Preparation method of self-cleaning TPU film with high yellowing resistance

Abstract

The invention relates to a preparation method of a high-yellowing-resistance self-cleaning TPU (thermoplastic polyurethane) film, which comprises the following steps: mixing polyether glycol with nano silicon dioxide which accounts for 1-5% of the total weight of a base material; adding a solvent of ethanol or methanol, wherein the dosage of the solvent is 150-300% of the weight of the base material; stirring for 30-60 minutes at room temperature to form uniform dispersion liquid; adding a metal chelating agent solution containing EDTA (Ethylene Diamine Tetraacetic Acid) into the dispersion liquid, wherein the dosage is 0.2-1% of the total weight of the dispersion liquid; an anti-yellowing agent comprising anti-UV-385 and anti-UV-328 is added into the solution, the total amount of the anti-yellowing agent is 2%-5% of the weight of the solution, and the anti-yellowing agent is added after being mixed according to the proportion of 1: 1 or 1: 2; the base material solution is added into a reaction kettle, isocyanate containing MDI is slowly added, and the use amount of the isocyanate is 40%-60% of the total weight of the base material; adding a chain extender which accounts for 10%-20% of the total weight of the base material, and adding a catalyst; adding activated titanium dioxide nano-particles into the prepolymer, wherein the use amount of the activated titanium dioxide nano-particles is 0.5%-2% of the total weight; the activation method adopts plasma treatment.

Description

Technical Field

[0001] The invention relates to a method for preparing a TPU film, in particular to a method for preparing a highly yellowing-resistant self-cleaning TPU film. Background Art

[0002] Although the current method for preparing highly yellowing-resistant self-cleaning TPU films is innovative in application, it still has many shortcomings and drawbacks. By analyzing the technical solutions in the "Chinese Invention Patent, Patent No. 202111235010X "Method for preparing yellowing-resistant TPU and TPU protective film", the limitations and potential problems of this technology can be clearly seen. These shortcomings not only affect its competitiveness in the market, but may also affect its widespread promotion in the field of high-performance film applications.

[0003] First, in the patent scheme, the preparation method of the yellowing-resistant TPU film mainly relies on the traditional chemical reaction process, and realizes the high yellowing resistance and self-cleaning function of the film through a multi-step complex process. Specifically, the method reacts isocyanate with a dihydroxy water-repellent in a reaction vessel and treats it at a temperature of 85 to 95°C. Although this approach can achieve the yellowing resistance of the film to a certain extent, high temperature conditions will lead to the formation of thermal decomposition products, which may have a negative impact on the mechanical strength and chemical stability of the film. In addition, although the control of temperature and stirring time improves the yellowing resistance effect, excessive processing time and high temperature conditions are likely to lead to the decomposition of certain active substances, thereby affecting the final quality and performance of the film. For example, in step a2, multiple chemical components such as polyglycol, 1,4-butanediol, graphene, yellowing resistance agent, antioxidant and catalyst need to be mixed and stirred. This process requires extremely high precision control of the ratio and time. Once there is a deviation, it may cause the molecular structure to be unstable, thereby affecting the functionality of the film.

[0004] Secondly, one of the biggest drawbacks of this technology is the complex preparation process of the yellowing-resistant pressure-sensitive adhesive. In the patent scheme, the preparation of the yellowing-resistant pressure-sensitive adhesive requires multiple reactions, and operations such as vacuuming and standing are performed at different stages. The preparation of the yellowing-resistant pressure-sensitive adhesive mentioned in steps b1 to b3 involves the synthesis of multiple chemical substances, and the ratio of these substances (such as the 1:1 mixing ratio of the first pressure-sensitive adhesive raw material and the second pressure-sensitive adhesive raw material) and the reaction temperature require highly precise control. More importantly, this preparation process not only consumes a large amount of raw materials and energy, but also increases the complexity of production, resulting in a long production cycle and high cost. In particular, in the preparation process of the first pressure-sensitive adhesive raw material, chemical substances such as difunctional isocyanates and antioxidants are used. These chemical substances are easily decomposed under high-temperature reactions, which may affect the stability and durability of the final product, especially in the long-term application process, and may not be able to maintain its initial performance. In addition, although the use of graphene can enhance the yellowing resistance of the film, its dispersibility and stability in the TPU substrate is an issue that cannot be ignored. Graphene nanoparticles are often difficult to integrate well with TPU materials, and are prone to aggregation during the preparation process, resulting in uneven distribution in the film. This uneven distribution will directly affect the mechanical properties of the film, especially in high stress environments such as stretching and impact, the film is prone to cracks or partial detachment, thereby reducing the overall quality and service life of the film. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a highly yellowing-resistant self-cleaning TPU film, thereby solving some of the drawbacks and deficiencies pointed out in the background technology.

[0006] The present invention solves the above-mentioned technical problems by adopting the following technical solution, which includes the following steps:

[0007] S1. Preparation and pretreatment of basic materials:

[0008] S1.1, mixing polyether diol with nano-silicon dioxide, wherein the nano-silicon dioxide accounts for 1% to 5% of the total weight of the substrate; adding ethanol or methanol solvent, wherein the amount of the solvent is 150% to 300% of the weight of the substrate; stirring at room temperature for 30 to 60 minutes to form a uniform dispersion;

[0009] S1.2, adding a metal chelating agent solution including EDTA to the dispersion in an amount of 0.2% to 1% of the total weight of the dispersion;

[0010] S1.3, adding anti-yellowing agents including anti-UV-385 and anti-UV-328 to the solution, the total amount of the anti-yellowing agent is 2% to 5% of the weight of the solution, and adding after mixing in a ratio of 1:1 or 1:2;

[0011] S2, TPU synthesis treatment:

[0012] S2.1. Add the substrate solution into the reaction kettle, and slowly add isocyanate including MDI in an amount of 40% to 60% of the total weight of the substrate;

[0013] S2.2, adding a chain extender in an amount of 10% to 20% of the total weight of the substrate, and adding a catalyst;

[0014] S2.3, adding activated titanium dioxide nanoparticles to the prepolymer in an amount of 0.5% to 2% of the total weight; the activation method is plasma treatment;

[0015] S3, film forming and performance optimization:

[0016] S3.1, filter the prepared TPU solution, control the filter pore size to 80-120 μm, and remove impurities;

[0017] S3.2, use the casting equipment to process the film, the casting speed is controlled at 1.2-1.8 m / min, the temperature range is 180-200°C, and the tension is maintained at 10-20 MPa; adjust the equipment parameters to form a film with a thickness of 20-40 μm;

[0018] S4. Surface coating treatment:

[0019] S4.1. Use a fluorinated silicone resin coating solution with a concentration of 1% to 3% by mass to cover the surface of the film by spraying; after spraying, place the film in an environment of 70 to 90°C for curing for 1.5 to 3 hours to form a dense coating.

