TPU (thermoplastic polyurethane) air bag film and preparation method thereof

Abstract

The invention discloses a TPU (thermoplastic polyurethane) air bag film and a preparation method thereof. The preparation method comprises the following steps: drying food-grade TPU resin, and adding a hydrolysis inhibitor and an antioxidant stabilizer for pretreatment; the preparation method comprises the following steps: carrying out prepolymerization reaction on a polyhydric alcohol modified reinforcing agent, terminated isocyanate, a chain extender and a catalyst to prepare a modified prepolymer; carrying out organic silicon coupling agent surface modification on an inorganic filler, and then carrying out melt blending on the inorganic filler, the TPU base material and the modified prepolymer to prepare master batches; the master batch is subjected to film casting, two-way stretching and heat setting, and the TPU air bag film is obtained; the TPU resin is fully dried, and the hydrolysis inhibitor and the anti-oxidation stabilizer are added, so that the melting film forming defect can be reduced; the polyhydric alcohol modified component is subjected to prepolymerization reaction and introduced into a TPU system, so that the stress uniformity and the resilience retention capability of the airbag film under the condition of repeated inflation and deflation can be improved; the surface modified inorganic filler and stretching treatment are matched, so that the long-term use reliability of the airbag film can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of airbag membranes, and more particularly to a TPU airbag membrane and its preparation method. Background Technology

[0002] TPU airbag film is a polymer film material that uses thermoplastic polyurethane (TPU) resin as the main film-forming material. It is formed by extrusion and heat sealing to create a sealed air chamber, providing cushioning, protection, or sealing functions when inflated. Due to the advantages of TPU material, such as good flexibility, high transparency, heat-sealing capability, and recyclability, TPU airbag film has been widely used in the fields of cushioning packaging airbags and flexible sealing airbags.

[0003] However, in the preparation and use of existing TPU airbag films, the TPU molecular chain contains structural units such as urethane bonds that are sensitive to moisture and heat. When trace amounts of moisture are present in the raw materials or processing environment, hydrolysis and related side reactions can easily occur during high-temperature melt extrusion, leading to a decrease in molecular weight and fluctuations in melt viscosity. This results in defects such as bubbles, silver streaks, or rough film surfaces during film formation, which in turn affect the thickness uniformity and film quality of the airbag film. In addition, in practical applications, airbag films often need to undergo repeated inflation, deflation, folding, and extrusion, and are subjected to cyclic mechanical stress over a long period of time. Traditional TPU airbag films are prone to insufficient fatigue durability or decreased dimensional stability in this process, which can lead to failure risks such as local thinning, decreased resilience, and even microcrack propagation.

[0004] Therefore, existing technologies have shortcomings and need to be improved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a TPU air-filled membrane with stable film quality, excellent fatigue resistance and high dimensional stability, and a method for preparing the same.

[0006] To achieve this objective, the present invention adopts the following technical solution: A method for preparing a TPU air-filled membrane includes the following steps: S1. Select food-grade TPU resin as the matrix material, dry the TPU resin at 80-100℃ for 4-8 hours, control the moisture content to be below 0.02wt%, then add 0.1-0.3wt% hydrolysis inhibitor and 0.2-0.5wt% antioxidant stabilizer, stir at low speed for 20-40 minutes to obtain the pretreated TPU matrix material; S2. Take at least one of polycarbonate-type polyol, polycaprolactone-type polyol or siloxane-modified polyol as a modifier and reinforcing agent. Add the modifier and reinforcing agent, end-capped isocyanate, chain extender and catalyst in proportion to the reaction vessel. Under nitrogen protection, carry out prepolymerization reaction at 70-95℃ for 1-3 hours. After degassing, obtain the modified prepolymer. The amount of the modified reinforcing agent added is 60-88 wt% of the total mass of the modified prepolymer, the amount of the end-capped isocyanate added is 8-28 wt% of the total mass of the modified prepolymer, the amount of the chain extender added is 0.3-6 wt% of the total mass of the modified prepolymer, and the amount of the catalyst added is 50-5000 ppm of the total mass of the modified prepolymer. S3. Select an inorganic filler and disperse it in an alcohol-water solvent, wherein the amount of inorganic filler added is 2-15 wt% of the mass of the alcohol-water solvent; add an organosilicon coupling agent under stirring conditions, wherein the amount of organosilicon coupling agent added is 1-5 wt% of the mass of the inorganic filler; adjust the pH value to 4-6; and after stirring, centrifugation, washing and drying, obtain the modified functional filler. S4. TPU base material, modified prepolymer, modified functional filler and processing aid are added as mixed raw materials into a twin-screw extruder, and after melt shear extrusion, water cooling and pelletizing, modified TPU masterbatch is obtained. S5. The modified TPU masterbatch is fed into the extrusion casting machine, and the molten material is transported to the casting die head by the melt metering pump, so that the molten TPU forms a uniform primary air bladder film. The thickness of the primary air bladder film is controlled at 0.10-0.60mm. S6. The primary airbag film is fed into a film stretching device for bidirectional stretching treatment, wherein the longitudinal stretching ratio is 1.3-2.8 times and the transverse stretching ratio is 1.2-2.5 times. After stretching, heat setting treatment is performed for 1-5 minutes, and after cooling, it is wound up to obtain TPU airbag film.

