Preparation method of ultraviolet yellowing-resistant TPU glass laminated film

Abstract

The application discloses a kind of UV yellowing-resistant TPU glass interlayer film preparation methods, belong to UV yellowing-resistant glass interlayer film technical field.It is specifically to be pre-polymerized under catalyst with polycarbonate dihydric alcohol, dicyclohexyl methane diisocyanate, partial chain extender, reactive ultraviolet absorber and hindered amine light stabilizer, and obtain prepolymer;Nano titanium dioxide, nano zinc oxide, remaining chain extender and epoxy silane coupling agent modified by silane coupling agent are then added, chain extension and in-situ hybridization are carried out, and functional TPU sizing material is obtained;Then, the film of ABC structure is prepared by three-layer co-extrusion casting, and then the surface is treated by plasma, to obtain UV yellowing-resistant TPU glass interlayer film.The application realizes the permanent fixation and synergistic effect of ultraviolet absorber and nanoparticles by the double stabilization strategy of chemical bonding and in-situ hybridization of nanoparticles, and greatly improves the yellowing resistance durability, mechanical properties and interfacial bonding strength of the interlayer film.

Description

Technical Field

[0001] This invention belongs to the field of UV-resistant yellowing glass laminated film technology, specifically a method for preparing a UV-resistant TPU glass laminated film. Background Technology

[0002] Laminated glass is a safety glass product made by laminating two or more panes of glass with an interlayer polymer film under high temperature and pressure. It is widely used in building curtain walls, automotive windshields, and aircraft windows. The polymer interlayer is the core component that determines the safety, optical, and weather resistance of laminated glass. Currently, polyvinyl butyral (PVB) film accounts for over 95% of the interlayer market share, but it suffers from poor resistance to damp heat, yellowing, and a significant decrease in adhesion strength to glass with humidity. Polyurethane (PU) film, due to its high strength, high elasticity, abrasion resistance, and solvent resistance, has become an important alternative to PVB film. However, traditional polyurethanes are mostly prepared by using aromatic isocyanates (such as MDI and TDI) with polyester or polyether polyols. The benzene ring in the aromatic isocyanate molecule is directly connected to the isocyanate group, and the large π bond on the benzene ring forms a conjugated structure with the nearby NCO. Under light, heat and oxygen environments, it easily absorbs 290-400nm ultraviolet light, which leads to photo-oxidative breakage or cross-linking of the polyurethane chain. At the same time, it degrades to generate quinone chromophores, causing severe yellowing of the film and a significant reduction in its service life.

[0003] To address the aforementioned issues, existing technologies have proposed several improvement schemes. Chinese patent CN118440654A discloses a yellowing-resistant polyurethane glass interlayer film for laminated glass, which improves yellowing resistance by synthesizing a special silicone oil curing agent. However, the preparation of this curing agent involves multiple organic synthesis steps (olefin addition, Gabriel reaction, hydrazine hydrolysis, methoxy carbonylation, pyrolysis, etc.), resulting in complex processes, high costs, and the use of an aromatic isocyanate system, thus offering limited improvement in yellowing resistance. Chinese patent CN116854930A discloses a yellowing-resistant TPU material that achieves yellowing resistance by constructing a metal-organic framework (MOF) structure. However, this scheme involves complex monomer synthesis and zinc ion coordination processes, and does not address optimization of adhesion to glass. Furthermore, existing technologies often use physical blending to add ultraviolet absorbers, which are prone to migration, precipitation, and volatilization during long-term use, leading to a significant decline in yellowing resistance over time. Therefore, developing a method for preparing a TPU glass laminated film that permanently immobilizes ultraviolet absorbers, uniformly disperses nanoparticles, and possesses excellent resistance to yellowing, high light transmittance, strong interfacial adhesion, and good mechanical properties is of significant practical importance and application value. This invention is proposed based on this technical need. Summary of the Invention

[0004] (a) Purpose of the invention The purpose of this invention is to provide a method for preparing a TPU glass laminated film resistant to ultraviolet yellowing. This method aims to solve the technical problems of insufficient yellowing resistance, easy migration of ultraviolet absorbers, easy agglomeration of nanoparticles, and low adhesion strength to glass in existing polyurethane glass laminated films. By adopting a dual stabilization strategy of chemical bonding and in-situ hybridization of nanoparticles, combined with a three-layer composite structure design and plasma surface activation treatment, a TPU laminated film with excellent yellowing resistance, good mechanical properties, high light transmittance, and strong adhesion to glass is obtained.

[0005] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a TPU glass laminated film resistant to ultraviolet yellowing includes the following steps: S1: Polycarbonate diol, dicyclohexylmethane diisocyanate, a first chain extender accounting for 30-50% of the chain extender mass, a reactive ultraviolet absorber, and a hindered amine light stabilizer are subjected to a prepolymerization reaction under the action of a catalyst to obtain an isocyanate-terminated TPU prepolymer. S2: Add nano-titanium dioxide modified with silane coupling agent, nano-zinc oxide modified with silane coupling agent, a second chain extender and epoxy silane coupling agent to the TPU prepolymer obtained in S1, and carry out chain extension reaction and in-situ hybridization reaction to obtain functionalized TPU compound. S3: The functionalized TPU material obtained in S2 is cast into a film by three-layer co-extrusion to form an ABC three-layer composite film, wherein layer A and layer C are functionalized TPU material, and layer B is pure TPU material without added nanoparticles. S4: The three-layer composite film obtained in S3 is subjected to nitrogen plasma surface activation treatment to obtain the UV-resistant TPU glass laminated film.

[0006] Preferably, the prepolymerization reaction temperature in S1 is 75-95℃, and the reaction time is 2-5h; the sum of the masses of the first and second chain extenders is the total mass of the chain extender; the reactive ultraviolet absorber is a benzophenone compound or a benzotriazole compound containing polymerizable double bonds and active hydroxyl groups; the reaction temperature in S2 is 75-90℃, and the reaction time is 1-3h.

