Breathable and water-resistant membranes, their preparation methods, and applications

Abstract

This invention provides a breathable and water-blocking membrane, its preparation method, and its application, belonging to the field of polymer thin film technology. The breathable and water-blocking membrane comprises: a single-layer membrane containing a fluoropolymer film layer, or a composite membrane consisting of a fluoropolymer film layer and a polymer film layer stacked together. The crystallinity of the single-layer membrane and the composite membrane is <70%, and the CO2 permeability is ≥20000 mL / m³. 2 • 24hrs • 0.1MPa, water vapor transmission rate ≤ 5g / m 2 • 24hrs. The breathable and water-resistant membrane of the present invention has both high air permeability and low water permeability, and can be widely used in many application fields.

Description

Technical Field

[0001] This invention relates to the field of polymer film technology, and in particular to a breathable and water-resistant membrane, its preparation method, and its application. Background Technology

[0002] In fields such as new energy, video packaging, biomedicine, electronic devices, and environmental membrane separation, there is a core requirement for functional membrane materials: high air permeability (such as CO2, O2, etc.) and low water permeability. Taking the lithium battery field in new energy as an example, functional membrane materials are needed for encapsulation in lithium batteries. Lithium batteries need to promptly expel gases such as CO2 generated during the reaction, while simultaneously preventing external moisture penetration to avoid battery failure. Similarly, the food packaging field needs to maintain a suitable gas atmosphere inside the packaging and prevent moisture penetration to extend shelf life; the biomedical field needs to ensure gas exchange while blocking moisture to prevent reagent deterioration; and the electronic device field needs to prevent moisture erosion while achieving gas heat dissipation.

[0003] Therefore, there is an urgent need to find a functional membrane material that can balance high gas permeability with low water permeability. Summary of the Invention

[0004] In view of this, in order to at least partially solve the aforementioned technical problems, the present invention provides an air-permeable and water-resistant membrane, its preparation method, and its application.

[0005] According to one embodiment of the present invention, a breathable and water-resistant membrane is provided, comprising a single-layer membrane containing a fluoropolymer membrane layer, or a composite membrane comprising a fluoropolymer membrane layer and a polymer membrane layer stacked together; the crystallinity of the single-layer membrane and the composite membrane is <70%, and the CO2 permeability is ≥20000 mL / m³. 2 • 24hrs • 0.1MPa, water vapor transmission rate ≤ 5g / m 2 24hrs.

[0006] According to another aspect of the present invention, a method for preparing the above-mentioned breathable and water-resistant membrane is provided, comprising: drying a fluoropolymer resin, an optional polymer resin and an optional compatibilizer to obtain a dried raw material; preparing a breathable and water-resistant membrane sample by extrusion casting or blown film preparation of the dried raw material; and sequentially subjecting the breathable and water-resistant membrane sample to heat setting, cooling, edge trimming and winding to obtain a breathable and water-resistant membrane.

[0007] According to another aspect of the present invention, an application is provided for the above-described air-permeable and water-blocking membrane or the air-permeable and water-blocking membrane prepared by the above-described preparation method in the fields of new energy, biomedicine, electronic devices, membrane separation, and packaging film.

[0008] According to another aspect of the present invention, a battery-grade gas-permeable and water-resistant encapsulation device is provided, comprising two annular metal sheets and the aforementioned gas-permeable and water-resistant membrane or the gas-permeable and water-resistant membrane prepared by the aforementioned method located between the two annular metal sheets; the two annular metal sheets and the gas-permeable and water-resistant membrane form a sandwich structure.

[0009] According to the embodiments of the present invention, the gas-permeable and water-blocking membrane, whether a single-layer membrane or a composite membrane, has low crystallinity, which can simultaneously achieve high gas permeability, such as CO2 permeability, and can remove gas in a timely manner according to actual needs when applied in different fields; and low water vapor permeability, which can prevent external water vapor from penetrating into the interior, thus helping to further expand the application fields.

[0010] According to embodiments of the present invention, the preparation method of the present invention, through extrusion casting and blown film preparation, enables the prepared air-permeable and water-blocking membrane to have low water vapor permeability while having high gas (CO2 / O2, etc.) permeability, while also taking into account excellent dimensional stability and corrosion resistance, thus meeting the air-permeable and water-blocking requirements of multiple fields such as new energy, food packaging, biomedicine, and electronic devices.