[0007] Using the above technical solution, in step S3, the inorganic filler is nano-montmorillonite, nano-mica, hexagonal boron nitride or a combination thereof, and the organosilicon coupling agent is one of aminosilane coupling agents, epoxysilane coupling agents or vinylsilane coupling agents.

[0008] Using the above technical solution, in step S3, the inorganic filler has a sheet structure with a length of 50-500 nm and a sheet thickness of 10-100 nm.

[0009] Using the above technical solution, in step S4, the amount of TPU base material added accounts for 75-92 wt% of the total mass of the mixture, the amount of modified prepolymer added accounts for 2-10 wt% of the total mass of the mixture, the amount of modified functional filler added accounts for 0.5-6 wt% of the total mass of the mixture, and the amount of processing aid added accounts for 0.2-1 wt% of the total mass of the mixture.

[0010] Using the above technical solution, in step S2, the end-capped isocyanate is isophorone diisocyanate or hexamethylene diisocyanate, the chain extender is one of 1,4-butanediol, 1,6-hexanediol, neopentyl glycol or trimethylolpropane; and the catalyst is one of organotin catalysts, bismuth catalysts, zinc catalysts or tertiary amine catalysts.

[0011] Using the above technical solution, in step S5, before the modified TPU masterbatch is fed into the extrusion casting machine, it is dehumidified and dried, with the drying temperature controlled at 70-90℃ and the time being 2-6 hours.

[0012] Using the above technical solution, in step S1, the hydrolysis inhibitor is a carbodiimide compound, and the antioxidant stabilizer is a hindered phenolic antioxidant or a phosphite antioxidant.

[0013] Using the above technical solution, in step S4, the processing aid is a lubricant, a heat stabilizer, a flow modifier, or a combination thereof; wherein, the lubricant is at least one of fatty acid ester lubricant, amide lubricant, or wax lubricant, the heat stabilizer is a hindered phenolic stabilizer or a phosphite stabilizer, and the flow modifier is an organosilicon processing aid or a fluoropolymer processing aid.

[0014] Using the above technical solution, in step S6, after biaxial stretching and heat setting, the thermal shrinkage rate of the TPU air-filled film under the condition of 80℃×1h is not higher than 2%.

[0015] The above technical solution is adopted.

[0016] This technical solution also provides a TPU air bladder membrane, which is prepared using any of the above-mentioned methods for preparing TPU air bladder membranes.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention effectively suppresses the adverse effects of hydrolysis and thermal oxidation on the molecular chain structure by thoroughly drying TPU resin and adding hydrolysis inhibitors and antioxidant stabilizers, thereby reducing defects during the melt film formation process. Introducing polyol-modified components into the TPU system after prepolymerization effectively improves the stress uniformity and resilience of the airbag membrane under repeated inflation and deflation conditions. Simultaneously, surface-modified inorganic fillers form a stable dispersion structure in the TPU matrix, enhancing the dimensional stability of the membrane without significantly reducing flexibility. Combined with subsequent film formation and orientation processes, the film maintains a low shrinkage tendency under heating conditions, thereby improving the fatigue resistance and long-term reliability of the airbag membrane. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Furthermore, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., described below refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the technical features involved in the various embodiments of the invention can be combined with each other as long as they do not conflict with each other.

