Tpu film and method for producing the same

Abstract

The application discloses a TPU film and a preparation method thereof. The preparation method of the TPU film comprises the following steps: granulating and flow-casting a raw material composition to prepare the TPU film; wherein the raw material composition comprises a composite filler and a TPU resin, and the composite filler comprises, in 100 parts by weight of the TPU resin, 3-8 parts of nano-silicon dioxide, 1-6 parts of micron-aluminum oxide, a lubricant, a silane coupling agent and a fatty acid substance; the flow-casting process comprises extrusion and setting in sequence, the setting is carried out between a front roller and a middle roller, the temperature of the front roller is higher than that of the middle roller, and the hardness of the front roller is lower than that of the middle roller; the hardness of the front roller is 70A-80A; and the hardness of the middle roller is 89A-95A. The TPU film provided by the application has good aging property, high mechanical strength and good stability.

Description

Technical Field

[0001] This invention relates to TPU films and their preparation methods. Background Technology

[0002] Traditional TPU film surface modification often uses corona treatment, but it has problems such as poor timeliness (rapid decay of dyne value) and high energy consumption; modification with a single filler (such as nano calcium carbonate) is prone to a decrease in mechanical properties and the improvement of dyne value is limited (dyne value ≤38); conventional casting process roller configuration cannot form a stable micro-nano structure.

[0003] How to achieve a sustained increase in the surface energy of TPU films without corona treatment; how to balance the relationship between high filler addition and material mechanical properties; and how to achieve precise control of surface microstructure through optimization of rolling process parameters. Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing TPU films, such as poor aging performance, poor mechanical properties, and structural instability, by providing a TPU film and its preparation method. The TPU film provided by this invention exhibits good aging performance, high mechanical strength, and good stability.

[0005] In a first aspect, the present invention provides a method for preparing a TPU film, comprising the following steps: granulating and casting a raw material composition to obtain the TPU film;

[0006] The raw material composition includes a composite filler and a TPU resin. Based on 100 parts by weight of the TPU resin, the composite filler includes:

[0007] 3-8 parts of nano-silica;

[0008] 1-6 parts of micron-sized alumina;

[0009] Lubricant;

[0010] Silane coupling agents;

[0011] fatty acids;

[0012] The casting process includes extrusion and setting in sequence. The setting is carried out between the front roller and the middle roller. The temperature of the front roller is higher than that of the middle roller, and the hardness of the front roller is lower than that of the middle roller. The hardness of the front roller is 70A-80A, and the hardness of the middle roller is 89A-95A.

[0013] In this invention, the fatty acid substance may be a fatty acid and / or a fatty acid amide; the fatty acid preferably has 12-20 carbon atoms, such as one or more of palmitic acid, lauric acid and stearic acid; the fatty acid amide preferably has 12-20 carbon atoms, such as stearamide.

[0014] In this invention, with 100 parts by weight of TPU resin, the fatty acid substances in the composite filler can be 0.5-2 parts by weight, for example, 0.5 parts or 2 parts.

[0015] In this invention, the silane coupling agent can be any silane coupling agent conventionally used in the art, preferably an aminosilane coupling agent, such as γ-aminopropyltriethoxysilane (KH550).

[0016] In this invention, with 100 parts by weight of TPU resin, the silane coupling agent in the composite filler can be 0.5-2 parts by weight, for example, 0.5 parts or 2 parts.

[0017] In this invention, the particle size of the micron-sized alumina can be 1-2 μm, for example, 2 μm.

[0018] In this invention, with 100 parts by weight of TPU resin, the part by weight of micron-sized alumina in the composite filler can be 2-5 parts, for example, 2 parts, 3 parts or 5 parts.

[0019] In this invention, the particle size of the nano-silica can be 20-50 nm, for example, 30 nm.

[0020] In this invention, with 100 parts by weight of TPU resin, the nano-silica in the composite filler can be 3-6 parts by weight, for example, 5 parts.

[0021] In this invention, the lubricant may be one or more of polyalkane wax, polyolefin wax and tungsten disulfide; the polyalkane wax is preferably Fischer-Tropsch wax; the polyolefin wax is preferably polytetrafluoroethylene (PTFE) wax and / or polyethylene wax.

[0022] In this invention, the lubricant can be a conventional lubricant used in the art, preferably meeting the following conditions: (1) good thermal stability, does not decompose or volatilize during TPU processing (150-200℃), and does not chemically react with TPU resin and composite filler; (2) moderate migration, can slowly migrate to the film surface during processing, fill the gaps in the micron protrusion structure to form a lubricating layer, but the migration rate should not be too fast to avoid a large amount of migration in a short period of time leading to a decrease in surface energy; (3) good compatibility with modified filler, can be uniformly attached to the surface of modified micron alumina, and does not affect the formation of micron protrusion structure.

