Preparation method of windproof moisture-permeable polyurethane film and fabric

Abstract

The invention discloses a preparation method of a windproof moisture-permeable polyurethane film and a fabric, the preparation method comprises the following steps: step S10: mixing and stirring polyurethane resin and an N, N-dimethylformamide solvent until the polyurethane resin is completely dissolved to obtain a polyurethane film casting slurry; s20, the surface of release paper is coated with the polyurethane film casting slurry to form a wet film, and the wet film is subjected to three-section type drying through a drying tunnel with different temperature zones; in the first-stage drying procedure, the product stays in a first temperature zone of 60-80 DEG C for 1-2 minutes; in the second-stage drying process, the product stays in a second temperature zone of 90-120 DEG C for 3-5 minutes; and in the third-section drying process, staying in a third temperature zone of 120-160 DEG C for 6-8 minutes. After the polyurethane film prepared by the preparation method is applied to garment materials, functional garments can be balanced in efficient moisture permeability and effective wind resistance.

Description

Technical Field

[0001] This invention relates to the field of polyurethane membrane technology, specifically to a method for preparing a windproof and breathable polyurethane membrane and its fabric. Background Technology

[0002] In recent years, the functional apparel market has developed rapidly, especially in the outdoor sector, where the requirements for the "waterproof and breathable" performance of outdoor jackets are extremely high. However, in the broader everyday wear market, such as woven jackets and down jackets, the core wearing scenarios are urban commuting and business travel. These scenarios are characterized by frequent switching between indoor and outdoor environments, large temperature fluctuations, easy sweating, and exposure to strong winds in urban areas. Currently, most fabrics for such clothing on the market use non-porous PU or TPU films for bonding in pursuit of fabric crispness and down-proof effects. These films are completely non-breathable, preventing moisture from escaping. This results in severe stuffiness and stickiness, and even causes chills, when there is slight activity or when entering a warm indoor environment. While ordinary woven fabrics have some breathability, they are completely windproof. When encountering strong winds outdoors, the heat from the insulating layer (such as down) will be rapidly lost, resulting in a feeling of cold. Therefore, there is currently an unbalanced relationship between the two functional characteristics of highly efficient moisture permeability and effective windproofing in current functional clothing. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned defects or problems in the background art and to provide a method for preparing a windproof and breathable polyurethane membrane and a fabric. When the polyurethane membrane prepared by this method is applied to clothing fabric, it can enable functional clothing to achieve a balance between high-efficiency moisture permeability and effective windproofness.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] Technical Solution 1: A method for preparing a windproof and breathable polyurethane membrane, comprising the following steps: Step S10: Mixing and stirring polyurethane resin with N,N-dimethylformamide solvent until the polyurethane resin is completely dissolved to obtain a polyurethane casting slurry; Step S20: Coating the polyurethane casting slurry onto the surface of release paper to form a wet film, and drying the wet film in three stages through drying tunnels with different temperature zones; In the first stage drying process, the film is kept in the first temperature zone of 60-80℃ for 1-2 minutes; In the second stage drying process, the film is kept in the second temperature zone of 90-120℃ for 3-5 minutes; In the third stage drying process, the film is kept in the third temperature zone of 120-160℃ for 6-8 minutes.

[0006] Technical Solution 2 based on Technical Solution 1: In step S10, a leveling agent is also added to the polyurethane resin and N,N-dimethylformamide solvent; wherein the weight ratio of the polyurethane resin, N,N-dimethylformamide solvent and leveling agent is 80-90:100-120:0.5-1.

[0007] Technical Solution 3 based on Technical Solution 2: The mixing and stirring process in step S10 is carried out at a temperature of 50-60℃.

[0008] Technical Solution 4 based on Technical Solution 3: In step S10, the viscosity of the polyurethane casting slurry is 1500±200mPa·s.

[0009] Technical solution five, based on technical solution four, further includes a step of vacuum degassing treatment of the polyurethane casting slurry after step S10 and before step S20.

[0010] Technical Solution Six based on Technical Solution Five: In step S20, the polyurethane casting slurry is coated onto the surface of the release paper using a reverse roller coating method.

[0011] Technical solution seven based on technical solution six: In step S20, the dry film thickness of the polyurethane film formed after three-stage drying is 0.01-0.02 mm.

[0012] Technical solution eight, based on technical solution seven, further includes step S30 after step S20: using a cooling roller with a temperature of 0-5℃ to quickly shape the dried polyurethane film.

[0013] Technical solution nine based on technical solution eight: After step S30, it further includes step S40: curing the polyurethane film in a constant temperature and humidity environment for 24-72 hours.

[0014] In addition, the present invention also provides technical solution ten: a fabric comprising a base fabric, wherein a polyurethane film prepared by the method of preparing a windproof and breathable polyurethane film according to any one of technical solutions one to nine is bonded to one side of the base fabric by means of adhesive.

