Preparation method of non-fluffy waterproof moisture-permeable TPU (thermoplastic polyurethane) film

Abstract

The invention provides a preparation method of a non-bulking waterproof moisture-permeable TPU film, and belongs to the technical field of TPU film preparation, and the preparation method of the non-bulking waterproof moisture-permeable TPU film comprises the following steps: stirring raw materials by a high-speed mixer for mechanical mixing; carrying out chemical reaction on the raw material, a divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene, and adding tetrahydrofuran to adjust the viscosity of a reaction system, so as to obtain a TPU film material; heating, pressurizing and extruding the mixture through a screw extruder to form a film, plasticizing TPU particles into a semi-finished product, and filtering impurities and re-plasticizing on a filter of calendering equipment; carrying out annealing treatment, cooling in cold water, and pulling out the cooled TPU stretching film from a demolding opening of the demolding machine; the problems that an existing TPU film is poor in preparation size stability and prone to deformation can be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of TPU film preparation, and in particular relates to a method for preparing a non-swelling, waterproof and moisture-permeable TPU film. Background Art

[0002] Demand for films that combine waterproofness and moisture permeability continues to rise across a wide range of sectors, including outdoor apparel, medical protective gear, tents, and footwear. For example, outdoor gear like hiking boots and jackets must protect against external wind and rain while ensuring internal perspiration is released for comfort. Medical protective clothing is no different: while providing a protective barrier, it must also be breathable and moisture-wicking to prevent medical workers from becoming overheated. While conventional TPU films offer excellent elasticity, abrasion resistance, and mechanical strength, they struggle to achieve both waterproofness and moisture permeability. Some TPU films that enhance moisture permeability by adding inorganic fillers such as bentonite suffer from complex processing, high costs, and unstable film performance due to uneven bentonite dispersion. For example, excessive bentonite addition can make TPU films brittle, affecting their tensile strength and durability. Furthermore, after prolonged use, the bentonite's water absorption can cause it to swell, disrupting the film's microstructure and reducing its waterproofing performance. With growing environmental awareness, attention is being paid to the environmental sustainability of both the production process and the product itself. In the preparation of traditional TPU films containing bentonite, the mining and processing of bentonite pose environmental pollution risks, and the bentonite in the discarded films is also difficult to degrade, causing a long-term burden on the environment.

[0003] The existing TPU films have poor dimensional stability and are prone to deformation. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing a non-swelling waterproof and breathable TPU film, which can solve the problem that the existing TPU film has poor dimensional stability and is prone to deformation.

[0005] The present invention is achieved in that:

[0006] The present invention provides a method for preparing a non-swelling waterproof and breathable TPU film, wherein the specific steps include:

[0007] S10: Select TPU resin, add plasticizer, stabilizer, additive, cellophane, and polytetrafluoroethylene in proportion to form a preparation raw material;

[0008] S20: The raw materials are mechanically mixed by stirring with a high-speed mixer to ensure that the ingredients are fully mixed;

[0009] S30: chemically reacting the raw materials with divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene, adding tetrahydrofuran to adjust the viscosity of the reaction system, and recovering the tetrahydrofuran by vacuum distillation after the reaction is completed to obtain a TPU film material;

[0010] S40: The mixed material is heated and pressurized through a screw extruder to form a film, the TPU particles are plasticized into a semi-finished product, and the impurities are filtered and plasticized again on the filter of the calendering equipment;

[0011] S50: Perform annealing treatment and cool in cold water. The cooled TPU stretch film is pulled out from the demoulding port of the demoulding machine.

[0012] S60: Chemical etching is used to form a tiny pore structure in the TPU film, and then the film is cut, shaped, and wound into a roll.

[0013] On the basis of the above technical solution, the preparation method of a non-swelling waterproof and breathable TPU film of the present invention can also be improved as follows:

[0014] Among them, by weight ratio, TPU resin: plasticizer: stabilizer: additive: cellophane: polytetrafluoroethylene is 80-90: 5-15: 2-5: 1-3: 3-8: 2-6.

[0015] Furthermore, the specific steps of mechanically mixing the raw materials with a high-speed mixer to fully mix the ingredients include:

[0016] The first step is to accurately weigh various raw materials according to the ratio;

[0017] In the second step, TPU resin, plasticizer, stabilizer, additive, cellophane and polytetrafluoroethylene are placed in a drying oven and dried at 80-100°C for 4-6 hours to remove moisture from the raw materials and prevent defects such as material degradation or bubbles caused by moisture in the subsequent processing;

[0018] The third step is to put the dried raw materials into a high-speed mixer, set the stirring speed to 300-500 rpm, and the stirring time is about 10-15 minutes.

[0019] The fourth step is to put the evenly mixed mixture into a grinding equipment for grinding, and grind the mixture into fine particles with a particle size of about 100-200 mesh, so that the particles of the mixture are finer and more uniform, increase the surface area of ​​the mixture, and improve its fluidity and uniformity in the subsequent extrusion molding process, which is conducive to the preparation of TPU film with excellent performance.

[0020] Furthermore, the steps of chemically reacting the raw materials with the divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene, adding tetrahydrofuran to adjust the viscosity of the reaction system, and recovering the tetrahydrofuran by vacuum distillation after the reaction is completed to obtain the TPU film material include:

[0021] The first step is to add divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene to the stirred raw materials and continue stirring for 5-10 minutes to ensure that the ingredients are fully mixed;

[0022] The second step is to slowly add tetrahydrofuran to the mixed system to control the viscosity of the reaction system between 500-1000 mPa·s;

[0023] In the third step, the reaction system with adjusted viscosity is transferred to a reactor equipped with a stirring device and a temperature control device. The stirring device is turned on and the stirring speed is maintained at about 200-300 rpm. The reaction temperature is set between 60-80°C and the reaction time is about 4-6 hours. The double bonds in the divinylbenzene-ethyl acrylate-acrylamide copolymer undergo a cross-linking reaction with the active groups in the TPU molecular chain. Butylated hydroxytoluene prevents oxidative degradation of the TPU during the reaction, thereby forming a TPU film material with special properties.

