Heat insulation car window film and preparation method thereof

Abstract

The invention discloses a heat-insulating car window film and a preparation method thereof, and relates to the technical field of films. The heat-insulating car window film prepared by the invention comprises modified polyurethane and modified vanadium dioxide, the modified polyurethane is obtained by polymerizing polycarbonate diol, hexamethylene diisocyanate and a dihydric alcohol monomer and then carrying out end capping by using 2, 3, 3-trimethyl-3H-indole-7-alcohol; the modified vanadium dioxide is obtained by polymerizing pre-treated vanadium dioxide coated with methyl methacrylate, 1-(pent-4-ene-1-yl)-1H-pyrrole, squaric acid and an intermediate, and the pre-treated vanadium dioxide is coated with 1-(pent-4-ene-1-yl)-1H-pyrrole. The heat-insulating car window film prepared by the invention has good heat-insulating, flame-retardant and anti-aging properties.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, specifically to a heat-insulating car window film and its preparation method. Background Art

[0002] Heat-insulating window film is a functional material widely used in automobiles, construction and other fields. Its main function is to reduce indoor temperature by blocking infrared and ultraviolet rays in solar radiation, reduce air conditioning energy consumption, protect the interior decoration from ultraviolet damage, and improve the explosion-proof and privacy performance of car windows.

[0003] When used as a raw material for heat insulation films, polyurethane provides good flexibility and adhesion, while also possessing certain weather resistance and impact resistance, enabling it to remain stable in complex environments. However, polyurethane itself does not possess direct heat insulation functionality because its molecular structure cannot efficiently reflect or absorb infrared radiation, and its high thermal conductivity makes it difficult to independently perform heat insulation tasks. Furthermore, polyurethane materials suffer from insufficient flame retardancy; it is prone to decomposition or even combustion under high temperatures or open flame conditions, leading to a decline in the overall performance of the heat insulation film. Simultaneously, polyurethane is susceptible to aging under long-term exposure to ultraviolet radiation, humidity, and other environmental conditions, such as yellowing, embrittlement, or decreased adhesion, which affects the light transmittance and durability of the heat insulation film. Therefore, endowing polyurethane with excellent heat insulation, flame retardant, and anti-aging properties can meet the high performance requirements of heat insulation films in practical applications. Summary of the Invention

[0004] The purpose of this invention is to provide a heat-insulating window film and its preparation method to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing a heat-insulating automotive window film includes the following preparation steps: (1) 1-Allyl-3,5-bis(2-hydroxyethyl)isocyanurate was reacted with DOPO to obtain a diol monomer; (2) Polycarbonate diol, diol monomer, hexamethylene diisocyanate and 2,3,3-trimethyl-3H-indole-7-ol were reacted to obtain modified polyurethane; (3) Vanadium pentoxide, concentrated sulfuric acid, pure water and sulfur dioxide gas are reacted to obtain vanadium pentoxide stock solution; the stock solution, urea and ethylene glycol are reacted to obtain a precursor; the precursor is reacted in a tube furnace to obtain hollow vanadium dioxide; vinyltrimethoxysilane and hollow vanadium dioxide are reacted to obtain pretreated vanadium dioxide. (4) Pretreated vanadium dioxide, methyl methacrylate, and 1-(pent-4-en-1-yl)-1H-pyrrole were reacted to obtain pre-modified vanadium dioxide; (5) The intermediate was obtained by reacting N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one; the modified vanadium dioxide was obtained by reacting the pre-modified vanadium dioxide, the intermediate, and squaric acid. (6) A heat-insulating car window film is obtained by mixing modified polyurethane, modified vanadium dioxide and squaric acid.

[0006] As an optimization, the preparation method of the diol monomer in step (1) is as follows: at 80-90℃, 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate and N-methylpyrrolidone are mixed, and under nitrogen protection, the temperature is raised to 150-160℃ and DOPO is added for 8-10h to obtain the diol monomer; the molar ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to DOPO is 1:(1.05-1.1); the mass ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to N-methylpyrrolidone is 1:(10-12).

[0007] As an optimization, the preparation method of the modified polyurethane in step (2) is as follows: Weigh the following components by mass fraction: 50 parts of polycarbonate diol, 18-20 parts of hexamethylene diisocyanate, 3-5 parts of diol monomer, 2-3 parts of 2,3,3-trimethyl-3H-indole-7-ol, 80-100 parts of N,N-dimethylformamide, and 0.05-0.1 parts of dibutyltin dilaurate; Mix the polycarbonate diol, diol monomer, and N,N-dimethylformamide, heat to 70-80℃, add hexamethylene diisocyanate and dibutyltin dilaurate, heat to 85-90℃ and react for 3-4 hours, add 2,3,3-trimethyl-3H-indole-7-ol and continue the reaction for 2-3 hours to obtain the modified polyurethane.

