Heat-resistant breathable TPU film and preparation process thereof

Abstract

The application relates to the field of TPU materials, and particularly discloses a heat-resistant and air-permeable TPU film and a preparation process thereof. The heat-resistant and air-permeable TPU film comprises a surface dense layer and a bottom porous layer. The surface dense layer comprises the following raw materials: TPU particles, a first pore-forming agent, a hydrophobic agent, polyethylene glycol, an antioxidant, hydrophobic nano silicon dioxide and nano carbon fibers. The bottom porous layer comprises the following raw materials: TPU particles, a second pore-forming agent, polyvinylpyrrolidone, hexamethylene diisocyanate, polycarbonate diol and modified glass fibers and epoxy-based modified mica powder. The preparation process comprises the following steps: S1, melting and extruding the raw materials of the bottom porous layer after mixing according to proportions, washing with water and drying to obtain the bottom porous layer; S2, melting and extruding the raw materials of the surface dense layer after mixing according to proportions to form the surface dense layer, and obtaining the heat-resistant and air-permeable TPU film after hot-pressing and compounding. The application has the characteristics of improving the heat resistance of the TPU material and excellent air permeability.

Description

Technical Field

[0001] This application relates to the field of TPU materials, and more specifically, to a heat-resistant and breathable TPU film and its preparation process. Background Technology

[0002] With the diversified development of outdoor sports, professional competitions, and daily commuting, the footwear material industry's requirements for material performance have shifted from single-function to composite and high-performance. TPU (thermoplastic polyurethane), as a polymer material that combines the elasticity of rubber with the processing properties of plastics, has become a core material in the field of sports footwear materials, replacing traditional PVC and rubber, thanks to its excellent mechanical strength, low-temperature impact resistance, and recyclability.

[0003] In footwear, TPU membranes are widely used in upper support layers, insole breathable membranes, and midsoles through melt extrusion and casting processes. More specifically, when used as an upper protective layer, such as in outdoor hiking boots where TPU membrane composite fabrics are often used to resist rainwater penetration while allowing sweat vapor to escape through the microporous structure. When applied to midsole support and cushioning, such as embedding TPU membranes at the edge of the basketball shoe midsole and combining them with the EVA / ETPU midsole, it enhances rebound performance and acts as a support frame to prevent midsole collapse. When used as insoles and linings, TPU breathable membranes are embedded in the insoles of athletic shoes, combined with activated carbon particles, to achieve long-lasting antibacterial and deodorizing effects.

[0004] While TPU membranes offer some waterproof and breathable properties in footwear, achieving a balance between heat resistance and breathability remains challenging. TPU membranes need to maintain their shape and physical properties under high temperatures, exhibiting a certain degree of thermal stability. However, the breathability of TPU membranes depends on their microporous structure, and the increased molecular chain movement at high temperatures can lead to pore collapse and reduced breathability.

[0005] With the development of kinematics, higher requirements have been placed on the heat resistance and breathability of footwear materials, and there is an urgent need to improve the heat resistance and breathability of TPU materials. Summary of the Invention

[0006] In order to improve the heat resistance of TPU materials while maintaining excellent air permeability, this application provides a heat-resistant and breathable TPU film and its preparation process.

[0007] In a first aspect, this application provides a heat-resistant and breathable TPU film, employing the following technical solution:

[0008] A heat-resistant and breathable TPU film includes a dense surface layer and a porous bottom layer, wherein the dense surface layer comprises the following raw materials in parts by weight:

[0009] 60-80 parts TPU particles, 3-5 parts primary pore-forming agent, 5-10 parts hydrophobic agent, 2-5 parts polyethylene glycol, 1-3 parts antioxidant, 5-10 parts hydrophobic nano silica and 8-15 parts carbon nanofibers;

[0010] The underlying porous layer comprises the following raw materials in parts by weight:

[0011] 60-80 parts TPU granules, 5-10 parts secondary pore-forming agent, 4-8 parts polyvinylpyrrolidone, 3-5 parts hexamethylene diisocyanate, 3-5 parts polycarbonate diol, 10-15 parts modified glass fiber, and 5-10 parts epoxy-modified mica powder.

[0012] The modified glass fiber is prepared by loading Peek micro powder onto glass fiber and then modifying it with aminosilane.

[0013] By adopting the above technical solution, the heat-resistant and breathable TPU membrane in this application is composed of a dense surface layer and a porous bottom layer. The dense surface layer acts as a surface barrier of the membrane material, undertaking heat resistance, hydrophobicity, and anti-aging functions, while preventing liquid penetration. The porous bottom layer achieves efficient water vapor transport by adjusting the pores, and the addition of modified glass fiber and other raw materials enhances heat resistance and mechanical support, reducing the problem of pore collapse at high temperatures leading to a decrease in breathability. Moreover, in this application, the dense layer uses nano-silica and nano-carbon fiber as nanoscale fillers, while the porous layer contains polyvinylpyrrolidone as a pore-forming template. Combined with the pore structure formed between modified glass fiber and mica powder and other fillers, a gradient pore structure is formed, improving breathability.

[0014] In this application, the dense surface layer contains carbon nanofibers, hydrophobic nano-silica, and carbon nanofibers possessing heat resistance, hydrophobic properties, and mechanical reinforcement. The addition of hydrophobic nano-silica and hydrophobic agents reduces surface energy, forming a lotus leaf effect to prevent water droplet penetration. The addition of carbon nanofibers improves surface heat resistance and provides a high-strength skeleton, preventing pore collapse at high temperatures and achieving a balance between waterproofing and slight breathability. Furthermore, the network structure of carbon nanofibers and the dotted distribution of hydrophobic nano-silica form a three-dimensional support skeleton, inhibiting pore shrinkage caused by the movement of TPU molecular chains at high temperatures. The addition of a small amount of the first pore-forming agent forms a dense microporous structure, which, together with the hydrophobic agent, forms a hydrophobic surface.

