Highly transparent anti-glare optical pre-coated film based on particle size gradient sedimentation and preparation method thereof

Abstract

This invention discloses a high-transmittance, anti-glare optical pre-coated film based on particle size gradient sedimentation and its preparation method. The optical pre-coated film includes an optical base film and a functional coating. The functional coating contains first nano-silica particles and second nano-silica particles, with the first nano-silica particles having a larger particle size than the second nano-silica particles. In the vertical direction of the functional coating, from the side closer to the optical base film to the air interface side farther away, the content of the first nano-silica particles continuously decreases, while the content of the second nano-silica particles continuously increases. This results in the average particle size of the nano-silica particles continuously decreasing from the optical base film side to the air interface side, forming a continuous gradient distribution structure with a large to small average particle size. By constructing a continuous refractive index gradient structure, this invention achieves higher light transmittance after coating than the base film itself, while simultaneously realizing a synergistic improvement in low haze, excellent anti-glare, anti-fingerprint, and wear-resistant properties.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, and in particular to a high-transmittance, anti-glare optical pre-coated membrane based on particle size gradient sedimentation and its preparation method. Background Technology

[0002] Optical pre-coated films refer to films on which functional coatings are pre-coated onto the surface of optical-grade base films, endowing them with properties such as anti-glare, anti-reflection, anti-fingerprint, and high hardness. They are widely used for surface protection or optical compensation in displays such as smartphones, tablets, automotive displays, and high-end televisions. As display technology continues to advance towards higher brightness and higher resolution, specular reflection glare from the screen surface under ambient light severely impacts the viewing experience. Therefore, anti-glare functionality has become a standard feature of optical films used in high-end displays. However, achieving anti-glare functionality usually comes at the cost of sacrificing light transmittance. How to maintain or even improve light transmittance while achieving excellent anti-glare performance has long been a technical challenge in this field.

[0003] In existing technologies, the anti-glare function of optical pre-coated films is mainly achieved through the following methods: The first method is the surface matting particle method. This approach adds micron-sized (1-10 μm) inorganic matting particles, such as silica or polymethyl methacrylate microspheres, to the coating. The particles create a rough surface, converting specular reflection into diffuse reflection and achieving an anti-glare effect. For example, CN101257980A discloses an "anti-glare and anti-reflection coating of surface-active nanoparticles," which achieves anti-reflection by forming a self-assembled gradient layer between a low-refractive-index phase and a high-refractive-index phase. However, this method requires complex interface control, and the nanoparticles still need to form a gradient through self-assembly, making process control difficult. A common drawback of this type of approach is that the particle size (1-10 μm) of the micron-sized matting particles is on the same order of magnitude as the wavelength of visible light (0.38-0.78 μm). According to Mie scattering theory, scattering efficiency is highest when the particle size is close to the wavelength. Simultaneously, there is a refractive index difference between the particles and the resin matrix, forming numerous interfaces with abrupt refractive index changes. Light is scattered and reflected at each interface it passes through, and the cumulative effect leads to a significant decrease in transmittance and an increase in haze. Simultaneously, the addition of a large number of inorganic particles reduces the coating's flexibility and adhesion. The fundamental reason for this is that the optical-grade base film has low surface energy and high crystallinity, meaning the interface between the coating and the base film relies solely on weak van der Waals forces. The micron-sized particles added to achieve anti-glare effects form protrusions on the coating surface, but these protrusions also disrupt the continuous contact surface between the coating and the base film, further reducing interfacial adhesion. With prolonged use or wiping, the coating easily peels off from the particle-base film interface.

[0004] The second method is multilayer interferometry. This approach achieves antireflection by alternating layers of materials with different refractive indices, utilizing the principle of optical interference. For example, JP2002341104A discloses an antireflective film whose optical functional layer consists of alternating stacked high-refractive-index and low-refractive-index layers. The disadvantages of this approach are: it requires precise control of the thickness and refractive index of the multilayer deposition, typically necessitating vacuum deposition processes (such as vacuum evaporation, sputtering, plasma deposition, etc.), resulting in high equipment investment, complex processes, low production efficiency, and unsuitability for large-area roll-to-roll continuous production; furthermore, the multilayer structure is prone to interlayer delamination during bending, exhibiting poor bending resistance.

[0005] The third method is the microstructure array method. For example, CN115016048B discloses an "anti-reflection microstructure and its fabrication method," which involves setting at least two stacked microstructure array layers on the upper and / or lower surfaces of a substrate. Each microstructure array layer contains a different microstructure material, thus effectively creating a thin film with a gradient refractive index distribution. The advantage of this method is its good anti-reflection effect, but its disadvantages are that it requires precision processing such as photolithography to form the microstructure array, which is complex and costly. It is not suitable for roll-to-roll production of large-area flexible thin films, and the microstructure size is usually in the micrometer range, making it prone to diffraction.

