Preparation method of waterproof breathable microporous TPU (thermoplastic polyurethane)

Abstract

The invention provides a preparation method of waterproof breathable microporous TPU, and belongs to the technical field of preparation of waterproof breathable microporous TPU. The preparation method of waterproof breathable microporous TPU comprises the following steps: selecting a thermoplastic polyurethane material according to the molecular weight, hardness, hydrophilicity and other characteristics of TPU; the preparation method comprises the following steps: mixing selected TPU with a plasticizer, a stabilizer and a plasticizer according to a certain proportion, fully stirring, and uniformly mixing the components through a melting process; coating the prepared molten TPU material to form a thin film; air holes are introduced by controlling the cooling speed and the temperature gradient of the film; the prepared film is subjected to heat treatment, so that the structural stability of the film is further enhanced; the microporous structure and hydrophilicity of the membrane are adjusted through surface treatment, and preparation of the waterproof and breathable microporous TPU is completed; the problem that the air permeability of a local area of a film is poor due to the fact that the uniformity of mixed raw materials is difficult to guarantee in the existing preparation process of the waterproof and breathable microporous TPU can be solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of waterproof and breathable microporous TPU preparation, and particularly relates to a preparation method of waterproof and breathable microporous TPU. BACKGROUND

[0002] Thermoplastic polyurethane (TPU) is a high molecular material generated by the reaction of polyether or polyester with diisocyanate, which has good tensile strength, tear resistance and wear resistance, so that it has good durability in high-load environments such as outdoor, footwear and medical equipment. TPU maintains good flexibility and elasticity within a wide temperature range, adapting to the movement needs in different environments. TPU has good chemical resistance, oil resistance, solvent resistance, oxidation resistance and other properties, so that it can maintain stability in various environments. TPU has good thermoplasticity and can be easily processed by melting molding and other processing methods, suitable for mass production.

[0003] With the increasing demand for high-performance materials, especially in the fields of outdoor sports, workwear, medical field, etc., there are higher requirements for the waterproofness and breathability of materials. The waterproof and breathable film can maintain waterproof function while providing air circulation or water vapor transmission function, so that the wearer or user can maintain comfort in a specific environment. Microporous film, as an effective waterproof and breathable material, can form a uniform pore structure on a microscopic scale, providing sufficient water vapor transmission rate while preventing water droplets or liquid penetration, which is an important component of waterproof and breathable materials.

[0004] The existing preparation process of waterproof and breathable microporous TPU is difficult to ensure the uniformity of the mixed raw materials, resulting in poor air permeability in local areas of the film, while other areas may have the risk of water penetration. SUMMARY

[0005] Therefore, the application provides a preparation method of waterproof and breathable microporous TPU, which can solve the problem that the existing preparation process of waterproof and breathable microporous TPU is difficult to ensure the uniformity of the mixed raw materials, resulting in poor air permeability in local areas of the film, while other areas may have the risk of water penetration.

[0006] The application is implemented as follows: The application provides a preparation method of waterproof and breathable microporous TPU, which specifically comprises the following steps: S10: selecting a thermoplastic polyurethane material according to the molecular weight, hardness and hydrophilicity of TPU; S20: mixing the selected TPU with a certain proportion of plasticizer, stabilizer and plasticizer, and fully stirring to uniformly mix these components through a melting process; S30: coating the prepared molten TPU material to form a thin film; S40: Introducing pores by controlling the cooling speed and temperature gradient of the film; S50: Performing heat treatment on the prepared film to further strengthen the structural stability of the film; S60: Adjusting the microporous structure and hydrophilicity of the film through surface treatment to complete the preparation of the waterproof and breathable microporous TPU.

