Spectral selective window film with high visible light barrier property and preparation method thereof

Abstract

The invention discloses a spectrally selective window film with high visible light barrier property and a preparation method of the spectrally selective window film. The window film sequentially comprises a transparent polymer base film, an ultraviolet blocking layer, a spectrum selection layer and a high-transparency pressure-sensitive adhesive layer. The preparation method comprises the following steps: carrying out surface treatment on the base film; coating and drying an ultraviolet blocking layer made of an ultraviolet light absorber, nano zinc oxide and the like; a spectrum selection layer coating composed of cesium tungsten bronze (Cs0. 33WO3) and lanthanum hexaboride (LaB6) nanoparticles, resin and the like is coated, and ultraviolet light curing is carried out; and finally compounding the high-transparency pressure-sensitive adhesive layer and curing. According to the window film, through the synergistic effect of cesium tungsten bronze and lanthanum hexaboride, high-strength blocking (the light transmittance is 10%-40%) for visible light and efficient reflection (the reflectivity is larger than or equal to 60%) for near-infrared light are achieved, and meanwhile the window film has the ultraviolet blocking rate exceeding 99% and excellent weather resistance stability. The product provided by the invention is especially suitable for automobile side windows and rear windshield glass, and can effectively improve privacy, reduce glare and improve heat insulation effect.

Description

Technical Field

[0001] This invention relates to a functional window film and its preparation method, and more particularly to a spectrally selective window film with high visible light blocking properties, belonging to the technical fields of polymer composite materials and automotive products. Background Technology

[0002] Solar control window films are widely used in the automotive and construction industries. Their main function is to selectively block ultraviolet, visible, and infrared rays in the solar spectrum to protect interior materials, reduce glare, decrease heat intake, and save energy. With increasing user demands for driving comfort, privacy, and energy conservation, developing multifunctional window films that combine excellent ultraviolet blocking, near-infrared reflection, and specific visible light modulation capabilities has become an important development direction in this field.

[0003] In terms of ultraviolet (UV) blocking, existing technologies typically achieve this by adding UV absorbers to the adhesive layer or coating. For example, CN106956486A discloses a heat insulation film with high UV blocking performance, which uses a UV-absorbing coating to construct a UV blocking layer between two base films and in the mounting adhesive layer. It achieves a high blocking rate in the UVA band through a high proportion of benzotriazole or hydroxybenzene triazine UV absorbers and emphasizes its weather resistance. However, this approach mainly focuses on UV blocking and basic heat insulation, and does not provide clear technical guidance on how to synergistically achieve high-intensity visible light blocking (e.g., to meet the privacy requirements of automotive side windows) and efficient selective reflection of the infrared spectrum.

[0004] In terms of infrared blocking and spectral selectivity, utilizing functional nanoparticles is an effective way to achieve selective heat insulation. CN120209382A discloses a transparent coating film using nano-cesium tungsten bronze (Cs). x WO3 (Cesium tungsten bronze) is used as an infrared absorbing material and combined with fluorocarbon resins to block both infrared and ultraviolet rays. This approach offers high light transmittance, making it suitable for applications requiring high transmittance. However, for applications that need to significantly reduce visible light transmittance (e.g., below 40%) to enhance privacy and anti-glare effects (such as automotive side windows) while maintaining high infrared reflectivity to reduce heat accumulation, this technology has limitations. The infrared reflection efficiency and stability of a single cesium tungsten bronze system may face challenges under low visible light transmittance.

[0005] Therefore, current technology still lacks a window film product that can comprehensively solve the following problems: achieving extremely low visible light transmittance to meet privacy and glare control requirements, maintaining high reflectivity in the near-infrared band for excellent heat insulation, providing durable and efficient UV blocking capabilities, and ensuring stable performance under harsh environments. Especially in applications such as automotive side windows, there is an urgent need for a spectrally selective window film with these comprehensive performance characteristics. Summary of the Invention

[0006] To address the above problems, this invention discloses a spectrally selective window film with high blocking visible light and its preparation method.