[0008] As an optimization, the preparation method of the pretreated vanadium dioxide in step (3) is as follows: vanadium pentoxide, concentrated sulfuric acid, and pure water are mixed at a mass ratio of 1:(5-7):(25-30), sulfur dioxide gas is introduced, and the reaction is carried out for 2-3 hours to obtain a vanadium oxide sulfuric acid solution. The vanadium oxide sulfuric acid solution is then prepared into a 5mM stock solution using pure water. The stock solution, urea, and ethylene glycol are mixed at a mass ratio of 50:(3-5):(5-7), and reacted in a polytetrafluoroethylene reactor at 80-90℃ for 24 hours to obtain the precursor. The precursor was reacted in a tube furnace at 500℃ under nitrogen protection for 5-6 hours to obtain hollow vanadium dioxide; the pH of a 90wt% ethanol solution was adjusted to 4.5-5.5 with acetic acid, vinyltrimethoxysilane was added and stirred at room temperature for 2-3 hours, then a hollow vanadium dioxide-ethanol dispersion was added, and the mixture was heated to 60-70℃ and reacted for 5-6 hours to obtain pretreated vanadium dioxide; the mass ratio of hollow vanadium dioxide, vinyltrimethoxysilane, and 90wt% ethanol solution was 1:(1-2):(5-6).

[0009] As an optimization, the preparation method of the pre-modified vanadium dioxide in step (4) is as follows: disperse the pretreated vanadium dioxide in pure water, add isobutanol, adjust the pH to 8-9 with ammonia, add emulsifier, stir for 12h, add sodium bicarbonate, potassium persulfate, methyl methacrylate, and 1-(pent-4-en-1-yl)-1H-pyrrole under nitrogen protection, heat to 75-85℃, react for 5-6h to obtain pre-modified vanadium dioxide; 10 parts of pretreated vanadium dioxide, 200-250 parts of pure water, 7-9 parts of isobutanol, 1-2 parts of emulsifier, 6-8 parts of sodium bicarbonate, 0.8-1 parts of potassium persulfate, 15-20 parts of methyl methacrylate, and 10-15 parts of 1-(pent-4-en-1-yl)-1H-pyrrole.

[0010] As an optimization, the preparation method of the modified vanadium dioxide in step (5) is as follows: pre-modified vanadium dioxide, toluene, and n-butanol are ultrasonically mixed, an intermediate and squaric acid are added, and the mixture is heated to 110-120℃ and refluxed for 16-20h to obtain modified vanadium dioxide; the mass ratio of pre-modified vanadium dioxide, toluene, n-butanol, intermediate and squaric acid is 1:(10-12):(30-50):(3-5):(1-2).

[0011] As an optimization, the intermediate is prepared by dissolving N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one in tetrahydrofuran, adding concentrated hydrochloric acid and reacting for 24 hours to obtain the intermediate; the molar ratio of N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one is (2.01-2.05):1; the mass ratio of N-methyl-2-pyrrolecarboxaldehyde, tetrahydrofuran and concentrated hydrochloric acid is 1:(10-12):(0.02-0.03).

[0012] As an optimization, the preparation method of the heat-insulating window film in step (6) is as follows: modified polyurethane, modified vanadium dioxide, squaric acid, and N,N-dimethylformamide are mixed in a mass ratio of 1:(0.25-0.35):(0.01-0.02):(4-6) and coated onto the surface of a glass substrate and cured into a film to obtain the heat-insulating window film.

[0013] The present invention also provides a heat-insulating window film prepared according to the above-described method for preparing heat-insulating window film.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are: In preparing the heat-insulating window film, this invention first involves a hydrophosphorylation reaction between 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate and DOPO to generate a phosphorus-nitrogen diol monomer containing a diol. This monomer effectively participates in the construction of the polyurethane backbone. Isocyanurate and DOPO can simultaneously impart excellent flame-retardant properties to the window film. The rigid triazine ring of isocyanurate and the phosphaphenanthrene ring of DOPO form a synergistic flame-retardant system. During high-temperature decomposition, this system can both generate a char layer and release phosphoric acid free radical quenching substances, thus endowing the window film with highly efficient flame-retardant properties. To further optimize material stability, a 2,3,3-trimethyl-3H-indole-7-ol end-capping structure was introduced into the polyurethane chain. This indole derivative forms a dynamic cross-linking network through a condensation reaction with subsequent squaric acid, which not only enhances the mechanical strength of the polyurethane matrix, but its unique wide-range conjugated system can also absorb ultraviolet radiation, effectively mitigating photoaging.

[0015] In terms of functional nanofiller design, hollow vanadium dioxide particles constructed using the urea template method form a physical thermal barrier due to their hollow structure. The vanadium dioxide lattice phase transition characteristics allow it to reversibly transform into the rutile phase at high temperatures, reducing radiative heat transfer efficiency through plasma resonance reflection of near-infrared spectra (700-2500 nm). To address the issue of vanadium dioxide's susceptibility to oxidation and deactivation under humid and ultraviolet environments, a copolymer of methyl methacrylate and 1-(pent-4-en-1-yl)-1H-pyrrole is used for surface grafting. This polymer layer not only physically blocks water and oxygen penetration but also maintains vanadium dioxide stability through the optical transparency of polymethyl methacrylate. The α,β-unsaturated ketone intermediate formed by the condensation of N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one is specifically introduced into the system. Its core conjugated enone system can capture free radicals to generate a stable benzoquinone structure, while the thioether group continuously consumes reactive oxygen species through a redox cycle mechanism, forming a multi-pathway synergistic antioxidant protection. The preparation of the intermediate is illustrated below: .