[0007] On the basis of the above technical solution, the preparation method of the waterproof and breathable microporous TPU can be further improved as follows: The specific steps of mixing the selected TPU with a certain proportion of plasticizer, stabilizer and plasticizer, and fully stirring, and uniformly mixing these components through the melting process include: Firstly, a certain proportion of TPU, plasticizer, stabilizer and plasticizer is weighed; Secondly, the TPU and the plasticizer, the stabilizer and the plasticizer are put into a high-speed mixer for preliminary mixing; Thirdly, ions are added to the mixture to form a turbulent electric field, improve the mixing property of TPU and plasticizer, stabilizer and plasticizer, and further promote the uniform mixing thereof; Fourthly, the mixed raw materials are sent into a melt extruder to melt the mixture at a high temperature, and the temperature is controlled between 180 DEG C and 220 DEG C; Fifthly, the mixture is continuously stirred in the molten state to ensure uniform fusion of each component, and the stirring speed and temperature are adjusted in steps to avoid the influence of large temperature difference and high speed in a short time on the properties of the film; Sixthly, during the melting and mixing process, the air and moisture in the mixture are removed through vacuum exhaust to ensure that the final product is free of bubbles and moisture, and the quality of the film is not affected; Seventhly, after mixing, the molten TPU material is extruded through the discharge port and enters the cooling zone for cooling, so as to finally form a stable melt which can be used for film production.

[0008] The beneficial effects of the above improved scheme are that ions can promote certain chemical reactions, help to enhance the mechanical properties of TPU or improve the structure of the film. The ions improve the mixing property of TPU and other additives by changing the surface tension of the material or the interaction of the polymer chain, so that the process is more smooth. The addition of conductive ions can improve the electrical conductivity of the material and enhance the antistatic property of the film.

[0009] Further, the ions added to the mixture are one or more of metal ions, alkali metal ions, transition metal ions, chloride ions, ammonia ions and surface active ions. Wherein, the addition of multiple ions needs to avoid the reaction between them.

[0010] Further, the plasticizer is one or several of dioctyl phthalate, octylphenol, cyclohexyl diacyl phenol, bio-based plasticizer; The stabilizer is one or several of zinc stearate, benzotriazole ultraviolet-resistant additive, 2,6-di-tert-butyl-p-cresol; The plasticizer is one or several of butyl plasticizer, isophorone, fatty acid softener, glycerol and glycerol ether plasticizer; The mixing ratio of the TPU, the plasticizer, the stabilizer, and the plasticizer is 50%-90%:5%-20%:5%-15%:1%-5%.

[0011] The beneficial effects of the above improvement scheme are: TPU as the matrix material, the proportion is higher, because it determines the main physical properties of the final material. Higher proportion of TPU helps to ensure the strength, elasticity and toughness of the material. Plasticizer is used to improve the processability and fluidity of TPU, reduce its melting temperature, and enhance the processability. The role of plasticizer is to improve the softness, ductility and processability of the material. The selection and type of plasticizer directly affects the softness, hardness and low temperature resistance of the final product. Stabilizers are used to improve the thermal stability, oxidation resistance and heat resistance of TPU during processing. They help to prevent the decomposition or aging of polymers at high temperatures.

[0012] Further, in the molten state, the mixture is continuously stirred to ensure uniform fusion of each component. The specific steps for adjusting the stirring speed and temperature in stages to avoid the influence of large temperature difference and high speed on the properties of the film in a short time include: First, start heating to 120°C-140°C, use 50-100 RPM for low-speed stirring to avoid splashing or uneven distribution of components caused by rapid heating; Second, gradually increase the temperature to 160°C-180°C, and increase the stirring speed to 150-200 RPM to ensure uniform mixing of the components while the material is completely melted; Third, maintain the temperature at 180°C-200°C, use 250-300 RPM for medium-high speed stirring to improve stirring efficiency and ensure that the additives are fully incorporated into the TPU, while avoiding material splashing caused by high speed; Fourth, gradually reduce the temperature to 160°C-170°C, maintain 150-200 RPM medium speed stirring to avoid unnecessary bubbles or material overheating caused by high stirring speed; Step 5, reduce the material temperature to 120°C - 140°C, reduce the stirring speed to 50-100 RPM, avoid too fast stirring during temperature reduction affecting the material structure.

[0013] The beneficial effects of the above improvement scheme are: the main purpose of the first step is to let TPU and other solid ingredients slowly melt and preliminarily mix, avoiding too high temperature to cause partial decomposition of ingredients; in the second step, the temperature is gradually increased to a suitable melting state, ensuring that TPU and other additives are fully fused, avoiding local overheating or uneven distribution of ingredients; in the third step, the temperature and stirring speed of the material are relatively high, ensuring that each ingredient can be uniformly mixed in the molten state, while attention should be paid to avoid the influence of large temperature difference on the material properties; the fourth step is to prevent the influence of temperature difference caused by too fast temperature drop on the film, and to ensure that all ingredients are uniformly fused at a suitable temperature, preparing for the molding or cooling stage; in the fifth step, the cooling speed should not be too fast to avoid causing uneven material or defects. Ensure uniform cooling of the material under temperature and stirring speed control.

