Fluorine-free high-temperature-resistant waterproof moisture-permeable film as well as preparation method and application thereof

Abstract

The invention discloses a fluoride-free high-temperature-resistant waterproof moisture-permeable membrane and a preparation method and application thereof.The preparation method comprises the steps that S1, polyamide acid and polyurethane are blended and dissolved in an organic solvent, and a nanofiber membrane substrate is formed through electrostatic spinning; carrying out high-temperature calcination treatment on the nanofiber membrane substrate under the protection of inert gas, so that polyamide acid is converted into polyimide, and a composite fiber membrane is formed; carrying out electrostatic spinning on a mixed solution of polyurethane and polysiloxane on the surface of the composite fiber membrane to form a middle layer with a microporous structure; depositing polysiloxane microspheres on the surface of the middle layer through electrostatic spraying to form a star-like topology-imitated hydrophobic surface layer; carrying out hot-pressing treatment on the composite membrane, so that interlayer interfaces are welded, the pore distribution is regulated and controlled, and the interlayer bonding strength is enhanced; dipping the composite film in a fluorine-free water repellent agent containing siloxane, and forming a hydrophobic coating on the surface through a padding process to obtain the fluorine-free high-temperature-resistant waterproof moisture-permeable film. The fabric has excellent water resistance, moisture permeability and environmental stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electronic device protection materials, and particularly relates to a fluorine-free high-temperature-resistant waterproof and moisture-permeable film and a preparation method and application thereof. BACKGROUND

[0002] In the field of electronic technology, with the continuous progress of technology and the widening of application scenarios, electronic components, especially flexible components, are developing towards smaller size, more functionality and higher integration. This trend has led to a significant increase in power density and heat output per unit volume of electronic components, posing unprecedented challenges to the sealing reliability of electronic components.

[0003] In particular, under harsh conditions such as humidity and high temperature, the performance degradation and shortened life of electronic components are increasingly prominent, thereby imposing more stringent requirements on protective materials. As a material with a unique microporous structure, waterproof and moisture-permeable film plays an important role in the protection of electronic components. However, traditional waterproof and moisture-permeable films, such as fluoropolymer waterproof films (such as polytetrafluoroethylene PTFE film), while to some extent can meet the needs of waterproofing and moisture-proofing, have significant environmental and health hazards. Fluoride poses a threat to human health due to its potential carcinogenic risk, especially in some sensitive application fields such as food packaging and medical devices, its use is strictly limited. In addition, fluorine-based waterproof and moisture-permeable films also have the problem of being difficult to bond, which requires complex surface modification treatment to effectively combine with other materials. At the same time, such film materials are prone to absorb dust, salt, oil and other contaminants in sweat during use, resulting in a decrease in waterproof performance, making it difficult to meet the needs of long-term stable operation of electronic components.

[0004] On the other hand, fluorine-free waterproof and moisture-permeable films, while avoiding the use of fluoride, have poor water washing resistance, and the waterproof effect is easily weakened after multiple washes; are prone to uneven waterproof effect and color change problems, affecting the appearance and performance of electronic components; have poor versatility, require high cleanliness of the processed fabric, and are difficult to apply to different types of electronic components.

[0005] Therefore, it is necessary to improve the fluorine-free high-temperature-resistant waterproof and moisture-permeable film and the preparation method and application thereof in the prior art to solve the above problems. SUMMARY

[0006] The present application overcomes the shortcomings of the prior art and provides a fluorine-free high-temperature-resistant waterproof and moisture-permeable film and a preparation method and application thereof, aiming to solve the problems of sudden decrease in waterproofness caused by easy cracking of flexible electronic devices, difficulty in optimizing waterproof and moisture-permeable performance, insufficient interlayer interface bonding strength, large environmental hazard of fluorine-containing hydrophobic agent, and leakage risk caused by dispersed pore size distribution of electrospun film.

[0007] To achieve the above object, the technical scheme adopted by the present application is as follows: a preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, comprising the following steps:

[0008] S1, polyamide acid and polyurethane are blended and dissolved in an organic solvent to form a nanofiber membrane base through electrospinning;

[0009] S2, the nanofiber membrane base is subjected to high-temperature calcination treatment under inert gas protection to convert the polyamide acid into polyimide and form a composite fiber membrane;

[0010] S3, a mixed solution of polyurethane and polysiloxane is electrospun on the surface of the composite fiber membrane to form an intermediate layer with a microporous structure;

[0011] S4, polysiloxane microspheres are deposited on the surface of the intermediate layer through electrostatic spraying to form a star-shaped topological hydrophobic surface layer, and a three-layer structure forms a composite membrane;

[0012] S5, the composite membrane is subjected to heat pressing treatment to fuse the interfaces between the layers, regulate the pore distribution, and enhance the interlayer bonding strength;

[0013] S6, the composite membrane is immersed in a fluorine-free hydrophobic agent containing siloxane, and a hydrophobic coating is formed on the surface through the padding process to obtain a fluorine-free high-temperature-resistant waterproof and moisture-permeable film.

[0014] In a preferred embodiment of the present application, in step S1, diamine-p-phenylenediamine and dianhydride-4,4'-biphenyl ether dianhydride are dissolved in a dimethylformamide solution according to a molar ratio of 1:0.97-1.03, stirred for 10-18 hours under an ice water bath at-10-0℃, and a polyamide acid solution with a total concentration of 15% is obtained; the molecular weight of the diamine is 60-500, and the molecular weight of the dianhydride is 180-500.