[0016] Based on this, squaric acid cyanine compounds were synthesized in situ by initiating the grafting of 1-(pent-4-en-1-yl)-1H-pyrrole onto the surface of vanadium dioxide. A functional layer of squaric acid cyanine with a strong D-π-A electron-donating structure was constructed. This narrow bandgap molecule can efficiently absorb near-infrared radiation and convert it into heat energy for dissipation. At the same time, it condenses with the indole groups at the end of polyurethane to form a three-dimensional cross-linked network, which not only enhances the interfacial bonding force but also extends the ultraviolet absorption to the visible light region. Finally, a multi-dimensional structure integrating flame-retardant framework, phase change heat insulation, anti-oxidation interface, and spectral regulation layer was formed, which meets the stringent requirements of the automotive environment for long life and high stability of window film. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] The polycarbonate diols described in the following examples and comparative examples have a molecular weight of 1000; the DOPO is 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0019] Example 1: A method for preparing a heat-insulating car window film, the method is as follows: (1) At 90°C, 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate and N-methylpyrrolidone were mixed, and under nitrogen protection, the temperature was raised to 160°C and DOPO was added to react for 10 h. After the reaction was completed, the mixture was cooled to room temperature, and 4°C cold ethanol was added. The mixture was filtered and washed with cold ethanol, and dried under vacuum to obtain a diol monomer. The molar ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to DOPO was 1:1.05; the mass ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to N-methylpyrrolidone was 1:10. (2) Weigh the following components by mass fraction: 50 parts of polycarbonate diol, 18 parts of hexamethylene diisocyanate, 3 parts of diol monomer, 2 parts of 2,3,3-trimethyl-3H-indole-7-ol, 80 parts of N,N-dimethylformamide, and 0.05 parts of dibutyltin dilaurate; mix polycarbonate diol, diol monomer, and N,N-dimethylformamide, heat to 80°C, add hexamethylene diisocyanate and dibutyltin dilaurate, heat to 90°C and react for 4 hours, add 2,3,3-trimethyl-3H-indole-7-ol and continue the reaction for 3 hours. After the reaction is completed, cool to room temperature, precipitate with 4°C ice-cold ether, filter, wash and dry to obtain modified polyurethane; (3) Vanadium pentoxide, concentrated sulfuric acid, and pure water were mixed in a mass ratio of 1:5:25. Sulfur dioxide gas was introduced (flow rate 20 mL / min), and the mixture was reacted for 3 h to obtain a vanadium oxide sulfuric acid solution. The solution was stirred for 12 h under open conditions to remove dissolved sulfur dioxide. The vanadium oxide sulfuric acid solution was then prepared into a 5 mM stock solution using pure water. The stock solution, urea, and ethylene glycol were mixed in a mass ratio of 50:3:5 and reacted in a polytetrafluoroethylene reactor at 90 °C for 24 h. The precipitate was centrifuged, washed with ethanol, and dried to obtain the precursor. The precursor was then subjected to nitrogen treatment at 500 °C. Hollow vanadium dioxide was obtained by reacting in a gas-protected tubular furnace for 6 hours. The pH of a 90 wt% ethanol solution was adjusted to 5.5 using acetic acid, and vinyltrimethoxysilane was added and stirred at room temperature for 3 hours. Then, a hollow vanadium dioxide-ethanol dispersion was added, and the mixture was heated to 70°C and reacted for 6 hours. After filtration, washing, and drying, pretreated vanadium dioxide was obtained. The hollow vanadium dioxide-ethanol dispersion was obtained by ultrasonically mixing hollow vanadium dioxide and ethanol at a mass ratio of 1:80, and the mass ratio of hollow vanadium dioxide, vinyltrimethoxysilane, and 90 wt% ethanol solution was 1:1:5. (4) Disperse the pretreated vanadium dioxide in pure water, add isobutanol, adjust the pH to 9 with ammonia, add emulsifier OP-10, stir at 200 r / min for 12 h, add sodium bicarbonate, potassium persulfate, methyl methacrylate, and 1-(pent-4-en-1-yl)-1H-pyrrole under nitrogen protection, heat to 85℃, react for 6 h, filter, wash and dry to obtain pre-modified vanadium dioxide; 10 parts of pretreated vanadium dioxide, 200 parts of pure water, 7 parts of isobutanol, 1 part of emulsifier, 6 parts of sodium bicarbonate, 0.8 parts of potassium persulfate, 15 parts of methyl methacrylate, and 10 parts of 1-(pent-4-en-1-yl)-1H-pyrrole; (5) N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one were dissolved in tetrahydrofuran, concentrated hydrochloric acid was added, and the reaction was carried out for 24 h. After the reaction was completed, the insoluble matter was removed by filtration, extracted with ethyl acetate, washed with pure water, dried with anhydrous sodium sulfate, distilled under reduced pressure, and column chromatography (V) 乙酸乙酯 / V 石油醚 The intermediate was obtained by purification and recrystallization from ethanol (1:1 ratio); the molar ratio of N-methyl-2-pyrrolecarboxaldehyde to tetrahydrothiaran-4-one was 2.01:1; the mass ratio of N-methyl-2-pyrrolecarboxaldehyde, tetrahydrofuran, and concentrated hydrochloric acid was 1:10:0.02; the pre-modified vanadium dioxide, toluene, and n-butanol were ultrasonically mixed, the intermediate and squaric acid were added, and the mixture was heated to 120℃ and refluxed for 20 h. After filtration, washing, and drying, the modified vanadium dioxide was obtained; the mass ratio of pre-modified vanadium dioxide, toluene, n-butanol, intermediate, and squaric acid was 1:10:30:3:1. (6) Mix modified polyurethane, modified vanadium dioxide, squaric acid and N,N-dimethylformamide in a mass ratio of 1:0.25:0.01:4 and degas under vacuum to obtain a slurry. Pour the slurry onto a glass substrate and use a wire bar coater to scrape the surface of the glass substrate at a uniform speed of 10 mm / s to form a wet film of uniform thickness on the substrate with a thickness of 500 μm. Set and execute the following stepped temperature curing program: cure at 60℃ for 2 h, raise the temperature to 80℃ (heating rate 2℃ / min), cure at 80℃ for 2 h, raise the temperature to 100℃ (heating rate 2℃ / min), cure at 80℃ for 1 h to obtain a heat-insulating car window film.