[0007] This invention includes the following technical solutions: A method for preparing a high-barrier visible light spectrally selective window film includes the following steps: S1. Base film surface treatment: Surface treatment of the transparent polymer base film; S2. Preparation of UV coating solution: Disperse UV absorber, nano zinc oxide and acrylate binder in solvent to prepare UV blocking layer coating solution; S3. UV coating and drying: The UV barrier coating liquid is coated on one side of the treated base film and dried to form a film, thus forming a UV barrier layer; S4. Preparation of spectrally selective layer coating solution: Cesium tungsten bronze nanoparticles, lanthanum hexaboride nanoparticles, resin base and additives are dispersed in a solvent to prepare spectrally selective layer coating solution; S5. Spectral Selective Layer Coating: The spectral selective layer coating liquid is coated onto the surface of the ultraviolet blocking layer; S6. Curing of the spectral selective layer: The coated spectral selective layer is cured with ultraviolet light to form a solid spectral selective layer; S7. Preparation and coating of pressure-sensitive adhesive layer: Mix acrylate monomer, tackifying resin and initiator to prepare a highly transparent pressure-sensitive adhesive, and coat it on the surface of the cured spectral selective layer or another independent release film; S8. Composite and curing: The layer structure coated with pressure-sensitive adhesive is composited with the other side of the spectral selective layer or base film, and then cured to obtain the window film.

[0008] Furthermore, in the above preparation method, in step S1, the surface treatment is corona treatment or plasma treatment; the transparent polymer base film is a polyethylene terephthalate film with a thickness of 25-100 μm.

[0009] Furthermore, in the above preparation method, in step S2, the ultraviolet blocking layer coating liquid comprises, by weight: 8-15 parts of benzotriazole ultraviolet absorber, 2-5 parts of nano zinc oxide, 3-8 parts of acrylate adhesive resin, and 65-85 parts of anhydrous ethanol.

[0010] Furthermore, in the above preparation method, in step S4, the spectral selective layer coating liquid comprises, by weight: 10-25 parts of cesium tungsten bronze nanoparticles, 5-12 parts of lanthanum hexaboride nanoparticles, 10-20 parts of polyurethane acrylate prepolymer, 3-8 parts of photocurable monomer, 0.5-2 parts of photoinitiator, 1-3 parts of surfactant, and 40-60 parts of propylene glycol methyl ether acetate.

[0011] Furthermore, in the above preparation method, in step S6, the ultraviolet curing is carried out under nitrogen protection, with an ultraviolet wavelength of 365 nm and an irradiation intensity of 100-300 mW / cm². 2 The irradiation time is 10-30 seconds.

[0012] The present invention also discloses a high-barrier visible light spectrally selective window film prepared by the above preparation method, comprising, in sequence, a transparent polymer base film, an ultraviolet blocking layer, a spectrally selective layer and a highly transparent pressure-sensitive adhesive layer; the spectrally selective layer comprises cesium tungsten bronze and lanthanum hexaboride nanoparticles.

[0013] Furthermore, in the aforementioned window film, the thickness of the highly transparent pressure-sensitive adhesive layer is 10-30 μm, and it is prepared by weight from the following raw materials: 50-70 parts of isooctyl acrylate, 15-25 parts of methyl methacrylate, 5-10 parts of hydroxyethyl acrylate, 8-15 parts of hydrogenated rosin glycerol ester, 0.5-2 parts of silane coupling agent, and 0.1-0.5 parts of photoinitiator.

[0014] Furthermore, the above-mentioned window film has a total thickness of 50-200 μm and a haze of less than 3%.

[0015] The present invention also discloses the application of the above-mentioned high-barrier visible light spectral selectivity window film on automotive glass, wherein the window film is bonded to the inner surface of the side window or rear window of an automobile through the high-transparency pressure-sensitive adhesive layer.