[0015] In a preferred embodiment of the present application, in step S1, the mass ratio of polyamide acid and polyurethane is 2.0-2.3:1, and after being mixed with an organic solvent, a mixed base solution with a concentration of 13-18wt% is formed; the polyurethane is thermoplastic polyurethane, the hard segment content is 30-40%, the soft segment is polyether type or polyester type, and the molecular weight range is 50,000-100,000; the electrospinning parameters include: needle diameter 0.6-0.9mm, voltage 15-22kV, pushing rate 0.3-0.6mL / h, ambient temperature 20-25℃, and relative humidity 30-40%.

[0016] In a preferred embodiment of the present application, in step S2, the high-temperature calcination treatment includes three stages:

[0017] The first stage is to heat up to 80-100℃ at a rate of 2-5℃ / min and keep the temperature for 1-2h to remove the solvent;

[0018] The second stage is raised to 280-320 DEG C at 3-8 DEG C / min, and the imidization is completed in 2-4 h;

[0019] The third stage is cooled to room temperature;

[0020] The inert gas flow rate is 100-200 mL / min, and the pore size of the composite fiber membrane after calcination is 0.5-1.5 mu m.

[0021] In a preferred embodiment of the present application, the mass ratio of the polyurethane and the polysiloxane is 2:1-3:1, and the concentration of the intermediate layer solution is 12-18 wt %;

[0022] The polysiloxane is a hydroxyl-terminated polydimethylsiloxane with a molecular weight of 5000-10000;

[0023] The electrospinning parameters include: a needle diameter of 0.8-1.2 mm, a voltage of 15-20 kV, a pushing rate of 0.4-0.8 mL / h, and an ambient humidity of 30-40 %.

[0024] In a preferred embodiment of the present application, in step S4, the polysiloxane microspheres are vinyl-terminated polydimethylsiloxane containing 1-3 wt % platinum catalyst; the electrostatic spraying parameters include: a needle diameter of 0.5-0.8 mm, a voltage of 12-18 kV, a pushing rate of 0.2-0.5 mL / h; the microspheres are loaded with 50-100 nm SiO2 nanoparticles on the surface, and the solution contains 2-5 wt % nano-SiO2 suspension.

[0025] In a preferred embodiment of the present application, in step S5, the hot-pressing temperature is 100-120 DEG C, the pressure is 0.5-1.0 MPa, and the pressure holding time is 30-90 min; the gradient cooling rate is 2-5 DEG C / min, and the average pore size of the composite membrane after hot-pressing is 0.3-0.8 mu m.

[0026] In a preferred embodiment of the present application, the fluorine-free hydrophobic agent contains 70-80 wt % polymethylhydrogen siloxane, 20-30 wt % amino silicone oil, and 0.05-0.1 wt % chloroplatinic acid, and the solvent is toluene; the padding process includes: a padding rate of 70-80 %, pre-drying at 80-100 DEG C for 1-2 min, and curing at 120-150 DEG C for 10-20 min.

[0027] In a preferred embodiment of the present application, in the intermediate layer formed in step S3, the soft segment of the polyurethane is polytetrahydrofuran ether, and the hard segment content is 35-45 %; the intermediate layer fiber diameter is 300-800 nm, the micropore size is 0.5-2 mu m, and the initial contact angle is 130-140 DEG.

[0028] The application provides a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, comprising a substrate layer formed of a polyimide-polyurethane interpenetrating network, an intermediate layer containing a polyurethane-polydimethylsiloxane microporous structure, and a star-like topological hydrophobic surface layer; the star-like topological hydrophobic surface layer has a multi-level rough structure reinforced by SiO2 nanoparticles.

[0029] The application solves the defects in the background art and has the following beneficial effects:

[0030] (1) The application provides a fluorine-free high-temperature-resistant waterproof and moisture-permeable film and a preparation method thereof. The film is prepared by synergistic design of a polyamide acid / polyurethane (PAA / PU) blended electrospun substrate, a PU / polydimethylsiloxane (PDMS) microporous intermediate layer and a star-like topological hydrophobic surface layer, combined with gradient high-temperature imidization, interlayer hot pressing interlocking and fluorine-free hydrophobic modification process. The substrate layer is converted into polyimide (PI) at high temperature and forms an interpenetrating network with PU, giving temperature resistance and high flexibility. The intermediate layer builds through holes through PU / PDMS hydrogen bond microphase separation, balancing the moisture permeability and liquid water breakthrough pressure. The surface layer forms a multi-level rough structure by loading SiO2 nanoparticles on electrostatically sprayed PDMS microspheres, combined with polydimethylhydrogen siloxane padding and curing, realizing superhydrophobicity and fluorine-free environmental protection. The film has excellent waterproofness, moisture permeability and environmental stability, solving the problems of brittleness and cracking of traditional PI films, dispersion of pore size of electrospun films and high-temperature failure of fluorine coatings.

[0031] (2) The application forms an intermediate layer by mixing a polyurethane and a polydimethylsiloxane solution through electrospinning, and a star-like topological hydrophobic surface layer by depositing polydimethylsiloxane microspheres through electrostatic spraying, and simultaneously performs hot pressing treatment on the composite film. The intermediate layer formed by electrospinning has a microporous structure, and the through holes of the micropores allow water vapor to diffuse quickly and the pore size is smaller than the critical value of liquid water capillary penetration, which ensures good moisture permeability while effectively preventing liquid water from penetrating. The star-like topological hydrophobic surface layer further enhances the hydrophobic effect, and the hot pressing treatment makes the interlayer interface welded, regulates the pore distribution and enhances the interlayer bonding strength. Compared with the prior art, the application realizes more excellent waterproof and moisture-permeable balance, avoids the decline of waterproof performance caused by film hole defects, and is more suitable for the protection of electronic components in a humid environment.

