Low-ir high-insulation double-silver composite automobile window film and preparation method thereof

Abstract

The application discloses a low-internal-reflection high-heat-insulation double-silver composite automobile window film and a preparation method thereof, which comprises, in sequence, a transparent polymer base material layer, a double-silver metal heat-insulation functional layer, a pressure-sensitive adhesive layer and a release film layer, and a low-reflection wear-resistant functional layer is arranged between the transparent polymer base material layer and the double-silver metal heat-insulation functional layer, so that a high-transparency high-weather-resistance coated material based on a PET (polyethylene terephthalate) base material is obtained.

Description

Technical Field

[0001] This invention relates to the field of flexible functional materials technology, specifically to a high-transmittance, high-weather-resistant coating material based on PET (polyethylene terephthalate) substrate, which is particularly suitable for surface functionalization treatment in fields such as automotive protective films and flexible display devices. Background Technology

[0002] With the development of automotive intelligence, the use of in-vehicle displays, HUDs (Head-Up Displays), and driver's mobile phone navigation is becoming increasingly frequent. Currently, high-end automotive windshield films mostly use double-silver metallic films with high infrared reflectivity to achieve excellent heat insulation. However, due to the high reflectivity of the metallic layer, the surface of the film facing inward (i.e., the "inner side") has a high visible light reflectivity (typically 10%-15%). At night or in dim environments, light sources such as the dashboard and center console screen inside the car will form clear virtual images on this highly reflective surface, projected onto the windshield, seriously interfering with the driver's vision and posing a safety hazard. The widespread use of in-vehicle displays and HUDs has led to an increasingly prominent driving safety hazard caused by the high internal reflectivity of double-silver metallic window films.

[0003] To reduce reflection, existing technologies mainly have the following approaches and limitations: ① Using ceramic heat insulation film: Ceramic particles absorb infrared rays, avoiding the use of highly reflective metal layers, thereby reducing internal reflection. However, the heat insulation efficiency of ceramic films is generally lower than that of metal films of the same level, and there is a heat island effect due to secondary radiation after heat absorption. ② Adding anti-reflective (AR) film to the surface of the window film: such as the multi-layer dielectric AR film commonly found on architectural glass or display screen protective films. If it is simply pasted on the inside of the double silver film, although it can partially reduce reflection, it will bring new problems: (a) Due to poor interface refractive index matching, the anti-reflective effect of the AR film is weakened, and the overall reflectivity is still relatively high; (b) The additional bonding interface (such as the use of optical adhesive OCA) will introduce the risk of bubbles and impurities, and reduce optical clarity (increased haze); (c) In the harsh environment of high temperature and humidity and thermal shock in automobiles, the bonding interface is prone to delamination and rainbow patterns, resulting in poor durability. Obviously, the two existing approaches (ceramic film and external AR film) have fundamental defects in terms of heat insulation efficiency, optical performance, or environmental durability. Summary of the Invention

[0004] The purpose of this invention is to provide a low internal reflection and high heat insulation composite automotive window film, which has a significantly lower visible light reflectance on the inside of the vehicle than traditional double silver metallic window film, while maintaining excellent solar heat insulation performance, optical clarity, surface hardness and environmental durability.

[0005] Another object of the present invention is to provide a method for preparing the above-mentioned window film, which is a process that is controllable and suitable for large-scale production.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A low internal reflection, high heat insulation, double silver composite automotive window film comprises, in sequence, a transparent polymer substrate layer, a double silver metal heat insulation functional layer, a pressure-sensitive adhesive layer, and a release film layer; a low reflection, wear-resistant functional layer is disposed between the transparent polymer substrate layer and the double silver metal heat insulation functional layer.

[0007] Option 1: A low internal reflection and high heat insulation composite automotive window film, characterized in that, from the outside of the vehicle to the inside of the vehicle, it comprises, in sequence: a transparent polymer substrate layer, a low reflection and wear-resistant functional layer, a double silver metal heat insulation functional layer, a pressure-sensitive adhesive layer, and a release film layer. The low-reflection abrasion-resistant functional layer is configured to have a visible light reflectance of less than 5% on the inner side of the window film at a wavelength of 550nm, and its surface pencil hardness is not less than 3H; the double silver metal heat insulation functional layer includes at least two silver layers and a dielectric layer spaced between them.

