Waterproof breathable TPU film and preparation method thereof

Abstract

The invention relates to the technical field of synthetic materials, in particular to a waterproof breathable TPU film and a preparation method thereof. The provided waterproof breathable TPU film is prepared from the following substances in parts by mass: 100 to 120 parts of TPU, 1 to 2 parts of sodium bicarbonate, 1.2 to 2 parts of citric acid monohydrate, 1 to 2 parts of polyvinylpyrrolidone K30, 0.3 to 0.8 part of zinc stearate, 1 to 2 parts of nano cellulose, 3 to 5 parts of cross-linking agent and 10 to 15 parts of pore-foaming agent. The preparation method comprises the following steps: S1, mixing; s2, extruding, water-cooling and pelletizing to obtain master batches; s3, preparing a thin film with the thickness of 20-30 microns; s4, preparing a dissolved film; s5, treating with a tannic acid ethanol solution, and drying to obtain the waterproof breathable TPU film. The prepared film has excellent waterproof air permeability, excellent mechanical performance and durability, and the preparation method and process are simple and efficient, suitable for large-scale production and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of synthetic materials technology, and in particular to a waterproof and breathable TPU film and its preparation method. Background Technology

[0002] Thermoplastic polyurethane (TPU) films are widely used in outdoor clothing, medical protective equipment, and electronic product packaging due to their excellent elasticity, abrasion resistance, low-temperature resistance, and processability. An ideal TPU film needs to have "waterproof and breathable" functions, that is, it can block the penetration of external liquid water while allowing water vapor molecules such as sweat to escape, maintaining wearing comfort.

[0003] In existing technologies, the main approaches to achieving air permeability in TPU films include: 1) Microporous air permeability method, which involves forming a large number of interconnected submicron-sized pores within the film, allowing water vapor to diffuse but blocking liquid water. However, the microporous structure is prone to clogging or failure due to stains and washing under long-term use or water pressure, resulting in poor waterproof durability. 2) Hydrophilic non-porous air permeability method, which relies on the adsorption-diffusion-desorption of water molecules by hydrophilic segments in the film body or added hydrophilic agents. Although this method avoids pore clogging problems, it usually has low air permeability efficiency, and hydrophilic components are prone to migration and precipitation under high temperature and high humidity environments, leading to performance degradation.

[0004] CN115537139B specifically relates to a waterproof and breathable TPU high and low temperature film and its preparation method. The waterproof and breathable TPU high and low temperature film includes, from top to bottom, a breathable and waterproof membrane layer, a TPU foam membrane layer, a mesh hot melt adhesive layer, and a release film layer. The TPU foam membrane layer has multiple spaced-apart air vents penetrating both the upper and lower surfaces of the TPU foam membrane layer. The TPU foam high and low temperature film of this invention has a simple structure, good breathability and waterproof performance, excellent mechanical properties, is easy to use, and highly practical. Its preparation method is simple to operate, easy to control, has low production costs, and stable product quality, which is conducive to large-scale industrial production. However, it has the following drawbacks: the multi-layer composite process is complex, resulting in low production efficiency and high costs; and the penetrating air vents easily lead to liquid water leakage, resulting in poor waterproof durability.

[0005] Therefore, developing a dense, non-porous, waterproof, and breathable TPU film is a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention provides a waterproof and breathable TPU film comprising the following components by weight: 100-120 parts TPU, 1-2 parts sodium bicarbonate, 1.2-2 parts citric acid monohydrate, 1-2 parts polyvinylpyrrolidone K30, 0.3-0.8 parts zinc stearate, 1-2 parts nanocellulose, 3-5 parts crosslinking agent, and 10-15 parts pore-forming agent. Zinc stearate, acting as a dispersant and heat stabilizer, decomposes first during extrusion, forming a micro-regional thermal barrier around the polyvinylpyrrolidone K30. Sodium bicarbonate then decomposes, and citric acid begins to melt and react with sodium bicarbonate; the temperature difference between their decomposition forms a time gradient. Polyvinylpyrrolidone K30 exhibits partial compatibility in molten TPU and migrates to the film surface in a shear flow field, carrying some sodium bicarbonate along with it, thus forming a spatial gradient. Sodium bicarbonate decomposes to produce carbon dioxide, and citric acid decomposes to produce carbon dioxide and release water of crystallization. The water vapor expands rapidly at high temperatures, creating a dual foaming dynamic. Polyvinylpyrrolidone K30 not only serves as a dispersion medium for the foaming agent, but its amide groups also act as bubble stabilizers during the foaming process, preventing bubble coalescence and ultimately forming a gradient pore size distribution from the surface to the inner layer. Nanocellulose forms a three-dimensional network structure in the film, significantly reinforcing and toughening it. It also refines the microphase separation structure of TPU, extending the tortuosity of the diffusion path for water vapor molecules. This improves mechanical properties, while its surface hydrophilic groups also participate in water molecule transfer, synergistically promoting moisture permeability.