[0016] Compared with the prior art, the present invention has the following outstanding advantages: 1. Excellent spectral selectivity: By using a specific ratio of cesium tungsten bronze and lanthanum hexaboride nanoparticles in synergy, visible light transmittance is significantly reduced while maintaining high near-infrared reflectivity, achieving differentiated spectral management that "blocks light but not heat".

[0017] 2. Balanced overall performance: While providing privacy protection and glare control (low visible light transmittance), it also has excellent ultraviolet blocking and infrared heat radiation reflection performance, resulting in significant overall heat insulation effect.

[0018] 3. Good stability: The functional nanoparticles are firmly bonded to the resin matrix, and the layered structure design is reasonable. Accelerated aging tests show that its core optical performance has a low decay rate and good long-term reliability.

[0019] 4. High practicality: The manufacturing process is mature, the range of raw materials is wide, and the product is easy to bond with pressure-sensitive adhesive layer, making it especially suitable for use as automotive window film. Attached Figure Description

[0020] Figure 1 The preparation process of the window film of the present invention is as follows; Figure 2 This is a schematic diagram of the structure of the window film of the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Table 1: Raw Material List

[0023] Example 1 A method for preparing a high-barrier visible light spectrally selective window film, such as... Figure 1 As shown, the specific steps are as follows: S1. Base film surface treatment: Select a transparent polyethylene terephthalate (PET) base film with a thickness of 50μm and a haze of less than 0.3%. Perform corona treatment on one side of the film with a treatment power of 500W and a treatment time of 30 seconds to increase the surface energy to more than 50 dynes.

[0024] S2. Preparation of UV coating solution: Weigh 12 parts of benzotriazole UV absorber UV-P, 3 parts of nano zinc oxide with an average particle size of 30nm, and 5 parts of acrylic adhesive resin (solid content 50%) by weight, add them to 80 parts of anhydrous ethanol, and stir in a 50℃ water bath for 3 hours to obtain a uniform UV blocking layer coating solution.

[0025] S3. UV Coating and Drying: Using a microgravure coating machine, the coating solution prepared in step 2 is coated onto the corona-treated PET base film, with the wet film thickness controlled at 20 μm. It is then placed in a 100°C drying oven for 5 minutes to form a UV barrier layer with a dry film thickness of approximately 3 μm.

[0026] S4. Preparation of the spectrally selective layer coating solution: a. Weigh out 18 parts by weight of cesium tungsten bronze (Cs0.33WO3) nanoparticles with an average particle size of 50 nm, 8 parts of lanthanum hexaboride (LaB6) nanoparticles with an average particle size of 40 nm, 2 parts of polyethylene glycol octylphenyl ether (surfactant), and 15 parts of polyurethane acrylate prepolymer, and add them to 50 parts of propylene glycol methyl ether acetate (PMA).

[0027] b. Place the above mixture in a ball mill and disperse it at a speed of 300 rpm for 8 hours to obtain a uniform and stable nano slurry.

[0028] c. Add 5 parts of photocurable monomer (dipropylene glycol diacrylate) and 1 part of photoinitiator (2-hydroxy-2-methyl-1-phenylpropanone) to the nano-slurry, stir evenly, and pass through a 400-mesh sieve to obtain the spectrally selective layer coating solution.

[0029] S5. Spectral Selective Layer Coating: Using a slit extrusion coating machine, the coating liquid prepared in step 4 is coated on the surface of the UV blocking layer obtained in step 3, and the wet film thickness is controlled to be 35μm.

[0030] S6. Curing of the spectral selective layer: Immediately transfer the coated film to a UV curing chamber filled with a nitrogen protective atmosphere, and use a 365nm UV lamp for irradiation and curing. The irradiation intensity is 200 mW / cm², and the irradiation time is 20 seconds, forming a solid spectral selective layer with a dry film thickness of about 8μm.