[0015] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0016] Technical Solution 1 provides a method for preparing a windproof and breathable polyurethane membrane. The polyurethane membrane prepared by this method has a permeable microporous structure, which, when applied to clothing fabrics, can effectively improve the performance contradiction between high-efficiency breathability and effective windproofing in existing technologies. In existing technologies, dense, non-porous membranes, due to the lack of molecular transport channels, can effectively block wind as macroscopic gas convection, but also hinder moisture as individual water molecules from diffusing, resulting in poor windproof but poor moisture permeability. The macroscopic pores of conventional fabrics do not effectively hinder either. Conventional film preparation processes typically aim to remove solvents as quickly as possible to improve production efficiency, generally employing single-stage high-temperature rapid drying. However, when this conventional method is applied to polyurethane membrane raw material systems, the instantaneous and violent evaporation of solvents on the wet membrane surface causes the surface polyurethane polymers to rapidly aggregate and solidify, forming a dense, impermeable skin. This skin immediately blocks the escape path of the solvent inside the membrane, ultimately leading to uneven film formation, internal solvent residue, and the inability to form any effective permeable pores.

[0017] The core of this scheme lies in the three-stage drying process in step S20. The first drying stage is conducted at a lower temperature range of 60-80℃, fully utilizing the physical properties of N,N-dimethylformamide solvent, which has a high boiling point and a slow evaporation rate in this temperature range. By gently heating, the solvent evaporation flux on the wet film surface is controlled, matching its rate with the rate of internal solvent diffusion to the surface. This ensures that the surface of the wet film remains open to solvent molecules during shrinkage, thus reserving the necessary physical channels for the smooth discharge of large amounts of internal solvent in subsequent processes. After completing the permeable surface preparation established in the first stage, the wet film enters the second temperature range of 90-120℃. The significant temperature increase significantly increases the saturated vapor pressure of N,N-dimethylformamide, driving a rapid acceleration of its evaporation rate. At this point, due to the open channels ensured in the first step, a large amount of solvent inside the membrane can escape rapidly. The rapid removal of the solvent causes the concentration of polyurethane polymer in the system to quickly exceed the phase separation critical point, triggering a violent liquid-liquid phase separation process throughout the entire membrane volume. During this process, regions with higher polymer concentrations precipitate to form an interconnected continuous phase, i.e., the solid framework of the micropores; while regions with higher solvent concentrations form discontinuous liquid phase regions enclosed by the framework, i.e., the future pore volume. The third drying process is carried out at a higher temperature range of 120-160℃, significantly higher than the glass transition temperature of the polyurethane material used. At this temperature, the polyurethane polymer chains constituting the pore wall framework gain sufficient mobility to relax and rearrange. This process not only releases the internal stress generated by rapid phase separation, preventing the final film from curling or cracking, but more importantly, it optimizes the formed microporous network structure and achieves a thermodynamically stable state.

[0018] The specific temperature and time parameters in the three-stage drying process play a crucial role in the formation and effectiveness of the polyurethane film. In the first drying stage, a temperature range of 60-80°C is chosen because this range provides sufficient energy to initiate effective solvent evaporation while being sufficiently gentle to ensure the evaporation rate remains below the critical skinning rate. If the temperature is below 60°C, solvent evaporation is too slow, leading to low production efficiency and an inability to establish the necessary concentration gradient for subsequent processes. If the temperature is above 80°C, the surface evaporation flux is too high, easily forming a dense skin layer, thus causing the entire micropore construction process to fail. A residence time of 1-2 minutes ensures that sufficient solvent escapes from the surface at this gentle rate to form a stable permeable surface, while avoiding over-drying due to excessive time. In the second drying stage, a temperature range of 90-120°C is ideal for triggering rapid phase separation. This temperature range provides sufficient driving force to cause an exponential increase in the solvent evaporation rate, instantly pushing the system into an unstable phase region. If the temperature is below 90℃, the phase separation process will be too slow, potentially leading to excessive growth and coalescence of solvent regions, resulting in an uneven macroporous structure. If the temperature is above 120℃, the phase separation process may be too violent and difficult to control, easily causing pore wall rupture or structural collapse. A residence time of 3-5 minutes provides the necessary time for the phase separation process to proceed fully along the entire film thickness, ensuring the formation of a continuous and uniform microporous network. In the third drying stage, the temperature range of 120-160℃ is set based on the dual objectives of ensuring sufficient polymer chain activity and complete solvent removal. This temperature must be stably higher than the glass transition temperature of the polyurethane used to provide sufficient mobility for stress relaxation and structural stabilization of the polymer chains. Simultaneously, this temperature range also ensures that even residual solvent physically adsorbed or encapsulated deep within the polymer network can obtain sufficient energy to escape completely. The longer residence time of 6-8 minutes is because the relaxation of polymer chains and the final diffusion of residual solvent are relatively slow processes that require sufficient time to complete.

[0019] In technical solution two, by introducing a leveling agent in a specific ratio, it is ensured that the polyurethane casting slurry can form a wet film with a macroscopically uniform thickness in the subsequent coating process. Without a leveling agent, the slurry, due to its inherent surface tension, is prone to defects such as orange peel, streaks, or uneven thickness during coating. These macroscopic inhomogeneities directly lead to significant differences in the heat received and solvent evaporation rates of different areas of the wet film during the drying process, thus completely disrupting the precise thermodynamic and kinetic balance upon which the three-stage drying process relies. The addition of the leveling agent synergizes the physical properties of the polyurethane resin and solvent, improving the wetting and spreading ability of the slurry on the release paper surface by reducing the surface tension of the slurry, thereby ensuring the uniformity of the initial wet film.