[0007] Furthermore, the pore-forming agent is composed of 10-12 parts sodium chloride and 3-5 parts PEG-10000. Water-soluble pore-forming agents are a common method for creating pores, but they are difficult to form interconnected channels. This invention achieves better technical results through the synergistic effect of two pore-forming agents. Sodium chloride forms a hard template in TPU, and after dissolving, it forms the main channels. PEG-10000 is partially compatible with TPU, forming nanopores during phase separation, and after dissolving, it forms secondary channels. The two types of channels are interconnected to form a tertiary channel structure. At the same time, PEG-10000 has a dual function of plasticizing and pore-forming. During processing, PEG-10000 acts as a plasticizer, reducing the melt viscosity of TPU and promoting the uniform dispersion of sodium chloride. After cooling, PEG-10000 crystallizes and separates from the TPU phase, and after dissolving, it forms micropores.

[0008] Furthermore, the crosslinking agent is composed of 2-3 parts urea, 1-2 parts boric acid, and 0.2-0.5 parts ammonium dihydrogen phosphate. At the TPU processing temperature, urea reacts with boric acid to form a borate-urea complex. This complex can form coordination bonds and hydrogen bonds with urethane bonds, urea bonds, etc., in the TPU. Simultaneously, urea itself can form hydrogen bonds with the TPU, enhancing intermolecular forces. Ammonium dihydrogen phosphate promotes the reaction.

[0009] Furthermore, the TPU is polyether-type 58887A, manufactured by Lubrizol. Polyether-type 58887A TPU is a high-performance, low-temperature resistant thermoplastic polyurethane material with excellent elasticity and abrasion resistance. It maintains good mechanical properties at low temperatures and has excellent chemical resistance, making it suitable for film preparation.

[0010] Furthermore, the TPU film also includes 1-2 parts of a nano-sized gallic acid-zinc coordination compound, which is prepared by dissolving gallic acid and zinc chloride in ethanol at a molar ratio of 2:1, reacting for 1 hour, adding water to precipitate the precipitate, filtering, washing, and drying to obtain the nano-sized gallic acid-zinc coordination compound. In the gallic acid-zinc coordination compound, zinc ions and ortho-diphenol hydroxyl groups form dynamic coordination bonds, forming a gallic acid-zinc ion cross-linked network. When damaged by water, it self-repairs, forming a self-healing waterproof layer.

[0011] Furthermore, the sodium chloride particle size is 10~20μm.

[0012] Furthermore, the foaming process in the TPU film is carried out by a synergistic gradient foaming of sodium bicarbonate-citric acid monohydrate-polyvinylpyrrolidone K30, wherein polyvinylpyrrolidone migrates to the surface during processing, carrying some of the foaming agent, forming a gradient distribution of small pores on the surface and large pores in the inner layer.

[0013] Furthermore, the above-mentioned method for preparing the waterproof and breathable TPU film includes the following steps: S1. Add all components to a high-speed mixer in proportion, mix for 8 minutes, and then vacuum dry to obtain the mixture; S2. Add the mixture obtained in step S1 into a co-rotating twin-screw extruder, gradually increase the temperature between 170 and 220°C, stir, melt, extrude, water cool, and pelletize to obtain masterbatch. By gradually increasing the temperature, the components can melt and decompose at different stages, achieving the ideal foaming effect. S3. Add the masterbatch obtained in step S2 to a single-screw blown film machine, set the barrel temperature to 180°C and the die temperature to 180°C, and obtain a film with a thickness of 20~30μm. S4. The film obtained in step S3 is first immersed in water at 40~60℃ to dissolve sodium chloride, and then immersed in warm water at 30~50℃ to dissolve PEG-10000, to obtain the dissolved film; S5. Immerse the dissolved film obtained in step S4 into a tannic acid ethanol solution with a concentration of 1~3g / L for 0.5~2min, and dry to obtain a waterproof and breathable TPU film. After tannic acid treatment and impregnation, the tannic acid is adsorbed on the surface of the pores, providing abundant phenolic hydroxyl groups and enhancing hydrophilicity.