[0011] According to embodiments of the present invention, a breathable and water-resistant encapsulation device is formed by combining a breathable and water-resistant membrane with an annular metal sheet, replacing the one-time failure structure of a traditional bursting disc. When applied to batteries, the device of the present invention can operate continuously, achieving high breathability and strong water resistance performance over a long period without replacement. For example, when applied to lithium batteries, it can significantly improve the safety and reliability of lithium batteries during long-term cycle use, and is particularly suitable for various lithium battery systems such as power lithium batteries, energy storage lithium batteries, and consumer lithium batteries. Detailed Implementation

[0012] The following describes embodiments of the present invention; however, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0013] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0014] In this invention, "crystallinity" can be understood as a parameter representing the proportion of crystalline regions in the total volume or mass of a thin film material. It is an important indicator used to measure the degree of orderliness of the atomic and molecular arrangement within the thin film material. Crystallinity can be determined by X-ray diffraction or differential scanning calorimetry.

[0015] In numerous fields such as new energy, food packaging, biomedicine, electronic devices, and environmental membrane separation, there is a core requirement for functional membrane materials: high air permeability and low water permeability. However, existing membrane materials currently struggle to simultaneously achieve both high gas permeability and low water vapor permeability. Therefore, there is a need to find a membrane material that can possess both of these dual functions.

[0016] In the process of realizing the concept of this invention, it was found that fluoropolymers have excellent hydrophobicity, chemical stability, high temperature resistance and corrosion resistance, but fluoropolymer films still have difficulty in achieving both high gas permeability and low water vapor permeability.

[0017] Furthermore, by optimizing the preparation process of the membrane material, the resulting membrane structure has a lower degree of crystallinity, thereby achieving both high air permeability and low water permeability.

[0018] Specifically, according to one embodiment of the present invention, a breathable and water-resistant membrane is provided, comprising a single-layer membrane containing a fluoropolymer membrane layer, or a composite membrane comprising a fluoropolymer membrane layer and a polymer membrane layer stacked together, wherein the crystallinity of the single-layer membrane and the composite membrane is <70%, and the CO2 permeability is ≥20000 mL / m³. 2 • 24hrs • 0.1MPa, water vapor transmission rate ≤ 5g / m 2 24hrs.

[0019] It is understandable that the materials of the fluoropolymer membrane layer in a single-layer membrane and the fluoropolymer membrane layer in a composite membrane can be the same or different, and can be selected according to actual needs.

[0020] Single-layer or composite membranes can be selected for use according to actual needs. Composite membranes can also be set as two-layer composite membranes or extended to more membrane layers to form multi-layer composite membranes.

[0021] According to embodiments of the present invention, the single-layer membrane and composite membrane of the present invention possess both high gas permeability (such as CO2) and low water vapor permeability. The high gas permeability balances the pressure difference between the inside and outside of the membrane structure, preventing damage to the sealing structure or equipment failure due to pressure buildup. The low water vapor permeability endows the membrane structure with excellent water-blocking properties, effectively preventing external water vapor from penetrating into the equipment, thus helping to protect electronic components, medical consumables, and new energy batteries. By adjusting specific parameters in extrusion casting and blown film production, the crystallinity of the membrane structure can be controlled to be below 70%, which helps provide channels for the dissolution and diffusion of gas molecules, indirectly supporting the achievement of high gas permeability. Furthermore, the membrane with moderate crystallinity has a low shrinkage rate, avoiding sealing failure or poor adhesion due to deformation.

[0022] Preferably, the crystallinity of the breathable and water-resistant membrane is less than or equal to 50%, which further improves the gas permeability and maintains good dimensional stability at higher temperatures (e.g., 100~120°C).

[0023] Optionally, the crystallinity of the breathable and water-resistant membrane may be, for example, 30%, 35%, 40%, 45%, 50%, 54%, 55%, 60%, 65%, or 69%, or a range consisting of any two of the above values.

[0024] In some embodiments, the thickness of the monolayer membrane is 1~60μm, preferably 20~50μm. Adjusting the thickness of the monolayer membrane within the above range facilitates subsequent direct bonding with the substrate, achieving a low-cost upgrade of the existing substrate to be breathable and water-resistant.

[0025] In some embodiments, the total thickness of the composite membrane, such as a two-layer composite membrane, is 50-300 μm, preferably 50-200 μm. The thickness of the fluoropolymer membrane layer is 1-60 μm, preferably 10-40 μm, and the thickness of the polymer membrane layer is 40-260 μm, preferably 50-150 μm. This configuration helps to tightly bond the fluoropolymer membrane layer and the polymer membrane layer, improving the functional consistency of the breathable and water-resistant membrane, meeting the breathable and water-resistant requirements of various fields, and, based on the introduction of a compatibilizer, preventing delamination between the two composite membrane layers.

