A breathable barrier film and method of making the same

Abstract

The present application relates to the technical field of composite forming auxiliary materials, and particularly relates to a breathable release film and a preparation method thereof. The method comprises the following steps: 1) dispersing a polymer and a nano functional filler in a solvent to configure an electrospinning solution; 2) performing electrospinning on a substrate layer to form a nanofiber film; 3) performing functionalization treatment on the surface of the nanofiber film, coating epoxy modified silicone oil and catalyzing curing; and 4) performing post-treatment on the cured material to obtain the breathable release film. The present application constructs a small-aperture PVDF nanofiber film through electrospinning, realizes high breathability, forms a physical anchoring functional layer on the fiber surface through self-crosslinking of the epoxy modified silicone oil, and obtains a stable low-surface-energy resin-repellent interface, thereby breaking through the contradiction between the breathability and the barrier property of traditional materials, and having excellent solvent resistance and moisture and heat aging resistance, and the comprehensive performance is significantly better than that of traditional foaming coatings and PTFE microporous films.

Description

Technical Field

[0001] This invention relates to the field of auxiliary materials for composite material molding, specifically to a breathable insulating membrane and its preparation method. Background Technology

[0002] In the vacuum infusion molding process of composite materials, unidirectional isolation materials (or unidirectional breathable membranes) are one of the key auxiliary materials. Their function is to allow air to pass through smoothly under vacuum while effectively blocking the penetration of liquid resin, ensuring that the resin flows within the predetermined channels and impregnates the reinforcing fibers. In existing technologies, mainstream unidirectional isolation membranes are mostly prepared by coating a non-woven or plain-weave fabric substrate with a foamed microporous coating (such as polyurethane or acrylic foam coating) or a wet coating process. However, these traditional technologies have the following prominent drawbacks: 1) The contradiction between micropore uniformity and reliability: To achieve high air permeability, the coating needs to form a sufficient number of interconnected channels. Traditional foaming or pore-forming processes struggle to precisely control the uniformity of micropore size, easily leading to areas with excessively large pore sizes or weak structures in the coating. When used in high-flow resin systems (such as low-viscosity epoxy resins), the resin easily leaks through these defects, causing the one-way barrier function to fail and resulting in product scrap.

[0003] 2) Uncontrollable interfacial adhesion: To ensure the adhesion between the coating and the substrate, traditional coating materials often have similar chemical properties or higher surface energy to the subsequently poured resin matrix, resulting in excessively strong interfacial adhesion between the release film and the cured resin after molding. Peeling is not only laborious but also more likely to leave coating material residue on the product surface, severely affecting the surface quality of composite parts and subsequent coating and bonding processes.

[0004] 3) Difficulty in achieving a balance between overall performance: Existing technologies are mostly based on the physical "sieving" principle, relying on the size of micropores to block resin. This is essentially a balancing act: increasing air permeability requires increasing porosity or pore size, but this weakens the reliability of the barrier; enhancing barrier properties requires decreasing the pore size or increasing the coating density, which sacrifices air permeability and may increase interfacial adhesion. Therefore, it is difficult to simultaneously achieve high air permeability, high-reliability resin barrier properties, and easy tearing in a single material.

[0005] Therefore, this invention aims to overcome the limitations of existing technologies and propose a novel unidirectional isolation material solution based on the synergistic design of nanofiber membrane structure and surface interface engineering. Summary of the Invention

[0006] The present invention addresses the technical challenges of poor micropore uniformity in traditional coatings, uncontrollable adhesion between coatings and resin substrates, and difficulty in achieving multiple properties simultaneously. It provides a method for preparing a breathable barrier membrane, as well as the resulting breathable barrier membrane.

[0007] The main objective of this invention is: 1. A unidirectional insulating material is provided, which has a highly uniform and controllable micro-nano-scale pore structure, achieving high air permeability while ensuring reliable barrier to liquid resin; 2. By constructing a resin-repellent functional layer with chemical stability and low surface energy on the material surface, the isolation material can be easily and completely removed after molding without any residue. Third, a preparation method with controllable process and suitable for large-scale production is provided to ensure the consistency and stability of material properties.

[0008] To achieve the above objectives, the present invention adopts the following technical solution.

[0009] A method for preparing a breathable insulating membrane, The method includes: 1) Disperse the polymer and nanofunctional fillers in a solvent to prepare an electrospinning solution; 2) Electrospinning is performed on the substrate layer to form a nanofiber membrane; 3) Functionalize the surface of the nanofiber membrane by coating it with epoxy-modified silicone oil and catalytic curing; 4) The cured material is then post-treated to obtain a breathable isolation membrane.

[0010] As a preferred option Step 1) The polymer is polyvinylidene fluoride (PVDF), with a weight-average molecular weight range of 4 × 10⁻⁶. 5 ~5×10 5 g / mol; Step 1) The nanofunctional filler is nano-silica and / or nano-magnesium silicate surface-treated with silane coupling agent, with a particle size range of 10-50 nm; Step 1) The solvent is a mixture of N,N-dimethylacetamide (DMAc) and acetone, wherein the mass ratio of N,N-dimethylacetamide to acetone is (6-8):(2-4).

[0011] As a preferred option In step 1), the concentration of polyvinylidene fluoride (PVDF) in the electrospinning solution is 10–16 wt%, and the amount of nanofunctional filler added is 1–5 wt% of PVDF. In particular, when the concentration of PVDF is 13–16 wt% and the amount of nanofunctional filler added is 3–5 wt% of PVDF, the product blocking effect is better.

[0012] As a preferred option Step 2) The electrospinning is carried out at a temperature of 20-30 ℃ and a relative humidity of 40-60%. The spinning voltage is controlled at 15-25 kV, the distance from the spinneret tip to the substrate layer is 15-18 cm, and the solution propulsion rate is 1.0-1.2 mL / h. The optimal spinning voltage should be controlled at 20-25 kV.

[0013] As a preferred option Step 2) The surface density of the nanofiber membrane formed by electrospinning is controlled to be 5–20 g / m³. 2 .

[0014] As a preferred option Step 3) The epoxy-modified silicone oil has an epoxy value of 0.1–0.2 mol / 100g and a viscosity of 1000–2000 mPa·s; Step 3) The catalyst is an aliphatic tertiary amine catalyst; The aliphatic tertiary amine catalyst is triethylenediamine (DABCO), and its addition amount is 1.0 to 2.0 wt% of the epoxy-modified silicone oil.

[0015] As a preferred option Step 3) The coating method is slot coating, and the wet film thickness is 10-30 μm; Step 3) The curing reaction is carried out in an oven and cured for 20 to 40 minutes in an air atmosphere, at a pressure of 0.08 to 0.12 MPa and a temperature of 70 to 90 °C.

[0016] As a preferred option Step 4) The post-treatment of the cured material is to perform calendering. During the calendering process, the temperature of the calendering roller is controlled at 50-70 ℃ and the linear pressure is 30-60 N / mm. After calendering, the material is dried in an oven at 70-90 ℃ for 10-30 min.

[0017] A breathable insulating membrane, comprising a substrate layer, a PVDF nanofiber layer, and a surface epoxy silicone oil cross-linked functional layer, wherein the layers are physically anchored together.

[0018] The core of this invention lies in the system integration of PVDF nanofiber membrane, epoxy-modified silicone oil interface engineering, and nanofiller composite reinforcement to construct a unidirectional barrier material with high air permeability, reliable barrier properties, and easy tearing.

[0019] PVDF-based nanofiber membranes achieve excellent air permeability and barrier properties based on their unique molecular structure and electrospinning process. The PVDF material selected in this invention, with its unique semi-crystalline nature and electric field-induced crystallization behavior during electrospinning, is key to constructing a stable three-dimensional network structure. Specifically, the PVDF molecular chains are highly oriented under a high-voltage electric field, promoting the formation of a piezoelectric β-crystal form. This β-crystal form not only endows the fiber membrane with excellent mechanical strength and structural rigidity, but more importantly, its regular crystalline structure acts as physical cross-linking points at the nanoscale, effectively inhibiting creep and shrinkage of the fibers during subsequent coating, curing, and high-temperature use, ensuring the long-term thermodynamic stability of the pore structure. Compared to amorphous polymers, the crystalline characteristics of PVDF are the fundamental reason why it can serve as a "skeleton," stably supporting subsequent functionalization processes and resisting the stress of complex molding environments. This is a material basis that is difficult for other non-crystalline or weakly crystalline polymers to replicate. The strong electronegativity of fluorine atoms and the high bond energy of CF bonds in the PVDF molecular chains endow the material with excellent chemical and thermal stability, allowing it to maintain structural integrity over a wide temperature range. Compared to polyurethane materials, PVDF has better solvent resistance and anti-aging properties.

[0020] This invention employs electrospinning technology to achieve refined fiber formation from a polymer solution driven by a high-voltage electric field. Under the influence of the electric field, charged droplets undergo Taylor cone instability, forming an ultrafine fiber jet. During its flight, the jet undergoes stretching deformation and solvent evaporation, ultimately depositing to form a three-dimensional network structure. This preparation method allows for precise control of fiber diameter at the nanometer level, resulting in a porous membrane structure with narrow pore size distribution and high porosity. The pore size of the fiber membrane is controlled through the synergistic optimization of polymer concentration, molecular weight, and process parameters. Appropriately increasing the polymer concentration is beneficial for forming continuous fibers, but excessively high concentrations lead to increased fiber diameter and coarsened pores. The molecular weight selection needs to balance spinning performance and the final membrane structure; excessively high molecular weight affects spinnability, while excessively low molecular weight affects membrane strength.