[0015] The addition of a second pore-forming agent and the synergistic effect of polyvinylpyrrolidone in the bottom porous layer form a porous bottom layer with higher porosity, significantly improving water vapor permeability. The modified glass fiber improves thermal stability through the loading of Peek micro powder, and the epoxy-modified mica powder forms a thermal barrier through a layered structure, reducing pore deformation at high temperatures. By utilizing the rigidity of the modified fiber and the layered structure of the epoxy-modified mica powder, the pore morphology is maintained, solving the problem of reduced air permeability caused by pore collapse due to high temperatures. This improves the heat resistance of TPU film while also providing better air permeability.

[0016] After modification with an aminosilane coupling agent, the glass fiber surface forms chemical bonds with the isocyanate end groups in TPU, enhancing the interfacial bonding strength and reducing pore collapse caused by interfacial debonding at high temperatures. After ring opening, the epoxy groups form covalent bonds with the hydroxyl groups of TPU, improving the dispersibility and interfacial bonding of mica powder and enhancing the heat barrier effect. The addition of hexamethylene diisocyanate can also react with the hydroxyl groups in TPU to form a cross-linked network, fixing the pore structure and preventing pore collapse at high temperatures. The ester groups of polycarbonate diol provide hydrogen bonding sites, enhancing the interaction between molecular chains at high temperatures. Finally, through nanocomposite modification and the formation of gradient pore structures, this application breaks through the bottleneck of traditional TPU films that are difficult to balance heat resistance and breathability, producing a heat-resistant and breathable TPU film that meets the requirements of high-performance TPU films.

[0017] Optionally, the first pore-forming agent is a mixture of fumed silica and ammonium bicarbonate in a mass ratio of 1:(2-3).

[0018] The second pore-forming agent is a mixture of ammonium bicarbonate and polyvinylpyrrolidone in a mass ratio of 1:(2-2.5).

[0019] By adopting the above technical solution, in this application, ammonium bicarbonate and fumed silica are selected as the first pore-forming agents in the dense surface layer. During the processing of ammonium bicarbonate, it decomposes into amino and carbon dioxide gases, forming nanoscale closed pores. After the gas overflows, the pores collapse and close, allowing only water vapor to pass through. Fumed silica, as a nano-nucleating agent, forms hydrogen bonds between its surface hydroxyl groups and TPU segments, inducing phase separation to form microphase regions and small pores. When polyvinylpyrrolidone is selected in the bottom porous layer, it forms interconnected pores after processing and water permeation. Combined with sodium bicarbonate, the pore connectivity is significantly improved, forming a porous structure with excellent air permeability. Furthermore, the cross-linking reaction of polycarbonate diol and hexamethylene diisocyanate fixes the pore structure and solves the problem of pore deformation and collapse at high temperatures.

[0020] Optionally, the modified glass fiber is prepared by the following method:

[0021] 1) Glass fibers are plasma treated, then cleaned and dried to obtain pretreated glass fibers;

[0022] 2) Peek micro powder was first ultrasonically dispersed in an ethanol solution of γ-aminopropyltriethoxysilane, filtered and dried to obtain pretreated Peek micro powder.

[0023] 3) The pretreated glass fiber obtained in step 1) is impregnated in polyamic acid solution, and then the pretreated Peek micro powder obtained in step 2) is added. After ultrasonic impregnation for 1-2 hours, it is filtered and treated at 150-200℃ for 40-60 minutes to obtain the initial modified glass fiber.

[0024] 4) The modified glass fiber is impregnated in an impregnation solution containing N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, starch, emulsifier, water and PAMAM for 1-2 hours, then filtered and dried to obtain the modified glass fiber.

[0025] By adopting the above technical solution, this application first introduces oxygen-containing functional groups into the glass fiber after plasma treatment. Then, Peek powder is modified with γ-aminopropyltriethoxysilane and loaded onto the pretreated glass fiber in a polyamic acid solution. The polyamic acid solution acts as a polar binder, which binds to the hydroxyl groups of the glass fiber through hydrogen bonds and simultaneously encapsulates the Peek powder to form a preliminary adhesion. The surface of the Peek powder treated with the silane coupling agent has amino or alkoxy groups, which form covalent bonds with the carboxylic acid groups of the polyamic acid. Then, under subsequent high-temperature treatment, the polyamic acid is imidized to form polyimide, forming molecular chain crosslinking and volume shrinkage to form a three-dimensional network, which tightly anchors the Peek to the glass fiber, thus achieving the loading of Peek powder on the glass fiber.

[0026] Finally, the product is impregnated in an impregnation solution of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane and PAMAM. N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane contains a diamino functional group. Its primary amino group can form an amide bond with the isocyanate group in TPU to achieve strong chemical bonding. The secondary amino group can form a dynamic hydrogen bond with the carbonyl group in TPU to buffer interfacial stress. The amino group in the dendritic macromolecule of PAMAM can form multi-point anchoring with the hydroxyl group on the glass fiber surface and TPU segments to improve the interfacial bonding strength. The rigid link between the glass fiber and TPU segments by diaminosilane and PAMAM inhibits relative slippage and improves heat resistance. The addition of starch can enhance the anchoring stability of silanized Peek on the fiber surface, and it can also enhance the modified anchoring performance of diaminosilane and PAMAM on the glass fiber surface. Moreover, Peek micro powder can reduce the difference in thermal expansion coefficient between glass fiber and TPU, reduce interfacial thermal stress, and ultimately improve heat resistance while having excellent air permeability.

[0027] Optionally, during the preparation of modified glass fibers,

[0028] In step 2), the amount of γ-aminopropyltriethoxysilane added is 3-5 wt% of Peek micro powder, and the amount of ethanol solution added is 3-4 times the mass of γ-aminopropyltriethoxysilane.

[0029] In step 3), the mass fraction of the polyamic acid solution is 5-10%, and the amount of polyamic acid solution added is 4-5 times the mass of the pretreated glass fiber. The mass ratio of the pretreated glass fiber to the pretreated Peek micro powder is 1:(0.3-0.4).