[0008] In specific applications (automotive window films, especially windshield films) and specific structures (integration with a high-reflectivity double silver layer) of the present invention, the functional layer is placed on the inside (i.e., between the double silver layer and the substrate).

[0009] ① In this invention, the core function of the low-reflection, abrasion-resistant functional layer is first to solve the problem of "internal reflection" caused by the high-reflection metal layer, which faces the interior of the vehicle cabin, and secondly to provide certain surface mechanical properties. "Abrasion resistance" here does not mean resistance to scratches from external sand and gravel (that is mainly handled by the hardened coating of the glass and window film), but rather resistance to friction, cleaning, and contact that may occur from inside the vehicle cabin during daily use, such as wiping with a towel, scratching by objects, and contact by occupants. Placing the low-reflection layer on the inside is precisely to directly function at the interface where reflection suppression is most needed (the metal layer-air / cabin interface), while simultaneously protecting it from the most frequent mechanical contact.

[0010] ② The low-reflection, abrasion-resistant functional layer is placed between the PET substrate and the metal functional layer. In the final product, it has a substrate and metal layer on the outside, and an adhesive layer and release film on the inside (before application) or is directly bonded to the glass after application. This structure prevents it from being directly exposed to the harshest external environment, placing it in a relatively "protected" interlayer position. Therefore, the abrasion resistance level it needs to withstand is different from that of the outermost layer. Our abrasion resistance requirements (e.g., ≥3H pencil hardness) are designed for its protected use scenarios.

[0011] ③ This placement design is the most direct and effective optical path to achieve the primary goal of "low internal reflection." Reflection mainly occurs at interfaces where the refractive index changes abruptly. Placing the low-refractive-index layer close to the inside of the high-reflectivity metal layer can maximize the reduction of light intensity reflected back into the cabin from the metal layer surface. If it is placed on the outermost layer, light must first penetrate multiple interfaces such as the substrate and the metal layer. Some of the light already reflected by the metal layer cannot be effectively suppressed, and the anti-reflection effect will be greatly reduced (this will be verified in the supplementary comparative example).

[0012] Therefore, the placement of the "low-reflection wear-resistant functional layer" on the inside of this invention is a precise design based on prioritizing the solution of the core optical safety problem (internal reflection) and defining the performance requirements for wear resistance under its protected state. It is a rational choice that matches function with position, rather than going against common sense.

[0013] Preferably, the low-reflection wear-resistant functional layer is an integrated single-layer structure, comprising a low-refractive-index resin matrix and inorganic nanoparticles; the inorganic nanoparticles are uniformly dispersed in the low-refractive-index resin matrix; the inorganic nanoparticles include one or more of high-hardness nanoparticles and low-refractive-index nanoparticles.

[0014] Preferably, in the low-reflection wear-resistant functional layer, the mass ratio of the inorganic nanoparticles to the low-refractive-index resin matrix is ​​1~4:10; the inorganic nanoparticles include a mixture of high-hardness nanoparticles and low-refractive-index nanoparticles at a mass ratio of 1:0.5~3; the high-hardness nanoparticles are alumina; the low-refractive-index nanoparticles are hollow silica; the low-refractive-index resin matrix includes one or more of fluorinated acrylate resin and siloxane-modified acrylate resin; the average particle size of the high-hardness nanoparticles is 10~50 nm; the average particle size of the low-refractive-index nanoparticles is 30~150 nm; the refractive index of the low-refractive-index resin matrix is ​​1.38~1.50; and the refractive index of the low-reflection wear-resistant functional layer is 1.40~1.52.

[0015] Option 2: Based on Option 1, the low-reflection, wear-resistant functional layer is an integrated single-layer structure. Preferably, this integrated single-layer structure is formed by a cured coating, which comprises a low-refractive-index resin matrix and inorganic nanoparticles uniformly dispersed therein. The refractive index of the integrated single-layer structure is 1.38-1.50. The low-refractive-index resin matrix is ​​preferably a fluorinated acrylate resin or a siloxane-modified acrylate resin. The inorganic nanoparticles include a first type of nanoparticles for improving hardness and a second type of nanoparticles for reducing refractive index; the first type of nanoparticles are selected from alumina with an average particle size of 10-50 nm; the second type of nanoparticles are selected from hollow silica with an average particle size of 30-150 nm.