[0021] This invention utilizes epoxy-modified silicone oil to achieve dual functionalization through molecular chain entanglement anchoring and surface reconstruction. Under the catalysis of tertiary amines, epoxy groups undergo graft crosslinking reactions with the substrate, forming a "spot-welded" chemical anchoring structure between the silicone oil molecules and the substrate. This strong physical anchoring, combined with the surface enrichment of silicone oil segments, ensures the stability and durability of the functional layer during use, avoiding the migration or failure of the functional layer that is easily caused by simple physical adsorption. The surface enrichment of silicone oil segments achieves spontaneous reconstruction based on the difference in interfacial energy between them and the substrate. During curing, low surface energy silicone oil molecules tend to migrate towards the air interface, forming a silicone-rich layer on the material surface. This surface reconstruction phenomenon reduces the surface energy of the material, significantly lower than the surface tension of most resins. Furthermore, the unidirectional isolation mechanism is achieved based on the surface energy gradient and wettability difference. The low surface energy silicone oil layer on the air side of the material repels liquid resin, preventing it from wetting and penetrating due to surface tension; the substrate side maintains a relatively high surface energy, ensuring good adhesion to the substrate. This asymmetric wettability achieves the unidirectional barrier effect of the resin. It is worth emphasizing that the "physical anchoring" described in this invention is not a simple surface adsorption or mechanical interlocking, but rather a physical interlocking anchoring based on the "topological entanglement" effect of polymer chains within a nanoscale confined space. Specifically, it refers to the physical interlocking anchoring formed by the molecular chain segments of the epoxy-modified silicone oil crosslinking network and the micro-nano-uneven structure of the PVDF fiber surface. After curing, the molecular chain segment size of the epoxy-modified silicone oil crosslinking network is at the same scale as the micro-nano structure of the PVDF nanofiber surface (including the roughness of the fiber itself and the "anchor points" formed by the protrusions of the nanofillers). During the curing process, these flexible crosslinked network segments can penetrate, entangle, and "lock" themselves into the nanoscale grooves, protrusions, and three-dimensional framework constructed by the nanofillers on the PVDF fiber surface, forming an interlocking structure similar to "molecular-level rivets." This strong physical bond based on topology has a bonding energy far exceeding that of van der Waals forces and does not depend on specific chemical bonds. Therefore, it ensures the inertness of the functional layer under harsh chemical environments while providing sufficient interfacial bonding strength to resist resin erosion and peel stress. This explains why the functional layer of the present invention remains intact after solvent wiping and thermal aging, while simple physical adsorption or linear molecular coatings will quickly fail.

[0022] This invention utilizes modified nano-magnesium silicate or silica to achieve good compatibility with the polymer matrix through surface functionalization. Silane coupling agent treatment introduces reactive groups onto the nanoparticle surface, improving interfacial compatibility with PVDF molecular chains. This enhanced interfacial effect effectively prevents nanofiller agglomeration and phase separation, ensuring the uniformity of composite material properties. The reinforcing mechanism of the nanofiller used in this invention is based on stress transfer and crack passivation effects. Nanoparticles, as rigid reinforcing phases, can effectively bear external loads, improving the material's modulus and strength. When the material is subjected to external forces, the nanofiller can prevent crack propagation, consuming fracture energy through crack deflection and bifurcation mechanisms, thus improving the material's toughness. Simultaneously, the pore size control effect is achieved through the steric hindrance of the nanofiller. During electrospinning, the presence of the nanofiller affects the rheological behavior and jet stability of the polymer solution, thereby controlling the fiber diameter and membrane pore size distribution. Appropriate addition of nanofiller can refine the fiber structure, optimize the pore size distribution, and improve the material's filtration accuracy. The nanofiller surface-treated with silane coupling agent surpasses the effects of traditional stress transfer and crack passivation. First, these nanoscale rigid particles act as "physical cross-linking points" in the electrospinning solution, creating a "spatial confinement" effect on the movement of PVDF molecular chain segments. This confinement effect can regulate the tensile behavior of the jet in an electric field, suppress Rayleigh instability, and thus significantly refine the fiber diameter and make its distribution more uniform. Second, the high specific surface area of ​​the nanofiller and the surface chemical properties modified by the coupling agent can induce heterogeneous nucleation and oriented crystallization of PVDF molecular chains on their surface during spinning, forming an "interfacial transition layer." This transition layer not only enhances the interfacial bonding force between the filler and the matrix, but more importantly, it changes the internal crystalline morphology and microstructure of the fiber, resulting in a denser and more stable internal structure in the final composite fiber membrane. This explains why adding a small amount of nanofiller can significantly improve tensile strength while achieving precise control over the maximum pore size of the fiber membrane—a microstructure design that cannot be achieved with a single polymer system.

[0023] In this invention, the components are organically integrated and unified through material-level design. Specifically, a basic composite support layer is formed on the surface of polyester plain weave fabric through electrospinning to create a nanofiber membrane. This layer not only provides the material with necessary mechanical strength and stable air permeability channels, but also acts as a primary physical barrier against resin due to its uniform and dense nanoporous structure. Epoxy-modified silicone oil, as a functional surface layer, forms a cross-linked network through curing and is physically anchored on the surface of the substrate and nanofiber membrane, giving the material active resin-repellent interfacial characteristics and reliable barrier performance. Specifically, after coating, the epoxy-modified silicone oil functional layer undergoes ring-opening cross-linking at the epoxy groups at the ends of its molecular chains under the action of a tertiary amine catalyst, forming a three-dimensional cross-linked network. During the curing process, this network is physically anchored to the surface of the substrate and PVDF nanofibers through molecular chain entanglement and van der Waals forces. At the same time, siloxane segments accumulate at the air interface, thereby constructing a low surface energy and high stability resin-repellent interface on the material surface. Nanofillers, as reinforcing phases, are uniformly dispersed in the fiber membrane matrix, further improving the mechanical properties and structural stability of the material. This multi-layered, integrated structural design ensures that each functional component can work together to achieve the material's comprehensive performance of high breathability, high barrier properties, and easy tearing.

[0024] The synergy between the various functions in this invention is reflected in the complementary and synergistic mechanism of key performance indicators. High air permeability requires a highly open and interconnected pore structure within the material, which is mainly achieved through a three-dimensional network constructed by electrospun nanofibers. Reliable barrier properties require the material surface to have low surface energy characteristics and weak interfacial adhesion with the resin, which is achieved through a surface-grafted epoxy-modified silicone oil functionalized layer. Easy peelability specifically refers to the ability to completely peel the unidirectional barrier material from the surface of the fiberglass product after vacuum infusion molding without leaving any coating residue. This is achieved through a moderate and stable physical anchoring between the network formed by the cured epoxy-modified silicone oil and the fiber surface, ensuring strong bonding while ensuring clean separation of the interface under stress. Through the above multi-level performance design, the various functions are coordinated and optimized within the material, avoiding the common performance constraints between high air permeability and strong barrier properties, and between strong adhesion and easy peelability in traditional solutions, ultimately achieving a synergistic improvement in overall performance.

[0025] The inventiveness of this invention is not a simple superposition of single elements, but rather a synergistic innovation that integrates structure and performance through systematic material design and process integration. Its core lies in using the crystalline properties of PVDF as the "skeleton" and electrospinning technology as the "construction method" to build a thermodynamically stable and structurally precisely controllable nanoporous platform. Then, through topological entanglement as a "physical anchoring" method, a low-surface-energy epoxy-modified silicone oil functional layer is firmly "stitched" onto the platform surface, forming a composite interface that combines rigidity and flexibility. Simultaneously, the introduced nanofillers, through spatial confinement and interface-induced effects, further strengthen the "skeleton" and optimize the microstructure of the "platform" at the molecular and nanoscale. This full-scale synergy, from molecular chain arrangement and nanoscale phase interface regulation to macroscopic multilayer structure design, enables materials to simultaneously achieve three properties that are mutually restrictive in traditional technologies: high permeability (derived from the interconnected channels of the framework), high barrier properties (derived from the low surface energy and fine pore size of the interface), and easy tearing (derived from the appropriate combination of topological anchoring). This constitutes a complete, non-obvious, and significantly improved technical solution.

[0026] The process design of this invention emphasizes the smooth connection of each step, ensuring the feasibility of industrial implementation by constructing a continuously operable preparation process. Specifically, the electrospinning process is well matched with the subsequent coating and curing processes in terms of parameters and rhythm. This not only ensures efficiency in continuous production but is also crucial for maintaining consistent product quality. The core process sequence of "spinning first, then coating" has significant scientific importance: it first constructs a structurally complete and uniformly porous nanofiber membrane on the substrate, and then performs functionalization treatment on its surface. The "spinning first, then coating" process sequence is not only an operational procedure but also an inevitable choice based on the principles of material thermodynamics and kinetics. From a thermodynamic perspective, the formation process of PVDF fiber membrane is a non-equilibrium phase transition process from solution to solid, with solvent evaporation and molecular chain aggregation occurring simultaneously. If low surface energy epoxy-modified silicone oil is introduced during this process, it will preferentially occupy the gas-liquid interface as a surfactant, severely interfering with the jet formation of PVDF and the normal aggregation of molecular chains, leading to fiber defects and bead structures. From a kinetic perspective, only after the PVDF fiber membrane is fully formed and its structure is finalized can its enormous specific surface area and abundant surface micro / nanostructures provide an ideal "anchoring platform" for the subsequent coating of epoxy-modified silicone oil. At this point, the spreading, penetration, and curing processes of the functional layer solution occur on a stable, rigid framework, rather than competing with another dynamically changing process. Therefore, this process sequence is the only path to ensure that the fiber membrane obtains its optimal intrinsic structure and that the functional layers achieve the strongest interfacial bonding, a prerequisite for achieving the material's ultimate high performance. This sequence fundamentally avoids interference from functionalizing agents on fiber formation and deposition during electrospinning, thus ensuring the optimal structure of the nanofiber membrane itself. Simultaneously, this sequence also allows the functionalized coating to uniformly and completely cover the surface of the finalized fiber network, forming a continuous functional interface.

[0027] Subsequent calendering, drying, and other optimization processes further refine and enhance the material's structure and properties. Appropriate calendering improves the film's density and surface smoothness, increasing its reliability against resin penetration in practical applications; while thorough drying ensures the material's dimensional stability and performance durability. These post-processing steps work together to significantly improve the material's overall performance and its adaptability to different applications, completing the final step in the transformation from laboratory preparation to a stable and reliable industrial product.