[0019] This invention provides a method for preparing a TPU air-filled membrane, comprising the following steps: S1. Select food-grade TPU resin as the matrix material. Dry the TPU resin at 80-100℃ for 4-8 hours, controlling the moisture content to below 0.02wt%. Then add 0.1-0.3wt% of hydrolysis inhibitor and 0.2-0.5wt% of antioxidant stabilizer. Stir at low speed for 20-40 minutes to obtain the pretreated TPU base material. The TPU molecular chain contains structural units such as urethane bonds that are sensitive to moisture and heat. If the residual moisture in the raw material is too high, hydrolysis reaction is easily triggered during subsequent melt extrusion and film formation. The hydrolysis reaction is accompanied by side reactions, leading to a decrease in molecular weight and fluctuations in melt viscosity, which in turn causes defects such as bubbles and silver streaks during film forming. Therefore, by thoroughly drying at 80-100℃ and controlling the moisture content to below 0.02wt%, the hydrolysis reaction can be effectively suppressed. On this basis, adding an appropriate amount of hydrolysis inhibitor can further passivate the water or active groups involved in the reaction, providing continuous protection for the TPU molecular chain. At the same time, introducing antioxidant stabilizers can inhibit oxidative degradation under high temperature and shear conditions during thermal processing, preventing molecular chain breakage. S2. At least one of polycarbonate-type polyol, polycaprolactone-type polyol, or siloxane-modified polyol is used as a modifying agent. The modifying agent, along with end-capped isocyanate, chain extender, and catalyst, are added to a reaction vessel in a specific ratio. A prepolymerization reaction is carried out at 70-95°C for 1-3 hours under nitrogen protection. After degassing, a modified prepolymer is obtained. The amount of the modifying agent added is 60-88 wt% of the total mass of the modified prepolymer, the amount of the end-capped isocyanate added is 8-28 wt% of the total mass of the modified prepolymer, the amount of the chain extender added is 0.3-6 wt% of the total mass of the modified prepolymer, and the amount of the catalyst added is... The total mass of the polymer is 50-5000 ppm; polycarbonate-type polyols, polycaprolactone-type polyols, and siloxane-modified polyols all belong to flexible segments. Using them as modifiers and reinforcing agents in the prepolymerization reaction can introduce a compliant segment structure at the molecular level, thereby improving the deformation coordination performance of the material under stress. By prepolymerizing with end-capped isocyanates and chain extenders, polyols can be introduced into the prepolymer structure through chemical bonding, avoiding migration or phase separation during subsequent melt blending. Reaction under nitrogen protection and temperature control at 70-95℃ can suppress side reactions of isocyanates with moisture or oxygen, effectively improving the stability of the product structure.

[0020] S3. Select an inorganic filler and disperse it in an alcohol-water solvent, wherein the amount of inorganic filler added is 2-15 wt% of the mass of the alcohol-water solvent; add an organosilicon coupling agent under stirring conditions, wherein the amount of organosilicon coupling agent added is 1-5 wt% of the mass of the inorganic filler, adjust the pH value to 4-6, and after stirring, centrifugation, washing and drying, obtain the modified functional filler; dispersing the inorganic filler in an alcohol-water mixed solvent and controlling its addition amount to 2-15 wt% of the solvent mass can reduce the mutual adsorption and agglomeration tendency between inorganic fillers while taking into account dispersion efficiency and system flowability, and provide sufficient contact interface for subsequent surface modification reactions; introducing an organosilicon coupling agent under stirring conditions can cause the coupling agent molecules to form a coating layer on the surface of the inorganic filler; adjusting the pH value of the system to 4-6 can facilitate the moderate hydrolysis of the organosilicon coupling agent and the condensation reaction with the hydroxyl groups on the surface of the inorganic filler, thereby improving the sufficiency and stability of surface modification.

[0021] S4. TPU base material, modified prepolymer, modified functional filler and processing aids are added as a mixture to a twin-screw extruder. After melt shear extrusion, water cooling and pelletizing, modified TPU masterbatch is obtained. The twin-screw extruder can fully plasticize the TPU base material under melt shear action, and at the same time promote the entanglement and compatibility of the modified prepolymer and TPU molecular chains. The modified functional filler can be further peeled and dispersed under shear and melt conditions, and embedded into the continuous TPU phase with the assistance of processing aids, reducing the impact of agglomeration on the continuity of the film.

