Waterproof breathable acoustic membrane based on PVDF crystal link regulation and control, preparation method and wearable device

Abstract

The invention discloses a waterproof breathable acoustic membrane based on PVDF crystal link regulation and control, a preparation method and wearable equipment, and relates to the technical field of waterproof breathable membranes. According to the preparation method, a PET nuclear track membrane substrate with a specific structure and a PVDF solution system regulated step by step are introduced, and a PET nuclear track membrane with a preformed microporous structure is selected as a rigid substrate, so that the problem of shrinkage and hemming caused by non-uniform solvent removal and stress concentration during pure PVDF film casting is solved. Two silane coupling agents with complementary functions are introduced step by step, so that precise regulation and control of PVDF crystallization behavior and interface combination are realized. According to the preparation method, excellent solution machinability of PVDF and excellent dimensional stability of the PET film are combined, so that parameters in the whole technological process are easy to control, repeatability is good, the technical bottleneck that a PVDF material is difficult to be directly used for preparing functional films with consistent forms on a large scale is successfully solved, and meanwhile, the defects that an ePTFE material is difficult to process and high in cost are overcome.

Description

Technical Field

[0001] This invention relates to the field of waterproof and breathable membrane technology, and in particular to a waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation, its preparation method, and a wearable device. Background Technology

[0002] As wearable devices evolve from basic functionalities to intelligent interactive devices, their internal structure and usage environment have undergone fundamental changes. Early electronic watches and similar devices had simple functions, low power consumption, and no need for voice communication; a fully sealed design was sufficient for swimming-grade waterproofing. However, driven by advancements in chip technology and integration, intelligent wearable devices have gradually integrated diverse functions such as voice interaction, health monitoring, and environmental sensing. They now integrate sophisticated components such as microphones, speakers, high-density batteries, and MEMS sensors, significantly increasing heat generation during operation. In this context, traditional fully sealed structures are prone to pressure imbalances between the inside and outside of the device, potentially leading to speaker noise and casing bulging with prolonged use, severely impacting user experience and device reliability. Therefore, designing a sealing solution with pressure relief capabilities for intelligent wearable devices has become a critical technical requirement, balancing waterproofing, heat dissipation, and sound quality integrity.

[0003] Currently, expanded polytetrafluoroethylene (ePTFE) is the most widely used waterproof and breathable membrane material in the consumer electronics field. ePTFE is considered the "king of low damping" due to its extremely low damping characteristics and holds a dominant position in the preparation of waterproof and breathable membranes. However, this material has poor processing performance: it is insoluble in common solvents, has an extremely high melting point and melt viscosity, and cannot be formed using conventional casting or coating processes. It typically relies on sintering or stretching methods for preparation, leading to difficulties in controlling membrane thickness uniformity and hindering ultra-thin production. Furthermore, ePTFE membranes are soft and prone to creep, exhibiting problems such as excessive mechanical damping, high-frequency response attenuation, and insufficient transient characteristics when used as acoustic diaphragms. This may affect sound clarity and resolution, making it difficult to fully meet the requirements of high-fidelity audio transmission.

[0004] In contrast, polyvinylidene fluoride (PVDF) exhibits significant advantages in processability and acoustic properties. PVDF is soluble in specific polar solvents, making it suitable for various film-forming processes such as casting, coating, and electrospinning, and easily facilitating the preparation of ultrathin, uniform, and high-precision films. In terms of acoustic characteristics, PVDF films combine high stiffness with moderate damping, offering a wide and smooth frequency response, a warm and natural sound, high listenability, no obvious peaks or valleys, and excellent mechanical strength and shape retention, with low dependence on supporting structures. Despite its outstanding acoustic performance and processability, PVDF is prone to shrinkage and curling during individual film-forming processes, especially in large-scale production where controlling the consistency of the film surface morphology is difficult. This results in high process complexity and low material utilization, hindering its widespread adoption in practical applications.

[0005] Therefore, it is urgent to solve the problem of how to overcome the shrinkage and deformation problems in the film formation process of PVDF while retaining its excellent acoustic performance and processing convenience, so as to prepare a composite membrane material that has high audio transmission performance, good waterproof and breathable properties, stable shape and suitable for mass production, in order to meet the dual needs of smart wearable devices for precision acoustics and reliable protection. Summary of the Invention

[0006] To overcome the shortcomings mentioned in the background art, the present invention provides a waterproof and breathable acoustic membrane based on PVDF crystal linking regulation, a preparation method and a wearable device, which realizes audio signal transmission by regulating the linking mode of polyvinylidene fluoride (PVDF) crystals.