[0032] (3) The application dips the composite film in a fluorine-free hydrophobic agent containing siloxane and forms a hydrophobic coating layer by padding process. The use of fluorine-free hydrophobic agent avoids the potential harm of fluorine-containing substances to the environment, and through specific hydrophobic agent formula and padding process parameter control, the hydrophobic coating layer can fully penetrate into the submicron pores and form a dense gradient coating, which improves the hydrophobicity without affecting the moisture permeability, further enhances the comprehensive performance of the protective film in waterproof and moisture permeability, and realizes the balance of environmental protection and high performance compared with the prior art.

[0033] (4) The polyamide acid is blended and dissolved with the polyurethane in a specific organic solvent, and a nanofiber membrane substrate is formed by electrospinning, and then the polyamide acid is converted into polyimide by high-temperature calcination. On the one hand, the polyamide acid as a precursor of polyimide, after high-temperature calcination, the polyimide formed has excellent high-temperature resistance, and finally a PI / PU interpenetrating network is formed, which can meet the demand of electronic components working normally in high-temperature environment; on the other hand, the introduction of polyurethane makes up for the defects of high brittleness and insufficient flexibility of pure polyimide, and the blending of the two makes the substrate layer have high-temperature resistance and flexibility, and improves the comprehensive performance. Compared with the prior art, the stability and reliability of the protective film in the high-temperature running and repeated bending of electronic components are further ensured.

[0034] (5) The present application forms a star-shaped topological structure (microsphere diameter 1-5 μm, branch fiber 300-800 nm) by electrostatic spray deposition of Vi-PDMS microspheres, and constructs a multi-level rough surface in cooperation with SiO2 nanoparticle loading (addition of 2-5 wt %), which improves the temperature resistance compared with traditional fluorine-based coatings. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0036] Figure 1 The SEM image of the polyimide nanofiber of the preferred embodiment of the present application;

[0037] Figure 2 The SEM image of the middle layer after treatment of the preferred embodiment of the present application;

[0038] Figure 3 The flowchart of the preferred embodiment of the present application. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described clearly and completely in the embodiments of the present application combined with the drawings. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0040] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in this description, and that the scope of the present application is not limited to the details in this description.

[0041] In the description of the present application, it needs to be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the scope of protection of the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined with "first", "second" and the like can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0042] In the description of the present application, it needs to be understood that, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integral connection; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or it can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0043] SUMMARY

[0044] In terms of special requirements for electronic component protection, electronic components have very strict performance requirements for protective films. The protective film not only needs to have excellent waterproof and moisture permeability to ensure the normal operation of the electronic component in a humid environment, but also needs to have good high temperature resistance to withstand the heat generated by the electronic component during operation at high temperature. In addition, the protective film also needs to have good adhesion with the surface of the electronic component to ensure the integrity and reliability of the seal.

[0045] Flexible electronic devices need to withstand repeated bending, while traditional PI films have high brittleness and are prone to cracking after bending, resulting in a sharp drop in waterproofness. The pressure fluctuation inside the sealed cavity of the electronic component is easy to make liquid water penetrate through the larger film holes, while the existing electrospun membrane has a discrete pore size distribution, and the local large pore area becomes a weak point of waterproofness.

[0046] The present application adopts a three-layer structure of moisture permeable film to solve the above problems.

[0047] The exemplary method comprises the following steps:

[0048] As shown in the accompanying drawings, Figure 3 A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film comprises the following steps:

[0049] S1. Polyamide acid and polyurethane are blended and dissolved in an organic solvent to form a nanofiber film substrate through electrospinning;

[0050] S2. The nanofiber film substrate is subjected to high-temperature calcination treatment under inert gas protection to convert the polyamide acid into polyimide, thereby forming a composite fiber film;

[0051] S3. A mixed solution of polyurethane and polysiloxane is electrospun on the surface of the composite fiber film to form an intermediate layer with a microporous structure;

[0052] S4. Polysiloxane microspheres are deposited on the surface of the intermediate layer through electrostatic spraying to form a star-shaped topological hydrophobic surface layer, and a three-layer structure is formed to form a composite film;

[0053] S5. The composite film is subjected to heat pressing treatment to fuse the interfaces between the layers, regulate the pore distribution, and enhance the interlayer bonding strength;

[0054] S6. The composite film is immersed in a fluorine-free hydrophobic agent containing polysiloxane, and a hydrophobic coating is formed on the surface through the padding process to obtain a fluorine-free high-temperature-resistant waterproof and moisture-permeable film;

[0055] Polyamide acid (PAA) is the precursor of polyimide (PI) and will be imidized to form PI after high-temperature calcination, which has excellent high-temperature resistance; however, pure PI material has high brittleness and insufficient flexibility. Polyurethane (PU) has good flexibility and elasticity, but poor high-temperature resistance; the mixture of the two is to maintain the high-temperature resistance of PI while introducing the flexibility of PU to improve the comprehensive performance of the substrate layer.