[0022] S5. The modified TPU masterbatch is fed into the extrusion casting machine, and the molten material is delivered to the casting die by a melt metering pump, so that the molten TPU forms a uniform primary airbag film. The thickness of the primary airbag film is controlled between 0.10-0.60mm. Through the casting film formation method, the molten TPU can be spread and shaped under cooling conditions, thereby reducing the risk of film surface defects and internal stress. Controlling the thickness of the primary airbag film within the range of 0.10-0.60mm can ensure that the film has the mechanical support and puncture resistance required for inflation, while avoiding excessive film thickness, which would lead to increased material consumption and decreased flexibility.

[0023] S6. The primary airbag film is fed into a film stretching device for biaxial stretching treatment, with a longitudinal stretching ratio of 1.3-2.8 times and a transverse stretching ratio of 1.2-2.5 times. After stretching, it is heat-set for 1-5 minutes, cooled, and then wound up to obtain the TPU airbag film. By performing biaxial stretching in both the longitudinal and transverse directions, the TPU molecular chains can be oriented along the direction of force, thereby improving the mechanical uniformity and load-bearing capacity of the film during use. Controlling the longitudinal stretching ratio to 1.3-2.8 times and the transverse stretching ratio to 1.2-2.5 times helps to achieve a balance between improving mechanical properties and maintaining film flexibility, avoiding embrittlement or dimensional instability caused by excessive orientation.

[0024] Furthermore, in step S3, the inorganic filler is nano-montmorillonite, nano-mica, hexagonal boron nitride, or a combination thereof, and the organosilicon coupling agent is one of aminosilane coupling agents, epoxysilane coupling agents, or vinylsilane coupling agents. Nano-montmorillonite, nano-mica, and hexagonal boron nitride are all layered inorganic materials with large specific surface areas and high structural rigidity. By modifying the surface of the inorganic filler with aminosilane, epoxysilane, or vinylsilane coupling agents, one end of the coupling agent molecule can interact with the hydroxyl groups on the surface of the inorganic filler, while the other end forms good compatibility with the organic segments in TPU or modified prepolymer, thereby establishing a good interfacial transition layer between the inorganic filler and the organic matrix.

[0025] Furthermore, in step S3, the inorganic filler has a sheet structure with a length of 50-500 nm and a sheet thickness of 10-100 nm. This allows the inorganic filler to maintain a high specific surface area and structural rigidity while avoiding stress concentration due to excessive size.

[0026] Furthermore, in step S4, the amount of TPU base material added accounts for 75-92 wt% of the total mass of the mixture, the amount of modified prepolymer added accounts for 2-10 wt% of the total mass of the mixture, the amount of modified functional filler added accounts for 0.5-6 wt% of the total mass of the mixture, and the amount of processing aid added accounts for 0.2-1 wt% of the total mass of the mixture.

[0027] Furthermore, in step S2, the end-capped isocyanate is isophorone diisocyanate or hexamethylene diisocyanate, the chain extender is one of 1,4-butanediol, 1,6-hexanediol, neopentyl glycol or trimethylolpropane; and the catalyst is one of organotin catalysts, bismuth catalysts, zinc catalysts or tertiary amine catalysts. Isophorone diisocyanate and hexamethylene diisocyanate are both aliphatic isocyanates, with relatively mild reactivity and stable structure. They are less prone to rapid crosslinking or side reactions during prepolymerization, thus forming a prepolymer structure with uniform molecular weight distribution. Small chain extenders such as 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, or trimethylolpropane can be used to regulate the flexibility and mechanical support properties of the prepolymer by adjusting the chain extension mode and branching degree, thereby avoiding excessive chain rigidity or phase separation. Meanwhile, organotin, bismuth, zinc, and tertiary amine catalysts are commonly used high-efficiency catalytic systems in polyurethane systems. Their moderate catalytic activity and selectivity can promote the reaction between isocyanate and hydroxyl groups at low addition levels, ensuring a stable prepolymerization process and effectively reducing side reactions. This results in a modified prepolymer with moderate activity, providing a stable reaction basis for subsequent melt blending and film formation processes.

[0028] Furthermore, in step S5, before feeding the modified TPU masterbatch into the extrusion casting machine, it undergoes dehumidification and drying treatment. The drying temperature is controlled at 70-90℃ for 2-6 hours. Modified TPU masterbatch inevitably absorbs moisture from the environment during storage, transportation, or pre-processing. Since the TPU system is quite sensitive to moisture, if it directly enters the extrusion casting process, hydrolysis can easily occur in the high-temperature molten state, leading to film defects such as bubbles, silver streaks, or thickness fluctuations on the film surface. By dehumidifying and drying at 70-90℃, the absorbed moisture can be effectively removed without causing thermal aging or adhesion of the masterbatch. This ensures that the masterbatch is in a low-moisture state when entering the extrusion casting machine, thereby guaranteeing the continuity of melt flow. This is beneficial for obtaining a smooth primary air-filled film and improving the processing stability of subsequent stretching and heat-setting processes.