[0007] In a first aspect, the present invention provides a method for preparing a waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation, comprising the following steps: S1. Base film preparation: Provide PET core-pore membranes that have undergone heavy ion bombardment and etching treatment; S2. Precursor preparation: Polyvinylidene fluoride (PVDF), N,N-dimethylformamide (DMF), acrylate and first silane coupling agent are mixed, heated and stirred to obtain casting solution precursor; S3. Crosslinking reaction: Cool the casting solution precursor to 15-30°C, add the second silane coupling agent, and stir to carry out the crosslinking reaction to obtain the casting solution; S4. Coating and film formation: The casting solution is coated onto the surface of the PET core-porous membrane, and a first phase separation and a second phase separation are performed sequentially. After drying, the waterproof and breathable acoustic membrane is obtained; wherein, the first silane coupling agent is an amino-containing silane coupling agent, and the second silane coupling agent is an epoxy-containing silane coupling agent.

[0008] The further technical solution is that step S1 specifically includes: A PET base film is subjected to heavy ion bombardment treatment, followed by etching pores in an alkaline solution. After cleaning and drying, a PET core-pore membrane is obtained. The heavy ion bombardment density is 80,000-120,000 ions / cm², and the concentration of the alkaline solution is 6-10 mol / L.

[0009] A further technical solution is that the PET core pore membrane has a pore size of 3-10 μm and a membrane thickness of 4-6 μm.

[0010] A further technical solution is that, in step S2, based on the total mass of the casting solution precursor, the mass percentage concentration of PVDF is 10-16 wt%; the mass ratio of PVDF to acrylate is (15-25):(2-4); and the mass ratio of PVDF to the first silane coupling agent is (40-60):1.

[0011] A further technical solution is that, in step S3, the mass ratio of the PVDF to the second silane coupling agent is (15-25):1.

[0012] A further technical solution is that, in step S4, before the coating and film-forming steps, the casting solution is filtered, and the filtered casting solution is aged at 15-30°C for 12-24 hours.

[0013] A further technical solution is that, in step S4, the first phase separation is to let it stand in the air for 1-6 minutes; the second phase separation is to soak it in a deionized water coagulation bath for 1-3 minutes.

[0014] A further technical solution is that, in step S4, a doctor blade is used for coating, with a coating gap of 20-80μm.

[0015] In a second aspect, the present invention provides a waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation, which is prepared by the preparation method described in the first aspect.

[0016] Thirdly, the present invention provides a wearable device, including the aforementioned waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation.

[0017] Beneficial effects: This invention provides a method for preparing a waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation. It uses a PET core-porous membrane with a pre-formed microporous structure as a rigid substrate, overcoming the shrinkage and curling problems caused by uneven solvent removal and stress concentration during pure PVDF casting. Furthermore, by introducing two functionally complementary silane coupling agents in stages, precise regulation of PVDF crystallization behavior and interfacial bonding is achieved. Specifically, the amino-containing first silane coupling agent effectively improves the compatibility of PVDF with acrylate and initially affects crystal growth; the subsequently added epoxy-containing second silane coupling agent reacts with the previously introduced amino group at a mild temperature (15-30℃) to construct a moderately cross-linked network between molecular chains. The synergistic effect of the two different silane coupling agents not only stabilizes the PVDF crystal linkage and inhibits disordered shrinkage, but also forms a strong and tough chemical bond interface between the PVDF coating and the PET base film.

[0018] Furthermore, the stepwise addition of two silane coupling agents with different functional groups not only optimized the piezoelectric crystal phase of PVDF, but also integrated the brittle crystal structure and flexible polymer chains into a stable system that combines rigidity and flexibility with high responsiveness by constructing a three-dimensional cross-linked network and strong interfaces. Specifically, the amino-containing first silane coupling agent added during the casting solution precursor preparation stage allows its amino groups to weakly interact with fluorine atoms on the PVDF molecular chains or acrylates in the system. This interaction helps promote the orderly arrangement of PVDF molecular chains during heating and stirring, and induces their transformation to the β-crystal phase with high piezoelectric activity. The increased β-crystal phase content is the key structural basis for the excellent electromechanical conversion efficiency (i.e., acoustic-to-electric / electro-acoustic conversion capability) of PVDF materials, preparing the material for high-sensitivity, wide-frequency response acoustic performance. The epoxy-containing second silane coupling agent, added after the casting solution precursor has cooled, undergoes a highly efficient ring-opening addition reaction with the introduced amino groups at room temperature. This results in the in-situ formation of a moderately cross-linked network between PVDF molecular chains and between PVDF and acrylate. This cross-linked network locks and stabilizes the β-phase structure induced in the previous step, preventing crystal transformation or relaxation during subsequent phase separation, drying, or use, thus ensuring the durability and stability of piezoelectric properties. More importantly, this cross-linking reaction also occurs on the surfaces of the PVDF coating and the PET core-porous membrane. The siloxane end of the first silane coupling agent has been hydrolyzed and combined with the hydroxyl groups on the PET surface, while the second silane coupling agent reacts with the amino groups of the first silane coupling agent through epoxy groups, thereby chemically bridging the PVDF functional layer and the PET substrate. This greatly enhances the interfacial adhesion, making the composite film a mechanically unified whole. The final product was a composite film with a high content and stability of piezoelectric β crystal phase at the microscopic level and exhibiting "high stiffness and low damping" at the macroscopic level. It can maintain the warm tone of PVDF while overcoming the shortcomings of traditional materials such as high frequency attenuation and transient blurring, and achieve high-fidelity audio transmission.