[0026] In some embodiments, the tensile strength of the single-layer membrane and / or composite membrane is 30~100MPa. This setting ensures that the membrane has a certain mechanical strength, thereby meeting the requirements of various application scenarios.

[0027] In some embodiments, the fluoropolymer in the fluoropolymer membrane layer includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-ethylene copolymer, perfluoroethylene propylene, and tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer. These materials possess excellent hydrophobicity, chemical stability, high-temperature resistance, and corrosion resistance. When subsequently forming single-layer or composite membranes, they can simultaneously meet the dual requirements of high gas permeability and low water vapor permeability, while also exhibiting high dimensional stability, thus broadening their large-scale general application in various breathable and water-blocking fields.

[0028] In some embodiments, the fluoropolymer in the fluoropolymer membrane has a molecular weight greater than 50,000 Da. This configuration enables the formation of a continuous and dense membrane during the film-forming process, improving the mechanical properties of the membrane structure and further optimizing the microstructure for both air permeability and water resistance.

[0029] In some embodiments, the polymer membrane layer comprises 95-97 wt% polymer and 3-5 wt% compatibilizer, wherein the compatibilizer is a maleic anhydride-modified polymer. This configuration helps optimize the composite membrane bonding process, improves the compatibility between the membrane layers, and avoids membrane delamination.

[0030] In some embodiments, the polymer includes at least one selected from polyamide, polyester, polypropylene, and polyethylene. The melt index of the polymer is 0.1 to 15 g / 10 min, preferably 5 to 12 g / 10 min. Selecting the melt index of the raw material in this way facilitates the simultaneous melting, merging, and casting of the fluoropolymer layer and the polymer layer during co-extrusion and heat treatment, contributing to the formation of a stable film structure.

[0031] In some embodiments, the melt index of the fluoropolymer in the fluoropolymer film layer is 0.1~30 g / 10 min, preferably 10~20 g / 10 min. This setting helps to achieve casting molding and optimizes the interlayer compatibility of multilayer co-extrusion composites, further avoiding delamination. According to another aspect of the present invention, a method for preparing the above-described air-permeable and water-resistant film is provided, comprising steps 1 to 3.

[0032] In step 1, the fluoropolymer resin, optional polymer resin and optional compatibilizer are dried to obtain a dried raw material.

[0033] In step 2, the dried raw material is used to prepare an air-permeable and water-resistant membrane sample by extrusion casting or blown film.

[0034] In step 3, the air-permeable and water-blocking membrane sample is cooled, trimmed, and rolled up sequentially to obtain the air-permeable and water-blocking membrane.

[0035] It is understandable that in the case of preparing a single-layer membrane, step 1 only requires drying the fluoropolymer resin. However, in the case of preparing a composite membrane, step 1 requires simultaneously drying the fluoropolymer resin, the polymer resin, and the compatibilizer.

[0036] According to embodiments of the present invention, a gas-permeable and water-blocking membrane is prepared by extrusion casting and blown film blowing, resulting in a membrane structure that combines high gas permeability and low water vapor permeability, thereby expanding its application areas. The addition of a compatibilizer further optimizes the compatibility between the membrane structures in the composite membrane.

[0037] In some embodiments, when preparing a breathable and water-resistant membrane sample by extrusion casting, the extrusion casting parameters include: screw extruder temperature of 200~340℃, die temperature of 220~330℃, cooling roller temperature of 20~100℃, and draw ratio of 1~5. The cooling roller temperature is preferably 20~40℃; this setting, within a lower temperature range, facilitates rapid quenching, freezes the amorphous structure, and forcibly reduces crystallinity. The draw ratio is preferably 1~2 to reduce molecular chain stretching and avoid the formation of a dense, highly crystalline layer. With these settings, based on the adjustment of the extrusion casting parameters, the membrane structure achieves high air permeability and low water permeability, with a CO2 permeability ≥20000mL / m³. 2 • 24hrs • 0.1MPa, water vapor transmission rate ≤ 5g / m 2 • 24hrs, meeting the core performance requirements of multiple fields.

[0038] It is understood that during the screening of experiments related to this invention, it was found that the screening of extrusion casting parameters has a significant impact on air permeability and water resistance performance. In particular, adjusting the temperature of the cooling roller and the traction ratio within the above-mentioned range can balance the high air permeability and water resistance performance of the film structure.