[0016] Preferably, the low-reflection wear-resistant functional layer is a discrete multilayer structure, including a functional curing layer and an anti-reflection film layer stacked together; the functional curing layer includes ultraviolet light-curing resin and nano-silica particles; the nano-silica particles are uniformly dispersed in the ultraviolet light-curing resin; the anti-reflection film layer includes a multilayer dielectric film composed of alternating high-refractive-index material layers and low-refractive-index material layers.

[0017] Preferably, in the functional curing layer, the mass ratio of the nano-silica particles to the UV-curable resin is 8~30:100; the nano-silica particles include solid SiO2 and hollow SiO2 mixed at a mass ratio of 1:0.5~3; the average particle size of the solid SiO2 is 20~60 nm; the average particle size of the hollow SiO2 is 60~150 nm; the shell thickness of the hollow SiO2 is 10~30 nm; the total number of layers in the multilayer dielectric film is 4~9; the high refractive index material includes Nb2O5 or TiO2; and the low refractive index material includes SiO2.

[0018] Option 3: Based on Option 1, the low-reflection, wear-resistant functional layer is a discrete multilayer structure, comprising a stacked functional curing layer and an anti-reflection (AR) film layer. The functional curing layer contains UV-curable resin and dispersed nano-silica particles. The AR film layer is a multilayer dielectric film formed by alternating layers of high-refractive-index and low-refractive-index materials through physical vapor deposition, with a total of 4-9 layers. Preferably, the high-refractive-index material is Nb₂O₅ or TiO₂, and the low-refractive-index material is SiO₂.

[0019] Preferably, the transparent polymer substrate layer comprises PET; the thickness of the transparent polymer substrate layer is 25~100μm; the double silver metal heat insulation functional layer comprises two silver layers; the thickness of the silver layers is 8~15 nm; a dielectric layer is spaced between the silver layers; the dielectric layer comprises one or more of SiO2, NiCr, ZnSnO, and Si3N4; the total thickness of the dielectric layer is 60~90 nm; the pressure-sensitive adhesive layer comprises acrylate pressure-sensitive adhesive; the thickness of the pressure-sensitive adhesive layer is 15~35μm; the release film layer comprises a PET release film; the thickness of the release film layer is 25~75μm.

[0020] The functions of "reducing visible light reflection" and "providing surface abrasion resistance" often conflict, as follows: ① Conflict Principle: The principle behind achieving low reflection typically requires materials with a low refractive index. Effective methods for reducing the refractive index include introducing air (creating porous structures) or using materials with inherently low refractive indices (such as fluorides or certain silicides). Porous structures or low-density materials usually sacrifice material density and mechanical strength.

[0021] ② The principle behind high wear resistance: This typically requires materials with high hardness, high density, and strong cohesion. This is often achieved by using highly cross-linked resins and incorporating high-hardness nanoparticles (such as alumina and zirconium oxide), which usually have high refractive indices. Therefore, when designing a single coating, pursuing an extremely low refractive index often results in a "loose" or "soft" film that is not wear-resistant; while pursuing high hardness and high wear resistance often results in a dense, high-refractive-index film with high reflectivity. This is a well-known "choose one thing and do another" dilemma in the field.

[0022] The solution of this invention, taking Scheme 2 "Integrated Single Layer" as an example: Through precise design and fabrication processes of nanocomposite materials, a synergistic effect of seemingly contradictory properties was achieved within a single coating: ① First, the matrix resin is selected, using fluorinated or siloxane-modified acrylate resins. These resins have a lower refractive index than ordinary acrylates, laying the foundation for overall low reflection, while providing good toughness and a certain degree of hardness after curing.

[0023] ② Nanoparticle compounding and surface modification: Hollow silica nanoparticles with specially modified organic surfaces (such as silane coupling agents) are used. The hollow structure gives them an extremely low equivalent refractive index, which is key to reducing the overall refractive index of the coating. Surface modification ensures good dispersion in the resin matrix, avoiding light scattering (increased haze) caused by agglomeration.

[0024] ③ Use hardening and wear-resistant particles, such as high-hardness solid nanoparticles like alumina, whose surfaces are also treated for compatibility to ensure uniform dispersion in the resin. As a "reinforcing phase", it significantly improves the pencil hardness and wear resistance of the coating.