[0023] In this invention, with 100 parts by weight of TPU resin, the weight of the lubricant in the composite filler can be 0.5-1.5 parts, for example, 1 part.

[0024] In this invention, the composite filler may further include a titanate coupling agent, such as isopropyl tris(dioctylpyrophosphoryloxy) titanate and / or bis(dioctylpyrophosphoryloxy) ethylene titanate. The commercially available titanate coupling agent may optionally be TMC-105 and / or TMC-201.

[0025] Wherein, based on 100 parts by weight of the TPU resin, the titanium ester coupling agent in the composite filler is 0.5-2 parts by weight, for example 0.5 parts.

[0026] In this invention, the TPU resin can be any TPU resin conventionally used in the art, preferably a polyether-type TPU resin. Because the polyether-type TPU resin contains ether bonds in its molecular chain, it exhibits good flexibility and hydrolysis resistance, and has good compatibility with nano-silica, thus better leveraging the surface polarity-enhancing effect of nano-silica.

[0027] In this invention, the Shore hardness of the TPU resin can be 80A-90A, for example 85A.

[0028] In this invention, the number-average molecular weight of the TPU resin can be 80,000-120,000. TPU resins with a number-average molecular weight in this range have moderate melt flowability, which facilitates uniform mixing with composite fillers and subsequent casting molding.

[0029] In this invention, the hydroxyl value of the TPU resin can be 28-35 mgKOH / g.

[0030] In this invention, with 100 parts by weight of TPU resin, the composite filler can be 8-13 parts by weight, preferably 8-12 parts, for example 8.3 parts, 9.3 parts, 10.3 parts, 10.8 parts, 11.8 parts, 12.3 parts or 13.3 parts.

[0031] In this invention, the composite filler may further include an antioxidant, preferably a hindered phenolic antioxidant and / or a phosphite antioxidant.

[0032] The hindered phenolic antioxidant may optionally be pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010) and / or octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (antioxidant 1076).

[0033] The phosphite antioxidant is preferably tris[2,4-di-tert-butylphenyl]phosphite (antioxidant 168).

[0034] Preferably, the antioxidant is antioxidant 1010 and antioxidant 168; more preferably, the mass ratio of antioxidant 1010 and antioxidant 168 is 1:(1-2).

[0035] Preferably, the antioxidant is antioxidant 1010 and antioxidant 1076; more preferably, the mass ratio of antioxidant 1010 and antioxidant 168 is 1:(1-2).

[0036] In this invention, based on 100 parts by weight of TPU resin, the antioxidant can be 0.2-0.5 parts by weight, for example, 0.3 parts.

[0037] In some specific embodiments, the composite filler is composed of the following components: 0.5 parts silane coupling agent, 5 parts nano silica, 0.5 parts stearic acid, 1-6 parts micron-sized alumina, 1 part PTFE wax, and 0.3 parts antioxidant. Preferably, the micron-sized alumina is in the following weight parts: 1 part, 2 parts, 3 parts, 4 parts, 5 parts, and 6 parts. The silane coupling agent is preferably KH550, and the antioxidant is preferably antioxidant 1010.

[0038] In some specific embodiments, the composite filler is composed of the following components: 0.5 parts silane coupling agent, 3 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part PTFE wax and 0.3 parts antioxidant; the silane coupling agent is preferably KH550 and the antioxidant is preferably antioxidant 1010.

[0039] In some specific embodiments, the composite filler is composed of the following components: 0.5 parts silane coupling agent, 8 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part PTFE wax and 0.3 parts antioxidant; the silane coupling agent is preferably KH550 and the antioxidant is preferably antioxidant 1010.

[0040] In some specific embodiments, the composite filler is composed of the following components: 0.5 parts silane coupling agent, 5 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part Fischer-Tropsch wax and 0.3 parts antioxidant; the silane coupling agent is preferably KH550 and the antioxidant is preferably antioxidant 1010.

[0041] In some specific embodiments, the composite filler is composed of the following components: 0.5 parts silane coupling agent, 5 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part PTFE wax, 0.5 parts titanate coupling agent, and 0.3 parts antioxidant; the silane coupling agent is preferably KH550, and the antioxidant is preferably antioxidant 1010.