[0019] The preparation method of this invention combines the excellent solution processability of PVDF with the excellent dimensional stability of PET film, making the process parameters easy to control and highly repeatable. It successfully solves the technical bottleneck that PVDF material is difficult to use directly for large-scale preparation of functional films with consistent morphology, while avoiding the disadvantages of difficult processing and high cost of ePTFE material.

[0020] The waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation provided by this invention uses a PET core-porous membrane as a permeable microporous channel, ensuring excellent breathability and pressure relief capacity, and effectively balancing the internal and external pressure difference of smart devices. Furthermore, a PVDF functional layer, formed by precise coating and phase separation, covers the pore surface and membrane surface of the PET core-porous membrane, providing a reliable waterproof barrier. This waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation successfully integrates and enhances the dimensional stability and breathability of the PET membrane, as well as the high-efficiency acoustic performance and good waterproofness of the PVDF material, simultaneously meeting the multiple stringent requirements of smart wearable devices for reliable waterproofing, high-efficiency breathability, high pressure difference balancing, and high-fidelity audio transmission. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The results are performance test results of acoustic composite membranes with different pore sizes formed in Example 1 and Comparative Example 1. Figure 2 The results are the performance test results of the acoustic composite membranes formed with different PVDF concentrations in Example 2 and Comparative Example 2. Figure 3 Here are some SEM images and audio test results of the acoustic composite films in Example 3 and Comparative Example 3; Figure 4 The images show SEM images of the acoustic composite membrane in Example 4 and the performance test results of the acoustic composite membranes in Example 4 and Comparative Example 4. Figure 5 The flowchart illustrates the preparation method of a waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation, as provided in this embodiment of the invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0025] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0026] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0027] See Figure 5 This is a flowchart illustrating the preparation method of a waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation provided in this embodiment of the invention. This embodiment of the invention provides a preparation method of a waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation, comprising the following steps: S1. Base film preparation: Provide PET core-pore membranes that have undergone heavy ion bombardment and etching treatment; S2. Precursor preparation: Polyvinylidene fluoride (PVDF), N,N-dimethylformamide (DMF), acrylate and first silane coupling agent are mixed, heated and stirred to obtain casting solution precursor; S3. Crosslinking reaction: Cool the casting solution precursor to 15-30°C, add the second silane coupling agent, and stir to carry out the crosslinking reaction to obtain the casting solution; S4. Coating and film formation: The casting solution is coated onto the surface of the PET core-porous membrane, and a first phase separation and a second phase separation are performed sequentially. After drying, the waterproof and breathable acoustic membrane is obtained; wherein, the first silane coupling agent is an epoxy-containing silane coupling agent, and the second silane coupling agent is an amino-containing silane coupling agent.

[0028] In some embodiments, step S1 specifically includes: A PET substrate film is subjected to heavy ion bombardment, followed by etching to create pores in an alkaline solution. After cleaning and drying, a PET core-pore membrane is obtained. It is important to note that the heavy ion bombardment density is fundamental for forming regular pores. Generally, it is 80,000-120,000 pores / cm², such as 80,000, 90,000, 100,000, and 120,000 pores / cm². Too low a density (<80,000 pores / cm²) results in a sparse pore count and insufficient air permeability; too high a density (>120,000 pores / cm²) may reduce the overall mechanical strength of the substrate film and cause excessively thin interpore walls after etching, making it vulnerable.

[0029] The concentration of the alkaline solution directly controls the etching rate and pore size. A suitable alkaline solution concentration is 6-10 mol / L, such as 6 mol / L, 8 mol / L, or 10 mol / L. Too low a concentration (<6 mol / L) results in a slow etching rate and difficulty in creating pores; too high a concentration (>10 mol / L) results in an excessively fast etching rate, making it difficult to control pore size uniformity and potentially damaging the film material.

[0030] In some embodiments, the PET core-pore membrane has a pore size of 3-10 μm, such as 3μm, 5μm, 6μm, 8μm, or 10μm, to achieve a balance between waterproofing and breathability. A pore size smaller than 3μm provides excellent waterproofing, but excessive air resistance hinders rapid pressure balance; a pore size larger than 10μm may significantly reduce waterproofing performance (water pressure resistance) due to weakened capillary action.

[0031] In some embodiments, the PET core-pore membrane has a thickness of 4-6 μm, such as 4 μm, 5 μm, or 6 μm, to provide suitable support performance. If the membrane is too thin (<4 μm), the support is insufficient and it is prone to deformation during coating; if the membrane is too thick (>6 μm), it does not help improve core performance but instead increases material costs and equipment packaging difficulty.