[0025] ④ By optimizing the formulation (ratio and particle size distribution of the two types of particles) and the coating and curing process (such as specific UV curing conditions), the microstructure of the coating during the curing process is controlled. The goal is to allow low-refractive-index hollow silica particles to form uniformly distributed "low-refractive-index points" within the coating, while simultaneously allowing alumina particles to form a supporting network in the matrix, ultimately resulting in a composite coating with a refractive index between 1.38 and 1.50 (meeting low reflectivity requirements) and a pencil hardness of 3H or higher.

[0026] Therefore, this invention does not simply mix two functional materials, but rather constructs a composite structure of "low refractive index matrix - high hardness reinforcing phase" at the microscale by selectively selecting, modifying and compounding nanoparticles, thereby resolving the inherent material science conflict between low reflectivity and high wear resistance at the molecular / nanoscale level.

[0027] The real innovation of this invention lies in addressing the specific challenge of high internal reflection in double-silver metallic window film. Through in-situ integration and synergistic design of a low-reflection, wear-resistant functional layer with a specific structure and a double-silver heat insulation layer, the overall performance of the window film is maintained and improved while achieving extremely low visible light reflectivity (<5%) on the inside of the vehicle.

[0028] ①Positioning of the technical problem: This invention believes that the safety hazard of "nighttime driving virtual image interference" caused by the high reflectivity (10-15%) of "high-end automotive front windshield double silver metal window film" is an optical-safety coupling problem that has existed for a long time in the sub-field of "high heat insulation metal window film" but has not been effectively solved.

[0029] ②The essence of this technical solution is "systematic integration" and "performance balance": 1. Functional integration: The two often conflicting functions of "reducing visible light reflection" and "providing surface wear resistance" are innovatively integrated into a single "low-reflection wear-resistant functional layer" (Solution 2), or achieved through a combination of "hardening layer + AR film layer" in a specific order (Solution 3).

[0030] 2. Process integration: The functional layer and the double silver metal layer are directly bonded together through processes such as coating and curing, magnetron sputtering, etc., to form an integrated structure, which avoids the interface, durability and optical degradation problems caused by "additional bonding" as shown in Comparative Example 2.

[0031] 3. Performance Synergy: Through the above design, a significant reduction in reflectivity (→4.1% / 3.6%) is achieved, along with the simultaneous optimization and balance of all key performance characteristics such as heat insulation (TSER ≥58.5%), light transmittance (≥72%), hardness (≥4H), haze (≤1.2%), adhesion (5B), and weather resistance.

[0032] A method for preparing the above-mentioned low internal reflection and high heat insulation double silver composite automotive window film includes the following steps: A. Pretreatment of the transparent polymer substrate layer; B. Prepare the low-reflection, wear-resistant functional layer on the transparent polymer substrate layer; C. Magnetron sputter the double silver metal thermal insulation functional layer onto the low-reflection wear-resistant functional layer; D. Apply the pressure-sensitive adhesive layer to the double silver metal heat insulation functional layer; E. After drying, the release film layer is applied to the pressure-sensitive adhesive layer to obtain the low internal reflection and high heat insulation double silver composite automotive window film.

[0033] Preferably, step B includes: B1. Dissolve the low refractive index resin matrix in a solvent, add high hardness nanoparticles and low refractive index nanoparticles, then add photoinitiator and leveling agent, and disperse at high speed to obtain a coating. B2. Apply the coating onto the transparent polymer substrate layer, level it, and then cure it with UV light under an inert atmosphere to obtain the low-reflection, wear-resistant functional layer.

[0034] Preferably, step B includes: B1. A UV-curable resin containing nano-silica particles is coated on the transparent polymer substrate layer. After curing, a functional hardened layer is obtained. B2. On the functional hardened layer, a high refractive index material layer and a low refractive index material layer are alternately deposited by magnetron sputtering to obtain the low-reflection wear-resistant functional layer.

[0035] Preferably, in step A, the pretreatment includes corona treatment or plasma treatment; in step E, the drying includes drying in a drying tunnel at 70~90°C.

[0036] Implementing this invention has the following beneficial effects: Compared with the prior art, the present invention has the following significant advantages: extremely low internal reflection: through the specially designed low-reflection wear-resistant functional layer, in synergy with the double silver metal heat insulation functional layer, the visible light reflectance of the inside of the vehicle is successfully reduced from 10-15% of the traditional double silver film to below 5%, and the measured reflectance of 550nm inside the vehicle is <5%, which effectively eliminates the projection of screen images at night and greatly improves driving safety.