[0042] In some specific embodiments, the composite filler is composed of the following components: 2 parts silane coupling agent, 5 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part PTFE wax and 0.3 parts antioxidant; the silane coupling agent is preferably KH550 and the antioxidant is preferably antioxidant 1010.

[0043] In some specific embodiments, the composite filler is composed of the following components: 0.5 parts silane coupling agent, 5 parts nano silica, 2 parts stearic acid, 3 parts micron alumina, 1 part PTFE wax and 0.3 parts antioxidant; the silane coupling agent is preferably KH550 and the antioxidant is preferably antioxidant 1010.

[0044] In this invention, the granulation method may optionally be twin-screw extrusion granulation, and the extrusion temperature is preferably 150℃-180℃.

[0045] In some specific embodiments, the twin-screw extrusion granulation includes the following steps:

[0046] The raw material composition was extruded, pelletized, and screened using a twin-screw extruder to obtain the TPU masterbatch;

[0047] The extrusion temperatures of the twin-screw extruder are set as follows: Zone 1: 150℃; Zone 2: 155℃; Zone 3: 160℃; Zone 4: 170℃; Zone 5: 170℃; Zone 6: 170℃; Zone 7: 160℃; Zone 8: 160℃.

[0048] In this invention, the hardness of the front roller can be 72-80A, for example 75A.

[0049] In this invention, the temperature of the front roller can be 50℃-70℃, for example 50℃, 58℃ or 70℃.

[0050] In this invention, the roughness Ra of the front roller can be 0.4-0.6 μm, for example, 0.5 μm. This roughness range ensures that the TPU masterbatch melt spreads uniformly during the setting process, avoiding scratches on the film surface due to an excessively rough roller surface, or an insufficiently fine roller surface that cannot provide a stable surface foundation for subsequent precision pressing.

[0051] In this invention, the pressure of the front roller can be 3-5 MPa, for example, 3 MPa, 4 MPa, or 5 MPa. When the pressure is below 3 MPa, the TPU melt does not adhere sufficiently to the pressure roller, resulting in uneven stretching; when the pressure is above 5 MPa, it easily leads to excessive extrusion of the TPU melt, making it difficult for micron-sized alumina to form a raised structure during subsequent fine pressing. A pressure range of 3-5 MPa can achieve the connection between the initial film forming and subsequent processing.

[0052] In this invention, the hardness of the intermediate roller can be 90-95A, for example 92A.

[0053] In this invention, the roughness Ra of the intermediate roller can be Ra≥1.2μm, for example 1.3μm.

[0054] In this invention, the temperature of the middle roller can be 20-55°C, preferably 40-55°C, for example 40°C, 47°C or 55°C.

[0055] In this invention, the pressure of the intermediate roller can be 8-12 MPa, for example 10 MPa.

[0056] In some specific embodiments, the hardness of the front roller can be 75A, and the temperature of the front roller can be 58°C; the hardness of the middle roller can be 92A, and the temperature of the middle roller can be 47°C.

[0057] In some specific implementations, the hardness of the front roller can be 75A, and the temperature of the front roller can be 50°C; the hardness of the middle roller can be 92A, and the temperature of the middle roller can be 47°C.

[0058] In some specific implementations, the hardness of the front roller can be 75A, and the temperature of the front roller can be 70°C; the hardness of the middle roller can be 92A, and the temperature of the middle roller can be 47°C.

[0059] In some specific implementations, the hardness of the front roller can be 75A, and the temperature of the front roller can be 58°C; the hardness of the middle roller can be 92A, and the temperature of the middle roller can be 40°C.

[0060] In some specific implementations, the hardness of the front roller can be 75A, and the temperature of the front roller can be 58°C; the hardness of the middle roller can be 92A, and the temperature of the middle roller can be 55°C.

[0061] In this invention, the casting process can be carried out in a single-screw casting machine, and the temperature setting of the single-screw casting machine can optionally be: the temperature settings of the five zones of the screw are 175°C, 185°C, 195°C, 200°C and 195°C respectively.

[0062] The flow channel temperature of the single-screw casting machine is preferably 190-200°C, for example, 195°C.

[0063] The mold temperature of the single-screw casting machine is preferably 185-200°C, for example, 190°C.

[0064] Secondly, the present invention provides a TPU film, which is prepared by the TPU film preparation method described above.

[0065] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0066] The reagents and raw materials used in this invention are all commercially available.

[0067] The positive and progressive effects of this invention are as follows:

[0068] This invention uses a specific composite filler combined with a gradient rolling process in the casting process to produce a TPU film, which achieves a high dyne value and a low dyne decay rate, resulting in high surface energy and durability, as well as good mechanical properties.