[0032] In some embodiments, in step S2, based on the total mass of the casting solution precursor, the mass percentage concentration of PVDF is 10-16 wt%, for example, 10 wt%, 12 wt%, or 16 wt%. If the PVDF concentration is too low, the formed film is too thin and discontinuous, resulting in poor water resistance; if the concentration is too high, the solution viscosity is too high, making coating difficult, and the film layer is too thick, affecting air permeability and acoustic response speed. The mass ratio of PVDF to acrylate is (15-25):(2-4), for example, 15:2, 18:3, 20:3, 20:4, or 25:3; acrylate can improve the film-forming properties and toughness of PVDF. Too high a ratio (too little acrylate) results in a weak modification effect; too low a ratio (too much acrylate) may degrade the inherent piezoelectric and mechanical properties of PVDF. The mass ratio of PVDF to the first silane coupling agent is (40-60):1, for example, 40:1, 50:1, or 60:1. This ratio ensures that there are enough coupling agent molecules to improve the compatibility of PVDF and acrylate and guide crystallization, while an excess will introduce too many small molecules and affect the quality of the crosslinked network.

[0033] In some embodiments, in step S3, the mass ratio of the PVDF to the second silane coupling agent is (15-25):1, for example, 15:1, 18:1, 20:1, or 25:1. This ratio determines the number of crosslinking points. A ratio that is too low (too much coupling agent) will result in excessive crosslinking, making the film brittle and increasing acoustic vibration damping; a ratio that is too high (too little coupling agent) will result in insufficient crosslinking, failing to effectively stabilize the crystal structure and enhance the interface, leading to decreased dimensional stability and rigidity of the film.

[0034] In some embodiments, step S4, prior to the coating and film-forming steps, further includes filtering the casting solution and aging the filtered solution at 15-30°C for 8-36 hours, preferably 12-24 hours. Filtration removes undissolved particles or gel impurities, preventing defects during coating. Aging the casting solution helps the solution system reach thermodynamic equilibrium, eliminates internal stress introduced by stirring, allows bubbles to escape fully, and ensures a more complete hydrolysis and condensation reaction of the silane coupling agent. Too short an aging time (less than 8 hours) will result in insufficient effect; too long a time (more than 36 hours) may lead to changes in solution viscosity or pre-crosslinking.

[0035] In some embodiments, in step S4, the first phase separation is to stand in air for 1-6 minutes; the second phase separation is to soak in a deionized water coagulation bath for 1-3 minutes.

[0036] It should be noted that the first phase separation (standing in air) allows for an initial exchange between the solvent (DMF) and the non-solvent (water vapor in the air), initiating the formation of polymer-depleted phase nuclei and laying the foundation for the pore structure. If the phase separation time is too short (less than 1 minute), the skin layer will be too thin; if the time is too long (more than 6 minutes), the skin layer will be too thick and dense, affecting subsequent phase separation and air permeability.

[0037] The second phase separation (water bath solidification) aims to rapidly complete the exchange of solvent and non-solvent, solidify the structure formed by the first phase separation, and create a sponge-like porous bottom layer. The phase separation time is controlled within 1-3 minutes to ensure complete phase separation and sufficient film strength for removal from the bath.

[0038] In some embodiments, in step S4, a doctor blade is used for coating, with a coating gap of 20-80 μm, such as 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, or 80 μm. The coating gap is the most direct and effective process parameter for controlling film thickness. If the gap is too small (<20 μm), the wet film is too thin, which may lead to discontinuities or pinholes in the dry film; if the gap is too large (>80 μm), the wet film is too thick, which is prone to defects during phase separation due to the long solvent removal path, and also results in high internal stress after drying.

[0039] Based on the above preparation method, this embodiment of the invention also provides a waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation, which is prepared by the above preparation method.

[0040] It should be noted that this membrane is a thin film material with a "PET core-porous membrane-PVDF functional layer" composite structure, which significantly reduces costs and offers greater controllability compared to ePTFE waterproof and breathable membranes. Furthermore, macroscopically, compared to single-layer PVDF membranes, its surface is smoother, its shape is more stable, and it exhibits no curling or wrinkling. This composite membrane combines excellent waterproof and breathable performance with high-fidelity acoustic properties. Thanks to its well-defined PET core-porous membrane substrate with a pore size of 3-10 μm, this membrane allows gases (such as air and water vapor) to pass through rapidly, effectively balancing the pressure difference between the inside and outside of the device. Simultaneously, the dense PVDF functional layer coated on the surface of the PET core-porous membrane provides excellent waterproof barrier properties, effectively preventing the penetration of liquid water. The combination of these two features enables the membrane to meet the dual requirements of pressure relief and waterproof sealing for smart wearable devices.