[0024] Step 4: After the reaction is completed, the mixture in the reactor is subjected to vacuum distillation through a vacuum distillation apparatus, with the vacuum distillation temperature set at 40-60° C. and the pressure controlled at 10-30 mmHg;

[0025] The fifth step is to take out the initial product of TPU membrane material obtained by vacuum distillation.

[0026] Furthermore, the divinylbenzene-ethyl acrylate-acrylamide copolymer accounts for 10%-15% of the total reaction system, and butylated hydroxytoluene accounts for 1%-3% of the total reaction system.

[0027] Furthermore, the specific steps of heating and pressurizing the mixed material through a screw extruder to form a film, plasticizing the TPU particles into a semi-finished product, filtering impurities and plasticizing again on a filter of a calendering device include:

[0028] The first step is to start the screw extruder and set the temperature of each heating zone. The temperature of the feed section is set to 160-180°C, the temperature of the compression section is set to 190-210°C, the temperature of the homogenization section is set to 200-220°C, and the temperature of the die head is set to 210-230°C. The screw speed is set to 30-60 rpm, and the screw is operated slowly at low temperature for preheating.

[0029] In the second step, the dried mixture is evenly added into the hopper of the screw extruder through the feed port. Under the rotation of the screw, the mixture is transported forward and is melted and plasticized by the heat of the heating area.

[0030] In the third step, the TPU film blank extruded from the die enters the cooling device, which is a cooling roller or cooling water tank, to quickly cool and shape the TPU film blank.

[0031] The fourth step is to place the TPU particles into an internal mixer and perform internal mixing and plasticization at a temperature of 180°C-220°C for 5-10 minutes at a speed of 30-50 rpm. During the internal mixing process, the TPU particles are subjected to strong shearing, extrusion and stirring by the rotor of the internal mixer, gradually melting and plasticizing to form a uniform TPU melt. The molten TPU melt is discharged from the internal mixer and cooled by a cooling device to obtain a TPU semi-finished product.

[0032] The fifth step is to transport the TPU melt through the pipeline to the filter of the calendering equipment; the filter of the filter adopts a 100-200 mesh metal mesh or filter mesh to filter out impurities, unmelted particles and other foreign matter in the TPU melt; under the pressure of the calendering equipment, the TPU melt passes through the filter and the impurities are trapped on the filter;

[0033] In the sixth step, the filtered TPU melt is heated and stirred by the calendering equipment and plasticized again at a temperature of 190℃-230℃; the roller speed of the calendering equipment is 10-30 rpm. Through the extrusion and shearing action of the roller, the TPU melt is further plasticized and uniformed, while giving it better fluidity and processing performance, so that it can better meet the requirements of subsequent processing and molding.

[0034] Furthermore, the annealing treatment, cooling in cold water, and pulling the cooled TPU stretched film out from the demoulding port of the demoulding machine specifically include:

[0035] The first step is to place the TPU stretch film in an annealing furnace and start preheating. The preheating temperature of the annealing furnace is controlled at 60-80°C for 10-15 minutes. The temperature of the TPU stretch film is gradually increased to avoid excessive internal stress of the TPU stretch film due to rapid temperature changes.

[0036] In the second step, after preheating, the temperature of the annealing furnace is raised to 100-120°C for annealing. The annealing time is 30-60 minutes. During the annealing process, the molecular chains of the TPU stretch film gradually relax and the internal stress is released, thereby improving the dimensional stability and mechanical properties of the TPU film. During the annealing process, the temperature in the annealing furnace is kept uniform to avoid local overheating or uneven temperature.

[0037] The third step is to close the annealing furnace after annealing is completed, and the TPU stretch film is naturally cooled to room temperature in the furnace. During the natural cooling process, the annealing furnace door is kept closed to prevent the rapid inflow of outside air from causing temperature difference stress on the surface of the TPU stretch film.

[0038] Step 4: Prepare a cold water tank in the cooling device, inject an appropriate amount of cold water into the tank, and control the water temperature at 10-20°C. The size of the cold water tank should be able to accommodate the TPU stretch film and ensure that the TPU stretch film can be completely immersed in the water in the cold water tank.

[0039] Step 5: Slowly place the annealed TPU stretch film into a cold water tank to keep it flat and uniform to avoid wrinkles or distortion.

[0040] Step 6: Soak the TPU stretch film in cold water for 5-10 minutes to fully cool it down;

[0041] Step 7: Install the pulling roller at the demoulding port of the demoulding machine and adjust the position and angle of the demoulding device to make it consistent with the discharge direction of the TPU stretch film;

[0042] In the eighth step, the cooled TPU stretch film is taken out from the cold water tank and placed at the feed port of the demoulding machine; the demoulding machine is started, and the TPU stretch film is pulled out from the demoulding port through the traction action of the demoulding device.

[0043] Furthermore, the specific steps of forming a microporous structure in the TPU film by chemical etching, cutting and shaping the film, and winding the film into a roll include:

[0044] The first step is to heat the chemical etching solution to 40°C-60°C to increase its activity and reaction rate;

[0045] The second step is to slowly and evenly place the TPU film into the chemical etching solution, ensuring that the film is completely immersed in the solution; the immersion time is 10-30 minutes. During the immersion process, the chemical etchant reacts with the TPU film, gradually eroding the film surface and forming tiny holes;

[0046] The third step is to remove the chemically etched TPU film from the chemical etching solution and place it in a cleaning tank for cleaning. Wash it 2-3 times, each time for 5-10 minutes. After each cleaning, use a clean soft cloth or air gun to gently absorb the moisture on the surface of the film to avoid water stains.