[0028] The beneficial effects of this invention are as follows: This invention constructs a small-pore PVDF nanofiber membrane through electrospinning, achieving high air permeability while simultaneously obtaining a stable low surface energy resin-repellent interface through the self-crosslinking of epoxy-modified silicone oil and the formation of a physically anchored functional layer on the fiber surface. This overcomes the contradiction between air permeability and barrier properties in traditional materials, achieving "permeability-free" barrier to low-viscosity epoxy resin under vacuum, while maintaining peel force within the easy-to-tear range. Combined with nanofiller reinforcement, the material has high tensile strength and excellent solvent resistance and damp heat aging resistance. Its comprehensive performance is significantly better than traditional foamed coatings and PTFE microporous membranes. Detailed Implementation

[0029] The present invention will be further described clearly and in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0030] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0031] Unless otherwise specified, the nanoparticles (nano silica or nano magnesium silicate) treated with KH-550 silane coupling agent used in the embodiments of this invention are all prepared by the following methods: A solution with a KH550 mass concentration of 10 g / L was prepared by mixing deionized water, anhydrous ethanol, and glacial acetic acid in a mass ratio of 5:95:0.5 as a solvent and adding KH550 coupling agent. The solution was magnetically stirred at 500 rpm for 30 min at room temperature to obtain a clear and transparent pre-hydrolyzed solution. Nanoparticles (nano-silica or nano-magnesium silicate) were added to an appropriate amount of anhydrous ethanol to prepare a suspension with a concentration of 50 g / L. The suspension was ultrasonically dispersed at 300 W for 30 min to obtain a pre-dispersion. The pre-dispersion was transferred to a three-necked flask equipped with a mechanical stirrer and reflux condenser, preheated to 70 °C in a water bath, and continuously stirred at 300 rpm. The pre-hydrolyzed solution was taken at a volume ratio of 1:10.5 (pre-hydrolyzed solution to pre-dispersion) and dispensed using a constant pressure dropping funnel at 20 °C. The solution was added dropwise to the pre-dispersion solution at a uniform rate within 1 minute. After the addition was complete, the reaction was continued at a constant temperature of 70°C in a water bath for 2 hours. After the reaction was completed, the reaction system was naturally cooled to room temperature. The solid was collected by centrifugation at 8000 rpm for 10 minutes, and the supernatant was discarded. The solid was washed three times by centrifugation with anhydrous ethanol. Finally, the washed wet powder was placed in a vacuum drying oven at 80°C for 6 hours. After drying, it was ground and passed through a 200-mesh sieve to obtain nanoparticles (nano silica or nano magnesium silicate) treated with KH-550 silane coupling agent.

[0032] Example 1 Preparation of a highly breathable unidirectional insulating material: 1) Select an areal density of 40 g / m³ 2 The polyester taffeta plain weave fabric is used as the base layer, cleaned and fixed on the electrospinning receiving device.

[0033] 2) PVDF particles with a weight-average molecular weight of approximately 400,000 were added to a mixed solvent of DMAc and acetone in a 6:4 mass ratio to achieve a PVDF mass concentration of 10%. The mixture was stirred in a 50°C water bath until completely dissolved. 1% of the PVDF mass of nano-silica treated with KH-550 silane coupling agent was added, and the mixture was further ultrasonically dispersed and mechanically stirred for 4 hours to obtain a homogeneous spinning solution.

[0034] 3) Spinning was carried out in an environmental chamber at 20 ℃ and 40% relative humidity. The spinning voltage was 15 kV, the distance from the spinneret tip to the substrate layer was 12 cm, and the solution propulsion rate was 0.8 mL / h. Spinning continued until an areal density of approximately 5 g / m³ was formed on the substrate. 2 PVDF / SiO2 composite nanofiber membrane.

[0035] 4) Epoxy-modified silicone oil with an epoxy value of 0.10 mol / 100g was mixed evenly with 0.5 wt% DABCO catalyst. The mixture was then coated onto the surface of the nanofiber membrane using a slot coater, with the wet film thickness controlled at 10 μm.

[0036] 5) The coated material is fed into a 70 ℃ drying tunnel and cured for 40 min. Then, it is calendered by passing it through heated calendering rollers at a roller temperature of 50 ℃ and a linear pressure of 30 N / mm. Finally, it is dried in a 70 ℃ oven for 30 min and then wound up to obtain a highly breathable unidirectional insulating material.

[0037] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are as follows.

[0038] Air permeability test: According to GB / T 5453-1997 "Determination of Air Permeability of Textile Fabrics", a digital fabric air permeability meter was used. Three circular samples without creases or obvious defects were cut from the sample, with a diameter at least 2 cm larger than the test head diameter. The instrument was preheated for 30 minutes before testing. The sample was held flat in the test head, ensuring a leak-proof seal. The test pressure difference was set to 100 Pa, and the measurement was started. The instrument automatically recorded the airflow per unit area. Each sample was tested at least three times in different areas, and the average value was taken as the air permeability (L / m²) of that sample. 2 ( / s), and finally calculate the arithmetic mean of the air permeability of all samples.

[0039] Resin Barrier Test: The test used a 15×15 cm flat glass mold, a vacuum pump and sealing system, a vacuum gauge, and a low-viscosity epoxy resin system with a viscosity of approximately 500 mPa·s, along with a release cloth and a flow guide net. A 10×10 cm square sample was cut. Before testing, the glass mold was cleaned, and the release cloth, the sample to be tested (functional layer facing up), and the flow guide net were laid out sequentially. The sample was then sealed with a vacuum bag film (sealing edge distance greater than 5 cm). 5.0 g of mixed resin was injected into the center of the sample through the pre-drilled injection port. The vacuum pump was started to evacuate the system pressure to -0.095 MPa and maintained for 10 min. After the test, the vacuum system was turned off, and the vacuum bag was opened to observe the resin penetration. The results were judged as follows: no penetration meant no resin traces on the back of the sample and the sealed area; trace penetration meant tiny or dot-like resin traces with a maximum size of less than 1 mm appeared on the back; partial / complete penetration meant a clear, continuous resin penetration area appeared. The resin barrier effect of the material was quantitatively evaluated.

[0040] Peel strength test: The peel performance of adhesive tapes was evaluated using the 180° peel method, according to GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes". A universal testing machine equipped with a 50 N force sensor was used. For sample preparation, two 25×150 mm samples were cut. One sample (functional side down) was flatly adhered to a clean glass plate (100×150 mm). A 2 kg standard roller was used to roll the sample back and forth three times at a speed of 10 mm / s to ensure no air bubbles. A 0.5 mm thick layer of epoxy resin was applied to the adhered sample and cured at room temperature for 24 h. After curing, the unattached end was bent upwards at a 180° angle to the glass plate and clamped onto the testing machine fixture. During testing, the glass plate with the adhered sample was vertically fixed to the lower fixture. The peel speed was set to 100 mm / min. The test was started, and force-displacement data were recorded within a 50–100 mm stroke. At least three parallel samples were tested, and the average peel force was calculated from the stable peel segment, converted to N / 25 mm.

[0041] Surface Energy Testing: Based on the Owens-Wendt-Rabel-Kaelble (OWRK) method, the total surface energy and its components are evaluated by measuring the contact angles of the material with two liquids of known surface tension components. An optical contact angle meter is used as the testing instrument. Ultrapure water and diiodomethane are used as the test liquids. Samples are cut into 10×10 cm square, flat, and uncontaminated blocks, fixed to the sample stage with the functional layer facing upwards. During the operation, 2 μL droplets are added to the sample surface using a microsyringe. The droplet profile is fitted using the Young-Laplace equation, and the static contact angle θ is automatically calculated. Each liquid is measured at least five times at different locations on the same sample, and the average value is calculated. The average contact angles of the two liquids are substituted into the OWRK equation to simultaneously solve for the dispersive and polar components of the material's solid surface energy, obtaining the total surface energy and accurately characterizing the material's surface wetting and compatibility properties.

[0042] Maximum pore size test: Following ASTM F316-03, "Standard Test Methods for Maximum Pore Size and Pore Size Distribution of Porous Membranes," the bubble point method pore size analyzer was used to determine the through-pore size characteristics of the material. A low surface tension liquid compatible with the material was used. A 5 mm diameter circular sample was cut and completely immersed in the test liquid, ensuring all pores were filled and no air bubbles remained. The wetted sample was placed flat into the test chamber. A slowly and uniformly increasing air pressure was applied to one side, while the other side was left open to the atmosphere, and the escaping of air bubbles was observed. The pressure at which the first continuous flow of air bubbles appeared was recorded as the bubble point pressure. The maximum pore size was calculated using the following formula.

[0043] In the formula: γ — Surface tension of the test liquid; Θ—Contact angle between the test liquid and the material; 0 for complete wetting. P – Bubble point pressure.

[0044]

[0045] Analysis of the above characterization results shows that the material prepared in Example 1 has an air permeability of 12.5 L / m³. 2 / s, fully demonstrating the high air permeability brought by the electrospinning structure, which can meet the process requirements of rapid degassing during vacuum infusion molding; the surface energy is in the typical low surface energy range, verifying that the epoxy modified silicone oil functional layer successfully endows the material with resin-repellent interface characteristics; the tensile strength is significantly improved compared with the pure PVDF fiber membrane without nano-SiO2, indicating that the uniform dispersion of nanofillers effectively enhances the mechanical properties and structural stability of the fiber membrane. The resin barrier test showed local penetration. Based on the result of a maximum pore size of 1.15 μm, it is speculated that this is because the fiber packing density in some areas during spinning was slightly lower, resulting in the maximum pore size slightly exceeding the target range. This caused a small amount of low viscosity resin to locally penetrate under a high pressure of -0.095 MPa. That is, when the parameters deviate from the optimal range of this invention, especially when the voltage is <20 kV, the polyvinylidene fluoride concentration is <13 wt%, and the amount of nano-functional filler added is <3 wt% of polyvinylidene fluoride, the barrier performance will decrease; the peel force is in a reasonable range of easy tearing, which ensures stable adhesion between the material and the product surface during molding and allows for complete peeling after molding without coating residue.

[0046] Example 2 Preparation of a highly breathable unidirectional insulating material: 1) Select an area density of 60 g / m³ 2 The polyester taffeta plain weave fabric is used as the base layer, cleaned and fixed on the electrospinning receiving device.

[0047] 2) PVDF particles with a weight-average molecular weight of approximately 450,000 were added to a mixed solvent of DMAc and acetone in a mass ratio of 7:3, resulting in a PVDF mass concentration of 13%. The mixture was stirred in a 60 °C water bath until completely dissolved. Then, 3% (by mass) of nano-silica treated with KH-550 silane coupling agent was added, and the mixture was further ultrasonically dispersed and mechanically stirred for 6 h to obtain a homogeneous spinning solution.

[0048] 3) Spinning was carried out in an environmental chamber at 25 ℃ and 50% relative humidity. The spinning voltage was 20 kV, the distance from the spinneret tip to the substrate layer was 16 cm, and the solution propulsion rate was 1.1 mL / h. Spinning continued until an areal density of approximately 12 g / m² was formed on the substrate. 2 PVDF / SiO2 composite nanofiber membrane.

[0049] 4) Epoxy-modified silicone oil with an epoxy value of 0.15 mol / 100g was mixed evenly with 1.0 wt% DABCO catalyst. The mixture was then coated onto the surface of the nanofiber membrane using a slot coater, with the wet film thickness controlled at 20 μm.

[0050] 5) The coated material is fed into an 80 ℃ drying tunnel and cured for 30 min. Then, it is calendered by heating calendering rolls at 60 ℃ and linear pressure of 45 N / mm. Finally, it is dried in an 80 ℃ oven for 20 min and wound up to obtain a highly breathable unidirectional insulating material.