[0030] In step 4), the impregnation solution is prepared by mixing N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, starch, emulsifier, water and PAMAM in a mass ratio of 1:(0.1-0.2):(0.05-0.1):(4-5):(0.4-0.6), and the amount of impregnation solution added is 4-6 times the mass of the original modified glass fiber.

[0031] Optionally, the epoxy-modified mica powder is prepared by the following method:

[0032] A coupling agent solution was prepared by dissolving γ-glycidoxypropyltrimethoxysilane in an ethanol solution with a mass concentration of 30-40%. Mica powder was then added, and the solution was subjected to pressure impregnation. After filtration and drying, epoxy-modified mica powder was obtained.

[0033] By adopting the above technical solution, γ-glycidoxypropyltrimethoxysilane is selected as the epoxy silane coupling agent. The epoxy silane coupling agent is hydrolyzed in ethanol solution to generate silanol groups. These silanol groups have high reactivity and can react with the hydroxyl groups on the surface of mica powder. The hydrolyzed epoxy silane coupling agent forms covalent bonds with the hydroxyl groups on the surface of mica powder, thereby achieving epoxy modification treatment of mica powder. Under high temperature treatment, the epoxy groups open the ring and form covalent bonds with TPU, improving the interfacial bonding between mica powder and TPU, enhancing the thermal barrier effect, and reducing the decrease in air permeability caused by pore deformation and collapse due to high temperature.

[0034] Optionally, in the preparation of epoxy-modified mica powder, the amount of γ-glycidoxypropyltrimethoxysilane added is 8-15 wt% of the mica powder, and the amount of ethanol solution added is 3-5 times the mass of γ-glycidoxypropyltrimethoxysilane.

[0035] Optionally, the pressure impregnation time is 40-60 min, the impregnation pressure is 0.5-0.8 MPa, and the impregnation temperature is 40-50℃.

[0036] By adopting the above technical solution and the above impregnation system, it is helpful to achieve epoxy group modification of mica powder.

[0037] Optionally, the epoxy-modified mica powder obtained may undergo post-treatment, the post-treatment operation being as follows:

[0038] The epoxy-modified mica powder was first impregnated in an ethanol solution of vinyltriethoxysilane for 20-30 minutes, then cinnamic acid and methyl methacrylate were added, the temperature was raised to 65-75℃, benzoyl peroxide was added, the reaction was carried out for 1-2 hours, then cooled, filtered and dried.

[0039] By adopting the above technical solution, epoxy-modified mica powder is first impregnated in an ethanol solution of vinyltriethoxysilane. The silanol after ethoxyl hydrolysis reacts with the hydroxyl groups of mica powder to introduce vinyl unsaturated functional groups. Then, under the action of benzoyl peroxide initiator, it polymerizes with methyl methacrylate and cinnamic acid, introducing acrylate polymer segments onto the surface of mica powder, thereby significantly improving its compatibility with TPU substrate. Moreover, the addition of cinnamic acid also introduces carboxyl functional groups and benzene ring groups on the surface, which can form chemical reactions with the amino groups on the modified glass fiber. This further realizes the cross-linking network in the TPU system, achieving the fixation of the pore structure. The introduction of benzene ring groups as rigid groups further improves its thermal stability and reduces the decrease in air permeability caused by pore collapse at high temperatures. The final TPU film has excellent heat resistance and good air permeability.

[0040] Optionally, during the post-treatment of epoxy-modified mica powder, the mass ratio of epoxy-modified mica powder to vinyltriethoxysilane is 1:(0.1-0.2), the mass ratio of vinyltriethoxysilane to cinnamic acid and methyl methacrylate is 1:(0.2-0.3):(0.4-0.5), and the amount of benzoyl peroxide added is 1-3 wt% of epoxy-modified mica powder.

[0041] Optionally, the hydrophobic agent is selected from polydimethylsiloxane, and the antioxidant is selected from antioxidant 1010.

[0042] Optionally, the bottom porous layer is provided with tapered vent holes along its thickness direction, and the diameter of the tapered vent holes gradually decreases along the dense layer near the surface.

[0043] By adopting the above technical solution, the setting of the conical vent holes and the setting of the pore size on the bottom porous layer allows water vapor to pass through the bottom porous layer and the dense layer better, while the small pore size of the outer layer can effectively block the entry of liquid, thus achieving a balance between waterproofing and breathability.

[0044] Secondly, this application provides a process for preparing a heat-resistant and breathable TPU film, using the following technical solution:

[0045] A process for preparing a heat-resistant and breathable TPU film includes the following steps:

[0046] S1. The raw materials of the bottom porous layer are mixed in proportion and then melt-extruded to form a bottom membrane. After washing with water to remove polyvinylpyrrolidone, the bottom porous layer is then dried to obtain the bottom porous layer.

[0047] S2. The raw materials for the surface dense layer are mixed in proportion and then melted and extruded to form a surface dense layer. Then, the surface dense layer is hot-pressed and laminated with the bottom porous layer to obtain a heat-resistant and breathable TPU film.

[0048] By adopting the above technical solution, which involves separate melt extrusion followed by hot pressing and composite, the process is more flexible and allows for the removal of polyvinylpyrrolidone from the bottom porous layer after water washing to form a porous structure, resulting in a gradient pore structure distribution.

[0049] In summary, this application has the following beneficial effects:

[0050] 1. The heat-resistant and breathable TPU membrane in this application is composed of a dense surface layer and a porous bottom layer. The dense surface layer acts as a surface barrier of the membrane material, undertaking the functions of heat resistance, hydrophobicity and anti-aging, while preventing liquid penetration. The porous bottom layer achieves efficient water vapor transmission by adjusting the pores. At the same time, the addition of modified glass fiber and other raw materials improves heat resistance and mechanical support, reducing the problem of pore collapse at high temperatures leading to a decrease in breathability.