[0020] Furthermore, the dispersion treatment method includes: using an ultrasonic processor for treatment, with the ultrasonic frequency set to 30 to 50 kHz, the power to 300 to 500 W, and the treatment time to 20 to 40 minutes to improve the dispersion uniformity of silicon dioxide.

[0021] Furthermore, in step S1.2, the solution is heated to 70-90° C., maintained for 30-60 minutes, and filtered to remove undissolved impurities to obtain a clear solution.

[0022] Furthermore, in step S1.3, the solution is stirred at 60 to 70° C. for 60 to 120 minutes to uniformly disperse the anti-yellowing agent.

[0023] Furthermore, in step S2.1, the reaction temperature is controlled in the range of 75 to 85° C.; the concentration of the NCO group is monitored by continuous stirring for 60 to 90 minutes to ensure that the NCO content is in the range of 3% to 5%.

[0024] Furthermore, the chain extender is 1,4-butanediol, the catalyst is stannous octoate, and the catalyst accounts for 0.01% to 0.05% of the total weight; stirring is continued at 80 to 90° C. for 60 to 90 minutes until a uniform prepolymer is formed.

[0025] Furthermore, the plasma treatment is carried out at a power of 200 to 400 W, a gas flow rate of 0.3 to 0.7 L / min, and a treatment time of 10 to 20 minutes; and stirring is carried out at 70 to 80° C. for 90 to 120 minutes to ensure that the particles are evenly dispersed and stable.

[0026] Furthermore, the method for controlling parameters of the film processed by the casting device includes:

[0027] A dynamic real-time thickness control system is used, combining online sensors, laser scanning technology and feedback control mechanism to monitor the actual thickness of the film in real time, and dynamically adjust the casting speed and cooling system operation according to the feedback signal; the film thickness adjustment formula is as follows:

[0028]

[0029] in,

[0030] V(t) represents the casting speed at time t; k1 and k2 are adjustment constants, which respectively reflect the film thickness change rate and the influence of the current thickness on the casting speed; is the rate of change of the film thickness H(t) at time t, indicating the speed of increase or decrease of the thickness over time; H(t) is the film thickness monitored in real time, which will change as the casting process proceeds; C(t) is the adjustment coefficient of the cooling rate, indicating the influence of the cooling rate on the film thickness during the cooling stage.

[0031] Furthermore, the method for controlling parameters of the film processed by the casting device includes:

[0032] A multi-zone temperature control system was introduced, which uses multiple independent heating zones to adjust according to the material fluidity and viscosity of each zone, and control the uniform temperature and material fluidity of each zone during the film forming process; the specific operation of the temperature control system is calculated based on the following formula:

[0033]

[0034] in,

[0035] T i (t) is the temperature of the i-th section, which determines the softening degree of the material in this section at time t; T i-1(t) is the temperature of the previous section, indicating the temperature influence of the previous heating section; ΔT is the temperature difference between two consecutive temperature control sections, reflecting the amplitude of the section temperature change; max(ΔT) is the maximum temperature difference between each temperature control section, which is used to standardize the control range of the temperature difference.

[0036] Furthermore, the method for controlling parameters of the film processed by the casting device includes:

[0037] An intelligent tension control system is used, combined with sensors and feedback algorithms, to monitor the stretching state of the film in real time, and dynamically adjust the tension distribution to control the uniform force in each area of ​​the film. The tension distribution control is dynamically adjusted using the following formula:

[0038]

[0039] in,

[0040] T i (t) is the tension in the i-th region. At time t, the morphology and physical properties of the film are ensured by adjusting the tension distribution; T ref is the reference tension, indicating the tension standard under ideal conditions; S i (t) is the real-time stretching rate of the ith region, reflecting the extension of the film in the region; S ref is the reference stretch rate, which is the elongation ratio of the film under ideal conditions; α is the tension distribution adjustment coefficient, which is used to adjust the sensitivity of tension to changes in stretch rate.

[0041] The method for preparing the highly yellowing-resistant self-cleaning TPU film provided by the present invention has significant beneficial effects by combining multiple innovative technologies, and improves the performance and application value of the film in many aspects. The following are several key beneficial effects of the present invention:

[0042] By introducing anti-yellowing agents such as Anti-UV-385 and Anti-UV-328, combined with special formulations and process control, the yellowing index (ΔYI) of the film is kept below 1.0, which is much lower than the ΔYI value of traditional TPU films, ensuring that the film can maintain its good appearance and performance for a longer period of time in outdoor environments or under high UV radiation.

[0043] The TPU film of the present invention has excellent hydrophobicity, an initial contact angle greater than 120°, and can quickly recover to more than 100° after artificial pollution. By coating a fluorinated silicone resin layer on the surface of the film and adopting technologies such as dynamic adjustment of cooling rate, casting speed and tension, the film surface is ensured to be smooth and have excellent water slipperiness, greatly improving the self-cleaning performance. Stains such as oil stains, dust, etc. can be quickly taken away by water droplets when they come into contact with the surface of the film, thereby reducing the cleaning frequency and maintaining the long-term cleanliness of the film surface.

[0044] The present invention adopts a multi-segment temperature control system, so that the temperature of each area of ​​the TPU film during the casting process is uniform and precisely controlled, and the fluidity of the material is optimized, thereby avoiding uneven thickness or surface defects caused by temperature fluctuations. Especially in the film forming process, combined with the tension control system, it can ensure that the physical properties of the film are uniform and the thickness is stable within the range of 20 to 40 μm, further improving the mechanical properties and durability of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention is a flow chart of a method for preparing a highly yellowing-resistant self-cleaning TPU film.

[0046] Figure 2 The present invention is a flow chart of the method for controlling parameters of film processing by the casting equipment. DETAILED DESCRIPTION

[0047] The specific implementation modes of the present invention will be described in detail below in conjunction with the accompanying drawings.

[0048] Example 1: Preparation and implementation of highly yellowing-resistant self-cleaning TPU film:

[0049] Combined with Figure 1 Flowchart, materials and equipment preparation:

[0050] 1. Polyether Polyol

[0051] Molecular weight: 2000g / mol

[0052] It provides a soft segment structure suitable for TPU synthesis, with good elasticity and toughness.

[0053] 2. Nano-silicon dioxide (SiO2)

[0054] Particle size: 10-50nm

[0055] Used to enhance the mechanical strength and wear resistance of TPU and improve its self-cleaning performance.

[0056] 3. Ethanol

[0057] Solvent, used to disperse nano-silica in polyether glycol solution.

[0058] 4.EDTA (ethylenediaminetetraacetic acid)

[0059] Metal chelators are used to remove possible metal impurities.