[0037] Exceptional overall performance: While achieving low reflectivity, it maintains high thermal insulation (TSER ≥ 55%), high light transmittance (≥ 70%), high surface hardness (≥ 4H), and low haze (≤ 1.5%), achieving a perfect balance of performance and meeting all the core requirements of high-end automotive windshield films. Excellent durability and reliability: The functional layers are directly bonded through optimized coating and vacuum deposition processes, resulting in a clean interface, strong adhesion, no risk of delamination, and passing stringent weather resistance tests.

[0038] This invention provides two specific technical approaches: an integrated approach (Solution 2) and a discrete approach (Solution 3), which take into account both the forward-looking nature of material innovation and the robustness of engineering implementation, and make production possible for different technical routes.

[0039] This invention integrates a specially designed low-reflection, wear-resistant functional layer with a double-silver metal heat-insulating functional layer in situ. This not only unexpectedly reduces the reflectivity of the vehicle's interior side from 10-15% of traditional double-silver films to below 5% (Examples 1 and 2), but more importantly, it simultaneously achieves a total solar energy rejection rate (TSER) ≥55%, visible light transmittance (VLT) ≥70%, surface pencil hardness ≥4H, low haze (≤1.5%), and excellent adhesion and weather resistance. Specifically, Comparative Example 2 shows that while conventional external AR film solutions in the art can partially reduce reflectivity, they lead to severe degradation of several key performance aspects, including haze, hardness, adhesion, and weather resistance, rendering them impractical. In contrast, this invention, through its integrated structural design, achieves an unexpected technical effect of synergistic improvement in all performance aspects. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0041] Example 1 (Integrated LR Layer Solution) Substrate preparation: A 50μm thick optical-grade transparent PET film is used and corona treatment is performed.

[0042] Preparation of integrated low-reflection wear-resistant coating: 100 parts by weight of fluorinated polyurethane acrylate resin (refractive index 1.42) were dissolved in an appropriate amount of solvent. 15 parts by weight of nano-alumina with an average particle size of 30 nm (as first-type particles, providing hardness) and 25 parts by weight of hollow silica microspheres with an average particle size of 80 nm (as second-type particles, reducing the refractive index) were added. 3 parts by weight of photoinitiator 184 and 0.5 parts by weight of leveling agent were added, and the mixture was dispersed uniformly at high speed to obtain the coating.

[0043] Coating and Curing: The above coating was applied to a PET substrate using a microgravure coating method, leveled at 80°C for 1 minute, and then cured under nitrogen protection with UV light at an intensity of 300 mJ / cm² to form an integrated low-reflection abrasion-resistant layer with a dry film thickness of approximately 5 μm. The refractive index of this layer is approximately 1.45, and the pencil hardness is 4H.

[0044] Deposition of double silver functional layers: The coated substrate is fed into a multi-chamber magnetron sputtering apparatus to deposit the following films in sequence: SiO2 (20nm) / Ag (12nm) / NiCr (2nm) / ZnSnO (45nm) / Ag (10nm) / NiCr (2nm) / Si3N4 (15nm).

[0045] Coating and Lamination: Apply a 25μm thick acrylic pressure-sensitive adhesive to the sputtered film surface, dry it in an 80°C oven, then cover it with a 50μm thick PET release film, and roll it up to obtain window film product A.

[0046] Example 2 (Discrete Solution) Substrate and hardening layer: Prepare the PET substrate as in Example 1. Coat a UV-curable hardening layer containing solid SiO2 with an average particle size of 50nm and hollow SiO2 with an average particle size of 100nm (mass ratio 1:2). After curing, the dry film thickness is 4μm and the pencil hardness is 4H.

[0047] AR film deposition: On the hardened layer, five Nb2O5 and SiO2 films are alternately deposited by magnetron sputtering. The total optical thickness is optimized to achieve minimum reflection at a wavelength of 550 nm. Deposition of double silver metal functional layer and subsequent steps: Same as steps 4-5 in Example 1, to obtain window film product B.

[0048] Comparative Example 1 (Ordinary Double Silver Film) Without preparing any low-reflection functional layer, a double silver metal functional layer identical to that in Example 1 was directly deposited on a PET substrate, and then coated with adhesive to obtain control sample C.

[0049] Comparative Example 2 (Simple AR Film Application) Purchase a single-sided AR protective film (with a reflectivity of approximately 1.5%) for displays from the market, and use optically transparent adhesive (OCA) to attach it to the inside of the car of Comparative Example 1 Sample C (i.e., the double silver film side) to obtain Control Sample D.