[0029] Furthermore, in step S1, the hydrolysis inhibitor is a carbodiimide compound, and the antioxidant stabilizer is a hindered phenolic antioxidant or a phosphite antioxidant. The carbodiimide compound can react with moisture present in the TPU system or acidic substances generated by hydrolysis, thereby effectively inhibiting further hydrolysis of the carbamate bonds, reducing the probability of molecular chain breakage, and allowing the TPU to maintain a relatively stable molecular weight structure during subsequent high-temperature melt processing. The hindered phenolic antioxidant and the phosphite antioxidant can synergistically inhibit oxidative degradation under thermal processing and shear conditions by capturing free radicals and decomposing peroxides, respectively.

[0030] Further, in step S4, the processing aid is a lubricant, a heat stabilizer, a flow modifier, or a combination thereof; wherein the lubricant is at least one of a fatty acid ester lubricant, an amide lubricant, or a wax lubricant; the heat stabilizer is a hindered phenolic stabilizer or a phosphite stabilizer; and the flow modifier is an organosilicon processing aid or a fluoropolymer processing aid. The lubricant reduces the frictional resistance between the TPU melt and the screw and barrel, thereby improving the flow continuity of the melt during extrusion and reducing the risk of heat accumulation and melt degradation due to excessive local shear; the heat stabilizer inhibits the thermal oxidation reaction of the TPU molecular chains under high temperature and shear conditions, preventing molecular chain breakage or performance degradation and ensuring the stability of the blending process; while the flow modifier reduces melt viscosity fluctuations and improves melt spreading performance, making the modified prepolymer and inorganic filler more uniformly dispersed in the TPU matrix.

[0031] Furthermore, in step S6, after biaxial stretching and heat setting, the thermal shrinkage rate of the TPU air-filled membrane under 80℃×1h conditions is no higher than 2%.

[0032] Example 1 Embodiment 1 of the present invention provides a method for preparing a TPU air-filled membrane, comprising the following steps: S1. Select food-grade TPU resin as the matrix material, dry the TPU resin at 95℃ for 6 hours, control the moisture content to be below 0.02wt%, then add 0.3wt% hydrolysis inhibitor and 0.4wt% antioxidant stabilizer, stir at low speed for 30 minutes to obtain the pretreated TPU matrix material. The hydrolysis inhibitor is a carbodiimide compound, and the antioxidant stabilizer is a hindered phenolic antioxidant. S2. Take polycarbonate-type polyol as a modifier and reinforcing agent, add the modifier and reinforcing agent, end-capped isocyanate, chain extender and catalyst to the reaction vessel in proportion, and carry out prepolymerization reaction at 85°C for 2 hours under nitrogen protection. After degassing, a modified prepolymer is obtained. The end-capped isocyanate is isophorone diisocyanate, the chain extender is 1,4-butanediol, and the catalyst is an organotin catalyst. The amount of the modified reinforcing agent added is 75 wt% of the total mass of the modified prepolymer, the amount of the end-capped isocyanate added is 20 wt% of the total mass of the modified prepolymer, the amount of the chain extender added is 5 wt% of the total mass of the modified prepolymer, and the amount of the catalyst added is 1000 ppm of the total mass of the modified prepolymer. S3. Select an inorganic filler and disperse it in an alcohol-water solvent, wherein the amount of inorganic filler added is 4 wt% of the mass of the alcohol-water solvent; add an organosilicon coupling agent under stirring conditions, wherein the amount of organosilicon coupling agent added is 1 wt% of the mass of the inorganic filler; adjust the pH value to 5; and after stirring, centrifugation, washing and drying, obtain the modified functional filler. The inorganic filler is nano-montmorillonite, and the inorganic filler has a sheet structure with a length of 200 nm and a sheet thickness of 20 nm. The organosilicon coupling agent is an aminosilane coupling agent. S4. TPU base material, modified prepolymer, modified functional filler and processing aid are added as mixed raw materials into a twin-screw extruder, and after melt shear extrusion, water cooling and pelletizing, modified TPU masterbatch is obtained. The TPU base material accounts for 86 wt% of the total mass of the mixture, the modified prepolymer accounts for 8 wt% of the total mass of the mixture, the modified functional filler accounts for 5 wt% of the total mass of the mixture, and the processing aid accounts for 1 wt% of the total mass of the mixture; the processing aid is a lubricant, and the lubricant is a fatty acid ester lubricant. S5. The modified TPU masterbatch is dehumidified and dried at a temperature of 80°C for 3 hours. Then it is fed into an extrusion casting machine and the molten material is transported to the casting die by a melt metering pump to form a uniform primary air bladder film. The thickness of the primary air bladder film is controlled at 0.5 mm. S6. The primary airbag film is fed into a film stretching device for bidirectional stretching treatment, wherein the longitudinal stretching ratio is 2.4 times and the transverse stretching ratio is 2.1 times. After stretching, heat setting treatment is performed for 2 minutes to ensure that the heat shrinkage rate under the condition of 80℃×1h is not higher than 2%. After cooling, the TPU airbag film is obtained by winding.