[0060] 5. Anti-yellowing agent: anti-UV-385, anti-UV-328

[0061] Each accounts for 2%-5% of the formula mass (at a 1:1 ratio) and is used to enhance the UV resistance of TPU and prevent discoloration due to prolonged exposure to sunlight.

[0062] 6.MDI (isocyanate)

[0063] Used in the synthesis of TPU as a source of hard segments.

[0064] 7.1,4-Butanediol (BDO)

[0065] Used as a chain extender to connect the soft segment and the hard segment and enhance the toughness of TPU.

[0066] 8. Stannous octoate

[0067] Used as a catalyst to promote the reaction of MDI and 1,4-butanediol.

[0068] 9. Titanium dioxide nanoparticles (TiO2)

[0069] Used to provide additional anti-yellowing properties, plasma treated to enhance its dispersibility.

[0070] 10. Silicon Fluoride Resin

[0071] Used in film surface coating to enhance self-cleaning performance.

[0072] 11. Casting equipment

[0073] Temperature control system: used to accurately control the casting temperature between 180-200℃.

[0074] Tension control system: ensure uniform film thickness and control the tension between 10-20MPa.

[0075] Step S1: Base material preparation and pretreatment

[0076] S1.1 Polyether diol mixed with nano-silicon dioxide

[0077] Raw material preparation: polyether diol weight: 50g; nano-silicon dioxide weight: 1.5g (3% of the total weight); ethanol solvent weight: 100g (200% of the substrate weight)

[0078] Operation steps: 1. Add 50g of polyether diol, 1.5g of nano-silicon dioxide and 100g of ethanol into a stirring container and stir for 30 minutes until uniform. 2. Use an ultrasonic processor to treat the dispersion, with the frequency set to 40kHz, the power to 400W, and the treatment time to 30 minutes. Ultrasonic treatment makes the nano-silicon dioxide more evenly dispersed in the polyether diol, improving the uniformity of the material.

[0079] S1.2 Adding metal chelating agents

[0080] Raw material preparation: The amount of EDTA solution used is 0.5% of the total weight of the dispersion, i.e. 0.75 g.

[0081] Operation steps: 1. Add 0.75 g of EDTA metal chelating agent solution to the above dispersion. 2. Heat to 80°C and continue stirring for 45 minutes to allow the metal impurities to chelate with EDTA and then be removed by filtration to obtain a clear solution.

[0082] S1.3 Add anti-yellowing agent

[0083] Raw material preparation: The total amount of anti-UV-385 and anti-UV-328 is 3% of the solution weight, that is, the amount of each anti-UV agent is 0.45g.

[0084] Operation steps: 1. At a temperature of 60°C, mix anti-UV-385 and anti-UV-328 in proportion and add them to the solution.

[0085] 2. Stir for 90 minutes to ensure that the anti-yellowing agent is completely dispersed in the solution. Step S2: TPU synthesis treatment

[0086] S2.1 Addition of MDI isocyanate

[0087] Raw material preparation: Base material solution mass: 50g

[0088] MDI isocyanate dosage: 50% of the total weight of the substrate, i.e. 25g

[0089] Steps:

[0090] 1. Add 50g of substrate solution into the reactor and slowly add 25g of MDI isocyanate.

[0091] 2. The reaction temperature was set at 80°C and stirring was continued for 60 minutes. The NCO group concentration was monitored to ensure that the NCO content was 4%, which was confirmed by infrared spectrometer (IR) testing.

[0092] S2.2 Adding chain extender

[0093] Raw material preparation: Chain extender 1,4-butanediol dosage: 15% of the total weight of the substrate, i.e. 7.5 g; Auxiliary catalyst (stannous octoate) dosage: 0.02% of the total weight, i.e. 0.01 g

[0094] Operation steps: 1. Add 7.5g 1,4-butanediol and 0.01g stannous octoate into the reaction kettle and continue stirring at 85°C for 75 minutes until a uniform prepolymer is formed.

[0095] S2.3 Addition of titanium dioxide nanoparticles

[0096] Raw materials preparation:

[0097] Titanium dioxide nanoparticle dosage: 1% of the total weight, i.e. 0.75g

[0098] Operation steps: 1. Add activated titanium dioxide nanoparticles into the reactor, set the temperature to 75°C, and continue stirring for 90 minutes to ensure that the particles are evenly dispersed.

[0099] Step S3: Film Forming and Performance Optimization

[0100] S3.1 Filtration of TPU solution

[0101] Operation: 1. Filter the prepared TPU solution through a filter pore size of 80μm to 120μm to remove impurities and ensure the purity of the solution. S3.2 Casting:

[0102] Operation parameter setting:

[0103] Casting speed: 1.5m / min

[0104] Casting temperature: 190℃

[0105] Tension range: 15MPa

[0106] Final film thickness: 30μm

[0107] Calculate the effect of casting speed on thickness:

[0108] According to the control formula

[0109] Set k1 = 0.8, k2 = 0.5, (set film thickness change rate),

[0110] H(t)=30 μm, C(t)=1.2 (cooling rate adjustment coefficient).

[0111] Then the casting speed V(t) is:

[0112] V(t)=(0.8·0.05+0.5·30)·1.2=(0.04+15)·1.2=18.048m / min

[0113] Through this calculation, the casting speed is precisely controlled to ensure uniform film thickness.

[0114] Step S4: Surface coating treatment

[0115] S4.1 Spraying fluorinated silicone resin

[0116] Ratio setting: Fluorinated silicone resin solution concentration: 2% Spraying amount: 0.5g / cm2 ; Operation: Spray the film surface with fluorinated silicone resin solution, and then place the film in an 80°C environment to cure for 2 hours.

[0117] Anti-yellowing and self-cleaning performance test:

[0118] 1.UV aging test

[0119] Purpose: The UV aging test is designed to evaluate the yellowing resistance of the film under long-term ultraviolet radiation, to ensure that the film does not turn yellow or its physical properties deteriorate due to ultraviolet radiation during use. The test accelerates the film aging process by ultraviolet radiation, and detects the yellowing index (ΔYI) to evaluate the material's anti-yellowing ability.

[0120] Experimental steps:

[0121] 1. Sample preparation:

[0122] The prepared TPU film samples were cut into small square pieces of 10 cm x 10 cm, ensuring that the thickness of each sample was consistent, about 30 μm.

[0123] 2. UV aging test chamber settings:

[0124] Irradiation intensity: set at 1000W / m 2 , is the irradiance of the ultraviolet light source.

[0125] Temperature control: The temperature inside the box is set at 60°C to simulate the conditions of long-term exposure to sunlight.

[0126] Test time: 200 hours of UV radiation test to simulate long-term outdoor lighting conditions.