[0020] Example 2: A method for preparing a heat-insulating car window film, the method is as follows: (1) At 85°C, 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate and N-methylpyrrolidone were mixed, and under nitrogen protection, the temperature was raised to 155°C and DOPO was added to react for 9 h. After the reaction was completed, the mixture was cooled to room temperature, and 3°C cold ethanol was added. The mixture was filtered and washed with cold ethanol, and dried under vacuum to obtain a diol monomer. The molar ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to DOPO was 1:1.07; the mass ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to N-methylpyrrolidone was 1:11. (2) Weigh the following components by mass fraction: 50 parts of polycarbonate diol, 19 parts of hexamethylene diisocyanate, 4 parts of diol monomer, 2.5 parts of 2,3,3-trimethyl-3H-indole-7-ol, 90 parts of N,N-dimethylformamide, and 0.07 parts of dibutyltin dilaurate; mix polycarbonate diol, diol monomer, and N,N-dimethylformamide, heat to 75°C, add hexamethylene diisocyanate and dibutyltin dilaurate, heat to 87°C and react for 3.5 h, add 2,3,3-trimethyl-3H-indole-7-ol and continue the reaction for 2.5 h, after the reaction is completed, cool to room temperature, precipitate with 3°C ice-cold ether, filter, wash and dry to obtain modified polyurethane; (3) Vanadium pentoxide, concentrated sulfuric acid, and pure water were mixed in a mass ratio of 1:6:27. Sulfur dioxide gas was introduced (flow rate 20 mL / min), and the reaction was carried out for 2.5 h to obtain a vanadium pentoxide sulfuric acid solution. The solution was stirred for 12 h under open conditions to remove dissolved sulfur dioxide. The vanadium pentoxide sulfuric acid solution was then prepared into a 5 mM stock solution using pure water. The stock solution, urea, and ethylene glycol were mixed in a mass ratio of 50:4:6 and reacted in a polytetrafluoroethylene reactor at 85 °C for 24 h. The precipitate was retained by centrifugation, washed with ethanol, and dried to obtain the precursor. The precursor was then subjected to nitrogen protection at 500 °C. The reaction was carried out in a tube furnace for 5.5 h to obtain hollow vanadium dioxide. The pH of the 90 wt% ethanol solution was adjusted to 5 using acetic acid, and vinyltrimethoxysilane was added and stirred at room temperature for 2.5 h. Then, the hollow vanadium dioxide-ethanol dispersion was added, and the temperature was raised to 65 °C and reacted for 5.5 h. After filtration, washing and drying, pretreated vanadium dioxide was obtained. The hollow vanadium dioxide-ethanol dispersion was obtained by ultrasonically mixing hollow vanadium dioxide and ethanol at a mass ratio of 1:90. The mass ratio of hollow vanadium dioxide, vinyltrimethoxysilane and 90 wt% ethanol solution was 1:1.5:5.5. (4) Disperse the pretreated vanadium dioxide in pure water, add isobutanol, adjust the pH to 8.5 with ammonia, add emulsifier OP-10, stir at 200 r / min for 12 h, add sodium bicarbonate, potassium persulfate, methyl methacrylate, and 1-(pent-4-en-1-yl)-1H-pyrrole under nitrogen protection, heat to 80℃, react for 5.5 h, filter, wash and dry to obtain pre-modified vanadium dioxide; 10 parts of pretreated vanadium dioxide, 240 parts of pure water, 8 parts of isobutanol, 1.5 parts of emulsifier, 7 parts of sodium bicarbonate, 0.9 parts of potassium persulfate, 17 parts of methyl methacrylate, and 13 parts of 1-(pent-4-en-1-yl)-1H-pyrrole; (5) N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one were dissolved in tetrahydrofuran, concentrated hydrochloric acid was added, and the reaction was carried out for 24 h. After the reaction was completed, the insoluble matter was removed by filtration, extracted with ethyl acetate, washed with pure water, dried with anhydrous sodium sulfate, distilled under reduced pressure, and column chromatography (V) 乙酸乙酯 / V 石油醚 The intermediate was obtained by purification and recrystallization from ethanol (1:1 ratio); the molar ratio of N-methyl-2-pyrrolecarboxaldehyde to tetrahydrothiaran-4-one was 2.04:1; the mass ratio of N-methyl-2-pyrrolecarboxaldehyde, tetrahydrofuran, and concentrated hydrochloric acid was 1:11:0.025; the pre-modified vanadium dioxide, toluene, and n-butanol were ultrasonically mixed, the intermediate and squaric acid were added, and the mixture was heated to 115℃ and refluxed for 18 h. After filtration, washing, and drying, the modified vanadium dioxide was obtained; the mass ratio of pre-modified vanadium dioxide, toluene, n-butanol, intermediate, and squaric acid was 1:11:40:4:1.5. (6) Mix modified polyurethane, modified vanadium dioxide, squaric acid, and N,N-dimethylformamide in a mass ratio of 1:0.3:0.015:5 and degas under vacuum to obtain a slurry. Pour the slurry onto a glass substrate and use a wire bar coater to scrape the surface of the glass substrate at a uniform speed of 10 mm / s to form a wet film of uniform thickness on the substrate with a thickness of 500 μm. Set and execute the following stepped temperature curing program: cure at 60℃ for 2 h, raise the temperature to 80℃ (heating rate 2℃ / min), cure at 80℃ for 2 h, raise the temperature to 100℃ (heating rate 2℃ / min), and cure at 80℃ for 1 h to obtain a heat-insulating car window film.