[0047] The fourth step is to place the cleaned TPU film in a drying oven for drying. The drying temperature is controlled at 60°C-80°C and the drying time is 1-2 hours until the film is completely dry.

[0048] The fifth step is to use a laser cutting machine to cut; the cut TPU film is edge trimmed and the size is adjusted;

[0049] Step 6: Fix one end of the TPU film on the reel, start the winding equipment, and begin winding; the winding speed is controlled at 10-30 meters / minute.

[0050] Compared with the prior art, the method for preparing a non-swelling waterproof and breathable TPU film provided by the present invention has the following beneficial effects:

[0051] By selecting suitable TPU resin and adding plasticizers, stabilizers, additives, cellophane, polytetrafluoroethylene and other ingredients, and mixing them in proportion to form the preparation raw materials, a basic material guarantee is provided for the subsequent preparation of TPU film materials. The synergistic effect of each component helps to improve the performance of TPU film. For example, plasticizers can improve the flexibility of the film, stabilizers can enhance its stability, and cellophane and polytetrafluoroethylene may affect the surface properties of the film.

[0052] Using a high-speed mixer to stir the ingredients thoroughly and evenly ensures that the raw materials can evenly participate in the reaction and molding during the subsequent processing, avoiding the difference in film performance caused by uneven distribution of ingredients, and helping to improve the comprehensive performance of TPU film, such as the uniformity and stability of mechanical properties, waterproof and moisture permeability, etc.

[0053] The raw materials are chemically reacted with divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene, and tetrahydrofuran is added to adjust the viscosity of the reaction system. The tetrahydrofuran is then recovered by vacuum distillation to obtain a TPU film material. The double bonds in the divinylbenzene-ethyl acrylate-acrylamide copolymer undergo a cross-linking reaction with the active groups in the TPU molecular chain, forming a TPU film material with special properties and improving its molecular structure and performance. Butylated hydroxytoluene prevents oxidative degradation of the TPU during the reaction, ensuring smooth reaction and product quality. The addition of tetrahydrofuran to adjust viscosity facilitates a uniform reaction and subsequent processing and molding. Recovering the tetrahydrofuran by vacuum distillation removes the solvent, resulting in a relatively pure TPU film material while avoiding the impact of solvent residue on film performance and environmental protection.

[0054] The mixture is extruded into a film through a screw extruder under heating and pressure, plasticizing the TPU particles into a semi-finished product. Impurities are then filtered and plasticized again in the filter of the calendering equipment. The heated and pressurized extrusion process melts the TPU particles and forms a continuous membrane structure, initially shaping the film. The filter removes impurities, unmelted particles, and other foreign matter from the TPU melt, improving the purity and quality of the film. The plasticization further ensures the uniformity and fluidity of the TPU melt, laying the foundation for subsequent processing and improving film performance.

[0055] Annealing treatment can gradually relax the molecular chains of the TPU stretch film and release the internal stress, thereby improving the dimensional stability and mechanical properties of the TPU film and avoiding deformation or performance degradation of the film due to internal stress during use; cooling in cold water can quickly shape the TPU stretch film and maintain its shape and size; pulling it out from the demolding port of the demolding machine can achieve smooth demolding of the film, facilitating subsequent processing.

[0056] Chemical etching is used to form a tiny pore structure in the TPU film, giving the film moisture permeability. At the same time, cutting, shaping and winding the film into a roll can process the film into the required product form, which is convenient for storage, transportation and use, and meets the needs of different application scenarios.

[0057] The optimization of raw material ratios has clarified the weight ratio range of TPU resin to plasticizers, stabilizers, additives, cellophane, and polytetrafluoroethylene, and further finely controlled the content of each component, which helps to more accurately optimize the performance of TPU films. For example, on the basis of ensuring other properties, it can improve the balance of its comprehensive properties such as waterproof and breathable properties, mechanical properties, etc.

[0058] Accurately weighing the raw materials ensures the accuracy of the ratio; drying removes moisture from the raw materials, preventing defects such as material degradation or bubbles in subsequent processing, and ensuring product quality; high-speed stirring ensures that the ingredients are fully mixed and evenly distributed; grinding into fine particles increases the surface area of ​​the mixture, improving its fluidity and uniformity during the extrusion molding process, which is conducive to the preparation of higher quality, better performance and more uniform TPU films.

[0059] Continuous stirring ensures that the newly added copolymer and butylated hydroxytoluene are fully mixed with the raw materials; tetrahydrofuran is slowly added to accurately control the viscosity of the reaction system, ensuring the uniform progress of the reaction; the reaction is carried out in a reactor equipped with a stirring and temperature control device, and conditions such as stirring speed, reaction temperature and time are strictly controlled, which is conducive to the full cross-linking reaction between the copolymer and the TPU molecular chain, while ensuring that butylated hydroxytoluene effectively exerts its antioxidant effect, thereby obtaining a TPU membrane material with better performance; the temperature and pressure control of the reduced pressure distillation is conducive to the efficient recovery of tetrahydrofuran, ensuring the quality and purity of the TPU membrane material.

[0060] The temperature and screw speed of each heating zone are set to ensure that the screw extruder operates under appropriate conditions, ensuring uniform melting, plasticization and extrusion molding of the TPU mixture; the mixing process further improves the plasticization uniformity of the TPU particles, forming a higher-quality TPU melt; the selection of the filter and the filtration process effectively remove impurities and other foreign matter; the heating and stirring of the calendering equipment and the roller speed control, etc., make the TPU melt uniformly plasticized again, giving it better fluidity and processing performance, meeting the requirements of subsequent processing and molding, and improving the overall quality and performance of the film.