[0127] 3. Yellowing index (ΔYI) measurement:

[0128] Use a colorimeter (such as Konica Minolta CM-2600d) to measure the color change of the film surface, and evaluate the anti-yellowing ability by calculating the yellowing index (ΔYI). The calculation formula of the yellowing index is:

[0129]

[0130] Among them, L0, a0, b0 and L1, a1, b1 are the color difference data of the sample before and after exposure.

[0131] Test results: Initial yellowing index ΔYI: 0.5

[0132] Yellowing index ΔYI after 200 hours of UV irradiation: 1.8

[0133] Conclusion: The yellowing index of the film remained at 1.8 after the UV aging test, which is significantly lower than the standard of 2, indicating that the film has excellent anti-yellowing properties and can maintain transparency and stable color for a long time.

[0134] Comparative test (comparison with traditional TPU film):

[0135] product Initial ΔYI 200 hours ΔYI evaluate High yellowing resistance TPU film of the present invention 0.5 1.8 Excellent, meets anti-yellowing standards Traditional TPU film (commercially available) 0.2 5.5 Poor, obvious yellowing Commercial low yellowing TPU film 0.3 3.0 Medium, slightly yellowing

[0136] 2. Self-cleaning performance test

[0137] Purpose: To test the self-cleaning performance of the film, that is, whether the film surface can restore its surface contact angle after being contaminated by natural or external factors, thereby restoring its self-cleaning properties. This test mainly examines the hydrophobicity and anti-pollution ability of the film surface material.

[0138] Experimental steps:

[0139] 1. Initial contact angle measurement: Use a contact angle meter (such as Krüss DSA100) to measure the initial contact angle of the film surface. A contact angle greater than 120° indicates that the film has good hydrophobicity, can effectively prevent water droplets from attaching, and has strong self-cleaning ability.

[0140] 2. Artificial pollution:

[0141] Artificial pollution was carried out using the following pollutants:

[0142] Dust: Fine dust particles are evenly sprayed on the film surface through a sprayer.

[0143] Oil stain: To simulate common oil stains, drop specific grease or lubricant on the film surface.

[0144] Sewage: Soak the film in sewage for a certain period of time, then take it out and dry it.

[0145] These contaminants can affect the hydrophilicity and hydrophobicity of the film surface.

[0146] 3. Contact angle recovery test:

[0147] After contamination, use distilled water to gently rinse the film surface, observe the change in contact angle, and test whether the surface can restore its original hydrophobicity. Standard requirements:

[0148] Initial contact angle ≥120°.

[0149] The contact angle recovery after contamination is ≥100°.

[0150] Test results:

[0151] Initial contact angle: 125°

[0152] Contact angle recovery after contamination: 102° (recovered after washing)

[0153] Comparative test (compared with commercially available films):

[0154]

[0155] Conclusion: This film has excellent self-cleaning properties and can quickly restore its hydrophobicity after contamination, ensuring its long-term self-cleaning effect.

[0156] 3. Cooling and storage

[0157] Purpose: To ensure that the film is morphologically stable after cooling and is ready for end use or further processing.

[0158] Experimental steps:

[0159] 1. Low temperature cooling: Cool the treated film in an environment with a temperature of 5℃-10℃ for 24 hours. This process can reduce the internal stress of the material and ensure the stability of the physical form of the film.

[0160] 2. Cutting and storage: After low temperature cooling, the film is cut into standard sizes of 10cmx10cm and stored in a dry environment, with relative humidity kept at <50% to avoid the influence of moisture on the film properties.

[0161] Conclusion: The cooling process does not affect the performance of the film, the surface of the film remains clean, and the thickness is stable, which meets the requirements of industrial production.

[0162] Embodiment 2:

[0163] Combined with Figure 1 Flowchart, a detailed implementation case of the TPU film preparation method of the present invention, including specific operating steps, formula ratios, material dosages and related calculations.

[0164] S1: Basic material preparation and pretreatment

[0165] S1.1: Mixture of polyether diol and nano-silica

[0166] Formula ratio: polyether diol (molecular weight 2000) is mixed with nano silicon dioxide, and the nano silicon dioxide accounts for 3% of the total weight of the substrate (the total weight of the substrate is assumed to be 100g).

[0167] Solvent: Ethanol was used as the solvent, and the amount of the solvent used was 200% (ie, 200 g) of the weight of the substrate.

[0168] Steps: Mix 3g of nano-silicon dioxide with 100g of polyether diol, add 200g of ethanol, and stir for 30 minutes to form a uniform dispersion. Use an ultrasonic processor, set the frequency to 40kHz, the power to 400W, and the processing time to 30 minutes to evenly disperse the silicon dioxide particles in the polyether diol solution.

[0169] S1.2: Addition of metal chelating agents

[0170] Addition amount: Add EDTA metal chelating agent solution, the amount used is 0.5% of the total weight of the dispersion.

[0171] calculate:

[0172] EDTA amount = (100g + 3g + 200g) × 0.5% = 1.515g

[0173] The temperature was raised to 80°C and maintained for 30 minutes. Undissolved impurities were removed by filtration to obtain a clear solution.

[0174] S1.3: Addition of anti-yellowing agent: Ratio of anti-yellowing agent: The total amount of anti-UV-385 and anti-UV-328 anti-yellowing agents is 3% of the solution weight (mixed in a 1:1 ratio).

[0175] calculate:

[0176] Total amount of anti-yellowing agent = (100g + 3g + 200g) × 3% = 6.09g

[0177] Among them, anti-UV-385 and anti-UV-328 each account for 3.045g, and stir for 1 hour to ensure that the anti-yellowing agent is evenly dispersed.

[0178] S2: TPU synthetic treatment

[0179] S2.1: Add isocyanate (MDI)

[0180] Formula ratio: The amount of MDI is 50% of the total weight of the substrate.

[0181] calculate:

[0182] MDI dosage = (100g + 3g + 200g) × 50% = 151.5g

[0183] Reaction temperature: 75-85°C, by continuous stirring for 60 minutes, ensure that the NCO group concentration is in the range of 3% to 5%.

[0184] S2.2: Addition of chain extenders and catalysts

[0185] Chain extender ratio: The amount of 1,4-butanediol added is 15% of the total weight of the substrate.

[0186] calculate:

[0187] 1,4-Butanediol dosage = (100g + 3g + 200g) × 15% = 30.45g

[0188] Catalyst: Stannous octoate is used in an amount of 0.03% of the total weight of the substrate.

[0189] calculate:

[0190] Catalyst dosage = (100 g + 3 g + 200 g) × 0.03% = 0.609 g

[0191] Reaction temperature: 80°C, stirring continued for 90 minutes until the reaction was complete.

[0192] S2.3: Addition of activated titanium dioxide nanoparticles

[0193] Titanium dioxide ratio: The dosage is 1% of the total weight.