[0069] In some preferred embodiments, the dyn value of the TPU film can be increased to 40-42 dyn / cm (ASTM D2578 standard test); tensile strength ≥25MPa, surface roughness Ra greater than 13μm; dyn value decay rate after 30 days of aging <4.5%, indicating good durability. Detailed Implementation

[0070] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0071] Equipment Model List:

[0072] equipment model Key parameter requirements high-speed mixer SHR-100A 100L capacity, speed ≥3000rpm Twin-screw extruder TSE-35 (Corperon) Length-to-diameter ratio 40:1, torque ≥12Nm Single screw extruder JWS50 / 32 The surface hardness of the middle roller is 92±2A, and the heating accuracy is ±1℃.

[0073] The types and manufacturers of the raw materials used in the following examples and comparative examples are shown in the table below:

[0074]

[0075] Example 1

[0076] (1) By weight, 100 parts of TPU resin, 5 parts of nano silica (particle size 30nm), 0.5 parts of KH550, 3 parts of micron alumina (particle size 2μm), 0.5 parts of stearic acid, 1 part of PTFE wax and 0.3 parts of antioxidant 1010 were blended in a high-speed mixer at a speed of 3000rpm for 15min. The mixture was then reacted in a drying oven at 60℃ for 2h, and then extruded, granulated underwater and dried in a twin-screw extruder to obtain TPU masterbatch. The temperature of the twin-screw extruder was set as follows: Zone 1 temperature 150℃; Zone 2 temperature 155℃; Zone 3 temperature 160℃; Zone 4 temperature 170℃; Zone 5 temperature 170℃; Zone 6 temperature 170℃; Zone 7 temperature 160℃; Zone 8 temperature 160℃.

[0077] (2) The TPU masterbatch obtained in step (1) is cast into a film in a single screw casting machine. The temperature of the five zones of the screw is set to 175°C, 185°C, 195°C, 200°C and 195°C, the flow channel temperature is 195°C, and the mold temperature is 190°C. Then, the TPU film is obtained by shaping through the front roller and the middle roller.

[0078] The process parameters for the front and middle rollers are as follows:

[0079] The front roller has a hardness of 75A, a temperature of 58℃, and a linear speed of 5m / min.

[0080] The hardness of the intermediate roll is 92A, the temperature of the intermediate roll is 47℃, the linear speed of the intermediate roll is 5m / min, and the pressure of the intermediate roll is 10MPa.

[0081] The gap between the front roller and the middle roller is -0.4mm.

[0082] Example 2-11

[0083] The main parameters of the formulations in Examples 2-11 are shown in Table 1. The casting process and parameter settings are the same as those in Example 1.

[0084] Examples 12-17

[0085] The formulations of Examples 12-17 are the same as those of Example 1. The main parameters for casting are shown in Table 2. Other conditions are the same as those of Example 1.

[0086] Comparative Examples 1-8

[0087] The main parameters of the formulations of Comparative Examples 1-8 are shown in Table 1, and the main process parameters of the casting process are shown in Table 2. Other conditions are the same as those in Example 1.

[0088] Table 1 Formulation of the raw material composition

[0089]

[0090] Table 2. Process parameters for preparing TPU films

[0091]

[0092] Example 1: Dyne value and attenuation rate

[0093] (1) Dyne value: Select a dyne pen with a dyne value 2-3 mN / m lower than the estimated dyne value and draw lines on the surface of the TPU film prepared in each embodiment and comparative example; observe the state of the lines: if the lines do not shrink or break within 2 seconds, it indicates that the surface tension of the film is ≥ the dyne value of the pen; if the lines shrink quickly into water droplets or thin lines, it is necessary to replace with a dyne pen with a lower value and retest; gradually replace with a dyne pen with a higher value until a dyne pen that can keep the lines from shrinking for 2 seconds is found, and its marked value is the dyne value of the film. The results are shown in Table 3.

[0094] (2) 30-day decay rate test: The TPU films prepared in each example and comparative example were stored in an environment with a temperature of 23±2℃ and a relative humidity of 50±5% for 30 days. The dyne values ​​before and after storage were tested according to the method in (1). The 30-day decay rate was calculated according to the formula (initial dyne value - dyne value after 30 days) / initial dyne value × 100%. The results are shown in Table 3.