[0020] In technical solution three, mixing and stirring at a temperature of 50-60℃ ensures the complete and uniform dissolution of polyurethane resin in N,N-dimethylformamide solvent, thereby obtaining a polyurethane casting slurry with a uniform molecular level. Polyurethane, as a high molecular weight polymer, dissolves slowly at room temperature and easily forms difficult-to-eliminate microgel clusters. These microscopic inhomogeneities are the root cause of defects in the final film formation, clogging or destroying the microporous structure formed during the three-stage drying process. Heating and stirring at 50-60℃ can efficiently prepare a truly uniform solution without causing significant solvent evaporation or polymer degradation.

[0021] In technical solution four, the viscosity of the polyurethane casting slurry is precisely controlled within the range of 1500±200 mPa·s, providing stable and ideal rheological conditions for subsequent precision coating processes. The viscosity of the slurry is a macroscopic reflection of its internal polymer concentration, molecular weight, and interaction with the solvent, and is a key parameter determining its processing performance. If the viscosity is too low, the slurry is prone to flow and spread during coating, making it difficult to maintain the set wet film thickness and potentially penetrating the release paper; if the viscosity is too high, the slurry has poor fluidity, making it difficult to form a uniform thin layer through the coating equipment and easily trapping air bubbles. This viscosity range ensures that the slurry has both sufficient fluidity for uniform coating and sufficient consistency to maintain the uniformity of the wet film thickness before entering the drying tunnel.

[0022] In technical solution five, vacuum degassing of the polyurethane casting slurry eliminates the microbubbles inevitably introduced into the slurry during mixing. These bubbles are macroscopic defects; if not removed, they will form randomly distributed pinholes on the final polyurethane film during subsequent coating and drying processes. These pinholes are much larger than the micron-sized pores that this invention aims to create; they impair the windproof properties of the film, become stress concentration points, and reduce the film's mechanical strength.

[0023] In technical solution six, a high-precision coating method called reverse roller coating is used to transform the polyurethane casting slurry, which has been optimized in the previous process, into a wet film with a highly accurate and uniform thickness.

[0024] In technical solution seven, the dry film thickness of the final polyurethane film is controlled within a specific range of 0.01-0.02 mm to achieve a good balance between moisture permeability and mechanical strength.

[0025] In technical solution eight, a cooling roller at 0-5℃ is used to rapidly shape the dried high-temperature polyurethane film, instantly fixing and preserving the stable microporous structure formed in the third drying process. When the polyurethane film leaves the third drying tunnel, its temperature is much higher than its glass transition temperature, and its polymer chains are still in a mobile state. If it is allowed to cool slowly and naturally, the continuous movement and rearrangement of the molecular chains may cause the already formed fine micropores to collapse or shrink to a certain extent, thereby impairing the film's moisture permeability. The use of a rapid cooling roller allows the film temperature to drop sharply below its glass transition temperature in a very short time, instantly suppressing the mobility of the polymer chains, thus ensuring that the film with a specific microstructure constructed in the aforementioned steps can be completely preserved in the final polyurethane film product.

[0026] In technical solution nine, the polyurethane film is cured in a constant temperature and humidity environment to further release and homogenize the residual stress inside the film, thereby improving the dimensional stability and long-term reliability of the final product.

[0027] Technical solution ten provides a fabric comprising a base fabric and a polyurethane film prepared by the above method. The polyurethane film is bonded to the base fabric by dispensing adhesive. This fabric can achieve a good balance between high-efficiency moisture permeability and effective windproofing, which is reflected in the final functional clothing. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments are briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the microstructure of the polyurethane membrane prepared by the method for preparing the windproof and moisture-permeable polyurethane membrane according to Embodiment 1 of the present invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] In the claims and description of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0032] This invention relates to a fabric comprising a base fabric, on one side of which a polyurethane membrane, prepared using the method described in this invention for creating a windproof and breathable polyurethane membrane, is bonded together with adhesive. Specifically, the base fabric can be made of 50D polyester plain weave fabric, a widely used basic material in the clothing industry known for its good strength and softness.