[0021] Example 3: A method for preparing a heat-insulating car window film, the method is as follows: (1) At 80°C, 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate and N-methylpyrrolidone were mixed, and under nitrogen protection, the temperature was raised to 150°C and DOPO was added to react for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, 0°C cold ethanol was added, the mixture was filtered and washed with cold ethanol, and dried under vacuum to obtain a diol monomer; the molar ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to DOPO was 1:1.1; the mass ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to N-methylpyrrolidone was 1:12. (2) Weigh the following components by mass fraction: 50 parts of polycarbonate diol, 20 parts of hexamethylene diisocyanate, 5 parts of diol monomer, 3 parts of 2,3,3-trimethyl-3H-indole-7-ol, 100 parts of N,N-dimethylformamide, and 0.1 parts of dibutyltin dilaurate; mix polycarbonate diol, diol monomer, and N,N-dimethylformamide, heat to 70°C, add hexamethylene diisocyanate and dibutyltin dilaurate, heat to 85°C and react for 3 hours, add 2,3,3-trimethyl-3H-indole-7-ol and continue the reaction for 2 hours. After the reaction is completed, cool to room temperature, precipitate with 0°C ice-cold ether, filter, wash and dry to obtain modified polyurethane; (3) Vanadium pentoxide, concentrated sulfuric acid, and pure water were mixed in a mass ratio of 1:7:30. Sulfur dioxide gas was introduced (flow rate 20 mL / min), and the mixture was reacted for 3 h to obtain a vanadium oxide sulfuric acid solution. The solution was stirred for 12 h under open conditions to remove dissolved sulfur dioxide. The vanadium oxide sulfuric acid solution was then prepared into a 5 mM stock solution using pure water. The stock solution, urea, and ethylene glycol were mixed in a mass ratio of 50:5:7 and reacted in a polytetrafluoroethylene reactor at 80 °C for 24 h. The precipitate was centrifuged, washed with ethanol, and dried to obtain the precursor. The precursor was then subjected to nitrogen treatment at 500 °C. Hollow vanadium dioxide was obtained by reacting in a gas-protected tubular furnace for 5 hours. The pH of a 90 wt% ethanol solution was adjusted to 4.5 using acetic acid, and vinyltrimethoxysilane was added and stirred at room temperature for 2 hours. Then, a hollow vanadium dioxide-ethanol dispersion was added, and the mixture was heated to 60°C and reacted for 5 hours. After filtration, washing, and drying, pretreated vanadium dioxide was obtained. The hollow vanadium dioxide-ethanol dispersion was obtained by ultrasonically mixing hollow vanadium dioxide and ethanol at a mass ratio of 1:100, and the mass ratio of hollow vanadium dioxide, vinyltrimethoxysilane, and 90 wt% ethanol solution was 1:1:5. (4) Disperse the pretreated vanadium dioxide in pure water, add isobutanol, adjust the pH to 8 with ammonia, add emulsifier OP-10, stir at 200 r / min for 12 h, add sodium bicarbonate, potassium persulfate, methyl methacrylate, and 1-(pent-4-en-1-yl)-1H-pyrrole under nitrogen protection, heat to 75℃, react for 5 h, filter, wash and dry to obtain pre-modified vanadium dioxide; 10 parts of pretreated vanadium dioxide, 250 parts of pure water, 9 parts of isobutanol, 2 parts of emulsifier, 8 parts of sodium bicarbonate, 1 part of potassium persulfate, 20 parts of methyl methacrylate, and 15 parts of 1-(pent-4-en-1-yl)-1H-pyrrole; (5) N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one were dissolved in tetrahydrofuran, concentrated hydrochloric acid was added, and the reaction was carried out for 24 h. After the reaction was completed, the insoluble matter was removed by filtration, extracted with ethyl acetate, washed with pure water, dried with anhydrous sodium sulfate, distilled under reduced pressure, and column chromatography (V) 乙酸乙酯 / V 石油醚 The intermediate was obtained by purification and recrystallization from ethanol (1:1 ratio); the molar ratio of N-methyl-2-pyrrolecarboxaldehyde to tetrahydrothiaran-4-one was 2.05:1; the mass ratio of N-methyl-2-pyrrolecarboxaldehyde, tetrahydrofuran, and concentrated hydrochloric acid was 1:12:0.03; the pre-modified vanadium dioxide, toluene, and n-butanol were ultrasonically mixed, the intermediate and squaric acid were added, and the mixture was heated to 110℃ and refluxed for 16 h. After filtration, washing, and drying, the modified vanadium dioxide was obtained; the mass ratio of pre-modified vanadium dioxide, toluene, n-butanol, intermediate, and squaric acid was 1:12:50:5:2. (6) Mix modified polyurethane, modified vanadium dioxide, squaric acid, and N,N-dimethylformamide in a mass ratio of 1:0.35:0.02:6 and degas under vacuum to obtain a slurry. Pour the slurry onto a glass substrate and use a wire bar coater to scrape the surface of the glass substrate at a uniform speed of 10 mm / s to form a wet film of uniform thickness on the substrate with a thickness of 500 μm. Set and execute the following stepped temperature curing program: cure at 60℃ for 2 h, raise the temperature to 80℃ (heating rate 2℃ / min), cure at 80℃ for 2 h, raise the temperature to 100℃ (heating rate 2℃ / min), and cure at 80℃ for 1 h to obtain a heat-insulating car window film.