[0095] Example 2: Mechanical Properties

[0096] (1) Tensile strength: According to ASTM D412-2021 standard, the TPU films prepared in each embodiment and comparative example were cut into dumbbell-shaped specimens using a universal testing machine. The testing speed was 500 mm / min. The maximum tensile force when the specimen broke was recorded. The tensile strength was calculated according to the formula: tensile strength = maximum tensile force / original cross-sectional area of ​​the specimen. The results are shown in Table 3.

[0097] (2) Peel strength: According to GB / T 2790-1995 standard, the peel strength of Example 1 and Comparative Example 2 was tested by 180° peel test. The test speed was 300 mm / min. Peel strength = peel force / sample width (unit: N / cm).

[0098] Example 3: Surface Roughness (Ra)

[0099] According to the GB / T 1031-2009 standard, the TPU films prepared in each embodiment and comparative example were made into sampling lengths of 0.8 mm and evaluation lengths of 4 mm. Five test points were randomly selected on the film surface, and the Ra value was tested using a surface roughness meter. The average value was taken as the final surface roughness. The results are shown in Table 3.

[0100] Table 3

[0101]

[0102] As can be seen from the data in Table 3, the TPU film provided by the present invention has a high dyne value (above 39 N / m) and a low dyne value decay rate (below 4.5%), indicating excellent aging performance; at the same time, it also has good mechanical properties (tensile strength above 25 MPa) and high surface roughness (1 μm and above).

[0103] The difference between Comparative Example 1 and Example 1 is that the raw material composition of Comparative Example 1 is 100 parts of pure TPU resin (Shore hardness 85A). As can be seen from the data in Table 3, the dyne value and surface roughness of Comparative Example 1 are significantly lower than those of Example 1. Furthermore, the surface contact angle of Comparative Example 1 was tested to be 93°, indicating a hydrophobic surface (contact angle > 90°), which fails to meet the printing / adhesion requirements for medical packaging materials (reference standard: YY / T0681.15-2019), thus affecting the application of TPU film.

[0104] The difference between Comparative Example 2 and Example 1 lies in the absence of micron-sized alumina in the raw material composition formulation and the surface roughness of the intermediate roller being 0.8 μm. According to the data in Table 3, the dyne value, surface roughness, and tensile strength of Comparative Example 2 are significantly lower than those of Example 1. Furthermore, surface defects in Comparative Example 2 and Example 1 were observed. It can be seen that filler agglomeration (agglomerate size greater than 500 nm) occurred in 12% of the area of ​​Comparative Example 2, while no agglomeration was observed in Example 1. This indicates that Comparative Example 2 has significant surface defects, resulting in limited surface energy improvement. Moreover, the peel strength of Example 1 was measured to be 8.2 N / m, while that of Comparative Example 2 was 5.1 N / cm, indicating that the peel strength of Comparative Example 2 is significantly lower than that of Example 1.

[0105] The difference between Comparative Example 3 and Example 1 is that the raw material composition was formulated as 100 parts of pure TPU (85A hardness), and step (2) was replaced with corona treatment power. The dyne decay rate of Comparative Example 3 was as high as 15.8%, with very poor aging performance, and the dyne value and tensile strength were also low. This is because the corona plasma caused the TPU molecular chain to break (FTIR can detect an increase in C=O groups), triggering surface degradation and leading to the overall deterioration of the PTU film performance.

[0106] Comparative Example 4 used the same raw material composition as Example 1, and its front roller temperature, pressure, and roughness were the same as those of the middle roller in terms of process parameters. The dyne value of Comparative Example 4 decreased by approximately 9% compared to Example 1, with a high attenuation rate, indicating poor tensile properties. Thickness testing of the TPU film in Comparative Example 4 showed a thickness deviation of ±12%, while the thickness deviation of the TPU film in Example 1 was ±4%, indicating very poor thickness uniformity of the TPU film in Comparative Example 4. Furthermore, during the preparation process, the film in Comparative Example 4 adhered to the roller surface 3 times / 8 hours, while in Example 1 it only adhered once. This is because Comparative Example 4 used high-hardness dual rollers, resulting in insufficient TPU melt extensibility and an inability to form effective micro-protrusions (surface roughness Ra was only 0.7 μm).

[0107] In Comparative Example 5, no fatty acids were added. The dyne value was reduced by 9.8% compared to Example 1, the 30-day decay rate was increased by 181% compared to Example 1, the surface roughness was reduced by 58% compared to Example 1, and the tensile strength was reduced by 15%.