[0051] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are as follows.

[0052] Air permeability test: According to GB / T 5453-1997 "Determination of Air Permeability of Textile Fabrics", a digital fabric air permeability meter was used. Three circular samples without creases or obvious defects were cut from the sample, with a diameter at least 2 cm larger than the test head diameter. The instrument was preheated for 30 minutes before testing. The sample was held flat in the test head, ensuring a leak-proof seal. The test pressure difference was set to 100 Pa, and the measurement was started. The instrument automatically recorded the airflow per unit area. Each sample was tested at least three times in different areas, and the average value was taken as the air permeability (L / m²) of that sample. 2 ( / s), and finally calculate the arithmetic mean of the air permeability of all samples.

[0053] Resin Barrier Test: The test used a 15×15 cm flat glass mold, a vacuum pump and sealing system, a vacuum gauge, and a low-viscosity epoxy resin system with a viscosity of approximately 500 mPa·s, along with a release cloth and a flow guide net. A 10×10 cm square sample was cut. Before testing, the glass mold was cleaned, and the release cloth, the sample to be tested (functional layer facing up), and the flow guide net were laid out sequentially. The sample was then sealed with a vacuum bag film (sealing edge distance greater than 5 cm). 5.0 g of mixed resin was injected into the center of the sample through the pre-drilled injection port. The vacuum pump was started to evacuate the system pressure to -0.095 MPa and maintained for 10 min. After the test, the vacuum system was turned off, and the vacuum bag was opened to observe the resin penetration. The results were judged as follows: no penetration meant no resin traces on the back of the sample and the sealed area; trace penetration meant tiny or dot-like resin traces with a maximum size of less than 1 mm appeared on the back; partial / complete penetration meant a clear, continuous resin penetration area appeared. The resin barrier effect of the material was quantitatively evaluated.

[0054] Peel strength test: The peel performance of adhesive tapes was evaluated using the 180° peel method, according to GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes". A universal testing machine equipped with a 50 N force sensor was used. For sample preparation, two 25×150 mm samples were cut. One sample (functional side down) was flatly adhered to a clean glass plate (100×150 mm). A 2 kg standard roller was used to roll the sample back and forth three times at a speed of 10 mm / s to ensure no air bubbles. A 0.5 mm thick layer of epoxy resin was applied to the adhered sample and cured at room temperature for 24 h. After curing, the unattached end was bent upwards at a 180° angle to the glass plate and clamped onto the testing machine fixture. During testing, the glass plate with the adhered sample was vertically fixed to the lower fixture. The peel speed was set to 100 mm / min. The test was started, and force-displacement data were recorded within a 50–100 mm stroke. At least three parallel samples were tested, and the average peel force was calculated from the stable peel segment, converted to N / 25 mm.

[0055] Surface Energy Testing: Based on the Owens-Wendt-Rabel-Kaelble (OWRK) method, the total surface energy and its components are evaluated by measuring the contact angles of the material with two liquids of known surface tension components. An optical contact angle meter is used as the testing instrument. Ultrapure water and diiodomethane are used as the test liquids. Samples are cut into 10×10 cm square, flat, and uncontaminated blocks, fixed to the sample stage with the functional layer facing upwards. During the operation, 2 μL droplets are added to the sample surface using a microsyringe. The droplet profile is fitted using the Young-Laplace equation, and the static contact angle θ is automatically calculated. Each liquid is measured at least five times at different locations on the same sample, and the average value is calculated. The average contact angles of the two liquids are substituted into the OWRK equation to simultaneously solve for the dispersive and polar components of the material's solid surface energy, obtaining the total surface energy and accurately characterizing the material's surface wetting and compatibility properties.

[0056] Maximum pore size test: Following ASTM F316-03, "Standard Test Methods for Maximum Pore Size and Pore Size Distribution of Porous Membranes," the bubble point method pore size analyzer was used to determine the through-pore size characteristics of the material. A low surface tension liquid compatible with the material was used. A 5 mm diameter circular sample was cut and completely immersed in the test liquid, ensuring all pores were filled and no air bubbles remained. The wetted sample was placed flat into the test chamber. A slowly and uniformly increasing air pressure was applied to one side, while the other side was left open to the atmosphere, and the escaping of air bubbles was observed. The pressure at which the first continuous flow of air bubbles appeared was recorded as the bubble point pressure. The maximum pore size was calculated using the following formula.

[0057] In the formula: γ — Surface tension of the test liquid; Θ—Contact angle between the test liquid and the material; 0 for complete wetting. P – Bubble point pressure.

[0058]

[0059] Analysis of the above characterization results shows that the air permeability of the material prepared in Example 2 is 8.2 L / m³. 2 / s, still within the high permeability range, effectively meeting the core requirement of rapid venting in vacuum injection molding; the resin barrier effect reaches the non-permeability level, and the analysis of the result with a maximum pore size of 0.85 μm indicates that through substrate selection and spinning parameter optimization, the material pore structure is more uniform and the maximum pore size is further reduced. Combined with the low surface energy characteristic of 22.5 mN / m, it completely blocks the penetration path of low viscosity resin; the peel force is in a reasonable balance range between stable adhesion and easy peeling, which can ensure reliable adhesion between the material and the product surface during molding, and can be completely peeled off after curing without coating residue; the tensile strength is significantly higher than that of Example 1, fully demonstrating the mechanical support of the polyester taffeta substrate and the synergistic effect of nano-SiO2 composite reinforcement, effectively enhancing the structural stability and tensile properties of the material.

[0060] Example 3 Preparation of a highly breathable unidirectional insulating material: 1) Select an area density of 80 g / m³ 2 Spring spun plain weave fabric is used as the base layer, cleaned and fixed on the electrostatic spinning receiving device.

[0061] 2) PVDF particles with a weight-average molecular weight of approximately 500,000 were added to a mixed solvent of DMAc and acetone in a mass ratio of 8:2, resulting in a PVDF mass concentration of 16%. The mixture was stirred in a 70 °C water bath until completely dissolved. Then, 5% (by mass) of nano-magnesium silicate treated with KH-550 silane coupling agent was added, and the mixture was further ultrasonically dispersed and mechanically stirred for 8 hours to obtain a homogeneous spinning solution.

[0062] 3) Spinning was carried out in an environmental chamber at 30 ℃ and 60% relative humidity. The spinning voltage was 25 kV, the distance from the spinneret tip to the substrate layer was 20 cm, and the solution propulsion rate was 1.5 mL / h. Spinning continued until an areal density of approximately 20 g / m² was formed on the substrate. 2 PVDF / magnesium silicate composite nanofiber membrane.

[0063] 4) Epoxy-modified silicone oil with an epoxy value of 0.20 mol / 100g was mixed evenly with 2.0 wt% DABCO catalyst. The mixture was then coated onto the surface of the nanofiber membrane using a slot coater, with the wet film thickness controlled at 30 μm.

[0064] 5) The coated material is fed into a 90 ℃ drying tunnel and cured for 20 min. Then it is calendered through a pair of heated calendering rollers at a roller temperature of 70 ℃ and a linear pressure of 60 N / mm. Finally, it is dried in a 90 ℃ oven for 10 min and wound up to obtain a highly breathable unidirectional insulating material.

[0065] The materials prepared in the examples were subjected to performance testing, and the specific characterization results are as follows.

[0066] Air permeability test: According to GB / T 5453-1997 "Determination of Air Permeability of Textile Fabrics", a digital fabric air permeability meter was used. Three circular samples without creases or obvious defects were cut from the sample, with a diameter at least 2 cm larger than the test head diameter. The instrument was preheated for 30 minutes before testing. The sample was held flat in the test head, ensuring a leak-proof seal. The test pressure difference was set to 100 Pa, and the measurement was started. The instrument automatically recorded the airflow per unit area. Each sample was tested at least three times in different areas, and the average value was taken as the air permeability (L / m²) of that sample. 2 ( / s), and finally calculate the arithmetic mean of the air permeability of all samples.

[0067] Resin Barrier Test: The test used a 15×15 cm flat glass mold, a vacuum pump and sealing system, a vacuum gauge, and a low-viscosity epoxy resin system with a viscosity of approximately 500 mPa·s, along with a release cloth and a flow guide net. A 10×10 cm square sample was cut. Before testing, the glass mold was cleaned, and the release cloth, the sample to be tested (functional layer facing up), and the flow guide net were laid out sequentially. The sample was then sealed with a vacuum bag film (sealing edge distance greater than 5 cm). 5.0 g of mixed resin was injected into the center of the sample through the pre-drilled injection port. The vacuum pump was started to evacuate the system pressure to -0.095 MPa and maintained for 10 min. After the test, the vacuum system was turned off, and the vacuum bag was opened to observe the resin penetration. The results were judged as follows: no penetration meant no resin traces on the back of the sample and the sealed area; trace penetration meant tiny or dot-like resin traces with a maximum size of less than 1 mm appeared on the back; partial / complete penetration meant a clear, continuous resin penetration area appeared. The resin barrier effect of the material was quantitatively evaluated.

[0068] Peel strength test: The peel performance of adhesive tapes was evaluated using the 180° peel method, according to GB / T 2792-2014 "Test Method for Peel Strength of Adhesive Tapes". A universal testing machine equipped with a 50 N force sensor was used. For sample preparation, two 25×150 mm samples were cut. One sample (functional side down) was flatly adhered to a clean glass plate (100×150 mm). A 2 kg standard roller was used to roll the sample back and forth three times at a speed of 10 mm / s to ensure no air bubbles. A 0.5 mm thick layer of epoxy resin was applied to the adhered sample and cured at room temperature for 24 h. After curing, the unattached end was bent upwards at a 180° angle to the glass plate and clamped onto the testing machine fixture. During testing, the glass plate with the adhered sample was vertically fixed to the lower fixture. The peel speed was set to 100 mm / min. The test was started, and force-displacement data were recorded within a 50–100 mm stroke. At least three parallel samples were tested, and the average peel force was calculated from the stable peel segment, converted to N / 25 mm.

[0069] Surface Energy Testing: Based on the Owens-Wendt-Rabel-Kaelble (OWRK) method, the total surface energy and its components are evaluated by measuring the contact angles of the material with two liquids of known surface tension components. An optical contact angle meter is used as the testing instrument. Ultrapure water and diiodomethane are used as the test liquids. Samples are cut into 10×10 cm square, flat, and uncontaminated blocks, fixed to the sample stage with the functional layer facing upwards. During the operation, 2 μL droplets are added to the sample surface using a microsyringe. The droplet profile is fitted using the Young-Laplace equation, and the static contact angle θ is automatically calculated. Each liquid is measured at least five times at different locations on the same sample, and the average value is calculated. The average contact angles of the two liquids are substituted into the OWRK equation to simultaneously solve for the dispersive and polar components of the material's solid surface energy, obtaining the total surface energy and accurately characterizing the material's surface wetting and compatibility properties.