[0033] Example 2 Embodiment 2 of the present invention provides a method for preparing a TPU air-filled membrane, comprising the following steps: S1. Select food-grade TPU resin as the matrix material, dry the TPU resin at 85℃ for 6 hours, control the moisture content to be below 0.02wt%, then add 0.2wt% hydrolysis inhibitor and 0.4wt% antioxidant stabilizer, stir at low speed for 40 minutes to obtain the pretreated TPU matrix material. The hydrolysis inhibitor is a carbodiimide compound, and the antioxidant stabilizer is a phosphite antioxidant. S2. Polycaprolactone-type polyol is used as a modifier and reinforcing agent. The modifier, end-capped isocyanate, chain extender and catalyst are added to the reactor in proportion. The prepolymerization reaction is carried out at 85°C for 3 hours under nitrogen protection. After degassing, the modified prepolymer is obtained. The end-capped isocyanate is hexamethylene diisocyanate, the chain extender is 1,6-hexanediol, and the catalyst is a bismuth-based catalyst. The amount of the modified reinforcing agent added is 82 wt% of the total mass of the modified prepolymer, the amount of the end-capped isocyanate added is 16 wt% of the total mass of the modified prepolymer, the amount of the chain extender added is 2 wt% of the total mass of the modified prepolymer, and the amount of the catalyst added is 500 ppm of the total mass of the modified prepolymer. S3. Select an inorganic filler and disperse it in an alcohol-water solvent, wherein the amount of inorganic filler added is 3wt% of the mass of the alcohol-water solvent; add an organosilicon coupling agent under stirring conditions, wherein the amount of organosilicon coupling agent added is 2wt% of the mass of the inorganic filler; adjust the pH value to 6; and after stirring, centrifugation, washing and drying, obtain the modified functional filler. The inorganic filler is nano-mica, and the inorganic filler has a sheet structure with a length of 100 nm and a sheet thickness of 30 nm. The organosilicon coupling agent is an epoxy silane coupling agent. S4. TPU base material, modified prepolymer, modified functional filler and processing aid are added as mixed raw materials into a twin-screw extruder, and after melt shear extrusion, water cooling and pelletizing, modified TPU masterbatch is obtained. The TPU base material accounts for 84 wt% of the total mass of the mixture, the modified prepolymer accounts for 9 wt% of the total mass of the mixture, the modified functional filler accounts for 6 wt% of the total mass of the mixture, and the processing aid accounts for 1 wt% of the total mass of the mixture; the processing aid is a flow modifier, and the flow modifier is a fluoropolymer processing aid. S5. The modified TPU masterbatch is dehumidified and dried at a temperature of 85°C for 3 hours. Then it is fed into an extrusion casting machine and the molten material is transported to the casting die by a melt metering pump to form a uniform primary air bladder film. The thickness of the primary air bladder film is controlled at 0.4 mm. S6. The primary airbag film is fed into a film stretching device for bidirectional stretching treatment, wherein the longitudinal stretching ratio is 2.2 times and the transverse stretching ratio is 1.8 times. After stretching, heat setting treatment is performed for 2 minutes to ensure that the heat shrinkage rate under the condition of 80℃×1h is not higher than 2%. After cooling, it is wound up to obtain TPU airbag film.