[0108] In Comparative Example 6, no silane coupling agent was added. The dyne value was reduced by 14.6% compared to Example 1, the 30-day decay rate was increased by 228% compared to Example 1, the surface roughness was reduced by 33% compared to Example 1, and the tensile strength was reduced by 22%.

[0109] In Comparative Example 7, no silane coupling agent or lubricant was added. The dyne value was reduced by 12.2% compared to Example 1, the 30-day decay rate was increased by 175% compared to Example 1, the surface roughness was reduced by 17% compared to Example 1, and the tensile strength was reduced by 26%.

[0110] The difference between Comparative Example 8 and Example 1 is that corona treatment was performed, resulting in a deterioration in the dyne value and 30-day decay rate of the obtained TPU film, especially with the 30-day decay rate increasing by 471%.

[0111] The difference between Examples 1-5 lies in the amount of micron-sized alumina used. It can be seen that when the amount of micron-sized alumina is 2-5 parts, the TPU film exhibits better performance in all aspects. The difference between Examples 1, 6, and 7 lies in the amount of nano-silica used. When the amount of nano-silica increases from 3 parts to 8 parts, the dyne value, surface roughness, and tensile strength all increase, while the 20-day dyne decay rate decreases. The difference between Examples 1 and 8 lies in the type of lubricant used. It can be seen that PTFE wax is more effective as the lubricant. The difference between Examples 1 and 9 lies in the addition of KR-138S in Example 9. It can be seen that adding KR-138S further improves the dyne value, surface roughness, and tensile strength of the TPU film, and achieves a lower 30-day decay rate.

[0112] This invention was discovered by chance that by combining nano-silica with micron-sized alumina and through the synergy of silane coupling agents, fatty acid substances and lubricants, a dual enhancement effect of "polarity-morphology" can be constructed in the TPU resin matrix.

[0113] Among them, after being treated with silane coupling agent, the silanol groups (-SiOH) on the surface of nano silica can form strong hydrogen bonds with the urethane groups (-NHCOO-) on the TPU molecular chain, which significantly increases the polar component (γ^p) of the material surface and provides a chemical basis for high surface energy.

[0114] In this process, micron-sized alumina, acting as a hard filler, partially punctures and protrudes from the TPU film surface due to its micron-scale size and hardness, forming a uniformly distributed micron-sized protrusion structure during the casting and rolling process of TPU film preparation. This structure significantly increases the surface roughness and specific surface area of ​​the TPU film, enhances the apparent contribution of the surface dispersion component (γ^d) according to the Wenzel model, and provides mechanical anchoring points.

[0115] During the rolling process, micron-sized Al2O3 acts as a "punch," locally breaking through or thinning the surface lubricant layer, exposing the highly polar nano-SiO2 / TPU composite interface beneath, which becomes an active site providing high surface energy. The lubricant layer in the unbroken areas remains, providing good processability and anti-adhesion properties. This "micro-area exposure" mechanism achieves a dynamic balance and unity between high surface energy (originating from the exposed polar region) and good processability (originating from the residual lubricant region), resolving the contradiction in traditional technologies where it is difficult to achieve both simultaneously.

[0116] The lubricant's role is not simply to reduce surface energy, as is commonly understood. In the formulation of this invention, after migrating to the surface, it primarily fills the gaps between micron-sized protrusions, forming a thin, continuous lubricating layer. This layer effectively prevents roller sticking during processing and protects the underlying polar surfaces and microstructures from damage during winding. During subsequent rolling or use, this lubricating layer can be partially penetrated, exposing highly polar active surfaces.

[0117] The long-chain alkyl groups of the stearic acid molecules can entangle with the TPU molecular chains, reducing the aggregation of micronized alumina in the matrix and ensuring its uniform dispersion. It can also regulate the surface polarity of micronized alumina, reducing its interfacial tension with the lubricant, so that the lubricant can adhere more uniformly to the surface of micronized alumina. In the subsequent rolling process, this ensures that micronized alumina can effectively form a surface protrusion structure, while avoiding the decline in mechanical properties caused by poor compatibility between the filler and the matrix.

[0118] Among them, the titanate coupling agent acts as a "molecular bridge". After hydrolysis, one end combines with the hydroxyl groups on the surface of inorganic fillers (nano silica, micron alumina), and the other end has long-chain organic groups that entangle with TPU molecular chains. This greatly improves the dispersion compatibility of the filler in the hydrophobic polymer matrix, prevents agglomeration, and ensures the uniform realization of the above effects.

[0119] The difference between Example 1 and Example 10 is the amount of KH550 used, but both achieve comparable results. The difference in the amount of stearic acid used between Example 1 and Example 11 shows that using less stearic acid can yield a better TPU film.