[0007] Preferably, after the three-layer co-extrusion casting in S3, the film is annealed at a temperature of 80-110℃ for 6-24 hours; the thickness ratio of the three layers of the ABC three-layer composite film is 1:6:1 to 1:10:1; the power of the nitrogen plasma surface activation treatment in S4 is 50-200W, and the treatment time is 30-120s.

[0008] Preferably, the reactive ultraviolet absorber is selected from one or more of 2-acrylate-2-(4-benzoyl-3-hydroxyphenoxy)ethyl ester, 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2-hydroxy-4-acryloyloxyethoxybenzophenone, and 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole; the hindered amine light stabilizer is 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine or 4-acryloyloxy-2,2,6,6-tetramethylpiperidine.

[0009] Preferably, the amounts of each raw material, by weight, are as follows: 40-70 parts polycarbonate diol, 35-60 parts dicyclohexylmethane diisocyanate, 3-10 parts total of the first and second chain extenders, 1-6 parts reactive ultraviolet absorber, 0.5-3 parts hindered amine light stabilizer, 0.02-0.5 parts catalyst, 0.5-5 parts silane coupling agent modified nano-titanium dioxide, 0.2-3 parts silane coupling agent modified nano-zinc oxide, and 0.1-1.5 parts epoxy silane coupling agent; the chain extender is one or more of 1,4-butanediol, ethylene glycol, and 1,6-hexanediol; the catalyst is an organobismuth catalyst or an organotin catalyst.

[0010] Preferably, the preparation method of the silane coupling agent modified nano-titanium dioxide is as follows: rutile nano-titanium dioxide with a particle size of 10-30 nm is dispersed in anhydrous ethanol, and 3%-10% (by weight of the rutile nano-titanium dioxide) of γ-methacryloyloxypropyltrimethoxysilane is added. The pH is adjusted to 3-5 using acetic acid or dilute hydrochloric acid, and the mixture is stirred and reacted at 60-80°C for 4-8 hours. The mixture is then centrifuged, washed with ethanol, and vacuum dried at 60-70°C. The silane coupling agent modified... The preparation method of nano-zinc oxide is as follows: Zinc oxide nanoparticles with a particle size of 20-50 nm are dispersed in anhydrous ethanol, and 2%-8% (by weight of the zinc oxide nanoparticles) of γ-aminopropyltriethoxysilane is added. The mixture is stirred and reacted at 50-70℃ for 3-6 hours, followed by centrifugation, washing with ethanol, and vacuum drying at 60-70℃. The centrifugation speed is 8000-12000 rpm, and the time is 10-20 minutes. The vacuum degree of the vacuum drying is ≤-0.095 MPa. (The particle size refers to the average primary particle size measured by transmission electron microscopy (TEM).) Preferably, the epoxy silane coupling agent is γ-glycidoxypropyltrimethoxysilane or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0011] Preferably, during the prepolymerization reaction in S1, the NCO / OH molar ratio in the reaction system is controlled to be 1.5-2.5:1; the polycarbonate diol has a number average molecular weight of 1000-4000, and its molecular structure is a linear diol obtained by polycondensation of C2-C10 aliphatic diols and carbonates; the trans-trans isomer content in the dicyclohexylmethane diisocyanate is not less than 70% (the trans-trans isomer content in the HMDI is determined by gas chromatography (GC)).

[0012] Preferably, the process conditions for the three-layer co-extrusion casting film in S3 are as follows: extruder temperature of A / C layers 180-210℃, extruder temperature of B layer 175-200℃, three-layer co-extrusion die temperature 190-215℃, casting roll temperature 65-85℃, casting speed 8-20m / min, and the total thickness of the resulting laminated film is 0.42-1.52mm, of which the thickness of each layer A and C is 0.05-0.15mm.

[0013] Preferably, before the nitrogen plasma surface activation treatment, the three-layer composite film is further preheated: the preheating temperature is 50-70℃, the preheating time is 1-3min; during plasma treatment, the nitrogen flow rate is 50-200mL / min, the treatment chamber pressure is 20-80Pa, the treatment power is 80-150W, and the treatment time is 45-90s.

[0014] The UV-resistant TPU glass laminated film prepared by this invention has the following excellent properties: light transmittance ≥87%, yellowing index Δb ≤2.1 (after QUV aging for 2400 h), and tensile strength ≥410 N / cm. 2 Elongation at break ≥400%, tensile shear strength of glass ≥7.8MPa, and resistance to damp heat aging (85℃ / 85%RH, 1000h) Δb≤1.5.

[0015] (III) Core Innovation Points 1. A two-component UV-resistant system chemically bonded to a reactive UV absorber and a hindered amine light stabilizer. This invention not only uses hydroxybenzophenone (or benzotriazole) containing polymerizable double bonds as a reactive UV absorber, but also simultaneously introduces a hindered amine light stabilizer (such as 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine) containing polymerizable double bonds. In the prepolymerization stage, the active hydroxyl groups (-OH) in the reactive UV absorber and hindered amine light stabilizer molecules preferentially react with isocyanate groups (-NCO) to form urethane bonds, thereby covalently linking the UV-resistant functional groups to the prepolymer molecular chain. The polymerizable double bonds (C=C) in the molecules remain inert at this stage, providing the possibility for in-situ thermal crosslinking reactions that may occur during subsequent extrusion processing at higher temperatures, or for reactions with double bonds on the surface of modified nanoparticles. The UV-absorbing functional groups and free radical trapping functional groups are simultaneously covalently bonded into the TPU backbone. The benzophenone structure efficiently absorbs 290-400nm ultraviolet light and converts it into heat energy, while the hindered amine structure captures alkyl and peroxy radicals generated during photo-oxidation, interrupting the free radical chain reaction. The two functional groups work synergistically at the molecular level to form a more efficient UV-resistant aging system.