[0031] S7. Preparation and Coating of Pressure-Sensitive Adhesive Layer: a. By weight, 60 parts of isooctyl acrylate, 20 parts of methyl methacrylate, 8 parts of hydroxyethyl acrylate, and 1 part of silane coupling agent (KH-570) are mixed, and 0.3 parts of photoinitiator (1-hydroxycyclohexyl benzophenone) are added. Partial prepolymerization is carried out under ultraviolet light to obtain a viscous prepolymer.

[0032] b. Add 10 parts of hydrogenated rosin glycerol ester to the prepolymer, stir and mix evenly, and then degas under vacuum to obtain a highly transparent pressure-sensitive adhesive.

[0033] c. Apply the pressure-sensitive adhesive to the release surface of another 50μm thick transparent PET release film and dry it at 110°C for 8 minutes to form a highly transparent pressure-sensitive adhesive layer with a thickness of about 25μm.

[0034] S8. Lamination and Curing: The adhesive side of the release film coated with pressure-sensitive adhesive is laminated with the surface of the spectral selective layer obtained in step 6, and a pressure of 0.4 MPa is applied. Then, it is left to stand in a curing chamber at 50°C for 36 hours to allow the adhesive layer to fully cure, finally obtaining the finished window film. The release film can be removed before application.

[0035] The final window membrane structure is shown in the diagram. Figure 2 As shown.

[0036] Example 2 The difference between this embodiment and Embodiment 1 is that the ratio of functional particles and the thickness of the base film in the spectral selective layer coating solution are adjusted.

[0037] 1. Base film: PET base film with a thickness of 75μm is selected.

[0038] 2. Preparation of spectral selective layer coating solution: The amount of cesium tungsten bronze nanoparticles was adjusted to 12 parts, the amount of lanthanum hexaboride nanoparticles was adjusted to 12 parts, and the remaining components and amounts were the same as in step 4 of Example 1.

[0039] 3. Pressure-sensitive adhesive layer: The thickness is adjusted to 15μm.

[0040] The other steps and conditions of the preparation method are the same as those in Example 1.

[0041] Example 3 The difference between this embodiment and Embodiment 1 is that a thermosetting resin system is used to construct the spectral selectivity layer.

[0042] Base film surface treatment and UV layer preparation: Same as in Example 1.

[0043] 1. Preparation of spectrally selective coating solution: By weight, 20 parts of cesium tungsten bronze nanoparticles and 6 parts of lanthanum hexaboride nanoparticles are dispersed in 40 parts of propylene glycol methyl ether acetate and ground until uniformly dispersed. Then, 25 parts of vinyl ether modified fluorocarbon resin (hydroxyl value 55 mgKOH / g), 15 parts of high hydroxyl value acrylic resin (hydroxyl value 58 mgKOH / g), 5 parts of HDI trimer isocyanate curing agent (Desmodur N3300), 2 parts of benzotriazole UV absorber, 2 parts of light stabilizer (hindered amine), 2 parts of silane coupling agent (KH-560), 0.5 parts of leveling agent, and 0.5 parts of defoamer are added, and PMA is added to bring the total solids to approximately 50%, and the mixture is stirred until uniform.

[0044] 2. Coating and curing of the spectral selective layer: The coating solution is applied to the UV blocking layer, with a wet film thickness of 40 μm. The layer is first dried in a 130℃ oven for 3 minutes to evaporate the solvent, and then cured at 60℃ for 48 hours to form a thermosetting spectral selective layer with a dry film thickness of approximately 10 μm.

[0045] 3. Pressure-sensitive adhesive layer lamination: Using the same high-transparency pressure-sensitive adhesive and release film as in Example 1, the adhesive is directly coated and laminated onto the surface of the cured spectral selective layer. After curing, the finished product is obtained.

[0046] Example 4 The difference between this embodiment and Embodiment 1 is that a higher curing energy and a different pressure-sensitive adhesive are used.