[0051] 2. The addition of a second pore-forming agent and the synergistic effect of polyvinylpyrrolidone in the bottom porous layer form a porous bottom layer with higher porosity, significantly improving water vapor permeability. The modified glass fiber improves thermal stability through the loading of Peek micro powder, and the epoxy-modified mica powder forms a thermal barrier through the layered structure, reducing pore deformation at high temperatures. The rigidity of the modified fiber and the layered structure of the epoxy-modified mica powder maintain the pore morphology, solving the problem of reduced air permeability caused by pore collapse due to high temperature. This improves the heat resistance of TPU film while providing better air permeability.

[0052] 3. In this application, the glass fiber surface is modified with an aminosilane coupling agent, which forms a chemical bond with the isocyanate end groups in TPU, enhancing the interfacial bonding strength and reducing pore collapse caused by interfacial debonding at high temperatures. After the epoxy groups open, they form covalent bonds with the hydroxyl groups of TPU, improving the dispersibility and interfacial bonding of mica powder and enhancing the heat barrier effect. The addition of hexamethylene diisocyanate can also react with the hydroxyl groups in TPU to form a cross-linked network, fixing the pore structure and preventing pore collapse at high temperatures. The ester groups of polycarbonate diol provide hydrogen bonding sites, enhancing the interaction between molecular chains at high temperatures. Finally, this application overcomes the bottleneck of traditional TPU films' difficulty in balancing heat resistance and breathability through nanocomposite modification and the formation of gradient pore structures, producing a heat-resistant and breathable TPU film that meets the requirements of high-performance TPU films. Detailed Implementation

[0053] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources.

[0054] Unless otherwise specified, the percentages in the following examples are mass percentages.

[0055] In the following examples, the hydrophobic nano-silica was selected from Jiangsu Tianxing New Materials Co., Ltd., specifically the TSP-L20 type.

[0056] In the following examples, the mica powder used is sericite powder; the Peek micro powder used is the L150 (powder) Peek micro powder from Shanghai Liancheng Plastics Co., Ltd.; and the TPU granules used are the UE-85AU10 TPU granules from Dongguan Changhong Plastics Co., Ltd.

[0057] The following preparation examples are examples of the preparation of modified glass fibers.

[0058] Preparation Example 1

[0059] An example of preparing modified glass fiber includes the following steps:

[0060] 1) The glass fiber was treated in a plasma processor with oxygen as the plasma atmosphere for 4 minutes, the power was 250W and the pressure was 20 mbar, and then it was cleaned and dried to obtain pretreated glass fiber.

[0061] 2) Peek micro powder was first ultrasonically dispersed in an ethanol solution of γ-aminopropyltriethoxysilane for 15 min, filtered, and dried to obtain pretreated Peek micro powder. The amount of ethanol solution added was 3 times the mass of γ-aminopropyltriethoxysilane, and the mass concentration of the ethanol solution was 30%. The amount of γ-aminopropyltriethoxysilane added was 4 wt% of the Peek micro powder.

[0062] 3) The pretreated glass fiber obtained in step 1) is immersed in a polyamic acid solution with a mass fraction of 8% for 25 minutes, and then the pretreated Peek micro powder obtained in step 2) is added. After ultrasonic impregnation for 1.5 hours with an ultrasonic power of 100W, the mixture is filtered and treated at 180℃ for 50 minutes to obtain the pre-modified glass fiber. The amount of polyamic acid solution added is 4.5 times the mass of the pretreated glass fiber, and the mass ratio of the pretreated glass fiber to the pretreated Peek micro powder is 1:0.3.

[0063] 4) N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, starch, emulsifier, water and PAMAM are mixed in a mass ratio of 1:0.1:0.08:4.5:0.5 to prepare an impregnation solution. The impregnation temperature is 55℃. Then, the pre-modified glass fiber obtained in step 3) is impregnated in the impregnation solution for 1.5h, filtered and dried to obtain modified glass fiber. The amount of impregnation solution added is 5 times the mass of the pre-modified glass fiber. The starch is corn starch and the emulsifier is sodium stearate.

[0064] Preparation Example 2

[0065] An example of preparing modified glass fiber includes the following steps:

[0066] 1) The glass fiber was treated in a plasma processor with oxygen as the plasma atmosphere for 3 minutes, the power was 300W and the pressure was 15mbar, and then it was cleaned and dried to obtain pretreated glass fiber.

[0067] 2) Peek micro powder was first ultrasonically dispersed in an ethanol solution of γ-aminopropyltriethoxysilane for 10 min, filtered, and dried to obtain pretreated Peek micro powder. The amount of ethanol solution added was 3 times the mass of γ-aminopropyltriethoxysilane, and the mass concentration of the ethanol solution was 30%. The amount of γ-aminopropyltriethoxysilane added was 3 wt% of the Peek micro powder.

[0068] 3) The pretreated glass fiber obtained in step 1) is immersed in a 5% polyamic acid solution for 20 minutes, and then the pretreated Peek micro powder obtained in step 2) is added. After ultrasonic impregnation for 1 hour with an ultrasonic power of 100W, the mixture is filtered and treated at 150℃ for 60 minutes to obtain the pre-modified glass fiber. The amount of polyamic acid solution added is 4 times the mass of the pretreated glass fiber, and the mass ratio of the pretreated glass fiber to the pretreated Peek micro powder is 1:0.3.

[0069] 4) N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, starch, emulsifier, water and PAMAM are mixed in a mass ratio of 1:0.1:0.05:4:0.4 to prepare an impregnation solution. The impregnation temperature is 50℃. Then, the pre-modified glass fiber obtained in step 3) is impregnated in the impregnation solution for 2 hours, filtered and dried to obtain modified glass fiber. The amount of impregnation solution added is 4 times the mass of the pre-modified glass fiber. The starch is corn starch and the emulsifier is sodium stearate.