[0039] In some embodiments, when preparing a breathable and water-resistant membrane sample by blown film, the blown film process includes sequential melt extrusion and blown film traction. The parameters for melt extrusion and blown film traction are as follows: Melt extrusion: extrusion temperature 200~340℃, die temperature 220~330℃, die gap 0.8~1.2mm; Blown film traction: air cooling temperature for blown film cooling 25~35℃, blown film ratio 1.2~3.0, and traction ratio 1.5~5.0. Preferably, the blown film ratio is 1.2~2.0, which allows for lower blowing ratios, avoids forced molecular orientation, and inhibits dense crystallization; low-temperature air cooling (25~35℃) ensures rapid cooling and shaping, retaining a large number of amorphous regions. The traction ratio of 1.5~2.0 prevents crystallization with low traction and avoids increased crystallinity with low stretching. This setup, based on adjustments to the blown film parameters, further achieves high air permeability and low water permeability in the membrane structure, with a CO2 permeability ≥20000 mL / m³. 2 • 24hrs • 0.1MPa, water vapor transmission rate ≤ 5g / m 2 • 24hrs, meeting the core performance requirements of multiple fields.

[0040] It is understood that during the screening of experiments related to this invention, it was found that the selection of blown film parameters has a significant impact on air permeability and water resistance performance. In particular, adjusting the parameters of air cooling temperature, blow-up ratio, and traction ratio of the blow-up cooling process within the above range can balance the high air permeability and water resistance performance of the film structure.

[0041] In one specific embodiment, taking extrusion casting as an example, this method is suitable for the preparation of high-precision, thin film materials, with good film thickness uniformity. It is applicable to fields such as electronic devices, biomedicine, and lithium batteries where high precision of film materials is required. It can prepare single-layer fluoropolymer films or fluoropolymer / polymer bilayer composite films (or multiple layers). The preparation process of this single-layer film or bilayer composite film can be as follows:

[0042] Raw material pretreatment: Dry the fluoropolymer resin (and other raw materials) at 60~80℃ for 4~6 hours to remove moisture and avoid bubbles and pinholes.

[0043] Casting into cast sheets: Melting and plasticizing is performed using a single-screw extruder, followed by casting with a T-die. The extrusion temperature is 200~340℃ (300~340℃ for polytetrafluoroethylene (PTFE) or ethylene-tetrafluoroethylene copolymer (ETFE), and 280~320℃ for polyvinylidene fluoride (PVDF)). The die temperature is 220~330℃, the cooling roller temperature is 20~40℃, the draw ratio is 1~2, and the cast sheet thickness is 10~60μm. Multi-layer (two-layer) co-extrusion casting processes add a maleic anhydride-modified polymer (MAH-g-polymer) compatibilizer (grafting rate 0.5%~1.0%, addition amount 3%~5% of the polymer), which can be co-extruded using a three-screw extruder.

[0044] Post-processing: cooling, thickness measurement, edge trimming and winding to obtain a single-layer film or a double-layer composite film.

[0045] In another specific implementation, taking blown film as an example, the blown film process is adapted to large-scale continuous mass production, the film material has good flexibility and high production efficiency, and it is suitable for large-scale application fields such as food packaging and lithium batteries. It is divided into single-layer blown film and two-layer composite blown film.

[0046] Raw material pretreatment: Dry the fluoropolymer resin (and other raw materials) at 60~80℃ for 4~6 hours to remove moisture and avoid bubbles and pinholes.

[0047] Melt extrusion: The film is melt-plasticized using a single-screw blown film extruder and extruded through a ring die. The extrusion temperature is 280~340℃, the die temperature is 290~330℃, and the die gap is 0.8~1.2mm. The blown film material is then inflated and drawn: It is inflated under air cooling at 25~35℃ with an inflation ratio of 1.2~2.0 and a draw ratio of 1.5~2.0 to balance air permeability and water resistance, resulting in an air-permeable and water-resistant membrane sample.

[0048] After post-processing, including thickness measurement, edge trimming, and winding, a single-layer or double-layer composite film is obtained.

[0049] According to another aspect of the present invention, an application is provided for the above-described air-permeable and water-resistant membrane or the air-permeable and water-resistant membrane prepared by the above-described preparation method in the fields of new energy, biomedicine, electronic devices, membrane separation, and packaging films.