[0120] The difference between Examples 1, 12, and 13 lies in the front roller temperature. When the front roller temperature increases from 50°C to 58°C, all aspects of the TPU film's properties improve. The difference between Examples 1, 14, and 15 lies in the middle roller temperature. When the middle roller temperature increases from 40°C to 47°C, all aspects of the TPU film's properties improve. The difference between Examples 1, 16, and 17 lies in the front roller pressure. When the front roller pressure increases from 3MPa to 4MPa, all aspects of the TPU film's properties improve.

[0121] This invention creatively designs a rolling system combining hardness gradient and temperature gradient: a low-hardness front roller is used to initially shape and extend the TPU melt at a higher temperature, allowing micron-sized fillers to be initially embedded in the surface, preparing for subsequent structural shaping; a high-hardness, high-roughness middle roller is used to press the material at a lower temperature and pressure, with the high pressure forcing the hard Al2O3 filler to completely penetrate and fix in the resin; the high-roughness roller surface replicates complex micro-nano structures on the film surface; this gradient energy input method of "extension before etching" avoids problems such as excessive filler embedding, unclear structure, or excessive film stress caused by a single high-hardness roller, and realizes the controllable construction and directional assembly of surface micro-protrusion structures.

[0122] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a TPU film, characterized in that, The process includes the following steps: granulating and casting the raw material composition to obtain the TPU film; The raw material composition comprises: a composite filler and a TPU resin, wherein the composite filler comprises, based on 100 parts by weight of the TPU resin, the composite filler comprises: 3-8 parts of nano-silica; 1-6 parts of micron-sized alumina; Lubricant; Silane coupling agents; fatty acids; The casting process includes extrusion and setting in sequence. The setting is carried out between the front roller and the middle roller. The temperature of the front roller is higher than that of the middle roller, and the hardness of the front roller is lower than that of the middle roller. The hardness of the front roller is 70A-80A, and the hardness of the middle roller is 89A-95A.

2. The method for preparing TPU film according to claim 1, characterized in that, The raw material composition satisfies one or more of the following conditions: (a) The fatty acid is a fatty acid and / or a fatty acid amide; the fatty acid preferably has 12-20 carbon atoms, such as one or more of palmitic acid, lauric acid and stearic acid; the fatty acid amide preferably has 12-20 carbon atoms, such as stearamide; (b) The silane coupling agent is an aminosilane coupling agent, such as γ-aminopropyltriethoxysilane; (c) The particle size of the nano-silica is 20-50 nm, for example 30 nm; (d) The particle size of the micron-sized alumina is 1-2 μm, for example, 2 μm; (e) The lubricant is one or more of polyalkane wax, polyolefin wax and tungsten disulfide, wherein the polyalkane wax is preferably Fischer-Tropsch wax; and the polyolefin wax is preferably polytetrafluoroethylene wax and / or polyethylene wax.

3. The method for preparing TPU film according to claim 1, characterized in that, The raw material composition satisfies one or more of the following conditions: (a) The Shore hardness of the TPU resin is 80A-90A, for example 85A; (b) The number average molecular weight of the TPU resin is 80,000-120,000; (c) The hydroxyl value of the TPU resin is 28-35 mg KOH / g; (d) The TPU resin is a polyether-type TPU resin.

4. The method for preparing TPU film according to claim 1, characterized in that, The raw material composition satisfies one or more of the following conditions: (a) Based on 100 parts by weight of the TPU resin, the fatty acid substance in the composite filler is 0.5-2 parts by weight, for example, 0.5 parts or 2 parts; (b) Based on 100 parts by weight of the TPU resin, the silane coupling agent in the composite filler is 0.5-2 parts by weight, for example, 0.5 parts or 2 parts; (c) Based on 100 parts by weight of the TPU resin, the composite filler contains 2-5 parts by weight of the micron-sized alumina, for example, 2 parts, 3 parts or 5 parts. (d) Based on 100 parts by weight of the TPU resin, the composite filler contains 3-6 parts by weight of the nano-silica, for example, 5 parts; (e) Based on 100 parts by weight of the TPU resin, the lubricant in the composite filler is 0.5-1.5 parts by weight, for example, 1 part; (f) The composite filler further includes a titanate coupling agent, preferably, the titanate coupling agent is isopropyl tris(dioctyl pyrophosphoryloxy) titanate and / or bis(dioctyl pyrophosphoryloxy) ethylene titanate; for example, the commercial model of the titanate coupling agent is TMC-105 and / or TMC-201; preferably, based on 100 parts by weight of the TPU resin, the weight of the titanate coupling agent in the composite filler is 0.5-2 parts, for example 0.5 parts; (g) The composite filler further includes an antioxidant, preferably a hindered phenolic antioxidant and / or a phosphite antioxidant; the hindered phenolic antioxidant is preferably pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and / or octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate; the phosphite antioxidant is preferably tris[2,4-di-tert-butylphenyl] phosphite; Preferably, the antioxidant is 0.2-0.5 parts by weight, for example, 0.3 parts, based on 100 parts by weight of TPU resin.