[0070] Maximum pore size test: Following ASTM F316-03, "Standard Test Methods for Maximum Pore Size and Pore Size Distribution of Porous Membranes," the bubble point method pore size analyzer was used to determine the through-pore size characteristics of the material. A low surface tension liquid compatible with the material was used. A 5 mm diameter circular sample was cut and completely immersed in the test liquid, ensuring all pores were filled and no air bubbles remained. The wetted sample was placed flat into the test chamber. A slowly and uniformly increasing air pressure was applied to one side, while the other side was left open to the atmosphere, and the escaping of air bubbles was observed. The pressure at which the first continuous flow of air bubbles appeared was recorded as the bubble point pressure. The maximum pore size was calculated using the following formula.

[0071] In the formula: γ — Surface tension of the test liquid; Θ—Contact angle between the test liquid and the material; 0 for complete wetting. P – Bubble point pressure.

[0072]

[0073] Analysis of the characterization results above shows that the air permeability of the material prepared in Example 3 is 5.8 L / m³. 2 / s, still within the high permeability range required for vacuum injection molding, effectively ensuring efficient removal of air and volatiles during molding; the resin barrier effect reaches a non-permeable level, thanks to the uniform pore structure with a maximum pore size further reduced to 0.78 μm, combined with a low surface energy of 21.8 mN / m, forming a dual barrier effect against low-viscosity resin, completely inhibiting resin penetration; the peel force is in a reasonable balance range between stable adhesion and easy peeling, ensuring close adhesion between the material and the product surface during molding, and allowing for complete removal after curing without coating residue; the tensile strength is significantly improved to 35.2 MPa, which is closely related to the excellent mechanical support properties of the spring spun substrate, the composite reinforcement effect of nano-magnesium silicate modified with coupling agent, and the densification optimization of the material structure by the optimized calendering process, greatly enhancing the structural stability and tensile properties of the material, and better adapting to the mechanical requirements under complex molding conditions.

[0074] Comparative Example 1 Based on Example 2, this example only modifies the fabrication process of the core functional layer; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0075] The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0076]

[0077] Analyzing the above characterization results, D1-1 and D1-2 represent two mainstream traditional coating processes. Both suffer from poor uniformity of microporous structure and localized defects, leading to localized leakage under resin infusion pressure and low barrier reliability. Furthermore, their high surface energy, strong affinity with resin, and extremely high peel force make them difficult to remove. While the PTFE membrane used in D1-3 has small pore size, good barrier properties, and low surface energy, its excessively high permeability results in weak adhesion to the substrate, high cost, and poor process compatibility. Specifically: Group D1-1 uses a polyurethane microporous foam coating to replace the electrospun nanofiber layer, reducing its air permeability to 5.5 L / m³. 2The resin exhibited localized leakage—this was due to the polyurethane coating having a much larger pore size than in Example 2, and an uneven pore size distribution, making it unable to effectively block low-viscosity resin. Simultaneously, its surface energy reached 38.0 mN / m, enhancing its compatibility with the resin and further exacerbating the leakage risk. Furthermore, this group showed significantly higher peel strength, making it difficult to completely remove after curing; its tensile strength was only 15.0 MPa, and its high-temperature dimensional change rate reached 2.1%, indicating that its thermal stability and mechanical properties failed to meet molding requirements.

[0078] The acrylate wet-process porous coatings in group D1-2 performed worse: air permeability dropped to 4.8 L / m. 2 The resin exhibits more pronounced localized leakage, higher peel strength, larger surface energy, and significant issues with pore size and uneven distribution. The tensile strength is only 12.5 MPa, and the high-temperature dimensional change rate reaches 3.0%. This is because the wet pore-forming process struggles to precisely control the pore structure, and the strong surface polarity and poor thermal stability of acrylate materials lead to a comprehensive deterioration of all key properties.

[0079] Although the composite commercial PTFE stretched microporous membranes of groups D1-3 achieved zero leakage and high air permeability, they still had obvious shortcomings: the peel force was higher than that of Example 2, and the difficulty of tearing after curing increased; the tensile strength was lower than that of Example 2, due to the weak bonding force between the composite interface of the PTFE membrane and the substrate, and the failure to form an integrated structure; the surface energy was higher than that of Example 2 (22.5 mN / m), and the dimensional change rate at high temperature was slightly larger, so the overall performance was still inferior to that of Example 2.

[0080] A horizontal comparison reveals that neither foamed coatings, wet coatings, nor special microporous membranes can simultaneously achieve the high permeability, reliable barrier properties, easy peeling, and good process adaptability achieved by this invention. This result strongly demonstrates that constructing an electrospun nanofiber membrane as the core functional layer is the only effective way to achieve optimal comprehensive performance. The electrospun nanofiber functional layer used in Example 2, through precise control of pore structure, optimization of surface energy, and the integrated combination of substrate and functional layer, achieves a synergistic effect of high permeability, excellent resin barrier properties, moderate peeling force, strong mechanical properties, and good thermal stability, representing the optimal process path for preparing high-performance unidirectional insulating materials.

[0081] Comparative Example 2 Based on Example 2, this example only modifies the polymer composition of the electrospinning solution; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0082] The performance testing method for the comparative product was completely consistent with that of Example 1. Partial performance characterization was performed, and the results are shown in the table below. Additional chemical and physical stability of the membrane material's functional layer under elevated temperature conditions was also tested. The testing methods and characterization results are as follows: Standard dumbbell-shaped samples were used, with 10 x 10 mm samples cut from materials from Example 2, D2-1, D2-2, and D2-3, respectively. The samples were divided into a control group (Group A, 5 samples directly tested for initial tensile strength) and an experimental group (Group B, 5 samples subjected to epoxy resin immersion test). All samples were conditioned for 24 h at a standard environment of 23 ℃ and 50% RH. During the immersion process in the experimental group, the low-viscosity uncured epoxy resin premix was poured into a glass container and placed in a 60 ℃ constant temperature forced-air drying oven for 30 min to equilibrate. The samples were completely immersed after being separated by a PTFE film to avoid adhesion. The container lid was sealed with a slight gap to prevent pressure buildup, and the process environment was maintained for 4 h to accelerate the simulation. After soaking, the samples were quickly removed, and residual resin was scraped off. They were then cleaned three times at room temperature in an ultrasonic cleaner containing acetone, 5 minutes each time, to ensure complete removal of micropores and surface resin. After cleaning, the samples were dried in a 60°C oven for 2 hours and then transferred to a standard laboratory environment for 48 hours to reach moisture equilibrium. After soaking, the sample dimensions were remeasured using vernier calipers, and the soaked cross-sectional area was calculated. The maximum tensile force was determined using a universal testing machine under the same testing conditions as the control group. The tensile strength after soaking was calculated and averaged. Finally, the strength retention rate was calculated.

[0083]

[0084] Analyzing the characterization results above, the three comparative groups used different types of commonly used polymers. D2-1 and D2-3 exhibited poor resistance to polar solvents, and their functional layers were easily damaged, leading to a decline in long-term barrier reliability. D2-2 was prone to swelling and even softening upon contact with resins or solvents, exhibiting extremely poor dimensional stability and failing to maintain structural integrity during molding processes. The lateral comparison clearly demonstrates that PVDF, due to its unique CF bonds and excellent chemical inertness, solvent resistance, and thermal stability, is the best and irreplaceable matrix material for ensuring the long-term reliable operation of unidirectional barrier materials in complex chemical environments and thermal cycling processes. Other polymer materials all have significant shortcomings. Specifically: Group D2-1 used polyamide 6 instead of PVDF as the polymer component of the electrospinning solution. Although it could achieve no permeation barrier in the initial stage, after being soaked in epoxy resin, the amide bonds in the PA6 molecular chain easily interacted with the polar epoxy resin, causing the microporous structure of the functional layer to be destroyed, and the resin barrier performance changed from "no permeation" to "permeation". At the same time, its water contact angle dropped to 90° after solvent wiping, indicating a significant decrease in surface hydrophobicity; the high-temperature dimensional change rate reached 1.5%, which was much higher than that of Example 2; the strength retention rate was only 75.5%, and the structural integrity was significantly damaged, failing to meet the long-term process reliability requirements.

[0085] Group D2-2 uses thermoplastic polyurethane (TPU) instead of PVDF. Initially, the resin barrier effect is non-permeable; however, TPU has strong polarity and high compatibility with epoxy resin, easily causing swelling and softening upon contact, resulting in the functional layer losing its original structural support. Furthermore, after solvent resistance, the resin barrier state swells, and the softening of the film leads to a water contact angle of only 70° after solvent wiping. The high-temperature dimensional change rate is as high as 2.5%, and the strength retention rate is only 60.0%, accompanied by severe deformation, making it completely unsuitable for the thermal environment and chemical contact requirements of the molding process.

[0086] Group D2-3 uses polypropylene instead of PVDF. Although the initial air permeability is higher and the high-temperature dimensional change rate is lower, PP has insufficient tolerance to polar epoxy resin. After soaking, the microporous structure of the functional layer is eroded, and the resin barrier performance changes from non-permeable to permeable. After solvent wiping, the water contact angle drops to 95° and the surface hydrophobicity decreases. The strength retention rate is 81.1%, which is still lower than that of Example 2. Long-term use is prone to performance degradation.

[0087] In contrast, the PVDF material used in the examples, with its strong polarity and chemical inertness of the CF bonds in its molecular chain, not only has excellent initial properties, but also maintains a non-permeable barrier effect after being impregnated with epoxy resin. It also has a water contact angle >130° after solvent wiping, high high-temperature dimensional change rate, and high strength retention rate. It fully demonstrates the unique advantages of PVDF in chemical stability, thermal stability, and long-term structural integrity, making it the optimal matrix choice to ensure the reliable operation of unidirectional isolation materials in complex process environments.