[0056] In step S1, diamine, i.e., p-phenylenediamine (PPDA), and dianhydride, i.e., 4,4'-diphenyl ether dianhydride (ODPA), are dissolved in a dimethylformamide (DMF) solution according to a molar ratio of 1:0.97-1.03, stirred for 10-18 hours under an ice water bath at -10-0℃, and a PAA polyamide acid solution with a total concentration of 15% is obtained; the molecular weight of the diamine is 60-500, and the molecular weight of the dianhydride is 180-500, so as to ensure controllable polymerization degree and avoid gelation.

[0057] The mass ratio of polyamic acid and polyurethane is 2.0-2.3:1, and after being mixed with an organic solvent, a mixed base solution with a concentration of 13-18wt% is formed; the polyurethane is selected to be a thermoplastic polyurethane, the hard segment content is 30-40%, the soft segment is polyether type or polyester type, and the molecular weight range is 50,000-100,000, so as to balance flexibility and solvent resistance;

[0058] The organic solvent is one or more mixtures of dimethylacetamide (DMAC), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), acetone, cyclohexanone or N-methyl pyrrolidone (NMP) solution; specifically, the mass ratio of DMF and THF is 1:0.2-0.4, the high boiling point of DMF delays the solvent volatilization on the surface of the fiber, avoiding the premature solidification of the surface layer; the rapid volatilization of THF promotes the rapid phase separation inside the fiber, forming a skin-core porous structure, and the skin-core structure combines the inter-fiber pores, the bottom layer has a pore size distribution of 1-3μm, providing a fast channel for water vapor diffusion;

[0059] The mixed base solution is added to a syringe needle and clamped on a push column table, and the power is connected at the needle, to prepare a nanofiber membrane base; the needle diameter is 0.6-0.9mm, the receiving distance is 15-20cm, the rotation speed is 50-100rpm, the uniform rotation, the electrospinning parameters are voltage 15-22kV, push rate 0.3-0.6mL / h, ambient temperature 20-25℃, relative humidity 30-40%, to avoid high humidity leading to fiber adhesion;

[0060] The obtained fiber diameter is 200-500nm, the fibers are connected by the PU segment to form a physical entanglement network, the carboxylic acid group (-COOH) of PAA and the urethane group (-NHCOO-) of PU produce hydrogen bonding, inhibiting phase separation; during electrospinning, PU segments are inserted into the PAA fiber interior, PI provides a rigid skeleton, giving the base high temperature resistance, PU fills the pores and enhances flexibility, increasing the elongation at break; after high temperature imidization, a PI / PU interpenetrating network structure (IPN) is formed, enhancing the interface bonding.

[0061] As Figure 1The SEM image of the polyimide nanofiber shows that in step S2, the nanofiber membrane substrate is placed in a tube furnace, nitrogen (N2) or argon (Ar) is introduced, the gas flow rate is 100-200 mL / min, oxygen is continuously excluded to prevent PU degradation or PI carbonization caused by high temperature oxidation; temperature gradient control is performed for high temperature calcination treatment, the first stage is used for solvent removal, the temperature is raised to 80-100°C at a rate of 2-5°C / min, and the residual solvent is completely removed after 1-2h of heat preservation; the second stage is used for imidization reaction, the temperature is raised to 280-320°C at a rate of 3-8°C / min, and the PI is formed by making the PAA molecules dehydrate and cyclize; the third stage is used for cooling and shaping, and the furnace is cooled to room temperature to avoid stress cracking of the membrane layer caused by rapid cooling; high temperature makes the fiber shrink and densify, and the average pore size is reduced from 1-3pm in S1 to 0.5-1.5pm;

[0062] wherein the carboxylic acid group (-COOH) of PAA and the amino group (-NH2) are dehydrated and condensed at high temperature to form an imide ring (-CO-NR-CO-), forming a rigid PI segment; select a thermally stable PU that only undergoes physical softening rather than chemical decomposition in an inert atmosphere, the PU softens and penetrates into the PI fiber gap at high temperature, and forms a mechanical interlocking structure after cooling, forming an interpenetrating network (IPN) with PI.

[0063] Step S3 is to electrospin a mixed solution of polyurethane (PU) and polysiloxane (PDMS) on the surface of the composite fiber membrane to form an intermediate layer; the function of the intermediate layer is to balance the waterproof and moisture permeable properties, and to provide support for the subsequent hydrophobic surface layer.

[0064] As shown in Figure 2 In step S3, the polyurethane is a thermoplastic polyurethane with a hard segment content of 35-45%, and the soft segment is polytetrahydrofuran ether (PTMG) with a molecular weight of 2000-3000, which provides flexibility and elasticity; the polysiloxane (PDMS) is selected as a hydroxyl-terminated polydimethylsiloxane with a molecular weight of 5000-10000, which has strong hydrophobicity and good compatibility with PU; PU and PDMS are mixed in a mass ratio of 2:1-3:1, and after mixing with an organic solvent, an intermediate layer solution with a total concentration of 12-18wt% is formed; too high PDMS content will result in too low viscosity of the spinning solution, making it difficult to form fibers; PU provides mechanical support, and PDMS imparts hydrophobicity, avoiding the loss of moisture permeability caused by additional coating;