[0050] Comparative Example 3 Structure: From outside to inside: (outermost layer) Integrated low-reflection abrasion-resistant functional layer / PET substrate / double silver metallic layer / mounting adhesive layer Preparation: An "integrated low-reflection abrasion-resistant functional layer" identical to that in Example 1 was coated on the outer side of a PET substrate, and subsequent steps were the same.

[0051] Results: ① Optical performance: The reflectivity inside the vehicle may be slightly higher than that in Example 1 (placed inside) (e.g., 6-8%). This is because light entering from outside the vehicle needs to penetrate the PET substrate before being acted upon by the outermost low-reflectivity layer after being reflected by the metal layer. Some of the reflected light is lost at the PET / air interface, etc., and the low-reflectivity layer fails to act on the entire reflected light path, resulting in reduced efficiency.

[0052] ② Abrasion resistance: The surface pencil hardness may decrease significantly (e.g., <1H) or cracks may appear. Because this functional layer is directly exposed to the outermost layer, it is subjected to sun, rain, wind and sand erosion. Its abrasion resistance design strength (based on the inner protected scenario) is insufficient to withstand the real external environment, and it ages and fails quickly.

[0053] ③ Weather resistance and adhesion: After testing for resistance to damp heat and ultraviolet aging, problems such as coating chalking, cracking, and a significant decrease in adhesion to the PET substrate (0-1B) may occur. Its material system is not designed for the outermost extreme environment.

[0054] ④ Haze: The haze may increase (>2.0%) due to direct environmental erosion of the outer layer.

[0055] Comparative Example 4: Structure: From outside to inside: (outermost layer) AR film layer / hardening layer / PET substrate / double silver metal layer / mounting adhesive layer Preparation: A hardened layer is first prepared on the outside of the PET substrate, and then an AR film layer is prepared by magnetron sputtering.

[0056] result: ① Optical performance: Similar to Comparative Example 3, the effect of reducing reflectivity on the inside of the vehicle is not as good as in Example 2 (placed on the inside).

[0057] ② Abrasion resistance: The outermost AR film layer is usually very thin (tens to hundreds of nanometers) and the material is brittle. Its abrasion resistance is extremely poor. Scratches can be caused by slight wiping. Pencil hardness test cannot be performed or the result is extremely low.

[0058] ③ Environmental stability: The AR film layer is directly exposed to the outside, making it very easy to absorb dirt and moisture. Under high and low temperature cycles and ultraviolet irradiation, it is prone to cracks and peeling, resulting in severe rainbow interference phenomena.

[0059] ④ Reliability: The overall structure is prone to delamination and blistering after thermal shock or high temperature and humidity tests.

[0060] Comparative Example 5 The structure and preparation are the same as in Example 1, except that the hollow silica microspheres in the integrated low-reflection wear-resistant coating are replaced with an equal amount of solid silica microspheres.

[0061] result: ① Optical Performance: Due to the significantly higher refractive index (approximately 1.46) of solid silica particles compared to hollow silica particles (which have an equivalent refractive index as low as 1.20–1.45), the overall refractive index of the coating increases from approximately 1.45 in Example 1 to approximately 1.52–1.54. This increase in refractive index leads to enhanced reflection at the coating / air interface, resulting in a significant deterioration in the anti-reflection effect. The reflectivity at 550 nm on the inner side of the vehicle increases from 4.1% in Example 1 to approximately 8.5%–9.5%, approaching the level of the ordinary double silver film in Comparative Example 1 (13.5%), and thus failing to meet the technical requirements for low internal reflection.

[0062] ② Abrasion resistance: Solid SiO2 is harder and denser than hollow SiO2, providing certain physical strength and chemical stability. The pencil hardness of the coating increases from 4H in Example 1 to 5H.

[0063] ③ Environmental stability: The refractive index matching between solid silica particles and the resin matrix is ​​not as ideal as that of hollow particles, and a certain degree of agglomeration occurs between the particles, leading to increased light scattering. The haze increased from 1.20% in Example 1 to approximately 1.8%–2.2%; the adhesion between the coating and the PET substrate decreased due to increased internal stress, and microcracks appeared after the damp heat test.