[0033] The lamination process utilizes a hot melt adhesive dot-matrix lamination device. The specific steps of this lamination process are as follows: The polyurethane membrane is introduced into the lamination device. Moisture-curing polyurethane (PUR) hot melt adhesive is selected as the binder. This adhesive is heated and melted into a liquid state at 110-120℃. The liquid hot melt adhesive is uniformly transferred to one side of the polyurethane membrane in a discrete dot-like pattern through an engraving roller with precisely etched dots on its surface. By controlling the dot density of the engraving roller, the coverage of the adhesive dots on the membrane surface is precisely controlled to approximately 25%. Subsequently, a 50D polyester plain weave fabric is guided through guide rollers, aligned and bonded to the polyurethane membrane surface coated with the dot-matrix adhesive. This initial composite is then passed through a set of hot press rollers set to a temperature of 65℃ and a pressure of 0.7MPa. The hot press rollers apply uniform pressure and moderate heat, causing the dot-matrix PUR adhesive to fully wet and penetrate into the fiber gaps of the polyester fabric, thereby forming strong physical bonds with the polyurethane membrane. The entire lamination process is carried out continuously at a speed of 15-20 meters per minute. Finally, the laminated fabric is rolled up and left at room temperature for 48-72 hours for final curing. During this period, the PUR adhesive undergoes a chemical cross-linking reaction with moisture in the air, further enhancing the bonding strength and durability, ultimately resulting in the finished windproof and breathable fabric.

[0034] The preparation method of the aforementioned windproof and moisture-permeable polyurethane membrane includes the following steps:

[0035] Step S10: Mix and stir the polyurethane resin with N,N-dimethylformamide solvent until the polyurethane resin is completely dissolved to obtain polyurethane casting slurry;

[0036] Step S20: Coat the surface of the release paper with polyurethane casting slurry to form a wet film, and dry the wet film in three stages through drying tunnels with different temperature zones; in the first drying stage, stay in the first temperature zone of 60-80℃ for 1-2 minutes; in the second drying stage, stay in the second temperature zone of 90-120℃ for 3-5 minutes; in the third drying stage, stay in the third temperature zone of 120-160℃ for 6-8 minutes.

[0037] Step S30: Use a cooling roller with a temperature of 0-5℃ to quickly set the dried polyurethane film;

[0038] Step S40: Cure the polyurethane film in a constant temperature and humidity environment for 24-72 hours.

[0039] The following is a detailed explanation of step S10.

[0040] The specific implementation of this step involves precisely proportioning and uniformly mixing the components of the polyurethane casting slurry to achieve a state suitable for subsequent coating processes. The preparation process is carried out in a reactor equipped with a temperature-controlled jacket and a mechanical stirrer. First, each material is precisely weighed according to the ratio of 80 to 90 parts by weight of polyurethane resin, 100 to 120 parts by weight of N,N-dimethylformamide solvent, and 0.5 to 1 part by weight of leveling agent. During operation, a measured amount of N,N-dimethylformamide solvent and leveling agent are first added to the reactor, and medium-speed stirring is started. Subsequently, while stirring, the weighed solid polyurethane resin is slowly added to the solvent in batches.

[0041] After all materials have been added, activate the heating function of the temperature-controlled jacket to raise the temperature of the materials inside the reactor to the range of 50-60℃ and maintain it at this temperature. Continuously perform mechanical stirring at a speed sufficient to create a stable vortex on the liquid surface without excessively introducing air. Under these temperature and stirring conditions, the polyurethane resin gradually dissolves in the N,N-dimethylformamide solvent. The entire dissolution process lasts 2 to 3 hours, during which time samples need to be taken periodically from the reactor to monitor the viscosity of the slurry using a rotational viscometer. By precisely controlling the initial feed ratio and ensuring complete dissolution of the polyurethane resin, the final slurry viscosity stabilizes within the target range of 1500±200 mPa·s.

[0042] Once it is confirmed that the polyurethane resin has completely dissolved, the slurry is uniform and transparent, and the viscosity reaches the specified range, heating is stopped, but low-speed stirring can continue to allow the slurry to cool naturally to room temperature. After cooling, the slurry is removed from the reactor and transferred to a vacuum degassing device. A vacuum is applied inside the device to remove the tiny air bubbles introduced into the slurry during the previous mixing and stirring process. The vacuum degassing process continues until no new air bubbles are observed escaping from the slurry bulk. After this step, a uniform, bubble-free polyurethane casting slurry with suitable viscosity is obtained, ready for subsequent coating in step S20.

[0043] The following provides a detailed explanation of step S20.

[0044] This step is the core of the entire preparation method, transforming the liquid polyurethane casting slurry into a solid film with a specific microporous structure. This step consists of two closely linked processes: high-precision coating and programmed segmented drying, all completed on a continuous coating production line.

[0045] The first step is the coating process. This process uses a reverse roller coater to ensure high uniformity and precision in wet film thickness. Before operation, the key components of the reverse roller coater need to be precisely set. This includes calibrating the gap between the coating roller and the metering roller using a micrometer or feeler gauge. Precise setting of this gap, combined with the solid content of the polyurethane casting slurry determined in the previous steps, is fundamental to controlling the final dry film thickness of the polyurethane film. The goal of setting the process parameters is to ensure that after the N,N-dimethylformamide solvent is completely evaporated in the subsequent drying process, the resulting solid dry film thickness falls precisely within the target range of 0.01 to 0.02 mm. The bubble-free polyurethane casting slurry prepared in the previous step S10 is pumped into the coating machine's feed trough. At the start of coating, the coating roller rotates in the feed trough at the set speed, carrying a layer of slurry on its surface. Simultaneously, a metering roller parallel to the coating roller and with a calibrated gap rotates in the opposite direction or at a different speed, scraping away excess slurry from the coating roller surface, leaving only a highly uniform slurry film with a thickness equal to the set gap. Subsequently, the continuously traveling release paper substrate, supported by the back roller, comes into contact with the surface of the coating roller carrying the slurry. Because the rotation direction of the coating roller is opposite to the forward direction of the release paper, the slurry is smoothly and completely transferred from the coating roller to the release paper surface at this contact point, forming a macroscopically flawless wet film. Throughout the coating process, the unwinding and rewinding tensions of the release paper are maintained constant by an independent tension control system to prevent wrinkles or stretching of the substrate during its journey, thereby ensuring consistent wet film thickness throughout the process.