[0065] The intermediate layer solution is electrospun, with a diameter of 0.8-1.2 mm, a receiving distance of 12-18 cm, a rotation speed of 50-100 rpm, and uniform rotation; the electrospinning parameters are a voltage of 15-20 kV, a push rate of 0.4-0.8 mL / h, an ambient temperature of 20-25 °C, and a relative humidity of 30-40%, to avoid excessive humidity causing premature crosslinking of PDMS; the intermediate layer fiber diameter is 300-800 nm; the hydrophobic segment of PDMS migrates to the fiber surface during solvent evaporation, forming a surface-rich silicon region, and the PDMS surface enrichment makes the initial contact angle of the intermediate layer reach 130-140°; the hard segment of PU and PDMS form a microphase separation structure through hydrogen bonding, producing through holes of 0.5-2 μm, which allow water vapor to diffuse quickly, while the pore size is smaller than the critical value of liquid water capillary penetration; the intermediate layer solution (PU) partially dissolves the surface of the base layer (PI / PU), forming chemical anchoring points and molecular-level interpenetration, and improving the interfacial bonding strength;

[0066] In step S4, the polysiloxane is vinyl-terminated polydimethylsiloxane (Vi-PDMS) with a molecular weight of 8000-12000, and 1-3 wt% of platinum catalyst is mixed to achieve in-situ crosslinking and curing; the solvent is a 3-4:1 mixture of toluene and isopropanol, toluene dissolves PDMS, and isopropanol adjusts the surface tension to ensure uniform microsphere formation; the mass fraction of the microsphere solution is 5-8%, and the solution viscosity is 200-500 mPa·s (25 °C);

[0067] The electrostatic spraying needle has a diameter of 0.5-0.8 mm, a receiving distance of 10-15 cm, a rotation speed of 50-100 rpm, and uniform rotation to ensure uniform deposition of the microspheres; the electrostatic spraying parameters are a voltage of 12-18 kV, a push rate of 0.2-

[0068] 0.5 mL / h, a temperature of 22-27 °C, and a relative humidity of 20-30%, to avoid excessive humidity causing microsphere adhesion.

[0069] The spray droplets stretch in the electric field and evaporate the solvent, forming PDMS microspheres with a diameter of 1-5 μm, which are combined with the intermediate layer PU / PDMS fibers through physical adsorption and chemical bonding; the Vi-PDMS reacts with the hydroxyl groups in the intermediate layer to form a star-shaped topological structure with the microspheres at the center and the fibers as radial branches;

[0070] The three-layer structure of the nanofiber membrane base, the intermediate layer, and the star-shaped topological hydrophobic surface layer forms a composite membrane;

[0071] Further, the microsphere surface is further loaded with 50-100 nm SiO2 nanoparticles by adding 2-5 wt% nano-SiO2 suspension in the spraying solution; the sub-micron channels of 0.1-0.3 μm are reserved between the microspheres, which allows efficient diffusion of water vapor, while the microsphere structure blocks the liquid water penetration path, and the star-shaped structure combined with nano-SiO2 makes the contact angle increase to 155-160° and the rolling angle <5°, realizing super-hydrophobicity through multi-level roughness.

[0072] In step S5, the hot pressing temperature is 100-120℃, which is lower than the softening point of PU but higher than its glass transition temperature, and the applied pressure is 0.5-1.0 MPa, and the pressure holding time is 30-90 min, to ensure sufficient melting and bonding between the layers; after hot pressing, the temperature is lowered to room temperature at a gradient of 2-5℃ / min to avoid stress cracking between the layers caused by sudden cooling.

[0073] At the hot pressing temperature, the PU soft segment (PTMG) undergoes plastic flow and penetrates into the interfacial pores between the PI / PU base layer and the intermediate layer (PU / PDMS), forming a physical interpenetrating anchor; the surface layer Vi-PDMS is further crosslinked under platinum catalysis to form a Si-O-Si covalent network with the intermediate layer PDMS, improving the bonding strength of the surface layer; hot pressing melts the contact points between the fibers, reducing the average pore size to 0.3-0.8 μm, but preserving the sub-micron channels to maintain the moisture permeability.

[0074] In step S6, 70-80 wt% polymethylhydrogen siloxane (PMHS), 20-30 wt% amino silicone oil (ASO), and 0.05-0.1 wt% chloroplatinic acid are dissolved in toluene to prepare a hydrophobic agent with a concentration of 3-5 wt% and a viscosity of 50-150 mPa·s (25℃);

[0075] The composite membrane is immersed in the hydrophobic agent for 10-30 seconds at an immersion temperature of 25-40℃ to ensure that the solution penetrates into the sub-micron pores; a two-roller rolling machine is used, and the rolling rate is controlled at 70-80% to avoid excessive liquid removal leading to uneven coating; the immersion and rolling are repeated for 2-3 times, and after each rolling, the membrane is pre-dried at 80-100℃ for 1-2 min to form a dense gradient coating; finally, the membrane is cured in a hot air oven at 120-150℃ for 10-20 min to promote the crosslinking of the siloxane and grafting on the fiber surface, obtaining a fluorine-free high-temperature-resistant waterproof and moisture-permeable membrane.

[0076] Exemplary device:

[0077] A fluorine-free high-temperature-resistant waterproof and moisture-permeable membrane, comprising: a base layer composed of a polyimide-polyurethane interpenetrating network, an intermediate layer containing a polyurethane-poly-siloxane micro-porous structure, and a star-shaped topological hydrophobic surface layer; the star-shaped topological hydrophobic surface layer has a multi-level rough structure enhanced by SiO2 nanoparticles.