[0014] Further, the waterproof and breathable TPU film obtained in step S5 is treated with triethoxy-1H,1H,2H,2H-tridecylfluoro-N-octylsilane vapor for 20-40 minutes, and then dried to obtain the treated waterproof and breathable TPU film. The triethoxy-1H,1H,2H,2H-tridecylfluoro-N-octylsilane vapor treatment followed by vapor deposition forms a low surface energy monolayer on the surface, creating an asymmetric wettability gradient pore structure with an "inner hydrophilic and outer hydrophobic" orientation. Water vapor is rapidly adsorbed from the inner surface (hydrophilic), transported by capillary forces, and escapes from the outer surface (superhydrophobic), while liquid water cannot enter due to the high hydrophobicity of the outer surface and the tortuous nature of the pores.

[0015] Further, the dissolved film prepared in step S4 is transferred to a high-pressure reactor, heated to 40°C, and carbon dioxide is injected to 100 bar. This is maintained for 4 hours to allow for full carbon dioxide permeation. Then, the pressure is reduced at a programmed rate of 0.5 MPa / s to further open the pores, followed by the processing in step S5. The carbon dioxide further enhances permeability and improves product performance.

[0016] Compared with the prior art, the present invention has the following significant advantages: 1. Excellent waterproof and breathable properties: The prepared waterproof and breathable TPU film has both high hydrostatic pressure resistance (>30kPa) and high water vapor permeability (>10500g / (m²·24h)).

[0017] 2. Excellent mechanical properties and durability: The three-dimensional reinforcing network of nanocellulose and the rigid-tough combination of the TPU matrix endow the film with high strength and high toughness. The moderate cross-linking network constructed by the reactive cross-linking agent effectively locks in the functional components, and the hydrolysis-resistant stabilizer provides chemical protection. Together, they ensure that the film maintains stable performance under repeated washing, long-term use and harsh environments.

[0018] 3. Processability and environmental friendliness: All components are highly compatible and can be prepared using conventional melt processing methods (blown film). The process is simple and efficient, suitable for large-scale production. The film does not contain plasticizers or other easily migrating small molecules, making it environmentally friendly. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0020] Example 1

[0021] A waterproof and breathable TPU film comprises the following components by weight: 110 parts TPU, 2 parts sodium bicarbonate, 1.5 parts citric acid monohydrate, 1.5 parts polyvinylpyrrolidone K30, 0.5 parts zinc stearate, 1.5 parts nanocellulose, 4 parts crosslinking agent, and 14 parts pore-forming agent.

[0022] The pore-forming agent consists of 10 parts sodium chloride and 4 parts PEG-10000, wherein the sodium chloride has a particle size of 10~20μm.

[0023] The crosslinking agent is composed of 2.5 parts urea, 1.2 parts boric acid and 0.3 parts ammonium dihydrogen phosphate.

[0024] The TPU is polyether type 58887A, manufactured by Lubrizol.

[0025] The above-mentioned method for preparing a waterproof and breathable TPU film includes the following steps: S1. Add all components to a high-speed mixer in proportion, mix for 8 minutes, and then vacuum dry to obtain the mixture; S2. Add the mixture obtained in step S1 into a co-rotating twin-screw extruder, gradually increase the temperature between 170 and 220°C, stir, melt, extrude, cool with water, and pelletize to obtain masterbatch; S3. Add the masterbatch obtained in step S2 to a single-screw blown film machine, set the barrel temperature to 180°C and the die temperature to 180°C, and obtain a film with a thickness of 25μm. S4. The film obtained in step S3 is first immersed in water at 40~45℃ to dissolve sodium chloride, and then immersed in warm water at 30~35℃ to dissolve PEG-10000, to obtain the dissolved film. S5. Immerse the dissolved film obtained in step S4 into a 2 g / L tannic acid ethanol solution for 1 min, and then dry to obtain a waterproof and breathable TPU film.

[0026] Example 2

[0027] A waterproof and breathable TPU film comprises the following components by weight: 110 parts TPU, 2 parts sodium bicarbonate, 1.5 parts citric acid monohydrate, 1.5 parts polyvinylpyrrolidone K30, 0.5 parts zinc stearate, 1.5 parts nanocellulose, 4 parts crosslinking agent, 1 part nano-gallic acid-zinc coordination compound, and 14 parts pore-forming agent.