[0046] After the coating process is completed, the release paper carrying a uniform wet film is immediately and without contact introduced into a long-channel, multi-temperature zone horizontal hot air drying tunnel to begin three-stage drying.

[0047] The first drying process takes place in the entrance area of ​​the drying tunnel. The length of this area is precisely calculated to match the production line's travel speed, ensuring the wet film remains in this zone for 1 to 2 minutes. This zone is equipped with independent electric heating elements or heat exchangers, and the temperature is monitored in real time by multiple thermocouple sensors. Data from these sensors is fed back to the central PLC control system, which uses a PID algorithm to adjust the heating power, precisely stabilizing the air temperature in this zone within the target range of 60-80℃. Simultaneously, a circulating fan in this zone blows heated air evenly onto the wet film surface at a moderate speed through a series of specially designed nozzles, ensuring uniform heat transfer while preventing excessive airflow from disturbing the liquid film surface. The main task of this stage is to gently remove some of the solvent from the wet film surface, preparing it for subsequent processes.

[0048] The wet film travels continuously with the release paper, passing through the isolation zone between the first and second temperature zones, and enters the second drying process. This temperature zone is an independent temperature control unit, whose temperature control system stabilizes the temperature in this area at 90-120℃. Similarly, the length of this zone determines the residence time of the wet film there, which is 3 to 5 minutes. At this temperature, the solvent evaporation rate increases dramatically, which is a crucial stage for the formation of the microporous structure. To cope with the generation of a large amount of solvent vapor, the exhaust system in this zone increases its suction capacity accordingly to maintain a stable micro-negative pressure environment within the drying tunnel and ensure that the solvent vapor is efficiently discharged. During this stage, the physical state of the wet film transforms from a completely liquid state to a gel state, and the internal microporous network structure is formed.

[0049] Finally, the semi-cured film enters the third drying stage. This temperature zone, as the final section of the drying tunnel, is set at its highest level of 120-160°C. The wet film remains here for 6 to 8 minutes. The purpose of this stage is twofold: firstly, to utilize the energy provided by the high temperature to completely remove the last remaining solvent bound within the polymer network; secondly, to allow the polyurethane polymer chains constituting the microporous framework to fully relax and rearrange in an environment above their glass transition temperature, thereby eliminating internal stress and stabilizing the formed microporous structure. When the release paper carrying the completely dried polyurethane film leaves the outlet of the third temperature zone, step S20 is complete. Although the polyurethane film is now solid, its temperature is still high, and its structure is not yet fully locked, requiring immediate processing in step S30.

[0050] The following provides a detailed explanation of step S30.

[0051] This step involves forced and rapid cooling of the high-temperature polyurethane film exiting the third drying tunnel. This process is accomplished by one or a set of precision cooling rollers, which are installed directly downstream of the drying tunnel outlet to ensure that the polyurethane film immediately enters the cooling process after leaving the high-temperature environment, avoiding slow and uncontrolled natural cooling in the air.

[0052] The cooling roller has a hollow structure with spiral-shaped flow channels inside, allowing the cooling medium to flow efficiently and evenly through the roller body. The roller surface undergoes precision grinding and chrome plating to achieve a high degree of smoothness and hardness, ensuring good contact with the release paper and preventing condensation. The cooling roller is connected via piping to an independent industrial chiller or refrigeration unit, forming a closed-loop circulation system. This system uses a mixture of, for example, ethylene glycol and water as the cooling medium, which is forcibly cooled and maintained within a target range of 0 to 5°C by the refrigeration unit. Driven by a circulating pump, the cooling medium continuously flows through the internal channels of the cooling roller, carrying away heat from the roller surface and thus maintaining a constant surface temperature at the set value. A surface temperature sensor is installed on the roller, feeding real-time temperature data back to the control system. The system then adjusts the power of the refrigeration unit or the flow rate of the cooling medium to achieve precise closed-loop control of the roller surface temperature.

[0053] During production, release paper carrying a high-temperature polyurethane film (approximately 120-160°C) exits the drying tunnel and is immediately guided to wrap around and adhere tightly to the surface of a rotating cooling roller at a specific angle. The tension control system on the production line ensures the release paper adheres tightly to the roller surface with appropriate tension, eliminating air gaps between the film and the roller surface and maximizing heat transfer efficiency. When the high-temperature polyurethane film comes into contact with the 0-5°C cold roller surface, the significant temperature difference generates extremely high heat flux, causing the heat from the film to be rapidly and forcibly dissipated. During this process, the temperature of the polyurethane film drops rapidly from a state far above its glass transition temperature to a state far below its glass transition temperature within a very short time (usually within a few seconds).