[0047] Curing conditions for spectrally selective layers: During UV curing, the irradiation intensity is adjusted to 300 mW / cm². 2 The irradiation time is shortened to 15 seconds.

[0048] Preparation of pressure-sensitive adhesive layer: Commercially available solvent-based acrylic pressure-sensitive adhesive (40% solid content) was directly coated onto the surface of the spectral selective layer, dried at 90°C for 10 minutes, and then laminated with a 25μm thick PET release film and cured for 24 hours.

[0049] The remaining steps are the same as in Example 1.

[0050] Comparative Example 1: This comparative example is intended to illustrate that coatings without spectrally selective functional particles cannot achieve the technical effects of the present invention.

[0051] The preparation method is basically the same as in Example 1, except that cesium tungsten bronze (Cs) is not added in step 4 (preparation of spectral selective layer coating solution). 0.33 The membrane was prepared using WO3 and lanthanum hexaboride (LaB6) nanoparticles, retaining only the polyurethane acrylate prepolymer, photocurable monomer, photoinitiator, surfactant, and solvent, while maintaining a total solids content approximately equivalent to that of Example 1. The resulting window film did not exhibit significant spectral selectivity.

[0052] Comparative Example 2 This comparative example aims to illustrate that when cesium tungsten bronze is used alone without the addition of lanthanum hexaboride, its infrared reflectance performance under low visible light transmittance is insufficient.

[0053] The preparation method is basically the same as in Example 1, except that in step 4 (preparation of spectral selective layer coating solution), only 20 parts of cesium tungsten bronze (Cs) are added. 0.33 WO3 nanoparticles are used, but lanthanum hexaboride (LaB6) nanoparticles are not added. The amounts of other components are fine-tuned accordingly to maintain the stability of the coating solution.

[0054] Comparative Example 3 This comparative example is intended to illustrate that using conventional visible light absorbing dyes or pigments instead of the spectrally selected particle combination of the present invention cannot simultaneously achieve high visible light blocking and high near-infrared reflectance.

[0055] The preparation method is basically the same as in Example 1, except that in step 4, an equal amount of carbon black pigment (average particle size 100 nm) is used to replace the mixture of cesium tungsten bronze and lanthanum hexaboride to give the coating a dark color and achieve low visible light transmittance. Since carbon black has strong absorption across a wide spectral range, it does not possess spectral selectivity.

[0056] Test case To make the technical solution, effects, and advantages of this invention clearer, specific test examples are provided below. All tests are based on embodiments of this invention and comparative samples, and national standards, industry standards, or recognized testing methods are preferred. Test data are presented in tabular form and analyzed accordingly.

[0057] Test Example 1 Core verification of spectral selectivity performance 1. Test objective: To verify the composition of cesium tungsten bronze (Cs) in this invention. 0.33 The key role of the spectral selectivity layer composed of WO3 and lanthanum hexaboride (LaB6) nanoparticles is whether it can synergistically achieve the spectral selectivity function of "high-barrier visible light" and "high-reflectance near-infrared".

[0058] 2. Test Groups: Test group A: Window film sample prepared in Example 1.

[0059] Comparative Group B: Window film sample prepared in Comparative Example 1 (the spectral selectivity layer does not contain any functional nanoparticles).

[0060] Comparative Group C: Window film sample prepared in Comparative Example 2 (spectrally selective layer contains only cesium tungsten bronze and no lanthanum hexaboride).

[0061] Comparative group D: Window film sample prepared in Comparative Example 3 (carbon black pigment was used for the spectral selection layer).

[0062] 3. Test Method Description: The spectral transmittance (T%) and reflectance (R%) of the sample in the wavelength range of 300-2000 nm were measured using an ultraviolet-visible-near-infrared spectrophotometer equipped with an integrating sphere.

[0063] Visible light transmittance (Tv): Calculates the average transmittance in the 380-780 nm wavelength band.