[0022] Comparative Example 1: The difference between the preparation method of the heat-insulating car window film in Comparative Example 1 and Example 2 is that DOPO is not grafted onto 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate. Specifically, step (1) is omitted, and step (2) is modified as follows: Weigh the following components by mass fraction: 50 parts polycarbonate diol, 19 parts hexamethylene diisocyanate, 4 parts 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate, and 2.5 parts 2,3,3-trimethyl-3H-indole-7-ol. 90 parts of N,N-dimethylformamide and 0.07 parts of dibutyltin dilaurate were mixed with polycarbonate diol, 1-allyl-3,5-bis(2-hydroxyethyl)isocyanurate and N,N-dimethylformamide. The mixture was heated to 75°C, and then hexamethylene diisocyanate and dibutyltin dilaurate were added. The mixture was heated to 87°C and reacted for 3.5 h. Then 2,3,3-trimethyl-3H-indole-7-ol was added and the reaction was continued for another 2.5 h. After the reaction was completed, the mixture was cooled to room temperature, precipitated with ice-cold ether at 3°C, filtered, washed and dried to obtain the modified polyurethane. The remaining steps were the same as in Example 2.

[0023] Comparative Example 2: The difference between the preparation method of the heat-insulating car window film in Comparative Example 2 and Example 2 is that the hollow vanadium dioxide is not modified. Instead, the hollow vanadium dioxide is directly mixed with the modified vanadium dioxide described in step (6) and the modified polyurethane. Specifically, steps (4) to (5) are omitted. Step (3) is modified as follows: vanadium pentoxide, concentrated sulfuric acid, and pure water are mixed in a mass ratio of 1:6:27. Sulfur dioxide gas (flow rate 20 mL / min) is introduced and reacted for 2.5 h to obtain a vanadium oxide sulfuric acid solution. The solution is stirred for 12 h under open conditions to remove dissolved sulfur dioxide. The vanadium oxide sulfuric acid solution is then prepared into a 5 mM stock solution using pure water. The stock solution, urea, and ethylene glycol are mixed in a mass ratio of 50:4:6 and reacted in a polytetrafluoroethylene reactor at 85°C for 24 h. The precipitate is retained by centrifugation, washed and dried with ethanol to obtain a precursor. The precursor is reacted in a tube furnace at 500°C under nitrogen protection for 5.5 h to obtain modified vanadium dioxide. The remaining steps are the same as in Example 2.

[0024] Comparative Example 3: The difference between the preparation method of the heat-insulating window film in Comparative Example 3 and Example 2 is that squaric acid is not added in step (6). Specifically, step (6) is modified as follows: modified polyurethane, modified vanadium dioxide, and N,N-dimethylformamide are mixed in a mass ratio of 1:0.3:0.015 and vacuum degassed to obtain a slurry. The slurry is poured onto a glass substrate and coated at a uniform speed of 10 mm / s using a wire bar coater to form a uniform wet film with a thickness of 500 μm on the substrate. The following stepped temperature curing program is set and executed: constant temperature curing at 60°C for 2 hours, temperature increased to 80°C (temperature increase rate 2°C / min), constant temperature curing for 2 hours, temperature increased to 100°C (temperature increase rate 2°C / min), constant temperature curing for 1 hour, and the heat-insulating window film is obtained. The remaining steps are the same as in Example 2.

[0025] Test Example 1: Flame retardant performance testing: Test method: The limiting oxygen index of the window films prepared in the examples and comparative examples was tested according to standard GB / T 2406.1—2008. The results are shown in Table 1: A comparison of the experimental data of Examples 1-3 and Comparative Examples 1-3 in Table 1 shows that the window film prepared by the present invention has good flame retardant properties.