5. The method for preparing TPU film according to claim 1, characterized in that, The raw material composition satisfies any one of the following conditions: (a) The composite filler is composed of the following components: 0.5 parts silane coupling agent, 5 parts nano silica, 0.5 parts stearic acid, 1-6 parts micron alumina, 1 part polytetrafluoroethylene wax and 0.3 parts antioxidant; (b) The composite filler is composed of the following components: 0.5 parts silane coupling agent, 3 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part polytetrafluoroethylene wax and 0.3 parts antioxidant; (c) The composite filler is composed of the following components: 0.5 parts silane coupling agent, 8 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part polytetrafluoroethylene wax and 0.3 parts antioxidant; (d) The composite filler is composed of the following components: 0.5 parts silane coupling agent, 5 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part Fischer-Tropsch wax and 0.3 parts antioxidant; (e) The composite filler is composed of the following components: 0.5 parts silane coupling agent, 5 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part polytetrafluoroethylene wax, 0.5 parts titanate coupling agent and 0.3 parts antioxidant; (f) The composite filler is composed of the following components: 2 parts silane coupling agent, 5 parts nano silica, 0.5 parts stearic acid, 3 parts micron alumina, 1 part polytetrafluoroethylene wax and 0.3 parts antioxidant; (g) The composite filler is composed of the following components: 0.5 parts silane coupling agent, 5 parts nano silica, 2 parts stearic acid, 3 parts micron alumina, 1 part polytetrafluoroethylene wax and 0.3 parts antioxidant.

6. The method for preparing TPU film according to claim 1, characterized in that, It meets one or more of the following conditions: (a) The hardness of the front roller is 72-80A, for example 75A; (b) The temperature of the front roller is 50°C-70°C, for example, 50°C, 58°C or 70°C; (c) The surface roughness Ra of the front roller is 0.4-0.6 μm, for example 0.5 μm; (d) The pressure of the front roller is 3-5 MPa, for example 3 MPa, 4 MPa or 5 MPa.

7. The method for preparing TPU film according to claim 1, characterized in that, It meets one or more of the following conditions: (a) The hardness of the intermediate roller is 90-95A, for example 92A; (b) The surface roughness Ra of the intermediate roller is Ra≥1.2μm, for example 1.3μm; (c) The temperature of the intermediate roller is 20-55°C, preferably 40-55°C, for example 40°C, 47°C or 55°C; (d) The pressure of the middle roller is 8-12 MPa, for example 10 MPa.

8. The method for preparing TPU film according to claim 1, characterized in that, It satisfies any one of the following conditions: (a) The hardness of the front roller is 75A and the temperature of the front roller is 58°C; the hardness of the middle roller is 92A and the temperature of the middle roller is 47°C. (b) The front roller has a hardness of 75A and a temperature of 50°C; the middle roller has a hardness of 92A and a temperature of 47°C. (c) The hardness of the front roller is 75A and the temperature of the front roller is 70°C; the hardness of the middle roller is 92A and the temperature of the middle roller is 47°C. (d) The hardness of the front roller is 75A and the temperature of the front roller is 58°C; the hardness of the middle roller is 92A and the temperature of the middle roller is 40°C. (e) The hardness of the front roller is 75A and the temperature of the front roller is 58°C; the hardness of the middle roller is 92A and the temperature of the middle roller is 55°C.

9. The method for preparing TPU film according to claim 1, characterized in that, It meets one or more of the following conditions: (a) The granulation method is twin-screw extrusion granulation; the extrusion temperature is preferably 150℃-180℃; (b) The casting process is carried out in a single-screw casting machine, wherein the screw temperature is preferably 175-200°C; the runner temperature is preferably 190-200°C, for example 195°C; and the die temperature is preferably 185-200°C, for example 190°C.

10. A TPU film, characterized in that, It is prepared using the method for preparing TPU film as described in any one of claims 1-9.

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