[0050] According to embodiments of the present invention, the above-mentioned breathable and water-blocking membrane or the above-prepared breathable and water-blocking membrane can achieve high gas permeability and low water vapor permeability while also having excellent high-temperature dimensional stability, interlayer adhesion and corrosion resistance. In subsequent applications in the above-mentioned fields, it can solve problems that are difficult to be compatible with conventional membrane materials, such as gas dispersion, insufficient exchange, water vapor penetration, interlayer delamination and dimensional deformation, and meet the breathable and water-blocking requirements of multiple fields such as new energy, food packaging, biomedicine, and electronic devices.

[0051] According to embodiments of the present invention, by employing two common preparation methods—casting and blown film—and through precise control of the parameters of the fluoropolymer membrane material, combined with single-layer / two-layer composite membrane structure design, a membrane material that meets the requirements of high air permeability and low water permeability has been successfully prepared, while also taking into account excellent high-temperature dimensional stability and corrosion resistance. Specific beneficial effects are as follows:

[0052] The processes are versatile and widely adaptable: both processes are fully covered, adapting to the industrial needs of breathable and water-resistant fields such as new energy, food packaging, biomedicine, and electronic devices. Specifically, the casting process is suitable for high-precision scenarios, while the blown film process is suitable for large-scale mass production, and both are compatible with conventional equipment with low modification costs.

[0053] Core performance is balanced: Through precise control of process parameters, the gas (CO2) permeability of the above-mentioned single-layer membrane or composite membrane is ≥20000ml / m²·24hrs·0.1MPa and the water vapor permeability is ≤5g / m²·24hrs. This ensures timely gas dissipation and / or exchange while effectively preventing water vapor infiltration, thus fundamentally solving the product failure problems caused by gas accumulation and water vapor erosion in the above-mentioned fields.

[0054] A standardized process parameter system for fluoropolymer membrane materials has been established, ensuring high product performance consistency. The membranes can be flexibly designed as single-layer or two-layer composite membranes. The raw materials are commercially available conventional fluoropolymers and polymers, offering broad applicability, controllable costs, and enabling continuous industrial-scale production. Fluoropolymer-based membrane materials possess excellent corrosion resistance, high-temperature resistance, and weather resistance, exhibiting no performance degradation or aging under complex operating conditions in various fields, significantly improving the service life and safety of end products.

[0055] The fluoropolymer membrane material (single-layer membrane or composite membrane) of this invention specifically addresses the core technical needs of gas exchange and / or dissipation, water vapor barrier, structural stability, and process adaptability in the general breathable and water-blocking field. It fills the gap in the generalization and multi-process preparation of fluoropolymer membrane materials in multiple fields. Compared with existing conventional breathable and water-blocking membrane materials, its comprehensive performance and industrial adaptability are greatly improved. It provides a general technical solution for the upgrading of membrane materials in various fields, and has significant technical advantages, wide application scenarios, and extremely high industrialization value.

[0056] According to another embodiment of the present invention, a battery-use breathable and water-resistant encapsulation device is provided, comprising two annular metal sheets and a breathable and water-resistant membrane as described above or a breathable and water-resistant membrane prepared by the above method located between the two annular metal sheets, wherein the two annular metal sheets and the breathable and water-resistant membrane form a sandwich structure.

[0057] In related technologies, a safety valve with a rupture disc is typically installed on the battery top cover. This rupture disc is designed to precisely rupture when the internal pressure of the battery rises beyond a preset threshold due to overcharging, short circuits, thermal runaway, or other reasons, releasing the high-temperature, high-pressure gases and electrolytes inside the battery and preventing a violent explosion of the battery casing. However, the rupture disc is only usable once and cannot be reused after damage.

[0058] According to embodiments of the present invention, the above-mentioned breathable and water-resistant device can replace the bursting disc in a traditional lithium battery, allowing gases such as carbon dioxide generated during the charging / discharging process of the lithium battery to be quickly discharged to the outside through the breathable and water-resistant membrane, preventing the battery from bulging, deforming, or cracking. Furthermore, external water vapor is effectively blocked by the breathable and water-resistant membrane, preventing it from entering the lithium battery, thus preventing electrolyte hydrolysis and battery corrosion, and ensuring battery performance and safety.

[0059] In some implementations, the annular metal sheet can be circular, elliptical, or square, etc., to provide a fixation effect on the breathable and water-resistant membrane.