[0034] Comparative Example 1 Compared with Example 1, the difference is that in step S2, the prepolymerization reaction of the modifier, the end-capped isocyanate, and the chain extender is not performed. Instead, the prepolymerization reaction process in step S2 is omitted, and the polycarbonate polyol is directly used as an additive component. In step S4, it is added to a twin-screw extruder together with the TPU base material, the modified functional filler, and the processing aid for melt blending. The remaining steps and process parameters are the same as in Example 1.

[0035] Comparative Example 2 Compared with Example 1, the difference is that in step S3, the inorganic filler is not subjected to surface modification treatment with organosilicon coupling agent. Instead, unmodified nano-montmorillonite is directly used as an inorganic filler for melt blending in the subsequent step S4. The remaining steps and process conditions are the same as in Example 1.

[0036] Comparative Example 3 Compared with Example 1, the difference is that in step S6, the primary airbag film is not subjected to biaxial stretching and subsequent heat setting after molding. Instead, after completing step S5, the primary airbag film is directly cooled and wound to obtain the TPU airbag film. The remaining steps are the same as in Example 1.

[0037] Comparative Example 4 Compared with Example 1, the difference is that in step S4, the modified prepolymer obtained in step S2 is not added. Instead, the TPU base material, the modified functional filler obtained in step S3, and the processing aid are added to a twin-screw extruder for melt shear extrusion. The remaining steps and process parameters are the same as in Example 1.

[0038] Comparative Example 5 Compared with Example 1, the difference is that in step S1, the TPU resin is not dried and no hydrolysis inhibitor or antioxidant stabilizer is added. The unstabilized TPU resin is directly used for melt blending in the subsequent step S4. The remaining steps and process conditions are the same as in Example 1.

[0039] The following experiments were conducted on the above Examples 1-2 and Comparative Examples 1-5 to verify or understand their performance in the airbag membranes prepared in the above Examples 1-2 and Comparative Examples 1-5.

[0040] Table 1 Comparison of Airbag Membrane Performance Test Data According to Table 1 above: The comparison results between Example 1 and Comparative Example 1 show that, in step S2, by introducing a modifier and forming a modified prepolymer through a prepolymerization reaction, compared with the method of directly adding the modifier in Comparative Example 1, the stress state of the airbag membrane during repeated inflation and deflation can be effectively improved, thereby effectively reducing fatigue damage and improving the resilience. The comparison results between Example 1 and Comparative Example 2 show that the surface modification treatment of inorganic fillers with organosilicon coupling agent in step S3 can improve the dispersion uniformity and interfacial bonding effect of inorganic fillers in TPU matrix, thereby improving the appearance quality of the film surface. As can be seen from the comparison between Example 1 and Comparative Example 3, the biaxial stretching and heat setting treatment of the primary airbag film in step S6 can effectively stabilize the molecular chain orientation structure and release internal stress, thereby effectively improving the dimensional stability and heat shrinkage resistance of the airbag film. The film without this treatment is prone to deformation under heat conditions. The comparison results between Example 1 and Comparative Example 4 show that introducing modified prepolymer and modified functional filler to form a synergistic blend structure in step S4 can effectively improve the fatigue resistance and structural stability of the airbag membrane without affecting the film quality. The comparison results between Example 1 and Comparative Example 5 show that thoroughly drying the TPU base material and adding hydrolysis inhibitors and antioxidant stabilizers in step S1 can effectively reduce the adverse effects of moisture and thermal oxidation factors in the raw materials on the film formation process, thereby reducing the generation of film defects and improving the performance stability of the airbag membrane during long-term use.