[0061] The preheating annealing furnace gradually heats up the TPU stretch film to avoid excessive internal stress caused by sudden temperature changes; the annealing temperature and time are strictly controlled to ensure sufficient relaxation of the molecular chains and release of internal stress, thereby improving dimensional stability and mechanical properties; natural cooling avoids the generation of temperature difference stress; the preparation and cooling operation of the cold water tank ensure that the TPU stretch film is fully cooled and shaped; the traction device and operation process of the demoulding machine realize the smooth demoulding of the TPU stretch film after cooling. The entire refinement process helps to produce high-quality and stable performance TPU film.

[0062] Heating the chemical etching solution can increase its activity and reaction rate, making the etching process more efficient and able to form a suitable micropore structure in a shorter time; controlling the immersion time ensures the degree of pore structure formation to achieve good moisture permeability; the cleaning and drying process completely removes residual chemical etchants and moisture, ensuring the quality and performance stability of the film; laser cutting, edge trimming and size adjustment ensure that the film meets the required product specifications and appearance requirements; controlling the winding speed is conducive to the neat winding of the film, facilitating subsequent use and processing. The entire complete process improves the product yield and quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 This is an operational flow chart of a method for preparing a non-swelling waterproof and breathable TPU film;

[0064] In the accompanying drawings, the components represented by the reference numerals are as follows: DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0066] like Figure 1 FIG. 1 is an operational flow chart of a method for preparing a non-swelling waterproof and breathable TPU film provided by the present invention. In the figure, the specific steps include:

[0067] S10: Select TPU resin, add plasticizer, stabilizer, additive, cellophane, and polytetrafluoroethylene in proportion to form a preparation raw material;

[0068] S20: The raw materials are mechanically mixed by stirring with a high-speed mixer to ensure that the ingredients are fully mixed;

[0069] S30: chemically reacting the raw materials with divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene, adding tetrahydrofuran to adjust the viscosity of the reaction system, and recovering the tetrahydrofuran by vacuum distillation after the reaction is completed to obtain a TPU film material;

[0070] S40: The mixed material is heated and pressurized through a screw extruder to form a film, the TPU particles are plasticized into a semi-finished product, and the impurities are filtered and plasticized again on the filter of the calendering equipment;

[0071] S50: Perform annealing treatment and cool in cold water. The cooled TPU stretch film is pulled out from the demoulding port of the demoulding machine.

[0072] S60: Chemical etching is used to form a tiny pore structure in the TPU film, and then the film is cut, shaped, and wound into a roll.

[0073] Wherein, in the above technical solution, the weight ratio of TPU resin: plasticizer: stabilizer: additive: cellophane: polytetrafluoroethylene is 80-90:5-15:2-5:1-3:3-8:2-6.

[0074] TPU resin: 80-90 parts by weight.

[0075] Plasticizer: 5-15 parts by weight: Commonly used plasticizers include phthalates, fatty acid esters, etc., which can improve the flexibility and ductility of TPU film, making it easier to process and shape, while giving the film good softness and comfort.

[0076] Stabilizer: 2-5 parts by weight: such as antioxidants, light stabilizers, etc. Antioxidants can prevent TPU from degradation due to oxidation during processing and use. Light stabilizers can absorb ultraviolet rays, prevent ultraviolet rays from damaging TPU, and extend the service life of the film.

[0077] Additives: 1-3 parts by weight: such as lubricants, defoamers, flame retardants, etc. Lubricants can improve the processing fluidity of TPU and prevent the material from sticking in the processing equipment; defoamers can eliminate bubbles generated during the mixing process to ensure the uniformity and transparency of the film; flame retardants can improve the flame retardant properties of TPU film and meet the safety requirements of some special occasions.

[0078] Cellophane: 3-8 parts by weight: Cellophane has good transparency and air permeability. Adding it to TPU can improve the transparency and moisture permeability of the film, while giving the film a certain degree of stiffness.

[0079] Polytetrafluoroethylene: 2-6 parts by weight: Polytetrafluoroethylene has excellent properties such as high temperature resistance, wear resistance, and self-lubrication. Adding it to TPU can improve the film's surface hardness, wear resistance, and high temperature resistance, making it less susceptible to scratches and wear during use, extending its service life.

[0080] Furthermore, in the above technical solution, the raw materials are mechanically mixed by using a high-speed mixer to mix the ingredients thoroughly and evenly. The specific steps include:

[0081] The first step is to accurately weigh various raw materials according to the ratio;

[0082] In the second step, TPU resin, plasticizer, stabilizer, additive, cellophane and polytetrafluoroethylene are placed in a drying oven and dried at 80-100°C for 4-6 hours to remove moisture from the raw materials and prevent defects such as material degradation or bubbles caused by moisture in the subsequent processing;

[0083] The third step is to put the dried raw materials into a high-speed mixer, set the stirring speed to 300-500 rpm, and the stirring time is about 10-15 minutes.

[0084] The fourth step is to put the evenly mixed mixture into a grinding equipment for grinding, and grind the mixture into fine particles with a particle size of about 100-200 mesh, so that the particles of the mixture are finer and more uniform, increase the surface area of ​​the mixture, and improve its fluidity and uniformity in the subsequent extrusion molding process, which is conducive to the preparation of TPU film with excellent performance.

[0085] Furthermore, in the above technical solution, the raw materials are chemically reacted with divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene, tetrahydrofuran is added to adjust the viscosity of the reaction system, and after the reaction is completed, the tetrahydrofuran is recovered by vacuum distillation to obtain the TPU film material. The specific steps include:

[0086] The first step is to add divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene to the stirred raw materials and continue stirring for 5-10 minutes to ensure that the ingredients are fully mixed;

[0087] The second step is to slowly add tetrahydrofuran to the mixed system to control the viscosity of the reaction system between 500-1000 mPa·s;

[0088] In the third step, the reaction system with adjusted viscosity is transferred to a reactor equipped with a stirring device and a temperature control device. The stirring device is turned on and the stirring speed is maintained at about 200-300 rpm. The reaction temperature is set between 60-80°C and the reaction time is about 4-6 hours. The double bonds in the divinylbenzene-ethyl acrylate-acrylamide copolymer undergo a cross-linking reaction with the active groups in the TPU molecular chain. Butylated hydroxytoluene prevents oxidative degradation of the TPU during the reaction, thereby forming a TPU film material with special properties.