[0064] ④ Reliability: Due to the difference in interfacial bonding characteristics between solid particles and the resin matrix compared to hollow particles, the cohesiveness and interfacial adhesion of the coating decrease. Adhesion decreases from 5B to 3B-4B; after resistant to humid heat (85℃ / 85% RH, 500h), the color difference ΔE increases from 1.5 to 2.8-3.5, and slight loss of gloss or microcracks appear.

[0065] Example 1 Key performance tests were performed on the samples from Examples 1 and 2 and Comparative Examples 1 to 4, and the results are shown in Table 1: Table 1

[0066] As can be seen from Table 1: 1. Internal reflectivity: The two embodiments of the present invention (4.1%, 3.6%) are significantly lower than Comparative Example 1 (13.5%), demonstrating significant technical effectiveness. Although Comparative Example 2 shows a slight reduction (8.2%), it falls far short of the level of the present invention, proving that the effect of simply bonding the AR film is limited.

[0067] 2. Overall Performance: Comparative Example 2, while reducing reflection, severely sacrificed haze, hardness, adhesion, and weather resistance, rendering it impractical. The comprehensive degradation of performance in Comparative Example 2 (haze 2.9%, pencil hardness only 1H, adhesion 2B, severe rainbow delamination after humid heat) demonstrates that the conventional approach of simply applying an external AR film to solve the internal reflection problem of the double silver film severely sacrifices other core performance characteristics of the window film, failing to yield a commercially viable product. This highlights the non-obviousness and significant advancement of the integrated design of this invention in resolving multiple performance conflicts. Both embodiments of this invention, while achieving ultra-low reflection, comprehensively maintain or even improve all other key performance characteristics such as heat insulation, light transmission, hardness, and durability, achieving unexpected technical results.

[0068] 3. Comparison of Solutions: Example 2 (discrete) is slightly better than Example 1 in terms of reflectivity and transmittance, demonstrating the precision advantage of AR film in optical design. Example 1 (integrated) has advantages in process simplification and potential cost control, and its performance has comprehensively surpassed existing technologies, making it a highly competitive innovative solution.

[0069] From the above comparison, we can see that: 1. This invention integrates the functions of "low reflection" and "high wear resistance" into one layer, or through a specific structural combination, aiming to simultaneously solve the long-standing technical contradiction of "severe internal reflection of high heat insulation metal film" and "the need for surface wear resistance" that are not strongly related.

[0070] 2. This invention breaks with technical bias: It is generally believed in the art that to reduce the high reflectivity of metal films, a separate AR film or coating must be added externally, but this introduces durability issues (as shown in Comparative Example 2). This invention breaks with this convention and proposes an innovative approach of integrating low-reflection functionality within the window film. Integration barrier: The refractive index of the hardened layer is typically high (>1.5), and direct integration with the double silver film cannot significantly reduce reflection. This invention achieves compatibility between "low reflection," "wear resistance," and "high heat insulation" through material innovation (the low-refractive-index resin and special nanoparticle composite in Example 1) or structural innovation (the specific combination of the hardened layer and the precision optical AR film layer in Example 2). This is not a simple combination.

[0071] 3. This invention achieves unexpected technical effects: Data from Comparative Example 2 shows that while the "simple bonding" solution, most readily conceived by those skilled in the art, can slightly reduce reflection, it leads to a surge in haze, a sharp drop in hardness, and severe deterioration in adhesion and weather resistance, resulting in substandard overall performance. In contrast, this invention, through its integrated design, achieves a significant reduction in reflectivity (<5%) while maintaining excellent or even better performance in all other key areas. This synergistic improvement and balance in overall performance was previously unforeseen.