[0028] The pore-forming agent consists of 10 parts sodium chloride and 4 parts PEG-10000, wherein the sodium chloride has a particle size of 10~20μm.

[0029] The crosslinking agent is composed of 2.5 parts urea, 1.2 parts boric acid and 0.3 parts ammonium dihydrogen phosphate.

[0030] The preparation method of the nanoscale gallic acid-zinc coordination compound is as follows: gallic acid and zinc chloride are dissolved in ethanol at a molar ratio of 2:1, reacted for 1 hour, water is added to precipitate the precipitate, and the precipitate is obtained by filtration, washing and drying.

[0031] The above-mentioned method for preparing a waterproof and breathable TPU film includes the following steps: S1. Add all components to a high-speed mixer in proportion, mix for 8 minutes, and then vacuum dry to obtain the mixture; S2. Add the mixture obtained in step S1 into a co-rotating twin-screw extruder, gradually increase the temperature between 170 and 220°C, stir, melt, extrude, cool with water, and pelletize to obtain masterbatch; S3. Add the masterbatch obtained in step S2 to a single-screw blown film machine, set the barrel temperature to 180°C and the die temperature to 180°C, and obtain a film with a thickness of 25μm. S4. The film obtained in step S3 is first immersed in water at 40~45℃ to dissolve sodium chloride, and then immersed in warm water at 30~35℃ to dissolve PEG-10000, to obtain the dissolved film. S5. Immerse the dissolved film obtained in step S4 into a 2 g / L tannic acid ethanol solution for 1 min, and then dry to obtain a waterproof and breathable TPU film.

[0032] Example 3

[0033] A waterproof and breathable TPU film comprises the following components by weight: 110 parts TPU, 2 parts sodium bicarbonate, 1.5 parts citric acid monohydrate, 1.5 parts polyvinylpyrrolidone K30, 0.5 parts zinc stearate, 1.5 parts nanocellulose, 4 parts crosslinking agent, and 14 parts pore-forming agent.

[0034] The pore-forming agent consists of 10 parts sodium chloride and 4 parts PEG-10000, wherein the sodium chloride has a particle size of 10~20μm.

[0035] The crosslinking agent is composed of 2.5 parts urea, 1.2 parts boric acid and 0.3 parts ammonium dihydrogen phosphate.

[0036] The above-mentioned method for preparing a waterproof and breathable TPU film includes the following steps: S1. Add all components to a high-speed mixer in proportion, mix for 8 minutes, and then vacuum dry to obtain the mixture; S2. Add the mixture obtained in step S1 into a co-rotating twin-screw extruder, gradually increase the temperature between 170 and 220°C, stir, melt, extrude, cool with water, and pelletize to obtain masterbatch; S3. Add the masterbatch obtained in step S2 to a single-screw blown film machine, set the barrel temperature to 180°C and the die temperature to 180°C, and obtain a film with a thickness of 25μm. S4. The film obtained in step S3 is first immersed in water at 40~45℃ to dissolve sodium chloride, and then immersed in warm water at 30~35℃ to dissolve PEG-10000, to obtain the dissolved film. S5. Immerse the dissolved film obtained in step S4 into a 2 g / L tannic acid ethanol solution for 1 min, and then dry to obtain a waterproof and breathable TPU film.

[0037] Example 4

[0038] A waterproof and breathable TPU film comprises the following components by weight: 110 parts TPU, 2 parts sodium bicarbonate, 1.5 parts citric acid monohydrate, 1.5 parts polyvinylpyrrolidone K30, 0.5 parts zinc stearate, 1.5 parts nanocellulose, 4 parts crosslinking agent, and 14 parts pore-forming agent.

[0039] The pore-forming agent consists of 10 parts sodium chloride and 4 parts PEG-10000, wherein the sodium chloride has a particle size of 10~20μm.

[0040] The crosslinking agent is composed of 2.5 parts urea, 1.2 parts boric acid and 0.3 parts ammonium dihydrogen phosphate.

[0041] The TPU is polyether type 58887A, manufactured by Lubrizol.