[0006] In summary, existing technologies cannot simultaneously achieve high light transmittance, low haze, excellent anti-glare effect, and high adhesion in a single coating. Furthermore, existing solutions either suffer from light transmittance loss or involve complex processes and high costs. Therefore, developing an optical pre-coated film that can achieve anti-glare functionality without sacrificing light transmittance, and which is simple to process and uses readily available materials, has significant industrial value. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a high-transmittance, anti-glare optical pre-coated film based on particle size gradient sedimentation and its preparation method. This invention constructs a continuous refractive index gradient structure, resulting in a higher transmittance after coating compared to the base film itself. Simultaneously, it achieves a synergistic improvement in low haze, excellent anti-glare, anti-fingerprint, and wear-resistant properties. Furthermore, the process is simple and suitable for roll-to-roll mass production.

[0008] To achieve the above-mentioned technical objectives and effects, the present invention is implemented through the following technical solution: In one aspect, the present invention provides a high-transmittance anti-glare optical pre-coated film based on particle size gradient sedimentation, comprising an optical base film and a functional coating disposed on at least one side of the optical base film; The functional coating contains first nano-silica particles and second nano-silica particles, wherein the particle size of the first nano-silica particles is larger than that of the second nano-silica particles. In the vertical direction of the functional coating, from the side closer to the optical base film to the air interface side farther away from the optical base film, the content of the first nano-silica particles continuously decreases, while the content of the second nano-silica particles continuously increases, so that the average particle size of the nano-silica particles in the functional coating continuously decreases from the optical base film side to the air interface side, forming a continuous gradient structure with the average particle size decreasing from large to small.

[0009] Furthermore, the functional coating has a continuous refractive index gradient in the vertical direction, with a refractive index of 1.58 to 1.64 near the optical base film and a refractive index of 1.45 to 1.50 near the air interface.

[0010] Furthermore, the particle size range of the first nano-silica particles is 80–120 nm, the particle size range of the second nano-silica particles is 20–30 nm, and the particle size ratio of the first nano-silica particles to the second nano-silica particles is ≥2.5.

[0011] Furthermore, the optical pre-coated film has a light transmittance ≥92.5%, a haze ≤3%, and a 60° gloss <45GU.

[0012] Furthermore, at least a portion of the surface of the second nano-silica particles is modified with fluorosilane, so that the side of the functional coating near the air interface is hydrophobic and oleophobic.

[0013] Another aspect of the present invention provides a method for preparing a high-transmittance, anti-glare optical pre-coated film based on particle size gradient sedimentation, comprising the following steps: Step 1: Provide the optical base film; Step 2: Prepare a bottom coating liquid and a top coating liquid. The bottom coating liquid contains first nano-silica particles, and the top coating liquid contains second nano-silica particles, wherein the particle size of the first nano-silica particles is larger than the particle size of the second nano-silica particles. Step 3: Apply the bottom coating liquid onto the optical base film to form a bottom wet film; Step 4: Pre-dry the bottom wet film to form a semi-dry film; Step 5: Coat the semi-dry film with the surface coating liquid to form a wet surface film; Step 6: Gradient drying is performed on the film coated with the base layer and the surface layer. By controlling the drying temperature and time, interdiffusion occurs between the base layer and the surface layer at the interface. At the same time, the difference in sedimentation velocity and surface energy between the first nano-silica particles and the second nano-silica particles is utilized to form a continuous gradient structure with a continuous transition in particle size from the base film side to the air interface side. Step 7: Perform a curing process to obtain the functional coating.

[0014] Furthermore, the gradient drying employs a three-stage drying process: The first stage involves drying at 40–60°C for 20–40 seconds to maintain the fluidity of the coating, allowing particles to settle and migrate driven by surface energy. The second stage involves drying at 60–80°C for 40–80 seconds, which triggers interdiffusion between the bottom and surface layers, forming a particle size transition zone. The third stage involves drying at 80–100°C for 20–40 seconds to completely eliminate the fluidity of the coating and lock in the continuous gradient structure.

[0015] Furthermore, the second nano-silica particles are surface-modified with fluorosilane to make their surface energy lower than that of the first nano-silica particles and the resin matrix of the functional coating; during the gradient drying process, the second nano-silica particles migrate toward the air interface, which works synergistically with the difference in settling velocity to form the continuous gradient structure.

[0016] Further, the bottom coating liquid comprises: 20-30 parts by weight of first nano-silica particles, 40-50 parts by weight of high-refractive-index UV acrylate resin, 10-20 parts by weight of reactive diluent, 2-5 parts by weight of silane coupling agent, and 1-5 parts by weight of photoinitiator; the particle size range of the first nano-silica particles is 80-120 nm; the top coating liquid comprises: 10-20 parts by weight of second nano-silica particles, 3-6 parts by weight of fluorosilane, 35-45 parts by weight of UV acrylate resin, 10-15 parts by weight of reactive diluent, and 1-5 parts by weight of photoinitiator; the particle size range of the second nano-silica particles is 20-30 nm.

[0017] Furthermore, in step four, the pre-drying temperature is 40–70°C, and the drying time is 20–60 seconds; after gradient drying in step six, the residual solvent content in the functional coating is ≤1%; in step seven, curing is performed using ultraviolet light under nitrogen protection, with a light intensity of 500–1000 mW / cm². 2 Energy density is 300–500 mJ / cm³ 2 .