[0016] 2. In-situ hybridization of two modified nanoparticles (TiO2 and ZnO) and complementary effects of dual coupling agents. This invention utilizes KH570-modified nano-TiO2 (with polymerizable double bonds on the surface) and KH550-modified nano-ZnO (with amino groups on the surface), while simultaneously incorporating the epoxy-based silane coupling agent KH560. During the chain extension reaction, the double bonds on the surface of the modified TiO2 participate in TPU polymerization to form chemical grafts, and the amino groups on the surface of the modified ZnO react with isocyanate groups to form urea bonds. The epoxy groups of KH560 can react with the amino groups, and their alkoxy groups can condense with the hydroxyl groups on the surface of the nanoparticles, thereby forming a network structure in the TPU matrix with nanoparticles as crosslinking points. The combined use of TiO2 and ZnO produces a broad-spectrum ultraviolet shielding effect: TiO2 mainly absorbs and scatters near-ultraviolet light in the 350-400 nm range, while ZnO mainly absorbs ultraviolet light in the 300-380 nm range. The two complement each other, achieving highly efficient shielding across the entire ultraviolet band. Meanwhile, the different surface modifications and particle size differences of the two nanoparticles (TiO2 10-30nm, ZnO 20-50nm) formed a "dual particle size distribution" effect, with small-sized TiO2 filling the gaps between large-sized ZnO particles, thus improving the packing density and dispersion uniformity of the nanoparticles.

[0017] 3. ABC Three-Layer Composite Structure Design. This invention uses functionalized TPU material (containing nanoparticles and UV-resistant components) as the surface layer (layers A and C), while the core layer (layer B) uses pure TPU material without added nanoparticles. This design has multiple advantages: First, the high concentration of UV-resistant components in the surface layer directly faces UV light irradiation, acting as a "barrier" to protect the core layer; second, the nanoparticles exist only in the surface layer, avoiding excessive influence of nanoparticles on light transmittance (the core layer has no nanoparticles and high light transmittance); third, the high-toughness pure TPU in the core layer ensures the overall flexibility and impact resistance of the laminated film; fourth, it reduces the amount of expensive nanoparticles and UV-resistant additives, lowering costs. The thickness ratio of the three layers is optimized to 1:6:1 to 1:10:1, ensuring both the shielding effect of the surface layer and the mechanical strength of the core layer, resulting in a scientifically balanced design.

[0018] 4. Nitrogen Plasma Surface Activation Treatment. Traditional TPU-glass bonding relies primarily on physical wetting and hydrogen bonding during hot pressing, resulting in limited bond strength. This invention involves treating the film with nitrogen plasma after casting. Nitrogen plasma introduces nitrogen-containing functional groups (such as amino, imino, and cyano groups) onto the film surface. These functional groups react with the silanol groups on the glass surface to form stronger chemical bonds (such as CN-Si bonds). Simultaneously, plasma etching increases surface roughness, enhancing mechanical interlocking. The tensile shear strength of the laminated film and glass is improved after plasma treatment, and its resistance to damp heat aging is also enhanced.

[0019] 5. Stepwise addition of chain extender and microphase structure regulation through annealing. The chain extender in this invention is added in two steps: the first step involves adding 30%-50% of the chain extender (the first portion) to control the molecular weight of the prepolymer within a low range, facilitating the uniform dispersion of nanoparticles; the second step involves adding the remaining chain extender (the second portion) to further extend the molecular chains and form a polymer. Combined with annealing after S3 (80-110℃, 6-24h), this promotes the ordered arrangement of hard segment microregions and microphase separation, contributing to improved mechanical strength and light transmittance.

[0020] (iv) Reaction Mechanism The core chemical reaction mechanism of this invention includes the following aspects: (1) Reaction mechanism of the prepolymerization stage: Under the action of an organobismuth catalyst, the hydroxyl group of polycarbonate diol (HO-R-OH) reacts with excess dicyclohexylmethane diisocyanate (OCN-R'-NCO) in a nucleophilic addition reaction with the isocyanate group to form a urethane bond (-NH-CO-O-), forming a linear prepolymer with isocyanate group end capping. At the same time, the primary hydroxyl group in the reactive ultraviolet absorber 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone reacts with the isocyanate group to attach the benzophenone structural unit to the end or middle of the prepolymer chain; the hydroxyl group in the hindered amine light stabilizer 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine also reacts with the isocyanate group to attach to the prepolymer. These reactions belong to typical polyurethane addition polymerization chemistry.

[0021] (2) Reaction mechanism of chain extension and in-situ hybridization stage: The added second small molecule chain extender (such as 1,4-butanediol) reacts with the isocyanate groups at the end of the prepolymer, causing the molecular chain to grow further. At the same time, the methacryloyloxy group (double bond) on the surface of KH570 modified nano-TiO2 can undergo graft copolymerization with the double bond or active hydrogen in the TPU molecular chain under the catalysis and thermal initiation, forming a stable CC bond connection. The amino group (-NH2) on the surface of KH550 modified nano-ZnO reacts with the isocyanate group to generate urea bond (-NH-CO-NH-), realizing the chemical anchoring of nanoparticles. The epoxy group of the epoxy silane coupling agent KH560 can undergo ring-opening addition reaction with the amino group on the surface of ZnO, and its methoxy group condenses with the hydroxyl group on the surface of nanoparticles to form Si-O-Ti or Si-O-Zn bonds, thereby constructing a three-dimensional chemical network between nanoparticles-coupling agent-TPU. This in-situ hybrid structure transforms nanoparticles from simple physical fillers into part of the TPU cross-linked network.