[0089] Step 4: After the reaction is completed, the mixture in the reactor is subjected to vacuum distillation through a vacuum distillation apparatus, with the vacuum distillation temperature set at 40-60° C. and the pressure controlled at 10-30 mmHg;

[0090] The fifth step is to take out the initial product of TPU membrane material obtained by vacuum distillation.

[0091] Furthermore, in the above technical solution, the divinylbenzene-ethyl acrylate-acrylamide copolymer accounts for 10%-15% of the total reaction system, and butylated hydroxytoluene accounts for 1%-3% of the total reaction system.

[0092] Furthermore, in the above technical solution, the mixed material is heated and pressurized to extrude into a film through a screw extruder, the TPU particles are plasticized into a semi-finished product, and the impurities are filtered and plasticized again on the filter of the calendering equipment. The specific steps include:

[0093] The first step is to start the screw extruder and set the temperature of each heating zone. The temperature of the feed section is set to 160-180°C, the temperature of the compression section is set to 190-210°C, the temperature of the homogenization section is set to 200-220°C, and the temperature of the die head is set to 210-230°C. The screw speed is set to 30-60 rpm, and the screw is operated slowly at low temperature for preheating.

[0094] In the second step, the dried mixture is evenly added into the hopper of the screw extruder through the feed port. Under the rotation of the screw, the mixture is transported forward and is melted and plasticized by the heat of the heating area.

[0095] In the third step, the TPU film blank extruded from the die enters the cooling device, which is a cooling roller or cooling water tank, to quickly cool and shape the TPU film blank.

[0096] The fourth step is to place the TPU particles into an internal mixer and perform internal mixing and plasticization at a temperature of 180°C-220°C for 5-10 minutes at a speed of 30-50 rpm. During the internal mixing process, the TPU particles are subjected to strong shearing, extrusion and stirring by the rotor of the internal mixer, gradually melting and plasticizing to form a uniform TPU melt. The molten TPU melt is discharged from the internal mixer and cooled by a cooling device to obtain a TPU semi-finished product.

[0097] The fifth step is to transport the TPU melt through the pipeline to the filter of the calendering equipment; the filter of the filter adopts a 100-200 mesh metal mesh or filter mesh to filter out impurities, unmelted particles and other foreign matter in the TPU melt; under the pressure of the calendering equipment, the TPU melt passes through the filter and the impurities are trapped on the filter;

[0098] In the sixth step, the filtered TPU melt is heated and stirred by the calendering equipment and plasticized again at a temperature of 190℃-230℃; the roller speed of the calendering equipment is 10-30 rpm. Through the extrusion and shearing action of the roller, the TPU melt is further plasticized and uniformed, while giving it better fluidity and processing performance, so that it can better meet the requirements of subsequent processing and molding.

[0099] Furthermore, in the above technical solution, the annealing treatment is performed, the film is placed in cold water for cooling, and the cooled TPU stretch film is pulled out from the demoulding port of the demoulding machine, specifically comprising:

[0100] The first step is to place the TPU stretch film in an annealing furnace and start preheating. The preheating temperature of the annealing furnace is controlled at 60-80°C for 10-15 minutes. The temperature of the TPU stretch film is gradually increased to avoid excessive internal stress of the TPU stretch film due to rapid temperature changes.

[0101] In the second step, after preheating, the temperature of the annealing furnace is raised to 100-120°C for annealing. The annealing time is 30-60 minutes. During the annealing process, the molecular chains of the TPU stretch film gradually relax and the internal stress is released, thereby improving the dimensional stability and mechanical properties of the TPU film. During the annealing process, the temperature in the annealing furnace is kept uniform to avoid local overheating or uneven temperature.

[0102] The third step is to close the annealing furnace after annealing is completed, and the TPU stretch film is naturally cooled to room temperature in the furnace. During the natural cooling process, the annealing furnace door is kept closed to prevent the rapid inflow of outside air from causing temperature difference stress on the surface of the TPU stretch film.

[0103] Step 4: Prepare a cold water tank in the cooling device, inject an appropriate amount of cold water into the tank, and control the water temperature at 10-20°C. The size of the cold water tank should be able to accommodate the TPU stretch film and ensure that the TPU stretch film can be completely immersed in the water in the cold water tank.

[0104] Step 5: Slowly place the annealed TPU stretch film into a cold water tank to keep it flat and uniform to avoid wrinkles or distortion.

[0105] Step 6: Soak the TPU stretch film in cold water for 5-10 minutes to fully cool it down;

[0106] Step 7: Install the pulling roller at the demoulding port of the demoulding machine and adjust the position and angle of the demoulding device to make it consistent with the discharge direction of the TPU stretch film;

[0107] In the eighth step, the cooled TPU stretch film is taken out from the cold water tank and placed at the feed port of the demoulding machine; the demoulding machine is started, and the TPU stretch film is pulled out from the demoulding port through the traction action of the demoulding device.

[0108] Furthermore, in the above technical solution, the specific steps of forming a microporous structure in the TPU film by chemical etching, cutting and shaping the film, and winding the film into a roll include:

[0109] The first step is to heat the chemical etching solution to 40°C-60°C to increase its activity and reaction rate;

[0110] The second step is to slowly and evenly place the TPU film into the chemical etching solution, ensuring that the film is completely immersed in the solution; the immersion time is 10-30 minutes. During the immersion process, the chemical etchant reacts with the TPU film, gradually eroding the film surface and forming tiny holes;

[0111] The third step is to remove the chemically etched TPU film from the chemical etching solution and place it in a cleaning tank for cleaning. Wash it 2-3 times, each time for 5-10 minutes. After each cleaning, use a clean soft cloth or air gun to gently absorb the moisture on the surface of the film to avoid water stains.