[0070] Preparation Example 3

[0071] An example of preparing modified glass fiber includes the following steps:

[0072] 1) The glass fiber was treated in a plasma processor with oxygen as the plasma atmosphere for 5 minutes, the power was 200W and the pressure was 20 mbar, and then it was cleaned and dried to obtain pretreated glass fiber.

[0073] 2) Peek micro powder was first ultrasonically dispersed in an ethanol solution of γ-aminopropyltriethoxysilane for 20 min, filtered, and dried to obtain pretreated Peek micro powder. The amount of ethanol solution added was 4 times the mass of γ-aminopropyltriethoxysilane, and the mass concentration of the ethanol solution was 40%. The amount of γ-aminopropyltriethoxysilane added was 5 wt% of the Peek micro powder.

[0074] 3) The pretreated glass fiber obtained in step 1) is immersed in a 10% polyamic acid solution for 30 minutes, and then the pretreated Peek micro powder obtained in step 2) is added. After ultrasonic impregnation for 2 hours with an ultrasonic power of 100W, the mixture is filtered and treated at 200℃ for 40 minutes to obtain the pre-modified glass fiber. The amount of polyamic acid solution added is 5 times the mass of the pretreated glass fiber, and the mass ratio of the pretreated glass fiber to the pretreated Peek micro powder is 1:0.4.

[0075] 4) N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, starch, emulsifier, water and PAMAM are mixed in a mass ratio of 1:0.2:0.1:5:0.6 to prepare an impregnation solution. The impregnation temperature is 60℃. Then, the pre-modified glass fiber obtained in step 3) is impregnated in the impregnation solution for 1 hour, filtered and dried to obtain modified glass fiber. The amount of impregnation solution added is 6 times the mass of the pre-modified glass fiber. The starch is corn starch and the emulsifier is sodium stearate.

[0076] Preparation Example 4

[0077] A process for preparing modified glass fiber is carried out according to the method in Preparation Example 1, except that PAMAM is not added to the impregnation solution in step 4).

[0078] Comparative Preparation Example 1

[0079] A process for preparing modified glass fiber is carried out according to the method in Preparation Example 1, except that steps 2)-3) are not performed, and step 4) is performed directly after step 1), and in step 4), the initial modified glass fiber is replaced with pretreated glass fiber in an equal amount.

[0080] Example 1

[0081] A process for preparing a heat-resistant and breathable TPU film includes the following steps:

[0082] S1. Mix 70 kg TPU granules, 8 kg secondary pore-forming agent, 5 kg polyvinylpyrrolidone, 4 kg hexamethylene diisocyanate, 4 kg polycarbonate diol, 12 kg modified glass fiber prepared in Preparation Example 1, and 8 kg epoxy-modified mica powder in a high-speed mixer at a speed of 1000 r / min for 10 min to obtain the bottom layer mixture.

[0083] Then the bottom mixture is added to the screw extruder for melt extrusion to produce the bottom film. The temperature of the feeding section is 160℃, the temperature of the compression section is 180℃, the temperature of the metering section is 190℃, the temperature of the die head is 200℃, and the screw speed is 30r / min.

[0084] The prepared bottom membrane was washed with water to remove polyvinylpyrrolidone and then dried to obtain a bottom porous layer with a thickness of 0.2 mm.

[0085] S2. 70kg TPU particles, 4kg primary pore-forming agent, 8kg hydrophobic agent, 3kg polyethylene glycol, 2kg antioxidant, 8kg hydrophobic nano silica and 12kg nano carbon fibers are mixed in a high-speed mixer at a speed of 800r / min for 10min to obtain a surface mixture.

[0086] The surface mixture is added to a screw extruder and melt-extruded to obtain a dense surface layer with a thickness of 0.2 mm. The temperature of the feeding section is 160℃, the temperature of the compression section is 180℃, the temperature of the metering section is 190℃, the temperature of the die head is 200℃, and the screw speed is 30 r / min.

[0087] Then, the bottom porous layer and the surface dense layer are hot-pressed together with a pressing plate temperature of 180℃ and a pressure of 10MPa to obtain a heat-resistant and breathable TPU film.

[0088] In step S1, the second porogen is a mixture of ammonium bicarbonate and polyvinylpyrrolidone in a mass ratio of 1:2.2; in step S2, the first porogen is a mixture of fumed silica and ammonium bicarbonate in a mass ratio of 1:2.5; and in step S2, the hydrophobic agent is polydimethylsiloxane and the antioxidant is antioxidant 1010.

[0089] The epoxy-modified mica powder in step S1 is obtained by the following method:

[0090] A coupling agent solution was prepared by dissolving γ-glycidoxypropyltrimethoxysilane in a 35% ethanol solution, with the amount of ethanol solution added being 4 times the mass of γ-glycidoxypropyltrimethoxysilane.

[0091] Then, mica powder was added to the coupling agent solution, and the amount of γ-glycidyl etheroxypropyltrimethoxysilane added was 10 wt% of the mica powder. The mixture was then subjected to pressure impregnation treatment for 50 min, with an impregnation pressure of 0.6 MPa and an impregnation temperature of 45 °C. After filtration, the mixture was dried to obtain epoxy-modified mica powder.

[0092] Example 2

[0093] A process for preparing a heat-resistant and breathable TPU film includes the following steps:

[0094] S1. Mix 60 kg of TPU granules, 5 kg of secondary pore-forming agent, 4 kg of polyvinylpyrrolidone, 3 kg of hexamethylene diisocyanate, 3 kg of polycarbonate diol, 10 kg of modified glass fiber prepared in Preparation Example 2, and 5 kg of epoxy-modified mica powder in a high-speed mixer at a speed of 1000 r / min for 10 min to obtain the bottom layer mixture.

[0095] Then the bottom mixture is added to the screw extruder for melt extrusion to produce the bottom film. The temperature of the feeding section is 160℃, the temperature of the compression section is 180℃, the temperature of the metering section is 190℃, the temperature of the die head is 200℃, and the screw speed is 30r / min.