[0088] Comparative Example 3 Based on Example 2, this example only modifies the surface functionalization treatment in a different way; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0089] The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0090] Additional tests were conducted on the wetting behavior and dynamic stability of the unidirectional isolation material functional surface on liquid epoxy resin. The specific methods and characterization results are as follows: The test employed an optical contact angle measuring instrument equipped with an electric precision liquid injection system and high-speed imaging, along with an ultra-flat sample stage and temperature control unit to maintain a constant temperature environment of 23 ℃. The test liquid was a low-viscosity epoxy resin premix. Samples were cut into 20×20 mm flat, defect-free pieces, fixed with the functional layer facing upwards. Before testing, the samples were conditioned in a standard environment (23 ℃, 50%RH) for 24 hours, and surface dust was removed using an air blower to ensure cleanliness. During operation, approximately 2 μL of liquid was added using a micro-syringe, and the left and right contact angles were calculated and averaged. In dynamic testing, 5 μL of liquid was slowly added and removed at a rate of 0.5 μL / s, and the advancing and receding contact angles were measured respectively. Measurements were repeated at three different points, and the difference in contact angle hysteresis was calculated.

[0091]

[0092] Analyzing the above characterization results, D3-1 directly proves that without a low surface energy interface layer, the material completely loses its barrier function. While D3-2 uses hydroxyl silicone oil to temporarily reduce surface energy, its lack of reactive groups results in weak bonding and poor wiping resistance, leading to insufficient barrier reliability. D3-3 uses a fluorinated surfactant that achieves extremely low initial surface energy, but it is only physically adsorbed and easily desorbs under prolonged liquid resin action or slight friction, exhibiting penetration after standing and a large dynamic contact angle hysteresis, indicating surface instability. A horizontal comparison shows that a durable and stable resin-repellent interface cannot be obtained solely through physical adsorption or the use of non-reactive low surface energy substances. Only by using epoxy-modified silicone oil with reactive epoxy groups, which can form a stable network through self-crosslinking and physically anchor to the substrate, as described in this invention, can a durable low surface energy interface be constructed, thereby achieving reliable long-term barrier properties and stable easy-to-remove performance. Specifically: Group D3-1 completely omits surface functionalization treatment. The surface of the electrospun PVDF fibers retains a large number of polar groups, with an initial surface energy as high as 42.3 mN / m, far exceeding the surface energy of the epoxy resin premix. Dynamic contact angle tests show that the resin is extremely easy to wet and spread, and directly and completely penetrates the functional layer under molding pressure. At the same time, the strong polar interaction between the fiber and the resin causes the peel force to soar. When torn off, the fiber is easy to break and leave residue, completely losing its unidirectional isolation function.

[0093] Group D3-2, coated with unmodified hydroxyl silicone oil, initially showed a surface energy reduction to 25.1 mN / m. However, the terminal hydroxyl groups of the silicone oil molecules lacked stable chemical bonds or strong physical interactions with the PVDF fiber surface, relying solely on weak van der Waals forces for bonding. After solvent wiping, the surface energy rebounded, the dynamic contact angle lags by 35°, and the interface stability is poor. Resin droplets slowly penetrate under prolonged static conditions or slight pressure. Furthermore, the silicone oil layer does not bond firmly to the fiber and is prone to detachment during processing, leading to localized barrier failure. The peel strength remains significantly higher than in Example 2.

[0094] Group D3-3 employs a fluorinated surfactant physical adsorption layer with an initial surface energy as low as 18.0 mN / m and a static contact angle of 120°, temporarily achieving no permeation barrier. However, this simple physical adsorption layer lacks effective and strong physical anchoring, making it prone to desorption under prolonged resin droplet immersion or slight friction. After solvent-resistant wiping, the surface energy increases sharply, and the dynamic contact angle lags by 40°, resulting in gradual resin penetration after standing. The residual surfactant after desorption also enhances the affinity between the resin and the fiber, and the peeling force cannot meet the requirements for long-term process stability.

[0095] In contrast, Example 2 employs an epoxy-modified silicone oil surface functionalization process that forms a stable physically anchored interface layer. This interface layer retains the low surface energy characteristics of the siloxane segments while exhibiting excellent adhesion stability; the dynamic contact angle hysteresis is only 5°, the interface wetting behavior is stable, and the resin droplets remain in a non-wetting state; at the same time, it effectively weakens the polar interaction between the fiber and the resin, maintaining a moderate peel force of 3.8 N / 25 mm, making it easy to remove without residue.

[0096] Comparative Example 4 Based on Example 2, this example only modifies the type and bonding method of the functionalized coating; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0097] The performance testing methods for the comparative product are completely consistent with those for Example 1, with a focus on durability tests such as aging resistance and abrasion resistance. The specific methods and characterization results are as follows: According to ISO 2409:2020 "Paints and varnishes—Cross-cut test", a multi-bladed cutting tool is used to cut a grid-like pattern through the coating surface to the substrate. Standard pressure-sensitive adhesive tape is then applied and quickly removed. The coating peeling off in the grid areas is observed and compared with a standard chart for evaluation, directly reflecting the bonding strength between the coating and the substrate. The test uses a six-bladed tool (1 mm blade spacing), a cutting guide ruler, 25 mm wide transparent pressure-sensitive adhesive tape, and a stereomicroscope with illumination, all meeting standard requirements. Three 50×50 mm samples were cut from materials from Example 2, D4-1, D4-2, and D4-3, placed flat on a rigid platform with the functional surface facing up, and conditioned for 16 hours at 23 ℃ and 50%RH before testing. During operation, at least three defect-free representative areas are selected on the sample surface, and dust particles are removed with a soft brush. If necessary, an eraser is used to clean and brush away debris. Six parallel cuts were made vertically along the guide ruler at a speed of 20 mm / s to the substrate. After rotating 90°, the cuts were repeated to form a 5×5 grid. Coating debris was removed with a brush. Then, 75 mm tape was applied to the grid area and pressed firmly to seal it. The tape was then quickly peeled off at a 180° angle within 120 seconds. Results were immediately observed under a microscope in good lighting and rated according to the ISO 2409 standard: Grade 0: no peeling; Grade 1: minor peeling at intersections (≤5%); Grade 2: peeling at edges / intersections (>5% to ≤15%); Grade 3: large fragment peeling (>15% to ≤35%); Grade 4: extensive peeling (>35% to ≤65%); Grade 5: severe peeling. The rating results for each test area were recorded.

[0098]

[0099] Analysis of the above characterization results shows that all comparative groups initially possessed low surface energy and a certain degree of liquid repellency. However, significant differences were observed in durability tests simulating harsh usage conditions. The physical adsorption layer of D4-1 was easily removed by solvents or migrated by heat. D4-2 used a linear polysiloxane with epoxy groups without a catalyst. Although its molecular chains contained reactive epoxy groups, they could not effectively construct a three-dimensional cross-linked network on the fiber surface. Under the same curing conditions, only a small amount of coupling occurred between molecular chains in the D4-2 group, failing to form a through-linked network, mainly relying on linear molecules adsorbing onto the fiber surface. After curing, it mainly formed a physical adsorption layer of linear molecules, lacking the strong entanglement and anchoring effect brought by the cross-linked network. Therefore, its adhesion was significantly worse than that of Example 2, and its performance in durability tests was also poor. The fluorocarbon resin coating of D4-3 was brittle and had poor compatibility with flexible fiber membranes, easily cracking and detaching after cyclic stress. The lateral comparison strongly demonstrates that simply possessing low surface energy characteristics is insufficient to guarantee the long-term effectiveness of the functional layer. This invention employs an epoxy-modified silicone oil catalytic crosslinking scheme. Its core innovation lies in the fact that the functional layer can form a stable network through self-crosslinking and achieve strong physical anchoring with the nanofiber membrane substrate. This combination ensures the functional layer's superior adhesion, solvent resistance, heat resistance, and fatigue resistance, which is unmatched by simple physical adsorption, physical crosslinking, or other non-bonding methods, and is the fundamental guarantee of material durability. Specifically: Group D4-1 used ordinary dimethyl silicone oil without a catalyst. The coating adhered to the PVDF fiber surface only through physical adsorption, and its cross-cut test rating was 4, indicating extremely weak adhesion between the coating and the substrate. After 50 acetone wiping cycles, the physically adsorbed silicone oil layer was almost completely removed, the functional layer lost its low surface energy protection, and the resin barrier effect became completely ineffective. After 24 hours of heat aging at 80 ℃, the silicone oil molecules migrated and agglomerated due to heat, the coating structure was destroyed, and the peel force increased sharply. After 10 simulated vacuum cycles, the maximum pore size change rate reached +25.3%, the microporous structure of the functional layer was severely damaged, and the unidirectional isolation function was completely lost.

[0100] Group D4-2 uses a linear polysiloxane with epoxy groups and no catalyst. Although its molecular chain contains reactive epoxy groups, it cannot effectively construct a three-dimensional cross-linked network on the fiber surface. After curing, it mainly forms a physical adsorption layer of linear molecules, lacking the strong entanglement and anchoring effect brought by the cross-linked network. Therefore, although its cross-cut adhesion is better than that of D4-1 with pure physical adsorption, it is significantly worse than that of Example 2. In the durability test, its structural instability was exposed: local failure occurred after solvent wiping; the interfacial bonding force decreased after thermal aging; after simulated vacuum cycling, the linear molecular layer was prone to relaxation or displacement, resulting in a maximum pore size change rate as high as +18.5%, which could not guarantee long-term reliable barrier. This proves that simply introducing reactive groups without forming a stable cross-linked network reduces structural stability and cannot meet the requirements for long-term cyclic use.

[0101] Group D4-3 used a non-reactive fluorocarbon resin solution. The fluorocarbon resin and PVDF fiber membrane were only physically bonded, and the resin itself was highly brittle, resulting in poor compatibility with the flexible fiber membrane. The cross-cut test rating was 4. After 50 acetone wiping cycles, the brittle coating developed numerous microcracks and peeled off due to friction, completely failing its barrier function. After 24 hours of heat aging at 80 °C, the fluorocarbon resin coating underwent catalytic degradation, with the peel force increasing to 7.0 N. After 10 simulated vacuum cycles, the maximum pore size change rate reached +20.6%, severely damaging the structural integrity of the functional layer.

[0102] In contrast, the epoxy-modified silicone oil in this embodiment forms a self-crosslinking network through catalytic crosslinking and achieves strong physical anchoring with PVDF fibers, resulting in a cross-cut adhesion rating of 0, indicating excellent coating adhesion. It maintains its non-penetrating barrier effect after 50 acetone wiping cycles; after 24 hours of heat aging at 80°C, the peel force only slightly increases to 4.0 N; and after 10 simulated vacuum cycles, the maximum pore size change rate is only +2.2%, fully verifying the long-term stability and durability of the anchoring functional layer under harsh environments.