[0026] The flame retardant properties of Examples 1-3 are superior to those of the comparative examples, indicating that the hydrophosphorization reaction of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate and DOPO generates a phosphorus-nitrogen diol monomer with a diol. This monomer effectively participates in the construction of the polyurethane backbone. Isocyanurate and DOPO can simultaneously impart good flame retardant properties to the window film. The rigid triazine ring of isocyanurate and the phosphaphenanthrene ring of DOPO form a synergistic flame retardant system. During high-temperature decomposition, it can both generate a barrier char layer and release phosphoric acid free radical quenching substances, thus giving the window film highly efficient flame retardant properties.

[0027] Test Example 2: Testing of thermal insulation performance; Test method: The window film prepared in the examples and comparative examples was cut into 7cm×7cm square strips and covered the opening of the heat preservation box. A light source was set above for illumination at a distance of 10cm. The temperature control probe of the electronic thermometer was fixed at the geometric center of the heat preservation box. The temperature change value was recorded after 40 minutes. The results are shown in Table 2.

[0028] The insulated box is made of polystyrene foam board, with internal dimensions of 10cm (length) × 8cm (width) × 6cm (height), and a wall thickness of 5cm. A 5cm × 5cm square opening is located at the center of the top. The light source is a solar simulator with a spectral distribution conforming to the standard solar spectrum (AM 1.5G), and the output power density is set to 0.6W / cm². 2 The actual solar radiation conditions were simulated by vertically irradiating the sample surface.

[0029] Testing of anti-aging properties; Test method: The window films prepared in the examples and comparative examples were cut into 7cm×7cm square strips. These strips were then exposed to 340 nm ultraviolet light, at a temperature of 60°C and a relative humidity of 95% for 30 days. The thermal insulation performance was tested according to the test method for thermal insulation performance, and the retention rate of thermal insulation performance before and after aging was calculated. The results are shown in Table 2. A comparison of the experimental data of Examples 1-3 and Comparative Examples 1-3 in Table 2 shows that the window film prepared by the present invention has good heat insulation and anti-aging properties.

[0030] Examples 1-3 exhibit superior heat insulation and anti-aging properties compared to the comparative examples. This demonstrates that the hollow vanadium dioxide particles constructed using the urea template method form a physical heat insulation barrier due to their hollow structure. Surface grafting with a copolymer of methyl methacrylate and 1-(pent-4-en-1-yl)-1H-pyrrole provides a polymer layer that both physically blocks water and oxygen penetration and maintains vanadium dioxide stability through the optical transparency of polymethyl methacrylate. The α,β-unsaturated ketone intermediate formed by the condensation of N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one, specifically introduced into the system, has a core conjugated enone system that can capture free radicals to generate a stable benzoquinone structure. Meanwhile, the thioether group continuously consumes reactive oxygen species through a redox cycle mechanism, forming a multi-pathway synergistic antioxidant protection. Based on this, a functional layer of squaric acid cyanine compounds was constructed by in-situ synthesis of 1-(pent-4-en-1-yl)-1H-pyrrole grafted onto the surface of vanadium dioxide. This narrow bandgap molecule can efficiently absorb near-infrared radiation and convert it into heat energy for dissipation. At the same time, it can condense with the indole group at the end of polyurethane to form a three-dimensional cross-linked network, which can also absorb ultraviolet radiation and effectively alleviate photoaging.

[0031] Test Example 3: Mechanical property testing; Test method: The tensile strength of the window film was tested according to standard GB / T 1040-2018; the window films prepared in the examples and comparative examples were cut into strips with a size of 100mm × 10mm and placed on a fixture to test the tensile strength; the results are shown in Table 3: A comparison of the experimental data of Examples 1-3 and Comparative Examples 1-3 in Table 3 shows that the window film prepared by the present invention has good mechanical properties. The mechanical properties of Examples 1-3 are superior to those of the comparative examples, indicating that the introduction of a 2,3,3-trimethyl-3H-indole-7-ol end-capping structure into the polyurethane chain ends allows this indole derivative to form a dynamic crosslinking network through a subsequent condensation reaction with squaric acid, thereby enhancing the mechanical strength of the polyurethane matrix.

[0032] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a heat-insulating car window film, characterized in that, The preparation steps include the following: (1) 1-Allyl-3,5-bis(2-hydroxyethyl)isocyanurate was reacted with DOPO to obtain a diol monomer; (2) Polycarbonate diol, diol monomer, hexamethylene diisocyanate and 2,3,3-trimethyl-3H-indole-7-ol were reacted to obtain modified polyurethane; (3) Vanadium pentoxide, concentrated sulfuric acid, pure water and sulfur dioxide gas are reacted to obtain vanadium pentoxide stock solution; the stock solution, urea and ethylene glycol are reacted to obtain a precursor; the precursor is reacted in a tube furnace to obtain hollow vanadium dioxide; vinyltrimethoxysilane and hollow vanadium dioxide are reacted to obtain pretreated vanadium dioxide. (4) Pretreated vanadium dioxide, methyl methacrylate, and 1-(pent-4-en-1-yl)-1H-pyrrole were reacted to obtain pre-modified vanadium dioxide; (5) The intermediate was obtained by reacting N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one; the modified vanadium dioxide was obtained by reacting the pre-modified vanadium dioxide, the intermediate, and squaric acid. (6) A heat-insulating car window film is obtained by mixing modified polyurethane, modified vanadium dioxide and squaric acid.