[0018] The beneficial effects of this invention are as follows: In this invention, the nano-silica particles in the first particle size range (large particle size) and the second particle size range (small particle size) of the functional coating form a continuous gradient distribution in the vertical direction. Particles in the first particle size range have a higher refractive index and settle quickly, accumulating on the optical substrate side; particles in the second particle size range settle slowly and tend to remain in the upper part of the coating, thus forming a gradient structure with a continuously decreasing refractive index from the optical substrate to air within a single coating. Furthermore, the particles in the second particle size range can be modified with fluorosilanes to further reduce their surface energy, causing them to spontaneously migrate towards the air interface during curing, thereby strengthening the gradient distribution and imparting anti-fingerprint properties to the coating.

[0019] This structure addresses the transmittance loss problem of existing technologies on two levels: First, in traditional anti-glare coatings, the refractive index difference between micron-sized particles and the resin creates numerous abrupt interfaces. Fresnel reflection occurs at each interface, and the cumulative effect leads to a decrease in transmittance. This invention uses a particle size gradient distribution to continuously change the refractive index in the vertical direction, eliminating abrupt refractive index changes within the functional coating and at the interfaces between the functional coating and the optical substrate, and between the functional coating and air, thus significantly suppressing reflection loss. Second, in traditional solutions, micron-sized particles are on the same order of magnitude as visible light wavelengths, resulting in strong Mie scattering. This invention eliminates micron-sized particles; all particles are nanometer-sized, much smaller than the visible light wavelength, producing only negligible Rayleigh scattering and no Mie reflection. The synergistic effect of these two aspects results in higher transmittance after coating compared to the uncoated substrate, overcoming the technical defect of traditional anti-glare coatings that sacrifice transmittance, and actually increasing the transmittance of the coated film.

[0020] Meanwhile, the anti-glare function of this invention no longer relies on surface roughness, but achieves diffuse reflection by guiding light to bend and propagate within the coating through a refractive index gradient structure, with a gloss level controllable below 42 GU at 60°. Because the coating surface is smooth and free of micron-level protrusions, adhesion reaches a 5B rating; furthermore, the surface layer can be enriched with small-diameter fluorinated particles, giving the coating excellent anti-fingerprint properties.

[0021] This invention provides a process route of undercoating → pre-drying → topcoating → gradient drying → curing. Through a three-stage gradient drying process (low temperature → medium temperature → high temperature), three physical processes are coordinated to transform the initial layered structure of a "double-layer coating" into a gradient structure with a continuous transition in particle size within a single coating. Specifically, the low-temperature stage maintains fluidity, with particles migrating to the bottom and top based on differences in sedimentation velocity and surface energy, respectively. The medium-temperature stage induces interdiffusion between the undercoat and the top layer, transforming the double-layer structure into a continuous gradient structure with a continuous transition in particle size. The high-temperature stage locks in this structure. Compared to single-layer mixed coating, this method can improve light transmittance, reduce haze, and enhance anti-glare performance. Moreover, this invention employs a fully wet coating process, uses commercially available raw materials, requires no custom synthesis, is suitable for roll-to-roll production, and eliminates the need for complex processes such as vacuum coating or photolithography. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. 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.

[0023] This invention provides a high-transmittance, anti-glare optical pre-coated film based on particle size gradient sedimentation, comprising an optical base film and a functional coating coated on at least one side of the optical base film. The functional coating contains first nano-silica particles and second nano-silica particles, wherein the particle size of the first nano-silica particles is larger than that of the second nano-silica particles. The functional coating is formed by sequential coating, gradient drying, and UV curing of a double-layer coating liquid. In the vertical direction of the functional coating, from the side closer to the optical base film to the air interface side farther away from the optical base film, the content of the first nano-silica particles continuously decreases, while the content of the second nano-silica particles continuously increases, forming a continuous gradient structure with decreasing particle size. That is, the region near the optical base film contains larger nano-silica particles with a higher refractive index; the region near the air interface contains smaller nano-silica particles with a lower refractive index; and the intermediate region is a gradient region with a continuous transition in particle size. This particle size gradient distribution is formed by the combined effect of the difference in sedimentation velocity of two different particle size nano-silica particles in the coating liquid and the migration driven by surface energy, ultimately achieving a continuous gradient change in refractive index from the base film side to the air side.

[0024] It should be noted that the "continuous gradient distribution of particle size from large to small" or "particle size gradient distribution" described in this invention refers to the statistical average particle size of the nano-silica particles in the coating continuously decreasing in the vertical direction from the optical substrate side to the air side. This is a statistical result caused by the gradual decrease in the content of large-size particles and the gradual increase in the content of small-size particles. Near the optical substrate side, large-size particles dominate, with a larger average particle size; near the air side, small-size particles dominate, with a smaller average particle size; in the intermediate region, the proportions of both are relatively equal, and the average particle size is between the two.

[0025] The anti-glare effect of the functional coating of the present invention is achieved by the gradient refractive index structure and Rayleigh scattering generated by the small-diameter particles on the surface. Since the size of the small-diameter particles is much smaller than the wavelength of visible light, Mie scattering will not occur, thus avoiding loss of transmittance. At the same time, the gradient refractive index structure eliminates abrupt changes in refractive index inside the coating and at the interface, further reducing reflection loss, resulting in an overall transmittance higher than that of the uncoated base film after coating.