[0103] Comparative Example 5 Based on Example 2, this example only modifies the type and bonding method of the functionalized coating; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0104] The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0105] Additional compression resilience tests were conducted on the fiber membrane. The specific methods and characterization results are as follows: The tests were performed using a universal testing machine or a dedicated compression resilience tester, equipped with a 50 mm diameter parallel pressure plate, a high-precision displacement sensor, and a pressure sensor. Five 50 mm diameter circular samples were cut from the materials of each embodiment after the functional layer was peeled off, ensuring they were flat and undamaged, and conditioned for 24 hours at 23 ℃ and 50%RH. The test parameters were set as follows: compression pressure 0.10 MPa, loading speed 0.5 mm / min, holding time 60 s, and free recovery for 180 s after unloading. A non-contact laser thickness gauge was used to measure the average value at three points in the center area of ​​the sample. The sample was then placed centered on the lower pressure plate, compressed to the target pressure according to the set program, and held. The displacement value at the end of the holding period was recorded to calculate the thickness after compression. After unloading, the sample recovered unconstrained for 180 s, and the recovered thickness was measured using the same method. The thickness recovery rate was calculated, and the material's compression resilience recovery rate was evaluated by the average value of the five parallel samples.

[0106]

[0107] Analysis of the above characterization results shows that D5-1, without nanofillers, results in a relatively coarse and loose fiber structure with large and widely distributed pores, leading to decreased barrier reliability and the lowest mechanical strength. D5-2 uses untreated hydrophilic nano-SiO2, which, although its fine particles can block small pores, has poor compatibility with hydrophobic PVDF, making it prone to agglomeration, potentially blocking pores, reducing air permeability, and increasing material brittleness. D5-3 uses micron-sized fillers, whose excessively large particle size fails to provide nanoscale reinforcement and fine pores, limiting its effect on pore size optimization and strength improvement. Lateral comparisons indicate that the reinforcing effect of nanofillers depends on their nanoscale effect, good dispersion in the matrix, and interfacial bonding with the polymer. The hydrophobic nano-SiO2 or magnesium silicate surface-treated with a silane coupling agent, preferred in this invention, can optimally exert multiple synergistic effects of fiber refinement, pore size optimization, and reinforcement and toughening during composite spinning, which cannot be achieved by filler-free, filler-agglomerated, or filler-appropriate particle size solutions. Specifically: Group D5-1 did not contain any nanofillers. The electrospun PVDF fibers exhibited a random, coiled pure polymer network structure with a wide and generally coarse fiber diameter distribution, resulting in a maximum pore size of 1.4 μm, significantly higher than in Example 2; although the air permeability increased to 10.2 L / m³. 2 While the resin droplets can penetrate locally through the large pore area, the barrier effect is unstable. Furthermore, lacking the reinforcing effect of nanofillers, the tensile strength of the fiber membrane is only 18.5 MPa, a decrease of 33.9% compared to Example 2; the compression recovery rate is 85.1%, indicating that the pure PVDF fiber membrane is difficult to fully recover its original shape after being compressed, and long-term use is prone to structural collapse leading to a decline in air permeability and barrier performance.

[0108] Group D5-2 uses untreated hydrophilic nano-silica. Due to the high hydroxyl content on the particle surface and poor compatibility with the hydrophobic PVDF matrix, agglomeration easily occurs during spinning. Some nanoparticles accumulate on the fiber surface or within the pores, causing localized pore blockage and reducing air permeability to 7.5 L / m. 2 / s; Simultaneously, the agglomerates become stress concentration points, causing the elongation at break of the fiber membrane to decrease from 45.2% in Example 2 to 30.7%, and the brittleness to increase significantly. Although the barrier effect of this group of resins temporarily meets the standard, the structural inhomogeneity caused by agglomeration will exacerbate performance fluctuations during long-term use, and the compression rebound recovery rate of 88.9% also does not reach the level of Example 2.

[0109] Group D5-3 uses micron-sized silica, whose particle size is much larger than that of nanofillers. This makes it impossible for the silica to effectively embed within the PVDF fibers or refine the fiber diameter, resulting in a weak effect on pore size optimization (the maximum pore size is still 1.3 μm), leading to localized resin penetration. Simultaneously, the interfacial bonding area between the micron-sized particles and the fiber matrix is ​​small, resulting in a tensile strength of only 20.0 MPa, and the reinforcing effect is far inferior to that of the nanofillers in Example 2. The compression rebound rate is only 80.0%, indicating that the micron-sized fillers are unable to support the fiber network structure and are prone to irreversible deformation under pressure, further affecting the long-term stability of the material.

[0110] In contrast, Example 2 uses hydrophobic nano-SiO2 surface-treated with a silane coupling agent. The particles are uniformly dispersed in the PVDF matrix, which not only refines the fiber diameter and pore size distribution, but also strengthens the interfacial bonding between the particles and the matrix through the bridging effect of the coupling agent. This increases the tensile strength to 28.0 MPa and maintains a relatively high elongation at break of 45.2%. At the same time, the three-dimensional network structure constructed by the nanofiller significantly enhances the compression resilience of the fiber membrane, ensuring that it can maintain stable air permeability and barrier properties under repeated pressure or vacuum cycling conditions.

[0111] Comparative Example 6 Based on Example 2, this example only modifies the type and bonding method of the functionalized coating; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0112] The performance testing method for the comparative product was exactly the same as that for Example 1, with a focus on observing the cross-sectional structure of the material. The characterization results are shown in the table below.

[0113]

[0114] Analysis of the above characterization results shows that any attempt to alter the core sequence of "first forming a complete nanofiber membrane, then constructing a functional layer on its surface" leads to structural defects and performance degradation in the product. D6-1 struggles to spin a uniform and continuous fiber membrane on a hydrophobic silicone oil layer. The "one-step" method of D6-2 severely interferes with the electrospinning process and results in functional materials being embedded internally, unable to effectively accumulate on the surface. The "sandwich structure" formed by D6-3 introduces a fragile internal interface. The horizontal comparison irrefutably proves that the "spinning first, coating later" process sequence is the optimal and only reasonable path to ensure the structural integrity of the nanofiber membrane, the uniformity and effectiveness of the functional layer surface, and the strong interlayer bonding of the final product. This sequence is a key technological prerequisite for the material to achieve its designed performance. Specifically: Group D6-1 employed a reversed sequence, and the pre-coated low surface energy silicone oil layer severely hindered the effective adhesion and overlap of subsequent PVDF fibers. This resulted in a loose fiber membrane structure, with the functional layer thickness variation coefficient exceeding 35% and extremely uneven coating distribution. Locally excessively thick areas blocked pores, reducing air permeability to 7.8 L / m³. 2 / s, uneven penetration occurs in areas with local fiber deficiency; the interlayer bonding strength is only 2.0 N / 25mm, far lower than that of Example 2, and the interface bonding is fragile and easily peeled off.

[0115] Group D6-2 attempted a "one-step" method by incorporating epoxy-modified silicone oil into the spinning solution. The silicone oil molecules interfered with the electrostatic stretching process of the PVDF polymer chains, leading to deterioration of fiber formability and the formation of numerous bead-like structures. Functional substances could not accumulate on the surface but instead became embedded within the fiber or aggregated. The air permeability abnormally decreased to 6.5 L / m³. 2 / s, defects in the fiber's structure cause localized penetration, and the interlayer bonding strength is only 3.0 N / 25mm, mainly due to the fracture of the fiber itself. The surface liquid repellency of the functional layer is completely lost.

[0116] Group D6-3 employs a sandwich process, where the silicone oil layer in the middle lacks a stable anchoring effect with the subsequent spun fibers, forming a distinct internal delamination interface. The functional layer thickness (CV%) exceeds 25%, and this internal delamination leads to resin penetration at the interface. Despite a peel strength of 6.5 N / 25mm, there is a significant risk of delamination, and the interlayer bonding strength is only 2.8 N / 25mm, making it prone to cracking from the inside under stress.

[0117] In contrast, Example 2 strictly follows the core sequence of complete spinning followed by surface functionalization: first, a uniform and dense PVDF nanofiber membrane substrate is formed by electrospinning, and then epoxy-modified silicone oil is coated on its surface and catalytically crosslinked. This process ensures the integrity of the fiber membrane structure, with a functional layer thickness CV% < 10%, and achieves a strong bond between the functional layer and the substrate, as well as between layers, through the physical entanglement and anchoring of the epoxy network.

[0118] Comparative Example 7 Based on Example 2, this example only modifies the conditions and methods of the post-processing; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0119] The performance testing method for the comparative product is completely consistent with that of Example 1. Partial performance characterization was performed, and the characterization results are shown in the table below.

[0120] Additional flexural fatigue tests were conducted on the fiber membranes. The specific methods and characterization results are as follows: An MIT-type flexural fatigue tester was used. The specimens were bent 180° around a mandrel with a radius of 3.0 mm at a frequency of 50 times / minute for 100 bends. The specimen size was 150 × 25 mm wide. Five parallel samples were cut along the longitudinal (MD) and transverse (CD) directions from materials of Example 2 and D7-1 to D7-3, with smooth, defect-free edges and a reference line marked in the center. The test environment was controlled at 23 ℃ and 50% RH. During the test, the two ends of the specimen were clamped and a slight tension was applied to ensure straightness and uniform bending around the mandrel in the bending area. After the test, a magnifying glass was used to carefully inspect the functional layer and substrate surface and edges within a 10 mm radius around the marked line, recording cracks, delamination, and fracture. The judgment levels included no cracking, edge micro-cracks (≤2 mm and not extending to the center), surface cracking (surface network cracks), and delamination or fracture. Five samples were tested in the same direction for each material group, and the test was repeated.

[0121]

[0122] Analysis of the characterization results above, D7-1 and D7-2 show that the absence of the calendering process results in a rougher material surface and slightly larger pore size, posing a risk to the absolute reliability of the barrier in practical applications. D7-3 demonstrates that while excessive calendering can achieve a smoother surface and smaller pore size, it severely sacrifices air permeability and may lead to coating embrittlement and decreased bending resistance due to over-compaction. The lateral comparison clearly reveals the necessity and optimization value of post-processing, particularly moderate calendering. The calendering conditions employed in this invention represent the optimal balance between improving surface smoothness, optimizing pore structure, enhancing barrier reliability, and product uniformity through gentle compaction without significantly sacrificing air permeability. Omitting or over-performing this step will adversely affect the overall performance. Specifically: Group D7-1 omitted all post-processing steps, resulting in incomplete removal of residual solvent from the fiber membrane, loose fiber overlap, and uneven pore distribution. This led to a surface roughness as high as 280 nm and a maximum pore size increased to 1.1 μm, although the air permeability was slightly improved to 8.8 L / m³. 2 / s, but the presence of tiny pores causes trace resin infiltration; the material thickness uniformity CV% reaches 8.0%, and stress concentration occurs in the edge area when bending, resulting in edge microcracks ≤2 mm, which can easily exacerbate the risk of damage with long-term use.