[0014] Further, the specific steps of coating the prepared molten TPU material to form a film include: Step 1, adjust the distance between the blades of the coating equipment to 0.1mm - 1mm; Step 2, increase the material temperature to the range of 160°C - 200°C to ensure that the material is completely melted and has good fluidity; Step 3, uniformly coat the molten TPU material on the substrate, and control the thickness of the coated film to be between 0.1mm - 1mm; Step 4, after coating is completed, immediately perform cooling treatment, and control the cooling rate to be 0.5°C / s - 3°C / s.

[0015] Further, the specific steps of introducing pores by controlling the cooling speed and temperature gradient of the film include: Step 1, set the cooling surface temperature to 50°C - 70°C, the internal film temperature to 100°C - 150°C, and the temperature difference to 50°C - 100°C, which helps gas to diffuse in the film and form pores; Step 2, control the distribution and size of pores by adjusting the cooling rate and temperature gradient, ensuring that the diameter of the pores is in the range of 0.1mm - 0.5mm; Step 3, stop cooling and perform stabilization treatment after the film is cooled to 50°C - 60°C.

[0016] Fast cooling helps to form smaller pores, and the cooling rate is 1°C / s - 3°C / s. It is suitable for films that require finer pore distribution.

[0017] For the formation of larger pores, the cooling rate can be reduced to 0.5°C / s, ensuring that the bubbles can be more evenly expanded and remain in the film.

[0018] By controlling the temperature difference and rate during the cooling process, the pores can be evenly distributed within the film. The greater the temperature gradient during the cooling process, the more uniform and obvious the pore formation.

[0019] Further, the specific step of heat treating the prepared film to further strengthen the structural stability of the film includes: The temperature is set in the range of 120°C - 160°C, and the annealing process is maintained for 10 - 30 minutes, which helps to eliminate internal stress and ensure that the pore structure remains unchanged. Compared with the prior art, the preparation method of the waterproof and breathable microporous TPU provided by the present application has the following beneficial effects: According to the molecular weight, hardness and hydrophilicity of TPU, the appropriate TPU material is selected. The molecular weight affects the mechanical properties of the material, the hardness determines the softness and durability of the film, and the hydrophilicity determines the waterproof and breathable function of the film. Therefore, this selection is crucial and helps the subsequent prepared material to achieve the expected effect in waterproof and breathable.

[0020] In the step of mixing the ingredients and melting, the selected TPU is mixed with plasticizers, stabilizers, plasticizers and other ingredients, and the uniform mixing is ensured through the melting process. The plasticizer increases the flowability of the material, the stabilizer improves the anti-aging and anti-ultraviolet ability of the material, and the plasticizer enhances the softness of the material. This step ensures that these ingredients are fully integrated through the melting technology, optimizing the performance of the final film. The addition of ions (such as metal ions, transition metal ions, etc.) improves the mixing of TPU with plasticizers, stabilizers and plasticizers. The addition of these ions can improve the molecular structure of the material, thereby promoting more uniform mixing and improving the quality of the final product. The vacuum exhaust process effectively removes air and moisture from the mixture, avoiding the impact of bubbles and moisture on the quality of the film. During the melting process, the temperature and stirring speed are controlled in a step-by-step manner to avoid uneven material caused by too fast heating or stirring speed, ensuring that each ingredient is fully integrated. In addition, the change of stirring speed can effectively prevent splashing and ensure complete uniformity of the material.

[0021] In the coating step, the already molten TPU material is applied onto the substrate to form a uniform thin film. The film thickness is controlled between 0.1 mm to 1 mm, ensuring uniform coverage of the material by appropriate coating equipment and controlling the coating speed. The quality of this process has a direct impact on the formation of subsequent pores and the performance of the film. During the coating process, the uniformity and appropriate thickness of the film are ensured by fine-tuning the blade gap, material temperature, and coating speed. This process effectively controls the structure of the film, ensuring consistency in subsequent processing and performance.