[0078] Example one:

[0079] A method for preparing a fluorine-free high-temperature resistant waterproof and moisture-permeable film, comprising:

[0080] A diamine, p-phenylenediamine, and a dianhydride, 4,4'-biphenyl ether dianhydride, are dissolved in a mixed solvent at a molar ratio of 1:1, stirred for 12 hours under an ice water bath at 0°C, and a PAA polyamic acid solution with a total concentration of 15% is obtained. The mass ratio of the polyamic acid and the polyurethane is 2.1:1, the hard segment content of the polyurethane is 30-40%, the soft segment is polyether type or polyester type, the molecular weight range is 80,000, and after being mixed with an organic solvent, a mixed base solution with a concentration of 15wt% is formed, and the organic solvent is DMF and THF at a ratio of 1:0.3. The mixed base solution is added to a syringe and clamped on a push column table, the needle diameter is 0.7mm, the receiving distance is 18cm, the rotation speed is 75rpm, the electrospinning parameters are a voltage of 18kV and a pushing rate of 0.4mL / h, the environmental temperature is 20°C, and the relative humidity is 35%. A nanofiber film base is formed by electrospinning, and the obtained fiber diameter is 300-400nm.

[0081] The nanofiber film base is placed in a tube furnace, nitrogen is introduced, and the gas flow rate is 150mL / min. In the first stage, the temperature is raised to 90°C at a rate of 3°C / min, and the temperature is kept constant for 1.5h; in the second stage, the temperature is raised to 300°C at a rate of 5°C / min, and the temperature is kept constant for 3h; finally, the furnace is cooled to room temperature. The polyamic acid is converted into polyimide, and a composite fiber film is formed, and the average pore size is reduced to 0.8-1.2μm.

[0082] The polyurethane is a thermoplastic polyurethane (hard segment content 40%, soft segment polytetrahydrofuran ether, molecular weight 2500), and the polysiloxane is a hydroxyl-terminated polydimethylsiloxane (molecular weight 7500). The PU and PDMS are mixed at a mass ratio of 2.5:1, and after being mixed with the above-mentioned mixed solvent, an intermediate layer solution with a total concentration of 15wt% is formed. The intermediate layer solution is electrospun, the needle diameter is 1.0mm, the receiving distance is 15cm, the rotation speed is 75rpm, the electrospinning parameters are a voltage of 17kV and a pushing rate of 0.6mL / h, the environmental temperature is 22°C, and the relative humidity is 35%. An intermediate layer is formed, the intermediate layer fiber diameter is 500-700nm, the contact angle reaches 135°, and the through-hole size is 1-1.5μm.

[0083] The polysiloxane adopts vinyl-terminated polydimethylsiloxane (molecular weight 10000), mixed with 2 wt% platinum catalyst, the solvent is 3.5:1 toluene and isopropyl alcohol mixed solvent, the mass fraction of the microsphere solution is 6%, and the solution viscosity is 300 mPa·s (25℃). The electrostatic spraying needle diameter is 0.6 mm, the receiving distance is 12 cm, the rotating speed is 75 rpm, the electrostatic spraying parameters are voltage 15 kV, propelling rate 0.3 mL / h, temperature 25℃, and relative humidity 25%. PDMS microspheres with a diameter of 2-4 μm are formed, the submicron channels between the microspheres are retained by 0.15-0.25 μm, the contact angle is increased to 157°, and the rolling angle is less than 3°.

[0084] The hot-pressing temperature is 110℃, the applied pressure is 0.8 MPa, the pressure maintaining time is 60 min, and the temperature is decreased to room temperature at a gradient of 3℃ / min. The layers are fully fused and combined, and the average pore size is reduced to 0.5-0.6 μm.

[0085] 75 wt% polymethylhydrosiloxane, 24 wt% amino silicone oil and 0.05 wt% chloroplatinic acid are dissolved in toluene to prepare a hydrophobic agent with a concentration of 4 wt% and a viscosity of 80 mPa·s (25℃). The composite film is immersed in the hydrophobic agent for 20 seconds at an immersion temperature of 30℃, a two-roller rolling vehicle is used, the rolling rate is controlled at 75%, and the film is immersed and rolled twice, and after each rolling, the film is pre-dried at 90℃ for 1.5 min, and finally cured in a hot air oven at 135℃ for 15 min to obtain a fluorine-free high-temperature-resistant waterproof and moisture-permeable film.

[0086] Example Two:

[0087] A method for preparing a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of this embodiment and example one are not repeated, and the difference between this embodiment and example one is:

[0088] The mass ratio of polyamide acid and polyurethane is 2.0:1.

[0089] Example Three:

[0090] A method for preparing a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of this embodiment and example one are not repeated, and the difference between this embodiment and example one is:

[0091] The mass ratio of polyamide acid and polyurethane is 2.3:1.

[0092] Example Four:

[0093] A method for preparing a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of this embodiment and example one are not repeated, and the difference between this embodiment and example one is:

[0094] The intermediate layer PU and PDMS are mixed in a mass ratio of 2:1.

[0095] Example Five

[0096] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example two are not repeated, the difference between the present embodiment and example two is:

[0097] The intermediate layer PU and PDMS are mixed in a mass ratio of 2:1.

[0098] Example Six

[0099] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example three are not repeated, the difference between the present embodiment and example three is:

[0100] The intermediate layer PU and PDMS are mixed in a mass ratio of 2:1.