[0041] The PVDF functional layer of this membrane has an optimized crystal structure and bonding state with the substrate due to the aforementioned preparation method. This results in: a broad and smooth frequency response, with no significant signal attenuation, especially in the high-frequency range; clear sound reproduction, high resolution, fast transient response, and no trailing or muffled sound, while maintaining the soft, warm listening feel characteristic of PVDF materials. This enables the membrane to achieve high-fidelity sound output and pickup when used as a speaker diaphragm or microphone acoustic structure.

[0042] This membrane structure is robust, possessing excellent mechanical strength and toughness, and is not easily damaged by vibration or deformation. Furthermore, due to the use of a chemical cross-linking process, its structural stability is high, and it is more adaptable to environmental changes such as temperature and humidity.

[0043] This invention also provides a wearable device, including the aforementioned waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation.

[0044] Given that the above-mentioned waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation has excellent "breathability", "waterproof", and "high-fidelity audio transmission" functions, it is an ideal material for acoustics and protection of the next generation of smart wearable devices and other highly integrated electronic products.

[0045] To verify the comprehensive performance of the aforementioned waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation, particularly its superior balance between waterproofness, breathability, and acoustic transmission, detailed descriptions and comparative examples are provided below. Each embodiment will demonstrate the performance of the composite membrane prepared under the preferred process parameters of this invention, while the comparative examples, by changing a single key parameter, further reveal the influence of various process conditions on the final performance, thereby confirming the effectiveness and advancement of the technical solution of this invention.

[0046] Example 1 1) PET core pore membrane etching: The membrane is etched using a heavy particle density of 100,000 particles / cm². 2 The original PET membrane bombarded in a heavy ion accelerator was etched with an 8 mol / L potassium hydroxide solution, resulting in a pore size of 6 μm and a membrane thickness of 5 μm. The nucleopore membrane was then rinsed in a deionized water bath to remove any residual alkali, dried, and then laminated onto a micro-adhesive membrane.

[0047] 2) Preparation of casting solution precursor: Weigh a certain amount of DMF solvent, and place it in a mixing bottle with 15 wt% acrylate and 5 wt% silane coupling agent KBM403 (PVDF by mass ratio) and stir until homogeneous. Then, slowly add 12 wt% PVDF powder while stirring, and place the mixing bottle in a 50 ℃ water bath for heating and stirring for 8 h.

[0048] 3) Solution system crosslinking: Cool the casting solution precursor to room temperature, add 0.5 wt% silane coupling agent KBM 603 with PVDF mass ratio, and continue stirring at room temperature for 2 hours.

[0049] 4) Casting solution treatment: Filter the casting solution with 300-mesh gauze to remove impurities from the solution, and age the solution at room temperature for 12 hours.

[0050] 5) Coating: Adjust the doctor blade gap to 60 μm, and evenly coat the casting solution onto the PET core-pore membrane. Place it in the air for 3 min for the first phase separation, and then immerse it in a deionized water coagulation bath for 40 s for the second phase separation. After drying, an acoustic composite membrane with waterproof and breathable functions is formed.

[0051] Comparative Example 1 The difference between Comparative Example 1 and Example 1 lies in the size of the nuclear pore membrane pores, specifically: 1) PET core pore membrane etching: The membrane is etched using a heavy particle density of 100,000 particles / cm². 2 The original PET membrane bombarded in a heavy ion accelerator was etched with an 8 mol / L potassium hydroxide solution to create pores of 3 μm, 5 μm, 8 μm, and 10 μm, resulting in a membrane thickness of 5 μm. The nucleopore membranes were then rinsed in a deionized water bath to remove any residual alkali, dried, and finally laminated onto a micro-adhesive membrane.

[0052] 2) Preparation of casting solution precursor: Weigh a certain amount of DMF solvent, and place it in a mixing bottle with 15 wt% acrylate and 5 wt% silane coupling agent KBM403 (PVDF by mass ratio) and stir until homogeneous. Then, slowly add 12 wt% PVDF powder while stirring, and place the mixing bottle in a 50 ℃ water bath for heating and stirring for 8 h.

[0053] 3) Solution system crosslinking: Cool the casting solution precursor to room temperature, add 0.5 wt% silane coupling agent KBM 603 with PVDF mass ratio, and continue stirring at room temperature for 2 hours.

[0054] 4) Casting solution treatment: Filter the casting solution with 300-mesh gauze to remove impurities from the solution, and age the solution at room temperature for 12 hours.

[0055] 5) Coating: Adjust the doctor blade gap to 60 μm, and evenly coat the casting solution onto the PET core-pore membrane. Place it in the air for 3 min for the first phase separation, and then immerse it in a deionized water coagulation bath for 40 s for the second phase separation. After drying, an acoustic composite membrane with waterproof and breathable functions is formed.

[0056] Appendix Figure 1 The figures show the performance test results of acoustic composite membranes with different pore sizes formed in Example 1 and Comparative Example 1. It can be seen that (a) in the figure compares the frequency response values ​​at 1K Hz. The larger the pore size of the nuclear pore membrane, the better the frequency response. However, when the pore size of the nuclear pore membrane exceeds 6 μm, the improvement in frequency response is relatively small. (b) in the figure compares the air permeability results; the larger the pore size of the nuclear pore membrane, the greater the air permeability.