[0026] The functional coating has a continuous refractive index gradient in the vertical direction, with a refractive index of 1.58–1.64 near the optical base film and a refractive index of 1.45–1.50 near the air interface. Exemplarily, the first nano-silica particles have a particle size range of 80–120 nm, the second nano-silica particles have a particle size range of 20–30 nm, and the particle size ratio of the first nano-silica particles to the second nano-silica particles is ≥2.5 (e.g., a particle size ratio of 3–4). The optical pre-coated film has a transmittance ≥92.5%, haze ≤3%, and a 60° gloss <45 GU, and the transmittance is higher than that of the optical base film itself. Further, at least a portion of the surface of the second nano-silica particles is modified with fluorosilane, making the functional coating hydrophobic and oleophobic on the side near the air interface, with a water contact angle ≥100° (preferably ≥108°), which imparts excellent anti-fingerprint properties to the functional coating.

[0027] This invention provides a method for preparing a high-transmittance, anti-glare optical pre-coated film based on particle size gradient sedimentation, comprising the following steps: (1) Preparation of coating solution The bottom coating solution is used to form a high refractive index layer close to the base film. For example, its preparation steps are as follows: First, take 20-30 parts by weight of nano-silica sol with a particle size range of 80-120 nm, add 2-5 parts by weight of silane coupling agent (e.g., γ-methacryloyloxypropyltrimethoxysilane KH-570), stir in a water bath at 50-60°C for 1 hour, and perform surface modification treatment so that the silane coupling agent forms a chemical bond with the hydroxyl groups on the surface of silica through hydrolysis and condensation reaction, introduce acrylate groups that can participate in UV curing, and improve the compatibility between particles and resin. Then, the modified silica sol is mixed with 40-50 parts by weight of high-refractive-index UV acrylate resin (e.g., Changxing Chemical 6195, refractive index 1.56-1.58) and 10-20 parts by weight of reactive diluent (e.g., dipentaerythritol hexaacrylate DPHA). The mixture is stirred at 1000-1200 rpm for 30 minutes to ensure thorough mixing. Next, 1-5 parts by weight of photoinitiator (e.g., 1-hydroxycyclohexylphenyl ketone Irgacure 184) is added, and stirring continues for 15 minutes until completely dissolved. Finally, an organic solvent (e.g., a 1:1 volume ratio mixture of propylene glycol methyl ether (PM) and butanone (MEK)) is added to adjust the solid content to approximately 45%. After stirring for 10 minutes, the mixture is filtered under positive pressure using a 0.45 μm pore size polytetrafluoroethylene (PTFE) membrane to remove any trace amounts of insoluble matter and gel particles. The mixture is then allowed to stand for 1 hour to remove bubbles, yielding the bottom coating solution.

[0028] The surface coating solution is used to form a low refractive index layer near the air interface. Exemplarily, its preparation steps are as follows: First, 10-20 parts by weight (e.g., 15 parts by weight) of nano-silica sol with a particle size range of 20-30 nm are taken, and 3-6 parts by weight of fluorosilane (e.g., perfluorodecyltrimethoxysilane FAS-17) are added. The mixture is stirred in a water bath at 60-70°C for 2 hours to perform fluorination modification treatment, allowing the fluorosilane to be grafted onto the silica surface through a hydrolysis-condensation reaction, forming a low surface energy fluorinated layer. Then, the fluorinated silica sol is mixed with 35-45 parts by weight of conventional UV acrylate resin (e.g., Changxing Chemical 6123 type, refractive index 1.52-1.54) and 10-15 parts by weight of reactive diluent (e.g., DPHA), and stirred at high speed at 1000-1200 rpm for 30 minutes. Next, add 1-5 parts by weight of a photoinitiator (e.g., Irgacure 184) and continue stirring for 15 minutes until completely dissolved. Finally, add an organic solvent (e.g., a 1:1 volume ratio mixture of isopropanol and butanone) to adjust the solid content to about 35%, stir for 10 minutes, filter through a 0.45 μm pore size polytetrafluoroethylene filter membrane, and allow to stand for 1 hour to remove bubbles, thus obtaining the surface coating solution.

[0029] All the above raw materials are commercially available products: nano-silica sols with particle sizes in the range of 80–120 nm and 20–30 nm can be purchased from Zhejiang Yuda Chemical Co., Ltd. or Shandong Baite New Materials Co., Ltd.; high-refractive-index UV acrylate resin 6195 and conventional UV acrylate resin 6123 can be purchased from Changxing Chemical Industry (China) Co., Ltd.; silane coupling agent KH-570 can be purchased from Nanjing Shuguang Chemical Group Co., Ltd.; fluorosilane FAS-17 can be purchased from Harbin Xuejia Fluorosilicon Chemical Co., Ltd.; reactive diluent DPHA can be purchased from Changxing Chemical; photoinitiator Irgacure 184 can be purchased from IGM Resins or its agents; organic solvents (PM, MEK, isopropanol) can be purchased from chemical markets in various regions. All raw materials do not require custom synthesis and have immediate industrialization capabilities.