[0060] In some implementations, the breathable and water-resistant membrane can be tightly clamped by an annular metal sheet, and the membrane can be sealed and fixed by laser welding of the outer ring, riveting, or hot pressing, so that the device is clamped evenly, without wrinkles, damage, or side leakage.

[0061] In some embodiments, a wire mesh or porous membrane may be optionally added to the portions of the upper and lower surfaces of the breathable and water-resistant membrane that are not covered by the annular metal sheet, in order to achieve structural protection of the breathable and water-resistant membrane.

[0062] In some embodiments, the annular metal sheet may be made of at least one of aluminum alloy, stainless steel, or nickel-plated steel.

[0063] In some implementations, the battery-grade breathable and water-resistant encapsulation device is mounted at the battery's vent and / or pressure relief interface, aligning the breathable and water-resistant membrane with the vent and / or pressure relief interface. This configuration ensures long-term stable operation of high breathability and strong water resistance without replacement, significantly improving the long-term stable operation of lithium batteries and guaranteeing battery performance and safety. It is particularly suitable for various lithium battery systems, including power lithium batteries, energy storage lithium batteries, and consumer lithium batteries.

[0064] In some embodiments, after the gas-permeable and water-resistant encapsulation device for lithium batteries is sealed by an annular metal sheet, the inner diameter of the portion exposed at the annular metal sheet seal ranges from 5 to 50 mm.

[0065] The present invention will be further illustrated below through embodiments and related test experiments and results. In the following detailed description, numerous specific details are set forth for ease of explanation to provide a comprehensive understanding of the embodiments of the present invention. However, it will be apparent that one or more embodiments may be practiced without these specific details. Moreover, the details in the following embodiments can be arbitrarily combined to form other feasible embodiments without conflict.

[0066] It should be noted that the specific embodiments described below are merely illustrative examples, and the scope of protection of this invention is not limited thereto. The chemicals and raw materials used in the following embodiments are all commercially available or prepared using recognized processing methods.

[0067] Example 1: Perfluoroethylene propylene (FEP), molecular weight 200,000 Da. A monolayer film (30 μm thick) was prepared by extrusion casting.

[0068] FEP resin with a melt index of 10 g / 10 min was used and dried in an oven at 70°C for 5 h to obtain dried FEP resin.

[0069] The dried FEP resin was cast into a film using a single-screw extruder with the temperature of the single-screw extruder at 320°C, the temperature of the T-die at 320°C, the temperature of the cooling roller at 30°C, the draw ratio at 1.5, and the film thickness at 30 μm, to obtain a breathable and water-resistant membrane sample.

[0070] After post-processing, namely cooling, thickness measurement, edge trimming and winding, a 30 μm thick FEP monolayer film was obtained. The crystallinity of the FEP monolayer film was determined to be 45% by X-ray diffraction.

[0071] Comparative Example 1:

[0072] Using the same FEP resin as in Example 1, the resin was dried in an oven at 70°C for 5 hours to obtain the dried FEP resin.

[0073] The dried FEP resin was cast into a sheet using a single-screw extruder. The temperature of the single-screw extruder was 320℃, the temperature of the T-die was 320℃, the temperature of the cooling roller was 120℃, the traction ratio was 6.0, and the thickness of the sheet was 30μm, thus obtaining a breathable and water-resistant membrane sample.

[0074] After cooling, thickness measurement, edge trimming, and winding, a 30 μm thick FEP monolayer film was obtained. X-ray diffraction analysis showed that the crystallinity of this FEP monolayer film was 78%.

[0075] Example 2: Two-layer composite film of perfluoroethylene propylene (FEP) and polypropylene (total thickness 200 μm)

[0076] FEP resin (molecular weight 200,000 Da) with a melt index of 10 g / 10 min, polypropylene resin with a melt index of 8 g / 10 min, and maleic anhydride-modified polypropylene (MAH-g-PP) (maleic anhydride grafting rate of 0.8%, added at 4% of the mass of polypropylene resin) were used and dried in an oven at 70°C for 5 h to obtain the dried raw materials.

[0077] The dried raw materials were co-extruded and cast using a three-screw extruder. The temperature of the three-screw extruder was 310℃, the temperature of the composite die was 310℃, the temperature of the cooling roller was 30℃, and the traction ratio was 1.2 to obtain a breathable and water-resistant membrane sample.

[0078] After post-processing, namely cooling, thickness measurement, edge trimming and winding, a two-layer composite film with a thickness of 20 μm FEP and a thickness of 180 μm polypropylene was obtained. The crystallinity of the two-layer composite film was determined to be 50% by X-ray diffraction.