[0054] This rapid cooling process instantly suppresses the mobility of the polyurethane polymer chains that make up the microporous framework, transforming them from an active, elastic state to a frozen, glassy state. After rapid cooling and shaping, the microstructure of the polyurethane film is stabilized, and it leaves the cooling roller along with the release paper, entering the curing stage in step S40.

[0055] The following provides a detailed explanation of step S40.

[0056] This step is a final stress-relieving and performance-stabilizing treatment for the rapidly cooled and shaped polyurethane film. This process is carried out in a dedicated curing chamber or constant temperature and humidity chamber with strictly controlled environmental parameters. Its purpose is to eliminate residual stresses inevitably generated within the polymer material during the aforementioned processing, thereby ensuring that the final film product has excellent dimensional stability and long-term reliability.

[0057] The curing chamber is a sealed space equipped with an industrial-grade environmental control system. This system integrates precision air conditioning, humidifiers, dehumidifiers, and air circulation fans. Multiple high-precision temperature and humidity sensors distributed throughout the chamber feed real-time environmental data back to the central PLC control system. Through a closed-loop control algorithm, the system continuously adjusts the cooling / heating power of the air conditioning and the operation of the humidifiers / dehumidifiers, thereby precisely and constantly maintaining the indoor temperature and relative humidity within preset process parameter ranges. For example, the temperature can be set at 23±2℃, and the relative humidity at 60±5%RH. The continuous operation of the air circulation fans ensures a uniform temperature and humidity field throughout the chamber, avoiding localized environmental differences.

[0058] In practice, the polyurethane film rolls (along with their release paper substrate) wound on the core and coming off the cooling roller station in step S30 are transferred off the production line as a whole. These film rolls are carefully placed on dedicated storage racks or A-frames. The racks are designed to ensure that the film rolls do not come into contact with each other, and that the rolls are supported only by the cores or edges at both ends, avoiding compression deformation or contact damage due to their own weight. Direct stacking of film rolls is strictly prohibited, as this will create irreversible indentations and stress concentration.

[0059] The storage rack containing the membrane rolls was moved into a curing chamber pre-set at the set temperature and humidity, and the sealed door was closed. Timing was then initiated. In this constant temperature and humidity environment, the membrane rolls were left to stand for 24 to 72 hours. Under constant temperature and humidity, slightly above room temperature, and moderate humidity, the polymer chains fixed under high stress acquired slight mobility, allowing for small-scale, slow creep and rearrangement. This microscopic movement gradually released and redistributed the internal non-uniform stress locked during rapid cooling, ultimately reaching a lower-energy, more balanced state.

[0060] After the curing time reaches the preset value of 24 to 72 hours, open the curing chamber door and remove the storage rack. At this point, the internal stress of the polyurethane film has been fully eliminated, and its dimensional stability has been significantly improved. This means that during subsequent slitting, lamination, or other processing, the film will not shrink, curl, or wrinkle due to stress release. The polyurethane film treated in this final step is a qualified and stable intermediate product, which can be used at any time to laminate with the base fabric to prepare the final functional fabric.

[0061] To further illustrate the technical solutions involved in this invention, the following embodiments and comparative examples are provided. It should be noted that the following embodiments and comparative examples do not constitute a limitation of this invention.

[0062] To make the description of the present invention clearer and more reproducible, the main raw materials used in the following embodiments and comparative examples are as follows:

[0063] Polyurethane resin: Polyester-type thermoplastic polyurethane elastomer produced by BASF (Germany), brand name: 1185A.

[0064] N,N-Dimethylformamide (DMF): Analytical grade (AR) solvent produced by Sinopharm Chemical Reagent Co., Ltd., with a purity ≥99.5%.

[0065] Leveling agent: A silicone surfactant manufactured by Dow Chemical Company, USA, brand name Dow. Q2-5211 Superwetting Agent.

[0066] The non-porous polyurethane membrane used in Comparative Example 1 was a commercially available, dense waterproof polyurethane membrane manufactured by Dongguan Weixin Polymer Materials Co., Ltd., model WX-2010, with a thickness of 10μm and an areal density of 10g / m³. 2 .

[0067] Base fabric: All fabrics are 50D*50D polyester plain weave fabric with an areal density of 75g / m². 2 .

[0068] Adhesive: Henkel moisture-curing polyurethane hot melt adhesive (PUR) TECHNOMELT PUR 270 / 7 is used.

[0069] Example 1

[0070] (1) Step S10: In a reactor, 85 parts by weight of polyester-type thermoplastic polyurethane elastomer, 110 parts by weight of DMF, and 0.8 parts by weight of silicone surfactant are mixed. The mixture is stirred at medium speed for 2.5 hours at 55°C until the polyurethane resin is completely dissolved. The viscosity of the obtained polyurethane casting slurry is measured to be 1550 mPa·s. The slurry is then subjected to vacuum degassing treatment.

