature or stretching rate hinders micropore formation, resulting in significant differences in micropore size distribution; excessively high stretching temperature or stretching rate can easily lead to tensile fracture. Too low or too high a stretching rate results in insufficient uniformity, causing inconsistent thickness on both sides and in the middle of the ion exchange membrane, thus affecting the overall performance of the membrane. Optimizing the stretching ratio helps to ensure the pore structure of the interlayer is within a reasonable range; excessively high stretching ratios lead to relatively low material strength, while excessively low stretching ratios may affect the material's ion conductivity.

[0047] In some embodiments, in step (3), the heat treatment temperature is 180-350℃, specifically, for example, 180℃, 200℃, 220℃, 240℃, 250℃, 300℃, 350℃; and / or, the heat treatment time is not less than 10 min, specifically, for example, 10 min, 12 min, 15 min, 20 min, 30 min. In this embodiment of the invention, by optimizing the heat treatment process, it is beneficial to further promote the composite of the reinforcing membrane and the perfluorosulfonate fluorine resin membrane, while eliminating the residual stress of the biaxial stretching process. Moreover, the micropore size formed on the membrane surface by biaxial stretching is relatively large. Heat treatment causes the pore size to shrink, and reduces or even eliminates the pores on the perfluorosulfonate fluorine resin layer caused by biaxial stretching. By optimizing the heat treatment temperature and time, it is beneficial to further increase the mechanical strength of the ion exchange membrane, ensure the ion exchange capacity of the ion exchange membrane, have higher tensile strength, higher proton conductivity, stronger proton exchange capacity, and better overall performance.

[0048] In some embodiments, the alkali treatment and acid treatment in step (3) are not particularly limited. Non-limiting examples include: the alkali treatment uses an alkali solution, preferably with a concentration of 2-20 wt%; the alkali solution includes at least one of NaOH or KOH; the temperature of the alkali treatment is 50-70°C; the time of the alkali treatment is 4-6 hours, optionally 5 hours; the acid treatment uses an acid; preferably with a concentration of 1-10 wt%; the acid includes sulfuric acid; the temperature of the acid treatment is 50-70°C; the time of the acid treatment is 4-6 hours, optionally 5 hours.

[0049] An ion exchange membrane according to an embodiment of the present invention is prepared using the method described in the embodiment of the present invention. The embodiment of the present invention possesses the corresponding advantages of the ion exchange membrane preparation method, which will not be elaborated further here.

[0050] In some embodiments, the thickness of the ion exchange membrane is 10-300 μm, specifically, for example, 10 μm, 50 μm, 60 μm, 70 μm, 90 μm, 100 μm, 150 μm, 200 μm, 300 μm.

[0051] In some embodiments, the ion exchange membrane includes two perfluorosulfonic acid resin layers on both sides and an intermediate layer. In this embodiment of the invention, the perfluorosulfonic acid fluoride resin membrane, the reinforcing membrane, and the perfluorosulfonic acid fluoride resin membrane are respectively prepared by the ion exchange membrane preparation method to obtain two perfluorosulfonic acid resin layers on both sides and an intermediate layer.

[0052] In some embodiments, the pore size of the intermediate layer of the ion exchange membrane is 5-20 μm, specifically, for example, 5 μm, 6 μm, 7 μm, 10 μm, 12 μm, 15 μm, 18 μm, and 20 μm. In this embodiment of the invention, the pore size of the intermediate layer of the ion exchange membrane is 5-20 μm, which is beneficial for the transport of hydrogen protons. Existing reinforcing mesh materials have relatively large pore sizes, for example, 40-50 μm. Even when using reinforcing mesh materials with small pore sizes, directly using the reinforcing mesh material and perfluorosulfonic acid fluorinated resin membrane for hot pressing to prepare the ion exchange membrane results in the inability to effectively and tightly bond the reinforcing mesh material with the perfluorosulfonic acid fluorinated resin membrane through hot pressing, thus failing to produce a composite ion exchange membrane. The method of the present invention forms micropores with even smaller pore sizes through biaxial stretching.

[0053] This invention discloses an application of an ion exchange membrane in water electrolysis, batteries, or electrodialysis. In this embodiment, the ion exchange membrane can be used in fields such as water electrolysis and batteries, for example, in water electrolysis hydrogen production devices and proton exchange membranes.

[0054] In some embodiments, it is used for fuel cells.

[0055] In some embodiments, it is used for a proton exchange membrane.

[0056] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0057] Example 1

[0058] A method for preparing an ion exchange membrane includes the following steps:

[0059] (1) Fluoropolymer resin is melt-extruded to obtain a fluoropolymer resin film. The extrusion temperature is 320℃, the die temperature is 350℃, and the extrusion thickness is 200 micrometers.