[0022] (3) Plasma surface activation mechanism: High-energy electrons and ions in nitrogen plasma bombard the TPU film surface, causing the surface molecular chains to break and generate free radicals. At the same time, active nitrogen species (N, N2, etc.) in nitrogen plasma react with surface free radicals, introducing nitrogen-containing polar groups such as -NH2, -CN, and -NH-. These groups increase the surface energy and improve the wettability of TPU to glass. On the other hand, during the hot-pressing process, -NH2 can undergo dehydration condensation with the silanol groups on the glass surface to form Si-NH- bonds (or Si-N- bonds), which significantly enhances chemical adhesion. In addition, plasma etching creates micro-nano uneven structures on the surface, increasing the physical anchoring effect.

[0023] (4) Synergistic mechanism of UV resistance to yellowing: When ultraviolet light irradiates the laminated film, the nano-TiO2 and ZnO in the surface layer first attenuate part of the ultraviolet light through scattering and absorption; the transmitted ultraviolet light is absorbed by the benzophenone structure, and the benzophenone molecule undergoes a reversible enol-keto tautomerism, dissipating the ultraviolet light energy in the form of heat; even if a small amount of free radicals are generated, the hindered amine structure can quickly capture the free radicals and prevent the propagation of the chain oxidation reaction. This triple protection mechanism of "physical shielding - chemical absorption - free radical capture", combined with the inherent advantage of aliphatic isocyanates without benzene ring structure, fundamentally inhibits the generation of chromophores and achieves ultra-durable resistance to UV yellowing.

[0024] Beneficial technical effects of the present invention 1. Ultra-durable resistance to UV yellowing. This invention constructs a triple synergistic UV-resistant system through the chemical bonding of a reactive UV absorber and a hindered amine light stabilizer, as well as in-situ hybridization of modified nano-TiO2 / ZnO. The system was tested under QUV accelerated aging conditions (UVA-340, 0.75W / m²). 2 Tested at 340nm, 60℃, and 2400h, the yellowing index Δb of the laminated film of this invention is ≤2.1, and the phenol resistance yellowing grade reaches 5.0, which is superior to the physical blend comparative example and the single-component comparative example. More importantly, since all functional components are fixed by chemical bonds, after 1000h boiling water test, the Δb value of most examples is less than 1.5, while the Δb value of the physical blend sample increases by more than 1.5, proving the migration resistance and durability of this invention.

[0025] 2. Excellent balance between mechanical properties and light transmittance. This invention utilizes a stepwise addition of chain extenders and annealing treatment to optimize the microphase separation structure, combined with an ABC three-layer structure design (without nanoparticles in the core layer), enabling the laminated film to maintain high light transmittance (≥87%) while achieving a tensile strength ≥410 N / cm. 2 Elongation at break ≥400%.

[0026] 3. Significantly enhanced interfacial bonding strength. Through nitrogen plasma surface activation treatment and the introduction of epoxy silane coupling agents, the tensile shear strength of the laminated film and glass of this invention is ≥8.0 MPa in most embodiments (7.8 MPa in Example 2), which is more than 40% higher than that of the untreated sample. After 1000 hours of humid heat aging at 85℃ / 85%RH, the shear strength retention rate is ≥85%, demonstrating excellent aging-resistant bonding performance.

[0027] 4. High process integration and controllable cost. This invention integrates chemical synthesis, nanoparticle modification, multilayer co-extrusion, and plasma treatment into a complete continuous production process. Although there are many steps, each unit operation is a mature industrial technology, which is easy to scale up for mass production. At the same time, through the three-layer structure design, expensive nanoparticles and UV-resistant additives are used only in the thin surface layer, reducing raw material costs.

[0028] 5. Comprehensive performance meets the needs of high-end applications. The TPU glass laminated film prepared by this invention can be applied to automotive windshields, architectural safety glass, aviation windows, and other fields. It is especially suitable for scenarios with extremely high requirements for resistance to UV yellowing and long-term outdoor reliability, such as photovoltaic module encapsulation and high-end building curtain walls. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the preparation process of the UV-resistant yellowing TPU glass laminated film of Embodiment 1 of the present invention.

[0030] Figure 2 This is a side view of a schematic diagram illustrating the chemical bonding of a reactive ultraviolet absorber and a hindered amine light stabilizer into the TPU backbone in Example 1 of the present invention.

[0031] Figure 3 This is a top view of the reaction schematic diagram of the chemical bonding of reactive ultraviolet absorber and hindered amine light stabilizer into the TPU backbone in Example 1 of the present invention.

[0032] Figure 4 This is a front view of the reaction diagram of the chemical bonding of the reactive ultraviolet absorber and the hindered amine light stabilizer into the TPU backbone in Example 1 of the present invention.

[0033] Figure 5 This is a cross-sectional schematic diagram of the ABC three-layer composite sandwich membrane of Embodiment 1 of the present invention.

[0034] Figure 6 This is a schematic diagram showing the changes in the functional groups on the TPU surface before and after nitrogen plasma surface activation treatment in Example 1 of the present invention.

[0035] Figure 7 This is a comparison chart of the UV resistance to yellowing performance of Example 1 and Comparative Examples 1-4 of the present invention (△b value changes with aging time).

[0036] Figure 8 This is a comparison diagram of the tensile shear strength of Embodiment 1 and Comparative Examples 1-4 of the present invention.

[0037] The names of the components shown in the diagram are as follows: Figure 2In the middle, 201—isocyanate group (-NCO) reaction end, 202—TPU backbone (polyurethane skeleton), 203—reactive ultraviolet absorber (benzophenone), 204—active hydroxyl group (-OH), 205—polymerizable double bond (C=C), 206—urethane bond (-NH-CO-O-), 207—auxiliary link / carbon chain; Figure 3 , Figure 4 Chinese logo and Figure 2 Consistent.

[0038] Figure 5 In the middle, 501-A layer (functionalized TPU), 502-B layer (pure TPU), and 503-C layer (functionalized TPU).

[0039] Figure 6 In the process, 601—TPU surface, 602—hydroxyl (-OH), 603—-NH2 (amino) introduced after nitrogen plasma treatment, and 604—-NH- (imino) introduced after nitrogen plasma treatment. Detailed Implementation

[0040] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0041] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in this invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of those skilled in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or identical to those described in the embodiments of this invention may be used to implement this invention.