[0041] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a TPU air-filled membrane, characterized in that, Includes the following steps: S1. Select food-grade TPU resin as the matrix material, dry the TPU resin at 80-100℃ for 4-8 hours, control the moisture content to be below 0.02wt%, then add 0.1-0.3wt% hydrolysis inhibitor and 0.2-0.5wt% antioxidant stabilizer, stir at low speed for 20-40 minutes to obtain the pretreated TPU matrix material; S2. Take at least one of polycarbonate-type polyol, polycaprolactone-type polyol or siloxane-modified polyol as a modifier and reinforcing agent. Add the modifier and reinforcing agent, end-capped isocyanate, chain extender and catalyst in proportion to the reaction vessel. Under nitrogen protection, carry out prepolymerization reaction at 70-95℃ for 1-3 hours. After degassing, obtain the modified prepolymer. The amount of the modified reinforcing agent added is 60-88 wt% of the total mass of the modified prepolymer, the amount of the end-capped isocyanate added is 8-28 wt% of the total mass of the modified prepolymer, the amount of the chain extender added is 0.3-6 wt% of the total mass of the modified prepolymer, and the amount of the catalyst added is 50-5000 ppm of the total mass of the modified prepolymer. S3. Select an inorganic filler and disperse it in an alcohol-water solvent, wherein the amount of inorganic filler added is 2-15 wt% of the mass of the alcohol-water solvent; add an organosilicon coupling agent under stirring conditions, wherein the amount of organosilicon coupling agent added is 1-5 wt% of the mass of the inorganic filler; adjust the pH value to 4-6; and after stirring, centrifugation, washing and drying, obtain the modified functional filler. S4. TPU base material, modified prepolymer, modified functional filler and processing aid are added as mixed raw materials into a twin-screw extruder, and after melt shear extrusion, water cooling and pelletizing, modified TPU masterbatch is obtained. S5. The modified TPU masterbatch is fed into the extrusion casting machine, and the molten material is transported to the casting die head by the melt metering pump, so that the molten TPU forms a uniform primary air bladder film. The thickness of the primary air bladder film is controlled at 0.10-0.60mm. S6. The primary airbag film is fed into a film stretching device for bidirectional stretching treatment, wherein the longitudinal stretching ratio is 1.3-2.8 times and the transverse stretching ratio is 1.2-2.5 times. After stretching, heat setting treatment is performed for 1-5 minutes, and after cooling, it is wound up to obtain TPU airbag film.

2. The method for preparing the TPU air-filled membrane according to claim 1, characterized in that, In step S3, the inorganic filler is nano-montmorillonite, nano-mica, hexagonal boron nitride or a combination thereof, and the organosilicon coupling agent is one of aminosilane coupling agents, epoxysilane coupling agents or vinylsilane coupling agents.

3. The method for preparing the TPU air-filled membrane according to claim 1, characterized in that, In step S3, the inorganic filler has a sheet structure with a length of 50-500 nm and a sheet thickness of 10-100 nm.

4. The method for preparing the TPU air-filled membrane according to claim 1, characterized in that, In step S4, the amount of TPU base material added accounts for 75-92 wt% of the total mass of the mixture, the amount of modified prepolymer added accounts for 2-10 wt% of the total mass of the mixture, the amount of modified functional filler added accounts for 0.5-6 wt% of the total mass of the mixture, and the amount of processing aid added accounts for 0.2-1 wt% of the total mass of the mixture.

5. The method for preparing the TPU air-filled membrane according to claim 1, characterized in that, In step S2, the end-capped isocyanate is isophorone diisocyanate or hexamethylene diisocyanate, the chain extender is one of 1,4-butanediol, 1,6-hexanediol, neopentyl glycol or trimethylolpropane, and the catalyst is one of organotin catalysts, bismuth catalysts, zinc catalysts or tertiary amine catalysts.

6. The method for preparing the TPU air-filled membrane according to claim 1, characterized in that, In step S5, before the modified TPU masterbatch is fed into the extrusion casting machine, it is dehumidified and dried. The drying temperature is controlled at 70-90℃ and the time is 2-6h.

7. The method for preparing the TPU air-filled membrane according to claim 1, characterized in that, In step S1, the hydrolysis inhibitor is a carbodiimide compound, and the antioxidant stabilizer is a hindered phenolic antioxidant or a phosphite antioxidant.

8. The method for preparing the TPU air-filled membrane according to claim 1, characterized in that, In step S4, the processing aid is a lubricant, a heat stabilizer, a flow modifier, or a combination thereof; wherein the lubricant is at least one of fatty acid ester lubricants, amide lubricants, or wax lubricants, the heat stabilizer is a hindered phenolic stabilizer or a phosphite stabilizer, and the flow modifier is an organosilicon processing aid or a fluoropolymer processing aid.

9. The method for preparing the TPU air-filled membrane according to claim 1, characterized in that, In step S6, after biaxial stretching and heat setting, the thermal shrinkage rate of the TPU air-filled membrane under the condition of 80℃×1h is not higher than 2%.

10. A TPU air-filled membrane, characterized in that, It is prepared by the method for preparing TPU air-filled membrane according to any one of claims 1-9.

Images