[0060] (2) Polyether ether ketone was melt-extruded to obtain a polyether ether ketone film. The extrusion temperature was 360°C, the die temperature was 390°C, and the extrusion thickness was 12 micrometers.

[0061] (3) Stack the fluoropolymer membrane, polyether ether ketone membrane and fluoropolymer membrane in sequence, cover the top and bottom with 2 breathable substrates, and hot press in a flat plate hot press at 400℃ for 20 minutes at a pressure of 10 MPa to obtain the composite base film.

[0062] (4) Cool the composite base film and perform bidirectional stretching in a biaxial stretching machine at 400℃. The stretching rate is 3m / min, and the stretching ratio of MD and TD is 2 times to obtain a microporous composite film.

[0063] (5) Heat-treat the microporous composite membrane at 300℃ for 10 min;

[0064] (6) After heat treatment, alkali treatment and acid treatment are performed sequentially to obtain an ion exchange membrane. The ion exchange membrane has a uniform thickness and a uniform pore size in the intermediate layer.

[0065] Example 2

[0066] A method for preparing an ion exchange membrane includes the following steps:

[0067] (1) Fluoropolymer resin is melt-extruded to obtain a fluoropolymer resin film. The extrusion temperature is 320℃, the die temperature is 350℃, and the extrusion thickness is 140 micrometers.

[0068] (2) Polyether ether ketone was melt-extruded to obtain a polyether ether ketone film. The extrusion temperature was 360°C, the die temperature was 390°C, and the extrusion thickness was 4 micrometers.

[0069] (3) Stack the fluoropolymer membrane, polyether ether ketone membrane and fluoropolymer membrane in sequence, cover the top and bottom with 2 breathable substrates, and hot press in a flat plate hot press at 400℃ for 20 minutes at a pressure of 10 MPa to obtain the composite base film.

[0070] (4) Cool the composite base film and perform bidirectional stretching in a biaxial stretching machine at 400℃. The stretching rate is 4m / min, and the stretching ratio of MD and TD is 2 times to obtain a microporous composite film.

[0071] (5) Heat-treat the microporous composite membrane at 300℃ for 10 min;

[0072] (6) After heat treatment, alkali treatment and acid treatment are performed sequentially to obtain an ion exchange membrane. The ion exchange membrane has a uniform thickness and a uniform pore size in the intermediate layer.

[0073] Example 3

[0074] A method for preparing an ion exchange membrane includes the following steps:

[0075] (1) Fluoropolymer resin is melt-extruded to obtain a fluoropolymer resin film. The extrusion temperature is 320℃, the die temperature is 350℃, and the extrusion thickness is 100 micrometers.

[0076] (2) Sulfonated polyether ether ketone was melt-extruded to obtain a sulfonated polyether ether ketone film. The extrusion temperature was 260°C, the die temperature was 290°C, and the extrusion thickness was 3 micrometers.

[0077] (3) The fluoropolymer membrane, sulfonated polyether ether ketone membrane and fluoropolymer membrane are stacked in sequence, and two breathable substrates are placed on the top and bottom. The membrane is then hot-pressed in a flatbed hot press at 290°C for 20 minutes at a pressure of 10 MPa to obtain a composite base membrane.

[0078] (4) Cool the composite base film and perform bidirectional stretching in a biaxial stretching machine at 290℃. The stretching rate is 3m / min, and the stretching ratio of MD and TD is 2 times to obtain a microporous composite film.

[0079] (5) Heat-treat the microporous composite membrane at 290℃ for 10 min;

[0080] (6) After heat treatment, alkali treatment and acid treatment are performed sequentially to obtain an ion exchange membrane. The ion exchange membrane has a uniform thickness and a uniform pore size in the intermediate layer.

[0081] Example 4

[0082] A method for preparing an ion exchange membrane includes the following steps:

[0083] (1) Fluoropolymer resin is melt-extruded to obtain a fluoropolymer resin film. The extrusion temperature is 320℃, the die temperature is 350℃, and the extrusion thickness is 100 micrometers.

[0084] (2) Soluble polytetrafluoroethylene is melt-extruded to obtain a soluble polytetrafluoroethylene film. The extrusion temperature is 350℃, the die temperature is 360℃, and the extrusion thickness is 3 micrometers.

[0085] (3) The fluoropolymer membrane, soluble polytetrafluoroethylene membrane and fluoropolymer membrane are stacked in sequence, and two breathable substrates are placed on the top and bottom. The membrane is then hot-pressed in a flatbed hot press at 360°C for 20 minutes at a pressure of 10 MPa to obtain a composite base membrane.