2. The method for preparing the heat-insulating car window film according to claim 1, characterized in that, The preparation method of the diol monomer in step (1) is as follows: at 80-90℃, 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate and N-methylpyrrolidone are mixed, and under nitrogen protection, the temperature is raised to 150-160℃ and DOPO is added for 8-10h to obtain the diol monomer; the molar ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to DOPO is 1:(1.05-1.1); the mass ratio of 1-allyl-3,5-bis(2-hydroxyethyl) isocyanurate to N-methylpyrrolidone is 1:(10-12).

3. The method for preparing the heat-insulating car window film according to claim 1, characterized in that, The modified polyurethane in step (2) is prepared by weighing the following components by mass fraction: 50 parts of polycarbonate diol, 18-20 parts of hexamethylene diisocyanate, 3-5 parts of diol monomer, 2-3 parts of 2,3,3-trimethyl-3H-indole-7-ol, 80-100 parts of N,N-dimethylformamide, and 0.05-0.1 parts of dibutyltin dilaurate; mix the polycarbonate diol, diol monomer, and N,N-dimethylformamide, heat to 70-80℃, add hexamethylene diisocyanate and dibutyltin dilaurate, heat to 85-90℃ and react for 3-4 hours, add 2,3,3-trimethyl-3H-indole-7-ol and continue the reaction for 2-3 hours to obtain the modified polyurethane.

4. The method for preparing the heat-insulating car window film according to claim 1, characterized in that, The preparation method of the pretreated vanadium dioxide in step (3) is as follows: vanadium pentoxide, concentrated sulfuric acid, and pure water are mixed at a mass ratio of 1:(5-7):(25-30), sulfur dioxide gas is introduced, and the reaction is carried out for 2-3 hours to obtain a vanadium oxide sulfuric acid solution. The vanadium oxide sulfuric acid solution is then prepared into a 5mM stock solution using pure water. The stock solution, urea, and ethylene glycol are mixed at a mass ratio of 50:(3-5):(5-7), and reacted in a polytetrafluoroethylene reactor at 80-90℃ for 24 hours to obtain a precursor. The precursor is then... Hollow vanadium dioxide was obtained by reacting in a tube furnace at 500℃ under nitrogen protection for 5-6 hours. The pH of a 90wt% ethanol solution was adjusted to 4.5-5.5 with acetic acid, vinyltrimethoxysilane was added and stirred at room temperature for 2-3 hours, followed by the addition of a hollow vanadium dioxide-ethanol dispersion. The mixture was then heated to 60-70℃ and reacted for 5-6 hours to obtain pretreated vanadium dioxide. The mass ratio of hollow vanadium dioxide, vinyltrimethoxysilane, and 90wt% ethanol solution was 1:(1-2):(5-6).

5. The method for preparing the heat-insulating car window film according to claim 1, characterized in that, The preparation method of the pre-modified vanadium dioxide in step (4) is as follows: Disperse the pretreated vanadium dioxide in pure water, add isobutanol, adjust the pH to 8-9 with ammonia, add emulsifier, stir for 12h, add sodium bicarbonate, potassium persulfate, methyl methacrylate, and 1-(pent-4-en-1-yl)-1H-pyrrole under nitrogen protection, heat to 75-85℃, react for 5-6h to obtain pre-modified vanadium dioxide; 10 parts of pretreated vanadium dioxide, 200-250 parts of pure water, 7-9 parts of isobutanol, 1-2 parts of emulsifier, 6-8 parts of sodium bicarbonate, 0.8-1 parts of potassium persulfate, 15-20 parts of methyl methacrylate, and 10-15 parts of 1-(pent-4-en-1-yl)-1H-pyrrole.

6. The method for preparing the heat-insulating car window film according to claim 1, characterized in that, The method for preparing the modified vanadium dioxide in step (5) is as follows: pre-modified vanadium dioxide, toluene, and n-butanol are ultrasonically mixed, an intermediate and squaric acid are added, and the mixture is heated to 110-120℃ and refluxed for 16-20h to obtain modified vanadium dioxide; the mass ratio of pre-modified vanadium dioxide, toluene, n-butanol, intermediate and squaric acid is 1:(10-12):(30-50):(3-5):(1-2).

7. The method for preparing the heat-insulating car window film according to claim 6, characterized in that, The intermediate is prepared by dissolving N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one in tetrahydrofuran, adding concentrated hydrochloric acid and reacting for 24 hours to obtain the intermediate; the molar ratio of N-methyl-2-pyrrolecarboxaldehyde and tetrahydrothiaran-4-one is (2.01-2.05):1; the mass ratio of N-methyl-2-pyrrolecarboxaldehyde, tetrahydrofuran and concentrated hydrochloric acid is 1:(10-12):(0.02-0.03).

8. The method for preparing the heat-insulating car window film according to claim 1, characterized in that, The method for preparing the heat-insulating window film in step (6) is as follows: modified polyurethane, modified vanadium dioxide, squaric acid, and N,N-dimethylformamide are mixed in a mass ratio of 1:(0.25-0.35):(0.01-0.02):(4-6) and coated onto the surface of a glass substrate and cured to form a film, thereby obtaining the heat-insulating window film.

9. A heat-insulating window film prepared by the method according to any one of claims 1-8.

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