[0030] (2) Base film pretreatment Optical-grade BOPET film was selected as the optical base film, with an exemplary thickness of 50–125 μm, a light transmittance ≥91%, a haze ≤0.8%, and a surface roughness Ra ≤0.03 μm. The optical base film was subjected to corona treatment before coating using a corona treatment machine with a power density of 8 W·min / m². 2 The processing speed is 30–50 meters per minute. After treatment, the surface area of ​​the optical substrate film reaches over 52 dynes per centimeter (dyne / cm), and the water contact angle is reduced to below 40°. Corona treatment introduces polar groups such as hydroxyl and carboxyl groups onto the surface of the optical substrate film, improving its wettability and adhesion to the coating solution. The treated substrate film is then cleaned with an ion air gun to remove electrostatically adsorbed dust particles.

[0031] Furthermore, this invention is also applicable to other transparent optical base films, such as cellulose triacetate (TAC) films, cyclic olefin polymer (COP) films, and polyimide (PI) films. Different base films have different surface energies, and coating adhesion can be optimized by adjusting corona treatment parameters or adding a primer.

[0032] (3) Double-layer coating process The coating process adopts a roll-to-roll continuous coating method. The coating environment requires a cleanliness level of 10,000, with the temperature controlled at 20-25℃ and the relative humidity controlled at 45-55%.

[0033] First, the undercoat is applied. The prepared undercoat solution is injected into a microgravure coating system, using a microgravure roller with a line count of 200–300 lines per inch and a gravure depth of 15–25 μm. The coating speed is 20–30 meters per minute, and the wet film thickness is controlled at 8–12 μm. The coated film enters the first stage of a three-stage hot air drying oven and is pre-dried at 50–60°C for 30 seconds to allow partial evaporation of the solvent. The coating solution loses its fluidity but is not completely dry, forming a semi-dry film. During this stage, the solvent evaporation rate should not be too fast to ensure sufficient time for particle sedimentation and migration. Immediately after the undercoat pre-drying, the topcoat is applied. A slot extrusion coating method is used, with the slot gap set at 0.15–0.25 mm. The coating speed is consistent with that of the undercoat, and the wet film thickness is controlled at 6–10 μm. The surface coating liquid is applied to the bottom semi-dry film, and interdiffusion occurs at the interface between the two layers to form a transition layer, thus obtaining a surface wet film.

[0034] It should be noted that the coating method is not limited to the above combination. For example, two-layer microgravure coating or two-layer slot extrusion coating can also be used, as long as double-layer coating can be achieved and the pre-baking degree of the underlying layer is well controlled. In addition, the present invention is not limited to UV curing systems, but can also use thermosetting systems, such as epoxy resin, polyester resin, etc., with appropriate curing agents and curing conditions, to form a gradient refractive index structure.

[0035] (4) Gradient forming drying The double-coated film enters a three-section hot air drying oven for gradient drying. The oven is 15-20 meters long and divided into three temperature zones. First stage (low temperature zone): The temperature is set at 40–60℃, and the residence time is 20–40 seconds (e.g., 30 seconds). During this stage, a small amount of solvent evaporates, and the coating liquid maintains high fluidity. Nano-silica particles with two different particle size ranges begin to settle under the influence of gravity. According to Stokes' law, the settling velocity of spherical particles in a Newtonian fluid is proportional to the square of the particle diameter. Particles with a larger particle size range (80–120 nm) settle faster and begin to migrate towards the optical base film; particles with a smaller particle size range (20–30 nm) settle slower and tend to remain on the upper part of the coating.

[0036] The second stage (medium temperature zone): The temperature is set at 60–80℃, and the residence time is 40–80 seconds (e.g., 60 seconds). During this stage, a large amount of solvent evaporates, the coating begins to shrink, the particle settling speed accelerates, and a particle size gradient gradually forms. Particles with larger particle sizes basically settle to the bottom, while particles with smaller particle sizes remain in the upper and middle parts. At the same time, because the surface energy of the small-particle-size nano-silica in the surface coating solution is extremely low after being modified with fluorosilane (approximately 15–20 dyne / cm), which is much lower than that of the resin matrix (approximately 30–35 dyne / cm) and the surface of the optical base film (approximately 52 dyne / cm after corona treatment), according to thermodynamic principles, low surface energy components tend to migrate to the air interface, which has even lower surface energy. Therefore, these small-particle-size fluorinated particles will spontaneously accumulate on the coating surface, further enhancing the particle size gradient distribution. Furthermore, resin interpenetration and particle interdiffusion occur at the interface between the bottom semi-dry film and the surface wet film, transforming the "particle size abrupt change interface" into a "particle size slope gradual change zone," thus eliminating the abrupt change in refractive index.

[0037] The third stage (high-temperature zone): The temperature is set at 80–100℃, and the residence time is 20–40 seconds (e.g., 30 seconds). During this stage, residual solvents completely evaporate, the coating loses its fluidity, and the continuous particle size gradient structure is "frozen." Throughout the drying process, the hot air velocity in each zone is controlled at 2–5 meters per second. Too low a velocity results in insufficient drying efficiency, while too high a velocity can easily generate surface turbulence, leading to an uneven coating. After drying, the residual solvent content in the coating should be ≤1%, which can be monitored using an online infrared moisture meter.

[0038] Through the above three-stage gradient drying, three physical processes (particle size gradient sedimentation, surface energy-driven self-migration, and interdiffusion at the bilayer interface) are coordinated to transform the initial layered structure of "bilayer coating" into a continuous gradient structure of "continuous particle size transition within a single coating".