[0057] Example 2 1) PET core pore membrane etching: The membrane is etched using a heavy particle density of 100,000 particles / cm². 2 The original PET membrane bombarded in a heavy ion accelerator was etched with an 8 mol / L potassium hydroxide solution, resulting in a pore size of 6 μm and a membrane thickness of 5 μm. The nucleopore membrane was then rinsed in a deionized water bath to remove any residual alkali, dried, and then laminated onto a micro-adhesive membrane.

[0058] 2) Preparation of casting solution precursor: Weigh a certain amount of DMF solvent, and place it in a mixing bottle with 15 wt% acrylate and 5 wt% silane coupling agent KBM403 (PVDF by mass ratio) and stir until homogeneous. Then, slowly add 12 wt% PVDF powder while stirring, and place the mixing bottle in a 50 ℃ water bath for heating and stirring for 8 h.

[0059] 3) Solution system crosslinking: Cool the casting solution precursor to room temperature, add 0.5 wt% silane coupling agent KBM 603 with PVDF mass ratio, and continue stirring at room temperature for 2 hours.

[0060] 4) Casting solution treatment: Filter the casting solution with 300-mesh gauze to remove impurities from the solution, and age the solution at room temperature for 12 hours.

[0061] 5) Coating: Adjust the doctor blade gap to 60 μm, and evenly coat the casting solution onto the PET core-pore membrane. Place it in the air for 3 min for the first phase separation, and then immerse it in a deionized water coagulation bath for 40 s for the second phase separation. After drying, an acoustic composite membrane with waterproof and breathable functions is formed.

[0062] Comparative Example 2 The difference between Comparative Example 2 and Example 2 lies in the different amounts of PVDF powder added, specifically: 1) PET core pore membrane etching: The membrane is etched using a heavy particle density of 100,000 particles / cm². 2The original PET membrane bombarded in a heavy ion accelerator was etched with an 8 mol / L potassium hydroxide solution, resulting in a pore size of 6 μm and a membrane thickness of 5 μm. The nucleopore membrane was then rinsed in a deionized water bath to remove any residual alkali, dried, and then laminated onto a micro-adhesive membrane.

[0063] 2) Preparation of casting solution precursor: Weigh 4 portions of DMF solvent, 15 wt% acrylate and 5 wt% silane coupling agent KBM403 (by mass ratio of PVDF) into a mixing bottle and stir until homogeneous. Then, while stirring, slowly add 8 wt%, 10 wt%, 14 wt%, and 16 wt% PVDF powder respectively, and place the mixing bottle in a 50 ℃ water bath for heating and stirring for 8 h.

[0064] 3) Solution system crosslinking: Cool the casting solution precursor to room temperature, add 0.5 wt% silane coupling agent KBM 603 with PVDF mass ratio, and continue stirring at room temperature for 2 hours.

[0065] 4) Casting solution treatment: Filter the casting solution with 300-mesh gauze to remove impurities from the solution, and age the solution at room temperature for 12 hours.

[0066] 5) Coating: Adjust the doctor blade gap to 60 μm, and evenly coat the casting solution onto the PET core-pore membrane. Place it in the air for 3 min for the first phase separation, and then immerse it in a deionized water coagulation bath for 40 s for the second phase separation. After drying, an acoustic composite membrane with waterproof and breathable functions is formed.

[0067] Appendix Figure 2 The figures show the test results of the acoustic composite membranes with different pore sizes formed in Example 2 and Comparative Example 2 regarding their waterproof and breathable performance. Figure (a) shows the comparison of the frequency response values ​​at 1K, indicating that the frequency response first increases and then decreases with increasing PVDF concentration. Figure (b) shows the breathability test results, where higher PVDF concentration results in lower breathability. Figure (c) shows the waterproof effect, indicating that higher PVDF concentration leads to better waterproofing.

[0068] Example 3 1) PET core pore membrane etching: The membrane is etched using a heavy particle density of 100,000 particles / cm². 2 The original PET membrane bombarded in a heavy ion accelerator was etched with an 8 mol / L potassium hydroxide solution, resulting in a pore size of 6 μm and a membrane thickness of 5 μm. The nucleopore membrane was then rinsed in a deionized water bath to remove any residual alkali, dried, and then laminated onto a micro-adhesive membrane.

[0069] 2) Preparation of casting solution precursor: Weigh a certain amount of DMF solvent, and place it in a mixing bottle with 15 wt% acrylate and 5 wt% silane coupling agent KBM403 (PVDF by mass ratio) and stir until homogeneous. Then, slowly add 12 wt% PVDF powder while stirring, and place the mixing bottle in a 50 ℃ water bath for heating and stirring for 8 h.

[0070] 3) Solution system crosslinking: Cool the casting solution precursor to room temperature, add 0.5 wt% silane coupling agent KBM 603 with PVDF mass ratio, and continue stirring at room temperature for 2 hours.