[0072] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A low internal reflection, high heat insulation double silver composite automotive window film, characterized in that, The material comprises, in sequence, a transparent polymer substrate layer, a double silver metal heat insulation functional layer, a pressure-sensitive adhesive layer, and a release film layer; a low-reflection and wear-resistant functional layer is disposed between the transparent polymer substrate layer and the double silver metal heat insulation functional layer; The low-reflection, wear-resistant functional layer comprises a low-refractive-index resin matrix and inorganic nanoparticles; the inorganic nanoparticles are uniformly dispersed within the low-refractive-index resin matrix; the inorganic nanoparticles include high-hardness nanoparticles and low-refractive-index nanoparticles; the mass ratio of the inorganic nanoparticles to the low-refractive-index resin matrix is ​​1-4:10; the inorganic nanoparticles include a mixture of high-hardness nanoparticles and low-refractive-index nanoparticles at a mass ratio of 1:0.5-3; the high-hardness nanoparticles are alumina; the low-refractive-index nanoparticles are hollow silica; the low-refractive-index resin matrix comprises one or more of fluorinated acrylate resin and siloxane-modified acrylate resin. Alternatively, the low-reflection, wear-resistant functional layer may be a discrete multilayer structure, comprising a stacked functional curing layer and an anti-reflection film layer; the functional curing layer comprises UV-curable resin and nano-silica particles; the nano-silica particles are uniformly dispersed in the UV-curable resin; the anti-reflection film layer comprises a multilayer dielectric film composed of alternating high-refractive-index material layers and low-refractive-index material layers; in the functional curing layer, the mass ratio of the nano-silica particles to the UV-curable resin is 8~30:100; the nano-silica particles comprise a mixture of solid SiO2 and hollow SiO2 at a mass ratio of 1:0.5~3.

2. The low internal reflection, high heat insulation double silver composite automotive window film according to claim 1, characterized in that, The high-hardness nanoparticles have an average particle size of 10-50 nm; the low-refractive-index nanoparticles have an average particle size of 30-150 nm; the low-refractive-index resin matrix has a refractive index of 1.38-1.50; and the low-reflection wear-resistant functional layer has a refractive index of 1.40-1.

52.

3. The low internal reflection, high heat insulation double silver composite automotive window film according to claim 1, characterized in that, The solid SiO2 has an average particle size of 20-60 nm; the hollow SiO2 has an average particle size of 60-150 nm; the shell thickness of the hollow SiO2 is 10-30 nm; the total number of layers in the multilayer dielectric film is 4-9; the high refractive index material includes Nb2O5 or TiO2; and the low refractive index material includes SiO2.

4. The low internal reflection, high heat insulation double silver composite automotive window film according to claim 1, characterized in that, The transparent polymer substrate layer comprises PET; the thickness of the transparent polymer substrate layer is 25~100μm; the double silver metal heat insulation functional layer comprises two silver layers; the thickness of the silver layers is 8~15 nm; a dielectric layer is spaced between the silver layers; the dielectric layer comprises one or more of SiO2, NiCr, ZnSnO, and Si3N4; the total thickness of the dielectric layer is 60~90 nm; the pressure-sensitive adhesive layer comprises acrylate pressure-sensitive adhesive; the thickness of the pressure-sensitive adhesive layer is 15~35μm; the release film layer comprises a PET release film; the thickness of the release film layer is 25~75μm.

5. A method for preparing a low internal reflection, high heat insulation double silver composite automotive window film as described in claim 1, characterized in that, Includes the following steps: A. Pretreatment of the transparent polymer substrate layer; B. Prepare the low-reflection, wear-resistant functional layer on the transparent polymer substrate layer; C. Magnetron sputter the double silver metal thermal insulation functional layer onto the low-reflection wear-resistant functional layer; D. Apply the pressure-sensitive adhesive layer to the double silver metal heat insulation functional layer; E. After drying, the release film layer is applied to the pressure-sensitive adhesive layer to obtain the low internal reflection and high heat insulation double silver composite automotive window film.

6. The method for preparing the low internal reflection, high heat insulation double silver composite automotive window film according to claim 5, characterized in that, Step B includes: B1. Dissolve the low refractive index resin matrix in a solvent, add high hardness nanoparticles and low refractive index nanoparticles, then add photoinitiator and leveling agent, and disperse at high speed to obtain a coating. B2. Apply the coating onto the transparent polymer substrate layer, level it, and then cure it with UV light under an inert atmosphere to obtain the low-reflection, wear-resistant functional layer.

7. The method for preparing the low internal reflection, high heat insulation double silver composite automotive window film according to claim 5, characterized in that, Step B includes: B1. A UV-curable resin containing nano-silica particles is coated on the transparent polymer substrate layer. After curing, a functional hardened layer is obtained. B2. On the functional hardened layer, a high refractive index material layer and a low refractive index material layer are alternately deposited by magnetron sputtering to obtain the low-reflection wear-resistant functional layer.

8. The method for preparing the low internal reflection, high heat insulation double silver composite automotive window film according to claim 5, characterized in that, In step A, the pretreatment includes corona treatment or plasma treatment; in step E, the drying includes drying in a drying tunnel at 70~90℃.

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