[0039] (5) UV curing The dried film is then placed in a UV curing unit for curing. A high-pressure mercury lamp is used as the light source, with a wavelength range of 200–400 nm and a peak wavelength of 365 nm. Curing is carried out under a nitrogen protective atmosphere, with the oxygen content controlled below 200 ppm to avoid oxygen inhibition affecting the surface curing effect. The peak light intensity is set to 500–1000 mW / cm². 2 (Example: 600-800 mW / cm) 2 The total energy density is 300–500 mJ / cm³. 2 The total thickness of the cured coating is 4–6 μm.

[0040] (6) Post-processing and testing After curing, the film rolls are placed in a curing chamber at 40–50°C for 24–48 hours to further improve the cross-linking network of the coating and fully release internal stress. Performance testing is then performed, including: testing transmittance and haze using a haze meter and transmittance meter according to ASTM D1003; testing 60° gloss using a gloss meter according to ASTM D523; testing pencil hardness using a pencil hardness tester according to ASTM D3363; testing coating adhesion using a cross-cut adhesion tester according to ASTM D3359; testing water contact angle using a contact angle tester; and testing abrasion resistance using a steel wool abrasion tester according to JIS K-5600. After passing the tests, the film rolls are cut to the width required by the customer, the coating surface is protected with anti-static PE film, and vacuum-packed.

[0041] In this invention, the nano-silica particles in the first particle size range (e.g., 80–120 nm) and the second particle size range (e.g., 20–30 nm) of the functional coating form a continuous gradient distribution in the vertical direction. Particles in the first particle size range have a higher refractive index and settle quickly, accumulating on the optical substrate side; particles in the second particle size range settle slowly and tend to remain in the upper part of the coating, thus forming a continuous gradient structure within a single coating where the refractive index decreases continuously from the optical substrate to air. As a preferred embodiment, the particles in the second particle size range can be modified with fluorosilane to further reduce their surface energy, causing them to spontaneously migrate towards the air interface during curing, thereby strengthening the gradient distribution and imparting anti-fingerprint properties to the coating.

[0042] This structure addresses the transmittance loss problem of existing technologies on two levels: First, in traditional anti-glare coatings, the refractive index difference (Δn≈0.05~0.1) between micron-sized particles and the resin creates numerous abrupt interface changes. Fresnel reflection occurs at each interface, and the cumulative effect leads to a decrease in transmittance. This invention, through a particle size gradient distribution, ensures a continuous change in refractive index in the vertical direction, eliminating abrupt refractive index changes within the functional coating and at the interfaces between the functional coating and the optical substrate, and between the functional coating and air, thus significantly suppressing reflection loss. Second, in traditional solutions, micron-sized particles (1~10μm) are on the same order of magnitude as visible light wavelengths (0.38~0.78μm), resulting in strong Mie scattering. This invention eliminates micron-sized particles; all particles are nanometer-sized (≤120nm), much smaller than the visible light wavelength, producing only negligible Rayleigh scattering and no Mie scattering. The synergistic effect of the two aspects makes the light transmittance after coating (e.g., 93.8%) higher than that of the uncoated base film (e.g., 91.2%), achieving a light transmittance enhancement effect that the existing anti-glare coating cannot achieve, surpassing that of the base film.

[0043] Meanwhile, the anti-glare function of this invention no longer relies on surface roughness, but rather achieves diffuse reflection by guiding light to bend and propagate within the coating through a refractive index gradient structure. The gloss level at 60° can be controlled below 42 GU (exemplarily 38–42 GU). Due to the smooth surface of the coating and the absence of micron-level protrusions, the adhesion reaches the highest level of 5B; and the fluorinated small-diameter particles enriched on the surface result in a water contact angle ≥108°, giving the coating excellent anti-fingerprint properties. In addition, the uniform particle distribution and small particle size in the coating, with no stress concentration points, combined with a high cross-linking density resin matrix, achieves abrasion resistance of 1800–2000 cycles (0000# steel wool, 500g load) without scratches.

[0044] The process route provided by this invention, namely, undercoating → pre-drying → topcoating → gradient drying → curing, transforms the initial layered structure of "double-layer coating" into a continuous gradient structure of "continuous particle size transition within a single coating" through three-stage gradient drying (low temperature → medium temperature → high temperature) in synergy with three physical processes. Compared with single-layer mixed coating (e.g., mixing the undercoating and topcoating liquids and then coating once), this method can increase the light transmittance from approximately 89.5% to 93.8%, reduce the haze from approximately 4.8% to 2.1%, improve the 60° gloss from approximately 52 GU to 38 GU, and significantly improve anti-glare performance. Moreover, this invention adopts a fully wet coating process (microgravure coating, slot extrusion coating, etc.), uses commercially available raw materials, requires no custom synthesis, is suitable for roll-to-roll continuous production, and eliminates the need for complex and expensive processes such as vacuum coating, sputtering, plasma deposition, or photolithography. It features low equipment investment, high production efficiency, and immediate industrialization capability.

[0045] The technical solution and effects of the present invention are further illustrated below through specific embodiments. Example 1

[0046] The following formulation and process conditions were used in Example 1: The formulation of the base coat is as follows: 20 parts of 80-120nm nano silica sol, 3 parts of KH-570 silane coupling agent, 45 parts of high refractive index UV resin (Changxing 6195), 15 parts of DPHA, 3 parts of Irgacure 184, and an appropriate amount of PM / MEK mixed solvent to adjust the solid content to 45%.