[0071] 4) Casting solution treatment: Filter the casting solution with 300-mesh gauze to remove impurities from the solution, and age the solution at room temperature for 12 hours.

[0072] 5) Coating: Adjust the doctor blade gap to 60 μm, and evenly coat the casting solution onto the PET core-pore membrane. Place it in the air for 3 min for the first phase separation, and then immerse it in a deionized water coagulation bath for 40 s for the second phase separation. After drying, an acoustic composite membrane with waterproof and breathable functions is formed.

[0073] Comparative Example 3 The difference between Comparative Example 3 and Example 3 lies in the different amounts of silane coupling agent KBM 403 added. Specifically: 1) PET core pore membrane etching: The membrane is etched using a heavy particle density of 100,000 particles / cm². 2 The original PET membrane bombarded in a heavy ion accelerator was etched with an 8 mol / L potassium hydroxide solution, resulting in a pore size of 6 μm and a membrane thickness of 5 μm. The nucleopore membrane was then rinsed in a deionized water bath to remove any residual alkali, dried, and then laminated onto a micro-adhesive membrane.

[0074] 2) Preparation of casting solution precursor: Weigh two portions of DMF solvent, 15 wt% acrylate (PVDF by mass), and 0 wt% and 6 wt% silane coupling agent KBM403 by mass in a mixing bottle and stir until homogeneous. Then, slowly add 12 wt% PVDF powder while stirring, and place the mixing bottle in a 50 ℃ water bath for heating and stirring for 8 h.

[0075] 3) Solution system crosslinking: Cool the casting solution precursor to room temperature, add 0.5 wt% silane coupling agent KBM 603 with PVDF mass ratio, and continue stirring at room temperature for 2 hours.

[0076] 4) Casting solution treatment: Filter the casting solution with 300-mesh gauze to remove impurities from the solution, and age the solution at room temperature for 12 hours.

[0077] 5) Coating: Adjust the doctor blade gap to 60 μm, and evenly coat the casting solution onto the PET core-pore membrane. Place it in the air for 3 min for the first phase separation, and then immerse it in a deionized water coagulation bath for 40 s for the second phase separation. After drying, an acoustic composite membrane with waterproof and breathable functions is formed.

[0078] Appendix Figure 3 The figures show SEM images and audio test results of the acoustic composite membranes of Example 3 and Comparative Example 3. In Figure (a), the left image shows the acoustic composite membrane of Example 3 with 0.5 wt% KBM 403 added, and the right image shows the acoustic composite membrane of Comparative Example 3 with 0 wt% KBM 403 added. It can be seen that Example 3 (left image) has more pores and stronger PVDF crystal dispersion, indicating that KBM 403 has a certain dispersion effect on PVDF crystals, thus increasing air permeability. Combining the comparison of the 1K-point frequency response values ​​in Figure (b), it can be seen that with the addition of KBM 403, the K-point frequency response values ​​show less dispersion and better consistency, but the dispersion increases after exceeding 0.5 wt%.

[0079] Example 4 1) PET core pore membrane etching: The membrane is etched using a heavy particle density of 100,000 particles / cm². 2 The original PET membrane bombarded in a heavy ion accelerator was etched with an 8 mol / L potassium hydroxide solution, resulting in a pore size of 6 μm and a membrane thickness of 5 μm. The nucleopore membrane was then rinsed in a deionized water bath to remove any residual alkali, dried, and then laminated onto a micro-adhesive membrane.

[0080] 2) Preparation of casting solution precursor: Weigh a certain amount of DMF solvent, and place it in a mixing bottle with 15 wt% acrylate and 5 wt% silane coupling agent KBM403 (PVDF by mass ratio) and stir until homogeneous. Then, slowly add 12 wt% PVDF powder while stirring, and place the mixing bottle in a 50 ℃ water bath for heating and stirring for 8 h.

[0081] 3) Solution system crosslinking: Cool the casting solution precursor to room temperature, add 0.5 wt% silane coupling agent KBM 603 with PVDF mass ratio, and continue stirring at room temperature for 2 hours.

[0082] 4) Casting solution treatment: Filter the casting solution with 300-mesh gauze to remove impurities from the solution, and age the solution at room temperature for 12 hours.

[0083] 5) Coating: Adjust the doctor blade gap to 60 μm, and evenly coat the casting solution onto the PET core-pore membrane. Place it in the air for 3 min for the first phase separation, and then immerse it in a deionized water coagulation bath for 40 s for the second phase separation. After drying, an acoustic composite membrane with waterproof and breathable functions is formed.

[0084] Comparative Example 4 The difference between Comparative Example 4 and Example 4 lies in the amount of silane coupling agent KBM 603 added, specifically: 1) PET core pore membrane etching: The membrane is etched using a heavy particle density of 100,000 particles / cm². 2 The original PET membrane bombarded in a heavy ion accelerator was etched with an 8 mol / L potassium hydroxide solution, resulting in a pore size of 6 μm and a membrane thickness of 5 μm. The nucleopore membrane was then rinsed in a deionized water bath to remove any residual alkali, dried, and then laminated onto a micro-adhesive membrane.