[0194] calculate:

[0195] Titanium dioxide dosage = (100g + 3g + 200g) × 1% = 3.03g

[0196] Activation method: plasma treatment, power of 300W, gas flow rate of 0.5L / min, treatment time of 15 minutes, ensuring that the particles are evenly dispersed and stable.

[0197] S3: Film Forming and Performance Optimization

[0198] S3.1: TPU solution filtration

[0199] Filter pore size: 80~120μm, to remove impurities.

[0200] S3.2: Processing of films using cast tape equipment

[0201] Casting speed: controlled at 1.5m / min.

[0202] Casting temperature: controlled at 190°C.

[0203] Tension: set at 15MPa.

[0204] Target film thickness: 20-40μm, finally determined to be 30μm.

[0205] Calculate the film casting parameters:

[0206] The width of the casting equipment was set to 50 cm and the target film thickness was set to 30 μm (ie 0.03 mm).

[0207] The relationship between casting speed and thickness can be approximately calculated by the material flow equation. Assuming that the film forming area remains unchanged, the relationship between casting speed and thickness is:

[0208]

[0209] in:

[0210] Q is the mass flow rate (g / s), w is the casting width (50 cm = 0.5 m), v is the casting speed (1.5 m / min), m is the film mass (the production mass per minute is set to 60 g), ρ is the TPU solution density (1.1 g / cm 3 ), h is the film thickness (0.03 mm).

[0211] First, calculate the mass flow rate:

[0212] Q=60g / min=1g / s

[0213] Then, solve for the desired casting speed:

[0214]

[0215] Therefore, the required casting speed is 1.5 m / min and the final thickness is 30 μm.

[0216] S4: Surface coating treatment

[0217] S4.1: Fluorinated silicone resin coating solution: solution concentration: 1% (mass percentage), use the fluorinated silicone resin coating solution to cover the film surface by spraying.

[0218] S4.2: Curing: Curing conditions: The film is placed in an environment of 70-90°C for 2 hours to ensure the formation of a dense self-cleaning coating. This implementation scheme ensures that the prepared TPU film has excellent anti-aging, anti-pollution and self-cleaning properties through strict anti-yellowing and self-cleaning performance tests. The following is a detailed test method and test data analysis, covering aspects such as UV aging test, contact angle measurement and pollution recovery ability.

[0219] 1. UV aging test: Purpose: To verify the anti-yellowing performance of TPU film under long-term ultraviolet radiation, that is, to evaluate its yellowing resistance by testing the yellowing index (ΔYI). A lower ΔYI value indicates that the film has good aging resistance. Test method: Place the TPU film sample in a UV aging test box and set the irradiation intensity to 800W / m 2 Up to 1200W / m 2The test time is set to 150 to 250 hours, during which the UV lamp provides continuous UV radiation to simulate the UV exposure conditions in the actual environment. Film samples are taken out regularly and their yellowing index (ΔYI) is measured using a standard photometer. The yellowing index ΔYI is measured by colorimetry, and the lower the value, the lighter the yellowing of the material.

[0220] Experimental data:

[0221] <![CDATA[Irradiation intensity W / m 2 > Test time hours Sample 1ΔYI Sample 2ΔYI Sample 3ΔYI 800 150 1.2 1.4 1.3 1000 200 1.1 1.3 1.2 1200 250 1.0 1.2 1.1

[0222] Result analysis: According to the UV aging test results, the ΔYI values ​​of all samples are far below 2, indicating that the prepared TPU film has excellent anti-yellowing performance. Under 150 to 250 hours of ultraviolet radiation, the yellowing index always remains between 1.0 and 1.4, meeting the high yellowing resistance requirements.

[0223] 2. Surface contact angle test: Purpose: To evaluate the self-cleaning properties of TPU film, especially its hydrophobicity and anti-pollution ability. A higher contact angle indicates that the material has strong hydrophobicity, can effectively avoid the adhesion of stains, and can restore its cleanliness through moisture. Test method: Initial contact angle test: Add a drop of water to the surface of the film, use a contact angle measuring instrument (such as ThetaLite or Krüss) to measure the contact angle between the water droplet and the film surface, and record the initial contact angle value. The larger the initial contact angle, the stronger the hydrophobicity of the film surface. Artificial contamination and recovery test: By spraying common pollutants (such as ink or sewage) on the surface of the film, simulate the actual pollution in use. After contamination, rinse the film surface with distilled water, and measure the contact angle after recovery to evaluate the self-cleaning ability of the film.

[0224] Experimental data:

[0225]

[0226] Result analysis:

[0227] Initial contact angle: The initial contact angles of all samples are greater than 120°, meeting the requirements of high hydrophobicity and having good anti-pollution performance. Recovery contact angle: After contamination, the contact angles of all samples can be restored to more than 100°, especially sample 1, which can be restored to 105° after contamination, showing excellent self-cleaning ability. Self-cleaning property: Even after artificial contamination, the TPU film can quickly restore the contact angle, indicating that the film has a good self-cleaning effect.

[0228] 3. Temperature, humidity and cooling storage treatment

[0229] Purpose: To verify the stability of the film in a low-temperature environment, to ensure that the material will not deform due to thermal expansion or cold contraction during low-temperature cooling and storage, and to maintain its excellent surface properties.

[0230] Test method: Cool the treated film sample in a low temperature environment (5-10°C). The cooling process lasts for 2 hours to ensure that the film is completely cooled to room temperature. After cooling, cut the film sample into the target size and store it in a dry environment (20-25°C, humidity ≤60%) for 1 month to ensure the performance stability of the sample during storage.

[0231] Experimental data:

[0232] Sample No. Contact angle before cooling° Contact angle after cooling° Contact angle after storage° ΔYI after storage Sample 1 125 124 123 1.1 Sample 2 130 129 128 1.2 Sample 3 122 121 120 1.0

[0233] Result analysis:

[0234] Cooling stability: The cooling process has little effect on the contact angle of the TPU film, and the contact angle changes within 1°, indicating that the film has good low-temperature stability.

[0235] Storage stability: After 1 month of storage, the contact angle remained stable and the yellowing index (ΔYI) was always below 2, indicating that the film did not degrade during long-term storage.

[0236] 4. Product comparison data

[0237] The following is a comparison table of the anti-yellowing and self-cleaning properties of the TPU film prepared by the present invention and conventional TPU films on the market.

[0238] Test items The present invention prepares TPU film Conventional TPU film on the market ΔYIUV aging 150 hours 1.1 3.5 ΔYIUV aging 250 hours 1.0 4.0 Initial contact angle° 125 105 Contact angle recovery after contamination° 105 85 Storage stability ΔYI 1.1 3.2 Contact angle after storage° 123 98

[0239] Result analysis: Yellowing index (ΔYI): The yellowing index of the TPU film prepared by the present invention after UV aging is much lower than that of conventional TPU films on the market, showing a stronger anti-yellowing ability.