[0047] Surface coating solution formulation: 15 parts of 20-30nm nano silica sol, 5 parts of FAS-17 fluorosilane, 40 parts of conventional UV resin (Changxing 6123), 12 parts of DPHA, 3 parts of Irgacure 184, and an appropriate amount of isopropanol / MEK mixed solvent to adjust the solid content to 35%.

[0048] Optical substrate: 125μm optical-grade BOPET, corona treatment power density 8W·min / m 2 .

[0049] Coating process: The bottom layer wet film thickness is 10μm, and it is pre-baked at 50℃ for 30 seconds; the top layer wet film thickness is 8μm.

[0050] Drying conditions: Zone 1 45℃, 30 seconds; Zone 2 65℃, 60 seconds; Zone 3 85℃, 30 seconds.

[0051] UV curing: Peak light intensity 700mW / cm 2 Energy density 400 mJ / cm³ 2 Nitrogen protection.

[0052] Test results: Light transmittance 93.8%, haze 2.1%, 60° gloss 38GU, pencil hardness 2H, coating adhesion 5B, water contact angle 112°, abrasion resistance (0000# steel wool, 500g load) 2000 times without scratches. Example 2

[0053] In Example 2, the content of nano-silica in the bottom coating liquid was adjusted to 25 parts, and the content of nano-silica in the top coating liquid was adjusted to 10 parts. The other conditions were the same as in Example 1.

[0054] Test results: Light transmittance 93.5%, haze 2.3%, 60° gloss 40GU, ​​pencil hardness 2H, coating adhesion 5B, water contact angle 108°, abrasion resistance 1800 cycles without scratches. Example 3

[0055] In this embodiment 3, the drying conditions are adjusted as follows: Zone 1: 40°C for 40 seconds; Zone 2: 60°C for 80 seconds; Zone 3: 80°C for 20 seconds; and the remaining conditions are the same as in embodiment 1.

[0056] Test results: Light transmittance 93.2%, haze 2.5%, 60° gloss 42GU, pencil hardness 2H, coating adhesion 5B, water contact angle 110°, abrasion resistance 1900 cycles without scratches.

[0057] Comparative Example 1 A commercially available anti-glare film from a certain brand was selected, with 3μm silica matting powder added to the coating.

[0058] Test results: Light transmittance 86.5%, haze 12.5%, 60° gloss 45GU, pencil hardness H, coating adhesion 3B, water contact angle 75°, abrasion resistance 500 times of minor scratches.

[0059] Comparative Example 2 Uncoated BOPET base film was selected; test results: light transmittance 91.2%, haze 0.8%, 60° gloss 155GU, pencil hardness HB, water contact angle 68°.

[0060] Comparative Example 3 A single-layer coating of BOPET base film was used. The coating solution was a 1:1 mixture of the bottom coating solution and the top coating solution from Example 1. After one coating, the film was dried and cured. The remaining conditions were the same as in Example 1.

[0061] Test results: Light transmittance 89.5%, haze 4.8%, 60° gloss 52GU, pencil hardness H, coating adhesion 4B, water contact angle 95°, abrasion resistance 1200 minor scratches.

[0062] A comparison between the examples and the comparative examples shows that: Regarding transmittance, the transmittance of Example 1 of this invention reaches 93.8%, higher than the 91.2% of the uncoated base film, achieving an anti-reflection effect where the transmittance of the coated film surpasses that of the base film. This phenomenon is due to the fact that the gradient refractive index structure eliminates the abrupt changes in refractive index at the interfaces between the functional coating and the optical base film, as well as between the functional coating and the air, significantly reducing Fresnel reflection loss. Simultaneously, small-diameter particles on the surface do not produce Mie scattering, thus improving the overall transmittance. Comparative Example 3, using a single-layer mixed coating, does not form a continuous gradient structure, resulting in a significant decrease in transmittance, demonstrating that a continuous gradient structure is key to achieving anti-reflection.

[0063] Regarding haze, the haze of this embodiment of the invention is controlled between 2.1% and 2.5%, which is far lower than the 12.5% ​​of commercially available micron-sized anti-glare films. This is because this invention abandons micron-sized extinction particles, and all particles are below 120nm in size, which do not produce Mie scattering of visible light, thus resulting in extremely low haze.

[0064] Regarding the anti-glare effect, the 60° gloss level of this invention is 38~42 GU, which meets the anti-glare standard and is comparable to or even better than commercially available micron-particle type anti-glare films (45 GU), but with a smooth surface and no particle feel, resulting in a better visual experience. This effect comes from the gradient refractive index structure guiding the bending and propagation of light to achieve diffuse reflection, rather than relying on surface roughness.

[0065] Regarding coating adhesion, the embodiments of this invention achieve the highest grade 5B, far superior to the 3B grade of commercially available products. This is because the functional coating of this invention does not contain large-sized particles, allowing it to form a continuous contact surface with the optical base film.

[0066] Regarding the anti-fingerprint performance, the water contact angle of the embodiments of the present invention reaches 108°~112°, exhibiting good hydrophobicity and oleophobicity.