[0123] Group D7-2 underwent only heat drying without calendering, which partially resolved the solvent residue problem and enhanced the inter-fiber bonding force. The bending resistance showed no cracking, but the lack of calendering compaction resulted in local protrusions on the fiber membrane surface. The roughness remained at 250 nm and the maximum pore size was 1.1 μm, leading to trace permeation. The thickness uniformity CV% of 6.5% also did not reach the optimized level of Example 2.

[0124] Group D7-3 uses high-pressure calendering at 80 N / mm. Excessive linear pressure forces the fiber membrane structure to compact, reducing the surface roughness to 90 nm and the maximum pore size to 0.7 μm. The thickness uniformity CV% is only 3.0%. Although it achieves zero permeation, excessive pore blockage leads to a sharp drop in air permeability. At the same time, the functional layer and fiber matrix generate irreversible internal stress due to high-pressure extrusion. After 100 bends, a network crack appears on the surface, which seriously affects the flexibility and durability of the material.

[0125] In contrast, Example 2 employs an optimized moderate calendering process, which smooths the surface of the fiber membrane, refines the pore size, and improves thickness uniformity through calendering, ensuring no resin penetration; it also avoids over-compaction and maintains high air permeability; at the same time, the residual stress inside the fiber membrane is released during the calendering process, and the bending fatigue test shows no cracking.

[0126] Comparative Example 8 Based on Example 2, this example only combines, deletes, or replaces the operation steps; the remaining steps are the same as in Example 2. The specific settings are as follows:

[0127] The performance testing method for the comparative product was completely consistent with that of Example 1. A comprehensive performance characterization was performed, and the results are shown in the table below.

[0128] Additional comprehensive performance evaluation tests were conducted after high-temperature and high-humidity aging. The specific methods and characterization results are as follows: A constant temperature and humidity test chamber with a temperature control accuracy of ±1 ℃ and a humidity control accuracy of ±3 %RH was used to accelerate aging the samples in an environment of 70 ℃ and 95 %RH for 168 hours. Samples of 10×10 cm were cut from materials in Example 2 and D8-1 to D8-3. Three parallel samples were prepared for each aging group (set A) and control group (set B). Before testing, all samples were conditioned in a standard environment of 23 ℃ and 50 %RH for 48 hours, and the initial mass was recorded. During aging, the samples were vertically suspended on a non-hygroscopic sample rack to ensure uniform airflow and avoid frequent door opening interference. After aging, the samples were quickly transferred to a desiccator with built-in fresh silica gel and left at room temperature for 1 hour to remove surface condensation. The wet weight was then weighed, and the samples were transferred to a standard environment for 24 hours of conditioning. The final equilibrium mass was recorded. The performance test after aging used the same resin barrier test method as the control group, and the degree of resin penetration of the samples was comprehensively observed and recorded.

[0129]

[0130] Analyzing the above characterization results, D8-1, combining two traditional technologies, exhibits the worst overall performance, proving that traditional approaches cannot solve the technical problems of this invention. D8-2, with its dual simplification of materials, performs far worse than Example 2, demonstrating that the combination of PVDF matrix and nanofiller is fundamental to high performance. D8-3 makes two erroneous changes to key processes, resulting in fundamental defects in the product structure and significantly reduced performance uniformity and reliability. Most importantly, the overall performance degradation of these defective combinations is far more than a simple summation of individual comparative performance losses; rather, it represents a systemic collapse in performance. This profoundly demonstrates the strong synergistic effect and interdependence among the various innovative aspects of this invention, forming an inseparable organic whole. Any attempt to adopt only some features or replace them with approximate features cannot reproduce the high level of overall performance achieved by this invention. Specifically: Group D8-1 uses a traditional PU foam coating instead of a nanofiber membrane and fixes the silicone oil functional layer through physical adsorption, completely lacking the core innovative elements of this invention. The wide pore size distribution and strong connectivity of the PU foam result in an air permeability of only 4.5 L / m³. 2 The permeability is far lower than that of Example 2, and it cannot form an effective barrier; the physically adsorbed silicone oil layer has no strong force constraint and completely falls off after aging in high temperature and high humidity. It also fails rapidly due to external force in the solvent wiping test; lacking the reinforcing support of the nanofiber membrane, the tensile strength is only 10.0 MPa. The overall performance is inferior to that of Example 2, proving that the traditional technical approach cannot solve the contradiction between high permeability and reliable barrier.

[0131] Group D8-2 had its polymer matrix replaced with PA6 and the nanofillers removed. PA6 itself has weak resistance to damp heat aging, and after accelerated aging at 70℃ and 95%RH, it undergoes hydrolytic degradation, resulting in the destruction of the material's structural integrity. The pore structure of the PA6 fiber membrane without nanofillers is unstable, with some areas exhibiting excessively large pore sizes that cause leakage. PA6's chemical stability is inferior to PVDF, and the functional layer is easily dissolved in solvent wiping tests. Ultimately, all key performance characteristics fail to meet application requirements, highlighting the necessity of combining a PVDF matrix with nanofillers.

[0132] The D8-3 group suffers from the dual defects of reversed stacking process sequence and omission of calendering. Coating before spinning results in weak bonding between the fiber membrane and functional layer, while omitting calendering leads to high surface roughness and uneven pore size. Both factors synergistically exacerbate interface defects. After high-temperature and high-humidity aging, the weak points at the interface further expand, and permeation becomes more severe. Uneven distribution of the functional layer leads to solvent-resistant wiping failure, resulting in an air permeability of 7.2 L / m³. 2Although / s is similar to Example 2, the barrier reliability is completely lost, fully demonstrating the destructive cumulative effect of process simplification on product performance.

[0133] The chemical and hygrothermal stability of the PVDF matrix, the reinforcement and pore structure optimization of the nanofiller, the pre-spinning and post-coating process ensuring uniform adhesion of the functional layers, the moderate calendering improving structural uniformity, and the strong anchoring all combine to form a close synergy. This results in a comprehensive advantage of maintaining impermeability, high air permeability, and strong mechanical properties even after high-temperature and high-humidity aging, verifying the scientific validity and completeness of the invention. This result demonstrates that the various technical features of the invention are not isolated but rather mutually supportive and indispensable organic wholes, jointly constructing the material's excellent comprehensive performance.

Claims

1. A method for preparing a breathable insulating membrane, characterized in that, The method includes: 1) Disperse the polymer and nanofunctional fillers in a solvent to prepare an electrospinning solution; 2) Electrospinning is performed on the substrate layer to form a nanofiber membrane; 3) Functionalize the surface of the nanofiber membrane by coating it with epoxy-modified silicone oil and catalytic curing; 4) Post-process the cured material to obtain a breathable isolation membrane; Step 1) The nano-functional filler is nano-silica and / or nano-magnesium silicate surface-treated with silane coupling agent; Step 1) said polymer is polyvinylidene fluoride having a weight average molecular weight ranging from 4 x 10 5 ~ 5 x 10 5 g / mol; Step 1) The particle size range of the nanofunctional filler is 10–50 nm; Step 1) The solvent is a mixture of N,N-dimethylacetamide and acetone, wherein the mass ratio of N,N-dimethylacetamide to acetone is (6-8):(2-4). In step 1), the concentration of polyvinylidene fluoride in the electrospinning solution is 10–16 wt%, and the amount of nano-functional filler added is 1–5 wt% of the polyvinylidene fluoride. Step 2) The electrospinning voltage is controlled at 20-25 kV; Step 2) the electrospinning controls the surface density of the formed nanofiber membrane to be 5-20 g / m 2 ; Step 3) The epoxy-modified silicone oil has an epoxy value of 0.1–0.2 mol / 100g and a viscosity of 1000–2000 mPa·s; The catalyst used for catalytic solidification in step 3) is an aliphatic tertiary amine catalyst; The aliphatic tertiary amine catalyst is triethylenediamine, and its addition amount is 1.0–2.0 wt% of the epoxy-modified silicone oil. Step 3) The coating method is slot coating, and the wet film thickness is 10-30 μm; Step 3) The curing reaction is carried out in an oven and cured for 20 to 40 minutes under an air atmosphere, a pressure of 0.08 to 0.12 MPa, and a temperature of 70 to 90 °C. Step 4) The post-treatment of the cured material is to perform calendering. During the calendering process, the temperature of the calendering roller is controlled at 50-70 ℃ and the linear pressure is 30-60 N / mm. After calendering, the material is dried in an oven at 70-90 ℃ for 10-30 min.

2. The method for preparing a breathable insulating membrane according to claim 1, characterized in that, Step 2) The electrospinning is carried out at a temperature of 20-30 ℃ and a relative humidity of 40-60%, with a distance of 15-18 cm from the tip of the spinneret to the substrate layer and a solution propulsion rate of 1.0-1.2 mL / h.

3. A method for preparing a breathable insulating membrane according to claim 1 or 2, characterized in that, The method is as follows: 1) Fix the substrate layer onto the electrospinning receiving device; 2) Add PVDF particles with a weight average molecular weight of 450,000 to a mixed solvent of DMAc and acetone in a mass ratio of 7:3 to make the PVDF mass concentration 13%. Stir in a 60 ℃ water bath until completely dissolved. Add nano-silica treated with KH-550 silane coupling agent at a mass of 3% of PVDF. Continue ultrasonic dispersion and mechanical stirring for 6 h to obtain a uniform spinning solution. 3) Spinning was performed in an environmental chamber at a temperature of 25 °C and a relative humidity of 50%, a spinning voltage of 20 kV, a distance of the spinneret tip to the substrate layer of 16 cm, a solution advance rate of 1.1 mL / h, and continuous spinning until a PVDF / SiO2 composite nanofiber membrane with an areal density of about 12 g / m2 was formed on the substrate; 2 of about 12 g / m2 was formed on the substrate; 4) Epoxy-modified silicone oil with an epoxy value of 0.15 mol / 100g was mixed evenly with 1.0 wt% DABCO catalyst, and the mixture was coated onto the surface of the nanofiber membrane using a slot coater, with the wet film thickness controlled at 20 μm. 5) The coated material is fed into an 80 ℃ drying tunnel and cured for 30 min. Then it is calendered by heating a calendering roller at a roller temperature of 60 ℃ and a linear pressure of 45 N / mm. Finally, it is dried in an 80 ℃ oven for 20 min and then wound up to obtain a highly breathable unidirectional insulating material.

4. A breathable insulating membrane prepared by any one of claims 1 to 3.

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