[0085] 2) Preparation of casting solution precursor: Weigh 3 portions of DMF solvent, 15 wt% acrylate and 5 wt% silane coupling agent KBM403 (by mass ratio of PVDF) into a mixing bottle and stir until homogeneous. Then, while stirring, slowly add 12 wt% PVDF powder and place the mixing bottle in a 50 ℃ water bath for heating and stirring for 8 h.

[0086] 3) Crosslinking of solution system: Cool the casting solution precursor to room temperature, add 0 wt% and 1 wt% of silane coupling agent KBM 603 with PVDF respectively, and continue stirring at room temperature for 2 hours.

[0087] 4) Casting solution treatment: Filter the casting solution with 300-mesh gauze to remove impurities from the solution, and age the solution at room temperature for 12 hours.

[0088] 5) Coating: Adjust the doctor blade gap to 60 μm, and evenly coat the casting solution onto the PET core-pore membrane. Place it in the air for 3 min for the first phase separation, and then immerse it in a deionized water coagulation bath for 40 s for the second phase separation. After drying, an acoustic composite membrane with waterproof and breathable functions is formed.

[0089] Appendix Figure 4Figure 4 shows the SEM image of the acoustic composite membrane of Example 4 and the performance test results of the acoustic composite membranes of Example 4 and Comparative Example 4. Figure (a) shows the SEM image of the acoustic composite membrane of Example 4 with 0.5 wt% KBM 603 added. It can be seen that KBM 603 has a stronger dispersion effect on PVDF crystals, and KBM 603 can react with amino groups in the solution to form a cross-linked network, adhering the PVDF crystals to the cross-linked network. Figure (b) shows the air permeability comparison, indicating that the air permeability decreases with the addition of KBM 603. Figure (c) shows the comparison of the 1K frequency response values ​​of the audio signal, indicating that the 1K frequency response values ​​have smaller dispersion and better consistency with the addition of KBM 603.

[0090] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0091] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Since these modifications and variations fall within the scope of the claims and their equivalents, this invention also intends to include these modifications and variations.

[0092] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a waterproof and breathable acoustic membrane based on PVDF crystal linking regulation, characterized in that, Includes the following steps: S1. Base film preparation: Provide PET core-pore membranes that have undergone heavy ion bombardment and etching treatment; S2. Precursor preparation: Polyvinylidene fluoride (PVDF), N,N-dimethylformamide (DMF), acrylate and first silane coupling agent are mixed, heated and stirred to obtain casting solution precursor; S3. Crosslinking reaction: Cool the casting solution precursor to 15-30°C, add the second silane coupling agent, and stir to carry out the crosslinking reaction to obtain the casting solution; S4. Coating and film formation: The casting solution is coated onto the surface of the PET core-porous membrane, and a first phase separation and a second phase separation are performed sequentially. After drying, the waterproof and breathable acoustic membrane is obtained; wherein, the first silane coupling agent is an amino-containing silane coupling agent, and the second silane coupling agent is an epoxy-containing silane coupling agent.

2. The preparation method according to claim 1, characterized in that, Step S1 specifically includes: A PET base film is subjected to heavy ion bombardment treatment, followed by etching pores in an alkaline solution. After cleaning and drying, a PET core-pore membrane is obtained. The heavy ion bombardment density is 80,000-120,000 ions / cm², and the concentration of the alkaline solution is 6-10 mol / L.

3. The preparation method according to claim 2, characterized in that, The PET core pore membrane has a pore size of 3-10 μm and a membrane thickness of 4-6 μm.

4. The preparation method according to claim 1, characterized in that, In step S2, based on the total mass of the casting solution precursor, the mass percentage concentration of PVDF is 10-16 wt%; the mass ratio of PVDF to acrylate is (15-25):(2-4); and the mass ratio of PVDF to the first silane coupling agent is (40-60):

1.

5. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of PVDF to the second silane coupling agent is (15-25):

1.

6. The preparation method according to claim 1, characterized in that, In step S4, before the coating and film-forming steps, the casting solution is filtered and aged at 15-30°C for 12-24 hours.

7. The preparation method according to claim 1, characterized in that, In step S4, the first phase separation is to let it stand in the air for 1-6 minutes; the second phase separation is to soak it in a deionized water coagulation bath for 1-3 minutes.

8. The preparation method according to any one of claims 1 to 7, characterized in that, In step S4, a doctor blade is used for coating, with a coating gap of 20-80 μm.

9. A waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation, characterized in that, It is prepared by any one of claims 1 to 8.

10. A wearable device, characterized in that, Including the waterproof and breathable acoustic membrane based on PVDF crystal linkage regulation as described in claim 9.

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