[0071] (2) Step S20: The slurry obtained in step (1) is coated onto the surface of the release paper using a reverse roller coater, and the coating gap is set so that the final dry film thickness is 0.015 mm. Then the wet film is sent into a three-stage drying tunnel for drying. First stage: 70℃, 1.5 minutes. Second stage: 110℃, 4 minutes. Third stage: 140℃, 7 minutes.

[0072] (3) Step S30: Use a cooling roller with a surface temperature of 2℃ for rapid cooling and shaping.

[0073] (4) Step S40: Grind at 23°C and 60% RH for 48 hours.

[0074] (5) The obtained polyurethane film is laminated by dispensing process to obtain fabric sample.

[0075] Example 2

[0076] (1) Step S10: Mix 80 parts by weight of polyester thermoplastic polyurethane elastomer, 100 parts by weight of DMF and 0.5 parts by weight of silicone surfactant. Stir at 50°C for 3 hours to obtain a slurry with a viscosity of 1320 mPa·s. Perform vacuum degassing.

[0077] (2) Step S20: Coating, setting the coating gap to achieve a final dry film thickness of 0.01 mm. Three-stage drying. First stage: 60°C, 2 minutes. Second stage: 90°C, 5 minutes. Third stage: 120°C, 8 minutes.

[0078] (3) Step S30: Cooling is performed using a cooling roller with a surface temperature of 5°C.

[0079] (4) Step S40: Mature for 24 hours.

[0080] (5) The composite material is used to obtain a fabric sample.

[0081] Example 3

[0082] (1) Step S10: Mix 90 parts by weight of polyester thermoplastic polyurethane elastomer, 120 parts by weight of DMF and 1.0 part by weight of silicone surfactant. Stir at 60°C for 2 hours to obtain a slurry with a viscosity of 1680 mPa·s. Perform vacuum degassing.

[0083] (2) Step S20: Coating, setting the coating gap to achieve a final dry film thickness of 0.02 mm. Three-stage drying. First stage: 80℃, 1 minute. Second stage: 120℃, 3 minutes. Third stage: 160℃, 6 minutes.

[0084] (3) Step S30: Cooling is performed using a cooling roller with a surface temperature of 0℃.

[0085] (4) Step S40: Mature for 72 hours.

[0086] (5) The composite material is used to obtain a fabric sample.

[0087] Comparative Example 1

[0088] This comparative example aims to simulate fabrics prepared using conventional dense non-porous membranes in existing technologies.

[0089] A commercially available dense waterproof polyurethane membrane was laminated with a base fabric using the same dispensing and lamination process as in Example 1 to obtain a fabric sample.

[0090] Comparative Example 2

[0091] This comparative example aims to demonstrate the non-obviousness of the "three-stage drying" process in this invention compared to conventional processes in the art.

[0092] (1) Step S10: Prepare polyurethane casting slurry exactly according to the formulation and operation of Example 1.

[0093] (2) Step S20: The same coating settings as in Example 1 are used. The difference is that a single-stage high-temperature rapid drying method, which is commonly used by those skilled in the art for the purpose of pursuing efficiency, is adopted: the wet film is directly sent into a single-temperature zone drying tunnel, the temperature is set at 140°C, and it stays for 9 minutes.

[0094] (3) Steps S30 and S40: are exactly the same as in Example 1.

[0095] (4) Composite to obtain fabric samples.

[0096] Comparative Example 3

[0097] This comparative example is intended to demonstrate, in isolation, the necessity and key role of the first low-temperature process in the "three-stage drying" of this invention.

[0098] (1) Step S10: Prepare polyurethane casting slurry exactly according to the formulation and operation of Example 1.

[0099] (2) Step S20: The same coating settings as in Example 1 are used. The difference is that the first low-temperature drying process is omitted. The wet film is directly sent into the drying tunnel with the temperature set at 110°C and stays for 5.5 minutes (1.5 + 4 minutes). Then it enters the third drying process at 140°C and stays for 7 minutes.

[0100] (3) Steps S30 and S40: are exactly the same as in Example 1.

[0101] (4) Composite to obtain fabric samples.

[0102] Comparative Example 4

[0103] This comparative example is intended to demonstrate, in isolation, the necessity and key role of the third high-temperature process in the "three-stage drying" of this invention.

[0104] (1) Step S10: Prepare polyurethane casting slurry exactly according to the formulation and operation of Example 1.

[0105] (2) Step S20: The same coating settings as in Example 1 are used. The difference is that the third high-temperature drying process is omitted. After the wet film has been dried in the first stage (70°C, 1.5 minutes) and the second stage (110°C, 4 minutes), it is considered that the solvent has basically evaporated and it is directly sent to cooling.

[0106] (3) Steps S30 and S40: are exactly the same as in Example 1.

[0107] (4) Composite to obtain fabric samples.

[0108] The final fabric samples obtained from Examples 1-3 and Comparative Examples 1-4 were subjected to performance testing according to the following Chinese national standards:

[0109] (1) Moisture permeability: Tested according to Method A (calcium chloride method) in GB / T 12704.1-2009 "Textiles - Test Methods for Moisture Permeability of Fabrics - Part 1: Moisture Absorption Method".