[0064] Near-infrared reflectance (R_NIR): Calculate the average reflectance in the 780-1400 nm band.

[0065] UV Block Ratio: The blocking ratio is obtained by subtracting the average transmittance in the 280-400 nm band from 100%.

[0066] Total Solar Infrared Rejection Rate (TSER): Calculated based on spectral data and the ISO 13837 standard method, representing the percentage of total solar infrared energy blocked in the 300-2500 nm range.

[0067] 4. Test data are shown in Table 2.

[0068] Table 2: Spectral Selectivity Performance Test Results

[0069] 5. Results Analysis: Compared to control group B, test group A, while maintaining the same excellent ultraviolet blocking capability (>99.7%), significantly reduced visible light transmittance from 85.2% to 22.5%, and significantly increased near-infrared reflectance from 8.5% to 68.3%, with TSER jumping from 15.3% to 78.5%. This fully demonstrates that the introduction of the spectral selective layer in this invention is the core of realizing the transformation from a "high-transmittance" ordinary film to a functional film with "high visible light blocking and high infrared reflectance".

[0070] Compared to control group C, test group A, while achieving a similarly low visible light transmittance (~22%), exhibited a significantly higher near-infrared reflectance (68.3%) than the sample using only cesium tungsten bronze (41.2%), and its TSER was also 23 percentage points higher. This indicates that the addition of lanthanum hexaboride (LaB6) played a crucial synergistic role in maintaining high near-infrared reflectance under low transmittance conditions, an effect that a single cesium tungsten bronze system could not achieve.

[0071] Compared to control group D, test group A, although having slightly higher visible light transmittance (22.5% vs 15.3%), had a much higher near-infrared reflectance (68.3%) than the sample using carbon black (9.8%), with a TSER more than four times that of the latter. This clearly reveals the fundamental difference between the spectrally selective nanoparticles (reflecting / absorbing specific wavelengths) used in this invention and the broadband absorbing pigments (indiscriminate absorption). This invention achieves "selective" blocking, effectively blocking visible light while reflecting most of the near-infrared heat, whereas carbon black converts light energy (including infrared) into heat energy, resulting in low heat insulation efficiency and potentially causing the membrane to heat up.

[0072] Test Example 2 Performance balance verification at different visible light transmittance levels.

[0073] Test objective: To verify that by adjusting the ratio of functional particles in the spectral selection layer, this invention can maintain a good balance between near-infrared reflection and ultraviolet blocking performance over a wide range of visible light transmittance, so as to meet the needs of different application scenarios (such as different privacy levels of automotive side windows).

[0074] Test Groups: Test group A1: Sample from Example 1 (Tv≈22%).

[0075] Test group A2: Sample from Example 2 (Tv≈35%).

[0076] Comparative Group E (simulating commercially available dark heat insulation film): using a carbon black system similar to Comparative Example 3, but with the formula adjusted to achieve a TV of about 22% for commercially available common dark car film samples.

[0077] Test method description: Same as in Test Example 1, measure Tv, R_NIR, UV Block and TSER.

[0078] Additional measurements were taken of the haze of the samples to assess their visual clarity, in accordance with GB / T 2410.

[0079] The test data is shown in Table 3.

[0080] Table 3: Performance Balance Verification at Different Visible Light Transmittance Levels

[0081] Results analysis: Test groups A1 and A2 show that the technical solution of this invention has good adjustability. As the visible light transmittance increases from 22.5% to 35.1%, its near-infrared reflectance remains at a high level of over 62%, the TSER is consistently above 72%, and the ultraviolet blocking rate is consistently better than 99.5%. This provides a technical foundation for the serialization and development of products.