[0042] Unless otherwise stated, the test methods, detection methods and preparation methods disclosed in this invention all adopt conventional techniques in this technical field.

[0043] I. Raw material sources and their functions

[0044] The raw materials used in the following embodiments and comparative examples of the present invention are sourced from the following sources: (1) Polymer polyol: Polycarbonate diol (PCDL, number average molecular weight 2000 g / mol) was purchased from BASF, brand name UH-200. PCDL, as the soft segment component of TPU, endows the material with good flexibility, low-temperature performance and hydrolysis resistance. Its molecular structure is a linear diol obtained by polycondensation of C2-C10 aliphatic diol and carbonate, without ether bonds, and its heat oxidation stability is better than that of polyether polyol.

[0045] (2) Isocyanates: Dicyclohexylmethane diisocyanate (HMDI, trans-trans isomer content ≥75%) was purchased from Covestro, Germany. HMDI is an aliphatic (alicyclic) isocyanate that does not contain benzene rings, thus fundamentally avoiding the yellowing problem of aromatic isocyanates due to the formation of quinone chromophores by photothermal oxidation.

[0046] (3) Chain extenders: 1,4-Butanediol (BDO), ethylene glycol (EG), and 1,6-hexanediol (HDO) were purchased from Sinopharm Chemical Reagent Co., Ltd., and were of analytical grade (≥99%). The chain extenders were used to adjust the hard segment content and molecular weight of TPU and were added in steps to optimize the microphase separation structure.

[0047] (4) Reactive UV absorber: 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, which has polymerizable double bonds and active hydroxyl groups, can react with isocyanates and chemically bond into the TPU backbone.

[0048] (5) Hindered amine light stabilizer: 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine was purchased from Beijing Additives Research Institute. It also contains polymerizable double bonds, which can be chemically bonded into the TPU backbone to capture free radicals.

[0049] (6) Catalysts: Bismuth neodecanoate was purchased from Jiangsu Evergreen New Material Technology Co., Ltd., and organotin catalyst was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0050] (7) Other reagents: Anhydrous ethanol and dimethylformamide (DMF, anhydrous grade) were purchased from Sinopharm Group. All raw materials were dried before use: polycarbonate diol was dried under vacuum at 100℃ for 2h (vacuum degree -0.095MPa), nano TiO2 and ZnO were dried at 120℃ for 4h, and HMDI was dried under vacuum at 60℃ (vacuum degree -0.095MPa) for 30min.

[0051] Example 1 A method for preparing a TPU glass laminated film resistant to ultraviolet yellowing includes the following steps: S1 (Prepolymerization): 50 parts by weight of polycarbonate diol (Mn=2000), 45 parts by weight of dicyclohexylmethane diisocyanate (HMDI, trans isomer content 75%), 2 parts by weight of 1,4-butanediol (BDO) (accounting for 40% of the total mass of chain extender), 4 parts by weight of reactive ultraviolet absorber HMBP, and 1.5 parts by weight of hindered amine light stabilizer (4-methacryloyloxy-2,2,6,6-tetramethylpiperidine) were added to a reactor. Nitrogen gas was introduced for protection (after replacing the air in the reactor, nitrogen gas was continuously introduced for protection). The temperature was raised to 85°C, and 0.12 parts by weight of bismuth neodecanoate catalyst were added. The mixture was stirred and reacted for 3.5 h to obtain isocyanate-terminated TPU prepolymer (NCO content was determined to be 4.2%, and the NCO content was determined by di-n-butylamine titration method (refer to GB / T 12009.4-2016)).

[0052] S2 (Nanoparticle Modification): 2.5 parts by weight of nano-titanium dioxide (20 nm particle size) were dispersed in anhydrous ethanol. 6% by weight of KH570 (based on the mass of nano-TiO2) was added, and the pH was adjusted to 4. The mixture was stirred at 70℃ for 6 hours, centrifuged, washed three times with ethanol, and dried under vacuum (-0.095 MPa) at 60℃ for 12 hours to obtain modified nano-TiO2. 1.5 parts by weight of nano-zinc oxide (30 nm particle size) were dispersed in anhydrous ethanol. 5% by weight of KH550 (based on the mass of nano-ZnO) was added, and the mixture was stirred at 60℃ for 5 hours. The mixture was centrifuged, washed three times with ethanol, and dried under vacuum (-0.095 MPa) at 60℃ for 12 hours to obtain modified nano-ZnO.

[0053] S2 (chain extension and in-situ hybridization): Add the above modified nano TiO2, modified nano ZnO, 3 parts by weight of the remaining 1,4-butanediol, and 0.8 parts by weight of epoxy silane coupling agent KH560 to the TPU prepolymer obtained in S1, and continue to stir and react at 80°C for 2.5 h to obtain functionalized TPU compound.

[0054] S3 (Three-layer co-extrusion casting): Functionalized TPU compound was used as the raw material for layers A and C. Pure TPU compound without added nanoparticles (prepared from the same proportions of PCDL, HMDI, and BDO, but without nanoparticles and UV-resistant additives) was used as the raw material for layer B. The mixture was extruded using a three-layer co-extrusion casting machine. The extruder temperature for layers A and C was 195℃, the extruder temperature for layer B was 185℃, the co-extrusion die temperature was 205℃, the casting roller temperature was 75℃, and the casting speed was 12 m / min. This yielded an ABC three-layer composite film with a total thickness of 0.76 mm. Layers A and C each had a thickness of 0.076 mm (10% each), and layer B had a thickness of 0.608 mm (80%). The film was then annealed at 100℃ for 12 hours.

[0055] S4 (Plasma Surface Activation): The annealed film is placed in a nitrogen plasma treatment device with a nitrogen flow rate of 100 mL / min, a treatment chamber pressure of 40 Pa, a treatment power of 120 W, and a treatment time of 60 s to obtain the final product.