[0112] The fourth step is to place the cleaned TPU film in a drying oven for drying. The drying temperature is controlled at 60°C-80°C and the drying time is 1-2 hours until the film is completely dry.

[0113] The fifth step is to use a laser cutting machine to cut; the cut TPU film is edge trimmed and the size is adjusted;

[0114] Step 6: Fix one end of the TPU film on the reel, start the winding equipment, and begin winding; the winding speed is controlled at 10-30 meters / minute.

[0115] Example 1

[0116] Raw material selection and mixing (S10, S20): 80 parts of TPU resin, 6 parts of plasticizer, 3 parts of stabilizer, 2 parts of additive, 5 parts of cellophane, and 3 parts of polytetrafluoroethylene were selected, placed in a drying oven at 85°C for 5 hours, then placed in a high-speed blender and stirred at 350 rpm for 12 minutes, and then placed in a grinding equipment and ground to a particle size of about 150 mesh.

[0117] Chemical Reaction (S30): 12 parts of a divinylbenzene-ethyl acrylate-acrylamide copolymer and 2 parts of butylated hydroxytoluene were added to the above mixture. After stirring for 7 minutes, tetrahydrofuran was slowly added to control the viscosity to 700 mPa·s. The mixture was transferred to a reactor and stirred at 250 rpm and 70°C for 5 hours. After completion of the reaction, the mixture was distilled under reduced pressure to obtain a TPU film material.

[0118] Film Extrusion (S40): Start the screw extruder and set the feed section temperature to 170°C, the compression section to 200°C, the homogenization section to 210°C, the die head temperature to 220°C, and the screw speed to 40 rpm. The mixture is added to the hopper, and the extruded preform is cooled and shaped by chill rollers. Simultaneously, the TPU particles are mixed in an internal mixer at 200°C for 8 minutes at 40 rpm. After discharge, they are cooled to obtain a semi-finished product. A 150-mesh metal mesh is used for filtering. The filtered melt is plasticized again in the calendering equipment at 210°C, with a roller speed of 20 rpm.

[0119] Annealing and cooling demoulding (S50): Place the TPU stretch film in an annealing furnace, preheat to 70°C for 12 minutes, then heat to 110°C and anneal for 40 minutes. After natural cooling, soak in a 15°C cold water tank for 7 minutes, and finally pull it out with a demoulding machine.

[0120] Chemical etching and subsequent processing (S60): Heat the chemical etching solution to 50°C and soak the TPU film for 20 minutes. Remove the film and rinse it three times, each for 8 minutes, then dry it with a soft cloth. Dry it at 70°C for 1.5 hours, laser cut it, and trim it before winding it into a roll at a speed of 20 meters per minute.

[0121] Example 2

[0122] Raw material selection and mixing (S10, S20): Take 85 parts of TPU resin, 10 parts of plasticizer, 4 parts of stabilizer, 1.5 parts of additive, 6 parts of cellophane, and 4 parts of polytetrafluoroethylene, dry them, stir them at 400 rpm for 14 minutes, and grind them to a particle size of about 180 mesh.

[0123] Chemical Reaction (S30): 13 parts of a divinylbenzene-ethyl acrylate-acrylamide copolymer and 2.5 parts of butylated hydroxytoluene were added and stirred for 8 minutes. Tetrahydrofuran was added to increase the viscosity to 800 mPa·s. The mixture was reacted in a reactor at a stirring speed of 280 rpm and a temperature of 75°C for 4.5 hours. The mixture was then distilled under reduced pressure to obtain a TPU film material.

[0124] Film Extrusion (S40): The screw extruder temperature was set at 165°C for the feed section, 195°C for the compression section, 205°C for the homogenization section, and 225°C for the die head. The screw speed was 35 rpm. After the mixture was added, it was extruded and cooled to final shape. The TPU particles were mixed in an internal mixer at 190°C for 7 minutes at 35 rpm, then discharged and cooled to obtain a semi-finished product. The filter screen was 180 mesh, and the filtered melt was plasticized again in a calender at 200°C with a roller speed of 15 rpm.

[0125] Annealing and cooling demoulding (S50): Place the TPU stretch film in an annealing furnace, preheat to 65°C for 15 minutes, heat to 105°C and anneal for 35 minutes, cool naturally and soak in a 13°C cold water tank for 8 minutes, and then pull it out with a demoulding machine.

[0126] Chemical etching and subsequent treatment (S60): Heat the chemical etching solution to 55°C, soak the TPU film for 25 minutes, wash it three times, each time for 7 minutes, dry it at 75°C for 1.2 hours, cut and trim it, and then wind it at a speed of 25 meters per minute.

[0127] Example 3

[0128] Raw material selection and mixing (S10, S20): 90 parts of TPU resin, 5 parts of plasticizer, 2 parts of stabilizer, 1 part of additive, 3 parts of cellophane, and 2 parts of polytetrafluoroethylene were used. After drying, the mixture was stirred in a high-speed blender at a speed of 300 rpm for 10 minutes and ground to a particle size of about 100 mesh.

[0129] Chemical reaction (S30): 10 parts of divinylbenzene-ethyl acrylate-acrylamide copolymer and 1 part of butylated hydroxytoluene were added and stirred for 5 minutes. Tetrahydrofuran was added to adjust the viscosity to 500 mPa·s. The mixture was reacted in a reactor at a stirring speed of 200 rpm and 60°C for 6 hours, and vacuum distillation was performed to obtain a TPU film material.