[0096] The prepared bottom membrane was washed with water to remove polyvinylpyrrolidone and then dried to obtain a bottom porous layer with a thickness of 0.2 mm.

[0097] S2. 60kg TPU particles, 3kg primary pore-forming agent, 5kg hydrophobic agent, 2kg polyethylene glycol, 1kg antioxidant, 5kg hydrophobic nano silica and 8kg nano carbon fibers are mixed in a high-speed mixer at a speed of 800r / min for 10min to obtain a surface mixture.

[0098] The surface mixture is added to a screw extruder and melt-extruded to obtain a dense surface layer with a thickness of 0.2 mm. The temperature of the feeding section is 160℃, the temperature of the compression section is 180℃, the temperature of the metering section is 190℃, the temperature of the die head is 200℃, and the screw speed is 30 r / min.

[0099] Then, the bottom porous layer and the surface dense layer are hot-pressed together with a pressing plate temperature of 170℃ and a pressure of 5MPa to obtain a heat-resistant and breathable TPU film.

[0100] In step S1, the second porogen is a mixture of ammonium bicarbonate and polyvinylpyrrolidone in a mass ratio of 1:2; in step S2, the first porogen is a mixture of fumed silica and ammonium bicarbonate in a mass ratio of 1:2; and in step S2, the hydrophobic agent is polydimethylsiloxane and the antioxidant is antioxidant 1010.

[0101] The epoxy-modified mica powder in step S1 is obtained by the following method:

[0102] A coupling agent solution was prepared by dissolving γ-glycidoxypropyltrimethoxysilane in a 30% ethanol solution, with the amount of ethanol solution added being 3 times the mass of γ-glycidoxypropyltrimethoxysilane.

[0103] Then, mica powder was added to the coupling agent solution, and the amount of γ-glycidyl etheroxypropyltrimethoxysilane added was 8 wt% of the mica powder. The mixture was then subjected to pressure impregnation treatment for 40 min, with an impregnation pressure of 0.8 MPa and an impregnation temperature of 50 °C. After filtration, the mixture was dried to obtain epoxy-modified mica powder.

[0104] Example 3

[0105] A process for preparing a heat-resistant and breathable TPU film includes the following steps:

[0106] S1. Mix 80 kg TPU granules, 10 kg secondary pore-forming agent, 8 kg polyvinylpyrrolidone, 5 kg hexamethylene diisocyanate, 5 kg polycarbonate diol, 15 kg modified glass fiber prepared in Preparation Example 3, and 10 kg epoxy-modified mica powder in a high-speed mixer at a speed of 1000 r / min for 10 min to obtain the bottom layer mixture.

[0107] Then the bottom mixture is added to the screw extruder for melt extrusion to produce the bottom film. The temperature of the feeding section is 160℃, the temperature of the compression section is 180℃, the temperature of the metering section is 190℃, the temperature of the die head is 200℃, and the screw speed is 30r / min.

[0108] The prepared bottom membrane was washed with water to remove polyvinylpyrrolidone and then dried to obtain a bottom porous layer with a thickness of 0.2 mm.

[0109] S2. 80kg TPU particles, 5kg primary pore-forming agent, 10kg hydrophobic agent, 5kg polyethylene glycol, 3kg antioxidant, 10kg hydrophobic nano silica and 15kg nano carbon fibers are mixed in a high-speed mixer at a speed of 800r / min for 10min to obtain a surface mixture.

[0110] The surface mixture is added to a screw extruder and melt-extruded to obtain a dense surface layer with a thickness of 0.2 mm. The temperature of the feeding section is 160℃, the temperature of the compression section is 180℃, the temperature of the metering section is 190℃, the temperature of the die head is 200℃, and the screw speed is 30 r / min.

[0111] Then, the bottom porous layer and the surface dense layer are hot-pressed together with a pressing plate temperature of 190℃ and a pressure of 15MPa to obtain a heat-resistant and breathable TPU film.

[0112] In step S1, the second porogen is a mixture of ammonium bicarbonate and polyvinylpyrrolidone in a mass ratio of 1:2.5; in step S2, the first porogen is a mixture of fumed silica and ammonium bicarbonate in a mass ratio of 1:3; and in step S2, the hydrophobic agent is polydimethylsiloxane and the antioxidant is antioxidant 1010.

[0113] The epoxy-modified mica powder in step S1 is obtained by the following method:

[0114] A coupling agent solution was prepared by dissolving γ-glycidoxypropyltrimethoxysilane in a 40% ethanol solution, with the amount of ethanol solution added being 5 times the mass of γ-glycidoxypropyltrimethoxysilane.

[0115] Then, mica powder was added to the coupling agent solution, and the amount of γ-glycidyl etheroxypropyltrimethoxysilane added was 15 wt% of the mica powder. The mixture was subjected to pressure impregnation treatment, with an impregnation time of 60 min, an impregnation pressure of 0.5 MPa, and an impregnation temperature of 40 °C. After filtration, the mixture was dried to obtain epoxy-modified mica powder.

[0116] Example 4

[0117] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that the modified glass fiber in step S1 is the modified glass fiber obtained in Preparation Example 4.

[0118] Example 5

[0119] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that the epoxy-modified mica powder obtained in step S1 is added after undergoing the following post-treatment steps, specifically as follows:

[0120] The epoxy-modified mica powder was first impregnated in an ethanol solution of vinyltriethoxysilane for 20-30 minutes, then cinnamic acid and methyl methacrylate were added, the temperature was raised to 70°C, benzoyl peroxide was added, the reaction was carried out for 1.5 hours, cooled, filtered and dried.

[0121] The mass ratio of epoxy-modified mica powder to vinyltriethoxysilane is 1:0.1, the mass concentration of the ethanol solution is 30%, and the amount of ethanol solution added is 4 times the mass of vinyltriethoxysilane. The mass ratio of vinyltriethoxysilane to cinnamic acid and methyl methacrylate is 1:0.25:0.45, and the amount of benzoyl peroxide added is 2 wt% of epoxy-modified mica powder.