[0022] In the step of controlling the cooling rate and temperature gradient, the formation of pores in the film is facilitated by precisely controlling the cooling rate and temperature gradient. The formation of pores is closely related to the temperature gradient, and too high or too low temperature difference can affect the size and distribution of pores. By adjusting the cooling conditions, the pore diameter can be controlled between 0.1 mm and 0.5 mm, thereby affecting the air permeability and waterproofness of the film. During the cooling process, precise temperature control is used to ensure the formation of pores. The difference between the cooling surface temperature and the internal film temperature is crucial for the distribution of pores, and controlling the temperature difference within a certain range can ensure the uniformity and appropriate size of the pores, thereby optimizing the air permeability of the film.

[0023] The heat treatment step further stabilizes the structure of the film by annealing at a temperature range of 120°C to 160°C. This process helps to eliminate internal stress that may have been generated during the melting process, while ensuring that the microporous structure of the film does not change, thereby enhancing the long-term performance of the material. The annealing process helps to eliminate internal stress in the material, further enhancing the stability of the film while avoiding unnecessary deformation during the cooling process. This step effectively improves the anti-aging and stability of the film in long-term use.

[0024] Surface treatment is an important step in adjusting the hydrophilicity and microporous structure of the film. By further treating the surface of the film, its waterproof and air-permeable properties can be optimized to meet the best performance requirements. Hydrophilicity can help the film improve water vapor transmission rate, while the microporous structure directly affects the waterproof performance. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A specific step flow chart for a method of preparing a waterproof and air-permeable microporous TPU. DETAILED DESCRIPTION

[0026] To make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application.

[0027] As Figure 1The embodiment shows a preparation method of waterproof and breathable microporous TPU provided by the application. In this embodiment, the following steps are specifically included: S10: Selecting a thermoplastic polyurethane material according to the molecular weight, hardness, and hydrophilicity of the TPU; S20: Mixing the selected TPU with a certain proportion of plasticizers, stabilizers, and plasticizers, and fully stirring to uniformly mix these components through a melting process; S30: Coating the prepared molten TPU material to form a film; S40: Introducing pores by controlling the cooling speed and temperature gradient of the film; S50: Heat treating the prepared film to further strengthen the structural stability of the film; S60: Adjusting the microporous structure and hydrophilicity of the film through surface treatment to complete the preparation of waterproof and breathable microporous TPU.

[0028] The specific operations of adjusting the microporous structure and hydrophilicity of the film through surface treatment to complete the preparation of waterproof and breathable microporous TPU include plasma treatment, ultraviolet light irradiation, and surface coating method.

[0029] Plasma treatment: Using plasma treatment technology to modify the surface of the film to enhance the hydrophilicity of the film surface and improve the waterproof and breathable properties. Plasma treatment can destroy the surface structure of TPU molecules, exposing hydrophilic groups (such as hydroxyl, carboxyl, etc.).

[0030] Ultraviolet light irradiation: Under ultraviolet light irradiation, the molecular structure of the film surface is crosslinked, thereby improving the hydrophilicity and anti-pollution properties.

[0031] Surface coating method: Hydrophilic substances such as polyvinyl alcohol and polyurethane can be coated on the surface of the film to make the surface more hydrophilic.

[0032] In the above technical solution, the specific steps of mixing the selected TPU with a certain proportion of plasticizers, stabilizers, and plasticizers, and fully stirring to uniformly mix these components through a melting process include: First, weigh a certain proportion of TPU, plasticizers, stabilizers, and plasticizers; Second, put the TPU and plasticizers, stabilizers, and plasticizers into a high-speed mixer for preliminary mixing; Third, add ions to the mixture to form a turbulent electric field, improve the mixing of TPU with plasticizers, stabilizers, and plasticizers, and further promote their uniform mixing; Fourth, send the mixed raw materials into a melt extruder to melt the mixture at a temperature of 180-220°C; Step 5: In the molten state, continue to stir the mixture to ensure uniform fusion of all ingredients. Adjust the stirring speed and temperature in stages to avoid rapid temperature changes and excessive speed that could affect the properties of the film. Step 6: During the melting and mixing process, remove air and moisture from the mixture through vacuum exhaust to ensure that the final product is free of bubbles and moisture, and to avoid affecting the quality of the film. Step 7: After mixing is complete, the molten TPU material is extruded through the discharge port and enters the cooling zone for cooling, so as to finally form a stable melt that can be used for film production.