[0056] For details of the preparation process and mechanism of Embodiment 1 of this invention, please refer to the accompanying drawings. Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 .

[0057] Example 2 The difference between this embodiment and Example 1 is that the amount of HMBP is 2 parts by weight, the amount of hindered amine light stabilizer is 0.8 parts by weight, the amount of modified nano-TiO2 is 1.0 parts by weight, and the amount of modified nano-ZnO is 0.5 parts by weight. The remaining raw materials and steps are the same as in Example 1.

[0058] Example 3 The difference between this embodiment and Example 1 is that: the amount of HMBP is 6 parts by weight, the amount of hindered amine light stabilizer is 2.5 parts by weight, the amount of modified nano-TiO2 is 4.5 parts by weight, and the amount of modified nano-ZnO is 2.5 parts by weight. The remaining raw materials and steps are the same as in Example 1.

[0059] Example 4 The difference between this embodiment and Embodiment 1 is that the thickness ratio of the three layers is 1:6:1 (layer A 0.095mm, layer B 0.57mm, layer C 0.095mm, total thickness 0.76mm). The remaining raw materials and steps are the same as in Embodiment 1.

[0060] Example 5 The difference between this embodiment and Embodiment 1 is that the plasma processing power in S4 is 80W and the processing time is 90s. The remaining raw materials and steps are the same as in Embodiment 1.

[0061] Example 6 The difference between this embodiment and Example 1 is that the chain extender used is 1,6-hexanediol (HDO). In the first step, 2.5 parts by weight of HDO (accounting for 50%) are added, and in the second step, 2.5 parts by weight are added. The remaining raw materials and steps are the same as in Example 1.

[0062] Comparative Example 1 (Physical blend of UV absorber and hindered amine) The difference between this comparative example and Example 1 is that, instead of adding reactive HMBP and reactive hindered amine, equal masses of the commercial UV absorber UV-531 (2-hydroxy-4-n-octyloxybenzophenone) and the commercial hindered amine light stabilizer UV-770 (bis(2,2,6,6-tetramethyl-4-piperidinyl) sebacate are physically blended during the S2 chain extension stage. The rest is the same as in Example 1.

[0063] Comparative Example 2 (without nanoparticles) The difference between this comparative example and Example 1 is that modified nano-TiO2 and modified nano-ZnO, as well as KH560, are not added in S2. Everything else is the same as in Example 1.

[0064] Comparative Example 3 (Aromatic Isocyanate) The difference between this comparative example and Example 1 is that HMDI was replaced by diphenylmethane diisocyanate (MDI) at the same mass. Everything else is the same as in Example 1.

[0065] Comparative Example 4 (No two-component UV-resistant system) The difference between this comparative example and Example 1 is that HMBP and hindered amine light stabilizers are not added; the comparison relies solely on the physical shielding effect of nano-TiO2 / ZnO. Everything else is the same as in Example 1.

[0066] Comparative Example 5 (single-layer structure, without plasma treatment) The difference between this comparative example and Example 1 is that: instead of using three-layer co-extrusion, the functionalized TPU compound is directly cast into a single-layer film (film thickness is the same as in Example 1), and no plasma treatment is performed. Everything else is the same as in Example 1.

[0067] Comparative Example 6 (no chemical bonding, only physical blending of nanoparticles) The difference between this comparative example and Example 1 is that the nano-TiO2 and ZnO are not modified with silane coupling agents, but are added directly in the S2 stage as unmodified powder. Everything else is the same as in Example 1.

[0068] Performance testing (a) Testing methods The following performance tests were performed on the TPU glass laminated films prepared in Examples 1-6 and Comparative Examples 1-6 of the present invention: 1. Mechanical property testing: Tensile strength and elongation at break were tested using a universal testing machine according to GB / T 1040.4-2006 standard. The specimen was a 1A dumbbell type (gauge length 50 mm), with an initial clamping distance of 115 mm, a tensile speed of 50 mm / min, a test temperature of 23±2℃, and a relative humidity of 50±5%. Five parallel samples were tested for each specimen, and the average value was taken.

[0069] 2. UV resistance to yellowing test: Following GB / T 16422.3-2022 standard, a QUV UV aging test chamber (Q-Lab, model QUV / spray) was used with UVA-340 lamps and an irradiance of 0.75W / m². 2 @340nm, test temperature 60℃, blackboard temperature 65℃, light / condensation cycle: 4h light exposure, 4h condensation. Total aging time 2400h. Samples were taken every 500h, and the yellowing index Δb (D65 light source, 10° viewing angle) was measured using a colorimeter (KonicaMinolta CM-3600A). Calculations were made according to GB / T 7921-2008 "Uniform Color Space and Color Difference Formula", with D65 as the standard illuminant and a 10° observer angle, using unaged samples as a reference. The smaller the Δb value, the better the yellowing resistance.

[0070] 3. Phenolic yellowing resistance test: According to GB / T 11039.3-2005 standard, the sample is brought into contact with phenolic compounds and placed at 50℃ and 80% relative humidity for 24 hours. The yellowing level is evaluated using ISO 105 gray scale (level 5 is the best).

[0071] 4. Transmittance Test: Transmittance at 550 nm was measured using a UV-Vis spectrophotometer (PerkinElmer Lambda 950) according to GB / T 2680-2021 standard. The sample thickness was 0.76 mm. The surface was wiped with anhydrous ethanol before testing (using a spectrophotometer with a wavelength range of 380-780 nm; five different locations were tested for each sample, and the average value was taken).

[0072] 5. Adhesion strength test with glass: According to GB / T 7124-2008 standard, the laminated film was cut into 25mm×12.5mm specimens, sandwiched between two pieces of glass (76mm×25mm×3mm), and hot-pressed at 120℃ under vacuum for 30min to prepare laminated glass specimens. Tensile shear tests were performed using a universal testing machine with a loading speed of 5mm / min. The maximum breaking load was recorded, and the shear strength (MPa) was calculated. Simultaneously, the shear strength retention rate after damp heat aging (85℃ / 85%RH, 1000h) was tested.