[0086] (4) Cool the composite base film and perform bidirectional stretching in a 360°C biaxial stretching machine at a stretching rate of 3 m / min. The stretching ratios of MD and TD are both 2 times to obtain a microporous composite film.

[0087] (5) Heat-treat the microporous composite membrane at 300℃ for 10 min;

[0088] (6) After heat treatment, alkali treatment and acid treatment are performed sequentially to obtain an ion exchange membrane. The ion exchange membrane has a uniform thickness and a uniform pore size in the intermediate layer.

[0089] Example 5

[0090] A method for preparing an ion exchange membrane includes the following steps:

[0091] (1) Fluoropolymer resin is melt-extruded to obtain a fluoropolymer resin film. The extrusion temperature is 320℃, the die temperature is 350℃, and the extrusion thickness is 200 micrometers.

[0092] (2) Polyethersulfone was melt-extruded to obtain a polyethersulfone film. The extrusion temperature was 350°C, the die temperature was 360°C, and the extrusion thickness was 12 micrometers.

[0093] (3) Stack the fluoropolymer membrane, polyethersulfone membrane and fluoropolymer membrane in sequence, cover each with two breathable substrates, and hot press them in a flat plate hot press at 360°C for 20 minutes at a pressure of 10 MPa to obtain the composite base film.

[0094] (4) Cool the composite base film and perform bidirectional stretching in a 360°C biaxial stretching machine at a stretching rate of 3 m / min. The stretching ratios of MD and TD are both 2 times to obtain a microporous composite film.

[0095] (5) Heat-treat the microporous composite membrane at 300℃ for 10 min;

[0096] (6) After heat treatment, alkali treatment and acid treatment are performed sequentially to obtain an ion exchange membrane. The ion exchange membrane has a uniform thickness and a uniform pore size in the intermediate layer.

[0097] Example 6

[0098] A method for preparing an ion exchange membrane includes the following steps:

[0099] (1) Fluoropolymer resin is melt-extruded to obtain a fluoropolymer resin film. The extrusion temperature is 320℃, the die temperature is 350℃, and the extrusion thickness is 200 micrometers.

[0100] (2) Polyvinylidene fluoride was melt-extruded to obtain a polyvinylidene fluoride film. The extrusion temperature was 200℃, the die temperature was 210℃, and the extrusion thickness was 12 micrometers.

[0101] (3) Stack the fluoropolymer membrane, polyvinylidene fluoride membrane and fluoropolymer membrane in sequence, cover each with two breathable substrates, and hot press them in a flat plate hot press at 210℃ for 20 minutes at a pressure of 10 MPa to obtain a composite base film.

[0102] (4) Cool the composite base film and perform bidirectional stretching in a biaxial stretching machine at 210℃. The stretching rate is 3m / min, and the stretching ratio of MD and TD is 2 times to obtain a microporous composite film.

[0103] (5) Heat-treat the microporous composite membrane at 210℃ for 10 min;

[0104] (6) After heat treatment, alkali treatment and acid treatment are performed sequentially to obtain an ion exchange membrane. The ion exchange membrane has a uniform thickness and a uniform pore size in the intermediate layer.

[0105] Example 7

[0106] A method for preparing an ion exchange membrane includes the following steps:

[0107] (1) Fluoropolymer resin is melt-extruded to obtain a fluoropolymer resin film. The extrusion temperature is 320℃, the die temperature is 350℃, and the extrusion thickness is 200 micrometers.

[0108] (2) Ethylene-tetrafluoroethylene copolymer was melt-extruded to obtain ethylene-tetrafluoroethylene copolymer film. The extrusion temperature was 260℃, the die temperature was 270℃, and the extrusion thickness was 12 micrometers.

[0109] (3) The fluoropolymer membrane, ethylene-tetrafluoroethylene copolymer membrane and fluoropolymer membrane are stacked in sequence, and two breathable substrates are placed on the top and bottom. The membrane is then hot-pressed in a flatbed hot press at 270°C for 20 minutes at a pressure of 10 MPa to obtain a composite base membrane.

[0110] (4) Cool the composite base film and perform bidirectional stretching in a biaxial stretching machine at 270℃. The stretching rate is 3m / min, and the stretching ratio of MD and TD is 2 times to obtain a microporous composite film.

[0111] (5) Heat-treat the microporous composite membrane at 270℃ for 10 min;

[0112] (6) After heat treatment, alkali treatment and acid treatment are performed sequentially to obtain an ion exchange membrane. The ion exchange membrane has a uniform thickness and a uniform pore size in the intermediate layer.