[0101] Example Seven

[0102] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example one are not repeated, the difference between the present embodiment and example one is:

[0103] The intermediate layer PU and PDMS are mixed in a mass ratio of 3:1.

[0104] Example Eight

[0105] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example two are not repeated, the difference between the present embodiment and example two is:

[0106] The intermediate layer PU and PDMS are mixed in a mass ratio of 3:1.

[0107] Example Nine

[0108] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example three are not repeated, the difference between the present embodiment and example three is:

[0109] The intermediate layer PU and PDMS are mixed in a mass ratio of 3:1.

[0110] Example Ten

[0111] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example one are not repeated, the difference between the present embodiment and example one is:

[0112] The mass fraction of the microsphere solution is 5%.

[0113] Example Eleven

[0114] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example one are not described again, the difference between the present embodiment and example one is that:

[0115] The mass fraction of the microsphere solution is 7%.

[0116] Example twelve:

[0117] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example one are not described again, the difference between the present embodiment and example one is that:

[0118] The mass fraction of the microsphere solution is 8%.

[0119] Comparative example one:

[0120] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example one are not described again, the difference between the present embodiment and example one is that:

[0121] Only PI is used as the base material.

[0122] Comparative example two:

[0123] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example one are not described again, the difference between the present embodiment and example one is that:

[0124] No intermediate layer.

[0125] Comparative example three:

[0126] A preparation method of a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, the same parts of the present embodiment and example one are not described again, the difference between the present embodiment and example one is that:

[0127] No star-shaped topological hydrophobic surface layer.

[0128] Experimental example one:

[0129] In this experimental example, examples one to nine, and comparative examples one and two are selected for experiments to verify the performance of the fluorine-free high-temperature-resistant waterproof and moisture-permeable film, and to explore the influence of the base layer (PAA / PU ratio) and the intermediate layer (PU / PDMS ratio) on the film performance, focusing on evaluating the synergistic optimization effect of flexibility, moisture permeability, and waterproofness.

[0130] Hydrostatic pressure test: fix the film sample on the test device, press at a rate of 6kPa / min, and record the pressure value when liquid water penetrates;

[0131] Moisture permeability test: cover the film on the moisture permeability cup, and place it in a 38℃, 90%RH environment, weigh and calculate the moisture permeability after 24h;

[0132] Elongation at break: The film was cut into dumbbell-shaped specimens and stretched to break at a rate of 50 mm / min, and the elongation was calculated.

[0133] Table 1 Performance comparison of experimental example one

[0134]

[0135] When the PAA / PU mass ratio is 2.1:1, the hydrostatic pressure, moisture permeability and elongation at break reach the best synergistic effect. The increase of PAA proportion will enhance the compactness of PI rigid skeleton, and the hydrostatic pressure will slightly rise, but the low proportion of PU will sacrifice flexibility; on the contrary, the high proportion of PU will lead to the decrease of substrate rigidity, and the hydrostatic pressure will decrease to 123.7 kPa; when the PU / PDMS mass ratio is 2.5:1, the balance of hydrostatic pressure and moisture permeability is the best.

[0136] PU / PDMS = 2.5:1: The hydrophobic segment of PDMS is enriched on the surface of the fiber, and PU provides microporous support, which not only blocks the penetration of liquid water, but also allows the diffusion of water vapor; high proportion of PDMS: the low viscosity of PDMS leads to the difficulty of fiber forming, and the through-hole is enlarged to the hydrostatic pressure is decreased to the moisture permeability is slightly increased due to the increase of porosity.

[0137] Without an intermediate layer, the PDMS hydrophobic barrier and the PU microporous regulation are lacking, and the hydrostatic pressure drops sharply, but the moisture permeability increases due to the increase of the pore structure of the substrate, which verifies the key role of the intermediate layer in the balance of waterproof and moisture permeability; from the elongation at break, the introduction of PU inhibits the brittleness of PI through physical entanglement and hydrogen bonding. The elongation at break of pure PI substrate is only 180.3% due to the lack of PU toughening, and the PU proportion of Example 1 realizes the optimal balance of rigidity and flexibility.

[0138] Experimental example two:

[0139] In this experimental example, Examples 1, 10 to 12, and Comparative Example 3 are selected for experiments to verify the performance of the fluorine-free high-temperature resistant waterproof and moisture permeable film, and to evaluate the influence of the concentration of the hydrophobic surface layer microspheres on the superhydrophobic performance and the moisture permeability;

[0140] Rolling angle test: 10 μL of water droplets is placed on the surface of the film, and the platform is slowly inclined until the water droplets roll, and the inclination angle is recorded.

[0141] Table 2 Performance comparison of experimental example two

[0142]

[0143] When the concentration of the microsphere solution is 6%, the number and distribution of the PDMS microspheres are moderate, the sub-micron channels between the microspheres are sufficient for water vapor diffusion while the super-hydrophobic performance is ensured. When the concentration of the microsphere solution is low, the water vapor permeability is improved but the water repellency is slightly weakened; too many microspheres may block some sub-micron channels, resulting in a decrease in the water vapor permeability.