[0240] Contact angle recovery ability: The contact angle of the TPU film prepared by the present invention recovers faster and can recover to 105° after contamination, while the contact angle of conventional TPU films on the market recovers slower and the recovery value is lower than 100°.

[0241] Storage stability: The yellowing index and contact angle data after storage for one month show that the performance of the film of the present invention is more stable and is not prone to aging or performance degradation.

[0242] Through the anti-yellowing and self-cleaning performance tests of this embodiment, the excellent performance of the prepared TPU film in terms of UV aging, surface contact angle, pollution recovery, etc. has been successfully verified. Compared with conventional TPU films on the market, the film of the present invention has significant advantages in anti-yellowing, hydrophobicity and self-cleaning ability, and has good stability in low-temperature cooling and storage environments, providing a solid technical guarantee for practical applications.

[0243] Embodiment 3:

[0244] Combined with Figure 2 Flowchart, this example shows how to achieve precise control of the thickness of the TPU film through a dynamic real-time thickness control system, combined with online sensors, laser scanning technology and feedback control mechanisms, and ultimately produce a film with high yellowing resistance and self-cleaning properties. This case will explain in detail each step, formula, and how to verify the feasibility of these methods through actual data and calculations. In the production process of highly yellowing-resistant and self-cleaning TPU films, the thickness uniformity of the cast film is one of the key factors affecting the performance of the film. If the thickness is uneven, the physical properties and surface quality of the film will be affected, especially the self-cleaning performance and anti-aging ability of the film. Therefore, the present invention proposes to monitor and adjust the casting speed and cooling rate in real time through a dynamic real-time thickness control system, so as to achieve high-precision film forming.

[0245] The goal of this embodiment is to ensure that the thickness of the film is uniform and stable within the range of 20 to 40 microns through this control system, and to optimize the surface quality of the film so that it performs well in terms of UV aging, contact angle recovery, and yellowing resistance.

[0246] The dynamic real-time thickness control system used combines online sensors, laser scanning technology and feedback control mechanism to monitor the thickness of the film in real time and adjust the casting speed and cooling rate through feedback signals. In this system, the real-time change of film thickness is controlled by the following formula:

[0247]

[0248] in:

[0249] V(t) is the casting speed at time t, in meters per minute (m / min).

[0250] k1 and k2 are adjustment constants, which respectively reflect the film thickness change rate and the influence of the current thickness on the casting speed. In this example, the range of k1 is 0.05-0.15, and the range of k2 is 0.2-0.5. k1=0.1 and k2=0.3 are selected as preliminary parameters.

[0251] It is the rate of change of the film thickness H(t) at time t, indicating the rate of increase or decrease of the film thickness over time during the casting process. This value is acquired in real time by the laser scanning sensor.

[0252] H(t) is the film thickness monitored in real time, in micrometers (μm), which changes as the casting process proceeds.

[0253] C(t) is the adjustment coefficient of the cooling rate, which indicates the effect of the cooling rate on the film thickness during the cooling stage. The coefficient of the cooling rate C(t) ranges from 0.5 to 1.5, indicating the adjustment from slow cooling to fast cooling. C(t) = 1.0 was selected as the normal cooling condition.

[0254] In actual production, a 50cm wide casting device was used to process the prepared TPU solution into a film. The initial solution temperature was set to 180°C and the thickness was set to 30μm (i.e. 0.03mm). During the production process, the thickness of the film was monitored in real time, and the casting speed was adjusted through a formula.

[0255] The initial film thickness H(t0)=30 μm.

[0256] At time t0, the real-time thickness change rate measured by the laser scanning sensor It indicates that the film thickness is decreasing. The initial cooling rate C(t0) is set to 1.0, that is, the production is carried out at a normal cooling speed.

[0257] Substituting into the formula:

[0258] V(t0)=(0.1·(-1)+0.3·30)·1.0

[0259] V(t0)=(-0.1+9)=8.9m / min

[0260] Therefore, at this moment, the casting speed needs to be adjusted to 8.9 m / min to keep the film thickness stable.

[0261] As production progresses, the film thickness may change, and the system will dynamically adjust the casting speed based on the real-time monitored thickness information. It is assumed that in the subsequent production process, the laser scanning sensor monitors the film thickness H(t) = 32μm, and its thickness change rate is Indicates that the film thickness is increasing.

[0262] Substituting into the formula:

[0263] V(t)=(0.1·0.5+0.3·32)·1.0

[0264] V(t)=(0.05+9.6)=9.65m / min

[0265] Therefore, at this moment, the casting speed should be adjusted to 9.65m / min to keep the thickness within the target range. Through this real-time adjustment, the casting equipment can ensure that the film thickness is always stable within the range of 30μm±5μm, thus avoiding performance fluctuations caused by uneven thickness.

[0266] After the film is formed by the casting equipment, the cooling system starts working to further help control the final thickness of the film. The cooling rate C(t) plays a crucial role in the final stability of the film thickness. The cooling rate is set to remain at the conventional 1.0, that is, cooling at a normal speed. Under this condition, the film thickness adjusted by system feedback is stabilized at 30μm, and the speed and cooling rate of the casting equipment will remain stable according to the real-time monitoring data, ensuring the consistency of the film surface quality. In the production of highly yellowing-resistant self-cleaning TPU film, temperature control is crucial to the quality of the final product. The film forming process requires heating to give it good fluidity and uniform thickness distribution, while uneven temperature distribution will cause surface defects, thickness fluctuations and other problems, affecting the self-cleaning performance and anti-yellowing ability of the film. Therefore, a multi-segment temperature control system came into being, which independently adjusts the temperature of different heating zones to ensure that the temperature of each zone is uniform during film forming and the fluidity of the material is optimal.

[0267] The core of the multi-zone temperature control system is the dynamic adjustment of temperature differences. The system achieves precise control by setting different heating zones, and each zone adjusts the temperature according to the requirements of its location (such as viscosity, fluidity, etc.). In each heating zone, the temperature will be calculated and adjusted by the following formula:

[0268]

[0269] in:

[0270] T i (t) is the temperature of the i-th section at time t, which determines the softening degree of the material in this section. i-1 (t) is the temperature of the previous section, reflecting the impact of the temperature of the previous heating section on the current section. ΔT is the temperature difference between two consecutive temperature control sections, indicating the amplitude of the temperature difference between the two sections. max(ΔT) is the maximum temperature difference between each temperature control section, ensuring that the temperature difference is not too large to avoid uneven heating of the material.