[0122] Example 6

[0123] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that the epoxy-modified mica powder obtained in step S1 is added after undergoing the following post-treatment steps, specifically as follows:

[0124] The epoxy-modified mica powder was first impregnated in an ethanol solution of vinyltriethoxysilane for 20-30 minutes, then cinnamic acid and methyl methacrylate were added, the temperature was raised to 65°C, benzoyl peroxide was added, the reaction was carried out for 2 hours, cooled, filtered and dried.

[0125] The mass ratio of epoxy-modified mica powder to vinyltriethoxysilane is 1:0.1, the mass concentration of the ethanol solution is 30%, and the amount of ethanol solution added is 3 times the mass of vinyltriethoxysilane. The mass ratio of vinyltriethoxysilane to cinnamic acid and methyl methacrylate is 1:0.2:0.4, and the amount of benzoyl peroxide added is 1 wt% of epoxy-modified mica powder.

[0126] Example 7

[0127] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that the epoxy-modified mica powder obtained in step S1 is added after undergoing the following post-treatment steps, specifically as follows:

[0128] The epoxy-modified mica powder was first impregnated in an ethanol solution of vinyltriethoxysilane for 20-30 minutes, then cinnamic acid and methyl methacrylate were added, the temperature was raised to 75°C, benzoyl peroxide was added, the reaction was carried out for 1 hour, cooled, filtered and dried.

[0129] The mass ratio of epoxy-modified mica powder to vinyltriethoxysilane is 1:0.2, the mass concentration of the ethanol solution is 30%, and the amount of ethanol solution added is 5 times the mass of vinyltriethoxysilane. The mass ratio of vinyltriethoxysilane to cinnamic acid and methyl methacrylate is 1:0.3:0.5, and the amount of benzoyl peroxide added is 3 wt% of epoxy-modified mica powder.

[0130] Example 8

[0131] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that the bottom porous layer is provided with tapered vent holes along its thickness direction, and the diameter of the tapered vent holes gradually decreases along the dense layer near the surface. The diameter of the tapered vent holes on the side near the dense layer is 0.03 mm, and the diameter on the other side is 0.08 mm.

[0132] Comparative Example 1

[0133] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that the modified glass fiber in step S1 is the modified glass fiber obtained in Comparative Preparation Example 1.

[0134] Comparative Example 2

[0135] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that the modified glass fiber in step S1 is replaced by an equal amount of glass fiber.

[0136] Comparative Example 3

[0137] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that the epoxy-modified mica powder in step S1 is replaced with an equal amount of mica powder.

[0138] Comparative Example 4

[0139] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that epoxy-modified mica powder is not added in step S1.

[0140] Comparative Example 5

[0141] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that hexamethylene diisocyanate is not added in step S1.

[0142] Comparative Example 6

[0143] A process for preparing a heat-resistant and breathable TPU film is carried out according to the method in Example 1, except that polycarbonate diol is not added in step S1.

[0144] Performance testing

[0145] The water vapor transmission rate of the prepared TPU membrane was tested according to the method in section 6.6 of GB / T 20991-2007, and the water vapor transmission rate (mg / (cm)) was calculated. 2 The results are shown in Table 1 below. Then, referring to GB / T 5453-2025 "Determination of Air Permeability of Textile Fabrics", the air permeability (mm / s) of the PTU membrane was measured, and the statistical results are shown in Table 1 below.

[0146] In addition, to consider the effect of high temperature on water vapor transmission rate, the initial water vapor transmission rate of the sample at room temperature was measured according to the above detection method. Then, the sample was placed in a high-temperature oven at 100℃ for 2 hours. After cooling to room temperature, the water vapor transmission rate was measured again according to the above detection method. The moisture permeability retention rate of the sample at high temperature was calculated as (water vapor transmission rate after high temperature treatment / initial water vapor transmission rate) × 100%. The results are shown in Table 1 below. In addition, the temperature resistance of the prepared TPU was tested. The specific method was as follows: the shrinkage rate of the prepared TPU film with a size of 100*100mm was calculated after baking at 150℃ for 2 hours. The statistical results are shown in Table 1 below.

[0147] Table 1:

[0148]

[0149] Referring to the test results in Table 1 above, the TPU film prepared in this application embodiment has excellent heat resistance and breathability, especially excellent breathability retention rate after long-term high-temperature treatment. In addition, the TPU film prepared in this application embodiment was tested for Vicat softening point according to GB / T 1633-2000, and its Vicat softening point is 120-130℃. Moreover, the mechanical properties of the TPU film prepared in Examples 1-8 of this application meet the requirements of tensile strength ≥25 MPa and elongation at break ≥300%. In addition, the TPU film obtained in Examples 1-8 of this application was tested for waterproof performance by hydrostatic pressure method according to GB / T 4744-2013, and it meets the requirement of 10000mmH2O. Furthermore, when water with a pressure of 10 kPa was applied to the dense surface layer of the TPU film and kept for 24 hours, no water droplets were observed to penetrate into the TPU film, indicating excellent waterproof performance.

[0150] Referring to the test results of Examples 1 and 4, it can be seen that when modifying glass fibers, the air permeability retention rate and heat resistance temperature are reduced when PAMAM is not added to the impregnation solution. The addition of PAMAM introduces amino functional groups into the glass fibers, which can form chemical bonds with epoxy-modified mica powder and crosslink with polycarbonate diol, etc., improving its temperature resistance and playing a fixing role to reduce pore deformation at high temperatures, thereby improving its air permeability at high temperatures. Combining the test results of Examples 5-7, the epoxy-modified mica powder further improves its air permeability retention rate and heat resistance temperature at high temperatures after post-treatment. Combining the test results of Example 8, the setting of conical pores can further improve its air permeability.