[0079] Example 3: A single-layer film (50 μm thick) of ethylene-tetrafluoroethylene copolymer (ETFE, molecular weight 630,000 Da) was prepared by blown film method.

[0080] ETFE resin with a melt index of 8 g / 10 min was used and dried in an oven at 70°C for 5 hours to obtain dried ETFE resin.

[0081] The dried ETFE resin was melt-extruded into a blown film using a single-screw blown film extrusion process. The temperature of the blown film extruder was 320℃, the temperature of the annular die head was 310℃, and the die gap was 1.0mm. The blown film material was then subjected to blow-in and traction processes, with a cooling air temperature of 30℃, a blow-in ratio of 1.5, and a traction ratio of 1.5, resulting in a breathable and water-resistant membrane sample.

[0082] After post-processing, namely cooling, thickness measurement, edge trimming and winding, an ETFE monolayer film with a thickness of 50 μm was obtained. The crystallinity of the ETFE monolayer film was determined to be 54% by X-ray diffraction.

[0083] Comparative Example 2

[0084] Using the same ETFE resin as in Example 3, the resin was dried in an oven at 70°C for 5 hours to obtain the dried ETFE resin.

[0085] The dried ETFE resin was melt-extruded and blown into a film. The temperature of the single-screw blown film machine was 320℃, the temperature of the annular die head was 310℃, and the die gap was 1.0mm. The air-cooling temperature of the blow-up and traction stage was set to 45℃, the blow-up ratio was 1.5, and the traction ratio was set to 6.0 to obtain a breathable and water-resistant film sample.

[0086] After cooling, thickness measurement, edge trimming, and winding, an ETFE monolayer film with a thickness of 50 μm was obtained. X-ray diffraction analysis showed that the crystallinity of this ETFE monolayer film was 75%.

[0087] Example 4: Two-layer composite film of poly(perfluoroethylene propylene) (FEP, molecular weight 200,000 Da) / polyamide (PA) (total thickness 220 μm)

[0088] FEP resin with a melt index of 10 g / 10 min, PP resin with a melt index of 10 g / 10 min, and maleic anhydride-modified PA (MAH-g-PA) (maleic anhydride grafting rate of 0.8%, added at 4% of PA resin mass) were used and dried in an oven at 70°C for 5 hours to obtain the dried raw materials.

[0089] The dried raw materials were co-extruded into blown films. The temperature of the twin-screw blown film extruder was 310℃, the temperature of the double-layer annular die head was 300℃, and the die gap was 1.2mm. The blown film material was then inflated and drawn: the cooling air temperature was 30℃, the inflation ratio was 1.3, and the draw ratio was 1.5, resulting in a breathable and water-resistant membrane sample.

[0090] After post-processing, namely cooling, thickness measurement, edge trimming and winding, a two-layer composite film with a FEP layer thickness of 25 μm and a PA layer thickness of 195 μm was obtained. The crystallinity of the two-layer composite film was determined to be 40% by X-ray diffraction.

[0091] The different single-layer or two-layer composite membranes prepared in Examples 1 to 4, Comparative Examples 1 and 2 were tested according to national standards and industry-standard methods. Each sample was tested 3 to 6 times and the average value was taken. The test items included: gas (CO2) transmission rate (GB / T1038-2000), water vapor transmission rate (GB / T26253-2010), and tensile strength (GB / T1040.3-2006). The performance test results are shown in Table 1 below.

[0092] Table 1

[0093]

[0094] As shown in Table 1, this invention uses two common preparation processes, casting and blown film, to finely control the parameters of fluoropolymer membrane materials. Combined with the structural design of single-layer membrane / two-layer composite membrane, it can successfully prepare membrane materials that meet the requirements of general high air permeability and low water permeability, while also having high tensile strength, which is conducive to their application in different fields.

[0095] Application Example 1:

[0096] Fabrication of breathable and water-resistant encapsulated devices:

[0097] Using the FEP monolayer membrane (thickness 30μm) prepared in Example 1 as the core membrane material, a circular monolayer membrane with a diameter of 12mm was taken, and two 304 stainless steel rings with an outer diameter of 14mm and an inner diameter of 8mm were selected. The air-permeable and water-blocking membrane was placed flat between the two rings to form a sandwich structure. Laser continuous welding was used along the outer ring of the stainless steel rings to make the circular monolayer membrane uniformly clamped and sealed without leakage, thus obtaining an air-permeable and water-blocking device for lithium batteries.