[0073] 6. Migration Resistance Test: The laminated film sample was immersed in deionized water at 60℃ for 1000h, with the water changed every 200h. The UV absorber content (quantified by UV-Vis spectroscopy using the characteristic absorption peak of benzophenone) and Δb value were measured before and after immersion.

[0074] 7. Microscopic morphology characterization: The cross-section and surface morphology of the thin film were observed using a scanning electron microscope (SEM, ZeissSigma 300), and the distribution of nanoparticles was analyzed using an energy dispersive spectroscopy (EDS).

[0075] Table 1 shows the performance test results for Examples 1-6. Table 2 shows the performance test results for each item in Comparative Examples 1-6. Although the test results of Examples 1-6 fluctuated, they were generally excellent. The slight differences mainly stemmed from the systematic control of key formulation parameters and process conditions. Example 3, due to the highest dosage of reactive UV absorber (6 parts), hindered amine (2.5 parts), and modified nano-TiO2 / ZnO (4.5 / 2.5 parts), constructed a triple protection of "physical shielding-chemical absorption-free radical capture," resulting in a high yellowing index (Δb2400h of 1.08) and mechanical strength (465 N / cm²). 2 Example 1 is the best, but the high filler content slightly reduces the transmittance to 88.8%. Example 2 has the lowest amount of UV-resistant additives and nanoparticles (2 parts HMBP, 1.0 parts TiO2), so the protective effect is relatively weaker, and Δb increases to 2.02, but the transmittance is high (93.2%) and the elongation at break is large (530%), which reflects the improved flexibility brought about by the low crosslinking density. Example 4 increases the surface layer thickness ratio to 1:6:1 (0.095 mm for each of the A and C layers). The thickened surface layer strengthens the UV shielding barrier. Δb (1.42) is slightly worse than that of Example 1 (1.35). In Table 1, the Δb 2400h of Example 4 is 1.42, which is slightly higher than that of Example 1 (1.35). This may be due to the slight decrease in the overall toughness caused by the reduced core layer ratio, and the shear strength retention rate is slightly lower (89.4%). Example 5 reduces the plasma power to 80W, the surface activation is slightly weaker, and the shear strength (8.6 MPa) is slightly lower than that of Example 1 (8.7 MPa). Example 6 uses 1,6-hexanediol as a chain extender, which increases the flexibility of the hard segment and slightly reduces the tensile strength to 412 N / cm. 2 These differences reflect the fine-tuning of performance trade-offs in formulation composition and process parameters. (For details on UV resistance to yellowing in Example 1 and Comparative Examples 1-4, please refer to...) Figure 7 The tensile shear strength of Example 1 and Comparative Examples 1-4 are shown in the figure. Figure 8 ) Comparative Example 1 replaced the reactive UV absorber and hindered amine with equal masses of conventional physically blended UV-531 and UV-770. Although the initial performance was acceptable, after 2400 hours of QUV aging, the Δb value reached as high as 3.52, and after 1000 hours of boiling in water, the UV absorber residue rate was only 62.5%, with Δb rising to 4.85. This is because the physically blended additives are not covalently bonded to the TPU matrix, and are prone to migration and precipitation under humid and photothermal conditions, leading to a rapid decline in UV resistance. In contrast, the example achieved permanent fixation of the additives through chemical bonding, significantly improving migration resistance and durability. Comparative Example 2, without any addition of nano-TiO2 and ZnO, relied solely on chemically bonded UV-resistant additives. Although its phenolic yellowing resistance rating was still 4.0, its Δb (2400h: 2.68) was higher than that of Example 1 (1.35), and its shear strength (6.0MPa) was lower. This indicates that the physical shielding effect of the nanoparticles and the three-dimensional network constructed with the coupling agent are indispensable for UV attenuation and enhanced interfacial adhesion. In Comparative Example 3, the aliphatic HMDI was replaced with aromatic MDI. The Δb (2400h) deteriorated sharply to 5.15, and the phenolic yellowing resistance rating was only 3.0. This is because the benzene ring in the MDI molecule is prone to forming quinone chromophores under photothermal oxidation, leading to severe yellowing. HMDI, on the other hand, has a saturated alicyclic structure, fundamentally avoiding this problem. Comparative Example 4, lacking reactive UV-resistant additives (no two-component UV-resistant system), relied solely on physical shielding by nano-TiO2 / ZnO, resulting in a high Δb (2400h) of 6.2 and a phenolic yellowing resistance rating of only 2.5. This demonstrates that simple nanoparticle shielding cannot effectively capture generated free radicals and must be combined with chemical absorption and free radical capture. Comparative Example 5, employing a single-layer structure without plasma treatment, showed all functional components uniformly distributed throughout the entire layer. Not only did the transmittance drop to 86% due to nanoparticle scattering, but the core layer also lacked pure TPU buffering, leading to decreased toughness. More importantly, the absence of plasma activation resulted in the absence of nitrogen-containing polar groups on the surface, weakening the chemical bond with the glass. The shear strength was only 5.2 MPa, decreasing to 3.8 MPa after damp heat aging (73.1% retention), far lower than the 8.7 MPa and 90.8% of the examples. Comparative Example 6: Nano-TiO2 and ZnO were directly physically blended without modification by a silane coupling agent. Due to the high surface energy and easy aggregation of nanoparticles, the dispersion was uneven, resulting in poor mechanical properties (tensile strength 367 N / cm). 2 The performance of the unmodified nanoparticles was inferior to that of the example in terms of both resistance to yellowing (Δb2400h was 2.8) and UV absorber residue rate after boiling in water (92%), which was also lower than the 97% or more of the example. This indicates that the unmodified nanoparticles had weak bonding with the matrix interface and were easy to detach or migrate.