[0042] The above-mentioned method for preparing a waterproof and breathable TPU film includes the following steps: S1. Add all components to a high-speed mixer in proportion, mix for 8 minutes, and then vacuum dry to obtain the mixture; S2. Add the mixture obtained in step S1 into a co-rotating twin-screw extruder, gradually increase the temperature between 170 and 220°C, stir, melt, extrude, cool with water, and pelletize to obtain masterbatch; S3. Add the masterbatch obtained in step S2 to a single-screw blown film machine, set the barrel temperature to 180°C and the die temperature to 180°C, and obtain a film with a thickness of 25μm. S4. The film obtained in step S3 is first immersed in water at 40~45℃ to dissolve sodium chloride, and then immersed in warm water at 30~35℃ to dissolve PEG-10000, to obtain the dissolved film. S5. Immerse the dissolved film obtained in step S4 into a 2 g / L tannic acid ethanol solution for 1 min, and dry to obtain a waterproof and breathable TPU film. The obtained waterproof and breathable TPU film is then treated with triethoxy-1H,1H,2H,2H-tridecylfluoro-N-octylsilane vapor for 20-40 min, and dried to obtain the treated waterproof and breathable TPU film.

[0043] Example 5

[0044] A waterproof and breathable TPU film comprises the following components by weight: 110 parts TPU, 2 parts sodium bicarbonate, 1.5 parts citric acid monohydrate, 1.5 parts polyvinylpyrrolidone K30, 0.5 parts zinc stearate, 1.5 parts nanocellulose, 4 parts crosslinking agent, and 14 parts pore-forming agent.

[0045] The pore-forming agent consists of 10 parts sodium chloride and 4 parts PEG-10000, wherein the sodium chloride has a particle size of 10~20μm.

[0046] The crosslinking agent is composed of 2.5 parts urea, 1.2 parts boric acid and 0.3 parts ammonium dihydrogen phosphate.

[0047] The TPU is polyether type 58887A, manufactured by Lubrizol.

[0048] The above-mentioned method for preparing a waterproof and breathable TPU film includes the following steps: S1. Add all components to a high-speed mixer in proportion, mix for 8 minutes, and then vacuum dry to obtain the mixture; S2. Add the mixture obtained in step S1 into a co-rotating twin-screw extruder, gradually increase the temperature between 170 and 220°C, stir, melt, extrude, cool with water, and pelletize to obtain masterbatch; S3. Add the masterbatch obtained in step S2 to a single-screw blown film machine, set the barrel temperature to 180°C and the die temperature to 180°C, and obtain a film with a thickness of 25μm. S4. The film obtained in step S3 is first immersed in water at 40~45℃ to dissolve sodium chloride, and then immersed in warm water at 30~35℃ to dissolve PEG-10000 to obtain a dissolved film. The dissolved film is then transferred to a high-pressure reactor, heated to 40℃, and carbon dioxide is injected to 100 bar. The reactor is kept for 4 hours to allow the carbon dioxide to fully penetrate. Then the pressure is reduced at a rate of 0.5 MPa / s to further open the pores. Then the processing in step S5 is carried out. S5. Immerse the dissolved film obtained in step S4 into a 2 g / L tannic acid ethanol solution for 1 min, and dry to obtain a waterproof and breathable TPU film. The obtained waterproof and breathable TPU film is then treated with triethoxy-1H,1H,2H,2H-tridecylfluoro-N-octylsilane vapor for 20-40 min, and dried to obtain the treated waterproof and breathable TPU film.

[0049] The foaming process in the TPU film is achieved through a synergistic gradient foaming of sodium bicarbonate, citric acid monohydrate, and polyvinylpyrrolidone K30. During processing, polyvinylpyrrolidone migrates to the surface, carrying some of the foaming agent, forming a gradient distribution of small pores on the surface and large pores in the inner layer.

[0050] The gradient heating process in step S2 is as follows: heat to 170°C and hold for 15 minutes, continue heating to 195°C and hold for 20 minutes, and then heat to 220°C and hold for 5 minutes.

[0051] Comparative Example 1 The only difference is that the monohydrate citric acid component in Example 1 is removed; otherwise, it is the same as in Example 1 and will not be repeated.

[0052] Comparative Example 2 The sodium chloride component in Example 1 was removed, and everything else was the same as in Example 1, so it will not be described again.

[0053] Comparative Example 3 The only difference is that the urea component in Example 1 is removed; everything else is the same as in Example 1, and will not be repeated here.

[0054] The performance test results of the waterproof and breathable TPU films prepared in the embodiments and comparative examples of the present invention are shown in Table 1.

[0055] Table 1

[0056] Note: The test conditions for strength retention rate after hydrolysis are 70℃ / 95%RH, 168h strength retention rate.