[0082] At a similar visible light transmittance (~22%), test group A1 outperformed control group E in all aspects. Particularly in the core heat insulation indicators, A1's near-infrared reflectance (68.3%) and TSER (78.5%) were approximately 6 times and 3.7 times that of commercially available dark-colored films, respectively. Simultaneously, A1's haze (2.1%) was significantly lower than control group E (4.5%), indicating that this invention achieves high heat insulation while ensuring better visual clarity, solving the common problems of "blurred vision" or "excessive mirror effect" associated with dark-colored films. This demonstrates the technical superiority of this invention over traditional colored heat insulation films.

[0083] Test Example 3 Weathering stability verification.

[0084] Test objective: To verify the retention rate of key optical properties of the window film of the present invention, especially its spectral selective layer, under harsh conditions simulating long-term sunlight exposure, and to evaluate its reliability for long-term use.

[0085] Test Groups: Test group A: Sample of Example 1.

[0086] Test group A3: Sample of Example 3 (thermosetting system).

[0087] Comparative Group C: Sample 2 (containing only cesium tungsten bronze).

[0088] Test method description: Accelerated aging tests were conducted using a xenon lamp aging test chamber according to ISO 105-B06 standard. Conditions were set as follows: black panel temperature 65°C, chamber temperature 40°C, relative humidity 50%, continuous illumination (no dark circulation). Irradiance was controlled at 0.55 W / m². 2 @340 nm.

[0089] Samples were taken out at 0 hours (initial), 500 hours and 1000 hours of aging, respectively, and after cooling to room temperature, their visible light transmittance (Tv) and near-infrared reflectance (R_NIR) were remeasured according to the method of Test Example 1.

[0090] Calculate the retention rate of each performance (value after aging / initial value × 100%).

[0091] The test data is shown in Table 4: Table 4: Changes in key optical properties over aging time

[0092] Results analysis: After 1000 hours of rigorous xenon lamp aging, the visible light transmittance of test group A (UV curing system) and test group A3 (thermocuring system) remained above 97.5%, and the near-infrared reflectance remained above 96.8%, with minimal performance degradation. This indicates that the layered structure and stable integration of functional nanoparticles with the resin matrix employed in this invention can effectively resist aging caused by environmental factors such as light and heat, and possesses excellent weather resistance and stability.

[0093] In contrast, group C (containing only cesium tungsten bronze) showed a significant performance degradation during aging, with only 90.1% of its near-infrared reflectance retained after 1000 hours. This indirectly confirms that the introduction of lanthanum hexaboride (LaB6) not only improved the initial infrared reflectance but also contributed to enhancing the stability of the entire spectral selective layer under long-term illumination. This may be due to the excellent chemical stability of LaB6 itself or its interaction with Cs. 0.33 WO3 forms a more stable composite system, which together resists aging and degradation.

[0094] In summary, the window film product of the present invention can meet the stringent requirements for long-lasting performance in outdoor application scenarios such as automobiles.

[0095] In summary, the technical effectiveness of this invention has been verified through the series of comparative tests above. The tests show that the spectral selective layer composed of cesium tungsten bronze and lanthanum hexaboride is key to achieving a synergistic effect of high visible light blocking and high near-infrared reflectance. The example sample (visible light transmittance 22.5%) achieved a near-infrared reflectance of 68.3% and a total solar infrared rejection ratio (TSER) of 78.5%, significantly better than the comparative samples using only cesium tungsten bronze (reflectance 41.2%, TSER 55.4%) or carbon black pigment (reflectance 9.8%, TSER 18.9%). At different visible light transmittance levels (e.g., 22% and 35%), the product of this invention maintains a near-infrared reflectance above 62% and an ultraviolet rejection rate exceeding 99.5%. After 1000 hours of accelerated aging under a xenon lamp, the core optical performance retention rate was above 97%, confirming its excellent weather resistance and stability.