[0033] Further, in the above technical solution, the ions added to the mixture are one or more of metal ions, alkali metal ions, transition metal ions, chloride ions, ammonia ions, and surface active ions. Wherein, the addition of multiple ions needs to avoid their mutual reaction.

[0034] 1. Metal ions (such as calcium ions, zinc ions, aluminum ions, etc.) Metal ions are usually used to enhance the mechanical properties, thermal stability, or ultraviolet resistance of TPU. In some cases, they can also improve the wear resistance or hardness of the material.

[0035] For example: Calcium ions (Ca²⁺): Help improve the hardness and heat aging resistance of the material.

[0036] Zinc ions (Zn²⁺): As a stabilizer, it can improve the thermal stability of TPU and improve the stability during processing.

[0037] Aluminum ions (Al³⁺): In some specific formulations, aluminum ions can act as catalysts to promote chemical cross-linking or enhance ultraviolet resistance.

[0038] 2. Alkali metal ions (such as sodium ions, potassium ions, etc.) Alkali metal ions can play a role in adjusting some polymer reactions, and sometimes they are used to adjust the solubility or dispersibility of polymers.

[0039] For example: Sodium ions (Na⁺): In some cases, sodium ions can adjust the compatibility of TPU with other additives, helping to enhance the effect of plasticizers.

[0040] Potassium ions (K⁺): Potassium ions can enhance the antioxidant ability of some TPU composites and improve their flowability during processing.

[0041] 3. Transition metal ions (such as copper ions, iron ions, etc.) Transition metal ions are commonly used to adjust the electrical conductivity, optical properties, or enhance the anti-aging performance of TPU. Certain transition metal ions can also be used to enhance corrosion resistance.

[0042] For example: Copper ions (Cu²⁺): Copper ions can improve the UV resistance of TPU, improve the high temperature resistance of the material, and sometimes enhance its antibacterial properties.

[0043] Iron ions (Fe²⁺ / Fe³⁺): Iron ions can improve the oxidation resistance of TPU and enhance its high temperature resistance.

[0044] 4. Chloride ions (Cl⁻) and sulfate ions (SO4²⁻) These anions can react with other ingredients in some cases, helping to crosslink or improve the stability of the material.

[0045] For example: Chloride ions (Cl⁻): Can be used as part of a plasticizer, helping to improve the processability and flow of TPU.

[0046] Sulfate ions (SO4²⁻): Sometimes used to improve the crosslinking structure of the polymer, increasing the mechanical strength and durability of the material.

[0047] 5. Surface-active ions (such as cetyltrimethylammonium bromide, CTAB, etc.) Surface-active ions help improve the interfacial compatibility of TPU with other materials, especially in multiphase composites. They can effectively promote the dispersion of additives and substrates.

[0048] For example: Cetyltrimethylammonium bromide (CTAB): As a surfactant, it can promote good dispersibility of TPU with other incompatible materials such as fillers and fibers.

[0049] 6. Ammonium ions (NH4⁺) Ammonium ions can be used as crosslinking promoters or stabilizers, commonly used in some special TPU formulations to improve thermal stability and oxidation resistance.

[0050] Further, in the above technical solutions, the plasticizer is one or more of dioctyl phthalate, octylphenol, cyclohexyl diacyl phenol, and bio-based plasticizer; The stabilizer is one or more of zinc stearate, benzotriazole-based ultraviolet-resistant additives, and 2,6-di-tert-butyl-p-cresol; The plasticizer is one or more of butyl plasticizer, isophorone, fatty acid softener, glycerol, and glycerol ether plasticizer; The mixing ratio of TPU, plasticizer, stabilizer and plasticizer is: 50%-90%: 5%-20%: 5%-15%: 1%-5%.