[0076] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of the present invention and not to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a TPU glass laminated film resistant to ultraviolet yellowing, characterized in that, Includes the following steps: S1: Polycarbonate diol, dicyclohexylmethane diisocyanate, a first chain extender accounting for 30-50% of the chain extender mass, a reactive ultraviolet absorber, and a hindered amine light stabilizer are subjected to a prepolymerization reaction under the action of a catalyst to obtain an isocyanate-terminated TPU prepolymer. S2: Add nano-titanium dioxide modified with silane coupling agent, nano-zinc oxide modified with silane coupling agent, a second chain extender and epoxy silane coupling agent to the TPU prepolymer obtained in S1, and carry out chain extension reaction and in-situ hybridization reaction to obtain functionalized TPU compound. S3: The functionalized TPU material obtained in S2 is cast into a film by three-layer co-extrusion to form an ABC three-layer composite film, wherein layer A and layer C are functionalized TPU material, and layer B is pure TPU material without added nanoparticles. S4: The three-layer composite film obtained in S3 is subjected to nitrogen plasma surface activation treatment to obtain a TPU glass laminated film resistant to ultraviolet yellowing.

2. The preparation method according to claim 1, characterized in that: The prepolymerization reaction temperature in S1 is 75-95℃, and the reaction time is 2-5h; the sum of the mass of the first chain extender and the second chain extender is the total mass of the chain extender; the reactive ultraviolet absorber is a benzophenone compound or a benzotriazole compound containing polymerizable double bonds and active hydroxyl groups; the reaction temperature in S2 is 75-90℃, and the reaction time is 1-3h.

3. The preparation method according to claim 1, characterized in that: After the three-layer co-extrusion casting in S3 is completed, the film is annealed at a temperature of 80-110℃ for 6-24 hours. The thickness ratio of the three layers of the ABC three-layer composite film is 1:6:1 to 1:10:

1. In S4, the power of the nitrogen plasma surface activation treatment is 50-200W, and the treatment time is 30-120s.

4. The preparation method according to claim 1, characterized in that: The reactive ultraviolet absorber is selected from one or more of 2-acrylate-2-(4-benzoyl-3-hydroxyphenoxy)ethyl ester, 2-hydroxy-4-(3-methacryloyloxy-2-hydroxypropoxy)benzophenone, 2-hydroxy-4-acryloyloxyethoxybenzophenone, and 2-[2-hydroxy-5-[2-(methacryloyloxy)ethyl]phenyl]-2H-benzotriazole; the hindered amine light stabilizer is 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine or 4-acryloyloxy-2,2,6,6-tetramethylpiperidine.

5. The preparation method according to claim 1, characterized in that, The amounts of each raw material, by weight, are as follows: 40-70 parts polycarbonate diol, 35-60 parts dicyclohexylmethane diisocyanate, 3-10 parts chain extender, 1-6 parts reactive ultraviolet absorber, 0.5-3 parts hindered amine light stabilizer, 0.02-0.5 parts catalyst, 0.5-5 parts silane coupling agent modified nano-titanium dioxide, 0.2-3 parts silane coupling agent modified nano-zinc oxide, and 0.1-1.5 parts epoxy silane coupling agent; the chain extender is one or more of 1,4-butanediol, ethylene glycol, and 1,6-hexanediol; the catalyst is an organobismuth catalyst or an organotin catalyst.

6. The preparation method according to claim 1, characterized in that, The preparation method of the silane coupling agent modified nano-titanium dioxide is as follows: rutile nano-titanium dioxide with a particle size of 10-30 nm is dispersed in anhydrous ethanol, and 3%-10% (by weight of rutile nano-titanium dioxide) of γ-methacryloyloxypropyltrimethoxysilane is added. The pH is adjusted to 3-5, and the mixture is stirred and reacted at 60-80℃ for 4-8 hours. After centrifugation, the mixture is washed with ethanol and dried under vacuum at 60-70℃. The preparation method of the silane coupling agent modified nano-zinc oxide is as follows: nano-zinc oxide with a particle size of 20-50 nm is dispersed in anhydrous ethanol, and 2%-8% (by weight of zinc oxide) of γ-aminopropyltriethoxysilane is added. After stirring and reacting at 50-70℃ for 3-6 hours, the mixture is centrifuged, washed with ethanol, and dried under vacuum at 60-70℃. The centrifugation speed is 8000-12000 rpm, and the time is 10-20 min. The vacuum degree of the vacuum drying is ≤-0.095 MPa.

7. The preparation method according to claim 1, characterized in that, The epoxy silane coupling agent is γ-glycidyl etheroxypropyltrimethoxysilane or β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

8. The preparation method according to claim 1, characterized in that, During the prepolymerization reaction in S1, the NCO / OH molar ratio in the reaction system is controlled to be 1.5-2.5:1; the number average molecular weight of the polycarbonate diol is 1000-4000, and its molecular structure is a linear diol obtained by polycondensation of C2-C10 aliphatic diols and carbonates; the trans-trans isomer content in the dicyclohexylmethane diisocyanate is not less than 70%.

9. The preparation method according to claim 1, characterized in that, The process conditions for the three-layer co-extrusion casting film in S3 are as follows: extruder temperature for A / C layers is 180-210℃, extruder temperature for B layer is 175-200℃, co-extrusion die temperature is 190-215℃, casting roll temperature is 65-85℃, casting speed is 8-20m / min, and the total thickness of the resulting laminated film is 0.42-1.52mm, of which the thickness of each layer (A and C) is 0.05-0.15mm.

10. The preparation method according to claim 1, characterized in that, In step S4, before the nitrogen plasma surface activation treatment, a preheating step is also included for the three-layer composite film: the preheating temperature is 50-70℃ and the preheating time is 1-3min; during plasma treatment, the nitrogen flow rate is 50-200mL / min, the treatment chamber pressure is 20-80Pa, the treatment power is 80-150W, and the treatment time is 45-90s.

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