[0096] The above are merely a few preferred embodiments of the present invention, described in a relatively specific and detailed manner, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-barrier visible light spectrally selective window film, characterized in that, Includes the following steps: S1. Base film surface treatment: Surface treatment of the transparent polymer base film; S2. Preparation of UV coating solution: Disperse UV absorber, nano zinc oxide and acrylate binder in solvent to prepare UV blocking layer coating solution; S3. UV coating and drying: The UV barrier coating liquid is coated on one side of the treated base film and dried to form a film, thus forming a UV barrier layer; S4. Preparation of spectrally selective layer coating solution: Cesium tungsten bronze nanoparticles, lanthanum hexaboride nanoparticles, resin base and additives are dispersed in a solvent to prepare spectrally selective layer coating solution; S5. Spectral Selective Layer Coating: The spectral selective layer coating liquid is coated onto the surface of the ultraviolet blocking layer; S6. Curing of the spectral selective layer: The coated spectral selective layer is cured with ultraviolet light to form a solid spectral selective layer; S7. Preparation and coating of pressure-sensitive adhesive layer: Mix acrylate monomer, tackifying resin and initiator to prepare a highly transparent pressure-sensitive adhesive, and coat it on the surface of the cured spectral selective layer or another independent release film; S8. Composite and curing: The layer structure coated with pressure-sensitive adhesive is composited with the other side of the spectral selective layer or base film, and then cured to obtain the window film.

2. The preparation method according to claim 1, characterized in that, In step S1, the surface treatment is corona treatment or plasma treatment; the transparent polymer base film is a polyethylene terephthalate film with a thickness of 25-100 μm.

3. The preparation method according to claim 1, characterized in that, In step S2, the ultraviolet blocking layer coating liquid comprises, by weight: 8-15 parts of benzotriazole ultraviolet absorber, 2-5 parts of nano zinc oxide, 3-8 parts of acrylate adhesive resin, and 65-85 parts of anhydrous ethanol.

4. The preparation method according to claim 1, characterized in that, In step S4, the spectral selective layer coating liquid comprises, by weight: 10-25 parts of cesium tungsten bronze nanoparticles, 5-12 parts of lanthanum hexaboride nanoparticles, 10-20 parts of polyurethane acrylate prepolymer, 3-8 parts of photocurable monomer, 0.5-2 parts of photoinitiator, 1-3 parts of surfactant, and 40-60 parts of propylene glycol methyl ether acetate.

5. The preparation method according to claim 1, characterized in that, In step S6, the ultraviolet curing is carried out under nitrogen protection, with an ultraviolet wavelength of 365 nm and an irradiation intensity of 100-300 mW / cm². 2 The irradiation time is 10-30 seconds.

6. A high-barrier visible light spectrally selective window film prepared by the preparation method according to any one of claims 1-5, characterized in that, It comprises, in sequence, a transparent polymer base film, an ultraviolet blocking layer, a spectral selective layer, and a highly transparent pressure-sensitive adhesive layer; the spectral selective layer contains cesium tungsten bronze and lanthanum hexaboride nanoparticles.

7. The window film according to claim 6, characterized in that, The window film has an average transmittance of 10%-40% in the visible light band of 380-780nm, an average reflectance of not less than 60% in the near-infrared band of 780-1400nm, and a blocking rate of not less than 99% for ultraviolet rays of 280-400nm.

8. The window film according to claim 6, characterized in that, The thickness of the highly transparent pressure-sensitive adhesive layer is 10-30 μm, and it is prepared by weight from the following raw materials: 50-70 parts of isooctyl acrylate, 15-25 parts of methyl methacrylate, 5-10 parts of hydroxyethyl acrylate, 8-15 parts of hydrogenated rosin glycerol ester, 0.5-2 parts of silane coupling agent, and 0.1-0.5 parts of photoinitiator.

9. The window film according to claim 6, characterized in that, The total thickness of the window film is 50-200μm, and the haze is less than 3%.

10. The application of the high-barrier visible light spectrally selective window film as described in any one of claims 6-9 on automotive glass, characterized in that, The window film is adhered to the inner surface of the car's side window or rear windshield via the highly transparent pressure-sensitive adhesive layer.

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