[0271] In order to achieve precise temperature control, the casting process is divided into three main heating sections, namely:

[0272] The first section: used for the initial softening and flow of the material.

[0273] The second section: optimizes the viscosity of the material and helps form a uniform film surface.

[0274] The third section: During the cooling phase, the film is ensured to maintain a high morphological stability.

[0275] The temperature of each heating zone will be adjusted in real time using the above formula.

[0276] The following initial parameters were chosen:

[0277] The temperature of the first section T1 = 180°C;

[0278] The temperature of the second section T2 = 190°C;

[0279] The temperature of the third section is T3 = 200°C.

[0280] In addition, the temperature difference ΔT is set to 10°C, that is, T2T1 = 10°C, T3T2 = 10°C, and the maximum temperature difference max(ΔT) = 10°C.

[0281] According to the given parameters, the temperature of the first section is set to T1 = 180°C, and then the actual temperatures of the second section T2 and the third section T3 are calculated by the formula.

[0282] Calculate the temperature of the second zone:

[0283]

[0284] Substituting the values:

[0285] T2(t)=190℃

[0286] Therefore, the temperature of the second zone is 190°C.

[0287] Calculate the temperature of the third zone:

[0288]

[0289] Substituting the values:

[0290] T3(t)=200℃

[0291] Therefore, the temperature of the third zone is 200°C.

[0292] These temperature values ​​ensure that the degree of heating of the material in different areas is suitable for its fluidity requirements, thereby optimizing the film forming process. During the production process, the temperature control system will dynamically adjust the temperature of the heating section based on real-time sensor data (such as temperature and thickness information provided by temperature sensors and laser scanning sensors). If the real-time temperature in the second section deviates from the target temperature within 10°C, the system will adjust the temperature of the second section according to the feedback signal, and adjust the temperature of other sections accordingly to maintain a uniform temperature distribution.

[0293] In actual operation,

[0294] The temperature T1(t) of the first section rises slightly to 185°C.

[0295] The temperature T2(t) of the second section rises to 195°C.

[0296] The temperature T3(t) of the third section reaches 205°C.

[0297] In this case, through the feedback control mechanism, the system will update the above temperature control formula in real time to ensure that the fluidity and viscosity of the material always remain within the ideal range.

[0298] Through the above precise temperature control process, the TPU film can be uniformly formed and the surface quality is significantly improved. The precise temperature adjustment makes the viscosity and fluidity of the film in each heating section in the best state, avoiding defects caused by too high or too low temperature, and ensuring the flatness and uniformity of the film surface.

[0299] In the production process of the film of this embodiment, tension control is a crucial link. The film is subjected to stretching and stress in different areas during the casting process. Uneven tension may cause deformation, cracks or uneven surface of the film, thereby affecting its performance. In order to ensure the morphological stability and uniform physical properties of the film, an intelligent tension control system is introduced. By real-time monitoring of the elongation of the film and dynamically adjusting the tension distribution according to the feedback signal, it is ensured that the film is uniformly stressed during the entire molding process. The intelligent tension control system combines real-time sensors, feedback algorithms and tension distribution control formulas. It can avoid local over-stretching or under-stretching by adjusting the tension distribution at each stage of film molding. The system dynamically adjusts the tension distribution of the film through the following formula:

[0300]

[0301] in:

[0302] T i (t) is the tension of the i-th region at time t, in Newtons, which determines the tensile strength of the film in that region. refThe reference tension represents the tension standard under ideal conditions. The unit is N. It is usually obtained through experiments and represents the tension of the material under standard conditions. i (t) is the real-time stretching rate of the i-th region, expressed as a ratio, reflecting the extension of the film in this region. ref is the reference stretch rate, which indicates the stretch rate under ideal conditions, usually the elongation ratio of the film under standard production conditions. α is the tension distribution adjustment coefficient, usually between 0.5 and 1.5, which is used to adjust the sensitivity of tension to the change of stretch rate. α = 1 is selected as the preliminary parameter.

[0303] In actual production, the casting equipment is divided into three tension control sections:

[0304] The first section: the initial stretching stage of the material.

[0305] The second section: the stretching speed increases and the film morphology gradually stabilizes.

[0306] The third section: the final stretching stage to ensure the integrity and uniformity of the film.

[0307] For each segment, a preliminary tension reference value is set:

[0308] Reference tension T of the first section ref1 =20N.

[0309] Reference tension T of the second section ref2 =25N.

[0310] Reference tension T of the third section ref3 =30N.

[0311] Set the ideal stretching ratio S of the film ref It is 1.1 (indicating the elongation of the film under standard conditions).

[0312] In the actual production process, the real-time stretching rate S of the film is monitored by the tension sensor. i (t). It is assumed that during the production process, the real-time stretching rate of the first section is S1(t)=1.05, the real-time stretching rate of the second section is S2(t)=1.08, and the real-time stretching rate of the third section is S3(t)=1.10.

[0313] According to the real-time stretch rate, the tension control system will dynamically adjust the tension of each section. Substitute into the formula to calculate the tension of each section:

[0314] Tension calculation for the first section:

[0315]

[0316] Therefore, the tension of the first section is 19.09N, which is slightly lower than the reference tension of 20N, ensuring moderate stretching.

[0317] Tension calculation for the second section:

[0318]

[0319] Therefore, the tension of the second section is 24.54N, which is close to the reference tension of 25N, showing a proper stretching effect.

[0320] Tension calculation of the third section:

[0321]

[0322] Therefore, the tension of the third section is 30N, which fully meets the reference tension and ensures that the final film morphology is stable.

[0323] In the actual production process, the tension sensor will continuously monitor the stretching of the film. It is set that in the subsequent stage of production, the stretching rate of the first section increases to S1(t) = 1.07, the stretching rate of the second section is S2(t) = 1.09, and the stretching rate of the third section remains unchanged S3(t) = 1.10.

[0324] Substitute this into the formula and recalculate the tension:

[0325] New tension in the first segment:

[0326]

[0327] New tension in the second segment:

[0328]

[0329] The tension of the third section is maintained at T3(t)=30N and no adjustment is required.

[0330] Through such adjustments, the tension control system can dynamically adjust the tension distribution according to the real-time stretch rate data to ensure the uniformity and stability of the film.

[0331] Through the above precise tension control, the prepared TPU film has excellent physical properties. After UV aging test, the yellowing index (ΔYI) of the film is 1.2, indicating that the film has strong anti-yellowing performance. At the same time, the contact angle recovery performance of the film also reached 105°, demonstrating its excellent self-cleaning ability.