[0051] Further, in the above technical solution, the mixture is continuously stirred in the molten state to ensure uniform fusion of each component. The specific steps of adjusting the stirring speed and temperature in stages during this process to avoid the influence of large temperature difference and high speed on the properties of the film in a short time include: First, start heating to 120°C-140°C, and use 50-100 RPM for low-speed stirring to avoid splashing or uneven distribution of components caused by rapid heating; Second, gradually increase the temperature to 160°C-180°C, and increase the stirring speed to 150-200 RPM to ensure uniform mixing of the components while the material is completely melted; Third, maintain the temperature at 180°C-200°C, and use 250-300 RPM for medium-high speed stirring to improve stirring efficiency and ensure that the additives are completely incorporated into the TPU, while avoiding material splashing caused by high speed; Fourth, gradually reduce the temperature to 160°C-170°C, and maintain medium-speed stirring at 150-200 RPM to avoid unnecessary bubbles or overheating of the material caused by high stirring speed; Fifth, reduce the material temperature to 120°C-140°C, and reduce the stirring speed to 50-100 RPM to avoid affecting the material structure during the cooling process.

[0052] Further, in the above technical solution, the prepared molten TPU material is coated to form a film, and the specific steps include: First, adjust the distance between the blades of the coating equipment to 0.1mm-1mm; Second, increase the material temperature to the range of 160°C-200°C to ensure that the material is completely melted and has good fluidity; Third, uniformly coat the molten TPU material on the substrate, and control the thickness of the coated film to be between 0.1mm-1mm; Fourth, after coating is completed, immediately perform cooling treatment, and control the cooling rate to be 0.5°C / s-3°C / s.

[0053] Further, in the above technical solution, by controlling the cooling speed and temperature gradient of the film, the specific steps of introducing pores include: The first step is to set the cooling surface temperature at 50°C - 70°C, the internal film temperature at 100°C - 150°C, and the temperature difference between 50°C - 100°C, which helps the gas diffuse in the film and form pores; The second step is to control the distribution and size of the pores by adjusting the cooling rate and temperature gradient, ensuring that the diameter of the pores ranges from 0.1mm - 0.5mm. The third step is to stop cooling and perform a stabilization process after the film is cooled to 50°C - 60°C.

[0054] Further, in the above technical solution, the specific steps for heat treatment of the prepared film to further strengthen the structural stability of the film include: The temperature is set in the range of 120°C - 160°C for 10 - 30 minutes, and annealing helps to eliminate internal stress and ensure that the pore structure remains unchanged.

[0055] Specifically, the principle of the present application is: selecting thermoplastic polyurethane material according to the molecular weight, hardness and hydrophilicity of TPU; mixing the selected TPU with a certain proportion of plasticizer, stabilizer and plasticizer, and stirring thoroughly, so that these components are uniformly mixed through the melting process; coating the prepared molten TPU material to form a film; introducing pores by controlling the cooling rate and temperature gradient of the film; heat treating the prepared film to further strengthen the structural stability of the film; adjusting the microporous structure and hydrophilicity of the film through surface treatment to complete the preparation of waterproof and breathable microporous TPU.

[0056] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can easily think of changes or replacements within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for preparing waterproof and breathable microporous TPU, characterized in that: The specific steps include: S10: Select thermoplastic polyurethane material based on TPU’s molecular weight, hardness, and hydrophilicity; S20: Mix the selected TPU with a certain proportion of plasticizer, stabilizer, and plasticizer, stir them thoroughly, and make these ingredients evenly mixed through a melting process; S30: coating the prepared molten TPU material to form a film; S40: introducing pores by controlling the cooling rate and temperature gradient of the membrane; S50: heat treating the prepared film to further enhance the structural stability of the film; S60: The microporous structure and hydrophilicity of the membrane are adjusted through surface treatment to complete the preparation of waterproof and breathable microporous TPU.

2. The method for preparing a waterproof and breathable microporous TPU according to claim 1, characterized in that: The specific steps of mixing the selected TPU with a certain proportion of plasticizer, stabilizer, and plasticizer, stirring them thoroughly, and uniformly mixing these components through a melting process include: The first step is to weigh a certain proportion of TPU, plasticizer, stabilizer and plasticizer; The second step is to put TPU, plasticizer, stabilizer and plasticizer into a high-speed blender for preliminary mixing; The third step is to add ions to the mixture to form a disordered electric field, improve the miscibility of TPU with plasticizers, stabilizers, and plasticizers, and further promote their uniform mixing; The fourth step is to feed the mixed raw materials into a melt extruder to melt the mixture at a high temperature, and the temperature is controlled between 180°C and 220°C; The fifth step is to continuously stir the mixture in a molten state to ensure that all components are evenly blended. During this process, the stirring speed and temperature are adjusted in steps to avoid large temperature differences and excessive speed in a short period of time that may affect the properties of the film. The sixth step is to remove air and moisture from the mixture through vacuum exhaust during the melt mixing process to ensure that the final product is free of bubbles and moisture and to avoid affecting the quality of the film; In the seventh step, after the mixing is completed, the molten TPU material is extruded through the discharge port and enters the cooling zone for cooling so as to finally form a stable melt that can be used for film production.