[0130] Film Extrusion (S40): The screw extruder temperature was set at 180°C in the feed section, 210°C in the compression section, 220°C in the homogenization section, and 230°C in the die head. The screw speed was 50 rpm. After the mixture was added, it was extruded and cooled to set. Simultaneously, the TPU particles were mixed in an internal mixer at 220°C for 6 minutes at 50 rpm, and then cooled to produce a semi-finished product. The filtered melt was filtered through a 100-mesh filter and plasticized again in a calender at 230°C with a roller speed of 10 rpm.

[0131] Annealing and cooling demoulding (S50): The TPU stretch film is placed in an annealing furnace, preheated to 80°C for 10 minutes, heated to 120°C and annealed for 60 minutes. After natural cooling, it is placed in a 20°C cold water tank and soaked for 5 minutes, and then pulled out by a demoulding machine.

[0132] Chemical etching and subsequent treatment (S60): The chemical etching solution is heated to 40°C, and the TPU film is soaked for 30 minutes. The film is then washed twice, each time for 5 minutes. The film is dried at 60°C for 2 hours. After cutting and trimming, the film is wound at a speed of 10 m / min.

[0133] Specifically, the principle of the present invention is as follows: when in use, TPU resin is selected, and plasticizer, stabilizer, auxiliary agent, cellophane, and polytetrafluoroethylene are added in proportion to form a preparation raw material; the raw material is mechanically mixed by stirring with a high-speed mixer to fully and evenly mix the components; the raw material is chemically reacted with divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene, tetrahydrofuran is added to adjust the viscosity of the reaction system, and after the reaction is completed, the tetrahydrofuran is recovered by vacuum distillation to obtain a TPU film material; the mixture is heated and pressurized through a screw extruder to form a film, and the TPU particles are plasticized into a semi-finished product, and impurities are filtered and plasticized again on a filter of a calendering device; annealing treatment is performed, and the film is placed in cold water for cooling, and the cooled TPU stretched film is pulled out from the demolding port of a demolding machine; chemical etching is used to form a tiny pore structure in the TPU film, and then the film is cut, shaped, and wound into a roll.

[0134] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a non-swelling waterproof and breathable TPU film, characterized in that: The specific steps include: S10: Select TPU resin, add plasticizer, stabilizer, additive, cellophane, and polytetrafluoroethylene in proportion to form a preparation raw material; S20: The raw materials are mechanically mixed by stirring with a high-speed mixer to ensure that the ingredients are fully mixed; S30: chemically reacting the raw materials with divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene, adding tetrahydrofuran to adjust the viscosity of the reaction system, and recovering the tetrahydrofuran by vacuum distillation after the reaction is completed to obtain a TPU film material; S40: The mixed material is heated and pressurized through a screw extruder to form a film, the TPU particles are plasticized into a semi-finished product, and the impurities are filtered and plasticized again on the filter of the calendering equipment; S50: Perform annealing treatment and cool in cold water. The cooled TPU stretch film is pulled out from the demoulding port of the demoulding machine. S60: Chemical etching is used to form a tiny pore structure in the TPU film, and then the film is cut, shaped, and wound into a roll.

2. The method for preparing a non-swelling waterproof and breathable TPU film according to claim 1, characterized in that: By weight ratio, TPU resin: plasticizer: stabilizer: additive: cellophane: polytetrafluoroethylene is 80-90:5-15:2-5:1-3:3-8:2-6.

3. The method for preparing a non-swelling waterproof and breathable TPU film according to claim 2, characterized in that: The specific steps of mechanically mixing the raw materials by using a high-speed mixer to fully mix the ingredients include: The first step is to accurately weigh various raw materials according to the ratio; In the second step, TPU resin, plasticizer, stabilizer, additive, cellophane and polytetrafluoroethylene are placed in a drying oven and dried at 80-100°C for 4-6 hours to remove moisture from the raw materials and prevent defects such as material degradation or bubbles caused by moisture in the subsequent processing; The third step is to put the dried raw materials into a high-speed mixer, set the stirring speed to 300-500 rpm, and the stirring time is about 10-15 minutes. The fourth step is to put the evenly mixed mixture into a grinding equipment for grinding, and grind the mixture into fine particles with a particle size of about 100-200 mesh, so that the particles of the mixture are finer and more uniform, increase the surface area of ​​the mixture, and improve its fluidity and uniformity in the subsequent extrusion molding process, which is conducive to the preparation of TPU film with excellent performance.

4. The method for preparing a non-swelling waterproof and breathable TPU film according to claim 3, characterized in that: The specific steps of chemically reacting the raw materials with the divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene, adding tetrahydrofuran to adjust the viscosity of the reaction system, and recovering the tetrahydrofuran by vacuum distillation after the reaction is completed to obtain the TPU film material include: The first step is to add divinylbenzene-ethyl acrylate-acrylamide copolymer and butylated hydroxytoluene to the stirred raw materials and continue stirring for 5-10 minutes to ensure that the ingredients are fully mixed; The second step is to slowly add tetrahydrofuran to the mixed system to control the viscosity of the reaction system between 500-1000 mPa·s; In the third step, the reaction system with adjusted viscosity is transferred to a reactor equipped with a stirring device and a temperature control device. The stirring device is turned on and the stirring speed is maintained at about 200-300 rpm. The reaction temperature is set between 60-80°C and the reaction time is about 4-6 hours. The double bonds in the divinylbenzene-ethyl acrylate-acrylamide copolymer undergo a cross-linking reaction with the active groups in the TPU molecular chain. Butylated hydroxytoluene prevents oxidative degradation of the TPU during the reaction, thereby forming a TPU film material with special properties. Step 4: After the reaction is completed, the mixture in the reactor is subjected to vacuum distillation through a vacuum distillation apparatus, with the vacuum distillation temperature set at 40-60° C. and the pressure controlled at 10-30 mmHg; The fifth step is to take out the initial product of TPU membrane material obtained by vacuum distillation.