[0067] Regarding abrasion resistance, the abrasion resistance of the embodiments of the present invention reaches 1800-2000 cycles without scratches, which is better than the 500 cycles of commercially available products. This is because the functional coating of the present invention has uniform particle distribution and small particle size, which prevents the formation of stress concentration points, while the high cross-linking density of the resin matrix provides good mechanical support.

[0068] 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 the spirit or essential characteristics of the invention. 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, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0069] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A high-transmittance, anti-glare optical pre-coated film based on particle size gradient sedimentation, characterized in that, Includes an optical base film and a functional coating disposed on at least one side of the optical base film; The functional coating contains first nano-silica particles and second nano-silica particles, wherein the particle size of the first nano-silica particles is larger than that of the second nano-silica particles. In the vertical direction of the functional coating, from the side closer to the optical base film to the air interface side farther away from the optical base film, the content of the first nano-silica particles continuously decreases, while the content of the second nano-silica particles continuously increases, so that the average particle size of the nano-silica particles in the functional coating continuously decreases from the optical base film side to the air interface side, forming a continuous gradient structure with the average particle size decreasing from large to small.

2. The high-transmittance anti-glare optical pre-coated film according to claim 1, characterized in that, The functional coating has a continuous refractive index gradient in the vertical direction, with a refractive index of 1.58 to 1.64 near the optical base film and a refractive index of 1.45 to 1.50 near the air interface.

3. The high-transmittance anti-glare optical pre-coated film according to claim 1, characterized in that, The particle size range of the first nano-silica particles is 80-120 nm, the particle size range of the second nano-silica particles is 20-30 nm, and the particle size ratio of the first nano-silica particles to the second nano-silica particles is ≥2.

5.

4. The high-transmittance anti-glare optical pre-coated film according to claim 1, characterized in that, The optical pre-coated film has a light transmittance of ≥92.5%, a haze of ≤3%, and a gloss of <45GU at 60°.

5. The high-transmittance anti-glare optical pre-coated film according to claim 1, characterized in that, The second nano-silica particles have at least a portion of their surface modified with fluorosilane, making the side of the functional coating near the air interface hydrophobic and oleophobic.

6. A method for preparing a high-transmittance, anti-glare optical pre-coated film based on particle size gradient sedimentation, characterized in that, Includes the following steps: Step 1: Provide the optical base film; Step 2: Prepare a bottom coating liquid and a top coating liquid. The bottom coating liquid contains first nano-silica particles, and the top coating liquid contains second nano-silica particles, wherein the particle size of the first nano-silica particles is larger than the particle size of the second nano-silica particles. Step 3: Apply the bottom coating liquid onto the optical base film to form a bottom wet film; Step 4: Pre-dry the bottom wet film to form a semi-dry film; Step 5: Coat the semi-dry film with the surface coating liquid to form a wet surface film; Step 6: Gradient drying is performed on the film coated with the base layer and the surface layer. By controlling the drying temperature and time, interdiffusion occurs between the base layer and the surface layer at the interface. At the same time, the difference in sedimentation velocity and surface energy between the first nano-silica particles and the second nano-silica particles is utilized to form a continuous gradient structure with a continuous transition in particle size from the base film side to the air interface side. Step 7: Perform a curing process to obtain the functional coating.

7. The preparation method according to claim 6, characterized in that, The gradient drying process employs a three-stage drying process: The first stage involves drying at 40–60°C for 20–40 seconds to maintain the fluidity of the coating, allowing particles to settle and migrate driven by surface energy. The second stage involves drying at 60–80°C for 40–80 seconds, which triggers interdiffusion between the bottom and surface layers, forming a particle size transition zone. The third stage involves drying at 80–100°C for 20–40 seconds to completely eliminate the fluidity of the coating and lock in the continuous gradient structure.

8. The preparation method according to claim 6, characterized in that, The second nano-silica particles are surface modified with fluorosilane to make their surface energy lower than that of the first nano-silica particles and the resin matrix of the functional coating; during the gradient drying process, the second nano-silica particles migrate toward the air interface, which works in synergy with the difference in settling velocity to form the continuous gradient structure.

9. The preparation method according to claim 6, characterized in that, The bottom coating liquid comprises: 20-30 parts by weight of first nano-silica particles, 40-50 parts by weight of high-refractive-index UV acrylate resin, 10-20 parts by weight of reactive diluent, 2-5 parts by weight of silane coupling agent, and 1-5 parts by weight of photoinitiator; the particle size range of the first nano-silica particles is 80-120 nm; the top coating liquid comprises: 10-20 parts by weight of second nano-silica particles, 3-6 parts by weight of fluorosilane, 35-45 parts by weight of UV acrylate resin, 10-15 parts by weight of reactive diluent, and 1-5 parts by weight of photoinitiator; the particle size range of the second nano-silica particles is 20-30 nm.

10. The preparation method according to claim 6, characterized in that, In step four, the pre-drying temperature is 40–70°C, and the drying time is 20–60 seconds; after gradient drying in step six, the residual solvent content in the functional coating is ≤1%; in step seven, curing is performed using ultraviolet light under nitrogen protection, with a light intensity of 500–1000 mW / cm². 2 Energy density is 300–500 mJ / cm³ 2 .