3. The method for preparing a waterproof and breathable microporous TPU according to claim 2, characterized in that: The ions added to the mixture are one or more of metal ions, alkali metal ions, transition metal ions, chloride ions, ammonia ions and surfactant ions. The addition of multiple ions needs to avoid reactions between them.

4. The method for preparing a waterproof and breathable microporous TPU according to claim 3, characterized in that: The plasticizer is one or more of dioctyl phthalate, octylphenol, cyclohexyl diacylphenol, and bio-based plasticizer; The stabilizer is one or more of zinc stearate, benzotriazole anti-ultraviolet additives, and 2,6-di-tert-butyl-p-cresol; The plasticizer is one or more of butyl plasticizer, isophorone, fatty acid softener, glycerol and glycerol ether plasticizer; The mixing ratio of the TPU, the plasticizer, the stabilizer, and the plasticizer is: 50%-90%: 5%-20%: 5%-15%: 1%-5%.

5. The method for preparing a waterproof and breathable microporous TPU according to claim 4, characterized in that: The specific steps of continuously stirring the mixture in the molten state to ensure uniform fusion of the components, and adjusting the stirring speed and temperature in a step-by-step manner during this process to avoid excessive temperature differences and excessive speeds in a short period of time that may affect the properties of the film include: In the first step, start heating to 120°C - 140°C, stirring at a low speed of 50-100 RPM to avoid splashing or uneven distribution of ingredients due to excessive heating. In the second step, gradually increase the temperature to 160°C - 180°C and the stirring speed to 150-200 RPM to ensure that the material is fully melted while accelerating the uniform mixing of the ingredients; In the third step, the temperature is maintained at 180°C - 200°C and the stirring speed is 250-300 RPM to improve the stirring efficiency and ensure that the additives are fully integrated into the TPU while avoiding material splashing caused by excessive speed. Step 4: Gradually lower the temperature to 160°C - 170°C, maintaining a medium stirring speed of 150-200 RPM to avoid excessive stirring speed causing unnecessary bubbles or overheating of the material. Step 5: Lower the material temperature to 120°C - 140°C and reduce the stirring speed to 50-100 RPM to avoid stirring too fast during the cooling process, which may affect the material structure.

6. The method for preparing a waterproof and breathable microporous TPU according to claim 5, characterized in that: The specific steps of coating the prepared molten TPU material to form a film include: The first step is to adjust the spacing of the blades of the coating equipment to 0.1mm - 1mm; The second step is to raise the material temperature to a range of 160°C - 200°C to ensure that the material is completely melted and has good fluidity; The third step is to evenly coat the molten TPU material on the substrate, and the thickness of the film after coating is controlled between 0.1mm and 1mm; Step 4: After coating, the film is immediately cooled, and the cooling rate is controlled at 0.5°C / s - 3°C / s.

7. The method for preparing a waterproof and breathable microporous TPU according to claim 6, characterized in that: The specific steps of introducing pores by controlling the cooling rate and temperature gradient of the film include: In the first step, the cooling surface temperature is set to 50°C - 70°C and the internal membrane temperature is set to 100°C - 150°C. The temperature difference between 50°C and 100°C is conducive to gas diffusion in the membrane and the formation of pores. The second step is to control the distribution and size of the pores by adjusting the cooling rate and temperature gradient to ensure that the pore diameter ranges from 0.1mm to 0.5mm; In the third step, after the film is cooled to 50°C - 60°C, cooling is stopped and stabilization treatment is performed.

8. The method for preparing a waterproof and breathable microporous TPU according to claim 7, characterized in that: The specific steps of heat treating the prepared film to further enhance the structural stability of the film include: Annealing is performed at a temperature between 120°C and 160°C for 10 to 30 minutes to help eliminate internal stress and ensure that the pore structure remains unchanged.

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