[0151] Combining the test results of Example 1 and Comparative Example 1, when the glass fiber was not subjected to Peek loading, its heat resistance and high-temperature air permeability retention rate were significantly reduced. Combining the test results of Comparative Example 2, when the glass fiber was added directly without modification, its air permeability and heat resistance were significantly reduced, and its interface bonding with TPU was poor. The difference in thermal expansion coefficients at high temperatures led to severe pore collapse, resulting in an even lower air permeability retention rate. Combining the test results of Comparative Examples 3 and 4, when mica powder was added directly without modification, its air permeability and heat resistance were slightly better than when epoxy-modified mica powder was not added, but still far weaker than in Example 1. Its layered structure had a certain heat insulation effect, but its bonding with TPU and its effect in combination with other raw materials were weak. Combining the test results of Comparative Examples 5 and 6, when polycarbonate diol or hexamethylene diisocyanate was not added to the raw materials, its heat resistance and high-temperature air permeability retention rate were significantly reduced.

[0152] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A heat-resistant and breathable TPU film, characterized in that, It includes a dense surface layer and a porous bottom layer, wherein the dense surface layer comprises the following raw materials in parts by weight: 60-80 parts TPU particles, 3-5 parts primary pore-forming agent, 5-10 parts hydrophobic agent, 2-5 parts polyethylene glycol, 1-3 parts antioxidant, 5-10 parts hydrophobic nano silica and 8-15 parts carbon nanofibers; The underlying porous layer comprises the following raw materials in parts by weight: 60-80 parts TPU granules, 5-10 parts secondary pore-forming agent, 4-8 parts polyvinylpyrrolidone, 3-5 parts hexamethylene diisocyanate, 3-5 parts polycarbonate diol, 10-15 parts modified glass fiber, and 5-10 parts epoxy-modified mica powder. The first pore-forming agent is a mixture of fumed silica and ammonium bicarbonate with a mass ratio of 1:(2-3); The second pore-forming agent is a mixture of ammonium bicarbonate and polyvinylpyrrolidone in a mass ratio of 1:(2-2.5); The modified glass fiber is prepared by the following method: 1) Glass fibers are plasma treated, then cleaned and dried to obtain pretreated glass fibers; 2) Peek micro powder was first ultrasonically dispersed in an ethanol solution of γ-aminopropyltriethoxysilane, filtered and dried to obtain pretreated Peek micro powder. 3) The pretreated glass fiber obtained in step 1) is impregnated in polyamic acid solution, and then the pretreated Peek micro powder obtained in step 2) is added. After ultrasonic impregnation for 1-2 hours, it is filtered and treated at 150-200℃ for 40-60 minutes to obtain the initial modified glass fiber. 4) The modified glass fiber is impregnated in an impregnation solution containing N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, starch, emulsifier, water and PAMAM for 1-2 hours, then filtered and dried to obtain the modified glass fiber. The epoxy-modified mica powder is prepared by the following method: A coupling agent solution was prepared by dissolving γ-glycidoxypropyltrimethoxysilane in an ethanol solution with a mass concentration of 30-40%. Mica powder was then added, and the solution was subjected to pressure impregnation. After filtration and drying, epoxy-modified mica powder was obtained.

2. The heat-resistant and breathable TPU film according to claim 1, characterized in that: During the preparation of modified glass fibers, In step 2), the amount of γ-aminopropyltriethoxysilane added is 3-5 wt% of Peek micro powder, and the amount of ethanol solution added is 3-4 times the mass of γ-aminopropyltriethoxysilane. In step 3), the mass fraction of the polyamic acid solution is 5-10%, and the amount of polyamic acid solution added is 4-5 times the mass of the pretreated glass fiber. The mass ratio of the pretreated glass fiber to the pretreated Peek micro powder is 1:(0.3-0.4). In step 4), the impregnation solution is prepared by mixing N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, starch, emulsifier, water and PAMAM in a mass ratio of 1:(0.1-0.2):(0.05-0.1):(4-5):(0.4-0.6), and the amount of impregnation solution added is 4-6 times the mass of the original modified glass fiber.

3. The heat-resistant and breathable TPU film according to claim 1, characterized in that: In the preparation of epoxy-modified mica powder, the amount of γ-glycidoxypropyltrimethoxysilane added is 8-15 wt% of the mica powder, and the amount of ethanol solution added is 3-5 times the mass of γ-glycidoxypropyltrimethoxysilane.

4. The heat-resistant and breathable TPU film according to claim 1, characterized in that: The epoxy-modified mica powder also undergoes post-processing, which includes the following steps: The epoxy-modified mica powder was first impregnated in an ethanol solution of vinyltriethoxysilane for 20-30 minutes, then cinnamic acid and methyl methacrylate were added, the temperature was raised to 65-75℃, benzoyl peroxide was added, the reaction was carried out for 1-2 hours, then cooled, filtered and dried.

5. The heat-resistant and breathable TPU film according to claim 4, characterized in that: During the post-treatment of epoxy-modified mica powder, the mass ratio of epoxy-modified mica powder to vinyltriethoxysilane is 1:(0.1-0.2), the mass ratio of vinyltriethoxysilane to cinnamic acid and methyl methacrylate is 1:(0.2-0.3):(0.4-0.5), and the amount of benzoyl peroxide added is 1-3 wt% of epoxy-modified mica powder.

6. The heat-resistant and breathable TPU film according to claim 1, characterized in that: The hydrophobic agent is selected from polydimethylsiloxane, and the antioxidant is selected from antioxidant 1010.

7. A preparation process for the heat-resistant and breathable TPU film as described in any one of claims 1-6, characterized in that: Includes the following steps: S1. The raw materials of the bottom porous layer are mixed in proportion and then melt-extruded to form a bottom membrane. After washing with water to remove polyvinylpyrrolidone, the bottom porous layer is then dried to obtain the bottom porous layer. S2. The raw materials for the surface dense layer are mixed in proportion and then melted and extruded to form a surface dense layer. Then, the surface dense layer is hot-pressed and laminated with the bottom porous layer to obtain a heat-resistant and breathable TPU film.

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