[0057] As shown in Table 1 above, the comparison of data from Examples 1 and 2 indicates that the nano-sized gallic acid-zinc coordination compound can significantly improve the strength retention rate after hydrolysis. The comparison of data from Examples 1 and 4 shows that vapor treatment with triethoxy-1H,1H,2H,2H-tridecylfluoro-N-octylsilane can improve the water vapor transmission rate of the product, with other properties remaining comparable. The comparison of data from Examples 1 and 5 shows that high-pressure carbon dioxide treatment can further improve the product's air permeability. Data from Comparative Example 1 shows that removing the citric acid monohydrate component reduces foaming performance and water vapor transmission rate. Data from Comparative Example 2 shows that removing the sodium chloride component reduces water vapor transmission rate and the strength retention rate after hydrolysis. Data from Comparative Example 3 shows that removing the urea component significantly reduces the strength retention rate after hydrolysis.

Claims

1. A waterproof and breathable TPU film, characterized in that, The substance comprises the following components by weight: 100-120 parts TPU, 1-2 parts sodium bicarbonate, 1.2-2 parts citric acid monohydrate, 1-2 parts polyvinylpyrrolidone K30, 0.3-0.8 parts zinc stearate, 1-2 parts nanocellulose, 3-5 parts crosslinking agent, and 10-15 parts pore-forming agent.

2. The waterproof and breathable TPU film according to claim 1, characterized in that, The pore-forming agent consists of 10-12 parts sodium chloride and 3-5 parts PEG-10000.

3. The waterproof and breathable TPU film according to claim 1, characterized in that, The crosslinking agent is composed of 2-3 parts urea, 1-2 parts boric acid and 0.2-0.5 parts ammonium dihydrogen phosphate.

4. The waterproof and breathable TPU film according to claim 1, characterized in that, The TPU is polyether type 58887A.

5. The waterproof and breathable TPU film according to claim 1, characterized in that, The TPU film also includes 1-2 parts of a nano-sized gallic acid-zinc coordination compound, which is prepared by dissolving gallic acid and zinc chloride in ethanol at a molar ratio of 2:1, reacting for 1 hour, adding water to precipitate the precipitate, filtering, washing, and drying to obtain the nano-sized gallic acid-zinc coordination compound.

6. The waterproof and breathable TPU film according to claim 2, characterized in that, The sodium chloride particles have a diameter of 10~20μm.

7. The waterproof and breathable TPU film according to claim 1, characterized in that, The foaming process in the TPU film is achieved through a synergistic gradient foaming of sodium bicarbonate, citric acid monohydrate, and polyvinylpyrrolidone K30. During processing, polyvinylpyrrolidone migrates to the surface, carrying some of the foaming agent, forming a gradient distribution of small pores on the surface and large pores in the inner layer.

8. A method for preparing a waterproof and breathable TPU film according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Add all components to a high-speed mixer in proportion, mix for 8 minutes, and then vacuum dry to obtain the mixture; S2. Add the mixture obtained in step S1 into a co-rotating twin-screw extruder, gradually increase the temperature between 170 and 220°C, stir, melt, extrude, cool with water, and pelletize to obtain masterbatch; S3. Add the masterbatch obtained in step S2 to a single-screw blown film machine, set the barrel temperature to 180°C and the die temperature to 180°C, and obtain a film with a thickness of 20~30μm. S4. The film obtained in step S3 is first immersed in water at 40~60℃ to dissolve sodium chloride, and then immersed in warm water at 30~50℃ to dissolve PEG-10000, to obtain the dissolved film; S5. Immerse the dissolved film obtained in step S4 into a tannic acid ethanol solution with a concentration of 1~3g / L for 0.5~2min, and then dry to obtain a waterproof and breathable TPU film.

9. The method for preparing the waterproof and breathable TPU film according to claim 8, characterized in that, The waterproof and breathable TPU film obtained in step S5 is treated with triethoxy-1H,1H,2H,2H-tridecylfluoro-N-octylsilane vapor for 20-40 minutes and then dried to obtain the treated waterproof and breathable TPU film.

10. The method for preparing the waterproof and breathable TPU film according to claim 8, characterized in that, The dissolved film prepared in step S4 is transferred to a high-pressure reactor, heated to 40°C, and carbon dioxide is injected to 100 bar. It is kept for 4 hours to allow the carbon dioxide to fully permeate. Then, the pressure is reduced at a rate of 0.5 MPa / s to further open the pores, and then the processing in step S5 is carried out.

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