[0113] Comparative Example 1

[0114] The preparation method is exactly the same as that in Example 1, except that step (5) is omitted, that is, the heat treatment step is omitted.

[0115] Comparative Example 2

[0116] The preparation method is exactly the same as that in Example 1, except that the stretching rate in step (4) is 1 m / min.

[0117] Comparative Example 3

[0118] The preparation method is exactly the same as that in Example 1, except that the stretching rate in step (4) is 10 m / min.

[0119] Comparative Example 4

[0120] The preparation method is exactly the same as that in Example 1, except that in step (4), the temperature of biaxial stretching is 450°C and no film is formed during stretching.

[0121] Comparative Example 5

[0122] The preparation method is exactly the same as that in Example 1, except that in step (1), a 50-micron fluoropolymer film is extruded, and then the fluoropolymer film, polyetheretherketone mesh and fluoropolymer film are stacked in sequence and hot-pressed together. The polyetheretherketone mesh has a wire diameter of 50 microns, a mesh count of 100 mesh, an opening width of 25 microns and a thickness of 70 microns. Steps (4) and (5) are omitted, that is, biaxial stretching and heat treatment are omitted.

[0123] Comparative Example 6

[0124] A commercially available ion exchange membrane prepared by casting method, wherein the intermediate layer is a polyetheretherketone (PEEK) mesh.

[0125] Table 1

[0126]

[0127] As shown in Table 1, the ion exchange membrane preparation method provided by this invention can prepare multilayer ion exchange membranes using different intermediate materials. The conductivity and tensile strength of the ion exchange membranes in the examples are slightly better than those of the commercially available ion exchange membranes in Comparative Example 6. This is because the commercially available membranes are prepared by casting, resulting in lower crystallinity. The main function of the reinforcing layer is to provide support strength. In Comparative Examples 1-3, when heat treatment was not performed or the bi-stretching rate was inappropriate, the pore structure of the membrane material changed significantly. The intermediate layer lacked a suitable pore structure, and the pore structure was uneven with a large difference in micropore size distribution, leading to poor mechanical properties of the material. In Comparative Example 4, the excessively high bi-stretching temperature resulted in poor membrane formation and stretching failure. Comparative Example 5 directly used resin and mesh fabric for lamination. Because the diameter of the polyether ether ketone (PEEK) mesh fabric was 50 micrometers, the resin distribution in local areas along the thickness direction was less, directly leading to lower membrane strength.

[0128] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0129] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing an ion exchange membrane, characterized in that, Includes the following steps: (1) The perfluorosulfonic acid fluorine resin film, the reinforcing film, and the perfluorosulfonic acid fluorine resin film are stacked in sequence and hot-pressed to obtain a composite base film; the reinforcing film is obtained by melt extrusion; the hot-pressing temperature is 200-500℃; (2) After cooling the composite base film, it is subjected to biaxial stretching; (3) The biaxially stretched membrane in step (2) is subjected to heat treatment, followed by alkali treatment and acid treatment to obtain an ion exchange membrane; the heat treatment temperature is 180-350℃; the pore size of the intermediate layer of the ion exchange membrane is 5-20μm. In step (1), the reinforcing film includes at least one of polyetheretherketone, sulfonated polyetheretherketone, soluble polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, and polyethersulfone. In step (2), the temperature of the biaxial stretching is 200-420℃; The biaxial stretching rate is 2-9 m / min; The bidirectional stretching includes longitudinal stretching and transverse stretching, wherein the longitudinal stretching multiple is 1.5-10 times; and the transverse stretching multiple is 1.5-10 times. In step (3), the heat treatment time shall not be less than 10 min.

2. The method for preparing the ion exchange membrane according to claim 1, characterized in that, In step (1), the perfluorosulfonic acid fluorine resin film is obtained by melt extrusion of perfluorosulfonic acid fluorine resin; And / or, the thickness of the perfluorosulfonic acid fluorinated resin film is 50-200 μm.

3. The method for preparing the ion exchange membrane according to claim 1, characterized in that, In step (1), the thickness of the reinforcing film is 1-20 μm.

4. The method for preparing the ion exchange membrane according to claim 1, characterized in that, In step (1), the pressure of the hot pressing is 2-10 MPa; And / or, the hot pressing time is 5-30 min.

5. An ion exchange membrane, characterized in that, The ion exchange membrane is prepared by any one of claims 1-4.

6. The ion exchange membrane according to claim 5, characterized in that, The thickness of the ion exchange membrane is 10-300 μm.

7. An application of the ion exchange membrane as described in claim 5 or 6, characterized in that, Used in water electrolysis, batteries, or electrodialysis.

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