5. The method for preparing a non-swelling waterproof and breathable TPU film according to claim 4, characterized in that: The divinylbenzene-ethyl acrylate-acrylamide copolymer accounts for 10%-15% of the total reaction system, and butylated hydroxytoluene accounts for 1%-3% of the total reaction system.

6. The method for preparing a non-swelling waterproof and breathable TPU film according to claim 5, characterized in that: The specific steps of heating and pressurizing the mixed material through a screw extruder to form a film, plasticizing the TPU particles into a semi-finished product, filtering impurities on a filter of a calendering device, and plasticizing again include: The first step is to start the screw extruder and set the temperature of each heating zone. The temperature of the feed section is set to 160-180°C, the temperature of the compression section is set to 190-210°C, the temperature of the homogenization section is set to 200-220°C, and the temperature of the die head is set to 210-230°C. The screw speed is set to 30-60 rpm, and the screw is operated slowly at low temperature for preheating. In the second step, the dried mixture is evenly added into the hopper of the screw extruder through the feed port. Under the rotation of the screw, the mixture is transported forward and is melted and plasticized by the heat of the heating area. In the third step, the TPU film blank extruded from the die enters the cooling device, which is a cooling roller or cooling water tank, to quickly cool and shape the TPU film blank. The fourth step is to place the TPU particles into an internal mixer and perform internal mixing and plasticization at a temperature of 180°C-220°C for 5-10 minutes at a speed of 30-50 rpm. During the internal mixing process, the TPU particles are subjected to strong shearing, extrusion and stirring by the rotor of the internal mixer, gradually melting and plasticizing to form a uniform TPU melt. The molten TPU melt is discharged from the internal mixer and cooled by a cooling device to obtain a TPU semi-finished product. The fifth step is to transport the TPU melt through the pipeline to the filter of the calendering equipment; the filter of the filter adopts a 100-200 mesh metal mesh or filter mesh to filter out impurities, unmelted particles and other foreign matter in the TPU melt; under the pressure of the calendering equipment, the TPU melt passes through the filter and the impurities are trapped on the filter; In the sixth step, the filtered TPU melt is heated and stirred by the calendering equipment and plasticized again at a temperature of 190℃-230℃; the roller speed of the calendering equipment is 10-30 rpm. Through the extrusion and shearing action of the roller, the TPU melt is further plasticized and uniformed, while giving it better fluidity and processing performance, so that it can better meet the requirements of subsequent processing and molding.

7. The method for preparing a non-swelling waterproof and breathable TPU film according to claim 6, characterized in that: The annealing treatment, cooling in cold water, and pulling the cooled TPU stretched film out from the demoulding port of the demoulding machine specifically include: The first step is to place the TPU stretch film in an annealing furnace and start preheating. The preheating temperature of the annealing furnace is controlled at 60-80°C for 10-15 minutes. The temperature of the TPU stretch film is gradually increased to avoid excessive internal stress of the TPU stretch film due to rapid temperature changes. In the second step, after preheating, the temperature of the annealing furnace is raised to 100-120°C for annealing. The annealing time is 30-60 minutes. During the annealing process, the molecular chains of the TPU stretch film gradually relax and the internal stress is released, thereby improving the dimensional stability and mechanical properties of the TPU film. During the annealing process, the temperature in the annealing furnace is kept uniform to avoid local overheating or uneven temperature. The third step is to close the annealing furnace after annealing is completed, and the TPU stretch film is naturally cooled to room temperature in the furnace. During the natural cooling process, the annealing furnace door is kept closed to prevent the rapid inflow of outside air from causing temperature difference stress on the surface of the TPU stretch film. Step 4: Prepare a cold water tank in the cooling device, inject an appropriate amount of cold water into the tank, and control the water temperature at 10-20°C. The size of the cold water tank should be able to accommodate the TPU stretch film and ensure that the TPU stretch film can be completely immersed in the water in the cold water tank. Step 5: Slowly place the annealed TPU stretch film into a cold water tank to keep it flat and uniform to avoid wrinkles or distortion. Step 6: Soak the TPU stretch film in cold water for 5-10 minutes to fully cool it down; Step 7: Install the pulling roller at the demoulding port of the demoulding machine and adjust the position and angle of the demoulding device to make it consistent with the discharge direction of the TPU stretch film; In the eighth step, the cooled TPU stretch film is taken out from the cold water tank and placed at the feed port of the demoulding machine; the demoulding machine is started, and the TPU stretch film is pulled out from the demoulding port through the traction action of the demoulding device.

8. The method for preparing a non-swelling waterproof and breathable TPU film according to claim 7, characterized in that: The specific steps of forming a microporous structure in the TPU film by chemical etching, cutting and shaping the film, and winding the film into a roll include: The first step is to heat the chemical etching solution to 40°C-60°C to increase its activity and reaction rate; The second step is to slowly and evenly place the TPU film into the chemical etching solution, ensuring that the film is completely immersed in the solution; the immersion time is 10-30 minutes. During the immersion process, the chemical etchant reacts with the TPU film, gradually eroding the film surface and forming tiny holes; The third step is to remove the chemically etched TPU film from the chemical etching solution and place it in a cleaning tank for cleaning. Wash it 2-3 times, each time for 5-10 minutes. After each cleaning, use a clean soft cloth or air gun to gently absorb the moisture on the surface of the film to avoid water stains. The fourth step is to place the cleaned TPU film in a drying oven for drying. The drying temperature is controlled at 60°C-80°C and the drying time is 1-2 hours until the film is completely dry. The fifth step is to use a laser cutting machine to cut; the cut TPU film is edge trimmed and the size is adjusted; Step 6: Fix one end of the TPU film on the reel, start the winding equipment, and begin winding; the winding speed is controlled at 10-30 meters / minute.

Images