[0110] (2) Air permeability: Tested according to GB / T 5453-1997 "Textiles - Determination of Air Permeability of Fabrics". Test conditions: pressure difference 100 Pa, test area 20 cm². 2 .

[0111] (3) Hydrostatic pressure resistance: Tested according to GB / T 4744-2013 "Test and evaluation of waterproof performance of textiles - hydrostatic pressure method".

[0112] The test results are as follows:

[0113]

[0114] Reference Figure 1 By comparing Examples 1-3 with Comparative Example 1 (Prior Art), it can be seen that the fabric prepared by the present invention has a moisture permeability (7530-8160) that is more than 2.3 times that of conventional non-porous membrane fabrics (3200), greatly solving the problem of stuffiness and dampness pointed out in the background art. At the same time, although its air permeability (9.8-13.5) is higher than that of dense membranes, it is still at a very low level, providing effective windproof performance. This indicates that the present invention has successfully achieved a good balance between high-efficiency moisture permeability and effective windproofing.

[0115] Comparative Example 2 used the exact same raw materials as Example 1, but employed a conventional process most readily conceived by those skilled in the art (single-stage high-temperature rapid drying). The resulting performance was almost indistinguishable from that of a conventional non-porous membrane (Comparative Example 1). This demonstrates that the raw material formulation of this invention alone is far from sufficient; the beneficial effects of this invention do not derive from a simple combination of raw materials, but rather rely on its unique, non-obvious "three-stage drying" process. Comparative Example 3 omitted the first low-temperature step, and its moisture permeability (3810) was significantly lower than that of Example 1. This demonstrates that the first stage of gentle drying is indispensable for preventing surface crusting and reserving channels for subsequent pore formation, and is not a dispensable preheating step. Comparative Example 4 omitted the third high-temperature step, and its moisture permeability (4250) was also significantly lower than that of Example 1. This demonstrates that the third high-temperature step is crucial for stabilizing the microporous structure and preventing its collapse during cooling, and is not simply for removing residual solvent. These two comparative examples together demonstrate that the "three-stage drying" of this invention is an organic, interconnected whole. Its three stages are interdependent and indispensable, together forming the complete technical logic for achieving the final effect.

[0116] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A method for preparing a windproof and moisture-permeable polyurethane membrane, characterized in that, Includes the following steps: Step S10: Mix and stir the polyurethane resin with N,N-dimethylformamide solvent until the polyurethane resin is completely dissolved to obtain polyurethane casting slurry; Step S20: The polyurethane casting slurry is coated onto the surface of the release paper to form a wet film, and the wet film is dried in three stages through drying tunnels with different temperature zones; in the first drying stage, the film stays in the first temperature zone of 60-80℃ for 1-2 minutes; in the second drying stage, the film stays in the second temperature zone of 90-120℃ for 3-5 minutes; in the third drying stage, the film stays in the third temperature zone of 120-160℃ for 6-8 minutes.

2. The method for preparing a windproof and moisture-permeable polyurethane membrane as described in claim 1, characterized in that, in In step S10, a leveling agent is also added to the polyurethane resin and N,N-dimethylformamide solvent; wherein the weight ratio of the polyurethane resin, N,N-dimethylformamide solvent and leveling agent is 80-90:100-120:0.5-1.

3. The method for preparing a windproof and moisture-permeable polyurethane membrane as described in claim 2, characterized in that, The mixing and stirring process in step S10 is carried out at a temperature of 50-60℃.

4. The method for preparing a windproof and moisture-permeable polyurethane membrane as described in claim 1, characterized in that, in In step S10, the viscosity of the polyurethane casting slurry is 1500±200 mPa·s.

5. The method for preparing a windproof and moisture-permeable polyurethane membrane as described in claim 1, characterized in that, After step S10 and before step S20, a step of vacuum degassing the polyurethane casting slurry is also included.

6. The method for preparing a windproof and moisture-permeable polyurethane membrane as described in claim 1, characterized in that, In step S20, the polyurethane casting slurry is coated onto the surface of the release paper using a reverse roll coating method.

7. The method for preparing a windproof and moisture-permeable polyurethane membrane as described in claim 1, characterized in that, In step S20, the dry film thickness of the polyurethane film formed after the three-stage drying process is 0.01-0.02 mm.

8. The method for preparing a windproof and moisture-permeable polyurethane membrane as described in claim 1, characterized in that, in Step S20 is followed by step S30: using a cooling roller with a temperature of 0-5℃ to quickly shape the dried polyurethane film.

9. The method for preparing a windproof and moisture-permeable polyurethane membrane as described in claim 8, characterized in that, After step S30, step S40 is also included: curing the polyurethane film in a constant temperature and humidity environment for 24-72 hours.

10. A fabric comprising a base fabric, characterized in that, One side surface of the base fabric is bonded with a polyurethane membrane prepared by the method described in any one of claims 1-9 using adhesive bonding.

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