[0144] The above is based on the ideal embodiment of the present application, and through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims

1. A method for preparing a fluorine-free high-temperature-resistant waterproof and moisture-permeable film, characterized by, The method comprises the steps of: S1, polyamide acid and polyurethane are blended and dissolved in an organic solvent to form a nanofiber membrane base by electrospinning; S2, the nanofiber membrane base is treated by high-temperature calcination under inert gas protection, polyamide acid is converted into polyimide, and a composite fiber membrane is formed; S3, a mixed solution of polyurethane and polysiloxane is electrospun on the surface of the composite fiber membrane to form an intermediate layer with a microporous structure; S4, polysiloxane microspheres are deposited on the surface of the intermediate layer by electrostatic spraying to form a star-shaped topological hydrophobic surface layer, and a three-layer structure is formed to form a composite membrane; S5, the composite membrane is subjected to heat pressing treatment to fuse the interfaces between the layers, regulate the pore distribution, and enhance the interlayer bonding strength; S6, the composite membrane is immersed in a fluorine-free hydrophobic agent containing siloxane, and a hydrophobic coating is formed on the surface by padding process to obtain a fluorine-free high-temperature resistant waterproof and moisture permeable membrane.

2. The method for preparing a fluorine-free high-temperature-resistant waterproof and moisture-permeable film according to claim 1, characterized in that: In step S1, diamine-p-phenylenediamine and dianhydride-4,4'-biphenyl ether dianhydride are dissolved in dimethylformamide solution according to a molar ratio of 1:0.97-1.03, stirred in an ice water bath at-10-0℃ for 10-18 hours, and a polyamide acid solution with a total concentration of 15% is obtained; the molecular weight of the diamine is 60-500, and the molecular weight of the dianhydride is 180-500.

3. The method for preparing a fluorine-free high-temperature-resistant waterproof and moisture-permeable film according to claim 1, characterized in that: In step S1, the mass ratio of polyamide acid and polyurethane is 2.0-2.3:1, and after being mixed with an organic solvent, a mixed base solution with a concentration of 13-18wt% is formed; the polyurethane is thermoplastic polyurethane, the hard segment content is 30-40%, the soft segment is polyether type or polyester type, and the molecular weight range is 50,000-100,000; the electrospinning parameters include: needle diameter 0.6-0.9mm, voltage 15-22kV, pushing rate 0.3-0.6mL / h, ambient temperature 20-25℃, and relative humidity 30-40%.

4. The method for preparing a fluorine-free high-temperature-resistant waterproof and moisture-permeable film according to claim 1, characterized in that: In step S2, the high-temperature calcination treatment includes three stages: The first stage is to remove the solvent by heating at 2-5℃ / min to 80-100℃ and keeping for 1-2h; The second stage is to complete the imidization by heating at 3-8℃ / min to 280-320℃ and keeping for 2-4h; The third stage is to cool to room temperature with the furnace; The inert gas flow rate is 100-200mL / min, and the pore size of the composite fiber membrane after calcination is 0.5-1.5μm.

5. The method for preparing a fluorine-free high-temperature-resistant waterproof and moisture-permeable film according to claim 1, characterized in that: The mass ratio of the polyurethane and the polysiloxane is 2:1-3:1, and the concentration of the intermediate layer solution is 12-18wt%; The polysiloxane is hydroxyl-terminated polydimethylsiloxane with a molecular weight of 5000-10000; The electrospinning parameters include: needle diameter 0.8-1.2mm, voltage 15-20kV, pushing rate 0.4-0.8mL / h, and ambient humidity 30-40%.

6. The method for preparing a fluorine-free high-temperature resistant waterproof and moisture-permeable film according to claim 1, characterized in that: In step S4, the polysiloxane microspheres are vinyl-terminated polydimethylsiloxane containing 1-3wt% platinum catalyst; the electrostatic spraying parameters include: needle diameter 0.5-0.8mm, voltage 12-18kV, pushing rate 0.2-0.5mL / h; the microsphere surface is loaded with 50-100nm SiO2 nanoparticles, and the solution contains 2-5wt% nano-SiO2 suspension.

7. The method for preparing a fluorine-free high-temperature resistant waterproof and moisture-permeable film according to claim 1, characterized in that: In step S5, the hot-pressing temperature is 100-120℃, the pressure is 0.5-1.0MPa, the pressure maintaining time is 30-90min; the gradient cooling rate is 2-5℃ / min, and the average pore size of the composite membrane after hot-pressing is 0.3-0.8μm.

8. The method for preparing a fluorine-free high-temperature-resistant waterproof and moisture-permeable film according to claim 1, characterized in that: The fluorine-free hydrophobic agent comprises 70-80wt% polymethyl hydrogen siloxane, 20-30wt% amino silicon oil and 0.05-0.1wt% chloroplatinic acid, and the solvent is toluene; the padding process comprises: padding rate 70-80%, pre-drying 80-100℃ / 1-2min, curing 120-150℃ / 10-20min.

9. The method for preparing a fluorine-free, high-temperature resistant, waterproof, and breathable membrane according to claim 1, characterized in that: In the intermediate layer formed in step S3, the soft segment of the polyurethane is polytetrahydrofuran ether, and the hard segment content is 35-45%; the fiber diameter of the intermediate layer is 300-800nm, the micropore size is 0.5-2μm, and the initial contact angle is 130-140°.

10. A fluorine-free high temperature resistant waterproof and moisture permeable film, characterized in that, based on the preparation method of the fluorine-free high temperature resistant waterproof and moisture permeable film according to any one of claims 1-9, Comprise: a base layer of polyimide-polyurethane interpenetrating network, an intermediate layer containing polyurethane-polysiloxane microporous structure, and a star-like topological hydrophobic surface layer; the star-like topological hydrophobic surface layer has a multi-level rough structure reinforced by SiO2 nanoparticles.

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