[0332] According to production data, after adopting the intelligent tension control system, the thickness uniformity of the film is improved, the surface defects are reduced, and the tensile and yellowing resistance are significantly enhanced. Compared with the traditional control method, it has higher production efficiency and product consistency. Through the intelligent tension control system, combined with real-time sensors and feedback algorithms, precise tension adjustment can be achieved during the film forming process to ensure uniform tensile force in each area. This method not only optimizes the physical properties of the TPU film, but also significantly improves the self-cleaning and yellowing resistance of the film. In practical applications, this system can be widely used in the production of various high-performance films, especially in the field of high-end products that require strict control of film quality.

Claims

1. A method for preparing a highly yellowing-resistant self-cleaning TPU film, characterized in that The following steps are involved: S1. Preparation and pretreatment of basic materials: S1.1, mixing polyether diol with nano-silicon dioxide, wherein the nano-silicon dioxide accounts for 1% to 5% of the total weight of the substrate; adding ethanol or methanol solvent, wherein the amount of the solvent is 150% to 300% of the weight of the substrate; stirring at room temperature for 30 to 60 minutes to form a uniform dispersion; S1.2, adding a metal chelating agent solution including EDTA to the dispersion in an amount of 0.2% to 1% of the total weight of the dispersion; S1.3, adding anti-yellowing agents including anti-UV-385 and anti-UV-328 to the solution, the total amount of the anti-yellowing agent is 2% to 5% of the weight of the solution, and adding after mixing in a ratio of 1:1 or 1:2; S2, TPU synthesis treatment: S2.

1. Add the substrate solution into the reaction kettle, and slowly add isocyanate including MDI in an amount of 40% to 60% of the total weight of the substrate; S2.2, adding a chain extender in an amount of 10% to 20% of the total weight of the substrate, and adding a catalyst; S2.3, adding activated titanium dioxide nanoparticles to the prepolymer in an amount of 0.5% to 2% of the total weight; the activation method is plasma treatment; S3, film forming and performance optimization: S3.1, filter the prepared TPU solution, control the filter pore size to 80-120 μm, and remove impurities; S3.2, use the casting equipment to process the film, the casting speed is controlled at 1.2-1.8 m / min, the temperature range is 180-200°C, and the tension is maintained at 10-20 MPa; adjust the equipment parameters to form a film with a thickness of 20-40 μm; S4. Surface coating treatment: S4.

1. Use a fluorinated silicone resin coating solution with a concentration of 1% to 3% by mass to cover the surface of the film by spraying; after spraying, place the film in an environment of 70 to 90°C for curing for 1.5 to 3 hours to form a dense coating.

2. The method for preparing a highly yellowing-resistant self-cleaning TPU film according to claim 1, characterized in that The dispersion treatment method comprises: using an ultrasonic processor for treatment, with the ultrasonic frequency set to 30-50 kHz, the power to 300-500 W, and the treatment time to 20-40 minutes to improve the dispersion uniformity of silicon dioxide.

3. The method for preparing a highly yellowing-resistant self-cleaning TPU film according to claim 1, characterized in that In step S1.2, the solution is heated to 70-90° C. and maintained for 30-60 minutes, and undissolved impurities are removed by filtration to obtain a clear solution.

4. The method for preparing a highly yellowing-resistant self-cleaning TPU film according to claim 1, characterized in that In step S1.3, the solution is stirred at 60-70° C. for 60-120 minutes to uniformly disperse the anti-yellowing agent.

5. The method for preparing a highly yellowing-resistant self-cleaning TPU film according to claim 1, characterized in that In step S2.1, the reaction temperature is controlled in the range of 75-85° C.; the concentration of the NCO group is monitored by continuous stirring for 60-90 minutes to ensure that the NCO content is in the range of 3%-5%.

6. The method for preparing a highly yellowing-resistant self-cleaning TPU film according to claim 1, characterized in that The chain extender is 1,4-butanediol, the catalyst is stannous octoate, and the catalyst accounts for 0.01% to 0.05% of the total weight; stirring is continued for 60 to 90 minutes at 80 to 90° C. until a uniform prepolymer is formed.

7. The method for preparing a highly yellowing-resistant self-cleaning TPU film according to claim 1, characterized in that The plasma treatment is carried out at a power of 200-400 W, a gas flow rate of 0.3-0.7 L / min, and a treatment time of 10-20 minutes; and stirring is carried out at 70-80° C. for 90-120 minutes to ensure that the particles are evenly dispersed and stable.

8. The method for preparing a highly yellowing-resistant self-cleaning TPU film according to claim 1, characterized in that The method for controlling parameters of film processing by the casting device comprises: A dynamic real-time thickness control system is used, combining online sensors, laser scanning technology and feedback control mechanism to monitor the actual thickness of the film in real time, and dynamically adjust the casting speed and cooling system operation according to the feedback signal; the film thickness adjustment formula is as follows: in, V(t) represents the casting speed at time t; k1 and k2 are adjustment constants, which respectively reflect the film thickness change rate and the influence of the current thickness on the casting speed; is the rate of change of the film thickness H(t) at time t, indicating the speed of increase or decrease of the thickness over time; H(t) is the film thickness monitored in real time, which will change as the casting process proceeds; C(t) is the adjustment coefficient of the cooling rate, indicating the influence of the cooling rate on the film thickness during the cooling stage.

9. The method for preparing a highly yellowing-resistant self-cleaning TPU film according to claim 8, characterized in that The method for controlling parameters of film processing by the casting device comprises: A multi-zone temperature control system was introduced, which uses multiple independent heating zones to adjust according to the material fluidity and viscosity of each zone, and control the uniform temperature and material fluidity of each zone during the film forming process; the specific operation of the temperature control system is calculated based on the following formula: in, T i (t) is the temperature of the i-th section, which determines the softening degree of the material in this section at time t; T i-1 (t) is the temperature of the previous section, indicating the temperature influence of the previous heating section; ΔT is the temperature difference between two consecutive temperature control sections, reflecting the amplitude of the section temperature change; max(ΔT) is the maximum temperature difference between each temperature control section, which is used to standardize the control range of the temperature difference.

10. The method for preparing a highly yellowing-resistant self-cleaning TPU film according to claim 9, characterized in that The method for controlling parameters of film processing by the casting device comprises: An intelligent tension control system is used, combined with sensors and feedback algorithms, to monitor the stretching state of the film in real time, and dynamically adjust the tension distribution to control the uniform force in each area of ​​the film. The tension distribution control is dynamically adjusted using the following formula: in, T i (t) is the tension in the i-th region. At time t, the morphology and physical properties of the film are ensured by adjusting the tension distribution; T ref is the reference tension, indicating the tension standard under ideal conditions; S i (t) is the real-time stretching rate of the ith region, reflecting the extension of the film in the region; S ref is the reference stretch rate, which is the elongation ratio of the film under ideal conditions; α is the tension distribution adjustment coefficient, which is used to adjust the sensitivity of tension to changes in stretch rate.

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