[0098] Assembly and Testing:

[0099] The device is installed at a pre-set venting interface on the lithium battery casing, replacing the traditional rupture disc. During a 7-day charge-discharge cycle test at 0.5C, gases such as CO2 generated inside the lithium battery are rapidly expelled through the device, resulting in stable gas pressure inside the battery casing without accumulation, and no bulging or deformation of the battery. Tests show that the device's water vapor permeability is ≤4.8 g / m²·24hrs, preventing external moisture from penetrating the battery and maintaining stability of the electrolyte and electrodes.

[0100] This device can continuously allow air to pass through and block water for a long time without replacement, solving the problem of traditional rupture discs failing once and being unusable, and significantly improving the lifespan and operational safety of lithium batteries.

[0101] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A breathable and water-resistant membrane, characterized in that, The breathable and water-resistant membrane includes a single-layer membrane containing a fluoropolymer membrane layer, or a composite membrane consisting of a fluoropolymer membrane layer and a polymer membrane layer stacked together. The crystallinity of the single-layer membrane and the composite membrane is <70%, and the CO2 permeability is ≥20000 mL / m. 2 • 24hrs • 0.1MPa, water vapor transmission rate ≤ 5g / m 2 24hrs.

2. The air-permeable and water-resistant membrane according to claim 1, characterized in that, The thickness of the monolayer film is 1~60μm; The thickness of the composite membrane is 50~300μm.

3. The air-permeable and water-resistant membrane according to claim 1, characterized in that, The tensile strength of the single-layer membrane and / or the composite membrane is 30~100MPa.

4. The air-permeable and water-resistant membrane according to claim 1, characterized in that, The fluoropolymer in the fluoropolymer film layer includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-ethylene copolymer, perfluoroethylene propylene, and tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride terpolymer, wherein the molecular weight of the fluoropolymer is greater than 50,000 Da. The polymer film layer comprises 95-97 wt% polymer and 3-5 wt% compatibilizer, wherein the compatibilizer is a maleic anhydride-modified polymer, and the polymer comprises at least one of polyamide, polyester, polypropylene, and polyethylene. The melt index of the polymer is 0.1~15 g / 10 min, and the melt index of the fluoropolymer in the fluoropolymer film is 0.1~30 g / 10 min.

5. A method for preparing an air-permeable and water-resistant membrane as described in any one of claims 1 to 4, characterized in that, include: The fluoropolymer resin, optional polymer resin, and optional compatibilizer are dried to obtain a dried raw material. A breathable and water-resistant membrane sample was prepared by extrusion casting or blown film method from dried raw materials. The air-permeable and water-blocking membrane sample was successively cooled, trimmed, and rolled up to obtain an air-permeable and water-blocking membrane.

6. The preparation method according to claim 5, characterized in that, When preparing a breathable and water-resistant membrane sample by extrusion casting, the parameters of extrusion casting include: The temperature of the screw extruder is 200~340℃, the die temperature is 220~330℃, the cooling roller temperature is 20~100℃, and the draw ratio is 1~5; In the case of preparing a breathable and water-resistant membrane sample by blown film, the blown film process includes sequential melt extrusion and blown film traction. The parameters for melt extrusion and blown film traction are as follows: Melt extrusion: extrusion temperature is 200~340℃, die temperature is 220~330℃, and die gap is 0.8~1.2mm; Inflation and traction: The air-cooling temperature for inflation and cooling is 25~35℃, the inflation ratio is 1.2~3.0, and the traction ratio is 1.5~5.

0.

7. The application of a breathable and water-resistant membrane according to any one of claims 1 to 4 or a breathable and water-resistant membrane prepared by any one of claims 5 to 6 in the fields of new energy, biomedicine, electronic devices, membrane separation and packaging films.

8. A gas-permeable and water-resistant encapsulation device for batteries, characterized in that, It includes two annular metal sheets, and a breathable and water-resistant membrane as described in any one of claims 1 to 4 or a breathable and water-resistant membrane prepared by any one of claims 5 to 6 located between the two annular metal sheets; The two annular metal sheets and the breathable and water-resistant membrane form a sandwich structure.

9. The battery-grade gas-permeable and water-resistant encapsulation device according to claim 8, characterized in that, The battery-use breathable and water-resistant encapsulation device is installed at the battery's vent and / or pressure relief interface position so that the breathable and water-resistant membrane is aligned with the vent and / or pressure relief interface.

Images